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Show - 2 - although not directly affecting the NOx reduction performance, may react with excess ammonia to form objectionable ammonium salts. As the flue gases are cooled below 600 degrees F, ammonia can react with sulfur trioxide (S03) to form ammonium sulfate or . bisulfate. These compounds could deposit on the surface of heat recovery equipment operating in this temperature range, however, this has not been a problem when the THERMAL DeNOx process is operated within the prescribed design specifications. Sulfur dioxide (S02) may also react with ammonia at temperatures below 150 degress F, but since this is usually far below the stack exit temperature, it is not of concern. Glass Furnace Applications The THERMAL DeNOx process has been applied to two types of glass melting furnaces: regenerative and recuperative. These designations refer to the method used to recover heat from the flue gas and to heat the incoming air. The first applications were to regenerative type furnaces. Please refer to Figure 2 for a brief description of this type furnace. The batch mixture is melted in the tank by combustion of fuel in the space above the molten glass. The flue gas flows from this space through ports and into the checkers. Checkers are loosely stacked refractory bricks which absorb the heat from the flue gas. The flue gas is collected at the outlet of the checkers and flows through a flue to the stack. After about 15 minutes the air flow is reversed. That is the the fuel and air flows are stopped. The air flow is then passed through the checkers which had recently contained the flue gas. The fuel is then introduced through the opposite set of firing ports. In addition to the obvious effects of this reversal, there is a heating and cooling cycle for the bricks resulting in constantly changing flue gas temperature at any selected location. Figure 3 illustates a typical variation of flue gas temperature over one 15 minute half-cycle. This effect is of paramount importance to the THERMAL DeNOx process with its strong temperature dependence. Regenerative glass furnace may contain one large checker on each side, or multiple checkers in series with interconnecting flues. The first application of the THERMAL DeNOx process to a glass melting furnace was a demonstration on a furnace with three sets of checkers in 1980. The layout of this furnace is shown schematically in Figure 4. The injection nozzles were located in the flue between the first and second checkers where the flue gas temperature was near optimum for the THERMAL DeNOx process. Figure 5 is a simplified flow plan showing the major equipment required for this installation. In this application low pressure compressed air was used as the carrier medium. The flue gas temperature at the injection location is shown in Figure 6, as well as untreated and treated NOx levels. The |