«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
The products can be applied similarly to conventional products. The kind and amount of catalyst have to be adjusted, as well as curing time and temperature.
Required quantity of formaldehyde-free products is approximately twice as high as conventional products.
Economics Prices for formaldehyde-free products are significantly higher than for formaldehyde-low products.
Reference plants Formaldehyde-free and low-formaldehyde easy-care finishing auxiliaries are supplied by various companies and applied worldwide.
Driving force for implementation Regulations concerning formaldehyde in the off-gas and compliance with various codes of conduct concerning consumer health (e.g. European Eco-label, etc.) are the main motivation for the use of the formaldehyde-free or low-formaldehyde products.
Reference literature [179, UBA, 2001], [51, OSPAR, 1994] (P016) 4.8.3 Avoiding batch softening Description In batch processing softening agents are often applied after the dyeing process directly in the dyeing machine (e.g. jet, overflow) using the exhaustion method.
Unfortunately, this limits the choice of softening agents to environmentally harmful cationic agents and gives rise to a 10 – 20 % loss of the whole volume of the warm softening bath [78, Danish EPA, 1999].
Alternative techniques are the application of softeners by pad mangles or by spraying and foaming application systems (see Sections 2.9.1 and 2.9.3).
The advantages of these techniques are that the use of cationic softening agents can be avoided and any chemical loss can be reduced to a few percent [78, Danish EPA, 1999].
The amount of residual liquors is also reduced compared with the waste water volume produced by a batch process. In this respect, the best performances are achieved with application techniques such as spraying and foaming, which allow minimum system-losses (residual liquor in the chassis, residual liquor in the pipes and leftovers in the batch storage containers).
However, the concentration of active substance is much higher, which makes these liquors not suitable for treatment in a biological system.
Another advantage of applying the softeners in separate equipment after the batch dyeing process is that it is then possible to re-use the dyeing or rinse baths as there is no longer a problem with the presence of residual cationic softeners, which would otherwise limit the adsorption of the dye in the subsequent dyeing process.
Main achieved environmental benefits Savings in water, energy and chemicals. Introduction of less environmentally harmful softening agents.
Operational data No information was made available.
Cross-media effects When softening is done in separate equipment after the dyeing process, the volume of the residual liquor is reduced (limited to system-losses), but the concentration of the active substance is higher. Provided that this concentrated stream is not mixed with the other effluents and sent to a biological waste water treatment, no cross-media effects need to be considered.
Applicability The technique has general applicability in the textile and carpet sectors.
Economics Economic benefits can be derived from savings in water, energy and chemicals consumption.
Reference plants Many plants.
Reference literature [78, Danish EPA, 1999].
4.8.4 Minimisation of emissions in the application of mothproofing agents The next three figures (Figure 4.29, Figure 4.30, Figure 4.31) illustrate the baseline processes used by the sector to apply insect resist (IR) agents and identifies the point of application in wet processing and potential points of emission of residual active substance to water. The application method(s) adopted by any manufacturer will depend on the specific yarn production/process sequence used and it is not uncommon to find more than one application procedure in use on one site.
Techniques to minimise the emission of residual insect resist agent may take a number of forms:
· general practices applicable to the majority of processes, for example material handling and storage and selection of the correct application rate · specific process modifications which include, for example, changes to the chemistry of the process or the substitution of interfering chemicals · alternative processes such as the use of specialised machinery dedicated to insect resist application. Application at a different point in the carpet manufacturing sequence is also considered under this heading · on site pretreatment of specific waste water streams – destruction of residual active substance by alkali hydrolysis.
The following discussion first describes general techniques and then specific modifications
applicable to each of the three identifiable processing routes for yarn manufacture:
· yarn production by the “dry spinning” route · yarn production by the “oil spinning” route · yarn dyed production route.
188.8.131.52 General techniques to minimise the emission of insect resist agent active substance
General techniques to minimise the emission of insect resist agent active substance include:
appropriate material handling and dyeing auxiliary selection.
Material handling The handling of environmentally sensitive materials such as formulated mothproofing agent requires the use of special techniques to minimise spillage during dispensing and transport within the dyehouse. The majority of commercial formulations are supplied as self-emulsifying concentrates- referred to as concentrate, below.
For handling and transfer of concentrate to dyeing machines the following measures should be
· bulk containers should be transferred to a safe bunded store on receipt · in the event of a fire, provision to inform the fire authority and sewage treatment undertaker of the presence and nature of the substance should be in place · concentrate should only be dispensed from bulk containers within the colour store · automated dispensing systems should be considered to minimise spillage and improve accuracy
· concentrate should not be pre-dissolved in the colour room, but:
· concentrate should be transferred from the colour store to the point of addition to the process in sealed shockproof containers · concentrate should be added directly to the process liquor only when the dyeing is underway and the dye bath volume is stable (prevents displacement spillage).
For handling concentrate in relation to semi-continuous application the following measures
should be adopted:
· concentrate should be stored in the original containers, within a bund and protected from accidental impact · concentrate should be dispensed directly into the process liquor – stock solutions should not be used · dispensing should not be a manual operation. Dosing pumps should be used.
Dyeing Auxiliary selection
Some dyeing auxiliaries are known to exert a retarding action on the uptake (exhaustion) of insect resist agents in all dyeing processes. The choice of, for example levelling agent and polyamide blocking agent can significantly affect the final dye bath and rinse residues. These effects are known to depend on both dye liquor pH and auxiliary concentration. Dyeing auxiliaries should therefore be screened for retarding action. Products with a significant retarding action should be substituted, if possible.
Main achieved environmental benefits The correct timing of additions to the dye bath has been shown to play an important role in reducing overall emissions of IR agent by minimising the spillage of the concentrated treatment liquor at the start of the dyeing process.
A targeted selection of the dyeing auxiliaries allows a reduction of the concentration of mothproofing agent in spent dye bath liquors.
Operational data Quantification of the impact of the materials handling regime described above on overall mill effluent residues is difficult to assess, but measurements on individual dyeing machines suggest that between 10 and 20 % of the total emissions can arise from liquor spillage.
Cross-media effects Cross-media effect are believed to be unlikely as regards the adoption of the proposed material handling regime. The choice of auxiliaries should be made taking into account overall effects on the environment.
Applicability The above techniques are applicable to all installations. However, it should be recognised that substitute auxiliaries with equivalent technical performance are not always available Economics Many of the above measures regarding material handling are of low or no cost. Accurate metering and dispensing systems for use in the colour store and as part of a continuous application system are estimated to cost in the range EUR 8000 –16000.
Reference literature [32, ENco, 2001], [51, OSPAR, 1994], [50, OSPAR, 1997].
184.108.40.206 Specific process modifications to minimise the emission of insect resist agent active substance during yarn production by “dry-spinning route” Figure 4.29 illustrates the baseline process used for the application of mothproofer to “dry spun” production during fibre wet processing. Insect resist agent is applied in loose fibre dyeing by addition to the dye bath at the commencement of the dyeing. In the baseline process the dye bath and the rinse liquor are discharged to drain and may carry residual agent not taken up by the fibre. Dewatering the dyed fibre using either a centrifuge or with squeeze rollers also generates an additional potential source of residues.
Candidate process modifications with potential to reduce mothproofer emissions in loose fibre
· acid aftertreatment & re-use of the rinse bath · proportional overtreatment of loose fibre.
220.127.116.11.1 Acid aftertreatment & re-use of the rinse bath Description
The procedure illustrated in Figure 4.29 combines:
1. acid aftertreatment: dyeing conditions can be modified to incorporate an acidification step at the end of the dyeing cycle. Lowering the dye liquor pH ( 4.0) increases the uptake of mothproofer active substance at the end of the cycle and reduces overall residues.
2. re-use of the rinse bath: reusing the liquor for the next dyeing can eliminate residues from the rinse bath. This approach is only feasible if the machine can be unloaded without emptying the dye vessel or if the machine is equipped with an external liquor storage tank to which the liquor can be transferred between unloading and loading.
Main achieved environmental benefits Reduction of residues from the dyeing process. Emissions of IR agent active substance are reduced by approximately 90 % when compared with the baseline process.
The example given in the table below illustrates the effectiveness of acid after-treatment.
Table 4.37: Indicative emissions from loose fibre dyeing Cross-media effects None believed likely.
Applicability The above techniques are applicable to all installations.
It is reported that this mothproofing technique may affect the quality of the product after dyeing [281, Belgium, 2002].
Economics The aftertreatment process requires additional time to complete, adding an average 30 minutes to a dyeing cycle. Productivity is reduced accordingly and the energy required to maintain the dye bath at elevated temperature increases overall consumption.
Reference plants Acid aftertreatment is reported to be used extensively by UK industry. A number of installations apply this technique in combination with rinse liquor recycling.
Reference literature [32, ENco, 2001] 18.104.22.168.2 Proportional overtreatment of loose fibre Description This technique utilises the fact that an intimate blend of treated and untreated fibres will be resistant to insect attack providing that the overall blend treatment level is maintained. In practice only a proportion of the fibre is treated, by adding mothproofer at an increased rate to one or more dyeings. The remaining fibre receives no treatment. Mixing of the two fibre types is achieved during mechanical blending.
The technique can be used for the preparation of both solid shades and yarns with mixed colour effects. The ratio of treated to untreated fibre can be varied, but normally between 5 and 20 % of the total blend weight would be treated.
Fewer dyeings are carried out in the presence of mothproofer, but the higher application rates required would under normal circumstances result in higher emissions from those dyeings, which may exceed the emissions arising from the normal production sequence. In practice it has been found that plant using this techniques for more than a very small proportion of their production must install some form of dedicated dye liquor re-use system to manage waste water concentrations.
Moreover, both the spent dye liquor and the rinse liquor may need to be re-used, which implies the construction of dedicated machinery, a revised drainage system and the installation of liquor storage tanks. A revision of the dyeing methods and dyestuff / auxiliary selection may be required to minimise colour contamination.
Main achieved environmental benefits
Using a dedicated installation and treating only 5 % of the total fibre blend with insect resist agent is an efficient way of providing protection to a large volume of finished carpet. Estimates of the waste water emissions from such an installation show values of less than 0.2mg active substance/kg fibre, which at a 5 % blending ratio is equivalent to 0.01mg active substance /kg of spun yarn.
Cross-media effects None believed likely when compared with the baseline process. However, as stated above, the application of this measure alone without dedicated dyeing machinery and waste water recycling systems does not provide sufficient reduction of the emissions of IR agent.
Applicability The technique can only be adopted on a significant scale by using specially constructed equipment and is not, therefore, applicable to the majority of dyehouses.
Economics On a self-build basis the cost of constructing a dedicated installation from available materials is said to be in excess of EUR 130000.
Reference plants One installation is known to exist in the UK. No design or operational details are available.
Reference literature [32, ENco, 2001]
Mothproofer Application Point Potential for emission to water Figure 4.29: Process Map for Mothproofing Dry-Spun Production [32, ENco, 2001]
22.214.171.124 Specific process modifications to minimise the emission of insect resist agent active substance during the treatment of stock dyed-yarn scoured production Figure 4.30 illustrates the baseline process used for the application of mothproofer to yarn produced by the loose fibre dyeing – yarn scouring route. In the baseline process insect resist agent is applied during loose fibre dyeing. The fibre is then converted to yarn and scoured to remove mill dirt and spinning lubricant.
Emissions of mothproofer arise from the dyeing and rinsing operations and from the yarn scouring operation, as mothproofer is removed from the spun yarn during this operation and concentrates in the scour liquor.
Figure 4.30 indicates that there are three possible alternative modifications to the baseline
process that may be applied to reduce mothproofer emissions:
· Process A: application of agent from the final bowl of the yarn scour – uses conventional, existing equipment and eliminates emissions at the dyeing stage · Process B: uses dedicated application machinery designed to operate at very low volumes – eliminates emissions from the dyeing process and fugitive emissions from the conventional scour bowl application · Process C: application of the insect resist agent directly to the carpet pile using dedicated foam application machinery – equipment is self contained and can be operated without emissions to water.