To study the influence of bed height on oil removal the amount of sawdust was increased, keeping constant the amount of coagulant salt. As shown in Fig. 4, an increase in the bed height, which is directly related to bed mass, allows to treat a larger volume of
emulsion, until a critical bed height value is reached.
Above this critical height the pressure drop across the bed increases exponentially with time, while for shorter beds, the pressure drop remains constant or increases linearly (Fig. 5). The exponential increase in pressure drop suggests the occurrence of surface straining or clogging in a deep layer of the bed. As the bed height is increased, higher inlet pressures are needed to maintain a certain flow rate of the feed emulsion.
Hence, the bed porosity is reduced, the void spaces become smaller and the
velocity is increased. An increased velocity increases the drag forces between the liquid and the granular media. Moreover, in this set of experiments, the amount of calcium sulphate mixed with the sawdust was relatively low (0.4 g CaSO4·2H2O). In
conclusion, the oil droplets are not easily retained but driven deeper into the bed, coalescing and reaching a size large enough to cause clogging of an inner layer.
At that moment, the linear increase of pressure with time shifts suddenly to an exponential increase and the filtration must be discontinued.
To study the influence of bed height on oil removal the amount of sawdust was increased, keeping constant the amount of coagulant salt. As shown in Fig. 4, an increase in the bed height, which is directly related to bed mass, allows to treat a larger volume of
emulsion, until a critical bed height value is reached.
Above this critical height the pressure drop across the bed increases exponentially with time, while for shorter beds, the pressure drop remains constant or increases linearly (Fig. 5). The exponential increase in pressure drop suggests the occurrence of surface straining or clogging in a deep layer of the bed. As the bed height is increased, higher inlet pressures are needed to maintain a certain flow rate of the feed emulsion.
Hence, the bed porosity is reduced, the void spaces become smaller and the
velocity is increased. An increased velocity increases the drag forces between the liquid and the granular media. Moreover, in this set of experiments, the amount of calcium sulphate mixed with the sawdust was relatively low (0.4 g CaSO4·2H2O). In
conclusion, the oil droplets are not easily retained but driven deeper into the bed, coalescing and reaching a size large enough to cause clogging of an inner layer.
At that moment, the linear increase of pressure with time shifts suddenly to an exponential increase and the filtration must be discontinued.
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