The burner swirl intensity plays an important role in membrane wall safety and the gasification performance of pulverized coal, swirl gasifiers. The comprehensive gasification model (CGM), having two reaction regions and one radial heat transfer region, was used to simulate the influence of the swirl number (SN) on gasification performance, multiphase flow, reactions in the space, and reactions regarding the membrane wall. The results show that an SN of 0.66 is a critical point to divide low-swirl and high-swirl flows for the single-swirl-burner gasifiers of this study. Gasifier performance increases sharply with increased SN for low-swirl burners, whereas SN has little influence on gasifier performance (and multiphase flow) for high-swirl cases. In this paper, we examine the relationship between burner swirl and flow fields, temperature distributions in the space and on membrane wall, slag thickness, and the molten slag velocity distribution on the membrane wall. The influence of SN on these parameters is more remarkable at the top of the reattachment point than below it. The slag layer formed on the membrane wall isolates high-temperature gas effectively, except around the reattachment point. To guarantee gasifier performance and membrane wall safety, the burner SN should be between 0.66 and 0.9 for the single-swirl-burner gasifiers of this study.