OPERATION OF LAFER SOLVENT SCOURING PLANT

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Percival Farmer
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1 OPERATION OF LAFER SOLVENT SCOURING PLANT INDEX Operation principle... page 2 Machine attachments... page 3 Plant service s... page 4 Machine start-up and stop... page 5 Safety systems of plant... page 5 Environmental impact... page 6 Page 1 of 6

2 OPERATION OF LAFER SOLVENT SCOURING PLANT The washing process is developed on a new system aimed to recover almost totally the solvent used and to completely avoid intakes (water and air). The following diagram shows the processing and recovery steps of perchloroethylene. FABRIC Inlet ACTIVE CARBON FILTER Unit Fabric WASHING Unit Fabric DRYING Unit Fabric DEODORIZING Unit MAIN DISTILLER CONDENSING AND DISTILLATION MUD DISTILLER PERCHLORO filtering DRYER condensing FABRIC exit WATER RECOVERY OPERATION PRINCIPLE The above processing exploits the excellent features of perchloroethylene to dissolve oils and greases coming from the previous preparing processes of the yarns and fabrics. Perchloroethylene used as a washing agent is totally recovered, purified and recycled in continuous. The only resulting product is the waste mud. The continuous fabric washing process starts and ends with dry fabric. The washing process includes the following steps: Step 1: solubilisation of fabric oils and greases by perchloroethylene washing. Washing is carried out by: Perchloroethylene spraying at adjustable pressure on both fabric sides, by means of flat spray nozzle showers Air vacuum extraction of perchloroethylene from the fabric, by means of slit pipes in contact with the fabric Final rinse of the immersed fabric by using clean solvent Step 2: after washing the solvent soaked fabric runs on a special net cylinder where, thanks to a forced hot air circulation system, the perchloroethylene is evaporated. Page 2 of 6

3 Step 3: after drying, the fabric is deodorized to remove the residual perchloroethylene. Deodorizing is carried out by air in a closed circuit on a net cylinder; air circulation is provided by an electric fan. At the end of step 3 the fabric is ready for the next finishing processing. MACHINE ATTACHMENTS PERCHLORO filtering : the perchloroethylene used in washing, is moved by electropumps and filtered by a belt system. The continuous intake of clean solvent coming from the distillation in the washing tank causes the overflow of perchloroethylene charged with greases removed from the fabric into the filter where solid particles (fibres, impurities, etc.) are hold back, while the filtered product is conveyed to the distiller. DRYER condensing : the perchloroethylene evaporated from the fabric in the drying chamber, is recovered by a closed circuit system. A part of the air of the drying circuit, goes through the condensing water cooled exchanger. The condensed perchloroethylene is clean and can be re-used, while the air returns to the drying circuit. ACTIVE CARBON FILTER : this is essential to purify the air during deodorizing and to collect the air mass movements of the plant. The particular affinity of perchloroethylene with plant active carbon makes the filtered air practically perchloroethylene-free. The recovery of perchloroethylene from active carbon is carried out by means of direct steam and is condensed by a water cooled exchanger. The is equipped with a pad (safety) filter which ensures the maximum efficiency during absorption. Page 3 of 6

4 PLANT SERVICE UNITS The perchloroethylene used in fabric washing and containing the weaving oils and greases, is regenerated and re-used at clean condition. The regeneration is carried out by distillation for which purpose the machine is equipped with the following s: MAIN DISTILLER : aimed to regenerate the perchloroethylene used for rinsing in the washing. The perchloroethylene coming from the washing filtering enters the main distiller where a steam heat exchanger provides for its regeneration. Steams are conveyed to distiller condensing, while a continuous perchloroethylene quantity is sent to the mud distiller. MUD DISTILLER : aimed to separate the greases (mud) from perchloroethylene. The distillation includes two stages: perchloroethylene evaporation and mud drainage. The constant flow of perchloroethylene coming from the main distiller enters the steam heat exchanger which evaporates it. The mud concentration increase in the distiller will involve a temperature rise of perchloroethylene/mud mixture. When a preset temperature value is achieved, the distiller will automatically carry out the mud concentration and discharge. The perchloroethylene steams are conveyed to the distiller condensing. DISTILLER CONDENSING : aimed to condensate the steams coming from the main distiller, mud distiller and active carbon filter s. The condensation is carried out by means of a water cooled exchanger. The condensed perchloroethylene is collected at the bottom of the condenser where, by specific gravity difference, it is separated from the water coming from direct steam used in carbon filter and mud distiller s. The perchloroethylene is sent to washing, while the water is collected in water recovery. WATER RECOVERY : aimed to recycle water coming from the separator of distiller condensing. A new system allows to reuse the water in the plant. Page 4 of 6

5 PLANT START AND STOP In order to avoid mistakes of the operator during the machine start or stop, the operator s board includes the control for automatic operation. SAFETY SYSTEMS OF THE PLANT The washing plant was designed with particular care to the environment, safety and operator s protection. For this purpose, different technical measures have been taken in order to prevent any leak of perchloroethylene. The special technical measures are the following: 1) No air discharge in the working room or outside. 2) No processing water discharge (water that came in contact with the perchloroethylene). 3) Machine equipped with metal seats at fabric entry and exit. 4) Machine equipped with immersion seat at washing entry. 5) Safety system for possible irregular pressure in distillation s. 6) Air purifying system with active carbon filters connected in series (the first filter restrains the perchloroethylene, the second one has a safety function). 7) System checking the correct operation of the active carbon filters. 8) System checking the correct operation of the main distiller and mud s. 9) System constantly checking the plant which, besides controlling the functions during normal operation, also provides for management of the emergency functions. 10) Use of particular radial seals made of special material to avoid the wear and tear of the shafts in the contact area. 11) Portholes equipped with thick glass to avoid possible breaks and with a heat resistant diaphragm on the portholes on high temperature s. 12) Machine access doors equipped with soft gasket for a perfect seal which can be opened only by the tools supplied to the maintenance staff. 13) VITON OR seals. 14) AISI 304 steel electropumps with mechanical seal. 15) Ball valves for perchloroethylene flow, in AISI 304 steel with TEFLON seal. Page 5 of 6

6 16) The operator cannot get in contact with perchloroethylene wet filters during the processing. 17) Safety sensors to detect perchloroethylene in the working room. ENVIRONMENTAL IMPACT Fabric washing by using perchloroethylene is the best solution to remove the spinning oils and greases. In the heatsetting a considerable reduction of smokes coming from the sublimation of residual grease is achieved. In addition to a better colour uniformity and brightness, dyeing offers a higher performance of the dyestuff with a lower consumption of the same. Perchloroethylene washing has a fairly restricted environmental impact compared to washing in water: the current fabric washing technology with perchloroethylene, besides a considerable energy saving compared to water washing (the machine processes dry to dry fabric), does not involve air or water discharge in the environment. The only hazardous waste subject to disposal is the distillation waste mud (greases released by the fabric) containing a perchloroethylene quantity <1% in weight: - code CER (Decision 2001/118/CE). Water washing, besides the considerable energy consumption to dry the wet fabric water content, involves high consumption of water that needs to be purified. Page 6 of 6

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