OCR Text |
Show the reburning natural gas prior to furnace injection. The results are shown in Figure 4. With preferential contacting between the reburning gas and NO, exhaust NOx emissions were lower than the baseline case. When oxygen was premixed with the reburning fuel, a substantial increase in NOx emissions was witnessed, regardless of whether NOx was premixed with the gases. Higher primary NOx concentrations resulted in increased reduction in all cases. The results, which demonstrated the competition between primary NOx and oxygen species for hydrocarbon radicals, showed that NOx-CH contacting was not rate 1 i mi ti ng. Fuel Composition The presence of CH radi ca 1 sis necessary for the reburning process to p rocee d. An app roach to improve CH avai 1 abi 1 i ty is to use a reburni ng fuel which favors CH as a decomposition product. Several gaseous hydrocarbon fuels were tested to investigate CH generation. The fuels included acetylene, ethylene (an olefin), isobutane (a parafin), and natural gas, which was primarily methane. The fuels had an H/C ratio of one to four. The data are presented in Figure 5 and indicated the reduction efficiency with all of the fuels was similar. Acetylene, the closest stable hydrocarbon to CH (as illustrated in the decomposition chemistry shown in Figure 5), did not appear superior to natural gas as a reburning fuel. Another method to improve interaction between NO and CH is to slow the rate of reburning fuel oxidation. A solid hydrocarbon fuel, naphthalene (CIoHe), was selected and tested as the reburning fuel. Lower reduction efficiency was obtained with the solid fuel, however. Figure 5 also shows resul ts obtai ned with methanol as the reburni ng fuel. Methanol, whi ch favored CO as a decomposition product, yielded substantially lower reduction efficiency. As expected, reburning with CO resulted in the lowest reduction in NOx emissions. 4 |