«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
· select raw material processed with low add-on techniques (e.g. pre-wetting of the warp yarn, see 4.2.5) and more effective bioeliminable sizing agents (see 4.2.4) combined with the use of efficient washing systems for desizing and low F/M waste water treatment techniques (F/M 0.15 kg BOD5/kg MLSS·d, adaptation of the activated sludge and temperatures higher than 15 °C – see 4.10.1) to improve the bioeliminability of the sizing agents · adopt the oxidative route when it is not possible to control the source of the raw material (see Section 4.5.2) · combine desizing/scouring and bleaching in one single step, as described in Section 4.5.3 · recover and re-use the sizing agents by ultrafiiltration as described in Section 4.5.1.
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BAT is to:
· use hydrogen peroxide bleaching as preferred bleaching agent combined with techniques for minimising the use of hydrogen peroxide stabilisers, as described in Section 4.5.6, or using biodegradable/bioeliminable complexing agents described in Section 4.3.4 · use sodium chlorite for flax and bast fibres that cannot be bleached with hydrogen peroxide alone. A two-step hydrogen peroxide-chlorine dioxide bleaching is the preferred option. It must be ensured that elemental chlorine-free chlorine dioxide is used. Chlorine-free chlorine dioxide is produced using hydrogen peroxide as the reducing agent of sodium chlorate (see Section 4.5.5) · limit the use of sodium hypochlorite only to cases in which high whiteness has to be achieved and to fabrics that are fragile and would suffer depolymerisation. In these special cases, to reduce the formation of hazardous AOX, sodium hypochlorite bleaching is carried out in a two-step process in which peroxide is used in the first step and hypochlorite in the second. Effluent from hypochlorite bleaching is kept separate from the other streams and mixed effluents in order to reduce formation of hazardous AOX.
BAT is to either:
· recover and re-use alkali from mercerising rinsing water as described in Section 4.5.7 · or re-use the alkali-containing effluent in other preparation treatments.
DYEING Dosage and dispensing of dye formulations
BAT is to do all the following:
· reduce the number of dyes (one way to reduce the number of dyes is by using trichromatic systems) · use automated systems for dosage and dispensing of dyes, only considering manual operation for dyes that are used infrequently · in long continuous lines where the dead volume of the distribution line is comparable with the volume in the padder, give preference to decentralised automated stations that do not premix the different chemicals with the dyes before the process and that are fully automatically cleaned.
General BAT for batch dyeing processes
BAT is to:
· use machinery fitted with: automatic controllers of fill volume, temperature and other dyeing cycle parameters, indirect heating & cooling systems, hoods and doors to minimise vapour losses · choose the machinery that is most fitted to the size of the lot to be processed to allow its operation in the range of nominal liquor ratios for which it is designed.
Modern machines can be operated at approximately constant liquor ratio whilst being loaded at a level as low as 60 % of their nominal capacity (or even 30 % of their nominal capacity with yarn dyeing machines) (see Section 4.6.19) · select new machinery according as far as possible to the requirements described in Section 4.6.19:
Ø low- or ultra-low liquor ratio Ø in-process separation of the bath from the substrate Ø internal separation of process liquor from the washing liquor Ø mechanical liquor extraction to reduce carry-over and improve washing efficiency Ø reduced duration of the cycle.
Textiles Industry 451 Chapter 5 · substitute overflow-flood rinsing method in favour of drain and fill or other methods (smart rinsing for fabric) as described in Section 4.9.1 · re-use rinse water for the next dyeing or reconstitution and re-use the dye bath when technical considerations allow. This technique (see Section 4.6.22) is easier to implement in loose fibre dyeing where top-loading machines are used. The fibre carrier can be removed from the dyeing machine without draining the bath. However, modern batch dyeing machines are equipped with built-in holding tanks allowing for uninterrupted automatic separation of concentrates from rinsing water BAT for continuous dyeing processes Continuous and semi-continuous dyeing processes consume less water than batch dyeing, but highly concentrated residues are produced.
BAT is to reduce losses of concentrated liquor by:
· using low add-on liquor application systems and minimising volume capacity of the dip trough when using pad dyeing techniques · adopting dispensing systems where the chemicals are dispensed on-line as separate streams, being mixed only immediately before being fed to the applicator · using one of the following systems for dosing the padding liquor, based on measurement of
the pick up (see 4.6.7):
Ø measure the amount of dyeing liquor consumed by reference to the quantity of processed fabric (length of the fabric multiplied by its specific weight); the resulting values are automatically processed and used for the preparation of the next comparable batch Ø use the rapid batch dyeing technique, where rather than being prepared for the whole batch before starting the dyeing batch, the dyestuff solution is prepared just in time, in several steps, based on on-line measurement of the pick up. This second technique is preferred when economic considerations allow (see 4.6.7) · increase washing efficiency according to the principles of countercurrent washing and reduction of carry-over described in Section 4.9.2.
PES & PES blends dyeing with disperse dyes
BAT is to:
· avoid the use of hazardous carriers by (in order of priority):
Ø using non-carrier dyeable polyester fibres (modified PET or PTT-type) as described in Section 4.6.2, when product market considerations allow Ø dyeing in HT conditions without use of carriers. This technique is not applicable to PES/WO and elastane/WO blends Ø substituting conventional dye carriers with compounds based on benzylbenzoate and Nalkylphthalimide, when dyeing WO/PES fibres (see Section 4.6.1) · substitute sodium dithionite in PES aftertreatment, by applying one of the two proposed
techniques (as described in Section 4.6.5):
Ø replace sodium dithionite with reducing agent based on sulphinic acid derivatives. This should be combined with measures in order to ensure that only the strict amount of reducing agent needed to reduce the dyestuff is consumed (e.g. by using nitrogen to remove oxygen from the liquor and from the air in the machine) Ø use of disperse dyes that can be cleared in alkaline medium by hydrolitic solubilisation instead of reduction (see Section 4.6.5) · use optimised dye formulations that contain dispersing agents with high degree of bioeliminability as described in Section 4.6.3.
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Chapter 5Dyeing with sulphur dyes
BAT is to (see 4.6.6):
· replace conventional powder and liquid sulphur dyes with stabilised non-pre-reduced sulphide-free dyestuffs or with pre-reduced liquid dye formulations with a sulphide content of less than 1 % · replace sodium sulphide with sulphur-free reducing agents or sodium dithionite, in that order of preference · adopt measures to ensure that only the strict amount of reducing agent needed to reduce the dyestuff is consumed (e.g. by using nitrogen to remove oxygen from the liquor and from the air in the machine) · use hydrogen peroxide as preferred oxidant.
Batch dyeing with reactive dyes
BAT is to:
· use high-fixation, low-salt reactive dyes as described in Sections 4.6.10 and 4.6.11 · avoid the use of detergents and complexing agents in the rinsing and neutralisation steps after dyeing, by applying hot rinsing integrated with recovery of the thermal energy from the rinsing effluent (see Section 4.6.12).
Pad-batch dyeing with reactive dyes BAT is to use dyeing techniques that perform at equivalent levels to those described in Section 4.6.13. The technique described is more cost effective than pad-batch dyeing in terms of total processing costs, but the initial capital investment in switching to the new technology is significant. However, for new installations and those seeking to replace equipment the cost factor is not so significant. In all cases, BAT is to avoid the use of urea and to use silicate-free fixation methods (see Section 4.6.9).
BAT is to:
· substitute chrome dyes with reactive dyes or, where not possible, use ultra-low chroming
methods that fulfil all the following requirements as defined in Section 4.6.15:
Ø an emission factor of 50 mg chromium per kg of wool treated is achieved, which corresponds to a chromium concentration of 5 mg/l in the spent chroming bath when a 1:10 liquor ratio is used Ø no chromium (VI) is detectable in the waste water (using a standard method able to detect Cr VI at concentrations 0.1 mg/l) · ensure minimum discharge of heavy metals in the waste water when dyeing wool with metal complex dyes. BAT associated values are emission factors of 10 - 20 mg/kg of treated wool, which correspond to 1 - 2 mg/l of chromium in the spent dye bath when a 1:10 liquor
ratio is used. These performances can be achieved by:
Ø using auxiliaries that enhance dye uptake like, for instance, the process described in Section 4.6.17 for loose wool and tops Ø using pH control methods to maximise final bath exhaustion for other make-ups · give preference to a pH-controlled process when dyeing with pH-controllable dyes (acid and basic dyes) so that level dyeing is obtained with maximum exhaustion of dyes and insect resist agents and minimum use of organic levelling agents (see Section 4.6.14).
Process in general
BAT is to:
· reduce printing paste losses in rotary screen printing by:
Ø minimising the volume of printing paste supply systems (see 4.7.4) Ø recovering printing paste from the supply system at the end of each run by adopting the technique described in Section 4.7.5 Ø recycling residual printing paste (see Section 4.7.6) Textiles Industry 453 Chapter 5
· reduce water consumption in cleaning operations by a combination of (see Section 4.7.7):
Ø start/stop control of cleaning of the printing belt Ø re-use of the cleanest part of the rinsing water from the cleaning of the squeegees, screens and buckets Ø re-use of the rinsing water from cleaning of the printing belt · use digital ink-jet printing machines for the production of short runs (less than 100 m) for flat fabrics, when product market considerations allow (see Section 4.7.9). It is not considered BAT to flush with solvent to prevent blocking while the printer is not in use · use digital jet printing machines described in Section 4.7.8 for printing carpet and bulky fabrics, except for resist and reserve printing and similar situations.
BAT is to avoid the use of urea by either:
· the one-step process with the controlled addition of moisture, where the moisture is applied either as foam or by spraying a defined quantity of water mist (see Section 4.7.1) OR · the two-steps printing method (see 4.7.2).
For silk and viscose, with the one-step process, the spraying technique is not reliable due to the low moisture add-on required for these fibres. The foaming technique with complete elimination of urea is proven for viscose, but not yet for silk. There is a high initial investment cost of about 200000 euros for a foaming machine related to a production capacity of up to about 80000 linear metres per day. The technique has been operated under economically viable conditions in plants of capacity of about 30000, 50000 and 140000 linear metres per day. There is a question whether the technique is economically viable for smaller plants.
Where the foam technique is not used, the amount of urea consumed can be reduced to about 50 g/kg of printing paste for silk and to 80 g/kg for viscose.
BAT is to use optimised printing pastes that fulfil the following requirements (see 4.7.3):
· thickeners with low-emission of volatile organic carbon (or not containing any volatile solvent at all) and formaldehyde-poor binders. The associated air emission value is
0.4 g Org.-C/kg textile (assuming 20 m3 air/kg textile) · APEO-free and high degree of bioeliminability · reduced ammonia content. Associated emission value: 0.6 g NH3/kg textile (assuming 20 m3 air/kg textile).
Process in general
BAT is to:
· minimise residual liquor by:
Ø using minimal application techniques (e.g. foam application, spraying) or reducing volume of padding devices Ø re-using padding liquors if quality is not affected
· minimise energy consumption in stenter frames by (see Section 4.8.1):
Ø using mechanical dewatering equipment to reduce water content of the incoming fabric Ø optimising exhaust airflow through the oven, automatically maintaining exhaust humidity between 0.1 and 0.15 kg water/kg dry air, considering the time taken to reach equilibrium conditions Ø installing heat recovery systems Ø fitting insulating systems Ø ensuring optimal maintenance of the burners in directly heated stenters · use low air emission optimised recipes. An example for classification/ selection of finishing recipes is the “Emission factor concept” described in Section 4.3.2.
Easy-care treatment BAT is to use formaldehyde-free cross-linking agents in the carpet sector, and formaldehydefree or formaldehyde-poor (0.1 % formaldehyde content in the formulation) cross-linking agents in the textile industry (see Section 4.8.2).
Mothproofing treatments · Process in general
BAT is to:
Ø adopt appropriate measures for material handling as described in Section 22.214.171.124 Ø ensure that 98 % efficiency (transfer of insect resist agent to the fibre) is achieved Ø adopt the following additional measures when the insect resist agent is applied from a dye
§ ensure that a pH4.5 is reached at the end of the process and if this is not possible, apply the insect resist agent in a separate step with re-use of the bath § add the insect resist agent after dye bath expansion in order to avoid overflow spillages § select dyeing auxiliaries that do not exert a retarding action on the uptake (exhaustion) of the insect-resist agent during the dyeing process (see Section 126.96.36.199).
· Mothproofing of yarn produced via the dry spinning route
BAT is to use one or both of these techniques (described in Section 188.8.131.52):
Ø combine acid aftertreatment (to increase the uptake of mothproofer active substance) and reuse of the rinse bath for the next dyeing step Ø apply proportional over-treatment of 5 % of the total fibre blend combined with dedicated dyeing machinery and waste water recycling systems to minimise active substance emissions to water.
· Mothproofing of loose fibre dyed / yarn scoured production
BAT is to (see Section 184.108.40.206):
Ø use dedicated low-volume application systems located at the end of the yarn scouring machine Ø recycle low-volume process liquor between batches and use processes designed specifically to remove active substance from spent process liquor. These techniques may include adsorptive or degradative treatments Ø apply mothproofer directly to the carpet pile (when mothproofing during carpet manufacture) using foam application technology.
· Mothproofing of yarn dyed production
BAT is to (see Section 220.127.116.11):