Today: the principle and operation of centrifugal fans

 I. Definition of centrifugal fan Centrifugal fan is a kind of driven fluid machinery, which depends on the input mechanical energy, improves the gas pressure and sends gas side by side. Centrifugal fan is widely used in grease factory, mainly including 1, ventilation and dust removal : Used for oil cleaning, meal/skin grinding, oil/meal conveying process ventilation dust removal; 2, pneumatic conveying: such as bean skin wind transport, white soil transport, skin/kernel wind separation, coal ash transport; 3. Ventilation Drying: such as conditioning tower ventilation, swelling material drying/cooling, meal drying/cooling, etc. Two, the principle of centrifugal fan When the impeller rotates with the rotating shaft, the gas between the blades also rotates with the impeller and obtains the inertial centrifugal force, and the gas is thrown out from the outlet between the blades. The expelled gas pushes into the housing, increasing the pressure of the gas inside the housing And is finally directed to the exit. After the gas is ejected, the pressure in the center of the impeller decreases. The outside gas can be inhaled from the inlet of the fan through the hole in the center of the front disk of the impeller, and the gas is continuously transmitted. Three, the structure of centrifugal fan The centrifugal fan is mainly composed of impeller, casing, air inlet, regulating damper and driving device. Impeller: composed of a front disk, a rear disk and a blade installed in two disks; Shell: the shell of the fan is volute shape, welded with thin steel plate, its role is to gather the gas from the impeller, and make it smoothly along the impeller rotation direction is directed to the fan outlet, and pressurize the gas; Air inlet: the first part of the suction pipe segment, plays the role of gas collection, so it is also called the collector. Iv. Main performance parameters Flow Q: fluid volume transported by the fan within a unit time, commonly expressed in volume flow, unit m3/s or m3/h, and related to the structure, size and speed of the fan; Pressure head p: the effective energy provided by the fan to the unit volume flow rate, in pa; Efficiency η : in the actual operation of the fan, due to the existence of various energy loss, resulting in The actual (effective) head and flow rate are lower than the theoretical value, and the input power is higher than the theoretical value. The parameter that reflects the amount of energy lost is called efficiency. Efficiency and fan type, size, processing accuracy, gas flow It has to do with things like properties. Usually, the efficiency of small fans is 50% ~ 70%, while the efficiency of large fans can reach 90%. Shaft power N and effective power Ne: Shaft power is the power unit of the motor input to the fan shaft in W or kW. The effective power of the centrifugal fan refers to the energy obtained by the gas from the impeller in unit time, then there is Ne=Qp , N=Ne/η= Qp/η. Rotational speed n: revolutions per minute of the fan and the fan impeller, that is, r/min. 5. Use and operation of fan 1. Prepare the fan before starting 1) Close the regulating damper and close the inlet and outlet damper of the fan; 2) Manually turn the engine, check the clearance of each fan component, and rotate the impeller and the housing to see if there is friction; 3) Coupling, belt wheel protection passport installed in place; 4) Whether the oil level of the bearing box meets the lubricating oil level during operation; 5) For the fan with water cooling bearing, it is necessary to check whether the water supply of the cooling water pipe is good; 6) Determine the steering of the fan electrically, and check whether there is water leakage, oil leakage, vibration, abnormal sound, odor and other phenomena. 2. Start the fan 1) Start the fan (pay attention to whether it runs smoothly); 2) After the fan starts, gradually open the wind door until the air volume required by the actual production; Pay attention to the running current of the motor when opening the wind door to prevent the wind door from overloading; 3) The temperature of the fan bearing shall be detected after starting, and the temperature rise of the bearing shall not exceed 40 degrees of the ambient temperature on site; 3. Check the fan during operation 1) Listen to whether the fan runs smoothly, has no abnormal sound or friction; 2) Check whether the foot bolts are loose; 3) Test the temperature and lubrication of bearings; 4) Whether the bearing lubricating oil cooling water is smooth and whether the inlet and outlet pipes have temperature differences; 5) Whether there is lubricating oil leakage in the bearing box; 6) Whether there is abnormal noise in the operation of the bearing box and bearing, and whether the rotation is smooth; 7) Check whether the current runs stably; 4. Make an emergency stop 1) The fan is found to have a strong noise; 2) There is friction between the impeller and the casing; 3) the vibration of the casing suddenly intensifies; 4) The bearing temperature continues to rise and exceeds the allowable temperature rise range; 5) The sudden rise of current cannot be recovered within 2 minutes; 6) Serious oil leakage in the bearing box; 7) Cooling water is interrupted for more than half an hour. 5. Stop the fan 1) Stop the fan operation after reducing the load; 2) Close the inlet and outlet valve of cooling water; 3) If the hot air is transported, stop the fan when the air outlet temperature of the fan is reduced to 40 degrees after stopping the heater; 4) After the fan is shut down, the drainage valve at the bottom of the housing should be opened for drainage; Close the fan inlet and outlet damper at the same time. Six: Matters needing attention in the selection of leaching fan in the leaching workshop: The fans in the leaching workshop include the immersion scraper supporting fan FN300, mineral oil FN361, DTDC supporting fan FN305, sweeping fan in the leaching workshop FN381. The selection of these fans in addition to meet the technical requirements In addition, explosion-proof must also be required, the drive of the fan should not be selected belt drive, fan speed should not exceed 1440RPM.