Bio-SNG production — concepts and their assessment

Abstract

A major goal of today’s energy policy is to establish an energy system with less greenhouse gas emissions (cf. “Renewable energy roadmap” [1]). The energetic use of biomass seems to be a very promising option to contribute to this goal: biomass can be used demand-oriented and to produce different energy carriers (e.g. power, heat and biofuels) needed within the energy system. Due to high overall efficiencies, especially the thermo-chemical conversion of solid biofuels to the natural gas substitute Bio-SNG (Synthetic Natural Gas) seems to be very promising. Therefore, it is the goal of this paper to analyse Bio-SNG production processes as a part of integrated polygeneration processes. Different Bio-SNG concepts using a gas slip stream in a gas engine or a gas turbine and process heat in an organic rankine cycle or conventional steam cycle are assessed. Based on mass and energy balances these concepts are discussed from an energetic, economic and environmental point of view. The analysis shows increasing exergetic efficiencies as well as improved economic and environmental process characteristics with increasingly integrated processes. However, the economic competitiveness still remains a bottleneck for a Bio-SNG market implementation. Therefore, two possible options to improve this competitiveness are discussed in detail.