Exhaust air purification in the textile industry
In the textile industry, fabric surfaces are coated from different materials, such as wool, cotton, polyacrylic, polyamide, polyester, or viscose/acetate. The fabrics are preliminary products for different textile areas such as home textiles, technical textiles or clothing.
The respective fabric surfaces are first treated with a coating process and then thermally treated in a segmented stenter frame (flatbed dryer) with 2 to 10 fields.
In the stenter frame, fresh air is directly heated with town gas and fed to the individual fields at different operating temperatures.
The exhaust air generated by this process can be discharged from the stenter frame using either one or two exhaust ducts. Temperatures can range from 120 to 230°C depending on the treatment process and material.
During the thermal treatment process, organic products such as ketones, amines, stearates, alcohols, but also water are used and released into the exhaust air together with condensation products such as formaldehyde or reaction products of the coating materials as well as excess methane from the direct heating.
In addition, blue smoke can be generated by the thermal treatment of PES. The operation of the drying plants for textile applications is carried out in discontinuous operation.
The emissions are strongly dependent on the respective coating formulations. In addition, ammonium stearates can be used, which react to form sodium stearates (candle wax) when unsoftened water is used. The waxes form irreversible deposits on UV-C equipment. The effectiveness of the UV-C lamps is reduced to the point of ineffectiveness.
UV ozone technology is used in many plants to purify textile exhaust air. To cope with the technical conditions, the configuration usually consists of an air-to-air heat exchanger to reduce the temperature from approx. 180 to 220°C to approx. 130°C and the cost-reducing energy recovery as well as a scrubber with condensate separator. With the scrubber, the exhaust air temperature is reduced to approx. 40 to 50°C, stearates and solvents are separated from the exhaust air.
However, because the water-soluble organic exhaust air constituents return proportionally from the water to the gaseous phase after the dissolution process in the scrubbing water according to the vapor pressure, only gaseous VOCs are present in the UV-C reactor, which are degraded oxidatively and radically. A catalyst may be used to extend the reaction time for degradation of the organic matrix.
The VOCs or odor units are measured and determined either with an FID or olfactorily.
- The TA Luft is fulfilled.
- Odors are practically no longer perceptible outside production.
- The recovered heat can be fed back into production.
- The UV lamps remain clean
- The maintenance effort is low.