Measures for the reduction of water consumption and process water recycling. Brigitte Zietlow German Federal Environment Agency

Transcription

1 Measures for the reduction of water consumption and process water recycling Brigitte Zietlow German Federal Environment Agency

2 2 Outline General technical measures to reduce water consumption Water re-use/recycling in batch dyeing processes Efficient washing processes Efficient cleaning processes Recycling of textile waste water

3 3 General technical measures to reduce water consumption Education/ training of employees: All staff should understand clearly the precautions needed to avoid water wastage Monitoring of water consumption in the various processes, Leak control: audits should be carefully conducted for broken and leaking pipes, drums, pumps and valves Use of flow control devices and automatic stop valves on continuous machinery Use of automatic controllers for control of fill volume and liquor temperature in batch machines

4 4 General technical measures to reduce water consumption optimisation of scheduling in production (e.g. in dyeing: dyeing dark shades after pale shades reduces water and chemicals consumption for machine cleaning; in finishing: proper scheduling minimises machine stops and heating-up/cooling down steps) adjustment of processes in pretreatment to quality requirements in downstream processes (e.g. bleaching is often not necessary if dark shades are produced) combination of different wet treatments in one single step (e.g. combined scouring and desizing, combined scouring/desizing and bleaching) Use of low- and ultra-low liquor ratio machinery in batch processes

5 5 Minimisation of dye liquor losses in pad dyeing techniques Reduction of residual dyeing liquor can be achieved by minimising the capacity of the dip trough (e.g. flexshaft, 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%. BREF Textile Industry Chapter 4.6.7

6 6 Water re-use/recycling in batch dyeing processes exhausted hot dye baths are analysed for residual colourant and auxiliary concentration, replenished and re-used to dye further batches holding tanks for the spent baths are needed modern batch dyeing machines have built-in holding tanks for uninterrupted automatic separation of concentrates from rinsing water easiest systems for re-use are dye classes with high affinity (exhaustion) and mimimum changes during the dyeing process (e.g. acid dyes for nylon and wool, basic dyes for acrylic, direct dyes for cotton and disperse dyes for synthetic fibres) on average four cycles of the same shade are possible Reduction of overall water consumption of 33 % Cost savings (depending on water price and effluent disposal costs) BREF Textile Industry Chapter

7 Airflow jet dyeing machines the use of air, either in addition to or instead of water in jet dyeing machines dyestuffs, chemicals and auxiliaries are injected into the gas stream for woven PES fabric: Liquor ratios of 1:2 may be reached for woven cotton fabric lowest liquor ratio is 1:4 separated circuit for liquor circulation without contacting the textile extremely low liquor ratio and the continuous rinsing system results in a virtually non-stop process with Benefits: up to 50 % water savings are achieved compared to conventional machines about 40 % reduced consumption of chemicals ((e.g. salt) less energy needed thanks to quicker heating/cooling and optimum heat recovery Illustration of an airflow dyeing machine THEN-Airflow LOTUS Source: FONG S EUROPE, 2010 The THEN-Airflow LOTUS is developed for the processing of surface and crease sensitive knit and woven fabrics as well as for technical fabrics. Fabrics with lengths up to 1200 m respectively 200 kg can be treated. 7

8 8 Example for reduction of specific water consumption in yarn finishing Company finishing Yarn implemented several measures for reduction of water and energy consumption: Reuse of low loaded water from washing Minimisation of number of process baths via optimisation of washing and rinsing processes and selection of chemicals for removal of dye hydrolysates (reactive dyes) Use of single-head centrifuges for dewatering of polyester cones (reduction of water content from 30-40% with old technique to 8%) Use of waste heat from compressors for drying of cones 29 % reduction of specific water consumption 44 % reduction of gas consumption

9 9 Example for reduction of specific water consumption in continuous washing Optimisation of an old washing machine for continuous washing of dyed fabrics: analysing of washing process (monitoring of colour, ph value, conductivity) Stepwise optimisation with consideration of quality (colour fastness as main parameter), e.g. re-use of parts of washing water Installation of extractors Use of tensides not longer needed Subsequently installed Extractor 70 % reduction of water consumption 80 % reduction of energy consumption

10 10 Efficient washing processes Replacement of overflow rinsing with drain and fill rinsing or smart rinsing. Use of Drain and fill in combination with low liquor ratio machines equipped with time-saving devices (power draining and filling, combined cooling and rinsing, full volume heated tanks) % less water consumption Water conservation in continuous washing and rinsing: Water flow control countercurrent washing Use of squeeze rollers or vacuum extractors for the reduction of carry-over Achievable specific water consumption levels for continuous washing processes Pretreatment process Water consumption (l/kg) Washing for desizing 3 4 Washing after bleaching 4 5 Washing to remove NaOH after mercerisation Washing after dyeing 4 5 Reactive dyestuffs Vat dyestuffs 8 12 Washing after printing Reactive dyestuffs Vat dyestuffs BREF Textile Industry Chapter 4.9.1, 4.9.2

11 11 Reduction of water consumption in cleaning operations equipment used around the printing machine (e.g. screens, buckets and the print paste feed system) needs careful cleaning before it can be used for new colours Measures for reducing water consumption in cleaning operations: a) start/stop control of cleaning of the printing belt b) mechanical removal of printing paste c) re-use of the cleanest part of the rinsing water from the cleaning of the squeegees, screens and buckets d) re-use of the rinsing water from the cleaning of the printing belt. Data of a pigment print hous: 55 % reduction of annual water consumption Option a) savings of about 2 m³ for every hour of stop Option c) 50 % of the water can be re-used Option d) 70 % of the water can be recycled

12 12 Examples after optimised water consumption reduction Technique Polyester knitted goods, continuous prewashing on perforated drum washing machine at 80 C to 35 m/min fabric speed with vacuum sucking technique and discontinuous dyeing (Jet and HT beam) at 130 C with reductive aftercleaning for dark shades in the dyebath Cotton, outerwear, oxidative desizing, cold pad batch reaktive dyeing, mainly continuous technique with roller tub washing machines and vacuum sucking technique Polyester/polyamide yarn dyeing, only discontinuous technique, optimised liqour ratio by using displacement devices and adapted aggregate dimensions Cotton cord fabric, desizing and hot bleaching continuously in two steps, reaktive dyeing in discontinuous technique (Jigger) Dyeing and printing, only continuous technique, mainly cellulosic fabrics, reactive and vat dyeing and printing Polyester/cotton dyeing, continuous technique with polyester Thermosol dyeing with subsequent continuous reactive or vat dyeing on pad steam aggregate Water consumption approx. [l/kg]

13 13 Recycling of textile waste water by treatment of selected streams with membrane techniques Membrane techniques like ultrafiltration, nanofiltration and reverse osmosis are used for treatment of waste water fractions waste water with a high COD value can be treated and directly re-used low-molecular substances can be recovered from the waste water (e.g. dispersants) heat content of waste water can be recovered Composition of a ceramic membrane Source: C. Kahl (2006)

14 14 Recycling of textile waste water by treatment of selected streams with membrane techniques Company A treats woven fabric, mainly consisting of cotton and polyester Process sequence: pretreatment, dyeing (cold pad batch), pigment printing and finishing waste water treatment plant, with a pre-treatment, ultrafiltration, nanofiltration and reverse osmosis. 90% of water is recovered and can be used for most processes in the company (except for bleaching, dyeing and finishing liquors) Waste water from pretreatment (scouring and bleaching) and finishing (residual padding liquors) is not treated in the membrane plant Benefits: reduction in water consumption and waste water discharge of about 60 % COD load in the remaining effluent discharged is reduced by about 50 % Flow sheet of waste water treatment

15 15 Thank you for your attention!