The paper presents the results of exergy analysis for a biomass-to-synthetic natural gas (SNG) conversion process. The presented study is based on wood gasification, which is analysed for different gasification conditions like temperature and/or pressure. The analysed temperature was varied in the range from 650 to 800°C and the pressure range was from 1 to 15bar. The main process units of biomass-to-SNG conversion technology are gasifier, gas cleaning, synthesis gas compression, CH4 synthesis and final SNG conditioning. The results showed that the largest exergy losses take place in the biomass gasifier, CH4 synthesis part and CO2 capture unit. The overall exergetic efficiency of the biomass-to-SNG process was estimated in the range of about 69.5–71.8%.

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.

Biomass availability is rather limited in Europe and, hence, it is of crucial importance to determine the optimal biomass-to-energy conversion pathway. This selection is somehow complex as there could be antagonistic motivations coming from industrial stake-holders, politicians, scientists or the society. Consequently, the aim of this paper is to present different biomass-to-biofuels alternatives that follows various economic, environmental and/or social drivers. Results are also compared with European Directives 2001/77/EC and 2009/28/EC. In General, maximizing bio-electricity over other biofuels turns out to be the best economical and environmental option. Combined with solar and wind energy, about 31% of the electricity production by 2020 could be renewable, i.e., 10 points higher than the target of Directive 2001/77/EC. If biomass is conducted to SNG production, fossil natural gas imports could be reduced by 1.63 EJ/yr in 2020, although this alternative implies higher costs and less CO2 savings than the previous bio-electricity solution. In case of promoting Fischer-Tropsch fuels, the share of biofuels in transport will be 9.5%, which is slightly below the 10% share target of Directive 2009/28/EC. H-2 is disregarded as feasible option for transport due to several technological barriers, although it would lead to substantial CO2 savings at a moderate price. Conversely, methanol results in the worst environmental solution as CO2 emissions are larger than those of conventional fossil fuels.

Consumption of hexoses and pentoses and production of ethanol by Mucor indicus were investigated in both synthetic media and dilute-acid hydrolyzates. The fungus was able to grow in a poor medium containing only carbon, nitrogen, phosphate, potassium, and magnesium sources. However, the cultivation took more than a week and the ethanol yield was only 0.2 gg−1. Enrichment of the medium by addition of trace metals, particularly zinc and yeast extract, improved the growth rate and yield, such that the cultivation was completed in less than 24 h and the ethanol and biomass yields were increased to 0.40 and 0.20 gg−1, respectively. The fungus was able to assimilate glucose, galactose, mannose, and xylose, and produced ethanol with yields of 0.40, 0.34, 0.39, and 0.18 gg−1, respectively. However, arabinose was poorly consumed and no formation of ethanol was detected. Glycerol was the major by-product in the cultivation on the hexoses, while formation of glycerol and xylitol were detected in the cultivation of the fungus on xylose. The fungus was able to take up the sugars present in dilute-acid hydrolyzate as well as the inhibitors, acetic acid, furfural, and hydroxymethyl furfural. M. indicus was able to grow under anaerobic conditions when glucose was the sole carbon source, but not on xylose or the hydrolyzate. The yield of ethanol in anaerobic cultivation on glucose was 0.46 g g−1.