In a cement plant in 2500t / D production line, the coal grinding is used in ZENITH LM series vertical grinding mill, capacity of 25t / h. Ready to use anthracite calcined anthracite, the ignition temperature is high, the burnout time longer, in order to improve the combustion velocity of anthracite coal in the burning system, to ensure the full burn anthracite, coal fineness requirements into the kiln control sieve sieve residue in 0.08ram about 3%, so the special request for the vertical roller mill for coal mill.
The main structure and working principle of the vertical roller mill coal grinding cement factory: the vertical grinding mill is a roller disc, the grinding part is composed of a rotating disc and 3 disc rolling along the rotation of the grinding roller is fixed and can be composed of. Coal required grinding by the central coal feeding tube into the millstone central, rotating disc by means of centrifugal force will send to coal vertical roller mill grinding roller, through, the milling force is generated by the hydraulic loading system. Coal crushing and drying can be carried out at the same time, a wind through the nozzle ring evenly into the millstone around, will pass through the separator grinding tangential Shuaichu material drying and sent to the mill from the upper part of the disc, coarse powder is separated out back to the millstone, fine powder is the wind out qualified mill.
As a result of anthracite and bituminous coal properties vary greatly, so use different mill test, found that the use of LM vertical grinding mill grinding pure anthracite effect is the best, and the debugging process encountered some problems and made some experience, for your reference.
Vertical Roller Mill Operation
Usually in the coal mill with vertical roller mill operation, a certain gap is left between the grinding roller and the grinding disc, this is mainly to prevent the mill in abnormal state of roller and the grinding disc direct contact, the size of the gap reflects just grinding efficiency. However, in the grinding of bituminous coal and anthracite operation reflects different. Vertical mill grinding coal grinding roller and the grinding disc, the gap is lOmm, whether the product fineness, yield and mill stabilization system is normal. But change of anthracite, but no effect on the coal grinding mill, this point from the operating current mill can be seen (basically the same with the empty load operation of the motor), is also in the disc is difficult to form material layer. Whether it is adjusting the grinding pressure and adjust the clearance between the grinding roller and the grinding disc change feeding, (from 10 to 2.7mm), running state can not change the mill.
Analysis of the use of cement factory of anthracite, we found that not only the high hardness, and the internal friction coefficient is less than bituminous coal, this should be one of the main reasons is difficult to form material layer on the grinding disk. This method considering the forced feeding device is added in the grinding roll, namely the material before entering the following pre pressure grinding roller. In the vertical roller mill on the test, this method is basically feasible. But in the practical application of the scene to see, although than original state change (there is a gap between the rollers and millstones remain at this time), but because the individual feed grain through the large, often caused by forced feeding device blocking material, not only failed to play its due role, instead of the grinding roll without material. After the factory’s suggestion, the grinding roller and the grinding disc will be vertical mill gap adjustment between zero, by adjusting the feeding ratio of bituminous and anthracite (30%, 50%, 70%) of the repeated test, largely succeeded, that within a small coefficient of friction material only disc effectively drive the grinding roller to rotate after to make the material is normally meshing under the grinding roller.
Through the observation of the adjustment, vertical coal mill run smoothly, but the material layer is relatively thin, it is further validated in the anthracite small friction coefficient is the reason for difficulty in forming material layer.