NOVELTY - Hydrothermal synthetic natural gas (SNG) production from carbon containing substrate, comprises: generating a pumpable slurry, pressuring and heating the slurry at 50 bar and 200 degrees C; gasifying the hydrolyzed slurry; performing liquid-vapor (LV) separation and gas separation at high pressure; for the liquid stream, liquid expanding with or without power recovery or evaporating and turbine expanding followed by LV separation; and valve expanding/reheating and turbine expanding of the vapor stream followed by combustion and expansion in a turbine; and waste water treating of the liquid stream.    USE - The process and the system are useful for the hydrothermal synthetic natural gas (SNG) production from carbon containing substrate (claimed) e.g. biomass and biomass waste, and industrial residues.    ADVANTAGE - The process is less expensive, has a more versatile process design particularly flexible with respect to the co-production of fuel and power, and exhibits increased robustness, increased thermal efficiency and prevents an expansion too far into the two-phase region.    DETAILED DESCRIPTION - Hydrothermal synthetic natural gas (SNG) production from carbon containing substrate, comprises: (a) generating a pumpable slurry having a predetermined solids content as calculated in dry mass; (b) pressuring and heating the slurry at above 50 bar and 200 degrees C; (c) gasifying the hydrolyzed slurry, from which precipitated solids are optionally separated before and/or after the gasification; (d) performing liquid-vapor (LV) separation and gas separation at high pressure or lower pressure to generate a liquid stream and a vapor stream; (e) for the liquid stream, liquid expanding with or without power recovery or evaporating and turbine expanding followed by LV separation; (f) valve expanding or reheating and turbine expanding of the gasified crude product or vapor stream followed by combustion and expansion in a turbine, and/or electrochemical conversion to heat and/or power of the so-generated SNG gas and/or supply of the so-generated SNG gas to a gas grid; and (g) waste water treating of the liquid stream. An INDEPENDENT CLAIM is also included for a system, comprising means for generating the pumpable slurry, means for pressuring and heating the slurry, means for gasifying the hydrolyzed slurry, means for performing LV separation and gas separation, means (for the liquid stream) for the liquid expanding with or without power recovery or evaporating and turbine expanding followed by LV separation, and means for valve expanding or reheating and turbine expanding of the vapor stream.