Development of techniques for the on-line determination of unburnt carbon in fly ash

The development of an accurate on-line monitor for the determination of unburnt carbon in fly ash would greatly assist in improving boiler efficiency in coal fired power stations. Nuclear and microwave techniques have been investigated for the rapid and accurate analysis of fly ash samples which, in an industrial instrument, would be extracted from the duct via a cyclone, filter or similar device. Laboratory measurements have been carried out on 123 fly ash samples, each weighing about 10 kg, which were provided by six Australian power stations. These measurements have shown that carbon content can be determined, using either microwave or neutron inelastic scattering techniques to within a root mean square (RMS) error of 0.08-0.29 wt%, for individual power stations. For combined data of less than 5 wt% carbon from all power stations, the RMS errors were 0.23 and 0.30 wt% carbon for the microwave and nuclear techniques, respectively. The neutron inelastic scattering technique has the advantage of measuring elemental carbon directly. However, microwave techniques have the advantages of rapid analysis time, higher accuracy at low carbon content, adaptability to small sample sizes and no requirement for bulky radiation shielding. Consequently, the microwave technique has been selected as being the most suitable technique for field trials. (author). 6 refs, 7 figs, 5 tabs