Apparatus and method for treating sewage sludge

Claim 2

A sludge treatment system which comprises: (a) a furnace capable of burning sludge and producing heat; (b) a dryer capable of receiving wet sludge and removing sufficient moisture from the sludge so that it is dry enough to be burned in the furnace; (c) a heat-exchanger through which the dryer is indirectly heated by hot gas produced by the furnace, so that no contaminants pass from the furnace hot gas to the dryer hot gas; (d) means for transporting the dried sludge to the furnace for combustion therein; (e) means for introducing at least some dryer discharge gas released during the drying of the sludge for combustion in the furnace.

Claim 3

A system as in Claim 1, wherein the discharge gas is cooled so as to reduce the moisture content of the discharge gas so that it can be used as combustion gas in the furnace.

Claim 4

A system as in Claim 2, whereby the cooling takes place in a scrubber and water used in the scrubber is heated and drawn off for use in anaerobic digestion of sewage sludge.

Claim 5

A system as in Claim 3, wherein the hot gas produced by the furnace also passes through a cyclone and a second scrubber for precipitation of solid matter contained in the hot gases.

Claim 6

A system as in Claim 4, wherein the second scrubber uses water which is heated by the hot gas and drawn off for use in anaerobic digestion of sewage sludge.

Claim 7

A system as in Claim 5, in which the dryer hot gas is composed of a mixture of dryer discharge gas and fresh air.

Claim 8

A system as in Claim 1 or 6 including means for introducing dry sludge produced by the dryer into wet sludge entering the dryer and in which the means include a means for breaking the dry sludge so that the wet sludge dries a predetermined grain size.

Claim 9

A sludge treatment system including a dryer for exposing sludge to hot gases, a furnace for burning sludge from the dryer, means for heating and circulating part of the dryer discharge gas back to the dryer, means for delivering the remainder of the dryer discharge gas into the furnace for combustion therein whereby no dryer discharge gas is discharged to atmosphere without passing through the furnace.

Claim 10

A sludge treatment system including a dryer for exposing sludge to hot gases, a furnace for burning sludge from the dryer, means for heating and circulating part of the dryer discharge gas back to the dryer, means for delivering the remainder of the dryer discharge gas into the furnace for combustion therein whereby no dryer discharge gas is discharged to atmosphere without passing through the furnace.

Claim 11

A sludge treatment system as claimed in Claim 8, wherein the means for heating dryer discharge gas comprise a heat exchanger having a passage for furnace discharge gas and a separate passage for dryer discharge gas whereby the latter is not exposed to contaminants in the furnace discharge gas.

Claim 12

A sludge treatment system as claimed in Claim 9, including means for cleaning the furnace discharge gas.

Claim 13

A sewage sludge treatment system comprising: (a) means for dewatering the sludge; (b) a rotary dryer for exposing dewatered sludge to hot gas; (c) a furnace for burning sludge from the dryer; (d) means for mixing part of the sludge from the dryer with dewatered sludge supplied to the dryer; (e) a first cyclone for separating solids from dryer discharge gas; (f) means for heating and circulating part of the dryer discharge gas back to the dryer, including a heat exchanger having a passage for furnace discharge gas and a separate passage for the circulating dryer discharge gas whereby the latter is heated by the furnace discharge gas without exposure to contaminants thereon; (g) means for delivering the remainder of the dryer discharge gas into the furnace for com-bustion therein whereby no dryer discharge gas is discharged directly to the atmosphere; (h) a first water scrubber for said remainder of dryer discharge gas delivered into the furnace, to reduce the moisture content of said remainder of dryer discharge gas by cooling; (i) a second cyclone for separating solids from the furnace discharge gas emanating from the heat exchanger; (j) a second water scrubber for further cleaning of the furnace discharge gas emanating from the second cyclone; (k) an anaerobic sludge digester heated by water from the scrubbers, and said digester producing a gaseous fuel for use in the furnace; (1) means for introducing fresh air into the circulating dryer discharge gas, including means for heating the fresh air in the heat exchanger without contact with furnace discharge gas; (m) means for introducing fresh air into the furnace.

Claim 14

A sewage sludge treatment system comprising: (a) means for dewatering the sludge; (b) a rotary dryer for exposing dewatered sludge to hot gas; (c) a furnace for burning sludge from the dryer; (d) means for mixing part of the sludge from the dryer with dewatered sludge supplied to the dryer; (e) a first cyclone for separating solids from dryer discharge gas; (f) means for heating and circulating part of the dryer discharge gas back to the dryer, including a heat exchanger having a passage for furnace discharge gas and a separate passage for the circulating dryer discharge gas whereby the latter is heated by the furnace discharge gas without exposure to contaminants thereon; (g) means for delivering the remainder of the dryer discharge gas into the furnace for com-bustion therein whereby no dryer discharge gas is discharged directly to the atmosphere; (h) a first water scrubber for said remainder of dryer discharge gas delivered into the furnace, to reduce the moisture content of said remainder of dryer discharge gas by cooling; (i) a second cyclone for separating solids from the furnace discharge gas emanating from the heat exchanger; (j) a second water scrubber for further cleaning of the furnace discharge gas emanating from the second cyclone; (k) an anaerobic sludge digester heated by water from the scrubbers, and said digester producing a gaseous fuel for use in the furnace; (1) means for introducing fresh air into the circulating dryer discharge gas, including means for heating the fresh air in the heat exchanger without contact with furnace discharge gas; (m) means for introducing fresh air into the furnace.

Claim 15

A process for treating sludge comprising the steps of: (a) introducing wet sludge into a dryer and drying it to a moisture content capable of being burned in a furnace and thereby releasing dryer discharge gas; (b) reintroducing some of the dried sludge so produced into the wet sludge entering the dryer; (c) introducing the dried sludge into a furnace and burning it to produce hot gas; (d) heating the dryer by indirect contact with the hot gas produced by the furnace so as to dry the sludge; (e) circulating part of the dryer discharge gas through the dryer for use in drying the sludge; (f) cooling the remainder of the discharge gas to remove some of its moisture; (g) circulating this remainder through the furnace as combustion gas.

Claim 16

A process for treating sludge comprising the steps of: (a) introducing wet sludge into a dryer and drying it to a moisture content capable of being burned in a furnace and thereby releasing dryer discharge gas; (b) reintroducing some of the dried sludge so produced into the wet sludge entering the dryer; (c) introducing the dried sludge into a furnace and burning it to produce hot gas; (d) heating the dryer by indirect contact with the hot gas produced by the furnace so as to dry the sludge; (e) circulating part of the dryer discharge gas through the dryer for use in drying the sludge; (f) cooling the remainder of the discharge gas to remove some of its moisture; (g) circulating this remainder through the furnace as combustion gas.