Overview of biomass conversion and generation technologies

The total energy stored in terrestrial biomass outnumbers the annual world energy consumption by a factor of more than fifty. Being highly available, renewable and geographically dispersed, biomass can form a substantial part of future energy sources and biomass-derived energy generation can result in both CO2-neutral and stable long-term energy supply for most areas in the world. Having a relatively low energy density, biomass processing in decentralised plants seems best suited to minimise transport cost of both the raw material and the products. To facilitate a wide-spread use of decentralised plants, their design has to be simple and they need to be easy-to-operate and flexible. This paper covers the two sequential steps of biomass power: conversion technologies to transform the raw feedstock into suitable intermediate energy carriers, and generation technologies to gain energy in the form of heat and/or electric power. A broad number of conversion technologies currently exist for both wet and dry biomass, ranging from research-stage up to commercialisation. In this paper the main ways of converting dry as well as wet feedstock will be discussed: combustion, gasification, pyrolysis and liquefaction for the further and fermentation and anaerobic digestion for the latter. Additionally, the common generation technologies will be analysed: internal combustion engines, Stirling engines and internally- and externally fired microturbines. Finally it will be recommended which technologies to use to meet a substantial part of the future energy demand on the basis of biomass in micro- or small-scale applications.