Numerical investigations of combustion and emissions of syngas as compared to methane in a 200 MW package boiler Mohamed A. Habib, Esmail M.A. Mokheimer ⇑ , Sofihullahi Y. Sanusi, Medhat A. Nemitallah Mechanical Engineering Department, Faculty of Engineering, KFUPM, Dhahran 31261, Saudi Arabia article info Article history: Received 8 February 2014 Accepted 19 March 2014 Available online 20 April 2014 Keywords: Excess air Methane reforming NO x emissions Package boiler Syngas combustion abstract 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 inves- tigated and compared with the case of pure methane combustion in a two-burner 200 MW package boi- ler. 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 includ- ing 67% CO:33% H 2 , 50% CO:50% H 2 and 33% CO:67% H 2 . The results showed a combustion delay in case of pure methane combustion as compared to syngas combustion. The case of 33% CO:67% H 2 syngas com- position 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% H 2 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% H 2 syngas composition had the lowest emissions with the best combustion characteristics. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Synthesis gas (syngas) is a source of environmentally clean fuels and has the potential to become a major fuel toward the near zero pollutant emissions. The use of syngas as a fuel is in line with meet- ing the ever increasing stringent environmental policy. Syngas has also been adjudged a potential energy source for the future due to its wide availability as a product of biofuel and fossil fuel gasification [1], as well as a product of methane reforming. Syngas produced from steam methane reforming consists of varying proportion of carbon monoxide (CO) and hydrogen (H 2 ) and may also contain methane (CH 4 ) depending on its conversion efficiency. Syngas (25% CO and 75% H 2 ) derived from 100% methane reforming pro- vides a unique opportunity of enhancing the fuel (syngas) energy per unit volume of methane by about 30%. The steam required for this process can be generated from solar energy thereby converting solar thermal energy into chemical energy of the fuel. The continu- ous variations in solar radiation through the day and across the year have strong effects on the syngas conversion efficiency and the resultant fuel thermal energy. This affects the heat release rate, emission characteristics and stability of the flame making pilot study necessary. Syngas has been successfully used and proved to be beneficial in commercial plants. Gadde et al. [2] carried out extensive testing on SGT6-5000F combustion system over a range of syngas fuels and achieved NO x and CO emissions of less than 15 ppm and 10 ppm, respectively, over the expected load range. They also observed less than 5 ppm NO x and less than 1 ppm CO emissions when syngas are tested on SGT5-4000F combustion sys- tem which shows improvement as compared to less than 25 ppm NO x and less than10 ppm CO on natural gas combustion system with steam injection. Sainchez et al. [3] showed that the use of syngas increases the gas turbine power by 3–7% at generator terminals and 5–10% increase in gas turbine efficiency (LHV based) but resulted in much higher carbon dioxide emissions. Oluyede et al. [4] reported that firing syngas in conventional gas turbine has the potential to result in enhanced power output with an increase of 20–25% when compared with the natural gas due to significant flow rate increase (14% increase over natural gas). However, they noted the increase in power output is accompanied by an increase in the moisture content of the combustion products due to higher hydro- gen content in the syngas which can contribute significantly to the http://dx.doi.org/10.1016/j.enconman.2014.03.056 0196-8904/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +966 3 860 2959. E-mail address: esmailm@kfupm.edu.sa (E.M.A. Mokheimer). Energy Conversion and Management 83 (2014) 296–305 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman