UK – CAT gets biomass generator for heat and power

Engineers at the Centre for Alternative Technology (CAT) are busy installing a new woodchip-powered generator, which will be more than 80% efficient when running at full power.



The woodchip-powered combined heat and power plant (CHP) will generate up to 100kW of electricity, enough to meet the instantaneous power demands of 40-60 households, and up to 250kW of heat. The unit will be run to match the CAT site’s power and heating requirements as closely as possible



In traditional power generation, the heat is wasted, released into the atmosphere via cooling systems. With a CHP system, that energy is used to heat water, which is then used for hot water supply, or for heating buildings through radiators or under floor heating.



CAT is growing rapidly – next year the £6.2million Wales Institute for Sustainable Education (WISE) will open at CAT, to cater for the rapidly growing numbers of students and professionals studying courses at the eco-centre.



With more buildings and people on the site, the demand for energy is also increasing. Engineers have been busy laying thick, highly insulated pipes under the CAT site to take the heat to the different buildings, extending the existing heat main system on site.



The new Talbotts BG100 CHP unit uses a hot air turbine spinning at 56,000rpm, which operates in a similar way to a jet engine. Woodchip is burnt in the combustion chamber to heat air. This hot air passes through an air-to-air heat exchanger to heat more air which drives the turbine. The primary hot air carries on to a further air-to-water heat exchanger in which the water is heated and then piped around the site. The whole unit is the size of a pair of stacked shipping containers.



“This will be the first small-scale woodchip CHP system in Britain where both the electricity and heat are used, ” CAT Engineer Katie Brown said. “The woodchip is forestry waste from trees four miles up the road, so there are very few emissions caused by transporting the fuel. The scheme supports a local business. We intend to do extensive monitoring of the system which will produce very interesting data that other sites can use in the future. “



Wood is considered to be a carbon neutral fuel because the CO2 that the wood releases as it is burnt is equivalent to the CO2 the tree absorbs as it grows. Furthermore, if the trees come from sustainably managed forests where new trees are planted as mature ones are felled, then the fuel is renewable.



Energy efficiency has been considered when planning the large building to house the new CHP. The walls are made from Ibstock Ecoterre clay blocks, which are not fired but dried using waste heat from a brick kiln – using a lot less energy than conventional cement blocks. The high density of these blocks make them ideal for sound attenuation, a very important consideration in this building as the turbine is quite loud – we have designed the building so that it will be inaudible outside.



This is the first building in the UK to use these blocks – another interesting trial for CAT’s researchers and students.