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Method for producing chemical pulp from hardwood chips

  • US 5,413,677 A
  • Filed: 04/05/1993
  • Issued: 05/09/1995
  • Est. Priority Date: 04/05/1993
  • Status: Expired due to Term
First Claim
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1. A method of producing chemical pulp from hardwood chips, using a vertical digester having a top and a bottom and a cooking zone, and a high pressure feeder, comprising the steps of continuously and substantially sequentially:

  • (a) steaming the hardwood chips;

    (b) entraining the hardwood chips in alkaline cooking liquor at a relatively cool temperature, so that the liquor will not significantly flash into steam in a high pressure feeder;

    (c) feeding the chips entrained in relatively cool liquor under high pressure to a point external of the top of the digester using the high pressure feeder;

    (d) at said point external of the digester, replacing the relatively cool liquor entraining the chips with relatively hot cooking liquor, at cooking temperature, and recirculating the replaced relatively cool liquor to the high pressure feeder, so as to thermally isolate the high pressure feeder from the digester;

    (e) feeding the hardwood chips entrained in cooking liquor at cooking temperature directly to the cooking zone at the top of the digester;

    (f) at the top of the digester, separating some liquor from the chips;

    (g) recirculating and reheating the liquor separated from the chips in step (f), to provide a significant part of the cooking liquor in step (d); and

    (h) cooking the chips in the digester in a cooking zone, to ultimately produce chemical hardwood pulp, and removing the hardwood pulp from the bottom of the digester.

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