402
Alternative Fuels for Transportation
composition of biomass fuels and the operating conditions. The heating value
of the gas produced during the pyrolysis process is low (3.5–8.9 MJ/m 3 ).
Oxidation: introduced air in the oxidation zone contains, besides oxygen
and water vapors, inert gases such as nitrogen and argon. These inert gases
are considered to be nonreactive with fuel constituents. Oxidation takes p lace
at the temperature range of 700–2000°C. Hydrogen in the biomass reacts with
oxygen in the air blast and produces steam.
C + O 2 ⇔ CO 2 + 406 MJ/kmol
1
H 2 + O 2 ⇔ H O
2
+ 242 MJ/kmol.
2
Reduction: in the reduction zone, a number of high temperature chemical
reactions take place in the absence of oxygen. The principal reactions that
take place in reduction are as follows:
Boudouard reaction: CO 2 + ⇔
C
2C O − 172 . 6 MJ/kmol
Water-gas reaction: C H
+ 2 O ⇔ CO H
+ 2 − 131 4
. MJ/kmol l
Water-shift reaction: CO 2 + H 2 ⇔ CO H
+ 2 O + 41 . 2 MJ/kmol k
Methane production reaction:C + 2H 2 ⇔ CH 4 + 75 MJ/kmol k
.
Fixed bed gasifiers operate at 26 bar and closely resemble a blast furnace.
The residence time of fixed bed gasifiers is between 30 and 60 minutes.
Coal size distribution must be controlled to ensure good bed permeability. To ensure stable fluid bed operation, gasification temperatures are kept
below the ash fusion temperature of the coal. Above this temperature, particles become sticky and excessive levels of agglomeration will occur, resulting in bed defluidization (http://www.ccsd.biz/factsheets/igcc.cfm).
13.5.1.2 Fluidized-Bed Gasifiers
A fluidized bed reactor is a vessel in which fine solids are kept in suspension by a gas such that the whole bed exhibits a fluid like behavior. This
type of reacting system is characterized by high heat and mass transfer rates
between the solid and gas. In a fluidized bed gasifier, air, oxygen, or steam
is passed through distributor plates at the bottom of the gasifier. Limestone
is mixed with coal to remove the sulfur present in the coal. Char/ash taken
Alternative Fuels for Transportation
composition of biomass fuels and the operating conditions. The heating value
of the gas produced during the pyrolysis process is low (3.5–8.9 MJ/m 3 ).
Oxidation: introduced air in the oxidation zone contains, besides oxygen
and water vapors, inert gases such as nitrogen and argon. These inert gases
are considered to be nonreactive with fuel constituents. Oxidation takes p lace
at the temperature range of 700–2000°C. Hydrogen in the biomass reacts with
oxygen in the air blast and produces steam.
C + O 2 ⇔ CO 2 + 406 MJ/kmol
1
H 2 + O 2 ⇔ H O
2
+ 242 MJ/kmol.
2
Reduction: in the reduction zone, a number of high temperature chemical
reactions take place in the absence of oxygen. The principal reactions that
take place in reduction are as follows:
Boudouard reaction: CO 2 + ⇔
C
2C O − 172 . 6 MJ/kmol
Water-gas reaction: C H
+ 2 O ⇔ CO H
+ 2 − 131 4
. MJ/kmol l
Water-shift reaction: CO 2 + H 2 ⇔ CO H
+ 2 O + 41 . 2 MJ/kmol k
Methane production reaction:C + 2H 2 ⇔ CH 4 + 75 MJ/kmol k
.
Fixed bed gasifiers operate at 26 bar and closely resemble a blast furnace.
The residence time of fixed bed gasifiers is between 30 and 60 minutes.
Coal size distribution must be controlled to ensure good bed permeability. To ensure stable fluid bed operation, gasification temperatures are kept
below the ash fusion temperature of the coal. Above this temperature, particles become sticky and excessive levels of agglomeration will occur, resulting in bed defluidization (http://www.ccsd.biz/factsheets/igcc.cfm).
13.5.1.2 Fluidized-Bed Gasifiers
A fluidized bed reactor is a vessel in which fine solids are kept in suspension by a gas such that the whole bed exhibits a fluid like behavior. This
type of reacting system is characterized by high heat and mass transfer rates
between the solid and gas. In a fluidized bed gasifier, air, oxygen, or steam
is passed through distributor plates at the bottom of the gasifier. Limestone
is mixed with coal to remove the sulfur present in the coal. Char/ash taken