GB835216A - Improvements in or relating to the drying of sewage sludge - Google Patents

Abstract

835,216. Sludge driers. DORR-OLIVER Inc. March 6, 1956 [March 7, 1955], No. 6637/55. Class 34(2) Digested sewage sludge is fed through a pipe 10 to an apparatus 12 in which it is miexd with dry sludge pellets and particles rejected from a rotary sizer 19 and a cyclone separator 20 respectively, until its moisture content is reduced to within the range of 45-55% by weight. It is then made into pellets in a rotary drum 13 before passing through a pipe 15 to a fluidized bed drier 16. The drying and fluidizing gas, e.,g., propane, is burnt in a chamber 18 and conducted to a chamber 16b below a grate 16a. Entrained solids in the pipe 16d are removed in the separator 20 and passed to the apparatus 12. The dried pellets enter the sizer 19 through a valve 16c and those of an acceptable size are withdrawn through a pipe 19a. Various alternative arrangements are indicated by dotted lines 21, 22, 23. Line 21 shows a return of oversize green pellets to the apparatus 12. From this line pellets may be directed to the chamber 18 through a valve 21a if combustion of such pellets is desired. The line 22 indicates the return of undersize green pellets to the drum 13 whilst the line 23 shows the feeding of undersized pellets to the drum 13 instead of the apparatus 12. Fertiliser or other soil conditioning additives may be introduced into the drum 13 during pellet formation (through a valve 25), or into the fluidized bed 17 (through a valve 26). The gas velocity in the bed may be 2-5 ft. per sec. (drier empty).