A combined heat and power peak shaving system using molten salt heated by gas turbine flue gas bypass

Abstract

This invention relates to a combined heat and power (CHP) peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt. The system includes a low-load peak-shaving circuit and a shutdown peak-shaving circuit. The low-load peak-shaving circuit comprises an interconnected gas turbine module and a molten salt thermal storage module. The gas turbine module includes an air compressor, a combustion chamber, a turbine, and a gas turbine generator. The molten salt thermal storage module comprises, in sequence, a low-temperature molten salt tank, a low-temperature molten salt pump, a flue gas heat exchanger, and a high-temperature molten salt tank. The gas turbine module and the flue gas heat exchanger are connected. The shutdown peak-shaving circuit comprises, in sequence, a high-temperature molten salt tank, a high-temperature molten salt pump, a brine heat exchanger, and a low-temperature molten salt tank. Compared to existing technologies, this invention adds a molten salt thermal storage module to the original structure, maintaining the advantages of CHP based on the principle of energy cascade utilization. During low-load peak-shaving, the gas turbine module's exhaust gas is used for heating and molten salt thermal storage, while during shutdown peak-shaving, the molten salt releases heat for heating, enabling flexible peak-shaving.

Description

Technical Field

[0001] This invention relates to the field of energy technology, and in particular to a combined heat and power peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt. Background Technology

[0002] CO2 emission reduction has had a profound impact on energy and power technologies in various countries, leading to a shift in the power generation industry towards renewable energy. However, renewable energy sources such as wind and solar power are characterized by randomness, intermittency, volatility, and lack of adjustability, necessitating improved peak-shaving capabilities from the power grid. Gas-fired combined cycle units, with their rapid start-up and shutdown speeds and flexible operation, are commonly used peak-shaving units in power grids.

[0003] However, the peak-shaving range of gas-fired combined cycle (CHP) units is greatly limited due to the influence of heat demand from users, resulting in a loss of flexibility. Many CHP units participate in deep peak shaving by shutting down for peak shaving, and during shutdown, they use standby gas-fired boilers for heating. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a cogeneration peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt. Based on the original structure, a molten salt thermal storage module is added. Under low load conditions of the gas turbine module, the gas turbine module exhaust gas is used to heat low-temperature molten salt through the bypass flue. The resulting high-temperature molten salt is stored in a high-temperature molten salt tank. The flue gas after heating the low-temperature molten salt is used to further heat water to generate steam for heating. Based on the principle of energy cascade utilization, the advantages of cogeneration are maintained. Simultaneously, the stored high-temperature molten salt can be used to heat water to generate steam for heating when the unit is shut down. Thus, during low-load peak shaving, the gas turbine module exhaust gas is used for heating and molten salt thermal storage, while during shutdown peak shaving, the molten salt releases heat for heating, enabling flexible peak shaving.

[0005] The objective of this invention can be achieved through the following technical solutions: This invention addresses gas-steam combined cycle cogeneration units that are shut down for peak shaving by introducing a molten salt thermal storage system. During high load periods, the original heating scheme is followed, with steam extracted from the turbine modules for heating. During low load peak shaving, only the gas turbine modules generate electricity at low load, and the exhaust gas from the gas turbine modules is used to heat feedwater for heating and for molten salt thermal storage. During shutdown for peak shaving, the high-temperature molten salt releases heat to heat the feedwater into steam, which is then supplied to heat users, thus preserving as much of the waste heat generated by the gas turbine modules as possible for heating during the peak shaving process.

[0006] This invention provides a cogeneration peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt, comprising: a low-load peak-shaving circuit, a high-load power generation circuit, and a shutdown peak-shaving circuit; The low-load peak-shaving circuit includes interconnected gas turbine modules and molten salt thermal storage modules. The molten salt thermal storage module includes a low-temperature molten salt tank, a flue salt heat exchanger, and a high-temperature molten salt tank connected in sequence. The gas turbine module and the flue salt heat exchanger are connected. The flue gas generated by the gas turbine module enters the flue salt heat exchanger through a pipeline. The flue gas heats the molten salt that is fed from the low-temperature molten salt tank into the flue salt heat exchanger. The heated high-temperature molten salt is then fed into the high-temperature molten salt tank for heat storage. After entering the flue salt heat exchanger, the flue gas enters the flue water heat exchanger through a pipeline to heat the water in the flue water heat exchanger. The water is heated into steam and then supplied to the heat users. The high-load power generation circuit includes a gas turbine module, a waste heat boiler, and a steam turbine module connected in sequence. The steam turbine module includes a steam turbine and a steam turbine generator. The flue gas generated by the gas turbine module enters the waste heat boiler through a pipeline. The flue gas heats water to generate steam, which enters the steam turbine to do work and drives the steam turbine generator to generate electricity. The steam turbine extracts steam to supply heat to heat users. The shutdown peak shaving circuit includes a high-temperature molten salt tank, a brine heat exchanger, and a low-temperature molten salt tank connected in sequence. The high-temperature molten salt stored in the high-temperature molten salt tank enters the brine heat exchanger to heat the water in the brine heat exchanger. The water is heated into steam and then supplied to the heat users. The molten salt after heating the water enters the low-temperature molten salt tank for storage.

[0007] Furthermore, the gas turbine module includes an air compressor, a combustion chamber, a turbine, and a gas turbine generator connected in sequence.

[0008] Furthermore, the turbine is connected to the flue gas heat exchanger and the waste heat boiler respectively. An inlet baffle is provided between the turbine and the waste heat boiler, and a bypass baffle is provided between the turbine and the flue gas heat exchanger.

[0009] Furthermore, the air compressor inlet is connected to an air duct to introduce air.

[0010] Furthermore, the natural gas inlet of the combustion chamber is connected to a natural gas pipeline.

[0011] Furthermore, the flue gas outlet of the flue gas heat exchanger is connected to a flue gas duct for exhausting the flue gas.

[0012] Furthermore, the turbine module also includes a feedwater pump, a condenser, a waste heat boiler, a steam turbine, a condenser, and a feedwater pump in a circulating connection, and the steam turbine and turbine generator are connected.

[0013] Furthermore, a high-temperature molten salt pump and regulating valve A are installed between the high-temperature molten salt tank and the brine heat exchanger.

[0014] Furthermore, a cryogenic molten salt pump and regulating valve B are installed between the cryogenic molten salt tank and the flue salt heat exchanger.

[0015] Furthermore, the turbine generator is a twin-cylinder, three-pressure reheat extraction condensing turbine, and the waste heat boiler is a three-pressure, single-reheat natural circulation boiler.

[0016] Compared with the prior art, the present invention has the following advantages: (1) A molten salt thermal storage module was added to the original structure. Under the low load of the gas turbine module, the exhaust gas of the gas turbine module was heated to low temperature molten salt through the bypass flue. The high temperature molten salt was stored in the high temperature molten salt tank. The flue gas after heating the low temperature molten salt continued to heat water to generate heating steam. Based on the principle of energy cascade utilization, the advantages of cogeneration were maintained. (2) The stored high-temperature molten salt can heat water to generate heating steam when the unit is shut down. In this way, the exhaust gas from the gas turbine module can be used for heating and molten salt heat storage during low load peak shaving, while the molten salt can be used to release heat for heating during shutdown peak shaving, which can flexibly adjust the peak. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a cogeneration peak-shaving system that uses gas turbine flue gas bypass to heat molten salt.

[0018] Attached reference numerals: 1-Air compressor, 2-Combustion chamber, 3-Turbine, 4-Gas turbine generator, 5-Inlet baffle, 6-Bypass baffle, 7-Fluorite heat exchanger, 8-Regulating valve A, 9-High-temperature molten salt pump, 10-High-temperature molten salt tank, 11-Brine heat exchanger, 12-Low-temperature molten salt pump, 13-Regulating valve B, 14-Low-temperature molten salt tank, 15-Fluorite water heat exchanger, 16-Waste heat boiler, 17-Feed water pump, 18-Condenser, 19-Steam turbine generator, 20-Steam turbine. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0020] Example 1 This embodiment provides a combined heat and power peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt, including: a low-load peak-shaving circuit, a high-load power generation circuit, and a shutdown peak-shaving circuit; The low-load peak-shaving circuit includes interconnected gas turbine modules and molten salt heat storage modules. The molten salt heat storage module includes a low-temperature molten salt tank 14, a flue salt heat exchanger 7, and a high-temperature molten salt tank 10 connected in sequence. The gas turbine module and the flue salt heat exchanger 7 are connected. The flue gas generated by the gas turbine module enters the flue salt heat exchanger 7 through a pipeline. The flue gas heats the molten salt in the flue salt heat exchanger 7 from the low-temperature molten salt tank 14. The heated high-temperature molten salt is then passed into the high-temperature molten salt tank 10 for heat storage. After entering the flue salt heat exchanger 7, the flue gas enters the flue water heat exchanger 15 through a pipeline to heat the water in the flue water heat exchanger 15. The water is heated into steam and then supplied to the heat users. The high-load power generation circuit includes a gas turbine module, a waste heat boiler 16, and a steam turbine module connected in sequence. The steam turbine module includes a steam turbine 20 and a steam turbine generator 19. The flue gas generated by the gas turbine module enters the waste heat boiler 16 through a pipeline. The flue gas heats water to generate steam, which enters the steam turbine 20 to do work and drive the steam turbine generator 19 to generate electricity. The steam turbine 20 extracts steam to supply heat to heat users. The shutdown peak shaving circuit includes a high-temperature molten salt tank 10, a brine heat exchanger 11, and a low-temperature molten salt tank 14 connected in sequence. The high-temperature molten salt stored in the high-temperature molten salt tank 10 enters the brine heat exchanger 11 to heat the water in the brine heat exchanger 11. The water is heated into steam and then supplied to the heat users. The molten salt after heating the water enters the low-temperature molten salt tank 14 for storage.

[0021] The gas turbine module includes an air compressor 1, a combustion chamber 2, a turbine 3, and a gas turbine generator 4 connected in sequence. The steam turbine module also includes a feedwater pump 17, a condenser 18, a waste heat boiler 16, a steam turbine 20, and the condenser 18 and feedwater pump 17 are connected in a loop. The steam turbine 20 and the steam turbine generator 19 are connected. The steam turbine 20 receives steam at a certain pressure and temperature, and drives the shaft to rotate through the force of the steam on the blades.

[0022] The specific connection method is as follows: air compressor 1, turbine 3, and gas turbine generator 4 are connected together via shafts; the inlet of air compressor 1 is connected to an air pipeline to introduce air, and the outlet of air compressor 1 is connected to the air inlet of combustion chamber 2; the natural gas inlet of combustion chamber 2 is connected to a natural gas pipeline, and the outlet of combustion chamber 2 is connected to the inlet of turbine 3; the outlet flue gas pipeline of turbine 3 is divided into two paths, which are respectively connected to the flue gas side inlet of waste heat boiler 16 and the flue gas side inlet of flue gas heat exchanger 7, and inlet baffles are installed at their respective inlets. Plate 5 and bypass baffle 6; the flue gas outlet of the flue gas heat exchanger 7 is connected to the flue gas inlet of the flue gas water heat exchanger 15, and then the flue gas outlet of the flue gas water heat exchanger 15 is discharged through the flue gas pipeline; the water inlet of the flue gas water heat exchanger 15 is connected to the feed water pipeline, and after heat exchange, the water outlet of the flue gas water heat exchanger 15 is discharged in the form of steam through the steam pipeline to supply heat to heat users; the inlet of the low-temperature molten salt tank 14 is connected to the outlet of the brine heat exchanger 11, introducing low-temperature molten salt for storage; the outlet of the low-temperature molten salt tank 14 is connected to the molten salt inlet of the flue gas heat exchanger 7, and A low-temperature molten salt pump 12 and a regulating valve B13 are installed at the outlet of the low-temperature molten salt tank 14; the molten salt side outlet of the flue salt heat exchanger 7 is connected to the inlet of the high-temperature molten salt tank 10, storing high-temperature molten salt in the high-temperature molten salt tank 10; the outlet of the high-temperature molten salt tank 10 is connected to the molten salt side inlet of the brine heat exchanger 11, and a high-temperature molten salt pump 9 and a regulating valve A8 are installed at the outlet of the high-temperature molten salt tank 10; the water side inlet of the brine heat exchanger 11 is connected to the feed water pipeline to introduce feed water, and the water side outlet of the brine heat exchanger 11 discharges steam through a steam pipeline, transferring the steam to the heat exchanger 11. Heat is supplied to users; the flue gas outlet of the waste heat boiler 16 is connected to the flue gas pipeline to discharge flue gas; the water inlet of the waste heat boiler 16 is connected to the feedwater pipeline to introduce feedwater for heating; the water outlet of the waste heat boiler 16 sends steam to the steam turbine 20 in the form of steam through the steam pipeline to do work, driving the steam turbine generator 19 to generate electricity; in addition, a portion of steam extracted from the steam turbine 20 is discharged through the steam pipeline to supply heat to users; the steam after doing work is discharged into the condenser 18 to form condensate, and the condensate is sent to the water inlet of the waste heat boiler 16 through the feedwater pump 17.

[0023] The flue gas discharged from turbine 3 is divided into two paths, which enter waste heat boiler 16 and flue gas heat exchanger 7 respectively; with the inlet damper 5 closed and the bypass damper 6 opened, the flue gas discharged from turbine 3 only enters the flue gas heat exchanger 7, which sequentially heats the low-temperature molten salt at the outlet of low-temperature molten salt tank 14 and the water at the inlet of flue gas water heat exchanger 15 before being discharged through the flue gas pipe; with the inlet damper 5 opened and the bypass damper 6 closed, the flue gas discharged from turbine 3 only enters waste heat boiler 16.

[0024] With the inlet damper 5 closed and the bypass damper 6 opened, the flue gas discharged from the turbine 3 enters only the flue gas heat exchanger 7, heating the low-temperature molten salt delivered by the low-temperature molten salt pump 12 into high-temperature molten salt, which is then sent to the high-temperature molten salt tank 10 for heat storage. The flue gas outlet on the flue gas side of the flue gas heat exchanger 7 enters the flue water heat exchanger 15, which heats the feedwater and then discharges it through the flue gas pipeline. The feedwater is heated into steam and then supplied to heat users. At this time, only the gas turbine module generates electricity, and the system is in a low-load peak-shaving state.

[0025] With the inlet damper 5 open and the bypass damper 6 closed, the flue gas discharged from the turbine 3 enters the waste heat boiler 16 to heat the inlet feedwater. The generated steam enters the steam turbine 20 to do work, and the heat for the heat users is provided by the steam extracted from the steam turbine 20. At this time, the gas turbine module and the steam turbine 20 generate electricity simultaneously, and the system is in a high-load power generation state.

[0026] During the molten salt heat storage stage, the outlet of the low-temperature molten salt tank 14 is pressurized by the low-temperature molten salt pump 12 and sent into the flue salt heat exchanger 7. The flow rate of the low-temperature molten salt is controlled by the regulating valve B13. The high-temperature molten salt heated by the flue gas enters the high-temperature molten salt tank 10 for storage. During the molten salt exothermic phase, the high-temperature molten salt stored in the high-temperature molten salt tank 10 is pressurized by the high-temperature molten salt pump 9 and sent to the brine heat exchanger 11. The flow rate of the high-temperature molten salt is controlled by the regulating valve A8. The exothermic molten salt is stored in the low-temperature molten salt tank 14. The feedwater is heated into steam by the molten salt and then supplied to the heat users. At this time, both the gas turbine module and the steam turbine module are shut down and do not generate electricity. The system is in a shutdown and peak shaving state.

[0027] Waste heat boiler 16 and steam turbine 20 are not limited to twin-cylinder, triple-pressure reheat extraction condensing steam turbines, but can also be other types of waste heat boilers and steam turbines, as long as there is steam turbine inlet or extraction for external heat supply.

[0028] The system works as follows: The working fluids at the system inlet are generally taken under design conditions, with both air and natural gas in their design states. Air compressor 1 is connected to an air pipeline at its inlet, introducing air. After compression, the air enters combustion chamber 2, where it mixes and burns with natural gas entering combustion chamber 2 via a natural gas pipeline. The resulting flue gas enters turbine 3 to perform work. The flue gas outlet of turbine 3 is divided into two paths, connected to the flue gas inlet of waste heat boiler 16 and the flue gas inlet of flue gas heat exchanger 7, respectively. Inlet baffles 5 and bypass baffles are installed at their respective inlets. With the inlet damper 6 closed and the bypass damper 5 opened, the flue gas discharged from the turbine 3 enters only the flue salt heat exchanger 7, sequentially heating the low-temperature molten salt at the outlet of the low-temperature molten salt tank 14 and the inlet water of the flue water heat exchanger 15 before being discharged through the flue gas pipeline; the low-temperature molten salt delivered by the low-temperature molten salt pump 12 is heated into high-temperature molten salt and sent to the high-temperature molten salt tank 10 for heat storage, and the flow rate of the low-temperature molten salt is regulated by the regulating valve B13; the water is heated into steam and then supplied to the heat users; at this time, only the gas turbine module generates electricity, and the system is in a low-load peak-shaving state. With the inlet damper 5 open and the bypass damper 6 closed, the flue gas discharged from turbine 3 enters only the waste heat boiler 16 to heat the inlet feedwater. The generated steam enters the steam turbine 20 to do work, driving the turbine generator 19 to generate electricity. The heat for the users is provided by the steam extracted from the steam turbine 20. The steam after doing work is discharged into the condenser 18 to form condensate, which is then sent to the water-side inlet of the waste heat boiler 16 via the feedwater pump 17. At this time, both the gas turbine module and the steam turbine module generate electricity simultaneously, and the system is in a high-load power generation state. During the molten salt exothermic stage, the high-temperature molten salt stored in the high-temperature molten salt tank 10 is pressurized by the high-temperature molten salt pump 9 and sent to the brine heat exchanger 11. The flow rate of the high-temperature molten salt is controlled by the regulating valve A8. The exothermic molten salt is stored in the low-temperature molten salt tank 14, and the feedwater is heated into steam by the molten salt and then supplied to the users. At this time, both the gas turbine module and the steam turbine are shut down and do not generate electricity, and the system is in a shutdown peak-shaving state.

[0029] In practical applications, the system utilizes an SGT5-4000F (4+) heavy-duty gas turbine module, a twin-cylinder, three-pressure reheat condensing steam turbine (generator 19), and a three-pressure, single-reheat natural circulation boiler (boiler 16). The gas turbine module operates at 30% load, with all exhaust gas entering the thermal storage system for molten salt thermal storage and heating. At this point, the power generation is 86.73MW, representing 31.03% of the minimum power generation of current gas-steam combined cycle cogeneration units, thus increasing the unit's peak-shaving range. The molten salt thermal storage capacity is 39.64MW, simultaneously meeting 145t / h of industrial heating needs. When the unit is shut down, the molten salt releases 48.33t / h of heat, and after 6 hours of thermal storage, the heat release process can meet 2 hours of 145t / h of heating needs.

[0030] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0031] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A cogeneration peak-shaving system that utilizes gas turbine flue gas bypass to heat molten salt, characterized in that, include: Low-load peak shaving circuit, high-load generation circuit, and shutdown peak shaving circuit; The low-load peak-shaving circuit includes a gas turbine module and a molten salt heat storage module connected to each other. The molten salt heat storage module includes a low-temperature molten salt tank (14), a flue salt heat exchanger (7), and a high-temperature molten salt tank (10) connected in sequence. The gas turbine module and the flue salt heat exchanger (7) are connected. The flue gas generated by the gas turbine module enters the flue salt heat exchanger (7) through a pipeline. The flue gas heats the molten salt that is introduced into the flue salt heat exchanger (7) from the low-temperature molten salt tank (14). The heated high-temperature molten salt is introduced into the high-temperature molten salt tank (10) for heat storage. After the flue gas enters the flue salt heat exchanger (7), it enters the flue water heat exchanger (15) through a pipeline to heat the water in the flue water heat exchanger (15). The water is heated into steam and then supplied to the heat users. The high-load power generation circuit includes a gas turbine module, a waste heat boiler (16), and a steam turbine module connected in sequence. The steam turbine module includes a steam turbine (20) and a steam turbine generator (19). The flue gas generated by the gas turbine module enters the waste heat boiler (16) through a pipeline. The flue gas heats water to generate steam, which enters the steam turbine (20) to do work and drive the steam turbine generator (19) to generate electricity. The steam turbine (20) extracts steam to supply heat to heat users. The shutdown peak-shaving circuit includes a high-temperature molten salt tank (10), a brine heat exchanger (11), and a low-temperature molten salt tank (14) connected in sequence. The high-temperature molten salt stored in the high-temperature molten salt tank (10) enters the brine heat exchanger (11) to heat the water in the brine heat exchanger (11). The water is heated into steam and then supplied to the heat users. The molten salt after heating the water enters the low-temperature molten salt tank (14) for storage. The gas turbine module includes an air compressor (1), a combustion chamber (2), a turbine (3), and a gas turbine generator (4) connected in sequence. The turbine module also includes a feedwater pump (17) and a condenser (18). The waste heat boiler (16), steam turbine (20), condenser (18), and feedwater pump (17) are connected in a loop. The steam turbine (20) and the turbine generator (19) are connected.

2. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, The turbine (3) is connected to the flue gas heat exchanger (7) and the waste heat boiler (16) respectively. An inlet baffle (5) is provided between the turbine (3) and the waste heat boiler (16), and a bypass baffle (6) is provided between the turbine (3) and the flue gas heat exchanger (7).

3. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, The air compressor (1) is connected to an air duct to introduce air.

4. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, The natural gas inlet of the combustion chamber (2) is connected to a natural gas pipeline.

5. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, The flue gas side outlet of the flue gas heat exchanger (15) is connected to the flue gas pipe for discharging flue gas.

6. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, A high-temperature molten salt pump (9) and a regulating valve A are provided between the high-temperature molten salt tank (10) and the brine heat exchanger (11).

7. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, A low-temperature molten salt pump (12) and a regulating valve B are provided between the low-temperature molten salt tank (14) and the flue salt heat exchanger (7).

8. A cogeneration peak-shaving system for heating molten salt using gas turbine flue gas bypass as described in claim 1, characterized in that, The turbine generator (19) is a twin-cylinder, triple-pressure reheat extraction condensing turbine, and the waste heat boiler (16) is a triple-pressure, single-reheat natural circulation boiler.

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