| 摘要 |
A method and apparatus are provided for the treatment of comminuted cellulosic fibrous material to effect prehydrolysis, and then subsequently kraft digestion, thereof, to produce paper pulp. The material is steamed, entrained in liquid to form a suspension, and transferred by a high pressure feeder in a first circulation loop to the top of a first vertical vessel. At the top of the vessel, a liquid/solids separator is provided, and the liquid withdrawn from the top of the first vessel into the return conduit of the first circulation loop includes recoverable hydrolysate (which contains hemicellulose, sugars, and the like). In the first vessel, countercurrent acid hydrolysis takes place in the top of the vessel, and a countercurrent wash is effected in the bottom of the vessel. A part of the liquid in the return conduit of the first circulatory loop is diverted to one or more flash tanks, to produce steam and a liquid with a high concentration of hydrolysate. After hydrolysis and washing, the material is withdrawn from the bottom of the first vessel and passed through a second circulatory loop to the top of a kraft digester, preferably one having a steam phase at the top.
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