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Water conservation for textile mills
Water is expensive to buy, treat, and dispose. If your firm
does not have a water conservation program, you are pouring money down the drain.
A water conservation program can cut water consumption by up to 30 percent
or more, and the cost savings can pay for the required materials in a very short
time. For example, at average water and sewage rates of about $2 per 1,000 gallons,
a reduction of the flow to the washers by just 1 gallon per minute can save
$250 per year. Since the average plant has a large number of washers, the savings
can add up to thousands of dollars per year.
Numerous methods have been developed to conserve water at textile mills. The
sections below discuss some of the techniques applicable to a wide variety of
firms.
Counter-Current Washing
For both water and energy savings, counter-current washing is employed frequently
on continuous preparation and dye ranges. Clean water enters at the final wash
box and flows counter to the movement of the fabric through the wash boxes.
Thus, when the fabric enters the actual wash process, the most contaminated
wash water contacts it first, and, later, the cleanest water contacts the cleanest
fabric.
This method of water reuse is contrary to the traditional method of providing
clean water at every stage of the wash cycle. Water and energy savings are related
to the number of boxes provided with the counterflow. Counter-current washing
can be applied at desize washers, scour washers, mercerizing washers, bleach
washers, dye ranges, and printhouse soaper ranges.
Reuse of final rinse water from dyeing for dye bath make-up
The rinse water from the final rinse in a batch dyeing operation is fairly clean
and can be used directly for further rinsing or to make up subsequent dye baths.
Several woven fabric and carpet mills use this rinse water for dye bath make-up.
Reuse of soaper wastewater
The colored wastewater from the soaping operation can be reused at the backgrey
washer, which does not require water of a very high quality. Alternatively,
the wastewater can be used for cleaning floors and equipment in the print and
color shop.
Reuse of scouring rinses for desizing
The rinse water from the scouring operation is adequate for reuse in other processes
such as desizing that do not require water of an extremely high quality. This
reuse is particularly true with scouring wastes from synthetic or cotton/synthetic
blend fabrics. Scouring rinses may, in certain cases, also be reused to wash
floors and equipment.
Reuse of mercerizing or bleach wash water for scouring
or desizing
Mercerizing or bleaching rinse water can be used in scouring and desizing operations
as long as size recovery is not practiced. Generally, the caustic or bleach
stream will degrade many size compounds to an extent that they cannot be recovered.
Recycle/reuse of water jet weaving wastewater
The jet weaving wastewater can be reused within the jet looms. Alternatively,
it can be reused in the desizing or scouring process, provided that fabric impurities
and oils are removed by in-line filters.
Use of automatic shut-off valves
An automatic shut-off valve set to time, level, or temperature will control
the flow of water into a process unit. One plant estimated that a reduction
in water use of up to 20 per cent could be achieved with thermally controlled
shut-off valves.
Use of flow control valves
A flow- or pressure-reduction valve can reduce the quantity of water used in
a wash or clean-up step. These valves are particularly useful in cleaning areas
where operators are not always aware of the need for water conservation.
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