PRODUCTION COSTS OF LIQUID FUELS FROM BIOMASS

There has been considerable interest in producing fuels from biomass a nd wastes since the oil crises of the last two decades which has been reinforced by subsequent environmental concerns and recent political e vents in the Middle East. This project was undertaken to provide a con sistent and thorough review of the full range of processes for produci ng liquid fuels from biomass to compare both alternative technologies and processes within those technologies in order to identify the most promising opportunities that deserve closer attention. Thermochemical conversion of wood, straw and refuse includes both indirect liquefacti on through gasification, and direct liquefaction through pyrolysis and liquefaction in pressurised solvents. Biochemical conversion is based on a different set of feedstocks that includes wood as well as wheat and sugar beet. Both acid and enzyme hydrolysis are included as option s, followed by fermentation. The liquid products considered include ga soline and diesel hydrocarbons that would in some cases would require minor refining to convert them into marketable products, and conventio nal alcohol fuels of methanol and ethanol which have established oppor tunities for utilisation, and fuel alcohol which is as yet unproven in the market place. Results are given both as absolute fuel costs and a s a comparison of estimated cost to market price. The results from the se two interpretations are quite different. In terms of absolute fuel costs, thermochemical conversion offers the lowest cost products, with the least complex processes generally having an advantage. Exceptions are the unproven direct liquefaction route through zeolites which may be very optimistic, and the Shell SMDS process. Biochemical routes ar e the least attractive. The most attractive processes from comparing p roduction costs to product values are generally the alcohol fuels whic h enjoy a higher market value. This final analysis should be viewed ca utiously since product values are very uncertain and can change signif icantly over short periods of time, and feedstock prices are also subj ect to substantial variation with time and location, and this is often the major cost item in the production costs. There is still considera ble analysis to be carried out on results from the model, including pr oduction cost analyses and sensitivity studies, as well as continued d evelopment to improve accuracy and extend the range of technologies co nsidered.