261
1. The energy efficiency for SCW gasification of biomass is generally high,
particularly for the feedstock containing large water content, because no
drying is required.
2. Most organic materials of biomass and other carbonaceous feedstock can
be dissolved in SCW due to their high solubility in SCW and high dielectric
constant of SCW. These features make the gasification in SCW a homogeneous reaction, with no mass transfer resistance between the two phases.
3. While the SCW requires high pressure of 22.1 MPa and high temperature
of 374°C, these conditions are still milder than what is required for conventional gasification and pyrolysis to obtain the same level of conversion
efficiency. For example, conventional steam gasification generally requires
1000°C, whereas the complete gasification of glucose can be achieved at
650°C and 35.4 MPa pressure in SCW.
4. SCW gasification produces very little impurities; no NO x and SO x and low
CO concentration are generated. The use of catalyst to enhance water–gas
shift reaction further reduces the gas-phase impurities.
10
Fuel Production by
Supercritical Water
10.1 intrOdUCtiOn
In recent years, the interest in the use of supercritical water (SCW) for the
production of fuels and chemicals as well as for waste treatment has been rapidly
expanding. The main reason for this is the unique properties of SCW that allow a
variety of organic reactions to occur in SCW, where water not only plays a benign
role of solvent but also plays a role as an active reactant or a catalyst. Water under
these conditions possesses properties such that important organic reactions can be
carried out in a homogeneous medium [1–13] (Aljishi et al., 2010, pers. comm.).
SCW can provide five different functions: (1) a medium in which numerous types
of organic chemical synthesis occur, (2) a medium for partial or complete oxidation of numerous hazardous or nonhazardous materials, (3) a medium in which
complex materials decompose and produce liquids and gases, (4) a medium for
thermal or catalytic gasification of simple and complex materials to produce fuels
like methane and hydrogen, and (5) a medium to generate hydrogen by catalytic
reforming of various carbonaceous materials. This chapter examines the role of
SCW in each of these functions, with a special emphasis on the functions that
generate synthetic fuels.
SCW technologies offer many advantages [1–13] (Aljishi et al., 2010, pers. comm.):
1. The energy efficiency for SCW gasification of biomass is generally high,
particularly for the feedstock containing large water content, because no
drying is required.
2. Most organic materials of biomass and other carbonaceous feedstock can
be dissolved in SCW due to their high solubility in SCW and high dielectric
constant of SCW. These features make the gasification in SCW a homogeneous reaction, with no mass transfer resistance between the two phases.
3. While the SCW requires high pressure of 22.1 MPa and high temperature
of 374°C, these conditions are still milder than what is required for conventional gasification and pyrolysis to obtain the same level of conversion
efficiency. For example, conventional steam gasification generally requires
1000°C, whereas the complete gasification of glucose can be achieved at
650°C and 35.4 MPa pressure in SCW.
4. SCW gasification produces very little impurities; no NO x and SO x and low
CO concentration are generated. The use of catalyst to enhance water–gas
shift reaction further reduces the gas-phase impurities.
10
Fuel Production by
Supercritical Water
10.1 intrOdUCtiOn
In recent years, the interest in the use of supercritical water (SCW) for the
production of fuels and chemicals as well as for waste treatment has been rapidly
expanding. The main reason for this is the unique properties of SCW that allow a
variety of organic reactions to occur in SCW, where water not only plays a benign
role of solvent but also plays a role as an active reactant or a catalyst. Water under
these conditions possesses properties such that important organic reactions can be
carried out in a homogeneous medium [1–13] (Aljishi et al., 2010, pers. comm.).
SCW can provide five different functions: (1) a medium in which numerous types
of organic chemical synthesis occur, (2) a medium for partial or complete oxidation of numerous hazardous or nonhazardous materials, (3) a medium in which
complex materials decompose and produce liquids and gases, (4) a medium for
thermal or catalytic gasification of simple and complex materials to produce fuels
like methane and hydrogen, and (5) a medium to generate hydrogen by catalytic
reforming of various carbonaceous materials. This chapter examines the role of
SCW in each of these functions, with a special emphasis on the functions that
generate synthetic fuels.
SCW technologies offer many advantages [1–13] (Aljishi et al., 2010, pers. comm.):