Kalgoorlie Nickel Smelter
Introduction
Located about 10 km South East of Kalgoorlie Boulder city, the Kalgoorlie Nickel Smelter has been operational for about 50 years. It all started as a concept in the Belmont office of Western Mining Corporation.
Originally there were two sites considered, one in Kwinana and the other in Kalgoorlie, but after much debate Kalgoorlie became the chosen site. The original plant was commissioned in December 1972, with a design capacity of 200,000 tpa of concentrate. The plant design consisted of a conventional Outokumpu flash furnace, an electric slag furnace and two converters, all supported by the matt and slag handling systems, and the usual equipment and utilities found at any mine processing site.
Commissioning
Commissioning of the original equipment produced some exciting experiences, as there was little smelting knowledge in Western Australia at the time. Most of the equipment relied on pneumatic instrument air which was problematic, as the loss of instrument air pressure resulted in a total shutdown of the site. An engineer walking casually through the air compressor building noticed the cooling water pump on the plant air compressor rotating backwards, thereby returning hot cooling water to the instrument air compressor located adjacent. A quick phone call resulted in several mobile diesel air compressors being hired from Kalgoorlie and plugged into the instrument and plant air ring main, allowing the air compressor building to be taken out of service and piping to be revised. This was just one of the lessons learned during the start up.
Another lesson learned related to the main pneumatic concentrate lines between the storage silos and the flash furnace feed bins which blocked up on a daily basis. With two pressure pots alternating the delivery of concentrate to the furnace bins, the smelter never had to shut down. The cause of the blockages was traced to a cross wiring of the valves on the two pots providing transport air to the concentrate in the feed lines.
There were many challenging moments during commissioning and matt granulation was one of them. In early days, the matt granulation exploded in an unpredictable manner. The problem appeared to be a lack of consistent matt feed to the granulating launder which dropped into the water jet. It was months later that a hydraulic tipping table was designed and built to ensure a steady flow of nickel matt to the granulation point. A simplified explanation of the problem as the molten matt sometimes solidifies at the granulation jet, resulting in an explosion.
Expansion
In November 1978 a larger furnace was commissioned to raise production to its current capacity of 550,000 to 580,000tpa. The new furnace integrated smelting and slag cleaning into one piece of equipment. This included many design changes and innovations initiated by Western Mining. Most relate to the cooling requirements of the furnace, including
- Replacement of the irrigated shell design of the reaction shaft with internal copper water elements.
- The introduction of horizontal copper elements in the settler side walls.
- Horizontal cooling elements in the uptake shaft
- Rearrangement of the concentrate burners in the main flash smelting reaction shaft.
- Redesign of the reaction shaft settler transition.
The Process
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The term ‘Flash Smelting’ refers to the smelting action that takes place in the main reaction shaft as the concentrate is falling in the reaction shaft into the bath below. In addition, two sets of three Soderberb electrodes have been introduced into the settler section introducing up to 8.5MW to maintain temperatures in the extended settler known as the ‘Appendage’.
The flux used in the smelting process is a blend of silica sand, reverts material, laterite, coal and secondary material (containing nickel values). Silica sand and laterite material is sourced locally and brought by road to the smelter site. Coal is railed from Western Collieries in Collie and used as a substitute for fuel oil in the smelter. The flux is mixed, dried and ball milled before storage in a 200t silo.
Process air heaters preheat the air to 450 C in coal fired air preheaters with oxygen supplied by Linde oxygen plants. Waste heat is removed and recovered in two 10.7MW steam turbines generating electricity which is exported to the WA grid. The smelter is self sufficient in terms of its power requirements.
Dust from the smelter off gas is removed in the waste heat boiler and a subsequent balloon flue, with a final clean up by electrostatic precipitators and returned to the flash furnace as approximately 10 to 14 % of the concentrate feed.
Slag is skimmed off the top of the settler, granulated and stored in silos. The low grade matte from the flash furnace is tapped and taken by ladles to two of the three converters. Two grades of matt are produced; export matt at about 72% nickel and a high iron matt at about 65% Nickel. The latter is not dried, but is railed to the Kwinana Nickel refinery for conversion to nickel powder and briquettes. Both are granulated prior to packaging and transport.
Prior to the inclusion of an acid plant to convert the metallurgical off gas to sulphuric acid for local sale in the goldfields, the off gas was discharged to a 185 metre stack. Special environmental requirements were put in place such that if weather conditions dictated unacceptable levels of SO2 in the Kalgoorlie Boulder areas, the smelter had to shut down discharge of metallurgical gas from their operations. Instrumentation in Kalgoorlie and Boulder determined if the air quality was adequate to continue operations. This all changed when the acid plant was added.
Acknowledgements:
Engineering Heritage WA would like to specifically thank BHP for access to process related material to prepare this introductory paper for visitors to the EHWA website. In particular the WA Heritage Committee would like to thank:
- A G Hunt, Senior Metallurgist, and for access to the article written for the Australasian Mining and Metallurgy, Volume 2 Second Edition 1993
- Alison Brooks (Née Bugno) for flowsheet and photographs.
This article was prepared by Mark Wanshaw, July 2020
