The authors have modeled turbulent combustion of natural gas in the reverse flame of fire-tube boiler using the ANSYS Fluent 12.1.4. The complete geometric model of the dead-end furnace based on boiler drawings was considered. Finite element model was used for the following processes and phenomena: the combustion of methane in air oxygen, radiant and convective heat transfer, turbulence. Aerodynamic structure and volumetric pressure fields of the flame were calculated for different degrees of spin-fuel jet. The effect of the twist parameter on a drag coefficient of dead-end furnace was estimated. The authors calculated critical twist parameter values when the disruption of the flow and reversal currents zone in the axial region occurs. The results are presented in graphical form.