摘要 |
<p>A pressure filter and a method of filtering of the type employing a particulate filter aid may be operated substantially continuously through an operating cycle composed of a cleaning stage of short duration, say on the order of 4 or 5 seconds, in which the filter aid layer and accumulated filter cake are purged from an open-work, supporting filter element, a coating stage in which a new layer of filter aid is formed on the filter element and involving a time of about 10 seconds, and a filtering stage. A rapid coating of the element with a layer of filter aid is facilitated by using a filter aid having a mean particle size approximately equal to the size of the openings in the support. The filter aid purged from the filter chamber during each cleaning cycle is recovered by conducting the mixture of filter aid, impurities, and raw liquid from the filter, upon cleaning, to a holding tank and then recycling, over a period of time or continuously, the mixture from the holding tank through a separator. The filter aid fraction is separated and conducted into a filter aid storage tank for use during the next cycle, make-up filter aid and filtrate being added to the filter aid storage tank as required. The level in the holding tank is reduced just before each cleaning to the extent required to provide a capacity sufficient to receive the mixture purged from the filter during cleaning. Continuous filtrate output may be achieved by accumulating filtrate in a storage reservoir during the filtering stage (for delivery) during the cleaning and filter aid coating stages.</p> |