| OCR Text |
Show cracking by direct mixing with the cracking gas. As a result, the soot yield (-1.5 X) obtained in the test 9-12 was considerably greater than the similar yield i~ test 9-10 (-0.05%). In any case, the use of air was to verify the extent of reforming reactions and it is not recommended for use in the "cracker" proj ect, since the presence of nitrogen in the air opposes the objective for reducing thermal NOx . We believe that the reforming reactions have prevented us from producing the design soot concentration (approx. 20- 30% yield or 0.0063 - 0.0095 lb/cf of cracking gas). The most soot we produced in Campaign #9 was around 0.00053 lb/cf, which is one order of magnitude smaller than the overall objective of this program of NOx reduction. Further, evidence of reforming reactions is seen by analyzing the cracked gas composition, which invariably shows large proportions of H2 and CO. B. Summary of present tests with original test equipment: Efforts are underway currently to enhance cracking by modifying the existing cracker (see top sketch on Table-l). The modifications include complete reversal of flow configurations. This means that oxy/fuel burner is fired in tangential direction, whereas the cracking gas is introduced axrally through the center of the combustion chamber front face. The tangential burner firing is accomplished by series of tangential holes along the length of the combustion chamber. Alternate oxygen and natural gas connections are also made. We expect that this firing configuration would create a swirling flame close to the wall of the combustion chamber and would heat the wall to a sufficient temperature (- 2400° F) . This heated combustion chamber wall is expected to radiate energy to the cracking gas more efficiently without too much mixing or reforming. The basic approach is to utilize the wall and flame radiation to a greater extent than the previous design. The soot yield from the present tests would indicate a proper combustion chamber design to meet our obj ectives. However, a sub-stoichiometric firing ratio is recommended to prevent refractory damage. C. Future: 1. R&D tests with new "MODUlATIVE GAS CRACKER" The basic concept here is to crack the natural gas in a periodic fashion. As shown in Figure 3, the oxy/fuel burners, mounted at four tangential locations, is set to fire SOX stoichiometric during the heating cycle, (which will maintain the combustion chamber to about 2600°F) , and then modulated to fire rich. (38% stoichiometric) during the cracking cycle. During the cracking cycle, the cracked gas is introduced tangentially in the narrow combustion chamber (1" annular gap) to thermally crack by forced convection due to the heat stored -5- |
