A DC boiler water supply system and control method for coupling a steam-driven water supply pump group and a hydraulic turbine booster pump group

Abstract

The present invention discloses a DC boiler water supply system and control method that couples a steam-driven water supply pump group and a hydraulic turbine booster pump group. Compared with a conventional DC boiler water supply system, the DC boiler water supply system of the present invention is coupled with a full-flow water supply bypass system including a water supply bypass header, a hydraulic turbine booster pump group, a water storage tank and other equipment, which is put into use during deep peak regulation of the DC boiler. On this basis, a detailed control strategy is elaborated, including control methods for the full-flow water supply bypass system at different stages such as commissioning and dry-wet state conversion. The present invention not only improves the economy and regulation performance of the DC boiler during deep peak regulation, but also increases the inlet flue gas temperature and denitrification efficiency of the SCR denitrification system by increasing the dry-wet state conversion load point of the DC boiler, thereby improving the environmental protection performance of the DC boiler during deep peak regulation.

Description

Technical Field

[0001] The present invention belongs to the field of flexible operation of efficient coal-fired power plants, and in particular to the field of deep peak-shaving operation of supercritical direct current furnaces, and specifically to a direct current furnace water supply system and a control method for coupling a steam-driven water supply pump group and a hydraulic turbine booster pump group. Background Art

[0002] The new power system needs to further improve the high-efficiency regulation capabilities of coal-fired power units, such as deep peak regulation and rapid ramping, improve the regulation capabilities of the power grid, and lay a solid foundation for the consumption of new energy. DC boiler technology has become the main type of high-efficiency coal-fired power units, and the regulation performance of its water supply system is a key factor restricting its deep peak regulation and rapid ramping capabilities. At present, the DC boiler water supply system with steam-driven water supply pumps as the power source faces two main problems in the operation of deep peak regulation:

[0003] The steam-driven feedwater pump unit has high energy consumption and poor regulation ability during deep peak regulation. This is mainly because the feedwater pump flow rate during operation needs to be greater than the minimum flow rate of the corresponding working condition to prevent feedwater pump cavitation and vibration. When the unit is deeply peak shaving, it is generally necessary to open the feedwater pump recirculation valve to ensure that the feedwater pump flow rate meets the requirements. At this time, not only the pressure energy of the recycled feedwater is wasted, but also the pressure difference before and after the feedwater pump recirculation valve is large, the valve core is easily blown and eroded, causing valve internal leakage, and it cannot be operated at a small opening for a long time. In addition, the feedwater pump recirculation valve has poor regulation linearity, and regulation will cause fluctuations in the feedwater flow rate, resulting in a significant reduction in the regulation performance of the feedwater system in the deep peak regulation range. (2) In order to prevent the uneven distribution of the feedwater flow rate on the heating surface of the DC furnace from causing uneven temperature distribution and large thermal stress on the heating surface, the feedwater flow rate entering the furnace water-cooled wall must be higher than its designed minimum flow rate and cannot be reduced synchronously with the furnace heat load. When the unit is deeply peak shaving, the working medium at the outlet of the DC furnace water-cooled wall will change from dry to wet. If the energy in the high-pressure saturated water separated by the vapor-liquid separator at the furnace outlet is not recycled, the energy consumption of the DC boiler will increase significantly when it enters wet operation. If this part of the energy is recovered through the electric boiler water circulation pump configured by the DC boiler startup system, the electric boiler water circulation pump will be frequently started and stopped when the DC furnace is switched between dry and wet states, which places extremely high requirements on the reliability and performance of the boiler water circulation pump motor. In addition, starting and stopping the electric boiler water circulation pump will cause huge disturbances to the water supply system. In severe cases, it will cause the DC furnace to switch frequently between dry and wet states, which is extremely detrimental to boiler safety. This puts greater demands on the regulation performance of the water supply system, exacerbating the contradiction of the reduced regulation capacity of the water supply system in the deep peak regulation interval.

[0004] In summary: the current water supply system with steam-driven water supply pump group as the power source cannot meet the requirements of deep peak regulation operation of DC boiler, which restricts the rapid climbing ability and economic performance of the unit's deep peak regulation. Summary of the invention

[0005] In response to the above-mentioned problems, the present invention is based on the limitations of conventional DC boiler water supply systems using a steam-driven feed water pump group as a power source in the deep peak-shaving period, and invents a DC boiler water supply system and a control method that couples a steam-driven feed water pump group and a hydraulic turbine booster pump group, so as to solve the above-mentioned limitations faced by the DC boiler water supply system using a steam-driven feed water pump group as a power source during deep peak-shaving.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A DC boiler water supply system coupling a steam-driven feed water pump group and a hydraulic turbine booster pump group, wherein the DC boiler water supply system is improved on the basis of a conventional DC boiler water supply system using a steam-driven feed water pump group as a power source, wherein the conventional DC boiler water supply system comprises a deaerator, a steam-driven feed water pump group, a high-pressure heater system, an economizer system, a water-cooled wall system, a steam-water separator, a superheater system and a water storage tank, wherein the outlet of the deaerator is connected to the inlet of the steam-driven feed water pump group, the outlet of the steam-driven feed water pump group is connected to the inlet of the high-pressure heater system, and the high-pressure The outlet of the heater system is connected to the inlet of the economizer system, the outlet of the economizer system is connected to the inlet of the water-cooled wall system, the outlet of the water-cooled wall system is connected to the inlet of the steam-water separator, the steam outlet of the steam-water separator is connected to the superheater system, the liquid phase outlet of the steam-water separator is connected to the inlet of the water storage tank, and the other branch of the outlet of the steam-driven feed water pump group is connected to the inlet of the deaerator through the steam-driven feed water pump recirculation regulating valve to realize feed water recirculation; a full-flow feed water bypass system is set on the main feed water pipeline between the high-pressure heater system and the economizer system.

[0008] Furthermore, the full-flow water supply bypass system includes a water supply bypass manifold and a booster pump which are connected in sequence, the water supply bypass manifold is also connected to the outlet of the water storage tank, the booster pump is connected to a hydraulic turbine for driving, and the inlet and outlet of the hydraulic turbine are respectively connected to the pipelines before and after the steam-driven water supply pump recirculation regulating valve through the hydraulic turbine inlet regulating valve and the hydraulic turbine outlet regulating valve.

[0009] Furthermore, the hydraulic turbine booster pump unit is composed of a hydraulic turbine directly connected to a booster pump through a coupling or a speed change gear box, or directly adopts an integrated hydraulic turbine booster pump. The hydraulic turbine can be regulated by guide vanes or regulating valves to achieve variable frequency regulation.

[0010] Furthermore, a water supply bypass inlet regulating valve is arranged at the inlet of the water supply bypass system, and a water supply bypass outlet regulating valve and a water supply bypass outlet check valve are arranged at the outlet of the water supply bypass system.

[0011] Furthermore, a main water supply pipeline check valve is provided on the main water supply pipeline between the water supply bypass systems to prevent the water supply bypass from flowing back, and an economizer inlet regulating valve is provided on the main water supply pipeline before the economizer system inlet.

[0012] Furthermore, the hydraulic turbine and booster pump are connected to their corresponding inlet pipes through the hydraulic turbine warm-up valve and the booster pump warm-up valve respectively, ensuring that the hydraulic turbine booster pump group is in hot standby state after shutdown and can be put into operation at any time.

[0013] Furthermore, the feed water bypass system is a full-flow bypass. When the feed water bypass system is put into operation, all the feed water entering the economizer system is pressurized through the bypass, and the main feed water pipeline is only used for hot standby.

[0014] Furthermore, the outlet of the superheater system is connected to the steam turbine system, and the steam separated by the steam-water separator enters the superheater system to continue to be heated to the rated temperature, and finally enters the steam turbine system to perform external work.

[0015] Furthermore, the outlet of the water storage tank is divided into two routes, one route is connected to the startup drain system, and a first regulating valve is arranged on its pipeline; the other route is connected to the water supply bypass manifold, and a second regulating valve is arranged on its pipeline.

[0016] The conventional water supply system of a DC boiler is generally as follows: the boiler water supply comes from the deaerator, enters the steam-driven feedwater pump group to increase pressure, enters the high-pressure heater system for heating, enters the economizer system for further heating, enters the water-cooled wall system for further absorption of heat and vaporization, enters the steam-water separator to complete steam-water separation, and the separated steam enters the superheater system to continue heating to the rated temperature, and finally enters the steam turbine system to perform external work. After separation, the saturated water enters the water storage tank, and then enters the startup drain system, which is recovered by the boiler water pump or discharged to the drain expansion tank. The outlet of the steam-driven feedwater pump is connected to the deaerator through the steam-driven feedwater pump recirculation regulating valve to achieve feedwater recirculation.

[0017] The difference between the present invention and the conventional water supply system of the DC furnace is that: a full-flow water supply bypass is designed to improve the flexibility of the DC furnace water supply system. Its starting point is the main water supply pipeline after the high-pressure heater system, and the end point is the main water supply pipeline before the economizer inlet regulating valve. The water supply bypass is connected to the water supply bypass header and the booster pump and other equipment in sequence. The water supply bypass header is also connected to the water storage tank to collect the drain water in the water storage tank, which is mixed with the water supply introduced by the water supply bypass and then sent to the booster pump for pressure increase. The booster pump is driven by a hydraulic turbine. The inlet and outlet of the hydraulic turbine are respectively connected to the pipelines before and after the recirculation regulating valve of the steam-driven water supply pump through regulating valves. Its power water source is the high-pressure water supply at the outlet of the steam-driven water supply pump.

[0018] The present invention also proposes a control method for a DC boiler water supply system coupling a steam-driven water supply pump group and a hydraulic turbine booster pump group as described above, comprising the following features:

[0019] When the DC boiler load is high and the feed water flow is greater than the minimum flow of the steam-driven feed water pump, the full-flow feed water bypass does not participate in the feed water regulation, the hydraulic turbine inlet regulating valve, the feed water bypass inlet regulating valve, and the second regulating valve from the water storage tank to the feed water bypass header are closed, the hydraulic turbine outlet regulating valve and the feed water bypass outlet regulating valve, the hydraulic turbine warm-up valve, and the booster pump warm-up valve are opened, and the system is in hot standby state;

[0020] When the DC boiler begins to perform deep peak regulation, when the feed water flow rate approaches the minimum flow rate of the steam-driven feed water pump, the full-flow feed water bypass is merged into the feed water system, and the full-flow feed water is gradually introduced. After the merging process is completed, the main feed water pipeline is only in hot standby mode, and no feed water is circulated. The merging method is: before merging, close the hydraulic turbine warm-up valve and the booster pump warm-up valve, fully open the hydraulic turbine inlet regulating valve and the feed water bypass inlet regulating valve, and close the hydraulic turbine outlet regulating valve and the feed water bypass outlet regulating valve to the set small opening; then, by opening the hydraulic turbine inlet guide vane or regulating valve, slowly increase the speed of the hydraulic turbine booster pump group to the set speed, and then gradually fully open the feed water bypass outlet regulating valve to introduce all the feed water in the main pipeline into the feed water bypass; during the merging process, the hydraulic turbine outlet regulating valve automatically follows and adjusts the hydraulic turbine outlet pressure to control it above the saturation pressure corresponding to the hydraulic turbine outlet temperature;

[0021] After the full-flow water supply bypass is incorporated into the water supply system, the hydraulic turbine booster pump group automatically controls the pressure difference before and after the booster pump, and the control target value is the pressure difference between the booster pump outlet and the water tank. The control target of the pneumatic water supply pump group remains unchanged and is still the water supply flow rate. The target value is output by the water supply main control.

[0022] When the DC furnace further performs deep peak regulation and the water supply flow rate approaches the minimum flow rate of the water-cooled wall, the water supply flow rate target value output by the water supply master control is the sum of the minimum flow rate of the water-cooled wall and a certain value, and no longer decreases synchronously with the load. The larger the fixed value, the larger the water supply flow rate entering the DC furnace, the load point at which the DC furnace switches to wet operation will increase synchronously, and the inlet flue gas temperature of the SCR denitrification system will also increase synchronously. The operating parameters that meet the minimum requirements for the inlet flue gas temperature of the SCR denitrification system can be obtained through field tests, and the difference between the corresponding water supply flow rate and the minimum flow rate of the water-cooled wall is the fixed value.

[0023] When the DC boiler further performs deep peak regulation, with the decrease of furnace heat load, the steam superheat at the outlet of the steam-water separator gradually decreases to 0, and the water-cooled wall enters wet operation; at this time, the second regulating valve from the water storage tank to the feedwater bypass header is gradually fully opened to recover the working fluid energy; the control mode of the steam-driven feedwater pump group is changed from controlling the feedwater flow to controlling the liquid level in the water storage tank to stabilize it at the set value; the control mode of the hydraulic turbine booster pump group is changed from controlling the pressure difference before and after the booster pump to controlling the feedwater flow, and the target value remains unchanged, which is still the sum of the minimum flow of the water-cooled wall and a certain value. The control mode of the feedwater system after switching is similar to that of the subcritical drum boiler, and the technology is mature and reliable; at the same time, before and after the control mode is switched, the head and flow corresponding to the steam-driven feedwater pump and the hydraulic turbine booster pump remain basically unchanged, and the control target values ​​such as the speed are continuous and stable, and will not change suddenly, so the switching process is non-disturbing to the steam-driven feedwater pump group and the hydraulic turbine booster pump group, and the relevant parameters of the feedwater system will not fluctuate, and the regulation accuracy is high. At the same time, during the switching process, the hydrophobic energy in the water storage tank can be collected throughout the process without throttling or external discharge, which will not affect the energy consumption during the dry-wet state conversion of the DC furnace.

[0024] The beneficial effects of the present invention in terms of economy, flexibility, environmental protection, reliability, etc. of DC furnace deep peak regulation are as follows:

[0025] (1) The hydraulic turbine booster pump group uses the pressure energy of the steam-driven feedwater pump recirculating water as an additional power source for the feedwater system. During the deep peak regulation period, there is no need to open the recirculation valve of the steam-driven feedwater pump. Compared with the conventional DC boiler feedwater system, it not only avoids the problems of poor reliability and adjustment accuracy of the recirculation valve, but also reduces the head of the steam-driven feedwater pump, so that its working point moves to the optimal efficiency working point, improves the efficiency of the steam-driven feedwater pump, and greatly reduces the energy consumption of the feedwater system. At the same time, during the dry-wet state conversion of the DC boiler and when it is in wet state operation, the drain energy in the water storage tank is collected throughout the process without throttling or external discharge. Compared with the dry state, the energy consumption will not be reduced, which lays the foundation for increasing the load point for transitioning to wet state operation, and helps to solve the problem of reduced denitrification efficiency and increased ammonia escape rate due to insufficient inlet flue gas temperature in the SCR denitrification system.

[0026] (2) The DC boiler water supply system of the coupled hydraulic turbine booster pump group is non-disturbing to the water supply system, whether it is incorporated into the water supply system at the initial stage of deep peak regulation or during the control mode switching process during the dry-wet state conversion of the DC boiler at the later stage of deep peak regulation. The relevant parameters will not be disturbed, the automatic control is simple, the reliability is high, and the water supply system can be continuously adjusted throughout the process, thereby improving the unit's rapid climbing ability during deep peak regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a system flow chart of the present invention;

[0028] In the figure: 1. Deaerator; 2. Steam-driven feedwater pump group; 3. High-pressure heater system; 4. Economizer inlet regulating valve; 5. Economizer system; 6. Water-cooled wall system; 7. Steam-water separator; 8. Superheater system; 9. Steam-water separator outlet check valve; 10. Water storage tank; 11. First regulating valve; 12. Steam-driven feedwater pump recirculation regulating valve; 13. Hydraulic turbine; 14. Booster pump; 15. Hydraulic turbine inlet regulating valve; 16. Hydraulic turbine outlet regulating valve; 17. Hydraulic turbine warm-up valve; 18. Booster pump warm-up valve; 19. Feedwater bypass inlet regulating valve; 20. Feedwater bypass header; 21. Feedwater bypass outlet regulating valve; 22. Second regulating valve; 23. Feedwater bypass outlet check valve; 24. Main feedwater pipeline check valve. DETAILED DESCRIPTION

[0029] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0030] The conventional direct current boiler feed water system is as follows: the boiler feed water comes from the deaerator 1, enters the steam-driven feed water pump group 2 for boosting, enters the high-pressure heater system 3 for heating, then enters the economizer system 5 through the economizer inlet regulating valve 4 for further heating, enters the water-cooled wall system 6 for further absorption of heat and vaporization, enters the steam-water separator 7 to complete the steam-water separation, and the separated steam enters the superheater system 8 for further heating to the rated temperature, and finally enters the turbine system to perform external work. After separation, the saturated drain enters the water storage tank 10 through the check valve 9 at the outlet of the steam-water separator. The water level of the water storage tank 10 is controlled by the first regulating valve 11 to discharge the drain to the startup drain system. The drain discharged to the startup drain system is recovered by the boiler water pump to the inlet of the economizer system 5 or discharged to the drain expansion tank. The outlet of the steam-driven feed water pump is connected to the deaerator 1 through the steam-driven feed water pump recirculation regulating valve 12 to realize the feed water recirculation.

[0031] The DC boiler water supply system of the present invention is different from the conventional system in that a full-flow water supply bypass is designed. Figure 1As shown, the starting point is the main water supply pipeline after the high-pressure heater system 3, and the end point is the main water supply pipeline before the economizer inlet regulating valve 4. The water supply bypass is connected to the water supply bypass header 20 and the booster pump 14 and other equipment in sequence. The water supply bypass header 20 is also connected to the water storage tank 10, collects the drain water in the water storage tank 10, mixes it with the feed water introduced by the water supply bypass, and then sends it to the booster pump 14 for pressure increase. The pipeline between the water supply bypass header 20 and the water storage tank 10 is provided with a second regulating valve 22 to participate in the water level regulation of the water storage tank 10. The booster pump 14 is driven by the hydraulic turbine 13, and the hydraulic turbine inlet and outlet are respectively connected to the pipeline before and after the steam-driven feed water pump recirculation regulating valve 12 through the hydraulic turbine inlet regulating valve 15 and the hydraulic turbine outlet regulating valve 16, and its power water source is the high-pressure feed water at the outlet of the steam-driven feed water pump group 2. A small warm-up pump bypass and a booster pump warm-up pump valve 18 are set in the pipelines before and after the feed water bypass inlet regulating valve 19, and a small warm-up machine bypass and a hydraulic turbine warm-up machine valve 17 are set between the pipeline before the hydraulic turbine inlet regulating valve 15 and the hydraulic turbine 13 to ensure that the hydraulic turbine 13 and the booster pump 14 are in hot standby state. A feed water bypass inlet regulating valve 19 is set at the feed water bypass inlet, and a feed water bypass outlet regulating valve 21 and a feed water bypass outlet check valve 23 are set in sequence at the feed water bypass outlet to participate in the regulation of the feed water bypass. A main feed water pipeline check valve 24 is set on the main feed water pipeline between the feed water bypasses to prevent the feed water of the feed water bypass from flowing back.

[0032] The hydraulic turbine booster pump group is composed of a hydraulic turbine 13 directly connected to a booster pump 14 through a coupling or a speed change gear box, or directly adopts an integrated structure turbine booster pump. The hydraulic turbine 13 can be regulated by guide vanes or regulating valves to achieve variable frequency operation. The regulation performance is better than that of an electric boiler water circulation pump operating at a fixed frequency, which improves the regulation performance of the water supply system during deep peak regulation.

[0033] There are two main types of hydraulic turbines in this embodiment: the first type is the most widely used reverse pump. Ordinary pumps with a specific speed between 35 and 500 can be used as reverse pumps. According to the classification of impeller structure, radial flow and mixed flow pumps are often used as hydraulic (hydraulic) turbines. The advantages are that the operating conditions of the reverse pump meet the system requirements, low cost, high reliability, and have been widely used in pumped storage power stations. The technical risk is small and the reliability has been verified. The second type is an impact hydraulic turbine suitable for small flow and high head. By changing the guide vane opening, the speed and output are adjusted. The adjustment performance is excellent, and the currently developed high head and small flow power station turbine technology can be used. In addition, the hydraulic turbine booster pump group in this embodiment can also directly adopt a hydraulic turbine booster pump with an integrated structure. The advantages are that the hydraulic turbine and the booster pump adopt an integrated design, and the comprehensive performance and overall efficiency are higher than the ordinary hydraulic turbine booster pump combination. The overall efficiency can reach more than 80%, and it has been widely used in petrochemical processes.

[0034] When selecting the hydraulic turbine booster pump unit in the present invention, the high-efficiency flow and lift point of the booster pump are the actual feed water flow entering the economizer system 5 during deep peak regulation of the unit, and the actual pressure drop between the corresponding feed water bypass outlet position and the steam-water separator 7. At the same time, its efficiency and lift curves should be as flat as possible. The designed working pressure head of the hydraulic turbine is the pressure difference before and after the steam-driven feed water pump during deep peak regulation, and the flow rate is calculated according to the output required by the booster pump. When the optimal operating speed points of the hydraulic turbine and the booster pump are close, they can be directly connected through a coupling; when the difference is large, they can be connected through a variable speed gearbox, and generally a fixed ratio type with high reliability is adopted.

[0035] The water source of the booster pump 14 in the present invention comes from the bypass header, which combines the saturated drain in the water tank 10 and all the subcooled feed water at the outlet of the high-pressure heater system 3. Compared with the inlet working medium of the conventional electric boiler water circulation pump of the boiler starting system (generally a mixture of saturated drain in the water tank 10 and part of the subcooled feed water), its temperature is significantly reduced, the effective cavitation margin of the booster pump inlet is significantly increased, and it is not easy to cavitation. Its working environment is significantly improved compared with the boiler water pump, the selection range is significantly widened, and the cost is effectively controlled.

[0036] The feed water bypass described in the present invention is a full-flow bypass. When the feed water bypass is put into operation, all the feed water entering the economizer is pressurized through the bypass, and the main feed water pipeline is only used for hot standby. The purpose of setting a warm-up (pump) valve to connect the hydraulic turbine booster pump group with its inlet pipeline is to ensure that it is in hot standby state after shutdown and can be put into operation at any time, which is beneficial to improving the climbing performance and regulation rate of the unit during deep peak regulation.

[0037] In this embodiment, the inlet and outlet of the hydraulic turbine 13 are respectively connected to the pipelines before and after the steam-driven feed water pump recirculation regulating valve 12, and a hydraulic turbine inlet regulating valve 15 and a hydraulic turbine outlet regulating valve 16 are respectively arranged in the inlet and outlet pipelines of the hydraulic turbine 13 to participate in the regulation and control. The purpose of arranging the hydraulic turbine outlet regulating valve 16 at the hydraulic turbine outlet is to control the pressure inside the hydraulic turbine 13 so that it is higher than the saturation pressure corresponding to the corresponding temperature, so as to prevent the feed water in the hydraulic turbine 13 from vaporizing and affecting the stable operation of the unit. The working water source of the hydraulic turbine 13 is the deoxygenated feed water, and the non-condensable gas in the water has been removed. As long as the feed water is guaranteed not to vaporize, the hydraulic turbine is not prone to cavitation, and its working environment will be better than that of a general turbine.

[0038] The control method of the DC boiler water supply system coupling the steam-driven water supply pump and the hydraulic turbine booster pump is as follows:

[0039] The DC boiler load is high, the feed water flow is greater than the minimum flow of the steam-driven feed water pump, the full-flow feed water bypass does not participate in the feed water regulation, and the feed water system operates in a conventional manner. The hydraulic turbine inlet regulating valve 15 and the feed water bypass inlet regulating valve 19, and the second regulating valve 22 from the water storage tank 10 to the feed water bypass header 20 are closed, the hydraulic turbine outlet regulating valve 16 and the feed water bypass outlet regulating valve 21, the hydraulic turbine warm-up valve 17, and the booster pump warm-up valve 18 are opened, and are in hot standby state;

[0040] When the DC boiler starts deep peak regulation, when the water supply flow rate is close to the minimum flow rate of the steam-driven water supply pump, the full-flow water supply bypass is merged into the water supply system, and the full-flow water supply is gradually introduced. After the merging process is completed, the main water supply pipeline is only in hot standby without water supply circulation. The specific incorporation method is as follows: before incorporation, close the hydraulic turbine warm-up valve 17 and the booster pump warm-up valve 18, fully open the hydraulic turbine inlet regulating valve 15 and the feed water bypass inlet regulating valve 19, and close the hydraulic turbine outlet regulating valve 16 and the feed water bypass outlet regulating valve 21 to a set small opening; then slowly increase the speed of the hydraulic turbine booster pump group to the set speed by opening the hydraulic turbine 13 inlet guide vane or regulating valve, and then gradually fully open the feed water bypass outlet regulating valve 21 to introduce all the feed water in the main pipeline into the feed water bypass; during the incorporation process, the hydraulic turbine outlet regulating valve 16 automatically follows and adjusts the hydraulic turbine outlet pressure to control it above the saturation pressure corresponding to the hydraulic turbine outlet temperature; finally, the hydraulic turbine booster pump group automatically controls the pressure difference before and after the booster pump 14, and the control target value is the pressure difference between the outlet of the booster pump 14 and the water storage tank 10; the control target of the steam-driven feed water pump group 2 remains unchanged, which is still the feed water flow, and the target value is output by the feed water main control.

[0041] In this embodiment, the full-flow feedwater bypass is selected to be incorporated into the water supply system before the feedwater flow approaches the minimum flow of the steam-driven feedwater pump, which can not only prevent the steam-driven feedwater pump from entering the dangerous range, but also calmly deal with the risks of the merging process. The main reasons are: at this time, the feedwater flow of the DC boiler is relatively large, and it is running in a dry state, and its own anti-interference ability is relatively strong; and during the merging process, the input power of the steam-driven feedwater pump group 2 gradually increases, and its main feedwater bypass is in a connected and hot standby state; during the merging process, if the hydraulic turbine booster pump group exits operation due to a fault, the steam-driven feedwater pump can automatically send the feedwater to the boiler through the main pipeline, and the restored feedwater flow is greater than the flow before merging, which can prevent the fluctuation of the feedwater flow during the merging process from causing the DC boiler to overheat or trigger the DC boiler water cut-off protection.

[0042] In this embodiment, before the full-flow water supply bypass is incorporated, the water supply bypass outlet regulating valve 21 is switched from full switch to a set small opening, mainly to reduce the torque and power of the booster pump 14 at the initial start-up, which is conducive to the rapid speed increase of the hydraulic turbine booster pump group and entering a stable and safe working range. The set opening can be determined in combination with factors such as valve flow characteristics and hydraulic turbine booster pump group power characteristics.

[0043] When the DC furnace is further deeply peak-regulated and the feed water flow rate approaches the minimum flow rate of the water-cooled wall, the target value of the feed water flow rate output by the feed water master control is the sum of the minimum flow rate of the water-cooled wall and a certain value, and it will no longer decrease synchronously with the load. The larger the fixed value, the larger the feed water flow rate entering the DC furnace, the load point at which the DC furnace switches to wet operation will increase synchronously, and the inlet flue gas temperature of the SCR denitrification system will also increase synchronously. The operating parameters that meet the minimum requirements for the inlet flue gas temperature of the SCR denitrification system can be obtained through field tests. The corresponding difference between the feed water flow rate and the minimum flow rate of the water-cooled wall is the fixed value, which helps to solve the problem of reduced denitrification efficiency and increased ammonia escape rate due to insufficient inlet flue gas temperature in the SCR denitrification system.

[0044] When the DC furnace is further deeply peaked, with the decrease of furnace heat load, the steam superheat at the outlet of the steam-water separator 7 gradually decreases to 0, and the water-cooled wall enters wet operation; at this time, the second regulating valve 22 from the water storage tank 10 to the feed water bypass header 20 is gradually fully opened to recover the working fluid energy; the control mode of the steam-driven feed water pump group 2 is changed from controlling the feed water flow to controlling the liquid level in the water storage tank 10, so that it is stable at the set value; the control mode of the hydraulic turbine booster pump group is changed from controlling the pressure difference before and after the booster pump 14 to controlling the feed water flow, and the target value remains unchanged, which is still the sum of the minimum flow of the water-cooled wall and a certain value. The control mode of the water supply system after switching is similar to that of the subcritical drum boiler, and the technology is mature and reliable. At the same time, before and after the control mode is switched, the head and flow corresponding to the steam-driven feed water pump and the hydraulic turbine booster pump remain basically unchanged, and the control target values ​​such as the rotation speed are continuous and stable, and will not change suddenly, so the switching process is non-disturbing to the steam-driven feed water pump group 2 and the hydraulic turbine booster pump group, and the relevant parameters of the water supply system will not fluctuate, and the regulation accuracy is high. At the same time, during the switching process, the drain water in the water tank 10 can be collected throughout the process without throttling or external discharge, which will not affect the energy consumption during the dry-wet state conversion of the DC furnace. The load point for switching to wet operation can be freely set, which greatly improves the economy and flexibility of the DC furnace during the deep peak-shaving period.

[0045] In this embodiment, after the feed water bypass is incorporated into the feed water system, the feed water entering the economizer system 5 comes from the feed water bypass header 20 and is boosted by the hydraulic turbine booster pump group. After the DC furnace is switched to wet operation, its flow rate is controlled at a fixed value and remains basically unchanged. However, as the load of the DC furnace is further reduced, the proportion of drain water in the water storage tank 10 collected by the feed water bypass header 20 increases, and the proportion of feed water from the high-pressure heater system 3 decreases synchronously, resulting in a gradual increase in the feed water temperature entering the economizer, and the corresponding SCR denitrification system inlet flue gas temperature is also increased synchronously, which greatly alleviates the environmental protection dilemma of the SCR denitrification system during the deep peak regulation period, which is caused by the inlet flue gas temperature not meeting the requirements and the increase in the ammonia escape rate.

[0046] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A direct current boiler water supply system coupling a steam-driven water supply pump group and a hydraulic turbine booster pump group, characterized in that: The DC boiler water supply system is improved on the basis of a conventional DC boiler water supply system using a steam-driven water supply pump group as a power source. The conventional DC boiler water supply system comprises a deaerator (1), a steam-driven water supply pump group (2), a high-pressure heater system (3), an economizer system (5), a water-cooled wall system (6), a steam-water separator (7), a superheater system (8) and a water storage tank (10). The outlet of the deaerator (1) is connected to the inlet of the steam-driven water supply pump group (2), the outlet of the steam-driven water supply pump group (2) is connected to the inlet of the high-pressure heater system (3), and the outlet of the high-pressure heater system (3) is connected to the economizer system (5). The inlet of the steam-driven feedwater pump group (2) is connected, the outlet of the economizer system (5) is connected to the inlet of the water-cooled wall system (6), the outlet of the water-cooled wall system (6) is connected to the inlet of the steam-water separator (7), the steam outlet of the steam-water separator (7) is connected to the superheater system (8), the liquid outlet of the steam-water separator (7) is connected to the inlet of the water storage tank (10), and the other branch of the outlet of the steam-driven feedwater pump group (2) is connected to the inlet of the deaerator (1) through the steam-driven feedwater pump recirculation regulating valve (12) to realize feedwater recirculation; a full-flow feedwater bypass system is arranged on the main feedwater pipeline between the high-pressure heater system (3) and the economizer system (5); The full-flow water supply bypass system comprises a water supply bypass header (20) and a booster pump (14) which are connected in sequence. The water supply bypass header (20) is also connected to the outlet of the water storage tank (10). The booster pump (14) is connected to a hydraulic turbine (13) for driving. The inlet and outlet of the hydraulic turbine (13) are respectively connected to the pipelines before and after the steam-driven water supply pump recirculation regulating valve (12) through a hydraulic turbine inlet regulating valve (15) and a hydraulic turbine outlet regulating valve (16).

2. A direct current boiler water supply system coupling a steam-driven water supply pump unit and a hydraulic turbine booster pump unit according to claim 1, characterized in that: The hydraulic turbine booster pump assembly is composed of a hydraulic turbine (13) directly connected to a booster pump (14) via a coupling or a speed change gear box, or directly adopts an integrated hydraulic turbine booster pump. The hydraulic turbine (13) can be regulated by guide vanes or a regulating valve to achieve variable frequency regulation.

3. A direct current boiler water supply system coupling a steam-driven water supply pump group and a hydraulic turbine booster pump group according to claim 2, characterized in that: A feed water bypass inlet regulating valve (19) is provided at the inlet of the feed water bypass system, and a feed water bypass outlet regulating valve (21) and a feed water bypass outlet check valve (23) are provided at the outlet of the feed water bypass system; a main feed water pipeline check valve (24) is provided on the main feed water pipeline between the feed water bypass systems, and an economizer inlet regulating valve (4) is provided on the main feed water pipeline before the inlet of the economizer system (5).

4. A direct current boiler water supply system coupling a steam-driven water supply pump unit and a hydraulic turbine booster pump unit according to claim 2, characterized in that: The hydraulic turbine (13) and the booster pump (14) are connected to their corresponding inlet pipes through the hydraulic turbine warm-up valve (17) and the booster pump warm-up valve (18) respectively, so as to ensure that the hydraulic turbine booster pump group is in a hot standby state after shutdown and can be put into operation at any time.

5. A direct current boiler water supply system coupling a steam-driven water supply pump unit and a hydraulic turbine booster pump unit according to claim 2, characterized in that: The feed water bypass system is a full-flow bypass. When the feed water bypass system is put into operation, all the feed water entering the economizer system (5) is pressurized through the bypass, and the main feed water pipeline is only used for hot standby.

6. A direct current boiler water supply system coupling a steam-driven water supply pump unit and a hydraulic turbine booster pump unit according to claim 1, characterized in that: The outlet of the superheater system (8) is connected to the steam turbine system. The steam separated by the steam-water separator (7) enters the superheater system (8) and continues to be heated to the rated temperature, and finally enters the steam turbine system to perform external work.

7. A direct current boiler water supply system coupling a steam-driven water supply pump unit and a hydraulic turbine booster pump unit according to claim 2, characterized in that: The outlet of the water storage tank (10) is divided into two routes, one route being connected to the start-up drain system, and a first regulating valve (11) is provided on its pipeline; and the other route being connected to the water supply bypass header (20), and a second regulating valve (22) is provided on its pipeline.

8. The control method of the DC boiler water supply system coupling the steam-driven water supply pump group and the hydraulic turbine booster pump group as claimed in any one of claims 3 to 7, characterized in that: Features include: When the DC boiler load is high and the feed water flow rate is greater than the minimum flow rate of the steam-driven feed water pump, the full-flow feed water bypass does not participate in the feed water regulation, the hydraulic turbine inlet regulating valve (15) and the feed water bypass inlet regulating valve (19), and the second regulating valve (22) from the water storage tank (10) to the feed water bypass header (20) are closed, and the hydraulic turbine outlet regulating valve (16) and the feed water bypass outlet regulating valve (21), the hydraulic turbine warm-up valve (17), and the booster pump warm-up valve (18) are opened, and the system is in a hot standby state; When the DC boiler starts deep peak regulation, when the water supply flow rate approaches the minimum flow rate of the steam-driven water supply pump, the full-flow water supply bypass is merged into the water supply system, and the full-flow water supply is gradually introduced; after the full-flow water supply bypass is merged into the water supply system, the hydraulic turbine booster pump group automatically controls the pressure difference before and after the booster pump (14), and the control target value is the pressure difference between the outlet of the booster pump (14) and the water storage tank (10), and the control target of the steam-driven water supply pump group (2) remains unchanged, which is still the water supply flow rate, and the target value is output by the water supply main control; When the DC boiler is further deeply peak-regulated and the feed water flow rate is close to the minimum flow rate of the water-cooled wall, the target value of the feed water flow rate output by the feed water master control is the sum of the minimum flow rate of the water-cooled wall and a certain value, and it will no longer decrease synchronously with the load. The larger the fixed value is, the higher the inlet flue gas temperature of the SCR denitrification system is. The operating parameters that meet the minimum requirements for the inlet flue gas temperature of the SCR denitrification system can be obtained through field tests, and the difference between the corresponding feed water flow rate and the minimum flow rate of the water-cooled wall is the fixed value; When the DC furnace is further deeply peaked, as the furnace heat load decreases, the steam superheat at the outlet of the steam-water separator (7) gradually decreases to 0, and the water-cooled wall enters wet operation; at this time, the second regulating valve (22) from the water storage tank (10) to the feed water bypass header (20) is gradually fully opened to recover the working fluid energy; the control mode of the steam-driven feed water pump group (2) is changed from controlling the feed water flow to controlling the liquid level in the water storage tank (10) to stabilize it at the set value; the control mode of the hydraulic turbine booster pump group is changed from controlling the pressure difference before and after the booster pump (14) to controlling the feed water flow, and the target value remains unchanged, which is still the sum of the minimum flow of the water-cooled wall and a certain value.

9. The control method of the DC boiler water supply system coupling the steam-driven water supply pump group and the hydraulic turbine booster pump group according to claim 8 is characterized in that: The full-flow water supply bypass is incorporated into the water supply system. The specific incorporation method is as follows: before the incorporation, the hydraulic turbine warm-up valve (17) and the booster pump warm-up valve (18) are closed, the hydraulic turbine inlet regulating valve (15) and the water supply bypass inlet regulating valve (19) are fully opened, and the hydraulic turbine outlet regulating valve (16) and the water supply bypass outlet regulating valve (21) are closed to a set small opening; then, the hydraulic turbine (13) inlet guide vane or regulating valve is opened to slowly increase the speed of the hydraulic turbine booster pump group to the set speed, and then the water supply bypass outlet regulating valve (21) is gradually fully opened to introduce all the water supply in the main pipeline into the water supply bypass; During the merging process, the hydraulic turbine outlet regulating valve (16) automatically follows and adjusts the hydraulic turbine outlet pressure to control it above the saturation pressure corresponding to the hydraulic turbine outlet temperature.

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