Measurement of specific energy, ash and moisture in bulk coal samples by a combined neutron and gamma-ray method

Abstract

The specific energy, ash and moisture contents of bulk coal samples can be determined simultaneously by a method based on the accurate measurement of carbon and hydrogen contents. The method for specific energy depends on a combination of a measurement of 4.43 MeV 12C γ-rays from neutron inelastic scattering and a separate 60Co γ-ray scattering measurement on essentially the same sample volume. The γ-ray scattering measurement corrects the neutron gauge for variables such as sample bulk density, bulk density gradients and sample thickness. By “matching” the response of the two gauges, an accuracy can be obtained that is higher than has been previously reported for bulk coal samples. Ash and moisture are determined by combining the above measurements with a simultaneous measurement of 2.22 MeV H neutron capture γ-rays. The method has been tested by many laboratory measurements on ∼50 kg coal samples from coalfields in southern N.S.W., Australia. Rms deviations between chemical laboratory and nuclear gauge assays were 0.92 wt.%, 0.44 MJ/kg and 1.4 wt.% for respectively, carbon, specific energy and ash. However, if the data was restricted to coal samples containing > 70 wt.% C, these errors reduced to 0.38 wt.%, 0.26 MJ/kg and 0.81 wt.% respectively. Accurate moisture values can be obtained provided that the C/H ratio in the coal matter remains constant. Measured rms deviations for moisture varied from 0.2 wt.% for a single sample with a number of different added water contents to 0.85 wt.% for a variety of samples from the different mines. The main potential applications of the method are for the on-line analysis of coal on conveyor belts and in chutes or hoppers; this analysis is required for the control of power stations and coal washeries.