Thermodynamic approach to biogas production

Abstract

This dissertation determines theoretical targets for producing biogas. Calculations were based on the relationship between the mass of substrate used (assumed to be glucose) versus the amount and composition of gas produced. Methane, hydrogen and carbon dioxide were considered as gases produced by biogas processes. The calculations undertaken to determine the production rates and environmental targets of the biogas production system were based on mass and energy balances as well as the second law of thermodynamics. These were applied to determine the limits of performance of the process. These limits are important due to the fact that they cannot be exceeded even if we genetically engineer organisms or change the equipment design or operation. Combining the results enabled us to plot an attainable region that showed the achievable composition of the gas as well as the minimum work and energy requirements for biogas production. It shows that the process is hydrogen and enthalpy (heat) limited. Furthermore the results show that a maximum of 3 moles of methane per mole of glucose are produced sustainably which in turn produces a large heat load of 142 kJ/mol of glucose.