Molten salt system and control method of molten salt system

Abstract

The present application provides a molten salt system and a control method for the molten salt system, which can heat the energy release part of the molten salt system while realizing rapid steam production of the unit to support the rapid load increase of the coal-fired unit, and is economical and safe. The molten salt system includes a molten salt energy storage part and a molten salt energy release part, the molten salt energy storage part includes a high-temperature molten salt tank and a low-temperature molten salt tank, the molten salt energy release part includes a preheater, an evaporator and a superheater, the high-temperature molten salt tank, the low-temperature molten salt tank and the molten salt energy release part's molten salt side circuit are connected in series to the first circuit, and the steam-water measuring circuit of the molten salt energy release part and the steam turbine are connected in series to the second circuit; the molten salt system also includes a steam lead-out circuit, the steam lead-out circuit is provided with a first control valve, one end of the steam lead-out circuit is connected to the steam outlet of the superheater, and the other end of the steam lead-out circuit is a steam interface, and the steam interface is used to connect steam-using components or steam pipelines other than the steam turbine.

Description

Technical Field

[0001] This application relates to the field of energy storage power station technology, specifically to a molten salt system and a control method for the molten salt system. Background Technology

[0002] Molten salt has become a primary working medium in the field of energy storage technology due to its numerous advantages, including a wide operating temperature range, low saturated vapor pressure, high energy density, low viscosity, good stability, long lifespan, low cost and availability, high thermal conductivity, and strong heat exchange capacity. Currently, molten salt systems are one of the steam sources for turbines in generator units.

[0003] Molten salt systems store heat through molten salt. When the molten salt needs to release heat, it can exchange heat through a heat exchanger to heat water and generate steam, which is then supplied to the turbine. However, when the generator unit needs to rapidly increase load, the molten salt side and steam-water side piping temperatures of the heat exchanger are both low, requiring a cold start, making it practically impossible to respond to rapid load increases. Related technical solutions include electric heat tracing, which involves installing electric heaters in the heat exchanger equipment and corresponding piping. When the molten salt is not releasing heat, electric heating is used to maintain the temperature and facilitate timely responses to rapid load increases. However, electric heating struggles to establish a temperature field on the heat exchanger tube side, resulting in thermal stress shocks during rapid load increases. Furthermore, continuous use of electric heating is obviously costly and uneconomical. Summary of the Invention

[0004] The purpose of this application is to provide a molten salt system and a control method for the molten salt system, which can provide heat tracing for the energy release part of the molten salt system while enabling the unit to quickly generate steam to support the rapid load increase of the coal-fired unit, and is both economical and safe.

[0005] To solve the above-mentioned technical problems, the molten salt system provided in this application includes a molten salt energy storage section and a molten salt energy release section. The molten salt energy storage section includes a high-temperature molten salt tank and a low-temperature molten salt tank. The molten salt energy release section includes a preheater, an evaporator, and a superheater. The molten salt side circuits of the high-temperature molten salt tank, the low-temperature molten salt tank, and the molten salt energy release section are connected in series in a first circuit. The steam-water measurement circuit of the molten salt energy release section is connected in series with the steam turbine in a second circuit.

[0006] The molten salt system also includes a steam extraction circuit, which is equipped with a first control valve. One end of the steam extraction circuit is connected to the steam outlet of the superheater, and the other end of the steam extraction circuit is a steam interface for connecting to steam-using components or steam pipelines other than the steam turbine.

[0007] Optionally, the steam-using component is the extraction steam pipe of the power plant's thermal system, or the deaerator of the power plant's thermal system, or the auxiliary steam header of the power plant's thermal system.

[0008] Optionally, it also includes a first connecting pipe that connects to the molten salt inlet of the high-temperature molten salt tank, wherein the high-temperature molten salt tank and the superheater form a circulation loop through the first connecting pipe and part of the first loop, and the first connecting pipe is provided with a second control valve.

[0009] Optionally, it also includes a molten salt temperature control pump and a second connecting pipe connecting the molten salt outlet of the low-temperature molten salt tank and the molten salt inlet of the evaporator; the molten salt temperature control pump is located in the second connecting pipe; the evaporator, the preheater and the low-temperature molten salt tank form a circulation loop through the second connecting pipe and part of the first loop, and the second connecting pipe is provided with a third control valve.

[0010] Optionally, it also includes a third connecting pipeline connecting the molten salt outlet of the high-temperature molten salt tank and the molten salt inlet of the low-temperature molten salt tank, the third connecting pipeline being provided with a fourth control valve.

[0011] Optionally, it also includes a molten salt heater and a fourth connecting pipe, the fourth connecting pipe connecting the molten salt outlet of the high-temperature molten salt tank and the molten salt inlet of the molten salt heater, and the fourth connecting pipe is provided with a fifth control valve.

[0012] Optionally, the molten salt energy storage section further includes a molten salt heater and a cryogenic molten salt pump. The molten salt inlet of the cryogenic molten salt pump is connected to the molten salt outlet of the cryogenic molten salt tank, the molten salt outlet of the cryogenic molten salt pump is connected to the molten salt inlet of the molten salt heater, and the molten salt outlet of the molten salt heater is connected to the molten salt inlet of the high-temperature molten salt tank.

[0013] The heat source of the molten salt heater includes at least one of the following: waste electricity, off-peak electricity, steam, and flue gas.

[0014] Optionally, it also includes a molten salt system water source and a molten salt system water pump, wherein the inlet of the molten salt system water pump is connected to the water source, and the outlet of the molten salt system water pump is connected to the inlet of the preheater;

[0015] It also includes a bypass, which connects the outlet of the molten salt system water pump to the water source, and the bypass is equipped with a twelfth control valve.

[0016] Optionally, the water source is water from the energy storage power station that has been heated by multi-stage steam extraction.

[0017] This application also provides a control method for a molten salt system. Based on any of the above-mentioned molten salt systems, the control method includes controlling the molten salt system to operate in at least one of the following modes:

[0018] In the thermal storage operation mode, the molten salt in the low-temperature molten salt tank is heated by the molten salt heater and then stored in the high-temperature molten salt tank.

[0019] In the exothermic operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first loop and back to the low-temperature molten salt tank. The energy-releasing part of the molten salt exchanges heat through the second loop and the first loop in a countercurrent manner, and provides steam to the steam turbine.

[0020] In the dynamic heat tracing operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first circuit and back to the low-temperature molten salt tank, and the steam outlet of the superheater and the steam turbine are disconnected. The steam outlet of the superheater is connected to the steam use component or steam pipeline through the steam lead-out circuit.

[0021] Optionally, the control method further includes controlling the molten salt system to operate in the following conditions:

[0022] In the static heat tracing operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow to the superheater and then back to the high-temperature molten salt tank; and / or, the molten salt in the low-temperature molten salt tank is controlled to flow sequentially to the evaporator and the preheater and then back to the low-temperature molten salt tank.

[0023] Optionally, the control method further includes controlling the molten salt system to operate in the following conditions:

[0024] In the high / low temperature molten salt tank heat tracing operation mode, the high temperature molten salt tank and the molten salt heater are connected, so that the molten salt in the high temperature molten salt tank flows to the molten salt heater for heating and then flows back to the high temperature molten salt tank; and / or, the high temperature molten salt tank and the low temperature molten salt tank are connected, so that the molten salt in the high temperature molten salt tank flows to the low temperature molten salt tank.

[0025] Optionally, the temperature and / or pressure of the molten salt energy release section are detected, and when the temperature or pressure is lower than a preset value, the static heat tracing operation mode is activated.

[0026] Optionally, the temperature of the high / low molten salt tank is detected, and when the temperature is lower than the set temperature value, the high / low temperature molten salt tank heat tracing operation mode is activated.

[0027] Optionally, the heat storage operation mode and the static heat tracing operation mode can be operated in combination;

[0028] Alternatively, the thermal storage operation mode and the dynamic heat tracing operation mode can be operated in combination;

[0029] Alternatively, it can operate in a combination of high / low temperature molten salt tank heat tracing mode and static heat tracing mode;

[0030] Alternatively, it can operate in a combined high / low temperature molten salt tank heat tracing mode and a dynamic heat tracing mode.

[0031] Optionally, when the load of the generator set reaches a predetermined value and it is not operating in the heat release mode, the molten salt system is controlled to operate in the dynamic heat tracing mode; when the load of the generator set is lower than the predetermined value and it is not operating in the heat release mode, the molten salt system is controlled to operate in the static heat tracing mode.

[0032] Optionally, the peak steam flow rate entering the turbine in the heat release operation mode is defined as the first steam flow rate, and the steam flow rate of the steam outlet circuit in the dynamic heat tracing mode is defined as the second steam flow rate, wherein the second steam flow rate is not greater than 5% of the first steam flow rate.

[0033] The molten salt system and control method in this application have the following technical advantages:

[0034] First, the molten salt system is equipped with a steam extraction circuit, allowing it to operate in a dynamic heat tracing mode with a small flow of steam. This establishes a temperature field similar to that of the equipment and pipelines in the molten salt energy release section, and the system pressure is adjusted to a suitable value through dynamic heat tracing. When a generator unit receives a command to rapidly increase its load, it can switch to the heat release mode without delay, quickly generating steam to support the generator unit's rapid load increase, demonstrating strong flexibility.

[0035] Secondly, by using the dynamic heat tracing operation mode, the pipelines and equipment of the molten salt energy release section are established to have a temperature field similar to that of the heat release operation mode, so that the molten salt energy release section is in a hot standby state, reducing the thermal stress impact on the equipment and pipelines during the switch to the heat release operation mode, and ensuring the safety of the molten salt system operation.

[0036] Third, in the dynamic heat tracing operation mode, the heat for insulation of the pipelines and equipment in the molten salt energy release section comes from the high-temperature molten salt tank, that is, from the molten salt heat storage. Compared with the pure electric heat tracing mentioned in the background technology, it can obviously improve the economic efficiency of the molten salt system operation. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the molten salt system in an embodiment of this application;

[0038] Figure 2 for Figure 1 A schematic diagram of the molten salt system in thermal storage operation mode;

[0039] Figure 3 for Figure 1 A schematic diagram of the molten salt system in exothermic operation mode;

[0040] Figure 4 for Figure 1 A schematic diagram of the molten salt system in dynamic heat tracing operation mode;

[0041] Figure 5 for Figure 1 A schematic diagram of the molten salt system in static heat tracing operation mode;

[0042] Figure 6 for Figure 1 A schematic diagram of the molten salt system in the high / low temperature molten salt tank heat tracing operation mode.

[0043] The annotations in the figure are explained as follows:

[0044] 1-Molten salt energy storage section, 2-Molten salt energy release section, 3-Cryogenic molten salt tank, 4-Cryogenic molten salt pump, 5-Ninth control valve, 6-Molten salt heater, 7-Heat source, 8-Eighth control valve, 9-High temperature molten salt tank, 10-High temperature molten salt pump, 11-Fifth control valve, 12-Fourth control valve, 13-Molten salt temperature regulating pump, 14-Third control valve, 15-Evaporator, 16-Preheater, 17-Seventh control valve, 18-Superheater, 19 - Second control valve, 20-Water source, 21-Molten salt system water pump, 22-Eleventh control valve, 23-Twelfth control valve, 24-Sixth control valve, 25-Steam turbine, 26-Tenth control valve, 27-First control valve, 28-Steam interface, A-First circuit, B-Second circuit, C-Steam outlet circuit, D-First connecting pipe, E-Second connecting pipe, F-Third connecting pipe, G-Fourth connecting pipe, H-Bypass. Detailed Implementation

[0045] To enable those skilled in the art to better understand the technical solutions of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] In the embodiments of this application, the numerically defined features such as the terms "first," "second," and "third" are used only for the purpose of distinguishing different components and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0047] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the molten salt system in an embodiment of this application.

[0048] The molten salt system in this embodiment includes a molten salt energy storage section 1 and a molten salt energy release section 2. Figure 1The diagram shows two parts within a dashed box. The molten salt energy storage section 1 includes a high-temperature molten salt tank 9 and a low-temperature molten salt tank 3. The molten salt energy storage section 1 also includes a low-temperature molten salt pump 4, a high-temperature molten salt pump 10, and a molten salt heater 6. The molten salt heater 6 is connected to a heat source 7. The low-temperature molten salt tank 3 is equipped with the low-temperature molten salt pump 4. The low-temperature molten salt tank 3, the low-temperature molten salt pump 4, the molten salt heater 6, and the high-temperature molten salt tank 9 are connected in series.

[0049] You can continue to refer to this. Figure 2 understand, Figure 2 for Figure 1 A schematic diagram of the molten salt system in thermal storage operation mode. (See attached diagram of an embodiment of this application.) Figure 2-6 In the diagram, dark colors indicate connected pathways and components in the corresponding operating mode, while light colors indicate disconnected pathways and components in the corresponding operating mode.

[0050] In thermal storage operation mode, the cryogenic molten salt pump 4 can send cryogenic molten salt into the molten salt heater 6 for heat exchange with the heat source 7. The molten salt heated by the heat source 7 then enters the high-temperature molten salt tank 9 for storage, thus storing thermal energy. In thermal storage operation mode, the molten salt energy release section 2 does not operate.

[0051] The heat source 7 here can take many forms, such as at least one of waste electricity (generally referring to electricity unsuitable for grid connection), off-peak electricity, steam, or flue gas. Waste electricity and off-peak electricity include, for example, electricity generated by photovoltaic / wind power, while steam and flue gas include, for example, steam and flue gas generated by various power plants. This allows for full utilization of thermal energy and improves its efficiency.

[0052] Look again Figure 1 , Figure 1 The molten salt energy release section 2 includes a heat exchanger group, which comprises a preheater 16, an evaporator 15, and a superheater 18. The preheater 16 is a molten salt-water heat exchanger, where molten salt and water exchange heat. The evaporator 15 is a molten salt-steam-water heat exchanger, where molten salt and steam-water two-phase media exchange heat. The superheater 18 is a molten salt-steam heat exchanger, where molten salt and steam exchange heat. Each heat exchanger has a molten salt side loop for flowing molten salt and a steam-water side loop for flowing water, steam-water, or steam. The preheater 16, evaporator 15, and superheater 18 are three types of heat exchangers. The number of each type of heat exchanger is not limited to one; multiple exchangers can be used. When multiple exchangers are used, heat exchangers of the same type can be connected in parallel to meet usage requirements, while heat exchangers of different types are connected in series. The molten salt side loops of the heat exchanger group of the high-temperature molten salt tank 9, the low-temperature molten salt tank 3, and the molten salt energy release section 2 are connected in series, and the steam-water side loops of the heat exchanger group of the molten salt energy release section 2 are connected in series with the steam turbine 25. For example... Figure 1As shown, the high-temperature molten salt tank 9, superheater 18, evaporator 15, preheater 16, and low-temperature molten salt tank 3 are connected in series in the first loop A, and the preheater 16, evaporator 15, superheater 18, and steam turbine 25 are connected in series in the second loop B.

[0053] The molten salt energy release section 2 also includes a molten salt system water pump 21 and a water source 20. The molten salt system water pump 21 is connected to the water source 20 and the steam-water side inlet of the preheater 16. Water from the water source 20 is pumped into the preheater 16 via the molten salt system water pump 21. In this embodiment, the water source 20 can come from the generator unit itself, such as feedwater from an energy storage power station that has been heated to a certain temperature through multi-stage steam extraction. Steam extraction refers to steam extracted from the steam turbine.

[0054] Please continue to refer to this. Figure 3 understand, Figure 3 for Figure 1 A schematic diagram of the molten salt system in exothermic operation mode.

[0055] In the exothermic operation mode, the high-temperature molten salt in the high-temperature molten salt tank 9 flows through the first loop A, specifically after being pumped by the high-temperature molten salt pump 10, and then sequentially enters the superheater 18, evaporator 15, and preheater 16 to release heat, and the temperature of the molten salt gradually decreases; the water pumped by the molten salt system water pump 21 flows through the second loop B, specifically, the water first enters the preheater 16, is preheated by the molten salt in the preheater 16, then enters the evaporator 15 to exchange heat with the molten salt and is further heated, and finally enters the superheater 18, where it is heated into steam by the high-temperature molten salt from the high-temperature molten salt tank 9, and then flows to the steam turbine 25 to provide the steam required by the steam turbine 25.

[0056] It should be emphasized that the molten salt system in this embodiment also includes a steam extraction loop C. The steam extraction loop C is equipped with a first control valve 27. One end of the steam extraction loop C is connected to the steam outlet of the superheater 18 of the molten salt energy release section 2, and the other end of the steam extraction loop C is a steam interface 28. The steam interface 28 is used to connect to steam-using components or steam pipelines other than the turbine 25. This differs from the second loop B, in which the heat exchanger assembly of the molten salt energy release section 2 is connected in series with the turbine 25, while the steam extraction loop C connects the heat exchanger assembly of the molten salt energy release section 2 in series with steam-using components or steam pipelines other than the turbine 25.

[0057] Please combine Figure 4 understand, Figure 4 for Figure 1 A schematic diagram of the molten salt system in dynamic heat tracing operation mode.

[0058] The reason for setting up the steam extraction loop C in the above embodiment is to maintain the continued operation of the molten salt energy release section 2 when steam is not needed to be supplied to the turbine 25. That is, the first loop A continues to operate, and the passage between the heat exchanger group in the second loop B and the turbine 25 is disconnected. In detail, Figure 4 A sixth control valve 24 is installed in the passage between the steam outlet of the superheater 18 and the steam inlet of the turbine 25. When steam is not needed to be supplied to the turbine 25, the sixth control valve 24 remains closed, but the first control valve 27 is opened. The steam outlet of the superheater 18 of the molten salt energy release section 2 is connected to the steam-using components or steam pipelines other than the turbine 25 through the steam lead-out circuit C, so the steam side circuit of the molten salt energy release section 2 basically maintains operation. In this way, the various pipelines of the first circuit A and the second circuit B, as well as multiple heat exchangers and other equipment, can always be kept in a heat-preserving state in the non-heat-releasing operation mode, and the heat source for heat preservation is also the heat stored in the molten salt. Compared with the electric heat tracing in the prior art, it has higher economic efficiency, and the dynamic heat tracing formed by molten salt is conducive to establishing a temperature field in various pipelines and heat exchangers that is similar to that in the heat-releasing operation mode.

[0059] As can be seen, with this configuration, the embodiments of this application can select to operate in thermal storage mode, thermal release mode, or dynamic heat tracing mode according to the load of the generator units in the power plant. When thermal release mode is not required, the molten salt system can be put into dynamic heat tracing mode as needed, ensuring that the high-temperature molten salt always flows in the first loop A of the molten salt energy release section 2 and heats the water or steam in the second loop B, thus ensuring that the molten salt system is in a hot standby state when called by the grid. Once the load requirements of the generator units necessitate switching to thermal release mode, the molten salt system can achieve a seamless switch to thermal release mode, thereby reducing cold start impact, shortening start-up time, and making the molten salt system more flexible. After this molten salt system is put into operation, most pipelines and equipment insulation do not require electric heat tracing, as the heat tracing energy for dynamic heat tracing comes entirely from the thermal storage heat source of the molten salt system. Therefore, this molten salt system is highly efficient, safe, and economical, and can better support the rapid load increase of generator units, meeting the requirements for the flexibility of energy storage systems.

[0060] It should be noted that, in this embodiment, the steam interface 28 of the steam outlet circuit C is a low-flow steam interface. Compared with the steam entering the turbine 25 from the second circuit B in the heat release operation mode, the flow rate is smaller. That is, the steam flowing through the steam outlet circuit C is low-flow steam. The flow rate of the molten salt flowing in the first circuit A is also small. The heat exchange of the two circuits is maintained at a low flow rate, which is sufficient to keep the pipes, heat exchangers and other equipment in a standby state.

[0061] Specifically, in the exothermic operation mode, the peak steam flow rate entering the turbine 25 from the second loop B is defined as the first steam flow rate, and the steam flow rate exiting from the steam interface 28 is defined as the second steam flow rate. The second steam flow rate is no more than 5% of the first steam flow rate; for example, it can be set to 2%, which is sufficient to achieve the purpose of heat preservation. Since the dynamic heat tracing operation mode consumes the heat of the molten salt in the high-temperature molten salt tank 9, it is sufficient to meet the basic heat preservation purpose, and the flow rates on both the molten salt side and the steam-water side should be as small as possible. Correspondingly, the molten salt flow rate in the first loop A in the dynamic heat tracing operation mode can be defined as the second molten salt flow rate, and the peak molten salt flow rate in the first loop A in the exothermic operation mode is defined as the first molten salt flow rate. The second molten salt flow rate is no more than 5% of the first molten salt flow rate; for example, it can also be set to 2%, which is approximately the same as the ratio of the second steam flow rate to the first steam flow rate.

[0062] At this point, you can continue to refer to... Figure 1 In this embodiment, the molten salt system also includes a bypass H, which connects the molten salt system pump 21 and the water source 20. This means that some of the pumped water can return directly to the water source 20 without entering the preheater 16. A twelfth control valve 23 can be installed on the bypass H to control its opening and closing. As described above, a small flow of steam flows from the steam interface 28, accounting for only a very small proportion of the peak steam flow. Therefore, the required pumping volume of the molten salt system pump 21 will be correspondingly reduced. When the molten salt system pump 21 cannot pump at a very low flow rate (for example, the minimum pumping volume of the molten salt system pump 21 is 30% of its rated capacity), a larger flow rate of water can be pumped. However, excess water can return to the molten salt system pump through the bypass H to satisfy the purpose of pumping a small flow rate of water to the preheater 16.

[0063] It is important to emphasize that, in order to achieve a small flow rate in the steam-side loop of the molten salt energy release section 2, the steam inlet 28 can be connected to any location other than the turbine 25 that requires steam. In the power plant's thermal system, there are many applications requiring steam besides the turbine 25. For example, steam-using components can be deaerators or auxiliary steam headers in the thermal system. Besides introducing steam into these components, steam can also be directly connected to steam pipelines. The aforementioned deaerators and auxiliary steam headers are connected to corresponding steam pipelines, and the steam inlet 28 can be directly connected to the steam pipeline connected to the steam-using component. For example, the steam pipeline can also be the extraction steam pipeline of the thermal system, connected to the cylinder of the turbine 25. When there is a large amount of steam in the turbine 25's cylinder, a certain amount of steam will be extracted from the extraction steam pipeline for use in other components. Therefore, the steam inlet 28 of the steam outlet loop C can be directly connected to the extraction steam pipeline. In summary, there are no specific restrictions on the connection position of the steam interface 28, as long as a small flow of steam can be introduced into the steam circuit of the thermal system. In this way, a small flow of steam can be introduced into the thermal system to participate in the circulation without causing waste, and the steam side circuit of the molten salt energy release section 2 can be kept running at a small flow rate to achieve the required heat preservation effect.

[0064] Please continue to refer to this. Figure 1 The molten salt system in this embodiment also includes a first connecting pipe D that connects to the high-temperature molten salt tank 9. The high-temperature molten salt tank 9 and the superheater 18 form a closed loop through the first connecting pipe D and part of the first loop A. The first connecting pipe D is equipped with a second control valve 19. Figure 1 In the passage between the high-temperature molten salt tank 9 and the molten salt side inlet of the superheater 18, a seventh control valve 17 is also provided.

[0065] At this point, please continue combining Figure 5 understand, Figure 5 for Figure 1 A schematic diagram of the molten salt system in static heat tracing operation mode.

[0066] from Figure 5 It can be seen that the high-temperature molten salt tank 9 and the superheater 18 are connected in series to form a small circulation loop. A high-temperature molten salt pump 10 is also provided between the molten salt outlet of the high-temperature molten salt tank 9 and the molten salt inlet of the superheater 18. The high-temperature molten salt pump 10 can be set upstream of the seventh control valve 17. The high-temperature molten salt pump 10 provides the power for the circulation of high-temperature molten salt. The seventh control valve 17 is used to control the on / off of molten salt and molten salt energy release section 2.

[0067] In addition, the molten salt system in this embodiment also includes a second connecting pipe E connecting the low-temperature molten salt tank 3. Specifically, the second connecting pipe E connects the low-temperature molten salt tank 3 and the molten salt side inlet of the evaporator 15. The molten salt system also includes a molten salt temperature regulating pump 13, which is located in the second connecting pipe E. That is, the low-temperature molten salt tank 3 is equipped with two pumps: a low-temperature molten salt pump 4, which provides power for pumping low-temperature molten salt in the heat storage operation mode, and a molten salt temperature regulating pump 13, which provides power for pumping low-temperature molten salt in the static heat tracing operation mode. The evaporator 15, preheater 16, and low-temperature molten salt tank 3 form a closed loop through the second connecting pipe E and part of the first loop A. The second connecting pipe E is equipped with a third control valve 14, meaning that the low-temperature molten salt tank 3, evaporator 15, and preheater 16 are connected in series to form another small loop. Figure 5 As can be seen, in the static heat tracing operation mode, the molten salt system can run two small circulation loops, namely the static heat tracing of the high-temperature molten salt tank and the static heat tracing of the low-temperature molten salt tank.

[0068] contrast Figure 4 , 5 Under static heat tracing operation mode, the steam-water side loop of the heat exchanger group in molten salt energy release section 2 can remain stationary. The high-temperature molten salt tank 9 and superheater 18 circulate, as do the low-temperature molten salt tank 3, evaporator 15, and preheater 16. This provides some insulation for the three types of heat exchangers, keeping the steam-water side loop in a hot standby state. However, compared to dynamic heat tracing mode, this saves heat from the molten salt. Furthermore, in static heat tracing operation mode, the high-temperature molten salt tank 9 and superheater 18 circulate, while the low-temperature molten salt tank 3, evaporator 15, and preheater 16 circulate, thus matching the temperature characteristics of each molten salt tank.

[0069] Look again Figure 1 The molten salt system in this embodiment also includes a third connecting pipe F. The high-temperature molten salt tank 9 is connected to the low-temperature molten salt tank 3 through the third connecting pipe F. The third connecting pipe F is equipped with a fourth control valve 12, that is, the high-temperature molten salt tank 9 and the low-temperature molten salt tank 3 are directly connected without going through a heat exchanger.

[0070] In addition, the molten salt system also includes a fourth connecting pipe G, which connects the high-temperature molten salt tank 9 and the molten salt heater 6. The fourth connecting pipe G is equipped with a fifth control valve 11, which means that the molten salt in the high-temperature molten salt tank 9 can directly enter the molten salt heater 6 for heating.

[0071] Please continue to refer to Figure 6 , Figure 6 for Figure 1 A schematic diagram of the molten salt system in the high / low temperature molten salt tank heat tracing operation mode.

[0072] In the high-temperature molten salt heat tracing operation mode, the fourth control valve 12 is opened, and the high-temperature molten salt in the high-temperature molten salt tank 9 can directly enter the low-temperature molten salt tank 3 and be mixed with the low-temperature molten salt in the low-temperature molten salt tank 3 to increase the temperature of the molten salt in the low-temperature molten salt tank 3.

[0073] In the low-temperature molten salt heat tracing operation mode, the fifth control valve 11 is opened, and the molten salt in the high-temperature molten salt tank 9 can enter the molten salt heater 6 for heating, replenish the heat, and then return to the high-temperature molten salt tank 9.

[0074] In summary, such as Figure 1 As shown, in this embodiment, an eighth control valve 8 is provided on the passage between the molten salt heater 6 and the high-temperature molten salt tank 9, a ninth control valve 5 is provided on the passage between the molten salt heater 6 and the low-temperature molten salt tank 3, a tenth control valve 26 is provided on the passage between the superheater 18 and the evaporator 15, and an eleventh control valve 22 is provided on the passage between the molten salt system water pump 21 and the preheater 16. The setting of these control valves is conducive to controlling the opening and closing of the corresponding passages, ensuring the switching of different modes, and maintaining the safety of the system.

[0075] In each mode, the on / off control of each control valve and the connection path of the loop are as follows:

[0076] Thermal storage operation modes: such as Figure 2 As shown, the molten salt outlet of the low-temperature molten salt tank 3 is connected to the molten salt inlet of the low-temperature molten salt pump 4; the molten salt outlet of the low-temperature molten salt pump 4 is connected to the molten salt inlet of the molten salt heater 6 through the ninth control valve 5; the molten salt outlet of the molten salt heater 6 is connected to the molten salt inlet of the high-temperature molten salt tank 9 through the eighth control valve 8.

[0077] Exothermic operation mode: such as Figure 3 As shown, the molten salt outlet of the high-temperature molten salt tank 9 is connected to the molten salt inlet of the high-temperature molten salt pump 10. The molten salt outlet of the high-temperature molten salt pump 10 is sequentially connected to the molten salt side of the seventh control valve 17, the superheater 18, the tenth control valve 26, the evaporator 15, and the preheater 16. The molten salt outlet of the preheater 16 is connected to the low-temperature molten salt tank 3. The molten salt system water source 20 is connected to the inlet of the molten salt system water pump 21. The outlet of the molten salt system water pump 21 is sequentially connected to the steam-water side of the eleventh control valve 22, the preheater 16, the evaporator 15, and the superheater 18. The steam outlet of the superheater 18 is connected to the steam turbine 25 through the sixth control valve 24.

[0078] Dynamic heat tracing operation mode: such as Figure 4As shown, the molten salt outlet of the high-temperature molten salt tank 9 is connected to the molten salt inlet of the high-temperature molten salt pump 10. The molten salt outlet of the high-temperature molten salt pump 10 is connected in sequence to the molten salt side of the seventh control valve 17, the superheater 18, the tenth control valve 26, the evaporator 15, and the preheater 16. The molten salt outlet of the preheater 16 is connected to the molten salt inlet of the low-temperature molten salt tank 3. The water source 20 of the molten salt system is connected to the inlet of the molten salt system water pump 21. The outlet of the molten salt system water pump 21 is connected in sequence to the steam and water side of the eleventh control valve 22, the preheater 16, the evaporator 15, and the superheater 18. The first control valve 27 is opened, the sixth control valve 24 is closed, and the steam outlet of the superheater 18 is connected to the steam-using component or the steam pipeline through the steam interface 28 of the steam lead-out circuit C.

[0079] Static heat tracing operation mode: such as Figure 5 As shown, the molten salt outlet of the high-temperature molten salt tank 9 is connected to the molten salt inlet of the high-temperature molten salt pump 10; the molten salt outlet of the high-temperature molten salt pump 10 is connected to the molten salt inlet of the superheater 18 through the seventh control valve 17; the molten salt outlet of the superheater 18 forms a closed loop with the molten salt inlet of the high-temperature molten salt tank 9 through the second control valve 19; the molten salt outlet of the low-temperature molten salt tank 3 is connected to the molten salt inlet of the molten salt temperature regulating pump 13; the molten salt outlet of the molten salt temperature regulating pump 13 is connected to the molten salt inlet of the evaporator 15 through the third control valve 14; the molten salt outlet of the evaporator 15 is connected to the molten salt inlet of the preheater 16; and the molten salt outlet of the preheater 16 is connected to the molten salt inlet of the low-temperature molten salt tank 3.

[0080] High / low temperature molten salt tank heat tracing operation mode: The high temperature molten salt tank 9 is connected in sequence with the high temperature molten salt pump 10, the fifth control valve 11, the molten salt side of the molten salt heater 6, the eighth control valve 8, and the high temperature molten salt tank 9 to form a closed loop, which is the high temperature molten salt tank heat tracing mode; the high temperature molten salt tank 9 is connected in sequence with the high temperature molten salt pump 10, the fourth control valve 12, and the low temperature molten salt tank 3, which is the low temperature molten salt tank heat tracing mode.

[0081] The molten salt system described above in this application embodiment has a heat storage operation mode, a heat release operation mode, a dynamic heat tracing operation mode, a static heat tracing operation mode, and a high / low temperature molten salt tank heat tracing operation mode. The switching logic for multiple operating modes is as follows:

[0082] When the low-temperature molten salt tank 3 is at a high liquid level and there is a suitable heat source 7 to heat the molten salt, the heat storage operation mode is activated. The molten salt in the low-temperature molten salt tank 3 is heated into high-temperature molten salt by the molten salt heater 6 and then transported to the high-temperature molten salt tank 9 for storage.

[0083] When the molten salt system receives the command to support the generator unit to quickly increase the load, it starts the heat release operation mode. The high temperature molten salt flows through the heat exchanger 18, evaporator 15 and preheater 16 in sequence, and exchanges heat with the molten salt system feedwater from the molten salt system water source 20 in a countercurrent manner. The generated steam is sent to the steam turbine 25 to do work, supporting the generator unit to quickly increase the load.

[0084] During rapid load increase, it is desirable for the molten salt system to switch to exothermic operation mode without delay. Therefore, based on the generator unit's operating load, the molten salt system can be switched to dynamic heat tracing operation mode in advance, i.e., hot standby state. The generator unit's rapid load increase command generally requires the current load to reach a predetermined value, such as between 50% and 100%. Only then will a rapid load increase command be generated based on demand. Once the load reaches the predetermined value (e.g., 50%) and is not in exothermic operation mode, the dynamic heat tracing operation mode can be activated. Through the dynamic heat tracing operation mode, the pipes and equipment (superheater 18, evaporator 15, preheater 16, etc.) of the molten salt energy release section 2 are established with a temperature and pressure field similar to that of the exothermic operation mode, so as to achieve a seamless switch to the exothermic operation mode.

[0085] If the molten salt system remains in dynamic heat tracing mode during periods when it is not supporting rapid load increases in the generator unit, it will consume a significant amount of stored heat, causing a drop in the temperature of the high-temperature molten salt tank 9. This could result in insufficient output from the molten salt system to support rapid load increases. Therefore, when the generator unit load is below a predetermined value (e.g., below 50%), the molten salt system will not receive a rapid load increase command. In this case, the molten salt system does not need to operate in dynamic heat tracing mode and can operate in static heat tracing mode. That is, a closed loop is formed by high-temperature molten salt tank 9 → superheater 18 → high-temperature molten salt tank 9, and a closed loop is formed by low-temperature molten salt tank 3 → evaporator 15 → preheater 16 → low-temperature molten salt tank 3. In this way, the heat loss of the molten salt energy release section 2 can be compensated by the temperatures of the high-temperature molten salt tank 9 and the low-temperature molten salt tank 3.

[0086] The static heat tracing operation mode includes two small cycles, meaning the aforementioned high-temperature molten salt tank static heat tracing can be performed separately and can be started according to actual needs. Both types of static heat tracing operate intermittently. For example, the need to operate the high-temperature molten salt tank static heat tracing mode and the low-temperature molten salt tank static heat tracing mode can be determined by monitoring the temperature and / or pressure of the molten salt energy release section 2. For instance, the temperature of the pipes in the molten salt side loop can be detected; if the temperature is lower than a preset value, the high-temperature molten salt tank static heat tracing mode and / or the low-temperature molten salt tank static heat tracing mode can be activated. As another example, for low-temperature molten salt tank static heat tracing, the pressure of evaporator 15 can be detected; if the pressure of evaporator 15 is lower than a preset value, the low-temperature molten salt tank static heat tracing mode can be activated; if the pressure of evaporator 15 reaches the preset value, the low-temperature molten salt tank static heat tracing mode can be deactivated. The static heating of the low-temperature molten salt tank is determined based on the pressure of the evaporator 15 to ensure that the pressure of the evaporator 15 is not lower than the preset value, so as to meet the requirements of good response capability. For the static heating of the high-temperature molten salt tank, the start-up can still be determined based on the temperature of the detection pipeline. Of course, the pressure of the superheater 18 can also be detected. However, in the static heating operation mode, the heat supplied to the heat exchanger group is relatively small. In order to further ensure the heating effect, the steam pipeline of the superheater 18 can be started with electric heating to maintain the steam state. At this time, the detection of the steam side pressure of the superheater 18 is not accurate enough. Therefore, the temperature of the molten salt side pipeline can still be used as the basis for judging whether to start the static heating of the high-temperature molten salt tank.

[0087] It is easy to understand that the static heat tracing operation mode can be started according to actual needs to detect the temperature or pressure of the equipment or pipeline in the molten salt energy release section 2. It can be set according to the actual application scenario, as long as static heat tracing can be achieved so that it can be switched to dynamic heat tracing operation mode in a timely manner according to load changes.

[0088] In the static heat tracing operation mode, heat exchange also occurs with the heat exchanger, causing a decrease in the temperature of the molten salt in both the high-temperature molten salt tank 9 and the low-temperature molten salt tank 3. This temperature decrease in the high-temperature molten salt tank 9 affects the quality of the steam generated in the exothermic operation mode, while a decrease in the temperature of the low-temperature molten salt tank 3 poses a condensation risk, impacting system safety. Therefore, the high-temperature and low-temperature molten salt tank heat tracing operation modes can be activated as needed. In the high-temperature molten salt tank heat tracing operation mode, the molten salt in the high-temperature molten salt tank 9 is pumped to the molten salt heater 6 via the fifth control valve 11 by the high-temperature molten salt pump 10. After multiple cycles, the temperature of the high-temperature molten salt tank 9 is set to the design value by the heat source 7 through the molten salt heater 6. Similarly, the molten salt in the high-temperature molten salt tank 9 is pumped to the low-temperature molten salt tank 3 via the fourth control valve 12 by the high-temperature molten salt pump 10. By mixing the high-temperature molten salt from the high-temperature molten salt tank 9 into the low-temperature molten salt tank 3, the temperature of the low-temperature molten salt tank 3 is also set to the design value.

[0089] In the high / low temperature molten salt tank heating mode, the high-temperature molten salt tank heating mode and the low-temperature molten salt tank heating mode can operate simultaneously or independently, depending primarily on the molten salt temperature in the high-temperature molten salt tank 9 and the low-temperature molten salt tank 3. The minimum set temperature values ​​for the molten salt in the high-temperature molten salt tank 9 and the low-temperature molten salt tank 3 vary depending on the type of molten salt. For example, if the molten salt is a ternary salt, the low-temperature molten salt tank 3 generally requires a minimum temperature of 235℃, and the high-temperature molten salt tank 9 generally requires a minimum temperature of 380℃; if the molten salt is a binary salt, the low-temperature molten salt tank 3 generally requires a minimum temperature of 290℃, and the high-temperature molten salt tank 9 generally requires a minimum temperature of 560℃. If the temperature of either the high-temperature molten salt tank 9 or the low-temperature molten salt tank 3 is detected to be lower than the set temperature value, the high-temperature molten salt tank heating mode and / or the low-temperature molten salt tank heating mode need to be activated to promptly raise the molten salt temperature to the set temperature value.

[0090] Furthermore, the heat storage operation mode, dynamic heat tracing operation mode, static heat tracing operation mode, and high / low temperature molten salt tank heat tracing operation mode mentioned in the above embodiments can be operated in combination according to actual needs. For example, the heat storage operation mode and the static heat tracing operation mode can be operated in combination, or the heat storage operation mode and the dynamic heat tracing operation mode can be operated in combination, or the high / low temperature molten salt tank heat tracing operation mode and the static heat tracing operation mode can be operated in combination, or the high / low temperature molten salt tank heat tracing operation mode and the dynamic heat tracing operation mode can be operated in combination. Obviously, the heat storage operation mode and the heat release operation mode cannot be operated in combination, and the high / low temperature molten salt tank heat tracing operation mode and the heat release operation mode cannot be operated in combination. In addition, the high / low temperature molten salt tank heat tracing operation mode does not need to be operated in combination with the heat storage operation mode, because the heat storage operation mode has already heated the low temperature molten salt in the low temperature molten salt tank 3 through the molten salt heater 6 and then sent it to the high temperature molten salt tank 9, so it is not necessary to directly heat the molten salt in the high temperature molten salt tank 9 or mix it with the molten salt in the low temperature molten salt tank 3.

[0091] In the above embodiments, the molten salt system can also be equipped with electric heating devices. For example, electric heating devices can be installed on the low-temperature molten salt tank 3, the high-temperature molten salt tank 9, and the molten salt pipeline to provide electric heat tracing when necessary to prevent the molten salt from solidifying. Of course, by setting up the above-mentioned multiple heat tracing modes, the use of electric heat tracing can be greatly reduced.

[0092] As can be seen, in this embodiment, the heat source for most of the pipelines and equipment heating in the molten salt energy release section 2 comes from the heat source 7 of the molten salt heater 6, which heats the molten salt, thus improving the economic efficiency of the molten salt system operation. By implementing the above multiple operating modes, the flexibility, safety, and economy of the molten salt system operation can be improved. The molten salt system of this application has a simple structure and is easy to implement, and can be widely used in molten salt systems for rapid load increase in energy storage power stations.

[0093] The above are merely preferred embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A molten salt system, comprising a molten salt energy storage section and a molten salt energy release section, wherein the molten salt energy storage section includes a high-temperature molten salt tank and a low-temperature molten salt tank, and the molten salt energy release section includes a preheater, an evaporator, and a superheater; the molten salt side circuits of the high-temperature molten salt tank, the low-temperature molten salt tank, and the molten salt energy release section are connected in series in a first circuit, and the steam-water measurement circuit of the molten salt energy release section is connected in series with a steam turbine in a second circuit; characterized in that: The molten salt system also includes a steam extraction circuit, which is equipped with a first control valve. One end of the steam extraction circuit is connected to the steam outlet of the superheater, and the other end of the steam extraction circuit is a steam interface for connecting to steam-using components or steam pipelines other than the steam turbine. The molten salt system has an exothermic operation mode and a dynamic heat tracing operation mode. In the exothermic operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first loop and back to the low-temperature molten salt tank. The energy release portion of the molten salt exchanges heat through the second loop and the first loop in a countercurrent manner, and provides steam to the turbine. In the dynamic heat tracing operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first loop and back to the low-temperature molten salt tank. The steam outlet of the superheater and the turbine are disconnected. The steam outlet of the superheater is connected to the steam-using components or steam pipeline through the steam lead-out loop. The peak steam flow rate entering the turbine under the exothermic operation mode is defined as the first steam flow rate, and the steam flow rate of the steam outlet circuit under the dynamic heat tracing mode is defined as the second steam flow rate, wherein the second steam flow rate is not greater than 5% of the first steam flow rate.

2. The molten salt system according to claim 1, characterized in that, The steam-using component is either the extraction steam pipe of the power plant's thermal system, or the deaerator of the power plant's thermal system, or the auxiliary steam header of the power plant's thermal system.

3. The molten salt system according to claim 1, characterized in that, It also includes a first connecting pipe that connects to the molten salt inlet of the high-temperature molten salt tank. The high-temperature molten salt tank and the superheater form a circulation loop through the first connecting pipe and part of the first loop. The first connecting pipe is equipped with a second control valve.

4. The molten salt system according to claim 3, characterized in that, It also includes a molten salt temperature control pump and a second connecting pipe that connects the molten salt outlet of the low-temperature molten salt tank and the molten salt inlet of the evaporator; the molten salt temperature control pump is located in the second connecting pipe; the evaporator, the preheater and the low-temperature molten salt tank form a circulation loop through the second connecting pipe and part of the first loop, and the second connecting pipe is provided with a third control valve.

5. The molten salt system according to claim 1, characterized in that, It also includes a third connecting pipeline that connects the molten salt outlet of the high-temperature molten salt tank and the molten salt inlet of the low-temperature molten salt tank, and the third connecting pipeline is equipped with a fourth control valve.

6. The molten salt system according to claim 5, characterized in that, It also includes a molten salt heater and a fourth connecting pipe, the fourth connecting pipe connecting the molten salt outlet of the high-temperature molten salt tank and the molten salt inlet of the molten salt heater, and the fourth connecting pipe is equipped with a fifth control valve.

7. The molten salt system according to any one of claims 1-5, characterized in that, The molten salt energy storage section also includes a molten salt heater and a cryogenic molten salt pump. The molten salt inlet of the cryogenic molten salt pump is connected to the molten salt outlet of the cryogenic molten salt tank, the molten salt outlet of the cryogenic molten salt pump is connected to the molten salt inlet of the molten salt heater, and the molten salt outlet of the molten salt heater is connected to the molten salt inlet of the high-temperature molten salt tank. The heat source of the molten salt heater includes at least one of the following: waste electricity, off-peak electricity, steam, and flue gas.

8. The molten salt system according to any one of claims 1-6, characterized in that, It also includes a molten salt system water source and a molten salt system water pump, wherein the inlet of the molten salt system water pump is connected to the water source, and the outlet of the molten salt system water pump is connected to the inlet of the preheater; It also includes a bypass, which connects the outlet of the molten salt system water pump to the water source, and the bypass is equipped with a twelfth control valve.

9. The molten salt system according to claim 8, characterized in that, The water source is the water from the energy storage power station, which has been heated by multi-stage steam extraction.

10. A control method for a molten salt system, characterized in that, Based on the molten salt system according to any one of claims 1-9, the control method includes controlling the molten salt system to operate in at least one of the following modes: In the thermal storage operation mode, the molten salt in the low-temperature molten salt tank is heated by the molten salt heater and then stored in the high-temperature molten salt tank. In the exothermic operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first loop and back to the low-temperature molten salt tank. The energy-releasing part of the molten salt exchanges heat through the second loop and the first loop in a countercurrent manner, and provides steam to the steam turbine. In the dynamic heat tracing operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow through the first circuit and back to the low-temperature molten salt tank, and the steam outlet of the superheater and the steam turbine are disconnected. The steam outlet of the superheater is connected to the steam use component or steam pipeline through the steam lead-out circuit.

11. The control method for the molten salt system according to claim 10, characterized in that, The control method also includes controlling the molten salt system to operate at: In the static heat tracing operation mode, the molten salt in the high-temperature molten salt tank is controlled to flow to the superheater and then back to the high-temperature molten salt tank; and / or, the molten salt in the low-temperature molten salt tank is controlled to flow sequentially to the evaporator and the preheater and then back to the low-temperature molten salt tank.

12. The control method for the molten salt system according to claim 11, characterized in that, The control method also includes controlling the molten salt system to operate in the following conditions: In the high / low temperature molten salt tank heat tracing operation mode, the high temperature molten salt tank and the molten salt heater are connected, so that the molten salt in the high temperature molten salt tank flows to the molten salt heater for heating and then flows back to the high temperature molten salt tank; and / or, the high temperature molten salt tank and the low temperature molten salt tank are connected, so that the molten salt in the high temperature molten salt tank flows to the low temperature molten salt tank.

13. The control method for the molten salt system according to claim 11, characterized in that, The temperature and / or pressure of the molten salt energy release section are detected. When the temperature or pressure is lower than the preset value, the static heat tracing operation mode is activated.

14. The control method for the molten salt system according to claim 12, characterized in that, The temperature of the high / low temperature molten salt tank is detected. When the temperature is lower than the set temperature value, the heat tracing operation mode of the high / low temperature molten salt tank is activated.

15. The control method for the molten salt system according to claim 12, characterized in that, The thermal storage operation mode and the static heat tracing operation mode are operated in combination. Alternatively, the thermal storage operation mode and the dynamic heat tracing operation mode can be operated in combination; Alternatively, it can operate in a combination of high / low temperature molten salt tank heat tracing mode and static heat tracing mode; Alternatively, it can operate in a combined high / low temperature molten salt tank heat tracing mode and a dynamic heat tracing mode.

16. The control method for the molten salt system according to claim 11, characterized in that, When the load of the generator set reaches the predetermined value and it is not operating in the heat release mode, the molten salt system is controlled to operate in the dynamic heat tracing mode; when the load of the generator set is lower than the predetermined value and it is not operating in the heat release mode, the molten salt system is controlled to operate in the static heat tracing mode.

17. The control method for the molten salt system according to any one of claims 10-15, characterized in that, The peak steam flow rate entering the turbine under the exothermic operation mode is defined as the first steam flow rate, and the steam flow rate of the steam outlet circuit under the dynamic heat tracing mode is defined as the second steam flow rate, wherein the second steam flow rate is not greater than 5% of the first steam flow rate.

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