Heat storage and supply

Abstract

A method of thermal energy storage and delivery is disclosed that includes supplying subcooled water to a pressure vessel (110), heating the liquid water in the pressure vessel using an electric heater such that the vessel contains saturated liquid water and steam at a variable storage pressure, controlling the heater (112) to raise the storage pressure to a peak storage pressure of at least 2 MPa, and selectively releasing steam from a discharge of the pressure vessel to a heat load (130, 40) in response to thermal energy demand such that the storage pressure drops by at least 1 MPa from the peak storage pressure during a depletion period.

Description

[Technical Field]

[0001] The present invention relates to methods and apparatus (eg, facilities) for thermal energy storage and supply. [Background technology]

[0002] It is known to provide industrial plants and other facilities requiring thermal energy with steam supply systems capable of generating steam for distribution to the heat load in the plant or other facility.

[0003] Such steam supply systems typically include a burner-type boiler and an accumulator. Because it is inefficient to operate the boiler over a large turndown ratio to accommodate fluctuations in steam demand, an accumulator is typically provided to accommodate such fluctuations in demand above and below the boiler's optimum steam discharge rate during the boiler's operating period.

[0004] There is a trend to replace fossil fuel-dependent systems with electric systems. Electric boilers with electric heating elements have been proposed, which offer variable power output and more consistent efficiency so that fluctuating steam demands can be met more efficiently by the boiler. Summary of the Invention

[0005] [Problem to be solved by the invention] [Means for solving the problem] According to a first aspect, there is provided a thermal energy storage and delivery method comprising: providing subcooled water to the pressure vessel; heating liquid water in a pressure vessel using an electric heater such that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to increase the storage pressure to a peak storage pressure of at least 2 MPa; and selectively releasing steam from a pressure vessel outlet to a heat load in response to a thermal energy demand such that the storage pressure drops by at least 1 MPa from the peak storage pressure during the depletion period.

[0006] Pressure figures disclosed herein are absolute pressures unless otherwise specified (e.g., as gauge pressures). A depletion period, as used herein, may be a period during which the enthalpy output corresponding to the released steam is greater than the energy input to the pressure vessel. The enthalpy output corresponding to the released steam may be the total enthalpy of steam released from the pressure vessel during the respective period, determined by referencing the respective storage pressure of the pressure vessel at the time the steam is released. This corresponds to the change in enthalpy of water in the pressure vessel due to the release of steam. The enthalpy output may also be referred to as the enthalpy loss corresponding to the released steam. The energy input to the pressure vessel is the sum of the enthalpy of the subcooled water supplied to the pressure vessel (i.e., newly supplied during the depletion period) and the energy input to the water in the pressure vessel by heating with a heater.

[0007] Steam can be selectively released from the outlet by control of a control valve, e.g., a control valve located at or downstream from the outlet, such that steam released from the outlet passes through the control valve. In some examples described herein, the control valve may be remote from the vessel and may be located on the condensate return line, for example, in a thermosiphon configuration (in such cases, the steam does not pass through the control valve).

[0008] During the depletion period, the total enthalpy output may be greater than the total energy input, while the instantaneous enthalpy output at any instant may be less than the instantaneous energy input at the same instant.

[0009] The depletion period can alternatively be described as the period during which the mass and energy (or enthalpy) fluctuations of the water in the pressure vessel are such that the storage pressure drops by at least 1 MPa from the peak storage pressure. The mass and energy fluctuations can be due to steam discharge, energy input from heating, and / or the supply of subcooled water.

[0010] The discharge steam may be supplied directly to the heat load without passing through an intermediate steam accumulator, or any one or more steam accumulators between the pressure vessel and the heat load may have a total volume less than the volume of the pressure vessel.

[0011] As used herein, the term "directly" should be interpreted with the intention of not passing through an accumulator. Thus, the discharge steam may be supplied to the heat load through one or more other components (e.g., through a desuperheater), but may not pass through an accumulator.

[0012] The method can include operating a heater during the depletion period. The heater can be operated during the depletion period concurrently with the selective release of vapor.

[0013] The method may include operating the heater during part or all of the depletion period without simultaneously supplying subcooled water to the pressure vessel and / or during part or all of the refill period during which the storage pressure increases by at least 1 MPa to a peak storage pressure of at least 2 MPa.

[0014] As used herein, a recharge period may refer to a period of time during which the energy input to the pressure vessel from heating is greater than the enthalpy output corresponding to the steam release to meet the thermal energy demand. Alternatively, a recharge period may be described as a period of time during which the mass and energy (or enthalpy) fluctuations of the water in the pressure vessel cause the storage pressure to rise by at least 1 MPa to the peak storage pressure. The mass and energy fluctuations may be due to heating, steam release, and / or the supply of subcooled water.

[0015] The steam may be released from the outlet so that the liquid water level in the pressure vessel (i.e., the surface of the liquid water or the interface between the liquid water and the steam) falls below a lower limit for operation of the heater during the depletion period. The controller may operate the heater during the depletion period while the steam is released when the water level is above the lower limit, and the controller may stop operation of the heater due to continued release of steam above the lower limit.

[0016] The liquid water level in the pressure vessel may fall below the minimum level for operation of the heater during an extended portion of the depletion period. By "extended," we mean that the ability to continue venting steam is extended by allowing the liquid level to fall below the minimum level, with the trade-off that the heater cannot be operated until the liquid level rises again by supplying additional water to the pressure vessel. After the extended depletion period ends (e.g., after venting steam has stopped, e.g., when a minimum pressure condition is reached), water may be supplied to the pressure vessel to restore the liquid level above the minimum level limit, and the heater may then be turned on again.

[0017] For example, the lower limit liquid level may be the lower limit liquid level height for operation of the heater (i.e., the lowest height of the liquid water / steam interface), which may correspond to or be the height to which the heating element of the heater extends within the vessel. The lower limit liquid level may also be the lower limit liquid volume of liquid water, which may be expressed as a volume fraction of liquid water within the pressure vessel (i.e., between 0 and 1).

[0018] In other words, steam may be released so that the liquid level margin is negative.

[0019] The steam may be discharged to the heat load at the discharge pressure, or subcooled water may be provided to the vessel if the storage pressure is greater than the discharge pressure.

[0020] The subcooled water is subcooled at the moment of delivery to the pressure vessel (e.g., from a condensate supply vessel), i.e., the water is delivered from a condensate supply vessel that stores condensate at a temperature lower than the temperature of the water in the pressure vessel.

[0021] The discharge pressure may be variable and subcooled water may be supplied when steam is not being discharged, in which case the discharge pressure is taken to be the discharge pressure at which steam was last discharged.

[0022] The peak storage pressure may exceed the maximum supply pressure at which subcooled water is supplied to the vessel.

[0023] Subcooled water may be supplied to the pressure vessel during the depletion period. The mass of subcooled water supplied to the pressure vessel during the depletion period may be 50% or less of the mass of steam released during the depletion period, e.g., 25% or less, 10% or less, or 5% or less.

[0024] The heat load may discharge a flow of condensate corresponding to the discharged steam to a subcooled water supply vessel, such as a hot well. A mass of condensate corresponding to at least 50%, e.g., at least 75%, at least 90%, or substantially all of the mass of steam discharged during the depletion period, or substantially all of the condensate generated by the steam discharged from the pressure vessel during the depletion period, may be supplied to the subcooled water supply during the depletion period for subsequent resupply to the pressure vessel.

[0025] The heat load may include a heat exchanger positioned relative to the pressure vessel such that a thermosiphon is established between the pressure vessel and the heat exchanger such that vent steam condensing in the heat exchanger forms a column of subcooled water that is returned to a condensate inlet at the bottom of the pressure vessel during depletion periods.

[0026] The heat exchanger may be located above the condensate inlet to provide sufficient head to return the subcooled water to the pressure vessel under the action of gravity. The heat exchanger may subcool the water therein by at least 10°C relative to a saturation temperature corresponding to the storage pressure.

[0027] The control valve for controlling the release of steam from the pressure vessel may be a condensate line control valve provided on a condensate line that returns condensate from the heat exchanger to the pressure vessel, and may be controllable by a controller to change or stop the flow rate of condensate from the heat exchanger to the pressure vessel, thereby also controlling the release of steam from the pressure vessel.

[0028] Subcooled water may be supplied to the pressure vessel at an injection rate such that the reservoir pressure decreases as the subcooled water is supplied.

[0029] The flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure to sustain the release of steam to the heat load.

[0030] The liquid level margin corresponds to the amount of liquid water in the pressure vessel above the lower limit for operation of the heater upon release of the flash potential.

[0031] The method may include evaluating a criterion corresponding to whether the level margin is positive or negative, and based on the evaluation, supplying subcooled water to the pressure vessel to increase the level margin and reduce the flash potential.

[0032] Subcooled water may be supplied to increase the level margin and reduce the flash potential when the rating corresponds to a negative level margin.

[0033] As an example, flash potential can correspond to or be defined as the mass of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a lower limit for sustaining the release of steam to the heat load. Flash potential can also be defined in other ways, such as by referring to the time a given peak rate of release of steam to the heat load can be sustained.

[0034] As an example, the liquid level margin can correspond to or be defined as the difference between the liquid level in the pressure vessel at the time of the release of the flash potential and the lower limit for the heater's operation (this difference is negative when the liquid level is below the lower limit). The liquid level margin can also be defined as the difference between the volume of liquid water in the pressure vessel at the time of the release of the flash potential and the lower limit for the heater's operation. The volume can be expressed as the volume fraction of liquid water in the pressure vessel (i.e., between 0 and 1).

[0035] The criteria may correspond to whether the liquid level margin is positive or negative, based on the release of an instantaneous flash potential, or based on the release of a predicted flash potential.

[0036] Evaluating the criteria may include determining a flash potential and determining a level margin based on the release of the flash potential (e.g., instantaneous flash potential or predicted flash potential). The instantaneous flash potential may be a function of the current storage pressure and water level in the pressure vessel and the floor pressure.

[0037] The flash potential may be a predicted flash potential that is a function of predicted demand and / or predicted power output of the heater over a period of time. The level margin may be a predicted level margin based on the release of the predicted flash potential over that period of time.

[0038] For example, evaluating the criteria can include evaluating criteria corresponding to whether a predicted level margin is positive or negative based on the release of the predicted flash potential over the time period. Evaluating the criteria can include determining a predicted flash potential, determining a predicted level margin based on the release of the predicted flash potential over the time period, and determining whether the predicted level margin is positive or negative.

[0039] The predicted flash potential may be determined based on the current liquid level and storage pressure, and based on the predicted demand and / or the predicted power output of the heater over the period. The demand may be, for example, a predicted thermal energy demand or a predicted steam demand.

[0040] The predicted demand may be based on historical demand data, such as historical steam or heat demand data for the facility, and / or the predicted demand may be based on forecasted weather conditions, and / or the predicted power output of the heater may be based on historical power capacity data for the heater, and / or the predicted power output of the heater may be based on forecasted weather conditions.

[0041] There may be a plurality of thermal loads, including a first thermal load and a second thermal load. Steam may be selectively released from the pressure vessel to each of the thermal loads through a respective control valve based on the respective thermal energy demands. The method may include evaluating a criterion corresponding to whether a flash potential is sufficient to meet the predicted demands of the plurality of loads. The method may include determining, based on the evaluation and priority data related to the thermal loads, to release steam to the first thermal load to meet the respective first thermal energy demand over releasing steam to the second thermal load to meet the respective second thermal energy demand.

[0042] The method is as follows: Discharging steam to a first heat load to satisfy a respective first heat energy demand; or releasing steam to a second heat load to only partially satisfy a respective second heat energy demand; Preventing the release of steam to the second heat load regardless of the respective second heat energy demand; or The method may include communicating a load shedding signal to a controller controlling at least a second heat load to indicate a reduced capacity to meet the second heat energy demand, whereby the controller may operate the second heat load to reduce the respective heat energy demand.

[0043] The method may include, during a refill period, heating liquid in the pressure vessel to raise the storage pressure by at least 1 MPa to a peak storage pressure of at least 2 MPa, and supplying subcooled water to the pressure vessel to reach a peak mass of water in the pressure vessel corresponding to a peak liquid level at the peak storage pressure. The duration of the refill period may be at least 100%, e.g., at least 125%, or at least 150% of the duration of the depletion period.

[0044] For example, the peak level at peak storage pressure may be 90%, or may be at least 80%.

[0045] The method may include staging a profile of water supply during the refill period so that it is front-loaded relative to a profile of heating during the refill period.

[0046] By front-loading the subcooled water supply, the temperature of the water within the pressure vessel during the refill period can be maintained relatively low (e.g., compared to a uniform feedwater profile or a back-loading feedwater profile), thereby reducing heat loss through the pressure vessel wall.

[0047] Staging the water supply and heating so that the water profile is front-loaded relative to the heating profile can include maintaining a minimum recharge flash potential (which can be a predetermined minimum flash potential or a flash potential corresponding to a forecasted demand) while the liquid level margin gradually rises to a peak mass of water, and then heating the liquid water to raise the pressure to the peak storage pressure.

[0048] The flash potential may be as defined elsewhere herein. The liquid level margin may be as defined elsewhere herein.

[0049] The flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure to sustain the release of steam to the heat load.

[0050] The liquid level margin corresponds to the amount of liquid water in the pressure vessel above the lower limit for operation of the heater upon release of the flash potential.

[0051] The method may include staging a feedwater profile relative to a heating profile to maintain a minimum recharge flash potential while increasing the amount of water in the pressure vessel to a target peak mass of water so as to progressively increase the liquid level margin during a water priority portion of the recharge period, and thereafter heating the liquid water during a flash priority portion of the recharge period to increase the storage pressure to the peak storage pressure.

[0052] The minimum recharge flash potential may be a predetermined minimum flash potential or may be a flash potential corresponding to a forecasted demand.

[0053] The minimum recharge flash potential may correspond to a predicted demand. The predicted demand may correspond to no demand for steam (e.g., may be no demand) during an idle portion of the recharge period, and the method may include supplying subcooled water during the idle portion to reduce the storage pressure below a lower limit pressure, the pressure then being increased by heat input to provide a flash potential corresponding to the non-zero demand.

[0054] The maximum flow rate of steam released during the depletion period per unit area of ​​water level in the pressure vessel is 150 kg / m 2 hours or less, for example 100 kg / m 2 hours or less, or 50 kg / m 2 The maximum rate of vapor release per unit area may be expressed as a percentage of the maximum unentrained vapor release rate (MSR) as described elsewhere herein, and may be 10% or less of the MSR, e.g., 5% or less, or 3% or less.

[0055] The method may include degassing an inlet stream of subcooled water supplied to the pressure vessel along a degassing path by conveying a degassed stream of steam from within the pressure vessel countercurrently along the degassing path. The inlet stream may be supplied to the pressure vessel over a range of storage pressures for the pressure vessel. The rate of the degassed stream of steam is varied as a function of the temperature of the inlet stream and / or the temperature difference between the inlet stream and the steam, with the goal of the inlet stream reaching a saturation temperature corresponding to the steam over the range of storage pressures. The rate may be varied by controlling a control valve for venting the degassed stream of steam and its associated entrained gases. The rate or control valve setting for controlling the rate may be determined by referencing a database of rates or control valve settings correlated with the temperature of the inlet stream and / or the temperature of the steam.

[0056] The inlet stream of subcooled water can be degassed during the depletion or recharge periods as described herein.

[0057] The peak storage pressure may be at least 2.5 MPa, such as at least 3 MPa, and / or the storage pressure may decrease during the depletion period to a value of 1.5 MPa or less, such as 1 MPa or less, or 0.8 MPa or less.

[0058] The average depleted power may be defined as the cumulative enthalpy of steam released from the pressure vessel during a depletion period divided by the duration of the depletion period. The maximum depleted power may be defined as the maximum enthalpy of steam released during any one-minute minimum power evaluation period within the depletion period divided by the minimum power evaluation period.

[0059] The method may further include heating the liquid water in the pressure vessel using a heater during a refill period during which the storage pressure increases by at least 1 MPa. The average refill power may be defined as the cumulative energy imparted to the liquid water by the heater during the refill period divided by the duration of the refill period. The maximum reheat power may be defined as the maximum power imparted to the liquid water by the heater within the refill period. The average reheat power may be less than or equal to 50% of the average depleted power, and / or the average reheat power may be less than or equal to 50% of the maximum depleted power, and / or the maximum reheat power may be less than or equal to 50% of the maximum depleted power.

[0060] The ratio of magnitude between (i) the cumulative enthalpy of steam released from the pressure vessel during the depletion period and (ii) the average reheat power of the heater during the recharge period is at least 25,000 seconds.

[0061] The method may be carried out using a thermal plant according to the second aspect of the present disclosure.

[0062] According to a second aspect, a pressure vessel for storing water containing saturated liquid water and steam at a storage pressure of 2 MPa, the pressure vessel having an outlet for releasing the steam to a heat load; an electric heater configured to heat liquid water stored in the pressure vessel to vary the storage pressure within the pressure vessel; controlling the heater to heat the liquid water in the pressure vessel to reach a peak storage pressure of saturated liquid water and steam of at least 2 MPa; controlling the control valve to selectively release steam from the outlet to the heat load in response to a heat energy demand; and releasing steam to meet the thermal energy demand so that the storage pressure is reduced by at least 1 MPa from the peak storage pressure. and a controller configured to operate the thermal storage facility.

[0063] The peak storage pressure may be at least 2.5 MPa, such as at least 3 MPa.

[0064] The steam can be selectively released from the outlet by control of the control valve, for example, the steam can be released to a heat load through the control valve. The control valve can be located at the outlet or downstream of the outlet so that steam released from the outlet passes through the control valve. In some examples described herein, the control valve can be remote from the vessel, for example, located on the condensate return line in a thermosiphon configuration (in which case the steam does not pass through the control valve).

[0065] The outlet may be in communication with the heat load to supply the discharged steam directly to the heat load without passing through an intermediate steam accumulator, or any one or more steam accumulators between the pressure vessel and the heat load may have a total volume less than the volume of the pressure vessel.

[0066] The controller may be configured to control the heater to heat liquid water in the pressure vessel independently of controlling the control valve for selectively releasing steam, thereby allowing simultaneous heating and release of steam in use, and allowing each of the heating and release of steam to occur without the other.

[0067] The controller may be configured to control the heater to heat liquid water in the pressure vessel independently of providing subcooled water to the pressure vessel, thereby allowing simultaneous heating and subcooled water supply in use, and allowing heating without simultaneous subcooled water supply.

[0068] The controller may be configured to cause the pressure vessel to supply subcooled water when the storage pressure is greater than a discharge pressure at which steam is discharged from the outlet (eg, via a control valve).

[0069] The facility may further include a water pump configured to supply subcooled water to the pressure vessel, optionally the water pump having a maximum water supply pressure that is less than the peak storage pressure.

[0070] The facility may further include a subcooled water supply vessel configured to store subcooled water for supply to the pressure vessel, wherein the ratio of the storage volume of the subcooled water supply vessel to the storage volume of the pressure vessel may be at least 5%, optionally at least 7.5% or at least 10%.

[0071] The controller may be configured to selectively operate in an extended depletion mode that allows steam release so that the liquid water level in the pressure vessel falls below a minimum liquid level for operation of the heater during the depletion period, and to prevent heating by the heater when the liquid level is below the minimum liquid level for operation of the heater. The controller may be configured to selectively operate the heater in a heating depletion mode that prevents steam release that would cause the liquid level to fall below the minimum liquid level, and to enable heating by the heater when the liquid level is below the minimum liquid level. The heat load may include a heat exchanger positioned relative to the pressure vessel to define a thermosiphon between the pressure vessel and the heat exchanger, whereby released steam condensing in the heat exchanger forms a column of subcooled water that is returned to a condensate inlet at a lower part of the pressure vessel. The heat load may be part of a facility.

[0072] The heat exchanger may be located above the pressure vessel, and the controller may be configured to discharge steam into the heat exchanger at a discharge pressure selected to provide sufficient head of water to return subcooled water to the pressure vessel under the action of gravity given the relative positions of the heat exchanger. The controller may be configured to control heat exchange in the heat exchanger such that the water is subcooled by at least 10°C.

[0073] The equipment may include a level sensor configured to provide a controller with a level signal corresponding to the level of water in the pressure vessel, and / or a storage pressure sensor configured to provide a controller with a pressure signal corresponding to the pressure of the water in the pressure vessel, and / or a storage temperature signal configured to provide a controller with a temperature signal corresponding to the temperature of the water in the pressure vessel, and / or a discharge pressure sensor configured to provide a controller with a pressure signal corresponding to the pressure at which steam is discharged from an outlet of the pressure vessel (via a respective control valve), and / or a discharge flow meter configured to provide a controller with a flow signal corresponding to the flow rate of steam downstream of the outlet (e.g., downstream of a respective control valve), and / or an injection flow meter configured to provide a flow signal corresponding to the flow rate of subcooled water supplied to the pressure vessel.

[0074] The flash potential may correspond to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a lower pressure limit to maintain the release of steam to the heat load.

[0075] The liquid level margin may correspond to the amount of liquid water in the pressure vessel above a lower limit for operation of the heater upon release of the flash potential.

[0076] The controller may be configured to select whether to operate the thermal storage facility in recharge mode or depletion mode based on predetermined settings, such as time-dependent settings, based on user input, or based on a predicted demand profile and / or a predicted power output profile of the heater. In depletion mode, the controller may be configured to evaluate a criterion corresponding to whether the level margin is positive or negative, and if the evaluation corresponds to the level margin being negative, to supply subcooled water to the pressure vessel to increase the level margin and reduce the flash potential. In recharge mode, the controller may be configured to (i) maintain a predetermined flash potential or a minimum recharge flash potential corresponding to the predicted demand while the level margin and the amount of water in the pressure vessel increase to a target mass of water corresponding to a target liquid level at the peak storage pressure, and (ii) thereafter stage a water supply profile relative to the heating profile to heat the liquid water to increase the storage pressure to the peak storage pressure.

[0077] The useful flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before either (i) the storage pressure reaches a lower limit for maintaining the release of steam to the heat load, or (ii) the amount of liquid water in the pressure vessel reaches a lower limit. The supply of subcooled water in the depletion mode to increase the level margin and reduce the flash potential when the assessment corresponds to a negative level margin may increase the useful flash potential.

[0078] The criteria may correspond to whether the liquid level margin is positive or negative, based on the release of an instantaneous flash potential, or based on the release of a predicted flash potential.

[0079] The controller may be configured to evaluate the criteria in the depletion mode and / or stage the feedwater profile in the refill mode by determining a flash potential and determining a level margin based on the release of the flash potential (e.g., instantaneous flash potential or predicted flash potential). The instantaneous flash potential may be a function of the current storage pressure and water level in the pressure vessel and the floor pressure. In other cases, the controller may be configured to evaluate the criteria and / or stage the feedwater profile in the refill without directly determining the flash potential and level margin, for example, based on a level signal received from a level sensor as described elsewhere herein.

[0080] The flash potential may be a predicted flash potential, in which case the controller may be configured to predict the flash potential as a function of predicted demand over a period of time and / or predicted power output of the heater. The level margin may be a predicted level margin, in which case the controller may be configured to predict the level margin based on a release of the predicted flash potential over the period of time.

[0081] The criteria evaluated may correspond to whether a predicted level margin is positive or negative based on the release of the predicted flash potential over the time period. The controller may be configured to evaluate the criteria by determining a predicted flash potential, determining a predicted level margin based on the release of the predicted flash potential over the time period, and determining whether the predicted level margin is positive or negative.

[0082] The controller may be configured to determine a predicted flash potential based on the current liquid level and storage pressure, and based on a predicted demand and / or a predicted power output of the heater over the time period. The demand may be, for example, a predicted thermal energy demand or a predicted steam demand.

[0083] The predicted power output profile of the heater may correspond to a predicted power budget for heating using the heater.

[0084] The controller may be configured to determine the predicted demand based on historical demand data, such as historical steam or heat demand data for the facility, and / or the controller may be configured to determine the predicted demand based on forecasted weather conditions, and / or the controller may be configured to determine the predicted power output of the heater based on historical power capacity data for the heater, and / or the controller may be configured to determine the predicted power output of the heater based on forecasted weather conditions.

[0085] In the refill mode, if the forecasted demand during the idle portion of the refill period corresponds to no demand for steam, the controller may be configured to cause subcooled water to be supplied to reduce the storage pressure below a lower pressure limit during the idle portion. The controller may then be configured to increase the storage pressure by heating liquid water in the pressure vessel to provide a flash potential corresponding to the non-zero demand.

[0086] The controller is 150 kg / m 2 hours or less, for example 100 kg / m 2 hours or less, or 50 kg / m 2 The control valve may be configured to control the steam to be selectively released at a maximum rate per unit area of ​​the water level (i.e., surface) within the pressure vessel that is equal to or less than 10% of the MRS, e.g., 5% or less, or 3% or less, as described elsewhere herein.

[0087] The pressure vessel may be configured to release steam to a plurality of thermal loads via respective control valves, including a first thermal load and a second thermal load. The controller may be configured to evaluate a criterion corresponding to whether the flash potential is sufficient to meet the forecasted demand of the plurality of loads. The controller may be configured to operate in a priority release mode, responsive to a result of the evaluation, where the controller evaluates priority data specifying relative priorities of the thermal loads and controls the selective release of steam to meet the thermal energy demand of a relatively higher priority thermal load over controlling the selective release of steam to meet the thermal energy demand of a relatively lower priority thermal load.

[0088] The results of the assessment may indicate that the flash potential is insufficient to meet the projected demand.

[0089] In the priority release mode, the controller may be configured to control the control valves associated with the relatively higher priority loads to release steam to meet their respective thermal energy demands (e.g., determined based on the respective demand signals received by the controller), (i) control the control valves associated with the relatively lower priority loads to release steam to only partially meet their respective thermal energy demands (e.g., determined based on the respective demand signals received by the controller), or (ii) control the control valves associated with the relatively lower priority loads to prevent the release of steam to the loads, and / or (iii) send load shedding signals to the controllers of the relatively lower priority thermal loads to indicate reduced capacity to meet their respective thermal energy demands.

[0090] The installation may be configured to supply water in the form of steam discharged from the pressure vessel to the heat load in an open configuration, whereby the heat load consumes the supplied water as steam without a corresponding return of water as condensate. The controller may be configured to discharge steam to the heat load at a minimum discharge pressure of between 0.5 MPa and 1.0 MPa, or the heat load is configured to receive discharged steam at a minimum discharge pressure of between 0.5 MPa and 1.0 MPa.

[0091] The equipment may be configured to supply steam discharged from the pressure vessel to at least two heat loads. The equipment may be configured to supply water to one of the heat loads in the form of steam discharged from the pressure vessel in an open configuration, whereby the water is contacted with a foreign process fluid or foreign matter and / or discharged from the heat load without a corresponding return of water as condensate. Additionally or alternatively, the equipment may be configured to supply water in the form of steam discharged from the pressure vessel to one of the heat loads in a closed loop, whereby the water is at least partially returned to the pressure vessel as subcooled water, for example via a subcooled water supply vessel.

[0092] In a closed loop, the water (supplied as steam) may be returned at least partially to the pressure vessel as subcooled water without contact with any extraneous process fluids or foreign matter.

[0093] The pressure vessel may include a degasser configured to receive an inlet flow of subcooled water along a degassing path and to direct a degassed stream of steam from within the pressure vessel countercurrently along the degassing path. The controller may be configured to vary the rate of the degassed stream of steam as a function of the temperature of the inlet flow and / or the temperature of the steam, with the goal of the inlet flow reaching a saturation temperature corresponding to the steam along the degassing path over a range of storage pressures. The controller may be configured to vary the rate by controlling a control valve for venting the degassed stream of steam and its associated entrained gases from the degasser. The controller may be configured to control the rate or a control valve setting for controlling the rate by referencing a database of rates or control valve settings correlated with the temperature of the inlet flow and / or the temperature of the steam.

[0094] The heater may be installed within the pressure vessel such that the lower liquid level for operation of the heater corresponds to a liquid fraction of water within the pressure vessel of 60% or less, e.g., 50% or less, 40% or less, or 30% or less.

[0095] According to a third aspect, a method for heat storage and supply is disclosed which corresponds to the first aspect and differs therefrom with respect to the peak storage pressure and the reduction in pressure during the depletion period (and other relevant numerical definitions as described below). A description of how the definitions of the third aspect may differ from the first aspect is defined below. In all other respects, except where mutually inconsistent, the features described with respect to the first aspect are also applicable to the third aspect mutatis mutandis.

[0096] According to a third aspect, the heater is controlled to raise the storage pressure to a peak storage pressure of at least 0.5 MPa, such as at least 1 MPa, or at least 2 MPa. The selective release of steam is such that, during the depletion period, the storage pressure drops by a depletion pressure differential that is at least 50% of the peak storage pressure.

[0097] According to a third aspect, the depletion period may be described as a period during which the mass and energy (or enthalpy) fluctuations of the water in the pressure vessel are such that the storage pressure drops by the depletion pressure difference.

[0098] The definition for the recharge period in the first aspect relates to an increase in storage pressure. The corresponding definition for the third aspect corresponds to a recharge pressure differential that is at least 50% of the peak storage pressure. Specifically, the method may include operating the heater without simultaneously supplying subcooled water to the pressure vessel during part or all of the depletion period and / or part or all of the recharge period during which the storage pressure increases to the peak storage pressure by the recharge pressure differential, the recharge pressure differential being at least 50% of the peak storage pressure. As noted above, the peak storage pressure is at least 0.5 MPa, e.g., at least 1 MPa, or at least 2 MPa.

[0099] According to a third aspect, a refill period may be described as a period of time during which the mass and energy (or enthalpy) fluctuations of the water in the pressure vessel are such that the storage pressure rises to the peak storage pressure by the refill pressure differential.

[0100] According to a third aspect, the method may include, during a refill period, heating liquid in the pressure vessel to raise the storage pressure by a refill pressure differential to the peak storage pressure, and supplying subcooled water to the pressure vessel to reach a peak mass of water in the pressure vessel corresponding to a peak liquid level at the peak storage pressure. The duration of the refill period may be at least 100% of the duration of the depletion period, e.g., at least 125%, or at least 150%.

[0101] The method according to the third aspect may be carried out using a thermal plant according to the second aspect or a thermal energy storage and supply device according to the fourth aspect.

[0102] According to a fourth aspect, there is provided a thermal energy storage and supply device (e.g., installation) that corresponds to the installation of the second aspect and differs from the second aspect with respect to peak storage pressure and pressure reduction during depletion periods (and other relevant numerical definitions as described below). A description of how the definitions of the fourth aspect may differ from the second aspect is defined below. In all other respects, except where inconsistent with each other, features described in relation to any of the first, second and third aspects are applicable to the fourth aspect mutatis mutandis.

[0103] According to a fourth aspect, a thermal energy storage and delivery device comprises: a pressure vessel for storing water comprising saturated liquid water and steam at a storage pressure of at least 0.5 MPa, e.g., at least 1 MPa or at least 2 MPa, the pressure vessel having an outlet for releasing the steam to a heat load; an electric heater configured to heat liquid water stored in the pressure vessel to vary the storage pressure within the pressure vessel; controlling the heater to heat the liquid water in the pressure vessel to reach a peak storage pressure of saturated liquid water and steam of at least 0.5 MPa, e.g., at least 1 MPa or at least 2 MPa; controlling the control valve to selectively release steam from the outlet to the heat load in response to a heat energy demand; and releasing steam to meet the thermal energy demand such that the storage pressure is reduced from the peak storage pressure by at least 50% of the peak storage pressure. and a controller configured to operate the thermal storage device.

[0104] The definition of discharge pressure is provided in connection with the second aspect. The thermal energy storage and delivery device according to the fourth aspect is configured to discharge steam at a variable discharge pressure (which may be equal to or lower than the current storage pressure). The controller described herein may include a processor. The controller and / or processor may include any suitable circuitry for performing the methods described herein and illustrated in the drawings. The controller or processor may include at least one application-specific integrated circuit (ASIC), at least one field-programmable gate array (FPGA), single or multi-processor architecture, sequential (von Neumann) / parallel architecture, at least one programmable logic controller (PLC), at least one microprocessor, at least one microcontroller, and / or a central processing unit (CPU) for performing the methods and / or described functions for which the controller or processor is configured.

[0105] The controller or processor may include or be in communication with one or more memories that store the data described herein and / or store machine-readable instructions (e.g., software) for implementing the processes and functions described herein (e.g., determining parameters and executing control routines).

[0106] The memory may be any suitable non-transitory computer-readable storage medium, one or more data storage devices, and may include a hard disk and / or solid-state memory (such as flash memory). In some examples, the computer-readable instructions may be transferred to the memory via wireless signals or via wired signals. The memory may be permanent, non-removable memory, or may be removable memory (such as a Universal Serial Bus (USB) flash drive). The memory may store a computer program including computer-readable instructions that, when read by a processor or controller, cause the method described herein and / or illustrated in the figures to be performed. The computer program may be software, or firmware, or a combination of software and firmware.

[0107] Except where mutually inconsistent, features described in relation to any one of the above embodiments are applicable to any other embodiment mutatis mutandis, and, except where mutually inconsistent, any feature described herein is applicable to any embodiment and / or can be combined with any other feature described herein.

[0108] The present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0109] [Figure 1] FIG. 1 is a schematic diagram of an exemplary thermal energy storage and supply facility for an industrial plant. [Figure 2] FIG. 2 illustrates an exemplary profile of steam demand. [Figure 3] 3a, 3b, 4a and 4b show exemplary profiles of operating conditions for a thermal energy storage and supply facility. [Figure 4] 3a, 3b, 4a and 4b show exemplary profiles of operating conditions for a thermal energy storage and supply facility. [Figure 5] FIG. 5 is a flow diagram of a method for controlling vapor emissions. [Figure 6] FIG. 6 is a flow diagram of a method for controlling heating. [Figure 7] 7a-7e are diagrams showing various liquid levels within a pressure vessel as a reference for illustrating the concept of flash potential. [Figure 8] 1 is a flow diagram illustrating a method for controlling the supply of subcooled water to a pressure vessel. [Figure 9] FIG. 10 shows a schematic diagram of a further example of a thermal energy storage and supply facility. DETAILED DESCRIPTION OF THE INVENTION

[0110] FIG. 1 shows a schematic representation of an industrial plant 10 as an example of a facility having at least one heat load equipped with a thermal energy storage and supply facility 100 .

[0111] The industrial plant 10 has first and second plant heat loads 30, 40, which in this particular embodiment are a room heating system and a sterilization system, respectively, but in alternative embodiments can be any system requiring thermal energy. The first plant heat load 30 (room heating system) is configured to receive thermal energy (heat) via a heat transfer circuit 132 extending between the facility 100 and the industrial plant 10, rather than receiving steam directly from the facility 100 as a process fluid for the heat load, as described in more detail below. In contrast, the second plant heat load 40 (sterilization system) is configured to receive steam discharged from the facility 100 directly as its own process fluid, for use, for example, in sterilizing an item. Steam consumed by the second plant heat load 40 (i.e., condensed to release latent heat) is discharged to a drain 50, but in alternative embodiments, may be returned to the water supply of the facility 100 as condensate.

[0112] In this example, the plant thermal loads 30, 40 are operated independently of the facility 100 and are operatively coupled to the facility's controller 200 (as described below) to communicate their respective thermal energy demands. The thermal energy demands may be communicated in any suitable form, for example, as a demand signal corresponding to a related parameter such as thermal power requirement (e.g., in kW), steam demand (e.g., in kg / sec), or a percentage of any type of predetermined maximum demand (e.g., coding "0.5" that is interpreted by the controller as a percentage of a maximum demand such as 300 kW, resulting in a demand of 150 kW).

[0113] The thermal storage and heat supply system 100 includes a pressure vessel 110 for storing water at high pressure and temperature. For completeness, the term “water” is used in this disclosure to refer to water in any phase, whereas the terms “liquid water” and “steam” are used to refer to water in the liquid and gas phases, respectively. The pressure vessel 110 is configured to store saturated liquid water and steam at a storage pressure of at least 2 MPa, e.g., at least 3 MPa or at least 4 MPa, or between 2 MPa and 6 MPa. In certain embodiments described below, the pressure vessel 110 is used to store water up to a target peak storage pressure of approximately 3 MPa (e.g., 3.101 MPa, corresponding to 30 bar gauge pressure for an installation at atmospheric pressure). It should be understood that these values ​​represent minimum requirements for the pressure vessel, and the pressure vessel can, of course, store water at lower storage pressures. As described elsewhere herein, in alternative embodiments, the pressure vessel may be configured to store saturated liquid water and steam at lower storage pressures (with lower minimum requirements depending on storage capacity), e.g., at least 0.5 MPa or at least 1 MPa.

[0114] The pressure vessel 110 includes an electric heater 112 configured to heat the liquid water stored in the pressure vessel to vary the storage pressure within the pressure vessel. The heater 112 is coupled to a power source 113, which may include a local power source, such as a renewable energy source (e.g., a solar or wind power source) and / or a generator (e.g., coupled to an engine such as a gas turbine). The power source may include a local power source and / or a grid connection to supply power from a non-local power grid (e.g., a national grid). The local power source may be a microgrid. A microgrid can be defined as a local power distribution grid consisting of multiple energy sources (e.g., electrical energy sources) that can operate independently of, and optionally connect to, a non-local power grid to power a dedicated local geographic area. A microgrid has defined boundaries and can function as a single, controllable entity. In contrast, a non-local power grid is understood to include multiple sources that serve a larger geographic area (e.g., a state) and where the entire grid is not controlled as a single entity. When the facility's power source includes (i) a local power source that is a microgrid and (ii) a grid connection to a non-local power grid, the grid connection can be a microgrid connection to the non-local power grid. While those skilled in the art will appreciate the differences in scale and control between a microgrid and a non-local power grid, when the power source includes (i) a local power source that includes a microgrid and (ii) a grid connection to a non-local power grid, it can be said that the generating capacity of the microgrid (when operating independently of any non-local power grid) is less than the generating capacity of the non-local power grid. For example, it may be 10% or less, 1% or less, or 0.1% or less of the generating capacity of the non-local power grid.

[0115] The pressure vessel 110 can provide energy storage for the microgrid in the form of thermal energy storage that can be delivered to local thermal loads.

[0116] In this embodiment, heater 112 is located at the bottom of pressure vessel 110 so that the lower limit of the water level within the pressure vessel, submerging the heater (or at least each heating element of the heater), is approximately 33% of the diameter of the pressure vessel, corresponding to a liquid fraction of approximately 30%. In other embodiments, the lower limit of the water level may be higher or lower, for example, between 20% and 70%, e.g., 20%-60%, or 25%-50%. Water level 114 within the pressure vessel is the interface between liquid water and a gas, such as saturated liquid water and steam.

[0117] Pressure vessel 110 includes sensor 210 coupled to controller 200 and configured to transmit a storage pressure signal to controller 200 corresponding to the storage pressure of the water in pressure vessel 110. Of course, when the vessel is saturated with water, such that it contains liquid water and steam, the pressure directly corresponds to the respective saturation temperatures. Accordingly, a suitable sensor may be a pressure sensor configured to monitor the pressure or a temperature sensor configured to monitor the temperature. In this particular example, sensor 210 is a pressure sensor configured to monitor the storage pressure and transmit a storage pressure signal to controller 200 encoding the monitored pressure.

[0118] Pressure vessel 110 further comprises a liquid level sensor 214, which may be of any suitable type known in the art, for example, a capacitance probe liquid level sensor having an elongated probe extending across the sensor's monitoring range and configured to output a continuously variable liquid level signal (e.g., in mA) that, with appropriate calibration in the liquid level sensor 214 or the controller, can be processed to determine the liquid level of water in the pressure vessel across the monitoring range. In other examples, the liquid level sensor may include multiple sensors, for example, each sensor configured to determine whether the liquid level is above or below a respective height / level within the pressure vessel such that the liquid level is determined as a discrete output quantity. Liquid level sensor 214 is configured to communicate a liquid level signal corresponding to the liquid level to controller 200.

[0119] The pressure vessel 110 includes a discharge outlet 116 for releasing steam from the pressure vessel via a control valve operable to reduce the steam to a lower downstream pressure (discharge pressure). In this example, the discharge outlet is located within the upper portion of the pressure vessel above the maximum operating level of the pressure vessel. The maximum operating level can be a target peak level (as described further below) or may be slightly higher to accommodate unintended operation above the target peak level. For example, the target peak level may correspond to a target peak liquid fraction of 90% of the vessel's volume. In this example, there are first and second discharge control valves 216, 217 associated with respective heat loads, each discharge control valve being downstream of the discharge outlet 116 and connected to the discharge outlet 116 by a discharge line 101, as described in more detail below. However, in other examples, a single or common discharge control valve may be downstream of the discharge outlet 116 (e.g., at location 215 marked with a dashed line in FIG. 1 ) or may be integrated with the discharge outlet 116 of the pressure vessel 110. Each discharge control valve 216, 217 is operably coupled to the controller 200 to receive a respective discharge control signal for operating the valve.

[0120] The pressure vessel 110 further includes a degasser 120, which may be an integrated degasser (i.e., integrated with the pressure vessel 110) as shown in FIG. 1 . The degasser is configured to remove oxygen and other dissolved components, such as carbon dioxide, from a supply of liquid water provided to the pressure vessel. The degasser 120 may be of any suitable type as known in the art, but in this example is shown schematically as having a configuration including multiple degassing trays vertically distributed throughout the degasser. The degasser 120 defines a degassing path 122 (in this example, a convoluted path through tray 121) for the inlet stream of water and is configured to direct a degassed stream of vapor from within the pressure vessel along the degassing path countercurrent to the inlet stream. Passing the degassing path raises the inlet stream of water to the saturation temperature of the vessel, and dissolved substances, such as oxygen and carbon dioxide, are removed from the inlet stream that exits the degassing path along with the degassed stream. The degassed flow can be discharged through a degassing outlet with a degasser outlet control valve 124, as shown in Figure 1. The degasser outlet control valve 124 is operably coupled to the controller 200 to receive a degassing flow control signal for operating the valve.

[0121] The inlet flow to the degasser is controlled to selectively supply water from a water supply to the pressure vessel 110 in response to demand, as described in more detail below. In this embodiment, the inlet flow is selectively directed to the degasser by an inlet pump 122. The inlet pump 122 is operably coupled to the controller 200 to receive a water feed signal, whereby the inlet pump 122 is controlled to direct the inlet flow to the pressure vessel 110 and the degasser 120 at a variable inlet flow rate and at an appropriate pressure. In an alternative embodiment, the inlet flow may be selectively enabled to flow to the degasser by an inlet control valve that controls the inlet flow rate based on the water feed signal received from the controller 200; the inlet control valve may be downstream of the inlet pump 122 that pressurizes the water, as described above, or may be coupled to a supply without an intermediate pump, or may pressurize the water.

[0122] In an alternative embodiment, the inlet stream of water may be supplied directly from the water source to pressure vessel 110 (i.e., without passing through a degasser, which degasses the inlet stream as it enters the pressure vessel), with the inlet stream being controlled by controller 200 via the inlet pump and / or inlet control valve, as described above. In an installation that includes a degasser, there may be a bypass line between the water source and the pressure vessel that bypasses the degasser, such as a bypass line extending from the inlet pump or from a valve mechanism (e.g., a three-way valve) downstream of the inlet pump, so that the inlet stream of water can be selectively supplied to the pressure vessel either through the degasser or bypassing the degasser. Such an arrangement may be advantageous when each water source is a water supply container to which water is returned in a closed loop (as described below) from within the installation, since the degasser can be used for the initial supply of water to the pressure vessel that may require degassing, and then the degasser can be bypassed if it is determined (or assumed) that the water supply container contains water that has already been degassed.

[0123] Steam storage and delivery facilities contemplated by the present disclosure can have an open configuration or a closed loop for delivery of steam to a heat load.

[0124] An open configuration is considered to be one in which the water supplied to the respective heat load (supplied as steam) is brought into contact with extraneous process fluids or materials and / or discharged from the heat load without a corresponding return of water as condensate. The expression "extraneous process fluids or materials" is intended to mean substances that can contaminate the water supplied to the heat load. For example, if water (supplied as steam) comes into direct contact with the heat load or another fluid downstream, the water can mix with that fluid. Similarly, if steam is used to heat extraneous materials, such as items to be sterilized in a sterilizer or heated and dried in a steam oven, the water (which may be steam) can be contaminated by materials from those items. Another definition of an open configuration would be one in which the water is not contained in a closed loop (a closed loop configured to recirculate the water to the pressure vessel without intervening treatment).

[0125] A closed loop can be considered as a configuration in which some or all of the water supplied to each heat load is returned as subcooled water to the pressure vessel, optionally via a subcooled water supply vessel (which can provide a discontinuous supply of water to the pressure vessel). The closed loop substantially prevents contamination of the water, such that the water does not come into contact with foreign process fluids or materials.

[0126] 1 is configured to supply steam to a first heat load 130, which is a heat exchanger in a closed-loop configuration, via a distribution line 102 downstream of a first discharge control valve 216. Water supplied (as steam) to the first heat load 130 is returned to the pressure vessel 110 via a water supply vessel 150, as described below. The heat exchanger 130 is thermally coupled to the first plant heat load 30 of the industrial plant 10 via a process fluid circuit 132, such that the steam supplied to the heat exchanger 130 does not directly contact the process fluid in the process fluid circuit. The controller 200 is configured to operate a heat transfer pump 133 associated with the heat transfer circuit 132 upon selective discharge of steam to the heat exchanger 130 for heat transfer. In other examples, process circuit 132 may not be necessary, and distribution line 102 may extend directly into first plant heat load 30 (still without directly contacting the process fluid of first plant heat load 30) before returning to feedwater reservoir 150. Controller 200 is configured to operate first discharge control valve 216 based on a demand signal received from first plant heat load 30 to control the flow rate of steam through heat exchanger 130. In this example, the flow rate is monitored by a first flow meter 218 positioned along distribution line 102, which provides a first flow rate signal to controller 200, and controller 200 may control first discharge control valve 216 based on the monitored flow rate to meet the thermal energy demand and / or based on other parameters, such as pressure and temperature, that may be monitored by additional sensors along distribution line 102.

[0127] The water supply vessel 150 has a return inlet for receiving return water from the first heat load 130 (heat exchanger 130) and a source inlet for receiving water from an external water supply (such as treated city water or the condensate recovery system of the industrial plant 10). The water supply vessel 150 has an outlet configured to supply water to the pressure vessel 110. In this example, the outlet supplies water to the pressure vessel 110 via the injection pump 122 and the degasser 120, although, as noted above, in other examples, the water may be supplied to the pressure vessel 110 through a bypass line.

[0128] The illustrated facility 100 is further configured to supply steam to a second heat load, which in the open configuration is a sterilizer system 40 (second plant heat load 40) as described above. The steam is supplied via a distribution line 103 downstream of a second discharge control valve 217. The controller 200 is configured to operate the second discharge control valve 217 based on a demand signal received from the second plant heat load 40 to control the flow of steam to the second plant heat load 40. It should be understood that the sterilizer 40 is representative of an industrial plant heat load, and that in practice there may be multiple heat loads configured to be supplied with steam by an industrial plant steam network that delivers steam to each individual load. For purposes of this disclosure, such a network and multiple loads may be considered equivalent to a single second heat load 40 with an associated total steam demand.

[0129] In this example, the flow rate to the second heat load is monitored by a second flow meter 219 located along the distribution line 103, which provides a second flow rate signal to the controller 200, which can control the second discharge control valve 217 based on the monitored flow rate to meet the heat energy demand and / or based on other parameters such as pressure and temperature that can be monitored by additional sensors along the distribution line 103. In this example, the second plant heat load 40 is a sterilizer in which steam is supplied in an open configuration for contact with foreign matter in the second heat load (i.e., items placed in the sterilizer for sterilization).

[0130] 1, the water supplied to the sterilizer 40 (supplied as steam) is discharged as condensate to the drain 50. In an alternative embodiment, the water may be treated (e.g., by a water treatment device such as a filter device and / or a reverse osmosis device) and then supplied to the water supply vessel 150, which would also constitute an open configuration as defined herein.

[0131] In this embodiment, the supplywater vessel 150 has a relatively large volume as a proportion of the storage volume of the pressure vessel 110 compared to previously considered steam supply systems. In this particular embodiment, the supplywater vessel 150 is sized to receive condensate corresponding to all of the steam released by reducing the water stored in the pressure vessel under peak conditions (e.g., a peak storage pressure of 3.101 MPa and a peak liquid level of 0.9 liquid fraction) to a lower pressure of 0.9101 MPa (8 bar gauge). This corresponds to a supplywater vessel having a volume of approximately 11.5% of the pressure vessel volume (corresponding to storage of subcooled water at 85°C at atmospheric pressure (0.101 MPa)). In other embodiments, this ratio may be higher or lower and is selected depending on the intended use. For example, a higher peak storage pressure may result in a larger ratio, and a lower peak storage pressure may result in a smaller ratio. Also, less water may be recirculated to the supplywater vessel when it is anticipated that a significant proportion of steam may be released to the heat load in the open configuration. In previously considered steam supply systems, there is typically a continuous water supply to each pressure vessel, resulting in such systems having a water supply vessel that is quite small relative to the size of the pressure vessel (e.g., a boiler or accumulator). In contrast, as will become apparent from the following description, the thermal energy storage and supply systems disclosed herein can be operated to discharge steam from the pressure vessel without necessarily requiring simultaneous water replenishment, with water being supplied at a later time when there is an opportunity to recharge the pressure vessel. Specifically, the mass of subcooled water supplied to the vessel during a depletion period can be relatively low compared to the mass of steam released during the depletion period, e.g., 50% or less, or 25% or less, 10% or less, or 5% or less. As discussed in more detail below, this mass may even be zero if thermal energy demands are met without requiring the addition of subcooled water to maintain a sustainable liquid level within the pressure vessel.

[0132] In use, the facility 100 stores and supplies thermal energy to a heat load. By heating water contained in the pressure vessel 110 to a storage pressure significantly higher than that required by the respective heat load, a significant reserve of thermal energy can be stored in the pressure vessel 110. Steam can then be generated (flashed) to supply the heat load by reducing the storage pressure in response to demand. This system is particularly suitable for use with heat loads that have highly variable heat energy demands or that require large amounts of energy for relatively short periods of time (e.g., during peak facility operating hours) with significant periods of low demand in between (e.g., overnight).

[0133] FIG. 2 shows an example plot of thermal energy demand (specifically, steam demand) for industrial plant 10. The thin dashed line labeled "Heating Demand" corresponds to the steam demand of heating system 30, which receives heat via a steam supply to heat exchanger 130. The steam demand is in kg / hr and corresponds to the steam supplied to heat exchanger 130 in a closed-loop configuration. The coarse dashed line labeled "Sterilizer Demand" corresponds to the steam demand of sterilizer 40, which receives steam directly from facility 100 in an open configuration. The solid line is the sum of the respective demands. As shown in FIG. 2, there is a relatively short period of time that contains the majority of the demand, from approximately 08:00 (8:00 AM) to 16:00 (4:00 PM), that is primarily driven by the sterilizer demand. The remaining time (nighttime) is relatively low demand.

[0134] The system is operated to store a significant amount of reserve thermal energy in the pressure vessel 110, which can be released during a depletion period 302 (shown above the plot along the x-axis of time) and then re-stored during a recharge period 304.

[0135] The expression "flash potential" as used herein corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a lower limit pressure for maintaining the release of steam to the heat load. When steam is supplied to a heat load in an open configuration, the associated lower limit pressure is a discharge pressure sufficient to maintain the steam flow received by the heat load at its minimum delivery pressure, which can be fixed or variable (the discharge pressure is typically about 0.1 MPa greater than the delivery pressure). If the delivery pressure is variable, it can be controlled independently of the steam plant. In the example plant 100 of FIG. 1, there is a pressure sensor 240 for monitoring the delivery pressure associated with the second heat load, operably coupled to the controller 200 to provide a delivery pressure signal to the controller 200, and the controller controls the respective control valve to release steam at a corresponding delivery pressure (e.g., a fixed amount above the delivery pressure). Although pressure sensor 240 is shown external to industrial plant 10 (i.e., outside the dashed line), in an alternative embodiment, it may be replaced by a pressure sensor installed within industrial plant 10 but remaining operably coupled to controller 200 to monitor the delivery pressure associated with second heat load 40 or the steam network of industrial plant 10 to which second heat load 40 belongs. For example, the delivery pressure of the heat load network may be set at 7 bar gauge (8.101 MPa) and the associated discharge pressure may be 8 bar gauge (9.101 MPa).

[0136] When steam is supplied to heat loads in a closed loop, the pressure floor may be variable and may depend on the flow rate required to meet the thermal energy demand of each heat load. For example, the pressure floor of a closed loop system may be atmospheric pressure (or lower). This pressure floor may be limited only by the associated saturation temperature and a flow rate high enough to maintain heat transferred to each load to meet its thermal energy demand.

[0137] When steam is supplied to the heat load in both open and closed loop configurations, the lower limit pressure for assessing flash potential is the highest of the respective lower limit pressures of the individual loads.

[0138] In this example, the lower pressure limit is the discharge pressure (8 bar gauge, 9.101 MPa) which corresponds to the delivery pressure (7 bar gauge, 8.101 MPa) of the second heat load.

[0139] The expression "level margin" corresponds to the amount of liquid water in the pressure vessel above the minimum amount for continued operation of the heater upon release of the flash potential. Thus, the level margin is positive if the release of the flash potential will leave more liquid water than the minimum amount, and negative if there will be less than the minimum amount.

[0140] Thus, the flash potential at any particular instant corresponds to the maximum demand that can be met. A negative liquid level margin associated with that flash potential indicates that the amount of liquid in the pressure vessel is a limiting factor in the ability to meet that demand while keeping the heater running, while a positive liquid level margin indicates that the demand (e.g., steam demand) corresponding to the flash potential can be met while keeping the heater running.

[0141] The flash potential can be readily calculated by one skilled in the art. The flash potential is proportional to the amount of liquid water in the pressure vessel and the difference in enthalpy of liquid water at the storage pressure and the lower pressure limit (which roughly corresponds to the pressure difference). The flash potential is inversely proportional to the enthalpy of evaporation at the lower pressure limit. Similarly, the level margin can be readily calculated based on the quality of a known saturated mass of water at a given pressure. However, both quantities can be indirectly monitored or indirectly controlled by monitoring related quantities. For example, as described in more detail below with reference to Figures 7a-7e, the flash potential and level margin for a given storage pressure and lower pressure limit can be determined based on the liquid level. Thus, operating the equipment by reference to the liquid level (e.g., by evaluating a level-based criterion) can correspond to operating the equipment to control the flash potential and / or the level margin as described herein. Except where explicit reference is made to calculating flash potential, level margin or related quantities, flash potential-based and / or level margin-based control as referred to herein can be performed without directly calculating flash potential and / or level margin, and a suitable implementation of control is based on monitored level and reservoir pressure, for example, by referencing a database of level thresholds correlated to reservoir pressure.

[0142] Storage pressure and liquid level are important quantities in the operation of equipment for storing and distributing thermal energy from a pressure vessel.

[0143] The basic variables affecting the conditions within a pressure vessel are (i) the release of steam by flashing, (ii) the addition of subcooled water, and (iii) heating using a heating element, each of which can occur alone or in combination with one another. (i) Flashing steam from the pressure vessel is achieved by reducing the storage pressure, which alone reduces the liquid level in the vessel. (ii) Adding subcooled water to the vessel alone reduces the storage pressure and raises the liquid level. (iii) Heating alone increases the storage pressure and raises the liquid level.

[0144] References herein to supplying subcooled water refer to water that is subcooled relative to its saturation temperature at the pressure vessel's storage pressure. As described elsewhere herein, the inlet stream of water to the pressure vessel may be heated to its saturation temperature as the inlet stream enters the pressure vessel, e.g., in degasser 120. However, such heating uses thermal energy from within the pressure vessel, and therefore, referring to the inlet condition as subcooled by reference to the condition prior to entry into the pressure vessel is deemed appropriate to aid in understanding the energy balance and the effect of supplying (subcooled) water to the pressure vessel.

[0145] Figures 3a and 3b are plots of operating conditions during an exemplary 24-hour operating cycle of the system 100, including depletion and recharge periods. Figure 3a shows trends in storage pressure (within the pressure vessel) and liquid level. Figure 3b shows trends in flash potential and liquid level margin.

[0146] Figures 3a and 3b are based on a simplified set of operating variables that includes a simplified profile of thermal energy demand relative to that shown in Figure 2. The exemplary operating variables include a steady maximum steam demand of approximately 330 kg / hr for the duration of the depletion period, which lasts approximately 6.5 hours, and no demand during the recharge period, which lasts the remainder of the 24 hour cycle.

[0147] During the depletion period, no power is available for use by the heater, but power for heating is available at a constant rate of 120 kW throughout the recharge period. Such a scenario may arise in practice, for example, if power is obtained from a local source (such as a renewable energy source) and is used for other purposes during the depletion period (e.g., during the day) and is only available for heating during the recharge period (e.g., at night).

[0148] Again, for simplicity, the plots in Figures 3 and 4 are shown with times starting from the start of the depletion period. The initial conditions for the pressure vessel at the start of the 24-hour cycle (i.e., the start of the depletion period) are a peak storage pressure of 30 bar gauge (3101 kPa) and a peak liquid moisture content of 90%. The lower pressure limit to maintain vapor release to the heat load is 8 bar gauge (9101 kPa), which corresponds to the delivery pressure for the heat load (e.g., delivery pressure is 7 bar gauge (8101 kPa) with an offset of 1 bar (100 kPa)). The lower liquid level limit for continued operation of the heater corresponds to a liquid fraction of 0.5. The vessel size is approximately 22.5 m 3 is.

[0149] In this simplified example, the steam demand is selected so that the flash potential is completely depleted at the end of the depletion period, and therefore, even though the flash potential drops to zero, the plots in Figures 3a and 3b do not represent an inability to meet the steam demand, which would end the depletion period.

[0150] As shown in Figures 3a and 3b, during the depletion period, the storage pressure is gradually reduced from a peak storage pressure of 30 bar gauge (3101 kPa) to flash enough steam to meet the (constant) steam demand, thereby reducing the flash potential. The liquid level also decreases as water (in the form of steam) is released from the pressure vessel. During the depletion period, the flash potential is always sufficient to meet demand, and because no condensate is added, the liquid level margin remains constant during the depletion period. The flash potential gradually decreases to reflect the gradual release of steam.

[0151] At the end of the depletion period, operation transitions to a demand-free recharge period that lasts for the remainder of the 24-hour cycle.

[0152] During the recharge period, the equipment is operated to both (i) resupply subcooled water to the pressure vessel to replace that released (in the form of steam) and (ii) add heat to repressurize the pressure vessel to the peak storage pressure. Specifically, water is added to reach a target (or peak) mass of water corresponding to the peak liquid fraction at the peak storage pressure, while heat is added to reach the peak storage pressure given the target mass of water.

[0153] The supply of subcooled water and heat during the recharge period may be managed or staged in any suitable manner.

[0154] In the particular example of Figures 3a and 3b, heat is provided at a constant rate (120 kW) while subcooled water is supplied according to a front-loading profile. By front-loading the subcooled water supply, the water in the pressure vessel is maintained at a relatively low pressure and temperature (and a relatively high liquid level) early in the refill period, and reaches higher pressures and temperatures only late in the refill period, thereby minimizing heat loss through the pressure vessel wall for as long as possible.

[0155] In this particular example, the supply of subcooled water is controlled based on the flash potential and level margin, as described below. The flash potential is zero at the beginning of the recharge period because the storage pressure has been reduced to a minimum pressure to maintain steam release to the heat load, and therefore there is no ability to supply additional steam when steam is required.

[0156] During the initial flash-dominant portion of the recharge period, heat is supplied without a corresponding subcooled water supply to build up flash potential up to the minimum recharge flash potential (a predetermined value of 500 kg in this example) that can be used if necessary. This initial flash-dominant portion of the recharge period reduces the level margin. Supplying subcooled water during this initial portion slows the rate of pressure rise (or even reduces the pressure), thereby slowing the buildup of flash potential.

[0157] During the subsequent water-dominant portion of the recharge period (starting around 9:00), subcooled water is supplied at a rate such that the minimum recharge flash potential is maintained while the liquid level margin rises. This water-dominant mode of operation is maintained until the water mass reaches the target (or peak) mass.

[0158] Once the target mass of water is reached (at approximately 11:00), the equipment is operated during a second flash priority portion of the refill period, supplying heat without a corresponding subcooled water supply until the target peak storage pressure is reached. In this example, the target peak storage pressure is reached at approximately 20:00, and no further water or heat is added during the final approximately four-hour period of the 24-hour cycle. Alternatively, subject to forecasted demand and forecasted heating power availability, the water supply and / or heating profile can be modified to delay the second flash priority period (e.g., by supplying no heat or subcooled water during the four-hour period between the water priority portion and the second flash priority portion). In other use cases, particularly those with steam demand during the refill period, additional subcooled water may be supplied during the second flash priority period to target or maintain the target (peak) mass of water in the pressure vessel.

[0159] Figures 4a and 4b are plots of operating conditions for a second example of operating the facility including depletion and recharge periods, showing the same quantities as Figures 3a and 3b. In the second example, power for heating (at the same 120 kW power) is available throughout both the depletion and reheat periods, and the operating variables are the same as in the second example, except that the steam demand is significantly higher at 500 kg / hr. To simulate the effect of a higher required liquid level, the lower liquid level limit is also higher, corresponding to a liquid fraction of 0.67.

[0160] The profiles in Figures 4a and 4b are similar to those in Figures 3a and 3b in that the pressure and liquid level drop during the depletion period. The significantly higher steam demand rate is compensated for by the available heating power during the depletion period. However, in this example, the liquid level margin reaches zero during the final portion of the depletion period, meaning that if the flash potential were released by lowering the reservoir pressure to the minimum pressure, the liquid level would be at the minimum level for continued heater operation. To maintain the level margin, subcooled water is added to the pressure vessel during this final portion of the depletion period, which accelerates the rate at which the reservoir pressure and flash potential drop, but the flash potential is still not exhausted. Specifically, because the full flash potential is not required (as shown in Figure 4a), the liquid level does not reach the minimum level during the depletion period.

[0161] During the recharge period, there is a short initial flash priority portion where the flash potential is increased to the minimum recharge flash potential (250 kg in this example). This is followed by a water priority portion where the minimum recharge flash potential is maintained while the liquid level margin is increased until the target mass of water is reached. This is then followed by a second water priority portion where heat is added without a corresponding subcooled water supply until the target peak storage pressure is reached. Finally, there is a period toward the end of the 24-hour cycle where the monitored quantity remains constant.

[0162] Other methods for staging the supply of subcooled water and heat are also applicable. For example, at the beginning of the refill period (or any time during the refill period), the controller may determine an additional mass of subcooled water to be added to the current mass of water in the pressure vessel to reach a target mass of water. The current mass of water may be determined based on the liquid level derived from the liquid level signal and the storage pressure derived from the storage pressure signal. The controller may determine the total amount of heat to add to the water (current and additional) during the refill period to reach a peak storage pressure. The controller may control the rate at which subcooled water is supplied to the pressure vessel in proportion to the heating power, thereby causing both the storage pressure and the liquid level ( / liquid fraction) to continuously and gradually increase during the refill period.

[0163] Because the pressure vessel is constructed and operated to provide a relatively large thermal energy reserve (e.g., a large flash potential) relative to the maximum expected rate of steam demand, in use the steam flow rate leaving the vessel is relatively low compared to the maximum value the pressure vessel can potentially accommodate. This has advantages with respect to steam dryness fraction. Specifically, for on-demand steam generation systems or short-term steam accumulator systems, it is conventional to determine whether the maximum expected rate at which steam is released from the liquid water surface is sufficiently low to suppress entrained liquid water. Empirical test studies conducted by the applicant and reported before the priority date have shown that the rate at which dry steam can be released from the water surface is a function of pressure, and is determined as the maximum unentrained steam release rate (MSR) (kg / m 2This figure shows an effective approximation that the maximum expected (or peak) steam release rate (MSR) for a properly sized vessel is equal to 220 times the absolute pressure in bar (or 22 times the absolute pressure in MPa). For example, in the design of steam accumulators, it is conventional practice to attempt to reduce the size of each vessel to reduce cost and installation size, thereby resulting in a relatively high maximum expected (or peak) steam release rate compared to the maximum steam release rate (MSR), e.g., between 25% and 90%. In contrast, the thermal energy storage and supply systems and methods described herein tend to result in much lower steam release rates. In the specific example described above with reference to FIGS. 3a and 3b, the maximum expected or peak steam release rate for a properly sized vessel, even when conservatively assessed assuming a 90% fill, is equal to approximately 0.7% of the MSR for the peak storage pressure and approximately 2.3% of the MSR for the lower pressure. For an 80% fill, these values ​​are 0.6% and 2%, respectively. Therefore, the risk of entrained liquid water in the released steam is low.

[0164] Figures 5-7 are flow diagrams of methods for operating a heat storage and heat supply facility by controlling the respective control variables of such a facility, which will be described with reference to the exemplary heat storage and heat supply facility of Figure 1 and with reference to the operating condition profiles shown in Figures 3a and 3b.

[0165] 5 illustrates a method 500 performed by the controller 200 for controlling the release of steam from the pressure vessel 100 to the heat loads, and is described with reference to the demand for thermal energy at a first plant heat load 30 as an example, although it should be understood that the method applies equally to the demand at another heat load or to the cumulative demand across multiple loads. The method steps described with reference to the "blocks" of FIG. 5 are repeated continuously or periodically during operation of the facility.

[0166] At block 502, the controller determines whether there is demand based on the demand signal received from the first plant heat load 30. If there is no demand, the method proceeds to block 510 where the respective discharge control valve 216 is closed or remains closed.

[0167] If there is demand, the method proceeds to block 504 where the controller determines whether the liquid level is above the lower level limit, for example, based on a level signal received from a level sensor. If the liquid level is not above the lower level limit, the method proceeds to block 510 where the respective discharge control valve 216 is closed or remains closed. This may continue until the liquid level is raised, for example, by adding heat and / or subcooled water to the pressure vessel, as described above with reference to Figures 3-4.

[0168] If the liquid level is above the lower liquid level limit, the method proceeds to block 520, where the controller controls each first discharge control valve 216 to open, reducing the storage pressure in the pressure vessel 110 and thereby causing liquid water to flash and be discharged through the discharge port 116, through the first discharge control valve 216 and down the distribution line 102 to the heat exchanger 130. As described elsewhere herein, the controller may control the first discharge control valve 216 based on monitored parameters corresponding to the supply of steam to the respective heat load (e.g., in a feedback loop), for example, based on a first flow signal provided by the first flow meter 218.

[0169] At block 522, the controller may determine whether the demand is met. For example, the controller may determine whether the flow rate of steam through each distribution line 102 is sufficient to meet the demand based on the first flow rate signal received from each first flow meter 218. If there is not enough water flash potential in the pressure vessel to meet the demand, the demand may not be met. If the controller determines that the demand is not met, the controller may decide to close the discharge control valve 216 until the flash potential is increased, for example, by further heating and / or feeding water to the pressure vessel. In response to determining that the demand is not met, the controller may control additional heat to be supplied, for example, using power from a secondary power source (e.g., from a grid connection rather than a local power source (e.g., a microgrid) that distributes renewable energy such as solar or wind power). Regardless of whether the demand is met, the method repeats throughout the operation of the facility 100 by returning to block 502.

[0170] Figure 6 illustrates a method 600 for controlling a heater when the heater is powered by a local power source, which may be performed in parallel with, and independently of, method 500 of Figure 5. As above, it will be described with reference to the example installation 100 of Figure 1. This example method does not address the optional provision of power from a secondary power source, such as a grid connection, as described elsewhere herein.

[0171] The thermal energy storage and supply system 100 is particularly advantageous when powered by a local power source, such as a microgrid. Local power sources, especially renewable sources, generally do not provide power with the same consistency and reliability as non-local power grids that distribute electricity from many different renewable and non-renewable power plants, for known reasons (e.g., variable amounts of wind or solar energy). The thermal energy storage and supply system 100 can provide large reserves by converting electrical energy to thermal energy for storage when available and later releasing the thermal energy upon demand. The inventors have found this to be more efficient than storing locally generated energy in batteries for later use in an electric boiler upon demand. Storing energy as thermal energy as described herein also has advantages over battery storage because it does not require the large amounts of chemicals and materials associated with battery technologies such as lithium, many of which are rare or pose environmental risks to mineral deposits.

[0172] The rates at which energy is stored and released by the facility are largely decoupled. Therefore, a large amount of stored thermal energy can be built up in the pressure vessel by heating the liquid water therein when electrical energy is available. Generally (i.e., across most of the operating map of the pressure vessel's conditions), heat can be supplied without requiring a corresponding supply of subcooled water to the vessel. The main exceptions are easily avoided scenarios: (i) when the pressure vessel is at peak storage pressure, but the mass of water in the pressure vessel is lower than the target peak mass of water, and (ii) when the liquid level falls below the lower limit for continued heater operation, e.g., the lower limit corresponding to the top position of the heater or its heating element within the pressure vessel. In case (i), additional subcooled water must be supplied to raise the mass of stored water and reduce the pressure. In case (ii), the heater cannot be operated to raise the liquid level, so additional water must be supplied to raise the liquid level.

[0173] At block 602, the controller determines whether power for heating is available from the local power source. This determination may be a determination of the power currently generated by the local power source and / or the power currently available from the local power source taking into account other loads (e.g., generated power minus power supplied to other electrical loads in facility 100 and / or the industrial plant). If power is not available, the method proceeds to block 610, where the controller does not operate the heater to heat the water in the pressure vessel. If power is available, the method proceeds to block 604.

[0174] At block 604, the controller determines (e.g., based on a storage pressure signal received at the controller) whether the storage pressure is already at the peak storage pressure. If so, the method proceeds to block 610 to not heat, as described above. If the storage pressure is less than the peak storage pressure, heat is supplied.

[0175] In block 606, the controller determines (based on the liquid level signal received by the controller) whether the liquid level is within a range for heating. In this example, this determination corresponds to (i) determining whether the liquid level is above a lower liquid level limit for continued operation of the heater, which may correspond to the top position of the heater or its heating element within the pressure vessel, as described above, and (ii) determining that the liquid level is not above an upper liquid level limit corresponding to a target peak mass of water in the pressure vessel. The upper liquid level limit may be pressure dependent. Specifically, heating the vessel alone (i.e., with no steam release or water supply) increases the pressure and raises the liquid level. Thus, if the vessel is at a target peak liquid fraction (e.g., 90%) at a storage pressure lower than the target peak storage pressure, further heating to reach the target peak storage pressure will further raise the liquid level. The controller can control the supply of water to the pressure vessel to avoid such a scenario, but can still optionally check in block 606.

[0176] If the liquid level is not within the heating range, the method proceeds to block 610 and no heat is applied, as described above. However, if the liquid level is within the heating range, the method proceeds to block 620 and heat is supplied at a rate corresponding to the available power.

[0177] Whether or not heat is supplied, the method repeats by returning to block 602 throughout operation of the facility 100 .

[0178] The heater may have a rating significantly lower than the rating (i.e., maximum power output) of a heater or burner that may be provided in an alternative steam supply system. While such alternative steam supply systems may size their heaters based on peak steam supply rates, heaters according to the present disclosure may be sized based on power and the total amount of heat that may be needed during an operating cycle, such as a day. Taking into account the operating mode of the facility (i.e., to accumulate a significant reserve of long-term thermal energy that can be released at a rate that far exceeds the power simultaneously available for heating), the inventors have provided a system that can meet a relatively high cumulative thermal energy demand and a relatively high demand rate with a relatively low heating power. The heater itself may have a relatively low rating, or may be coupled to a local power source with a relatively low power output, or a controller may limit the power output of the heater.

[0179] To quantify the relatively low heating power compared to the relatively high ability of the system to meet demand, this disclosure defines the following parameters:

[0180] - The average depletion power is defined as the cumulative enthalpy of steam released from the pressure vessel during the depletion period divided by the duration of the depletion period.

[0181] - Maximum depletion power is defined as the maximum enthalpy of steam released during any one minute minimum power evaluation period within the depletion period, divided by the minimum power evaluation period. It therefore typically corresponds to the peak rate of steam release, taking into account that steam released at lower pressures may have lower enthalpy than steam released at higher pressures.

[0182] - Average reheat power is defined as the cumulative energy imparted to the liquid water by the heater during the recharge period divided by the duration of the recharge period.

[0183] - Maximum reheat power is defined as the maximum power delivered by the heater to the liquid water within the recharge period.

[0184] According to the present disclosure, the average reheat power during the recharge period may be significantly lower than the average depleted power, e.g., 50% or less of the average depleted power, corresponding to a system configuration that uses a relatively low power source or a low-rated heater to meet a relatively high energy demand during a limited period. In the particular example of Figure 3, the average depleted power is 0.26 MW, while the average reheat power is 0.12 MW. This ratio would be lower if heat were provided during the depletion period.

[0185] According to the present disclosure, the average reheat power may be less than or equal to 50% of the maximum depleted power. In the specific example of Figure 3, the maximum depleted power corresponds to the release of steam when the pressure vessel is at peak storage pressure with a constant demand rate of about 330 kg / hr. This corresponds to a maximum depleted power of about 0.26 MW.

[0186] According to the present disclosure, the maximum reheat power may be less than or equal to 50% of the maximum depletion power, with corresponding values ​​for the specific example of Figure 3 as shown above.

[0187] According to the present disclosure, the magnitude ratio between (i) the cumulative enthalpy of steam released from the pressure vessel during the depletion period and (ii) the average reheat power of the heater during the recharge period is at least 25,000 seconds. This corresponds to a relatively low recharge power compared to the system's ability to meet the heat load, which is different in the present invention compared to previously considered steam supply systems for comparable applications. Although the units are seconds, this does not correspond to the duration of the recharge period. In the specific embodiment shown in FIG. 3, the magnitude ratio is approximately 50,000 seconds.

[0188] The heater rating may be selected based in part on the variability of the supply. For example, if power can be reliably drawn from the power source, the heater rating may be equal to the total expected thermal energy delivered by the heater over one cycle divided by the duration of the cycle. However, for power sources with variable output (such as wind or solar), the appropriate rating may be determined by evaluating the predicted power output profile of the local power source. The local power source may be capable of generating peak power that exceeds the heater rating. As described elsewhere herein, if the local power source is unable to meet the required power output to achieve the target storage pressure and / or target water mass (which may be the target peak storage pressure and target peak water mass), auxiliary power may be supplied (e.g., from a non-local power grid connection).

[0189] Before describing the method for controlling the supply of subcooled water with reference to Figure 8, it will be helpful to illustrate the terms "flash potential" and "liquid level margin" used in this specification, as shown in Figures 7a to 7e.

[0190] 7a-7e show a cylindrical vessel 710 corresponding to pressure vessel 110 of FIG. 1. Line L0 represents the lower liquid level limit in vessel 710 for continued operation of the heaters (i.e., corresponding to the height of the respective heater or at least the heating element of the heater). Line 714 represents the water level in vessel 710. As described elsewhere herein, the liquid level can be expressed as the height of the liquid water / vapor interface or as the liquid fraction in the vessel. In each figure, the current storage pressure of the water is the same (and is lower than the target peak storage pressure for the vessel), but the mass of water, and therefore the liquid level, is different.

[0191] In Figure 7a, the liquid level 714 is below the lower limit liquid level L0 so that the heater cannot operate. This condition can arise if, during operation, the equipment is intentionally operated to deplete the flash potential even while at a liquid level below the lower limit, thereby preventing further heat input during this operation until the liquid level is raised by the addition of more water to the vessel.

[0192] Each of Figures 7b-7d shows two side-by-side views of vessel 710. The left-hand view shows the current liquid level 714 at the current storage pressure, while the right-hand view shows what the liquid level 716 will be after the flash potential is released.

[0193] In FIG. 7c, the liquid level 714 is at a zero margin liquid level L1, which corresponds to a liquid level margin that is zero (i.e., the liquid level at the time of release of the flash potential is equal to the lower limit liquid level L0, as shown in the right diagram of the vessel 710).

[0194] In FIG. 7b, the liquid level 714 is at the midpoint between the liquid levels L0 (lower limit liquid level) and L1 (zero margin liquid level) so that the liquid level margin is negative.

[0195] In Figure 7e, the left view of vessel 710 shows the current water level 714 at the current storage pressure, and the right view of vessel 710 shows the water level 716 for the same mass of water if the water storage pressure is increased to the target peak storage pressure. In Figure 7e, the current water level 714 is at the peak fill level L2, e.g., 90%, which corresponds to the water level 716 at the (higher) target peak storage pressure, which is the target peak level.

[0196] In FIG. 7d, the liquid level 714 is at an intermediate level between levels L1 (zero margin level) and L2 (peak fill level).

[0197] As can be seen, the lower limit level is the same for all storage pressures, while the zero margin level L1 and peak fill level L2 vary with storage pressure.

[0198] With no further heat input while the flash potential is depleted, the optimum liquid level at any particular reservoir pressure is the zero margin liquid level L1, which represents depressurizing the pressure vessel to the lower limit pressure while reaching but not below the lower limit liquid level L0.

[0199] If the liquid level 714 is between L0 and L1 and there is no heat input while the flash potential is depleted, only a portion of the flash potential (the "useful flash potential") can be released before the liquid level reaches the lower limit L0. Generally, the flash potential (including the useful flash potential) increases in response to heat input because both the liquid level and the enthalpy of the liquid water increase. Generally, the flash potential decreases in response to the addition of subcooled water because the addition of subcooled water increases the total amount of liquid mass but decreases the temperature and enthalpy of the liquid water. However, when the liquid level 714 is between L0 and L1, the useful flash potential tends to increase in response to the addition of subcooled water because the amount of water acts as a limiting factor in allowing steam to be flashed and released to evaporate. Thus, adding water reduces the total flash potential but allows more flash potential to be used.

[0200] When the liquid level 714 is between L1 and L2, the flash potential (which is equal to the useful flash potential) will rise in response to heat input. The flash potential (which again corresponds to the useful flash potential) will fall in response to subcooled water input because the liquid level does not act as a limiting factor in allowing the flash potential to be released, while the addition of subcooled water reduces the pressure and enthalpy of the liquid water in the pressure vessel.

[0201] Therefore, useful flash potential is best conserved or increased by adding subcooled water when the liquid water level for a given pressure is between L0 and L1, and by adding heat without adding subcooled water when the liquid water level for a given pressure is between L1 and L2.

[0202] Of course, it may also be necessary to add subcooled water to the pressure vessel when the liquid water level is between L1 and L2, but such addition of water may depend on the operating mode of the facility.

[0203] The above description also applies to instantaneous flash potential, i.e., the amount of steam that can be flashed by reducing the pressure to a lower limit based on the current mass of water in the pressure vessel and the storage pressure. However, the above description also applies to predicted flash potential, predicted level margin, and predicted useful flash potential, which are determined based on predicted demand and / or predicted power output of the heater.

[0204] To illustrate how predicted flash potential can differ from instantaneous flash potential, consider a scenario where the liquid level is 0.75, the instantaneous flash potential is X kg (e.g., 500 kg), and there is a positive liquid level margin Y (e.g., 0.1 liquid fraction above the lower limit of 0.5). If the predicted demand corresponds to a steam release of 250 kg / hour per hour over a two-hour period, without additional heating and subcooled water supply, the flash potential will be exhausted at the end of the two-hour period, and the liquid level will be at the lower limit of L0. However, if there is a predicted heater power output of 100 kW over the same two-hour period, a lower pressure drop will be required over the two hours to release the same amount of steam (because the heat input also evaporates liquid water), and a positive flash potential will still exist at the end of the two-hour period. However, if the liquid margin becomes negative, the useful flash potential may be limited.

[0205] The flash potential, liquid margin, and / or useful flash potential can be evaluated over time based on predicted demand and predicted heater output, as described in further detail below. This can be particularly useful for controlling the supply of subcooled water during periods of depletion, as described below. In the context of liquid levels L0, L1, and L2 as described above in connection with FIG. 7, these predicted quantities can particularly affect the zero margin liquid level L1 (level L0 is only relevant for the current liquid level, while level L2 is most relevant during recharge periods).

[0206] Continuing with the particular example scenario above, the zero margin level L1 based on the instantaneous flash potential and level margin may be 0.65, corresponding to a level drop of 0.15 to reach the lower level limit of 0.5. However, the zero margin level L1 based on the predicted flash potential and predicted level margin may be lower, e.g., 0.6, because a lower drop in storage pressure may be required to output the same amount of steam during a two-hour period when the heater is providing additional energy to the pressure vessel. Also, at higher storage pressures, the level may drop at a slower rate.

[0207] A similar analysis can also be applied to determine the peak fill level L2 based on predicted demand and predicted power output. However, compared to an analysis based on the current condition of the pressure vessel, the effect of using the predicted quantity may be simply to determine that more water than the target peak mass of water is added to the pressure vessel in anticipation of some water being released to meet the predicted demand. While there may be efficiency benefits to doing this (particularly to lower the temperature of the pressure vessel to reduce heat loss), the actual control implementation may reflect the target peak mass of water as an upper limit. For example, if the pressure vessel is filled with a mass of water greater than the target peak mass at a relatively lower pressure, the liquid level will exceed its associated target peak level at the target peak storage pressure if the predicted demand does not occur.

[0208] Figure 8 illustrates a method 800 for controlling the supply of subcooled water to a pressure vessel that can be performed independently of, and in parallel with, the methods 500, 600 of Figures 5 and 6. As above, the method will be described with reference to the exemplary system 100 of Figure 1.

[0209] As discussed elsewhere herein, supplying subcooled water to the pressure vessel alone (i.e., separate from heating by a heater and / or releasing steam) reduces the storage pressure of the water within the pressure vessel. Thus, while operation of the system 100 to release steam is dependent on there being a sufficient mass of water within the pressure vessel, in many parts of the system's operating map, the act of resupplying water to the pressure vessel tends to reduce the pressure vessel's potential to release steam (i.e., flash potential).

[0210] The inventors have realized that the timing and rate of water supply can be controlled depending on the purpose of the facility's operation.

[0211] At block 802 of the method, the controller 200 determines whether the liquid level is below a lower limit level L0 for continued operation of the heater. This determination may be based on the liquid level signal received from the liquid level sensor 214. If the liquid level is below the lower limit level L0, the method proceeds to block 820.

[0212] At block 820, the amount of subcooled liquid to be added is determined. If the plant is operating in an extended depletion mode, where the liquid level is allowed to remain below the lower limit L0 for an extended period to release the full flash potential, the controller determines not to add subcooled water. In all other modes (i.e., a heat depletion mode, where the controller prevents the release of steam that would lower the liquid level below the lower limit for heater operation, or a recharge mode), the controller determines to add subcooled water.

[0213] The amount of subcooled water to supply can be determined based on both the liquid level and the reservoir pressure (block 820). For example, the controller can calculate the amount of subcooled water required to reach a lower liquid level limit, or can reference the amount from a database of predetermined values ​​correlated to the liquid level and reservoir pressure. The amount of subcooled water can be specified in any suitable manner, such as a mass of water, a duration of operation of the injection pump, and / or a flow rate.

[0214] In block 822, a flow rate for supplying subcooled water is determined. In the context of restoring the liquid level to the lower limit level L0, the heater must be deactivated, and therefore the flow rate is determined without reference to the rate of heating. If the controller determines to degas the subcooled water, the flow rate may be determined based on a predetermined injection flow rate associated with the operation of the degasser, which may correspond to an injection flow rate that enables the degasser to raise the temperature of the injection stream to the saturation temperature. Otherwise, the flow rate may be determined by the injection pump, for example, as an optimal or maximum flow rate.

[0215] At block 824, subcooled water is provided up to the amount and / or flow rate determined at blocks 820, 822.

[0216] While in this particular embodiment both the amount of subcooled water to add and the supply rate (block 822) are determined, in alternative embodiments the controller may proceed directly to block 824 to, for example, begin supplying subcooled condensate at a predetermined rate. Iteration of this method (as described above) may provide appropriate control for stopping the supply.

[0217] The method proceeds to block 802 to repeat the method. The method may be repeated such that the requirement for the supply of subcooled water to the pressure vessel is iteratively determined until the determined amount is supplied in the final iteration.

[0218] If, at block 802, it is determined that the liquid level is at or above the lower limit liquid level L0, the method proceeds to block 804. At block 804, it is determined whether the liquid level margin is negative. The liquid level margin corresponds to the amount by which the liquid level in the pressure vessel will be above or below the lower limit liquid level L0 upon release of the flash potential.

[0219] A determination that the level margin is negative corresponds to determining that the amount of water in the pressure vessel is currently the limiting factor on the pressure vessel's ability to release steam. The inventors have discovered that the available flash potential (as defined above) can be increased by adding subcooled water to the pressure vessel. This reduces the storage pressure and flash potential (at any given liquid level), but increases the available flash potential. If the level margin is negative, the method proceeds to block 820.

[0220] In blocks 820-824, as described above, the amount of subcooled water to be dispensed is determined (block 820), the flow rate for dispensing is determined (block 822), and the controller causes the determined amount to be dispensed, and then the method is repeated. As in the context of restoring the liquid level to the lower limit level L0, the amount of subcooled water to be dispensed can be calculated or can be referenced from a database of predetermined values ​​correlated to the liquid level and the reservoir pressure. As in the context of restoring the liquid level to the lower limit level L0, the flow rate can be determined without reference to the rate of heating, because the benefit of increasing the useful flash potential is based on the mass of water dispensed, regardless of the dispense rate.

[0221] The determination in block 804 that the level margin is zero or positive corresponds to a determination that the amount of water in the pressure vessel is not currently a limiting factor on the pressure vessel's ability to release steam. This determination may be based on the predicted flash demand and predicted level margin (which themselves are determined based on the current conditions (storage pressure, liquid level) of the pressure vessel), as well as the predicted demand and / or predicted power output of the heater, as described elsewhere herein.

[0222] If the liquid level margin is determined to be zero or positive, the method proceeds to block 806 .

[0223] At this stage, the decision to provide subcooled water to the pressure vessel may be based on the particular application in which the facility will be operated and / or the forecasted demand.

[0224] When operating a facility to meet substantial or uncertain demand, adding subcooled water may be considered unproductive because it reduces the flash potential (and thus the useful flash potential). Adding subcooled water may also be considered unnecessary because a zero or positive level margin corresponds to the flash potential being fully depleted, leaving enough liquid water in the pressure vessel for continued heater operation. If the level margin is the predicted level margin over a period of time and is zero or positive, this corresponds to the flash potential being fully depleted over that period, leaving enough liquid water in the pressure vessel for continued heater operation.

[0225] Therefore, when operating a facility to meet substantial or uncertain demand, the inventors have determined that the addition of subcooled water can be delayed to avoid unnecessarily reducing the useful flash potential.

[0226] In contrast, to recharge the vessel to the target peak conditions (i.e., to the target peak storage pressure at the target peak mass of water), both additional subcooled water to reach the target mass and heat to reach the target pressure must be resupplied to the vessel.

[0227] The inventors have determined that to meet this dual requirement, the installation may have different modes of operation, as described by way of example with reference to the method of FIG.

[0228] In block 806, the controller determines whether to operate the equipment in a depletion mode or a recharge mode. The depletion mode corresponds to operation of the equipment during a depletion period to meet thermal demands that generally deplete the thermal energy stored in the pressure vessel over a duration of time. The depletion period can be described as a period in which the enthalpy output (or loss) corresponding to the released steam is greater than the energy input to the pressure vessel, such that the storage pressure drops by a significant amount, such as at least 1 MPa, from the peak storage pressure. The recharge mode corresponds to operation of the equipment during a recharge period in which thermal energy generally accumulates in the pressure vessel over a duration of time. The recharge period can be described as a period in which the energy input to the pressure vessel by heating is greater than the enthalpy output (or loss) corresponding to the released steam to meet thermal energy demands, such that the storage pressure rises by at least 1 MPa to the peak storage pressure (e.g., at least 2 MPa). As described elsewhere herein, in alternative embodiments where the peak storage pressure may be lower (e.g., at least 0.5 MPa, or at least 1 MPa, or at least 2 MPa), the depletion period and refill period may be defined differently on the same basis, for example, by reference to a depletion pressure difference and / or a refill pressure difference that is at least 50% of the respective peak storage pressure.

[0229] The controller may determine whether to operate the equipment in depletion mode or refill mode in any suitable manner, examples of which include (i) a time-based schedule of operation in each mode (e.g., depletion mode from 09:00 to 17:00, refill mode from 17:00 to 09:00), (ii) by reference to projected demand and / or projected heater power output over a period of time, such as the next 6 hours or the next 12 hours, or (iii) by reference to a prediction of whether the pressure vessel is predicted to reach a depletion condition or a target peak condition first, based on the projected demand and / or projected heater power output. By way of example, in the case of (iii), the depletion condition may correspond to the flash potential being depleted to zero liquid margin remaining, or the useful flash potential being reduced to a minimum depletion potential, such as 500 kg. If, at block 806, it is determined that the equipment is to operate in depletion mode, the method proceeds to block 810. At block 810, the equipment is operated without adding subcooled liquid to the pressure vessel, and the method then returns to block 802 and repeats. By not adding subcooled water, the flash potential (useful flash potential) can be maintained as high as possible during the depletion period while still meeting steam demand.

[0230] If at block 806 it is determined that the equipment is to operate in a refill mode, the method proceeds to block 808 .

[0231] At block 808, a decision is made as to whether to operate in a refill mode that prioritizes flash potential ("flash priority") or to prioritize water mass accumulation within the pressure vessel (water priority). The inventors have determined that by prioritizing the storage of additional water only after a minimum flash potential has been established, an optimal balance can be achieved between conserving and storing instantaneous capacity to meet demand (i.e., flash potential) and storing additional water to meet even greater demand at a future time.

[0232] Considering that the level margin must be positive in block 808 of method 800, the flash potential and useful flash potential equal and correspond to the demand that can be met without additional heat input to the vessel. In this example, the controller determines whether the flash potential is below a minimum refill potential, which may be a predetermined minimum potential (e.g., determined from a database of predetermined minimum potentials that are generally applicable or, alternatively, correlated by operating variables such as time of day, day of week, etc.) or may be determined based on projected demand over a period of time and / or projected power output of the heater, as described above. For example, the minimum fill potential may correspond to 500 kg of flash potential.

[0233] The controller may determine whether the flush potential is below the minimum refill potential in any suitable manner, including based on the level signal received by the controller (e.g., by referencing a database of level signals corresponding to minimum refill potentials correlated with the storage pressure and optionally the minimum refill potential (if available)), or by calculating the flush potential and comparing it to the minimum refill potential.

[0234] If the flash potential is below the minimum recharge potential (e.g., if the liquid level is below the respective threshold for a given pressure), the controller determines not to add subcooled water until sufficient heat is supplied to raise the flash potential to the minimum recharge potential, referred to herein as operating in a flash-first recharge mode.

[0235] If the flash potential is greater than or equal to the minimum refill potential, the controller determines to add subcooled water to raise the mass of water in the pressure vessel to the target peak mass of water. The method proceeds to block 820, where in a water-first refill mode, the controller determines an amount of water to add to reach the target peak mass of water. At block 822, in a water-first refill mode, the controller determines a rate at which to add water to the pressure vessel. In this example, this rate is selected such that, despite the addition of subcooled water, the flash potential is maintained at (or above) the minimum refill potential possible by simultaneously heating the water in the pressure vessel at a rate that offsets the addition of water and steam release, if any. This can be achieved, for example, by calculating a water addition rate that maintains the minimum refill potential based on the heater's current and / or predicted power output (which may itself be limited by the power available from the power source) and current and / or predicted demand.

[0236] At block 824, subcooled water is supplied to the pressure vessel in the determined amount, and the method returns to block 802. As noted above, the method may iterate, such that the method continually reevaluates whether to supply subcooled liquid based on current and / or predicted conditions, until the determined amount of subcooled water is actually supplied.

[0237] When the amount of liquid reaches the target peak mass of water and the method returns to block 808 of method 800, the controller determines to operate in a flash-first refill mode, thereby preventing further addition of subcooled liquid while allowing the storage pressure to gradually increase to the target peak storage pressure.

[0238] The above description illustrates one example of operating the system to stage a subcooled water supply and heating profile to frontload the feedwater (while maintaining a minimum recharge flash potential). As described elsewhere herein, this allows the water temperature to remain low for a relatively long period of the recharge period, and only during the final stages of operation does it increase toward a temperature corresponding to the storage period. This reduces heat loss through the pressure vessel wall.

[0239] Please refer again to the exemplary profiles of storage pressure, level, flash potential and level margin described above with reference to Figures 3a-4b, which show the depletion periods corresponding to the depletion mode of operation and the recharge periods corresponding to the recharge mode of operation in relation to the flush priority and water priority stages, respectively.

[0240] In the exemplary methods described above, and in particular the exemplary method 500 of FIG. 5 for controlling the release of steam to one or more heat loads, all thermal energy demands of the respective heat loads can be (met) without reference to the priority of the loads until the flash potential (or useful flash potential) is exhausted.

[0241] However, to conserve flash potential, criteria may be evaluated to determine whether the thermal energy demand of each load is met, e.g., at block 520 of method 500 of FIG. 5 . For example, criteria corresponding to whether the flash potential is sufficient to meet the predicted demand of a plurality of loads may be evaluated. If the evaluation corresponds to the flash potential being sufficient to meet the predicted demand, the controller continues to operate the equipment to release steam to each of the loads at a rate that meets their respective demand. However, if the evaluation corresponds to the flash potential being insufficient to meet the predicted demand, the controller operates the equipment to preferentially release steam to one or more higher priority loads over lower priority loads. For example, the controller may store or otherwise access priority data specifying the relative priority of each thermal load. For example, a sterilization load (e.g., priority 10) may have a higher priority relative to heating (e.g., priority 4). The priority data may be defined in any suitable manner, and a simple implementation is data defining a high priority or a low priority (e.g., by 1 or 0, respectively).

[0242] The criteria may be any suitable criteria for assessing whether the predicted demand can be met by releasing steam from water stored in the pressure vessel. In a relatively simple example implementation, the criteria may correspond to determining whether the flash potential is higher or lower than a predetermined amount for each time point. For example, if the facility is operated to meet a relatively constant demand over a predetermined period of time, such as 200 kg / hr between 09:00 and 16:00, the facility may be configured to meet the corresponding addressable demand (e.g., 1400 kg) over that period by reducing the storage pressure in the pressure vessel from peak storage conditions (i.e., the liquid level is at the target peak liquid level and the storage pressure is at the target peak storage pressure). Continuing with this example, it may be expected that no more than 600 kg of steam has been released by 12:00, or that the storage pressure and / or liquid level in the pressure vessel at 12:00 corresponds to a flash potential of at least 800 kg while maintaining a zero or positive liquid level margin.

[0243] Criteria may be defined to determine whether the storage pressure is above or below a predetermined minimum storage pressure at a particular time corresponding to the available demand, or above or below a minimum storage pressure determined as a function of time. For example, at 12:00, there may be a minimum storage pressure of 1.8 MPa and at 14:00, there may be a minimum storage pressure of 1.6 MPa. A storage pressure below the minimum storage pressure would correspond to a higher-than-expected demand, thereby indicating that the flash potential in the vessel may not be sufficient to meet the forecasted demand (based on continued use at 200 kg / hr). Similar evaluations can be made based on any suitable parameters, such as storage temperature (which correlates with pressure), liquid level (height or volume / volume fraction), or direct calculation / estimation of flash potential and / or liquid level margin using, for example, monitored liquid level and storage pressure information. Such evaluations may also take into account the predicted power output of the heater, as described elsewhere herein.

[0244] In other example implementations, the criterion may be defined to compare the predicted demand to the addressable demand (i.e., the demand known to be addressable based on the thermal energy storage capacity of the pressure vessel). The addressable demand may be evaluated based on the current conditions of the pressure vessel (e.g., storage pressure and liquid level) or may be the total addressable demand corresponding to depletion from peak storage conditions (i.e., the liquid level is at the target peak liquid level and the storage pressure is at the target peak storage pressure). If the addressable demand is expressed in terms of the amount of vapor available for release, the addressable demand is equivalent to the flash potential when the liquid level margin is zero or positive (or equivalent to the useful flash potential as defined elsewhere herein). Similarly, the forecasted demand may be the forecasted demand for a future period (e.g., beginning at the moment the criterion is evaluated) or may instead include the demand already met by the release of steam during a drawdown period (i.e., the forecasted total demand for the drawdown period). In the latter case, the criteria may not directly reference the current addressable demand or the current flash potential of the pressure vessel, but may only consider whether the forecasted total demand exceeds the total addressable demand or total flash potential corresponding to depletion from peak storage conditions.

[0245] The determination of available demand, flash potential, liquid level margin and / or useful flash potential may take into account the predicted power output of the heater as described elsewhere herein, where the available amount of heating power has the effect of slowing the decline in storage pressure to release a given amount of steam.

[0246] In the example installation 100 of FIG. 1 , the controller 200 is configured to evaluate criteria that are repeatedly evaluated throughout the depletion period based on predicted demand during the depletion period from 09:00 to 17:00 and the determined flash potential during that period. The predicted demand is determined as the mass of steam (e.g., in kg) required during the depletion period, the demand corresponding to heating is the predicted demand determined by the controller as a function of forecasted weather conditions, and the demand corresponding to sterilization is the predicted demand corresponding to the average of historical demand for the same day of the week over the last six weeks (e.g., if today is Thursday, the last six Thursdays). For example, the controller may receive weather forecast data including the average forecast temperature for the day or depletion period and evaluate a function that accounts for baseline heating demand as a function of the average forecast temperature. In other examples, the heating demand and / or sterilization demand may be determined based at least in part on other data for that particular day. For example, the heating demand may be predicted based on the number of rooms predicted to be used based on a central calendar system of the plant 10, or the sterilization demand may be predicted based on a database storing information about the sterilization operations to be performed each day.

[0247] In this example, the flash potential is determined at each time based on the current storage conditions, i.e., the current storage pressure (based on the pressure signal) and the current liquid level (based on the level signal) in the pressure vessel, and is expressed as a mass of vapor (e.g., in kg). The flash potential is determined as a predicted flash potential based on the current storage conditions and based on a predicted power output of the heater as described elsewhere herein. For example, controller 200 may receive power forecast data received by the controller from a local power source (e.g., defining a predicted power availability for multiple 10-minute time segments predicted by a controller of a local power source, such as a wind turbine or microgrid, based on weather forecast data), and controller 200 may simulate a profile of storage conditions in the pressure vessel through the end of the depletion period based on the current storage conditions, the predicted demand, and the predicted power output of the heater.

[0248] In this example, a criterion corresponding to whether flash potential is sufficient to meet projected demand is evaluated by determining whether the level margin is predicted to be negative during the simulated depletion period.

[0249] If the controller 200 evaluates the criteria and determines that the flash potential is insufficient to meet the forecasted demand, the controller takes responsive action to reduce steam consumption by lower priority loads.

[0250] In this particular example, the controller 200 stores priority data defining the priority of each heat load, specifically, priority 0 (low priority) for the first heat load 30 (heating system) and priority 1 (high priority) for the second heat load 40 (sterilization system). Based on the priority data, the controller takes responsive action by transmitting a load shedding signal to the controller of the plant 10 controlling the first heat load to indicate a reduced capacity to meet the heat energy demand of the load. Thus, the plant 10 can transition to a lower power consumption mode (e.g., by setting a lower setpoint for the system), thereby reducing the heat energy demand.

[0251] In other embodiments, the controller 200 may take other response actions, such as controlling the respective control valves of the lower priority heat loads to prevent the release of steam to the respective loads regardless of the respective heat energy demand, or controlling the respective control valves to release steam to only partially meet the respective heat energy demand.

[0252] Figure 9 illustrates a further exemplary thermal energy storage and supply facility 900 installed for use with an industrial plant 90. Many of the components of this facility and industrial plant are substantially the same as those described above with reference to the embodiment of Figure 1, and like reference numbers are used for like components.

[0253] Specifically, similar components in the industrial plant 90 include a heating system with a single heat plant load 40 thermally coupled to a heat exchanger 930 of the facility 900 by a closed circuit 132 as described above with reference to the exemplary industrial plant 10 of FIG. 1.

[0254] Components within facility 900, all as described above with reference to FIG. 1, are described in this paragraph and include a pressure vessel 110 containing water having a liquid level 113, with a heater 112 and associated power source 113. The pressure vessel includes a degasser 120 supplied with subcooled liquid from a subcooled water supply 150 by an injection pump 122. The pressure vessel 110 has an outlet 116 that discharges steam into a discharge line 101. Sensing equipment includes a level sensor 214 and a pressure sensor 210 located within the pressure vessel as described above. A heat exchanger 930 is provided as the facility's heat load to receive the steam discharged from the pressure vessel, but is distinct from heat exchanger 130 as described below.

[0255] Installation 900 differs from the installation described above with reference to FIG. 1 in that heat exchanger 930 is positioned relative to pressure vessel 110 to define a thermosiphon between the pressure vessel and the heat exchanger, whereby vent steam condensing in the heat exchanger forms a column of subcooled water that is returned to a condensate inlet at the bottom of the pressure vessel via condensate return line 903. Specifically, heat exchanger 930 is positioned above the pressure vessel (and thus above the peak liquid water level in the pressure vessel, expressed in height) by a height difference of, for example, at least 0.5 m, measured between the top of the heat exchanger elements of the heat exchanger and the top of the pressure vessel (e.g., between 0.5 m and 2 m, e.g., 0.6 m or 1 meter). The heat exchanger can be positioned above the pressure vessel by virtue of the condensation location in the heat exchanger being above the top of the pressure vessel or above the operating range of fill level in the pressure vessel by a height difference of, for example, at least 0.1 m, e.g., at least 0.2 m, e.g., between 0.1 m and 2 m. The controller 920 is configured to discharge steam into the heat exchanger with a minimum pressure drop from the storage pressure so that there is sufficient head to return subcooled water to the pressure vessel under gravity at any fill level given the relative positions of the heat exchangers. The action of the heat exchanger to condense the steam is believed to promote the continuous flow of steam from the pressure vessel in the manner of a thermosiphon. The subcooling in the heat exchanger 930 also densifies the water, promoting its recirculation back to the pressure vessel 110.

[0256] The controller can control the control valve 915 to fully open so that steam is substantially discharged at storage pressure. In the event of excessive steam flow for the heat load, the controller can control the control valve to open on a fixed duty cycle to regulate flow over a period of time (e.g., open 60% of the time and closed 40% of the time in a given period). In an alternative embodiment, instead of or in addition to the discharge control valve 915 at the pressure vessel discharge, there can be a condensate line control valve 915' disposed along the condensate return line 903 that conveys condensate from the heat exchanger 930 to the pressure vessel 110. The controller can be operatively coupled (not shown) to control the condensate line control valve 915' to regulate (e.g., selectively enable) the condensate column formed in and downstream of the heat exchanger 930 back to the pressure vessel. When condensate line control valve 915' is closed, condensate accumulates within heat exchanger 930 to prevent further steam from entering heat exchanger 930, thereby limiting the release of steam from the pressure vessel.

[0257] The pressure reduction (if any) by the control valve 915 at the pressure vessel discharge can be controlled to vary the pressure exerted by the water column to allow condensate to return to the pressure vessel. Similarly, the amount of subcooling in the heat exchanger 930 can be controlled to vary the density of the subcooled water to control thermosiphon flow. Also, the appropriate height can be selected for any particular installation through modeling to ensure continuous operation as a thermosiphon over the desired range of conditions.

[0258] Because there is only a single heat load 930, in this example there is a single discharge control valve 915 operably coupled to the controller along discharge line 101 to control the discharge of steam to heat exchanger 930 (although this is optional as discussed above). Downstream of the discharge / discharge control valve 915 are a flow meter 916 and a pressure sensor 918 coupled to controller 920 to provide flow and pressure signals, respectively. In this simplified example, discharge line 101 discharges steam only to a single delivery line 902 that extends to heat exchanger 930, although it should be appreciated that in alternative embodiments there may be multiple branching delivery lines and this is discussed separately.

[0259] Controller 920 determines demand based on a demand signal from heat plant load 40 and controls heating of water in pressure vessel 930 using heater 112, substantially as described above with reference to controller 200 of FIG. 1 . Controller 920 is configured to control the release of steam based on the demand signal received from heat plant load 40 by controlling release control valve 915. In this example, controller 920 opens release control valve 915 to release steam at a variable release pressure at or slightly below the storage pressure to provide a steam flow rate that enables a target heat transfer rate in heat exchanger 930 that meets demand. As with heat exchanger 130 of FIG. 1 , controller 920 is configured to operate heat transfer pump 133 associated with heat transfer circuit 132 upon selectively releasing steam to heat exchanger 930 for heat transfer. In the alternative example described above, controller 920 can control condensate line control valve 915′ to control the release of steam to the heat exchanger at a steam flow rate that enables a target heat transfer rate in heat exchanger 930 that meets demand.

[0260] Because there is a thermosiphon arrangement for the return of condensate to the pressure vessel, subcooled water is naturally returned to the pressure vessel without the need for control by controller 920, except when the controller restricts return flow to control the release of steam from the pressure vessel. Controller 920 is configured to control the initial supply of subcooled water to the pressure vessel via deaerator 120, as described above, from a water supply, shown in this example as water supply vessel 150, but which may be a separate water supply source in other examples.

[0261] In use, an initial supply of water is supplied to pressure vessel 110 from a water supply source up to a target peak water mass as described above. Controller 920 operates heater 112 to heat the water to a target peak storage pressure, such as at least 2 MPa. In response to a demand for thermal energy (e.g., based on a demand signal received from heat plant load 40), controller 920 controls discharge control valve 915 to open to reduce the storage pressure in the pressure vessel, thereby flashing liquid water within the pressure vessel, which is selectively discharged via discharge control valve 915. Alternatively, condensate line control valve 915' may be controlled to discharge steam from the vessel.

[0262] The steam is supplied at discharge pressure to a heat exchanger 930 located above the pressure vessel 110 and condenses in the heat exchanger 930 to release latent heat of vaporization for heat transfer to a working fluid in a heat transfer circuit 132, which then transfers the heat to the thermal plant load 40 (heating system). In response to a demand for thermal energy, the controller 920 also operates a pump 133 in the heat transfer circuit 132 to prepare for heat transfer from the steam received at the heat exchanger 930.

[0263] The steam is subcooled in heat exchanger 930, for example by at least 10°C, and is returned to pressure vessel 110 by a thermosiphon mechanism due to the pressure head of the subcooled water column between heat exchanger 930 and the pressure vessel (together with the flow velocity head due to the steam flow rate). The condensate returning to the pressure vessel can cause thermal stratification of liquid water within the pressure vessel so that the liquid water at the interface with the steam remains at saturation temperature for immediate flashing upon lowering the storage pressure by opening the respective discharge control valve.

[0264] The controller 920 independently controls the heater 112 to heat the water in the pressure vessel according to the method 600 of FIG.

[0265] As described above, the system 900 can be operated to release and then recharge large reserves of thermal energy, e.g., during depletion and recharge periods as described above. Specifically, during depletion periods, steam can be released to the thermal load 930 at a rate such that the enthalpy loss from the pressure vessel (taking into account the enthalpy of the return flow of subcooled water from the heat exchanger 930) is greater than the input energy provided to the water in the pressure vessel via the heater, which can result in the storage pressure of the water in the pressure vessel dropping significantly, e.g., by at least 1 MPa, from a target peak storage pressure (e.g., of at least 2 MPa). Similarly, during periods of no or relatively low demand, the input energy from the heater via the release of steam can be greater than the enthalpy loss (again taking into account the enthalpy of the return flow of subcooled water from the heat exchanger 930), such that the storage pressure can rise over the recharge period, increasing by a significant amount, e.g., by at least 1 MPa.

[0266] Of course, operation of the thermosiphon system 900 of FIG. 9 does not require any procedure for determining the staging of the subcooled water supply, since subcooled water is continuously returned from the heat exchanger 930 through the thermosiphon arrangement.

[0267] The thermal energy storage and supply facilities described herein may have a connection to a non-local power grid (referred to herein as “grid power,” while power drawn from a microgrid is considered to be drawn from a local power source), and a controller of the facility may be configured to evaluate criteria for drawing grid power based on criteria corresponding to (i) the predicted power output of the heater based on power supply from the local power source being insufficient to meet thermal energy demand during a depletion period, and / or (ii) the predicted power output of the heater based on power supply from the local power source being insufficient to meet target peak storage conditions (e.g., target peak storage pressure for a target peak mass of water) during a recharge period.

[0268] Once the demand for auxiliary grid power is determined based on (i) or (ii), the controller can determine when and / or whether to draw grid power based on cost. For example, the cost of electricity may be relatively high during the day and relatively low at night. Thus, the criteria may be biased to allow power to be drawn from the grid source when the cost of electricity is relatively low. The criteria may be based on current or predicted conditions of the pressure vessel, such as the current or predicted flash potential or current or predicted liquid level margin over a period of time. As described elsewhere herein, the predicted flash potential may be based on the predicted demand for thermal energy and / or the predicted power output of the heater (corresponding to the predicted availability of power for heating). Thus, the criteria may allow power to be drawn from the source at a relatively higher cost if it is determined that doing so would otherwise compromise the facility's ability to meet demand. Additionally or alternatively, criteria may be defined such that when there is demand for auxiliary grid power but energy costs are relatively high, steam supply to relatively lower priority heat loads is restricted while steam supply is maintained to higher priority heat loads, as described elsewhere herein.

[0269] By way of example only, a facility may have a local power source including a wind power source and a grid connection to a non-local electrical grid, and an associated industrial plant may be operated such that there is a relatively high demand for thermal energy during daytime operating hours each day starting at 09:00, with a minimum demand for thermal energy between 18:00 and 09:00. Based on conditions within the pressure vessel at 18:00, the controller may determine to provide 700 kW of heating during an overnight recharge period to reach a target peak storage pressure and target liquid water level by 09:00. At the beginning of the recharge period, the controller may predict power availability from the wind-generated power source for the 900 kW heater based on historical power availability data for the heater and / or based on forecast weather conditions (both of which may be determined by reference to historical power availability data and / or weather forecast data provided to or stored in a database accessible to the controller). At an intermediate time within the recharge period (e.g., 03:00), the controller may determine, for example, based on updated forecast weather conditions, that the projected power availability for the recharge period is only 600 kW. Based on this determination, the controller may decide to draw auxiliary power from the grid power source. The controller may determine the latest time at which the withdrawal of auxiliary power can begin based on current and / or forecast conditions at the pressure vessel and delay the withdrawal of auxiliary power until that latest time. Specifically, the heater may have a maximum power output (e.g., 120 kW). Additionally, the rate at which subcooled liquid is introduced into the pressure vessel is limited by the amount of parallel heating (e.g., to maintain flash potential while raising the liquid level margin) and / or by the rate at which such subcooled liquid can be introduced while still being sufficiently degassed.

[0270] The present disclosure extends to the subject matter of the following numbered examples:

[0271] Example 1. A thermal energy storage and delivery method, comprising: providing subcooled water to the pressure vessel; heating liquid water in a pressure vessel using an electric heater such that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to increase the storage pressure to a peak storage pressure, wherein the peak storage pressure is at least 0.5 MPa, e.g., at least 1 MPa, or at least 2 MPa; and selectively releasing steam from a pressure vessel outlet to a heat load in response to a thermal energy demand such that the storage pressure drops from the peak storage pressure, e.g., by at least 50% of the peak storage pressure, during the depletion period.

[0272] Example 2. The discharge steam is supplied directly to the heat load without passing through an intermediate steam accumulator, or 2. The method of example 1, wherein any one or more steam accumulators between the pressure vessel and the heat load have a total volume less than the volume of the pressure vessel.

[0273] Example 3. The method of Example 1 or 2, including operating a heater during the depletion period, optionally simultaneously with the selective release of steam.

[0274] Example 4. For part or all of the attrition period, and / or over part or all of the refill period during which the storage pressure rises to the peak storage pressure, e.g., by at least 50% of the peak storage pressure; 4. The method of any of claims 1 to 3, comprising operating the heater without simultaneously supplying subcooled water to the pressure vessel.

[0275] Example 5. Steam is discharged from the outlet so that the liquid water level in the pressure vessel falls below the minimum liquid level for heater operation during the depletion period. Optionally, the controller operates the heater simultaneously with the release of steam when the water level is above the lower limit during the depletion period, and the controller shuts off the heater due to continued release of steam above the lower limit.

[0276] Example 6. Steam is discharged to a heat load at discharge pressure. 6. The method of any one of claims 1 to 5, wherein the vessel is supplied with subcooled water when the storage pressure is greater than the discharge pressure.

[0277] Example 7. The method of example 6, wherein the peak storage pressure exceeds the maximum supply pressure at which the vessel is supplied with subcooled water.

[0278] Example 8. The method of Example 6 or 7, wherein subcooled water is supplied to the pressure vessel during the depletion period, and optionally the mass of subcooled water supplied to the pressure vessel during the depletion period is 50% or less, e.g., 25% or less, 10% or less, or 5% or less, of the mass of steam released during the depletion period.

[0279] Example 9. The method of any of Examples 1 to 6, wherein the heat load includes a heat exchanger positioned relative to the pressure vessel such that a thermosiphon is established between the pressure vessel and the heat exchanger such that vent steam condensing in the heat exchanger during the depletion period forms a column of subcooled water that is returned to a condensate inlet at the bottom of the pressure vessel.

[0280] Example 10. The heat exchanger is located above the condensate inlet to provide sufficient head to return subcooled water to the pressure vessel under the action of gravity, and / or 10. The method of example 9, wherein the heat exchanger subcools the water in the heat exchanger by at least 10° C. relative to the saturation temperature corresponding to the storage pressure.

[0281] Example 11. The method of any of Examples 6 to 10, wherein subcooled water is supplied to the pressure vessel at an injection rate such that the reservoir pressure decreases as the subcooled water is supplied.

[0282] Example 12. The flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure to maintain the release of steam to the heat load; the liquid level margin corresponds to the amount of liquid water in the pressure vessel above the lower limit for heater operation upon release of the flash potential; The method is Evaluating a criterion corresponding to whether the liquid level margin is positive or negative; and providing subcooled water to the pressure vessel based on the assessment to increase the liquid level margin and reduce the flash potential.

[0283] Example 13. The method of example 12, wherein the flash potential is a predicted flash potential that is a function of predicted demand and / or predicted power output of the heater over a period of time, and the liquid level margin is a predicted liquid level margin based on the release of the predicted flash potential over the period of time.

[0284] Example 14. The forecasted demand is based on historical demand data, such as historical steam demand data or historical heat demand data for a device (e.g., facility), and / or forecast demand is based on forecasted weather conditions, and / or The predicted power output of the heater is based on historical power capacity data of the heater; and / or 14. The method of example 13, wherein the predicted power output of the heater is based on forecasted weather conditions.

[0285] Example 15. There are a plurality of heat loads including a first heat load and a second heat load; selectively releasing steam from the pressure vessel through a respective control valve based on the respective thermal energy demand for each of the heat loads; the flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure to maintain the release of steam to the heat load; The method is evaluating a criterion corresponding to whether the flash potential is sufficient to meet the forecasted demand of the plurality of loads; 15. The method of any of examples 1 to 14, further comprising: determining, based on the assessment and the priority data related to the thermal loads, to release steam to the first thermal load to satisfy each first thermal energy demand in preference to releasing steam to the second thermal load to satisfy each second thermal energy demand.

[0286] Example 16. During the refill period, heating the liquid in the pressure vessel to raise the storage pressure to a peak storage pressure by a recharge pressure differential that is at least 50% of the peak storage pressure; supplying subcooled water to the pressure vessel to reach a peak mass of water in the pressure vessel corresponding to a peak liquid level at the peak storage pressure; Optionally, the method of any of Examples 1 to 15, wherein the duration of the refill period is at least 100%, such as at least 125%, or at least 150% of the duration of the depletion period.

[0287] Example 17. The method of Example 16, including staging the water supply profile during the refill period so that it is frontloaded relative to the heating profile during the refill period.

[0288] Example 18. The flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure to maintain the release of steam to the heat load; the liquid level margin corresponds to the amount of liquid water in the pressure vessel above the lower limit for heater operation upon release of the flash potential; The method comprises staging a feedwater profile relative to a heating profile to maintain a minimum recharge flash potential while increasing the amount of water in the pressure vessel to a target peak mass of water so as to progressively increase the liquid level margin during a water priority portion of the recharge period; and thereafter heating the liquid water during the flash-preferential portion of the refill period to raise the storage pressure to the peak storage pressure.

[0289] Example 19. The method of example 18, wherein the minimum recharge flash potential corresponds to a forecasted demand, the forecasted demand corresponds to no demand for steam during an idle portion of the recharge period, and the method includes supplying subcooled water to reduce the storage pressure below a lower limit pressure during the idle portion, and thereafter the pressure is increased by heat input to supply a flash potential corresponding to the non-zero demand.

[0290] Example 20. The maximum rate of steam release per unit area of ​​water surface in a pressure vessel during the depletion period is 150 kg / m 2 hours or less, for example 100 kg / m 2 hours or less, or 50 kg / m 2 20. The method of any one of Examples 1 to 19, wherein the treatment is carried out for no more than 2 hours.

[0291] Example 21. A method for producing a pressure vessel comprising degassing an inlet stream of subcooled water supplied to the pressure vessel along a degassing path by conveying a degassed stream of steam from within the pressure vessel countercurrently therethrough along the degassing path; an inlet stream is provided into the pressure vessel over a range of storage pressures of the pressure vessel; the rate of the degassing stream of steam is varied as a function of the temperature of the inlet stream and / or the temperature difference between the inlet stream and the steam, with the goal that the inlet stream reaches a saturation temperature corresponding to the steam over a range of storage pressures; Optionally, the rate is varied by controlling a control valve for venting the degassing stream of steam and associated entrained gases; 21. The method of any of Examples 1 to 20, optionally wherein the rate, or control valve setting for controlling the rate, is determined by referencing a database of rates or control valve settings correlated to the temperature of the injection stream and / or the temperature of the steam.

[0292] Example 22. The peak storage pressure is at least 2.5 MPa, for example at least 3 MPa, and / or 22. The method of any of Examples 1 to 21, wherein the storage pressure drops during the depletion period to a value of 1.5 MPa or less, such as 1 MPa or less, or 0.8 MPa or less.

[0293] Example 23. The average depletion power is defined as the cumulative enthalpy of steam released from the pressure vessel during a depletion period divided by the duration of the depletion period; 23. The method of any one of Examples 1 to 22, wherein the maximum depletion power is defined as the maximum enthalpy of vapor released during any one minute minimum power evaluation period within the depletion period, divided by the minimum power evaluation period.

[0294] Example 24. The method further comprising using a heater to heat the liquid water in the pressure vessel during a refill period when the storage pressure increases by at least 50% of the peak storage pressure; Average refill power is defined as the cumulative energy imparted to the liquid water by the heater during the refill period divided by the duration of the refill period; The maximum reheat power is defined as the maximum power imparted by the heater to the liquid water within the recharge period; The average reheat power is less than or equal to 50% of the average depletion power, and / or The average reheat power is less than or equal to 50% of the maximum depleted power, and / or 24. The method of claim 23, wherein the maximum reheat power is less than or equal to 50% of the maximum depletion power.

[0295] Example 25. The method of Example 23 or 24, wherein the ratio of the magnitude of (i) the cumulative enthalpy of vapor released from the pressure vessel during the depletion period to (ii) the average reheat power of the heater during the recharge period is at least 25,000 seconds.

[0296] Example 26. The method of any of Examples 1 to 25, carried out using a thermal energy storage and delivery device (e.g., facility) of any of Examples 27 to 47.

[0297] Example 27. A pressure vessel for storing water containing saturated liquid water and steam at a storage pressure of 0.5 MPa, e.g., 1 MPa or 2 MPa, the pressure vessel having a discharge port for discharging the steam to a heat load; an electric heater configured to heat liquid water stored in the pressure vessel to vary the storage pressure within the pressure vessel; controlling the heater to heat the liquid water in the pressure vessel to reach a peak storage pressure of saturated liquid water and steam of at least 0.5 MPa, e.g., at least 1 MPa or at least 2 MPa; controlling the control valve to selectively release steam from the outlet to the heat load in response to a heat energy demand; and enabling steam release to meet thermal energy demand such that the storage pressure drops from the peak storage pressure by a depletion pressure difference of at least 50% of the peak storage pressure. and a controller configured to operate the thermal storage facility.

[0298] Example 28. The outlet is in communication with a heat load to supply discharge steam directly to the heat load without passing through an intermediate steam accumulator; or 28. The apparatus of example 27, wherein any one or more steam accumulators between the pressure vessel and the heat load have a total volume that is less than the volume of the pressure vessel.

[0299] Example 29. The apparatus of example 27 or 28, wherein the controller is configured to control the heater to heat the liquid water in the pressure vessel independently of controlling the control valve to selectively release steam, thereby enabling, in use, heating and steam release to occur simultaneously, and enabling each of heating and steam release to occur without the other.

[0300] Example 30. The apparatus of any of Examples 27 to 29, wherein the controller is configured to control the heater to heat liquid water in the pressure vessel independently of providing subcooled water to the pressure vessel, thereby enabling, in use, simultaneous heating and subcooled water supply, and heating without simultaneous subcooled water supply.

[0301] Example 31. The apparatus of any of Examples 27 to 30, wherein the controller is configured to provide subcooled water to the pressure vessel when the storage pressure is greater than a discharge pressure at which steam is discharged from the discharge port.

[0302] Example 32. The apparatus of any of Examples 27 to 31, further comprising a water pump configured to supply subcooled water to the pressure vessel, optionally wherein the water pump has a maximum water supply pressure that is less than the peak storage pressure.

[0303] Example 33. A system for supplying subcooled water to a pressure vessel, further comprising a subcooled water supply vessel configured to store subcooled water for supply to the pressure vessel; 33. The apparatus of any of examples 27 to 32, wherein the ratio of the storage volume of the subcooled water supply vessel to the storage volume of the pressure vessel is at least 5%, optionally at least 7.5% or at least 10%.

[0304] Example 34. The controller is configured to selectively operate in an extended depletion mode in which the controller allows steam to be released so that the liquid water level in the pressure vessel falls below a lower limit for operation of the heater during a depletion period, and the controller prevents heating by the heater when the liquid level is below the lower limit for operation of the heater; Optionally, the controller is configured to selectively operate the heater in a heat depletion mode in which the controller prevents vapor release that would cause the liquid level to drop below the lower limit, and the controller enables heating by the heater when the liquid level is below the lower limit.

[0305] Example 35. The apparatus of any of Examples 27 to 31, wherein the heat load includes a heat exchanger positioned relative to the pressure vessel to define a thermosiphon between the pressure vessel and the heat exchanger, whereby vent steam condensing in the heat exchanger forms a column of subcooled water that is returned to the condensate inlet at the bottom of the pressure vessel.

[0306] Example 36. The heat exchanger is located at a height above the pressure vessel, and the controller is configured to discharge steam into the heat exchanger at a discharge pressure selected such that there is sufficient head under gravity to return subcooled water to the pressure vessel given the relative positions of the heat exchanger; and / or 36. The apparatus of claim 35, wherein the controller is configured to control heat exchange in the heat exchanger such that the water is subcooled by at least 10°C.

[0307] Example 37. A pressure vessel includes a level sensor configured to provide a level signal to the controller corresponding to the level of water in the pressure vessel; and / or a reservoir pressure sensor configured to provide a pressure signal to the controller corresponding to the pressure of the water in the pressure vessel; and / or a storage temperature signal configured to provide a temperature signal to the controller corresponding to the temperature of the water in the pressure vessel; and / or a discharge pressure sensor configured to provide a pressure signal to the controller corresponding to a discharge pressure at which steam is discharged from the outlet of the pressure vessel; and / or a discharge flow meter configured to provide a flow signal to the controller corresponding to a flow rate of the steam downstream of the discharge outlet; and / or 37. The apparatus of any of claims 27 to 36, comprising an inlet flow meter configured to provide a flow rate signal to the controller corresponding to the flow rate of subcooled water supplied to the pressure vessel.

[0308] Example 38. The flash potential corresponds to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a lower pressure limit to maintain the release of steam to the heat load; the liquid level margin corresponds to the amount of liquid water in the pressure vessel above the lower limit for heater operation upon release of the flash potential; the controller is configured to select whether to operate the thermal storage device in a recharge mode or a depletion mode based on predetermined settings, such as time-dependent settings, or based on user input, or based on a predicted demand profile and / or a predicted power output profile of the heater; and / or wherein in the depletion mode, the controller is configured to evaluate a criterion corresponding to whether the level margin is positive or negative, and if the evaluation corresponds to the level margin being negative, to supply subcooled water to the pressure vessel to increase the level margin and reduce the flash potential; 38. The apparatus of any of Examples 27 to 37, wherein in a refill mode, the controller is configured to (i) maintain a minimum refill flash potential that is a predetermined flash potential or corresponds to a predicted demand while the liquid level margin and the amount of water in the pressure vessel are gradually increased to a target mass of water corresponding to the target liquid level at the peak storage pressure, and (ii) thereafter stage the water supply profile relative to the heating profile to heat the liquid water to raise the storage pressure to the peak storage pressure.

[0309] Example 39. The flash potential is a predicted flash potential, and the controller is configured to predict the flash potential as a function of predicted demand over a period of time and / or predicted power output of the heater; 39. The apparatus of example 38, wherein the liquid level margin is a predicted liquid level margin, and the controller is configured to predict the liquid level margin based on a predicted flash potential release over the period of time.

[0310] Example 40. The controller is configured to determine the predicted demand based on historical demand data, such as historical steam demand data or historical heat demand data, of the equipment; and / or the controller is configured to determine the predicted demand based on forecasted weather conditions; and / or the controller is configured to determine a predicted power output of the heater based on historical power capacity data of the heater; and / or 40. The apparatus of example 38 or 39, wherein the controller is configured to determine a predicted power output of the heater based on forecasted weather conditions.

[0311] Example 41. In a recharge mode, the controller is configured to, if the forecasted demand during an idle portion of the recharge period corresponds to no demand for steam, the controller causes subcooled water to be supplied to reduce the storage pressure below a lower limit pressure during the idle portion; Optionally, the controller is configured to subsequently increase the storage pressure by heating liquid water in the pressure vessel to provide a flash potential corresponding to the non-zero demand.

[0312] Example 42. The controller is 150 kg / m 2 hours or less, for example 100 kg / m 2 hours or less, or 50 kg / m 2 42. The apparatus of any one of claims 27 to 41, configured to control the control valve so that steam is selectively released at a maximum flow rate per unit area of ​​water level in the pressure vessel that is equal to or less than 1 hour.

[0313] Example 43. A pressure vessel is configured to release steam via respective control valves to a plurality of heat loads, including a first heat load and a second heat load; the controller is configured to evaluate a criterion corresponding to whether the flash potential is sufficient to meet the forecasted demand of the plurality of loads; 42. The apparatus of any of Examples 27 to 41, wherein, in response to a result of the evaluation, the controller is configured to evaluate priority data specifying a priority of each of the heat loads and operate in a priority release mode to control the selective release of steam to meet the thermal energy demand of a relatively high priority heat load in preference to controlling the selective release of steam to meet the thermal energy demand of a relatively lower priority heat load.

[0314] Example 44. A system configured to supply water to a heat load in the form of steam discharged from a pressure vessel in an open configuration, whereby the heat load consumes the water supplied as steam without a corresponding return of water as condensate; 44. The apparatus of any of Examples 27 to 43, wherein the controller is configured to discharge steam to the heat load at a minimum discharge pressure between 0.5 MPa and 1.0 MPa, or the heat load is configured to receive discharged steam at a minimum discharge pressure between 0.5 MPa and 1.0 MPa.

[0315] Example 45. A system configured to supply steam discharged from a pressure vessel to at least two heat loads, Optionally, the heat storage device is configured to supply water in the form of steam discharged from the pressure vessel in an open configuration to one of the heat loads, whereby the water is contacted with a foreign process fluid or foreign matter and / or discharged from the heat load without a corresponding return of water as condensate; and / or 45. The apparatus of any of Examples 27 to 44, wherein the heat storage device is configured to supply water in the form of steam discharged from the pressure vessel to one of the heat loads in a closed loop, whereby the water is at least partially returned to the pressure vessel as subcooled water, for example via a subcooled water supply vessel.

[0316] Example 46. A pressure vessel includes a degasser configured to receive an inlet flow of subcooled water along a degassing path and to direct a degassed flow of vapor from within the pressure vessel countercurrently along the degassing path; the controller is configured to vary the rate of the degassing flow of the vapor as a function of the temperature of the inlet stream and / or the temperature of the vapor with the goal of the inlet stream reaching a saturation temperature corresponding to the vapor along the degassing path over a range of storage pressures; Optionally, the controller is configured to vary the rate by controlling a control valve for exhausting the degassed stream of vapor and associated entrained gas from the degasser; Optionally, the controller is configured to control the rate or a control valve setting for controlling the rate by referencing a database of rate or control valve settings correlated with the temperature of the injection stream and / or the temperature of the steam.

[0317] Example 47. The apparatus of any of Examples 27 to 46, wherein the heater is installed within the pressure vessel such that the lower liquid level for operation of the heater corresponds to a liquid fraction of water within the pressure vessel of 60% or less, e.g., 50% or less, 40% or less, or 30% or less.

Claims

1. 1. A thermal energy storage and delivery method comprising: providing subcooled water to the pressure vessel; heating liquid water in the pressure vessel using an electric heater so that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to increase the storage pressure to a peak storage pressure of at least 2 MPa; and selectively releasing steam from a discharge outlet of said pressure vessel to a heat load in response to a thermal energy demand such that said storage pressure drops by at least 1 MPa from said peak storage pressure during a depletion period.

2. Discharging steam to the heat load at a discharge pressure; providing subcooled water to the vessel when the storage pressure is greater than the discharge pressure; The method of claim 1 , wherein the subcooled water is supplied to the pressure vessel during the depletion period.

3. there are a plurality of heat loads including a first heat load and a second heat load; selectively releasing steam from the pressure vessel through a respective control valve based on a respective thermal energy demand for each of the heat loads; a flash potential corresponding to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure limit for maintaining the release of steam to the heat load; evaluating a criterion corresponding to whether the flash potential is sufficient to meet the forecasted demand of the plurality of loads; 2. The method of claim 1, further comprising: determining, based on the evaluation and priority data relating to the thermal loads, to release steam to the first thermal loads to satisfy each first thermal energy demand in preference to releasing steam to the second thermal loads to satisfy each second thermal energy demand.

4. During the refill period, heating the liquid in the pressure vessel to increase the storage pressure by at least 1 MPa to a peak storage pressure of at least 2 MPa; supplying subcooled water to the pressure vessel to reach a peak mass of water in the pressure vessel corresponding to a peak liquid level at the peak storage pressure; 2. The method of claim 1, further comprising: staging a profile of water supply during said refill period so as to be frontloaded relative to a profile of heating during said refill period.

5. a pressure vessel for storing water containing saturated liquid water and steam at a storage pressure of 2 MPa, the pressure vessel having an outlet for releasing steam to a heat load; an electric heater configured to heat liquid water stored in the pressure vessel to vary the storage pressure within the pressure vessel; controlling the heater to heat the liquid water in the pressure vessel to reach a peak storage pressure of saturated liquid water and steam of at least 2 MPa; controlling a control valve to selectively discharge steam from the outlet to a heat load in response to a heat energy demand; and allowing steam release to meet the thermal energy demand such that the storage pressure drops by at least 1 MPa from the peak storage pressure. and a controller configured to operate the thermal energy storage and delivery facility.

6. a subcooled water supply vessel configured to store subcooled water for supply to the pressure vessel; 6. The installation of claim 5, wherein the ratio of the storage volume of the subcooled water supply vessel to the storage volume of the pressure vessel is at least 5%.

7. 7. The installation of claim 5 or 6, wherein the controller is configured to selectively operate in an extended depletion mode in which the controller allows steam to be released so that the liquid water level in the pressure vessel falls below a lower limit liquid level for operation of the heater during a depletion period, and the controller prevents heating by the heater when the liquid level is below the lower limit liquid level for operation of the heater.

8. 6. The system of claim 5, wherein the heat load includes a heat exchanger positioned relative to the pressure vessel to define a thermosiphon between the pressure vessel and the heat exchanger, whereby vent steam condensing in the heat exchanger forms a column of subcooled water that is returned to a condensate inlet at a lower portion of the pressure vessel.

9. the heat exchanger is located above the pressure vessel, and the controller is configured to cause the heat exchanger to discharge steam at a discharge pressure selected such that there is sufficient head to return the subcooled water to the pressure vessel under the action of gravity given the relative positions of the heat exchangers; and / or 9. The arrangement of claim 8, wherein the controller is configured to control heat exchange in the heat exchanger such that the water is subcooled by at least 10 degrees Celsius.

10. a flash potential corresponding to the amount of steam that can be flashed from the liquid water in the pressure vessel before the storage pressure reaches a minimum pressure limit for maintaining the release of steam to the heat load; a liquid level margin corresponds to an amount of liquid water in the pressure vessel above a lower limit for operation of the heater upon release of the flash potential; the controller is configured to select whether to operate the equipment in a recharge mode or a depletion mode based on predetermined settings, such as time-dependent settings, or based on user input, or based on a predicted demand profile and / or a predicted power output profile of the heater; and / or wherein in the depletion mode, the controller is configured to evaluate a criterion corresponding to whether the level margin is positive or negative, and if the evaluation corresponds to the level margin being negative, to supply subcooled water to the pressure vessel to increase the level margin and reduce the flash potential; 6. The system of claim 5, wherein in the refill mode, the controller is configured to (i) maintain a minimum refill flash potential that is a predetermined flash potential or corresponds to a forecasted demand while a liquid level margin and a volume of water in the pressure vessel are gradually raised to a target mass of water corresponding to a target liquid level at the peak storage pressure, and (ii) thereafter stage a water supply profile relative to a heating profile to heat the liquid water to raise the storage pressure to the peak storage pressure.

11. 11. The installation of claim 10, wherein in the refill mode, the controller is configured to cause subcooled water to be supplied to reduce the storage pressure below the lower pressure limit during an idle portion of a refill period if the predicted demand corresponds to no demand for steam during the idle portion.

12. the pressure vessel is configured to release steam via respective control valves to a plurality of heat loads, including a first heat load and a second heat load; the controller is configured to evaluate a criterion corresponding to whether flash potential is sufficient to meet the forecasted demand of the plurality of loads; 6. The facility of claim 5, wherein in response to a result of the evaluation, the controller is configured to evaluate priority data specifying a priority of each of the heat loads and operate in a priority release mode to control the selective release of steam to meet the thermal energy demands of relatively higher priority heat loads in preference to controlling the selective release of steam to meet the thermal energy demands of relatively lower priority heat loads.

13. configured to supply water to the heat load in the form of steam discharged from the pressure vessel in an open configuration, whereby the heat load consumes the water supplied as steam without a corresponding return of the water as condensate; 6. The installation of claim 5, wherein the controller is configured to discharge steam to the heat load at a minimum discharge pressure between 0.5 MPa and 1.0 MPa, or the heat load is configured to receive discharged steam at a minimum discharge pressure between 0.5 MPa and 1.0 MPa.

14. configured to supply steam discharged from the pressure vessel to at least two heat loads; the installation is configured to supply water in the form of steam discharged from the pressure vessel in an open configuration to one of the heat loads, whereby the water is contacted with a foreign process fluid or foreign matter and / or is discharged from the heat load without a corresponding return of the water as condensate; and / or 6. The installation of claim 5, wherein the installation is configured to supply water in the form of steam discharged from the pressure vessel to one of the heat loads in a closed loop, whereby the water is at least partially returned to the pressure vessel as subcooled water.

15. the pressure vessel comprising a degasser configured to receive an inlet flow of subcooled water along a degassing path and to direct a degassed flow of steam from within the pressure vessel countercurrently along the degassing path; 6. The system of claim 5, wherein the controller is configured to vary the rate of the degassing flow of steam as a function of the temperature of the injection stream and / or the temperature of the steam, with the goal of the injection stream reaching a saturation temperature corresponding to the steam along the degassing path over a range of storage pressures.

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