Existing problems

The raw mill model of a company is ATOX50. The grinding condition of this vertical mill is stable since it was put into production in March 2008. By the summer of 2015, in order to meet more stringent environmental emission requirements, electric dust collector at the end of the kiln has been replaced with electric bag compound dust collector. After technical modification, dust collection effect is improved, dust content decreases from 25mg/m³ to about 15mg/m³, pressure difference between inlet and outlet of dust collector increases from 1500Pa to about 2500Pa, and operating resistance increases a lot; The output of the mill decreased by 25t/h, the vibration of the mill was between 0.5 ~ 0.7mm, the pressure difference was as high as 6700 ~ 7200Pa, the fluctuation of the material layer was large, about 20 ~ 100mm, the amount of external circulation was too much, the mill electromechanical flow was more than 200A(after the input), the mill discharge was slow; The output cannot be increased, the raw material powder produced is only enough for the kiln, the raw material homogenizing warehouse does not expand, and the vertical mill has no downtime for fixing inspection, which reduces The Times of maintenance for normal maintenance and brings hidden dangers to the safe operation. Before the technical change, the power of the tail-exhaust fan in the kiln is 4100kW, and the air volume of the treatment is 850,00m ³/h. After the technical change, the motor is not replaced. In normal production, the maximum speed of the fan is 49.2Hz, and the power reaches 4100kW, so the air volume of the tail-exhaust fan is insufficient.

02 Measures

(1) To strengthen the sealing and plugging of the system. During the overhaul at the end of 2016, through inspection, it was found that there was a large air leakage at the dust inlet pipe at the end of the kiln, especially close to the air inlet of the dust collector, and the pipe was seriously worn. This place has carried on the thorough plugging seal, has repaired the large area air leakage.

When checking the two valves 5404A and 5404B on the bypass pipeline, it is found that the switch of the valve (butterfly valve) of 5404B is basically normal, and one of the valve plates of the louver of 5404A (louver valve) is seriously damaged and the wind locking is not strict, which results in the decrease of the air flow into the mill and the decrease of the wind speed. The materials in the mill return to the grinding plate for secondary grinding, and the external circulation is increased. The deformed louver valve was replaced during maintenance.

(2) Process equipment adjustment. In the mill, the retaining ring of the mill was mainly replaced. The height of the rear retaining ring was 200mm, and the height before the replacement was 216mm. The water spraying device in the mill is replaced, the original water spraying in the inner ring of the mill is transformed into the water spraying directly on the mill plate, and the original water spraying area is slightly adjusted. The water spraying will not be affected by the water pressure and affect the material layer.

(3) Operational adjustment. After the kiln feeding in March, the output of the vertical mill was increased to 380t/h, and the flow layer of the mill was very stable. According to the changes of the system, the operation was further adjusted, the water spraying quantity was reduced from 8m³/h to 3m³/h, the output was increased to 410t/h, the fluctuation of the material layer was small, the grinding condition was more and more stable, the discharging was fast, and the maximum electromechanical flow of the grinding hoist was up to 200A.

The speed of the separator was reduced from 1100r/min to 1000r/min, the raw material fineness was 2.0%, and now it is about 3.5%. The output increased to 440t/h at the grinding table. Although the raw material fineness was coarser, the quality of the clinker was not affected at the calcination of the rotary kiln. Parameter comparison before and after adjustment are shown in Table 1.

Table 1 Comparison of parameters before and after adjustment

03 Conclusions

By overhauling at the beginning of the year to deal with the leakage of the mill outlet pipe and bypass valve, and improving the operation, the ventilation condition of the system has been greatly improved. The output of raw material mill increased by more than 40t/h, and now the output of raw material mill is stable at 440t/h. The vertical mill stops twice a week to avoid the peak, which can save 192,000 kWh of electricity and 96,000 yuan of capital every month, and effectively reduce the cost.

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