Double inlet & outlet ball mill

Application

 

Double inlet & outlet ball mill is coal grinding system developed on the base of single inlet & outlet ball mill. It has functions of drying, pulverizing, coal particles classifying, coal particles conveying. Besides medium speed coal mill and high speed bleeder wheel mill, double inlet & outlet ball mill plays major role of direct fired pulverized coal preparation system in thermal power plant.

 

 

Working principle

 

Double inlet & outlet ball mill has two symmetric circuits shown in picture. Coal feeder sends coal into drop pipe. Coal falls down to screw conveyor and gets pushed into cylinder of ball mill. Inside, steel balls will grind coal into fine particles. Hot primary air enters cylinder through hollow pipe at two ends of coal mill. Hot air would dry pulverized coal and take them to classifier on the top. Coarse particles will be sent back to cylinder for grinding again, fine particles will be sent to boiler burner. Part of hot primary air will enter cylinder through mixing chamber, then drop pipe. It plays pre-drying function before coal grinding.

 

Advantages

 

1. High continuous operation ratio, low maintenance.

 

Steel balls are wearing parts, which can be charged without shutdown. Screw impeller service life is normally 2 years, while lining plate service life is normally 4-7 years. Coal mill could run a long time as long as boiler is not shut down. Screw impeller and lining plate could be changed during boiler overhaul.

 

2. Low air/coal ratio, stable output and particle size.

 

This coal mill structure results in a low air/coal ratio, which increase coal concentration in primary air. As it runs at low load, coal particle size is furtherly reduced. This could keep minimum sustained load low to reduce oil or gas consumption. Output is controlled by primary air quantity. Output is stable as long as primary air quantity remains the same. Coal particle size is decided by steel ball quantity. Coal particle size is stable as long as steel ball quantity remains the same.

 

3. Wide adaptability for coal types. It could grind hard and abrasive coals.

 

Wearing resistance of steel balls and lining plates could be improved by choosing different materials. Double input & outlet ball mill is not sensitive to iron block, wood block, rock.

 

4. Flexible operation, fast response within a wide load range.

 

Double input & output ball mill has large coal storage capacity, and output is linear to primary air quantity. This design gives it a fast response ability. According to load requirement, this coal mill has three working modes: double inlet and doublet outlet, single inlet and double outlet, or single input and single output. This brings user big convenient during operation.