An overview of the design, operation, and maintenance practices relating to tap-hole management on a PGM smelting furnace

Abstract

PGM smelting furnaces are known for operating at significant high superheats. Safe and efficient tapping of both the slag and matte phases can be achieved only through sound tap-hole management practices. This paper gives an overview of the tap-hole management approach followed at Lonmin's Western Platinum smelter. Five circular AC furnaces are operated, with each furnace comprising essentially a crucible and auxiliary equipment. Within the crucible, the slag and matte tap-holes are situated at different elevations. The slag phase is tapped at a higher elevation than the matte phase. At the three older furnaces, tapping is done by the conventional method of lancing open the tap-hole and closing it with a dolly. However, at the two newer furnaces, tap-holes are opened with the aid of a drill and closed with a mudgun. Tap-hole management can be divided in a number of aspects. In order to achieve a safe opening and closure every time, Lonmin distinguishes between three important aspects; namely, the design of the tap-hole system, the operating practices followed, and care and maintenance. The paper briefly explains the design of the tapping channel and cooling requirements in order to handle superheated matte, and the difference in design of the matte and slag tap-holes. Mention is also made of the importance of auxiliary equipment, which includes the launders, fume extraction, granulation water, and mudgun and drill units. Improvements made to the matte tap-block design are discussed. The monitoring, alarming, and safety systems related to matte and slag tapping are reviewed, and tap-hole life and different wear mechanisms are described. Tapping can be done in a safe manner only if the tap-holes and equipment are maintained properly. This topic includes tap-hole refractory repair practices, as well as improvements made in order to reduce repair time and to extend the time between deep repairs. The importance of the correct tap-hole clay selection in order to nurse the tapping channel after each tap is also discussed. Finally, the paper touches on some research and development work that was done in order to improve the monitoring of the condition of the tap-block by means of fibre optic temperature sensors.