GB828909A - Steaming and pulping fibrous material - Google Patents

Abstract

<PICT:0828909/IV (a)/1> Wood chips and like fibrous materials are subjected in a pressure vessel to treatment with steam under pressure in the absence of air, whereafter the pressure is reduced, but not completely released, and the material is treated with a cooking liquor and then discharged from the vessel, a superatmospheric pressure being maintained throughout the process. As shown, during the charging of fibrous material, e.g. wood chips, to the pressure vessel, valves 24, 27 are open and steam under pressure entering via valve 29 causes expulsion of air from the apparatus. Valves 24, 27 are closed when the charging of fibrous material is complete and steam pressure within the vessel rises rapidly, but preferably does not exceed 300 p.s.i. After a predetermined interval, e.g. up to five minutes, valve 27 is opened and the pressure in the vessel is rapidly reduced, say to 5-25 p.s.i.g., although a superatmospheric pressure is still maintained. Cooking liquor is drawn into the vessel by way of reservoir 33, placed under pressure and absorbed by the fibrous material. Following impregnation, the material can be cooked in the presence of free liquor or the latter may be evacuated and cooking conducted in the "vapour phase." Discharge of the cooked material is effected by opening valve 26.