Flexible operation system for coal-fired power unit to adapt to deep peak shaving

Abstract

Disclosed is a flexible operation system for a coal-fired power unit to adapt to deep peak shaving. In the system, a pressurization module is connected in a steam inlet pipe between a high-pressure cylinder and an existing final-stage high-pressure heater. The pressurization module is provided with a pressurization device. An inlet of the pressurization module is connected to steam having a pressure level lower than a target steam extraction pressure level. An outlet of the pressurization module is connected to the steam inlet pipe of the existing final-stage high-pressure heater, and the outlet of the pressurization module is located downstream of a steam extraction isolation valve, so that the steam having the pressure level lower than the target steam extraction pressure level is pressurized by the pressurization device and then enters the existing final-stage high-pressure heater to heat feedwater, thereby increasing an in-boiler feedwater temperature of the unit under a deep peak shaving condition, and thus increasing a water temperature at an inlet and a water temperature at an outlet of an economizer and a flue gas temperature at the outlet of the economizer, reducing subcooling enthalpy of an inlet of a water-cooled wall, shortening a hot water section in the water-cooled wall, and maintaining a superheat degree of steam at an outlet of the water-cooled wall, so as to achieve dry-state operation of the boiler of the unit under the deep peak shaving condition, maintain hydrodynamic stability, and maintain continuous and stable operation of a denitration system.

Description

A flexible operation system for coal-fired power units adapted to deep peak shaving

[0001] This application claims priority to Chinese Patent Application No. 2024118558181, filed on December 17, 2024. The entire contents of the aforementioned Chinese Patent Application are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of power generation technology, and in particular to a flexible operation system for coal-fired power units that adapts to deep peak shaving. Background Technology

[0003] Currently, high-parameter, large-capacity, high-efficiency, and low-carbon ultra-supercritical units have become the mainstream choice for new thermal power plant units. For ultra-supercritical units, their capacities are mainly in the 350MW, 660MW, and 1000MW range, with a small number in the 1200MW and 1350MW range.

[0004] New energy installed capacity and power generation have reached new highs. Due to the uncertainty of power generation from new energy sources, traditional thermal power units, especially coal-fired power units, must assume the role of basic backup power supply and flexible peak-shaving power supply to support new energy power generation.

[0005] Taking a 1000MW ultra-supercritical unit as an example, the power grid dispatch load range in this region is 40%-100% THA. The feedwater flow rate of the boiler equipment corresponding to the unit's load is higher than the minimum flow rate required for the boiler to maintain dry operation. Therefore, within the current normal load dispatch range, the boiler always maintains dry operation without any dry-wet transition process. However, with the rapid development of new energy sources, the unit needs to operate under deep peak shaving conditions, and the lower limit of load dispatch needs to be as low as 20%. The feedwater flow rate of the boiler equipment corresponding to 20% load of this unit is already lower than the minimum flow rate required for the boiler to maintain dry operation, and the boiler will have to switch to wet operation. Therefore, the unit faces numerous challenges during operation. For example, under deep peak-shaving conditions, frequent dry-to-wet boiler transitions make coal, water, and air control extremely difficult, drastically increasing the risk of boiler outages. Furthermore, the increased under-enthalpy of the feedwater at the water-cooled wall inlet leads to poor hydrodynamic stability of the boiler water-cooled wall, significantly increasing the risk of overheating and tube rupture. Additionally, under deep peak-shaving conditions, the economizer outlet flue gas temperature will fall below the lower limit of normal operation for conventional denitrification catalysts (e.g., 300℃), preventing the denitrification system from operating normally and leading to anticipated NOx emissions. X Emissions will surge and far exceed standard requirements (e.g., emission limits will be reduced from 25 mg / Nm³). 3 The concentration of Nm2 surged to 200 mg / Nm3 3 The above levels far exceed the standard value of 50 mg / Nm³. 3Under wet operation conditions, if the water separated from the steam-water separator at the boiler's water-cooled wall outlet is directly discharged into the atmospheric expansion tank, it will result in a significant loss of working fluid and energy, leading to a substantial increase in unit energy consumption and a significant decrease in operational economy. Therefore, how to maintain dry operation of the boiler under deep peak-shaving conditions, while ensuring hydrodynamic stability and the continuous and stable operation of the denitrification system, has become an urgent problem to be solved. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to maintain the dry operation of the boiler under deep peak shaving conditions, while maintaining hydrodynamic stability and continuous stable operation of the denitrification system, and to provide a flexible operation system for coal-fired power units to adapt to deep peak shaving.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution:

[0008] This invention provides a flexible operation system for coal-fired power units adapted to deep peak shaving. The system includes a deaerator, a booster pump, a feedwater pump, an existing final-stage high-pressure heater, a boiler, a main steam throttling assembly, a high-pressure cylinder, and an extraction steam isolation valve. Low-pressure condensate from the deaerator outlet is pressurized sequentially by the booster pump and feedwater pump before entering the existing final-stage high-pressure heater for heating. The heated feedwater then enters the boiler and is successively heated by the economizer, water-cooled walls, and superheater heating surfaces, ultimately producing main steam that enters the high-pressure cylinder to perform work. The final-stage extraction steam from the high-pressure cylinder enters the existing final-stage high-pressure heater through an inlet pipe. A high-pressure cylinder inlet valve assembly is arranged on the high-pressure cylinder inlet pipe. The extraction steam isolation valve is arranged on the inlet pipe of the existing final-stage high-pressure heater.

[0009] A booster module is connected to the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater. The booster module is equipped with a booster device in its pipe. The inlet of the booster module receives steam at a pressure lower than the target extraction pressure level. The outlet of the booster module is connected to the steam inlet pipe of the existing final-stage high-pressure heater and is located downstream of the extraction isolation valve. The steam entering the booster module is pressurized by the booster device and then enters the existing final-stage high-pressure heater to increase the boiler feedwater temperature of the unit under deep peak shaving conditions.

[0010] In this scheme, a booster module is connected to the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater, and a booster device is installed in the booster module's pipe. The booster module's inlet is connected to steam below the target extraction pressure level, and the booster module's outlet is connected to the steam inlet pipe of the existing final-stage high-pressure heater. The booster module's outlet is located downstream of the extraction isolation valve. When the booster device pressurizes the steam entering the existing final-stage high-pressure heater, the extraction isolation valve is closed upstream. This allows the steam below the target extraction pressure level entering the booster module to be pressurized by the booster device before entering the existing final-stage high-pressure heater to heat the feedwater, thereby increasing the unit's feedwater temperature under deep peak shaving conditions. This, in turn, increases the economizer inlet water temperature, economizer outlet water temperature, and economizer outlet flue gas temperature, and reduces the water-cooled wall inlet enthalpy deficit. This invention shortens the hot water section in the water-cooled wall and maintains a certain degree of superheat in the steam at the water-cooled wall outlet, ultimately enabling the unit to operate in a dry state under deep peak-shaving conditions, maintain hydrodynamic stability, and ensure the continuous and stable operation of the denitrification system. By introducing steam at a pressure lower than the target extraction pressure level, which is then pressurized by a booster device and enters the existing final-stage high-pressure heater to heat the feedwater, compared to the scheme of using main steam after cooling and depressurization to replace the steam inlet of the final-stage high-pressure heater, this method can save on the amount of high-temperature and high-pressure pipelines used and avoid the negative safety impacts caused by the instantaneous change in the heat absorption ratio of main and reheat steam due to the use of main steam. Furthermore, the extraction steam used in this invention at a pressure lower than the target extraction pressure level has better thermal economy than the main steam that does not perform work in the turbine. Therefore, this scheme has advantages such as relative safety, low cost, high operational flexibility, and good economy.

[0011] Preferably, the pressurizing device is a steam compressor.

[0012] In this scheme, steam below the target extraction pressure level is pressurized and heated by a steam compressor and then enters the existing final-stage high-pressure heater to heat the feedwater, thereby increasing the feedwater temperature of the unit under deep peak shaving conditions.

[0013] Preferably, a heat exchanger is added downstream of the steam compressor. Steam below the target extraction pressure level is pressurized by the steam compressor, then heat-exchanged by the heat exchanger before entering the existing final high-pressure stage.

[0014] And / or, a heat exchanger is added upstream of the steam compressor, so that steam below the target extraction pressure level first enters the heat exchanger for heat exchange before entering the steam compressor.

[0015] In this scheme, a heat exchanger is added downstream of the steam compressor; steam below the target extraction pressure level is pressurized by the steam compressor and then enters the heat exchanger to heat other working media, such as air, water, coal, etc., before entering the existing final stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the existing final stage high-pressure heater and relatively increases the steam flow rate of the existing final stage high-pressure heater.

[0016] A heat exchanger is added upstream of the steam compressor. Steam with a pressure lower than the target extraction pressure level enters the heat exchanger to heat other working media, such as air, water, and coal. After being pressurized by the steam compressor, it enters the existing final-stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the steam compressor and relatively increases the steam flow rate of the existing final-stage high-pressure heater.

[0017] Preferably, a heat exchanger is added downstream of the steam compressor, located on the steam inlet pipe of the existing final stage high-pressure heater or on the pipe of the booster module;

[0018] And / or, an additional heat exchanger may be installed upstream of the steam compressor, located on the inlet pipe of the existing final-stage high-pressure heating system or on the pipe of the booster module.

[0019] In this scheme, the heat exchanger located downstream of the steam compressor and / or the heat exchanger located upstream of the steam compressor can be installed on the inlet pipe of the existing final stage high-pressure heating or on the pipe of the booster module.

[0020] Preferably, the steam supplied to the inlet of the booster module, which is below the target extraction pressure level, is the final stage extraction steam of the high-pressure cylinder of the unit. The inlet of the booster module is connected to the existing final stage high-pressure heating steam inlet pipe and is located upstream of the extraction steam isolation valve.

[0021] In this scheme, the steam supplied to the inlet of the booster module, which is lower than the target extraction pressure level, is the final stage extraction steam of the high-pressure cylinder of the unit. That is, for the existing final stage high-pressure heater and its extraction steam, the final stage extraction steam is pressurized by the steam compressor and then enters the existing final stage high-pressure heater to heat the feedwater. The inlet of the booster module is connected to the steam inlet pipe of the existing final stage high-pressure heater and is located upstream of the extraction steam isolation valve. Upstream of the extraction steam isolation valve, the inlet of the booster module is connected. When the extraction steam isolation valve is closed, the final stage extraction steam of the high-pressure cylinder can enter the booster module, be pressurized, and then enter the existing final stage high-pressure heater to heat the feedwater.

[0022] Preferably, a new extraction steam isolation valve is installed in the existing steam inlet pipe of the final stage high-pressure heater, and the new extraction steam isolation valve is located upstream of the heat exchanger upstream of the steam compressor.

[0023] In this scheme, a new extraction steam isolation valve is installed in the existing steam inlet pipe of the final stage high-pressure heater. The new extraction steam isolation valve is located upstream of the heat exchanger upstream of the steam compressor. That is, when the steam connected to the inlet of the booster module is lower than the target extraction steam pressure level and is used for the final stage extraction steam of the high-pressure cylinder of this unit, the new extraction steam isolation valve is installed at the front end of the heat exchanger upstream of the steam compressor. In the event of equipment failure such as heat exchanger failure, the final stage exhaust steam of the high-pressure cylinder can be disconnected by closing the new extraction steam isolation valve, ensuring the safety of system operation and improving the flexibility of system operation.

[0024] Preferably, the steam below the target extraction pressure level is regenerative extraction steam or reheat system steam or superheater system steam in this unit or other units.

[0025] In this scheme, steam below the target extraction pressure level is optimized to be reheat extraction steam or reheat system steam or superheater system steam in this unit or other units. Under the premise that the steam compressor outlet steam pressure is higher than the existing final stage extraction steam, the operation flexibility of this unit is improved.

[0026] Preferably, the main steam throttling assembly is a high-pressure cylinder inlet steam regulating valve group or a regulating valve.

[0027] In this scheme, the main steam throttling component adopts a high-pressure cylinder inlet steam regulating valve group or regulating valve to facilitate the adjustment of the pressure and flow rate of the main steam.

[0028] Preferably, the flexible operation system is configured to: throttle the main steam using the main steam throttling component to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain degree of subcooling.

[0029] In this scheme, when the steam entering the existing final-stage high-pressure heater is pressurized by the booster module to increase the feedwater temperature of the unit under deep peak shaving conditions, the main steam is throttled by operating the high-pressure cylinder steam inlet valve group. The purpose is to maintain a certain feedwater pressure, keep the economizer outlet feedwater at a certain degree of subcooling, prevent vaporization from occurring while increasing the feedwater temperature, and ensure the normal operation of the unit.

[0030] Preferably, a throttling device is installed in the feedwater or steam pipeline system from the economizer outlet to the high-pressure cylinder inlet to maintain a certain feedwater pressure.

[0031] In this scheme, throttling components, such as regulating valves, can also be installed in the feedwater or steam pipeline system from the economizer outlet to the high-pressure cylinder inlet to maintain a certain feedwater pressure.

[0032] The positive and progressive effects of this invention are as follows: A booster module is connected to the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater, and a booster device is installed in the booster module's pipe. The inlet of the booster module receives steam at a pressure lower than the target extraction pressure level, and the outlet of the booster module is connected to the steam inlet pipe of the existing final-stage high-pressure heater. The outlet of the booster module is located downstream of the extraction isolation valve, so that the steam entering the booster module at a pressure lower than the target extraction pressure level is boosted by the booster device and then enters the existing final-stage high-pressure heater to heat the feedwater, thereby increasing the feedwater temperature of the unit under deep peak shaving conditions, and thus increasing the economizer inlet water temperature, economizer outlet water temperature, and economizer outlet flue gas temperature, while reducing the water-cooled wall temperature. By reducing the inlet enthalpy, shortening the hot water section in the water-cooled wall, and maintaining a certain degree of superheat in the steam at the outlet of the water-cooled wall, the unit can ultimately achieve dry-state operation of the boiler under deep peak shaving conditions, maintain hydrodynamic stability, and ensure the continuous and stable operation of the denitrification system. Compared with the scheme of replacing the inlet steam of the final stage high-pressure heater with the main steam after cooling and depressurization, this scheme can save the amount of high-temperature and high-pressure pipelines used, avoid the negative safety impacts caused by the instantaneous change in the heat absorption ratio of the main and reheat steam due to the use of main steam, and the extraction steam used in this invention is lower than the target extraction steam pressure level, which has better thermal economy than the main steam that does not do work in the turbine. Therefore, this scheme has advantages such as relative safety, low cost, high operational and adjustment flexibility, and good economy. Attached Figure Description

[0033] Figure 1 is a schematic diagram of a boiler feedwater heating system in the prior art.

[0034] Figure 2 is a schematic diagram (I) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0035] Figure 3 is a schematic diagram (II) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0036] Figure 4 is a schematic diagram (III) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0037] Figure 5 is a schematic diagram (IV) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0038] Figure 6 is a schematic diagram (V) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0039] Figure 7 is a schematic diagram (VI) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention.

[0040] Figure 8 is a schematic diagram (VII) of a preferred embodiment of the flexible operation system of a coal-fired power unit adapted to deep peak shaving of the present invention. Detailed Implementation

[0041] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0042] Figure 1 is a schematic diagram of an existing boiler feedwater heating system. The system includes, in sequence, a deaerator, a pre-pump, a feedwater pump, an existing final-stage high-pressure heater, a boiler, a high-pressure cylinder inlet valve assembly, a high-pressure cylinder, and an extraction steam isolation valve. The boiler includes an economizer, water-cooled walls, and a superheater. All these components are connected by pipelines. The high-pressure cylinder inlet valve assembly is located on the high-pressure cylinder inlet pipeline and can regulate the pressure and flow rate of the main steam. The extraction steam isolation valve is also located on the high-pressure cylinder inlet pipeline. The existing final-stage high-pressure heater receives its steam from the final-stage extraction steam of the high-pressure cylinder.

[0043] During system operation: Low-pressure condensate is pressurized by the deaerator, pre-pump, and feedwater pump before entering the existing high-pressure heater for heating. The heated feedwater enters the boiler and is heated by the economizer, water-cooled wall, superheater, and other heating surfaces in sequence, finally producing main steam that enters the high-pressure cylinder to do work.

[0044] To address the aforementioned technical problems, this invention, based on the existing boiler feedwater heating system, connects a booster module to the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater. A booster device is installed in the booster module's pipe. The booster module's outlet is connected to the existing final-stage high-pressure heater's steam inlet pipe and located downstream of the extraction steam isolation valve. By introducing steam at a pressure lower than the target extraction pressure level into the booster module, which is then boosted by the booster device, the steam enters the existing final-stage high-pressure heater to heat the feedwater. This increases the boiler feedwater temperature under deep peak-shaving conditions, thereby increasing the economizer inlet water temperature, economizer outlet water temperature, and economizer outlet flue gas temperature, reducing the water-cooled wall inlet enthalpy deficit, and shortening the hot water section in the water-cooled wall. Simultaneously, the high-pressure cylinder's steam inlet valve group throttles the main steam to maintain a certain feedwater pressure, keeping the economizer outlet feedwater at a certain degree of subcooling. The target extraction pressure level of steam can be understood as steam that, if the existing boiler feedwater heating system is used, directly enters the existing final stage high-pressure heater to heat the feedwater to the required temperature without setting a booster module; the extraction steam source below the target extraction pressure level can be the final stage extraction steam of the high-pressure cylinder of this unit, or other regenerative extraction steam or superheater system steam or reheat system steam of this unit, or regenerative extraction steam or superheater system steam or reheat system steam of other units, or a mixture of the aforementioned steam and other relatively low-pressure steam (such as regenerative extraction steam, reheat steam, etc. of the unit).

[0045] Compared to the scheme of replacing the steam inlet of the final stage high-pressure heater with the main steam after cooling and depressurization, the present invention can save the amount of high-temperature and high-pressure pipeline used, avoid the negative safety impact caused by the instantaneous change in the heat absorption ratio of main steam and reheat steam due to the use of main steam, and the extraction steam used in the present invention is lower than the target extraction steam pressure level, which has better thermal economy than the main steam that does not do work in the turbine. Therefore, the present invention has the advantages of relative safety, low cost, high operational and adjustment flexibility, and good economy.

[0046] Example 1

[0047] Figure 2 shows a schematic diagram of the flexible operation system of the coal-fired power unit adapted to deep peak shaving according to the present invention.

[0048] This invention, based on the existing boiler feedwater heating system, connects a booster module to the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater, and installs a booster device in the booster module's pipe. The outlet of the booster module is connected to the steam inlet pipe of the existing final-stage high-pressure heater and located downstream of the extraction steam isolation valve. By introducing steam at a pressure lower than the target extraction steam level into the booster module, the steam is pressurized by the booster device and then enters the existing final-stage high-pressure heater to heat the feedwater. In this embodiment, the source of the steam at a pressure lower than the target extraction steam level is the final-stage extraction steam from the high-pressure cylinder of the unit. The inlet of the booster module is connected to the steam inlet pipe of the existing final-stage high-pressure heater and located upstream of the extraction steam isolation valve. That is, a booster device is installed in parallel between the inlet and outlet of the extraction steam isolation valve of the steam inlet pipe of the existing final-stage high-pressure heater. The booster device is a steam compressor. After the final-stage extraction steam from the high-pressure cylinder is pressurized, it enters the existing final-stage high-pressure heater to heat the feedwater, thereby increasing the feedwater temperature of the unit under deep peak shaving conditions.

[0049] Compared to the scheme of replacing the inlet steam of the final stage high-pressure heater with the main steam after cooling and depressurization, this scheme can save the amount of high-temperature and high-pressure pipeline used, avoid the negative safety impact caused by the instantaneous change in the heat absorption ratio of main steam and reheat steam due to the use of main steam, and the final stage extracted steam in this scheme has already done work in the steam turbine, so its thermal economy is better than that of main steam that has not done work in the steam turbine. Therefore, this scheme has the advantages of relative safety, low cost, high operational flexibility and good economy.

[0050] For this system, when the unit is operating at partial load, the low-pressure condensate from the deaerator outlet is pressurized by the pre-pump and feedwater pump before entering the existing high-pressure heater for heating. The heated feedwater then enters the boiler and is heated by the economizer, water-cooled wall, superheater, and other heating surfaces in sequence, eventually producing main steam that enters the high-pressure cylinder to do work. The extraction steam isolation valve on the steam inlet pipe of the existing final-stage high-pressure heater is closed, and the final-stage extraction steam from the high-pressure cylinder enters the pressurization module. The steam compressor pressurizes the final-stage extraction steam before it enters the existing final-stage high-pressure heater to heat the feedwater, thereby increasing the feedwater temperature of the unit under deep peak shaving conditions.

[0051] The high-pressure cylinder inlet steam pipe is equipped with a main steam throttling component. In Figure 2, the main steam throttling component is the high-pressure cylinder inlet steam valve group. Of course, a regulating valve can also be used. The high-pressure cylinder inlet steam valve group regulates the pressure and flow rate of the main steam.

[0052] It is important to emphasize that when introducing a booster module to pressurize the final stage extraction steam before it enters the existing final stage high-pressure heater to heat the feedwater, thereby increasing the feedwater temperature at the boiler inlet under deep peak shaving conditions, the main steam is throttled by operating the high-pressure cylinder inlet valve group, maintaining a certain feedwater pressure. This ensures that the feedwater at the economizer outlet has a certain degree of subcooling, which increases the feedwater temperature at the boiler inlet under deep peak shaving conditions. This, in turn, increases the economizer inlet water temperature, economizer outlet water temperature, and economizer outlet flue gas temperature, reduces the underenthalpy at the water-cooled wall inlet, shortens the hot water section in the water-cooled wall, and maintains a certain degree of superheat in the steam at the water-cooled wall outlet. While increasing the feedwater temperature, this also prevents vaporization of the feedwater, ultimately enabling the unit to operate in dry state under deep peak shaving conditions, maintain hydrodynamic stability, and ensure the continuous and stable operation of the denitrification system. It should be noted that throttling components, such as regulating valves, can also be installed in the feedwater or steam pipeline system from the economizer outlet to the high-pressure cylinder inlet to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain degree of subcooling.

[0053] Thus, under deep peak shaving conditions, taking the 20% THA condition as an example:

[0054] The feedwater temperature of the unit can be increased to 75% THA or even 100% THA.

[0055] As the feedwater temperature into the boiler increases, the economizer inlet water temperature rises, leading to an increase in the economizer outlet water temperature and consequently, the economizer outlet flue gas temperature, which meets the denitrification inlet flue gas temperature requirements. While the economizer outlet water temperature increases, a certain feedwater pressure is maintained to ensure a certain degree of subcooling at the economizer outlet. This increase in economizer outlet water temperature also raises the water-cooled wall inlet water temperature, reducing the water-cooled wall inlet underenthalpy and enhancing hydrodynamic stability. Furthermore, the increased water-cooled wall inlet water temperature allows the steam at the water-cooled wall outlet to maintain a certain degree of superheat, thus achieving dry-state boiler operation.

[0056] Example 2

[0057] Figure 3 shows a schematic diagram of the flexible operation system for coal-fired power units adapted to deep peak shaving in this embodiment. Based on Embodiment 1, a heat exchanger is added downstream of the steam compressor. Steam with a pressure lower than the target extraction pressure level is pressurized by the steam compressor, then heat-exchanged by the heat exchanger before entering the existing final-stage high-pressure heater. In Figure 3, the heat exchanger is located on the inlet pipe of the existing final-stage high-pressure heater. Of course, the heat exchanger can also be set on the pipe of the pressurization module, as long as it meets the requirement of heat exchange for the steam pressurized by the steam compressor before entering the existing final-stage high-pressure heater. After the final-stage extraction steam is pressurized by the steam compressor, it enters the heat exchanger to heat other working media, such as air, water, and coal, before entering the existing final-stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the existing final-stage high-pressure heater and relatively increases the inlet steam flow rate of the existing final-stage high-pressure heater.

[0058] Take the data of a 1000MW unit under 20% THA operating conditions as an example.

[0059] Current configuration: The main generator load is 200MW. The existing final stage high-pressure heater has inlet steam parameters of 1.75MPa and 436℃ and outlet feedwater parameters of 6MPa and 192℃. The economizer outlet water temperature is 240℃ (subcooling 36℃, enthalpy deficit 176kJ / kg), and the economizer outlet flue gas temperature is 245℃. The water-cooled wall outlet is wet saturated steam, and the unit is operating in a wet state, so the denitrification system cannot be put into use.

[0060] This patented solution: The main generator load is 200MW. The existing final stage extraction steam parameters are 1.01MPa and 339℃. After being pressurized by the steam compressor and de-cooled by the heat exchanger, the existing final stage high-pressure heater inlet steam parameters are 6.2MPa and 390℃, and the outlet feedwater parameters are 11.9MPa and 279℃. The economizer outlet water temperature is 306℃ (subcooling degree 18℃, enthalpy deficit 112kJ / kg), the economizer outlet flue gas temperature is 311℃, and the water-cooled wall outlet superheat is 12℃. The unit is in a dry state of operation. The enthalpy deficit of the water-cooled wall inlet water is relatively reduced by 64kJ / kg. The steam temperature deviation at the water-cooled wall outlet is controlled, the hydrodynamic stability is enhanced, and the denitrification system is stably and continuously put into operation.

[0061] Example 3

[0062] Figure 4 shows a schematic diagram of the flexible operation system for coal-fired power units adapted to deep peak shaving in this embodiment. Based on Embodiment 1, a heat exchanger is added upstream of the steam compressor. Steam with a pressure lower than the target extraction pressure level first enters the heat exchanger for heat exchange before entering the steam compressor. In Figure 4, this heat exchanger is located on the inlet pipe of the existing final-stage high-pressure heater. Alternatively, the heat exchanger can be located on the pipeline of the booster module, as long as it is located upstream of the steam compressor. The final-stage extraction steam entering the heat exchanger can heat other working media, such as air, water, or coal. After being pressurized by the steam compressor, it enters the existing final-stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the steam compressor and relatively increases the inlet steam flow of the existing final-stage high-pressure heater. Simultaneously, a new extraction steam isolation valve is installed in the inlet pipe of the existing final-stage high-pressure heater, located upstream of the heat exchanger. When the steam supplied to the inlet of the booster module is at a pressure lower than the target extraction pressure level and is used as the final stage extraction steam for the high-pressure cylinder of the unit, an additional extraction steam isolation valve is installed at the front end of the heat exchanger upstream of the steam compressor. This allows the final stage exhaust steam of the high-pressure cylinder to be disconnected by closing the additional extraction steam isolation valve in case of equipment failure such as heat exchanger failure, thus ensuring the safety of system operation and improving the flexibility of system operation.

[0063] Example 4

[0064] Figure 5 shows a schematic diagram of the flexible operation system of the coal-fired power unit adapted to deep peak shaving in this embodiment. Based on Embodiment 1, heat exchangers are added upstream and downstream of the steam compressor, and a new extraction steam isolation valve is installed in the existing steam inlet pipe of the final stage high-pressure heater. The new extraction steam isolation valve is located at the front end of the heat exchanger upstream of the steam compressor.

[0065] The extracted steam enters the heat exchanger to heat other working media, such as air, water, and coal. After being pressurized by the steam compressor, it enters the heat exchanger again to heat other working media, such as air, water, and coal. Then, it enters the existing final-stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the steam compressor and the existing final-stage high-pressure heater, and relatively increases the steam flow rate into the existing final-stage high-pressure heater. The two heat exchanges before and after the steam compressor improve the efficiency of energy utilization in a cascade manner.

[0066] Example 5

[0067] Figure 6 shows a schematic diagram of the flexible operation system of the coal-fired power unit adapted to deep peak shaving in this embodiment. Based on Embodiment 1, the source of the inlet steam for the steam compressor is optimized from the last-stage extraction steam to other regenerative extraction steam of the unit, or steam from the superheater system, or steam from the reheater system, or steam from the regenerative extraction steam of other units. Under the premise that the outlet steam pressure of the steam compressor is higher than that of the existing last-stage extraction steam, the operational flexibility of the unit is improved. At the same time, a heat exchanger is added downstream of the steam compressor. The steam from the steam compressor outlet enters the heat exchanger to heat other working fluids, such as air, water, and coal, before entering the existing last-stage high-pressure heater to heat the feedwater. This reduces the steam temperature entering the existing last-stage high-pressure heater and relatively increases the steam flow rate of the existing last-stage high-pressure heater.

[0068] Example 6

[0069] Figure 7 shows a schematic diagram of the flexible operation system of the coal-fired power unit adapted to deep peak shaving in this embodiment. Based on Embodiment 1, the inlet steam of the steam compressor is optimized from the last-stage extraction steam to other regenerative extraction steam of the unit, or superheater system steam, or reheater system steam of other units. Under the premise that the outlet steam pressure of the steam compressor is higher than that of the existing last-stage extraction steam, the operational flexibility of the unit is improved. At the same time, a heat exchanger is added upstream of the steam compressor. The steam entering the heat exchanger can heat other working fluids, such as air, water, and coal, and then be pressurized by the steam compressor before entering the existing last-stage high-pressure heater to heat the feedwater. This can reduce the steam temperature entering the steam compressor and relatively increase the steam flow rate of the existing last-stage high-pressure heater.

[0070] Example 7

[0071] Figure 8 shows a schematic diagram of the flexible operation system of the coal-fired power unit adapted to deep peak shaving in this embodiment. Based on Embodiment 1, the inlet steam of the steam compressor is optimized from the last-stage extraction steam to other regenerative extraction steam of the unit, or superheater system steam, or reheater system steam of other units. Under the premise that the outlet steam pressure of the steam compressor is higher than that of the existing last-stage extraction steam, the operational flexibility of the unit is improved. At the same time, heat exchangers are added upstream and downstream of the steam compressor. Before entering the steam compressor, the steam first enters the heat exchanger to heat other working media, such as air, water, coal, etc., and then is pressurized by the steam compressor. After being pressurized by the steam compressor, it can enter the heat exchanger to heat other working media, such as air, water, coal, etc., and then enter the existing last-stage high-pressure heater to heat the feedwater. This can reduce the steam temperature entering the steam compressor, reduce the steam temperature entering the existing last-stage high-pressure heater, relatively increase the steam flow rate of the existing last-stage high-pressure heater, and also improve the energy cascade utilization efficiency.

[0072] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

1. A flexible operation system for coal-fired power units adapted to deep peak shaving, characterized in that, The system includes a deaerator, a booster pump, a feedwater pump, an existing final-stage high-pressure heater, a boiler, a main steam throttling assembly, a high-pressure cylinder, and an extraction steam isolation valve. Low-pressure condensate from the deaerator outlet is pressurized sequentially by the booster pump and the feedwater pump before entering the existing final-stage high-pressure heater for heating. The heated feedwater then enters the boiler and is successively heated by the economizer, water-cooled walls, and superheater heating surfaces, ultimately producing main steam that enters the high-pressure cylinder to perform work. The final-stage extraction steam from the high-pressure cylinder enters the existing final-stage high-pressure heater through an inlet pipe. The main steam throttling assembly is installed on the high-pressure cylinder inlet pipe, and the extraction steam isolation valve is installed on the inlet pipe of the existing final-stage high-pressure heater. A booster module is connected in the steam inlet pipe between the high-pressure cylinder and the existing final-stage high-pressure heater. A booster device is installed in the pipe of the booster module. The inlet of the booster module is connected to steam with a pressure lower than the target extraction pressure level. The outlet of the booster module is connected to the steam inlet pipe of the existing final-stage high-pressure heater and is located downstream of the extraction isolation valve. The steam entering the booster module is pressurized by the booster device and then enters the existing final-stage high-pressure heater to increase the feedwater temperature of the unit under deep peak shaving conditions.

2. The flexible operation system as described in claim 1, characterized in that, The booster device is a steam compressor.

3. The flexible operation system as described in claim 2, characterized in that, A heat exchanger is added downstream of the steam compressor. Steam that is lower than the target extraction pressure level is pressurized by the steam compressor, then heats the steam in the heat exchanger before entering the existing final stage high-pressure heater. And / or, a heat exchanger is added upstream of the steam compressor, so that steam below the target extraction pressure level first enters the heat exchanger for heat exchange before entering the steam compressor.

4. The flexible operation system as described in claim 3, characterized in that, The heat exchanger added downstream of the steam compressor is located on the steam inlet pipe of the existing final stage high-pressure heater or on the pipe of the booster module. And / or, the heat exchanger added upstream of the steam compressor is located on the steam inlet pipe of the existing final stage high-pressure heating or on the pipe of the booster module.

5. The flexible operation system as described in claim 4, characterized in that, The steam source at the inlet of the booster module, which is lower than the target extraction pressure level, is the final stage extraction steam from the high-pressure cylinder of the unit. The inlet of the booster module is connected to the existing final stage high-pressure heating steam inlet pipe and is located upstream of the extraction steam isolation valve.

6. The flexible operation system as described in claim 5, characterized in that, A new extraction steam isolation valve is installed in the existing steam inlet pipe of the final stage high-pressure heater. The new extraction steam isolation valve is located at the front end of the heat exchanger upstream of the steam compressor.

7. The flexible operation system as described in claim 3, characterized in that, Steam sources below the target extraction pressure level are reheat extraction steam or reheat system steam or superheater system steam in this unit or other units.

8. The flexible operation system as described in any one of claims 1-7, characterized in that, The main steam throttling component is a high-pressure cylinder inlet steam regulating valve group or regulating valve.

9. The flexible operation system as described in any one of claims 1-8, characterized in that, The flexible operation system is configured to: use the main steam throttling component to throttle the main steam in order to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain degree of subcooling.

10. The flexible operating system according to any one of claims 1-8, characterized in that, A throttling device is installed in the feedwater or steam pipeline system from the economizer outlet to the high-pressure cylinder inlet to maintain a certain feedwater pressure.

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