Coal mill

coal mill overview

Coal mill also called coal pulverzier or coal powder mill is grinding mill that is used in coal mining industry, such as vertical coal mill. And in general, vertical mill includes mineral series and coal series. The first series grinder can be widely used in cement making, power, metallurgy, chemical, ore industries. And the vertical coal mill also called coal grinder is the most used machine for coal grinding according to our mining experience. In some cases, coal mill is not just one grinder mill, it will include some optional equipment such as vibrating feeder, vibrating screen, belt conveyors and so on to finish the coal milling process. So, coal mill is also used widely in many industries besides coal mining.

Coal mill can be widely used in electricity generation, steel production, cement manufacturing, power, metallurgy and chemical and ore industries. SBM design a complete line of coal grinding mills and other assistant equipments, like bag-type dust collector and electric magnetic iron mover, to meet the requirements of any industry.

Coal mill process

Coal is mined by explosion, then crushed by coal crusher into small pieces. In this coal crushing process, several types of coal Crusher are used. jaw crusher, impact crusher, cone crusher can be used as coal pulverizer.

After crushing, crushed coal enter into the coal mill for grinding. Usually a complete coal milling line includes coal mill, impulse dust cleaner, piping device, cyclone collector device, classifier. The stones are squeezed by roller and ring into powder, the powder is collected by cyclone collector. In order to ptotect the environment, we also install the cloth deduster.

Coal mill classification

In steam powder plant, coal mill pulverizer is used to crush and grind coal into powder. In this coal milling process, several types of coal mill can be used.

Ball grinding mill is the early coal mill used in coal powder plant, there are two types: wet ball mill and dry ball mill. This type coal mill performance is rather good: the output is high, the maintenance is friendly, the operation is easy, safety control of this coal mill.

Vertical mill is the most common coal grinding mill in milling plant, so vertical mill is also called vertical coal mill, it set up the coal mill stardard.

Raymond mill is also the early coal mill, the capacity of this coal mill can be up to 6-8 t/h. The finess of the finished product can be adjusted from 100 mesh to 325 mesh according to the requirements.

SBM is a professional coal mill manufacturer in China, and supply coal crushers and coal mills for sale with best price all over the world. We also can design coal milling solution according to the special requirements of our customers.

Coal mill pulverizer working principle

Raw coal is fed through a central coal inlet at the top of the pulverizer and falls by gravity to the rotating grinding table, mixing with classifier rejects returned for re-grinding. Centrifugal action forces the coal outward to the grinding ring where it is pulverized between the ring and three grinding rollers. Grinding load, transmitted from the tension rods through the loading frame to the roller assemblies, holds the rollers in contact with the grinding ring. The rollers adjust vertically as the depth of the coal load increases or decreases.

A nozzle ring on the outside perimeter of the grinding ring feeds primary air to the pulverizer. Pyrites and tramp metal fall through the nozzle ring openings to be scraped into a rejects hopper.

A stream of low-velocity air carries the particles of pulverized coal upward where they enter the classifier inlet vanes. Fine particles travel to the burners in the primary air stream, but the larger, heavier particles are returned to the grinding zone for further pulverization.

How to operate coal mill safely

What is the proper method to operate coal mill to avoid the disaster?

1. change the piling method of the coal to make the coal accumulate little; thus avoid the spontaneous combustion of the coal.
2. change the gap of the great bar from 25mm to 22mm; thus decrease the wind speed and increase the drying speed.
3. add a settling chamber between the coal mill and the pipe; thus prevent the hot coal powder enter the coal mill.
4. add a explosion-proof valve at the opening.
5. increase the fineness of the coal from 10% to 15%.
6. make up strict safety rules.

If the coal mill stops for 3 days, empty the coal hopper or put a layer of raw meat powder on the surface to isolate the coal from the oxygen before stopping the coal mill, close the hot wind valve and open the close wind valve and then stop the feeding. remember to empty the coal in the coal mill before stopping the machine and not to stop the collector immediately.

Check the following things when operating the coal mill: the airing is ok; there is no overfeeding or underfeeding; the temperature is not too high; the order of starting and stopping the coal mill is right; the temperature of the air from the coal mill is higher the dew point.

Make an emergency plan; when an explosion happens, close the hot wind valve and the pneumatic valve, prevent the hot coal powder enter the collector and if the temperature is over 80 degree centigrade, start the carbon dioxide extinguisher.

we should pay attention to avoid safety problem in operating the coal mill. as long as we obey the safety rules, the safety problems surely can be avoided.