The aim of the research was to investigate the feasibility of using an
impedance cell and ratio-transformer bridge to measure solids content in
coal slurry pipelines. It appeared that this technique could be developed
to measure variations in conductance which correlate with solids content.
Successful implementation of the measurement technique would have a
variety of applications in existing coal wash plants and the potential for
automatic process control. A small pilot plant was designed for a feasibility study. This was a
closed loop system in which the coal was uniformly dispersed in a tank
with a variable speed agitator and then circulated through an external pipe
returning to the top of the tank. The impedance cell was located near the
end of the external pipe. Slurry concentrations were varied from clean
tap water to 50 per cent solids by weight with the addition of weighed
quantities of dry coal dust. Ratio-transformer bridge measurements
showed that variations in individual observations were equivalent to
measurement errors of about two per cent. These probably reflect
variations in concentration of the mixture in the pipe. Data for
increments in concentration of one per cent indicate that this is about the
limit of resolution of the current system. The paper discusses the principles of operation of the impedance cell
and measurement system. Results from the pilot study and proposed
improvements in the impedance cell design are examined.