Although there are significant differences in the capital investments for pyrolysis­upgrading, gasification-synthesis and biochemical conversion of lignocellulose to liquid biofuels for transportation, these technologies all require large-scale imple­mentation to make the high capital costs worthwhile (Anex et al. 2010; Kazi et al. 2010; Stephen et al. 2012; Kumar et al. 2012; Brown et al. 2013). Furthermore, it is also expected that the first commercial plants for these technologies will perform at less than design capacity and have capital costs that are higher than anticipated (Anex et al. 2010). Despite the need for bioenergy in transportation, the high capital costs and technology risks associated with newer technologies represent hurdles on the pathway to commercialisation (Stephen et al. 2012; Anex et al. 2010). The wide range of multiple, competing, commercially unproven technologies for the production of liquid transportation fuels from lignocellulose also indicates that standardisation of the conversion process, with associated economies-of-scale in plant component production to reduce capital costs, will not be achieved soon (Stephen et al. 2012).

The large production scales required for cost effective production of liquid transportation fuels from lignocellulose have to be balanced against the cost of feedstock supply. The transport cost of biomass supply generally increases with an increase in production capacity (Gnansounou and Dauriat 2010; Seabra et al. 2010; see Chap. 6). Regional conditions for the supply of biomass will determine optimal plant size, since the reduction of capital investment per unit energy produced as production scale increases is balanced by an increased requirement of feedstocks, the local cost and availability of which determines the maximum scale-dependant cost-benefit that can be achieved (Stephen et al. 2010). Various combinations of lignocellulose feedstock may therefore be used to increase biomass supply in order to reach the desired economies of scale (Seabra et al. 2010). In some scenarios the increase in cost effectiveness with an increase in production scale may outweigh the associated increase in feedstock cost (Amigun et al. 2010). It has been demonstrated that for torrefaction processes there is no benefit in terms of economies of scale for production scale beyond 40MWth (Uslu 2005; Uslu et al. 2008).

7.5 Conclusion

Combustion, pyrolysis and anaerobic digestion of lignocellulose are well — established technologies available for commercial application; while gasification, liquefaction, hydrolysis-fermentation and fractionation hold promise for future implementation.

Overall, it is expected that the production of bioenergy will increase in the Southern hemisphere, based on the overall sustainability of biomass production and cost comparisons with fossil-derived energy.