An innovative sustainable process for VOCs recovery from spray paint booths

摘要

Air emissions from surface coating operations result from the evaporation of the organic solvents in the coatings and consist primarily of volatile organic compounds (VOCs). These VOC emissions can occur in a number of places along the production line: during atomization and application of the coating, during initial air drying of the part after it leaves the spray paint booth, and, eventually, in the bake oven. The aim of this paper is to present an innovative and sustainable process based on VOC absorption. An absorption tower is fed on the top by oil, which efficiently absorbs at low temperature the VOCs contained by the off-gas that enters the tower at its bottom. The mass ratio between oil and gas is approximately 1, so that a tray configuration results more efficiently than an alternative packed column. Saturated oil from the column is then stripped at high temperature in a vacuum system that condenses VOCs at a temperature slightly below the ambient temperature. Stripped oil is then recycled to the absorption tower. Special utilities are foreseen to reduce the water content in the gas and for energy recovery all over the plant. An industrial site located in Italy works at 14,000 Nm~3/h off-gas absorbed with slightly more than 10 m~3/h of oil. VOCs content in the off-gas ranges daily from 1200 to 2500 ppm; an average efficiency of approx. 90% recovery is presently obtained. A further reduction to an expected value of about 95-98% will be achieved in the next months.