Energy-saving system for low-load operation of power station boiler

Abstract

The utility model discloses an energy-saving system for low-load operation of a power station boiler, which comprises a boiler, a first-stage reheater and a second-stage reheater, wherein the first-stage reheater and the second-stage reheater are connected through a pipeline; an outlet of the third-stage superheater is connected with a steam inlet of a steam turbine high-pressure cylinder through a main steam conveying pipe, a steam outlet of the steam turbine high-pressure cylinder is connected with an inlet of a first-stage reheater arranged in a boiler through a cold reheating steam pipe, and an outlet of a second-stage reheater is connected with a steam turbine intermediate-pressure cylinder through a reheating steam conveying pipe. A bypass superheated steam output pipe is connected to a pipeline between the first-stage superheater and the second-stage superheater, a bypass cold reheating steam pipe is arranged on the cold reheating steam pipe, the bypass superheated steam output pipe and the bypass cold reheating steam pipe are both connected with an ejector, and an outlet of the ejector is connected with a heat user through an ejection steam pipe.

Description

Technical Field

[0001] The utility model relates to an energy-saving system for low-load operation of a power station boiler, belonging to the technical field of energy-saving and emission-reduction of coal-fired boilers. Background Art

[0002] Existing coal-fired units such as Figure 1 As shown in the figure, the following problems are faced when operating under low load conditions: when the power station boiler is operating under low load conditions, the main steam temperature and reheat steam temperature will be under-temperature, which is particularly obvious in the tower furnace. The tower furnace has significant advantages: it is suitable for burning coal that is easy to slag, has a lower furnace outlet flue gas temperature, the flue gas temperature and heat load are more evenly distributed, and it starts faster. However, due to the particularity of the tower boiler, all the heating surfaces of the tower furnace are arranged on the upper part of the furnace and are all heating surfaces with convection characteristics. When the unit load is reduced, the flue gas volume is significantly reduced, resulting in a significant reduction in the heat transfer of the convection heating surface, which in turn reduces the heat absorption of each level of the heating surface in the boiler, and ultimately causes the main steam temperature and reheat steam temperature to be significantly lower than the design value. This leads to problems such as large steam temperature deviation, high steam turbine heat consumption, and high power coal consumption when the boiler is under low load. Taking 600MW and 1000MW ultra-supercritical coal-fired units as an example, the design temperature of superheated steam is 605℃ and the design temperature of reheated steam is 620℃. When the unit load is reduced to 30%, the main steam temperature is only about 530-550℃ and the reheated steam temperature is only about 520-530℃, which affects the power supply coal consumption by 10.8-13g / kwh. It not only affects the economy of the whole plant, but also is not conducive to the goal of reducing CO2 emissions under low load conditions of the unit. Utility Model Content

[0003] The technical problem to be solved by the utility model is to provide an energy-saving system for low-load operation of power station boilers.

[0004] In order to solve the above technical problems, the technical solution adopted by the utility model is: an energy-saving system for low-load operation of a power station boiler, comprising a boiler, a primary reheater and a secondary reheater connected by pipelines, the boiler is connected in series with an economizer, a primary superheater, a secondary superheater and a tertiary superheater through pipelines, the outlet of the tertiary superheater is connected to the steam inlet of the high-pressure cylinder of the turbine through a main steam delivery pipe, the steam outlet of the high-pressure cylinder of the turbine is connected to the inlet of the primary reheater arranged in the boiler through a cold reheat steam pipe, the outlet of the secondary reheater is connected to the medium-pressure cylinder of the turbine through a reheat steam delivery pipe, a bypass superheated steam output pipe is connected to the pipeline between the primary superheater and the secondary superheater, a bypass cold reheat pipe is provided on the cold reheat pipe, the bypass superheated steam output pipe and the bypass cold reheat pipe are both connected to an ejector, and the outlet of the ejector is connected to a heat user through an ejector steam pipe.

[0005] As a preferred solution, the outlet of the high-pressure cylinder of the steam turbine is connected to the heat medium inlet of the No. 1 high-pressure heater through a steam extraction pipe, and a steam extraction isolation valve is provided on the steam extraction pipe; the No. 1 high-pressure heater is provided with a low-temperature feed water pipe, and the high-temperature feed water pipe of the No. 1 high-pressure heater is connected to the inlet of the economizer.

[0006] As a preferred solution, a superheated steam output pipe is connected to the pipeline between the first-stage superheater and the second-stage superheater, and a superheated steam isolation valve is provided on the superheated steam output pipe. The outlet of the superheated steam isolation valve is connected to the heat medium inlet of the No. 1 high-pressure heater through a superheated steam transmission pipe.

[0007] As a preferred solution, a pressure reducing regulating valve is provided on the superheated steam transmission pipe.

[0008] The beneficial effects of the utility model are:

[0009] When the power plant boiler is operating under low load conditions, this system can significantly reduce the power supply coal consumption of the unit under low load conditions by reducing the superheated steam flow through the secondary superheater and the tertiary superheater, and reducing the reheated steam flow through the primary reheater and the secondary reheater, thereby increasing the main steam temperature and reheated steam temperature at the boiler outlet.

[0010] The outlet of the high-pressure cylinder of the steam turbine is connected to the heat medium inlet of the No. 1 high-pressure heater through a steam extraction pipe, and a steam extraction isolation valve is provided on the steam extraction pipe; the No. 1 high-pressure heater is provided with a low-temperature feed water pipe, and the high-temperature feed water pipe of the No. 1 high-pressure heater is connected to the inlet of the economizer, so that the steam discharged from the high-pressure cylinder of the steam turbine can be reused, further reducing the energy consumption of the overall system.

[0011] Since the pipeline between the first-stage superheater and the second-stage superheater is connected to a superheated steam output pipe, a superheated steam isolation valve is provided on the superheated steam output pipe, and the outlet of the superheated steam isolation valve is connected to the heat medium inlet of the No. 1 high-pressure heater through a superheated steam transmission pipe, when the power station boiler is operating under low-load conditions, the steam flow through the second-stage superheater and the third-stage superheater is reduced, thereby increasing the main steam temperature at the boiler outlet, and reducing the power supply coal consumption under low-load conditions; at the same time, the No. 1 high-pressure heater is a condensing heat exchanger, and the outlet feed water temperature depends on the feed water end difference of the No. 1 high-pressure heater, and the feed water end difference refers to the difference between the saturated temperature at the inlet steam pressure of the No. 1 high-pressure heater and the outlet feed water temperature. Since the superheated steam pressure after decompression is higher than the first-stage extraction pressure, the steam inlet pressure of the No. 1 high-pressure heater is increased, and then the feed water temperature at the outlet of the No. 1 high-pressure heater is increased, further reducing the energy consumption of the overall system. Moreover, the increase in feed water temperature is one of the important means to achieve SCR full-load denitrification.

[0012] Since a pressure reducing regulating valve is provided on the superheated steam transmission pipe, it is safer to use the superheated steam after it is decompressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the original system diagram. Figure 2 This is a system diagram of the utility model.

[0014] In the figure: 1. Boiler; 2. Turbine high-pressure cylinder; 3. Turbine intermediate-pressure cylinder; 4. Cold resteam; 5. Main steam; 6. Reheat steam; 7. Primary superheater; 8. Secondary superheater; 9. Third-stage superheater; 10. Primary reheater; 11. Secondary reheater; 12. Bypass cold resteam; 13. Bypass superheated steam; 14. Ejector; 15. Ejector steam; 16. Heat user.

[0015] 18. Economizer, 19. No. 1 high-pressure heater, 20. Low-temperature feed water pipe, 21. Superheated steam output pipe, 22. First-stage steam extraction pipe, 23. First-stage steam extraction isolation valve; 24. Superheated steam isolation valve, 25. Pressure reducing regulating valve, 26. Superheated steam transmission pipe, 27. High-temperature feed water pipe. DETAILED DESCRIPTION

[0016] The specific implementation scheme of the utility model is described in detail below in conjunction with the accompanying drawings.

[0017] like Figure 2 As shown, an energy-saving system for low-load operation of a power station boiler comprises a boiler 1, a primary reheater 10 and a secondary reheater 11 connected by pipelines. The boiler 1 is connected in series with an economizer 18, a primary superheater 7, a secondary superheater 8 and a tertiary superheater 9 in sequence by pipelines. The outlet of the tertiary superheater 9 is connected to the steam inlet of the high-pressure cylinder 2 of the steam turbine through a main steam delivery pipe 5. The steam outlet of the high-pressure cylinder 2 of the steam turbine is connected to the inlet of the primary reheater 10 arranged in the boiler through a cold reheat steam pipe 4. The outlet of the secondary reheater 11 is connected to the intermediate-pressure cylinder 3 of the steam turbine through a reheat steam delivery pipe 6. A bypass superheated steam output pipe 13 is connected to the pipeline between the primary superheater 7 and the secondary superheater 8. A bypass cold reheat steam pipe 12 is provided on the cold reheat steam pipe 4. The bypass superheated steam output pipe 13 and the bypass cold reheat steam pipe 12 are both connected to an ejector 14. The outlet of the ejector 14 is connected to a heat user 16 through an ejector steam pipe.

[0018] The outlet of the steam turbine high-pressure cylinder 2 is connected to the heat medium inlet of the No. 1 high-pressure heater 19 through a steam extraction pipe 22, and a steam extraction isolation valve 23 is provided on the steam extraction pipe 22; the No. 1 high-pressure heater 19 is provided with a low-temperature feed water pipe 20, and the high-temperature feed water pipe 27 of the No. 1 high-pressure heater 19 is connected to the inlet of the economizer 18.

[0019] Take 600MW and 1000MW supercritical units as an example: when the units are operating normally at low load, the temperature of the main steam and the temperature of the reheat steam are both much lower than the design values. The design temperature of the main steam is 605℃ and the design temperature of the reheat steam is 620℃. During actual operation, the temperature of the main steam is only about 530-550℃, and the temperature of the reheat steam is only about 520-530℃, which affects the power supply coal consumption by 10.8-13g / kwh.

[0020] By means of the method disclosed in the utility model, when the unit is operated under low load conditions, on the one hand, part of the bypass superheated steam is taken out from the outlet of the first-stage superheater 7, so that the steam flow rate through the second-stage superheater 8 and the third-stage superheater 9 is reduced, thereby increasing the temperature of the main steam at the outlet of the boiler 1 from 530-550°C to the rated value of 605°C; on the other hand, part of the bypass cold re-steam is extracted from the cold re-steam 4, and the steam flow rate through the first-stage reheater 10 and the second-stage reheater 11 is reduced, thereby increasing the temperature of the reheated steam at the outlet of the boiler 1 from 520-530°C to the rated value of 620°C, thereby ultimately reducing the heat consumption of the unit and reducing the power supply coal consumption of the unit under low load conditions by 10.8-13g / kwh.

[0021] In another embodiment, a superheated steam output pipe 21 is connected to the pipeline between the primary superheater 7 and the secondary superheater 8, and a superheated steam isolation valve 24 is provided on the superheated steam output pipe 21. The outlet of the superheated steam isolation valve 24 is connected to the heat medium inlet of the No. 1 high-pressure heater 19 through a superheated steam delivery pipe 26. A pressure reducing regulating valve 25 is provided on the superheated steam delivery pipe 26.

[0022] When the unit is operating normally at low load, the main steam temperature will be lower than the design temperature. At the same time, the pressure of a section of the extraction pipe 22 will decrease as the unit load decreases. Since the No. 1 high-pressure heater 19 is a condensing heat exchanger, the temperature of its outlet high-temperature feed water depends on the feed water end difference of the No. 1 high-pressure heater 19, and the feed water end difference refers to the difference between the saturated temperature at the inlet steam pressure of the No. 1 high-pressure heater 19 and the outlet high-temperature feed water temperature. Therefore, the temperature of the high-temperature feed water at the outlet of the No. 1 high-pressure heater 19 continues to decrease as the load decreases.

[0023] When the power station boiler 1 is operating under low load conditions, part of the superheated steam is taken out from the outlet of the first-stage superheater 7, so the steam flow through the second-stage superheater 8 and the third-stage superheater 9 is reduced, thereby increasing the main steam temperature at the outlet of the boiler 1, and ultimately reducing the power supply coal consumption under low load conditions; at the same time, since the pressure of the superheated steam at the outlet of the first-stage superheater 7 is much higher than the pressure of the first-stage extraction steam, the pressure of the superheated steam after being reduced by the pressure reducing regulating valve 25 is basically equivalent to the pressure of the first-stage extraction pipe 22 under 100% load of the unit, thereby increasing the temperature of the high-temperature feed water at the outlet of the No. 1 high-pressure heater 19.

[0024] The above-mentioned embodiments are only illustrative of the principles and effects of the invention, as well as some embodiments of its application, and are not intended to limit the invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the invention, and all of these belong to the protection scope of the invention.

Claims

1. An energy-saving system for low-load operation of a power station boiler, comprising a boiler (1), a primary reheater (10), and a secondary reheater (11) connected by pipelines, wherein the boiler (1) is connected in series with an economizer (18), a primary superheater (7), a secondary superheater (8), and a tertiary superheater (9) in sequence through the pipeline, and the outlet of the tertiary superheater (9) is connected to the steam inlet of the high-pressure cylinder (2) of the turbine through a main steam delivery pipe (5), characterized in that: The steam outlet of the high-pressure cylinder (2) of the steam turbine is connected to the inlet of the first-stage reheater (10) arranged in the boiler through a cold reheating pipe (4), the outlet of the second-stage reheater (11) is connected to the intermediate-pressure cylinder (3) of the steam turbine through a reheating steam delivery pipe (6), a bypass superheated steam output pipe (13) is connected to the pipeline between the first-stage superheater (7) and the second-stage superheater (8), a bypass cold reheating pipe (12) is provided on the cold reheating pipe (4), the bypass superheated steam output pipe (13) and the bypass cold reheating pipe (12) are both connected to an ejector (14), and the outlet of the ejector (14) is connected to a heat user (16) through an ejector steam pipe.

2. The energy-saving system for low-load operation of a power station boiler according to claim 1, characterized in that: The outlet of the steam turbine high-pressure cylinder (2) is connected to the heat medium inlet of the No. 1 high-pressure heater (19) through a steam extraction pipe (22), and a steam extraction isolation valve (23) is provided on the steam extraction pipe (22); the No. 1 high-pressure heater (19) is provided with a low-temperature feed water pipe (20), and the high-temperature feed water pipe (27) of the No. 1 high-pressure heater (19) is connected to the inlet of the economizer (18).

3. The energy-saving system for low-load operation of a power station boiler according to claim 1, characterized in that: A superheated steam output pipe (21) is connected to the pipeline between the first superheater (7) and the second superheater (8), and a superheated steam isolation valve (24) is provided on the superheated steam output pipe (21). The outlet of the superheated steam isolation valve (24) is connected to the heat medium inlet of the first high-pressure heater (19) through a superheated steam transmission pipe (26).

4. The energy-saving system for low-load operation of a power station boiler as claimed in claim 3, characterized in that: The superheated steam transmission pipe (26) is provided with a pressure reducing regulating valve (25).

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