CN214330815U - Solar thermal power generation system based on sensible heat and phase change latent heat composite energy storage - Google Patents
Solar thermal power generation system based on sensible heat and phase change latent heat composite energy storage Download PDFInfo
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Abstract
The utility model relates to a solar thermal power generation system based on sensible heat and the compound energy storage of phase transition latent heat belongs to solar thermal power generation technical field. Comprises a solar energy collecting and storing loop and a thermal power conversion circulating loop. The solar energy collecting and storing loop mainly comprises a solar energy collecting and heat accumulating unit, and comprises a solar energy collecting field, a high-temperature heat accumulating tank, a low-temperature heat accumulating tank and a phase-change material. Wherein the phase-change material is placed in the high-temperature heat storage tank. The heat-work conversion circulation loop comprises a high-pressure stage expander, a low-pressure stage expander, a valve, a mixer, a condenser, a first preheater, a second preheater and an evaporator. The utility model discloses have 4 kinds of mode, be solar energy collection power generation mode and the tertiary exothermic power generation mode respectively. The utility model discloses technical scheme combines sensible heat storage and phase change heat storage, has greatly improved the heat storage capacity of system and thermal power generation's stability, can effectively solve the problem that current phase change heat storage technique exists in solar thermal power generation field especially direct inflation formula electricity generation field.
Description
Technical Field
The utility model belongs to the technical field of solar thermal power generation, concretely relates to solar thermal power generation system based on sensible heat and the compound energy storage of phase transition latent heat.
Background
The direct expansion type solar thermal power generation technology is rapidly developing, and demonstration and commercialization systems are provided in the technical fields of parabolic trough type light condensation, Fresnel light condensation and tower type light condensation. The direct-expansion solar thermal power generation system adopts cheap and environment-friendly water working medium as a heat collecting medium. The latent heat of vaporization of water is large, so that the average heat absorption temperature of the heat collection field is high, and higher heat-power conversion efficiency is favorably obtained. The direct-expansion solar thermal power generation system commercialized at the present stage generally adopts a heat storage water tank as an energy storage means. In the process of heat release and power generation of the conventional heat storage water tank, the temperature and the pressure are unstable and can be reduced along with the heat release time, the thermodynamic cycle is in variable working condition operation, and the efficiency is not high. The heat collection field generally only produces saturated steam, a long-time large-scale heat storage system is not arranged, the requirements of stability and adjustability of a steam turbine power generation system can be met only by adding a fossil energy afterburning system, and the development is limited. The phase-change material has the characteristics of large heat storage capacity per unit mass (volume), small temperature fluctuation (approximately isothermal heat storage and release processes), good chemical stability, good safety and the like, and has good application prospect in the field of solar thermal power generation, particularly in the field of direct expansion technology. The heat storage density of the phase change material is 10 times or more that of sensible heat storage. The phase-change material is combined with the direct-expansion type solar thermal power generation system, so that the heat storage power generation capacity of the system can be improved under the given volume of the heat storage tank, and the heat source temperature stability of the thermodynamic cycle can be maintained.
Theoretically, the heat-power conversion efficiency of the direct-expansion solar thermal power generation system adopting the phase-change material for heat storage at the temperature of a heat collection field of 300 ℃ is equivalent to that of the traditional system adopting heat conduction oil for heat storage (about 30%), but the heat collection temperature of the latter is higher than 400 ℃. Compared with heat conducting oil, the water has low viscosity, low price, difficult cracking, low replacement cost and low power consumption of the circulating pump, can be organically combined with the phase-change material, and provides required heat for the phase-change material. However, if the phase change material is applied to an actual direct-expansion solar thermal power generation system, the phase change material still faces a great challenge:
first, the heat storage tank temperature and pressure may be significantly reduced during exothermic power generation. The phase-change material exchanges heat with water/steam from the heat collection field through the wall surface, the heat conductivity coefficient of the phase-change material is low, and the heat transfer performance in the phase-change process is poor. In practical application, materials with high thermal conductivity coefficient, such as copper powder, aluminum powder, graphite, etc., are generally required to be added. Or the heat exchange area is increased, for example, a fin heat exchanger is adopted, and the specific surface area of the phase change material unit is increased. However, none of these methods for enhancing heat transfer can fundamentally solve the problem of low thermal conductivity of phase change materials. During exothermic power generation, the phase change material changes from a liquid state to a solid state. The solid phase-change material is continuously attached to the wall surface, the thickness is increased, and the heat transfer resistance between the liquid phase-change material and water is increased due to the low heat conductivity coefficient of the solid phase-change material. For example, under the conditions of a given heat storage tank volume and phase change unit structure, assuming that the phase change temperature of the phase change material is 250 ℃, the nominal input heat of the thermodynamic cycle is Q (mw), and the water temperature corresponding to the released heat Q is 240 ℃ in the initial stage of heat release, the heat transfer resistance is increased in the final stage of heat release, and the water temperature corresponding to the released heat Q may be 210 ℃ or lower. In order to ensure that the power generation cycle stably operates near the rated working condition, the design temperature of the inlet of the steam turbine is lower than 210 ℃, otherwise, the heat stored by the phase-change material is difficult to completely release or the power generation cycle is difficult to maintain to operate at the rated working condition, so that energy loss is caused. At the phase transition temperature of 250 ℃, if the design temperature of the inlet of the steam turbine is 210 ℃ or lower, the thermodynamic cycle efficiency is low, which is not favorable for shortening the investment recovery period of the solar thermal power generation system.
Secondly, the temperature and pressure of the heat storage tank also fluctuate during the heat absorption of the phase change material. The solar irradiation intensity changes along with the time, and the heat collected by the heat collection field also changes along with the change of the solar irradiation intensity. Assuming that the irradiation intensity is 700W/m2When the water/steam temperature at the outlet of the heat collection field is 260 ℃, the temperature of the phase-change material is 250 ℃, the heat absorption power of the phase-change material is Q, the rated input heat of the thermodynamic cycle is Q, and the output heat of the heat collection field is 2Q, the irradiation intensity is 1000W/m2In the time, the heat output by the heat collection field can reach 3Q, and the heat absorption power of the phase change material can reach 2Q. An increase in heat flow density requires an increase in the heat transfer differential, and it is possible for the water/steam temperature to reach 270 ℃ or higher. The temperature and pressure of the water in the heat storage tank may vary with the irradiation. This can result in higher design pressure and increased cost for the regenerator, while the periodic pressure fluctuations tend to shorten the life of the regenerator.
To above problem, the utility model provides a solar thermal power generation system based on compound energy storage of sensible heat and phase transition latent heat combines sensible heat storage and phase transition heat storage organically, guarantees the high-efficient steady operation of heat storage tank and thermodynamic cycle.
SUMMERY OF THE UTILITY MODEL
In order to further improve the thermodynamic property and the technical feasibility of phase change heat accumulation formula solar thermal power generation system, the utility model provides a solar thermal power generation system based on sensible heat and the compound energy storage of phase change latent heat.
The solar thermal power generation system based on sensible heat and phase change latent heat composite energy storage comprises a solar energy collecting and storing loop and a thermal power conversion and circulation loop.
The solar energy collecting and storing loop comprises a high-temperature heat storage tank 11, a phase-change material 12, a first high-temperature pump 13, a low-temperature heat storage tank 14, a low-temperature pump 15, a second high-temperature pump 16 and a solar heat collecting field 17; the high-temperature heat storage tank 11 is filled with a phase-change material 12, the volume of the phase-change material 12 accounts for 30-70% of the volume of the high-temperature heat storage tank 11, and the phase-change temperature of the phase-change material 12 is 210-400 ℃; the solar energy collecting and storing loop is a heat transfer medium;
the thermal power conversion circulation loop comprises a high-pressure stage expander 21, a mixer 22, a low-pressure stage expander 23, a condenser 24, a low-temperature working medium pump 25, a first preheater 26, a high-temperature working medium pump 27, a second preheater 28 and an evaporator 29; the first preheater 26, the second preheater 28 and the evaporator 29 respectively comprise a heat transfer side and a working medium side which are arranged in parallel; working media are in the heat-work conversion circulation loop;
the working temperature of the heat transfer medium in the high-temperature heat storage tank 11 is 200-400 ℃, and the working temperature of the heat transfer medium in the low-temperature heat storage tank 14 is 30-170 ℃; the gaseous mass fraction of the heat transfer medium at the outlet of the solar heat collection field 17 is 5-95%;
the solar thermal power generation system has 4 working modes;
in a solar heat collection power generation mode, a solar heat collection field 17, a high-temperature heat storage tank 11, a first high-temperature pump 13, a low-temperature heat storage tank 14, a high-pressure-stage expander 21, a mixer 22, a low-pressure-stage expander 23, a condenser 24, a low-temperature working medium pump 25 and an evaporator 29 participate in work;
in a first-stage heat release power generation mode, the high-temperature heat storage tank 11, the first high-temperature pump 13, the high-pressure stage expander 21, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25 and the evaporator 29 participate in work;
in the second-stage heat release power generation mode, the high-temperature heat storage tank 11, the first high-temperature pump 13, the high-pressure stage expander 21, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25, the first preheater 26, the high-temperature working medium pump 27, the second preheater 28 and the evaporator 29 participate in work;
in the three-stage heat release power generation mode, the high-temperature heat storage tank 11, the low-temperature heat storage tank 14, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25, the first preheater 26 and the second preheater 28 participate in work.
The technical scheme for further limiting is as follows:
the bottom outlet of the high-temperature heat storage tank 11 is sequentially connected in series with the heat transfer side of a first preheater 26, the heat transfer side of a second preheater 28, the low-temperature heat storage tank 14 and the inlet of a low-temperature pump 15 through pipelines, and the outlet of the low-temperature pump 15 is respectively communicated with the inlet of a solar heat collection field 17 and the outlet of a second high-temperature pump 16 through a three-way pipe; the outlet of the solar heat collection field 17 is communicated with the inlet at the top of the high-temperature heat storage tank 11, and the inlet of the second high-temperature pump 16 is communicated with the outlet at the bottom of the high-temperature heat storage tank 11; an evaporator 29 and a first high-temperature pump 13 are connected in series between an inlet at one side of the upper part and an outlet at one side of the lower part of the high-temperature heat storage tank 11;
the inlet of the high-pressure stage expander 21 is sequentially connected with one side of a working medium of the evaporator 29, one side of a working medium of the second preheater 28 and the outlet of the high-temperature working medium pump 27 in series, the inlet of the high-temperature working medium pump 27 is communicated with the first outlet of the mixer 22, and the outlet of the high-pressure stage expander 21 is communicated with the first inlet of the mixer 22; the outlet of the low-pressure stage expander 23 is sequentially connected with the condenser 24, the low-temperature working medium pump 25 and the inlet of the working medium side of the first preheater 26 in series, the outlet of the working medium side of the first preheater 26 is communicated with the second inlet of the mixer 22, and the second outlet of the mixer 22 is communicated with the inlet of the low-pressure stage expander 23;
a first valve 31 is connected in series between the outlet of the low-temperature working medium pump 25 and the inlet of the working medium side of the first preheater 26, and a second valve 32 is connected in series between the outlet of the low-temperature working medium pump 25 and the second inlet of the mixer 22; a third valve 33 is connected in series between the working medium side inlet of the second preheater 28 and the outlet of the high temperature working medium pump 27, and a fourth valve 34 is connected in series between the outlet of the high temperature working medium pump 27 and the working medium side inlet of the evaporator 29.
The solar heat collection field 17 is one of a parabolic groove type heat collection field, a linear Fresnel heat collection field and a tower type heat collection field.
The heat transfer medium is one of water and heat transfer oil.
The phase change material 12 is an inorganic salt phase change material, and the inorganic salt phase change material is one of lithium nitrate inorganic salt, sodium nitrate-calcium nitrate binary mixed inorganic salt, sodium carbonate-sodium chloride-potassium carbonate ternary mixed inorganic salt, and sodium carbonate-sodium chloride-potassium carbonate quaternary mixed inorganic salt.
The working medium is water, toluene, benzene, pentane and octamethylcyclotetrasiloxane (molecular formula C)8H24O4Si4) Hexamethyldisiloxane (formula C)6H18OSi2) One kind of (1).
The utility model discloses beneficial technological effect who compares with prior art mainly embodies in following two aspects:
1. the double-tank sensible heat storage and the phase-change material heat storage are innovatively and organically combined to store energy in a composite mode. The technical scheme of combining sensible heat storage with phase-change material storage has been reported, including placing the phase-change material in the thermal storage oil/molten salt tank of the thermocline, and placing the phase-change material in the pressure water/steam thermal storage tank. Because the quality of the heat transfer medium (water, heat transfer oil, molten salt and the like) in the single-tank system is relatively constant, the temperature of the heat transfer medium in the tank body can be changed along with the change of the solar irradiation intensity and the heat collection amount in the daytime heat absorption process. And when the heat storage tank releases heat in cloudy days or at night, the temperature and the pressure of the heat transfer medium in the tank body are gradually reduced. Therefore, the problems existing when the phase-change material is applied to a solar thermal power generation system, particularly a direct expansion type system, can not be solved by the technical scheme of combining single-tank sensible heat storage and phase-change material heat storage. The composite energy storage technical scheme combining the double-tank sensible heat storage and the phase-change material heat storage has not been reported in the prior documents or patents.
The innovative technical scheme can effectively solve the problem of temperature and pressure fluctuation of the heat transfer medium in the tank body in the heat charging and discharging process of the phase change material. In the daytime, the heat transfer medium in the low-temperature heat storage tank 14 flows into the high-temperature heat storage tank 11 through the heat collection field 17, the flow of the heat transfer medium can be adjusted according to the intensity of solar radiation and the low-temperature pump 15, and the higher the radiation intensity is, the higher the flow is, the constant temperature of the heat transfer medium in the high-temperature heat storage tank 11 can be ensured, and meanwhile, solar energy resources are not wasted. For example, assuming an irradiation intensity of 700W/m2When the temperature of water/steam at the outlet of the heat collection field 17 is 260 ℃, the temperature of the phase-change material is 250 ℃, the heat absorption power of the phase-change material is Q, the rated input heat of the thermodynamic cycle is Q, the output heat of the heat collection field 17 is 2Q, and the flow of the low-temperature pump 15 is m, the irradiation intensity is 1000W/m2In the process, the heat absorption power Q of the phase-change material and the rated input heat Q of the thermodynamic cycle can still be kept unchanged, and the flow of the cryopump 15 is increased to be1.5 m so that the thermal field 17 outputs heat up to 3Q. When the heat storage tank releases heat in cloudy days or at night, the heat transfer medium of the high-temperature heat storage tank 11 flows back to the low-temperature heat storage tank 14 to convey heat to the thermal cycle, and the flow of the heat transfer medium is adjusted according to the heat release power of the phase-change material. The input flow of the thermodynamic cycle is composed of two parts, one part is latent heat released by the phase change material, and the other part is sensible heat brought by the temperature drop of the heat transfer medium flowing from the high-temperature heat storage tank 11 into the low-temperature heat storage tank 14. Latent heat is released through the evaporator 29 and sensible heat is released through the first and second preheaters 26 and 28. The latent heat and the sensible heat cooperate to ensure the efficient operation of the thermodynamic cycle. For example, in the initial stage of heat release, the phase change temperature of the phase change material is 250 ℃, the temperature of the heat transfer medium in the high-temperature heat storage tank 11 is 240 ℃, the rated input heat of the thermodynamic cycle is Q, the heat released by the phase change material is Q, and the flow rate of the heat transfer medium flowing into the low-temperature heat storage tank 14 from the high-temperature heat storage tank 11 is 0, so that in the final stage of heat release, the phase change temperature of the phase change material can still be kept at 250 ℃, the temperature of the heat transfer medium in the high-temperature heat storage tank 11 is 240 ℃, and the flow rate of the heat transfer medium flowing into the low-temperature heat storage tank 14 from the high-temperature heat storage tank 11 is increased to m, thereby ensuring that the low-pressure stage expander 23 operates under the rated working condition. At this time, the heat released from the phase change material may be reduced to 0.5Q due to the increase of the thermal resistance, but a part of the heat may be compensated by the second preheater 28, and the efficiency of the high-pressure stage expander may be maintained at a high level.
2. The utility model discloses have unique tertiary exothermic electricity generation mode, do respectively: driving the thermodynamic cycle by means of the heat released by the phase change material unit 12; secondly, the thermodynamic cycle is driven by the latent heat of phase change of the phase change material unit 12 and the sensible heat of the heat transfer medium; and thirdly, the thermodynamic cycle is driven by means of sensible heat of the heat transfer medium. The technical solution of the above single sub-mode has been reported, for example, the heat release mode (iii) can be found in utility model application CN 201710608229.7. However, a solar thermal power generation system having the above three-stage exothermic power generation mode has not been reported yet.
The unique heat-release power generation mode effectively improves the heat-storage power generation capacity of the system. Under the volumetric condition of given high temperature heat accumulation jar, the technical scheme of the utility model compare in the tradition based on phase change material heat accumulation's technical scheme, have higher heat accumulation generating capacity. For a traditional phase-change material heat storage tank, the phase-change units cannot fully occupy the space of the heat storage tank, gaps are formed among the units, and the volume proportion of the phase-change units is about 50% generally. For technical reasons, it is difficult for the conventional phase-change material thermal storage tank to generate electricity using sensible heat of the heat transfer medium. And to the utility model discloses technical scheme, the difference in temperature between high temperature heat accumulation jar 11 and the low temperature heat accumulation jar 14 can reach 200 ℃ or higher, and the sensible heat that heat transfer medium can release is huge to convert technical power into through low pressure steam turbine 23, therefore the heat accumulation generating capacity is higher. Simultaneously, the technical scheme of the utility model compare in not taking phase change material's two jar heat accumulation schemes (like CN 201710608229.7), also have higher heat accumulation generating capacity. The reason is that the heat storage density of the phase change material per unit volume is large, the temperature is relatively constant in the phase change process, the heat releasable amount is large in the heat release process, and the efficiency of the thermodynamic cycle is high (higher than that of the thermodynamic cycle which only uses a low-pressure stage expander to generate electricity).
Drawings
Fig. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a flow chart of a solar heat collection power generation mode.
FIG. 3 is a diagram of one design of a mixer.
Fig. 4 is a flow chart of the first stage heat and power generation mode.
Fig. 5 is a flow chart of the second stage heat and power generation mode.
Fig. 6 is a flow chart of the third stage heat-release power generation mode.
Sequence numbers in the upper figure: the system comprises a high-temperature heat storage tank 11, a phase-change material 12, a first high-temperature pump 13, a low-temperature heat storage tank 14, a low-temperature pump 15, a second high-temperature pump 16, a solar heat collection field 17, a high-pressure-stage expander 21, a mixer 22, a low-pressure-stage expander 23, a condenser 24, a low-temperature working medium pump 25, a first preheater 26, a high-temperature working medium pump 27, a second preheater 28, an evaporator 29, a first valve 31, a second valve 32, a third valve 33 and a fourth valve 34.
Detailed Description
The invention will now be further described by way of example with reference to the accompanying drawings.
Referring to fig. 1, the solar thermal power generation system based on the sensible heat and latent heat of phase change composite energy storage comprises a solar energy collection and storage loop and a thermal power conversion circulation loop.
The solar energy collecting and storing loop comprises a high-temperature heat storage tank 11, a phase-change material 12, a first high-temperature pump 13, a low-temperature heat storage tank 14, a low-temperature pump 15, a second high-temperature pump 16 and a solar heat collecting field 17. The high-temperature heat storage tank 11 is filled with a phase-change material 12, wherein the phase-change material 12 is inorganic salt, specifically lithium nitrate, and the melting point is 255 ℃. The volume of the phase-change material 12 accounts for 30-70% of the volume of the high-temperature heat storage tank 11, and the phase-change temperature of the phase-change material 12 is 255 ℃. The solar energy collecting and storing loop is provided with a heat transfer medium, and the heat transfer medium is water. The solar heat collection field 17 is a parabolic trough type heat collection field.
Referring to fig. 1, the specific structure of the solar energy collecting and storing circuit is illustrated as follows: the outlet at the bottom of the high-temperature heat storage tank 11 is sequentially connected in series with the heat transfer side of a first preheater 26, the heat transfer side of a second preheater 28, the low-temperature heat storage tank 14 and the inlet of a low-temperature pump 15 through pipelines, and the outlet of the low-temperature pump 15 is respectively communicated with the inlet of a solar heat collection field 17 and the outlet of a second high-temperature pump 16 through a three-way pipe; the outlet of the solar heat collection field 17 is communicated with the inlet at the top of the high-temperature heat storage tank 11, and the inlet of the second high-temperature pump 16 is communicated with the outlet at the bottom of the high-temperature heat storage tank 11; an evaporator 29 and a first high-temperature pump 13 are connected in series between an inlet on the upper side and an outlet on the lower side of the high-temperature heat storage tank 11.
The heat power conversion circulation loop comprises a high-pressure stage expander 21, a mixer 22, a low-pressure stage expander 23, a condenser 24, a low-temperature working medium pump 25, a first preheater 26, a high-temperature working medium pump 27, a second preheater 28 and an evaporator 29. The first preheater 26, the second preheater 28 and the evaporator 29 each comprise a heat transfer side and a working medium side in parallel, respectively. Working medium is in the heat-work conversion circulation loop, and the working medium is benzene.
The specific structure of the thermal power conversion circulation loop is illustrated as follows: the inlet of the high-pressure stage expander 21 is sequentially connected with one side of the working medium of the evaporator 29, one side of the working medium of the second preheater 28 and the outlet of the high-temperature working medium pump 27 in series, the inlet of the high-temperature working medium pump 27 is communicated with the first outlet of the mixer 22, and the outlet of the high-pressure stage expander 21 is communicated with the first inlet of the mixer 22; the outlet of the low-pressure stage expander 23 is sequentially connected with the condenser 24, the low-temperature working medium pump 25 and the inlet of the working medium side of the first preheater 26 in series, the outlet of the working medium side of the first preheater 26 is communicated with the second inlet of the mixer 22, and the second outlet of the mixer 22 is communicated with the inlet of the low-pressure stage expander 23;
a first valve 31 is connected in series between the outlet of the low-temperature working medium pump 25 and the inlet of the working medium side of the first preheater 26, and a second valve 32 is connected in series between the outlet of the low-temperature working medium pump 25 and the second inlet of the mixer 22; a third valve 33 is connected in series between the working medium side inlet of the second preheater 28 and the outlet of the high temperature working medium pump 27, and a fourth valve 34 is connected in series between the outlet of the high temperature working medium pump 27 and the working medium side inlet of the evaporator 29.
The utility model provides a solar thermal power generation system has 4 kinds of mode, is solar energy collection power generation mode and the tertiary heat release power generation mode respectively, and concrete theory of operation explains as follows:
(1) the solar heat collection power generation mode is shown in fig. 2, and the flow of the mode is indicated by a solid black line. In a solar heat collection power generation mode, a solar heat collection field 17, a high-temperature heat storage tank 11, a first high-temperature pump 13, a low-temperature heat storage tank 14, a high-pressure-stage expander 21, a mixer 22, a low-pressure-stage expander 23, a condenser 24, a low-temperature working medium pump 25 and an evaporator 29 participate in work. Under the condition of sufficient solar irradiation, solar heat collection, heat storage and thermodynamic cycle power generation are simultaneously carried out, and all pumps are operated. The cryopump 15 and the second high-temperature pump 16 pump the liquid heat medium from the low-temperature heat storage tank 14 and the high-temperature heat storage tank 11, respectively, into the heat collection field 17. The flow rates of the cryopump 15 and the second cryopump 16 may be adjusted according to the intensity of solar radiation, with the aim of ensuring a stable temperature of water in the high-temperature heat storage tank 11 while sufficiently collecting solar energy. Under normal conditions, water at the outlet of the solar heat collection field 17 is in a gas-liquid two-phase state. The gas-liquid two-phase state is beneficial to improving the heat transfer coefficient of water, reducing the heat loss of a heat collection field and being easy to control. Gaseous water at the outlet of the solar heat collection field 17 is condensed in the high-temperature heat storage tank 11, and the released heat can be released to the phase-change material 12 and the water. The water further transfers heat to the thermal cycle working medium benzene through a first high temperature pump 13. The thermodynamic cycle working medium obtains heat through the evaporator 29 and evaporates, the gaseous benzene enters the high-pressure stage expansion machine 21 to do work, and the outlet benzene of the high-pressure stage expansion machine 21 enters the mixer 22 and is mixed with the liquid benzene from the low-temperature working medium pump 25 and the second valve 32. The liquid benzene at the outlet of the mixer 22 flows into the high-temperature working medium pump 27, and the pressurized benzene enters the evaporator 29 through the fourth valve 34 to absorb heat again. The gaseous benzene at the outlet of the mixer 22 enters the low-pressure stage expansion machine 23 to do work, the benzene at the outlet of the low-pressure stage expansion machine 23 enters the condenser 24 to be condensed, the liquid benzene flows into the low-temperature working medium pump 25, and the pressurized benzene enters the mixer 22 again through the second valve 32. The mixer is constructed as shown in figure 3.
When the solar heat collection power generation mode is finished in the evening, the water in the high-temperature heat storage tank 11 becomes liquid, and simultaneously, most of the water in the low-temperature heat storage tank 14 is heated by the solar heat collection field 17 and transferred to the high-temperature heat storage tank 11 to prepare for heat release and power generation.
(2) The first stage heat-generation and power-generation mode is shown in fig. 4, and the flow of the mode is indicated by a solid black line. In the first-stage heat release power generation mode, the high-temperature heat storage tank 11, the first high-temperature pump 13, the high-pressure stage expander 21, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25 and the evaporator 29 participate in working; the heat required for the thermodynamic cycle is obtained by the latent heat of phase change of the phase change material 12. As the initial stage of heat release is realized, most of the phase-change material 12 is in a liquid state, the thermal resistance with the wall surface is small, and the rate of heat release of the phase-change material 12 is large at a given heat transfer medium temperature, so that the requirement of thermodynamic cycle can be met. In this mode, the solar heat collection field 17 does not operate, and the power generation mode of the thermodynamic cycle is the same as the power generation mode in the solar heat collection power generation mode. The benzene in thermodynamic cycle obtains heat through the evaporator 29 and is evaporated, the gaseous benzene enters the high-pressure stage expansion machine 21 to do work, the outlet working medium of the high-pressure stage expansion machine 21 enters the mixer 22 and is mixed with the liquid benzene from the low-temperature working medium pump 25 and the second valve 32. The liquid benzene at the outlet of the mixer 22 flows into the high-temperature working medium pump 27, and the pressurized benzene enters the evaporator 29 through the fourth valve 34 to absorb heat again. The gaseous benzene at the outlet of the mixer 22 enters the low-pressure stage expansion machine 23 to do work, the benzene at the outlet of the low-pressure stage expansion machine 23 enters the condenser 24 to be condensed, the liquid benzene flows into the low-temperature working medium pump 25, and the pressurized benzene enters the mixer 22 through the second valve.
(3) The second-stage heat-generation and power-generation pattern is shown in fig. 5, and the flow of the pattern is indicated by a solid black line. In the second-stage heat release power generation mode, the high-temperature heat storage tank 11, the first high-temperature pump 13, the high-pressure stage expander 21, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25, the first preheater 26, the high-temperature working medium pump 27, the second preheater 28 and the evaporator 29 participate in work; the phase-change material 12 with a larger proportion is solidified, the heat transfer resistance with the wall surface is increased, and the rate of heat release of the phase-change material 12 is smaller at a given heat transfer medium temperature, so that the requirement of thermodynamic cycle is difficult to meet. At this time, the sensible heat of the water in the high-temperature heat storage tank 11 is required to be used for replenishment. The water of the high temperature heat storage tank 11 flows into the low temperature heat storage tank 14 through the first and second preheaters 26 and 28, and the released sensible heat is used to make up for the shortage of the heat released from the phase change material 12. The gaseous benzene in the thermodynamic cycle enters the high-pressure stage expansion machine 21 to do work, and the benzene at the outlet of the high-pressure stage expansion machine 21 enters the mixer 22 to be mixed with the liquid benzene from the low-temperature working medium pump 25 and the second valve 32. The liquid benzene at the outlet of the mixer 22 flows into a high temperature working medium pump 27, and the pressurized benzene enters the second preheater 28 through a third valve 33, is increased in temperature and then flows into the evaporator 29 for further evaporation. The gaseous working medium at the outlet of the evaporator 29 enters the high-pressure stage expander 21 to do work again. The gaseous benzene at the outlet of the mixer 22 enters the low-pressure stage expander 23 to do work, the benzene at the outlet of the low-pressure stage expander 23 enters the condenser 24 to be condensed, the liquid benzene flows into the low-temperature working medium pump 25, the pressurized benzene enters the first preheater 26 through the first valve 31, and the heated benzene flows into the mixer 22. In the second stage heat release power generation mode, the low-pressure stage expander 23 is in a rated operation condition, the power output by the high-pressure stage expander 21 can be lower than the rated operation condition (the efficiency of the high-pressure stage expander 21 is slightly reduced), and the overall power output of the thermodynamic cycle can still be kept at a level of 80% or more of the rated operation condition.
(4) The third-stage heat-generation power generation mode is shown in fig. 6, and the flow of the mode is indicated by a solid black line. In a third-stage heat release power generation mode, in the third-stage heat release power generation mode, the high-temperature heat storage tank 11, the low-temperature heat storage tank 14, the mixer 22, the low-pressure stage expander 23, the condenser 24, the low-temperature working medium pump 25, the first preheater 26 and the second preheater 28 participate in work; most of the phase change material 12 is solidified, and the latent heat of phase change is fully utilized. At this time, it is necessary to generate electricity by relying entirely on the sensible heat of the water in the high-temperature heat storage tank 11. The water in the high temperature heat storage tank 11 flows into the low temperature heat storage tank 14 through the first preheater 26, and the released sensible heat is used for bottom thermodynamic cycle power generation. The gaseous benzene enters the low-pressure stage expander 23 to do work, the benzene at the outlet of the low-pressure stage expander 23 enters the condenser 24 to be condensed, the liquid benzene flows into the low-temperature working medium pump 25, and the pressurized benzene enters the first preheater 26 through the first valve 31 and is completely evaporated. The gaseous benzene passes through mixer 22 and then re-enters low pressure stage expander 23 to perform work. In the third stage heat release power generation mode, the low-pressure stage expander 23 is in the rated operation condition, and the high-pressure stage expander 21 does not work.
Table 1 shows the thermodynamic cycle parameters for each stage in the three-stage heat release mode. Assuming that the working fluid is benzene (chemical formula C)6H6The boiling point is 80.1 ℃, the critical temperature is 288.94 ℃, and the critical pressure is 4.898 MPa), the phase-change temperature of the phase-change material 12 is 270 ℃, the design efficiency of the high-pressure stage expander 21 and the low-pressure stage expander 23 is 85%, and the design efficiency of the high-temperature working medium pump 27 and the low-temperature working medium pump 25 is 80%. The thermodynamic cycle state of the heat collection and power generation mode is the same as that of the first-stage heat release mode. It can be seen from the table that the evaporator heat absorption (second stage heat release mode) can be reduced to less than 50% of the normal operation (first stage heat release mode) with supplementation of sensible heat of the heat transfer medium in the high temperature heat storage tank 11, while the cycle efficiency is only slightly reduced (2% because of the reduction in heat source temperature and the deviation of the high pressure stage expander from design work)A condition-induced decrease in internal efficiency). Therefore, the technical scheme of the utility model can effectively solve the problem that the existing phase change heat storage tank exists in the solar thermal power generation technical field, especially the direct expansion type technical field.
Claims (6)
1. Solar thermal power generation system based on sensible heat and latent heat of phase change complex energy storage, its characterized in that: the solar heat conversion system comprises a solar energy collection and storage loop and a heat-work conversion circulation loop;
the solar energy collecting and storing loop comprises a high-temperature heat storage tank (11), a phase-change material (12), a first high-temperature pump (13), a low-temperature heat storage tank (14), a low-temperature pump (15), a second high-temperature pump (16) and a solar heat collecting field (17); the high-temperature heat storage tank (11) is filled with a phase-change material (12), the volume of the phase-change material (12) accounts for 30-70% of the volume of the high-temperature heat storage tank (11), and the phase-change temperature of the phase-change material (12) is 210-400 ℃; the solar energy collecting and storing loop is a heat transfer medium;
the thermal power conversion circulation loop comprises a high-pressure stage expander (21), a mixer (22), a low-pressure stage expander (23), a condenser (24), a low-temperature working medium pump (25), a first preheater (26), a high-temperature working medium pump (27), a second preheater (28) and an evaporator (29); the first preheater (26), the second preheater (28) and the evaporator (29) respectively comprise a heat transfer side and a working medium side which are arranged in parallel; working media are in the heat-work conversion circulation loop;
the working temperature of the heat transfer medium in the high-temperature heat storage tank (11) is 200-400 ℃, and the working temperature of the heat transfer medium in the low-temperature heat storage tank (14) is 30-170 ℃; the gaseous mass fraction of the heat transfer medium at the outlet of the solar heat collection field (17) is 5-95%;
the solar thermal power generation system has 4 working modes;
in a solar heat collection power generation mode, a solar heat collection field (17), a high-temperature heat storage tank (11), a first high-temperature pump (13), a low-temperature heat storage tank (14), a high-pressure-stage expansion machine (21), a mixer (22), a low-pressure-stage expansion machine (23), a condenser (24), a low-temperature working medium pump (25) and an evaporator (29) participate in work;
in a first-stage heat release power generation mode, a high-temperature heat storage tank (11), a first high-temperature pump (13), a high-pressure stage expander (21), a mixer (22), a low-pressure stage expander (23), a condenser (24), a low-temperature working medium pump (25) and an evaporator (29) participate in work;
in a secondary heat release power generation mode, a high-temperature heat storage tank (11), a first high-temperature pump (13), a high-pressure stage expander (21), a mixer (22), a low-pressure stage expander (23), a condenser (24), a low-temperature working medium pump (25), a first preheater (26), a high-temperature working medium pump (27), a second preheater (28) and an evaporator (29) participate in working;
and in a three-stage heat release power generation mode, the high-temperature heat storage tank (11), the low-temperature heat storage tank (14), the mixer (22), the low-pressure stage expander (23), the condenser (24), the low-temperature working medium pump (25), the first preheater (26) and the second preheater (28) participate in work.
2. The solar thermal power generation system based on the composite storage of sensible heat and latent heat of phase change according to claim 1, wherein: the bottom outlet of the high-temperature heat storage tank (11) is sequentially connected in series with the heat transfer side of a first preheater (26), the heat transfer side of a second preheater (28), the low-temperature heat storage tank (14) and the inlet of a low-temperature pump (15) through pipelines, and the outlet of the low-temperature pump (15) is respectively communicated with the inlet of a solar heat collection field (17) and the outlet of a second high-temperature pump (16) through a three-way pipe; an outlet of the solar heat collection field (17) is communicated with an inlet at the top of the high-temperature heat storage tank (11), and an inlet of the second high-temperature pump (16) is communicated with an outlet at the bottom of the high-temperature heat storage tank (11); an evaporator (29) and a first high-temperature pump (13) are connected in series between an inlet at one side of the upper part and an outlet at one side of the lower part of the high-temperature heat storage tank (11);
an inlet of the high-pressure stage expansion machine (21) is sequentially connected with one side of a working medium of the evaporator (29), one side of a working medium of the second preheater (28) and an outlet of the high-temperature working medium pump (27) in series, an inlet of the high-temperature working medium pump (27) is communicated with a first outlet of the mixer (22), and an outlet of the high-pressure stage expansion machine (21) is communicated with a first inlet of the mixer (22); the outlet of the low-pressure stage expander (23) is sequentially connected with the condenser (24), the low-temperature working medium pump (25) and the inlet of the working medium side of the first preheater (26) in series, the outlet of the working medium side of the first preheater (26) is communicated with the second inlet of the mixer (22), and the second outlet of the mixer (22) is communicated with the inlet of the low-pressure stage expander (23);
a first valve (31) is connected in series between the outlet of the low-temperature working medium pump (25) and the inlet of the working medium side of the first preheater (26), and a second valve (32) is connected in series between the outlet of the low-temperature working medium pump (25) and the second inlet of the mixer (22); a third valve (33) is connected in series between the inlet at one side of the working medium of the second preheater (28) and the outlet of the high-temperature working medium pump (27), and a fourth valve (34) is connected in series between the outlet of the high-temperature working medium pump (27) and the inlet at one side of the working medium of the evaporator (29).
3. The solar thermal power generation system based on the composite storage of sensible heat and latent heat of phase change according to claim 1, wherein: the solar heat collection field (17) is one of a parabolic groove type heat collection field, a linear Fresnel heat collection field and a tower type heat collection field.
4. The solar thermal power generation system based on the composite storage of sensible heat and latent heat of phase change according to claim 1, wherein: the heat transfer medium is one of water and heat transfer oil.
5. The solar thermal power generation system based on the composite storage of sensible heat and latent heat of phase change according to claim 1, wherein: the phase change material (12) is an inorganic salt phase change material, and the inorganic salt phase change material is one of lithium nitrate inorganic salt, sodium nitrate-calcium nitrate binary mixed inorganic salt, sodium carbonate-sodium chloride-potassium carbonate ternary mixed inorganic salt and sodium carbonate-sodium chloride-potassium carbonate quaternary mixed inorganic salt.
6. Sensible heat and phase based according to claim 1The solar thermal power generation system of the compound energy storage of latent heat becomes, its characterized in that: the working medium is water, toluene, benzene, pentane and octamethylcyclotetrasiloxane (molecular formula C)8H24O4Si4) Hexamethyldisiloxane (formula C)6H18OSi2) One kind of (1).
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