Methods and systems for promoting hydrogen gas distribution within cellulosic biomass solids during hydrothermal digestion

A biomass conversion system comprising:

• a hydrothermal digestion unit;
• a plurality of spaced apart fluid inlets vertically disposed about the height of the hydrothermal digestion unit;
• and
• a gas recirculation line configured to remove a gas from the hydrothermal digestion unit and return at least a portion of the gas to the hydrothermal digestion unit via the plurality of spaced apart fluid inlets, the gas recirculation line being fluidly connected to the plurality of spaced apart fluid inlets.

A biomass conversion system comprising:

• a hydrothermal digestion unit;
• a plurality of spaced apart fluid inlets vertically disposed about the height of the hydrothermal digestion unit;
• and
• a fluid recirculation line configured to remove a mixture of a liquid and a gas from the hydrothermal digestion unit and return at least a portion of the gas to the hydrothermal digestion unit via the plurality of spaced apart fluid inlets, the fluid recirculation line being fluidly connected to the plurality of spaced apart fluid inlets.