Abstract
Organic waste is a good source of clean energy. However, different fractions of waste have to be utilized efficiently. One way is to find pathways to convert waste into useful products via various available processes (gasification, pyrolysis anaerobic digestion, etc.) and integrate them to increase the combined efficiency of the process. The syngas and hydrogen produced from the thermal conversion of biomass can be upgraded to biomethane via biological methanation. The current study presents the simulation model to predict the amount of biomethane produced by injecting the hydrogen and syngas. Hydrogen injection is modelled both in-situ and ex-situ while for syngas solely the ex-situ case has been studied. The results showed that 85% of the hydrogen conversion was achieved for the ex-situ reactor while 81% conversion rate was achieved for the in-situ reactor. The syngas could be converted completely in the bio-reactor. However, the addition of syngas resulted in an increase of carbon dioxide. Simulation of biomethanation of gas addition showed a biomethane concentration of 87% while for hydrogen addition an increase of 74% and 80% for in-situ and ex-situ addition respectively.
Highlights
Waste biomass is an exclusive source of renewable energy and can be utilized in various ways like incineration, gasification, anaerobic or aerobic digestion
Finding the alternate solutions for efficient utilization of different waste fractions is of importance
The two processes i.e. anaerobic digestion and gasification/pyrolysis can be integrated to increase the efficiency of biogas plants, efficient utilization of various fractions of waste within one facility and decrease the complexity of carbon dioxide separation in the downstream processes [2]
Summary
Waste biomass is an exclusive source of renewable energy and can be utilized in various ways like incineration, gasification, anaerobic or aerobic digestion. The two processes i.e. anaerobic digestion and gasification/pyrolysis can be integrated to increase the efficiency of biogas plants, efficient utilization of various fractions of waste within one facility and decrease the complexity of carbon dioxide separation in the downstream processes [2]. The conversion of hydrogen by biological Sabatier reaction can either be in-situ by introducing the hydrogen into an anaerobic digester or ex-situ i.e. in an external reactor with methanogens to favor the production of biomethane [4], [3]. The production of pure hydrogen is an energy intensive process either by hydrolysis of water or from thermochemical conversion, such as gasification or pyrolysis, of organic matter for example lingo-cellulosic biomass. The biological conversion of syngas can be carried out by a range of microorganisms which can simultaneously support the production of methane, hydrogen, and acetate [7]. The second pathway follows the conversion of CO to acetate followed by conversion of acetate to methane via following reactions [9]
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