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Show INTRODUCTION The continual increase in oil prices over the past years has prompted the search for immediate methods to conserve its consumption or to replace it with other less costly fuels, such as coal. However, the conversion of an oil to a coal-fired system in an industrial application is usually connected with enormous investment costs, especially when equipment for coal transportation, storage, processing, ash-removal and waste gas treatment are taken into consideration. One has to anticipate a long amortization period for this kind of investment. Under these circumstances, there is a great deal of interest in the utilization of other more economical fuels in existing oil firing system, in which the retrofit costs are minimal. Fuels that are eligible for this purpose are coal-oil mixtures (COM), coal-water mixtures (CWM) or any other viscous slurry with similar caloric value. The use of such fuels in systems that were designed for oil requires thorough examination of the expected changes in operation. Anticipated adverse effects in operation must be resolved as inexpensively as possible by technical measures. The controlling and optimizing of the preparation and combustion of the alternative fuel, present an additional challenge. The following presentation addresses this problem. THE ULTRASONIC BURNERS The ultrasonic burner developed by D U M A G , Vienna, Austria, was used for the combustion of C O M . Shown schematically in Figure 1, this burner has mainly been used for burning sludge or other viscous residues in the chemical industry. Tests conducted by Kali-Chemie A.G. in Hannover, Germany, have proven the suitability of the burner for the combustion of C O M. The center of the ultrasonic burner is the nozzle which can be of various designs. Figure 2 shows the simplest nozzle construction. The fundamental operating principle is based on the generation of an ultrasonic field by an atomizing gas which passes through a resonance chamber at high velocity. Compressed air, steam or even natural gas can be used as the atomizing medium. It flows through the outer transverse section of the nozzle tip and accelerates from there. Depending on the inlet pressure of the gas, ultrasonic waves of 18,000 to 23,000 16-2 |