3.1 Thermochemical Conversion Technologies
67
In China, a number of pyrolysis plants have been designed and manufactured for
industrialization through the R&D projects of some Chinese universities. A fluidizedbed fast pyrolysis process was developed by Zhejiang University and was then scaled
up to a 20 kg/h demonstration plant. A 50 kg/h rotating cone pyrolysis reactor was
introduced by the Biomass Technology Group at Shenyang Agricultural University.
A research group at the University of Science and Technology of China partnering
with Yinneng Bio-Energy Corporation, constructed a pilot auto-thermal pyrolysis
plant in 2006 with a capacity of 120 kg/h [35].
3.1.2.2 Slow Pyrolysis
In a slow pyrolysis process, biomass is heated to a moderate temperature at a slow
heating rate (less than 10 °C/s). The produced vapors remain in the reaction medium
between 10 and 60 min, which produces more char. It differs from fast pyrolysis
in terms of chemistry, overall yields and properties of the pyrolysis products. As
also shown previously in Table 3.3, the main products of this process are biochars
(35%) and gases (35%) and bio-oils (30%) [25, 26]. Slow pyrolysis may be further
divided into two groups: conventional pyrolysis and carbonization. In a conventional
pyrolysis process, the residence time of the product is in the order of minutes and the
main products are gas, char and bio-oils, while in carbonization the main products
are char and non-condensable gases.
3.1.2.3 Plasma Pyrolysis
Pyrolysis can process both biomass and plastic materials. Conversion of plastic materials into syngas is generally refered to as plasma pyrolysis. Commercial plasma
pyrolysis processes produce hydrogen-rich syngas and inert construction materials
[23]. Plasma processes use extremely high temperatures in an oxygen-starved environment. In this process, a thermal plasma field is created using an electric current
through a low-pressure gas stream, which produces a stream of plasma at temperatures of 5000–15,000 °C [6, 37]. In the plasma environment, organics are decomposed
into simple molecules and both chemical and physical reactions occur rapidly. The
intense and flexible heat generation of this technology enables it to safely dispose of
plastic-, polymer-, medical-, hazardous-wastes and MSW [37]. Although the technology requires relatively high capital and operating costs, it provides some environmental advantages such as the ultimate destruction of hazardous materials including
polychlorinated biphenyls (PCBs) and complex stable volatile organic compounds
[6]. Currently, there is however no commercial-scale plasma technology for MSW
in North America, except some patented systems proposed for future operations.
Pyrogenesis Inc. and Plasco Energy Group are two companies that proposed plasma
systems for conversion of MSW into syngas, heat and inert slag. The produced syngas
is composed of H 2 , N 2 , CO and CO 2 and is then cleaned and combusted in an engine
or turbine for energy recovery [6].
67
In China, a number of pyrolysis plants have been designed and manufactured for
industrialization through the R&D projects of some Chinese universities. A fluidizedbed fast pyrolysis process was developed by Zhejiang University and was then scaled
up to a 20 kg/h demonstration plant. A 50 kg/h rotating cone pyrolysis reactor was
introduced by the Biomass Technology Group at Shenyang Agricultural University.
A research group at the University of Science and Technology of China partnering
with Yinneng Bio-Energy Corporation, constructed a pilot auto-thermal pyrolysis
plant in 2006 with a capacity of 120 kg/h [35].
3.1.2.2 Slow Pyrolysis
In a slow pyrolysis process, biomass is heated to a moderate temperature at a slow
heating rate (less than 10 °C/s). The produced vapors remain in the reaction medium
between 10 and 60 min, which produces more char. It differs from fast pyrolysis
in terms of chemistry, overall yields and properties of the pyrolysis products. As
also shown previously in Table 3.3, the main products of this process are biochars
(35%) and gases (35%) and bio-oils (30%) [25, 26]. Slow pyrolysis may be further
divided into two groups: conventional pyrolysis and carbonization. In a conventional
pyrolysis process, the residence time of the product is in the order of minutes and the
main products are gas, char and bio-oils, while in carbonization the main products
are char and non-condensable gases.
3.1.2.3 Plasma Pyrolysis
Pyrolysis can process both biomass and plastic materials. Conversion of plastic materials into syngas is generally refered to as plasma pyrolysis. Commercial plasma
pyrolysis processes produce hydrogen-rich syngas and inert construction materials
[23]. Plasma processes use extremely high temperatures in an oxygen-starved environment. In this process, a thermal plasma field is created using an electric current
through a low-pressure gas stream, which produces a stream of plasma at temperatures of 5000–15,000 °C [6, 37]. In the plasma environment, organics are decomposed
into simple molecules and both chemical and physical reactions occur rapidly. The
intense and flexible heat generation of this technology enables it to safely dispose of
plastic-, polymer-, medical-, hazardous-wastes and MSW [37]. Although the technology requires relatively high capital and operating costs, it provides some environmental advantages such as the ultimate destruction of hazardous materials including
polychlorinated biphenyls (PCBs) and complex stable volatile organic compounds
[6]. Currently, there is however no commercial-scale plasma technology for MSW
in North America, except some patented systems proposed for future operations.
Pyrogenesis Inc. and Plasco Energy Group are two companies that proposed plasma
systems for conversion of MSW into syngas, heat and inert slag. The produced syngas
is composed of H 2 , N 2 , CO and CO 2 and is then cleaned and combusted in an engine
or turbine for energy recovery [6].