A coal mill manufacturer carries out four functions at the same time. The operations are called grinding, drying, classification and transportation. These functions are used to take the product to burners. A coal mill is not the lone part involved in the path of combustion which ought to be controlled. Also, there is combustion air entered into the mill for transporting the pulverized coal and the secondary air supply.
The function of grinding minimizes coal fed into the mill with dust particles of the required size for combustion. Commonly, two kinds of the mill are used: the drum type and the spindle type.
The spindle mill in vertical shape crushed coal through feeding it between the grinding roller and either;
-Bowl, at the bottom.
Coal enters through coal feed and goes into the grinding zone, where it gets crushed by the abrasive wheels. Through the rotation of the grinding table, coal particles are spun outwards and moved by the incoming heated air feed to the classifier. The classifier segregates particles on the basis of size. Particles with extra-large size are thrown back to the crusher. However, those that are fine are fed through the output to the burner.
The grinding function is controlled by differing both the rotation speed of the grinding table and pressure upon the rollers.
Instant contact with the air feed evaporates moisture retained in the ground coal particles so that the required temperature of mill outlet is achieved.
This process makes sure that the correct size of coal particles are fed into the boiler and bigger particles are thrown back to the crushing table.
There are two kinds of classifier: dynamic and static. Both static and dynamic uses centrifugal forces for carrying out the classification operation. In the static classifier, the coal particles pass through the angled vane structure. More massive particles crash with the vanes loses energy and fall into the grinder. The size of the particle is controlled through varying the vane’s angles.
A dynamic classifier includes rotating vanes apart from static blades. The rotation speed can be varied for altering the performance of the classifier. Only the fine particles go into the inlet.
The pulverized coal which transfers through the classifier goes to the burners through the primary airflow. It is mixed with secondary air for achieving the desired coal-to-air ratio. The feed pipe configuration may differ for each burner which results in different airflow and coal feed rates.
Pulverizes control and proper maintenance is vital for the efficient performance of the coal mill.