New innovations for the textile processing plants
by Alain Geiser and Fawad Ahmed Sheikh

1. Introduction

WAG-Freiburg GmbH, established in Germany, has, together with its branch office in Karachi, Pakistan, developed new technologies and equipment improving some processes in the textile processing thus reducing the overall costs.

These can be summarized as under:

• De-ironing Filters: Removal of iron and rust in water, steam and caustic solutions with magnetic filters. Especially for bleaching processes or any other processes using water, caustic or steam.
• Wedge Filters:  Filtration of fluffs from strong/weak lye of mercerizers, wastewater filtration,  or all liquid filtration down to 50 micron.
• De-coloring of strong or weak lye from mercerisers in Denim, followed by weak lye evaporation (CRU process) and reuse of strong lye.
• Wastewater Pre-Treatment (1st. stage):  Complete space saving and modular chemical treatment, de-coloring (Denim) and sludge separation.
• Wastewater total treatment: Total space saving plant with modular elements for future extensions.
• Water Recovery:  out of wastewater, Re-use for processing.
• Caustic Recovery Units: (CRU) Weak lye evaporation from mercerisers.
• Silt Removal: specially for ground water.

2. De-ironing Filters

Burnt-out holes on your fabric?

Rusty stains? or even reddish spots?

These problems are  solved with customized magnetic  filters by WAG Freiburg Engineering in Germany. De-ironing filters in the Textile Mills are recommended for de-ironing of supplied water to bleachers, J-Boxes, a.s.o, fresh water distribution, condensate, steam and weak and strong lye.

De-ironing filter for hot water.	De-ironing for strong lye.

De-ironing of supplied water is needed especially for the bleaching process in order to avoid attack of hydrogen peroxide with iron which results in holes in the fabric. If de-ironing is not done, iron particles coming with the water supply shall slip causing damage to the fabric.

The caustic solutions from outside sources can also contain impurities with iron contents. This iron  slippage into commercial caustic solution comes from corroded and dirty tankers and also due to inefficiency of post filtration process during manufacturing of caustic soda.

The Filters are specially conceived for the elimination of Iron particles for the textile industry. The coarse iron particles will be retained in a 100 ym sieve whereas the fine iron material will be sticking on strong magnetic elements placed within the sieve. This filter will separate all iron particles in suspension in water.

3.   Wedge filters

WAG Wedge filter  is best applicable for the filtration of fibres, fluffs, and all materials which are normally difficult to  filtrate  under pressure. WAG Hydro-Wedge filter  are especially effective at removing  particles from 100 to 1000 ym.   Wastewater flows downward along the Wedge filter. The material to be filtered will be retained on the surface of the wedge whereas wastewater will flow filtered through it. Filtered out material remains on the surface of the wedge and is constantly pushed downward the wedge into a sludge tank.

Wedge Filter, Denim WW.	Wedge Filter, Wastewater.

3. De-coloring of waste Indigo dyes in denim processing

Applications for weak and strong lye decoloring in mercerisers is given as under:

Indigo Weak lye	De-coloring- Indigo weak lye after treatment.

Weak Lye of mercerisers 

The use of Indigo dyes in the Denim processing  does not allow its recovery, i.e, its evaporation to a strong lye  with a caustic recovery plant (CRU). The Indigo dyes would  block off the evaporation processes. 2-6 m³/h weak lye with a concentration of 3-7 Be are reported to go down the drains and in other words, it is “money down the drains”.

Strong lye of Mercerisers

Strong lye have to be drained periodically due to the high Indigo concentration. New strong lye solution will have to be frequently set up. 

WAG Freiburg has found a process to remove the indigo dye from the caustic solution using a combined physico-chemical process. After 6 months trial period, the system is presently being installed in two Denim factories in Pakistan.

Wastewater decoloring

Wastewater from Denim Processing is dark blue or black, which is unesthetical and gives the impression of a poisonous wastewater at the drainage area. Denim factories often have complaints from the surrounding population or organisations.

WAG has installed 5 wastewater pre-treatment plants in Denim factories  in the last 6 months, where not only Indigo blue or black are removed, but also a reduction of 30-40% COD load is obtained and reported by the customers. These plants are worldwide unique for their flexibility, space saving  (130 m² for 70 m³/h) and modular conception.

Total wastewater treatment plants (physical and biological) can also be planed for all textile processing plants.

Process water recovery out of the cleared wastewater is possible, but still not very economical for the time being.

4.   Caustic Recovery units  (CRU)

A few Multiple Falling Film Evaporators unit are in operation in Pakistan, (examples include, Gul Ahmed Textiles Mills Ltd). Along with the units  tailor-made designed heat and water recovery unit for the entire process was also supplied, which is saving total water, and nearly the total heat energy input in the process.