| Efficient Recovery and Reuse of Caustic Soda from Mercerizing Washwaters | India | Prior to 1985 | Full scale |
MANUFACTURE OF TEXTILES # 27
Background:
A plant floor study examined mercerizing machines and a caustic soda recovery plant in a textile mill in India. It was observed that only 75% of the caustic soda from washwaters was collected, compared to the normal 85%. Additionally, the caustic soda recovery plant recovered only 81% of the soda, as opposed to the normal 90%. Cleaner production measures were then used to correct the situation and minimize environmental impact as well as improve the economics of the process at the mill.
Cleaner Production Principle:
Process modification; Housekeeping.
Cleaner Production Application:
Based on the findings of the plant floor study, the following corrective steps were taken to improve the collection and recovery rates were:
| improve the efficiency of washing of the mercerized material, |
| improve the squeeze on the fabric to prevent high quantities of caustic being left on the fabric, |
| stop overflowing/leakage of dilute caustic soda solutions from the washing tank, and |
| stop seepage from the underground storage tanks. |
To improve the caustic recovery process the following steps were taken:
| improve the filtration of caustic soda solution prior to recovery, |
| descaling of the metallic tubes of the heat exchanger thereby improving the heat transfer coefficient in the recovery plant |
| increase the efficiency of vacuum obtained by the barometric condenser, and |
| improve the efficiency of removal of non-condensate gases from the evaporation body. |
Environmental and Economic Benefits:
Environmental benefit would include discharge of lower concentrations of caustic soda in the wastewater. Savings in caustic produced monetary benefits of Rs. 684,750 per year and improved the quality of the fabric.
No information was available on the investment costs.
A comparison of the operational and maintenance costs before and after implementation of the CP measure are as follows:
| Parameters | Before (kg) | After (kg) |
| Mercerizing production / day of fabric | 10,000 | 10,000 |
| Caustic soda input /day | 3,500 | 3,500 |
| Collection from washwaters | 2,630 | 2,975 |
| Reuse of dilute solutions in bleaching | 310 | 475 |
| Caustic soda recoverable | 2,320 | 2,500 |
| Recovery of caustic soda | 2,000 | 2,225 |
| Total caustic soda consumed in mercerizing (Total input less recovery/reuse) | 1,190 | 775 |
| Saving of caustic soda/day = 415 kg Savings per day = 2,282.50 rupees Savings per year = 684,750 rupees |
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Constraints:
None reported.
Contacts:
Type of Source Material: Conference proceedings
Citation : "Seminar on avenues for Cost Reduction in Chemical Processing of Textiles", held on February 26, 1985 by Bombay Textile Research Association, Bombay 400 086, BTRA No.06.3.1 Bombay Textile Research Association (BTRA) Member Mill, Bombay, India
Review Status:
This case study was originally compiled by the UNEP Working Group of Textiles. It underwent a UNEP IE funded technical review in 1994 for quality and completeness. It was edited for the ICPIC diskette in July of 1995. Subsequently it underwent a technical review in September 1998 by Dr. Prasad Modak, Environmental Management Centre, Mumbai, India.