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Show removed with standard precipitator or bag house equipment. The urea Is decomposed Into the gas phase and thus does not contribute to the particulate loading of the flue gas. The principal advantage of the lime-urea hydrate technology over selective noncatalytic NOx reduction alone, or even SCR, is the potential for eliminating, or markedly decreasing, air heater deposits from ammonium sulfates. These deposits are formed when byproduct ammonia (NH:) reacts with S03 formed during the combustion of sulfur bearing fuels. By having the calcium available to remove any S03 at a relatively high temperature, it will not be available to react with any byproduct ammonia at air heater temperatures. In this manner a potential operational Impact Is minimized, thereby allowing the Implementation of a technology that might otherwise not be considered a viable candidate. SUMMARY OF PILOT SCALE COMBUSTOR RESULTS A series of pilot scale tests have been conducted in order to characterize the combined NOx and S02 removal performance of the lime-urea hydrate as well as to determine the effect of the urea on the CaO hydration process. Detailed results of these tests are presented elsewhere (Teague, et aI., 1989; Muzio, et aI., 1989). In sum, the pilot-scale tests showed that the lime-urea hydrate is effective In simultaneously removing S02 and NOx from the combustion products. The primary parameters that control the process are the combustion product temperature at the pOint of injection, the amount of lime-urea hydrate injected, and the composition of the lime-urea hydrate (urea/CaO ratio). As shown in Figure 2(a), peak S02 removals occur at an injection temperature of 1100-1150°C (2000-21 OO°F) while peak NOx removals occur at 950°C. Depending on a specific application, one can optimize the process for either S02 or NOx removal. At an intermediate Injection temperature of 1 OOO°C, simultaneous S02 and NOx removals of 45 percent and 50 percent were obtained at a hydrate injection rate corresponding to Ca/S=2 and N/NOx= 1. Increasing the hydrate injection rate to provide Ca/S=3 and N/NOx= 1.5 increased the S02 and NOx removals to 62 percent and 65 percent, respectively (Figure 2(b)). Ammonia is a byproduct emission from the process, and the levels depend on temperature as well as the amount of lime-urea hydrate injected. As shown in Figure 2, ammonia emissions are minimized if the injection temperature is above the temperature for peak NOx removal (e.g. >950°C). The pilot-scale tests also showed (Figure 3) that the hydrate formulation (e.g., urea/CaO ratio) can be modified to accommodate either: 1) different S02/NOx ratios in the flue gas, or 2) varying Ca/S and N/NOx ratios. Likewise, the effects of initial S02 and NOx levels on the process are similar to those seen with Ca(OH)2 or urea injection alone. Thus the technology provides a means for -5- |