CAUSTIC RECOVERY PLANT/CRP/CRU
DISTINCTIVE TRAITS
Integrated with Mercerizing Process
Seamlessly synchronized with mercerizing line operation for balanced Baume, stable lye quality, and zero interruption — proven at Nishat Mills.
Fast ROI — Within One Year
Investment pays back quickly through chemical and steam savings.
Hot Water & Energy Recovery
Condensate reuse delivers both water and heat energy savings across the plant.
Compact & Modular Design
High-Purity Output
Strong lye can be further refined with peroxide treatment for premium reuse.
Clean Condensate
Low-pH condensate reusable in bleaching or washing sections.
Local Manufacturing, Global Standards
Built in Pakistan under stringent international engineering standards.
Long Service Life — 30-Year Design
Performance-Based Consultancy
Environmentally Responsible
Complies with sustainability standards such as ZDHC and OEKO-TEX through waste minimization.
Product Outline
In the textile processing industry, particularly during the mercerizing process of cotton woven, knit, or yarn, the use of significant quantities of caustic soda is essential. For every kilogram of cotton, an approximate amount of 500 grams of 48Be caustic or 250 grams of 100% sodium hydroxide (NaOH) is required to facilitate the mercerization process. Subsequently, during the stabilizing phase, 84% of the sodium hydroxide is washed out, resulting in a weak lye with a 8Be,5.2% concentration.
Traditionally, this weak lye, having been drained into the sewer or directed to an effluent treatment plant for neutralization before disposal, represents a notable loss in terms of both resources and environmental impact. Addressing this challenge, RAFAE Engineering introduces a Caustic Recovery System designed to economically concentrate the purified weak lye. This innovative system not only minimizes waste but also facilitates the recycling of caustic soda and hot distilled water back into the mercerizing process.
A critical component of this integrated solution is the Weak Lye Concentration Control System, strategically installed to synchronize with the mercerizing machine. This control system ensures the optimized operation of the Caustic Recovery System, thereby maximizing the efficiency of the entire mercerizing process. In doing so, RAFAE Engineering not only contributes to resource conservation but also aligns with sustainable practices in the textile industry.
How it works:
The weak lye, 8 °Bé (5.2% NaOH), from the weak lye storage tank is re-concentrated to strong caustic soda, 30 °Bé (23.5% NaOH), in a multiple-stage evaporation plant. Steam from the boiler house is utilized only for the 1st stage. The further stages are heated by the off vapors created in the plant. The vapor (steam) generated in the 1st stage (water vapor evaporated from the caustic soda solution) is utilized to heat the 2nd evaporator, the vapor from the 2nd stage for heating the 3rd stage, and so on.
The system of evaporation applied is with natural circulation, with a vertical shell-and-tube evaporator and a separator (vessel for vapor/liquid phase separation). The steam from the boiler house condenses in the 1st stage without contact with caustic soda, and the condensate flows to the condensate piping system, back to the boiler house.
The vapor (steam) generated in the plant, by the evaporation of water from the caustic soda, condenses in the subsequent evaporators, in the pre-heaters, and in the condenser. This condensate – the distillate – normally has a pH value of 8-10 and can be utilized for washing/stabilizing in the mercerizer or for other uses. In the case of optional pH control, if the pH value of the distillate rises due to foam or other reasons, the distillate can be switched over to the sewer by the conductivity indicator and the actuated valves.
The re-concentrated caustic soda solution from the last stage separator is pumped to the sedimentation tank (precipitator). In the precipitator, solid impurities are separated from the caustic soda solution.
Particles lighter than the caustic soda specifically form a floating layer on top of the liquid, and an automatically operating cleaning device removes them periodically, directing them into the funnel leading to the sewer. Meanwhile, particles heavier than caustic soda sink to the bottom, creating sediment (sludge) in the lower part of the precipitator. The operator needs to drain this sediment periodically, with the frequency of draining intervals depending on the level of impurities in the re-concentrated caustic soda.
The cleaned caustic soda is then led by gravitation through an overflow tube to the tank for recovered caustic soda. From this storage tank, the recovered caustic soda is pumped to the mercerizing machine or other users.