Altex developed the Ultra Reduced NOx Burner (URNB), which can reduce NOx from 80 ppm to 5 ppmvd (at 3% O2).
This substantial 93% NOx reduction, at good combustion stability and CO burnout conditions, is achieved by breaking
the combustion into multiple flame zones, where all critical flame needs can be balanced. Other ultralow NOx burners
cannot achieve these benefits, because they use a single flame to address all flame needs. The advantage of the URNB
can be seen in the comparison of burner test results in a conventional firetube boiler, at 12 MM Btu/hr scale, versus
boiler results obtained on alternative ultralow NOx burners.
As shown in the figure above, the Altex URNB has
lower emissions than alternative ultralow burners, for a given percent Flue Gas Recirculation (FGR). Even without
FGR, the URNB can achieve a low 13 ppm NOx emissions, versus over 100 ppm for a fully premixed type ultralow
NOx burner without FGR. In addition, the alternative burners need over 40% FGR to achieve very low
NOx. However, this level of FGR is close to the stability limits of the burner. With the URNB, this is not the case, and
the burner can be ramped rapidly in load, and be out of adjustment without concern for flame blowout and safe
operation.
Presently, the URNB is being sold at scales from 5 MM Btu/hr (1465 kilowatts), to
25 MM Btu/hr (7325 kilowatts). URNB burners at scales up to 50 MM Btu/hr (14650 kilowatts) will be produced
and sold.
As an extension to the successful URNB, an ultralow NOx duct burner was developed and tested at Altex, at
a scale of 500,000 Btu/hr (147 kilowatts). This test unit represented a small segment of a multirow, full-scale duct
burner. NOx emissions as low as 2 ppmvd (at 15% O2) were measured under stable and low CO combustion
conditions. These burners will be critical to producing low cost and low emissions
gas turbine combined cycle powerplants and combined heat and power systems, which use supplemental firing. Lastly, Altex
developed a low NOx and high air preheat (1500F) burner, which reduced NOx by over 94%.