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Show 10 Effect of lifting up the burners on the furnace exit gas temperatures Table 6. Furnace exit gas temperature Flue gas Fuel input flow (kg/s) (MW) FEGT ( C) Base case1 Alternative l2 Alternative 22 Alternative 34 139 184 184 167 315 317 316 315 987 1172 1181 1132 In order to find out the effect of the lifting up of the burner on the furnace exit gas temperature, the different burner arrangements were studied by using A R D E M U S. The studied burner arrangements can be observed in Appendix 7 and the calculated furnace exit gas temperatures are presented in the Table 6. Coal + low-NOx-burners+FRG 32 % 2Coal+low-NOx-burners+FRG 3 2 % ^oal+low-NO^-burners+FRG 2 0 % 4.4 The new solution The most cost-effective solution proved to be a combination of flue gas recirculation (cold gas recirculation) and the lifting up of the burners. B y using only flue gas recirculation, the amount of recirculated flue gas should be very high and the flame stability would be poor, and hence the NOx-emissions and U B C would be high. Therefore the amount of recirculated flue gases must be limited to 2 0 % of the total flue gas flow, which is also the limit that has been established on the basis of operational experience gained. Also, the combination of flue gas recirculation and an added superheater area would have been a good alternative, but, because of the high cost, the solution with the F G R (20%) and lifting up the burners according to Alternative 3 turned out to be the most economical choice. The alternative 3 was chosen because, because the FEGT in this case was optimum for the boiler efficient operation. The fuel switching and all the modification related to it will be carried out during the year 1999. 5 Improvement of Low-NOx-burner performance Meri-Pori Power Plant is owned by IVO, and it consists of one 560 M W e boiler, which produces 440 kg/s of steam (HP 240 bar, 540 °C; L P 46 bar, 560 °C). The pulverised coal is blown into the furnace through 30 low-NOx burners located at three different levels against each other (opposite wall firing). |