liquefaction process is well suitable, whereas low moisture feedstocks are found
suitable for combustion or pyrolysis or gasification process.
6.3.1.1 Gasification
All constituents of biomass feedstock subjected to higher temperatures (700–900
C)
with a restricted amount of oxidizing agent (air/oxygen/steam) supply in a gasifier
can yield a gaseous biofuel. This gaseous fuel is referred to as syngas or producer
gas, which can be used as fuel in burners or dual-fuel engines for thermal
applications and electricity generation, respectively. In terms of typical calorific
value, the biogas (21–24 MJ/m
3 ) is lower than that of syngas (4–10 MJ/m
3 )
depending on biomass feedstocks and reaction conditions (Tumwesige et al. 2014;
Widjaya et al. 2018). The syngas is used as a chemical platform for biofuels or
biochemicals. Pre-processing of biomass feedstocks is carried out by drying and size
reduction process. The low moisture content of biomass (10–15%) is preferred for
the gasification process (Basu 2010), which can be achieved by sun-drying or
mechanical drying methods. Generally, the size and shape of the biomass materials
are not in uniform shape due to heterogeneous biomass feedstocks. Therefore, size
reduction is the main pre-processing step after drying. The size of biomass
feedstocks must be reduced to increase the biomass holding capacity of the gasifier
and also for enhancing the reaction rates. Most of the agro-residues would contain
alkali minerals, and it reacts with silica to form clinkers at time of thermal degradation. For example, the rice husk contains more silica content and forms clinkers in
the case of the combustion or gasification process. Therefore, the selection of
biomass feedstock for the gasification process is an important one, and feedstocks
are tested for their performance in the gasifier to assess their syngas potential.
6.3.1.2 Pyrolysis
The biomass materials subjected to medium temperature without air/oxygen in a
pyrolytic reactor yields useful bio-products such as pyrolytic gas, solid product, and
liquid biofuel. Typical end product yields (dry basis) produced from different modes
of the pyrolysis process is depicted in Fig. 6.2. It depends on reaction conditions
used in the pyrolysis process, either biochar or bio-oil generated from the biomass.
Biochar and charcoal can be used as a soil conditioner.
6.3.1.3 Combustion
Complete burning of biomass materials in an excess air/oxygen environment in a
combustor/furnace/stoves/chulha to produce heat energy. The steam is produced by
burning of biomass, which can be used for electricity generation. For example,
sugarcane bagasse is used as fuel in steam boiler and electricity is produced in
steam turbines. If the agro-residues with higher ash content are used as fuel in the
combustion process, ash removal setup should be incorporated in the combustion
system for continuous ash removal.
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D. Ramesh et al.
suitable for combustion or pyrolysis or gasification process.
6.3.1.1 Gasification
All constituents of biomass feedstock subjected to higher temperatures (700–900
C)
with a restricted amount of oxidizing agent (air/oxygen/steam) supply in a gasifier
can yield a gaseous biofuel. This gaseous fuel is referred to as syngas or producer
gas, which can be used as fuel in burners or dual-fuel engines for thermal
applications and electricity generation, respectively. In terms of typical calorific
value, the biogas (21–24 MJ/m
3 ) is lower than that of syngas (4–10 MJ/m
3 )
depending on biomass feedstocks and reaction conditions (Tumwesige et al. 2014;
Widjaya et al. 2018). The syngas is used as a chemical platform for biofuels or
biochemicals. Pre-processing of biomass feedstocks is carried out by drying and size
reduction process. The low moisture content of biomass (10–15%) is preferred for
the gasification process (Basu 2010), which can be achieved by sun-drying or
mechanical drying methods. Generally, the size and shape of the biomass materials
are not in uniform shape due to heterogeneous biomass feedstocks. Therefore, size
reduction is the main pre-processing step after drying. The size of biomass
feedstocks must be reduced to increase the biomass holding capacity of the gasifier
and also for enhancing the reaction rates. Most of the agro-residues would contain
alkali minerals, and it reacts with silica to form clinkers at time of thermal degradation. For example, the rice husk contains more silica content and forms clinkers in
the case of the combustion or gasification process. Therefore, the selection of
biomass feedstock for the gasification process is an important one, and feedstocks
are tested for their performance in the gasifier to assess their syngas potential.
6.3.1.2 Pyrolysis
The biomass materials subjected to medium temperature without air/oxygen in a
pyrolytic reactor yields useful bio-products such as pyrolytic gas, solid product, and
liquid biofuel. Typical end product yields (dry basis) produced from different modes
of the pyrolysis process is depicted in Fig. 6.2. It depends on reaction conditions
used in the pyrolysis process, either biochar or bio-oil generated from the biomass.
Biochar and charcoal can be used as a soil conditioner.
6.3.1.3 Combustion
Complete burning of biomass materials in an excess air/oxygen environment in a
combustor/furnace/stoves/chulha to produce heat energy. The steam is produced by
burning of biomass, which can be used for electricity generation. For example,
sugarcane bagasse is used as fuel in steam boiler and electricity is produced in
steam turbines. If the agro-residues with higher ash content are used as fuel in the
combustion process, ash removal setup should be incorporated in the combustion
system for continuous ash removal.
106
D. Ramesh et al.