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Metal Casting Technologies : March 2010
20 www.metals.rala.com.au Aluminium casthouse furnace energy efficiency T. Ireland-Hay1, R. Voyer2 Hatch Associates Pty Ltd 1171 LaTrobe St, Melbourne, Vic 3000, Australia 25 Place Vile Marie, Montreal, QC Canada H3B 2G2 O TECHNICAL FEATURE Abstract perational casthouses, although not one of the largest energy consumers of an aluminium smelter, do require significant amounts of energy to maintain accurate liquid metal temperature. However, the casthouse does consume approximately 50% of the non-reduction line energy across site. The high cost of fossil fuels and the need to reduce carbon emissions are forcing changes in casthouse equipment choice and practices. There is a need to assess the state of energy consumption to better plan for future energy reduction programs. This paper outlines the methodology used in completing energy assessment programs in a number of casthouse furnaces and outlines the potential savings smelters could see if these are completed. Introduction The purpose of this paper is to give an overview of energy consumed in casthouse furnaces, quantify potential energy and carbon emission savings based on previous experience and propose a proven methodology for implementing a cost-efficient energy reduction plan. This will be discussed based on surveys completed on fifty different furnaces over one year. Although the casthouse furnace energy consumption is a small part of the whole smelter energy requirement, it is one of the next highest energy consumers (along with the carbon bake furnace) and has one of the lowest energy efficiencies as shown by the data detailed later in this paper. With cost increases in fossil fuel and also the potential introduction of Australia's Carbon Pollution Reduction Scheme (CPRS), any reduction in energy will not only reduce direct fuel costs, but also carbon credit cost. Energy consumption Survey's completed on fifty different holding furnaces have shown significant variation in energy consumption both within type and between types of furnaces. This is expected due to differences in furnace equipment as well as operating practices such as scrap remelting. As shown in Figure 1 the energy consumption can range from 1000 to 4500Nm3/day per furnace with gas furnaces using significantly more energy than electric furnaces. The first part of the improving casthouse furnace efficiency is to complete an energy survey. The main objectives are to get a good overview of the actual energy consumption and quantify any potential fuel and carbon emission reduction opportunities. Completing these measurements and showing the potential for improvements increase the management awareness of potential savings. Methodology To improve energy efficiency of aluminum casthouse furnaces, a thorough and detailed work structure was used. Firstly, measurement of energy being used was completed and then compared against the benchmark performance possible. The energy efficiency program was carried out using the following steps; ● Discussions with the casthouse personnel were completed to collect and tabulate data on existing furnace combustion equipment, operating conditions, amount of metal re-melted and fuel consumption. If not all required data was available, an action plan was developed to gather the missing data, such as the installation of monitored gas flow meters. ● Secondly, a detailed computer model was developed for each of the furnaces surveyed which took into account furnace heat loss through walls, cooling from cold air infiltration and from Fig 1. Furnace energy consumption
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