REFLECTIONS ON INDIRECT HEATING OF LATERITE ORE SLURRIES IN HPAL PLANTS USING SELF-CLEANING FLUIDIZED BED HEAT EXCHANGERS

摘要

In this article, we have shown the unparalleled performance of self-cleaning fluidized bed heat exchangers for the implementation of indirect heat transfer in severely fouling fluid environments. Apparently, the recirculation of cleaning particles through the tubes of these vertical shell and tube heat exchangers provides the ability to solve any problems that arise as a consequence of tube-side fouling during indirect heat transfer to process fluids. In addition to the mitigation of fouling effects, a number of other significant benefits for process fluids heating are afforded by the mode of operation of the self-cleaning fluidized bed heat exchangers. Increased turbulence at the fluid / tube interface is imparted by the action of the fluidised particles, resulting in very high heat transfer at relatively low liquid velocities. We have also shown the consequences for the design of complete installations equipped with self-cleaning fluidized bed heat exchangers. Concentrating on process slurries, and given the thixotropic nature of most of these slurries, the action of the fluidised particles imparts additional shear to the process slurry, resulting in shear-thinning effects with a consequent reduction in pressure drop and enhancement of heat transfer across the heat exchanger. The benefits provided by the self-cleaning fluidized bed heat exchanger make it the ideal option for the indirect heating of laterite nickel slurry for High-Pressure-Acid-Leach (HPAL) plants. We have also presented an elegant approach for production increase through a 'brownfield expansion' of an existing HPAL plant, by changing its 'directly heated' mode of operation into an 'indirectly heated' configuration employing self-cleaning fluidized bed heat exchangers. However, we have also shown two different and rather revolutionary ideas for 'greenfield expansions' of newly designed HPAL plants, which do not require high pressure steam anymore for the final heating due to the very efficient heat recovery of the self-cleaning fluidized bed heat exchangers. Last but not least, we believe in a bright future for self-cleaning fluidized bed heat exchangers for a variety of metallurgical processes and, particularly, for the extraction of nickel and cobalt from laterite ores through HPAL processing.