Field trial of a pair production gauge for the on-line determination of ash in coal

The ash content of coal can be determined by a method based on pair production. Coal is irradiated with high energy gamma-rays and 0.511 MeV annihilation and Compton scattered gamma-rays measured. Earlier laboratory tests on 50 kg samples of high ash coals gave errors of 0.46 to 1.3 wt% ash. A plant test to assess the pair production gauge for direct on-line conveyor belt analysis is described. This test was carried out on a recirculating coal loop at a Broken Hill Pty. Ltd. coal washery pilot plant. Samples were measured on-belt as a function of sample depth, compaction, moisture and particle size. The technique was found to provide accurate measurements of the ash content of coal in a constant geometry. It can be used to determine ash content of coal of thickness 60-220 mm on a conveyor belt by an additional measurement of the weight per unit area of coal on the belt by γ-ray transmission