Innovative Biogas Configurations
T: 353 (0)21 490-1995
F: 353 (0)21 490-1932
Funding Body: Science Foundation Ireland, Ecoventi
Project Type: PhD
Period: Oct 2013 – Sept 2017
Storage of electricity is essential to facilitate large scale renewable energy penetration, in particular when the source of electricity is intermittent and variable. The concept proposed here includes for converting electricity to a gaseous fuel. Initially hydrogen will be produced via electrolysis. This may be converted to methane as described by the Sabatier Equation (4H2 + CO2 -> CH4 + 2H2O). The reason for choosing methane is that hydrogen is limited as a transport energy vector due to its volumetric energy density. For use in vehicular transport, hydrogen requires compression to 700 bar to achieve the same energy per unit compressed storage as methane at 220 bar. This compression requires 13% of the energy in hydrogen compared to 3.3% of the energy in methane. The energy balance or round trip efficiency of compressed hydrogen (as a transport energy vector) produced from electricity is of the order of 50%, whereas the overall efficiency of the conversion of electricity to compressed methane is 55%. Of great benefit is the potential to use the natural gas grid as a transportation infrastructure for the produced methane.
The Sabatier system requires a concentrated stream of CO2. This is readily available from a biogas facility. Typically biogas comprises 55% CH4 and 45% CO2. In order to gas grid inject biomethane, CO2 must be removed. The Sabatier system can act as an upgrading facility while also doubling the methane output (each m3 of CO2 is converted to approximately 1 m3 of CH4).
Methanation by application of the Sabatier equation can either be effected through catalytic or biological processes. This project entails a laboratory assessment combining a biological Sabatier system with a variety of bespoke single and multi-phase digester systems. The objective of this research is to assess the optimum operation of such systems and their application to biological conversion of hydrogen to methane.