| OCR Text |
Show rates were determined based on periodic velocity measurements using standard pitot tubes. Samples were collected at the locations listed in Table 2. Test results indicate that Radian's Hybrid Low NOz process can reduce diesel exhaust NOz levels as high as 1500 ppmv to less than 25 ppmv. The key to the NOz reduction process is controlling the reduction catalyst outlet CO between approximately 750 and 1500 ppmv. This is critical to obtaining a final effluent NOz level of below 25 ppmv because of the following: 1. As the CO falls below 750 ppmv, the reaction of the N02 with the combustibles decreases and the NOz levels in the reduction catalyst effluent (and in the oxidation catalyst effluent) begin to increase. 2. As the CO begins to rise above 1500 ppmv, the NOz in the reduction catalyst effluent remains unchanged, but the NOz in the oxidation catalyst effluent begins to increase. This difference in NOz levels is attributed to the reaction of N02 with CO and H2 to form bound nitrogen compounds (NH3 and HCN) across the reduction catalyst at reduction catalyst outlet CO levels above 2000 ppmv. These bound nitrogen compounds are subsequently reoxidized across the oxidation catalyst to form NOz • 3. As CO continues to increase, NOz levels in the reduction catalyst begin to increase. This may be due to the blanketing of the reduction catalyst with CO such that catalyst sites for the reaction of NO and CO to form N2 are not available. Evidence of these influences can be seen in Figures 2 through 4. These figures show data points taken approximately every three minutes from the recording charts for 87.5% diesel load operation. Figures 2 and 3 are the data points for reduction catalyst outlet NOz and oxidation catalyst outlet NOz ' respectively. Variation in the data points results from the difficulty in manually controlling the reduction catalyst outlet CO concentration at the levels necessary to minimize NOz emissions. The CO level tended to change abruptly, but responded fairly rapidly to control attempts. NOz levels, on the other hand, increased when the reduction catalyst outlet CO fell outside the required operating range and required a considerable amount of time to reach minimum when the CO was brought back to the required range. The difficulty in controlling the CO is attributed to several factors, including variation in fuel flow to the reduction furnace and the lack of effective manual control of the small volume (about 15 Nm3/h) of air to the reduction catalyst. Better control of the reduction catalyst outlet CO is considered achievable with automatic controllers. -5- |
