To Drive off Moisture (theoretical) per Ton (2,000 lbs.) of Dry Material. Total B.T.U. include 63,840 B.T.U. to raise temperature of material from 60° F. to 212° F. at which point evaporation takes place (at sea level); specific beat of material taken as 0.21.
Coal assumed to have 12,000 B.T.U. per’lb. as used and is for 100% efficiency as specified. Table of coal added to original data by The General Engineering Company.
ROTARY DRYERS have efficiencies of 50% to 70%; coal consumption may be determined from the above table by subtracting pounds of coal corresponding to percent moisture in the dried product from the pounds of coal to percent moisture the feed, and dividing by the efficiency expressed decimally.
Capacity 250 to 660 lbs. water evaporated per sq. ft. of section per 24 hours. Rabble Dryers are frequently used for drying concentrates; generally have a cast iron bottom, heated on the under side; the maternal being dried is moved along, counter to the flow of the heating gases, by rabbles; evaporated moisture usually goes direct into the room.
Capacity: 50 to 75 pounds of water evaporated per 24 hours, per sq. ft. Power: 3 to 10 H.P. hours per ton of water evaporated. Fuel efficiency: About 50%, at maximum rating- may go down to 30% on reduced load. The usual practice on flotation concentrates js to remove by drying about half to three-fourths of the moisture in the filter cake, which runs from 8% to 30%.
