Thermal sludge to energy transformer
Systems and processes provide for a thermal process to transform sludge (and a variety of other natural waste materials) into electricity. Dewatered sludge and other materials containing a high amount of latent energy are dried into a powdered biofuel using a drying gas produced in the system. The drying gas is recirculated and is heated by the biofuel produced in the system, waste heat (from turbines or internal combustion engines), gas (including natural gas or digester gas) and/or oil. The biofuel is combusted in a boiler system that utilizes a burner operable to burn biofuel and produce heat utilized in a series of heat exchangers that heat the recirculating drying air and steam that powers the turbines for electricity production.
1 . A system for generating electricity by combusting biofuel produced from dewatered sludge, the system comprising:
a dryer operable to:
receive a drying gas;
receive sludge; and
reduce the moisture content of the sludge in the presence of the drying gas, wherein the drying gas absorbs at least a portion of the moisture content of the sludge and forms a biofuel and at least partially saturated gas;
a boiler system operable to combust the biofuel to produce at least one of heat for use in the dryer or steam for a turbine;
a first separator operable to separate the biofuel from the at least partially saturated gas;
a first condenser operable to reduce a moisture content of the at least partially saturated gas by reducing a temperature of the at least partially saturated gas to form a reduced-moisture gas;
at least one fan operable to direct the reduced-moisture gas to a first heat exchanger to form the drying gas, the first heat exchanger disposed in the boiler system and to direct the reduced-moisture gas to the dryer to reduce the moisture content of the sludge;
a diverter valve operable to keep an overall system moisture balance by removing the volume of reduced-moisture gas out of the system that is equivalent to the volume of moisture removed from the sludge less the amount removed by the first condenser;
a make-up air supply to replace reduced-moisture gas diverted out of the system, wherein the make-up air is supplied to the system downstream of the diverter valve and upstream of the first heat exchanger, wherein the make-up air supply is preheated by a gas burner prior to being supplied to the system; and
a second heat exchanger incorporated into the boiler system to transfer heat to at least one of the turbine and dryer.
2 . The system of claim 1 , wherein the biofuel is a reduced-moisture powder.
3 . The system of claim 1 , wherein the sludge comprises at least one or a combination of digested sludge, undigested sludge, fresh animal waste, aged animal waste, agricultural waste, or food waste.
4 . The system of claim 1 , further comprising a mixer operable to mix a second portion of reduced-moisture gas with gas heated by the boiler to form the drying gas.
5 . The system of claim 2 , wherein the boiler system comprises a boiler burner operable to burn a mixture of at least one of ambient and pre-heated air and at least a portion of the reduced moisture powder.
6 . The system of claim 5 , wherein the boiler burner is further operable to burn a gas or oil.