Patent ID: 6171499
Filing Date: 2001-01-09
Classification: B09B,C02F,C05F,C12M,F23G,F26B,Y02A,Y02E,Y02P,Y02W,Y10S

Abstract:
A method for the treatment and the reuse as solid fuel of urban and industrial sewage sludge, characterized in that it comprises the following steps:a) the anaerobic sludge digestion (1), in one stage or in two stages, and biogas production;b) the mechanical dehydration (2) of the digested sludge;c) the biogas combustion, enriched with addition of natural gas, in a gas turbine (3) running with an overall energy yield of about 88%;d) the thermal drying of the dehydrated sludge by means of two apparatuses in series: the first apparatus is an indirect thin-layer dryer (4a) with a double-mantle heated by a circulating thermal oil (3b) through the boiler (3a) recovering the heat issued from the biogas combustion, the second apparatus is a vibrated fluid bed dryer and cooler (4b), heated by the exhaust hot gas (3c) out of the recovery heat exchanger and followed by a cyclone separator (4g) in the exhaust gas circuit;e) the condensation of the vapors coming out of the indirect thin-layer dryer, with a thermal deodorization of the uncondensable gases in the burner of the gas turbine, by means of a tubular condenser (5a) producing the hot water used to warm the digester and the premises, and a mix-condenser (5b), as stand-by, to condense the excess vapors in summer time by means of a spray of purified water issued from the sewage treatment plant;f) transporting the dried sludge to a household refuse incineration plant, and use of the dried sludge as a ""booster"" fuel which is easily storable in a silo (6a) and automatically conveyed (6b), according to the demand of the existing boiler-furnaces (7), in order to fill or to equalize their thermal load and to utilize the existing capacity of the incineration plant's equipment, including that related to the heavy metals elimination (8).