Defining solid biofuel standards for Europe
Solid biofuel includes wood chips, sawdust, charcoal, straw, plant remnants such as corn cobs and even solid municipal waste. Biofuel is a renewable and environmentally-friendly source of energy. However, one of the obstacles standing in the way of broader adoption of biofuels is the lack of standards. The Austrian Research Institute for Chemistry and Technology (OFI), member of the BioNorm consortium, tackled the issue of standardising the determination of sulphur, chlorine and nitrogen content of solid biofuel. Excess sulphur and chlorine causes premature corrosion of power plants burning solid biofuel and hence increases maintenance costs. Nitrogen and sulphur emissions to the atmosphere promote aerosol development that negatively impacts visibility and can lead to acid rain. OFI first focused on the requirements of sample preparation and found that a particle size of less than one millimetre is sufficient. Samples sizes must be adjusted in order to fall within the range for which the analytic instrument is calibrated. As a guide, a sample size on the order of one gram is usually sufficient. A number of different elemental analysis methods were evaluated by OFI for each of the three elements. For samples with ample amounts of sulphur and chlorine, combustion with an oxygen bomb followed by quantification of the resulting sulphate and chloride particles is suitable. The advantage is that this procedure is already standardised at the European level. However, this is not adequate for samples with very low concentrations of sulphur and chlorine for which other methods must be identified. In the case of nitrogen, automated analysers proved equivalent to the widely accepted Kjeldahl method. No differences were detected among the various methods employed by each analyser, therefore no specific recommendation for a reference method is made. Rather, the key issue turns out to be standardisation of the calibration and operation procedures. OFI's work in BioNorm will contribute to the development of CEN TC 335 "Solid Biofuels". They also identified the need to address other elements, namely bromine and iodine, in a similar fashion.
