Slurry capacitance methods

Capacitance Methods. Capacitance methods have been used to measure solids concentration in slurry pipelines (79). This method requires the dielectric constant of the solids and the carrying fluid to be significantly different. Sand-water slurry is a good example to use the capacitance method. In this case, the dielectric constant for water is 80, whereas that of the sand particles is 5. The method relies on the variation of the dielectric constant of the mixture, Em, with the solids concentration, C. For homogeneous slurries of spherical particles at low solids concentration, Maxwell s correlation can be used to predict the dielectric constant of the mixture. However, several investigators assumed that the relationship of the dielectric constant of the mixture and solids concentration was linear, as follows ... 

Capacitance methods have been used to measure the concentration of dispersed phase in slurry (79) and emulsion (65) pipelines in which the continuous phases have low conductivity, for example, water-in-oil emulsions. The advantage of the capacitance methods over the conductivity methods is that the effect of temperature on the dielectric constant of water is not significant. According to Pal (65), capacitance methods are not effective to measure the concentration of dispersed phase, when the continuous phase has high conductivity. 

Feed slurry is introduced into the basket through either single or multiple feed pipes, or by other means such as rotating feed cone to help distribute the solids on the basket wall. In most cases, feed slurry is introduced at an intermediate speed, although in some applications (FGD gypsum, for one), feeding is done at full speed. There are several methods available to control the feed and cake level such as mechanical, paddle-type feelers, capacitance probes, ultrasonic sensors, feed totalizer, or load cells. 

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