Numerical study of hot flow field in an entrained-flow gasifier with flat flame burner

Coal burners are considered to be one of the critical units in coal gasification furnaces. Nowadays, as most of the coal burners in entrained-flow gasifiers are designed in the coaxial type (oxygen-encapsulated coal or vice versa), it normally requires a large combustion chamber with a high aspect ratio to keep a good averaged residence time (ART) for the coal particles in order to achieve a good carbon conversion rate (CCR) for the gasifier. As a consequence, the investment of the gasifier has to be increased due to the large combustion/reaction chamber. In this article, a top mounted flat flame burner was proposed to overcome the drawbacks of the coaxial burners. Instead of one, it is designed with three burner units on top of the combustion chamber, which converts the single candle shape flame from the traditional coaxial burner into a shorter and flatter shape flame, so the length of the flame can be reduced in the combustion chamber and extra space for gasification reactions can be created. The combustion characteristics of the flat flame burner were investigated using numerical simulation tools, and the results were compared with a same gasifier but mounted with a coaxial burner, together with the combustion chamber, both of the burners were modeled under the Eddy Dissipation Concept (EDC), the flow field, temperature distribution, CCR, solid particle distribution and the residence time were calculated. The results show that the implementation of flat flame burner leads to more reverse flow (reverse flow rate:flat flame Kvmax=3.2; single Kvmax=1.3) in the upper part of the combustion chamber, which helps the coal particles and oxygen dispersing more evenly in the combustion chamber, and reduces heat concentration near the burner section, therefore, brings a much more uniform temperature and particles distribution along the gasifier. The fuller particle dispersion and more uniform temperature distribution are conductive to the effective utilization of gasifier combustion chamber volume and intensify the mass transfer near the impinging stream zones. After comparing the performance of the simulated gasifier, the results show that the CCR of the gasifier with the flat flame burner is higher than of the one with single coaxial burner (with calculated values of CCR at 0.5 m away from burner: flat flame burner=95.1%, single burner=77.0%) which implies that the reaction volume of the flat flame burner gasifier can be designed smaller than that of the single burner for the same production capacities. © 2019, Editorial Office of Journal of China Coal Society. All right reserved.