VOC reduction in the printing-, painting- and coating industry

VOC in the printing, painting and coating sector

Liquid paints, lacquers, varnishes, inks and adhesives based on organic solvents contain a certain quantity of volatile organic compounds (= VOC) such as alcohols, glycols, esters, hydrocarbons and ethers (e.g. toluene, benzene, butane, methane, isopentane, ethane, ethylene, pentane, propane). Many volatile organic compounds are released when, for example, mixing components in open mixing systems, cleaning machines with solvents or when coating is applied, at the level of the flash-off zones and in the drying ovens. The VOC content varies according to the printing methods. Heatset inks are among the largest polluters. They consist of 35-40% VOC. In gravure and flexographic printing, the inks can contain up to 70% VOC. In view of the negative impact on people and the environment, there are strict guidelines regarding VOC emissions. In addition to VOC, HAPs (hazardous air pollutants), unpleasant odours or toxic gases can also be released.

RTO as a solution

Ideally, as few organic solvents as possible should be used. However, in some situations, this is inevitable. A post-treatment of VOC emissions ensures controlled emission.

One way of rendering volatile organic compounds and other air pollutants harmless is to oxidise them with oxygen at high temperature. By initiating an incineration reaction, the air pollutants are oxidised and converted into harmless products such as CO2, H2O and usable heat. For this purpose, PCA Air offers the regenerative thermal oxidator (RTO) as the most effective and cost-efficient solution.

A RTO is an air pollution control device in which the polluted process air is in most cases pushed through three ceramic beds. In the first ceramic bed, the process air is heated to the combustion point. The air therefore undergoes oxidation. The warm and clean air is then led down through the second ceramic bed, where the air is cooled. Finally, there is also a third ceramic bed, which is cleaned. In this way we get an effluent flow that is as constant as possible. The heat released by such regeneration of the heat exchanger ensures a thermal efficiency of up to +- 95%, which is much higher than the traditional recuperative heat exchangers.

RTO is also designated by the Flemish BBT knowledge centre as one of the best available technique for the printing industry. Fuel is only used if the system has been idle for a weekend. The waste streams therefore often contain VOC concentrations around or above the autothermal point. Finally, there are also dryers with a built-in thermal burner, but according to the BBT knowledge centre it is more reliable and cheaper in the long run to install one central RTO. 

For the paints, lacquers, varnishes, printing inks and adhesives industry BBT recommends the following: if possible, try to use as few organic solvents as possible. In situations where it is unavoidable, they recommend treating the VOC emissions with a RTO in order to achieve controlled emissions.