Among the filter assemblies commonly used for removing solid particles from a fluid are those having a plurality of tubular filter means suspended in a housing wherein the tubular filter means are closed at the bottom and open at the top. Some examples of such filter assemblies are disclosed in U.S. Pat. Nos. 2,954,873, 3,169,109, 3,228,528, and 3,356,215; the disclosures of which are incorporated herein by reference.
In those types of filter assemblies, the tubular filter means are suspended from a partition which divides the housing into a lower inlet portion and an upper outlet portion. The partition has openings in it which allow fluid to flow from inside the filter means to the upper outlet portion of the housing. Filtering is accomplished with those filter assemblies by introducing the solids-containing fluid into the lower inlet portion of the housing. The fluid flows through the walls of the tubular filter means and up into the upper outlet portion of the housing. The solids removed remain on the outside of the tubular filter means.
Such filter assemblies have found a wide range of uses, including, for example, the filtering of boiler feedwater, cooling water pharmaceutical process solutions, salt water, and refinery process streams, such as coker gas oil or heavy vacuum gas oil streams. In some applications a filter cake is applied to the outside of the tubular filter means.
Generally, in all applications of such filter assemblies at some point in time the accumulation of solids on the outside of the tubular filter means becomes so great that it is necessary to backflush the tubular filter means. The backflush generally involves flowing filtrate or other backflush fluid in a reverse fashion through the filter means while the filtering is shifted to another filter assembly.
It is desirable to be able to clean the filter means as quickly as possible with a minimum amount of backflush fluid. It has been observed that if one tries to backwash all the tubular filter means simultaneously, more backflush liquid is needed than is generally desirable.
An object of the present invention is thus to provide a means for backflushing a plurality of tubular filter means to obtain adequate cleaning of the filter means with smaller quantities of backflush fluid.
Still another object of the present invention is to provide a means for controlling the backflush that is less complex, more reliable, and more economical than many means of the prior art.
Other aspects, objects, and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.