Filter underdrain with internal air scour laterals

Patent metadata

Field	Value
Publication number	US-10143944-B2
Application number	US-201615146770-A
Country	US
Kind code	B2
Filing date	May 4, 2016
Priority date	May 4, 2016
Publication date	Dec 4, 2018
Grant date	Dec 4, 2018

Abstract

Underdrain units in a sand medium or dual medium filtration system include efficient air, water and combined air/water cleaning. Air, water or both are delivered in backflow direction from a very low position on the underdrain unit, as well as water from a higher position, so as to effectively remove blocking contaminants on the outside the underdrain unit and in the surrounding filter media.

First claim

We claim:

1. A method for cleaning underdrain units and surrounding granular filter medium in an underdrain filtration system that has a series of such longitudinal underdrain units in a parallel array for collection of filtrate passing down through a filter medium or media and through perforations in the walls of the underdrain units, by air and water backflow cleaning to remove filter cake and contaminants surrounding the underdrain units, comprising:
each underdrain unit comprising an elongated metal shell having two sides and a top, and having perforations formed directly in the metal shell with perforations essentially through the height of the sides, including a first plurality of perforations at a lower position at each side and a second plurality of perforations at a higher position on each side above said first plurality of perforations, and the underdrain unit having a bottom at a floor of the underdrain filtration system such that the shell with the bottom define an internal filtrate-collecting plenum, the first plurality of perforations in each side of the underdrain unit including perforations at least as low as two inches above the bottom of the underdrain unit, and the underdrain unit including within the plenum two side ducts, one at each side and at the bottom of the underdrain unit such that a side of the shell, with said first plurality of perforations, forms an outer wall of each side duct, each side duct extending longitudinally through the unit,
in a first cleaning step, directing pressurized air into the side ducts of the plenum of the unit to distribute air near the filtration system floor through said first plurality of perforations throughout the length of the underdrain unit to exit the first plurality of perforations and to effect a scrubbing action that detaches trapped particles from grains of filter medium outside the unit;
in a second cleaning step, delivering both air and water simultaneously under pressure, into the side ducts to exit through the first plurality of perforations near the filtration system floor, with the water delivered at a sub-fluidization rate; and
in a third cleaning step, delivering water alone under pressure into the side ducts and into the remainder of the plenum so as to flush water through all perforations of the underdrain unit, thereby flushing substantially all detached particles from the filter medium bed.

2. The method of claim 1 , wherein, in the second cleaning step, water is also admitted into the remainder of the plenum of the underdrain unit, so that air and water together are delivered out through the first set of perforations, and water alone is flushed out through all remaining perforations of the unit.

3. The method of claim 1 , wherein, in the third cleaning step, the flow of water into the underdrain unit is gradually increased to a rate for fluidization of the filter medium, expanding the medium bed and flushing remaining detached particles from the bed.

4. The method of claim 1 , wherein the sides of the metal shell of the underdrain unit are sloped so as to be closer together at the top of the unit than at the bottom, defining a trapezoidal shape.

Assignees

• Ovivo Inc

Inventors

• Haggard Sr Gary D
• Kelly Brendan

Classifications

• B01D24/24

  Downward filtration, the container having distribution or collection headers or pervious conduits · CPC title

• B01D24/4631 Primary

  Counter-current flushing, e.g. by air · CPC title

• B01D24/22

  Downward filtration, the filter material being supported by pervious surfaces · CPC title