Combined Heat and Power (CHP) and Power Generation
Biomass can be used to generate both electricity and heat. Most biomass power plants use steam produced by biomass combustion to drive turbines which can generate electricity. Power can also be generated using gas turbines or combustion engines driven by low-energy gas produced by gasification of biomass.
Power generation
Electricity generation from biomass is generally on a large scale. The first woodfuel powered plant in Scotland is currently under construction by E.ON at Lockerbie. This will generate 44 MW of electricity.
Electricity generation alone generally has a low conversion efficiency, whether for fossil fuel or biomass, as a significant proportion of the energy available in the fuel is lost as heat. Some of this "low-grade" heat can be used, for example for industrial facilities.
Combined Heat and Power
CHP plants can be fired by any fuel, including coal, gas or biomass. The newest gas fired CHP plants can provide a reduction of over 50% of the CO2 emissions when compared to a coal-fired power station and individual boilers. If the CHP plant is fuelled by biomass, then the emissions savings are even greater.
The scale of the plant can range from less than 100 kW to over 100 MW. The heat produced in the process is used to heat water which is circulated via highly insulated, underground ‘heat mains’ to the end users. It is essential that the end users are situated close to the power plant to minimise the costs of installing the heating mains, and to reduce the heat lost from longer pipe lengths.
Biomass power plants tend to have lower conversion efficiencies that fossil-fuelled power stations, but this is not important if the heat can be recovered. CHP works best with smaller power plants; a large coal-fired power station could produce waste heat in the gigawatt range, and it would be difficult to use all this heat in a district heating scheme. Smaller-scale biomass plants produce more manageable levels of heat output.
Smaller scale biomass power plants are more suited to local production of biomass from forestry and short-rotation coppice: if local sources of fuel can be used, transport costs and emissions can be minimised.
The Scottish Renewables Forum published a regular update on all large-scale renewable energy projects in Scotland and their status.
Useful links
Scottish Renewables Forum
Combined Heat & Power Association
European BIO-CHP
Useful articles
Slough Heat and Power
[Locher, C. (2002) The Long Road to Renewables. Forest Machine Journal 11/05]