Energy efficiency and CO₂ emission assessment of Bio-SNG production - A methodology comparison

Fossil fuels applied in energy generation-, transport- and refinery processes can be replaced by biofuels. This offers plenty processing options for biomass resources such as thermo-chemical. For process evaluation different criteria is applied, usually including costs, energy efficiency and CO₂ emission. However, comparative evaluation of the energy efficiency is difficult since no general standard method exists. The objective of this paper is to compare different methods of energy efficiency and CO₂ emission assessment in order to systematically analyse their differences qualitatively and quantitatively. The methods include a general engineering approach, CO₂ assessment according to the EU's Renewable Energy Sources Directive, primary energy efficiency analysis (incl. CO₂ assessment) and exergy analysis. In this paper the methods are compared, based on a case study of Bio-SNG generation from woody biomass (simulated with Aspen+). The work shows the differences of the methods when applied to the same process allowing critical discussions of the methods applicability and providing a starting point for the future work on developing novel energy efficiency and CO₂ emission assessment methods.