| OCR Text |
Show recycle into the primary air stream. This is attributed to the less reducing atmosphere in the secondary air region which causes less radicals serving for NOx reduction and lower temperature unfavorable for reaction rates. NO Recycle into PA and SA Streams Simultaneously A few experiments were conducted for NO recycle into both primary air and secondary air streams simultaneously. The ratio of the amount of NO recycled into the PA stream to the amount of NO recycled into the SA stream was varied. As expected, the greater the percentage of NO recycled into the primary air stream, the higher the NOx reduction efficiency. The favorable recycle location is at the PA duct, which provides good mixing between the recycled NOx and the reducing atmosphere. NQz Recycle into Secondary Air Duct Because the NOx recycle stream may contain large portion of N02, experiments were conducted to recycle N02 into the secondary air stream. The results are shown in Figure 6. The data demonstrate a consistent trend similar to the NO recycle tests. The effect of exit O2 is also similar. The lower the exit O2 , the higher the NOx reduction efficiency due to the increased reducing atmosphere. Average N Ox reduction efficiencies were 61 %, 57 % and 47% for exit O2 concentrations of 2 %, 3 % and 4 % respectively. These values are higher than that for NO recycle at the corresponding conditions. This is positive to the overall NOx reduction efficiency, because the percentage of N02 is higher than Figure 6. N O2 recycle into secondary air stream NO in the N Ox recycle stream of NOXSO Process. However, the mechanisms need be explored. Generally, when N02 is recycled into the combustor, it is expected to be converted frrst to NO at high temperatures and then NO will be reduced in the flame. In addition to this, the experimental results implied that some other reactions contributed to the reduction of N02 directly. 10 |
