Low-carbon flexible coal-fired power generation system and method

Abstract

The invention discloses a low-carbon flexible coal-fired power generation system and method, and the method comprises the steps: constructing a low-carbon flexible coal-fired power generation system based on in-plant renewable power assistance, enabling renewable power not to be directly merged into a power grid, and determining the renewable output, the operation state of a unit and the peak regulation demand, different energy forms such as electricity / heat are selected for coupling to assist the coal-fired power plant to generate power in different operation modes, low-carbon and flexible operation of the unit is achieved, the initial investment cost of the system is relatively low, the operation modes are more flexible, and the variable load requirement is more rapidly responded.

Description

Technical Field

[0001] The present invention relates to the technical field of energy saving and low carbonization of thermal power units, and in particular to a low-carbon flexible coal-fired power generation system and method. Background Art

[0002] In the new energy utilization technology, deep coupling of solar thermal power generation and coal-fired power generation systems can share power and power generation equipment such as steam turbines, solving the problem of high initial investment in solar thermal power generation and improving the efficiency of solar thermal power generation; it can reduce the coal consumption of coal-fired units, significantly reduce fossil fuel consumption and carbon dioxide emissions, and also reduce the power generation load of coal-fired units to achieve flexible operation.

[0003] In recent years, the scale of renewable energy utilization has grown rapidly, and the proportion of solar power generation in renewable energy generation has continued to increase. However, due to the intermittent nature of solar energy, large-scale grid-connected power generation has led to increased fluctuations in the power grid, making it difficult to absorb renewable energy in some areas. In order to cope with the frequent peak-shaving and frequency-regulation needs of the power grid, it is necessary to improve the flexibility and economy of solar thermal power generation systems and coal-fired power generation systems, requiring them to be able to output electric power stably while quickly responding to the peak-shaving and frequency-regulation needs of the power grid, quickly changing loads, and operating flexibly and economically. However, the existing coupling method of solar thermal power generation systems and coal-fired power generation systems is not sufficient to cope with power fluctuations caused by frequent changes in solar radiation intensity, and there is no reasonable solution to make the flexibility of solar thermal power generation and coal-fired power generation units meet the requirements of the power grid and improve their economy.

[0004] Chinese patent document CN117432491A discloses a "light-coal-storage complementary low-carbon flexible power generation system and operation method". The system includes a coal-fired power generation system, a solar-coupled heat storage system and a carbon capture system including a carbon dioxide absorption tower, a solar-assisted reboiler, a steam-assisted reboiler, and a desorption tower; the solar-assisted reboiler and the steam-assisted reboiler are used to utilize solar energy and high-temperature and high-pressure steam to jointly provide the heat required for the reaction in the desorption tower, thereby reducing the impact of the carbon capture system on the efficiency of the coal-fired power generation system; the energy input from the solar-coupled heat storage system to the coal-fired power generation system and the energy input from the coal-fired power generation system to the carbon capture system are controlled to meet the requirements of low-carbon and flexible operation of the system. The above technical solution has high investment costs, a single coupling method and large thermal inertia, and is insufficient in its ability to respond to peak demand. Summary of the invention

[0005] The present invention mainly solves the technical problems of the original technical solution, such as high investment cost, single coupling method, large thermal inertia, and insufficient response ability to peak shaving demand. It provides a low-carbon flexible coal-fired power generation system and method, constructs a low-carbon flexible coal-fired power generation system assisted by in-plant renewable electricity. The renewable electricity is not directly incorporated into the power grid. By judging the renewable power output, unit operation status and peak shaving demand, different energy forms such as electricity / heat are selected for coupling to assist the coal-fired power plant to generate electricity in different operation modes, realizing the low-carbon and flexible operation of the unit. The initial investment cost of the system is relatively low, the operation mode is more flexible, and it can respond to variable load demands more quickly.

[0006] The above technical problems of the present invention are mainly solved by the following technical solutions: The present invention includes a molten salt side circulation loop and a steam side circulation loop. The steam side circulation loop includes a boiler, a steam turbine and a condenser connected in sequence. The output end of the molten salt side circulation loop is connected to the steam turbine, and the input end of the molten salt side circulation loop is connected to the condenser.

[0007] The unit can realize the efficient, flexible and low-carbon operation of the unit by coupling with in-plant renewable electricity in three modes: normal operation mode, load reduction operation mode and load increase operation mode.

[0008] S1: First, according to the power grid dispatching instruction, judge whether the unit needs to perform load increase / load reduction peak shaving operation. If load increase operation is required, go to S2; if load reduction operation is required, go to S3. If the unit maintains stable operation, go to S4.

[0009] S2: When the unit needs to perform load increase operation, If ΔP ps <F(load), the in-plant green electricity drives the heat pump system to heat part of the condensate water, reduce the extraction steam flow of the low-pressure heater, and meet the load increase demand of the unit. Further judge P RE and ΔP ps sizes. If P RE >ΔP ps , while the green electricity drives the heat pump system, the excess green electricity drives the electric heater to heat the low-temperature molten salt for heat storage. If P RE <ΔP ps , further start the molten salt heat storage system to release heat. The high-temperature molten salt flows out of the high-temperature molten salt tank, heats the feed water through the steam generator, cools down to the low-temperature molten salt, and enters the low-temperature molten salt tank to make up for the output gap of the unit.

[0010] If ΔP ps >F(load), start the heat pump system and the heat storage system to release heat and produce steam at the same time to synergistically increase the output of the unit. Further judge P RE and F(load) sizes. If P RE<F(load), all the green power drives the heat pump; if P RE >F(load), the excess green power drives the electric heater to heat the low-temperature molten salt for heat storage. Among them, P RE is the renewable power generation within the plant, and ΔP ps is the peak shaving depth required by the unit, and F(load) is the increased load that the unit can reach when all the condensate water of the unit is bypassed under different loads.

[0011] S3: When the unit needs to operate at a reduced load, start the molten salt heat storage system, drive the electric heater with part of the electric energy of the unit generator. The low-temperature molten salt flows out of the low-temperature molten salt tank, is heated to high-temperature molten salt by the electric heater, and flows into the high-temperature molten salt tank for storage. The green power within the plant selects the auxiliary unit method according to the following boiler operation state judgment criteria: If P - ΔP ps >P d-w , the green power heats the feed water temperature after the high-pressure heater, increases the feed water temperature at the boiler inlet, and reduces the coal input of the unit; If P - ΔP ps <P d-w , the green power is not coupled with the unit, and drives the electric heater to heat the molten salt for energy storage.

[0012] In the formula, P is the load before peak shaving of the unit, and P d-w is the load corresponding to the dry-wet conversion of the unit boiler.

[0013] S4: When the unit operates at normal load, the green power heats the feed water temperature after the high-pressure heater, increases the feed water temperature at the boiler inlet, reduces the coal input of the unit, and the unit enters the economizer operation mode.

[0014] Preferably, the molten salt side circulation loop includes a molten salt electric heater. The input end of the molten salt electric heater is connected to a low-temperature molten salt storage tank, the output end of the molten salt electric heater is connected to a high-temperature molten salt storage tank, and the input end of the low-temperature molten salt storage tank is connected to the output end of the high-temperature molten salt storage tank through a steam generator. For the molten salt side circulation loop, the inlet of the molten salt electric heater is connected to a molten salt pump, the outlet of the molten salt electric heater is connected to the high-temperature molten salt tank, the high-temperature molten salt tank is connected to the steam generator, and the outlet of the steam generator is connected to the low-temperature molten salt tank to form a molten salt circulation loop.

[0015] Preferably, the water inlet of the steam generator is connected to the condensate outlet of the condenser, and the water outlet of the steam generator is connected to the steam turbine. During the charging process, the molten salt is heated to a high temperature by the low-temperature molten salt tank through an electric heater and flows into the high-temperature molten salt storage tank. During the discharge process, it is cooled to a low-temperature molten salt through heat exchange with the feed water through the steam generator, and then flows into the low-temperature molten salt storage tank. The power consumed by the molten salt electric heater comes from the unit plant electricity and the renewable power in the plant. The condensate outlet of the condenser is connected to the water inlet of the steam generator after passing through the feed water pump after the deaerator.

[0016] Preferably, the steam side circulation loop also includes a low-pressure heater and a heat pump respectively connected to the condensate outlet of the condenser. For the steam side circulation loop, the outlet of the low-pressure cylinder of the unit is connected to the condenser, the outlet of the condenser is connected to the condensate pump, the outlet of the condensate pump is connected to the low-pressure heater and the heat pump respectively, and the condensate is divided into two streams, which are heated by the low-pressure heater and the heat pump respectively and then enter the deaerator. Among them, a flow regulating valve is set on the condensate bypass. Preferably, the water outlet of the low-pressure heater and the water outlet of the heat pump are connected to the water inlet of the deaerator, and the water outlet of the deaerator is connected to the water inlet of the water feed pump. The deaerator is connected to the water feed pump, and the water feed is divided into two streams after the water feed pump. One of the streams enters the boiler after passing through the high-pressure heater; the other stream of water feed is converted into steam after passing through the steam generator and enters the medium-pressure cylinder. A water feed bypass is provided after the high-pressure heater, and the bypass water feed returns to the main water feed after being heated by the electric heater. Among them, the water feed bypass is provided with a flow regulating valve.

[0017] Preferably, the water outlet of the feed water pump is connected to the water inlet of the steam generator, and the water outlet of the feed water pump is connected to the steam turbine through the high-pressure heater and the boiler in sequence. The deaerator is connected to the feed water pump, and the feed water after the feed water pump is divided into two streams. One stream enters the boiler after passing through the high-pressure heater; the other stream of feed water is converted into steam after passing through the steam generator and enters the medium-pressure cylinder.

[0018] Preferably, the steam turbine comprises a steam turbine high-pressure cylinder, a steam turbine medium-pressure cylinder and a steam turbine low-pressure cylinder connected in sequence, the outlet end of the steam turbine high-pressure cylinder is connected to the air inlet end of the steam turbine medium-pressure cylinder after passing through the boiler, the outlet end of the steam turbine low-pressure cylinder is connected to the condenser, and the steam turbine power output end is connected to the generator.

[0019] Preferably, an electric heater is provided between the high-pressure heater and the boiler, and the electric heater is connected to the in-plant renewable power source and the in-plant power supply respectively. The in-plant renewable power source is not connected to the power grid.

[0020] Preferably, the molten salt electric heater is connected to the in-plant renewable power source and the in-plant power respectively. The power consumed by the molten salt electric heater comes from the in-plant power and the in-plant renewable power, and the in-plant renewable power source is not connected to the power grid.

[0021] Preferably, the condenser external water outlet is connected to a heat pump. The condensed water is divided into two streams and heated by the low-pressure heater and the heat pump respectively before entering the deaerator. The condenser external water is circulating cooling water. The heated circulating cooling water enters the heat pump for heat exchange, realizing heat recovery of the unit and reducing the loss of the cold end of the unit.

[0022] The beneficial effects of the present invention are: 1. The present invention constructs renewable electricity in the plant, and the renewable electricity is not directly connected to the power grid. Different coupling methods are used to assist the coal-fired power plant to generate electricity in different operating modes, thereby realizing low-carbon and flexible operation of the unit.

[0023] 2. In the present invention, the heat pump driven by renewable electricity in the plant is used to utilize the waste heat of the circulating cooling water, thereby reducing the cold end loss of the unit, improving the overall energy efficiency of the system, and realizing the economical operation of the entire system.

[0024] 3. The operation strategy of the low-carbon fire-storage peak-shaving system proposed in the present invention can flexibly switch the operation mode for different working conditions by judging the renewable output, the operating status of the unit and the peak-shaving demand. When the unit is operating normally, renewable electricity continuously assists the unit in coal-saving operation; when the unit needs to flexibly peak-shave, the unit can quickly change its load by driving the heat pump with green electricity and releasing energy through the molten salt heat storage system. When peak-shaving is performed on a small scale, the heat pump system can be enabled to bypass the condensed water. When peak-shaving is performed on a large scale, the heat pump and the heat storage system can be enabled at the same time to quickly respond to changing load demands. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a principle connection structure diagram of the present invention.

[0026] In the figure, 1 is a generator, 2 is a steam turbine low-pressure cylinder, 3 is a steam turbine medium-pressure cylinder, 4 is a steam turbine high-pressure cylinder, 5 is a boiler, 6 is a condenser, 7 is a deaerator, 8 is a high-pressure heater, 9 is a low-pressure heater, 10 is an in-plant renewable power source, 11 is a high-temperature molten salt storage tank, 12 is a low-temperature molten salt storage tank, 13 is a molten salt electric heater, 14 is an electric heater, 15 is a heat pump, and 16 is a steam generator. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is further described in detail below through embodiments and in combination with the accompanying drawings. It should be understood that the specific implementation method described here is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] my country's coal-based energy structure is unlikely to change fundamentally in the short term. In 2022, China's coal-fired power generation will still account for 58.4% of total power generation, and will play the role of ballast in the long term. However, coal-fired power is also one of the main sources of CO2 emissions in my country's power industry. At the same time, the large-scale grid connection of my country's photovoltaic, wind power and other renewable energy power generation has aggravated the voltage and frequency fluctuations of the power grid, making it difficult to regulate the peak and frequency of the power grid, which has also put forward higher requirements for the flexibility of coal-fired power and the flexible and efficient use of solar energy. The coupling of carbon capture technology with coal-fired power generation can effectively reduce carbon emissions, but the impact of carbon capture technology on the efficiency of the unit is huge, causing the efficiency of the unit to drop by about 10%. At the same time, the existing coal-fired power generation system coupled with solar energy is difficult to meet the requirements of flexible and efficient operation of the system.

[0029] Carbon emissions from coal-fired power generation / heating in my country account for about 53% of the country's total carbon emissions. In the process of energy structure transformation and upgrading, traditional thermal power plants are facing tremendous pressure to reduce emissions. At the same time, coal-fired power, as a power generation technology that can achieve stable and reliable supply, will play an important role in supporting the rapid development of renewable energy power generation. The present invention proposes a low-carbon flexible coal-fired power generation system and operation strategy based on in-plant renewable power assistance to solve the technical problems of high carbon emission intensity of traditional coal-fired units and insufficient flexibility when switching to fast-changing load conditions.

[0030] At present, the technology of renewable energy-assisted coal-fired power generation mainly uses solar thermal effects to thermally couple with coal-fired units. The existing technology mainly uses solar thermal collection systems to achieve low-carbon peak-shaving operation of solar-assisted coal-fired units, but this technical solution still faces challenges such as high investment cost, single coupling method, and large thermal inertia. The present invention proposes a low-carbon flexible coal-fired power generation system and operation strategy based on in-plant renewable electricity assistance, adding off-grid renewable power sources in thermal power plants, coupling molten salt heat storage systems to achieve renewable energy-assisted coal-fired power generation in different forms of heat / electricity, reducing the carbon emission intensity of coal-fired power generation units and improving the flexibility of unit operation.

[0031] The solar thermal assisted coal-fired power generation system heats the thermal fluid in the heat collecting device through the action of solar thermal energy, thereby realizing the transfer and storage of thermal energy, and the whole process is transmitted in the form of heat. This technical solution has the problem of high investment cost of thermal collection equipment, and it can only interact with the coal-fired unit in the form of heat. Due to the thermal inertia, the overall response speed of the system is slow. The purpose of the present invention is to propose a low-carbon flexible coal-fired power generation system assisted by in-plant renewable electricity. The in-plant renewable electricity and coal-fired units can be coupled in different energy forms such as electricity / heat according to different operating conditions of the units. The initial investment cost of the system is relatively low, the operating mode is more flexible, and the response speed is faster.

[0032] Before discussing the exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts depict the operations (or steps) as sequential processes, many of the operations (or steps) can be implemented in parallel, concurrently, or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operations are completed, but there can also be additional steps not included in the figures; the process can correspond to a method, function, procedure, subroutine, subprogram, and so on.

[0033] The technical solution of the present invention will be further specifically described below through embodiments in conjunction with the accompanying drawings.

[0034] Embodiment: A low-carbon flexible coal-fired power generation system and method of this embodiment, as Figure 1 shown, includes a molten salt side circulation loop and a steam side circulation loop. The steam side circulation loop includes a boiler 5, a steam turbine, and a condenser 6 connected in sequence. The output end of the molten salt side circulation loop is connected to the steam turbine, and the input end of the molten salt side circulation loop is connected to the condenser 6. The steam turbine includes a high-pressure cylinder 4, an intermediate-pressure cylinder 3, and a low-pressure cylinder 2 of the steam turbine connected in sequence. The outlet end of the high-pressure cylinder 4 of the steam turbine is connected to the inlet end of the intermediate-pressure cylinder 3 of the steam turbine after passing through the boiler 5. The outlet end of the low-pressure cylinder 2 of the steam turbine is connected to the condenser 6, and the power output end of the steam turbine is connected to the generator 1.

[0035] The unit can achieve efficient, flexible, and low-carbon operation of the unit by coupling with in-plant renewable electricity in different ways under three modes: normal operating condition, load reduction operating condition, and load increase operating condition.

[0036] S1: First, according to the grid dispatching instruction, determine whether the unit needs to perform load increase / load reduction peak shaving operation. If load increase operation is required, go to S2; if load reduction operation is required, go to S3. If the unit maintains stable operation, go to S4.

[0037] S2: When the unit needs to perform load increase operation, If ΔP ps < F(load), the in-plant green power drives the heat pump system to heat part of the condensate water, reduce the extraction steam flow of the low-pressure heater, and meet the load increase demand of the unit. Further judge P RE and ΔP ps sizes. If P RE > ΔP ps , while the green power drives the heat pump system, the excess green power drives the electric heater to heat the low-temperature molten salt for heat storage. If P RE < ΔP ps, further start the molten salt thermal energy storage system for heat release. The high-temperature molten salt flows out of the high-temperature molten salt tank, heats the feed water through the steam generator, cools down to the low-temperature molten salt, and enters the low-temperature molten salt tank to make up for the output gap of the unit.

[0038] If ΔP ps > F(load), start the heat pump system and at the same time the thermal energy storage system releases heat to produce steam, synergistically increasing the output of the unit. Further judge P RE and the size of F(load). If P RE < F(load), all the green power drives the heat pump; if P RE > F(load), the excess green power drives the electric heater to heat the low-temperature molten salt for heat storage. Wherein, P RE is the renewable electricity power in the plant, ΔP ps is the peak shaving depth required by the unit, and F(load) is the increased load that the unit can achieve when all the low-pressure heaters are shut down with all the condensate water bypassed at different loads.

[0039] S3: When the unit needs to operate at a reduced load, start the molten salt thermal energy storage system, drive the electric heater with part of the electric energy of the unit generator. The low-temperature molten salt flows out of the low-temperature molten salt tank, is heated to high-temperature molten salt by the electric heater, and flows into the high-temperature molten salt tank for storage. The green power in the plant selects the auxiliary unit method according to the following boiler operation state judgment criteria: If P - ΔP ps > P d-w , the green power heats the feed water temperature after the high-pressure heater, increases the feed water temperature at the boiler inlet, and reduces the coal input of the unit; If P - ΔP ps < P d-w , the green power is not coupled with the unit and drives the electric heater to heat the molten salt for energy storage.

[0040] Wherein, P is the load before peak shaving of the unit, and P d-w is the load corresponding to the dry-wet state conversion of the unit boiler.

[0041] S4: When the unit operates at a normal load, the green power heats the feed water temperature after the high-pressure heater, increases the feed water temperature at the boiler inlet, reduces the coal input of the unit, and the unit enters the economizer operation mode.

[0042] The molten salt side circulation loop includes a molten salt electric heater 13, the input end of the molten salt electric heater 13 is connected to a low-temperature molten salt storage tank 12, and the output end of the molten salt electric heater 13 is connected to a high-temperature molten salt storage tank 11, and the input end of the low-temperature molten salt storage tank 12 is connected to the output end of the high-temperature molten salt storage tank 11 through a steam generator 16. For the molten salt side circulation loop, the inlet of the molten salt electric heater is connected to the molten salt pump, the outlet of the molten salt electric heater is connected to the high-temperature molten salt tank, the high-temperature molten salt tank is connected to the steam generator, and the outlet of the steam generator is connected to the low-temperature molten salt tank, forming a molten salt circulation loop. The molten salt electric heater 13 is connected to the in-plant renewable power supply 10 and the plant power supply respectively. The power source consumed by the molten salt electric heater includes the unit plant power supply and the in-plant renewable power supply, and the in-plant renewable power supply is not connected to the power grid.

[0043] The water inlet of the steam generator 16 is connected to the condensate outlet of the condenser 6, and the water outlet of the steam generator 16 is connected to the steam turbine. During the charging process, the molten salt is heated to a high temperature by the electric heater from the low-temperature molten salt tank and flows into the high-temperature molten salt storage tank. During the discharging process, the molten salt is cooled to a low-temperature molten salt by heat exchange with the feed water through the steam generator and flows into the low-temperature molten salt storage tank. The power consumed by the molten salt electric heater comes from the power used by the unit plant and the renewable power in the plant.

[0044] The steam side circulation loop also includes a low-pressure heater 9 and a heat pump 15 respectively connected to the condensate outlet of the condenser 6. For the steam side circulation loop, the outlet of the low-pressure cylinder of the unit is connected to the condenser, the outlet of the condenser is connected to the condensate pump, and the outlet of the condensate pump is connected to the low-pressure heater and the heat pump respectively. The condensate is divided into two streams and heated by the low-pressure heater and the heat pump respectively before entering the deaerator. Among them, a flow regulating valve is provided on the condensate bypass. The outlet of the low-pressure heater 9 and the outlet of the heat pump 15 are connected to the inlet of the deaerator 7, and the outlet of the deaerator 7 is connected to the inlet of the feed water pump. The deaerator is connected to the feed water pump, and the feed water is divided into two streams after the feed water pump. One of them enters the boiler after passing through the high-pressure heater; the other feed water is converted into steam after passing through the steam generator and enters the medium-pressure cylinder. A feed water bypass is provided after the high-pressure heater, and the bypass feed water returns to the main feed water after being heated by the electric heater. Among them, a flow regulating valve is provided on the feed water bypass.

[0045] The outlet of the feedwater pump is connected to the inlet of the steam generator 16, and the outlet of the feedwater pump is connected to the steam turbine through the high-pressure heater 8 and the boiler 5 in turn. The deaerator is connected to the feedwater pump, and the feedwater is divided into two streams after the feedwater pump. One stream enters the boiler after passing through the high-pressure heater; the other stream of feedwater is converted into steam after passing through the steam generator and enters the medium-pressure cylinder. An electric heater 14 is provided between the high-pressure heater 8 and the boiler 5, and the electric heater 14 is respectively connected to the renewable power source 10 in the plant and the plant power. The renewable power source in the plant is not connected to the power grid. The external water outlet of the condenser 6 is connected to the heat pump 15. The condensed water is divided into two streams and heated by the low-pressure heater and the heat pump respectively and then enters the deaerator. The external water of the condenser 6 is circulating cooling water. The heated circulating cooling water enters the heat pump for heat exchange, realizing heat recovery of the unit and reducing the cold end loss of the unit.

[0046] Example 1 A low-carbon flexible coal-fired power generation system based on in-plant renewable electricity assistance includes: boiler, steam turbine, generator, condenser, deaerator, high-pressure heater, low-pressure heater, in-plant renewable power source, high-temperature / low-temperature molten salt storage tank, molten salt electric heater, heat pump, steam generator. The in-plant renewable power source is not connected to the power grid.

[0047] For the molten salt side circulation loop, the inlet of the molten salt electric heater is connected to the molten salt pump, the outlet of the molten salt electric heater is connected to the high-temperature molten salt tank, the high-temperature molten salt tank is connected to the steam generator, and the outlet of the steam generator is connected to the low-temperature molten salt tank, forming a molten salt circulation loop. During the charging process, the molten salt is heated to a high temperature by the low-temperature molten salt tank through the electric heater and flows into the high-temperature molten salt storage tank. During the discharge process, the molten salt is cooled to a low-temperature molten salt through heat exchange with the feed water through the steam generator and flows into the low-temperature molten salt storage tank. The electricity consumed by the molten salt electric heater comes from the unit plant electricity and the renewable electricity in the plant.

[0048] For the steam side circulation loop, the outlet of the unit's low-pressure cylinder is connected to the condenser, the outlet of the condenser is connected to the condensate pump, the outlet of the condensate pump is connected to the low-pressure heater and the heat pump respectively, and the condensate is divided into two streams, which are heated by the low-pressure heater and the heat pump respectively and then enter the deaerator. Among them, a flow regulating valve is installed on the condensate bypass. The deaerator is connected to the feed water pump, and the feed water is divided into two streams after the feed water pump. One of them enters the boiler after passing through the high-pressure heater; the other feed water is converted into steam after passing through the steam generator and enters the medium-pressure cylinder.

[0049] A water supply bypass is provided after the high-pressure heater, and the bypass water supply returns to the main water supply after being heated by the electric heater. Among them, the water supply bypass is provided with a flow regulating valve.

[0050] The operation strategies of low-carbon flexible coal-fired power generation system based on on-site renewable power assistance include: The unit can achieve efficient, flexible, and low-carbon operation through different coupling methods with in-plant renewable electricity under three modes: normal operation mode, load reduction mode, and load increase mode.

[0051] S1: First, according to the grid dispatching instruction, judge whether the unit needs to perform load increase / load reduction peak shaving operation. If load increase operation is required, go to S2; if load reduction operation is required, go to S3. If the unit maintains stable operation, go to S4.

[0052] S2: When the unit needs to perform load increase operation, If ΔP ps <F(load), the in-plant green electricity drives the heat pump system to heat part of the condensate water, reduce the extraction steam flow of the low-pressure heaters, and meet the load increase demand of the unit. Further judge P RE and ΔP ps sizes. If P RE >ΔP ps , while the green electricity drives the heat pump system, the excess green electricity drives the electric heater to heat the low-temperature molten salt for heat storage. If P RE <ΔP ps , further start the molten salt heat storage system to release heat. The high-temperature molten salt flows out of the high-temperature molten salt tank, heats the feed water through the steam generator, cools down to the low-temperature molten salt, and enters the low-temperature molten salt tank to make up for the output gap of the unit.

[0053] If ΔP ps >F(load), start the heat pump system and the heat storage system to release heat and produce steam simultaneously to synergistically increase the output of the unit. Further judge the sizes of P RE and F(load). If P RE <F(load), all the green electricity power drives the heat pump; if P RE >F(load), the excess green electricity drives the electric heater to heat the low-temperature molten salt for heat storage. Where P RE is the in-plant renewable electricity power, ΔP ps is the peak shaving depth required by the unit, and F(load) is the load that the unit can increase when all the low-pressure heaters are shut down and all the condensate water is bypassed at different loads.

[0054] S3: When the unit needs to perform load reduction operation, Start the molten salt heat storage system, drive the electric heater with part of the electric energy of the unit generator, the low-temperature molten salt flows out of the low-temperature molten salt tank, is heated to high-temperature molten salt by the electric heater, and flows into the high-temperature molten salt tank for storage. The in-plant green electricity selects the auxiliary unit method according to the following boiler operation state judgment criteria: If P - ΔP ps >P d-w , the green electricity heats the feed water temperature after the high-pressure heater, increases the feed water temperature at the boiler inlet, and reduces the coal feeding amount of the unit; If P-ΔP ps <P d-w , green electricity is not coupled with the unit, driving the electric heater to heat the molten salt for energy storage.

[0055] Where, P is the pre-peak load of the unit, P d-w It is the corresponding load when the unit boiler is converted from dry to wet state.

[0056] S4: When the unit is operating under normal load, green electricity heats the feed water temperature after the high-pressure heater, which increases the feed water temperature at the boiler inlet, reduces the coal input of the unit, and the unit enters the coal-saving operation mode.

[0057] Example 2 For a certain 660MW unit, 10MW of photovoltaic power was built in the factory, and the capacity of the molten salt heat storage device was 56MW / 56MWh.

[0058] When the unit is running at peak load, the unit output can be increased by 4MW by completely bypassing the condensate water by driving the heat pump with green electricity at a low load of 25% THA; the unit output can be increased by 24MW by completely bypassing the condensate water by driving the heat pump with green electricity at 100% THA; the unit output can be increased by 70MW by activating the heat pump at maximum power at 100% THA and releasing heat and producing steam with the heat storage system at the same time.

[0059] During coal-saving operation, the unit is under 100% THA load, and green electricity heats the boiler feed water temperature, reducing the unit's coal consumption. Calculated based on the average daily utilization hours of photovoltaic power of 5 hours, the daily coal consumption is reduced by 6.2 tons and carbon emissions are reduced by 17.36 tons.

[0060] Advantages of the invention: 1. The present invention constructs renewable electricity in the plant, and the renewable electricity is not directly connected to the power grid. Different coupling methods are used to assist the coal-fired power plant to generate electricity in different operating modes, thereby realizing low-carbon and flexible operation of the unit.

[0061] 2. In the present invention, the heat pump driven by renewable electricity in the plant is used to utilize the waste heat of the circulating cooling water, thereby reducing the cold end loss of the unit, improving the overall energy efficiency of the system, and realizing the economical operation of the entire system.

[0062] 3. The operation strategy of the low-carbon fire-storage peak-shaving system proposed in the present invention can flexibly switch the operation mode for different working conditions by judging the renewable output, the operating status of the unit and the peak-shaving demand. When the unit is operating normally, renewable electricity continuously assists the unit in coal-saving operation; when the unit needs to flexibly peak-shave, the unit can quickly change its load by driving the heat pump with green electricity and releasing energy through the molten salt heat storage system. When peak-shaving is performed on a small scale, the heat pump system can be enabled to bypass the condensed water. When peak-shaving is performed on a large scale, the heat pump and the heat storage system can be enabled at the same time to quickly respond to changing load demands.

[0063] The specific embodiments described herein are merely examples of the spirit of the present invention. The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that technicians in the technical field to which the present invention belongs can make various modifications or supplements to the described specific embodiments or replace them in a similar manner, but will not deviate from the spirit of the present invention or exceed the scope defined in the attached claims. For ordinary technicians in this field, multiple deformations and improvements can also be made without departing from the concept of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A low-carbon flexible coal-fired power generation system, characterized in that: It comprises a molten salt side circulation loop and a steam side circulation loop, wherein the steam side circulation loop comprises a boiler (5), a steam turbine and a condenser (6) connected in sequence, the output end of the molten salt side circulation loop is connected to the steam turbine, and the input end of the molten salt side circulation loop is connected to the condenser (6).

2. A low-carbon flexible coal-fired power generation system according to claim 1, characterized in that: The molten salt side circulation loop comprises a molten salt electric heater (13), the input end of the molten salt electric heater (13) is connected to a low-temperature molten salt storage tank (12), the output end of the molten salt electric heater (13) is connected to a high-temperature molten salt storage tank (11), and the input end of the low-temperature molten salt storage tank (12) is connected to the output end of the high-temperature molten salt storage tank (11) via a steam generator (16).

3. A low-carbon flexible coal-fired power generation system according to claim 2, characterized in that: The water inlet end of the steam generator (16) is connected to the condensed water outlet end of the condenser (6), and the water outlet end of the steam generator (16) is connected to the steam turbine.

4. A low-carbon flexible coal-fired power generation system according to claim 2, characterized in that: The steam side circulation loop also includes a low-pressure heater (9) and a heat pump (15) respectively connected to the condensate outlet end of the condenser (6).

5. A low-carbon flexible coal-fired power generation system according to claim 4, characterized in that: The water outlet of the low-pressure heater (9) and the water outlet of the heat pump (15) are connected to the water inlet of the deaerator (7), the water outlet of the deaerator (7) is connected to the water inlet of the feed water pump, the water outlet of the feed water pump is connected to the water inlet of the steam generator (16), and the water outlet of the feed water pump is connected to the steam turbine through the high-pressure heater (8) and the boiler (5) in sequence.

6. A low-carbon flexible coal-fired power generation system according to claim 1, 4 or 5, characterized in that: The steam turbine comprises a steam turbine high-pressure cylinder (4), a steam turbine medium-pressure cylinder (3) and a steam turbine low-pressure cylinder (2) which are connected in sequence; the gas outlet of the steam turbine high-pressure cylinder (4) is connected to the gas inlet of the steam turbine medium-pressure cylinder (3) after passing through a boiler (5); the gas outlet of the steam turbine low-pressure cylinder (2) is connected to a condenser (6); and the steam turbine power output end is connected to a generator (1).

7. A low-carbon flexible coal-fired power generation system according to claim 5, characterized in that: An electric heater (14) is provided between the high-pressure heater (8) and the boiler (5), and the electric heater (14) is respectively connected to the in-plant renewable power source (10) and the plant power.

8. A method for operating a low-carbon flexible coal-fired power generation system, characterized in that: The following steps are involved: According to the grid dispatching instructions, determine whether the unit needs to increase load / reduce load for peak load regulation. If it needs to increase load, perform the load increase operation; if it needs to reduce load, perform the load reduction operation; if the unit maintains stable operation, enter the coal-saving operation mode.

9. The working method of a low-carbon flexible coal-fired power generation system according to claim 8, characterized in that: The load increase operation specifically includes: when the unit needs to increase load operation, If ΔP ps < F(load), the on-site renewable power source (10) drives the heat pump system to heat part of the condensate water, reduce the extraction steam flow of the low-pressure heater, meet the unit's load increase demand, and further judge P RE and ΔP ps sizes. If P RE > ΔP ps , while the on-site renewable power drives the heat pump system, the excess on-site renewable power drives the electric heater to heat the low-temperature molten salt for heat storage; if P RE < ΔP ps , further start the molten salt heat storage system to release heat. The high-temperature molten salt flows out of the high-temperature molten salt tank, heats the feed water through the steam generator, cools down to the low-temperature molten salt, and enters the low-temperature molten salt tank to make up for the unit output gap; If ΔP ps > F(load), start the heat pump system and at the same time the heat storage system releases heat to produce steam, synergistically improving the unit output; further judge P RE and the magnitude of F(load). If P RE < F(load), all the in-plant renewable electric power drives the heat pump; if P RE > F(load), the excess in-plant renewable electric power drives the electric heater to heat the low-temperature molten salt for heat storage; Where P RE is the renewable power in the plant, ΔP ps is the peak regulation depth required by the unit, F(load) is the load that can be increased when all low-pressure heaters are shut down and all condensing water of the unit is bypassed under different loads.

10. The working method of a low-carbon flexible coal-fired power generation system according to claim 8, characterized in that: The load reduction operation specifically includes: when the unit needs to reduce load, The molten salt heat storage system is started, and part of the electric energy of the unit generator drives the electric heater. The low-temperature molten salt flows out of the low-temperature molten salt tank, is heated to high-temperature molten salt by the electric heater, and flows into the high-temperature molten salt tank for storage. The renewable power source (10) in the plant selects the auxiliary unit mode according to the following boiler operation status judgment criteria: If P-ΔP ps >P d-w , the renewable electricity in the plant heats the feed water temperature after the high-pressure heater (8), so that the feed water temperature at the boiler inlet is increased, and the coal input of the unit is reduced; If P-ΔP ps <P d-w , the renewable electricity in the plant is not coupled with the unit, driving the electric heater to heat the molten salt for energy storage; Where, P is the pre-peak load of the unit, P d-w It is the corresponding load when the unit boiler is converted from dry to wet state.

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