Improvement of Biogas Upgrading Process Using Chemical Absorption at Ambient Conditions

Abstract

Biogas major components are methane, carbon dioxide and traces of hydrogen sulfide, ammonia and nitrogen. Biogas upgrading process is the process by which carbon dioxide (composing 40 % of the biogas) is removed. In this study chemical absorption process using three different solvents (10 – 30 % monoethanolamine, 4 – 12 % sodium hydroxide and 5 – 15 % aqueous ammonia) was performed to produce methane-enriched biogas. A laboratory-scale packed-column apparatus containing efficient and cheap packing material (plastic bioball) was used to perform the experimental work in this study. Initial absorption runs were performed to select the best solvent type and concentration. Monoethanolamine (MEA) was proven to have the highest ability in producing upgraded biogas using a single absorption column apparatus at ambient conditions. The liquid to gas flow ratio was investigated using 30 % MEA solution. Optimum liquid to gas flow ratio for biogas upgrading process was determined to be about 18 (on mass basis). Biogas with methane content up to 96.1 v/v% was produced with CO2 loading capacity up to 0.24 mole-CO2 per mole-MEA.

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“…The solvent is regenerated and can be recirculated to the absorption column, but now Ca(OH) 2 has to be regenerated (Equations ( 6) and ( 7)). The formation of CaO and CO 2 from CaCO 3 occurs under high temperatures, making this process very energy-extensive, even higher than MEA regeneration [85]. Similar reactions for KOH, Ca(OH) 2 , and NH 4 OH regeneration take place [68,92].…”

“…KOH is more expensive than NaOH, but K 2 CO 3 is formed, which is a compound with many industrial applications (e.g., the crystal industry, special glass production, potassium salts, inks and pigments, detergents, the food industry, and waste gas treatment) [68,83]. NH 4 OH is less corrosive than MEA and requires less energy for its regeneration [82,84], but it is highly volatile, and some traces can be present in the upgraded gas [85].…”