An overview of thermal biomass conversion technologies

Abstract

The major thermal biomass conversion techniques are combustion, gasification, pyrolysis, and torrefaction. Combustion means 100% oxidation of all organic contents of the fuel using air/oxygen, while gasification means partial combustion where some 15-30% of the oxygen is added in relation to what would be needed for 100% oxidation. In pyrolysis we only heat but without adding air and thereby gaseous components of the organic material are evaporated and later condensed as liquid hydrocarbons. Torrefaction is when you do partial pyrolysis but only to remove some of the gaseous components, where the purpose not is to produce liquid hydrocarbons but make a compact residue that can replace coal in coal fired power plants. Only combustion is really used on a large scale commercially today for biomass, although significant work has been done on development of the other techniques as well. The hurdle has been the cost as the fossil alternatives with natural gas, oil and coal have been “too cheap”. As different type of penalties are introduced on fossil fuels to compensate for the costs caused by environmental impact like greenhouse effects and acidification, the relative competitiveness will change. As the new technologies are improved they will also be cheaper, and with new system designs we can foresee a commercial expansion within the next coming 10 years also with respect to all other technologies apart from combustion. Several countries like the USA, Denmark, Finland, Germany, the Netherlands and Sweden all have strategies for research and demonstration of biomass for multiple uses such as for production of plastics, textile fibers, and many different chemicals (Andersson, 2012).