Biogas purification - Eliminating VOCs and siloxanes

At a time when the development of alternative energies to fossil fuels is particularly propitious, the prospect of integrating biogas into the French energy landscape is of undeniable interest from a political, economic and environmental point of view. Indeed, the recovery of domestic, industrial and agricultural organic residues, or the treatment of wastewater, satisfies the notions of sustainable development and renewable energy, clearly spelled out in recent international commitments and agreements. The environmental impact of implementing biogas recovery processes results in a significant reduction in greenhouse gas emissions. As methane's impact on the greenhouse effect is 20 to 25 times greater than that of carbon dioxide, it is preferable to recover the former by combustion rather than releasing it into the atmosphere. Recent fluctuations in the cost of importing fossil fuels have also had a positive impact on the renewed economic interest in producing energy from biogas, whether directly in the form of high-purity methane gas or in the form of electricity.

Nevertheless, the optimal integration of this resource into existing energy networks is not without technical challenges. Gas dehumidification and hydrogen sulfide reduction are two key steps in the biogas treatment process. However, research on this subject over the last ten years has highlighted the pressure exerted by the volatile organic compounds (VOCs) present in biogas on the operation of energy production plants. In fact, whatever the —value chain chosen, the presence of these compounds at concentrations in the ppm range represents a risk of premature plant degradation, as well as a reduction in biogas energy recovery yields.

This dossier successively covers :

• key concepts related to biogas, defining a classification of biogas, its quality and the resulting applications;

• Volatile organic compounds and siloxanes in biogas, from their presence to their impact on the industry;

• the various gas treatment processes that can be implemented to meet the specific demands of raw biogas purification, the —technological criteria for choosing the process according to biogas characteristics and possible recovery routes;

• a discussion on the prospects for biogas treatment processes.