Appeal No. 2001-2443
Application 09/108,541
CLAIMS
Claims 1, 11, and 20 are representative of the claims on appeal and read as
follows:
1. A method for bleaching a kraft brown stock pulp in a multi-stage elemental
chlorine-free bleach sequence which comprises treating the brown stock as the first
bleaching stage in the sequence with an initial alkaline extraction stage assisted by
oxygen or oxygen and peroxide (EO or EOP) before a first chlorine dioxide stage (D1) in
an EOD1EOPD2 or EOPD1EOPD2 bleaching sequence which produces a bleach plant
effluent which that is not recycled to a recovery boiler, wherein pulp from the D1 and D2
stages is washed after the stages to produce a D1 and D2 stage filtrate containing
chlorides and pulp from the initial EO or initial EOP stage is washed after the stage to
produce an initial EO or initial EOP stage filtrate and wherein at least a portion of the D1
and/or D2 stage filtrate is treated and the consistency of the brown stock entering the
initial EO or EOP stage is reduced by recycling the D1 and/or D2 stage filtrate to the initial
EO or initial EOP stage and mixing the recycled D1 and or D2 stage filtrate with brown
stock entering the initial EO or initial EOP stage so that treated D1 and/or D2 stage filtrate
is incorporated within the initial EO or initial EOP stage filtrate which in turn is ultimately
incorporated into the bleach plant effluent and thereby not recycled to the recovery
boiler, whereby the bleach plant effluent has a substantially reduced AOX, COD and
color relative to such effluent in the absence of such recycling.
11. A process for bleaching a kraft brown stock pulp in a multi-stage elemental
chlorine-free bleach sequence wherein the pulp has a consistency in the range of from
about 25% to about 30% and a pH in the range of from about 3 to about 11 which
comprises treating the brown stock pulp as the first bleaching stage in a bleaching
sequence with 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 from the first chlorine dioxide
stage D1 is washed in a pulp washer to produce a D1 stage filtrate containing chlorides,
and pulp from the initial EO or initial EOP stage is washed after the stage to produce an
initial EO or initial EOP stage filtrate, and at least a portion of the D1 stage filtrate is
treated and the consistency of the brown stock entering the initial EO or initial EOP stage
is reduced by recycling the D1 stage filtrate to the initial EO or EOP stage and mixing the
D1 stage filtrate with brown stock entering the initial EO or initial EOP stage so that the
treated D1 stage filtrate is incorporated with the initial EO or initial EOP stage filtrate which
is in turn incorporated within the bleach plant effluent and thereby nor recycled to the
recovery boiler, substantially all filtrates from later bleaching and extraction stages being
recycled to earlier stages of the bleaching sequence and ultimately incorporated with
the bleach plant effluent and thereby not recycled to a recovery boiler.
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