Characterisation of products from co-gasification of Nigerian biomass in a pilot scale down draft gasifier

The use of biomass for thermal conversion systems (alternative to fossil fuel) leads to increase in ash generation of up to 40 % of the biomass (depending on type and form of biomass) from thermal conversion systems. The disposal of ash poses different challenges including heavy metals components of the ash, while land filling is being discouraged for any types of waste products. Agricultural use of ash provides a sustainable option; therefore it is important to prioritise biomass residue qualitatively and quantitatively. This is important to ensure the ash generated through these processes is of beneficial and no harm to both the soil and crop, and generally the ecosystems. In terms of process practical operation point of view, it is important to avoid the formation of fused or partly-fused agglomerates and slag deposits. Co-gasification studies were carried out in a 25 kWth pilot scale down draft gasifier. The gasifier was operated over a temperature range of 750–900°C whilst varying air/fuel ratio. Three types of Nigerian biomass generated from oil processing units were studied: empty fruit bunch (EFB), mesocarp fibre (MF) and palm kernel shell (PKS). The gas compositions, gas yields, quality of liquid and solid products were determined and correlated with temperature, and types of biomass used. Online FTIR gas analyser was used for the analysis of the gaseous elements. A detailed analysis on tar sampling (tar probe developed based on BSI DD CEB/TS 15439:2006) and quantification are examined in this paper. The study showed that mixing the biomass affects residues yield from the downdraft gasifier plant, and consequently the performance of flue gas cleaning equipment, fouling of gasifier surface, and the handling and the utilisation/disposal of ash. This is particularly true for PKS, which increased the rate of sintering significantly when cofired with other biomass