Pollutant emission characteristics of staged combustion with hydrogen-enriched methane for gas-fired boiler based on Taguchi design

Hydrogen-enriched methane (HEM) combustion is an effective method to reduce the consumption of CH4. A Taguchi orthogonal method was proposed to investigate the effects of the H2-doping ratio XH2, air preheating temperature Tair, and excess air coefficient of burners arranged at the bottom Ex,b on the NOx and CO emissions from HEM combustion in a gas-fired boiler. According to the analyses, the significant order of the three parameters for NOx emissions is Tair > XH2>Ex,b. The optimal combination was XH2 = 0, Tair = 300 K, and Ex,b = 0.8, and the corresponding NOx emissions were 20.59 mg/m3. For CO emissions, the significant order of the three parameters is XH2>Tair > Ex,b, and the optimal combination was XH2 = 0, Tair = 400 K, and Ex,b = 0.9 where the corresponding CO emissions were 5.47 mg/m3. An entropy weight method was used to obtain the optimal combination of XH2, Tair, and Ex,b for the total NOx and CO emissions, and an index of comprehensive pollutant emissions (CPE) was proposed. Further investigation of the CPE in 25 trials showed that for the total emissions, the significance order of the three parameters was XH2>Tair > Ex,b. The optimal combination was XH2 = 0.4, Tair = 400 K, and Ex,b = 0.8, and the corresponding NOx and CO emissions were 33.68 mg/m3 and 6.53 mg/m3 respectively. These results provide guidance on the operating conditions of HEM combustion for emissions control.