Appeal No. 2001-2443
Application 09/108,541
20. A pulp bleaching process for reducing total bleach plant effluent volume
which comprises treating a kraft brown stock pulp having a consistency of from about 20
to about 30% by weight and a Kappa number greater than about 25 for softwood and
greater than about 15 for hardwood as the first bleaching stage of an elemental
chlorine-free bleaching bleach sequence in an initial alkaline extraction stage assisted
by oxygen or oxygen and peroxide (initial EO or initial EOP stage) before a first chlorine
dioxide stage (D1) in an EOD1EOPD2 or EOPD1EOPD2 bleaching sequence which produces
a bleach plant effluent that is not recycled to a recovery boiler, wherein pulp is washed
after the D1 stage, after the D2 stage, and after the EOP stage to provide filtrates, at least
a portion of filtrate from the D2 stage contains chlorides and is recycled to a washer for
the EOP stage for washing pulp after the EOP stage to produce an EOP stage filtrate, at
least a portion of the EOP stage filtrate is recycled to the D1 stage for washing pulp after
the D1 stage to produce a D1 stage filtrate containing chlorides, and at least a portion of
the D1 stage filtrate is recycled to brown stock entering the initial EO or initial EOP stage
and mixed with the brown stock to adjust the consistency of the brown stock entering
the initial EO or initial EOP stage to from about 5 to about 10 wt.% and to effect treatment
of the D1 stage filtrate, and wherein pulp is washed after the initial EO or initial EOP stage
to produce an initial EO or initial EOP stage filtrate containing chlorides from at least the
D1 stage filtrate mixed with brown stock entering the initial EO or initial EOP stage, the
filtrate of which is in turn ultimately incorporated within the bleach plant effluent and
thereby not recycled to the recovery boilers.
THE REFERENCES
In rejecting the appealed claims under 35 U.S.C. §103(a), the Examiner relies on
the following references:
Maples et al. (Maples) 5,853,535 Dec. 29, 1998
(filed Nov. 7, 1994)
Carles et al. (Carles) 4,274,912 Jun. 23, 1981
Farley 3,719,552 Mar. 6, 1973
Samuelson 3,843,473 Oct. 22, 1974
Ibister et al., “The Closed Cycle Concept Kraft Mill at Great Lakes - An Advanced
Report,” Pulp & Paper Canada, June 1979, pp. T174-180 (Ibister).
Li et al., “The Effects of Alkaline Leaching on Pulp Bleachability and Physical
Properties,” Tappi, J., Vol. 76, No. 12, pages 159 - 166, Dec. 1993 (Li).
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