Variable capacity continuous extended area filter

Abstract

A molten polymer filtration assembly includes at least three independently controllable and removable filter housings which extend from a common inlet passage to a common outlet passage, thereby providing parallel flow paths for polymer filtration. Each of the filter housings includes an inlet valve controlling the flow of polymer from the inlet passage, an outlet valve controlling the flow of polymer to the outlet passage, and a filtration passage which extends between the inlet and outlet valves and houses a candle-type filtration element. When the inlet and outlet valves are opened, the filter housing is on-stream and allows polymer to flow from the inlet to the outlet passage. Each filter housing is individually controllable, and can be set in an on-stream state independent of the state of any of the other filter housings, such that any number of filter housings can be on-stream at a given time. By setting the number of on-stream filter housing in correspondence with the polymer flow rate, the polymer residence time can be maintained in a relatively narrow range of durations over a wide range of polymer flow rates, thereby ensuring that the polymer residence time within the filtration system remains below an acceptable duration and that the polymer residence time is regulated to avoid significant fluctuation or variances in the polymer residence time. Interlocks prevent the closure of the outlet valve of each filter housing unless the inlet valve for that housing is closed. Removal of any filter housing is prevented unless its valves are both closed.