Solids Handling and Metering in an NPK Prilling Plant

The potassium chloride for an NPK prilling process requires special preparation not necessary in other granulation processes. A plant designed for handling the potash, based on a lean phase pneumatic conveying system incorporating heating, drying and grinding equipment is described.

Problems arose with some items of equipment and from tramp material and fines in the potash. The effects of modifications to improve the operation and of a change in the source of potash are reported.

The potash is metered to the melt by a variable speed screw feeder which has been unsatisfactory in some respects but there was no obviously better method of dealing with the material.

For recycle of NPK fines, a means of conveying the fines to the prill tower for addition to the melt along with the potash has recently been installed to avoid the risk of decomposition reactions from adding fines to the melt at an early stage. A dense phase pneumatic handling system has been found satisfactory.

Difficulties which were encountered in the early days were due to unreliability of some items of equipment and to insufficient data from small scale tests. Therefore, in the design of plant and selection of equipment for special applications, one cannot rely on preliminary tests alone to indicate the problems that might arise under production conditions.

W J Kelly, Albright and Wilson Ltd, UK.

34 pages, 5 figures, 2 tables, 6 references