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Show 1600r------------______ ---, <5 ~ 1400 o .Q 1200 "0 Q) ~ 1000 o o E 800 aa.. 6 600 () ~ 0 1'O 400 U5 200 * o .--- Kiln upset condition • 1.5 2.0 2.5 3.0 Preheater oxygen. % NSR = 0 0.3-0.7 0.8-1.1 1.3-1.4 1.6-1.8 2.0-2.4 ~ - --A--- - -Q- - _ ........ _. * Figure 6 - Effect of NOxOUT-A injection on stack CO <5 ::R 0 ~ .Q "0 Q) U e 0 0 E a. a. cS en ~ 0 1'O U5 60 50 40 30 - 20 10 0 1.6 1.8 , ,*, 2.0 2.2 2.4 2.6 Preheater oxygen. % NSR = 0 0.3-0.7 0.8-1 .1 1.3-1.4 1.6-1.8 2.0-2.4 -e-- ---A--- ·····0 ····· - .... - -. • o 2.8 3.5 3.0 Figure 7 - Effect of pre heater oxygen on stack 802 ports, CO was about the same as the baseline levels at N8R 1. The NOxOUT chemistry requires oxygen and appropriate temperature to react with NOx. At low 02 or at low temperatures, CO generated from the urea decomposition oxidizes to CO2 at a slower rate. In addition, combustion of gas, coal, or CO is delayed with a reduced 02 concentration caused by the NOxOUT reactions that consume 0 2' Both of these paths are likely to have contributed to the CO increase with NOxOUT injection at 0 2 less than 2.3%. As injection location moved to a higher temperature region (the bottom level), the rate of CO oxidation increased, which gave lower CO than the middle or top ports. Therefore, the NOxOUT-A injection into high temperature zones and/or increased oxygen can prevent a CO increase above a baseline level. S02 Emissions of802 increased with decreasing preheater exit oxygen concentration. Concentration of 802 corrected to 10% 02 was about 20 ppm at >2.4% 02' but increased to 36 ppm at lower 02' This increase is likely to be the result of very low oxygen and high CO concentrations which decrease the rate of sulfur capture by lime. In high temperature applications described in literature, the rate of sulfur capture with lime or limestone decreased as excess oxygen decreased close to stoichiometric condition.7 NOxOUT injection increased 802 with increasing N8R and decreasing 02' In Figure 7, 802 during injection was higher than baseline conditions but only at less than 2.3% oxygen. This oxygen level is also the level where CO started to increase. The 802 increase was the least when the reagent was injected through the bottom level ports. This correspondence between 802 and CO supports the role of high CO and low 02 concentrations in reducing the 802 capture efficiency. NHs Flue gas was analyzed for ammonia at the preheater exit. Many samples were obtained and analyzed during injection and baseline condition. The results, however, were erratic, ranging from 5 ppm to 20 ppm during injection and between 2 and 9 ppm with an average of6.5 ppm during baseline conditions. At N8R of 1, average of 7 data points were 10.4 ppm of ammonia. Further ammonia sampling and analysis is needed to validate these results. ECONOMIC ANALYSIS The cost to maintain NOx emissions to less than the limit of 422lb/hr will depend on the firing rate in the kiln to process a raw material mix to manufacture a certain type of clinker. Raw material variations and the product requirements change the firing rate which in turn affects the NOx levels such that the required NOxOUT-A feedrate will change constantly. In Figure 8, the average daily NOx emissions in pounds per hour for June, 1993, varied from 300 pph to 700 pph. Using this as a basis, the reagent cost for a ton of clinker was estimated as shown in Figure 9. This cost varied even more and ranged from no chemical feed to $0.50/ton of clinker. An average chemical cost for June, 1993 would have been $0.18 per ton of clinker. In addition to high chemical utilization, the NOxOUT Process is cost-effective because the chemical is injected only when necessary and the bulk of the operating cost is the chemical. The capital cost of the process for this cement kiln! calciner was estimated to be $0.08 per ton of clinker on a 15-year life, 85% average plant capacity of |
