Biogas purification with biomass ash.

Area of Science:

• Environmental Engineering
• Biomass Energy
• Waste Management

Background:

• Small-scale biogas plants produce biogas containing impurities like CO2 and H2S.
• Effective purification methods are crucial for biogas utilization.
• Biomass ash is a regionally available byproduct with potential adsorbent properties.

Purpose of the Study:

• To investigate the efficacy of using regionally available biomass ash for biogas purification.
• To assess the capacity of wood ash to adsorb CO2 and H2S from biogas.
• To evaluate the impact of biogas flushing on the properties of biomass ash.

Main Methods:

• Wood ash was used as an adsorbent in a 1 m³ container connected to a small-scale biogas plant.
• The biogas stream was passed through the wood ash to trap CO2 and H2S.
• The duration of CO2 and H2S removal was monitored.
• Cumulative H2S uptake was quantified.
• Leachability of heavy metals and plant toxicity of the ash were assessed before and after biogas flushing.

Main Results:

• Biomass ash successfully trapped CO2 for several hours, yielding pure methane.
• Significant and longer-lasting removal of H2S was achieved, lasting up to 34 days.
• Cumulative H2S uptake ranged from 0.56 to 1.25 kg H2S per ton of ash.
• Biogas flushing reduced ash pH and leachability of Lead and Barium.
• However, ash toxicity towards plants increased, limiting its agricultural application.

Conclusions:

• Biomass ash is a viable option for removing hydrogen sulfide from biogas in small and medium-scale biogas plants.
• The adsorption capacity for H2S is substantial.
• Economic feasibility is constrained by ash transportation logistics and post-treatment utilization challenges.