A theoretical analysis was made for the energy saving process of syngas methanation with reaction heat carried by steam recycling generated from waste heat. Calculations of the main parameters demonstrated that the heat carrying capacity was proportional to the parameter H

the molar ratio of steam to other components in the syngas mixture. From heat and mass transfer taking place in the coupled evaporation and condensation two-phase flow

H could reach the value of 3.0—4.0. Consequently the adiabatic temperature run-up in the catalytic methanation reactor could be controlled within 300—400℃. The energy efficiency of the process could be improved by over 6% because of omitting the mechanical compressor for recycling of process fluid. The experimental results obtained in a tubular reactor indicated that the performance of methanation catalyst remained the same owing to the high value of steam content.