GB910001A - Improvements in or relating to the cooking of lignocellulose fibrous material - Google Patents

Abstract

<PICT:0910001/IV(a)/1> Lignocellulosic fibrous material is treated with steam, mechanically compressed to remove liquid and air from the pores of the material, allowed to expand while immersed below the surface of a chemical solution, which applies a hydrostatic over-pressure to the material, cooked in a steam phase at superatmospheric pressure and corresponding temperature, and then cooked in a second chemical solution under substantially the same pressure as in the steam phase. The initial steam treatment may be effected at substantially 100 DEG C. and in the different cooking steps the material may be impregnated with solutions of chemicals of different composition. Preferably cooking a first time in the steam phase and in the liquid phase and a second time in the steam phase is effected while the material is contained within one and the same closed system. Thus the first cooking step in the steam phase may be effected within a container during downwardly directed movement of the material and the cooking step in the liquid phase effected during movement of the material in the same direction in the container and also during an upwardly-directed movement of the material in a second container communicating with the first container at the base of the latter, the second cooking step in the steam phase being effected in the top portion of the second container during upwardly-directed movement of the material within the second container. The material may be disintegrated mechanically while still under the superatmospheric pressure and elevated temperature produced by the cooking steps. Apparatus as shown comprises a plurality of vertical elongated containers 10, 36, 64, 98 traversed in series by the material and including a first container 10 fed with steam via pipe 24 for softening the material, which enters via duct 20, a second container 36 for a solution of chemicals (supplied from 38) within which the material is allowed to expand at a great depth after having been mechanically compressed by a pressing device 30 at a very high pressure in its travel between the two containers and means (56, 58 and cell feeder 62) to transfer the material from the second container to the upper part of a third container 64 intercommunicating with a fourth container 98 at their bases and forming together with the latter a closed system having a supply pipe 80 for steam at superatmospheric pressure, a supply duct 76 for a solution of chemicals and control members 84, 88 to maintain a predetermined level of the solution within these containers, whereby the material is subjected during downwardly directed movement within the third container to an initial cooking operation within a steam zone and to a subsequent cooking operation in a liquid zone, the latter operation also extending into the lower part of the fourth container provided with means 100 for conveying the material upwardly to a steam zone in its upper part. Chemical treatment of the material is conventional, varying according to the intended use of the product. Cooking solutions specified include mixtures of sodium sulphite with either sodium carbonate or sodium hydroxide and sodium sulphide and sodium sulphite solutions. Specification 761,179 is referred to.