«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
The next level is the process or machine level. Chapter 3 contains examples of analysis of consumption and emission levels for some specific processes. In many cases this level of information directly leads to identification of options for improvement and optimisation.
Figure 3.9 shows an example of input/output assessment at process-specific level (the example deals with energy and water consumption, but the same approach can be applied for other parameters).
Main achieved environmental benefits The described evaluation and inventory of input/output mass streams is an essential management tool for the identification of optimisation potential, both environmental and economic. It is the prerequisite for a continuous improvement process.
Operational data The application of such a management tool requires highly qualified staff and management commitment at the highest level. The work of such experts generally pays for itself, but this is not yet widely understood.
Cross-media effects There are no cross-media effects to be mentioned. On the contrary, the input/output streams assessment/inventory allows cross-media effects to be taken into consideration during the assessement of potential optimisation options. This means the achievement of a high level of protection of the environment as a whole.
Applicability The technique is applicable to both existing and new installations. Provided that the management of a company is convinced of the benefits of such a tool, there are no limitations in applicability, regardless of the size of the mill.
Economics There is no specific information available on economic aspects but, generally speaking, because of the big potential for improvements in the textile sector, the application of the described management tool pays for itself within a short time [179, UBA, 2001].
Driving force for implementation Saving on raw materials and production costs is good business. The application of this type of approach makes it easier to implement environmental management systems under EMAS/ISO 14001.
Reference plants There are various textile finishing industries in Western Europe which have implemented input/output streams evaluation and documentation as inventories on site level. Only a few are also systematically applying this instrument on process level.
References literature [179, UBA, 2001] 4.1.3 Automated preparation and dispensing of chemicals Description Great improvements have been made in recent years in the automation of traditionally manual process steps, such as the preparation and dosing/dispensing of chemicals (as either aqueous solutions, powder or pastes) and even laboratory operations.
Automated colour kitchens and automated chemicals dosing and dispensing systems are now commonly applied in many companies in the textile industry. Microprocessor-controlled dosing systems meter chemicals automatically according to a variety of profiles, such as constant rate or variable rate.
In the case of highly concentrated padding liquors for pretreatment, dyeing and finishing (continuous and semi-continuous processes), it is of environmental relevance to prevent or to minimise excess liquors. Today, there are automated systems available for just-in-timepreparations of liquors. With on-line measurement of the liquor pick-up and of the quantity of processed fabric, the exact amount of liquor can be prepared and added. Liquor surpluses and waste water pollution are therefore minimised.
Moreover, in modern dosing and dispensing systems, the water used for washing the preparation vessel and supply pipes is taken into account when the quantity of liquor to be prepared is calculated. This approach reduces waste water, but still involves premixing of chemicals. Other automated dosing systems are available where the chemicals are not premixed before being introduced into the applicator or dyeing machine. In this case, individual streams are used for each of the products. As a result, there is no need to clean the containers, pumps and pipes before the next step, saving even more chemicals, water and time. This is an important feature in continuous processing lines.
Figure 4.2 shows an example of an automated systems for dispensing chemicals for the preparation of pretreatment and finishing liquors (without premixing of the chemicals).
Similar devices can be used in semi-continuous (cold pad batch - see the relevant described technique in Section 4.6.7) and continuous dyeing.
Figure 4.2: Example of automated systems for dispensing chemicals
In addition to the improvements mentioned above, the most recent developments in dosing systems for carpets and bulky fabrics, although expensive, are still worth mentioning. The most advanced equipment allows on-line real-time preparation, dosing and application of each of the individual components. The most innovative machines and application systems work on the colour-on-demand principle. There is no longer any need to make measurements; the liquors are injected or applied digitally and quantitatively. As a result, there are no liquor residues at the end of the process.
Important improvements have also been made in laboratory operations. All laboratory operations needed in batch dyeing can now be carried out with fully automated systems with practically no need for manual intervention. These sophisticated systems have been succesfully applied in some large dyehouses.
Main achieved environmental benefits Automation leads to a number of environmental benefits.
First of all, tighter control of the process allows for improved right-first-time perfomance, which means minimising corrective measures such as reworks, redyes, stripping and shade adjustment.
Secondly, automated systems with just-in-time preparation of liquors and separate dispensing of the different chemicals (i.e. no premixing) allow a significant reduction of waste water pollution and wasted chemicals thanks to the minimisation/ avoidance of liquor residues that would otherwise need to be disposed of at the end of the process. This is particularly important in continuous and semi-continuous processing.
Another important issue to consider is a safer and healthier working environment. Eliminating human contact means no workers handling and breathing toxic and hazardous substances.
Operational data Highly automated systems generally require qualified personnel, but usually one person can easily operate the system.
Automated systems for powders are highly sophisticated, especially when very small amounts have to be metered. High precision in dosing is fundamental, especially for powder dyes.
Modern automated dosing systems can dose amounts of powders as small as 0.8 g [289, Comm., 2002].
Data from a textile dyehouse (size 5500 t/year) show the following improvements before and after the installation of an automated dosing and dispensing system for chemicals [289, Comm., 2002].
Another example comes from a well-known Italian manufacturer who, due to the installation of an automated dosing and dispensing system for dyes and auxiliaries, no longer needed a sampling operation on the batches and so was able to replace it with an extra daily batch on each machine [289, Comm., 2002].
Automated laboratories can reduce reworking to 2 – 3 % of total production.
Cross-media effects There are no cross-media effects to be mentioned.
Applicability Typical automated dosing and dispensing techniques described in this section are applicable to both new and existing installations. However, exception is made for highly sophisticated techniques such as dosing systems based on the colour-on-demand principle and automated laboratories, which are still very expensive and as a consequence more suitable for large installations.
According to information provided by equipment suppliers, the size and the age of the plant do not seem to represent a limitation in the applicability of automated dosing and dispensing systems in general. Examples are available of plants with production capacity ranging from 70 t/day to 5 t/day [289, Comm., 2002].
Space availability may represent an issue in existing companies, especially for the automation of dyes. Whereas liquid chemicals are easy to automatate due to the limited number of chemicals used in the process, some companies may regard the high number of dyes as a limitation due to lack of space and higher investment costs required.
It is not uncommon to find dyehouses with 150/200 different dyes for various reasons.
However, in most cases it should be possible to use a maximum of 15 colours for each fibre, which means 90 dyes for 6 different types of fibre [289, Comm., 2002].
Usually the colourants that are used more frequently (highest consumption) are selected for automation. A typical situation is the one in which a company uses 60 colourants with a daily consumption of 5 - 6 kg and 20 colourants in amounts as low as 10 g/day. In such a situation, it is likely that the company will decide to automatise the 60 dyes with higher consumption and leave the others for manual dosing and dispensing. Very often this choice encourages the company in giving preference to dyes that are automatised, gradually reducing the consumption of the other dyes [289, Comm., 2002].
In automated systems with separate dispensing of the different chemicals, the resulting environmental benefits are particularly important where chemicals and auxiliaries are used in large amounts in the mill and in long continuous lines (where the dead volume in the distribution system is comparable with the volume in the padder). When the different chemicals are not mixed before the process they can be easily re-used for the next run. Separate dispensing of each dye, although technically possible, is very expensive and advantageous only for trichromatic systems where a few dyes are used (maximum nine different dyes) and the volumes recovered are high enough to justify the investment.
Investment costs for the automated dosing of liquid chemicals, depending on the number of machines to be served, liquors to be prepared and chemicals to be used, range from EUR 230000 to EUR 310000. For powder dyes, the investment is between 250000 and 700000 euros, whereas for powder auxiliaries the prices range from a minimum of 110000 up to a maximum of 310000 euros. The reported figures do not include costs for pipes and conjunctions [289, Comm., 2002].
Cost savings can be derived from a reduction of consumption of chemicals and water, increase of reproducibility and decrease in staff costs. Savings of up to 30 % have been reported by [179, UBA, 2001].
Liquid chemicals are the most commonly automatised (first option in existing companies) due to health & safety reasons, but also due to the relatively low investment needed (limited number of chemicals used in the process) [289, Comm., 2002].
Driving force for implementation The main driving forces for implementation are increased reproducibility and productivity along with health and safety requirements defined by legislation.
Reference plants Plants with automated dosing and dispensing systems represent more than 60 % of the existing dye and printing houses in Europe. Automated systems for liquid chemicals are the most common (70 % of the plants), whereas automated dosing and dispensing for powder dyes and auxiliaries are present in 20 % of the European installations [289, Comm., 2002].
Some examples of installations using automated systems for just-in-time preparation of liquors
are in Germany:
- Brennet AG, D-79704 Bad Säckingen
- Schmitz Werke GmbH + Co., D-48282 Emsdetten
- Görlitz Fleece GmbH, D-02829 Ebersbach
- Thorey Gera Textilveredelung GmbH, D-07551 Gera.
There are many examples of installations equipped with fully automated in Europe and worldwide.
Reference literature [179, UBA, 2001], [171, GuT, 2001], [76, Colorservice, 2001], [289, Comm., 2002].
4.1.4 Optimising water consumption in textile operations Description Textile processing is known to be a water-intensive sector. Many techniques in this chapter, including some of the housekeeping measures already mentioned in other parts of this document, deal with reducing water consumption. Some aspects are common to many treatments. This section is intended to be a summary of the factors that may be of more importance for optimal water usage.
Controlling water consumption
A prerequisite of any programme to prevent unnecessary waste of water is to firstly collect information on the installation and the volumes consumed in the various processes. This kind of audit/assessment should actually be part of a wider programme involving the collection of information on types, quantities, composition and sources of all waste streams (see Section 4.1.2).
As with water consumption, data at site level is already a good benchmark in determining whether water consumption is excessive and is a good baseline against which to measure improvements. A process-specific analysis, however, is fundamental for setting priorities and identifying potential pollution prevention options. Water use should be monitored and recorded at machine/process level and water meters should be regularly maintained and calibrated.
Reducing water consumption · by improved working practices Inappropriate working practices and the absence of automated control systems can lead to
significant wastage of water, e.g.:
· during filling and rinsing, for example, where machines are equipped only with manual water control valves there is potential for overfilling · displacement spillage during immersion of the fibre in the machine may account for up to 20 % of total operating volume over the course of a dyeing cycle (this may also lead to losses of dyes and hazardous chemicals if these are introduced before the displacement takes place).
Well-documented production procedures and training are important. Dyeing machines should at least be fitted with modern process control equipment, capable of accurately controlling both the fill volume and the liquor temperature.
· by reducing liquor ratio In continuous dyeing, the dye is applied in the form of a concentrated liquor. The volume of water consumed per kg of processed fabric in the dyeing process is therefore fairly low even when using conventional application systems (e.g. padders). This volume can be even lower in more recently developed application systems (e.g. fluidyer, foam, flexnip application systems, etc. – see Section 10.4.2).
As already explained in Section 126.96.36.199, in batch operations the amount of water used per kg of processed substrate is higher, although there has been considerable improvement in this field, too. All major machine manufacturers now have units for dyeing at low liquor ratio. An investment in such units pays because it cuts operating costs (energy, water, chemicals, dyes, etc.) and raises productivity by reducing processing times (see also Sections 188.8.131.52 and 4.6.19).
· by improving washing efficiency
In both batch and continuous processing, water consumption for washing is significantly higher than for the treatment itself (e.g. dyeing, etc.) (see also Section 184.108.40.206). Modern continuous washing machines have greatly improved their washing efficiency. In batch processes, it is not straightforward to achieve a high washing efficiency with little water and in a short time and therefore low liquor ratio does not always correlate with reduced water use as one might expect.
Indeed it is not uncommon to find machines able to dye with a liquor ratio of 1:5 and then rinse with a liquor ratio of 1:10. Moreover conventional machines can only handle unloading by increasing the liquor ratio.