| OCR Text |
Show Introduction In the past, the only demand on LNG (Liquid Natural Gas) combustion was to reach a high carbon conversion efficiency. However, environmental considerations required combustion modifications for pollutant emission abatement. Recent concern about the reduction of NO x emission from LNG combustion has created the motivation to examine thermal NO x emission level from conventional combustion equipment and to develop new in-flame NO x reduction combustion techniques. Swirling flow has been used to stabilize flame in LNG burners [1]. Although staged combustion technique provides an effective way to reduce thermal NO x emission, but it has an adverse effect on carbon conversion efficiency. Azov et al [2] and Morgan [3] have demonstrated that a reduction of up to 60% NO x emissions can be achieved by this technology; however, carbon burnout drops up to 6.0%. Experimental studies have indicated the emission level of NO x could be affected by many factors, such as stoichiometry in the initial mIxIng zone, flame temperature, and the type of burners [4]. The availability of oxygen was one of the major factors controlling thermal NO x formation. Especially, modification of the combustion process to allow natural gas to react initially under oxygen-deficient condition is one of the most effective methods of controlling NO formation. Staged combustion could be accomplished by several different techniques. The combustion process will be staged either by physically separating the fuel rich zone from the burnout zone, or by using the burner to delay the mixing of the fuel with all of the combustion air. In this study, the combustion system was considered as a series of idealized reactors in which time/temperature history and stoichiometry could be controlled independently. The results obtained in bench scale studies define the optimem conditions for staged combustion, and the effects of other operating parameters on the formation and reduction of nitrogen oxides are also studied. |
