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Show particle. However, these two processes are not independent and Flament suggests that the total loss of surface or porosity be the m a x i m u m of the two. 2.0 Model Validation One of the most complete sets of information regarding the calcination and sulphation of sorbents in combustion flue gases is the work of Flament, 1993. In his work, particles were injected into flowing, turbulent flue gases. The particles were rapidly heated, as they would be in a utility boiler. The model developed here was validated using surface area and calcium utilization data (Flament, 1993) for the temperature range of 850 to 1150 °C, with and without S 0 2 in the flue gases. Without S 0 2 in the flue gas, the particle surface area can develop without pore plugging due to sulphation. This was a test of the calcination rate and sintering models. The calcination model reasonably predicted the change in surface area that was observed in the experiments. When 3000 ppm S02 was included in the simulations, the sulphate layer for gas temperatures between 850 and 950 °C reduced the surface area. The model and the data matched this behavior. At temperatures greater than 950 °C, there was little change in the surface area compared to surface area development in the absence of SO2. This suggests that sintering was the dominant effect in reducing pore surface area above 950°C. There was a significant reduction in surface area for temperature greater than 1150 °C. The model reasonably predicted the change in calcium utilization after 0.4 s for temperatures greater than 850 °C. In the first 0.1 s, the utilization was under predicted by 2-5%, but approached measured levels after this time. At temperatures greater than 1150°C, sintering had a dominant effect on the particle structure and calcium utilization decreased dramatically. 2.1 Sensitivity Study A sensitivity study was conducted for the sorbent reaction chemistry model. The baseline for this study was 10-micron diameter limestone particles in 3000 p p m SO2 at 1050 °C Varying several factors produced little change in the calcium utilization predictions. Varying the calcination activation energy had only minor effects on the calcium utilization. For this reason Ecai remained constant throughout the simulations at the recommended value of 3021 K. Varying the maximum calcined surface area value (Sexp) produced little effect on calcium utilization. This parameter was fixed throughout all simulations at a value of 30 m2/g. Altering the initial porosity was of minor importance. The initial porosity was fixed at a value of 0.05. Several factors proved to be of more importance in the sorbent model. As was expected, decreasing the concentration of SO2 in the flue gas significantly reduced the calcium utilization numbers. A variation in calcium utilization occurred when Esui was varied. From Flament, 1993 two sulphation rate equations were given, one for temperatures below about 1000 °C the other for temperatures above. If the low temperature rate equation was used with high temperature data the sulphur capture was over predicted. |