US20170030656A1

US20170030656A1 - Thermal energy storage facility having functions of heat storage and heat release

Info

Publication number: US20170030656A1
Application number: US14/814,644
Authority: US
Inventors: Ching-Hohn Lien; Kuang-Hsin CHU
Original assignee: SFI Electronics Technology Inc
Current assignee: SFI Electronics Technology Inc
Priority date: 2015-07-31
Filing date: 2015-07-31
Publication date: 2017-02-02

Abstract

A thermal energy storage facility for use in heat storage and heat release comprises a heat storage/release mechanism constituted by multiple heat storage/heat exchange units stacked up, each unit at least comprises a heat storage board having parallel grooves for loading phase-change material (PCM) therein and a heat exchange plate having micro-channel groups for heat transfer fluid (HTF) flowed through to exchange heat with the PCM; particularly two or more the thermal energy storage facilities can be worked together by combination in series or/and in parallel to input of thermal energy, absorption of thermal energy and both simultaneously from the PCM, and the thermal energy storage facility capably operating at a heat storage temperature higher than 1200° C. is suited for use in solar thermal power generation system to improve overall efficiency of solar thermal power to reach 35-40%.

Description

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Invention
The present invention relates to thermal energy storage facilities, and more particularly to thermal energy storage facilities having functions of heat storage and heat release and suited for increasing the efficiency of solar power generation system.
2. Description of Related Art
Electrical power can be continuously generated by a solar power generation process in combination with a thermal energy storage system. The solar power plants collect solar energy and store part of the solar-derived thermal energy in thermal energy storage systems, to generate electrical power continuously through day and night, or during cloudy and rainy periods. Hence, solar power is presently one of the most promising renewable energy resources. In this regard, thermal energy storage technology is crucial to solar power generation. According to the prior art, solar-derived thermal energy storage is typically implemented by one of the three following materials: a sensible heat storage material, a latent heat storage material, and a thermochemical reaction-based heat storage material.
Solar power generation most often requires the sensible heat storage material in the presence of a molten salt which has a melting point of 221° C. and comprises 66.3% NaNO₃and 33.7% KNO₃. However, the currently conventional molten salts solar heat storage systems, only use the sensible heat of molten salts. The molten salt also served as heat transfer fluids (hereinafter referred to as the HTF).
Thus, the conventional molten salts solar thermal energy storage systems use only the sensible heat of the molten salts. Resulted in the HTF has drawbacks as follows:

1. The sensible heat molten salts freeze and solidify at low temperature, thereby clogging a pipe; and
2. The sensible heat molten salts may undergo decomposition and degradation at high temperature and thus corrodes metallic pipes.

To avoid clog and corrosion of metallic pipes, the sensible heat molten salts HTF used in a solar power generation system has to operate from 290° C. to 565° C., and thus inevitably leads to the following limitations:

1. The heat storage temperature of the solar power generation system ranges from 290° C. to 565° C. only;
2. in consequence the thermal energy released from the solar power generation system can bring about steam of a maximum temperature less than 565° C.; and
3. Since the steam temperature cannot be higher than 600° C., the steam turbine efficiency will be less than 34%. The sensible heat molten salts HTF is conventionally in conjunction with tube solar receivers, which are made of vertical metallic pipes. Subject to the limitation on thermal stress of the metallic pipes, the maximum intensity of sunlight concentrated by the tube solar receivers, equal to the irradiation intensity of a few hundreds of the Suns and thus the overall receiver efficiency achieved is just 57%. The overall solar power generation efficiency of the solar power generation system equals 19.5% (=0.57×0.34), i.e., less than 20%.

Latent heat is energy absorbed or released by materials during phase transition. A phase-change material (hereinafter referred to as the PCM) is a latent heat storage material characterized by a large heat of fusion. The PCM effectuates heat storage by absorbing and releasing heat at constant temperature during phase transition, such as phase changed from solid state to liquid state to gas state, or reversibly. At a phase-transition temperature, the PCM absorbs heat when melting, and releases heat when solidifying, without significant change of temperature. Therefore, the PCM is capable of storing and releasing a large amount of thermal energy.
At low temperature, the PCM is in the solid state and thus unable to function directly as the HTF in the solar power generation system; as a result, a solar power generation system which relies upon a latent heat storage material is confronted with intricate design of a heat storage and heat release system. However, latent heat storage materials have much higher latent heat storage density than sensible heat storage materials and thus are more advantageous than sensible heat storage materials in terms of heat storage level and volume.
The higher the power generation system temperature, the higher is the solar power generation efficiency of the solar power generation system. High-temperature PCM heat storage system, can link with a volume solar receiver, with a gas HTF, such as air or supercritical CO2. The maximum intensity of sunlight concentrated by the volume receivers may equal to the irradiation intensity of more than a thousand of the Suns. The efficiency of volume solar heat receiver can be 70-80%, and can achieve a maximum temperature of 1200° C. The heat released can be used to heat up gas fed into a gas turbine and thus drive a gas turbine combined cycle generator. The waste heat of gas discharged from the gas turbine still reaches 600° C., can be used to drive a steam turbine to achieve an overall power generation efficiency of 50%. The solar power generation system will achieve an overall solar power generation efficiency of 35-40% (=0.7×0.5-0.8×0.5). Thus, when a combined power block combined with a high-temperature heat storage device. Overall efficiency of 50% can be achieved constantly, and can be served as a base load power cycle.
Hence, the solar power generation efficiency is enhanced by developing a heat storage device which uses a latent heat storage material and features high heat storage level, high heat storage temperature, withstand to high HTF pressure, and high efficiency of heat storage/heat release heat exchange.
According to the prior arts, a heat storage facility with multi-channel PCM heat storage boards stacked alternately with printed circuit heat exchanger (abbreviated as the PCHE) plates, was developed. In order to achieve high heat storage, high heat exchange efficiency and can withstand high HTF pressure.
Referring to FIG. 1, a conventional micro-channel heat exchanger 90 comprises multiple heat exchange units 91 stacked up. The heat exchange units 91 each comprise a first heat exchange plate 93 and a second heat exchange plate 95. The first heat exchange plates 93 and the second heat exchange plates 95 are stacked up, coupled together by diffusion bonded, and arranged in a manner that the first heat exchange plate 93 alternates with the second heat exchange plate 95. A plurality of first micro-channels 94 is disposed on the surface of each of the first heat exchange plates 93 to function as passages of a heat transfer fluid F1. A plurality of second micro-channels 96 is disposed on the surface of each of the second heat exchange plates 95. The second micro-channels 96 of the second heat exchange plates 95 cross the first micro-channels 94 of the first heat exchange plates 93 at 90 degrees and function as passages of a heat transfer fluid F2. When the heat transfer fluid F1 passes through the first micro-channels 94, the heat transfer fluid F1 undergoes heat exchange, at high heat transfer speed, with the heat transfer fluid F2 which passes through the second micro-channels 96 in a manner that the direction of the flow of the heat transfer fluid F1 crosses the direction of the flow of the heat transfer fluid F2 at 90 degrees.
The aforesaid technical features of the micro-channel heat exchanger 90, coupled with the first heat exchange plate 93 or the second heat exchange plate 95 which is very thin and serves to space apart the first micro-channels 94 and the second micro-channels 96, achieve a heat exchange efficiency of 94%.
Both the micro-channel heat exchanger and the PCHE exhibit high heat transfer rate, high heat exchange efficiency and withstand high pressure but are not capable of heat storage.

SUMMARY OF THE INVENTION

In view of the aforesaid drawbacks of the prior art, the motive of the present invention is to couple together a conventional micro-channel heat exchanger (or PCHE) and latent heat storage material to thereby build a thermal energy storage facility at least having functions of both heat storage and heat release.
The primary objective of the present invention is to provide a thermal energy storage facility using a latent heat storage material and having functions of both heat storage and heat release, characterized in that: the thermal energy storage facility is a single block, or multiple blocks of thermal energy storage facilities are connected in parallel, connected in series, or connected by a combination of parallel connection and series connection, to be applied to a solar power generation system to effectuate thermal energy storage; thermal energy from the volume solar receivers is absorbed by air or the other HTF; and operate in conjunction with a gas turbine combined cycle generator. Hence, the thermal energy storage facility of the present invention is conducive to increasing the overall solar power generation efficiency to 35-40%.
The thermal energy storage facility comprises a thermal effect mechanism and at least two convergence-divergence hoods. The thermal effect mechanism further comprises an external framework and a heat storage and heat release mechanism. The external framework forms a rigid framework of the thermal effect mechanism and contains the heat storage/release mechanism. The heat storage/release mechanism comprises multiple heat storage/heat exchange units stacked up. The heat storage/heat exchange units each comprise a heat storage board and a heat exchange plate stacked up. The heat storage board has a plurality of parallel grooves for holding therein the PCM. The heat exchange plate has at least one micro-channel group, preferably two spaced-apart Z-shaped micro-channel groups functioning as passages of the HTF. The micro-channel groups each comprise multiple micro-channel units arranged in parallel such that the HTF passing through the heat exchange plate exchanges heat with the PCM of the heat storage board.
The convergence-divergence hoods each comprise a hollow-core cavity and a pipe, wherein the hollow-core cavities are disposed outside the heat storage/release mechanism of the thermal effect mechanism and adapted to conceal inlet ends and outlet ends of micro-channel groups of each said heat storage/heat exchange unit of the heat storage/release mechanism, with the pipe communicating with the hollow-core cavity and functioning as the pipe for feeding or discharging the HTF.
The heat storage boards of the heat storage/heat exchange units are of a thickness T1 of 5-20 mm. The parallel grooves are of a bottom thickness T2 of 0.3-3 mm and a groove width T3 of 5-20 mm. Every two adjacent ones of the grooves are separated by a groove-to-groove spacing T4 of 0.3-3 mm.
The heat exchange plates of the heat storage/heat exchange units are of a thickness of 1-4 mm. The micro-channel units of the micro-channel groups are of a channel depth of 0.5-1.5 mm and a channel width of 1.0-3.0 mm. The least wall thickness between every two adjacent micro-channel units is 0.3-1.5 mm. Preferably, each micro-channel unit of the micro-channel groups is shaped as a semicircular having a diameter of 1.0-3.0 mm.
The PCM is selectively a molten salt of a mixture of Li₂CO₃, LiF, NaF, KF, MgF₂, CaF₂, CaO, 46.5% LiF/11.5% NaF/42% KF, a molten salt of a mixture of 80.5% LiF/19.5% CaF₂, or a molten salt of a mixture of 66.3% NaNO₃/33.7% KNO₃. Preferably, graphite or metal is added to the PCM.
The thermal energy storage facility operates at a heat storage temperature of 1000° C. or higher, preferably 1200° C.-1500° C., and most preferably 1500° C. or higher, in order to effectuate thermal energy storage in the solar power generation system.
Advantages of the thermal energy storage facility of the present invention are as follows:

1. The thermal energy storage facility is capable of input of thermal energy, absorption of thermal energy and both simultaneously.
2. The thermal energy storage facility uses a latent heat storage material and is capable of heat storage and heat release to thereby overcome a drawback of the prior art, that is, both conventional micro-channel heat exchanger and PCHE are not capable of heat storage.
3. The thermal energy storage facility is standalone, or the thermal energy storage facilities are connected in parallel, connected in series, or connected by a combination of parallel connection and series connection, operated at a heat storage temperature of 1200° C. or higher, and applied to the solar power generation system to effectuate thermal energy storage. Hence, the thermal energy storage facility is conducive to increasing the overall solar power generation efficiency to 35-40%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior conventional micro-channel heat exchanger;

FIG. 2 is a schematic view of a thermal energy storage facility having functions of heat storage and heat exchange according to the present invention;

FIG. 3 is a cutaway view of the thermal energy storage facility of FIG. 2;

FIG. 4 includes an exploded view and partial enlarged cross-sectional views of a heat storage/release mechanism and heat storage/heat exchange units of the thermal energy storage facility of FIG. 2; and

FIG. 5 is a schematic view of a large-scale thermal energy storage system comprising two or more thermal energy storage facilities of FIG. 2 connected in parallel or in series.

DETAILED DESCRIPTION OF THE INVENTION

Referring to from FIG. 2 to FIG. 4, a thermal energy storage facility 10 of the present invention exhibits heat storage efficiency of 94% or higher and heat storage temperature of 1200° C. or higher and comprises a thermal effect mechanism 15 and at least two (that is, two, four or multiple) convergence-divergence hoods 70.
The thermal effect mechanism 15 comprises an external framework 20 and a heat storage/release mechanism 30. In an embodiment of the present invention, the infrastructure of the thermal effect mechanism 15 includes a metallic material which is resistant to high temperature such that the thermal effect mechanism 15 is can withstand atmospheric pressure of 500-1000 atm at 900° C.
The external framework 20 comprises a top panel 21, a bottom panel 22, a front panel 23 and a rear panel 24 which together form a rigid framework of the thermal effect mechanism 15. In an embodiment of the present invention, the thermal effect mechanism 15 comprises the external framework 20 and the heat storage/release mechanism 30 and allows the heat storage/release mechanism 30 to be hermetically sealed and thus disposed inside the external framework 20.
The external framework 20 is made of a metallic material good at thermal insulation and resistant to high temperature. It is also feasible for the external framework 20 to be made of a sensible heat storage material in order to enhance the heat storage heat release capability of the thermal effect mechanism 15. Upon the production of the external framework 20, it is enclosed by a thermally insulating material.
Referring to FIG. 3 and FIG. 4, the heat storage/release mechanism 30 comprises multiple heat storage/heat exchange units 40 which are stacked up and alternate with each other. The heat storage/heat exchange units 40 each comprise a heat storage board 50 and a heat exchange plate 60 which are stacked up and form a block unit by a pressing process.
The heat storage board 50 is made of a sensible heat storage material and has a plurality of parallel grooves 52. The heat storage board 50 is of a thickness T1 of 5-20 mm. The grooves 52 are of a bottom thickness T2 of 0.3-3 mm and a groove width T3 of 5-20 mm. Every two adjacent ones of the grooves 52 are separated by a groove-to-groove spacing T4 of 0.3-3 mm.
The two ends of each of the grooves 52 of the heat storage board 50 are closed or open. The two ends of each of the grooves 52 are hermetically sealed with the top panel 21 and the bottom panel 22 of the external framework 20.
Further referring to FIG. 4, the opening of each of the grooves 52 of the heat storage board 50 is hermetically sealed with the other heat storage/heat exchange unit 40 which is stacked alternately by a diffusion bonding process. The outermost heat storage/heat exchange unit(s) 40 use the front panel 23 or the rear panel 24 of the external framework 20 to hermetically seal the opening of each of the grooves 52.
Therefore, the PCM is placed inside each groove 52 of the heat storage board 50 so that the heat storage board 50 is capable of heat storage and heat release. The PCM is selectively a molten salt of a mixture of Li₂CO₃, LiF, NaF, KF, MgF₂, CaF₂, CaO, 46.5% LiF/11.5% NaF/42% KF, 80.5% LiF/19.5% CaF₂or a molten salt of a mixture of 66.3% NaNO₃/33.7% KNO₃. To augment the coefficient of thermal conductivity of the PCM, a material with high coefficient of thermal conductivity, such as graphite or metal, is added to the PCM as appropriate.
Referring to FIG. 4, the heat exchange plate 60 is of a thickness of 1-4 mm and is made of a sensible heat storage material. At least one (including one, two or multiple) micro-channel group 62 is disposed on one side of the heat exchange plate 60. Preferably, two spaced-apart Z-shaped micro-channel groups 62 are disposed on one side of the heat exchange plate 60. The micro-channel groups 62 each comprise multiple micro-channel units 63 arranged in parallel. The channel cross-sections of the micro-channel units 63 are of any appropriate shape and are, preferably, characterized by a channel depth of 0.5-1.5 mm and a channel width of 1.0-3.0 mm, wherein the least wall thickness between every two adjacent ones of the micro-channel units 63 is 0.3-1.5 mm. Preferably, the micro-channel unit 63 is shaped as a semicircular having a diameter of 1.0-3.0 mm.
Referring to FIG. 3, the convergence-divergence hoods 70 each have a hollow-core cavity 71 and a pipe 72 in communication with the hollow-core cavity 71. The convergence-divergence hoods 70 are disposed outside the heat storage/release mechanism 30 of the thermal effect mechanism 15. The hollow-core cavities 71 of the convergence-divergence hoods 70 conceal inlet ends and outlet ends of the micro-channel groups 62 of each heat storage/heat exchange unit 40 of the heat storage/release mechanism 30 thoroughly.
Referring to FIG. 5, when the convergence-divergence hoods 70 are disposed at the inlet ends for concealing the micro-channel groups 62, the pipes 72 of the convergence-divergence hoods 70 function as a feed pipe 73 of the HTF. Likewise, when the convergence-divergence hoods 70 are disposed at the outlet ends for concealing the micro-channel groups 62, the pipes 72 of the convergence-divergence hoods 70 function as a discharge pipe 74 of the HTF.
Referring to from FIG. 2 to FIG. 5, the inlet ends and outlet ends of the micro-channel groups 62 of the heat exchange plate 60 are only connected to the convergence-divergence hoods 70, respectively, to form self-contained channels.
Referring to FIG. 5, in practice the thermal energy storage facility 10 of the present invention is optionally allowed either a high-temperature homogenous HTF or a low-temperature homogenous HTF to enter the feed pipe 73 of all the convergence-divergence hoods 70. In another embodiment, the thermal energy storage facility 10 of the present invention is also optionally allowed a high-temperature homogenous or heterogeneous HTF and/or a low-temperature homogenous or heterogeneous HTF to respectively enter the feed pipe 73 of two or more different convergence-divergence hoods 70 simultaneously.
After the homogenous and/or heterogeneous HTF provided with high or low temperature entered the feed pipe 73 of all the convergence-divergence hoods 70, the HTF goes from the hollow-core cavities 71 of the convergence-divergence hoods 70 to the micro-channel groups 62 of the heat storage/heat exchange units 40, undergoes thermal conduction-based heat exchange with the PCM placed inside each groove 52 of the heat storage board 50 of the heat storage/heat exchange units 40, exits the outlet ends of the micro-channel groups 62, then passes through the hollow-core cavities 71 which conceal the outlet ends of the micro-channel groups 62, and is eventually discharged from the discharge pipes 74 of the convergence-divergence hoods 70.
Hence, according to the present invention, the micro-channel groups 62 of the thermal energy storage facility 10 are either fully used to input of thermal energy transmitted heat from HTF to PCM or fully used to absorption of thermal energy transmitted heat from PCM to HTF. Alternatively, according to the present invention, one of two or more different micro-channel groups 62 of the thermal energy storage facility 10 is further used to input of thermal energy and the rest are used to absorption of thermal energy simultaneously.
Accordingly, the thermal energy storage facility 10 of the present invention in use therefore has basic functions capable of heat storage, heat release and both simultaneously.
More detailed speaking, after the HTF has been heated up with concentrated solar energy, the passage of the high-temperature HTF through the micro-channel units 63 of the micro-channel groups 62 is accompanied by the process of transferring (by heat conduction) the thermal energy to the PCM disposed at the heat storage board 50. Conversely, the passage of the low-temperature HTF through the micro-channel units 63 of the micro-channel groups 62 is accompanied by the process of absorbing (by heat conduction) the heat extract released from the PCM of the heat storage board 50 to thereby effectuate heating.
When passing through the micro-channel groups 62 of the heat exchange plate 60 of each heat storage/heat exchange unit 40, the HTF is only separated from the PCM of the heat storage board 50 of each heat storage/heat exchange unit 40 by a thin wall to enable heat exchange to take place therebetween. Hence, the thermal energy storage facility 10 of the present invention has a high heat transfer efficiency, exhibits a heat storage efficiency of 92% or higher, and achieves a heat storage temperature of 1000° C. or higher, preferably a heat storage efficiency of 94% or higher, a heat storage temperature of 1200° C.-1500° C., most preferably a heat storage efficiency of 99% or higher and a heat storage temperature of 1500° C. or higher, which are much higher than the 80% heat storage efficiency of a conventional heat storage device operating in conjunction with a conventional shell-and-tube heat exchanger.
Referring to FIG. 5, the discharge pipe 74 of a thermal energy storage facility 10 and the feed pipe 73 of another thermal energy storage facility 10 are connected in series. By analogy, multiple thermal energy storage facilities 10 of the same specification are connected in series to form a large-scale thermal energy storage facility.
Likewise the feed pipes 73 of two thermal energy storage facilities 10 are connected in parallel, and the corresponding discharge pipes 74 of the two thermal energy storage facilities 10 are connected in parallel. By analogy, multiple thermal energy storage facilities 10 of the same specification are connected in parallel to form another kind of a large-scale thermal energy storage facility. Furthermore, the thermal energy storage facilities 10 are connected by a combination of parallel connection and series connection to further form another kind of a large-scale thermal energy storage facility. Hence, according to the present invention, multiple thermal energy storage facilities 10 of the same specification can be connected in parallel, or connected in series, or connected by a combination of parallel connection and series connection.
The thermal energy storage facility 10 of the present invention not only uses the PCM of the thermal effect mechanism 15 to effectuate heat storage, but also uses the infrastructure of the thermal effect mechanism 15 further made of a sensible heat storage material to enhance an additional heat storage.

EMBODIMENT

The embodiments below illustrate the thermal energy storage facility 10 having functions of heat storage and heat release according to the present invention and applied to the solar power generation system for thermal energy storage to achieve an overall solar power generation efficiency of 35-40%.

Embodiment 1

The thermal energy storage facility 10 of FIG. 2 is produced and configured to resist pressure of at least 500 atm and has the highest operating temperature of 1095° C. and the lowest operating temperature of 565° C., with further details provided below.


volume (width × depth ×	= 65.32 cm × 64.4 cm × 103 cm = 433 L
length) of thermal effect
mechanism
15
volume of PCM	= 60 cm × 50 cm × 103 cm = 309 L
	accounts for 71.4% of volume of thermal
	effect mechanism
15
volume of structure of	= 433 L − 309 L = 124 L
thermal effect	accounts for 28.6% of volume of thermal
mechanism
15	effect mechanism 15

The PCM is NaF which has a melting point of 996° C., density of 2780 kg/m³, specific heat of 3.336 MJ/m³° C., latent heat (996° C.) of 2208 MJ/m³, where M is 10⁶.
The structure (infrastructure) of the thermal effect mechanism 15 is made of INCONEL 600 alloy which is resistant to a maximum temperature of 1095° C. and has a density of 8470 kg/m³and specific heat of 5.32 MJ/m³° C., where M is 10⁶.
At an operating temperature of 565° C.-1095° C., heat storage level per cubic meter (m³) of the thermal energy storage facility 10 in this embodiment equals the sum of three heat levels as follows: 1262 MJ+1577 MJ+806 MJ=3645 MJ.


sensible heat of PCM	= 0.714 m³× 3.336 MJ/m³° C. × (1095-565) ° C.
	= 1262 MJ
latent heat	= 0.714 m³× 2208 MJ/m³
(996° C.) of PCM	= 1577 MJ
sensible heat of	= 0.286 m³× 5.32 MJ/m³° C. × (1095-565) ° C.
structure of thermal	= 806 MJ
effect mechanism
15

Embodiment 2

The thermal energy storage facility 10 of embodiment 1 is applied to the solar power generation system and coupled to the volume-dependent solar receivers and supercritical CO₂gas turbine generator.
The high-temperature HTF F1 of the volume-dependent solar receivers passes through a Z-shaped micro-channel of the thermal energy storage facility 10 to thereby store thermal energy in the PCM of the thermal energy storage facility 10.
A supercritical CO₂working fluid F2 which operates at a pressure of 199.7 Bar, and another Z-shaped micro-channel passing through the thermal energy storage facility 10 takes up the thermal energy of the PCM of thermal energy storage facility 10, so as to drive the supercritical CO₂gas turbine generator when the temperature reaches 485.8° C.
The efficiency of the supercritical CO₂gas turbine generator is 44.2%. The efficiency of the volume-dependent solar receivers is 80%. The overall efficiency of the solar power generation system is 35.4%.

Embodiment 3

The thermal energy storage facility 10 of FIG. 2 is produced and configured to resist pressure of at least 500 atm and has the highest operating temperature of 1500° C. and the lowest operating temperature of 1200° C., with further details provided below.


volume (width × depth ×	= 65.32 cm × 83.07 cm × 103 cm = 558.9 L
length) of thermal
effect mechanism
15
volume of PCM	= 60 cm × 51 cm × 103 cm = 315.2 L
	accounts for 56.4% of volume of thermal
	effect mechanism
15
volume of structure	= 558.9 L − 315.2 L = 243.7 L
of thermal effect	accounts for 43.6% of volume of thermal
mechanism
15	effect mechanism 15

The PCM is MgF₂and has a melting point of 1263° C., a density of 3148 kg/m³, specific heat of 3.463 MJ/m³° C., and latent heat (1263° C.) of 2956 MJ/m³, where M is 10⁶.
The structure of the thermal effect mechanism 15 is made of silicon carbide (SiC) and has a density of 3100 kg/m³, a melting point of 2837° C., an operating temperature of 1700° C., rupture modulus of 110 Mpa, specific heat of 7.874 MJ/m³° C., and coefficient of thermal conductivity of 125 W/m-K (20° C.)-40 W/m-K (1000° C.), where M is 10⁶.
At an operating temperature of 1200° C.-1500° C., heat storage level per cubic meter (m³) of the thermal energy storage facility 10 in this embodiment equals the sum of three heat levels as follows: 586 MJ+1667 MJ+1030 MJ=3283 MJ


sensible heat of	= 0.564 m³× 3.463 MJ/m³° C. × (1500-1200)° C.
PCM	= 586 MJ
latent heat	= 0.564 m³× 2956 MJ/m³
(1263° C.) of PCM	= 1667 MJ
sensible heat of	= 0.436 m³× 7.874 MJ/m³° C. × (1500-1200)° C.
structure of thermal	= 1030 MJ
effect mechanism
15

Embodiment 4

The thermal energy storage facility of embodiment 3 is applied to the solar power generation system of embodiment 2 and substitutes for the thermal energy storage facility of embodiment 1.
The efficiency of the supercritical CO₂gas turbine generator is 50%. The efficiency of the volume-dependent solar receivers is 80%. The overall efficiency of the solar power generation system is 40%.

Comparative Example

A conventional heat storage system with two heat storage tanks is built in the solar power generation system and configured to operate in conjunction with area-dependent solar receivers and a steam turbine in power generation.
As regards the heat storage system, its high-temperature heat storage tank operates at a temperature of 565° C., and its low-temperature heat storage tank operates at a temperature of 290° C. The heat storage system stores heat by sensible heat of a molten salt rather than by phase-transition heat of the molten salt.
The HTF comes in the form of a molten salt which comprises a mixture of 66.3% NaNO₃and 33.7% KNO₃and has a melting point of 221° C., and its latent heat at the melting point (221° C.) is 232 MJ/m³, where M is 10⁶.
At an operating temperature of 290° C.-565° C., heat storage level per cubic meter (m³) of the heat storage system=molten salt specific heat (1.6 kJ/kg° C.⁻¹)×molten salt density 1870 (kg/m³)×(565° C.-290° C.)=823 MJ/m³.
The efficiency of the steam turbine is 34%. The efficiency of the area-dependent solar receivers is 57%. The overall efficiency of the solar power generation system is 19.5%, that is, less than 20%.

Results

1. Embodiment 1 has a heat storage level of 3645 MJ/m³which is 4.43 times of 66.3% NaNO₃/33.7% KNO₃molten salt sensible heat storage (823 MJ/m³) of the comparative example.
2. Embodiment 3 has a heat storage level of 3283 MJ/m³which is 3.99 times of 66.3% NaNO₃/33.7% KNO₃molten salt sensible heat storage (823 MJ/m³) of the comparative example.
3. The solar power generation systems of embodiment 2 and embodiment 4 use the thermal energy storage facilities of embodiment 1 and embodiment 3 to thereby attain a power generation efficiency of 35.4% and 40%, respectively, which is higher than the power generation efficiency of less than 20% in the comparative example.

Claims

What is claimed is:

1. A thermal energy storage facility having functions of heat storage, heat release and both, using a phase-change material (PCM) for storing heat and releasing heat, comprising a thermal effect mechanism and at least two convergence-divergence hoods, wherein the improvement comprises:

the thermal effect mechanism comprises

an external framework functioning as a rigid framework of the thermal effect mechanism; and

a heat storage/release mechanism hermetically sealed by the external framework and comprising multiple heat storage/heat exchange units stacked up, each heat storage/heat exchange unit comprises a heat storage board and a heat exchange plate stacked up, wherein

the heat storage board has a plurality of parallel grooves for loading the PCM therein, and

the heat exchange plate has one or more micro-channel groups functioning as a passage of a heat transfer fluid (HTF), each micro-channel group comprises multiple micro-channel units arranged in parallel to allow the HTF when passed through to exchange heat with the PCM of the heat storage board; and

the convergence-divergence hoods each comprise

a hollow-core cavity disposed outside the heat storage/release mechanism of the thermal effect mechanism and adapted to conceal inlet ends and outlet ends of micro-channel groups of each said heat storage/heat exchange unit of the heat storage/release mechanism; and

a pipe communicating with the hollow-core cavity for feeding or discharging the HTF.

2. The thermal energy storage facility as described in claim 1, wherein the heat storage boards of the heat storage/heat exchange units are of a thickness T1 of 5-20 mm, and wherein the grooves of the heat storage boards are of a bottom thickness T2 of 0.3-3 mm, a groove width T3 of 5-20 mm, and a groove-to-groove spacing T4 of 0.3-3 mm.

3. The thermal energy storage facility as described in claim 1, wherein the heat exchange plate has two spaced-apart Z-shaped micro-channel groups.

4. The thermal energy storage facility as described in claim 2, wherein the heat exchange plates of the heat storage/heat exchange units are of a thickness of 1-4 mm.

5. The thermal energy storage facility as described in claim 2, wherein the micro-channel units of the micro-channel groups of the heat exchange plates are of a channel depth of 0.5-1.5 mm, a channel width of 1.0-3.0 mm and a wall thickness of 0.3-1.5 mm between every two adjacent micro-channel units.

6. The thermal energy storage facility as described in claim 2, wherein the micro-channel unit of the heat exchange plate is shaped as a semicircular having a diameter of 1.0-3.0 mm.

7. The thermal energy storage facility as described in claim 1, wherein the PCM is one or more molten salts selected from the group consisting of Li₂CO₃, LiF, NaF, KF, MgF₂, CaF₂, CaO, mixture of 46.5% LiF/11.5% NaF/42% KF, mixture of 80.5% LiF/19.5% CaF₂and mixture of 66.3% NaNO₃/33.7% KNO₃, afore clamed PCMs materials in combination with graphite form, afore clamed PCMs encapsules.

8. The thermal energy storage facility as described in claim 6, wherein the PCM further contains graphite or metal added.

9. The thermal energy storage facility as described in claim 6, wherein the thermal energy storage facility operates at a heat storage temperature equal to or higher than of 1000° C.

10. The thermal energy storage facility as described in claim 6, wherein the thermal energy storage facility operates at a heat storage temperature ranged from 700° C. to 1500° C.

11. The thermal energy storage facility as described in claim 6, wherein the thermal energy storage facility operates at a heat storage temperature higher than 1500° C.

12. A large-scale thermal energy storage facility for use in a solar power generation system to effectuate thermal energy storage, comprising two or more thermal energy storage facilities of claim 1 are connected in parallel, connected in series or connected by a combination of both.