Various types of absorbents are used, and based on the types of absorbents, the
absorption methods can be categorised into the following types:
(a) Physical absorption method.
(b) Chemical absorption method.
(c) Physical absorption method.
9.3.1.1 Physical Water Scrubbing
Physical water scrubbing is one of the most commonly used biogas upgradation
technology for biogas cleaning and upgradation, which is commercially available
and manufactured with wide range of capacities (Thran et al. 2014). In this method,
the principle of solubility is applied between two gaseous components (Kapoor et al.
2017). The two gaseous components carbon dioxide and methane vary in the
property of solubility, specifically at low temperature. Carbon dioxide is more
soluble when compared to methane, and while leaving the column, the carbon
dioxide quantity gets increased in the liquid part and the methane quantity gets
increased in the gaseous phase (Cozma et al. 2013). The water that is left over the
column is passed to a flash tank with release in some amount of carbon dioxide and
again retransferred to the raw biogas inlet provided. If the water is allowed to
recycling process in desorption column which is filled with plastic packing, the
carbon dioxide gas will be released. The high difference in the solubility of the two
gases can be attained by cooling the water, before the next recycling process in the
column.
Genosorb 1753 is one of the most widely applied absorbent, and by using the
depressurising technique, the spent absorbents can be regenerated (Patterson et al.
2011). The hydrogen sulphide gas separation should be done since the absorption of
carbon dioxide tends to reduce in the presence of hydrogen sulphide gas (Sahota
et al. 2018). The operating parameters for the water scrubbing method include initial
pressure of 6–10 Bar and temperature of 40
C. From the bottom side of the column,
the biogas is passed, and from the top of the column, water is passed and injected
into the absorption column via the bottom side of the tank, while the water is passed
that expresses the countercurrent flow between the gas and the water (Bauer et al.
2013b).
The major disadvantage of this method is that during the process of regeneration,
gas components such as nitrogen and oxygen tend to get dissolved, and then it passes
along with the upgraded methane gas. This technique is more valuable if:
• The plant capacity is increased.
• The decompression process is discarded.
• The heating value is reduced (Report 2012).
9.3.1.2 Organic Physical Scrubbing
In organic physical scrubbing, the absorption of carbon dioxide occurs in the organic
solvents such as polyethylene glycol/methanol, and this absorption tendency is more
possible because the carbon dioxide gas is more soluble in solvent than in water.
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
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absorption methods can be categorised into the following types:
(a) Physical absorption method.
(b) Chemical absorption method.
(c) Physical absorption method.
9.3.1.1 Physical Water Scrubbing
Physical water scrubbing is one of the most commonly used biogas upgradation
technology for biogas cleaning and upgradation, which is commercially available
and manufactured with wide range of capacities (Thran et al. 2014). In this method,
the principle of solubility is applied between two gaseous components (Kapoor et al.
2017). The two gaseous components carbon dioxide and methane vary in the
property of solubility, specifically at low temperature. Carbon dioxide is more
soluble when compared to methane, and while leaving the column, the carbon
dioxide quantity gets increased in the liquid part and the methane quantity gets
increased in the gaseous phase (Cozma et al. 2013). The water that is left over the
column is passed to a flash tank with release in some amount of carbon dioxide and
again retransferred to the raw biogas inlet provided. If the water is allowed to
recycling process in desorption column which is filled with plastic packing, the
carbon dioxide gas will be released. The high difference in the solubility of the two
gases can be attained by cooling the water, before the next recycling process in the
column.
Genosorb 1753 is one of the most widely applied absorbent, and by using the
depressurising technique, the spent absorbents can be regenerated (Patterson et al.
2011). The hydrogen sulphide gas separation should be done since the absorption of
carbon dioxide tends to reduce in the presence of hydrogen sulphide gas (Sahota
et al. 2018). The operating parameters for the water scrubbing method include initial
pressure of 6–10 Bar and temperature of 40
C. From the bottom side of the column,
the biogas is passed, and from the top of the column, water is passed and injected
into the absorption column via the bottom side of the tank, while the water is passed
that expresses the countercurrent flow between the gas and the water (Bauer et al.
2013b).
The major disadvantage of this method is that during the process of regeneration,
gas components such as nitrogen and oxygen tend to get dissolved, and then it passes
along with the upgraded methane gas. This technique is more valuable if:
• The plant capacity is increased.
• The decompression process is discarded.
• The heating value is reduced (Report 2012).
9.3.1.2 Organic Physical Scrubbing
In organic physical scrubbing, the absorption of carbon dioxide occurs in the organic
solvents such as polyethylene glycol/methanol, and this absorption tendency is more
possible because the carbon dioxide gas is more soluble in solvent than in water.
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
249