Closer Process Control

Water is used various textile processes, they are mentioned below- cleaning the raw material,  many different industrial processes sizing, desizing, scouring, bleaching, mercerizing, d

Prepared By : Mazadul Hasan

sheshir

ID: 2010000400008

13 th Batch

Wet Processing Technology

Email:

mazadulhasan@yahoo.com

Southeast University

Southeast University

Department Of Textile Engineering

I/A 251,252 Tejgaon Dhaka Banglade sh

Waste water is very similar in textile processing, which do harms for environment and regular activities of mankind Water is used various

textile processes, they are mentioned

below- cleaning the raw material,

 many different industrial processes (sizing,

desizing, scouring, bleaching, mercerizing,

dyeing, printing and finishing), and

 rinsing steps during the whole production

What is closer process control:

 Closer process control is a process, which

control the pollution load in textile effluent

By this process, the pollution load can be

reduced by 30-40percent.

The closer process controlled by following implements:

 Reduction in chemical usage.

 Recovery and re-use of chemicals.

 Process modification.

 Flow or volume reduction.

Reduction in chemical usage:

in large quantities The unutilized eventually joins the effluent stream Its amount should

be optimized though it is estimated that it will always remain somewhat in excess of what is required Obviously, this excess

should be diverted for different ratio In

summer it should be sun-dried and in

winters it should be evaporated thus

obtained should be disposed of as solid

waste.

 In bleaching operations, chlorine and per

oxides are used They should be mixed

with dyeing effluent in order to decolorize it.

 In kiering mercerizing processes caustic

soda is used in large quantities It should be recycled by readjusting its concentration

Process modification:

 Certain change in processes can reduce the amounts and concentrations

of waste materials E.g.change in dyeing method(use of Exhaust dyeing , Standing bath dyeing , Pad-batch dyeing ).

 Exhaust dyeing:

 Exhaust dyeing in which a batch of fibre is dyed from a liquor that is used only once and then discarded This technique enables dyers to produce matching colours on different batches of fibre with relative case (provided that the composition of the dye liquor and the dyeing conditions are carefully controlled) but obviously leads to the wastage of chemicals that are not consumed in the dye bath However, provided that dyes which exhaust well are used, the loss of dyestuff is negligible and other chemicals used in the dye bath are relatively cheap.

 Standing bath dyeing:

dyeing However, after the first dyeing the dye bath is replenished with dyestuff and chemicals and a further dyeing is carried out This replenishment may be

repeated several times Experience is required to

calculate the exact amount of dyestuff and chemicals

needed for replenishment.

 Pad-batch dyeing:

on the use of reactive dyes It is often carried out in the cold and uses low liquor to fibre ratios (1: 1 compared with 20: 1 for exhaust dyeing).

Recovery and re-use of chemicals:

Size selection

Replace starch-based sizes with synthetic sizes The advantages of this is a reduced pollution load as synthetic sizes have lower BOD levels, and they can be recycled for reuse

Desizing

The effluent from desizing will contain the sizes that were added onto the yarn before

weaving/knitting Using and recycling synthetic sizes in place of starch sizes will reduce the

pollution load from desizing

Detergents should be easily biodegradable Avoid the following detergents: linear alkyl benzene

sulphonate; dialkyl-dimthyl ammonium chloride with poor biodegradability (e.g EDTA; phosphonic acid) Reuse scour wash water for desizing Recycle

continuous scour wash water to batch scouring

Bleaching

Replace the use of chlorites and hypochlorite's with hydrogen peroxide Ensure that bleaching is carried out efficiently Recycle bleach wash water for

scouring Use vacuum slots to remove excess

solution which can then be reused

Recycling of sodium hydroxide through evaporation for reuse in mercerizing or scouring will decrease the pollution load and chemical consumption

General

environmental impact.

Flow or volume reduction:

The waste flow may be reduced by the reuse of process water, counter flow waste, segregation of weak waste for disposer without treatment, changes in process and other similar means.

The textile industry emits a wide variety of

pollutants from all stages in the processing of

fibers and fabrics These include liquid effluent, solid waste, hazardous waste, emissions to air and noise pollution It is important to investigate all aspects of reducing wastes from the textile

industry, as not only will it result in improved

environmental performance, but also substantial savings for the individual companies