Reuse of vapour condensate of caustic soda recovery plant

 

Technical description

 

In some woven fabric textile finishing industries where mercerization process is carried out extensively, Caustic Soda Recovery Plant (CRP) is installed to recover caustic soda from the mercerization process. The purpose of the CRP is to concentrate dilute caustic soda solution (weak lye) of 5 to 10 oBé concentration discharged from the mercerization machines into 20-25 oBé concentration by evaporating water from the weak lye through evaporators. The vapors from weak lye is condensed into hot water through condensers. This hot water is at a high temperature of about 60 to 80oC with alkaline pH. Generally, this hot alkaline water is wasted in the industry.

This water can be collected and reused (see Figure 1) as:

  • Washing water for post mercerization washes
  • Pre and post washes of continuous textile pretreatment machines (desizing, scouring and bleaching)
  • Dilution water for caustic soda solution from 50 oBé to 25 oBé.

Figure 1: Vapor condensate from CRP is collected at over ground tank and then supplied to the pretreatment machine for post bleaching washing

 Achieved environmental benefits

  • Water conservation
  • Reduction in thermal energy (hot water will require less steam for heating, in case if this water is used as hot washes)
  • Reduction in greenhouse gases 
  • Reduction in hydraulic load of wastewater treatment plant

Operational data

The quantity of this water varies from 30 to 75 m3/day or 9,000 to 22,500 m3/year. The value of this hot water is about USD 10,660 to USD 26,660/yr (Rs. 1.6 to 4 million/year).

Cross media effects

No relevant cross media effect is known.

Technical considerations relevant to applicability

This measure is applicable to all the woven fabric textile finishing industries where CRP is installed to concentrate dilute caustic soda solution from mercerization machine. This measure does not require any major intervention in the process, no major infrastructure development and no technical human resource requirement. The vapor condensate will be collected in an over ground or underground tank. This tank will be attached with small pump and discharge pipeline. The discharge pipeline will be connected to multiple machines/sources with valves where this water is intended to be reused. In case of water requirement to specific machine, the valve for that machine or source will be opened for the water supply. The storage tank and pipelines will be insulated to avoid convectional and radiation energy losses into the atmosphere.

Economics

Capital cost for the tank, pump, pipeline and valves = USD 2,000 – 3,330 (Rs. 300,000 – 500,000)

Annual saving = USD 10,660 to 26,660 (Rs. 1.6 to 4 million)

Annual O&M cost = USD 1,330 – 2,660 (Rs. 200,000 - 400,000)

Simple payback period = 2 - 3 months

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

Driving force for implementation 

  • Financial benefits
  • Resource conservation
  • Sustainability of textile business

Reference industry

  • Kohinoor Mills Limited Dyeing Division), Raiwind Manga Road, Lahore
  • Sarena Textile Industry Pvt. Ltd, Sheikhupura Road, Lahore


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