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Show Fundamental flame research is required to verify the actual heat transfer achieved by various types of burners. The results of such work could then be used to improve the accuracy of the many reheat furnace models now in existence. It is recognized that such work does not fall into the category of a process improvement that will achieve near-term results. However, it is important that it is mentioned here. A program to examine possible solutions to this problem is reconmlended. 4.3 Metal Casting Industry The foundry industry is primarily involved in melting metal and introducing it into a mold cavity to form complex shapes. More broadly, however, it may include premelting operations such as metal reheating, and postcasting operations such as annealing and tempering. Heat treating operations are discussed in this section, though they also pertain to the steel industry. In its narrowest definition, the foundry industry is almost totally scrap-based, converting up to 20 million tons/year of scrap into castings used in over 90% of durable goods and 100% of machine tools. About 3,000 foundries employ nearly 200,000 workers. Since 1980, about 25% of U.S. foundries have closed. Output in 1991 was about half of what it was in 1972. Casting imports and exports are each about 7% of the U.S. market. When the metal being cast is steel, the division between the combustion research needs of the foundry industry and the steel industry becomes somewhat vague. An attempt is made to keep the two industries separate. Further complicating this assessment is the melting of aluminum, which is covered in the aluminum industry section. Foundries used 0.25 quads in 1988-660/0 from natural gas, and the remaining majority from electricity. Melting uses about 550/0 of the foundry industry 's energy, but many furnaces are only about 35% efficient. The foundry industry spent $3.3 billion for energy in 1992-170/0 of the value of shipments. The metal casting industry vision notes that this industry is vulnerable to the cost of increasingly stringent environmental and occupational regulations (DOE/GO 1995 b). The vision study for this industry identifies the following combustion-related research and development needs: waste heat recovery and reuse, cupola furnace modeling and control using neural networks, advanced sensors and process controls to optimize process energy use, and melting and holding furnace optimization. The foundry industry essentially melts scrap metal and produces a metal object of the desired shape by using a ladle to pour molten metal through a passageway into a mold and allowing the metal to cool and solidify. Melting is the single largest combustion-related processing step and can be effected in furnaces of several types, such as cupola, electric arc, induction, and gas fired. Cupolas are generally used for iron castings and account for 590/0 of all foundry metal. Gas-fired furnaces are used for nonferrous castings. Fundamental research needs to be conducted on coal and coke reactivity. The rate of carbon reaction within the cupola depends upon a nwuber of factors . Production of carbon dioxide rather than carbon monoxide for cupolas is preferred because a reduction atmosphere is not required. Reactions that favor carbon dioxide production should be encouraged. Some types of carbon react faster. The active diffusivity is not well understood, but could lead to the use of less expensive coal. About 33% of the energy of combustion in the cupola is lost through the discharge of the heat content of carbon monoxide. Foundries typically rebum the CO and recuperate as much of the energy as feasible, but the amount of CO discharge is still significant. One method to use this CO is to introduce oxygen at appropriate locations. This technique has been tried, but too much oxygen leads to melting in the upper layer which forms a sealing layer. CWTent research being perfomled for cupola modeling has increased the industy's ability to predict gas composition and exhaust stack temperatures. The use of this model to predict the location and amount of oxygen injection could lead to increased energy savings. Sand casting is the dominant method used in the foundry industry. Die casting is the second most common. In the die casting process, molten metal is injected at high pressure into a water cooled steel die, where it solidifies as a net shape product. The life of the die is aITected by materials properties and heat treating methods. Heat transfer to the die during heat treating has been a problem area. Studies that would determine improved methods of heat transfer are needed by the industry. Processes which improve heat transfer will reduce combustion energy. Reclamation of sand from sand casting requires further work. Regulations are increasingly limiting the amolmt of sand that can be disposed of in landfills. The sands contain organic and inorganic materials. One potential method of sand reclamation is the use of fluidized bed combustors where the organic is burned off. A demonstration of fluidized bed sand reclamation is needed (the heat produced could be used to preheat metal). 11 |
