Numerical investigations of combustion and emissions of syngas as compared to methane in a 200 MW package boiler

During the last decades, focus has been made on the use of syngas instead of conventional hydrocarbon fuels targeting NO_x emission reduction in the exhaust gases. With advances in solar-steam methane reforming for the production of synthesis gas, the applicability of syngas at industrial scale becomes imperative. In the present work, syngas combustion and emission characteristics are numerically investigated and compared with the case of pure methane combustion in a two-burner 200 MW package boiler. A detailed reaction kinetics mechanism of 21 steps and 11 species was considered for the modeling of syngas-air combustion. Different syngas compositions were considered for combustion with air including 67% CO:33% H₂, 50% CO:50% H₂ and 33% CO:67% H₂. The results showed a combustion delay in case of pure methane combustion as compared to syngas combustion. The case of 33% CO:67% H₂ syngas composition was found to have the shortest flame as compared to that of other syngas compositions. The case of 50% CO:50% H ₂ syngas resulted in lowest maximum boiler temperature while 67% CO:33% H₂ syngas resulted in highest maximum boiler temperature. The boiler exit temperature was found to increase with the increase of hydrogen content in the syngas. The excess air factor was found to have a significant effect on both CO and NO_x emissions. NO_x emission decreases by about 30% when the amount of excess air is increased from 5% to 25%, which is very promising. Among the tested syngas compositions, the 50% CO:50% H₂ syngas composition had the lowest emissions with the best combustion characteristics.