On-line microwave monitor for solid concentration in coal-water slurries. Final report

The feasibility of utilizing microwave techniques to measure coal concentration and linear flow velocity of coal-water slurries was investigated. The technique consisted of utilizing the slurry pipe as a circular waveguide and monitoring the frequency corresponding to the onset of power transmission in the waveguide (cut-off frequency) between recessed antennae. The cut-off frequency depends upon the dielectric constant of the slurry filling the pipe segment which is a function of the volume fraction of coal in the slurry. The technique was tested in 3/4 in. and 1-1/2 in. pipes using slurries containing 40 to 65% by weight Utah bituminous coal. The precision of the method was +-0.2% of the absolute value. The method was found to be independent of the direction of coal flow, particle size distribution, flow velocity above 0.15 m/s to the highest velocity tested, 3.8 m/s. The temperature dependence of the method was predictable from the measured dielectric constants of the slurries, and could therefore be correctable. Measurement variation with temperature was +-0.5% between 22/sup 0/C and 50/sup 0/C. Linear flow velocities could be determined by cross correlation of the noise from two microwave test sections separated by a known distance, and approximate values of the flowmore » rate and the flow/no flow condition could be determined from the noise spectrum of a single test section.« less