NOVELTY - Biomass conversion system (100) comprises first (104) and second (106) digestion units connected to one another; pressure isolation mechanism between digestion units; fluid circulation loop (110) for fluid communication between outlet of first digestion unit and inlet of second digestion unit; and bypass line (112) establishing fluid communication between outlet of second digestion unit and fluid circulation loop. The system further comprises catalytic reduction reactor unit comprising at least one catalyst which is capable of activating molecular hydrogen; and the loading mechanism.    USE - For processing cellulosic biomass such as wood, to provide biofuel; also to produce jet fuel.    ADVANTAGE - The systems allows cellulosic biomass to be efficiently digested to form soluble carbohydrates, which may subsequently be converted through catalytic reduction reactions e.g. hydrogenolysis and/or hydrogenation into reaction products comprising oxygenated intermediates that may be further processed into higher hydrocarbons. The higher hydrocarbons can be useful in forming industrial chemicals and transportation fuels i.e. biofuel, including e.g. synthetic gasoline, diesel fuels and jet fuels. The ability to continuously or semi-continuously feed pressurized digestion unit can be advantageous in terms of time, energy and cost savings, and thus fresh biomass introduction can take place more frequently than would otherwise be possible. The system is designed to favor high conversion of biomass into soluble carbohydrates under high pressure (of about 30 bar or more); also enables high conversion rates by minimizing the formation of degradation products during processing of biomass. The loading mechanism provides better heat integration, thus improving the overall energy efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method involving partially digesting cellulosic biomass in first or second digestion units, and forming hydrolysate comprising soluble carbohydrates within liquor phase; isolating first digestion unit from second unit and then partially depressurizing first digestion unit; after depressurizing the first unit and while digestion continues in second digestion unit, loading first digestion unit with cellulosic biomass, and re-pressurizing first unit to pressure less than or equal to pressure in second unit; and after re-pressurizing the first unit, transferring at least portion of cellulosic biomass from first unit to second unit.    DESCRIPTION OF DRAWING(S) - The figure shows schematic diagram of biomass conversion system having combined digestion unit/pressurization zone.    Biomass conversion system (100)    First digestion unit (104)    Second digestion unit (106)    Fluid circulation loop (110)    Bypass line (112)