Heater vessel

Abstract

This invention provides a heater comprising: a shell effective to contain a heat medium, the shell having a heat medium inlet and heat medium outlet; a tube bundle inside of the shell, said tube bundle containing multiple conduits, the conduits defining a plurality of volumes that are not in communication with the volume effective to contain the heat medium; and heating elements within the conduits, the heating elements being electrical resistance heating elements and being removable from the conduits.

Description

[0001] HEATER VESSEL

[0002] Field of the Invention

[0003] This invention relates to a heater and an energy storage system comprising said heater. Background of the invention

[0004] Sustainable energy is an ever-increasing concern in modern society. The drive to replace hydrocarbons as a direct source of power has led to a focus on the electrification of industrial processes. The ability to use renewable sources for such electricity production can greatly reduce the carbon footprint of such industrial processes. However, the supply of renewable energy fluctuates depending, for example, on weather conditions or time of day. In any electrical grid there will also be fluctuations in supply and demand. Such fluctuations can also result in cost fluctuations.

[0005] Therefore, there exists a need for more efficient methods to store energy during times of lower demand and / or higher availability and to return that energy to the system during periods of greater demand or lower supply .

[0006] US9523285 discloses a system to store energy by heating fluid using electrical resistance heating elements and storing the heated fluid. The fluid may be a molten salt. Molten salt is heated during hours of greater availability of energy and energy stored in the molten salt is then used to generate electricity or steam during periods of lesser availability. The assignee of US9523285 markets heaters using electrical resistance heating elements under the trade name DirectConnect™ Medium Voltage Heaters .

[0007] US20090200290 Al discloses a variable voltage transformer useful for powering electrical heaters. Further, segmented heaters are disclosed wherein the heat generated in different segments of the heater vary depending on the desired heat output profile of the heater. Self-regulating heaters are also disclosed in US20090200290 that rely on utilizing the Curie point of the materials used limit temperatures reached in heaters. Other self -regulating heaters are disclosed also utilizing the Curie point of the materials and induction heating.

[0008] US3515980 and US3239749 disclose different designs of tap changing voltage regulators .

[0009] The provision of improved higher density energy storage systems is high desirable to support the electrification of industrial processes as part of the energy transition. In particular, improved aspects of an energy storage system, including a heater would be highly advantageous .

[0010] Summary of the Invention

[0011] The present invention provides a heater comprising: a shell effective to contain a heat medium, the shell having a heat medium inlet and heat medium outlet; a tube bundle inside of the shell, said tube bundle containing multiple conduits, the conduits defining a plurality of volumes that are not in communication with the volume effective to contain the heat medium; and heating elements within the conduits, the heating elements being electrical resistance heating elements and being removable from the conduits.

[0012] The present invention also provides an energy storage system comprising: a first storage vessel effective for storing a heat medium at an elevated temperature; a second storage vessel effective for storing a heat medium at a base temperature; a heater effective for trans ferring heat medium from the second storage ves sel at the base temperature and increas ing the temperature of a heat medium to the elevated temperature and transferring heat medium at an elevated temperature to the first storage ves sel ; and an energy recovery system ef fective for trans ferring heat medium from the first storage ves sel , recovering energy from the heat medium at the elevated temperature thereby reducing the temperature of the heat medium f rom the elevated temperature to the base temperature , and trans ferring heat medium at the base temperature to the second storage ves sel , wherein said heater comprises a shell effective to contain a heat medium, the shell having a heat medium inlet and heat medium outlet ; a tube bundle inside of the shell , said tube bundle containing multiple conduits , the conduit s defining a plurality of volumes that are not in communication with the volume effective to contain the heat medium; and heating element s within the conduit s , the heating elements being electrical resi stance heating elements and being removable from the conduits .

[0013] Brief Description of the Drawings

[0014] Figure 1 a flow scheme for an energy storage scheme according to the present invention .

[0015] Figure 2 shows a heater according to the present invention .

[0016] Figure 3 is a lateral cros s section of an electrical resistance heating element .

[0017] Figure 4 depicts a schematic for a conventional design of tap changing voltage regulator .

[0018] Figure 5 depicts a schematic for a variable voltage , load tap changing transformer .

[0019] Figure 6 depicts a representation of_an embodiment of a trans former and a controller . Figure 7 is a plot of data showing hourly electricity prices for electrical power provided to or from three grids.

[0020] Detailed Description of the Invention

[0021] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques . Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the specification.

[0022] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0023] Figure 1 illustrates an energy storage system in which the heater of the present invention may be applied. In Figure 1, heater 102 converts electrical power 110 from the source of electrical energy 101 to heat energy. The heat energy is used to increase the temperature of a heat medium at a base temperature 111 from a base temperature heat medium storage 103 to an elevated temperature to provide a heat medium at the elevated temperature 112. The heat medium at the elevated temperature 112 is then sent to an elevated temperature heat medium storage 104. The heat medium could be, for example, a molten salt. The heat medium could be liquid sulfur. The heat medium is preferably a fluid that has a high heat capacity, is not corrosive to relatively inexpensive materials , such as carbon steel or stainles s steel at elevated temperature s . The heat medium is al so preferably a fluid that has a viscosity and other properties that permit it to be pumped and to transfer heat effectively .

[0024] The source of electrical energy 101 may have a variable demand and or supply so that at some times , exces s electrical energy is available , and at other times , there i s a need for additional electrical energy . For example , solar or wind power energy may be available at certain times , and not available at other times . The source of electrical energy may be a power grid or could be an electrical generation facility wherein the electrical generation facility may be operated at a constant output and f luctuations in demand provided for by an energy storage system utilizing the present invention . The source of electrical energy may be a generation facility operated at a variable output depending on the availability of electricity, depending on variable energy sources such as solar or wind power generation .

[0025] To minimi ze a need for stand by electrical generation capacity to supply electrical power or steam at times of high demand and / or low production ( or high low demand for other forms of energy provided by the facility utili zing the present invention ) , it is desirable to have systems that ta ke electrical power during times when there is exce ss supply or lower cost , convert that energy into a form that can be stored, and then utilize stored energy during times when demand is higher or supply is lower . Without an effective system to store energy, hydrocarbon fired electrical generation capacity may need to be kept on-line and operating at low production level s until the capacity i s needed . This is extremely inefficient and partially defeats the purpose of using renewable energy to supply electrical energy.

[0026] An acceptable heat medium is NitCal-K™, which is a molten salt available from Yara North America. It is a double salt of calcium and potassium nitrate having a melting point of 131 °C. This material is stable and is not corrosive to carbon steel at temperatures to above 400 °C when intermolecular water has been removed from the molten salt solution according to the supplier' s procedures .

[0027] The heater 102 may increase the temperature of the heat medium from a base temperature of between 100 °C and 290 C or preferably 150 C, and 240 C or more preferably about 190 °C to an elevated temperature of between 300 °C and 500°C, or preferably 350°C and 440°C, or more preferably about 390 °C. The base temperature is a temperature at which heat may be economically extracted from heat medium, and the elevated temperature is a temperature at which the heat medium is thermally stable and not corrosive to reasonable metals, such as carbon steel or stainless steel.

[0028] Heat medium at a base temperature 111 is provided from a base temperature heat medium storage system 103, and the heat medium at an elevated temperature 112 is sent to an elevated temperature heat medium storage 104. The base temperature heat medium storage 103 and elevated temperature heat medium storage 104 are preferably well insulated. Preferably, the temperature loss from the base temperature heat medium storage and elevated heat medium storage would not decrease by more than 20°C, or preferably, not more than 5 °C, over a time period of twelve hours. The capacity of the base temperature heat medium storage 103 and elevated heat medium storage 104 is preferably sufficient to provide the heater with heat medium at design rate s of heat medium flow for a period of four hours , or more preferably at least eight hours .

[0029] Heat medium at an elevated temperature 112 from storage 104 is provided to an energy recovery system 105 . The energy recovery system utilizes energy in the heat medium at elevated temperature 112 to produce an energy output 115 . The energy recovery system 105 may comprise a boiler , ef fective to vaporize water utili zing heat f rom the heat medium at the elevated temperature , a super heater , ef fective to further heat the vaporized water , and a turbine and generator effective to convert superheated steam to produced electrical energy as the energy output 115 . Heat medium at a base temperature 111 is then returned to the base temperature heat medium storage 103 .

[0030] Figure 2 shows a heater according to the present invention . The heater includes heating elements 201 within conduit s 202 . The heater has a structure similar to a conventional shell and tube heat exchanger . A shell 203 surrounds conduits and defines a volume effective to contain the heat medium . The conduits 202 def ine a plurality of volumes that are not in communication with the volume within the shell containing heat medium . The conduit s therefore separate the heat medium 204 from the electrical resi stance elements 201 .

[0031] The shell 203 includes a heat medium inlet 205 and a heat medium outlet 206 . The end of the conduits proximate the outlet end may be sealed in a f loating head to which the distal ends of the conduits are sealed, or the shell may be provided with a bellows 208 to accommodate differential expansion between the conduits 202 and the shell 203 . Providing bellows 208 rather than a floating head avoids a need to prevent leakage past the floating head . Conduits 202 and heating elements 201 may extend through the distal end of the shell 203 and may enter a jumper box 209. The jumper box 209 may be attached to the conduits 202 and the jumper box may move laterally as the tubes and heater elements 201 expand upon heating, or the conduits 202 outside surface could be sealed at the point the tubes enter the jumper box and slide in and out as the conduits 202 and heating elements 201 expand. The jumper box 209 could contain a dielectric fluid such as a transformer oil 210. The heating elements 201 may be connected to each other, for example in pairs by jumpers 211 inside of the jumper box 209. Conduits 202 are shown as extending into the jumper box 209 but they could terminate, for example, at the distal end of the shell 203 and only heating elements 201 extend into the jumper box 209.

[0032] The heater may contain baffles 216 (four shown) . These baffles may be arranged in a segmented or helical configuration. The baffles 216 direct flow of heat medium 204 across the conduits to provide for increased heat transfer of heat from the heating elements 201 to the heat medium 204 and provide for a more uniform temperature of the heat medium 204 and along the heating elements 201 as the heat medium flows through the shell side of the heater and a more uniform temperature along each of the conduits 202 and heating elements 201.

[0033] The heating system may have a fixed end 217. The fixed end 217 may contain tube sheet 218 may secure and seal the conduits 202. The electrical resistance heating element 201 may extend through tube sheet 218 into an electrical connection box 220. The heating element ends in the electrical connection box 220 may be connected, for example, in pairs, by electrical connector end jumpers 221 to provide series connections of heating elements 201. These groups of series connected heating elements may also be electrically interconnected in separate parallel circuits depending on the level of heat flux is needed to provide the necessary temperature increase in the heating medium. Heating element ends may also be connected, for example, by electrical connectors 222 to electrical power supply 223.

[0034] The heating elements 201, because they are not in contact with the heat medium and are contained in the volumes defined by the conduits, are provided with accessibility so that individual heating elements may be removed without opening the volume containing the heat medium and without having to provide for a seal between the heating element and the shell 203. Accessibility could be provided by having ends of the jumper box 209 and the electrical connection box 220 flanged so that they may be removed .

[0035] To avoid contamination of heat medium 204 with any fluids from the jumper box 209 or the electrical connection box 220, for example, transformer oil, the volume between the jumper box 209 and the inside of the shell 203 could be purged with an inert material such as nitrogen. An air gap or epoxy seals could also be utilized.

[0036] Electrical power supply 223 may be provided from a transformer 225. Electrical power supply may be provided at voltages of, for example, between 600 and 12,000 volts. Preferably, the electrical power supply is provided between 1000 and 10,000 volts or more preferably between 3000 and 9000 volts. Utilizing a power supply at these voltages reduces the electrical current needed to provide a given about of energy, and significantly reduces the amount of equipment needed to reduce voltage from typical system line voltages. Higher voltages are not preferred because electrical heating elements would require insulation to result in long and reliable heater element performance .

[0037] Transformer 225 may be a variable voltage trans former , and preferably a trans former with automatic tap changing provided . The automatic tap changing provi sions will be on-load type which permits the output voltage to change while the circuit is energi zed with the load connected and electrical current being supplied . This type of tap changer does not require the circuit to be deenergized nor the electrical load to be interrupted . Having on-load tap changing ability within the trans former allows for a constant current operation of the heating element s . By constant current , it i s to be understood that the current is within a reasonable range of currents , such as within 25 percent of a target current , or preferably within plus or minus 10 percent of a target current . Constant current power supply is preferred because a s the temperature of most material s increase , electrical resistance of the material decrease s . Thus , when heating element s get hotter than target temperatures , resistance decreases , and with a constant voltage power supply, the current increases . The increasing current then cause s further increases in heater element temperature . A power supply system that prevents electrical current from significantly increas ing will limit the amount of temperature increase . When temperature limited heating element s are utilized , constant current power supply is also preferred . When a temperature limited heating element such as the Curie point heaters taught by Patent Publication US20090200290 , the electrical res istance of the heating element also decreases . If the power supply system is configured to provide a f ixed voltage the current may increase until this system exceeds its current limitations. A transformer such as a variable voltage transformer that is configured to adjust taps in response to the increase of the electrical load or increase in temperature of the heating medium of the system will prevent the current from increasing in response to a decrease in electrical resistance of the system.

[0038] Electrical resistance heating elements are approximately a resistive load; thus load power is proportional to voltage squared. A variable voltage transformer design is derived from that of a distribution voltage regulator, which is generally designed for linear voltage stepping. Therefore, using a linearly stepped variable voltage transformer on a heater results in nonlinear (quadratic) adjustment of power in fixed steps.

[0039] Utilizing a variable voltage transformer as transformer 225 also provides for a more effective turndown when less than capacity operation is desired. Because the voltage to the heating elements may all be reduced, the heat input to the heater system may be decreased to any power level desired with minimal risk of creating hot spots within the heater system.

[0040] As the power output of a linearly tapped variable voltage transformer on the heater load is quadratic, the low-voltage end of the stepping range or power steps are very small. An improvement is to provide for the variable voltage transformer minimum voltage output to be greater than zero. Having this minimal output voltage will allow for compression of the stepping function into the higher- power range and therefore reduce power step sizes on the top end of the voltage output range. For example, with a linear 32-step variable voltage transformer ranging from, for example, 1.47 KV to 6.6KV, it is possible to limit the max stepping size at the system level to less than 1.2% (except for the lowest power position which would be 1.24% up from zero) . This is much improved compared to the zerobased variable voltage transformer tap range.

[0041] The electrical connection volume 220 and the jumper box 209 may be filled with a dielectric fluid 224, for example, transformer oil. The electrical connection box 220 and the jumper box 209 may be provided with fins 226 to help cool the electrical connection box 220 and the jumper box 209 respectively.

[0042] Use of a shell and conduit structure with heating elements inserted inside the conduits permits the heating elements to be fabricated from materials that may not be suitable for being in contact with a heat medium such as a molten salt. Further, the heating elements may be removed from the tubes and replaced without effecting the materials that are in contact with the heat medium material. Fabrication and performance of shell and tube heat exchangers are also well known and adaptable to the present invention. The conduits could also have more surface area than would be otherwise provided by having heating elements in direct contact with the heat medium. This larger conduit surface area has been found to provide much greater heat transfer for a given volume of shell 203. Conduit inside diameters could be, for example, 2 to 7 centimetres. Utilization of conduits of this diameter may provide heat transfer densities of 0.2 to 0.5 megawatts per m3of volume within the shell 203. Conduits may be provided with intermediate spacing (similar to tube pitch for shell and tube heat exchangers) of 1.25 to 1.5 times the conduit diameter, for example, 2 cm conduit at 30 degree pitch results in 0.25 cm intermediate spacing.

[0043] Providing conduits 202 within which heating elements 201 are provided avoids a need to weld or seal the heating elements to the tube sheets 218. This is a significant advantage because brazing, welding or otherwise sealing the sheath of a mineral insulated heating element will disturb the mineral insulation layer and cause cracks or voids within this insulating layer . The cracks or voids provide pathways for arcing and could cause failure of the heating element s .

[0044] Figure 3 is a lateral cros s section of an electrical resistance heating element that can be used a s heating element 201 . An electrical resistance heating element that is not temperature limited may be a mineral insulated heating cable . In the embodiment of a mineral insulated heating element that is not temperature limited , a sheath 301 may surround mineral insulation 302 . The mineral insulation may be magnesium dioxide , for example . The mineral insulation provides electrical insulation between the sheath 301 and a heating element 303 . The heating element may be , for example , a nickel alloy with an electrical resi stance and diameter effective to provide heat along the length of the heating element as electrical current is applied to the heating element .

[0045] The heating element 301 is shown divided into f ive sections . A lead in section 311 extends f rom inside the mineral insulation 302 and extends to out side of the mineral insulation and sheath 301 . The lead in section 311 is an electrically conductive material with a low electrical resi stance so that heat is not generated in the lead in section 311 . The lead in section 311 preferably is long enough to extend into shell 203 of the heater and past any tube sheet 218 .

[0046] An inlet end section 312 of the heating element 303 is connected to the lead in section 311 . The inlet section of the heater may be designed to provide a greater heat flux than the remaining heating element because heat medium entering the heater at this section will be cooler and transfer more heat from the heating element . A middle section 313 of the heating element 303 may be designed to operate at a lower heat flux than the inlet section 312 and / or a higher temperature to accommodate heat medium increasing in temperature as the heat medium passes through the heater. An outlet section 314 may be provided with a lower heat flux and / or higher temperature capability than the middle section 313 to accommodate further increase in heat medium temperature as the heat medium passes through the heater. A lead out section 315 may be provided that is an electrically conductive material with a low electrical resistance. The lead out section in this embodiment will not generate significant heat flux in a region where the heat element passes through a tube sheet such as a floating head, and into a jumper enclosure 209.

[0047] A temperature limited heating element 301 is preferred. A temperature limited heating element is an element that will produce less heat at an elevated temperature. An example of a temperature limited heating element is a heating element that utilizes a Currie point transition temperature to reduce the electrical resistance of the heating element as the heating element approaches or exceeds the Currie point temperature of a material. US10119366 and patent publication US20090200290 describes such a heating element.

[0048] Co-pending patent applications US63 / 489444 and US63 / 489447 disclose a different embodiment of a temperature limited heater. This temperature limited heater utilizes a semiconductor layer that has includes electrical characteristic that electrical resistance decreases with increasing temperature.

[0049] The preferred electrical supply for the heating systems of the present invention includes microprocessor controllers that monitor output voltage from the variable voltage transformer power supply and adj ust taps up or down to generate the appropriate output to provide the desired heater outlet temperature . These controllers include current and tap position monitoring and may be equipped with remote communications capabilitie s . The controller firmware of commercially available transformers may be modified for current based control ( for example , control de sired for maintaining constant wattage as heater resistance s vary with temperature ) . Load resi stance monitoring as well as other electrical analysi s-ba sed evaluation and control are a pos sibility because of the availability of both current and voltage sens ing by the controller . In addition to current , sensed electrical properties including , but not limited to power, voltage , power factor , resistance or harmonics may be used as control parameters . Typical tap changers have a 400% of nominal , short time current rating , Thus , the regulator controller may be programmed to respond to overload current s by means of tap changer operation .

[0050] Electronic heater controls such as silicon- controlled rectifiers ( SCRs ) are often used to provide power to and control resistive heating loads . SCRs may be expensive to use and may waste electrical energy in the power circuit . SCRs may also produce harmonic distortions during the nonlinear power control of the res istive heating loads . Harmonic distortion may re sult in unacceptable power quality on the power line feeding the heating system and negatively impact other electrical loads upstream of the heating load . This negative impact can be so significate that it may result in the electrical power utility requiring this electrical heating load being removed from service . In addition , SCRs may overly stre s s heaters by switching the power between being full on and full of f in short periodic bursts rather than regulating the power at or near the ideal current setting . Thus , there may be significant overshooting and / or undershooting at the target current for temperature limited heater element s ( for example , heaters using ferromagnetic materials for self-limiting temperature control ) . SCRs are also available in lower voltage ranges than are desirable for the present heating system . Because of the lower voltage required, more let down transformers and much higher current would be required .

[0051] A variable voltage , load tap changing transformer , which i s based on a load tap changing regulator design, may be used to provide power to and control res istive heater power supply more simply and without the harmonic distortion and power quality is sues as sociated with electronic semiconductor-based heater control . The variable voltage transformer may be connected to power distribution systems by simple , inexpensive fused cutouts . The variable voltage transformer may provide a cost effective , stand alone , fully functional heater controller and i solation transformer .

[0052] Figure 4 depicts a schematic for a conventional design of tap changing voltage regulator 401 . Regulator 401 provides plus or minus 10% adj ustment of the input or line voltage . Regulator 401 include s primary winding 402 . Primary winding 402 i s a series winding electrically coupled to the secondary winding of tap changer section 403 . Tap changer section 403 includes eight taps 404A-H that separate the voltage on the secondary winding into voltage steps . Moveable tap changer 405 i s a moveable preventive autotransformer with a balance winding . Tap changer 405 may be a s liding tap changer that moves between taps 404A-H in tap changer section 403 . Tap changer 405 may be capable of carrying high currents up to , for example , 668 A or more . Tap changer 405 contacts either one tap 404 or bridges between two taps to provide a midpoint between the two tap voltages. Thus, 16 equivalent voltage steps are created for tap changer 405 to couple to in tap changer section 403. The voltage steps divide the 10% range of regulation equally (5 / 8 % per step) . Switch 406 changes the voltage adjustment between plus and minus adjustment. Thus, voltage can be regulated plus 10% or minus 10% from the input voltage. In this version of transformer 225, voltage transformer 407 regulates the output voltage of transformer 409.

[0053] Voltage transformer 409 senses the potential at bushing 408. The potential at bushing 408 may be used for evaluation by a microprocessor controller. The controller adjusts the tap position to match a preset value. Control power transformer 409 provides power to operate the controller and the tap changer motor. Current transformer 410 is used to sense current in the regulator.

[0054] Figure 5 depicts a schematic for variable voltage, load tap changing transformer that could be utilized as transformer 225. The schematic for this version of transformer 225 is based on the load tap changing regulator schematic depicted in Figure 4. Primary winding 402 is isolated from the secondary winding of tap changer section 403 to create distinct primary and secondary windings. Primary winding 402 may be coupled to a voltage source using bushings 411, 412. The voltage source may provide a first voltage across primary winding 402. The first voltage may be a high voltage such as voltages of_at least 5 kV, at least 10 kV, at least 25 kV, or at least 35 kV up to about 50 kV. The secondary winding in tap changer section 403 may be coupled to an electrical load (for example, one or more subsurface heaters) using bushings 413, 414. The electrical load may include, but not be limited to, an insulated conductor heater (for example, mineral insulated conductor heater) , a conductor-in- conduit heater, a temperature limited heater, a dual leg heater, or one heater leg of a three-phase heater configuration.

[0055] The secondary winding in tap changer section 403 steps down the first voltage across primary winding 402 to a second voltage (for example, voltage lower than the first voltage or a second voltage) . In certain embodiments, the secondary winding in tap changer section 403 steps down the voltage from primary winding 402 to the second voltage that is between 5% and 20% of the first voltage across the primary winding. In some embodiments, the secondary winding in tap changer section 403 steps down the voltage from primary winding 402 to the second voltage that is between 1% and 30% or between 3% and 25% of the first voltage across the primary winding. In one embodiment, the secondary winding in tap changer section 403 steps down the voltage from primary winding to the second voltage that is 10% of the first voltage across the primary winding. For example, a first voltage of 7200 V across the primary winding may be stepped down to a second voltage of 720 V across the secondary winding in tap changer section 403.

[0056] In some embodiments, the step-down percentage in tap changer section 403 is preset. In some embodiments, the step-down percentage in tap changer section 403 may be adjusted as needed for desired operation of a load coupled to transformer 225.

[0057] Taps 404A-H (or any other number of taps) divide the second voltage on the secondary winding in tap changer section 403 into voltage steps. The second voltage is divided into voltage steps from a selected minimum percentage of the second voltage up to the full value of the second voltage . In certain embodiment s , the second voltage is divided into equivalent voltage steps between the selected minimum percentage and the full second voltage value . In some embodiments , the selected minimum percentage is 0 % of the second voltage . For example , the second voltage may be equally divided by the taps in voltage steps ranging between 0 V and 720 V. In some embodiment s , the selected minimum percentage is 25% or 50% of the second voltage .

[0058] This vers ion of transformer 225 includes tap changer 405 that contacts either one tap 404 or bridges between two taps to provide a midpoint between the two tap voltage s . The position of tap changer 405 on the taps determines the voltage provided to an electrical load coupled to bushings 413 , 414 . As an example , an arrangement with 8 taps in tap changer section 403 provide s 16 voltage steps for tap changer 405 to couple to in tap changer section 403 . Thus , the electrical load may be provided with 16 different voltages varying between the selected minimum percentage and the second voltage . As another example , an arrangement with 6 taps in tap changer section 403 provides 32 voltage steps for tap changer 405 to couple to in tap changer section 403 . Thus , the electrical load may be provided with 32 different voltages varying between the selected minimum percentage and the second voltage .

[0059] In certain embodiments of transformer 225 , the voltage steps divide the range between the selected minimum percentage and the second voltage equally ( the voltage steps are equivalent ) . For example , eight taps may divide a second voltage of 720 V into 16 voltage steps between 0 V and 720 V so that each tap increments the voltage provided to the electrical load by 45V . In some embodiment s , the voltage steps divide the range between the selected minimum percentage and the second voltage in non-equal increments (the voltage steps are not equivalent) .

[0060] Switch 406 may be used to electrically disconnect bushing 414 from the secondary winding and taps 404. Electrically isolating bushing 414 from the secondary winding turns off the power (voltage) provided to the electrical load coupled to bushings 413, 414. Thus, switch 406 provides an internal disconnect in transformer 225 to electrically isolate and turn off power (voltage) to the electrical load coupled to the transformer.

[0061] In this version of transformer 225, voltage transformer 407 controls power transformer 409, and current transformer 410 is electrically isolated from primary winding 402. Electrical isolation protects voltage transformer 407, control power transformer 409, and current transformer 410 from current and / or voltage overloads caused by primary winding 402.

[0062] In certain embodiments, transformer 225 is used to provide power to a variable electrical load (for example, a temperature limited heater using ferromagnetic material that self-limits at the Curie temperature or a phase transition temperature range) . Transformer 225 allows power to the electrical load to be adjusted in small voltage increments (voltage steps) by moving tap changer 405 between taps 404. Thus, the voltage supplied to the electrical load may be adjusted incrementally to provide essentially constant current to the electrical load in response to changes in the electrical load (for example, changes in resistance of the electrical load) . Voltage to the electrical load may be controlled from a minimum voltage (the selected minimum percentage) up to full potential (the second voltage) in increments. The increments may be equal increments or nonequal increments. Thus, power to the electrical load does not have to be turned full on or off to control the electrical load such as is done with a SCR controller. Using small increments may reduce cycling stress on the electrical load and may increase the lifetime of the device that is the electrical load. This version of transformer 225 changes the voltage using mechanical operation instead of the electrical switching used in SCRs . Electrical switching can add harmonics and / or noise to the voltage signal provided to the load. The mechanical switching of transformer 225 provides clean, noise free, incrementally adjustable control of the voltage provided to the electrical load.

[0063] Referring to Figure 6 in combination with Figure 5, transformer 225 may be controlled by controller 415. Controller 415 may be a microprocessor controller. Controller 415 may be powered by control power transformer 409. Controller 415 may assess properties of transformer 225, including tap changer section 403, and / or the electrical load coupled to the transformer. Examples of properties that may be assessed by controller 415 include, but are not limited to, voltage, current, power, power factor, harmonics, tap change operation count, maximum and minimum value recordings, wear of the tap changer contacts, measured temperatures of the heat medium 204, and electrical load resistance.

[0064] In certain embodiments, controller 415 is coupled to the electrical load to assess properties of the electrical load. For example, controller 415 may be coupled to the electrical load using an optical fibre. The optical fibre allows measurement of properties of the electrical load such as, but not limited to, electrical resistance, impedance, capacitance, and / or temperature. In some embodiments, controller 415 is coupled to voltage transformer 409 and / or current transformer 409 to assess the voltage and / or current output of transformer 225. In some embodiments, the voltage and current are used to assess a resistance of the electrical load over one or more selected time periods. In some embodiments, the voltage and current are used to assess or diagnose other properties of the electrical load (for example, temperature) .

[0065] In certain embodiments, controller 415 adjusts the voltage output of transformer 225 in response to changes in the electrical load coupled to the transformer or other changes in the power distribution system such as, but not limited to, input voltage to the primary winding or other power supply changes. For example, controller 415 may adjust the voltage output of transformer 225 in response to changes in the electrical resistance of the electrical load. Controller 415 may adjust the output voltage by controlling the movement of control tap changer 405 between taps 404 to adjust the voltage output of transformer 225. In some embodiments, controller 415 adjusts the voltage output of transformer 225 so that the electrical load (for example, a subsurface heater) is operated at a relatively constant current. In some embodiments, controller 415 may adjust the voltage output of transformer 225 by moving tap changer 405 to a new tap, assess the resistance and / or power at the new tap, and move the tap changer to another new tap if needed.

[0066] In some embodiments, controller 415 assesses the electrical resistance of the load (for example, by measuring the voltage and current using the voltage and current transformers or by measuring the resistance of the electrical load using the optical fibre) and compares the assessed electrical resistance to a theoretical resistance. Controller 415 may adjust the voltage output of transformer 225 in response to differences between the assessed resistance and the theoretical resistance. In some embodiments, the theoretical resistance is an ideal resistance for operation of_the electrical load. In some embodiments, the theoretical resistance varies over time due to other changes in the electrical load (for example, temperature of the electrical load) .

[0067] In some embodiments, controller 415 is programmable to cycle tap changer 405 between two or more taps 404 to achieve intermediate voltage outputs (for example, a voltage output between two tap voltage outputs) . Controller 415 may adjust the time tap changer 405 is on each of the taps cycled between to obtain an average voltage at or near the desired intermediate voltage output. For example, controller 415 may keep tap changer 405 at two taps approximately 50% of the time each to maintain an average voltage approximately midway between the voltages at the two taps.

[0068] In some embodiments, controller 415 is programmable to limit the numbers of voltage changes (movement of tap changer 405 between taps 404 or cycles of tap changes) over a period of time. For example, controller 415 may only allow 1 tap change event 30 minutes or 2 tap changes per hour. Limiting the number of tap changes over the period of time reduces the stress on the electrical load (for example, the heater system) from changes in voltage to the load. Reducing the stresses applied to the electrical heater elements may increase the lifetime of the electrical load. Limiting the number of tap changes may also increase the lifetime of the tap changer apparatus. In some embodiments, the number of tap changes over the period of time is adjustable using the controller. For example, a user may be allowed to adjust the cycle limit for tap changes on transformer 225. In some embodiments , controller 415 is programmable to power the electrical load in a start-up sequence . For example , restive heaters may require a certain start up protocol ( such as high current during early times of heating and lower current as the temperature of the heater reaches a set point ) . Ramping up power to the heaters in a desired procedure may reduce mechanical stres se s on the heaters from material s expanding at different rates . In some embodiment s , controller 415 ramps up power to the electrical load with controlled increases in voltage steps over time . In some embodiments , controller 415 ramps up power to the electrical load with controlled increase s in watts per hour . Controller 415 may be programmed to automatically start up the electrical load according to a user input start up procedure or a pre-programmed start up procedure .

[0069] In some embodiments , controller 415 is programmable to turn of f power to the electrical load in a shutdown sequence . For example , heater systems may require a certain shut down protocol to inhibit the heaters from cooling too quickly . Controller 415 may be programmed to automatically shut down the electrical load according to a user input shut down procedure or a pre-programmed shut down procedure .

[0070] In some embodiments , controller 415 is programmable to power the electrical load in a moisture removal sequence . For example , resistive heaters may require start up at second voltages to remove moi sture from the before application of higher voltages . In some embodiments , controller 415 inhibits increases in voltage “until required electrical load res istance value s are met . Limiting increa ses in voltage may inhibit trans former 225 from applying voltage s that result in a short circuit due to moisture in the system . Controller 415 may be programmed to automatically start up the electrical load according to a user input moisture removal sequence or a pre-programmed moisture removal procedure.

[0071] In some embodiments, controller 415 is programmable to reduce power to the electrical load based on changes in the voltage input to primary winding 402. For example, the power to the electrical load may be reduced during brownouts or other power supply shortages . Reducing the power to the electrical load may compensate for the reduced power supply.

[0072] In some embodiments, controller 415 is programmable to protect the electrical load from being overloaded. Controller 415 may be programmed to automatically and immediately reduce the voltage output if the current to the electrical load increases above a selected value. The voltage output may be stepped down as fast as possible while sensing the current. Sensing of the current occurs on a faster time scale than the step downs in voltage so the voltage may be stepped down as fast as possible until the current drops below a selected level. In some embodiments, tap changes (voltage steps) may be inhibited above higher current levels. At the higher current levels, secondary fusing may be used to limit the current. Reducing the tap setting in response to the higher current levels may allow for continued operation of_the transformer even after partial failure or quenching of electrical loads such as heaters.

[0073] In some embodiments, controller 415 records or tracks data from the operation of the electrical load and / or transformer 225. For example, controller 415 may record changes in the resistance or other properties of the electrical load or transformer 225. In some embodiments, controller 415 records faults in operation of transformer 225 (for example, missed step changes) . In certain embodiments, controller 415 includes communication modules. The communication modules may be programmed to provide status, data, and / or diagnostics for any device or system coupled to the controller such as the electrical load or transformer 225. The communication modules may communicate using serial communications, ethernet, fibre, wireless, and / or other communication technologies known in the art. The communication modules may be used to transmit information remotely to another site so that controller 415 and transformer 225 are operated in a self-contained or automatic manner but are able to report to another location (for example, a central monitoring location) . The central monitoring location may monitor several controllers and transformers (for example, controllers and transformers located in a separate production facility) . In some embodiments, users or equipment at the central monitoring location are able to remotely operate one or more of the controllers using the communications modules.

[0074] Figure 6 depicts a representation of an embodiment of transformer 225 and controller 415. In certain embodiments, transformer 225 is enclosed in enclosure 416. Enclosure 416 may be a cylindrical can. Enclosure 416 may be any other suitable enclosure known in the art (for example, a substation style rectangular enclosure) . Controller 415 may be mounted to the outside of enclosure 416. Bushings 411, 412, 413, and 414 may be open air, high voltage bushings located on the outside of enclosure 416 for coupling transformer 225 to the power supply and the electrical load.

[0075] The applicability of a system to store energy during periods of excess supply in order to convert that energy back into power that may be provided to a power grid may be seen from Figure 7. ERCOT (Electric Reliability Council of Texas) schedules power to electrical power grid covering most of Texas, and published demand and rates on a real time basis. Figure 7 is a plot of data from June 25, 2023, through June 27, 2023, showing hourly electricity prices for electrical power provided to or from three grids. The vertical axis 904 is the electricity price in $ / MWh. The horizontal axis 905 is time. Line 901, with data shown with circles, is the price of electricity in the Houston zone. Line 902, with data shown as triangles, is the price for the North zone. Line

[0076] 903, with data shown as squares, is the price in the south zone. The price of electricity from the grid can be seen to vary considerably over the course of the two days . The prices vary as a function of supply and demand. Over the two days shown, the prices peaked in the afternoon on June

[0077] 26thand, on June 25th, in the late afternoon and early evening .

Claims

SP3193- 28 -C L A I M S1. A heater comprising: a shell effective to contain a heat medium, the shell having a heat medium inlet and heat medium outlet; a tube bundle inside of the shell, said tube bundle containing multiple conduits, the conduits defining a plurality of volumes that are not in communication with the volume effective to contain the heat medium; and heating elements within the conduits, the heating elements being electrical resistance heating elements and being removable from the conduits.

2. A heater as claimed in Claim 1, wherein the tube bundle is removable from the shell.

3. A heater as claimed in Claim 1 or Claim 2, wherein baffles are arranged in a segmental or helical arrangement within the shell in order to direct the flow of the heat medium across the conduits.

4. A heater according to claim 3, wherein the baffles are spiral baffles.

5. A heater according to any one of claims 1 to 3, wherein the heating elements extend from the conduits to an electrical connection volume.

6. A heater according to claim 5, wherein the heating elements include a non-heating section which extends from the shell to within the electrical connection volume.

7. A heater according to claim 5 or claim 6, wherein a dielectric fluid is contained within the electrical connection box.

8. A heater according to any one of claims 1 to 7, wherein power for the heating elements is provided by a variable voltage transformer.

9. A heater according to any one of claims 1 to 8, wherein the heating elements comprise a plurality of segment having variable heat outputs .

10. A heater according to any one of claims 1 to 9, wherein the heating elements are temperature limited electrical heaters.

11. A heater according to any one of claims 1 to 10, wherein the heat medium is a molten salt heat medium.

12. An energy storage system comprising: a first storage vessel effective for storing a heat medium at an elevated temperature; a second storage vessel effective for storing a heat medium at a base temperature; a heater according to any one of claims 1 to 11, said heater being effective for transferring heat medium from the second storage vessel at the base temperature and increasing the temperature of a heat medium to the elevated temperature and transferring heat medium at an elevated temperature to the first storage vessel; and an energy recovery system effective for transferring heat medium from the first storage vessel, recovering energy from the heat medium at the elevated temperature thereby reducing the temperature of the heat medium from the elevated temperature to the base temperature, and transferring heat medium at the base temperature to the second storage vessel.

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