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Simple Introductions to Three Kinds of Coal Mills

Posted On : Oct-10-2011 | seen (273) times | Article Word Count : 652 |

Coal mill is a kind of machine that crushes the coal and grinds it into powders. It is an important supplementary equipment of pulverized coal furnace.
Coal mill is a kind of machine that crushes the coal and grinds it into powders. It is an important supplementary equipment of pulverized coal furnace. The coal grinding process is a process to crush coal and increase its superficial area continuously. To create new superficial area, the bond of molecules of solid must be broken, so this process needs to consume energy. There are three main ways to grind coal into powders: crushing, shattering and pulverizing. Among the three ways, crushing is the most energy-economical one, and pulverizing is the one consuming the most energy. Coal mill, nowadays, usually adopt two or all the three ways mentioned above when grinding coal, but it needs to depend on the type of coal mill to tell which way is the main one applied to the mill.

There are many types of coal mills, but according to the rotating speed of the coal grinding work pieces, coal mills can be divided into three types: low speed coal mill, medium speed mill and high speed mill.

Low speed mills mainly refer to the cylinder steel ball coal mills, which are commonly called steel ball mills or ball mill. Ball mill is a rotating cylinder or a cylinder with two taper heads, which contains steel balls. The rotating speed of the cylinder is about 10 to 25rpm. When ball mill is working, steel balls in the cylinder impacts and extrude coals and grinds the coals into powders. Then these powders are transmitted and dried by the hot air which is led to the cylinder. These powders are separated by the segregator. Parts of the powders with certain particle size are transmitted to pulverized coal bunker or to the combustor directly. Steel ball mill is of large size and heavy weight, a heavy electric consumer and makes lots of noise. But its merits are also obvious. It can be applied to many different kinds of coal, especially suitable to grinding the hard anthracite; what's more, it is more reliable.

Medium speed mills whose rotating speeds are 50 to 300rpm have relatively more types than low speed mill. Plate mill, bowl mill, E type mill and roller mill are commonly medium speed mills. The common thing those mills mentioned above have is that their grinding parts are all made up of two grinding bodies with relative movements. Coals are extruded and grinded between the grinding bodies. The hot air dries and transmits these powders to the segregator simultaneously. After segregating, the coal powders with certain particle size are transported out of the mill by hot air, but the larger ones have to be sent back to the mill and grinded again. Medium speed mill only occupies a small place and consumes less electricity than ball mill. It makes less noise. These are all its merits, but its drawbacks are obvious. Its structure and manufacture are too complicated. When it is broken, it spends more to repair it. Besides, it does not suit to those hard coals.

High speed mills are mainly made up of high speed rotator and mill shell, whose rotating speeds are 500 to 1500rpm. Fan mill and hammer swing sledge mill all belong to high speed mills. Coals are grinded because of the impact from the high speed rotator and other coals. The mill and segregator are made as a whole. Because of this, it is compact and has a simple structure, which is extremely suitable to grinding high moisture lignite and bituminous coal with high volatility. Fan mill can not work as long as other kind of coal mills because of its large wear. That is why it does not fit to grinding hard coal.

In a word, when choose coal mill, people should take both the hardness of the coal and the merits of different mills into consideration. Try to get more but consume less.

Article Source : Introductions to Three Kinds of Coal Mills_90058.aspx

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