Reuse of water lock water from steamers

 

Technical description

 

In the woven fabric textile finishing industry, continuous pretreatment and pad steam dyeing machines are used for pretreatment (desizing, scouring, bleaching) and dyeing of the fabric respectively. These machines are equipped with steamers (generally at the top) for heating the fabric and giving reaction time for the completion of the process (scouring/bleaching/dyeing). In the pretreatment machine where the scouring and bleaching process is carried out separately, there are two steamers (one after the scouring impregnator and the other after the bleaching impregnator) and for the pretreatment machine where the scouring and bleaching process is carried out simultaneously in the same impregnator, there is only one steamer.

In many cases, there is a continuous supply and wastage of fresh water at the fabric exit point of the steamer. This water is supplied to maintain a water lock so that the steam vapors cannot escape from the steamer along with the fabric into the atmosphere (loss of steam and increase of humidity of the environment) (see Figure 1 as an example). This is relatively a clean water stream that can be collected and reused at the wash boxes of the same machine.

Achieved environmental benefits:

  • Water conservation
  • Reduction in the hydraulic load of the wastewater treatment plant

Operational data:

The quantity of water lock water will vary from industry to industry depending upon the type of the pretreatment machine employed, and the production of the bleached and dyed fabric. Its quantity is in the range of 90 to 115 m3/day (29,070 - 37,145 m3/year). Its value is USD 3,860 to 4,930 (Rs. 0.58 to 0.74 million/year).

The implementation cost will be nominal as the discharge point of this water lock water will be directly connected to the wash boxes of the same machine.

Cross-media effects:

No relevant cross-media effect is known.

Technical considerations relevant to applicability:

This measure is applicable to all the woven fabric finishing industries where continuous pretreatment and pad steam dyeing machines are installed. This measure does not require any intervention in the process, no major infrastructure development, and no technical human resource requirement. The water lock water will be directly diverted to the wash boxes of the same machine.

Note: In principle, there are two types of dyestuffs applied for continuous dyeing of cotton or cotton/polyester woven fabric at pad steam dyeing machines: reactive and vat dyes. For dark shade reactive dyed fabric, this water lock water is generally contaminated with dyes whereas for vat dyed fabric, this water is relatively clean; the same is true for light shades with reactive dyes. In case water is contaminated due to dark shade reactive dyes, it should be discarded.

Economics:

Capital cost = Nominal

Annual saving = USD 3,860 to 4,930 (Rs. 0.58 - 0.74 million)

Annual O&M cost = Nil

Simple payback period = Few days

Additional benefits will be the reduction in hydraulic load and treatment cost of the wastewater treatment plant.

Driving force for implementation:

  • Financial benefits
  • Resource conservation
  • Sustainability of textile business

Reference industry:

All the woven fabric textile finishing industries where pretreatment and pad steam dyeing machines are installed.


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