OCR Text |
Show The natural gas burner performance requirements were best satisfied with the use of a center gas gun. The center gas gun provided a very high turndown ratio (almost 35: 1), yet offered an acceptable flame length at full-load conditions. As discussed above, combustion staging for NOx control was achieved by clustering the injection nozzles in discrete locations. Reduced NOx was achieved with combustion staging and FGR. NOx emissions with LFG were less of a concern because the total LFG available can only produce 10 MW, which is 50 percent load on Grayson Unit 3 and 25 percent load on Grayson Unit 4. Operating on predominantly LFG at reduced load would inherently result in lower NOx emissions. The presence of inem in LFG reduced the flame tempenture and the corresponding NOx generated. The availability of FGR. offered added NOx control. As such, the challenge with LFG combustion was to maintain flame stability rather than reduce NOr Thus, analytical modeling was directed at identifying approaches for enhancing flame stability with LPG firing. Enhanced mixing was promoted in favor of achieving improved stability without concern for NOx produced. Modeling examined two diametrically opposed approaches. The first approach was based on operating at a high burner header pressure using the gas pressure or jet momentum to achieve mixing. The second approach emphasized low burner header pressure, but used the combustion air momentum and swirl to achieve mixing. In the second approach, nozzle injection orientation relative to the swirl was identified to be critical, and various orientations were evaluated through analytical modeling. 3.5 Prototype Burner Testing Proof of design was obtained through full-scale prototype burner testing. The burner was tested at the research and development facility of Hamworthy Combustion Engineering Limited, the parent company of A USCC. Tests encompassed the -10- |