Green Energy Thermal Storage System

Abstract

The thermal energy storage system includes one or more containment vessels including an interior cavity including a bed of a phase change material (PCM) capable of storing thermal energy, an array of heaters embedded in the molten phase change material, and a tube bundle. The heaters are electrically connected to a power source and capable of heating the PCM to a molten state. The tube bundle includes heat exchanger tubes embedded in the molten PCM and is configured to convey a working fluid (e.g., water, etc.) through a tube side of the heat exchanger tubes. The tubes may be arranged in a plurality of separate tube cartridges, each of which is insertable into and removable from the vessel. During operation, the working fluid is heated by absorbing the stored thermal energy from the molten phase change material. The PCM is heated by energy extracted from the power grid during off-peak demand periods.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 297,899, filed January 10, 2022, and U.S. Provisional Patent Application No. 63 / 209,234, filed June 10, 2021. The foregoing applications are incorporated herein by reference in their entireties.

[0002] [Technical field] The present invention relates to energy storage systems, and more particularly to systems that utilize endothermic phase change materials (PCMs) that operate to store thermal energy from power absorbed from a power grid or other power source, such as to produce hot water for district heating or other purposes, or steam for generating electricity via a Rankine cycle during peak load demand periods on the power grid. [Background technology]

[0003] As the transition from traditional energy generation to non-polluting "green" energy accelerates, tens of thousands of fossil-fuel-fired power plants (especially coal-fired plants) around the world are heading for early shutdown and decommissioning. In fact, fueled by a new consensus to decarbonize the economy, the process of retiring older fossil-fuel power plants has already begun in favor of more environmentally friendly, non-polluting, "green" power generation alternatives. The resulting destruction and waste of capital assets is estimated to be in the trillions of dollars, even though other equipment in the traditional steam-electricity Rankine power generation cycle shown in Figure 1A, other than the fossil-fuel boiler (i.e., steam generator), often remains fully functional and operational.

[0004] Another consequence of the increase in green renewable energy is greater fluctuations in power generation levels (high and low), which necessitates energy storage systems to smooth out the power supplied to the grid by these green power generation systems. Summary of the Invention

[0005] The present disclosure provides an environmentally friendly, "green" thermal energy storage system that provides stored thermal energy when needed to heat a heat transfer working fluid. In some embodiments and applications, the working fluid may be water or a water mixture, although other types of working fluids may be used in other applications. The system includes one or more thermal energy storage vessels containing a bed of phase change material (PCM) that absorbs and stores heat from a power source. The PCM heats the working fluid flowing through the vessel on demand for various purposes.

[0006] In some embodiments, the thermal energy storage system of the present invention may be used to heat water for district heating or other uses. In other embodiments, the thermal energy storage system may be used to generate steam to generate electricity. In any of these applications, as further described herein, power is preferably extracted from a power source, such as a power grid, to heat the PCM in the vessel during periods of off-peak load demand on the power grid when energy prices are low. However, these thermal energy systems may also extract power from a power source during other periods, including periods of peak load demand, as needed. Therefore, the timing of drawing power from a power grid or other storage source and storing it as thermal energy is not limited to a specific time period.

[0007] In the latter application, the technology disclosed herein replaces the traditional fossil-fueled boiler portion of the Rankine power cycle with a "green boiler" that functions as both an energy storage device and a corresponding "on-demand" steam and power generation device without consuming fossil fuels, thus significantly saving the huge capital investment in fossil-fueled power plants and fully realizing humanity's energy decarbonization goals.

[0008] The green thermal energy storage and power generation system of the present disclosure provides a means of matching power output to fluctuating load demands on the power grid, and is given the name "green boiler" herein because the system can be retrofitted into existing fossil energy power plants and operated to provide steam and power as needed, eliminating the use of fossil fuels at the power plant. The turbogenerator and remaining Rankine cycle equipment infrastructure of a conventional fossil fuel-fired power plant is maintained; only the fossil fuel boiler and its associated subsystem components are removed and replaced.

[0009] Thus, the green boiler technology disclosed herein contemplates replacing fossil fuel-fired boilers in existing power plants with "green boiler systems," transforming the power plants into both energy storage and clean power generation facilities. In some embodiments, the green boiler system may also be a stand-alone energy storage device that receives input energy from an associated solar, wind, or nuclear power plant.

[0010] The current "green boiler" concept relies on the fact that for most of the 24-hour period, the power supplied to the power grid by power plants exceeds the actual real-time power demand of consumers (industrial, commercial, residential, etc.). This means that there are times when there is cheap surplus power that unfortunately goes to waste. Green boilers capture surplus energy directly from the power grid, or alternatively from an on-site green energy plant (solar, wind, nuclear, etc.), and in one embodiment, thermally store the energy in a phase change material (PCM), such as, but not limited to, a molten salt bed.

[0011] In terms of power generation, the PCM Green Boiler is configured and operated to boil and superheat boiler feedwater for the Rankine power cycle, producing electricity "on demand" whenever the grid faces a power shortage to meet current demand. Therefore, when the grid faces a power shortage, the Green Boiler can function as a peaking power generating unit, replacing traditional small natural gas or diesel peaking units used during periods of grid load fluctuation. In other words, the Green Boiler kicks in when power demand exceeds the grid's baseload capacity. In this way, traditional large, polluting fossil-fuel power plants equipped with fossil-fuel boilers are transformed into on-demand clean energy generators that serve as peaking power generators.

[0012] From a sociological perspective, the reconfigured power plant will continue to employ workers (with some retraining), resulting in little impact on the plant's host community. However, a source of hydrocarbon emissions will be advantageously eliminated. Furthermore, coal-fired power plants also eliminate the residual fly ash and bottom ash that result from burning coal in their boilers. Some coal-fired power plants use wet downspout flushing as a method of ash disposal, thereby removing suspended solids, "heavy metals," or other components contained in the ash from such waste streams and reducing the costs associated with wastewater treatment and purification to meet regulatory emission limits.

[0013] In principle, converting environmentally unclean boilers to green boiler technology is applicable to any fossil fuel plant worldwide, without exception. Thus, decarbonization of the power generation economy can be implemented without delay and with maximum expediency. Scoping calculations show that conversion to green boilers is by far the cheapest route, in terms of capital costs, for decarbonizing existing fossil fuel-fired power plants. Operating costs are similarly lower than any other energy storage and supply technology.

[0014] Replacing existing fossil fuel / coal-fired, oil-fired, or natural gas-fired boilers with "green boilers" consisting of an assembly of fluidly interconnected, heated phase change material (PCM) containment vessels, each of which in one embodiment stores thermal energy in molten salt, is one non-limiting aspect of the innovative green energy storage and power generation systems disclosed herein.

[0015] Each molten salt PCM containment vessel is configured and operable to heat and melt the solid salt particles contained therein with power extracted from the electric grid (or an associated clean energy power plant) via an array of heating elements embedded in the salt stock or bed when available electricity supplied to the electric grid exceeds demand. Each PCM containment vessel comprises a tube bundle containing multiple heat exchanger tubes fluidly isolated from the molten salt bed for conveying and flowing Rankine cycle boiler feedwater through the vessel on the interior tube side of the vessel. The shell side of the vessel (the exterior of the tubes within each vessel) contains molten salt in intimate and direct contact with the exterior of the tubes. During operation of the electric grid to which the Green Boiler Rankine cycle generator is electrically connected, the Green Boiler utilizes the thermal energy stored in the molten salt to heat boiler feedwater in cascaded salt beds of successively higher melting points contained in the heat exchanger vessel to generate steam. The steam is supplied to and drives a steam turbine. The steam turbine rotates an electrical generator that is mechanically coupled to the steam turbine in a known manner to generate electricity "on demand" during peak load periods on the power grid.

[0016] In one embodiment, the molten salt PCM containment vessel of the green boiler system is elongated and may include, in fluid communication on the water side, an optional preheater to preheat the boiler feedwater (still in liquid phase), a boiler to heat the water and convert it to wet (i.e., saturated) steam, and a superheater to dry the steam (i.e., remove moisture) to a superheated state that is supplied to the steam turbine. If the incoming boiler feedwater is sufficiently hot, the preheater may be omitted. Some embodiments include a steam recovery vessel upstream of the steam turbine that receives and recovers the superheated steam directly from the superheater vessel. All of the aforementioned vessels are preferably heavily insulated for thermal insulation and may be housed together within a common enclosure structure or housing. In one embodiment, the vessel is elongated and vertical, and may be placed on a reinforced concrete support pad on a slope or elevated elevation.

[0017] It is worth noting that in fossil boiler retrofit and replacement programs, the green boiler system is sized so that the superheated steam enthalpy is the design standard steam capacity of the fossil boiler it is replacing, and therefore can be used without changing the balance of the power plant's equipment, as there is no change in the equipment's heat load.

[0018] In district heating applications, one or more heated PCM containments, similar in construction to those described above, utilize the thermal energy stored in the molten salt bed to heat and produce hot water, which can then be pumped and distributed to local municipalities to heat buildings. The water is heated to approximately 93°C (approximately 200°F) and kept saturated but not boiling for heating purposes. Multiple heated molten salt containments may be arranged in parallel flow and fluidly coupled to provide the total hot water required for district heating. Advantageously, a modular system can be provided, allowing for additional PCM containments to be added as district heating demand increases with population and infrastructure growth.

[0019] In one aspect, a thermal energy containment vessel comprises an elongate body defining an interior cavity containing a bed of phase change material operable to store thermal energy, an array of heaters embedded in the phase change material, the heaters configured to be electrically coupled to a power source and operable to heat the phase change material to a molten state, and a tube bundle comprising a plurality of heat exchanger tubes embedded in the molten phase change material, the heat exchanger tubes configured to convey a working fluid through the heat exchanger tubes to absorb thermal energy from the molten phase change material. The phase change material may be a salt, and the working fluid may include water alone or a water mixture (e.g., water and glycol).

[0020] In another aspect, a thermal energy storage and power generation system includes a closed flow loop in fluid communication with a steam turbine, a steam condenser, a boiler assembly, and a pump operable to circulate boiler feedwater through the closed flow loop; a generator operably coupled to the steam turbine and an electric power grid; a boiler assembly including a thermal energy boiler vessel and a thermal energy superheater vessel fluidly coupled to the boiler vessel, each vessel including an elongated tubular body defining an interior cavity containing a bed of molten phase change material operable to store thermal energy; and an array of heaters embedded in the molten phase change material, the heaters electrically connected to the electric power grid. and a boiler assembly including an array of heaters coupled to the boiler vessel and energized to heat the molten phase change material, and a tube bundle of heat exchanger tubes embedded in the molten phase change material, the heat exchanger tubes configured to convey boiler feedwater through the tube sides of the heat exchanger tubes, wherein the thermal energy boiler vessel is configured to receive the feedwater in a liquid state, which is heated by the molten phase change material therein to produce saturated steam, and the thermal energy superheater vessel is configured to receive the saturated steam, which is heated to a superheated state by the molten phase change material therein, and the superheated steam flows through a steam turbine that rotates a generator to produce electricity. In some embodiments, the system further includes a thermal energy preheater vessel fluidly coupled in the closed flow loop upstream of the boiler vessel. The preheater vessel may be configured similarly to and have the same characteristics as the boiler vessel and the superheater vessel. The phase change material may be a salt, and different types of salts may be used in each vessel.

[0021] In another aspect, a method for heating a working fluid includes providing a thermal energy storage vessel including an internal cavity containing a bed of solid-state phase change material and a tube bundle comprising a plurality of tubes embedded in the bed of phase change material; applying energy to a plurality of heating elements embedded in the bed of phase change material to heat and transform the phase change material from a solid state to a molten state; and flowing the working fluid through the molten phase change material, which heats the working fluid at a first temperature to a second, higher temperature. The phase change material may be a salt, and the working fluid may include water alone or a water mixture (e.g., water and glycol). In some embodiments, the water is in a liquid state when it enters the thermal energy storage vessel and is heated by the phase change material from the first temperature to the second, higher, liquid temperature. In another embodiment, the water entering the vessel is in a liquid state and is heated by the phase change material to convert the water to steam. In yet another embodiment, the water is saturated steam when it enters the thermal energy storage vessel and is heated by the phase change material to superheated steam. [Brief explanation of the drawings]

[0022] Features of exemplary embodiments of the present invention are described with reference to the following drawings, where like elements are numbered like, and in which:

[0023] [Figure 1A] FIG. 1A is a schematic diagram of a conventional Rankine power cycle system that uses polluting fossil fuel boilers to generate steam.

[0024] [Figure 1B] FIG. 1B is a schematic diagram of a Rankine power cycle system according to the present disclosure, including a non-polluting thermal energy storage green boiler according to the present disclosure for generating steam for the cycle.

[0025] [Figure 2] FIG. 2 is a perspective view of a green boiler including a set of thermal energy storage vessels according to the present disclosure.

[0026] [Figure 3]3 is a partial perspective view of one of the tops of one of the thermal energy storage vessels of FIG. 2. FIG.

[0027] [Figure 4] FIG. 4 is a partial perspective view of the lower part.

[0028] [Figure 5] FIG. 5 is a partial perspective view similar to FIG. 3, but also showing the top opening lid of the container in cross section.

[0029] [Figure 6] FIG. 6 is a top perspective view showing the upper portion of the tube bundle of the container.

[0030] [Figure 7] FIG. 7 is a top perspective view of the lower portion of the tube bundle.

[0031] [Figure 8] FIG. 8 is a bottom perspective view of the top of the tube bundle.

[0032] [Figure 9] FIG. 9 is a bottom perspective view of the lower portion of the tube bundle.

[0033] [Figure 10] FIG. 10 is a side view of a thermal energy storage vessel.

[0034] [Figure 11] FIG. 11 is a top view thereof.

[0035] [Figure 12] FIG. 12 is a bottom view thereof.

[0036] [Figure 13] FIG. 13 is a longitudinal / longitudinal cross-section taken from FIG.

[0037] [Figure 14]FIG. 14 is an enlarged view from FIG.

[0038] [Figure 15] FIG. 15 is a cross-sectional view from FIG.

[0039] [Figure 16] FIG. 16 is a top perspective view of a first embodiment of a heat exchanger tube cartridge of a tube bundle configured for six-pass tube-side flow of working fluid through a vessel.

[0040] [Figure 17] FIG. 17 is a bottom perspective view thereof.

[0041] [Figure 18] FIG. 18 is a first side view thereof.

[0042] [Figure 19] FIG. 19 is a second side view thereof.

[0043] [Figure 20] FIG. 20 is a longitudinal / longitudinal cross-section taken from FIG.

[0044] [Figure 21] FIG. 21 is a top view thereof.

[0045] [Figure 22] FIG. 22 is a bottom view thereof.

[0046] [Figure 23] FIG. 23 is a top perspective view of a second embodiment of a heat exchanger tube cartridge of a tube bundle configured for three-pass tube-side flow of working fluid through a vessel.

[0047] [Figure 24] FIG. 24 is a bottom perspective view thereof.

[0048] [Figure 25] FIG. 25 is a first side view thereof.

[0049] [Figure 26] FIG. 26 is a second side view thereof.

[0050] [Figure 27] FIG. 27 is a perspective view showing the tube-side working fluid flow path passing through the tube cartridge.

[0051] [Figure 28] FIG. 28 is a longitudinal / longitudinal cross-sectional view thereof.

[0052] [Figure 29] FIG. 29 is a top view thereof.

[0053] [Figure 30] FIG. 30 is a bottom view thereof.

[0054] [Figure 31] FIG. 31 is a top perspective view of a third embodiment of a heat exchanger tube cartridge of a tube bundle configured for single-pass tube-side flow of working fluid through a vessel.

[0055] [Figure 32] FIG. 32 is a bottom perspective view thereof.

[0056] [Figure 33] FIG. 33 is a first side view thereof.

[0057] [Figure 34] FIG. 34 is a second side view thereof.

[0058] [Figure 35] FIG. 35 is a longitudinal / longitudinal cross-sectional view thereof.

[0059] [Figure 36]FIG. 36 is a top view thereof.

[0060] [Figure 37] FIG. 30 is a bottom view thereof.

[0061] All drawings are schematic and not necessarily to scale. Parts designated by reference numerals in one figure may be considered to be the same parts as parts appearing in other figures without a number designation for the sake of brevity, unless specifically labeled with a different part number and explained herein. Reference herein to a serial number consisting of multiple figures with the same serial number but different alphabetic suffixes shall be construed as a general reference to all figures sharing the same serial number unless otherwise indicated. DETAILED DESCRIPTION OF THE INVENTION

[0062] The features and advantages of the present invention are illustrated and described herein with reference to exemplary ("example") embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are considered part of this entire specification. Accordingly, the present disclosure should not be limited to such exemplary embodiments, which illustrate some possible non-limiting combinations of features that may exist alone or in other feature combinations.

[0063] In describing the embodiments disclosed herein, references to direction or orientation are intended merely for convenience of description and are not intended to limit the scope of the present invention in any way. Relative terms such as "bottom," "up," "horizontal," "vertical," "upward," "below," "up," "down," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downward," "upwardly," etc.) should be interpreted as referring to the orientation currently being described or shown in the drawings under discussion. These relative terms are for convenience of description only and do not require that the devices be constructed or operated in a particular orientation. Terms such as "mounted," "attached," "connected," "coupled," "interconnected," and the like refer to a relationship in which structures are fixed or attached to one another, directly or indirectly through intervening structures, and to both movable and fixed attachments or relationships, unless expressly stated otherwise.

[0064] As used throughout, the ranges disclosed herein are used as shorthand for describing each and every value within the range. Any value within the range can be selected as the boundary endpoint of the range. Furthermore, all references cited herein for prior patents or patent applications are incorporated herein by reference in their entirety. In the event of a discrepancy between the definitions in this disclosure and those in the references, the present disclosure shall control.

[0065] FIG. 1A illustrates a conventional steam-electric Rankine power cycle with a large fossil-fuel boiler to generate the steam needed to generate electricity. The basic cycle equipment (excluding auxiliary systems) includes a fossil-fuel-fired boiler (e.g., coal, oil, natural gas), a steam turbine-generator set, a condenser that condenses the steam discharged from the steam turbine back into a liquid, and a boiler feed pump that circulates boiler feedwater (heat exchange working fluid) extracted from the condenser through a closed-flow loop formed by piping that fluidly connects each component. A generator is mechanically coupled to the steam turbine and electrically coupled to a power grid (represented by the illustrated transmission tower). Steam generated in the boiler rotates a turbine shaft through a row of turbine blades, which in turn rotates a generator rotor within a stator (magnets), converting mechanical energy into electrical energy. Rankine cycle power generation systems and their power generation operation are well known to those skilled in the art and require no further explanation.

[0066] Rankine system fossil-fuel boilers (steam generators), which convert liquid boiler feedwater into steam, have traditionally been used for base electrical load operation to meet the base load demands of the power grid because such boilers and associated auxiliary equipment cannot be started quickly to generate electricity on demand. In fact, the entire start-up process of a fossil-fueled baseload plant can take many hours to bring all equipment up to full pressure and temperature operating conditions to achieve full load.

[0067] 1B illustrates a clean energy "green" Rankine power cycle system including a steam generator with non-polluting "green boiler" technology according to the present disclosure. The green boiler replaces the fossil fuel steam boiler of FIG. 1A with a thermal energy containment vessel configured as both a phase change material (PCM) containment vessel and a heat exchanger, as further described herein. In one embodiment, the PCM is a molten salt.

[0068] The thermal energy storage and power generation system 100 can be configured and used as a "peaking" power generation system that generates and supplies electricity to the power grid during peak load demand periods. Conversely, during "off-peak" load demand periods when the power grid has excess energy, electrical energy extracted from the power grid can be used to "charge" the molten salt bed of a green boiler, as previously described herein.

[0069] 1B may include, but is not limited to, a steam turbine 102, a generator 103 mechanically coupled thereto and operably connected to an electric power grid 104, a steam condenser 105, a boiler feedwater pump 106, and a molten salt-filled thermal energy storage boiler 120. The feedwater pump circulates boiler feedwater through a closed flow loop 110 formed by piping fluidly coupling the water-receiving components of the Rankine cycle, as shown. With the exception of the present green boiler assembly, the remaining components of the clean energy Rankine cycle operate and produce electricity in a known manner as previously described, similar to a conventional Rankine cycle.

[0070] For on-demand power generation applications using the aforementioned Rankine cycle, the thermal energy storage boiler 120 may be an assembly including multiple fluidly coupled and interconnected thermal energy storage vessels 121. The thermal energy storage vessels may include, in order of working fluid flow, an optional thermal energy preheater vessel 121A, a thermal energy boiler vessel 121B, and a thermal energy superheater vessel 121C. These vessels are plumbed in a serial flow arrangement as shown (see working fluid flow direction arrows). In the illustrated embodiment, the working fluid includes water, which may be the boiler feedwater in the Rankine cycle of FIG. 1B. In some embodiments, the preheater vessel may be omitted if the incoming feedwater from the condenser is sufficiently hot. If used, the preheater vessel receives "cold" liquid feedwater at a first temperature and heats it to a second, higher temperature while it remains in the liquid state. The heated feedwater flows to the boiler vessel, where it is further heated and undergoes a phase change from liquid to saturated vapor before flowing to the superheater vessel. The superheater vessel heats the saturated vapor to a superheated state. The superheated steam flows in a closed flow loop 110 to a steam turbine 102 (FIG. 1B) to drive the steam turbine 102, which rotates a generator shaft or rotor to generate electricity, which is supplied to the power grid.

[0071] Because the preheater vessel 121A, boiler vessel 121B, and superheater vessel 121C receive working fluids (e.g., liquid water or steam) at different temperatures and must heat the fluids to different temperatures and conditions, the PCMs (phase change materials) used in each vessel may differ in at least one property, including, for example, but not limited to, the melting temperature and / or type of PCM. The PCM may be a salt with properties suited to the required heat load.

[0072] 2-15, where applicable, each vessel has a similar structure generally comprising a longitudinally oriented elongated body 123 exhibiting a vertical centerline axis CA passing through the geometric center of each vessel. Each vessel body includes a longitudinal internal cavity 122 extending substantially the entire height of the vessel (excluding the thickness of the vessel's top and bottom closure structures). Each internal cavity contains a bed B of molten salt contained in a captive manner within the vessel such that molten salt does not flow into or out of the containment vessel 121 during boiler operation. Only a working fluid, such as boiler feedwater FW, flows through the vessels in a cascaded series manner, as further described herein.

[0073] The thermal energy containment vessel body 123 may be cylindrical in one embodiment, as defined by cylindrical, vertical sidewalls 124 that define the vessel's internal cavity 122. Each vessel includes a top closure lid 125 coupled to the upper end of the sidewalls 124 and defining the vessel's top, and a bottom closure plate 126 coupled to the lower end of the sidewalls and defining the vessel's bottom. The lid 125 and bottom closure plate 126 are sealed to the ends of the sidewalls, fluid-tightly enclosing the cavity 122 and serving to leak-tightly contain the molten salt bed. In one embodiment, the lid 125 and bottom closure plate 126 may be seal-welded to each end of the cylindrical vessel sidewalls 124. In another embodiment, the lid 125 may be removably coupled to the upper end of the vessel body 123 (e.g., sidewalls 124) via a plurality of threaded fasteners, such as bolts. Other removably fastening methods may also be used.

[0074] The thermal energy containment vessels 121 are supported by and vertically mounted on a reinforced concrete pad 135, as shown. In one embodiment, each vessel may include a number of structural legs 129 that elevate the bottom of the vessel above the concrete pad. The structural legs may be welded to the lower vessel body 123 and secured to the concrete pad via a number of anchor bolts (not shown) or other suitable methods to ensure stability, particularly during earthquakes.

[0075] The cylindrical sidewall 124 of the container body 123 may have a composite structure consisting of an innermost shell 130, an outermost shell 131, and an intermediate shell 132 disposed proximate to but radially spaced from the outermost shell (see, for example, FIGS. 13-15). Thus, the intermediate shell 132 is closer to the outermost shell than the innermost shell. Each shell 130-132 has a hollow, tubular, cylindrical shape.

[0076] The body 123 of the thermal energy containment vessel 121, including the shells 130-132, the top closure lid 125, and the bottom closure plate 126, may in one embodiment be formed of a suitable metal, such as steel, preferably including stainless steel. These components of the vessel body may be welded together to form a welded assembly, with the exception of the top closure lid 125, which in some embodiments may be removably coupled to the sidewall 124.

[0077] In one embodiment, a vacuum annulus 128 may be provided and formed between the outer shell 131 and the intermediate shell 132. The vacuum annulus is evacuated and sealed to subatmospheric pressure (i.e., negative pressure) or vacuum V and serves to thermally insulate the thermal energy containment vessel 121 within the sidewall structure. In one embodiment, the vacuum annulus may be evacuated to approximately 0.067 kPa (0.5 Torr). A plurality of longitudinally spaced annular shell support ribs 134 may be attached between the outermost shell 131 and the intermediate shell 132 to prevent collapse of the vacuum annulus 128 when exposed to a vacuum. The ribs 134 may be formed of a metallic material (e.g., steel or preferably stainless steel) and welded to the shells 131 and 132. The ribs 134 may be insulated in some embodiments to reduce conductive heat transfer from the vessel cavity 122 to the outermost shell 131.

[0078] In one embodiment, the opposing surfaces of the outermost shell 131 and the intermediate shell 132, which may be formed of stainless steel facing inward toward the vacuum annulus 128, are highly polished to form a reflective surface for reflecting heat inward and to increase the insulating value of the vacuum annulus.

[0079] To further insulate the thermal energy containment vessel 121, an insulating annulus 127 may be formed between the innermost shell 130 and the intermediate shell 132, as shown. The insulating annulus 127 has a greater radial width than the vacuum annulus 128 and may include suitable insulating material 133. It is worth noting that the insulating annulus 127 and the vacuum annulus 128 each extend across at least the entire height of the vessel cavity 122 containing the molten salt bed B, and in some embodiments, across the entire height of the sidewall 124 (see, e.g., FIGS. 13 and 14 ).

[0080] Each thermal energy containment vessel 121 further comprises a tube bundle 140 containing multiple heat exchanger tubes 141 embedded in but fluidly isolated from the molten salt bed B. Water (including boiler feedwater in the Rankine cycle of FIG. 1B) or other type of working fluid flows through the interior of the tubes (interior tube side) that penetrate each vessel. Molten salt is located on the shell side of the vessel (outside the heat transfer tubes), in intimate direct contact with the exterior of the heat transfer tubes for heat transfer. The heat exchanger tubes may extend 90% or more of the total height of the vessel cavity 122 to maximize the heat transfer surface area of ​​the tube bundle.

[0081] In one embodiment, the heat exchanger tubes 141 of the tube bundle 140 may be separated, arranged, or clustered into a plurality of individual tube cartridges 142, each removably insertable into the vessel 121 through a corresponding, complementary configured cartridge opening 146 formed in the vessel's top closure lid 125. The cartridges 142 are advantageously replaceable without removing the top closure lid 125 to access the interior cavity of the vessel 121, thereby facilitating tube replacement and reducing replacement costs. The tubes of each cartridge may be arranged and configured to make single or multiple longitudinal passes through the working fluid to absorb heat from the molten salt bed B within the vessel cavity 122 to heat the working fluid.

[0082] FIGS. 16-22 depict a first embodiment of a tube cartridge 142, including an illustrative six-pass tube cartridge 142A, variously shown installed in the thermal energy storage vessel 121 of FIGS. 3-15. As some additional examples, FIGS. 23-30 depict a three-pass tube cartridge 142B. FIGS. 31-37 depict a one-pass tube cartridge 142C. Any number of tube passes suitable for the intended application can be used to sufficiently heat a working fluid, such as water or another heated PCM-containing thermal energy storage vessel 121, to a desired temperature. Regardless of the number of passes, each tube cartridge 142 shares similar features, which will be described in more detail with respect to the six-pass tube cartridge 142A.

[0083] 3-22 , each tube cartridge 142 (e.g., 142A, 142B, 142C) includes a metal cylindrical head 147, which in one embodiment is a solid structure, including a top surface 147a and an opposing bottom surface 147b. The head 147 has a thickness substantially comparable to that of the vessel top closure lid 125 (see, e.g., FIGS. 5 and 14 ). The heads 147 are insertable into respective circular cartridge openings 146 in the top closure lid 125 and are coupled to the lid 125 in a fixed, fluid-tight manner, such as via a seal weld, to prevent molten PCM or associated vapors from leaking to the ambient atmosphere through the interface between the tube cartridge and the lid. Each tube cartridge 142 may be fully supported by the vessel lid 125 in a suspended, vertical cantilever manner, as shown, such that no portion of the tube cartridge 142 or heat exchanger tubes 141 is supported by any portion of the vessel below the lid. As shown in the figure, the tube cartridge 142 has a structure that is elongated in the hand direction.

[0084] The heat exchanger tubes 141 extend parallel to one another longitudinally from the tube cartridge head 147 to the metal lower tube support plate 145. The plate 145 may have any suitable shape, such as an annular flat ring as shown. The upper ends of the tubes are rigidly attached and coupled to the tube cartridge head 147 and extend completely therethrough, as best shown in FIG. 20 . The lower ends of the tubes 141 extend completely through and are rigidly coupled to the lower tube support plate 145. The tubes may be hermetically welded to the cartridge head 147 and the lower tube support plate 145. It is noteworthy that the lower tube support plate 145 is not fixedly attached to the vessel body 121 such that it is slidably removable from the vessel cavity 122 along with the tube cartridge 142.

[0085] Each tube cartridge 142 further comprises a cartridge fluid inlet 150 for introducing a working fluid, such as water (e.g., boiler feedwater) or, in some applications, steam, and a cartridge fluid outlet 151 for discharging the water or steam after it has been heated. The inlet and outlet may be formed by sections of pipe of any suitable configuration having a diameter larger than that of the heat exchanger tubes 141. The inlet and outlet are rigidly attached to and coupled to the tube cartridge head 147 for support. The inlet 150 extends vertically completely through the tube cartridge head 147 and is fluidly coupled to a downcomer 152 coupled to a lower tube support plate 145 (see, e.g., FIG. 20 ). In some embodiments, the downcomer may be coupled and seal-welded to the upper surface of the lower tube support plate. Flow holes (not visible) in the tube support plate 145 directly below and within the downcomer 152 allow the inlet water flow to pass under the plate to redirect to another upflow heat exchanger tube 141.

[0086] Continuing to refer generally to the six-pass tube cartridge 142A, shown generally in an installed state in FIGS. 3-15 and specifically in isolation in FIGS. 16-22. The six-pass tube cartridge 142A comprises heat exchanger tubes 141 configured to pass water through a bed of molten PCM (phase change material) multiple times (e.g., six times) as the water (or steam, as the case may be) is heated to successively higher temperatures by absorbing heat from the PCM bed. Thus, some of the heat exchanger tubes 141 in each tube cartridge of any multi-pass tube cartridge may be upflow tubes and some may be downflow tubes. The upflow tubes in each tube cartridge are fluidly coupled to corresponding downflow tube members by cross-flow conduits 153, or vice versa to form a multi-pass tube flow arrangement. Multiple cross-flow conduits 153 are sealably attached (e.g., welded) to the top surface of the tube cartridge head 147, which in turn is sealably attached to the lower tube support plate 145. The cross-flow conduit reverses the water / steam flow up and down 180 degrees within the tube cartridge 142 .

[0087] Note that the cross-flow conduit 153 may be configured to fluidly couple to a single heat exchanger tube 141 or to multiple tubes, depending on the flow path design within the tube cartridge 142. Thus, the cross-flow conduit may split and distribute the flow from the heat exchanger tube 141 or fluid inlet 150 to multiple tubes (see, e.g., the tee-shaped inlet cross-flow conduit 153a in FIG. 24 or FIG. 30), or may combine the flows from multiple heat exchanger tubes into a single flow (see, e.g., the tee-shaped outlet cross-flow conduit 153a in FIG. 23, FIG. 27, or FIG. 29).

[0088] Any suitable configuration of cross-flow conduit 153 may be used, including, for example, but not limited to, a box-shaped conduit (153b), a round pipe section conduit (153a), or the like, so long as a leak-tight fluid connection is made between the upflow tubes and the downflow tubes. It is noted that cross-flow conduit 153 may be used to fluidly couple fluid inlets 150 and outlets 151 to corresponding upflow tubes.

[0089] Figures 23-30 show a three-pass tube cartridge 142B that is similar in construction to the six-pass tube cartridge 142A described above. Similar features are similarly labeled and have been previously described. Some differences in configuration / construction are that the lower tube support plate 145 has a solid circular shape and the downcomer pipe 152 is centrally located, as opposed to being radially offset as in the six-pass tube cartridge 142A (see, e.g., Figure 16).

[0090] Figure 27, showing a three-pass tube cartridge 142B, includes tube-side fluid flow arrows showing the path that a working fluid, such as water (liquid or vapor state), takes through the tube cartridge 142B as it passes longitudinally through PCM bed B within thermal energy containment vessel 121. It can be seen that the heat exchanger tubes 141 function as both upflow and downflow tubes. The same technique is applicable to a six-pass tube cartridge 142A or any multiple-pass tube cartridge having any other number of passes through the PCM.

[0091] 31-37 depict a single-pass tube cartridge 142C, which is also generally similar in construction to the three-pass and six-pass tube cartridges 142A and 142A described above. Similar features are similarly labeled, as previously noted. One difference is that the lower tube support plate of the multi-pass tube cartridge is replaced with a lower annular header 148 formed from circular cross-section piping. A centrally located downcomer 152 is in fluid communication with the annular header. The lower ends of the heat exchanger tubes 141 are in turn in direct fluid communication with the annular header 148 as shown. During operation, working fluid (e.g., water) flows vertically downward through the downcomer 152 and into the annular header 148, from which the flow is evenly distributed among the heat exchanger tubes. The flow then travels upward within the tubes, making a single pass through the PCM bed B to absorb heat. In one embodiment, the single-pass tube cartridge may include an upper annular header 149 formed by a circular section of tubing that receives the working fluid flowing upward from the tubes to which the upper ends of the tubes are fluidly coupled. The annular header 149 is attached to the top surface of the upper head 147 of the tube cartridge, as shown.

[0092] Regardless of the number of passes, the tube cartridge 142, including the head 147 and lower tube support plate 145, is an entirely metal structure. The fluid inlet 150, fluid outlet 151, cross-flow conduit 153, and lower annular header 148 of the single-pass tube cartridge 142C are preferably formed from a suitable metal material, such as steel or stainless steel. Stainless steel is generally preferred and used whenever possible due to its corrosion resistance. The heat exchanger tubes 141 may be made from any suitable material, including stainless steel whenever possible. The type of tube material can be selected for compatibility with the particular type of PCM material being used, so as to avoid corrosive effects due to the chemistry of the PCM material. Other metal materials may also be used for any of the aforementioned components.

[0093] To distribute the incoming cooled working fluid (e.g., water or steam in one embodiment) to the tube cartridges 142 or collect the heated working fluid exiting the tube cartridges, each thermal energy containment vessel 121 includes multiple inlet and outlet headers. In one embodiment, metallic annular or circular ring headers may be provided, including an inlet ring header 160 and an outlet ring header 161, best shown in Figures 3, 5, 6, 8, and 11. In one embodiment, metallic annular or circular ring headers may be provided, including an inlet ring header 160 and an outlet ring header 161, best shown in Figures 3, 5, 6, 8, and 11. The illustrated embodiment includes a pair of inlet ring headers 160 and a pair of outlet ring headers 161. The inlet and outlet ring headers are concentrically positioned and aligned with each other. Thus, the ring headers may have different diameters to form the nested arrangement shown. Additionally, the inlet and outlet ring headers may be interspersed, rather than adjacent to each other. One inlet ring header 160 includes a header inlet pipe 162 that receives cooled working fluid for distribution, and one outlet ring header 161 includes a header outlet pipe 163 that discharges heated working fluid collected from the tube cartridges 142. Jumper pipes 164 may be used to fluidly couple the two inlet ring headers 160 so that the incoming working fluid is transferred from one ring header to the other. As shown, a similar arrangement and jumper pipe 164 may be used to fluidly couple the two outlet ring headers 161. The number of inlet and outlet ring headers depends on the number of tube cartridges 142 and their arrangement. The fluid inlet 150 from each tube cartridge 142 is fluidly coupled to one of the inlet ring headers 160. The fluid outlet from each tube cartridge is fluidly connected to one of the outlet ring headers 161.

[0094] In one embodiment, the vessel's inlet ring header 160 and outlet ring header 161 may be positioned above and supported by the top closure lid 125 of the thermal energy containment vessel 121. In one embodiment, structural standoff members 165 may be used to elevate each ring header upward and support it from the top surface of the lid (shown schematically in FIG. 3). Any type of structural member (rod, angle, etc.) may be used. The ring headers 160, 161 are formed of a suitable metal such as steel or preferably stainless steel.

[0095] During operation, an incoming cooling working fluid stream, such as water (liquid or vapor), enters the first inlet ring header 160 through the header inlet pipe 162. A portion of the stream is transferred to the second inlet ring header 160 via one or more jumper pipes 164. In other embodiments, instead of serial flow, the incoming working fluid may be split and distributed equally to both inlet ring headers simultaneously. The arrangement and flow scheme of the outlet ring header 161 would also be similar, but reversed.

[0096] In either case, the inlet stream is distributed from each inlet ring header 160 to the tube cartridges 142, where the fluid passes one or more times through the PCM beds in the vessel 121 and is heated. The heated working fluid (liquid or vapor form) is collected from the tube cartridges by a pair of outlet ring headers 161 and discharged through the vessel 121's fluid outlets 181. In one embodiment, the vessel fluid outlets 181 may be fluidly coupled and connected to one of the outlet ring headers 161. The header inlet pipe 162 may likewise be fluidly coupled and connected to one of the inlet ring headers 160. The inlet pipe 162 and outlet pipe 163 may be formed of any suitable metal piping having any suitable configuration.

[0097] The heat exchanger tubes 141 may crack and leak over time because the granular PCM undergoes cyclic phase changes between a liquid / molten state and an at least partially solid state each time heat (thermal energy) stored in the PCM is transferred to and absorbed by water flowing through the PCM bed B within the heat exchanger tubes 141. The corrosive nature of PCMs, such as some molten salts, can corrode the tube material, causing cracks and leaks over time. Either of these situations requires replacement of the tubes and downtime of the affected thermal energy containment vessel 121.

[0098] Advantageously, the tube cartridges 142 disclosed herein allow for the rapid replacement and replacement of individual cartridges and their associated tubing (some of which may be leaking) with identical new, completely pre-assembled tube cartridges without removing the closure lid 125 of the thermal energy storage vessel 121. This eliminates the need for time-consuming replacement or patching of individual leaking heat exchanger tubes. After the thermal energy containment vessel 121 is returned to service, damaged and leaking tubes in the old tube cartridge may be replaced / repaired. This dramatically simplifies vessel maintenance and repair, reducing downtime and, consequently, allowing the vessel to return to service sooner and minimizing lost revenue.

[0099] Each provided thermal energy containment vessel 121 includes an array of heaters embedded in a molten phase change material (PCM) and operable to heat the PCM. The heaters are configured to be electrically coupled to an available source of electrical power for the intended application, such as via suitable commercially available electrical contacts or connectors. The power source may be a commercial local power grid maintained by a public utility, or in some cases, may be a local power source, such as electricity generated at an industrial plant. The heaters convert electrical power received from the power source into thermal energy that is used to heat the PCM.

[0100] 3-14 illustrate various PCM heaters. In one embodiment, the heater 170 comprises a plurality of longitudinally elongated bayonet-type heating elements 170 having an inner ceramic core 172 and an outer metallic sheath 171 in direct contact with the PCM within the interior cavity 122 of the thermal energy containment vessel 121. The heating elements are longitudinally elongated / oriented and may have a cylindrical configuration. The heating elements 170 are radially interspersed between the longitudinal tube cartridges 142 and their associated heat exchanger tubes 141 as shown. Any number of heating elements may be provided as needed to sufficiently heat and melt the PCM.

[0101] Each upper end 174 of the heating elements 170 is positioned within and passes through a complementarily configured opening 175 in the top closure lid 125 of the thermal energy containment vessel 121 (see, e.g., FIGS. 5 and 14). The upper portions 174 define a radially projecting, annular mounting flange 176 that seats on the exposed upper surface of the vessel's top closure lid 125. An upper cylindrical electrical connection boss 173 of each heating element 170 projects upwardly from the lid and includes electrical contacts / terminals for electrical connection to a power supply or source for the vessel 121.

[0102] The heating element 170, similar to the individual heat exchanger tube cartridges 142 described earlier herein, is suspended and cantilevered vertically and removably attached to the top closure lid 125 of the thermal energy containment vessel 121. Thus, there is nothing within the vessel's interior cavity 122 to support the heating element other than below the top lid. The heating element 170 is advantageously replaceable without removing the top closure lid 125 to access the interior cavity of the vessel 121, which makes replacement of the heating element more convenient and reduces replacement costs.

[0103] In some embodiments, the heating element 170 has a vertical length or height that extends across a majority and substantially the entire height of the interior cavity 122 of the vessel 121 that contains the PCM (see, for example, FIG. 13 ). In some embodiments, the heating element 170 has a vertical height or length that is greater than the heat exchanger tube cartridge 142. This ensures that the entire captured bed of granular PCM (if in a solid state / form) within the vessel cavity 122 is exposed to heat from the heating element and melts when the heating element is energized.

[0104] When the tube cartridge 142 and heating element 170 are installed in the thermal energy containment vessel 121, the granular PCM fills the gap between the tube 141, downcomer 152, and heating element before the heating element is energized. When the heating element is energized, the granular PCM particles are converted to a liquid or molten state, occupying the same interior space within the vessel cavity 122 and in direct longitudinal contact with the components to maximize heat transfer to the working fluid within the tube.

[0105] To initially fill the thermal energy containment vessel 121 with a PCM, a combination fill and pressure relief device 166 is provided that is configured to penetrate the vessel's top closure lid 125 (see, for example, FIG. 5 ). The device 166 is in fluid communication with the interior vessel cavity 122 via suitably configured PCM transfer piping 167. The device can be opened and closed to fill the PCM, and can be closed after PCM filling is complete. If the pressure within the thermal energy containment vessel 121 exceeds the device's preset maximum set pressure, the device opens to release the excess pressure to atmosphere. Suitable commercially available or custom-built devices may be used to provide the required functionality.

[0106] According to another aspect of the present invention, the thermal energy storage system is advantageously modular in nature. In other words, multiple thermal energy storage vessels 121 may be provided for any installation to meet the design and operational requirements of the facility that utilizes them to heat a working fluid via thermal energy stored in a PCM (phase change material) bed within each vessel. Applications for this system include the production of hot water (or a mixture, such as glycol and water) for district heating, industrial processes, and other heated liquid applications, and the production of steam for steam heating, industrial processes, power generation, and other applications. The number of thermal energy storage vessels 121 deployed is selected to produce a liquid or gaseous (e.g., steam) working fluid at a volume / amount and temperature sufficient to meet the needs of the intended application. Additionally, the existing modular system allows for additional working fluid heating capacity to be added in response to increasing demand, such as, but not limited to, population and infrastructure (e.g., housing) growth in district heating or other applications.

[0107] To meet the volume and temperature requirements of the heated working fluid, the individual thermal energy storage vessels 121 may be fluidly coupled in a series flow arrangement (see, for example, FIG. 2) or a parallel flow arrangement. Thus, any suitable flow scheme may be used. It is within the skill of the art to select the number of thermal energy storage vessels 121, the thermal service load, and the fluid arrangement as needed.

[0108] A suitable PCM (phase change material) can be used that is customized and selected for the required heat load and operating parameters (i.e., heating the working fluid, which is a water-water mixture, from an inlet temperature entering the thermal energy storage vessel 121 to a desired outlet temperature). In a preferred, but non-limiting embodiment, the PCM is a salt, which may be transformed from a granular solid state to a molten state when heated by the heating element 170 when energized by power extracted from an available power source, such as the power grid or other source. A suitable salt selected depending on the required heat load can be used.

[0109] Some examples of salts that may be used to form the PCM bed B in each thermal energy storage vessel 121 are shown in the table below: [Table 1]

[0110] The melting temperature and latent heat properties of a salt are characteristics and factors that dictate the selection of a salt appropriate for the required heat load and temperature rise of the working fluid. Therefore, it should be noted that the type of salt used in each thermal energy storage vessel 121 of the green boiler 120 in the green thermal energy storage and power generation system 100 application (i.e., preheater, boiler, and superheater) shown in FIG. 1B may be customized and different. It will be apparent to those skilled in the art that the heat load and performance of the thermal energy storage vessel 121 are highly customizable to meet the required temperature rise target of the thermal energy system, whether for an application such as simply heating water for district heating.

[0111] The thermal energy storage vessel 121 disclosed herein is described without limitation for heating water for various purposes and uses (e.g., boiler feedwater, water-glycol and other blends, or regular water) via a thermal energy absorbing PCM bed, although the invention is not limited in this respect. Thus, the thermal energy storage vessel 121 can be used to heat any type of fluid that can flow through the vessel's heat exchanger tubes. Thus, countless applications of the green thermal energy storage system 100 are possible and within the scope of this disclosure.

[0112] While the foregoing description and drawings represent exemplary embodiments of the present disclosure, it will be understood that various additions, modifications, and substitutions can be made therein without departing from the spirit and scope of the appended claims and their equivalents. In particular, it will be apparent to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, dimensions, and other elements, materials, and components without departing from the spirit or essential characteristics thereof. Furthermore, numerous modifications of the methods / steps described herein can be made within the scope of the present disclosure. Those skilled in the art will further appreciate that the present embodiments can be used with many changes in the structure, arrangement, proportions, dimensions, materials, and components used in the implementation of the present disclosure that are particularly adapted to particular environments and operating requirements without departing from the principles described herein. Therefore, the presently disclosed embodiments are considered in all respects to be illustrative and not restrictive. The appended claims should be interpreted broadly to include other modifications and embodiments of the present disclosure that may be made by those skilled in the art without departing from the scope thereof and their equivalents.

Claims

1. 1. A thermal energy containment vessel comprising: an elongated body defining an interior cavity containing a bed of molten phase change material capable of storing thermal energy; a top closure lid defining an upper portion of the thermal energy containment vessel; a plurality of heaters embedded in the phase change material, the heaters configured to be electrically coupled to a power source and operable to heat the molten phase change material to a molten state; a tube bundle including a plurality of heat exchanger tubes embedded in the molten phase change material, the heat exchanger tubes configured to convey a working fluid therethrough to absorb thermal energy from the molten phase change material; the plurality of heat exchanger tubes of the tube bundle are disposed within a plurality of individual tube cartridges, each tube cartridge being removably insertable into the thermal energy containment vessel through a respective opening in the top closure lid; Thermal energy containment vessel.

2. the working fluid comprises water; 10. The thermal energy containment vessel of claim 1.

3. the thermal energy containment vessel is configured to convert the water entering the thermal energy containment vessel from a liquid state to vapor exiting the thermal energy containment vessel; 3. The thermal energy containment vessel of claim 2.

4. the thermal energy storage vessel is configured to receive the water in a liquid state at a first temperature and to discharge the water in a liquid state at a second temperature higher than the first temperature; 3. The thermal energy containment vessel of claim 2.

5. the thermal energy containment vessel is configured to receive saturated steam at a first steam temperature and discharge superheated steam at a second temperature higher than the first steam temperature; 3. The thermal energy containment vessel of claim 2.

6. the body of the thermal energy containment vessel is a longitudinally elongated cylinder, and the heat exchanger tubes are longitudinally elongated and parallel to one another such that the working fluid flows longitudinally through a bed of the molten phase change material within the heat exchanger tubes; 6. A thermal energy storage vessel according to any one of claims 1 to 5.

7. the heater comprises a plurality of longitudinally elongated bayonet-type heating elements having an inner ceramic core and an outer metallic sheath in direct contact with the molten phase change material, the heating elements being disposed between the heat exchanger tubes; 7. The thermal energy containment vessel of claim 6.

8. the heating element is cantilevered vertically from the top closure of the thermal energy containment vessel; 8. The thermal energy containment vessel of claim 7.

9. each of the tube cartridges includes an upper head coupled to the upper closure lid of the thermal energy storage vessel, and an upper end of the heat exchanger tube of each cartridge extends through and is coupled to the head; 10. The thermal energy containment vessel of claim 1.

10. The tube cartridge is cantilevered vertically from the top closure.

10. The thermal energy containment vessel of claim 9.

11. the heat exchanger tubes of each tube cartridge are configured to pass the working fluid through the bed of molten phase change material multiple times, heating the working fluid to successively higher temperatures with each pass; 11. The thermal energy containment vessel of claim 10.

12. Some of the heat exchanger tubes in each tube cartridge are upflow tubes and some of the heat exchanger tubes are downflow tubes.

12. The thermal energy containment vessel of claim 11.

13. a portion of the upflow tube of each tube cartridge is in fluid communication with a corresponding downflow tube by a cross-flow conduit attached to the upper head; 13. The thermal energy containment vessel of claim 12.

14. the tube cartridge further comprises a lower tube support plate coupled to a lower end of the heat exchanger tube, the lower tube support plate being unsecured to the body of the thermal energy containment vessel so as to be slidably removable from the cavity along with the tube cartridge; 14. The thermal energy containment vessel of claim 13.

15. the upflow tubes of each tube cartridge are fluidly coupled to corresponding downflow tubes by cross-flow conduits attached to the lower tube support plate; 15. The thermal energy containment vessel of claim 14.

16. each tube cartridge including a fluid inlet for introducing a working fluid into the tube of the tube cartridge and a fluid outlet for expelling the working fluid from the tube cartridge; 15. The thermal energy containment vessel of claim 14.

17. each tube cartridge comprising a downcomer pipe having a diameter greater than the diameter of each of the heat exchanger tubes within the tube cartridge; 10. The thermal energy containment vessel of claim 9.

18. The downcomer pipe is vertically disposed and fluidly coupled to a lower end of at least one heat exchanger tube.

20. The thermal energy containment vessel of claim 17.

19. the downcomer pipe is supported at its upper part by the upper head of the tube cartridge and at its lower part by a lower tube support plate; 20. The thermal energy containment vessel of claim 18.

20. a lower end of the downcomer pipe is supported by and fluidly coupled with a lower annular header, an upper end of the downcomer pipe is supported by and fluidly coupled with an upper annular header attached to the upper head of the tube cartridge, and the heat exchanger tubes are fluidly coupled with the lower annular header and the upper annular header; 20. The thermal energy containment vessel of claim 17.

21. an upper end of the downcomer pipe fluidly coupled to an inlet pipe configured to introduce a working fluid into the tube cartridge; The heat exchanger tubes of each cartridge are fluidly coupled to an outlet pipe configured to expel water from the tube cartridge.

20. The thermal energy containment vessel of claim 17.

22. The thermal energy storage vessel further comprises a plurality of ring headers disposed in an upper head of the thermal energy storage vessel, each ring header being in direct or indirect fluid communication with one of the inlet pipe and the outlet pipe of each tube cartridge.

22. The thermal energy containment vessel of claim 21.

23. some of the plurality of ring headers are inlet ring headers that supply working fluid to the heat exchanger tubes in the tube cartridge, and some of the plurality of ring headers are outlet ring headers that collect working fluid from the heat exchanger tubes in the tube cartridge; 23. The thermal energy containment vessel of claim 22.

24. The plurality of ring headers are arranged concentrically with one another.

24. The thermal energy containment vessel of claim 23.

25. the inlet ring header is fluidly isolated from the outlet ring header; 25. The thermal energy containment vessel of claim 24.

26. The inlet ring header comprises at least two headers fluidly coupled by a cross-flow conduit, and the outlet ring header comprises at least two headers fluidly coupled by a cross-flow conduit; 26. The thermal energy containment vessel of claim 25.

27. the elongated body of the thermal energy containment vessel comprises a longitudinally elongated sidewall having an innermost shell and an outermost shell, and a vacuum annulus formed between the innermost shell and the outermost shell, the vacuum annulus being evacuated to below atmospheric pressure; 10. The thermal energy containment vessel of claim 1.

28. further comprising an insulating annulus formed between the innermost shell and the outermost shell, the insulating annulus including insulation configured to retain heat within the cavity of the thermal energy containment vessel; 28. The thermal energy containment vessel of claim 27.

29. the vacuum annulus is formed between the outermost shell and an intermediate shell adjacent to the outermost shell, and the insulating annulus is formed between the intermediate shell and the innermost shell; 30. The thermal energy containment vessel of claim 28.

30. the innermost shell, the outermost shell, and the intermediate shell are formed of stainless steel; 30. The thermal energy containment vessel of claim 29.

31. The opposing surfaces of the outermost shell and the intermediate shell facing the inside of the vacuum annulus are polished to form reflective surfaces that reflect heat; 31. The thermal energy containment vessel of claim 30.

32. the molten phase change material is operable to change from a granular solid state to a liquid state when heated by thermal energy emitted from the heater; 10. The thermal energy containment vessel of claim 1.

33. the molten phase change material is a salt; 33. The thermal energy containment vessel of claim 32.

34. 1. A thermal energy storage and power generation system comprising: a closed flow loop in fluid communication with the steam turbine, the steam condenser, the boiler assembly, and a pump that circulates boiler feedwater through the closed flow loop; a generator operably connected to the steam turbine and to an electric power grid; The boiler assembly includes a thermal energy boiler vessel and a thermal energy superheater vessel fluidly coupled to the thermal energy boiler vessel, the thermal energy boiler vessel and the thermal energy superheater vessel comprising: an elongated tubular body defining an interior cavity containing a bed of molten phase change material capable of storing thermal energy; a top closure lid defining an upper portion of the thermal energy boiler vessel and the thermal energy superheater vessel; an array of heaters embedded in the molten phase change material, the heaters electrically coupled to the power grid and energized to heat the molten phase change material; a tube bundle including a plurality of heat exchanger tubes embedded in the molten phase change material, the plurality of heat exchanger tubes of the tube bundle being disposed within a plurality of individual tube cartridges, each tube cartridge being removably insertable into the thermal energy boiler vessel or the thermal energy superheater vessel through a respective opening in the top closure lid, the tube bundle including a plurality of heat exchanger tubes configured to convey boiler feedwater through the heat exchanger tubes; the thermal energy boiler vessel is configured to receive boiler feedwater in a liquid state that is heated by the molten phase change material therein to produce saturated steam, and the thermal energy superheater vessel is configured to receive saturated steam that is heated to a superheated state by the molten phase change material therein to produce superheated steam; The superheated steam passes through the steam turbine to rotate the generator to generate electricity; Thermal energy storage and power generation systems.

35. further comprising a thermal energy preheat vessel fluidly coupled to the closed flow loop upstream of the thermal energy boiler vessel, the thermal energy preheat vessel comprising: an elongated tubular body defining an interior cavity containing a bed of molten phase change material capable of storing thermal energy; an array of heaters embedded in the molten phase change material, the heaters electrically coupled to the power grid and operable to heat the molten phase change material; a tube bundle including a plurality of heat exchanger tubes embedded in the molten phase change material, the heat exchanger tubes configured to convey the boiler feedwater through tube sides of the heat exchanger tubes; the thermal energy preheat vessel is operable to receive the boiler feedwater in a liquid state at a first temperature from the closed flow loop and to heat the boiler feedwater in a liquid state to a second, higher temperature; the thermal energy boiler vessel receiving the boiler feedwater in the liquid state at the second temperature via the closed flow loop; 35. The thermal energy storage and power generation system of claim 34.

36. the heater is powered by electricity drawn from the power grid during off-peak load demand periods; 36. A thermal energy storage and power generation system according to claim 34 or claim 35.

37. the generator supplies power to the power grid during peak load demand periods on the power grid; 37. The thermal energy storage and power generation system of claim 36.

38. the phase change material in the thermal energy boiler vessel differs from the phase change material in the thermal energy superheater vessel by at least one characteristic; 36. A thermal energy storage and power generation system according to claim 34 or claim 35.

39. The property is melting temperature; 39. The thermal energy storage and power generation system of claim 38.

40. The property is the type of phase change material; 39. The thermal energy storage and power generation system of claim 38.

41. the phase change material is a salt; 35. The thermal energy storage and power generation system of claim 34.

42. the tubular bodies of the thermal energy boiler vessel and the thermal energy superheater vessel are cylindrical and include a longitudinally elongated sidewall with an innermost shell and an outermost shell, a vacuum annulus formed between the innermost shell and the outermost shell and evacuated to below atmospheric pressure, and an insulating annulus formed between the innermost shell and the outermost shell including insulation configured to retain heat within the cavity of the thermal energy boiler vessel and the thermal energy superheater vessel; 35. The thermal energy storage and power generation system of claim 34.

43. further comprising an intermediate shell disposed adjacent to the outermost shell, and a vacuum annulus formed between the outermost shell and the innermost shell; 43. The thermal energy storage and power generation system of claim 42.

44. providing a thermal energy containment vessel comprising an interior cavity containing a bed of solid-state phase change material and a tube bundle comprising a plurality of tubes embedded in the phase change material, the plurality of tubes being disposed within a plurality of individual tube cartridges, each tube cartridge being removably insertable into the thermal energy containment vessel through a respective opening in a top closure lid defining a top of the thermal energy containment vessel; supplying energy to a plurality of heating elements embedded in the bed of phase change material to heat the phase change material and change it from a solid state to a molten state; a flowing step of flowing a working fluid at a first temperature through the phase change material to heat the working fluid to a second, higher temperature; Methods for heating working fluids.

45. the working fluid comprises water; 45. The method of heating a working fluid according to claim 44.

46. the phase change material is a salt; 46. ​​The method of heating a working fluid according to claim 45.

47. the water is in a liquid state upon entering the thermal energy storage vessel and is heated in the liquid state from a first temperature to a second, higher temperature by the phase change material; 47. The method of heating a working fluid according to claim 46.

48. the water is in a liquid state when it enters the thermal energy storage vessel and is heated by the phase change material to convert the water to steam; 47. The method of heating a working fluid according to claim 46.

49. the water is saturated steam entering the thermal energy storage vessel and is heated to superheated steam by the phase change material; 47. The method of heating a working fluid according to claim 46.

50. the heating element is electrically connected to an electrical power grid; The step of supplying energy includes the heating element drawing power from the power grid during periods of off-peak load demand on the power grid; 45. The method of heating a working fluid according to claim 44.

51. the heating element is electrically connected to an electrical power grid; the step of supplying energy includes the heating element drawing electricity from the power grid during periods of off-peak load demand on the power grid; 50. The method of heating a working fluid according to claim 49.

52. passing the superheated steam to a steam turbine generator for generating electricity; supplying the generated electricity to the power grid during peak electricity demand periods; 52. The method of heating a working fluid according to claim 51.

53. The thermal energy containment vessel is cylindrical and includes a longitudinally elongated sidewall with an innermost shell and an outermost shell, a vacuum annulus formed between the innermost shell and the outermost shell and evacuated to below atmospheric pressure, and a cavity in the thermal energy containment vessel. an insulating annulus formed between the innermost shell and the outermost shell, the annulus including insulation configured to retain heat therein; 45. The method of heating a working fluid according to claim 44.

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