Are European bioenergy targets achievable? : an evaluation based on thermoeconomic and environmental indicators

Abstract

Nowadays, it is globally accepted the need of increasing the share of renewable energy to minimize global warming effects. Biomass is a potential alternative to partly fulfill energy policy targets, although unlike solar or wind energy, its availability is limited and stochastically distributed. Hence, the most effective biomass-to-bioenergy route should be selected which, in turn, would lead to more competitive prices with regard to conventional fossil fuels. However, selection of the best conversion technology generates some controversy as the politicians, industry or the scientific community have their own preferences. An inherent challenge is, thus, to develop a multidimensional model that integrates different perspectives. Another point of discussion is related to the different biomass sources that can be used for energy purposes. In effect, 1st generation biofuels are currently being questioned for using energy crops which may directly compete with food production. Moreover, some life-cycle studies reveal that several 1st generation biofuels exceed the emissions level of fossil fuels. Conversely, 2nd generation biofuels are now being developed as a possible better alternative to profit from inedible crops, while operating at higher efficiencies in larger conversion plants. In the thesis, we present the evaluation of five different 2nd generation biofuels (i.e., Synthetic Natural Gas (SNG), methanol, Fischer-Tropsch fuels, hydrogen and bioelectricity) for their potential implementation in the European Energy market. Evaluation is made following an own multidimensional 3E approach, which combines efficiency, economic and environmental parameters. For that purpose, forestry and straw wastes availability of EU-25 countries is firstly calculated and allocated within all regions. The five production chains are then modeled in Aspen Plus and Icarus for efficiency (exergy) and economic evaluation respectively, whereas a LCA is carried out to assess the environmental impact. Simulations are performed at different production scales to identify the optimal plant size for each biofuel. Evaluation is finally completed by considering the different motivations of policy makers, industry and scientific community. Hence, different scenarios are analyzed, ranging from maximizing biofuels for road transport in short and long-term future (i.e., ICE and FCV vehicles), optimizing SNG production, maximizing the renewable share in electricity production (i.e., new bio-based BIGCC plants or cofiring) and, ultimately, maximizing CO2 emissions reduction. Results determine how feasible is to fulfill the different European Energy Policy when using only forestry and straw residues, which are the potential global CO2 emissions reduction and the average biofuels and bioelectricity prices. Bioelectricity generation turns out to be the best alternative from a techno-economic and environmental point of view. About 381 to 461 Mtn CO2 could be saved annually if all European forest and straw residues were used in either cofiring or new BIGCC plants. The corresponding price difference between bioenergy and fossil alternatives are also the lowest for the bioelectricity scenario, i.e., 3-4 Billion €/year respectively, with an estimated ‘virtual’ ecocost lying in the range of 7-8 €/tn CO2. It is also observed that cofiring is preferred over other biofuels production when the aim is to reduce CO2 emissions. On the other hand, if bioelectricity is summed to 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. In case of prioritizing Fischer-Tropsch fuels, the share of biofuels in transport would be 8.0-9.5%, which is slightly below the 10% share target of Directive 2009/28/EC. However, this option implies relatively higher capital investments. In any case, there is not enough forest and straw residues in Europe to the targets of both Directives. Individual biofuels comparison reveals that SNG and bioelectricity yield the highest exergetic production efficiencies for wood-fuelled plants (i.e., up to 45.5%). This statement is translated into the lowest biofuel prices (i.e., 17-20 and 24 €/GJ for SNG and bioelectricity in the Netherlands). However, SNG prices are about 2-times higher than natural gas in most of the European countries, with the exception of Sweden. Fischer-Tropsch and methanol can be produced at similar end-user prices, which are relatively close to fossil diesel prices including taxes. However, they emit more CO2 than the other biofuel options. In particular, methanol even releases more CO2 emissions than fossil diesel in most of the European countries. When the efficiency analysis is extended to a well-to-wheel (WTW) perspective (i.e., from biomass collection to final biofuel use in vehicles), the bioelectricity option is again the most efficient route, with energy ratios in the range of actual oil-based systems (i.e., 17-19%). H2 attains the second best WTW efficiencies values (i.e., 14-15%), but it is also the most expensive biofuel per unit of output energy. Moreover, safety concerns about H2 distribution queries the viability of this biofuel for the long-term future. SNG and Fischer-Tropsch systems attain similar efficiencies (i.e., 9-11%) whereas methanol is the least efficient (i.e., 5-6%).