Expandable heat storage capacity system for trough type photo-thermal power station

Abstract

The utility model discloses an expandable heat storage capacity system for a trough type photo-thermal power station, a trough type mirror field is respectively communicated with an oil salt heat exchange system and a steam generator through a main circulating pump by pipelines to form a main circulating loop, and the steam generator is connected with the oil salt heat exchange system in parallel; one end of the bypass pipeline is communicated with the oil outlet end of the groove type mirror field, the other end of the bypass pipeline is connected to the switch valves on the tops of the overflow tanks in the overflow tank set, and the oil discharge ends of the overflow tanks in the overflow tank set are connected to the expansion tank through the oil discharge valves and the overflow pumps. The oil discharge end of the expansion tank is respectively connected to the oil inlet valves at the tops of the overflow tanks in the overflow tank group through an expansion tank oil discharge valve by virtue of a pipeline; and a bypass pipeline switching valve and a bypass pipeline regulating valve are arranged on the bypass pipeline. According to the utility model, the heat conduction oil overflow system of the original heat conduction oil tank type power station equipment is improved, so that the heat storage capacity of the power station is expanded under the condition of not increasing the use amount of the fused salt heat storage medium.

Description

Technical Field

[0001] The utility model belongs to the application technical field of solar thermal power generation, and particularly relates to an expandable heat storage capacity system for a trough solar thermal power station. Background Art

[0002] Solar thermal power generation (Concentrated Solar Power, abbreviated as "CSP") is a technology that uses a concentrating solar collector to convert solar radiant energy into heat energy, heats a fluid working medium, and then generates high-temperature steam through heat exchange, and finally drives a steam turbine to generate electricity. When the sunlight is strong during the day, a part of the fluid working medium can be directly stored, or the heat can be transferred to the heat storage medium through heat exchange for storage. When it is night or the sunlight is poor, the stored heat is released, so that the power station can generate electricity normally at sunset or on cloudy days.

[0003] The heat transfer oil trough solar thermal power station is the mainstream technology of solar thermal power generation, and has the advantages of the highest technical maturity, the richest historical experience, the most stable operation performance, etc. In the heat transfer oil trough power station, the fluid working medium is heat transfer oil, and the heat storage medium is molten salt. The heat is generally stored in the sensible heat of the molten salt medium. The heat transfer oil system is an important part of the power station, mainly transporting heat transfer oil through pump sets and pipelines, responsible for absorbing heat in the mirror field, and then transporting the heated heat transfer oil to the steam generator to generate high-temperature steam for power generation, or transporting the heated heat transfer oil to the oil-salt heat exchanger to transfer the heat of the heat transfer oil to the molten salt for storage. Since the temperature of the heat transfer oil will change continuously during the cyclic operation, its volume will also change accordingly. Therefore, the heat transfer oil system usually sets an expansion tank installed at a high place and several overflow tanks installed on the ground to absorb the volume change of the heat transfer oil during the working process and play a role in stabilizing the pressure of the heat transfer oil system.

[0004] Under normal working conditions, at sunrise every day, the average temperature of the thermal oil in the power plant is at its lowest value of the day. At this time, the volume of thermal oil in the thermal oil system is the smallest, and the amount of thermal oil stored in the overflow tank is also the smallest. After sunrise, the mirror field gathers sunlight to gradually heat the thermal oil in the collector tube. The average temperature of the thermal oil in the whole field gradually increases, the volume expands, and the liquid level in the expansion tank gradually rises. The thermal oil that exceeds the designed liquid level will flow to the overflow tank through the overflow pipe at a certain height set in the expansion tank for storage. When the operating temperature of the trough power plant reaches the designed operating conditions during the daytime, the average temperature of the thermal oil in the whole field is the highest, the volume of thermal oil reaches the maximum value, and the amount of thermal oil stored in the overflow tank also reaches the maximum value. After sunset, the temperature of the thermal oil in the whole field gradually decreases, and the volume gradually shrinks. At this time, it is necessary to pump the thermal oil from the overflow tank to the expansion tank to keep the liquid level of the expansion tank stable, until before sunrise in the early morning of the next day, the volume of thermal oil in the system is the smallest, and the amount of thermal oil stored in the overflow tank is the least, and this cycle is repeated. Therefore, during the daytime, a portion of the heat transfer oil in the power station is always stored in the overflow tank, and its heat capacity is not fully utilized.

[0005] Since the maximum allowable operating temperature of the heat transfer oil does not exceed 400°C, otherwise the heat transfer oil will undergo high-temperature cracking. Subject to this limitation, the operating temperature range of the heat transfer oil in the trough power station under the design conditions is generally 293~393°C, which determines that the heat storage temperature range of the molten salt is about 285~385°C, a total of about 100°C, and its upper temperature limit is much lower than the maximum allowable operating temperature of molten salt, 565°C. The molten salt heat storage temperature range of molten salt tower or molten salt line technology is generally 290~550°C, a total of 260°C. Therefore, under the premise of the same heat storage capacity, the amount of molten salt used in the trough power station is much higher than that of the tower or line power station, about 2.6 times, which is very unfavorable for further reducing the cost of electricity of the trough solar thermal technology. Therefore, how to use the existing equipment of the thermal oil trough power station to fully tap the heat storage potential of the system without increasing the amount of molten salt is a major problem that the thermal oil trough technology needs to face.

[0006] In summary, the heat storage system of thermal oil tank technology currently has the following problems:

[0007] 1. The thermal energy storage form of solar thermal power generation technology is the sensible heat of the molten salt medium. Therefore, for the same amount of molten salt, the larger the heat storage temperature range, the greater the heat storage capacity. Limited by the maximum allowable operating temperature of the thermal oil, the maximum heat storage temperature of the molten salt in the thermal oil tank power station is about 385°C, which is much lower than its maximum allowable operating temperature, and the designed heat storage temperature range of the molten salt is about 100°C. Therefore, under the same heat storage capacity requirement, the amount of molten salt required for the thermal oil tank power station is much higher than that of the molten salt tower or molten salt line power station.

[0008] 2. Without changing the working fluid of the heat transfer oil and without further increasing its maximum operating temperature, it is impossible to expand the system's heat storage capacity by increasing the maximum heat storage temperature of the molten salt.

[0009] 3. Although the system heat storage capacity can be increased by increasing the amount of molten salt, this will inevitably lead to an increase in system investment, which is not conducive to further reducing the cost of electricity of trough solar thermal technology.

[0010] 4. According to the working characteristics of the heat transfer oil system, when the power station collects heat during the day, a part of the heat transfer oil will overflow into the overflow tank for storage. The temperature of the naturally overflowing heat transfer oil is the temperature after the heat transfer oil in the expansion tank is mixed, which is generally within 300°C and cannot reach 393°C. Its heat capacity cannot be fully utilized, which is a waste of the heat storage capacity of the power station. Utility Model Content

[0011] In order to overcome the shortcomings of the above-mentioned prior art, the utility model provides a thermal oil overflow system for a trough type solar thermal power station with expandable heat storage capacity. By improving the thermal oil overflow system of the original thermal oil trough type power station equipment, the heat storage capacity of the power station can be expanded without increasing the amount of molten salt heat storage medium.

[0012] The main technical solutions adopted in this utility model are:

[0013] A scalable heat storage capacity system for a trough solar thermal power station, comprising a trough mirror field, an oil-salt heat exchange system, a main circulation pump, a steam generator, a bypass pipeline, an expansion tank and an overflow tank group, wherein the trough mirror field is connected to the oil-salt heat exchange system and the steam generator through a pipeline via the main circulation pump to form a main circulation loop, and the steam generator is connected to the oil-salt heat exchange system in parallel, one end of the bypass pipeline is connected to the oil outlet end of the trough mirror field, and the other end is respectively connected to the switch valve at the top of each overflow tank in the overflow tank group, the oil discharge end of each overflow tank in the overflow tank group is respectively connected to the expansion tank through the oil discharge valve through the overflow pump, and the oil discharge end of the expansion tank is respectively connected to the oil inlet valve at the top of each overflow tank in the overflow tank group through the pipeline via the expansion tank oil discharge valve, and the bypass pipeline is provided with a bypass pipeline switch valve and a bypass pipeline regulating valve, and the high-temperature heat transfer oil returned from the trough mirror field enters any one or more of the oil-salt heat exchange system, the bypass pipeline and the steam generator through valve control.

[0014] Preferably, the overflow tank group includes one or two or more overflow tanks, wherein the two or more overflow tanks are connected in parallel with each other.

[0015] Preferably, the expansion tank is connected to the main circulation loop between the steam generator and the main circulation pump through an oil inlet pipeline and an oil return pipeline respectively, and an expansion tank bypass valve is provided in the main circulation loop between the oil inlet pipeline and the oil return pipeline.

[0016] Preferably, an oil overflow port is provided at the highest liquid level of the expansion tank, and the oil overflow port is respectively connected to the oil inlet valves at the tops of the overflow tanks in the overflow tank group through an overflow pipeline.

[0017] Preferably, the bypass pipeline switch valve, the bypass pipeline regulating valve, the switch valve, the oil inlet valve, the oil drain valve, the expansion tank oil drain valve, and the expansion tank bypass valve are all automatic valves and all have valve position feedback functions.

[0018] Preferably, the outer peripheries of the bypass pipeline, the bypass pipeline switch valve, the bypass pipeline regulating valve, and the switch valve are all wrapped with a heat insulation layer.

[0019] Preferably, an electric tracing heating device is also laid in the heat insulation layer.

[0020] Beneficial effects: The utility model provides a heat-conducting oil overflow system for a trough solar thermal power station capable of expanding the heat storage capacity. Without increasing the amount of molten salt heat storage medium, high-temperature heat-conducting oil can be used to replace and store low-temperature heat-conducting oil in the overflow tank group by designing a bypass pipeline, so as to achieve the purpose of expanding the heat storage capacity of the power station by using the heat-conducting oil in the overflow tank, which is beneficial to improving the energy utilization rate and reducing the production cost of the power station. Description of the Drawings

[0021] Figure 1 The flow chart of trough solar thermal power generation in Embodiment 1 is shown.

[0022] In the figure: trough mirror field 1, oil-salt heat exchange system 2, oil-salt heat exchanger 2-1, hot salt tank 2-2, cold salt tank 2-3, main circulation pump 3, steam generator 4, bypass pipeline 5, bypass pipeline switch valve 5-1, bypass pipeline regulating valve 5-2, expansion tank 6, overflow tank group 7, first overflow tank 701, second overflow tank 702... nth overflow tank 70n, first switch valve 801, second switch valve 802... nth switch valve 80n, oil drain valve 9, first oil drain valve 901, second oil drain valve 902... nth oil drain valve 90n, overflow pump 10, expansion tank oil drain valve 11, oil inlet valve 12, oil inlet pipeline 13, oil return pipeline 14, expansion tank bypass valve 15, overflow pipeline 16. Detailed Embodiments

[0023] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application. Embodiment 1

[0024] An expandable heat storage capacity system for a trough solar thermal power station, as Figure 1 shown, includes a trough mirror field 1, an oil-salt heat exchange system 2, a main circulation pump 3, a steam generator 4, a bypass pipeline 5, an expansion tank 6, and an overflow tank group 7. Among them, the trough mirror field 1 is connected to the oil-salt heat exchange system 2 and the steam generator 4 respectively through pipelines via the main circulation pump 3 to form a main circulation loop, and the steam generator 4 and the oil-salt heat exchange system 2 are connected in parallel. One end of the bypass pipeline 5 is connected to the oil outlet end of the trough mirror field 1, and the other end is respectively connected to the switching valves at the tops of the overflow tanks in the overflow tank group 7. The oil outlet ends of the overflow tanks in the overflow tank group 7 are respectively connected to the expansion tank 6 through the oil discharge valves 9 via the overflow pumps 10. The oil discharge end of the expansion tank 6 is respectively connected to the oil inlet valves 12 at the tops of the overflow tanks in the overflow tank group 7 through pipelines via the expansion tank oil discharge valve 11. A bypass pipeline switching valve 5-1 and a bypass pipeline regulating valve 5-2 are arranged on the bypass pipeline 5. The high-temperature heat transfer oil returning from the trough mirror field 1 enters any one or more of the oil-salt heat exchange system 2, the bypass pipeline 5, and the steam generator 4 through valve control (not shown in the figure, which belongs to a conventional setting).

[0025] In the present utility model, the overflow tank group 7 includes one or two or more overflow tanks, among which, two or more overflow tanks 7-1 are connected in parallel with each other. In the first embodiment, the overflow tank group 7 includes the first overflow tank 701, the second overflow tank 702... the nth overflow tank 70n, a total of n parallel-connected overflow tanks (n≥2), and each overflow tank is correspondingly connected with a switching valve and an oil discharge valve 9.

[0026] In the first embodiment, the expansion tank 6 is respectively connected to the main circulation loop between the steam generator 4 and the main circulation pump 3 through an oil inlet pipeline 13 and an oil return pipeline 14, and an expansion tank bypass valve 15 is arranged on the main circulation loop between the oil inlet pipeline 13 and the oil return pipeline 14.

[0027] An oil overflow port is arranged at the highest liquid level of the expansion tank 6, and the oil overflow port is respectively connected to the oil inlet valves 12 at the tops of the overflow tanks in the overflow tank group 7 through an oil overflow pipeline 16.

[0028] In the first embodiment, the bypass pipeline switching valve 5-1, the bypass pipeline regulating valve 5-2, the switching valve, the oil inlet valve 12, the oil discharge valve 9, the expansion tank oil discharge valve 11, and the expansion tank bypass valve 15 are all automatic valves and all have a valve position feedback function for feedback of the current valve state. For example: if it is a regulating valve, the valve position feedbacks the current opening degree of the valve; if it is a switching valve, the valve position feedbacks whether the current valve is in an open or closed state.

[0029] In the first embodiment, the outer peripheries of the bypass pipeline 5, the bypass pipeline switching valve 5-1, the bypass pipeline regulating valve 5-2, and the switching valve are all wrapped with heat insulation layers.

[0030] In Embodiment 1, an electric tracing device is laid in the heat preservation layer for anti-condensation.

[0031] In the present utility model, the specific settings of the heat preservation layer and the electric tracing device belong to the conventional technical field, so no detailed description is given.

[0032] Taking the following working conditions as an example, the specific working principle of Embodiment 1 is described.

[0033] In Embodiment 1, the heat transfer oil fluid working medium and the heat storage medium are two different media, both of which are liquid within their respective working temperature ranges, and the energy forms of heat absorption, heat transfer, and heat storage are all sensible heat. Specifically: the heat transfer oil fluid working medium is 26.5% biphenyl - 73.5% diphenyl ether, with a freezing point of 12°C, a working temperature range of 50°C to 400°C, and a working temperature range under the design conditions of 293°C to 393°C; the heat storage medium is a binary molten salt of 60% sodium nitrate - 40% potassium nitrate, with a freezing point of 238°C, a working temperature range of 270°C to 400°C, and a working temperature range under the design conditions of 285°C to 385°C.

[0034] In Embodiment 1, after the heat transfer oil is heated by the sunlight focused in the trough mirror field 1, the temperature rises to 393°C. The high-temperature heat transfer oil returning from the trough mirror field 1 preferentially enters the steam generator 4 through valve control to generate high-temperature steam for driving the steam turbine unit to generate electricity. The surplus high-temperature heat transfer oil can be selectively controlled by valves to enter the oil-salt heat exchange system 2 to exchange the heat of the heat transfer oil to the molten salt for storage, or to enter the bypass pipeline 5 to directly store the high-temperature heat transfer oil in the overflow tank group 7, replacing the original low-temperature heat transfer oil in the overflow tank, so as to achieve the purpose of expanding the heat storage capacity of the power station using the heat transfer oil in the overflow tank.

[0035] In Embodiment 1, the operation of expanding the heat storage capacity of the system charging station includes the following steps:

[0036] Step 1: At the sunrise time of each day, the temperature of the heat transfer oil in the whole power station is about 150°C, the liquid level of the expansion tank 7 is about 50%, and the liquid level of each overflow tank in the overflow tank group 7 is about 15%. At this time, the bypass pipeline switch valve 5-1, the switch valves at the tops of each overflow tank, and the expansion tank oil discharge valve 11 are in the closed state, and the expansion tank bypass valve 15, the oil inlet valves 12 connecting the expansion tank 6 to the tops of each overflow tank, and the oil discharge valves 9 connecting the bottoms of each overflow tank to the overflow pump 10 are in the open state. Because the oil discharge valves 9 at the bottoms of each overflow tank are in the open state, the overflow tank group 7 is a set of communicating vessels. Since the expansion tank bypass valve 15 is open, the heat transfer oil at the outlet of the steam generator 4 directly enters the main circulation pump 3.

[0037] Step 2: After sunrise, the power station is preheated normally. The temperature of the heat-conducting oil rises, and its volume expands. The heat-conducting oil gradually overflows from the expansion tank 6 to the overflow tank group 7 through the overflow pipeline 16. Meanwhile, the temperature of the heat-conducting oil in the overflow tank group 7 also gradually increases. When the temperature of the heat-conducting oil at the outlet of the trough mirror field 1 reaches the designed working temperature of 393°C, the liquid levels of the overflow tanks 7-1 in the overflow tank group 7 also reach their maximum values. At this time, the expansion tank bypass valve 15 is set to the closed state, and the expansion tank 7 is connected to the main heat-conducting oil circulation loop through the oil inlet pipeline 13 and the oil return pipeline 14 (in the "double-leg" mode), that is, all the heat-conducting oil at the outlet of the steam generator 4 has to enter the expansion tank 6 through the oil inlet pipeline 13 for mixing and then enter the main circulation pump 3 through the oil return pipeline 14.

[0038] Step 3: Subsequently, the power station has been operating under the designed conditions. The temperature of the heat-conducting oil at the outlet of the trough mirror field 1 is maintained at 393°C. When the flow rate of the heat-conducting oil at the outlet of the trough mirror field 1 exceeds the flow rate of the heat-conducting oil required by the steam generator 4, the bypass pipeline switch valve 5-1 is opened.

[0039] Step 4: Open the first switch valve 801 connecting the bypass pipeline 5 to the top of the first overflow tank 701, keep the first oil discharge valve 901 connecting the bottom of the first overflow tank 701 to the overflow pump 10 in the open state, close the oil discharge valves 17 connecting the bottoms of other overflow tanks to the overflow pump 10, start the overflow pump 10, and control the valve opening of the bypass pipeline regulating valve 5-2 to keep the liquid level in the expansion tank 6 stable. At this time, the high-temperature heat-conducting oil at 393°C will enter the first overflow tank 701, causing the temperature and liquid level of the heat-conducting oil in the first overflow tank 701 to rise gradually.

[0040] Step 5: When the temperature of the heat-conducting oil in the first overflow tank 701 reaches 393°C, open the second switch valve 802 connecting the bypass pipeline 5 to the top of the second overflow tank 702 and the second oil discharge valve 902 connecting the bottom of the second overflow tank 702 to the overflow pump 10, and close the first switch valve 801 connecting the bypass pipeline 5 to the top of the first overflow tank 701 and the first oil discharge valve 901 connecting the bottom of the first overflow tank 701 to the overflow pump 10. At this time, the high-temperature heat-conducting oil changes to enter the second overflow tank 702, and the first overflow tank 701 is already full of high-temperature heat-conducting oil at 393°C.

[0041] Step 6: Repeat Step 4 and Step 5 until the heat-conducting oil in all the overflow tanks reaches 393°C. Then close the bypass pipeline switch valve 5-1 and the nth switch valve 80n connecting the bypass pipeline 5 to the top of the nth overflow tank 70n, and stop the operation of the overflow pump 10.

[0042] Thus, the entire process of heat charging and heat storage of the heat-conducting oil in the overflow tank group is completed.

[0043] In this Embodiment 1, the system heat release operation includes the following steps:

[0044] Step a: At sunset, the temperature of the heat transfer oil at the outlet side of the trough mirror field 1 starts to drop, the volume of the heat transfer oil shrinks, and the liquid level in the expansion tank 7 drops. At this time, keep the shut-off valve of the bypass pipe 5 connected to the top of the overflow pipe group 7 and the bypass pipe shut-off valve 5-2 in the closed state, and keep the oil inlet valve 12 of the expansion tank 6 connected to the top of the overflow pipe group 7 in the open state.

[0045] Step b: Open the first oil discharge valve 901 at the bottom of the first overflow tank 701 connected to the overflow pump 10, close the oil discharge valves 9 at the bottoms of other overflow tanks connected to the overflow pump 10 and the oil inlet valves 12 of the expansion tank 6 connected to the tops of other overflow tanks, start the overflow pump 10, and gradually supplement the high-temperature heat transfer oil in the first overflow tank 701 to the expansion tank 6 to keep the liquid level and temperature of the expansion tank 6 stable (by controlling the start and stop (non-variable frequency pump) or flow rate (variable frequency pump) of the overflow pump 10 to control the amount of heat transfer oil sent into the expansion tank, and its control method belongs to conventional technology). At this time, although the heat transfer oil in the expansion tank 6 may overflow and flow back to the first overflow tank 701, as long as the temperature of the heat transfer oil in the first overflow tank 701 is higher than that in the expansion tank 6, this operation should continue. The main part of the heat transfer oil in the expansion tank 6 is in the main circulation loop, and a small part will overflow to the overflow tank group 7. To ensure that the hot oil supplemented from the overflow tank can be fully mixed with the heat transfer oil in the main circulation loop, the expansion tank bypass valve 15 is in the closed state at this time.

[0046] Step c: When the liquid level in the first overflow tank 701 reaches the lowest liquid level, or when the temperature of the heat transfer oil in the first overflow tank 701 is the same as that in the expansion tank 6, open the second oil discharge valve 902 at the bottom of the second overflow tank 702 connected to the overflow pump, close the first oil discharge valve 901 at the bottom of the first overflow tank 701 connected to the overflow pump 10, and repeat step b, and cycle in this way until the nth overflow tank 70n reaches the lowest liquid level.

[0047] Step d: When the nth overflow tank 70n reaches the lowest liquid level, stop the overflow pump 10. In order to restore the valve state to the state before the heat charging step 1 and prepare for the heat charging the next day, and form a closed loop in the operation, it is necessary to open the oil inlet valves 12 of the expansion tank 6 connected to the tops of the respective overflow tanks in the overflow tank group 7 and the oil discharge valves 9 at the bottoms of the respective overflow tanks connected to the overflow pump 10. The high-temperature heat transfer oil in the expansion tank enters the steam generator 4, releases heat to generate steam, the temperature of the heat transfer oil drops, and it returns to the expansion tank 6. At this time, due to the shrinkage of the volume of the heat transfer oil, the liquid level of the expansion tank 6 drops, and it is necessary to supplement the heat transfer oil (the heat transfer oil that has released heat) from the overflow tank group to the expansion tank 6 to maintain the stable liquid level of the expansion tank. Thus, the entire process of heat release of the heat transfer oil in the overflow tank is completed.

[0048] In the present utility model, the oil-salt heat exchange system includes an oil-salt heat exchanger, a hot salt tank, and a cold salt tank, which are conventional technical devices and thus will not be elaborated in detail.

[0049] The above are only the preferred embodiments of the present utility model. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present utility model, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present utility model.

Claims

1. An expandable heat storage capacity system for a trough solar thermal power plant, characterized in that: The invention comprises a trough mirror field, an oil-salt heat exchange system, a main circulation pump, a steam generator, a bypass pipeline, an expansion tank and an overflow tank group, wherein the trough mirror field is connected to the oil-salt heat exchange system and the steam generator through a pipeline via the main circulation pump to form a main circulation loop, and the steam generator is connected to the oil-salt heat exchange system in parallel, one end of the bypass pipeline is connected to the oil outlet end of the trough mirror field, and the other end is respectively connected to the switch valves on the top of each overflow tank in the overflow tank group, the oil discharge end of each overflow tank in the overflow tank group is respectively connected to the expansion tank through the oil discharge valve via the overflow pump, the oil discharge end of the expansion tank is respectively connected to the oil inlet valve on the top of each overflow tank in the overflow tank group through the pipeline via the expansion tank oil discharge valve, the bypass pipeline switch valve and the bypass pipeline regulating valve are arranged on the bypass pipeline, and the high-temperature heat transfer oil returned from the trough mirror field enters any one or more of the oil-salt heat exchange system, the bypass pipeline and the steam generator through the valve control.

2. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 1, characterized in that: The overflow tank group includes one or two or more overflow tanks, wherein the two or more overflow tanks are connected in parallel with each other.

3. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 1, characterized in that: The expansion tank is connected to the main circulation loop between the steam generator and the main circulation pump through an oil inlet pipeline and an oil return pipeline respectively, and an expansion tank bypass valve is provided in the main circulation loop between the oil inlet pipeline and the oil return pipeline.

4. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 1, characterized in that: An oil overflow port is arranged at the highest liquid level of the expansion tank, and the oil overflow port is respectively connected to the oil inlet valve at the top of each overflow tank in the overflow tank group through an overflow pipeline.

5. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 1, characterized in that: The bypass pipeline switch valve, bypass pipeline regulating valve, switch valve, oil inlet valve, oil drain valve, expansion tank oil drain valve and expansion tank bypass valve are all automatic valves and have valve position feedback function.

6. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 1, characterized in that: The outer peripheries of the bypass pipeline, the bypass pipeline switch valve, the bypass pipeline regulating valve and the switch valve are all wrapped with a heat-insulating layer.

7. The expandable heat storage capacity system for a trough type solar thermal power plant according to claim 6, characterized in that: An electric heating device is also installed in the thermal insulation layer.

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