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【 Technical communication 】 Fan, induced draft fan, air volume and air pressure relationship

by:Tianwang     2020-06-26
【 Technical communication 】 Fan and induced draft fan air volume and air pressure relationship is 1 why induced draft fan, air blower is big? Only maximum evaporation into the boiler blower. The amount of air required for complete combustion. And induced draft fan in addition to send charging in the air and fuel all away, try to make the air leakage into the flue gas side. Blower into the boiler preheater is the average temperature is 20 ℃ cold air, and the fan is higher temperature ( 140~160℃) The hot flue gas, the cold air to higher temperature hot flue gas, the volume will increase. Therefore, induced draft fan air volume is bigger than the blower. Generally induced draft fan air volume to 50% ~ 60% larger than the supply air volume. 2, why often wind pressure is higher than induced draft fan wind pressure blower? Adopt blower overcome the resistance of the air side, adopts the induced draft fan to overcome the resistance of the flue gas side ventilation method called balanced ventilation. Because of the large advantages of balanced ventilation, so most of the boiler adopts balanced ventilation. The flue gas side of the induced draft fan to overcome resistance mainly includes the following several parts: the negative pressure of furnace; (2) prevent slag tube, superheater, reheater, steering room, economizer and air preheater and the dust collector and so on flow resistance; (3) shaft flue formed through wind resistance produced by itself. Although induced draft fan need to overcome the resistance of the project is more, but as a result of convection heating surface wear in the direct ratio, and the three times of flue gas flow, the convection heating surface in order to reduce wear and tear, the design of flue gas flow rate is low, about 10 m/s or so, at the same time, the average density of flue gas is small, so the flow resistance of flue gas side is not very big. Blower need to overcome flow resistance is mainly at the inlet and outlet of the air preheater and the corresponding air duct and flow resistance of the burner. Although the blower need to overcome the resistance of the project is less, but because of the air cleaner, do not need to consider wind speed increase after the air preheater wear problem. In order to improve the heating coefficient of air side, in order to improve the heat transfer coefficient of air preheater, air preheater of the wind speed up to about 20 m/s. Heat transfer area of the air preheater is one of the biggest, pulverized coal furnace period of high and low temperature air preheater with high and low temperature section of economizer cross to decorate, make the air preheater inlet and outlet duct, contact air duct forming more resistance to flow. In order to make the burner has good performance, need to be part of the air inside the burner to rotate, formed in the burner outlet reflux zone. In order to make the air into the interior of the flame, strengthen the fuel and air mixing and late for burner outlet of wind speed of 25 ~ 40 m/s. As a result, not only the resistance coefficient of the burner is very big, and the burner of the wind speed is high, make the burner flow resistance is very big, often burner flow resistance than flow resistance of air preheater. For example, in a 130 t/h boiler, the flue gas side of the flow resistance at 1710 pa; Total air preheater and the import and export air duct flow resistance is 1186 pa, burner flow resistance of 1860 pa, the total flow resistance for the air side is 3046 pa. Because of the boiler air side air velocity is higher, the density of air is larger, the total flow resistance is greater than the total flow resistance of flue gas side, so, the wind pressure blower is usually higher than induced draft fan wind pressure ( Is not absolute) 。
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