Dry furnace off-gas cleaning system improvements at the Polokwane metallurgical complex

Abstract

Anglo American Platinum (AAP) has completed the installation of a new furnace off-gas cleaning section at the Polokwane Metallurgical Complex (PMC) in the Limpopo Province of South Africa. This installation was part of the larger SO2 Abatement Project to remove dust and SO2 from the furnace off-gas in line with the group's ongoing efforts towards sustainable mining. The new dry gas cleaning plant, containing a spray cooler followed by a five-field electrostatic recipitator (ESP) and new ID fans, replaced the original dry gas cleaning train that had a forced draft cooler and baghouse. Major off-gas ducting modifications were also implemented and involved replacing the original horizontal off-gas ducts with a pair of inclined A-frame ducts that serve well to prevent dust settling and blockage. The new dry gas cleaning plant offered several operational improvements; the major being enhanced furnace freeboard draft control as the lower pressure drop system enables more effective response to pressure disturbances and especially positive pressure events (PPEs). This enabled furnace operation with much better sealing, resulting in lower off-gas flowrates, less dust carry-over and significant reduction in off-gas heat loss. Higher operating temperatures further away from acid dewpoint are also now achieved which prevents corrosion and subsequent air ingress leaks. Minimising ingress air is essential for optimal performance of the downstream SO2 Abatement Plant, and having the overall system operating at much less negative pressure was another key objective. The new off-gas system also allowed operating cost savings associated with costly filter-bag replacement and the bi-annual forced draft cooler (FDC) tube bundle replacement. This paper presents a short project history, options considered, process description, key technology and design considerations and the challenges that were encountered during commissioning and ramp-up. A discussion on the current performance of the new plant compared to the original is also provided.