A molten salt-based gas-steam combined heat storage system and capacity calculation method

Abstract

The embodiment of the present disclosure provides a molten salt-based gas-steam combined heat storage system and a capacity calculation method. The system comprises a gas turbine, a boiler, a gas heat exchanger, a steam heat exchanger, a high-temperature molten salt storage tank and a low-temperature molten salt storage tank. The outlet of the gas turbine is connected with the inlet of the flue of the boiler. The gas heat exchanger is connected with the flue between the gas turbine and the high-temperature reheater and the high-pressure superheater in the boiler. The steam heat exchanger is connected with the steam-water pipeline between the high-pressure superheater and the high-pressure drum and the low-pressure drum in the boiler. The low-temperature molten salt storage tank is connected with the high-temperature molten salt storage tank through a molten salt conveying pipeline. The molten salt conveying pipeline is sequentially connected with the steam heat exchanger and the gas heat exchanger. The low-temperature molten salt is heated to high-temperature molten salt when passing through the steam heat exchanger and the gas heat exchanger along the molten salt conveying pipeline. The system realizes reasonable distribution of steam flow and gas flow, significantly improves the heat exchange efficiency of the heat storage heat exchanger, improves the energy storage density per unit mass of the molten salt heat storage system, and reduces the cost.

Description

Technical Field

[0001] This disclosure pertains to the field of combined cycle gas-steam power generation technology, specifically relating to a combined gas-steam thermal energy storage system based on molten salt and its capacity calculation method. Background Technology

[0002] Gas-fired combined cycle (Gas-Steam) generator units offer rapid start-up and shutdown, high energy efficiency, and high peak-shaving flexibility, making them ideal for grid peak-shaving dispatch. In recent years, the proportion of combined cycle cogeneration units has been increasing. However, because most Cogeneration units operate on a "heat-driven power generation" principle, they cannot simultaneously respond effectively to both the grid and heating network loads, significantly reducing the economic efficiency and flexibility of unit operation. Furthermore, frequent shutdowns during actual operation of Gas-Steam combined cycle generator units compromise downstream heating security during outages, often requiring the use of backup gas-fired boilers for heating. This not only incurs substantial start-up and shutdown costs but also significantly reduces the economic efficiency of boiler heating.

[0003] Currently, thermal power units mainly employ additional energy storage (thermal storage) of a certain scale to enhance their deep peak-shaving, rapid ramp-up, and steam supply security capabilities. Molten salt thermal storage technology is a widely used technique. For gas-steam combined cycle power units, existing research primarily employs two approaches: either extracting steam to heat molten salt thermal storage or extracting gas to heat molten salt thermal storage. For the latter, utilizing the latent heat of steam to heat molten salt is limited by the pinch point temperature difference, resulting in a maximum heating temperature of approximately 200-250℃, leading to low thermal storage quality and low system cycle efficiency. For the gas-heating method, extracting large amounts of gas to heat molten salt can cause insufficient heat load on the waste heat boiler, affecting steam cycle operation.

[0004] To address the aforementioned issues, it is necessary to propose a rationally designed and effective solution for a gas-steam combined thermal storage system based on molten salt, along with a method for capacity calculation. Summary of the Invention

[0005] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide a gas-steam combined thermal storage system based on molten salt and a method for calculating its capacity.

[0006] One aspect of this disclosure provides a gas-steam combined thermal storage system based on molten salt, including a gas turbine, a boiler, a gas heat exchanger, a steam heat exchanger, a high-temperature molten salt storage tank, and a low-temperature molten salt storage tank;

[0007] The outlet of the gas turbine is connected to the flue inlet of the boiler;

[0008] The flue gas inlet of the gas heat exchanger is connected to the outlet of the gas turbine, and the flue gas outlet of the gas heat exchanger is connected to the flue between the high-temperature reheater and the high-pressure superheater in the boiler.

[0009] The gas heat exchanger is used to extract a portion of the outlet flue gas from the gas turbine, wherein the extracted flue gas enters the gas heat exchanger to release heat.

[0010] The steam inlet of the steam heat exchanger is connected to the outlet of the high-pressure superheater, and the steam outlet of the steam heat exchanger is connected to the steam-water pipeline between the high-pressure steam drum and the low-pressure steam drum in the boiler.

[0011] The steam heat exchanger is used to extract a portion of the outlet steam from the high-pressure superheater, wherein the extracted steam enters the steam heat exchanger to release heat.

[0012] The outlet of the low-temperature molten salt storage tank is connected to the inlet of the high-temperature molten salt storage tank through a molten salt conveying pipeline. The steam heat exchanger and the gas heat exchanger are connected in series on the molten salt conveying pipeline.

[0013] The low-temperature molten salt is heated into high-temperature molten salt as it passes sequentially through the steam heat exchanger and the gas heat exchanger along the molten salt conveying pipeline.

[0014] Optional features also include a smoke extraction valve;

[0015] The first end of the flue gas valve is connected to the gas turbine, and the second end of the flue gas valve is connected to the flue gas inlet of the gas heat exchanger.

[0016] Optionally, a flue gas temperature sensor may also be included;

[0017] The flue gas temperature sensor is located between the gas turbine and the flue gas valve.

[0018] Optionally, a smoke exhaust valve may also be included;

[0019] The first end of the flue gas valve is connected to the gas heat exchanger, and the second end of the flue gas valve is connected to the steam-water pipeline between the high-pressure steam drum and the low-pressure steam drum.

[0020] Optionally, a steam extraction valve may also be included;

[0021] The first end of the steam extraction valve is connected to the high-pressure superheater, and the second end of the steam extraction valve is connected to the steam inlet of the steam heat exchanger.

[0022] Optionally, a flow sensor may also be included;

[0023] The flow sensor is located between the steam extraction valve and the high-pressure superheater.

[0024] Optionally, it also includes a pressure sensor and a temperature sensor connected in sequence; wherein,

[0025] The pressure sensor and the temperature sensor are located between the steam extraction valve and the steam heat exchanger.

[0026] Optionally, a steam exhaust valve may also be included; wherein,

[0027] The first end of the steam exhaust valve is connected to the steam outlet of the steam heat exchanger, and the second end of the steam exhaust valve is connected to the steam-water pipeline between the high-pressure steam drum and the low-pressure steam drum.

[0028] Another aspect of this disclosure provides a capacity calculation method for a gas-steam combined thermal storage system based on molten salt, using the system described above, wherein the calculation method includes:

[0029] The extraction steam pressure, extraction steam temperature, extraction steam flow rate and extraction flue gas temperature are obtained respectively, and the temperature difference value at the lower end of the steam heat exchanger, the temperature difference value at the pinch point of the steam heat exchanger, the temperature difference value at the lower end of the gas heat exchanger, the temperature value of the high temperature molten salt storage tank and the temperature value of the low temperature molten salt storage tank are set respectively.

[0030] The flow rate of the flue gas extractor and the heat storage power are calculated based on the steam pressure, steam temperature, steam flow rate, flue gas temperature, temperature difference at the lower end of the steam heat exchanger, temperature difference at the pinch point of the steam heat exchanger, temperature difference at the lower end of the gas heat exchanger, temperature of the high-temperature molten salt storage tank, and temperature of the low-temperature molten salt storage tank.

[0031] Optionally, the smoke extractor flow rate and heat storage power can be calculated using the following formulas:

[0032] t s1 -Δt win =t w1

[0033] t(P w )-Δt min =t s2

[0034] q w (h(t(P w ),P w )-h(t w1 ,P w ))=q s (h(t s2 )-h(t s1 ))

[0035] q w (h(t w3 ,P w )-h(t(P w ),P w ))=q s (h(t s3)-h(t s2 ))

[0036] t gout =t s3 +Δt g

[0037] Q=(t s4 -t s1 )q s

[0038] in,

[0039] P w Indicates the steam extraction pressure, t w3 Indicates the steam extraction temperature, q w Indicates the steam flow rate, t gin The flue gas temperature and Δt are indicated. win This indicates the temperature difference value at the lower end of the steam heat exchanger, Δt. min This indicates the pinch temperature difference value of the steam heat exchanger, Δt. g This indicates the temperature difference value at the lower end of the gas heat exchanger, t s1 This indicates the temperature value and t of the high-temperature molten salt storage tank. s4 This indicates the temperature value of the low-temperature molten salt storage tank;

[0040] q g Q represents the flue gas flow rate, Q represents the thermal storage power, and t represents the heat storage capacity. w1 This indicates the water-side outlet temperature of the steam heat exchanger, t s2 The temperature of the flue gas at the pinch point of the steam heat exchanger is represented by q. s Indicates molten salt flow rate, t s3 This indicates the salt temperature at the salt side outlet of the steam heat exchanger and t. gout This indicates the outlet flue gas temperature of the gas heat exchanger 23;

[0041] The thermodynamic specific enthalpy of steam is represented by the function h(t, p), and the saturation temperature is represented by the function t(p). The thermodynamic specific enthalpy and temperature of flue gas are represented by the functions h(t) and t(h), respectively.

[0042] This disclosure discloses a molten salt-based combined gas-steam thermal energy storage system and its capacity calculation method. By adding a molten salt thermal energy storage system, when the grid requires deep peak shaving, a portion of the flue gas from the gas turbine outlet and steam from the high-pressure superheater outlet are extracted through the gas heat exchanger and steam heat exchanger, respectively. This reduces the boiler inlet flue gas and high-pressure superheater outlet steam, simultaneously lowering the boiler heat load and the steam turbine's work capacity, enabling the combined cycle unit to achieve deep peak shaving. Simultaneously, the extracted flue gas and steam release heat into the steam and gas heat exchangers, heating the low-temperature molten salt to a high-temperature molten salt, which is then stored in a high-temperature molten salt storage tank. During high-load phases in the unit, this heat is released for heating or power generation. This system not only improves the flexible operation capability of the gas-steam combined cycle power generation system but also solves the problem of the pinch temperature difference limiting the molten salt's ability to reach very high temperatures under a single steam heating method. It achieves a reasonable distribution of steam and gas flow, significantly improves the heat exchange efficiency of the thermal energy storage heat exchanger, increases the energy storage density per unit mass of the molten salt thermal energy storage system, and reduces system investment. It has broad application prospects in combined cycle power generation. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a gas-steam combined thermal storage system based on molten salt, according to one embodiment of the present disclosure. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of the embodiments of this disclosure, the embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0045] like Figure 1 As shown, one aspect of this disclosure provides a gas-steam combined thermal energy storage system based on molten salt, which comprises a gas-steam combined cycle power generation system and a molten salt thermal energy storage system.

[0046] The gas-steam combined cycle power generation system specifically includes a compressor 1, a combustion chamber 2, a gas turbine 3, a boiler 4, a high-pressure cylinder 5, an intermediate-pressure cylinder 6, a low-pressure cylinder 7, a condenser 8, a condensate pump 9, an intermediate-pressure feedwater pump 10, a high-pressure feedwater pump 11, a low-pressure economizer 12, a low-pressure superheater 13, a low-temperature reheater 14, a high-temperature reheater 15, a high-pressure superheater 16, a high-pressure steam drum 17, an intermediate-pressure steam drum 18, and a low-pressure steam drum 19.

[0047] Specifically, compressor 1 is connected in sequence to combustion chamber 2, gas turbine 3, and boiler 4. The outlet of high-pressure superheater 16 is connected to the inlet of high-pressure cylinder 5. The outlet of high-pressure cylinder 5 is connected to the outlet of low-temperature reheater 14, and together they enter high-temperature reheater 15. The outlet of high-temperature reheater 15 is connected to the inlet of intermediate-pressure cylinder 6. The outlet of intermediate-pressure cylinder 6 is connected to the inlet of low-pressure cylinder 7. Low-pressure superheater 13 is connected to the inlet of low-pressure cylinder 7. The outlet of low-pressure cylinder 7 is connected to the inlet of condenser 8. The outlet of condenser 8 is connected to the inlet of condensate pump 9. The outlet of condensate pump 9 is connected to the inlet of low-pressure economizer 12. Low-pressure economizer 12... The outlet of the steam drum 19 is connected to the inlet of the low-pressure steam drum 19. The steam outlet of the low-pressure steam drum 19 is connected to the inlet of the low-pressure superheater 13. The feedwater outlet of the low-pressure steam drum 19 is connected to the inlet of the medium-pressure feedwater pump 10 and the inlet of the high-pressure feedwater pump 11, respectively. The outlet of the medium-pressure feedwater pump 10 is connected to the inlet of the medium-pressure steam drum 18. The steam outlet of the medium-pressure steam drum 18 is connected to the inlet of the low-temperature reheater 14. The outlet of the high-pressure feedwater pump 11 is connected to the inlet of the high-pressure steam drum 17. The steam outlet of the high-pressure steam drum 17 is connected to the inlet of the high-pressure superheater 16.

[0048] The molten salt thermal storage system mainly includes a gas heat exchanger 23, a steam heat exchanger 22, a high-temperature molten salt storage tank 21, and a low-temperature molten salt storage tank 20.

[0049] The outlet of gas turbine 3 is connected to the flue inlet of boiler 4.

[0050] The flue gas inlet of the gas heat exchanger 23 is connected to the outlet of the gas turbine 3, and the flue gas outlet of the gas heat exchanger 23 is connected to the flue between the high-temperature reheater 15 and the high-pressure superheater 16 in the boiler 4.

[0051] The gas heat exchanger 23 is used to extract part of the outlet flue gas of the gas turbine 3, wherein the extracted flue gas enters the gas heat exchanger 23 for heat release.

[0052] The steam inlet of the steam heat exchanger 22 is connected to the outlet of the high-pressure superheater 16, and the steam outlet of the steam heat exchanger 22 is connected to the steam-water pipeline between the high-pressure steam drum 17 and the low-pressure steam drum 19 in the boiler 4.

[0053] Steam heat exchanger 22 is used to extract part of the outlet steam of high-pressure superheater 16, wherein the extracted steam enters the steam heat exchanger 22 for heat release.

[0054] The outlet of the low-temperature molten salt storage tank 20 is connected to the inlet of the high-temperature molten salt storage tank 21 through a molten salt conveying pipeline. A steam heat exchanger 22 and a gas heat exchanger 23 are connected in series on the molten salt conveying pipeline.

[0055] The low-temperature molten salt is heated into high-temperature molten salt as it passes through the steam heat exchanger 22 and the gas heat exchanger 23 in sequence along the molten salt conveying pipeline.

[0056] Specifically, when the power grid requires deep peak shaving by the unit, the gas heat exchanger 23 is connected to the gas turbine 3 and the boiler 4, respectively, and the steam heat exchanger 22 is connected to the steam-water pipeline between the high-pressure superheater 16 and the high-pressure steam drum 17 and the low-pressure steam drum 19 of the boiler 4, respectively. By extracting a portion of the flue gas from the gas turbine 3 outlet and the steam from the high-pressure superheater 16 outlet through the gas heat exchanger 23 and the steam from the high-pressure superheater 16 outlet, the amount of flue gas from the boiler 4 inlet and the steam from the high-pressure superheater 16 outlet is reduced, simultaneously lowering the heat load of the boiler 4 and the work capacity of the steam turbine, thus enabling the combined cycle unit to achieve deep peak shaving. Simultaneously, the extracted flue gas and steam release heat into the steam heat exchanger 22 and the gas heat exchanger 23, heating the low-temperature molten salt to high-temperature molten salt as it flows through them. This molten salt is then stored in the high-temperature molten salt storage tank 21 and releases heat during high-load periods in the unit for heating or power generation.

[0057] The gas-steam combined thermal energy storage system based on molten salt in this disclosure not only improves the flexible operation capability of the gas-steam combined cycle power generation system, but also solves the problem that the pinch temperature difference limits the molten salt from reaching a very high temperature under a single steam heating method. It achieves a reasonable distribution of steam flow and gas flow, significantly improves the heat exchange efficiency of the thermal energy storage heat exchanger, increases the energy storage density per unit mass of the molten salt thermal energy storage system, and reduces system investment. It has broad application prospects in combined cycles.

[0058] For example, such as Figure 1 As shown, the molten salt-based gas-steam combined thermal storage system also includes a flue gas valve 27. The first end of the flue gas valve 27 is connected to the gas turbine 3, and the second end of the flue gas valve 27 is connected to the flue gas inlet of the gas heat exchanger 23.

[0059] In this embodiment, the opening of the flue gas extraction valve 27 controls a portion of the flue gas entering the gas heat exchanger 23 for heat exchange. During normal unit operation, when deep peak shaving is not required, the flue gas extraction valve 27 is closed, and the gas heat exchanger 23 does not extract flue gas from the gas turbine 3 outlet. When the power grid requires deep peak shaving, the flue gas extraction valve 27 is opened, and a portion of the gas turbine 3 outlet flue gas is extracted through the gas heat exchanger 23, reducing the amount of flue gas entering the boiler 4.

[0060] For example, such as Figure 1 As shown, the gas-steam combined thermal storage system based on molten salt also includes a flue gas temperature sensor 31, which is located between the gas turbine 3 and the flue gas valve 27.

[0061] In this embodiment, the flue gas temperature entering the gas heat exchanger 23 can be monitored by the flue gas temperature sensor 31.

[0062] For example, such as Figure 1As shown, the molten salt-based gas-steam combined thermal storage system also includes a flue gas valve 26. The first end of the flue gas valve 26 is connected to the gas heat exchanger 23, and the second end of the flue gas valve 26 is connected to the steam-water pipeline between the high-pressure steam drum 17 and the low-pressure steam drum 19.

[0063] In this embodiment, by opening the flue gas exhaust valve 26, the flue gas that has undergone heat exchange in the flue gas heat exchanger 23 can be discharged to the steam-water pipeline between the high-pressure steam drum 17 and the low-pressure steam drum 19 for recycling.

[0064] For example, such as Figure 1 As shown, the molten salt-based gas-steam combined thermal storage system also includes a steam extraction valve 24. The first end of the steam extraction valve 24 is connected to the high-pressure superheater 16, and the second end of the steam extraction valve 24 is connected to the steam inlet of the steam heat exchanger 22.

[0065] In this embodiment, the steam outlet of the high-pressure superheater 16 can be controlled to enter the steam heat exchanger 22 for heat exchange by opening the steam extraction valve 24.

[0066] For example, such as Figure 1 As shown, the gas-steam combined thermal storage system based on molten salt also includes a flow sensor 30, which is located between the steam extraction valve 24 and the high-pressure superheater 16.

[0067] In this embodiment, the flow rate of steam entering the steam heat exchanger 22 can be monitored by the flow sensor 30.

[0068] For example, such as Figure 1 As shown, the gas-steam combined thermal storage system based on molten salt also includes a pressure sensor 28, which is located between the steam extraction valve 24 and the steam heat exchanger 22.

[0069] In this embodiment, the steam pressure entering the steam heat exchanger 22 can be monitored by setting a pressure sensor 28.

[0070] For example, the molten salt-based gas-steam combined thermal storage system also includes a temperature sensor 29; wherein the temperature sensor 29 is disposed between the pressure sensor 28 and the steam heat exchanger 22.

[0071] In this embodiment, the temperature of the steam entering the steam heat exchanger 2 can be monitored by setting a temperature sensor 29.

[0072] For example, such as Figure 1 As shown, the gas-steam combined thermal storage system based on molten salt also includes a steam exhaust valve 25; wherein, the first end of the steam exhaust valve 25 is connected to the steam outlet of the steam heat exchanger 22, and the second end of the steam exhaust valve 25 is connected to the steam-water pipeline between the high-pressure steam drum 17 and the low-pressure steam drum 19.

[0073] like Figure 1 As shown, the working principle of the molten salt-based gas-steam combined thermal storage system of this disclosure is as follows:

[0074] Normal operating mode: When the power grid does not require deep peak shaving of the unit, the steam extraction valve 24, steam exhaust valve 25, flue gas exhaust valve 26, and flue gas extraction valve 27 are closed. No gas or steam is extracted for energy storage. The compressor 1 compresses air into the combustion chamber 2 and burns it fully with the fuel. The high-temperature gas generated drives the gas turbine 3 to do work. The exhaust gas enters the boiler 4. The feedwater enters the boiler 4 to absorb heat and generate high-temperature and high-pressure steam. The steam enters the steam turbine to do work.

[0075] Energy storage peak shaving mode: When the grid requires deep peak shaving by the unit, the steam extraction valve 24, steam exhaust valve 25, flue gas exhaust valve 26, and flue gas extraction valve 27 are opened to extract a portion of the flue gas from the gas turbine 3 outlet and the steam from the high-pressure superheater 16 outlet, respectively. This reduces the flue gas at the boiler 4 inlet and the steam at the high-pressure superheater 16 outlet, simultaneously reducing the heat load of the boiler 4 and the work capacity of the steam turbine, enabling the combined cycle unit to achieve deep peak shaving. Simultaneously, the extracted flue gas and steam are used to release heat in the steam heat exchanger 22 and the gas heat exchanger 23, heating the low-temperature molten salt to a high-temperature molten salt, which is then stored in the high-temperature molten salt storage tank 21. During high-load periods in the unit, this heat is released for heating or power generation.

[0076] In this embodiment, by opening the steam exhaust valve 25, the steam after heat exchange in the steam heat exchanger 22 can be discharged into the steam-water pipeline between the high-pressure steam drum 17 and the low-pressure steam drum 19 for recycling.

[0077] During energy storage, it is necessary to adjust the steam flow rate and flue gas flow rate to ensure that the high-temperature molten salt temperature meets the requirements. Therefore, it is necessary to calculate the matching flue gas flow rate based on the steam extraction flow rate. At the same time, it is also necessary to calculate the maximum thermal storage power based on the maximum steam extraction flow rate to determine the maximum thermal storage scale. In view of this, another aspect of the present disclosure provides a capacity calculation method for a gas-steam combined thermal storage system based on molten salt.

[0078] In this embodiment of the present disclosure, a capacity calculation method for a gas-steam combined thermal storage system based on molten salt is adopted using the system described above. The specific structural features of the gas-steam combined thermal storage system based on molten salt have been described in detail above and will not be repeated here.

[0079] The capacity calculation method for this molten salt-based gas-steam combined thermal storage system includes:

[0080] The steam pressure is obtained through pressure sensor 28, the steam temperature is obtained through temperature sensor 29, the steam flow rate is obtained through flow sensor 30, and the flue gas temperature is obtained through flue gas temperature sensor 31.

[0081] The following values ​​are set: lower end temperature difference of steam heat exchanger, pinch point temperature difference of steam heat exchanger, lower end temperature difference of gas heat exchanger, temperature of high-temperature molten salt storage tank, and temperature of low-temperature molten salt storage tank.

[0082] The flow rate of the flue gas extractor and the heat storage power are calculated based on the steam pressure, steam temperature, steam flow rate, flue gas temperature, temperature difference at the lower end of the steam heat exchanger, temperature difference at the pinch point of the steam heat exchanger, temperature difference at the lower end of the gas heat exchanger, temperature of the high-temperature molten salt storage tank, and temperature of the low-temperature molten salt storage tank.

[0083] Specifically, the capacity of the thermal storage system is obtained using the following formula:

[0084] t s1 -Δt win =t w1

[0085] t(P w )-Δt min =t s2

[0086] q w (h(t(P w ),P w )-h(t w1 ,P w ))=q s (h(t s2 )-h(t s1 ))

[0087] q w (h(t w3 ,P w )-h(t(P w ),P w ))=q s (h(t s3 )-h(t s2 ))

[0088] t gout =t s3 +Δt g

[0089] Q=(t s4 -t s1 )q s

[0090] in,

[0091] P w Indicates the steam extraction pressure, t w3 Indicates the steam extraction temperature, qw Indicates the steam flow rate, t gin The flue gas temperature and Δt are indicated. win This indicates the temperature difference value at the lower end of the steam heat exchanger, Δt. min This indicates the pinch temperature difference value of the steam heat exchanger, Δt. g This indicates the temperature difference value at the lower end of the gas heat exchanger, t s1 This indicates the temperature value and t of the high-temperature molten salt storage tank. s4 This indicates the temperature value of the low-temperature molten salt storage tank;

[0092] q g Q represents the flue gas flow rate, Q represents the thermal storage power, and t represents the heat storage capacity. w1 This indicates the water-side outlet temperature of the steam heat exchanger, t s2 The temperature of the flue gas at the pinch point of the steam heat exchanger is represented by q. s Indicates molten salt flow rate, t s3 This indicates the salt temperature at the salt side outlet of the steam heat exchanger and t. gout This indicates the outlet flue gas temperature of the gas heat exchanger 23;

[0093] The thermodynamic specific enthalpy of steam is represented by the function h(t, p), and the saturation temperature is represented by the function t(p). The thermodynamic specific enthalpy and temperature of flue gas are represented by the functions h(t) and t(h), respectively.

[0094] This disclosure discloses a capacity calculation method for a gas-steam combined thermal storage system based on molten salt. According to the molten salt temperature of the high and low temperature molten salt storage tank and the steam-gas temperature, the ratio of steam flow rate to gas flow rate can be determined to achieve a reasonable distribution of heat between the two locations.

[0095] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the embodiments of this disclosure, and the embodiments of this disclosure are not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the embodiments of this disclosure, and these modifications and improvements are also considered to be within the protection scope of the embodiments of this disclosure.

Claims

1. A molten salt based gas-steam combined heat storage system, characterized by, The system comprises a gas turbine, a boiler, a gas heat exchanger, a steam heat exchanger, a high-temperature molten salt storage tank and a low-temperature molten salt storage tank. An outlet of the gas turbine is connected to an inlet of a flue duct of the boiler. A flue gas inlet of the gas heat exchanger is connected to an outlet of the gas turbine, and a flue gas outlet of the gas heat exchanger is connected to a flue duct between a high-temperature reheater and a high-pressure superheater of the boiler. The gas heat exchanger is used to extract part of flue gas at the outlet of the gas turbine, wherein the extracted flue gas is discharged into the gas heat exchanger to release heat. A steam inlet of the steam heat exchanger is connected to an outlet of the high-pressure superheater, and a steam outlet of the steam heat exchanger is connected to a water-steam pipeline between a high-pressure drum and a low-pressure drum of the boiler. The steam heat exchanger is used to extract part of steam at the outlet of the high-pressure superheater, wherein the extracted steam is discharged into the steam heat exchanger to release heat. An outlet of the low-temperature molten salt storage tank is connected to an inlet of the high-temperature molten salt storage tank through a molten salt conveying pipeline, and the steam heat exchanger and the gas heat exchanger are sequentially arranged on the molten salt conveying pipeline. The low-temperature molten salt is heated to high-temperature molten salt when passing through the steam heat exchanger and the gas heat exchanger in sequence on the molten salt conveying pipeline.

2. The system of claim 1, wherein, The system further comprises a flue gas extraction valve. A first end of the flue gas extraction valve is connected to the gas turbine, and a second end of the flue gas extraction valve is connected to the flue gas inlet of the gas heat exchanger.

3. The system of claim 2, wherein, The system further comprises a flue gas temperature sensor. The flue gas temperature sensor is arranged between the gas turbine and the flue gas extraction valve.

4. The system of claim 1, wherein, The system further comprises a flue gas discharge valve. A first end of the flue gas discharge valve is connected to the gas heat exchanger, and a second end of the flue gas discharge valve is connected to the flue duct between the high-temperature reheater and the high-pressure superheater of the boiler.

5. The system of claim 1, wherein, The system further comprises a steam extraction valve. A first end of the steam extraction valve is connected to the high-pressure superheater, and a second end of the steam extraction valve is connected to the steam inlet of the steam heat exchanger.

6. The system of claim 5, wherein, The system further comprises a flow sensor. The flow sensor is arranged between the steam extraction valve and the high-pressure superheater.

7. The system of claim 5, wherein, The system further comprises a pressure sensor and a temperature sensor which are sequentially connected. The pressure sensor and the temperature sensor are arranged between the steam extraction valve and the steam heat exchanger.

8. The system of claim 7, wherein, The system further comprises a steam discharge valve. A first end of the steam discharge valve is connected to the steam outlet of the steam heat exchanger, and a second end of the steam discharge valve is connected to the water-steam pipeline between the high-pressure drum and the low-pressure drum.

9. A method for calculating the capacity of a molten salt-based gas-steam combined heat storage system, characterized by, The system adopts the method according to any one of claims 1 to 8, wherein the method comprises: obtaining the steam extraction pressure, the steam extraction temperature, the steam extraction flow and the flue gas extraction temperature respectively, and setting the steam heat exchanger lower end temperature difference value, the steam heat exchanger pinch point temperature difference value, the gas heat exchanger lower end temperature difference value, the high-temperature molten salt storage tank temperature value and the low-temperature molten salt storage tank temperature value; calculating the flue gas extraction flow and the heat storage power respectively according to the steam extraction pressure, the steam extraction temperature, the steam extraction flow, the flue gas extraction temperature, the steam heat exchanger lower end temperature difference value, the steam heat exchanger pinch point temperature difference value, the gas heat exchanger lower end temperature difference value, the high-temperature molten salt storage tank temperature value and the low-temperature molten salt storage tank temperature value.

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