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Caustic Recovery Plants

Caustic Recovery Plants

A Caustic Recovery Plant is typically a multiple effect evaporation plant which will re-concentrate the weak lye by heating it in heat exchanger and when it reaches evaporator, vapour is released due to water evaporation that increases its concentration. This process is repeats itself by circulation in caustic recovery plant till the desired concentration is reached. Textile Mills involved in mercerizing of (Yarn, Woven, Knitted, Denim) cotton use caustic (NaOH) in mercerizing machines. After process in mercerizing machine this dilute caustic soda solutions come out from mercerizing machines as drain. The density of drain dilute caustic solution varies from 3% to 8% (31 to 87 gm/lt). The drained weak lye also causes financial loss not only by removal but also by process incurred to remove it, i.e. expense incurred in treating (neutralizing) at ETP as per pollution laws.


1) The system re-concentrates weak caustic lye from 40 to 50 gmfitr to 250 to 450 gmIltr as required by the process viz. dry-in-wet or wet-in-wet mercerizing.

2) Fresh caustic in the process is required only for concentration variation and make-up.

3) Payback period of the Plant is less than 4 months for a Triple Effect Caustic Recovery plant with Surface Condenser and Thermo-compressor.

4) The energy of heating steam can be completely transformed into hot water. Hot Water is generated at:
- The uncontaminated steam condensate from the first heat exchanger may be reused as boiler feed water.
- At surface condenser hot water is generated by soft water feed to the surface condenser for cooling vapour of the last effect.
- The result is eventually soft water of a high temperature, which saves cost in water softening before use in mercerizing machines .
- Alkaline condensate is generated as the vapour condensate, which can be used as hot wash water in the mercerizing machines.

5) Financial savings in neutralizing agents and waste water treatment costs.

Caustic Recovery Plant


It removes lint, fluff, and other fibre from wash liquor. This improves the efficiency of plant by reducing the fouling of heat transfer material.

It is basically a vibrating screen device with S.S. Screen of 100 mesh and an electric motor with eccentric load to generate vibration. This removes the solid from wash liquor and is collected for disposal. It is an automatic working device, not requiring any human intervention.


Different types of impurities are left in the lye during the mercerizing process like oils, paraffin, sizes and starches. Hydrogen Peroxide being a strong oxidizing agent reacts with OH-groups of organic materials. The lye viscosity is reduced and impurities float to the top and sludge sink down in the tank. Synthetic sizes cannot be removed by this process.

Specifically designed mixing and dosing tanks are provided for maximizing the residence time in settling tank with intricate baffles and piping inside to remove the floating impurities as well as settled sludge. This treatment also bleaches the dirt and reactive dye particals finely distributed in the lye. The exact peroxide dosage is set during plant operation and varied periodically.

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