Quantification of re-evaporated mass from loaded fibre-mist eliminators

Airborne lubricant emissions are a serious health hazard for employees in t he metal working industry. The basic components of lubricants are oils and additives for adapting the properties to achieve the process demands. The o ils used in lubricants are either mineral, synthetic or of biological origi n. The lubricants are used as water-emulsions and also as straight oils. Ex treme process conditions cause considerable amounts of aerosol and vapour e missions of lubricants into the working environment. Fibre filters are used in industrial demisters for pollution control and also for sampling purpos es. Re-evaporation of separated lubricants from loaded fibre filters causes increased vapour emissions. Quantification of lubricant vapour emission wa s the subject of this research. An apparatus and an appropriate procedure f or measuring the dynamic behaviour of evaporative losses from fibre filters were developed. The test piece of a loaded fibre filter was fixed in a sam pling probe according to VDI 2066. The vapour concentration of organic comp ounds in downstream air was measured in real-time by using a photo-ionisati on detector (PID). The PID was checked by sampling the vapour on an oleophi lic adsorbent resin, solvent extraction and quantitative IR analysis and al so gravimetrically. The two basic processes of filtering volatile aerosols are, on the one hand, collecting droplets on the fibres and. on the other h and, the evaporation of collected liquid. These two processes had to be sep arated in order to measure the increase of the vapour concentration caused by the tested fibre filler. The experiments were carried out using pure dod ecane and hexadecane in order to avoid difficulties due to the unknown chem ical composition of lubricant vapour. The variation of the air flow and the initial liquid mass on the filter covered the relevant range for industria l fibre demisters and for sampling methods based on collecting aerosols on fibre filters. It was found that the downstream air was saturated with lubr icant vapour for a wide range of filter loads and filtration velocities. Fr om the results obtained it can be concluded that loaded industrial filler s ystems emit air with saturation vapour concentration throughout their opera tion. Hence, vapour emissions can be estimated easily if the saturation vap our pressure and the mean relative molecular mass are known. Moreover, resu lts obtained from measurements of filters with low loads confirm that the p hase transition from liquid to vapour is influenced by the identified proce ss parameters. This is relevant for measurement methods using fibre filters for sampling volatile aerosols. A semi-empirical model to estimate the eva porative losses for low loadings is proposed. However, further research is necessary to determine the full range of parameters that are relevant for e vaporative losses from filters loaded with low masses of aerosols.