A flexible and efficient coal-fired power generation system coupled with renewable energy and a method of operating the same

Abstract

The application discloses a flexible and efficient coal-fired power generation system coupled with renewable energy and an operation method thereof. The system comprises a traditional coal-fired generator unit and a two-stage flash evaporation geothermal energy utilization system coupled with the traditional coal-fired generator unit. The geothermal energy utilization system adopts two-stage flash evaporation devices to generate steam with different pressures, which are injected into the medium-pressure cylinder and the low-pressure cylinder of a steam turbine respectively to generate power. In addition, a regenerative heater bypass of the coal-fired generator unit is arranged, and the high-temperature geothermal fluid after flash evaporation is used to heat the bypass condensate water and the bypass boiler feed water. In normal operation, the system combines the geothermal energy and the coal-fired generator unit, increases the power output of the unit without increasing the coal supply of the boiler, and promotes the renewable energy consumption of the power grid. When the coal-fired generator unit is rapidly loaded or unloaded, the working fluid flow of the two-stage flash evaporation geothermal energy utilization system is adjusted, so that the load change rate of the coal-fired generator unit is increased without changing the coal supply of the boiler, and the safety of the coal-fired unit in the rapid load change process is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of multi-energy fusion complementary power generation, and particularly relates to a flexible and efficient coal-fired power generation system coupled with renewable energy and an operation method thereof. BACKGROUND

[0002] All countries in the world actively take energy transformation actions to increase the proportion of renewable energy in energy consumption as much as possible, so as to effectively alleviate the environmental security problem of the world.

[0003] With the gradual consumption of fossil energy, vigorously developing renewable energy has become an inevitable trend in the development of the energy field. The development and utilization of geothermal energy has advantages such as small occupation area and small ecological impact, and compared with energy such as wind energy and solar energy which have intermittency and volatility, geothermal energy has the characteristics of less weather and seasonal influence and stable energy quality. Vigorously developing the development and utilization of geothermal energy is one of the effective ways to reduce coal consumption and reduce greenhouse gas emissions in China. However, the temperature of low-temperature geothermal energy is relatively low, and direct extraction of geothermal energy for power generation has low power generation efficiency and high investment cost. Therefore, efficient integration of geothermal energy utilization and coal-fired power generation system can realize the cascade utilization of energy and improve the energy use efficiency, which has great significance for promoting renewable energy consumption and reducing the energy consumption level of coal-fired units in China. SUMMARY

[0004] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a flexible and efficient coal-fired power generation system coupled with renewable energy and an operation method thereof, which comprises a traditional coal-fired power generation unit and a two-stage flash geothermal energy utilization system coupled therewith, wherein the geothermal energy utilization system first adopts two-stage flash devices to generate steam at different pressures, which are injected into the medium-pressure cylinder and the low-pressure cylinder of the steam turbine respectively for power generation, and a regenerative heater bypass of the coal-fired power generation unit is also provided, and the high-temperature geothermal fluid after flash evaporation is used to heat the bypass condensate water and the bypass boiler feed water. When the system is normally operated, the combination of geothermal energy and coal-fired power generation unit increases the power output of the system without increasing the coal supply of the boiler, which promotes the renewable energy consumption of the power grid; when the coal-fired power generation unit is rapidly loaded or unloaded, the working fluid flow of the two-stage flash geothermal energy utilization system is adjusted, so that the purpose of increasing the load change rate of the coal-fired power generation unit without changing the coal supply of the boiler is achieved. The present application efficiently integrates geothermal energy and coal-fired power generation unit, realizes the cascade utilization of geothermal energy, and effectively improves the load change rate of the coal-fired power generation unit.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A flexible and efficient coal-fired power generation system coupled with renewable energy, comprising a coal-fired power generation unit and a two-stage flash geothermal energy utilization system coupled with the coal-fired power generation unit;

[0007] The coal-fired power generating unit comprises a boiler 1, a high-pressure cylinder 2 of a steam turbine, a medium-pressure cylinder 3 of the steam turbine, a low-pressure cylinder 4 of the steam turbine, a generator 5, a condenser 6, a condensate pump 7, a low-pressure heater 8, a deaerator 9, a feedwater pump 10 and a high-pressure heater 11; a main steam outlet of the boiler 1 is connected with a steam inlet of the high-pressure cylinder 2 of the steam turbine; a steam extraction outlet of the high-pressure cylinder 2 of the steam turbine is connected with a steam inlet of the high-pressure heater 11, and a steam outlet of the high-pressure cylinder 2 of the steam turbine is connected with a reheat steam inlet of the boiler 1; a reheat steam outlet of the boiler 1 and a steam-side outlet of a primary flash evaporator 14 of the two-stage flash geothermal energy utilization system are connected with a steam inlet of the medium-pressure cylinder 3 of the steam turbine after being merged; a steam extraction outlet of the medium-pressure cylinder 3 of the steam turbine is connected with a steam inlet of the deaerator 9, and a steam outlet of the medium-pressure cylinder 3 of the steam turbine and a steam-side outlet of a secondary flash evaporator 15 of the two-stage flash geothermal energy utilization system are connected with a steam inlet of the low-pressure cylinder 4 of the steam turbine after being merged; a steam extraction outlet of the low-pressure cylinder 4 of the steam turbine is connected with a steam inlet of the low-pressure heater 8, and a steam outlet of the low-pressure cylinder 4 of the steam turbine is connected with an inlet of the condenser 6; a water working medium outlet of the condenser 6 is divided into two routes after passing through the condensate pump 7, one of which is connected with a water working medium inlet of the low-pressure heater 8, and the other of which is connected with a low-temperature side water working medium inlet of a bypass condensate-geothermal fluid heat exchanger 18 of the two-stage flash geothermal energy utilization system through a condensate diversion valve 19; a water working medium outlet of the low-pressure heater 8 and a low-temperature side water working medium outlet of the bypass condensate-geothermal fluid heat exchanger 18 of the two-stage flash geothermal energy utilization system are connected with a water working medium inlet of the deaerator 9 after being merged; a water working medium outlet of the deaerator 9 is divided into two routes after passing through the feedwater pump 10, one of which is connected with a water working medium inlet of the high-pressure heater 11, and the other of which is connected with a low-temperature side water working medium inlet of a bypass feedwater-geothermal fluid heat exchanger 16 of the two-stage flash geothermal energy utilization system through a feedwater diversion valve 17; a water working medium outlet of the high-pressure heater 11 and a low-temperature side water working medium outlet of the bypass feedwater-geothermal fluid heat exchanger 16 of the two-stage flash geothermal energy utilization system are connected with a feedwater inlet of the boiler 1 after being merged; the high-pressure cylinder 2 of the steam turbine, the medium-pressure cylinder 3 of the steam turbine and the low-pressure cylinder 4 of the steam turbine are connected through rotating shafts and drive the generator 5 to output electric power to the outside;

[0008] The double-stage flash geothermal energy utilization system comprises a geothermal fluid extraction well 12, a deep well pump 13, a first-stage flash evaporator 14, a second-stage flash evaporator 15, a bypass feedwater-geothermal fluid heat exchanger 16, a bypass condensate-geothermal fluid heat exchanger 18, and a geothermal fluid reinjection well 20; the geothermal fluid extracted from the geothermal fluid extraction well 12 by the deep well pump 13 is connected to the water side inlet of the first-stage flash evaporator 14; the steam side outlet of the first-stage flash evaporator 14 and the reheat steam outlet of the boiler 1 are connected to the steam inlet of the intermediate pressure cylinder 3 of the steam turbine; the water side outlet of the first-stage flash evaporator 14 is connected to the water side inlet of the second-stage flash evaporator 15; the steam side outlet of the second-stage flash evaporator 15 and the steam outlet of the intermediate pressure cylinder 3 of the steam turbine are connected to the steam inlet of the low pressure cylinder 4 of the steam turbine; the water side outlet of the second-stage flash evaporator 15 is connected to the high temperature side water working medium inlet of the bypass feedwater-geothermal fluid heat exchanger 16; the high temperature side water working medium outlet of the bypass feedwater-geothermal fluid heat exchanger 16 is connected to the high temperature side water working medium inlet of the bypass condensate-geothermal fluid heat exchanger 18; and the high temperature side water working medium outlet of the bypass condensate-geothermal fluid heat exchanger 18 is sent back to the geothermal fluid reinjection well 20.

[0009] Further, the bypass feedwater-geothermal fluid heat exchanger 16 and the bypass condensate-geothermal fluid heat exchanger 18 are both partitioned water-water heat exchangers.

[0010] Further, the geothermal energy utilization system comprises two-stage flash devices, the first-stage flash evaporator 14 and the second-stage flash evaporator 15.

[0011] Further, the bypass feedwater-geothermal fluid heat exchanger 16 and the bypass condensate-geothermal fluid heat exchanger 18 are arranged in parallel with the high pressure heater 11 and the low pressure heater 8 of the coal-fired power generating unit, respectively.

[0012] Further, the extracted geothermal fluid is first subjected to two-stage flash to generate steam at different pressures, which is injected into the steam turbine to generate power, and then the remaining high temperature geothermal fluid is used to heat the bypass condensate and the bypass boiler feedwater.

[0013] An operation method of a flexible and efficient coal-fired power generation system coupled with renewable energy sources, specifically as follows:

[0014] 1) When the coal-fired power generating unit is in a normal operation load range, the deep well pump 13 can be started to extract geothermal fluid; the extracted geothermal fluid is first subjected to the first-stage flash evaporator 14 and the second-stage flash evaporator 15 to generate steam at different pressures, which is injected into the intermediate pressure cylinder 3 of the steam turbine and the low pressure cylinder 4 of the steam turbine to generate power, and then the remaining high temperature geothermal fluid is used in the bypass feedwater-geothermal fluid heat exchanger 16 and the bypass condensate-geothermal fluid heat exchanger 18 to heat the bypass boiler feedwater and the bypass condensate; in this stage, the operation goal is to increase the power output of the system without increasing the coal consumption of the boiler by combining the geothermal energy and the coal-fired power generating unit, so as to promote the renewable energy consumption of the power grid;

[0015] 2) When the coal-fired generator needs to quickly reduce the electrical load rate, the mass flow rate of the deep well pump 13 is reduced to reduce the steam flow rate generated by the two-stage flash device, and the mass flow rate of the bypass boiler feed water and bypass condensate is correspondingly reduced, the steam extraction flow rate of the steam turbine heat recovery system is increased, and the output power of the coal-fired generator is rapidly reduced. The operation goal of this stage is to quickly reduce the output power of the coal-fired generator by adjusting the two-stage flash geothermal energy utilization system without reducing the coal supply of the boiler, effectively improving the variable load rate of the coal-fired generator;

[0016] 3) When the coal-fired generator needs to quickly increase the electrical load rate, the mass flow rate of the deep well pump 13 is increased to increase the steam flow rate generated by the two-stage flash device, and the mass flow rate of the bypass boiler feed water and bypass condensate is correspondingly increased, the steam extraction flow rate of the steam turbine heat recovery system is reduced, and the output power of the coal-fired generator is rapidly increased. The operation goal of this stage is to quickly increase the output power of the coal-fired generator by adjusting the two-stage flash geothermal energy utilization system without increasing the coal supply of the boiler, effectively improving the variable load rate of the coal-fired generator.

[0017] Compared with the prior art, the advantages of the present application are as follows:

[0018] (1) The present application proposes an efficient integration method of a coal-fired generator and a two-stage flash geothermal energy utilization system. First, geothermal fluid is used to generate steam at different pressures by a two-stage flash device, which is injected into the medium-pressure cylinder and the low-pressure cylinder of the steam turbine for power generation. A bypass of the heat recovery heater of the coal-fired power generation system is also provided, which uses high-temperature geothermal fluid after flashing to heat bypass condensate and bypass boiler feed water, achieving cascade utilization of energy and improving energy use efficiency.

[0019] (2) The present application efficiently integrates geothermal energy utilization with a coal-fired generator, which increases the system's electrical power output without increasing the coal supply of the boiler, which is of great significance to promoting renewable energy consumption and reducing the energy consumption of coal-fired generators in China.

[0020] (3) The present application adjusts the working fluid flow of the two-stage flash geothermal energy utilization system to assist the coal-fired generator in quickly increasing and decreasing the load, thereby effectively improving the variable load rate of the coal-fired generator without changing the coal supply of the boiler. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the system of the present application. DETAILED DESCRIPTION

[0022] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0023] AsFigure 1 As shown, the present application provides a flexible and efficient coal-fired power generation system coupled with renewable energy, which comprises a conventional coal-fired power generating unit and a two-stage flash evaporation geothermal energy utilization system coupled therewith;

[0024] The coal-fired power generating unit comprises a boiler 1, a high-pressure cylinder of a steam turbine 2, a medium-pressure cylinder of a steam turbine 3, a low-pressure cylinder of a steam turbine 4, a generator 5, a condenser 6, a condensate pump 7, a low-pressure heater 8, a deaerator 9, a feedwater pump 10 and a high-pressure heater 11; a main steam outlet of the boiler 1 is connected with a steam inlet of the high-pressure cylinder of the steam turbine 2; a steam extraction outlet of the high-pressure cylinder of the steam turbine 2 is connected with a steam inlet of the high-pressure heater 11, and a steam outlet of the high-pressure cylinder of the steam turbine 2 is connected with a reheat steam inlet of the boiler 1; a reheat steam outlet of the boiler 1 and a steam side outlet of a first flash evaporator 14 of the two-stage flash evaporation geothermal energy utilization system are connected with a steam inlet of the medium-pressure cylinder of the steam turbine 3 after being merged; a steam extraction outlet of the medium-pressure cylinder of the steam turbine 3 is connected with a steam inlet of the deaerator 9, and a steam outlet of the medium-pressure cylinder of the steam turbine 3 and a steam side outlet of a second flash evaporator 15 of the two-stage flash evaporation geothermal energy utilization system are connected with a steam inlet of the low-pressure cylinder of the steam turbine 4 after being merged; a steam extraction outlet of the low-pressure cylinder of the steam turbine 4 is connected with a steam inlet of the low-pressure heater 8, and a steam outlet of the low-pressure cylinder of the steam turbine 4 is connected with an inlet of the condenser 6; a water working medium outlet of the condenser 6 is divided into two routes after passing through the condensate pump 7, one of which is connected with a water working medium inlet of the low-pressure heater 8, and the other of which is connected with a low-temperature side water working medium inlet of a bypass condensate-geothermal fluid heat exchanger 18 of the two-stage flash evaporation geothermal energy utilization system through a condensate shunt valve 19; a water working medium outlet of the low-pressure heater 8 and a low-temperature side water working medium outlet of the bypass condensate-geothermal fluid heat exchanger 18 of the two-stage flash evaporation geothermal energy utilization system are connected with a water working medium inlet of the deaerator 9 after being merged; a water working medium outlet of the deaerator 9 is divided into two routes after passing through the feedwater pump 10, one of which is connected with a water working medium inlet of the high-pressure heater 11, and the other of which is connected with a low-temperature side water working medium inlet of a bypass feedwater-geothermal fluid heat exchanger 16 of the two-stage flash evaporation geothermal energy utilization system through a feedwater shunt valve 17; a water working medium outlet of the high-pressure heater 11 and a low-temperature side water working medium outlet of the bypass feedwater-geothermal fluid heat exchanger 16 of the two-stage flash evaporation geothermal energy utilization system are connected with a feedwater inlet of the boiler 1 after being merged; the high-pressure cylinder of the steam turbine 2, the medium-pressure cylinder of the steam turbine 3 and the low-pressure cylinder of the steam turbine 4 are connected through rotating shafts and drive the generator 5 to output electric power to the outside;

[0025] The double-stage flash geothermal energy utilization system comprises a geothermal fluid extraction well 12, a deep well pump 13, a first-stage flash evaporator 14, a second-stage flash evaporator 15, a bypass feedwater-geothermal fluid heat exchanger 16, a bypass condensate-geothermal fluid heat exchanger 18, and a geothermal fluid reinjection well 20; the geothermal fluid taken out from the geothermal fluid extraction well 12 by the deep well pump 13 is connected with a water side inlet of the first-stage flash evaporator 14; a steam side outlet of the first-stage flash evaporator 14 and a reheat steam outlet of the boiler 1 are connected with a steam inlet of a medium-pressure cylinder 3 of the steam turbine; a water side outlet of the first-stage flash evaporator 14 is connected with a water side inlet of the second-stage flash evaporator 15; a steam side outlet of the second-stage flash evaporator 15 and a steam outlet of the medium-pressure cylinder 3 of the steam turbine are connected with a steam inlet of a low-pressure cylinder 4 of the steam turbine; a water side outlet of the second-stage flash evaporator 15 is connected with a high-temperature water working medium inlet of the bypass feedwater-geothermal fluid heat exchanger 16; a high-temperature water working medium outlet of the bypass feedwater-geothermal fluid heat exchanger 16 is connected with a high-temperature water working medium inlet of the bypass condensate-geothermal fluid heat exchanger 18; and a high-temperature water working medium outlet of the bypass condensate-geothermal fluid heat exchanger 18 is sent back to the geothermal fluid reinjection well 20.

[0026] Further, the bypass feedwater-geothermal fluid heat exchanger 16 and the bypass condensate-geothermal fluid heat exchanger 18 are both partitioned water-water heat exchangers, and the geothermal fluid can heat the bypass condensate and the boiler feedwater, so as to reduce the steam extraction flow rate of the coal-fired power generation unit heat recovery system, thereby increasing the output electric power of the coal-fired unit.

[0027] Further, the geothermal energy utilization system comprises two-stage flash devices, i.e., the first-stage flash evaporator 14 and the second-stage flash evaporator 15, and the double-stage flash can effectively utilize the pressure of the geothermal fluid, thereby generating steam at different pressures, which is injected into the steam turbine to generate power.

[0028] Further, the bypass feedwater-geothermal fluid heat exchanger 16 and the bypass condensate-geothermal fluid heat exchanger 18 are arranged in parallel with the high-pressure heater 11 and the low-pressure heater 8 of the coal-fired power generation unit, respectively, so as to fully utilize the waste heat of the geothermal fluid to heat the bypass condensate and the boiler feedwater, thereby improving the variable load rate of the coal-fired unit.

[0029] Further, the extracted geothermal fluid is first subjected to the two-stage flash devices to generate steam at different pressures, which is injected into the steam turbine to generate power, and then the remaining high-temperature geothermal fluid is used to heat the bypass condensate and the bypass boiler feedwater, so as to realize the cascade utilization of the thermal energy in the geothermal fluid and improve the energy efficiency of the system.

[0030] An operation method of a flexible and efficient coal-fired power generation system coupled with renewable energy is as follows:

[0031] 1) When the coal-fired generating unit is in the normal operation load range, the deep well pump 13 can be started to extract geothermal fluid, the extracted geothermal fluid first passes through the first-stage flash evaporator 14 and the second-stage flash evaporator 15 to generate steam at different pressures, and is injected into the steam turbine intermediate pressure cylinder 3 and the steam turbine low pressure cylinder 4 respectively to generate power, and then the remaining high-temperature geothermal fluid is used to heat the bypass boiler feed water and the bypass condensate water in the bypass feed water-geothermal fluid heat exchanger 16 and the bypass condensate water-geothermal fluid heat exchanger 18, and the operation target in this stage is to increase the power output of the system while not increasing the coal consumption of the boiler by combining the geothermal energy and the coal-fired generating unit, so as to promote the renewable energy consumption of the power grid;

[0032] 2) When the coal-fired generating unit needs to quickly reduce the electric load rate, the mass flow of the deep well pump 13 extracting geothermal fluid is reduced, so that the steam flow generated by the two-stage flash evaporation device is reduced, and the mass flow of the bypass boiler feed water and the bypass condensate water is correspondingly reduced, the steam extraction flow of the steam turbine regenerative system is increased, and the output power of the coal-fired generating unit is rapidly reduced, and the operation target in this stage is to quickly reduce the output power of the coal-fired generating unit by adjusting the two-stage flash evaporation geothermal energy utilization system while not reducing the coal consumption of the boiler, so as to effectively improve the load change rate of the coal-fired generating unit.

[0033] 3) When the coal-fired generating unit needs to quickly increase the electric load rate, the mass flow of the deep well pump 13 extracting geothermal fluid is increased, so that the steam flow generated by the two-stage flash evaporation device is increased, and the mass flow of the bypass boiler feed water and the bypass condensate water is correspondingly increased, the steam extraction flow of the steam turbine regenerative system is reduced, and the output power of the coal-fired generating unit is rapidly increased, and the operation target in this stage is to quickly increase the output power of the coal-fired generating unit by adjusting the two-stage flash evaporation geothermal energy utilization system while not increasing the coal consumption of the boiler, so as to effectively improve the load change rate of the coal-fired generating unit.

[0034] In summary, the present application integrates the geothermal energy utilization and the coal-fired generating unit, first uses the two-stage flash evaporation device to generate steam at different pressures from the geothermal fluid, injects into the steam turbine intermediate pressure cylinder and the steam turbine low pressure cylinder respectively to generate power, and sets the bypass of the regenerative heater of the coal-fired generating unit, uses the high-temperature geothermal fluid after flash evaporation to heat the bypass condensate water and the bypass boiler feed water, realizes the cascade utilization of energy, and improves the energy use efficiency; in addition, the load of the coal-fired generating unit is quickly increased or decreased by adjusting the working fluid flow of the two-stage flash evaporation geothermal energy utilization system, so as to effectively improve the load change rate of the coal-fired generating unit without changing the coal consumption of the boiler.

Claims

1. An operation method for a flexible and efficient coal-fired power generation system coupled with renewable energy, characterized in that: The system includes a coal-fired power generation unit and a two-stage flash geothermal energy utilization system coupled with the coal-fired power generation unit; The coal-fired power generation unit includes a boiler (1), a high-pressure cylinder (2) of a steam turbine, an intermediate-pressure cylinder (3) of a steam turbine, a low-pressure cylinder (4) of a steam turbine, a generator (5), a condenser (6), a condensate pump (7), a low-pressure heater (8), a deaerator (9), a feedwater pump (10), and a high-pressure heater (11); the main steam outlet of the boiler (1) is connected to the steam inlet of the high-pressure cylinder (2) of the steam turbine; the extraction steam outlet of the high-pressure cylinder (2) of the steam turbine is connected to the steam inlet of the high-pressure heater (11), and the steam outlet of the high-pressure cylinder (2) of the steam turbine is connected to the reheat steam inlet of the boiler (1); the reheat steam of the boiler (1) The steam outlet of the first-stage flash evaporator (14) of the two-stage flash geothermal energy utilization system merges with the steam inlet of the intermediate-pressure cylinder (3) of the turbine; the extraction steam outlet of the intermediate-pressure cylinder (3) of the turbine is connected to the steam inlet of the deaerator (9); the steam outlet of the intermediate-pressure cylinder (3) of the turbine and the steam outlet of the second-stage flash evaporator (15) of the two-stage flash geothermal energy utilization system merge with the steam inlet of the low-pressure cylinder (4) of the turbine; the extraction steam outlet of the low-pressure cylinder (4) of the turbine is connected to the steam inlet of the low-pressure heater (8); the steam outlet of the low-pressure cylinder (4) of the turbine is connected to the steam inlet of the condenser (6). The water outlet of the condenser (6) is divided into two paths after passing through the condensate pump (7). One path is connected to the water inlet of the low-pressure heater (8), and the other path passes through the condensate diversion valve (19) to the low-temperature side water inlet of the bypass condensate-geothermal fluid heat exchanger (18) of the two-stage flash geothermal energy utilization system. The water outlet of the low-pressure heater (8) and the low-temperature side water outlet of the bypass condensate-geothermal fluid heat exchanger (18) of the two-stage flash geothermal energy utilization system merge and are connected to the water inlet of the deaerator (9). The water outlet of the deaerator (9) is divided into two paths after passing through the feed water pump (10). One path is connected to the water inlet of the high-pressure heater (11), and the other path is connected to the low-temperature water inlet of the bypass feedwater-geothermal fluid heat exchanger (16) of the two-stage flash geothermal energy utilization system via the feedwater diversion valve (17); the water outlet of the high-pressure heater (11) and the low-temperature water outlet of the bypass feedwater-geothermal fluid heat exchanger (16) of the two-stage flash geothermal energy utilization system are combined and connected to the feedwater inlet of the boiler (1); the high-pressure cylinder (2), the intermediate-pressure cylinder (3) and the low-pressure cylinder (4) of the turbine are connected by a rotating shaft and jointly drive the generator (5) to output electrical power. The two-stage flash geothermal energy utilization system includes a geothermal fluid extraction well (12), a deep well pump (13), a first-stage flash evaporator (14), a second-stage flash evaporator (15), a bypass feedwater-geothermal fluid heat exchanger (16), a bypass condensate-geothermal fluid heat exchanger (18), and a geothermal fluid reinjection well (20). The geothermal fluid extracted from the geothermal fluid extraction well (12) by the deep well pump (13) is connected to the water-side inlet of the first-stage flash evaporator (14). The steam-side outlet of the first-stage flash evaporator (14) and the reheat steam outlet of the boiler (1) are combined and connected to the steam inlet of the intermediate pressure cylinder (3) of the steam turbine. The water-side outlet of the first-stage flash evaporator (14) is connected to the steam inlet of the intermediate pressure cylinder (3) of the steam turbine. It is connected to the water-side inlet of the secondary flash evaporator (15); the steam-side outlet of the secondary flash evaporator (15) and the steam outlet of the intermediate pressure cylinder (3) of the steam turbine are combined and connected to the steam inlet of the low pressure cylinder (4) of the steam turbine; the water-side outlet of the secondary flash evaporator (15) is connected to the high-temperature water working medium inlet of the bypass feedwater-geothermal fluid heat exchanger (16); the high-temperature water working medium outlet of the bypass feedwater-geothermal fluid heat exchanger (16) is connected to the high-temperature water working medium inlet of the bypass condensate-geothermal fluid heat exchanger (18); the high-temperature water working medium outlet of the bypass condensate-geothermal fluid heat exchanger (18) is sent back to the geothermal fluid reinjection well (20); The bypass feedwater-geothermal fluid heat exchanger (16) and the bypass condensate-geothermal fluid heat exchanger (18) are arranged in parallel with the high-pressure heater (11) and the low-pressure heater (8) of the coal-fired power generation unit, respectively. The operating method is as follows: 1) When the coal-fired power generation unit is in the normal operating load range, the deep well pump (13) can be turned on to extract geothermal fluid. The extracted geothermal fluid first passes through the first-stage flash evaporator (14) and the second-stage flash evaporator (15) to generate steam at different pressures, which are then injected into the intermediate-pressure cylinder (3) and the low-pressure cylinder (4) of the turbine for power generation. The remaining high-temperature geothermal fluid is then used in the bypass feedwater-geothermal fluid heat exchanger (16) and the bypass condensate-geothermal fluid heat exchanger (18) to heat the bypass boiler feedwater and bypass condensate. The goal of this stage is to increase the power output of the system by combining geothermal energy with the coal-fired power generation unit without increasing the boiler coal supply, thereby promoting the consumption of renewable energy in the power grid. 2) When the coal-fired power generation unit needs to quickly reduce the load rate, reduce the mass flow rate of geothermal fluid extracted by the deep well pump (13), thereby reducing the steam flow rate generated by the two-stage flash evaporation device. At the same time, the mass flow rate of the bypass boiler feedwater and bypass condensate is reduced accordingly, the steam extraction flow rate of the turbine regenerative system increases, and the output power of the coal-fired power generation unit is rapidly reduced. The operating objective at this stage is to quickly reduce the output power of the coal-fired power generation unit by adjusting the two-stage flash geothermal energy utilization system without reducing the boiler coal feed rate, thereby effectively improving the load change rate of the coal-fired power generation unit. 3) When the coal-fired power generation unit needs to rapidly increase the load rate, the mass flow rate of geothermal fluid extracted by the deep well pump (13) is increased, thereby increasing the steam flow rate generated by the two-stage flash evaporation device. At the same time, the mass flow rate of the bypass boiler feedwater and bypass condensate is increased accordingly, the steam extraction flow rate of the turbine regenerator system is reduced, and the output power of the coal-fired power generation unit is rapidly increased. The operating objective at this stage is to rapidly increase the output power of the coal-fired power generation unit by adjusting the two-stage flash evaporation geothermal energy utilization system without increasing the boiler coal feed rate, thereby effectively improving the load change rate of the coal-fired power generation unit.

2. The operation method of a flexible and efficient coal-fired power generation system coupled with renewable energy as described in claim 1, characterized in that: Both the bypass feedwater-geothermal fluid heat exchanger (16) and the bypass condensate-geothermal fluid heat exchanger (18) are indirect-wall water-to-water heat exchangers.

3. The operation method of a flexible and efficient coal-fired power generation system coupled with renewable energy as described in claim 1, characterized in that: The geothermal energy utilization system includes a two-stage flash evaporation device, a primary flash evaporator (14) and a secondary flash evaporator (15).

4. The operation method of a flexible and efficient coal-fired power generation system coupled with renewable energy as described in claim 1, characterized in that: The extracted geothermal fluid is first passed through two-stage flash evaporators to generate steam at different pressures, which is then injected into a steam turbine to generate electricity. The remaining high-temperature geothermal fluid is then used to heat the bypass condensate and bypass boiler feedwater.

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