System for increasing low-load main steam temperature and feed water temperature of power station boiler

Abstract

The utility model discloses a system for improving low-load main steam temperature and feed water temperature of a power station boiler, which comprises a boiler, and an economizer, a first-stage superheater, a second-stage superheater and a third-stage superheater which are sequentially connected in series through pipelines in the boiler, and an outlet of the third-stage superheater is connected with a steam inlet of a steam turbine high-pressure cylinder through a main steam pipe. An outlet of a steam turbine high-pressure cylinder is connected with a heating medium inlet of a first high-pressure heater through a first-section steam extraction pipe, and a first-section steam extraction isolation valve is arranged on the first-section steam extraction pipe. A low-temperature water supply pipe is arranged on the first high-pressure heater, and a high-temperature water supply pipe of the first high-pressure heater is connected with an inlet of the economizer. A superheated steam pipe is connected to a pipeline between the first-stage superheater and the second-stage superheater, a superheated steam isolating valve is arranged on the superheated steam pipe, and an outlet of the superheated steam isolating valve is connected with a heating medium inlet of the first high-pressure heater through a superheated steam conveying pipe; and the opening and closing states of the superheated steam isolating valve and the pressure-reducing regulating valve are opposite to the opening and closing states of the first-section steam extraction isolating valve.

Description

Technical Field

[0001] The utility model relates to a system for improving the low-load main steam temperature and feed water temperature of a power station boiler, belonging to the technical field of energy conservation and emission reduction of coal-fired boilers. Background Art

[0002] Existing coal-fired units face the same problem when operating under low load conditions: on the one hand, power plant boilers have been upgraded with denitrification technology, and more than 90% of the units use selective catalytic reduction (SCR). In order to meet the temperature window of the SCR catalyst, the inlet flue gas temperature is required to be above 300°C during the operation of the unit. When the inlet flue gas temperature of the SCR is lower than 300°C, the SCR cannot operate normally, resulting in ultra-low NOx emission concentration, catalyst deactivation, increased ammonia slip, etc. Therefore, wide-load denitrification technology must be adopted to meet the NOx emission requirements and achieve full load and stable emission requirements at all times above the minimum technical output. The current wide-load denitrification technologies mainly include: economizer water side bypass, economizer flue gas bypass, economizer feed water recirculation, staged economizer, zero high-pressure heater, boiler water recirculation, etc. Although there are many wide-load denitrification technical means at present, they generally have problems such as limited layout space, limited temperature increase effect, high investment, and complex system.

[0003] On the other hand, when the power plant boiler is running under low load conditions, the main steam temperature may be insufficient, which is particularly evident in tower furnaces. Tower furnaces have significant advantages: they are suitable for burning coals that are prone to slagging, have lower furnace outlet flue gas temperatures, more uniform distribution of flue gas temperature and heat load, and faster startup. However, due to the particularity of the tower boiler, all 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 stage of the superheater in the boiler, and ultimately causes the main steam temperature to be significantly lower than the design value. This leads to problems such as large deviation of steam temperature at low load, high heat consumption of the steam turbine, and high coal consumption for power supply. Taking 600MW and 1000MW ultra-supercritical coal-fired units as an example, the design temperature of superheated steam is 605℃. When the unit load is reduced to 30%, the main steam temperature is only about 530-550℃, which affects the power supply coal consumption by 4.5-6g / kwh. This not only affects the economy of the whole plant, but also goes against the goal of reducing CO2 emissions under low load conditions. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a system for improving the low-load main steam temperature and feed water temperature of a power station boiler.

[0005] In order to solve the above technical problems, the technical solution adopted by the utility model is: a system for improving the low-load main steam temperature and feed water temperature of a power station boiler, comprising a boiler, wherein an economizer, a first-stage superheater, a second-stage superheater and a third-stage superheater are connected in series in sequence through a pipeline, the outlet of the third-stage superheater is connected to the steam inlet of the high-pressure cylinder of the turbine through a main steam pipe, the outlet of the high-pressure cylinder of the turbine is connected to the heat medium inlet of the No. 1 high-pressure heater through a section of extraction pipe, and a section of extraction pipe is provided with a section of extraction isolation valve; 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; an overheated steam 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 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; the opening and closing states of the superheated steam isolation valve and the pressure reducing regulating valve are opposite to those of the first-stage extraction isolation valve.

[0006] As a preferred solution, the superheated steam isolation valve, the pressure reducing regulating valve and the first stage steam extraction isolation valve are all solenoid valves electrically connected to the control center.

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

[0008] As a preferred solution, the pressure reducing regulating valve is a solenoid valve electrically connected to the control center.

[0009] As a preferred solution, the main steam pipe is provided with a main steam control valve electrically connected to the control center; the high-temperature water supply pipe is provided with a high-temperature water control valve electrically connected to the control center.

[0010] The beneficial effects of the utility model are:

[0011] In the utility model, when the power station boiler is operating under low load conditions, the steam flow through the secondary superheater and the tertiary 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 saturation 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 steam 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. The increase in feed water temperature is one of the important means to achieve SCR full-load denitrification.

[0012] Since the superheated steam isolation valve, the pressure reducing regulating valve and the first stage steam extraction isolation valve are all electromagnetic valves electrically connected to the control center, they can be controlled more conveniently and reliably.

[0013] Since the superheated steam transmission pipe is provided with a pressure reducing regulating valve, the transmission and use of the hot steam are safer.

[0014] Since the pressure reducing regulating valve is a solenoid valve electrically connected to the control center, it can be controlled more conveniently and reliably.

[0015] Since the main steam pipe is provided with a main steam control valve electrically connected to the control center; the high-temperature water supply pipe is provided with a high-temperature water control valve electrically connected to the control center, control can be performed more conveniently and reliably. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a system diagram of the utility model.

[0017] In the figure: 1. Boiler; 2. High-pressure cylinder of steam turbine; 3. No. 1 high-pressure heater; 4. First-stage extraction isolation valve; 5. Low-temperature feed water pipe; 6. High-temperature feed water pipe; 7. Main steam pipe; 8. First-stage extraction pipe; 9. Economizer; 10. First-stage superheater; 11. Second-stage superheater; 12. Third-stage superheater; 13. Superheated steam pipe; 14. Superheated steam isolation valve; 15. Pressure reducing regulating valve; 16. Superheated steam transmission pipe. DETAILED DESCRIPTION

[0018] The specific implementation scheme of the utility model is described in detail below in conjunction with the accompanying drawings.

[0019] like Figure 1 As shown, a system for increasing the low-load main steam temperature and feed water temperature of a power station boiler comprises a boiler 1, wherein the boiler 1 is connected in series with an economizer 9, a primary superheater 10, a secondary superheater 11, and a tertiary superheater 12 in sequence through a pipeline, wherein the outlet of the tertiary superheater 12 is connected to the steam inlet of a high-pressure cylinder 2 of a steam turbine through a main steam pipe 7, wherein the outlet of the high-pressure cylinder 2 of the steam turbine is connected to the heat medium inlet of a No. 1 high-pressure heater 3 through a section of extraction pipe 8, wherein a section of extraction pipe 8 is provided with a section of extraction isolation valve 4; a low-temperature feed water pipe 5 is provided on the No. 1 high-pressure heater 3, and a high-temperature feed water pipe 6 of the No. 1 high-pressure heater 3 is connected to the inlet of the economizer 9; a superheated steam pipe 13 is connected to the pipeline between the primary superheater 10 and the secondary superheater 11, wherein a superheated steam isolation valve 14 is provided on the superheated steam pipe 13, wherein the outlet of the superheated steam isolation valve 14 is connected to the heat medium inlet of the No. 1 high-pressure heater 3 through a superheated steam transmission pipe 16; and a pressure reducing regulating valve 15 is provided on the superheated steam transmission pipe 16. The pressure reducing regulating valve 15 is a solenoid valve electrically connected to the control center. The opening and closing states of the superheated steam isolation valve 14 and the pressure reducing regulating valve 15 are opposite to those of the first stage steam extraction isolation valve 4. The superheated steam isolation valve 14, the pressure reducing regulating valve 15 and the first stage steam extraction isolation valve 4 are all solenoid valves electrically connected to the control center.

[0020] The system disclosed in the present invention takes part of the superheated steam from the outlet of the primary superheater 10 arranged in the boiler 1 under low load conditions, closes the original first stage extraction steam isolation valve 4, isolates the first stage extraction steam, and no longer extracts the first stage extraction steam from the high pressure cylinder 2 of the steam turbine;

[0021] After passing through the superheated steam isolation valve 14, the superheated steam is reduced in pressure through the pressure reducing regulating valve 15, and the superheated steam becomes reduced-pressure superheated steam; the reduced-pressure superheated steam is sent to the No. 1 high-pressure heater 3 to replace the original first-stage extraction steam to heat the low-temperature feed water, and the low-temperature feed water is heated by the No. 1 high-pressure heater 3 to become high-temperature feed water, and the high-temperature feed water is finally sent to the economizer 9 in the boiler 1.

[0022] When the unit is operating normally at low load, the main steam temperature is much lower than the design value. The design main steam temperature is 605℃, and the actual operating main steam temperature is about 530-550℃. At the same time, the pressure of the first stage extraction steam changes with the change of the unit load. The pressure of the first stage extraction steam is 11MPa at 100% load, and the pressure of the first stage extraction steam is about 3MPa at 30% load. Since the No. 1 high-pressure heater 3 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 3, 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 3 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 3 continues to decrease with the decrease of load.

[0023] In the system and method disclosed in the present invention, when the power station boiler is operating under low load conditions, part of the superheated steam is taken out from the outlet of the first-stage superheater 10, so the steam flow through the second-stage superheater 11 and the third-stage superheater 12 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 10 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 15 is basically equivalent to the pressure of the first-stage extraction steam 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 3.

[0024] Therefore, the method disclosed in the present invention, on the one hand, achieves the goal of increasing the main steam temperature under low-load conditions of the unit, thereby reducing the unit's power supply coal consumption by 4 to 6.5 g / kwh; on the other hand, it achieves an increase in the steam pressure entering the No. 1 high-pressure heater 3 under low-load conditions of the unit, thereby greatly increasing the temperature of the high-temperature feed water at the outlet of the No. 1 high-pressure heater 3. After calculation, the feed water temperature can be increased by more than 40°C.

[0025] 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. A system for increasing the low-load main steam temperature and feed water temperature of a power station boiler, comprising a boiler (1), wherein the boiler (1) is connected in series with an economizer (9), a primary superheater (10), a secondary superheater (11), and a tertiary superheater (12) in sequence through a pipeline, wherein the outlet of the tertiary superheater (12) is connected to the steam inlet of a high-pressure cylinder (2) of a steam turbine through a main steam pipe (7), and wherein: The outlet of the high-pressure cylinder (2) of the steam turbine is connected to the heat medium inlet of the No. 1 high-pressure heater (3) through a steam extraction pipe (8), and a steam extraction isolation valve (4) is provided on the steam extraction pipe (8); a low-temperature feed water pipe (5) is provided on the No. 1 high-pressure heater (3), and the high-temperature feed water pipe (6) of the No. 1 high-pressure heater (3) is connected to the inlet of the economizer (9); a superheated steam pipe (13) is connected to the pipeline between the first superheater (10) and the second superheater (11), and a superheated steam isolation valve (14) is provided on the superheated steam pipe (13), and the outlet of the superheated steam isolation valve (14) is connected to the heat medium inlet of the No. 1 high-pressure heater (3) through a superheated steam transmission pipe (16); the opening and closing states of the superheated steam isolation valve (14) and the pressure reducing regulating valve (15) are opposite to those of the first steam extraction isolation valve (4).

2. A system for increasing the low-load main steam temperature and feed water temperature of a power station boiler as claimed in claim 1, characterized in that: The superheated steam isolation valve (14), the pressure reducing regulating valve (15) and the first stage steam extraction isolation valve (4) are all electromagnetic valves electrically connected to the control center.

3. A system for increasing the low-load main steam temperature and feed water temperature of a power station boiler as claimed in claim 2, characterized in that: The superheated steam transmission pipe (16) is provided with a pressure reducing regulating valve (15).

4. A system for increasing the low-load main steam temperature and feed water temperature of a power station boiler as claimed in claim 3, characterized in that: The pressure reducing regulating valve (15) is a solenoid valve electrically connected to a control center.

5. A system for increasing the low-load main steam temperature and feed water temperature of a power station boiler as claimed in claim 4, characterized in that: The main steam pipe (7) is provided with a main steam control valve electrically connected to the control center; the high-temperature water supply pipe (6) is provided with a high-temperature water control valve electrically connected to the control center.

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