The application of combined heat and power (CHP) run on biomass for district heat­ing has been applied widely in Scandinavia and Austria. CHP has the advantages of higher efficiency of electricity generation and lower costs, and these systems have also encouraged the development of a biomass market. The burning of straw for CHP has seen the development of more complex boilers and pre-treatment of the straw. An example of a system using biomass to produce electricity is shown in Fig. 4.6. Short rotation coppice or perennial grasses are chipped or made into pellets and dried using some of the waste heat from the turbine before use. The flue gas can be treated before release and the only waste that needs disposal is the slag from the boiler.

Co-firing

The addition of biomass to coal for use in power stations occurs in the UK and many European countries. The advantages are that overall emissions of GHGs are reduced by incorporating biomass, the efficiencies are high due to the large scale, and invest­ment costs are low making this an attractive GHG mitigation option. Co-firing with coal is used for the generation of electricity and has been shown to reduce emissions of sulfur dioxide and NOx. Normally the co-firing proportion is around 10% which changes the processes very little. The biomass that has been used includes straw, short rotation coppice (SRC), sawdust and other wastes such as sewage sludge, manure and municipal solid waste (Sami et al., 2001).