Column: Zinc concentrates squeeze but there’s no shortage of metal
Global zinc mine production continues to slide and the raw materials squeeze is now starting to bite, particularly in China.
Water cooled copper blocks designed by high capacity furnace and smelting plant specialist, Tenova Pyromet, are successfully operating on metal, matte and slag tapholes for a number of processes, including nickel, titanium dioxide, platinum group metals (PGMs) and mineral wool. Tenova Pyromet is part of the global total technology solutions provider to the mining and bulk materials handling industries, Tenova Mining & Minerals.
Water-cooled taphole blocks have proved to be an effective solution for those applications, where metal and/or slag are aggressive to the refractory, or where they operate at several hundred degrees of superheat. Most importantly, they provide an effective means of extending the life of taphole refractories, as the resulting lower temperature of the refractory material inhibits wear and other damage. Water-cooled taphole blocks promote the formation of a protective frozen slag layer, and are particularly beneficial during prolonged tapping cycles.
In addition, as the copper block forms an integral part of the lining, it provides mechanical support to the refractory, facilitating rapid replacement of tapping channel bricks, without disturbing the surrounding lining. Safety considerations are an important design factor, and positioning of the water channels is optimised to prevent leaks, although the copper is not in direct contact with the molten fluids during normal operation.
Tenova Pyromet’s “in-house” designed taphole systems, accommodate the specific requirements of smelting furnaces in the ferrous, non-ferrous and ferroalloy industries, optimising furnace reliability and efficiency, as well as costs. Taphole systems currently in use range from uncooled or indirectly cooled carbon metal and slag tapholes, where both slag and molten product are tapped through a single tap. This does not aggressively attack the refractory lining for systems requiring dedicated slag and metal/matte tapholes and the slag and, in some cases, the metal or matte, where the metal or matte is aggressive to the refractories, resulting in potentially rapid wear. The latter includes production of pig iron, titanium dioxide, ferronickel and PGMs.
As the wear mechanisms in these processes are all functions of temperature, either the actual temperature or the rate of change of temperature, maintaining an optimal temperature within the taphole is important for its successful operation. The refractory is required to conduct heat from the molten fluid at a rapid rate to ensure that the tapping channel material is not damaged or degraded, but not so rapidly that the fluid freezes inside the channel to the extent that the channel closes prematurely. This requires construction of tapholes to be optimised, to provide sufficient cooling of the inside of the tapping channel. This is what led to the development of copper taphole blocks by Tenova Pyromet.
“The taphole region of a furnace is critical to the successful operation of the furnace, providing the means by which to remove product from the furnace in a manner which does not compromise the integrity of the furnace, or the quality of the product,” says Isobel Mc Dougall, Tenova Pyromet Principle Design Engineer. “However, tapholes are also the most vulnerable area of the furnace, as they are subject to severe operating conditions, which include thermal cycling, erosion by molten metal or slag, chemical attack by slag or molten metal and wear, caused by taphole opening and plugging operations.
“There is no one-size-fits-all solution to taphole design. One of the major reasons for the continuing strong demand for Tenova Pyromet’s services is that all our product designs can be customised to suit a variety of furnace shapes and sizes and, cooling requirements.”
Tenova Pyromet presented a paper on water cooled copper blocks at the recent South African Institute of Mining & Metallurgy Furnace Tapping Conference 2014, held in Johannesburg, South Africa.
Tenova Pyromet is a leading company in design and supply of high capacity AC and DC furnaces and complete smelting plants for production of ferroalloys, base metals, slag cleaning and refining. Tenova Pyromet also designs and supplies equipment for material handling and pre-treatment, alloy conversion and refining, granulation of metal, matte and slag, furnace off-gas fume collection and treatment, and treatment of hazardous dusts and waste. Tenova Pyromet has several technologies to reduce operating costs and increase production power consumption.
Tenova Mining & Minerals is a total integrated solutions provider to the global mining, bulk materials handling and minerals beneficiation and processing sectors, offering innovative technological solutions and full process and commodity knowledge across the mining industry value chain.
Tenova is a worldwide supplier of advanced technologies, products, and engineering services for the metals and mining & minerals industries. More information is available at www.tenova.com.
