CN203784991U - Hot air recirculating system of coal-fired boiler - Google Patents

Abstract

The utility model discloses a hot air recirculation system for a coal-fired boiler, which mainly includes an air preheater, a blower (primary fan), a recirculation air duct, a recirculation air duct cut-off door, a recirculation air duct regulating valve and hot and cold air mixing chamber. The utility model adds a hot air recirculation device in the outlet air duct of the air preheater, and uses it to extract part of the hot air at the outlet of the air preheater, and introduces this part of hot air to the front of the blower (primary fan) through the recirculation air duct. The cold air extracted from the outside is mixed, and then the mixed air is passed into the air preheater together. The hot air recirculation system solves the problem of low air temperature at the inlet of the air preheater in some areas, and alleviates the common problems of low temperature corrosion and dust blocking in the normal operation of the air preheater to a large extent. The safe and stable operation of thermal power generating units in low temperature environment provides a strong guarantee.

Description

A coal-fired boiler hot air recirculation system

technical field

The utility model belongs to the technical field of preventing low-temperature corrosion of an air preheater, in particular to a hot air recirculation system for a coal-fired boiler. Specifically, a part of the hot air at the outlet of the air preheater is mixed with the cold air at the inlet to increase the air temperature at the inlet of the air preheater, increase the average wall temperature of the cold end, protect the heat transfer elements at the cold end of the air preheater, and reduce corrosion and blocking ash.

Background technique

The safe operation of the boiler unit is related to many factors, while the safe operation of the air preheater, supply (primary) fan, dust collector and other equipment is directly related to the temperature of the cold air. In order to ensure the safe operation of these equipment, certain requirements should be put forward for the cold air temperature according to different fuel characteristics and different operating conditions.

There are many ways to prevent low-temperature corrosion. One of the most widely used methods is to increase the temperature of the cold air to ensure that the average wall temperature at the cold end is higher than the acid dew point temperature. The corrosion and dust blocking of the preheater are mainly located at the cold end of the preheater, and sometimes also occur on the heating surface of the middle layer. Therefore, the average wall temperature of the cold end during operation is required to be higher than the recommended value, generally at least 5°C higher. And because the exhaust gas temperature is different under different loads of the boiler, so the required cold air temperature is also different when the boiler load is different. Still above the recommended value, a higher cold air temperature is required. In addition, when the (primary) blower directly draws air from the outside, the temperature of the air entering the fan is the local ambient temperature. In cold regions, the material and adjustment device of the fan are unbearable. When the air temperature entering the fan reaches the required value, it is also necessary to take measures to increase the temperature of the cold air. At the same time, a higher temperature of the cold air can also reduce the low-temperature condensation in the indoor cold air duct. In addition, for the safe operation of the electrostatic precipitator, it is generally stipulated that when the unit is started, it is only allowed to be used when the exhaust gas temperature is higher than the dew point, so as to avoid condensation on the lower temperature electrostatic precipitator plate. Therefore, it is of great significance to increase the temperature of the cold air entering the preheater to prolong the life of the equipment, improve the operating conditions of the equipment, and reduce environmental pollution. Under normal circumstances, it can be realized by setting the heater and recirculating hot air.

The hot air recirculation system is widely used because of its simplicity, convenient operation, and small maintenance workload, but it also has certain problems during operation. For systems equipped with recirculation fans, the wear and tear of recirculation fans, the increase in initial investment and operating costs all reduce their availability. In addition, the uneven mixing of the recirculating hot air and the cold air at the inlet of the air preheater often causes failures in the operation of the subsequent blower (primary blower) and reduces its service life.

Contents of the invention

The purpose of this utility model is to propose a more reasonable hot air recirculation system in view of the various disadvantages of the existing devices for increasing the air temperature at the inlet of the air preheater.

The hot air recirculation system of a coal-fired boiler mainly includes an air preheater (1), a blower (2), a recirculation air duct (3), a recirculation air duct cut-off door (4), a recirculation air duct adjustment The valve (5) and the hot and cold air mixing chamber (6); the blower (2) is respectively connected with the hot and cold air mixing chamber (6) and the inlet air duct of the air preheater; the recirculation air duct is respectively connected with the air preheater The hot air outlet air duct and the hot and cold air mixing chamber (6); the hot and cold air mixing chamber (6) is connected to the ambient cold air inlet (7); the recirculation air duct cut-off door (4) is connected to the recirculation air duct The regulating valve (5) is connected and arranged at the air inlet of the recirculation air duct.

The air outlet of the recirculation air duct is arranged with a cold and hot air mixing chamber (6) to enhance the mixing effect of cold and hot air, so as to avoid the difference in air temperature between the upper and lower parts of the air duct, resulting in unsafe operation of the blower (2).

The recirculated hot air is sent into the cold and hot air mixing chamber (6) through three paths a, b, and c, so as to enhance the mixing effect of the cold and hot air in the mixing chamber.

The recirculation air duct is sequentially arranged with a recirculation cut-off door (4) and a recirculation regulating valve (5). The recirculation cut-off door (4) is used to increase the tightness of the air duct after the hot air recirculation system is deactivated. The circulation regulating valve (5) regulates the flow of hot air entering the hot and cold air mixing chamber (6).

The hot and cold air mixing chamber (6) is arranged at the air inlet of the blower. It uses the pressure difference between the hot air at the outlet of the air preheater and the air inlet of the blower to extract the hot air.

This system realizes the hot air recirculation flow by using the pressure difference between the hot air at the outlet of the air preheater and the air at the inlet of the blower (primary fan), which saves the hot air recirculation fan and reduces the initial investment and operating costs. In addition, a cold and hot air mixer is arranged at the air outlet of the recirculation air duct, and the recirculation hot air is sent into the cold and hot air mixing chamber through three paths a, b, and c, so as to enhance the mixing effect of cold and hot air to avoid The air temperature in the upper and lower parts of the air duct is different, resulting in unsafe operation of the blower (primary fan). After analysis and demonstration, the system has great advantages in operation safety and economy.

Description of drawings

Figure 1 is a hot air recirculation system for a coal-fired boiler.

Figure 2 is a partial A-A view of the hot air recirculation system.

Labels in the figure:

1-air preheater; 2-supply fan (primary fan); 3-recirculation air duct;

4-recirculation air duct cut-off door; 5-recirculation air duct regulating valve; 6-hot and cold air mixing chamber;

7-Outdoor wind inlet.

Detailed ways

The utility model provides a hot air recirculation system for a coal-fired boiler. The following will be described in conjunction with the accompanying drawings and examples.

In the schematic diagram of a hot air recirculation system for a coal-fired boiler as shown in Figure 1, the system mainly includes an air preheater (1), a blower (2), a recirculation air duct (3), and a recirculation air duct cut-off door ( 4), recirculation air duct regulating valve (5) and hot and cold air mixing chamber (6).

The principle is as follows: the cold air from the external environment flows through the hot and cold air mixing chamber and the blower (primary fan) and then enters the air preheater to exchange heat with the flue gas in the air preheater. To the pulverizing system or the furnace, a small part of it is sent back to the cold and hot air mixing chamber through the recirculation air duct, mixed with the cold air from the external environment, and the air temperature at the inlet of the blower is increased, and then sent into the air preheater through the blower . For some thermal power plants located in the north and with low ambient temperature in winter, as long as a reasonable recirculation air volume is selected, the inlet air temperature of the air preheater can be guaranteed to meet the design requirements.

When the boiler load or ambient temperature changes, the recirculation air volume can be adjusted through the recirculation air duct regulating valve, thereby ensuring the stability of the air temperature at the inlet of the air preheater. When the external ambient temperature rises, gradually close the recirculation air duct regulating valve to reduce the recirculation air volume entering the hot and cold air mixing chamber until the external ambient temperature can fully meet the air temperature requirements of the air preheater inlet.

Claims (5)

1. A coal-fired boiler hot air recirculation system, characterized in that the system mainly includes an air preheater (1), a blower (2), a recirculation air duct (3), and a recirculation air duct cut-off door (4) , the recirculation air duct regulating valve (5) and the hot and cold air mixing chamber (6); the blower (2) is respectively connected with the hot and cold air mixing chamber (6) and the inlet air duct of the air preheater; the recirculation air The channels are respectively connected to the hot air outlet channel of the air preheater and the hot and cold air mixing chamber (6); the hot and cold air mixing room (6) is connected to the ambient cold air inlet (7); the recirculation air channel cut-off door (4 ) is connected with the recirculation air duct regulating valve (5), and is arranged at the air inlet of the recirculation air duct. 2. A hot air recirculation system for a coal-fired boiler according to claim 1, characterized in that: a cold and hot air mixing chamber (6) is arranged at the air outlet of the recirculation air duct to enhance the mixing effect of cold and hot air , so as to avoid the difference in air temperature between the upper and lower parts of the air duct, resulting in unsafe operation of the blower (2). 3. A hot air recirculation system for a coal-fired boiler according to claim 1, characterized in that: the recirculated hot air is sent into the cold and hot air mixing chamber (6) through three paths a, b, and c to strengthen the mixing chamber Mixed effect of hot and cold air. 4. A hot air recirculation system for a coal-fired boiler according to claim 1, characterized in that: a recirculation cut-off door (4) and a recirculation control valve (5) are sequentially arranged on the recirculation air duct, and the recirculation The cut-off door (4) increases the tightness of the air duct after the hot air recirculation system is disabled, and the recirculation regulating valve (5) is used to regulate the flow of hot air entering the hot and cold air mixing chamber (6). 5. A hot air recirculation system for a coal-fired boiler according to claim 1, characterized in that: the hot and cold air mixing chamber (6) is arranged at the air inlet of the blower, and uses the hot air at the outlet of the air preheater to enter the blower. The pressure difference between the tuyeres draws hot air.