How to choose the right industrial dust collector, you should know these

2021-11-19 10:37

Bag filter fan selection, select the right fan, and the dust removal effect is guaranteed. The bag filter has a wide range of applications: basically all applicable: mechanical equipment, workshop grinding, power plants, steel plants, cement plants, chemical plants, smelting, carbon , Foundry and other factories. There are many types of bag filter. The induced draft fan is the necessary equipment for the bag filter. The dust is processed by the bag filter under the action of the induced draft fan. Therefore, the calculation of its selection is particularly important. Larger equipment will cause unnecessary flow costs; small equipment will affect production, making it difficult to meet environmental protection requirements. Choosing the correct bag filter fan can better achieve the dust removal effect and solve the flue gas pollution.


The main technical parameters for the design and selection of bag filter fans include processing gas flow, filtration wind speed, dust removal efficiency, imported dust concentration, emission concentration, filter bag specifications, dust removal skeleton specifications, electromagnetic pulse valve specifications, pressure loss, and air leakage Rate, steel consumption, draft fan specifications and models, the length, width, and height of the dust collector, etc.


   General steps for the selection of the fan of the bag filter


  The air volume of the fan is defined as:


   The product of the wind speed V and the cross-sectional area F of the air duct. Large fans can accurately measure the air volume with an anemometer, so the air volume calculation is also very simple. Directly use the formula Q=VF. to calculate the air volume.


   Most of the fans used in the dust collector are general purpose fans, and a few explosive dusts use explosion-proof fans. Ordinary impellers are made of carbon steel. As the parts collide with each other, or impurities such as sand or iron filings are absorbed into the rotor, it is easy to cause sparks and cause gas combustion and explosion. In order to avoid such accidents, when the ventilator conveys explosive and flammable grades When the gas medium is lower, the volute of the fan is made of steel plate, and the impeller is made of aluminum. When the gas is flammable and explosive, both the volute and the impeller must be made of aluminum. There is not much difference in overall appearance and size between general-purpose fans and explosion-proof fans of the same specification and model, but the material used for the impeller is different.


  The direction of rotation fan can be made into two types of right-handed or left-handed. Viewed from one end of the motor, the impeller rotates in a clockwise direction into a right-handed fan, which is represented by "right"; otherwise, it is called a whirlwind and is represented by "left".


  The main parameters of the fan


   1. Air volume:


  The volume flow of gas delivered by the fan in a unit time is called the air volume or flow rate, which usually refers to the volume of gas delivered under working conditions. (Unit: m3/h, m3/min, m3/s).


  2, wind pressure:


  The wind pressure of the fan refers to the total pressure, which is the sum of the dynamic pressure and the static pressure. (Unit: Pa);


  Dynamic pressure: The pressure represented by the kinetic energy of the gas on the outlet section of the ventilator is called dynamic pressure;


  Static pressure: The vertical force received by the fan per unit area.


  3, power:


   The work done by the fan to the air per unit time. (Unit: kW, W)


  4. Efficiency:


   The ratio of the output power of the fan to the input power.


  5, rotation speed:


   The number of fan rotations per minute. (Unit: r/min)


  6. Ratio of revolutions:


  The specific speed is a characteristic parameter of the fan, which represents the relationship between the air volume, air pressure and speed of the fan at the highest efficiency point. A fan with a large specific speed has a large flow and low air pressure: a fan with a low specific speed has a small flow and high air pressure.


  2. Selection content


  (1) Air volume: Determined by the air volume required by the system;


   (2) Total pressure: determined by the resistance of the pipeline system and the dust removal equipment;


  (3) Angle of inlet and outlet: determined by the direction of inlet and outlet;


  (4) Optional installation direction: determined by the pipeline system;


  (5) Transmission mode: determines the transmission efficiency. The mechanical efficiencies of motor direct drive, coupling direct drive, and belt drive are 1, 0.98, and 0.95 respectively.


   (6) When selecting a fan, the ventilation duct system is not tight and the leakage of air and the resistance calculation error should be considered. In order to ensure the reliable operation of the fan, the air volume and pressure of the system should be left margin.


  Pipe system design and selection


  The wind pressure is determined according to the pipeline hydraulic calculation. The hydraulic calculation of the ventilation ducts is carried out on the basis that the system and equipment layout, air duct materials, the location and air volume of each air supply and exhaust point have been determined. Its main purpose is to determine the pipe diameter (or cross-section size) and resistance of each pipe section to ensure the required air volume distribution in the system. Finally, determine the model and power consumption of the fan.


   Air duct hydraulic calculation methods include assumed flow velocity method, pressure loss average method and static pressure recovery method.


   The assumed flow rate method is commonly used at present.


The characteristic of    pressure loss averaging method is to evenly distribute the known total pressure head to each pipe section according to the length of the main pipe, and then determine the section size of the air duct according to the air volume of each pipe section. If the pressure head of the fan used in the air duct system has been determined, or carry out the resistance balance calculation for the branch pipeline.


The characteristic of the    static pressure recovery method is to use the static pressure recovered at the branch of the air pipe to overcome the resistance of the pipe section, and determine the section size of the air pipe according to this principle. This method is suitable for hydraulic calculation of high-speed air-conditioning system.


   The characteristic of the assumed flow velocity method is that the flow velocity of the air duct is first selected according to the technical and economic requirements. Then determine the cross-sectional size and resistance of the air duct according to the air volume of the air duct. Most of our company calculates wind pressure according to this method.


   The calculation steps and methods of the assumed flow velocity method are as follows:


  (A) Draw an axonometric drawing of the ventilation or air-conditioning system, number each pipe section, and mark the length and air volume. The length of the pipe section is generally calculated according to the length of the center line between the two pipe fittings, without deducting the length of the pipe fittings (such as tees and elbows).


  (B) Determine a reasonable air velocity


   The air velocity in the duct has a great influence on the economy of the ventilation and air-conditioning system. The flow rate is high, the air duct section is small, the material consumption is small, and the construction cost is small; but the resistance of the system is large, the power consumption increases, and the operating cost increases. The dust removal system will increase the wear of equipment and pipes, and the air conditioning system will increase the noise. The flow rate is low, the resistance is small, and the power consumption is low; but the duct section is large, the material and construction costs are high, and the space occupied by the duct is also increased. Too low the flow rate of the dust removal system will cause dust deposits to block the pipeline. Therefore, a reasonable flow rate must be selected through a comprehensive technical and economic comparison.


  When determining the cross-sectional size of the air duct, the uniform specifications of the ventilation ducts should be used for duct selection to facilitate industrial processing and production. After the duct cross-section size is determined, the resistance should be calculated according to the actual flow velocity in the duct. The resistance calculation should start from the most unfavorable loop (ie the loop with the greatest resistance).


   (c) When the fan is working in a non-standard state, the performance of the fan should be converted according to the formula and formula, and then the fan should be selected from the fan sample based on this parameter.


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