Investigation on hydrogen sulphide poisoning in molten carbonate fuel cells used for waste-to-energy conversion.

Bioenergy addresses three important social concerns: security of energy supply, lower greenhouse gas emissions and support for agriculture. Bioenergy is energy produced from the direct or indirect combustion of biomass material, such as energy crops, wood, manures and slurries or organic waste converted to biogas. Different technologies are currently available for bioenergy conversion but fuel cells are one of the most interesting because of their environmental benefits and their high efficiency. High operating temperature of molten carbonate fuel cells (650°C) makes them particularly suitable for energy production from biogas, which is biomass derived gas rich in methane and carbon dioxide. In fact, methane can be internally reformed to hydrogen, carbon dioxide is a safe chemical participating in electrodic reactions, and carbon monoxide acts both as a hydrogen supplier and as a fuel. Unfortunately, biogas impurities, such as sulfur compounds, halogen compounds, nitrogen compounds, hydrocarbons and siloxanes, cause adverse effects on cell performances. The most dangerous impurities are sulfur compounds. Hydrogen sulphide is the predominant and the most harmful sulfur compound in biogas. It reacts with nickel-based anode to form nickel sulphides and blocks electrocatalytic sites. Poisoning mechanism of hydrogen sulphide depends on operational conditions such as current density, anodic gas composition, temperature and pressure. The aim of this work is to study hydrogen sulphide effects on MCFCs with multivariate mathematical approaches. In this way it is possible to define the main sulfur poisoning mechanism under MCFC operating conditions, quantify the effect of current density, hydrogen and hydrogen sulphide on sulfur poisoning and identify the interaction between these parameters. Also it is possible to formulate a multivariate model to predict sulfur poisoning.