The report gives results of an evaluation of the possibility that plant efficiency losses or combustion instability might limit NOx reduction by combustion modification. Data from natural-gas- and oil-fired boilers were used in the analyses. The study of effects on plant efficiency of combustion modifications for NOx reduction showed that the effects were negligible, at least within the scatter of available data. Nearly all plant efficiency variations (losses of up to 6%) resulted from plant load variation, which is not considered a combustion modification for NOx control. Combustion instability, however, appeared to be a possible limitation, if not properly understood and accounted for by hardware modifications. Fuel-rich burner operation, in the staged combustion technique, can create an unstable air-side feed system coupled mode of combustion instability. A method of analyzing such instability modes was developed for use in providing stable operating conditions, even with very fuel-rich burners.

Prepared by the Aerospace Corporation under Grant No. R803283-02, ROAP No. 21ADG-089, Program element No. 1AB014. Issued Sept. 1977. Includes bibliographical references (page 58).