same time the aqueous sodium hydroxide solution entering via the opening 6 is finely atomized mechanically by the blades 9 of the rotor 8 which also provide for immediate centrifugation of the extremely small droplets obtained these are introduced in this way into the thin tubular dynamic layer of straw particles with which they can 34 interact 34 the sodium hydroxide solution introduced in atomized form via the openings 10 further increases the interaction of the digesting agent with the straw particles after a residence time of about 40 seconds in the turboreactor 1 the reaction product consisting of a mixture of cellulose fibres and of spent digesting agent is continuously discharged from the opening 7 the reaction product is continuously fed to the turboreactor b of 350 mm internal diameter through the opening 105 in cocurrent with a flow of steam at a pressure of 3 5 bar and at a rate of 40 kg h in the turboreactor b the wall temperature is controlled at a value of 260 u00b0 c while the speed of the bladed rotor is maintained at a constant 700 rpm in this second turboreactor b the interaction between the sodium hydroxide and the straw particles is completed and the subsequent separation of the cellulose fibres from the black liquor is facilitated the constituents of the straw in particular the lignin which tend to encrust the cellulose being maintained in a softened state owing to the flow of steam after a residence time of about 6 minutes a product consisting essentially of cellulose and a black liquor consisting of a solution.