Systems having digestion units with capability for loading cellulosic biomass under high pressure and associated methods for cellulosic biomass processing

A method comprising:

• providing biomass conversion system comprising:
• a first digestion unit and a second digestion unit that are operatively connected to one another;
• a fluid circulation loop establishing fluid communication between an outlet of the first digestion unit and an inlet of the second digestion unit;
• and
• a bypass line establishing fluid communication between an outlet of the second digestion unit and the fluid circulation loop;
• at least partially digesting a cellulosic biomass in, optionally, the first digestion unit and the second digestion unit, thereby forming a hydrolysate comprising soluble carbohydrates within a liquor phase;
• isolating the first digestion unit from the second digestion unit and then at least partially depressurizing the first digestion unit;
• after at least partially depressurizing the first digestion unit and while digestion continues in the second digestion unit, loading the first digestion unit with a cellulosic biomass, and re-pressurizing the first digestion unit to a pressure less than or equal to a pressure in the second digestion unit;
• and
• after re-pressurizing the first digestion unit, transferring at least a portion of the cellulosic biomass from the first digestion unit to the second digestion unit.

A method comprising:

• at least partially digesting a cellulosic biomass contained in, optionally, a first digestion unit and a second digestion unit to produce a hydrolysate comprising soluble carbohydrates in a liquor phase, the first digestion unit and the second digestion unit being operatively connected to one another;
• circulating the liquor phase from the first digestion unit to the second digestion unit through a fluid circulation loop establishing fluid communication between an outlet of the first digestion unit and an inlet of the second digestion unit;
• isolating the first digestion unit from the second digestion unit, such that the liquor phase continues to flow through the second digestion unit to the fluid circulation loop via a bypass line establishing fluid communication between an outlet of the second digestion unit and the fluid circulation loop;
• while hydrolysis continues in the second digestion unit, adding a cellulosic biomass to the first digestion unit and pressurizing the first digestion unit to a pressure that is less than or equal to a pressure in the second digestion unit;
• equalizing the pressure between the first digestion unit and the second digestion unit;
• and
• transferring at least a portion of the cellulosic biomass from the first digestion unit to the second digestion unit.