We are currently developing an instrument for in-line particle size measurement in bulk solids systems and would like to invite comment on, or suggestions of, specific applications where this type of instrument would be of significant benefit (details of the instrument follow). We are also putting a prototype instrument together for use in field trials and would be interested in hearing from any one who could assist with a field evaluation of its performance.

The details;

The particle size measurement is based on measuring the transit time of acoustic waves through a bed of particles, and returns a surface mean diameter. The most effective measurement range is for free flowing materials in the size range 50 µm through to several mm. Measurements can be taken in any part of a process where the voidage is similar to that of a packed bed, or where (all or part of) a dispersed flow can be temporarily channelled into a dense bed. The measurement can be taken flush with the wall of a process vessel or with a probe inserted into a particle bed. The measurement is relatively independent of changes in voidage, occuring for example with changes in flow velocity, and almost completely independent of changes in particle density. Size distributions spanning up to two orders of magnitude in size still return a good surface mean value. Wider distributions would benefit from the use of multiple instruments tuned to different size ranges.

The instrument in its current form continuously measures a volume with a dimension of the order of 10 - 1000 particle diameters. For non-spherical particles, the instrument tends to measure the particle dimension in the transverse direction of propagation of the acoustic signal (ie for non-spherical particles that allign themselves with flow the measurement depends on the orientation of the instrument, for randomly alligned particles the returned value is an average one regardless of orientation).

I'm happy to supply more info to interested parties.

Steve Tallon

S.Tallon@irl.cri.nz ■