Sludge Drying Process

The press cake at approx. 20% solids from filter band presses or centrifuges is conveyed into a mixer where it is mixed with dried product of about 95% solids to form a loose and friable product of about 65% solids.

This mixture is conveyed into a direct fired air rotary dryer where it is dried to 90% solids or more through direct contact with air of 800-1000 Deg. F. inlet and about 250 Deg. F. outlet temperature. The product obtains a temperature of 175 to 180 Deg. F. The dried product is screened to remove tramp matter. Fines are recycled to the mixer. Product of acceptable size is recycled to the mixer while the net production is conveyed to a holding/load out bunker.

After the product has been separated from the air stream by a centrifugal cyclone, the air is cleaned in a venturi scrubber followed by a tangential demister. The scrubbing water is returned to the plant for treatment.

This type of process has been in successful operation for many years in Milwaukee, Wisconsin; Boston, Massachusetts; and other cities.