Bed boiler tests for safe bio-waste combustion
Greenhouse and particle emissions from small combined heating and power plants are of great environmental concern. To tackle the inherent problems, experiments were carried out using a fluidised bed (FB) boiler of input 1 MWth manufactured by the Dutch company Crone, a project partner. Gas and particle emissions were measured and process parameters such as fluidisation velocity, bed temperature, air staging and co-combustion of other types of biomass were investigated. Higher fluidisation velocity within the system resulted in reduced gaseous emissions from the combustion of B quality wood (demolition wood) due to better mixing within the bed zone of the combustor. Moreover, palletised demolition wood (BQW) combusted with acceptable gas emissions. However, it was discovered that combustion temperatures less than 850ο C had a negative effect on the combustion behaviour. When the boiler system contained a cyclone only, there were unacceptable levels of solid emissions and BQW was found to emit a relatively high concentration of lead. By contrast, pepper plant residue (PPR) pellets from greenhouses did not combust well. Even in co-combustion conditions with 25 % of PPR, there were very high gas emissions and agglomeration (production of a mass of solid) occurred, despite the use of an additive to prevent this process. From an environmental point of view, the use of high-efficiency FB boilers to combust biomass is an option to land fill waste disposal. The technology developed may be applicable in the treatment of household biowaste together with conventional fuels. Moreover, in developing tools to minimise operational problems and emissions, use of these boilers may be a viable method of energy production to replace fossil fuels in plants where appropriate.
