ABSTRACT
Converting solid or liquid biomass into a gaseous form can be achieved biologically (for example by using anaerobic bacteria to turn it into ‘biogas’ – Chapter 8) or thermochemically. Combustion, gasification, pyrolysis and liquefaction are all processes involving the thermal degradation of biomass fuels for which the available supply of air or oxygen (being the gasifying agent) determines the products. As discussed in Chapter 5, the combustion process and steam cycle is commercially available with minimum risk to investors but is limited by materials and technologies to around 30% conversion efficiency (from energy in the fuel to electricity) in the supercritical systems in large-scale units up to 600 MWth. Most smaller-scale boilers have thermal efficiencies below 70%, and because of poor-quality steam limitations most small electricity generation plant designs have higher heat value efficiencies of around 25%, giving an overall conversion efficiency of only 15–18%. Gasification (Figure 6.1) routes are therefore gaining interest as hot gas efficiencies for a gasifier can be over 95%, leading to around 35% overall conversion efficiency with 45–50% as a near-term possibility. Gasification of biomass to generate electricity and heat https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315067155/e6ca7006-8441-4586-b415-9e3480b24435/content/fig6_1_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>
