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Show heat the outside of the chamber. In either case, heat fluxes of at least 91 kW/m2 (200 BTU/HR/in 2) are required at operating temperatures of 12000C (22000F) to 14250C (26000 F). The tubes or the chamber must be gas tight and be able to withstand vacuums to 1.34 kPa (10 torr). Integrated heat recovery devices for combustion air preheating are essential for peak efficiency. DRYING - Much of this paper has been dedicated to high temperature processes. An important market for gas exists on the lower temperature regime in the field of drying. Materials to be dried range from dirty sludges to sensitive foodstuffs. Natural gas is the preferred fuel for sensitive drying, while dirty fuels, like coal and heavy oil, are more economical for the drying of materials where product quality is not an issue. Natural gas is preferred fuel for food drying because of its clean burning characteristics. Some competition is being felt from electrical processes such as microwave. In this area, control of the heat input, heat release pattern and temperature is critical. The latest technology in combustion, heat recovery and process control must be integrated into gas-fired equipment in order to keep gas the fuel of choice. When drying insensitive material, such as ore for example, the cost of the fuel becomes the dominant factor. Gas can overcome its premium price disadvantage by taking advantage of its form value. For example, GRI is now sponsoring the application of pulse combustors to the drying of sludges. The vibrations inherent in pulse combustors are used to shake loose water molecules trapped in the sludge. The overall process becomes more efficient and justifies the use of gas. CONCLUSION The development of new process equipment does not often require the invention of something entirely new, but rather the adaptation of technology used in one area to another. Good examples of this are the Advanced Glass Melter and the Oxy-Fuel Burner for Electric Arc Furnaces. The AGM built upon a coal combustor designed for MHO applications, and the Oxy-Fuel Burner used aerospace technology to solve a difficult problem in a very old basic industry. Albert Einstein once said that a genius is one who could understand principles from one discipline and apply them to another. This cross-fertilization of ideas is an excellent method of arriving at solutions to challenging problems. The foregoing discussion of plans for new gas-fired industrial process technology presents some interesting challenges for the combustion community. Fortunately, natural gas is extremely flexible and many combustion techniques already exist. For example, to 325 achieve higher temperatures, oxygen enrichment, preheating and plasma boosting could be employed. Surface burners or catalytic surfaces could be used to attain higher heat flux levels. Pulse combustors could be utilized to gain higher rates of convective heat transfer. Process control systems can be applied to improve the flexibility and accuracy of the system, thereby widening its application. The materials used in combustion system are a critical issue in the advancement of combustion technology. Recent progress in structural ceramics has made feasible the use of radiant tubes in processes over 11000C (20000F), the use of immersion tubes in molten metal, and the development of recuperators and regenerators and burners for high temperature heat recovery. In addition to ceramics, advances in high temperature metal alloys and composite materials may be employed to new process equipment. This materials work still has a long way to go, but the fate of advanced process equipment depends upon its success. The combustion system is a key element in the development of advanced natural gas fired industrial process equipment. Research must strive to increase the operating temperature and heat flux capability of these systems. Heat recovery devices must be integrated into these systems to assure peak efficiency. And last but not least, efforts must be continued to lower the cost of the equipment and the process to maximize the value to the consumer. |
