Determination of solids weight fraction and ash content of coal in slurries of variable voidage: Laboratory measurements

Abstract

Nuclear techniques have been used to determine the solids weight fraction (W) and ash content of (fine) coal in slurries independent of voidage. The basis of the techniques is the correlation between W and the hydrogen concentration (w/w) of the slurry. At constant ash content, W is determined by combining neutron moderation and γ-ray transmission (density) measurements. With varying ash content, both W and ash content of coal are determined by combining the above measurements with either of two well-established techniques for the determination of ash content of dry coal, namely x-ray backscatter compensated by iron K x-ray excitation, and low energy γ-ray transmission.

Radioisotope source and detector were incorporated into three probes which were immersed directly into coal slurry in a 200 L drum. Measurements were made on coal slurries with W in the range 5–22 wt%. ash in coal 20.7–30 wt%, and voidage 0–4 vol.%. The r.m.s. difference between W determined by probe measurements and W obtained from assay of slurry samples was 0.54 wt%, a factor of five better than that obtained from the γ-ray transmission (density) measurement alone. The r.m.s. difference for ash content, based on the x-ray backscatter method combined with neutron and γ-ray (density) count rates, was 0.78 wt% ash.