Coal to substitute natural gas based on combined coal-steam gasification and one-step methanation

In the face of the requirement of clean coal utilization and greenhouse gas emission reduction, coal to substitute natural gas (SNG) production attracts increasing attention worldwide. This work proposed a coal-to-SNG process, which combines a high-efficiency coal-steam gasification and one-step methanation. Through regenerative unit, the sensible heat of the syngas can be recovered via the oxidant steam and then finally converted into chemical energy of syngas, and thereby the cold gas efficiency can be 8.8 percentage points higher than the traditional GE gasification. The HZ/CO mole ratio of syngas leaving the gasifier is about 1.2 which can be used for one-step methanation directly and the traditional water gas shift process can be eliminated. Simulation and thermodynamic analysis of the whole plant are presented, and the experimental study of coke-steam gasification is carried out in a fixed bed reactor. Preliminary experiments show that when gasification temperature is higher than 1000 degrees C, the H-2/CO ratio of the syngas is approximately 1.3-1.4. Thermodynamic analysis shows that the SNG conversion efficiency of the proposed process increases from 61.3% to 71.7% and the energy consumption for SNG product has been reduced from 84 GJ/t to 60.5 GJ/t, mainly due to the cold gas efficiency enhancement of gasification and elimination of water gas shift process. Besides, through the one-step methanation, the concentration of CO2 before CO2 separation unit increases from 31.1% to 43.2%, and the unit energy consumption in the CO2 capture decreases from 15.3 kJ/mol to 11.7 kJ/mol.