Contributor, The Textile Industry and the Environment, UNEP

ANNEX C
• No aU1OQ1atic monitors are available to measure the concentration of impurities in the wash
water or on the fabric. Data on the effects of change must be gathered by painstaking laboratory
work.
• In the absence of other controls, the water flow is set to be sufficient for the most difficult
fabrics processed. It is generally changed for more easily washed fabrics. iA control was recently
introduced which allows automatic variation of wash water flow with the lb/hour of
fabric produced which assumes that the difficulty of washing is proponionaJ to the fabric weight,
something that is true for most fabric types.)
One valid way to reduce water flow is 10 use more efficient washers. Horizontal washers use about
one third 10 one quarter as much as vertical washers for the same washing job. Water and energy
use is reduced accordingly.
Reduce tbe number of water feeds:
a) Counterflow between stages
As stated earlier the standard open-width continuous bleach range has three separate water feeds.
Counterflowing water from the bleach washers to the caustic washers could eliminate 3,000 gal/hour
water feed and could save 2,600 Ib/hour steam. A mass energy balance of a typical bleach range
has shown that the total impurities in the bleach water when it is discharged are about 0.03 lb/gaJ
or 0.340/0 by weight. It is clean enough for re-use in the desize or caustic stages for most mills, and
many of them have recently begun to take advantage of this.
It is possible to recycle the same water through all ,hree stages but this is rarely done. Wash waler
used in both the bleach and caustic stages will contain around 1.3070 impurities by weight and its reuse
in desizing might lower efficiency tOo much. Coagulation of impurities due to cooling during
the counterflowing is another risk. In spite of the high incentive (6,000 gal/hour and 5,300 Ib
steam/hour) full counterflow is practiced on very few ranges.
b) Reduce the number of stages
Elimination of bleach range stages would save 3,100 gal/hour and 3,700 lb steam/hour. For this
lhere are three options:
I. Combining desize and caustic functions, something especially attractive for COlton polyester
blends because pYA desize can be removed by hot water washing and causlic muSI be kept
low to prOtecl the polyester. The system becomes in a sense a non-desize one. A small addition
of hydrogen peroxide stabilized with epsom salt can help remove PVA and other minor
sizing polymers which may be presenl.
2. Combining caustic and bleach functions. If the caustic is eliminated, the result is a desize
bleach system. Du Pont introduced this concept during the 1950s as the Solo Matic process.
The most popular configuration is rope desizing in bins followed by a single J-80x to perform
bot]l the caustic and bleaching stages. II is intended mainly for lightweight open weave
fabrics including soft-filled sheeting, polyester collon shirting and preparation for non-critical
dying. Its major limitations are development of absorbency and removal of motes, both of
which require strong caustic treatmen!.
The bleach bath in a desize bleach system uses a high alkali content and requi res sodium silicate
buffering to pH 10.8-11.00;
3. Single stage bleaching. The prospect of cutting out two stages is attractive. Present applications
include knit goods. bedsheets, terry cloth and lightweight polyester cotlon shirting.
There are very few open-width single-stage bleach ranges because of the limited steaming times
available. Few plants run corduroy and other fabrics for non-critical dyeing use on a single
stage range as results are often marginal. The conveyer steamer with 15-20 minutes steaming
ti me is of g,eatest interest here, although few such applications are currently running.
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