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CASE STUDIES- 6

CLEANER PRODUCTION CASE STUDY IN DYE MANUFACTURING

1. INTRODUCTION
2. PROCESS DESCRIPTION
3. STUDY FOCUS AREA:
4. WASTE ASSESSMENT:
5. CP OPPORTUNITIES THAT REDUCED ENVRIONMENTAL LOAD AND ACCRUED ECONOMIC BENEFITS:
6. POLLUTION STATUS BEFORE AND AFTER CP IMPLEMENTATION:




1. INTRODUCTION

This is a case of M/s. Dintex Dyechem Ltd located in Vatva Industrial Estate of Ahemdabad. The unit is engaged in manufacturing 150 tons per month of Vinyl sulfone ( Known chemically as Para amino Phenyl B-Hydoxy Ethyl Sulfate Ester).

This product is listed in the nine restricted items generating high and toxic pollution declared by the government, in 1996-97. The units producing this product were being increasingly monitored by regulatory agencies regarding the pollutant discharges.

This case represent the WM means adopted by the industry to reduce the environmental load but also conserving resources like raw material, energy etc.

2. PROCESS DESCRIPTION
Vinyl sulfone is manufactured from acetanilide. The production processes involves unit processes like sulfonation, drowning, reduction, condensation and esterification reactions and unit operations like filtration, drying, pulverizing and blending. The total process takes about 136 hours for completion.

Acetanilide is sulfonated with chloro-sulfonic acid in a sulfonation reactor. The reaction is exothermic. The temperature is maintained at 50oC for the reaction time of 4 hours. The product is then cooled to about 28 oC and dumped in ice to get acetyl sulfonyl chloride precipitate. The precipitate is separated by filtration in a neutsch filter. The product cake is given chilled water wash to remove the acid traces from the cake. The washed cake is then charged into the reactor containing sodium bi-sulfite slurry for reduction. The pH is maintained at 7.0 and the temperature is maintained at 50 oC for the reaction time of 4 hours. The reduced mass is passed through a filter press to remove the suspendable impurities and then taken in a next reactor for condensation.

Ethylene oxide is added to the reactor at a controlled feed rate for its reaction with reduced mass. A reaction time of 4hrs is allowed after the addition. The temperature is maintained at 55 oC during the reaction. The pH is maintained at 7.0 both during the addition and reaction by the dilute sulfuric acid. The condensed mass is then filtered in neutsch filter. The cake is given hot water washes in order to remove the salt impurities from the cake. The washed cake is centrifuged and flash dried. The dried product is then reacted with sulfuric acid in an esterification reactor. The temperature in the reactor is maintained at 150 oC for 3hrs to get vinyl sulfone product. The product is then pulverized, blended and packed.

3. STUDY FOCUS AREA:

The dye and dye intermediate industry is characterised by complex process chemistry. Since the Government has listed this product in the nine restricted items generating high and toxic pollution the unit as a first step has concentrated on recovery of by products from waste streams to reduce pollution load to the environment.

4. WASTE ASSESSMENT:

A waste assessment study was conducted to assess the existing pollutant load and the scope for reducing the load. The pollutant load generated per ton of product is given below:

S.No Parameter Quantity
1. Waste water generation 18.6 m3//ton
2. COD load 668 Kg/ton
3. BOD load 230 Kg/ton
4. Filter press waste 19 Kg/ton
5. ETP sludge 3400 Kg/ton


5. CP OPPORTUNITIES THAT REDUCED ENVRIONMENTAL LOAD AND ACCRUED ECONOMIC BENEFITS:

Based on the waste assessment study the unit identified ways and means to reduce waste. The most significant CP opportunities that are identified and implemented are as follows:

1. HCl gases are generated during sulfonation. To extract these gases the existing scrubber system is modified and two packed bed scrubbers are installed. A fan is also installed for sucking out gas through the scrubber system. In the first scrubber HCl is scrubbed with water along with cooling to recover HCl. The second scrubber acts as polishing scrubber in which scrubbing is done by dilute caustic soda to enable the industry to meet regulatory norms. The implementation of this recovery option has yielded following benefits:

Additional Acid recovered = 97 Tons/annum
Investment = Rs. 1,02,000/
Operational cost = Rs. 1,70,000/ per annum
Savings due to acid recovery = Rs 2,91,000/ per annum (@ Rs3/Kg of HCl)
Savings due to reduced treatment = Rs. 4,45,000/ per annum (@ Rs 7/Kg of NaoH)
Net savings = Rs.5,67,000 per annum.
Pay back period = About 3 months

2. The mother liquor stream and first wash liquor stream generated from the neutsch filter's acidity is about 17% and contains 1% sulfanilic acid. However, it was found that if acid concentration is more than 60% it can be sold in the market.

A multiple effect evaporator was installed to concentrate the acid. This system was not only able to concentrate the acid streams but also able to separate the sulfanilic acid from the waste as well as generating 65-70% concentrated sulfuric acid.

Sulfanilic Acid recovered = 105Tons/annum
Sulfuric acid recovered = 1680Tons/annum
Reduction in water consumption = 30,000 m3/annum
(due to avoidance of lime slurry preparation)
Investment = Rs. 90,00,000/
Operational cost = Rs. 95,50,000/ per annum

Savings due to acid recovery = Rs 73,50,000 / per annum
(@ Rs4/Kg of sulfuric acid and @ Rs 6/Kg sulfanilic acid)
Savings due to reduced treatment = Rs.1,08,00,000 / per annum (@ Rs 3/Kg of lime)
Net savings = Rs.86,00,000 per annum.
Pay back period = About 13 months

3. Waste stream from condensation reaction can not be biologically treated as it contains TDS in the range of 300 gms/lit. A spray drier was installed for recovering glauber salt and making waste amenable to biological treatment. The results are as given under:

Reduction in wastewater = 5700 m3/annum
Reduction in TDS load = 1710 T/ annum.
Investment = Rs. 35,00,000/
Operational cost = Rs. 49,50,000/ per annum
Net savings = Rs.86,40,000 per annum.
Pay back period = About 11 months

4. The codensation product after drying used to be recovered through multi clones. It was observed there is product loss through the off gas from multi clones. A bag filter was installed replacing multi-clones. Also the temperature of drying the product was increased resulting in reduced drying time.

Additional product recovery = 27 tons /day
Investment = Rs. 7,60,000
Operational cost = Rs 1,70,000 /annum
Savings = Rs 34,44,000/ per annum
Pay back period = about 3 months

6. POLLUTION STATUS BEFORE AND AFTER CP IMPLEMENTATION:

The overall results achieved by the unit are given in the following table.
OVERALL RESULTS ACHIEVED
Recovery of HCl per annum 224 Kg
Recovery of sulfuric acid per annum 8800 Kg
Recovery of sulfanilic acid per annum 2 200 Kg
Reduction in water consumption 22600 m3
Reduction in solid waste (gypsum and other process sludge) 6100 tons

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