PURPOSE: To prevent the aggravation of an environment as well as the deterioration of ash removing rate, which are accompanied by discharging high ash slurry to the outside of a system, by a method wherein a dehydrating machine, a slurry adjusting tank and an ash removed CWM manufacturing machine for manufacturing CWM (high density coal water slurry) are added newly.

CONSTITUTION: Low density slurry 14, crushed in a crusher 11, is supplied to an ash removing device 15 to separate low-ash slurry 16 from high-ash slurry 17. The low-ash slurry 16 is supplied into a dehydrating machine 18a for a low-ash slurry and is dehydrated whereby low-ash dehydrated cake 19a is obtained. Water 20a, produced by the dehydration, is re-utilized as one part of water 3 for supplying to a crusher 1. Dehydrated cake 19a is sent into a low-ash slurry regulating tank 22a through a conveyer 21a, small amount of water 23a and an adding agent 24a are added into the regulating tank 22a and are mixed and agitated by a low-ash slurry mixer 25a whereby low-ash CWM 26a may be obtained. On the other hand, the high-ash slurry 17 is supplied into the dehydrator 18b for high-ash slurry and high-ash dehydrated cake 19b may be obtained here.