The use of bag filter will be limited by the temperature resistance of filter material. Among the commonly used filter materials, glass fiber filter material has the highest temperature resistance, and the long-term working temperature can reach 280℃. But the smoke from industrial furnaces can reach hundreds or even thousands of degrees Celsius. In order to solve this problem, measures must be taken to reduce the temperature of flue gas to the allowable range of filter media. Common cooling methods are as follows.
(1) indirect cooling
High-temperature flue gas passes through a heat exchanger (generally made of steel pipe), flue gas flows through one side of the steel pipe, and cold water or outdoor air flows through the other side of the steel pipe. The temperature of flue gas is reduced without touching each other. The advantage of this method is that it does not increase the amount of flue gas, the actual flow of flue gas will decrease due to the decrease of temperature, and the moisture content of flue gas will not increase. At the same time, the heat of flue gas can be recycled. Its disadvantages are large volume of heat exchanger, large steel consumption and high investment. At the same time, the heat exchanger has certain resistance, which increases the power consumption of the fan.
(2) spray direct cooling
Water is sprayed into the high-temperature flue gas through the nozzle to form fine water mist, which evaporates and absorbs a lot of heat to cool the flue gas. The advantages of this method are fast flue gas cooling and low equipment and investment. Its disadvantage is that the moisture content of flue gas increases, which may cause flue gas condensation and endanger the dust removal filter bag. If the sprayed water mist is not fine enough to become larger water droplets, then the water droplets are likely to directly enter the bag filter before evaporation, and the dust filter bag is easily blocked. Therefore, it is necessary to select a nozzle with excellent performance and accurately control the spray amount with a microcomputer. This kind of equipment is expensive and difficult to control.
(3) mixing with cold air and cooling directly.
Usually, a three-way pipe is installed in the air inlet pipe of the dust collector, and the outside air can enter the flue from the three-way pipe and mix with the flue gas, thus reducing the temperature of the flue gas. The advantage of this method is that the cooling speed is fast, and only some simple components such as three-way pipe and valve for controlling air flow are needed. Its disadvantage is that the flue gas volume will increase, and the greater the cooling rate, the more the flue gas volume will increase. Therefore, it is necessary to increase the filtering area and equipment volume of the dust collector accordingly, thus increasing the investment of equipment, air ducts, fans and other facilities and increasing the operating cost.
The above cooling methods have their own scope of application, and we will choose them according to the specific characteristics of smoke and dust and the economic conditions of manufacturers.