Coal-water slurry producing process, system therefor, and slurry transfer mechanism

A system comprising:

• a first processing system for wet-grinding low grade coal to produce a ground coal slurry of particle size not greater than 3 mm;
• a second processing system for applying an upgrading treatment to said ground coal slurry under a pressurized hydrothermal atmosphere not less than 300.degree. C. to produce an upgraded coal slurry;
• a third processing system for applying a dehydration treatment to said upgraded coal slurry to produce an upgraded coal cake and a filtrate, adding water and an additive to said upgraded coal cake and mixing them to produce a high-concentration coal-water slurry;
• and
• a fourth processing system for recycling said filtrate as water for producing said ground coal slurry;
• wherein said first processing system comprises a wet grinder and a flotator arranged prior to said wet grinder, and wherein said filtrate produced in said third processing system is fed to said flotator for deashing said low grade coal using a foaming component in said filtrate.