GB806699A - Apparatus for the removal of water from sewage sludge by evaporation and drying - Google Patents

Abstract

In apparatus for removing water from sewage sludge, comprising a multiple-effect evaporator for concentrating the sludge, one or more driers for drying the concentrated sludge and one or more pre-heaters for the fresh sludge, means are <PICT:0806699/III/1> provided for connecting any one of the evaporators to a boiler for raising steam and for taking out of service any other evaporator so that the concentrated sludge therein can be transferred to a drier. The driers are supplied with steam evolved from the sludge in one of the evaportors; and the steam evolved in the driers is used for heating the pre-heaters. The system shown comprises pre-heaters 21 and 21a, a number of evaporators 3, 3a ... 3n of the shell and tube type, two driers 19, 19a, and a boiler 1. Sludge to be treated is supplied to the evaporators through conduits 6, 6a ... 6n. Steam from boiler 1 is introduced through conduit 2 into the tubes of evaporator 3; and the steam-condensate is discharged through conduit 4 to heat exchanger 5 where it pre-heats the sludge flowing through conduit 6. This pre-heated sludge passes through gas separator 8, and is then sprayed into the upper part of evaporator 3. This spray of fresh sewage breaks down foam in the lower part of the evaporator, and diminishes the entrainment of solids in the steam leaving the evaporator. This steam passes through purification vessel 14 where entrained water and solids are separated, and then returned to evaporator 3 via conduit 16. The purified steam from vessel 14 is used as heating-medium for evaporator 3a. The steam generated in evaporator 3a is purified and is introduced into the tubes of the next evaporator. The purified steam from the last evaporator 3n is passed through conduit 18 to driers 19, 19a. After a predetermined period of time each evaporator in turn is taken out of service by manipulation of the appropriate valves 2a and 2b; and the concentrated sewage is withdrawn through conduit 24, 24a ... or 24n, and transferred to the driers. The steam driven off from the sludge in the driers is used to pre-heat fresh sludge in pre-heaters 21, 21a, and to pre-heat boiler feedwater in pre-heater 26. The empty evaporator is refilled via conduit 25 with pre-heated sludge from pre-heaters 21, 21a. After the sludge has been sufficiently dried, the solids are removed and replaced with concentrated sludge from the next evaporator of the series.