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Milling Index for Pulverized Coal
The milling index is one of the important indicators of the pulverized coal quality. It is the basis for evaluating the milling efficiency of pulverized coal. Milling index is an import indicator to measure the pulverization ability of coal. It is the combination of the milling time, milling energy consumption, and pulverized coal fineness. The better the milling ability, the higher the index will be.
Definition
Milling index is defined as the weight ratio between the pre-milled coal to the total coal: the mass fraction of post-milled coal and the post-milled coal fineness ratio. The pre-milled coal is the original coal sample before being milled by the mill; the post-milled coal refers to the pulverized coal produced from the mill. Generally, the pre-milled coal means the raw coal; the post-milled coal means the pulverized coal. The post-milled coal fineness ratio is the ratio of the mass of pulverized coal with the sieve size ranging from 75 μm to the total mass of the pulverized coal.
Calculation
Milling index is calculated by the following formula:
Milling Index = ( Mass of post-milled coal )/( Mass of pre-milled coal ) X ( Mass fraction of post-milled coal passing through the sieve with 75 μm )
The pre-milled coal should be used as the original mass, and the post-milled coal should be based on the pulverization process. The sieving test should be performed after the process of pulverization to determine the post-milled coal fineness ratio. After obtaining the three items in the formula above, the milling index can be calculated.
Milling Efficiency Evaluation
The milling index is a quantitative indicator for evaluating the milling efficiency of pulverized coal. Generally, a higher milling index indicates better milling ability. In order to measure the milling efficiency of coal, it is necessary to control the parameters of the mill such as rotating speed, energy input, and milling time.
To achieve the better milling effect and minimize the energy consumption, it is necessary to adjust the mill parameters appropriately. For example, increasing the rotating speed can increase the fineness of the pulverized coal, while more energy input is also required: too slow rotating speed may cause the milling time to be longer thus causing the fineness of the pulverized coal to be insufficient. Therefore, in the process of milling, it is necessary to adjust the mill parameters according to the requirements of pulverized coal fineness. The actual evaluation should be done with the milling index to determine the ability of the mill.
Conclusion
Milling index is an important indicator for evaluating the quality of pulverized coal. It is the combination of milling time, milling energy consumption, and pulverized coal fineness. The better the milling ability, the higher the index will be. The milling index is a quantitative indicator for evaluating the milling efficiency of pulverized coal, and it is necessary to adjust the mill parameters according to the requirements of pulverized coal fineness.
