Thermodynamic and environmental assessment of systems including the use of gas from manure fermentation in the context of the Spanish potential

The EU energy policy focuses on reliable, flexible, environmentally friendly and secure ways of delivering energy to consumers. This favours the implementation of novel, often hybrid, technologies for electricity generation and storage that have not been present in the energy mix before. To introduce them into the energy market in the most proper and optimised way, there is a need for developing robust simulations of the most advanced electricity generation systems and projecting the life-cycle performance to future electricity energy generation systems, as such analyses are hardly met in the literature. One of the prospective technologies that can be used for energy generation in distributed systems is based on biogas production, usually involving fermentation process of various types of biomass and wastes. In this paper a case study of manure fermentation for the purpose of energy (and fuel) generation is assessed. The analysis is made for Spain, for which such a solution is very promising, due to availability of the feedstock. A detailed simulation model of the proposed system in two different cases was built in Aspen Plus software and VBA. Case 1 involves production of biogas in manure fermentation process, its upgrading (cleaning and removal of CO₂ from the gas) and injection to the grid. Case 2 assumes combustion of the biogas in gas engine to produce electricity and heat that can be used locally or sold to the grid. Thermodynamic assessment of these two cases was made allowing to determine the most important parameters and evaluation indices. The results served as input values for Life Cycle Assessment performed in SimaPro. Two impact categories were chosen here for assessment – global warming potential and cumulative non-renewable energy demand.