Air entrainment in kiln burners is helpful in multiple ways. Most importantly, though, entrainment significantly reduces the burner jet temperature and therefore promotes temperature uniformity and freedom from excessive hot spots in the kiln. An additional improvement in NOx emissions is a further benefit.
The article notes that all recessed installations promoted "far more entrainment...than the flush-mounted burner," but the temperature uniformity reported does not support this conclusion. The flush-mounted system produced a reported delta T of 120°F in the load. The recessed delta T values for 19 in. and 6 in. recessed burners were reported to be 280°F (worse) and 70°F, respectively, despite both burners having higher calculated entrainment ratios. This inconsistency in the data should be further evaluated.
I believe that the difference between flush-mounted vs. recessed has more to do with the fact that different burners were used in the flush vs. recessed models. The two burners selected have around a 10% difference in output, as well as different mixing characteristics, as indicated by the extreme differences in the excess air (XSA) capabilities of the two burners.
Ralph Ruark, Ruark Engineering
Bradenton, Fla., email@example.com
With regard to the apparent difference between the temperature uniformity and entrainment values, temperature uniformity is a function of the heat release profile and burner location, as well as the heat transfer in the furnace-not just entrainment.
There may be some differences in results between the recessed vs. flush-mounted burner cases as noted, since two different burners were modeled. However, modeling the two burners at the same average burner exit velocity mitigated the magnitude of such a difference. In the future, we plan to run the flush-mounted case using the same burner as the recessed cases to further validate the results.
Jim J. Feese, Director of Product Development
Hauck Manufacturing Co., Cleona, Pa. firstname.lastname@example.org