The main absorption tower of natural gas with high hydrogen sulfur content purification needs regular welding repair due to corrosion. Before and after repair, the internal combustion integral heat treatment technology can be used to perform hydrogen-eliminating treatment and eliminate stress. The arrangement of swirlers has an important impact on air distribution and flame control during the heat treatment. In this work, the fluid field characteristics of two-stage swirler, single-stage swirler I and II in the absorption tower are simulated, respectively. The results show that there is no obvious recirculation zone above the two-stage swirler and the velocity distribution is uniform. A large tangential velocity is generated above the inner and outer swirler blades. The maximum tangential velocity is 8.33 m/s when the inlet velocity is 9.8 m/s, followed by single-stage swirler II and single-stage swirler I, 4.5 m/s and 3.12 m/s, respectively. The pressure drop in the tower corresponding to the two-stage swirler has the smallest change. These prove that the two-stage swirler can effectively generate low resistance swirling flow field. The proportion of the streamline at the bottom of the tower corresponding to the two-stage swirler changes steadily with the gas mass flow rate, and is kept at about 14%, which is consistent with the percentage of the tower bottom wall in the total surface area of the tower body. It can ensure that enough gas media return to the tower bottom and promote gas convection. The 90% residence time of two-stage swirler increases linearly with the increase of gas mass flow rate. In general, the swirling effect of the two-stage swirler is better than that of the other two swirlers, and this study provides a reference for the optimization design of swirl device of internal combustion integral heat treatment process.