System for improving low-load pulverizing and drying output and feed water temperature of coal-fired boiler

Abstract

The utility model relates to the technical field of energy conservation of coal-fired boilers, in particular to a system for improving low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, which is innovatively designed and comprises a main steam, a turbine high-pressure cylinder, a hot air heat exchanger and other core components. The problems that the excess air coefficient of a hearth outlet is increased and the boiler efficiency is reduced during low-load operation are solved. According to the working principle, superheated steam is extracted from an outlet of the medium-temperature superheater, and after pressure reduction and temperature reduction, the steam is fed into the hot air heat exchanger, so that the hot air temperature is increased, the drying effect of the coal mill is enhanced, and meanwhile the feed water temperature is increased. The system not only improves the operation parameters of the boiler, but also remarkably improves the boiler efficiency and reduces the coal consumption by implementing an intelligent control strategy, and achieves the purposes of energy conservation and emission reduction.

Description

Technical Field

[0001] The utility model relates to the technical field of energy conservation of coal-fired boilers, in particular to a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. Background Art

[0002] With the continued development of the economy and the increasing demand for electricity, thermal power, as the mainstay of my country's power supply, continues to play a crucial role in the broader context of energy restructuring. To meet environmental protection requirements, the coal-fired power generation industry is actively seeking technological innovations for energy conservation and emission reduction. Currently, large-scale coal-fired units in China generally use selective catalytic reduction (SCR) for denitrification to reduce nitrogen oxide emissions. However, with increasingly stringent environmental standards, maintaining the SCR inlet flue gas temperature to ensure catalyst activity and denitrification efficiency, particularly under low-load conditions, has become a critical issue facing the industry.

[0003] To address the challenges faced by SCR technology under low-load conditions, various wide-load denitrification methods have been proposed and applied in existing technologies, such as economizer water-side bypass and flue gas bypass. These technologies primarily increase the flue gas temperature at the SCR inlet by adjusting the flue gas flow path or heat distribution. Although these technologies have improved denitrification efficiency to a certain extent, in actual application, they are often limited by installation space, limited temperature increase effects, high investment costs, and system complexity. At the same time, during low-load operation, increasing the air volume to ensure stable combustion in the boiler will lead to an increase in the excess air coefficient at the furnace outlet and a decrease in boiler efficiency, which in turn increases the coal consumption of the unit and has a negative impact on the overall economic efficiency of the power plant.

[0004] Under low-load conditions, the primary air temperature at the air preheater outlet decreases, ultimately leading to a decrease in the primary air temperature entering the boiler (particularly noticeable for units burning high-moisture lignite). This decrease in primary air temperature causes the center of the flame in the furnace to move upward, leading to a series of problems such as an increase in the excess air coefficient at the furnace outlet, decreased boiler efficiency, increased desuperheating water volume, and increased exhaust gas temperature. Consequently, this increases the unit's coal consumption, severely impacting the overall plant's economic performance.

[0005] The original system runs as shown in the attached Figure 1As shown: After entering the boiler, the high-temperature feed water is heated by the economizer, low-temperature superheater, medium-temperature superheater, and high-temperature superheater, becoming main steam. The main steam at the high-temperature superheater outlet enters the high-pressure cylinder of the steam turbine to perform work. The first extraction steam extracted from the high-pressure cylinder of the steam turbine passes through the first extraction steam isolation valve and enters the No. 1 high-pressure heater. The low-temperature feed water is heated by the No. 1 high-pressure heater and becomes high-temperature feed water. The high-temperature feed water is sent to the economizer in the boiler. The cold air is heated by the air preheater 9 and becomes hot secondary air at the air preheater outlet and hot primary air at the air preheater outlet. The hot secondary air at the air preheater outlet is sent to the boiler for combustion. The hot primary air at the air preheater outlet enters the coal mill to dry the raw coal, and the mill outlet primary air enters the boiler for parameters.

[0006] While wide-load denitrification technology can raise flue gas temperatures at the SCR inlet, it typically requires complex system modifications, resulting in high investment costs and poor economic returns. Furthermore, increasing air volume to maintain combustion stability during low-load operation compromises boiler efficiency and increases coal consumption, contradicting the primary goal of energy conservation and emission reduction. Therefore, the thermal power industry urgently needs to develop a new wide-load denitrification technology that can both meet environmental standards and maintain good economic returns. Utility Model Content

[0007] The utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, solving a series of problems such as a high excess air coefficient at the furnace outlet, a decrease in boiler efficiency, an increase in the amount of cooling water, and an increase in the exhaust gas temperature, which in turn lead to an increase in the coal consumption of the unit.

[0008] The utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, comprising:

[0009] The boiler is connected to the high-pressure cylinder of the steam turbine. A steam extraction isolation valve is installed between the high-pressure cylinder of the steam turbine and the No. 1 high-pressure heater. The hot air heat exchanger is connected to the coal mill, No. 1 high-pressure heater, air preheater, and desuperheater.

[0010] The hot air heat exchanger is connected to the air preheater, desuperheater, desuperheating water, No. 1 high-pressure heater, coal mill and boiler;

[0011] One end of the desuperheating water regulating valve is connected to the desuperheating water isolation valve, the other end of the desuperheating water regulating valve is connected to the desuperheater, and the bypass superheated steam isolation valve is connected to the desuperheater;

[0012] The boiler includes an economizer, a low-temperature superheater, a medium-temperature superheater and a high-temperature superheater. The economizer is connected to the low-temperature superheater, the low-temperature superheater is connected to the medium-temperature superheater, and the medium-temperature superheater is connected to the high-temperature superheater.

[0013] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The hot air heat exchanger is arranged in the hot primary air duct between the air preheater and the coal mill. After the cold air passes through the air preheater, a part of it enters the boiler as the hot secondary air at the air preheater outlet to participate in combustion, and the other part enters the hot air heat exchanger for reheating and becomes the hot air at the hot air heat exchanger outlet to enter the coal mill to dry the raw coal, thereby improving the temperature of the primary air at the mill outlet of the coal mill. The primary air at the mill outlet after temperature increase enters the boiler for combustion.

[0014] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, wherein part of the superheated steam is extracted from the outlet of the medium-temperature superheater arranged in the boiler as bypass superheated steam.

[0015] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The bypass superheated steam is reduced in pressure by a pressure reducing regulating valve and then cooled by a desuperheater to become cooled and reduced-pressure superheated steam.

[0016] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The cooled and reduced-pressure superheated steam enters the hot air heat exchanger, heats the hot primary air at the outlet of the air preheater and converts it into hot air at the outlet of the hot air heat exchanger. The cooled and reduced-pressure superheated steam after heat release becomes superheated steam at the outlet of the hot air heat exchanger.

[0017] The beneficial effects produced by the utility model are as follows:

[0018] Improve the drying output of the coal mill: The hot air temperature entering the coal mill is increased through the hot air heat exchanger, thereby enhancing the drying capacity of the coal mill and maintaining an efficient pulverizing process even under low load conditions.

[0019] Increase feed water temperature: Using superheated steam to heat feed water and increase feed water temperature helps improve the overall efficiency of the boiler and power generation performance.

[0020] Reduce coal consumption: By optimizing steam utilization and increasing hot air temperature, reducing excess air coefficient and lowering exhaust temperature, coal consumption can be reduced, achieving energy conservation and emission reduction.

[0021] In summary, the utility model significantly improves the pulverizing and drying output and feed water temperature of the coal-fired boiler under low-load conditions, providing strong support for the efficient and stable operation of the coal-fired boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is the original system operation diagram.

[0024] Figure 2 This is a schematic diagram of a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler provided by the utility model.

[0025] Illustration: 1. Boiler; 2. Turbine high-pressure cylinder; 3. No. 1 high-pressure heater; 4. First-stage extraction steam isolation valve; 5. Low-temperature feed water; 6. High-temperature feed water; 7. Main steam; 8. First-stage extraction steam; 9. Air preheater; 10. Cold air; 11. Hot secondary air at air preheater outlet; 12. Hot primary air at air preheater outlet; 13. Coal mill; 14. Primary air at mill outlet; 15. Desuperheater; 16. Superheated steam at hot air heat exchanger outlet; 17. Desuperheating water; 18. Bypass superheated steam; 19. Desuperheated and reduced-pressure superheated steam; 20. Hot air at hot air heat exchanger outlet; 21. Hot air exchanger; 22. Bypass superheated steam isolation valve; 23. Reduced-pressure superheated steam; 24. Desuperheating water regulating valve; 25. Desuperheating water isolation valve; 26. Economizer; 27. Low-temperature superheater; 28. Medium-temperature superheater; 29. ​​High-temperature superheater. DETAILED DESCRIPTION

[0026] See also Figure 2 The embodiment of the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, comprising: a boiler 1 connected to a high-pressure cylinder 2 of a steam turbine, a steam extraction isolation valve 4 installed between the high-pressure cylinder 2 of the steam turbine and a No. 1 high-pressure heater 3, a hot air heat exchanger 21 connected to a coal mill 13, a No. 1 high-pressure heater 3, an air preheater 9, and a desuperheater 15.

[0027] The hot air heat exchanger 21 is connected to the air preheater 9, the desuperheater 15, the desuperheating water 17, the No. 1 high-pressure heater 3, the coal mill 13 and the boiler 1;

[0028] One end of the desuperheating water regulating valve 24 is connected to the desuperheating water isolation valve 25, and the other end of the desuperheating water regulating valve 24 is connected to the desuperheater 15. The bypass superheated steam isolation valve 22 is connected to the desuperheater 15.

[0029] The boiler 1 includes an economizer 26, a low-temperature superheater 27, a medium-temperature superheater 28 and a high-temperature superheater 29. The economizer 26 is connected to the low-temperature superheater 27, the low-temperature superheater 27 is connected to the medium-temperature superheater 28, and the medium-temperature superheater 28 is connected to the high-temperature superheater 29.

[0030] The present invention provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. When the system is in operation, the first extraction steam isolation valve 4 is closed, and the superheated steam 16 at the outlet of the hot air heat exchanger replaces the first extraction steam 8 to enter the first high-pressure heater 3 to heat the low-temperature feed water 5; the low-temperature feed water 5 is heated by the first high-pressure heater 3 to become high-temperature feed water 6, and is finally sent to the boiler 1;

[0031] Steam turbine high-pressure cylinder 2: It is the main component of the steam turbine. Its function is to convert the thermal energy of steam into mechanical energy, thereby driving the generator to generate electricity.

[0032] No. 1 high-pressure heater 3: used to heat feed water and improve boiler efficiency by increasing feed water temperature.

[0033] Stage 1 extraction steam isolation valve 4: This valve is installed between the high-pressure cylinder of the steam turbine and the No. 1 high-pressure heater. Its main function is to control the extraction steam flow rate and ensure the stable operation of the No. 1 high-pressure heater.

[0034] Hot air heat exchanger 21: It is arranged in the hot primary air duct between the air preheater and the coal mill. Its main function is to heat part of the cold air, turning it into hot air that enters the coal mill to dry the raw coal, thereby increasing the primary air temperature at the coal mill outlet.

[0035] Coal mill 13: used to grind raw coal into coal powder, which is then mixed with hot air and then fed into the boiler for combustion.

[0036] Air preheater 9: Responsible for heating the cold air. Part of the hot air will enter the boiler to assist combustion, and the other part will enter the hot air heat exchanger for reheating.

[0037] Desuperheater 15: used to regulate the steam temperature to ensure that it operates within a safe temperature range.

[0038] Desuperheating water regulating valve 24 and desuperheating water isolation valve 25: These two valves together constitute part of the desuperheating system. Their main function is to achieve precise control of steam temperature by adjusting the flow of desuperheating water.

[0039] Bypass superheated steam isolation valve 22: This valve is used to control the flow of bypass superheated steam to ensure the stable operation of the entire system.

[0040] Boiler 1: It contains economizer, low-temperature superheater, medium-temperature superheater and high-temperature superheater. These components together constitute the boiler's superheating system, which is responsible for heating the steam to the predetermined temperature.

[0041] Economizer 26: Located at the boiler inlet, its primary function is to heat the feedwater and recover heat from the exhaust gas, thereby improving boiler efficiency. Low-temperature superheater 27, medium-temperature superheater 28, and high-temperature superheater 29: These three components are connected in sequence and work together to gradually heat the steam to the desired temperature required for turbine operation.

[0042] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The hot air heat exchanger 21 is arranged in the hot primary air duct between the air preheater 9 and the coal mill 13. After the cold air 10 passes through the air preheater 9, a part of it enters the boiler 1 as the hot secondary air 11 at the air preheater outlet to participate in combustion, and the other part enters the hot air heat exchanger 21 for reheating and becomes the hot air 20 at the hot air heat exchanger outlet to enter the coal mill 13 to dry the raw coal, thereby improving the temperature of the mill outlet primary air 14 at the outlet of the coal mill 13. The mill outlet primary air 14 after temperature increase enters the boiler 1 for combustion.

[0043] Specifically, the present invention provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, wherein part of the superheated steam is extracted from the outlet of the medium-temperature superheater 28 arranged in the boiler 1 as bypass superheated steam 18 .

[0044] Specifically, the present invention provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The bypass superheated steam 18 is reduced in pressure by a pressure reducing regulating valve 12 and then reduced in temperature by a desuperheater 15 to become reduced-temperature and reduced-pressure superheated steam 19.

[0045] Specifically, the utility model provides a system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler. The cooled and reduced-pressure superheated steam 19 enters the hot air heat exchanger 21, heats the hot primary air 12 at the outlet of the air preheater and converts it into hot air 20 at the outlet of the hot air heat exchanger. The cooled and reduced-pressure superheated steam 19 after heat release becomes superheated steam 16 at the outlet of the hot air heat exchanger.

[0046] Specifically, the utility model includes the following main parts and operation processes:

[0047] Main steam system: The main steam connects the boiler and the high-pressure cylinder of the turbine to ensure the effective conversion and utilization of steam energy.

[0048] High-pressure heater and extraction system: A steam extraction isolation valve is installed between the high-pressure cylinder of the turbine and the No. 1 high-pressure heater to control the extraction and distribution of steam.

[0049] Hot air heat exchange system: The hot air heat exchanger is connected to multiple key components, including the coal mill, high-pressure heater, air preheater, and desuperheater. Placed in the hot primary air duct between the air preheater and the coal mill, the hot air heat exchanger further heats the cold air, raising the air temperature entering the coal mill and thus enhancing the mill's drying capacity.

[0050] Desuperheating and pressure reduction system: includes desuperheating water regulating valve, desuperheating water isolation valve and desuperheater, which is used to adjust the temperature and pressure of superheated steam to ensure that the steam reaches appropriate conditions before being sent to the hot air heat exchanger.

[0051] Boiler internal system: including economizer, low-temperature superheater, medium-temperature superheater and high-temperature superheater. These components work together to ensure the gradual heating and efficient use of steam inside the boiler.

[0052] The utility model effectively solves the problems of increased excess air coefficient at the furnace outlet, decreased boiler efficiency, increased cooling water volume, and increased exhaust gas temperature, thereby reducing the coal consumption of the unit. The specific measures are as follows:

[0053] Increasing hot air temperature: Using hot air heating modules and superheated steam to increase the hot air temperature not only helps stabilize combustion in the boiler, but also reduces the excess air coefficient by reducing the hot air flow, thereby improving boiler efficiency.

[0054] Increased feedwater temperature: The No. 1 high-pressure heater module uses cooled superheated steam to heat the low-temperature feedwater, raising the feedwater temperature. This improves the efficiency of heat exchange within the boiler, reducing fuel consumption and exhaust gas temperature.

[0055] Steam decompression and temperature reduction treatment: The steam decompression and temperature reduction module can accurately control the steam parameters, avoid energy loss and improve energy utilization efficiency.

[0056] System control optimization: The system control module comprehensively monitors and regulates system operation, and automatically adjusts parameters according to actual operating conditions through intelligent control strategies to improve boiler efficiency and reduce coal consumption in the most optimized way.

[0057] Air preheater preheating: preheat the cold air entering the boiler, increase the initial temperature of the hot air, provide favorable conditions for subsequent hot air heating, and thus improve the thermal efficiency of the boiler.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler, characterized in that: include: The boiler (1) is connected to the high-pressure cylinder (2) of the steam turbine. A steam extraction isolation valve (4) is installed between the high-pressure cylinder (2) of the steam turbine and the No. 1 high-pressure heater (3). The hot air heat exchanger (21) is connected to the coal mill (13), the No. 1 high-pressure heater (3), the air preheater (9), and the desuperheater (15). The hot air heat exchanger (21) is connected to the air preheater (9), the desuperheater (15), the desuperheating water (17), the No. 1 high-pressure heater (3), the coal mill (13) and the boiler (1); One end of the desuperheating water regulating valve (24) is connected to the desuperheating water isolation valve (25), the other end of the desuperheating water regulating valve (24) is connected to the desuperheater (15), and the bypass superheated steam isolation valve (22) is connected to the desuperheater (15); The boiler (1) includes an economizer (26), a low-temperature superheater (27), a medium-temperature superheater (28) and a high-temperature superheater (29). The economizer (26) is connected to the low-temperature superheater (27), the low-temperature superheater (27) is connected to the medium-temperature superheater (28), and the medium-temperature superheater (28) is connected to the high-temperature superheater (29).

2. The system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler according to claim 1 is characterized in that: The hot air heat exchanger (21) is arranged in the hot primary air duct between the air preheater (9) and the coal mill (13). After the cold air (10) passes through the air preheater (9), a portion of the cold air (10) enters the boiler (1) as the hot secondary air (11) at the air preheater outlet to participate in combustion, and the other portion enters the hot air heat exchanger (21) to be heated again and becomes the hot air (20) at the hot air heat exchanger outlet to enter the coal mill (13) to dry the raw coal and increase the temperature of the mill outlet primary air (14) at the mill outlet (13). The mill outlet primary air (14) after the temperature increase enters the boiler (1) to be burned.

3. The system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler according to claim 1 is characterized in that: A portion of the superheated steam is extracted from the outlet of the medium-temperature superheater (28) arranged in the boiler (1) as bypass superheated steam (18).

4. The system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler according to claim 1 is characterized in that: The bypass superheated steam (18) is decompressed by the pressure reducing regulating valve (12) and then desuperheated by the desuperheater (15) to become desuperheated and pressure-reduced superheated steam (19).

5. The system for improving the low-load pulverizing and drying output and feed water temperature of a coal-fired boiler according to claim 4 is characterized in that: The desuperheated steam (19) enters the hot air heat exchanger (21), heats the hot primary air at the outlet of the air preheater and converts it into hot air (20) at the outlet of the hot air heat exchanger. The desuperheated steam (19) after releasing heat becomes superheated steam (16) at the outlet of the hot air heat exchanger.

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