System for synchronously increasing low-load hot air temperature and boiler feed water temperature of coal-fired boiler by using main steam

Abstract

The utility model discloses a system for synchronously increasing the low-load hot air temperature of a coal-fired boiler and the feed water temperature of the boiler by using main steam, which is characterized in that a part of superheated steam is extracted from a main steam pipeline at an outlet of the boiler and enters a hot air heat exchanger after being subjected to pressure reduction by a pressure reducing valve and temperature reduction by desuperheating water; the hot air heat exchanger achieves the effect that superheated steam obtained after temperature and pressure reduction heats hot primary air at an outlet of the air preheater, the heated hot primary air is sent to the coal mill to improve the drying output of the coal pulverizing system, steam obtained after heat release is sent to the first high-pressure heater, and steam at an inlet of the original first high-pressure heater is isolated. Inlet steam of the first high-pressure heater is changed into superheated steam subjected to pressure reduction and temperature reduction from original first-section extraction steam. According to the system, the flue gas temperature of the SCR inlet under the low-load working condition of the coal-fired boiler is increased, full-load denitration and deep peak regulation of a unit are facilitated, and combustion stability in the boiler is facilitated; and the coal consumption of the coal-fired boiler under the low-load working condition is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of energy conservation and emission reduction of coal-fired boilers, and in particular to a system that utilizes main steam to synchronously increase the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler. Background Art

[0002] All large coal-fired units in my country have undergone denitrification technology upgrades before, and more than 90% of them 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 SCR inlet flue gas temperature 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 used to meet NOx emission requirements and achieve full load and full-time stable emission requirements above the minimum technical output.

[0003] The current wide-load denitrification technologies mainly include: economizer water side bypass, economizer flue gas bypass, economizer feed water recirculation, graded economizer, zero-level 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, complex system, etc. The utility model increases the technical reserves in the field of wide-load denitrification technology, which is conducive to the demand for flexible transformation of coal-fired units as scheduled.

[0004] In addition, under low-load conditions, the temperature of the hot primary air at the outlet of the air preheater decreases, which eventually leads to a decrease in the temperature of the primary air entering the boiler (especially for units burning high-moisture lignite). As the temperature of the primary air entering the boiler decreases, the center height of the flame in the furnace moves upward, resulting in a series of problems such as a high excess air coefficient at the furnace outlet, a decrease in boiler efficiency, an increase in cooling water volume, and an increase in exhaust gas temperature, which in turn leads to an increase in the coal consumption of the unit, which seriously affects the economy of the entire plant. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a system which utilizes main steam to synchronously increase the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler.

[0006] In order to solve the above technical problems, the technical solution adopted by the utility model is: a system for synchronously increasing the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam, comprising: a boiler, a main steam pipe is provided on the boiler, and the main steam pipe is connected to a first bypass superheated steam pipe and a second bypass superheated steam pipe;

[0007] The end of the first bypass superheated steam pipe is connected to the high-pressure cylinder of the steam turbine, a steam extraction pipe is provided on the high-pressure cylinder of the steam turbine, and a steam extraction pipe isolation valve is provided on the steam extraction pipe; the end of the steam extraction pipe is connected to the No. 1 high-pressure heater, a low-temperature feed water pipe is provided on the No. 1 high-pressure heater, and a high-temperature feed water pipe connected to the boiler is provided on the No. 1 high-pressure heater;

[0008] The second bypass superheated steam pipe is provided with a pressure reducing regulating valve and a desuperheater. The outlet of the desuperheater is provided with a desuperheating and pressure reducing superheated steam pipe. The desuperheater is also connected with a desuperheating water pipe, and the desuperheating water pipe is provided with a desuperheating water pipe regulating valve.

[0009] The outlet of the superheated steam pipe for reducing temperature and pressure is connected to the section between the isolation valve of the first steam extraction pipe and the No. 1 high-pressure heater on the first steam extraction pipe; the superheated steam pipe for reducing temperature and pressure is connected to the section between the isolation valve of the first steam extraction pipe and the No. 1 high-pressure heater on the first steam extraction pipe through the outlet superheated steam pipe of the hot air heat exchanger provided with the hot air heat exchanger;

[0010] The inlet of the medium to be heated of the hot air heat exchanger is connected to the air preheater through the hot primary air duct at the outlet of the air preheater. The air preheater is provided with a cold air duct. The outlet of the medium to be heated of the hot air heat exchanger is connected to the boiler through a pipeline.

[0011] As a preferred solution, the outlet of the heated medium of the hot air heat exchanger is connected to the coal mill through an outlet hot air duct, the powder outlet of the coal mill is connected to the boiler through the mill outlet primary air duct, and the air preheater is connected to the boiler cavity through the air preheater outlet hot secondary air duct.

[0012] As a preferred solution, a cooling water pipe isolation valve is provided on the cooling water pipe.

[0013] As a preferred solution, a bypass superheated steam isolation valve is provided on the second bypass superheated steam pipe.

[0014] The beneficial effects of the utility model are:

[0015] In the utility model, under low load conditions, the temperature of the secondary air entering the boiler is increased through the heating of the hot air heat exchanger, which increases the heat in the boiler and is beneficial to stable combustion in the boiler; at the same time, due to the increase in the temperature of the hot air entering the boiler, the flow rate of the hot air can be appropriately reduced, thereby improving the boiler efficiency of the unit under low load conditions and generating considerable economic benefits. In addition, the No. 1 high-pressure heater is a condensing heat exchanger, and the level of its 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 cooling and pressure reduction 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. The increase in feed water temperature is one of the important means to achieve SCR full-load denitrification.

[0016] Since the outlet of the heated medium of the hot air heat exchanger is connected to the coal mill through the outlet hot air pipe, the powder outlet of the coal mill is connected to the boiler through the outlet primary air pipe of the mill, and the air preheater is connected to the inner cavity of the boiler through the outlet hot secondary air pipe of the air preheater, the temperature of the hot primary air entering the coal mill is increased through the heating of the hot air heat exchanger, thereby improving the drying output of the entire pulverizing system, and increasing the temperature of the primary air entering the boiler, thereby increasing the heat in the boiler, lowering the flame center, and being beneficial to the combustion in the boiler; at the same time, due to the increase in the temperature of the hot primary air entering the coal mill, the boiler can appropriately mix and burn economical coal with high moisture content, thereby generating considerable economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a system structure diagram of Example 1;

[0018] Figure 2 is a system structure diagram of Example 2;

[0019] 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. Air preheater; 10. Cold air pipe; 11. Hot secondary air pipe at air preheater outlet; 12. Hot primary air pipe at air preheater outlet; 13. Coal mill; 14. Primary air pipe at mill outlet; 15. Desuperheater; 16. Superheated steam pipe at hot air heat exchanger outlet; 17. Desuperheating water pipe; 18. Bypass superheated steam isolation valve; 19. Desuperheating and pressure-reducing superheated steam pipe; 20. Hot air pipe at hot air heat exchanger outlet; 21. Hot air heat exchanger; 22. Main superheated steam pipe; 23. Bypass superheated steam pipe; 24. Pressure reducing regulating valve; 25. Desuperheating water isolation valve; 26. Desuperheating water regulating valve. DETAILED DESCRIPTION

[0020] The specific implementation scheme of the utility model is described in detail below in conjunction with the accompanying drawings.

[0021] Example 1 Figure 1 As shown, a system for synchronously raising the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam comprises: a boiler 1, a main steam pipe 7 is provided on the boiler, and the main steam pipe 7 is connected to a first bypass superheated steam pipe 22 and a second bypass superheated steam pipe 23;

[0022] The end of the first bypass superheated steam pipe 22 is connected to the high-pressure cylinder 2 of the steam turbine, and a steam extraction pipe 8 is provided on the high-pressure cylinder 2 of the steam turbine, and a steam extraction pipe isolation valve 4 is provided on the steam extraction pipe 8; the end of the steam extraction pipe 8 is connected to the No. 1 high-pressure heater 3, and 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 connected to the boiler 1 is provided on the No. 1 high-pressure heater 3;

[0023] The second bypass superheated steam pipe 23 is provided with a bypass superheated steam isolation valve 18 and a pressure reducing regulating valve 24, and a desuperheater 15. The outlet of the desuperheater 15 is provided with a desuperheating and pressure reducing superheated steam pipe 19. The desuperheater 15 is also connected with a desuperheating water pipe 17. The desuperheating water pipe 17 is provided with a desuperheating water pipe isolation valve 25 and a desuperheating water pipe regulating valve 26.

[0024] The outlet of the desuperheated steam pipe 19 is connected to the section between the first steam extraction pipe isolation valve 4 and the first high-pressure heater 3 on the first steam extraction pipe 8; the desuperheated steam pipe 19 is connected to the section between the first steam extraction pipe isolation valve 4 and the first high-pressure heater 3 on the first steam extraction pipe 8 through the hot air heat exchanger outlet superheated steam pipe 16 provided with a hot air heat exchanger 21;

[0025] The inlet of the medium to be heated of the hot air heat exchanger 21 is connected to the air preheater 9 through the hot primary air duct 12 at the air preheater outlet. The air preheater 9 is provided with a cold air duct 10. The outlet of the medium to be heated of the hot air heat exchanger 21 is connected to the boiler 1 through a pipeline.

[0026] Under low load conditions, the main steam 7 at the outlet of the boiler 1 is divided into two parts: main path superheated steam and bypass superheated steam. The main path superheated steam enters the high-pressure cylinder 2 of the steam turbine to perform work; the original first stage extraction isolation valve 8 is closed, and the first stage extraction is isolated;

[0027] The bypass superheated steam passes through the bypass superheated steam isolation valve 18 and is decompressed through the pressure reducing regulating valve 12;

[0028] After the desuperheating water passes through the desuperheating water isolation valve 13, the desuperheating water regulating valve 14 is used to adjust the flow rate. The bypass superheated steam after decompression passes through the desuperheater 15 and uses the desuperheating water to reduce the temperature, and finally the bypass superheated steam becomes desuperheated and decompressed superheated steam.

[0029] The desuperheated steam is sent to the hot air heat exchanger 21, which is arranged between the air preheater 9 and the boiler 1. The hot air heat exchanger 21 heats the hot air at the outlet of the air preheater with the desuperheated steam, so that the temperature of the hot air at the outlet of the air preheater is increased to become hot air, and the hot air is sent to the boiler 1 to participate in combustion.

[0030] The superheated steam after cooling becomes superheated steam at the outlet of the hot air heat exchanger, and the superheated steam at the outlet of the hot air heat exchanger is sent to the No. 1 high-pressure heater 3, thereby replacing the original first-stage extraction steam to heat the low-temperature feed water. The low-temperature feed water is heated by the No. 1 high-pressure heater 3 and becomes high-temperature feed water, which is finally sent to the boiler 1.

[0031] When the system is operating normally, the pressure of the first stage of steam extraction changes with the change of the unit load. Taking a 350MW supercritical unit as an example, the pressure of the first stage of steam extraction under 100% THA load is 11MPa, and the pressure of the first stage of steam extraction under 30% THA load is about 3MPa. 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 under the inlet steam pressure of the No. 1 high-pressure heater 3 and the outlet high-temperature feed water temperature. Therefore, the feed water temperature at the outlet of the No. 1 high-pressure heater 3 continues to decrease with the decrease of load. In addition, as the load decreases, the temperature of the hot air entering the boiler 1 gradually decreases. The hot air temperature is about 220℃ under 30% THA load, and the hot air temperature is about 320℃ under 100% THA load.

[0032] In the system and method disclosed by the utility model, part of the steam is taken out from the main steam as bypass superheated steam, and the bypass superheated steam after being cooled and reduced in pressure first uses its superheat to heat the hot air at the air preheater outlet through the hot air heat exchanger 21, thereby raising the temperature of the hot air at the air preheater outlet to above 290°C; the steam after cooling becomes superheated steam at the hot air heat exchanger outlet and is sent to the No. 1 high-pressure heater 3 as the steam source of the No. 1 high-pressure heater 3, and the temperature and pressure of the cooled and reduced-pressure superheated steam entering the No. 1 high-pressure heater 3 can be adjusted by the cooling water regulating valve 14 and the pressure reducing regulating valve 12.

[0033] Since the temperature and pressure of the main steam are much higher than the temperature and pressure of the first stage extraction steam and it has a huge superheat, the system and method disclosed in the utility model, on the one hand, achieves the goal of using the superheat of steam to heat the temperature of the hot air entering the boiler, thereby reducing the coal consumption of the unit; 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.

[0034] Example 2 Figure 2As shown, it is different from Example 1 in that the outlet of the medium to be heated of the hot air heat exchanger 21 is connected to the coal mill 13 through the outlet hot air pipe 20, the powder outlet of the coal mill 13 is connected to the boiler 1 through the mill outlet primary air pipe 14, and the air preheater 9 is connected to the boiler cavity through the air preheater outlet hot secondary air pipe 11.

[0035] 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 synchronously increasing the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam, comprising: A boiler (1), wherein a main steam pipe (7) is provided on the boiler, and the main steam pipe (7) is connected to a first bypass superheated steam pipe (22) and a second bypass superheated steam pipe (23); The end of the first bypass superheated steam pipe (22) is connected to the high-pressure cylinder (2) of the steam turbine, a steam extraction pipe (8) is provided on the high-pressure cylinder (2) of the steam turbine, and a steam extraction pipe isolation valve (4) is provided on the steam extraction pipe (8); the end of the steam extraction pipe (8) is connected to the No. 1 high-pressure heater (3), 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) connected to the boiler (1) is provided on the No. 1 high-pressure heater (3); The invention is characterized in that: the second bypass superheated steam pipe (23) is provided with a pressure reducing regulating valve (24) and a desuperheater (15); the outlet of the desuperheater (15) is provided with a desuperheating and pressure reducing superheated steam pipe (19); the desuperheater (15) is also connected with a desuperheating water pipe (17); the desuperheating water pipe (17) is provided with a desuperheating water pipe regulating valve (26); The outlet of the desuperheated steam pipe (19) is connected to the section between the steam extraction pipe isolation valve (4) and the No. 1 high-pressure heater (3) on the first steam extraction pipe (8); The superheated steam pipe (19) for reducing temperature and pressure is connected to the portion between the steam extraction pipe isolation valve (4) and the No. 1 high-pressure heater (3) on a steam extraction pipe (8) through a hot air heat exchanger outlet superheated steam pipe (16) provided with a hot air heat exchanger (21). The inlet of the medium to be heated of the hot air heat exchanger (21) is connected to the air preheater (9) through the hot primary air pipe (12) at the air preheater outlet. The air preheater (9) is provided with a cold air pipe (10). The outlet of the medium to be heated of the hot air heat exchanger (21) is connected to the boiler (1) through a pipeline.

2. A system for synchronously increasing the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam as claimed in claim 1, characterized in that: The outlet of the medium to be heated of the hot air heat exchanger (21) is connected to the coal mill (13) via an outlet hot air pipe (20), the powder outlet of the coal mill (13) is connected to the boiler (1) via an outlet primary air pipe (14), and the air preheater (9) is connected to the inner cavity of the boiler via an outlet hot secondary air pipe (11).

3. A system for synchronously increasing the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam as claimed in claim 1, characterized in that: The desuperheating water pipe (17) is provided with a desuperheating water pipe isolation valve (25).

4. A system for synchronously increasing the low-load hot air temperature and boiler feed water temperature of a coal-fired boiler by using main steam as claimed in claim 1, characterized in that: The second bypass superheated steam pipe (23) is provided with a bypass superheated steam isolation valve (18).

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