FILTRATION-COALESCENCE OF A METALWORKING FLUID USING GLASS FIBER BEDS

摘要

Water-based coolants used in metalworking operations yield unwanted oil-in-water (O/W) emulsions that cannot be disposed without treatment in order to remove the emulsified oil and other pollutants. Emulsion destabilization by coalescence adding inorganic salts, may yield removal efficiencies above 90% after 5 or 10 minutes of settling [1, 2]. After the emulsion coalescence, the resulting aqueous phase shows a turbidity that remains for hours, even days. This turbidity is due to the presence of small droplets, less than a few microns in diameter and, therefore, with a very small settling velocity. This phase can be considered as a secondary emulsion [3]. A treatment method for removing the oil from these emulsions is to force them through a fibrous bed, which promotes coalescence of oil droplets [4, 5]. The larger droplets can then be easily removed by gravity settling. This kind of bed is often called as filter coalescer and, although it retains some of the dispersed phase, its behavior differs from that of a conventional filter. When steady state is reached in the filter coalescer, the mass flow of the dispersed phase entering the bed equals tha t of the mass flow of the phase leaving it. rnThe aim of this work is to study the performance of glass fiber packed filter coalescer at laboratory-scale, to treat a cutting oil emulsion. Glass fibers were coated with different silanizing compounds, in order to modify their surface properties and determine the influence of the zeta potential and wettability of the dispersed phase, on the filtration-coalescence process. The influence of surface properties, such as wettability and zeta potential of the packing medium, on the filter coalescer performance is reported and also the influence of bed length and emulsion flow rate on the separation process.