Prediction of Ash Formation Behaviour of Biomass During Combustion through Characterisation of Inorganic Matter
Abstract
The inorganic part in biomass, unlike in coal does not only consist of mineral matter, but also free ionic species and organically bound inorganic matter. Therefore, to be able to study the behaviour of the released inorganic matter from this fuel during thermal conversion, it is vital to be able to determine the speciation, particle size distribution and the chemical composition of the inorganic matter. Previously, Computer Controlled Scanning Electron Microscopy (CCSEM) and Chemical Fractionation (CF) methods have been used for this objective, whereby the former was used to determine the size and composition of particulates >1mm, while the latter was used to determine the organically bound inorganic matter and the free ionic species in the fuel. This paper presents a discussion on the existing literature concerning the characterisation and specification of inorganic matter in biomass fuels and its fate in thermal conversion processes. Work done on the CF method using a pH leaching technique that enables the prediction of the speciation of the inorganics in equilibrium stage, has also been addressed in the paper. Results from the extraction of biomass at various pH values have been incorporated into a chemical speciation model to calculate the most likely speciation of biomass inorganic matter. It is anticipated that the chemical speciation can be used to predict high-temperature mass transport and kinetics of the biomass inorganic material. Therefore, results obtained from this on-going work at the Energy research Centre of the Netherlands (ECN) are of practical significance in predicting the ash formation as well as associated problems such as ash deposition.