9.3
Biogas Upgradation: CO 2 Removal
Biogas upgrading is a necessary process to be executed in all countries since the
importance of upgraded biogas is wide. It requires cost-effective investment and
environmentally pleasing solutions, and hence optimisation must be done in terms of
providing high methane content, less energy consumption and minimised methane
emissions (Petersson and Wellinger 2009).
More biogas upgrading technologies are commercially available. The fuel efficiency is important and can be predicted using the parameter calorific value which is
21.5 MJ/m
3 for biogas and 35.8 MJ/m
3 for natural gas. The deviation in the calorific
values for biogas and natural gas is due to the presence of CO 2 , the incombustible
section of biogas, which may lead to the minimisation of heating value with high
compression value. In addition to CO 2 , H 2 S, nitrogen and methane gases are also
present that are strongly not factorable to the environment (Sahota et al. 2018).
Many techniques are available for biogas upgradation, and novel techniques
rectifying all the disadvantages (GHG emissions, hydrocarbon emission, nitrogen
oxide emission, carbon monoxide emission) (Zhao et al. 2010) are under development with environmental and economical perspective (Petersson and Wellinger
2009). The use of biogas as transportation fuel is a dream for developed and
developing countries. Various methods of biogas upgrading technologies
(Fig. 9.3) are described below:
9.3.1 Absorption Methods
In absorption method, the gaseous components have the capacity to undergo diffusion process (Report 2012). Gaseous impurity solubility is one of the crucial factors
for effective absorption. The solubility of carbon dioxide is more than the methane,
and so the liquid that is emitted from the column contains increased amount of
carbon dioxide and the gas emitted from the column contains more amount of
methane, which forms the base for the absorption principle (Petersson and Wellinger
2009).
The untreated biogas is allowed to pass through the column containing a plastic
pack for increasing the area of contact between the two phases in a countercurrent
manner. The solvent used in the absorption process should be selected based on the
various factors (Battino and Clever 1966). For obtaining maximum absorption of
components, factors such as volatility, non-hazardous nature and cost-effectiveness
should be considered (Sahota et al. 2018). The efficiency of absorption process can
also be enhanced by adding fresh liquid to the already used scrubbing liquid. Since,
absorption process requires lower flow rates, the method is economically feasible
(Singhal et al. 2017).
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
247
Biogas Upgradation: CO 2 Removal
Biogas upgrading is a necessary process to be executed in all countries since the
importance of upgraded biogas is wide. It requires cost-effective investment and
environmentally pleasing solutions, and hence optimisation must be done in terms of
providing high methane content, less energy consumption and minimised methane
emissions (Petersson and Wellinger 2009).
More biogas upgrading technologies are commercially available. The fuel efficiency is important and can be predicted using the parameter calorific value which is
21.5 MJ/m
3 for biogas and 35.8 MJ/m
3 for natural gas. The deviation in the calorific
values for biogas and natural gas is due to the presence of CO 2 , the incombustible
section of biogas, which may lead to the minimisation of heating value with high
compression value. In addition to CO 2 , H 2 S, nitrogen and methane gases are also
present that are strongly not factorable to the environment (Sahota et al. 2018).
Many techniques are available for biogas upgradation, and novel techniques
rectifying all the disadvantages (GHG emissions, hydrocarbon emission, nitrogen
oxide emission, carbon monoxide emission) (Zhao et al. 2010) are under development with environmental and economical perspective (Petersson and Wellinger
2009). The use of biogas as transportation fuel is a dream for developed and
developing countries. Various methods of biogas upgrading technologies
(Fig. 9.3) are described below:
9.3.1 Absorption Methods
In absorption method, the gaseous components have the capacity to undergo diffusion process (Report 2012). Gaseous impurity solubility is one of the crucial factors
for effective absorption. The solubility of carbon dioxide is more than the methane,
and so the liquid that is emitted from the column contains increased amount of
carbon dioxide and the gas emitted from the column contains more amount of
methane, which forms the base for the absorption principle (Petersson and Wellinger
2009).
The untreated biogas is allowed to pass through the column containing a plastic
pack for increasing the area of contact between the two phases in a countercurrent
manner. The solvent used in the absorption process should be selected based on the
various factors (Battino and Clever 1966). For obtaining maximum absorption of
components, factors such as volatility, non-hazardous nature and cost-effectiveness
should be considered (Sahota et al. 2018). The efficiency of absorption process can
also be enhanced by adding fresh liquid to the already used scrubbing liquid. Since,
absorption process requires lower flow rates, the method is economically feasible
(Singhal et al. 2017).
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
247