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Show 3.2.3 Site Results It is during commissioning that the ground work undertaken when doing the modelling really pays off. There is no need for lengthy trial and error to find the best operating conditions. It is possible to bring the kiln up to temperature and into production very quickly. The burner can then be quickly "fine tuned" to give its optimum performance in the kiln, the model study results providing valuable information of the behaviour of the system. This is particularly important when reburnering associated with a fuel conversion program owing to the changed operating conditions. Comparative data between the kiln firing oil and gas are given in table 4. It can be seen that the new burner is able to operate at a lower excess air than the oil burner (1.25% 02 as against nearly 3.5% before), and at this lower excess air the carbon monoxide concentration is also lower. As expected the product temperature near the burner is lower and the exhaust hotter, as a result of the change in heat flux profile. However, the increase in exhaust gas temperature is only 15°F which is significantly lower than often experienced. Parameter Original Burner FCT Burner (Oil) (Gas) Hot End Temperature (OF) 1497 1420 Cold End Temperature (OF) 630 645 Excess Oxygen ( %) 3.42 1.25 CO Concentration (ppm) 199 140 Table 4 Comparison of Gas and Oil Operating Parameters \,/hilst it is not possible to measure the heat flux profile within the kiln, the radiation from the outside of the kiln shell can be measured using an infra-red technique and, for alumina kilns, this gives an indication of the heat flux pattern of the flame, figure 17. This shows that the major region of flame heat flux release is at some 60 feet and 80 feet from the burner for the oil and gas flames respectively and that the region of maximum peak release has moved up the kiln by about 20-25 feet with gas firing. These trends show a good agreement with the predicted heat flux profiles. The flue gas carbon monoxide/excess oxygen relationships for the burners are presented in figure 18. This shows the curve for the original oil burner as well as that for the FCT burner on gas. The curves are 'best fi tted' around daily averaged recorded data. The curve profiles are similar to the flame length/excess air curves produced by the acid/alkali model studies. The profiles produced by the FCT burner is indicative of better fuel/air mixing leading to more efficient combustion conditions and show that the high momentum burner is capable of operating at lower excess air levels with less CO formation. |