A study of NOx emission characteristics in two stage combustion

NOx reduction mechanism of a methane–air Smithells flame

“…In this method the combustion is divided into two stages; in the first stage, fuel is burned with air in a rich premixed condition, and in the second stage, the remaining fuel is burned with secondary air. A variety of experimental studies [1][2][3][4] have been conducted on this method, mainly for development of large-scale furnaces and combustors, and it has been determined that the heat loss in the region behind the premixed flame of the first stage reduces the maximum temperature of the second stage flame, which suppresses the production of Zeldovich NO. Additionally, in the field of home combustion appliances, Umeda and co-workers recently developed a multiple-inner-port burner in which the NO x emission is considerably low [5].…”

Developments of Gas Turbine Combustors for Air-Blown and Oxygen-Blown IGCC

“…The body of research into the basic combustion characteristics of gasified fuel includes studies on the flammability limits of mixed gas, consisting of CH 4 or H 2 diluted with N 2 , Ar or He (Ishizuka & Tsuji, 1980); a review of the flammability and explosion limits of H 2 and H 2 /CO fuels (Cohen, 1992); the impact of N 2 on burning velocity (Morgan & Kane, 1952); the effect of N 2 and CO 2 on flammability limits (Coward & Jones, 1952;Ishibasi et al, 1978); and the combustion characteristics of low calorific fuel (Folsom, 1980;Drake, 1984); studies by Merryman et al (1997), on NOx formation in CO flame; studies by Miller et al (1984), on the conversion characteristics of HCN in H 2 -O 2 -HCN-Ar flames; studies by Song et al (1980), on the effects of fuel-rich combustion on the conversion of the fixed nitrogen to N 2 ; studies by White et al (1983), on a rich-lean combustor for lowBtu and medium-Btu gaseous fuels; and research of the CRIEPI into fuel-NOx emission characteristics of low-calorific fuel, including NH 3 through experiments using a small diffusion burner and analyses based on reaction kinetics (Hasegawa et al, 2001). It is widely accepted that two-stage combustion, as typified by rich-lean combustion, is effective in reducing fuel-NOx emissions (Martin & Dederick, 1976;Yamagishi et al, 1974). On the other hand, with respect to the combustion emission characteristics of oxygen-blown medium calorific fuel, Pillsbury et al (1976) and Clark et al (1982) investigated low-NOx combustion technologies using model combustors.…”

Gas Turbine Combustion and Ammonia Removal Technology of Gasified Fuels

“…The body of research into the basic combustion characteristics of gasified fuel includes studies on the flammability limits of mixed gas, consisting of CH 4 or H 2 diluted with N 2 , Ar or He [47]; a review of the flammability and explosion limits of H 2 and H 2 /CO fuels [48]; the impact of N 2 on burning velocity [49]; the effect of N 2 and CO 2 on flammability limits [50,51]; and the combustion characteristics of low calorific fuel [52,53]; studies by Merryman et al [54], on NOx formation in CO flame; studies by Miller et al [55], on the conversion characteristics of HCN in H 2 -O 2 -HCN-Ar flames; studies by Song et al [56], on the effects of fuel-rich combustion on the conversion of the fixed nitrogen to N 2 ; studies by White et al [57], on a rich-lean combustor for low-Btu and medium-Btu gaseous fuels; and research of the CRIEPI into fuel-NOx emission characteristics of low-calorific fuel, including NH 3 through experiments using a small diffusion burner and analyses based on reaction kinetics [58][59][60][61]. It is widely accepted that two-stage combustion, as typified by rich-lean combustion, is effective in reducing fuel-NOx emissions [62,63].…”

“…It is conceivable that the characteristics of the flame zone, such as the local temperature distributions, the local equivalence ratios, and the reaction behaviors of fuel constituents and radicals (O, OH, H, etc.) [63] are affected by the fuel constituents. Figure 12 shows the correlation between the equivalence ratio, φ ex , and the conversion rate of NH 3 in the fuel to NOx, C.R., with the fuel CO/H 2 molar ratio as a parameter, when the NH 3 concentration in the fuel and the calorific value are set and maintained at 1000 ppm and 4.4 MJ/m 3 respectively [82].…”

“…Since the temperature differences among the test cases are very small in comparison to the flame temperature itself, and the thermal-NOx emissions are very small compared to the fuel-NOx emissions, as shown in Figure 11, it is speculated that the temperature differences have no noticeable impact on NOx emission characteristics. Two-stage combustion with reducing flame (which has a primary combustion stage under fuel-rich conditions and a secondary stage in which remaining unburned fuel combusts completely), is widely accepted as a combustion technology for suppressing fuel-NOx production in conventional fuels [62,63,87]. It is also known that the fuel-NOx production mechanisms of conventional hydrocarbon fuels, such as CH 4 , are different from those of non-hydrocarbon fuels, such as CO and H 2 [88][89][90][91].…”