Potential use of combinable crop biomass as fuel for small heating boilers

Abstract

This report presents the findings of a research project to investigate the potential of certain combinable crop products as biomass fuels for heat generation in small scale heating systems. Initially, a review of boiler technology and existing expertise was conducted. The five fuels studied were: oats, wheat, wheat with a limestone additive, straw pellets and oilseed rape. Wood pellets were included as a reference fuel, since wood is the most widely used form of biomass fuel for heating.

Tests were conducted in two stoker burner boilers at a test facility using a heat meter, flue gas analyser and photographic equipment with reference to existing British Standards for solid fuel boilers rated up to 300kW. Relative efficiency calculations, flue gas emissions, operational and observational data were collected for each fuel during combustion periods ranging from 4 – 48 hours. Observations were made on ten small biomass heating systems during studies in Sweden Denmark, Finland, Luxembourg and Germany.

The results demonstrated that oats and wheat are viable fuels for small scale biomass boilers but only when automatic and/or manual intervention is available to remove ash and clinker build up. Combustion efficiencies for oats and wheat were comparable with those achieved when burning wood pellets and the addition of limestone to wheat appeared to improve combustion efficiency further. Carbon monoxide emissions from the combustion of oats and wheat were below the British Standard limits for solid fuel boilers. Emissions of NOx were above the Austrian limits for solid fuel boilers but currently no equivalent standard limits exist in Britain. Few existing small biomass heating systems were found to be suitable for burning grain fuels and no systems were as efficient when burning grain as they were when burning wood fuel. A few manufacturers have developed heating systems to reduce combustion and ash removal difficulties.

Data from the experimental work were used to produce an economic evaluation for oats and wheat as a biomass fuel. It was found that grain was cost effective fuel when it was priced at £60, but at a price of £130/tonne it is unlikely to be cost effective. Industrial crop production of grain on set aside land is now not considered to be an option. The experimental data were also used in a life cycle analysis to compare energy consumption and greenhouse gas emissions from cereals with other forms of heating fuel. Using oats and wheat grain for heating achieves substantial reductions in primary energy consumption and total green house gas emissions compared with heating based on conventional fossil fuels or electricity.