Analysis and design of flashtubes for pressure letdown in autoclave leaching operations

Theory and methodology have been developed to control slurry flashing during pressure letdown following high-pressure acid leaching (HPAL) of nickel laterites and pressure oxidation (POX) of refractory gold ores in order to minimize wear and tear of flash vessels and to facilitate steam/slurry separation. This is accomplished with the use of a “flashtube”, which is a valve-and-choke assembly which is specially contoured to control the expansion rate of the flashing slurry. By expanding the flow sufficiently to form a shock wave within the flashtube, it is shown that the amount of kinetic energy released at the flashtube exit can be reduced by nearly two orders of magnitude for a typical case.