Danish experience. Best Available Techniques – BAT - in the clothing and textile industry
1. Cleaner technology in pigment printing
In pigment printing, the printing paste is applied to the surface of the fabric through different types of screens perforated in patterns and figures – one screen for each colour. The fabric is transported under the screens on an endless belt – the printing belt – momentarily fixed with water-soluble glue to avoid dislocation of the fabric relatively to the screens. To keep the printing belt totally smooth and clean from printing paste, fluff and lint, the printing belt is rinsed with water on its way back to the start of the printing machine.
The pigments are bonded to the fibre with a bonding agent by heating and the printed fabric does not require washing or rinsing after printing.
The equipment used around the printing machine – screens, buckets (for mixing, transporting and storage) and the print paste feeding system (i.e. pumps, hoses, pipes and squeegees) needs careful cleaning before it can be used for new colours.
In pigment printing, several CT-options are related to reduction in the consumption and discharge of water and printing paste. Two options are described:
1.1 Reduction in water consumption in cleaning operations
In connection with cleaning operations, there are several possibilities to reduce the water consumption. The following CT-options are described:
- Start/stop control of cleaning of the printing belt.
- Mechanical removal of printing paste.
- Reuse of the cleanest part of the rinsing water from cleaning of the squeegees, screens and buckets.
- Reuse of the rinsing water from cleaning of the printing belt.
It should be emphasised that these options are also relevant in connection with printing with dyestuffs.
1.1.1 Description
A) Start/stop control of cleaning of the printing belt.
In many cases, water dosage for the cleaning of the printing belt continues when the fabric - and thereby the printing belt - is stopped for whatever reason. A start/stop of the water dosage can be automatically connected to the start/stop of the printing belt.
B) Mechanical removal of printing paste.
Large amounts of water for cleaning of squeegees, screens and buckets are used within the print-house. An improved printing paste removal before flushing of this equipment would lead to a reduced need for water for flushing. In Denmark, physical devices for removal of dye from buckets have been developed (e.g. scraper). Some modern printing machines have a built-in system for mechanical removal of residual printing paste from pipes and hoses.
C) Reuse of the cleanest part of the rinsing water from cleaning of the squeegees, screens and buckets.
Typically, the first half of the effluent from the washing equipment is heavily loaded with printing paste and will have to be discharged as wastewater. On the other hand, the water quality demand for reusable rinsing water in this first part of the washing process is low. In the last half of the washing process, clean water must be used, but the effluent can be collected for reuse.
D) Reuse of the rinsing water from cleaning of the printing belt.
The rinsing water from cleaning of the printing belt is only slightly coloured and contains small amount of fibres (depending on the fabric) and very small amounts of glue. The rinsing water can be mechanically filtered, collected in an overflow vessel and reused for the same purpose, if minor amounts of fresh water are added to the recycling system.
The following are common features for option 1.1.A – D unless otherwise specified.
1.1.2 Main achieved environmental benefits
The environmental benefit is a reduction in the water consumption. In a Danish pigment print-house, the implementation of all the above options has reduced the annual consumption of water by approximately 25,000 m3 (55% reduction). For option 1.1.A alone, the savings are estimated at approximately 2 m3 for every hour the printing machine stops and the water dosage for cleaning of the printing belt is still running for whatever reason. For option 1.1.C, 50% of the water is reused. For option 1.1.D, approximately 70% of the water is recycled.
1.1.3 Cross-media (whole environment) effects
 | Reduction in water consumption. |
| Ability to re-use wastewater. |
1.1.4 Applicability
Option 1.1.A – D can be implemented in all types of textile companies involved in printing; new or existing, large or small. Space availability is a minor factor – the company only needs space for collection tanks (option 1.1.C and 1.1.D). However, older printing machines can probably not be retrofitted with a device for mechanical removal of the residual printing paste from pipes and hoses in the printing machine (option 1.1.B).
1.1.5 Economics
In the Danish case mentioned above, the total capital costs (tanks, mechanical filters, pumps and pipes) for all options are estimated at approximately DKK 100,000 (» EUR 13,500). Option 1.1.C and 1.1.D together approximately DKK 95,000 – option 1.1.A approximately DKK 5,000 – option 1.1.B negligible. Change in operating costs (before and after implementation) for all options are negligible. The costs for fresh water and wastewater discharge are DKK 9 and DKK 18 per m3, respectively. Hence the total annual savings are approximately DKK 675,000 (» EUR 90,000). Payback time for all options together is estimated at about two months.
1.1.6 Driving force for implementation
High costs for fresh water and wastewater discharge.
1.1.7 References to literature and example plants
Example plants:
Danish Colour Design Textile Print A/S
Mylius Erichsensvej 52
7330 Brande
Denmark
| Att: | Mr Benny Hansen |
| Phone: | + 45 97 18 19 22 |
| Fax: | + 45 97 18 19 11 |
| E-mail: | dcd@teliamail.dk |
Literature:
DANCEE, 1999. Cleaner Technology Transfer to the Polish Textile Industry. Idea catalogue and selected options, 1999. Danish Ministry of Environment and Energy. Danish Environmental Protection Agency. DANCEE – Danish Co-operation for Environment in Eastern Europe.
Danish EPA, 1994. Survey of the handling of resources in the wet processing of textiles. Environmental project no. 268, 1994. Danish Ministry of Environment and Energy. Danish Environmental Protection Agency. (In Danish).
1.2 Reduction in consumption of printing paste. 1.2.1 DescriptionThe printing paste, which is left over after printing, can be collected and reused. The optimum solution implies collecting residual printing paste from as many pieces of equipment as possible, e.g. at least from squeegees and buckets. As mentioned for option I B, some modern printing machines have a built-in system for removal of printing paste from pipes and hoses. The use of PC-based recipe formation and a database can facilitate reuse of printing paste with information on the composition of the collected printing paste including information about the durability. Normally the durability is not a problem.
1.2.2 Main achieved environmental benefits
The main environmental benefit is reduction in the quantity of hazardous waste. In a Danish pigment print-house, this option has reduced the amount of hazardous waste for special treatment by approximately 25,000 kg printing paste / year (60% reduction).
1.2.3 Cross-media (whole environment) effectsPotential effects:
| Reduction in consumption and emission of chemicals. |
| Reduction in hazardous waste. |
| Less particulate matter (including micro-particles and metals) in the wastewater. |
| Ability to re-use printing paste. |
1.2.4 Applicability
This option can be implemented in all types of textile companies involved in pigment printing - new or existing, large or small. Space availability is a minor factor. However, to achieve the maximum benefits, it is necessary to be operating with or implement a PC-based recipe formation system. In addition, the print-house needs to be operating with an automatic colour dosage system (so-called "dye-kitchen"). Furthermore, operating with modern printing machines with a built-in system for mechanical removal of printing paste from pipes and hoses in the printing machines will increase the amount of printing paste that can be collected and reused.
1.2.5 Economics
In the Danish case mentioned above, the total capital costs (extension of printing paste weighing system, software and extra buckets) are estimated at approximately DKK 80,000 (» EUR 10,500). Change in operating costs (before and after implementation) are negligible. The economic value of the collected and reused printing paste is approximately DKK 5 per kg (savings DKK 125,000). The costs for disposal of hazardous waste in Denmark are DKK 1,500 per tonnes (savings DKK 37,500). Hence the total annual savings are approximately DKK 160,000 (» EUR 21,500). Payback time is estimated at about six months.
1.2.6 Driving force for implementation
High costs for printing paste and disposal of hazardous waste.
1.2.7 References to literature and example plants
Example plants:
Danish Colour Design Textile Print A/S
Mylius Erichsensvej 52
7330 Brande
Denmark
| Att: | Mr Benny Hansen |
| Phone: | + 45 97 18 19 22 |
| Fax: | + 45 97 18 19 11 |
| E-mail: | dcd@teliamail.dk |