NOVELTY - Distributing a slurry catalyst in cellulosic biomass solids, comprises: providing cellulosic biomass solids in a digestion solvent; heating the cellulosic biomass solids and the digestion solvent to form a phenolics liquid phase comprising lignin and an aqueous phase comprising an alcoholic component derived from the cellulosic biomass solids; conveying at least a portion of the phenolics liquid phase and the slurry catalyst in it to a location above at least a portion of the cellulosic biomass solids; and releasing them such that they come in contact with the cellulosic biomass solids.    USE - The method is useful for distributing a slurry catalyst in cellulosic biomass solids (claimed), which are useful for the production of fuel blends.    ADVANTAGE - The method ensures: adequate slurry catalyst distribution, thus reducing thermal gradients that may occur during hydrothermal digestion; and more rapid digestion and efficient conversion rate of cellulosic biomass into fuel blends under elevated temperature and pressure conditions with less energy consumption and reduced loss in catalytic activity of slurry catalyst in an economical manner.    DETAILED DESCRIPTION - Distributing a slurry catalyst in cellulosic biomass solids, comprises: providing cellulosic biomass solids in a digestion solvent; heating the cellulosic biomass solids and the digestion solvent in the presence of molecular hydrogen and a slurry catalyst capable of activating molecular hydrogen to form a phenolics liquid phase comprising lignin, an aqueous phase comprising an alcoholic component derived from the cellulosic biomass solids, and an optional light organics phase, where the slurry catalyst is distributed in the cellulosic biomass solids and at least a portion of the slurry catalyst accumulates in the phenolics liquid phase as it forms; conveying at least a portion of the phenolics liquid phase and the slurry catalyst in it to a location above at least a portion of the cellulosic biomass solids; and after conveying the phenolics liquid phase and the slurry catalyst, releasing them such that they come in contact with the cellulosic biomass solids. An INDEPENDENT CLAIM is included for a biomass conversion system (1) comprising: a hydrothermal digestion unit (2); a first fluid conduit configured to remove a first fluid from an upper portion of the hydrothermal digestion unit and return the first fluid to a lower portion of the hydrothermal digestion unit; and a second fluid conduit configured to remove a second fluid from a lower portion of the hydrothermal digestion unit and return the second fluid to an upper portion of the hydrothermal digestion unit.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a biomass conversion system.    Biomass conversion system (1)    Hydrothermal digestion unit (2)    Gas inlet line (9)    Fluid return line (11)    Fluid conduit (15)    Drying unit. (24)