Production costs of liquid fuels from biomass

Abstract

There has been considerable interest in producing fuels from biomass and wastes since the oil crises of the last two decades which has been reinforced by subsequent environmental concerns and recent political events in the Middle East. This project was undertaken to provide a consistent and thorough review of the full range of processes for producing 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 liquefaction through gasification, and direct liquefaction through pyrolysis and liquefaction in pressurized 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 options, followed by fermentation. The liquid products considered include gasoline and diesel hydrocarbons that in some cases would require minor refining to convert them into marketable products, and conventional alcohol fuels of methanol and ethanol which have established opportunities for utilization, and fuel alcohol which is as yet unproven in the market place. Results are given both as absolute fuel costs and as a comparison of estimated cost to market price. The results from these 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 middle distillate synthesis process. Biochemical routes are the least attractive. The most attractive processes from comparing production costs to product values are generally the alcohol fuels which enjoy a higher market value. This final analysis should be viewed cautiously since product values are very uncertain and can change significantly over short periods of time, and feedstock prices are also subject to substantial variation with time and location, and this is often the major cost item in the production costs. There is still considerable analysis to be carried out on results from the model, including production cost analyses and sensitivity studies, as well as continued development to improve accuracy and extend the range of technologies considered.