US 5,292,442 AGranted

Process for disposing of sewage sludge

AssigneeTexaco Inc.

InventorsMotasimur R. Khan, Harvey D. Schindler, Christine C. Albert, Stephan J. DeCanio

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Abstract

A process for disposing of sanitary sewage sludge by producing a pumpable slurry of sewage sludge with or without solid carbonaceous fuel and burning said slurry as fuel in a partial oxidation gas generator, furnace, or boiler. The aqueous slurry of sewage sludge is concentrated by removing water by means of a conventional belt filter press, centrifuge, or hydroclone. The dewatered slurry of sewage sludge is heated by direct contact with steam while air and organic vapors are simultaneously removed, to reduce the pressure in the system; hydrothermally treated in two steps with indirect and direct heat exchange with steam; dewatered by flash evaporation and centrifuging; and burned with or without admixture with solid carbonaceous fuel in a partial oxidation gasifier, furnace, boiler, or incinerator to produce synthesis gas or a hot raw effluent gas stream. In a preferred embodiment, the effluent gas stream is cleaned and purified and non-contaminating ash and slag are separated. By this process, noxious sewage sludge may be disposed of without contaminating the environment. Synthesis gas, reducing gas, or fuel gas may be produced.

Claims15

Dependent claims

A process for disposing of sewage sludge comprising:

(1) dewatering an aqueous slurry of sewage sludge to a solids content in the range of about 8 to 35 wt. %;
(2) heating the dewatered aqueous slurry of sewage sludge from (1) to a temperature in the range of about 120.degree. F. to 210.degree. F. and at atmospheric pressure by direct contact with steam, and holding said material at said elevated temperature for about 1.0 to 30.0 minutes while simultaneously removing off-gas comprising air, H.sub.2 O, and organic vapors;
(3) heating, mixing an shearing the aqueous slurry of sewage sludge from (2) by indirect heat exchange in the absence of air at a temperature in the range of about 210.degree. F. to 350.degree. F. and at a pressure of about 50 to 100 psig above the vapor pressure of water at that temperature, for a period in the range of about 2.0 to 10.0 minutes;
(4) hydrothermally treating the aqueous slurry of sewage sludge from (3) by direct steam injection in an autoclave in the absence of air and holding said material in said autoclave for about 15 to 120 minutes at a temperature in the range of about 450.degree. F. to 600.degree. F. and a pressure of about 50 to 100 psig above the vapor pressure of water at the holding temperature, while simultaneously removing off-gas comprising air, H.sub.2 O, organic vapors, CO.sub.2, H.sub.2 S, and COS;
(5) suddenly reducing the pressure of the aqueous slurry of sewage sludge from (4) to a value in the range of about 25 to 50 psig and flash evaporating water to increase the solids content of said aqueous slurry of sewage sludge to about 25 to 55 wt. %;
(6) centrifuging the aqueous slurry of sewage sludge from (5) to remove water and to provide a solids content in the range of about 28 to 58 wt. %;
and
(7) burning said pumpable slurry of sewage sludge with or without admixture with supplemental solid carbonaceous fuel either:
(a) in a furnace, boiler, or incinerator to produce a hot raw effluent gas stream;
or (b) in a partial oxidation gas generator to produce a hot raw stream of synthesis gas, reducing gas, or fuel gas.

7 more elements

A process for disposing of sewage sludge comprising:

(1) dewatering an aqueous slurry of sewage sludge to a solids content in the range of about 8 to 35 wt. %;
(2) heating the dewatered aqueous slurry of sewage sludge from (1) to a temperature in the range of about 120.degree. F. to 210.degree. F. and at atmospheric pressure by direct contact with steam, and holding said material at said elevated temperature for about 1.0 to 30.0 minutes while simultaneously removing off-gas comprising air, H.sub.2 O, and organic vapors;
(3) heating, mixing and shearing the aqueous slurry of sewage sludge from (2) by indirect heat exchange in the absence of air at a temperature in the range of about 210.degree. F. to 350.degree. F. and at a pressure of about 50 to 100 psig above the vapor pressure of water at that temperature, for a period in the range of about 2.0 to 10.0 minutes;
(4) hydrothermally treating the aqueous slurry of sewage sludge from (3) by direct steam injection in an autoclave in the absence of air and holding said material in said autoclave for about 15 to 120 minutes at a temperature in the range of about 450.degree. F. to 600.degree. F. and a pressure of about 50 to 100 psig above the vapor pressure of water at the holding temperature, while simultaneously removing off-gas comprising air, H.sub.2 O, organic vapors, CO.sub.2, H.sub.2 S, and COS;
(5) suddenly reducing the pressure of the aqueous slurry of sewage sludge from (4) to a value in the range of about 25 to 50 psig and flash evaporating water to increase the solids content of said aqueous slurry of sewage sludge to about 25 to 55 wt. %;
(6) grinding the aqueous slurry of sewage sludge from (5) together with solid carbonaceous fuel to produce a pumpable aqueous slurry of sewage sludge and solid carbonaceous fuel having a solids content in the range of about 45 to 67 wt. %;
and
(7) burning said pumpable aqueous slurry of sewage sludge and solid carbonaceous fuel in a furnace, boiler, or incinerator to produce a hot raw effluent gas stream;
or burning said aqueous slurry of sewage sludge in a partial oxidation gas generator to produce synthesis gas, reducing gas or fuel gas.

6 more elements

Dependencies are inferred from the claim text.