The application of refrigeration in mechanised mines

Australia has a long history of underground mining. Even with advances in open cut mining equipment, techniques and economics, many orebodies are still best mined by underground means. In addition, modern exploration tools are ‘uncovering’ orebodies that are at increasing depths. South African mines are currently producing from below 3 km, and developing down to 5 km depths – it is likely that Australian mines will also become much deeper over the next 20 years. One of the most significant technical challenges in deep mines is the problem of heat. Community expectations and legislated standards continue to drive operations towards improving the working conditions in mines. The hazards and costs associated with chronic hot working conditions (heat illness, poor safety, poor productivity, higher operating costs and poor morale) are also becoming increasingly recognised (Brake, Donoghue and Bates, 1998). The exposure of miners to many other occupational hazards has been reduced over the past 50 years. However, despite air-conditioned cabins greatly reducing the heat stress on mobile plant operators, there are still many Australian mine workers subject to levels of thermal stress that existed a century ago. There are several reasons for this, including a frequently-poor understanding of the physiology of working in heat by mine management, no agreed mining code of practice for working in heat, the lack of a robust, practical-sized instrument to measure heat stress, the cost pressures on the industry and, to some extent, deep-seated traditional management and worker practices. However significant progress has been made in many of these areas (Brake and Bates, in press), with the net result that there is likely to be a trend towards installation of refrigeration of some form in many Australian mines in the future. This will add directly to the cost of operation, but will also have direct and indirect benefits, including cost benefits. It should also be noted that Australia is not at the forefront of adopting practices to manage temperatures in the workplace: South African metal mines usually have refrigerated cooling, and Canadian mines spend large sums on heating, with heating costs (averaged over a full year) of up to $A1 per tonne mined (Bandopadhyay et al, 1997) The history of mine refrigeration dates back to 1919 when the first plant was installed at Morro Velho, Brazil. By 1965, the total installed capacity (worldwide) reached about 100 MW(R)i. Since 1965 the growth in mine refrigeration capacity has been exponential, with a doubling every six or seven years (Howes and Nixon, 1997). South Africa is by far the largest user of mine refrigeration, with over 300 refrigeration machines installed. This paper discusses the key design issues associated with the application of refrigeration in underground metal or coal mines. Whilst the emphasis is on large, surface plants, small, surface or underground refrigeration plants can also be very effective in the correct application and many of the principles of design and operation are the same.