01 Fault Analysis

The model of coal mill induced draft fan of a company is W4-73-15NO19F, the air volume is 100000m³/h, the wind pressure is 2200Pa, the rated current is 28A, the design speed is 960r/min, the motor power is 250kW, and the actual operating current is 19 ~ 20A. The fan is generally stable at the beginning of operation, and the vibration of the fan bearing house is generally about 0.6mm/s. However, with the continuous operation of the equipment, the vibration value of the fan bearing house rises gradually and has no slowing down trend. Generally speaking, the operator will actively stop when the fan bearing seat vibrates to 5.6mm/s, and it is required to use high pressure air to blow the dust on the non-working surface of the fan impeller. However, the wind after purging will continue the above process again. Basically, under the condition of stable working conditions, it needs to stop cleaning 6 ~ 7 times a day, and each purging will take about 20min. In order to solve this problem, we take measures to reduce dust concentration and avoid impeller dusting.

02 Solutions

(1) In order to reduce dust concentration, firstly lengthen the inner cylinder of the original cyclone dust collector in front of the induced draft fan to 200mm beyond the straight section, and the diameter of the inner cylinder remains unchanged; Secondly, a simple settlement chamber (which can store 3T of dust) is made in front of the induced draft fan, and the dust is regularly discharged by introducing a dividing wheel through a 400mm×400mm pipeline.

(2) Through analysis, the baffle opening of the coal mill induced draft fan is 33%, which seriously deviates from the working point (fan operation curve) and runs at the lowest efficiency point. After calibration, the operating efficiency is about 78.4% and the shaft power is 160.71kW, indicating that the motor selection is too large and the no-load loss is also large. And the fan blade is a veneer backward leaning blade, this form of impeller is easy to be stained with ash, in order to solve the problem of fan stained with ash, we need to change the impeller form.

To quickly solve the problem of stained with dust, has carried on the communication with the domestic some well-known air blower factory, we don’t have to adjust motor, simply change the impeller and transform inlet, the impeller blade by the veneer backward, changed to veneer front forward with arc, after a period of straight blade, can significantly reduce the impeller with grey situation, and makes the fan run more smoothly.

The newly made impeller matches the performance parameters of the fan again according to the actual working conditions, adjusts the outlet Angle of the blade, reduces the size of the impeller, changes the aerodynamic performance of the impeller, promotes the baffle opening of the fan, and eliminates the idle work loss caused by the baffle of the fan. The modified impeller is also thickened and treated with special wear resistance to improve the service life of the impeller.

03 Implementation Status

In order to shorten the installation time, we sent a fan spindle and two sets of bearings in stock of our company to the new fan manufacturer in advance. The fan manufacturer made the new impeller and air inlet according to the requirements, and sent them to our company after its company finished the assembly and debugging of the spindle, and they will be replaced at the end of the year when the overhaul is completed. The cost of this investment is 105,000 yuan for one spindle, two plates of bearings including impeller and air inlet, 21,000 yuan for disassembly and installation, 126,000 yuan in total.

04 Implementation effect

(1) After the inner cylinder of the cyclone dust collector is lengthened and the settlement chamber is added, the dust collecting efficiency is effectively improved, the safe operation of the coal mill induced draft fan is reduced due to the excessively high dust content of the air flow, and the dilution degree of coal powder into the kiln is reduced. The standard coal is saved about 0.05kg/t clinker, the annual coal is saved about 84t, and the cost is saved RMB 49,500 yuan.

(2) The calibrated operating efficiency of the modified fan is 87.05%, and the shaft power is 115KW. According to the annual operation for 8 months, the electricity cost can be saved (160.71-115) KW ×24h×240d×0.5 yuan /kWh= 131,600 yuan.

(3) There is no dust on the surface of the fan impeller, and the vibration of the fan bearing seat is below 1.2mm/s for a long time. The annual loss can be reduced at least 0.5(electricity price/yuan)×789(power consumption of coal mill equipment in idle operation hours)×6(reduced times of shutdown)×240(actual operating days)×0.33(idle operation time h)= 187,500 yuan.

(4) Greatly reduce the labor intensity of workers, and avoid the environmental risk caused by cleaning the fan dust.

(5) Before the transformation of the fan impeller, the newly added settlement chamber and grid wheel can discharge ash about 500kg once a day. After the technical reform of the fan impeller, it was first tried to suspend the discharge of ash once a day, and the vibration of the induced draft fan did not change, so the device was later removed during maintenance.

The transformation not only solves the vibration problem of the fan, but also achieves energy saving and consumption reduction, and reduces the labor intensity of workers. The social and ecological environment benefits are remarkable.

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