Process improvements for finishing operations - gpcb … · • allows a more homogeneous sizing...

Process improvements for finishing operations

Brigitte ZietlowGerman Federal Environment Agency

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“BAT in textile and pulp and paper sector” – 18th – 29th November 2013 B. Zietlow, Umweltbundesamt

Outline

Process integrated measures for

Selection of incoming fibres

Pretreatment

Dyeing

Printing

Finishing

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Selection of incoming fibresMan-made fibre preparation agents with improved environmental performance

Preparations are the major causes of the pollution in the downstream processes

Conventional preparation agents are mainly based on mineral oils with:

• high add-on (3-5%), • low temperature stability

(smoke during high-temperature treatments), • poor biodegradability, • presence of polyaromatic hydrocarbons,

Alternative preparation systems are based on:• polyester-/polyethercarbonate• special polyolesters• special steric hindered fatty acid esters

Achieved benefits:•Up to 50 % reduction of application amount •90% reduction of air pollution•Reduction of chemical load in waste water•Reduction of odour nuisance•savings in water and detergent consumption•Improved colour fastness

BREF Textile Industry Section 4.2.1

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Sizing/DesizingMinimising sizing agent add-on by pre-wetting the warp yarns

Sizing agents account for 50 to 70 % of the total COD in the waste water of finishing mills

Minimising the amount of size applied on the warp yarn is one of the most effective pollution prevention techniques for reducing the organic load

prewetting technology (running the warp yarn through hot water before the sizing process):

• allows a more homogeneous sizing effect, increased adhesion of the size and reduced hairiness of the yarn

Reduction of the size add-on of about 20 - 50 % Improved weaving efficiency in some cases

not applicable to small batches (<5000 m) as the add-on cannot be controlled adequately

Data of a weaving mill:• 27 % cost savings• 22 % increase in sizing machine speed


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PretreatmentOne-step desizing, scouring and bleaching of cotton fabric

New auxiliaries’ formulations and automatic dosing and steamers allow the one-step desizing, scouring and bleaching (“Flash Steam” procedure)

Leads to significant reductions in water and energy consumption

Needs only 2 - 4 minutes from loom-state goods to a white good suitable for dyeing


One of the possible recipes consists of: •15 - 30 ml/kg phosphorus-free mixture of bleaching agents, dispersant, wetting agent and detergent •30 - 50 g/kg NaOH 100 % •45 - 90 ml/kg H2O2 35 %

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PretreatmentOptimisation of cotton warp yarn pretreatment

For production of white, non-dyed cotton sheets cotton warp yarn is bleached before weaving (e.g. for under bed sheets and table-cloths )

Optimisation of the process:• combining wetting, scouring and bleaching in

one step and performing rinsing in two steps, re-using the second rinsing bath for making the bleaching/scouring bath

• heat from the scouring/bleaching bath (110°C) is recovered (by means of a heat exchanger) and used for heating the fresh water for the first rinsing to a temperature of 60 – 70 °C


Data of textile company:

50 % reduction of water consumption 50% reduction of process time80 % reduction of NaOH-consumption65% reduction of complexing agents70 % reduction of surfactants20 % reduction of COD load in waste waterEnergy savings: 1.2 kg steam/kg warp yarn

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Process improvements for dyeingAutomated preparation and dispensing of chemicals

Microprocessor-controlled dosing systems meter chemicals automatically according to a variety of profiles, such as constant rate or variable rate.

Usually the frequently used colourants (highest consumption) are selected for automation.

commonly applied in many companies in the textile industry (Examples of plants with production capacity ranging from 70 t/day to 5 t/day)

Benefits:• improved right-first-time perfomance minimising

corrective measures (e.g. reworks, redyes)• significant reduction of waste water pollution and

wasted chemicals thanks to the minimisation/ avoidance of liquor residues

BREF Textile Industry Chapter 4.1.3

Data ofa textile dyehouse(production capacity 5500 t/year):17% reduction of reworks11% reduction of costs for chemicals10% reduction of costs for labour5 % increased dye machine efficiency

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Process improvements for dyeingUse of non-carrier dyeable PES fibres

Fibres made from polytrimethylene terephthalate (PTT) can be dyed or printed in light or medium shades using standard disperse dyestuffs without the need for any special processing steps or carriers.

Higher temperatures are recommended for dark and full shades like red, navy-blue, and black.

for light and medium shades PTT is dyed atmospherically at 100 °C with excellent dye exhaustion and colourfastness

Advantages of PTT: soft handling, higher extensibility, higher stability with regard to UV-light, higher chlorine fastness preferred use in underwear, sportswear, and swimwear

Benefits:• emissions of carriers in the workplace and in the environment are

completely avoided • Reduced energy consumption compared with PETS dyed under high-

pressure-high –temperature (HT) conditions BREF Textile Industry Chapter 4.6.2

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Process improvements for dyeingSilicate-free fixation method for cold pad batch dyeing

Sodium silicate is used in cold pad-batch dyeing, to increase the pad liquor stability and to avoid selvage carbonisation

Silicate-free highly concentrated aqueous alkali solutions are available ready-made products (carefully adjusted mixture of alkali in aqueous

solution) can be easily applied with modern dosing systems particularly suitable for cold-pad-batch processes Benefits:

• no residues of alkali in the preparation tank (alkali can be added as ready‐made solution)

• no formation of difficult‐to‐wash‐off deposits on the substrate and on the equipment

• lower electrolyte content in the effluent Dosing curve for ready-made alkali solutionBREF Textile Industry Chapter 4.6.9

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Process improvements for dyeing Use of high-fixation polyfunctional reactive dyestuffs

Bifunctional (polyfunctional) reactive dyes offer very high levels of fixation in exhaust dyeing of cellulosic fibres

Combination of two reactive systems in the same dye delivers the advantages of the two individual groups (e.g. high degree of fixation with high fastness levels and wash-off)

Post-rinsing to obtain the required level of wet-fastness can be performed quickly and with reduced amounts of energy and water

dye manufacturers introduced small dye ranges each comprising highly compatible dyes with identical behaviour in the dye bath

dyeing compatibility matrixes are provided high reproducibility, low dependency on dyeing conditions (e.g. liquor ratio, dyeing temperature, salt concentration) and therefore right-first-time dyeing

Fixation rate is increased from 60 % to 80 % Reduction of waste water pollution (e.g. TDS)

Data for new dyes:90°C fixation temperature40 % reduction of water consumption40 % reduction of energy consumption30 % reduction of salt conumption


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Process improvements for dyeing Exhaust dyeing with low-salt reactive dyes

exhaust dyeing of cellulosic fibres with reactive dyestuffs requires usually 50 - 60 g salt/l (up to 100 g salt/l for dark shades)

Low-salt reactive dyes need only about two-thirds of this quantity

low-salt dyes can be kept in solution at a higher concentration use of low liquor ratio (L.R.) dyeing machines further reduction of salt consumption

low-salt reactive dyes are not combinable with other dyes, processing parameters have to be complied in an exact way

Winch (L.R. 1:20) Jet (L.R. 1:10) Low L.R. Jet (L.R. 1:5)

Traditional dyes (salt 60 g/l) 1200 kg 600 kg 300 kg

Low salt dyes (salt 40 g/l) 800 kg 400 kg 200 kg

Quantities of salt required for dyeing 1000 kg of fabric to a medium depth of shade BREF Textile Industry Chapter 4.6.11

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When carbon dioxide is heated to above 31°C and pressurized to above 74 bars, it becomes “supercritical” high (liquid-like) density that enables dissolution of compounds and the low viscosity that enables good penetration

For dyeing of textile the carbon dioxide is heated to 120°C and pressurized to 250 bars

During dyeing of polymer fibres, CO2 loaded with dyestuff penetrates deep into the polymer structure of the fibres and thus provides effective coloration of these materials

Benefits: no water consumption – and therefore no wastewater no off-gas emission (90-95% of the CO2 can be recycled) no drying step after dyeing no leveling and dispersing agents dyestuff residues can be recycled

Process improvements for dyeing Dyeing in supercritical carbon dioxide

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Process improvements for dyeing Minimisation of dye liquor losses in pad dyeing techniques

Main emission sources in pad dyeing processes arise from the discharge of the residual dyeing liquor in the pad, pumps and pipes

Reduction of these losses can be achieved by minimising the capacity of the dip trough (e.g. flex-shaft, U-shaft)

Further reduction of losses:• Dosing of dyestuff solution and auxiliaries based on the

specific recipe, dispensing as separate streams and mixing immediately before the pad

• dosage of the padding liquor based on measurement of the pick-up reduction of liquor loss in the tanks from 150 litres to 5 – 15 litres

The use of a U‐trough reduces the bath residue by 60–90%.


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Process improvements for dyeing After-soaping of reactive dyed or printed fabrics

New developed efficient products for after-soaping based on vinyl polymers prevents renewed uptake of unfixed dyestuff on the fibre in shortened rinsing passages

The number of rinsing bathes depends on the depth of shade. High savings can be reached for light shades by minimizing the number of the rinsing bathes (according to experiences in practice two rinsing processes can be saved).

Benefits:Savings in water consumption up to 25 %

Savings in energy consumption

Reduced process time

improved quality (higher fastness) of the final product

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Process improvements for printingRecovery of printing paste

Recovery of the printing paste remaining in the supply system in rotary screen printing machines at the end of each run

A ball is inserted in the squeegee and transported by the incoming paste to its end. After a print run, the ball is pressed back by air pressure, pumping the printing paste in the supply system back into the drum for re-use.

modern printing machines with minimum-volume feed systems should be used

Re-use rates of 50 – 75%

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Calculation of savings achievable in a typical textile mill

Number of changes of printing pastes per day 8

Number of working days per year 250

Average number of printing pastes per design 7

Saving of printing paste per supply system 3.7 kg

Price of printing paste 0.6 euros/kg

Savings per year 31080 euros/yr

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Thank you for your attention!

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Process improvements for finishing operations - gpcb … · • allows a more homogeneous sizing...

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