System configuration for flexible operation of coal power unit

Abstract

The utility model provides a system configuration for flexible operation of a coal power unit, which is characterized in that a newly-added external steam cooler is arranged at an existing final-stage high-pressure water supply outlet of a water supply pipeline, a steam side inlet of the newly-added external steam cooler is connected with a pressurization module, and steam lower than a target steam extraction pressure grade is introduced into an inlet of the pressurization module; a steam side outlet of the newly added external steam cooler is communicated with a steam inlet of the existing final-stage high-pressure heater; the steam lower than the target steam extraction pressure grade is pressurized by the pressurization module, firstly enters the newly-added external steam cooler to heat the feed water at the position, and then enters the existing final-stage high-pressure heater to heat the feed water, so that the temperature of the feed water entering the furnace of the unit is increased; and meanwhile, a certain feed water pressure is maintained, so that feed water at an outlet of the economizer is kept at a certain supercooling degree, dry-state operation of the boiler is maintained under the deep peak regulation working condition, the hydrodynamic stability is maintained, and the denitration system is continuously and stably put into operation.

Description

Technical Field

[0001] This utility model relates to the field of power generation technology, and in particular to a system configuration for flexible operation of coal-fired power units. Background Technology

[0002] 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.

[0003] Although the installed capacity and power generation of new energy sources have reached new highs, 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 due to the uncertainty of power generation from new energy sources.

[0004] 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 power grid in this region has now notified the unit 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.

[0005] For ultra-supercritical units that need to participate in deep peak shaving operation, if the load variation range is 20%-100% THA, and the deep peak shaving load range is 20%-30% THA or even lower, the following problems will be faced:

[0006] (1) Under deep peak shaving conditions, the boiler frequently switches between dry and wet states, making the control of coal, water, and air very difficult and drastically increasing the risk of boiler outages.

[0007] (2) Under deep peak shaving conditions, due to the increased under-enthalpy of the feedwater at the water-cooled wall inlet, the hydrodynamic stability of the boiler water-cooled wall is poor, and the risk of water-cooled wall overheating and tube rupture increases sharply.

[0008] (3) Under deep peak-shaving conditions, the economizer outlet flue gas temperature will be lower than the lower limit of the normal operating temperature of the denitrification catalyst, such as 300℃. The denitrification system will then be unable to operate normally, and NO2 is expected to rise. X Emissions will surge and far exceed standard requirements, such as the emission limit being raised 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 / Nm³.3 ;

[0009] (4) Under the wet operation of the boiler, if the water separated from the steam-water separator at the outlet of the boiler water-cooled wall is directly discharged into the atmospheric expansion tank, a large amount of working fluid and its energy will be lost, the unit's energy consumption will increase significantly and the operating economy will decrease significantly.

[0010] Therefore, how to maintain the boiler in dry state operation under deep peak shaving conditions, and maintain hydrodynamic stability and continuous stable operation of the denitrification system, has become an urgent problem to be solved. Utility Model Content

[0011] The technical problem to be solved by this utility model is how to maintain the dry operation of the boiler under deep peak shaving conditions, while maintaining hydrodynamic stability and continuous and stable operation of the denitrification system, and providing a system configuration for flexible operation of coal-fired power units.

[0012] The present invention solves the above-mentioned technical problems through the following technical solution:

[0013] This utility model provides a system configuration for flexible operation of a coal-fired power unit, comprising: a boiler, a deaerator system, a high-pressure cylinder, an existing final-stage high-pressure heater, a feedwater pipeline, and a steam pipeline. The boiler includes an economizer, a water-cooled wall, and a superheater connected sequentially by pipelines. The high-pressure cylinder adopts a partial steam inlet method and is equipped with a regulating stage. In the feedwater pipeline, the deaerator system, the existing final-stage high-pressure heater, and a newly added external steam cooler are sequentially arranged along the feedwater flow direction. The feedwater outlet of the newly added external steam cooler is connected to the boiler feedwater inlet. The steam pipeline includes a main steam pipeline connecting the boiler steam outlet and the high-pressure cylinder steam inlet, and an extraction steam pipeline connecting the high-pressure cylinder extraction steam inlet and the existing final-stage high-pressure heater steam inlet. The main steam pipeline is equipped with a regulating stage steam inlet valve group, and the extraction steam pipeline is equipped with an extraction steam isolation valve. The steam-side inlet of the newly added external steam cooler is connected to a booster module. The inlet of the booster module receives steam at a pressure lower than the target extraction steam pressure level, and the steam-side outlet of the newly added external steam cooler is connected to the steam inlet of the existing final-stage high-pressure heater.

[0014] In this scheme, a new external steam cooler is installed at the feedwater outlet of the existing final-stage high-pressure feedwater pipeline. The steam-side inlet of the new external steam cooler is connected to a booster module. The inlet of the booster module receives steam at a pressure lower than the target extraction pressure level. The steam-side outlet of the new external steam cooler is connected to the steam inlet of the existing final-stage high-pressure heater. The steam at a pressure lower than the target extraction pressure level is boosted by the booster module and first heats the feedwater in the new external steam cooler before heating it in the existing final-stage high-pressure heater. That is, the feedwater is heated twice, in the new external steam cooler and the existing final-stage high-pressure heater, to increase the feedwater temperature entering the boiler. As the feedwater temperature entering the boiler increases, the economizer inlet water temperature increases, which in turn increases the economizer outlet water temperature, and the economizer outlet flue gas temperature increases to meet the denitrification inlet flue gas temperature requirements.

[0015] Preferably, a steam compressor is installed in the pipeline of the booster module. The steam compressor is used to boost the steam entering the booster module that is below the target extraction pressure level, so that the steam below the target extraction pressure level is pressurized by the steam compressor to a pressure higher than the pressure of the final stage extraction steam of the high-pressure cylinder.

[0016] In this scheme, a steam compressor is installed in the pressurization module. The steam compressor pressurizes the steam that is below the target extraction pressure level and first heats the feedwater in the newly added external steam cooler. Then, the feedwater is heated in the existing final stage high-pressure heater. The steam that is below the target extraction pressure level is pressurized by the steam compressor to a pressure higher than the final stage extraction pressure of the high-pressure cylinder. This ensures that the steam pressure entering the newly added external steam cooler after being compressed by the steam compressor is higher than the final stage extraction pressure entering the existing final stage high-pressure heater. This ensures that the feedwater is heated to a higher temperature, thereby improving the boiler feedwater temperature of the unit under deep peak shaving conditions.

[0017] Preferably, when the steam from the steam-side outlet of the newly added external steam cooler enters the existing final stage high-pressure heater to heat the feedwater, the extraction steam isolation valve on the extraction steam pipeline of the existing final stage high-pressure heater is in the closed state, and the steam pressure at the steam-side outlet of the newly added external steam cooler is higher than the extraction steam pressure of the final stage of the high-pressure cylinder.

[0018] In this scheme, the extraction steam isolation valve is in the closed state, and the steam from the steam-side outlet of the newly added external steam cooler is sent into the existing final-stage high-pressure heater to replace the final-stage extraction steam of the high-pressure cylinder. The steam pressure at the steam-side outlet of the newly added external steam cooler is higher than the final-stage extraction steam pressure of the high-pressure cylinder, so that the steam pressure entering the existing final-stage high-pressure heater is higher than the final-stage extraction steam of the high-pressure cylinder, thereby further increasing the feedwater temperature entering the boiler.

[0019] Preferably, a new steam extraction isolation valve is provided in the pipeline of the booster module, and the new steam extraction isolation valve is located upstream of the steam compressor;

[0020] And / or, a heat exchanger is also provided in the pipeline of the booster module, the heat exchanger being located upstream of the steam compressor or between the steam compressor and the newly added external steam cooler.

[0021] In this solution, a new extraction steam isolation valve is installed in the booster module and positioned upstream of the steam compressor. The new extraction steam isolation valve regulates the fluid flow into the booster module. In the event of a failure in the steam compressor, the new external steam cooler, or other equipment, the new extraction steam isolation valve can be closed to prevent steam from entering the booster module, ensuring system safety and improving system operational flexibility.

[0022] A heat exchanger is installed in the pipeline of the booster module. Steam in the pipeline enters the heat exchanger to heat other working media, such as air, water, and coal, before entering the corresponding equipment. For example, after heat exchange, the heat exchanger is located upstream of the steam compressor. Steam with a pressure lower than the target extraction pressure level first 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 newly added external steam cooler to heat the feedwater. This reduces the steam temperature entering the steam compressor and relatively increases the steam flow rate of the newly added external steam cooler. Alternatively, the heat exchanger can be placed between the steam compressor and the newly added external steam cooler. Steam with a pressure lower than the target extraction pressure level is pressurized by the steam compressor before entering the heat exchanger to heat other working media, such as air, water, and coal, before entering the newly added external steam cooler to heat the feedwater. This reduces the steam temperature entering the newly added external steam cooler and relatively increases the steam flow rate of the newly added external steam cooler.

[0023] Preferably, the steam below the target extraction pressure level originates from the final stage extraction steam of the high-pressure cylinder, and the inlet of the booster module is connected to the extraction steam pipeline via a pipeline.

[0024] In this scheme, the steam connected 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. The inlet of the booster module is connected to the existing extraction steam pipeline of the final stage high-pressure heater. After being pressurized by the booster module, the final stage extraction steam of the high-pressure cylinder first goes to the newly added external steam cooler to heat the feedwater there, and then goes to the existing final stage high-pressure heater to heat the feedwater, so as to improve the feedwater temperature of the unit under deep peak shaving conditions.

[0025] Preferably, the interface of the booster module connected to the extraction steam pipeline is located upstream of the extraction steam isolation valve.

[0026] In this scheme, the interface of the booster module to the extraction steam pipeline is located upstream of the extraction steam isolation valve. The final stage extraction steam of the high-pressure cylinder is led out from the front end of the extraction steam isolation valve inlet. When the extraction steam isolation valve is closed, the final stage extraction steam of the high-pressure cylinder can enter the booster module, improving the flexibility of unit operation.

[0027] Preferably, the steam source below the target extraction pressure level is regenerative extraction steam or reheat system steam or superheater system steam in this unit or other units.

[0028] In this scheme, steam below the target extraction pressure level is optimized into reheat extraction steam or reheat system steam or superheater system steam in this unit or other units. Under the premise of ensuring that the steam compressor outlet steam pressure is higher than the final stage extraction steam of the high-pressure cylinder, the operation flexibility of this unit is improved.

[0029] Preferably, the number of valves in the regulating stage inlet valve group is four or six.

[0030] In this scheme, the number of valves in the regulating stage inlet valve group is four or six. By regulating the main steam flow through multiple valves, not only is the flow control accuracy high, but the flow of a single valve is relatively small, which makes the pressure control of the main steam more precise and convenient.

[0031] Preferably, the system is configured to: throttle the main steam using the regulating stage inlet steam valve group to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain degree of subcooling.

[0032] In this scheme, steam below the target extraction pressure level is pressurized by a booster module and then sequentially enters the newly added external steam cooler and the existing final-stage high-pressure heater to heat the feedwater. This is to increase the feedwater temperature at the boiler inlet of the unit under deep peak shaving conditions. At the same time, the main steam is throttled by operating the original regulating stage inlet valves. The purpose is to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain degree of subcooling. Furthermore, the regulating stage inlet valve group can control the main steam while also achieving a certain steam enthalpy drop, thereby relatively improving the unit's economy.

[0033] Preferably, a throttling component is installed in the feedwater or steam pipeline system from the economizer outlet to the high-pressure cylinder inlet, and the throttling component is adjusted to maintain a certain feedwater pressure.

[0034] In this scheme, throttling components, such as regulating valves, can also be installed in the feedwater or steam pipeline from the economizer outlet to the high-pressure cylinder inlet. The throttling components can be adjusted to maintain a certain feedwater pressure, thereby keeping the economizer outlet feedwater at a certain degree of subcooling.

[0035] The positive and progressive effects of this utility model are as follows: a new external steam cooler is installed at the feedwater outlet of the existing final-stage high-pressure feedwater pipeline, and the steam-side inlet of the new external steam cooler is connected to a booster module. The inlet of the booster module is connected to steam with a pressure lower than the target extraction pressure level, and the steam-side outlet of the new external steam cooler is connected to the steam inlet of the existing final-stage high-pressure heater. That is, the feedwater is heated twice, in the new external steam cooler and the existing final-stage high-pressure heater, to increase the feedwater temperature entering the boiler and at the same time maintain a certain feedwater pressure to keep the economizer outlet feedwater at a certain degree of subcooling. This enables the boiler to maintain dry operation under deep peak shaving conditions, and maintains hydrodynamic stability and continuous and stable operation of the denitrification system. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a boiler feedwater heating system in the prior art.

[0037] Figure 2 This is a schematic diagram of the system configuration for flexible operation of a coal-fired power unit according to an embodiment of the present invention. Detailed Implementation

[0038] The present invention will be described more clearly and completely below with reference to the accompanying drawings, using a preferred embodiment.

[0039] Figure 1 This is a schematic diagram of a current boiler feedwater heating system. The system includes a boiler, a deaerator system, a high-pressure cylinder, and an existing final-stage high-pressure heater. The boiler includes an economizer, water-cooled walls, and a superheater connected sequentially via pipelines. The deaerator system includes a deaerator, a pre-pump, and a feedwater pump connected sequentially via pipelines. The feedwater inlet of the existing final-stage high-pressure heater is connected to the feedwater outlet of the deaerator system, and the feedwater outlet of the existing final-stage high-pressure heater is connected to the boiler feedwater inlet. The boiler steam outlet is connected to the high-pressure cylinder via the main steam pipeline, and the steam inlet of the existing final-stage high-pressure heater is connected to the extraction port of the high-pressure cylinder via an extraction steam pipeline. The high-pressure cylinder uses a partial steam inlet method and is equipped with a regulating stage. A regulating stage inlet valve group is arranged on the main steam pipeline, and an extraction steam isolation valve is arranged on the extraction steam pipeline. The low-pressure condensate from the deaerator outlet is pressurized sequentially by the pre-pump and feedwater pump before entering the existing final-stage high-pressure heater for heating. The heated feedwater enters the boiler and is subsequently heated by the economizer, water-cooled walls, and superheater, ultimately producing main steam that enters the high-pressure cylinder to perform work.

[0040] This utility model provides a system configuration for the flexible operation of coal-fired power units, such as... Figure 2As shown, it includes: a boiler, a deaerator system, a high-pressure cylinder, an existing final-stage high-pressure heater, a feedwater pipeline, and a steam pipeline. The boiler includes an economizer, a water-cooled wall, and a superheater connected in sequence via pipelines. The deaerator system includes a deaerator, a pre-pump, and a feedwater pump connected in sequence via pipelines. The high-pressure cylinder adopts a partial steam inlet method and is equipped with a regulating stage. In the feedwater pipeline, the deaerator system, the existing final-stage high-pressure heater, and a newly added external steam cooler are sequentially arranged along the feedwater flow direction. The feedwater outlet of the newly added external steam cooler is connected to the boiler feedwater. The steam pipeline includes a main steam pipeline connecting the boiler steam outlet and the high-pressure cylinder inlet, and an extraction steam pipeline connecting the high-pressure cylinder extraction steam outlet and the existing final-stage high-pressure heater inlet. The main steam pipeline is equipped with a regulating stage inlet valve group, and the extraction steam pipeline is equipped with an extraction steam isolation valve. A booster module is connected to the steam-side inlet of the newly added external steam cooler. The booster module inlet receives steam at a pressure lower than the target extraction steam pressure level, and the steam-side outlet of the newly added external steam cooler is connected to the inlet of the existing final-stage high-pressure heater. The target extraction steam pressure level can be understood as the steam that, if using the existing boiler feedwater heating system (i.e., without a booster module, directly enters the existing final-stage high-pressure heater to heat the feedwater to the required temperature and pressure), is the steam required to heat the feedwater to the required pressure.

[0041] The feedwater is sequentially sent to the boiler feedwater inlet after passing through the deaeration system, the existing final-stage high-pressure heater, and the newly added external steam cooler. At the same time, a certain feedwater pressure is maintained to keep the economizer outlet feedwater at a certain degree of subcooling, so as to maintain the boiler dry operation under deep peak shaving conditions, and maintain hydrodynamic stability and continuous and stable operation of the denitrification system.

[0042] In this embodiment, when increasing the boiler feedwater temperature under deep peak-shaving conditions, the main steam is throttled by operating the regulating stage inlet steam valve group to maintain a certain feedwater pressure and keep the economizer outlet feedwater at a certain subcooling. Compared to the isenthalpic throttling method using valves without a regulating stage, the regulating stage inlet steam valve group achieves the same pressure control effect for the main steam while also obtaining a certain steam enthalpy drop, thus improving the unit's economy. Furthermore, because the flow rate of each valve in the regulating stage inlet steam valve group is relatively small, its pressure control of the main steam is more precise and convenient. Of course, in other embodiments, throttling components, such as regulating valves, can also be installed in the feedwater or steam pipeline from the economizer outlet to the high-pressure cylinder inlet. Adjusting the throttling components maintains a certain feedwater pressure, thereby keeping the economizer outlet feedwater at a certain subcooling.

[0043] This invention introduces steam at a pressure lower than the target extraction pressure level via a booster module, which is then pressurized and fed into a newly added external steam cooler to increase the feedwater temperature of the unit. Compared to the method of replacing the inlet steam of the final stage high-pressure heater with the main steam after cooling and depressurization, this invention saves on the amount of high-temperature and high-pressure pipelines used and avoids 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. 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 solution has advantages such as relative safety, low cost, high operational flexibility, and good economy.

[0044] like Figure 2 As shown, a steam compressor is installed in the pipeline of the booster module. The steam compressor is used to pressurize the steam entering the booster module that is below the target extraction pressure level, so that the pressure of the steam below the target extraction pressure level after being pressurized by the steam compressor is higher than the pressure of the final stage extraction steam of the high-pressure cylinder. After the steam below the target extraction pressure level is pressurized by the steam compressor, it first heats the feedwater in the newly added external steam cooler, and then heats the feedwater in the existing final stage high-pressure heater. The pressure of the steam below the target extraction pressure level after being pressurized by the steam compressor is higher than the pressure of the final stage extraction steam of the high-pressure cylinder. This ensures that the steam pressure entering the newly added external steam cooler after being compressed by the steam compressor is higher than the pressure of the final stage extraction steam entering the existing final stage high-pressure heater, thereby ensuring that the feedwater is heated to a higher temperature to improve the boiler feedwater temperature of the unit under deep peak shaving conditions.

[0045] When the steam from the steam-side outlet of the newly added external steam cooler enters the existing final-stage high-pressure heater to heat the feedwater, the extraction isolation valve on the extraction steam pipeline of the existing final-stage high-pressure heater is in the closed state. The steam pressure at the steam-side outlet of the newly added external steam cooler is higher than the final-stage extraction steam pressure of the high-pressure cylinder. With the extraction isolation valve closed, the steam from the steam-side outlet of the newly added external steam cooler is sent into the existing final-stage high-pressure heater to replace the final-stage extraction steam of the high-pressure cylinder. The steam pressure at the steam-side outlet of the newly added external steam cooler is higher than the final-stage extraction steam pressure of the high-pressure cylinder, resulting in the steam pressure entering the existing final-stage high-pressure heater being higher than the final-stage extraction steam of the high-pressure cylinder, thereby further increasing the feedwater temperature entering the boiler.

[0046] like Figure 2 As shown, a new steam extraction isolation valve is installed in the pipeline of the booster module. The new steam extraction isolation valve is located upstream of the steam compressor. The new steam extraction isolation valve can regulate the flow rate of fluid entering the booster module. In the event of failure of equipment such as the steam compressor or the new external steam cooler, the new steam extraction isolation valve can be closed to prevent steam from entering the booster module, thus ensuring the safety of system operation and improving the flexibility of system operation.

[0047] Of course, a heat exchanger can also be installed in the pipeline of the booster module. The steam in the pipeline enters the heat exchanger to heat other working media, such as air, water, and coal, before entering the corresponding equipment. For example, if the heat exchanger is located upstream of the steam compressor, steam with a pressure lower than the target extraction pressure level first enters the heat exchanger to heat other working media, such as air, water, and coal. After being pressurized by the steam compressor, it then enters the newly added external steam cooler to heat the feedwater. This reduces the steam temperature entering the steam compressor and relatively increases the steam flow rate of the newly added external steam cooler. If the heat exchanger is located between the steam compressor and the newly added external steam cooler, steam with a pressure lower than the target extraction pressure level is pressurized by the steam compressor before entering the heat exchanger to heat other working media, such as air, water, and coal, before entering the newly added external steam cooler to heat the feedwater. This reduces the steam temperature entering the newly added external steam cooler and relatively increases the steam flow rate of the newly added external steam cooler.

[0048] like Figure 2 As shown, the steam entering the booster module at a pressure lower than the target extraction pressure level is the final-stage extraction steam from the high-pressure cylinder of this unit. The booster module inlet connects to the existing extraction steam pipeline for the final-stage high-pressure heater. After being pressurized by the booster module, the final-stage extraction steam from the high-pressure cylinder first heats the feedwater in the newly added external steam cooler, and then heats the feedwater in the existing final-stage high-pressure heater to increase the feedwater temperature into the boiler under deep peak shaving conditions. The interface of the booster module connecting to the extraction steam pipeline is located upstream of the extraction steam isolation valve. The final-stage extraction steam from the high-pressure cylinder is led out from the front end of the extraction steam isolation valve inlet. When the extraction steam isolation valve is closed, the final-stage extraction steam from the high-pressure cylinder can enter the booster module, improving the operational flexibility of the unit.

[0049] Of course, in other embodiments, the steam source below the target extraction pressure level is regenerative extraction steam or steam in the reheat system or superheater system of this unit or other units. Optimizing the steam below the target extraction pressure level to regenerative extraction steam or steam in the reheat system or superheater system of this unit or other units improves the operational flexibility of the unit while ensuring that the steam compressor outlet steam pressure is higher than the final stage extraction steam of the high-pressure cylinder.

[0050] Figure 2 In the regulating stage, the number of valves in the steam inlet valve group is four, but it can also be set to six. By regulating the main steam flow through multiple valves, the main steam flow can be controlled, and a certain steam enthalpy drop can be obtained, which improves the economic efficiency of the unit. Not only is the flow control accuracy high, but the flow of a single valve is relatively small, making the pressure control of the main steam more precise and convenient.

[0051] The flexible operation system configuration for coal-fired power units provided by this utility model, under deep peak shaving conditions (taking 20% ​​THA as an example), allows the boiler feedwater temperature to be increased to 75% THA or even 100% THA. As the boiler feedwater temperature increases, the economizer inlet water temperature rises, leading to an increase in the economizer outlet water temperature and ultimately, an increase in the economizer outlet flue gas temperature, meeting the denitrification inlet flue gas temperature requirements. Simultaneously, a certain feedwater pressure is maintained to ensure a certain degree of subcooling at the economizer outlet. Furthermore, the increase in economizer outlet water temperature also raises the water-cooled wall inlet water temperature, reducing the water-cooled wall inlet enthalpy deficit and enhancing hydrodynamic stability. Moreover, the increased water-cooled wall inlet water temperature allows the water-cooled wall outlet steam to maintain a certain degree of superheat, achieving dry-state boiler operation. This avoids large-scale modifications to the boiler and turbine thermal systems, better adapts to a wide load range for deep grid peak shaving, and simultaneously improves the unit's operational economy and flexibility.

[0052] Taking a 1000MW ultra-supercritical unit with a partial steam inlet in its high-pressure cylinder and a regulating stage as an example, under 20% THA conditions.

[0053] Existing configuration: The main generator load is 200MW. The existing final stage high-pressure heater inlet steam parameters are 1.75MPa and 436℃, and the outlet feedwater parameters are 6MPa and 192℃. The economizer outlet water temperature is 240℃, subcooling is 36℃, under-enthalpy is 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.

[0054] This embodiment's scheme: The main generator load is 200MW. The existing final-stage extraction steam pressure and temperature parameters are 1.04MPa and 342℃. After being pressurized by the steam compressor and de-cooled by the newly added external steam cooler, the existing final-stage high-pressure heater inlet steam pressure and temperature parameters are 5.8MPa and 392℃, and the outlet feedwater pressure and temperature parameters are 12.1MPa and 275℃. The water-side temperature rise of the newly added external steam cooler is 7℃. The economizer outlet water temperature is 307℃, the subcooling degree is 18.3℃, the underenthalpy is 115kJ / kg, and the economizer outlet flue gas temperature is... With a temperature of 312℃ and a superheat of 12℃ at the water-cooled wall outlet, the unit operates in a dry state. The enthalpy deficit of the water-cooled wall inlet water is reduced by 61 kJ / 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. Meanwhile, the inlet and outlet flow rates, pressures, and temperatures of the regulating stage are 610 t / h, 13.2 MPa, and 591℃, and 610 t / h, 6.3 MPa, and 546℃, respectively. The effective enthalpy drop per unit working fluid is 46.9 kJ / kg, corresponding to a power output of 7.9 MW. Compared to the isenthalpic throttling method using valves without a regulating stage, the regulating stage inlet valve group achieves the same pressure control effect for the main steam, resulting in a relatively improved unit economy. Furthermore, because the flow rate of each valve in the regulating stage inlet valve group is relatively small, its pressure control of the main steam is more precise and convenient.

[0055] While specific embodiments of this utility model have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of this utility model is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of this utility model, but all such changes and modifications fall within the scope of protection of this utility model.

Claims

1. A system configuration for flexible operation of a coal-fired power plant, comprising: The boiler, deaerating system, high-pressure cylinder, existing last-stage high-pressure heater, feedwater pipeline and steam pipeline are characterized in that the boiler comprises, in sequence, an economizer, a water wall and a superheater connected by pipelines; the high-pressure cylinder adopts a partial admission mode and is provided with an adjusting stage; in the feedwater pipeline, a deaerating system, an existing last-stage high-pressure heater and a newly-added external steam cooler are arranged in sequence along the flow direction of the feedwater, and a feedwater outlet of the newly-added external steam cooler is connected to a boiler feedwater inlet; the steam pipeline comprises a main steam pipeline connected between a boiler steam outlet and a high-pressure cylinder steam inlet, and a steam extraction pipeline connected between a high-pressure cylinder steam extraction outlet and a steam inlet of the existing last-stage high-pressure heater, and the main steam pipeline is provided with an adjusting stage steam inlet valve group, and the steam extraction pipeline is provided with a steam extraction isolation valve; a steam side inlet of the newly-added external steam cooler is connected to a pressure boosting module, an inlet of the pressure boosting module is connected to steam at a pressure lower than a target steam extraction pressure level, and a steam side outlet of the newly-added external steam cooler is connected to the steam inlet of the existing last-stage high-pressure heater.

2. The system configuration of claim 1, wherein, A steam compressor is arranged in a pipeline of the pressure boosting module, and the steam compressor is used to boost the steam at a pressure lower than the target steam extraction pressure level entering the pressure boosting module, so that the pressure of the steam at a pressure lower than the target steam extraction pressure level after being boosted by the steam compressor is higher than the pressure of the last-stage steam extraction of the high-pressure cylinder.

3. The system configuration of claim 2, wherein, When steam at the steam side outlet of the newly-added external steam cooler enters the existing last-stage high-pressure heater to heat the feedwater, a steam extraction isolation valve on the steam extraction pipeline between the steam inlets of the existing last-stage high-pressure heater is in a closed state, and the steam pressure at the steam side outlet of the newly-added external steam cooler is higher than the last-stage steam extraction pressure of the high-pressure cylinder.

4. The system configuration of claim 2, wherein, A newly-added steam extraction isolation valve is arranged in the pipeline of the pressure boosting module, and the newly-added steam extraction isolation valve is located upstream of the steam compressor. Furthermore, a heat exchanger is arranged in the pipeline of the pressure boosting module, and the heat exchanger is located upstream of the steam compressor or between the steam compressor and the newly-added external steam cooler.

5. The system configuration of claim 4, wherein, The steam at a pressure lower than the target steam extraction pressure level is derived from the last-stage steam extraction of the high-pressure cylinder, and the inlet of the pressure boosting module is connected to the steam extraction pipeline by a pipeline.

6. The system configuration of claim 5, wherein, An interface of the pressure boosting module connected to the steam extraction pipeline is located upstream of the steam extraction isolation valve.

7. The system configuration of claim 4, wherein, The steam at a pressure lower than the target steam extraction pressure level is derived from regenerative extraction steam or steam in a reheat system or superheater system in the unit or other units.

8. The system configuration of claim 1, wherein, The number of valves of the adjusting stage steam inlet valve group is four or six.

9. The system arrangement according to any of the claims 1-8, characterized in that The system is configured to throttle the main steam by using the adjusting stage steam inlet valve group to maintain a certain feedwater pressure and maintain a certain subcooling degree of the feedwater at the economizer outlet.

10. The system arrangement according to any of the claims 1-8, characterized in that A throttling assembly is arranged in the feedwater or steam pipeline from the economizer outlet to the high-pressure cylinder inlet, and the throttling assembly is adjusted to maintain a certain feedwater pressure.

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