CHEMICALS CALCULATIONS IN EXHAUST AND CONTINUOUS PROCESS

EXAUST APPLICATION OF CHEMICALS

A cycle comprises one complete circulation of the complete volume of the dyebath

All the chemicals are added into the bath step by step after some intervals

Two main factors which are important in exhaust process i.e.,

1. Main component %age on the fabric

2. Liquor to goods ratio (L:R)

All chemicals quantity depends upon these two things

Let’s assume the following bleaching recipe

L:R = 1:50H2O2 = 4% o.w.fCaustic Soda = 4% o.w.fWetting Agent = 1g/lSquestering Agent = 1g/l

Assume that fabric weight = 2.15gTotal liquor = 2.15*50 = 107.5 mlQuantity of H2O2 = 4*2.15/100Caustic soda = 4*2.15/100

Wetting agent:

1000ml require = 1 g1 ml require = 1/1000107.5ml require = 1/1000*107.5 = .1075g

Squestering agent:

1000ml require = 1 g1 ml require = 1/1000107.5ml require = 1/1000*107.5 = .1075g

PAD APPLICATION OF CHEMICALS

Two types of pad applications:

Application of chemicals to dry fabric i.e., Wet on Dry. e.g, in finishing and dyeing process

Application of chemicals to wet fabric i.e., Wet on Wet. e.g., in bleaching process

The following conditions should be met to obtain consistent chemical application:

Uniform nip pressureUniform initial moisture contentConstant saturator levelConstant fabric speedConstant temperatureGood liquor penetration and interchange

PAD APPLICATION OF CHEMICALS TO DRY FABRIC

The amount of liquor taken up by the fabric is often described as the mangle expression i.e., ‘pick up’

Dry fabric is passed through the chemical solution and this process is called a ‘wet on dry’ process

Factors affecting fabric wet pickup

Factor Effect on wet pickupFiber type Higher wet pickup with hydrophilic fibersYarn construction Higher wet pickup with low twistFabric construction Higher wet pickup with loose constructionWettability Higher wet pickup with more easily wetted fabricPressure of squezz rolls Higher pressure will lead to low pickupNature and hardness of squezz rolls Harder coveribgs lead to low pickupLength of immersion time Higher wet pickup with longer immersion timeViscosity of solution Higher wet pickup with higher viscositySurface tension of solution Higher wet picup with faster wetting solutions

Temperature of solutionViscosity and surface tension changes with temp, changing pickup

Concentration of solution Change the conc. Change the pickup

Wet pickup of the fabric can be calculated by the following equation

%wpu = wt of solution applied*100/wt of dry fabric……(A)

amount of supplied chemical added to the fabric is calculated by

%add-on = %conc in sol(wt/wt)*%wpu/100………..(B)

Where %conc is the concentration of the chemical in the applied solution expressed as percentage by weight

Pick-up can also be calculated as

Pick-up(E) = Wet wt after pad-air dry wt/air dry wt*100……(C)

PAD APPLICATION OF CHEMICALS TO WET FABRIC

In scouring and bleaching chemicals are applied to wet fabric i.e., undried from preceding washers

Water is added to the saturator chemicals by the fabric

Let assume that the entry expression of the fabric is Ei and exit expression is Eo

if Ei>Eo…….then

if Ei<Eo…….then

The minimum difference in these entries is 10% adopted by most industries

In wet on wet case the effective pick-up is calculted

effective pick-up = (Eo-Ei)+(Ei*F)

F= interchange factor or fracrion by which the incoming water is exchanged

The value of F is usually about 0.7-0.8

CHEMICAL FEED SYSTEMSFor wet on dry application, the feed

sol. is made at same concentration as the saturator

For wet on wet padding, more concentrated chemical feed will be required

Concentrated chemical feed liqour will be 5-8 times the strength of saturator liquor

There are five basic systems available

1.Manual control2.Rotameter flow meters3.Metering pumps4.Proportioning cylinders, e.g. Texicon5.Fully automated units, e.g. Polymetron

MANUAL CONTROL SYSTEM

ROTAMETER FLOW METERS

METERING PUMPS

PROPROTIONING CYLINDERS

FULLY AUTOMATED UNITS

CONCENTRATION OF FEED LIQUOR CALCULATION

Let,exit mangle expression = Eo%entry mangle expression = Ei%percentage chemicals on the fabric = Xweight of fabric per minute = W kg/min

X = saturator conc(K1)*epu/1000

By putting the value of epu

X = K1*[(Eo-Ei)+(Ei*F)]/1000…….(A)

The volume change (V) per minute in the saturator is

V = W*(Eo-Ei)/SG*100 = W*(Eo-Ei)/100 l/min, assuming SG = 1

And the weight of chemical (w) used per min is

w = W*X/100 kg/min = W*X*1000/100 g/min

This then is the feed liquor concentration (K2)

K2 = w/V = W*X/100*1000*100/W*(Eo-Ei)

K2 = 1000*X/Eo-Ei g/l

or X = K2*(Eo-Ei)/1000……(B)

equating A and B, we have

K2 = K1[(Eo-Ei)+(E*F)]/Eo-Ei

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