coal processing plant

A Coal preperation plant, nestled among the mountains. Coal Preperation plants generally use gravity process equipment to separate the refuse from the product (coal). Coal has a specific gravity between 1.35 and 1.5, while the refuse rock has a Specific Gravity of 2.1 to 2.3. Heavy Media is the most popular method of cleaning coarse sizes, jig plants are probably the second most common method used for coarse coal. Heavy media cyclones are being used more often for fines size fractions. Flotation is generally used to clean the -28 mesh size fraction, although spirals and heavy media cyclones have shown success in cleaning down to 100 mesh coal feed. Spirals are generally used for middling sizes ( 10 mesh to 60 mesh)

Coal processing goes as follow:

Coal is first crushed by coal crushers to a size of 20 to 25 mm and is then fed to coal bunkers. Coal feeders feed this crushed coal continuously to coal mill as per requirement. Coal gets ground by grinding elements in stages. Coal particles get re-circulated around four times before achieving required fineness. Classifier allows finer particles to escape mill outlet while coarse particles are returned to mill for further grinding. Primary air is supplied by P.A. fan through air pre heaters to coal mill or in some boilers, P.A. fan pressurize hot air received from air pre heaters and then supply to mills. Hot primary air drives moisture from coal and acts as carrier to transport pulverized coal to the boiler through pipes.

Output is pulverized coal having required fineness. For complete combustion coal should have fineness of 75% through 200 mesh and 99.5% through 50 meshes. Primary air + coal mixture flowing through each coal pipes should have minimum velocity of 18 m/sec, Temp. Around 80 degrees C, and air/coal ratio of 1.8 -2. Fuel flow through pipes is balanced within range of +/-10%. Finer is the coal, better is the flow distribution.