3.1 Thermochemical Conversion Technologies
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sludge with 20% solids as the feedstock at a feeding rate of 30 L/h, and operates
at 300 °C, achieving 73% energy recovery in the forms of oil and char. In the early
1990s a demonstration plant based on the STORS process was constructed in Japan,
which had a processing capacity of 5 tonnes/d of dewatered sludge and operated
at 300 °C and 100 bar. The process produced a 38% yield of oil with an HHV of
31–39 MJ/kg. Another STORS demonstration plant was successfully constructed
in 2001 in Colton, California, USA by ThermoEnergy company, sponsored by the
United States Environmental Protection Agency, aiming to produce bio-oil from raw
sewage sludge [40]. In addition, Thermo-Depolymerization Process, LLC (TDP),
a subsidiary of the Changing World Technologies Inc. (CWT), built a test plant
based on the TDP technology in Philadelphia, Pennsylvania, and a demonstrationscale plant was inaugurated in Carthage, Missouri, USA in 2004, aiming to produce
approximately 500 barrels bio-oil per day by processing up to 250 tonnes/day of
turkey offal and fats [40].
3.1.4 Gasification
Gasification is a thermochemical technology for conversion of solid feedstocks (coal
or biomass) into gaseous products (mostly H 2 and CO with small amounts of CO 2 ,
H 2 O vapor and CH 4 ) by reaction with gasifying agents of air/oxygen, steam, supercritical water and flue gases [53–55]. This process usually takes place at 500–1400 °C
and atmospheric or elevated pressures up to 33 bar [55]. Similar to other thermochemical technologies (combustion/co-firing, and pyrolysis), the feedstock should be first
dried to a moisture content of <10–20% before it is fed into a gasifier (except supercritical water gasifier) [55]. Major process steps involved in a gasification process
are summarized as follows [54–58]:
– Drying: evaporation of the biomass moisture.
– Pyrolysis: decomposition and break down of biomass into char, various gases and
tar vapor/liquids in the absence of oxygen.
– Combustion: oxidation of the pyrolysis products to produce CO, CO 2 and H 2 O
vapor:
C + 1 / 2 O 2 → CO H = −111 kJ/mol
C + O 2 → CO 2 H = −395 kJ/mol
– Cracking: breaking down of the large complex molecules such as tar into lighter
gases through thermal cracking.
– Gasification or reduction: removal of oxygen from water vapor and carbon dioxide
at high temperatures and formation of combustible gases.
73
sludge with 20% solids as the feedstock at a feeding rate of 30 L/h, and operates
at 300 °C, achieving 73% energy recovery in the forms of oil and char. In the early
1990s a demonstration plant based on the STORS process was constructed in Japan,
which had a processing capacity of 5 tonnes/d of dewatered sludge and operated
at 300 °C and 100 bar. The process produced a 38% yield of oil with an HHV of
31–39 MJ/kg. Another STORS demonstration plant was successfully constructed
in 2001 in Colton, California, USA by ThermoEnergy company, sponsored by the
United States Environmental Protection Agency, aiming to produce bio-oil from raw
sewage sludge [40]. In addition, Thermo-Depolymerization Process, LLC (TDP),
a subsidiary of the Changing World Technologies Inc. (CWT), built a test plant
based on the TDP technology in Philadelphia, Pennsylvania, and a demonstrationscale plant was inaugurated in Carthage, Missouri, USA in 2004, aiming to produce
approximately 500 barrels bio-oil per day by processing up to 250 tonnes/day of
turkey offal and fats [40].
3.1.4 Gasification
Gasification is a thermochemical technology for conversion of solid feedstocks (coal
or biomass) into gaseous products (mostly H 2 and CO with small amounts of CO 2 ,
H 2 O vapor and CH 4 ) by reaction with gasifying agents of air/oxygen, steam, supercritical water and flue gases [53–55]. This process usually takes place at 500–1400 °C
and atmospheric or elevated pressures up to 33 bar [55]. Similar to other thermochemical technologies (combustion/co-firing, and pyrolysis), the feedstock should be first
dried to a moisture content of <10–20% before it is fed into a gasifier (except supercritical water gasifier) [55]. Major process steps involved in a gasification process
are summarized as follows [54–58]:
– Drying: evaporation of the biomass moisture.
– Pyrolysis: decomposition and break down of biomass into char, various gases and
tar vapor/liquids in the absence of oxygen.
– Combustion: oxidation of the pyrolysis products to produce CO, CO 2 and H 2 O
vapor:
C + 1 / 2 O 2 → CO H = −111 kJ/mol
C + O 2 → CO 2 H = −395 kJ/mol
– Cracking: breaking down of the large complex molecules such as tar into lighter
gases through thermal cracking.
– Gasification or reduction: removal of oxygen from water vapor and carbon dioxide
at high temperatures and formation of combustible gases.