Filtration apparatus and method

Claim 1

A pressure filter according to claim 1 and further comprising a receptacle for storing the filter aid in suspension in a liquid, means for selectively supplying filter aid from the storage receptacle to the inlet of the filter chamber, a holding tank, means for conducting material from the cleaning outlet of the filter chamber to the holding tank, means for separating a mixture of filter aid liquid and the impurities extracted upon filtering, such mixture constituting the aforesaid material, into a first fraction containing predominantly filter aid and a second fraction containing predominantly impurities, means for supplying the material from the holding tank to the separating means, means for supplying the first fraction from the separating means to the filter aid storage receptacle, and means for supplying the second fraction from the separating means to the holding tank.

Claim 11

A method of filtering liquids under pressure through a filter layer composed of particulate filter aid material in a pressure filter having a filter chamber enclosing an open-work partition having openings of given size and having an inlet and an outlet separated by said partition; means defining a gauged throttling passage associated with said inlet for connection thereof to a source of the liquid to be filtered under pressure while restricting the rate of inflow of said liquid to said chamber; means defining a filtrate reservoir in communication with said outlet, for receiving filtrate and maintaining it at a given pressure; a cleaning outlet in communication with the filter chamber on the inlet side thereof; a discharge valve associated with the cleaning outlet; and means for successively operating the valve to provide a rapid cyclic operation thereof including a closed stage for filtering and an opened stage for producing a sudden pressure drop in the liquid on the inlet side of the chamber to a value below said given pressure in the filtrate reservoir effective to cause an abrupt reversal of the pressure gradient across the partition and a removal of the layer of filter aid and impurities from the partition; said method comprising the steps of: (a) forming said filter layer during a brief period at the beginning of said closed stage of the discharge valve by choosing said filter aid material so that the mean particle size thereof is substantially equal to the size of the openings of said partition and by rapidly injecting into a stream of liquid flowing from said inlet to said outlet a given amount of said material corresponding to a filter layer of given thickness, such that substantially all the injected filter aid particles are carried by said stream to said partition and are retained thereby to form said layer, while the liquid stream substantially free of filter aid particles flows to said outlet; (b) thereafter filtering said liquid under pressure through said filter layer during said closed stage of the discharge valve while conducting the filtrate from said outlet partially to said reservoir; (c) after using said layer for filtering, providing sudden removal thereof from the partition during said opened stage of the discharge valve and rapid discharge of the material of the used layer through said cleaning outlet; and (d) cyclically repeating steps (a), (b) and (c) during the whole operation of said pressure filter, such as to provide substantially continuous filtrate delivery, with prolonged filtration during each step (b) and brief interruptions thereof during steps (c) and (a) for providing rapid renewal of the filter layer.