Classifying – separating – and assorting solids – Sifting – Plane sifters
Reexamination Certificate
2000-11-28
2002-07-02
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Plane sifters
C209S311000, C209S314000, C209S317000, C209S326000, C209S332000, C209S275000
Reexamination Certificate
active
06412644
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to vibratory separators; shale shakers; screens and screen assemblies for them; and methods of their use.
2. Description of Related Art
Vibrating screens have been employed for many years to separate particles in a wide array of industrial applications. One common application of vibrating screens is in drilling operations to separate particles suspended in drilling fluids. The screens are mounted generally horizontally on a vibrating mechanism or shaker that imparts a desired motion to the screen. Material from which particles are to be separated is poured onto a back end of the vibrating screen, usually from a pan mounted above the screen. The material generally flows toward the front end of the screen. Large particles are unable to move through the screen remaining on top of the screen and moving toward the front of the screen where they are collected. The smaller particles and fluid flows through the screen and collects in a tank, receptacle or pan beneath the screen.
Typically a vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by a vibrating mechanism, e.g. an unbalanced weight on a rotating shaft connected to a basket or frame. The screen is vibrated by vibratory equipment to create a flow of trapped solids on top surfaces of the screen for removal and disposal of solids. The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.
The need for solids control in drilling mud used in hydrocarbon well drilling is well known in the prior art. Drilling mud, typically a mixture of clay and water and various additives, is pumped down through a hollow drill string (pipe, drill collar, bit, etc.) into a well being drilled and exits through holes in a drillbit. The mud picks up cuttings (rock) and other solids from the well and carries them upwardly away from the bit and out of the well in a space between the well walls and the drill string. At the top of the well, the solids-laden mud is discharged over a shale shaker, a device which typically has a screen or a series of screens arranged in tiered or flat disposition with respect to each other. The prior art discloses a wide variety of vibrating screens, devices which use them, shale shakers, and screens for shale shakers. The screens catch and remove solids from the mud as the mud passes through them. If drilled solids and/or debris are not removed from the mud used during the drilling operation, recirculation of the drilled solids can create weight, viscosity, and gel problems in the mud, as well as increasing wear on mud pumps and other mechanical equipment used for drilling.
In many cases it is difficult if impossible to mount or hang a screen S in a vibratory separator or shale shaker so that the lateral plane of its surface is perfectly horizontal. Either the center of the screen bulges upward laterally from the longitudinal edges of the screen as shown in
FIG. 1
(an “over slung” screen as described in U.S. Pat. No. 4,820,407, incorporated fully herein), in which case the screen is said to be “crowned” or “over slung”, or the center bulges downward in which case the screen is said to be “under slung”. A screen that is “crowned” or “over slung” (FIG.
1
), causes solids to tend to congregate at the screen's longitudinal edges; if a screen is “under slung”, solids tend to congregate at its center.
FIG. 2
shows a typical prior art vibratory separator system A with a screen B (with screen or screening cloth or mesh as desired) according to the present invention mounted on vibratable screen mounting apparatus or “basket” C. The screen B may be any screen disclosed herein or have any combination of any feature or features of any screen or screen part disclosed herein; and any such screen may be used with any appropriate shaker or screening apparatus. The basket C is mounted on springs I (only two shown; two as shown are on the opposite side) which are supported from a frame D. The basket C is vibrated by a motor E and interconnected vibrating apparatus F which is mounted on the basket C for vibrating the basket and the screens. Elevator apparatus G provides for raising and lowering of the basket end. The screen B is any prior art screen, screens, and/or screen assembly.
FIG. 3
shows a prior art screen mounting basket J with a screen K mounted therein with a typical prior art “crown” disposition with a middle crown portion L. Typical mounting rails or channels M are used with typical mounting devices N to releasably secure the screen K in the basket J.
There has long been a need recognized by the present inventor for a vibratory separator screen which overcomes the problems of prior art crowned screens.
SUMMARY OF THE PRESENT INVENTION
The present invention discloses, in at least certain embodiments, screens and screen assemblies for vibratory separators (including, but not limited to screens for shale shakers for treating drilling fluid or “mud”) and vibratory separators with such screens and screen assemblies. In certain aspects screen assemblies according to the present invention have one or more screening members (screen, mesh, perforated plate, etc.) with a top surface that is higher in the middle than at one or both ends, i.e., when viewed from the side one or both ends of the screen assembly are at a level below the screen assembly's middle. In certain aspects the surface tapers from the middle down to the end(s). The “ends” of the screen assembly are a first end onto which material to be treated (e.g., but not limited to, drilling fluid from which mud is to be filtered) is introduced to the screen assembly and a second end from which separated material (e.g., but not limited to, solids like drilled cuttings and/or debris) exits from the vibratory separator.
In certain particular embodiments an exit end of such a screen assembly is positioned over a lower screen assembly and separated solids (which may still have some liquid therein) fall down onto the lower screen. The lower screen may be any known two- or three-dimensional screen and it may be, in particular aspects formed with a higher middle and one or both lower ends according to the present invention.
Any screen or screen assembly known in the prior art may be formed according to the present invention with a relatively higher middle and with one or both ends lower than the middle (in side view).
In certain embodiments the present invention discloses a vibratory separator with a screen or screens according to the present invention as described herein.
In other aspects a screen is mounted in a basket or screen cradle of a vibratory separator so that part of the screen is higher than one or both ends. In one aspect such a screen has sufficient flexibility to be bent into a desired configuration; in other aspects the screen is made in the desired configuration or multiple sub-screens and/or screen parts are positioned in the desired shape. Screens mounting or holding devices or apparatuses are used to hold the screen or screens in the desired shape (viewed from the side).
To the extent more screening area is available with a screen assembly according to the present invention, screening efficiency and capacity are increased.
In certain aspects, the present invention discloses a vibratory separator for separating components of material introduced to the vibratory separator (which in one aspect is a shale shaker for separating drilling fluid from a mixture of drilling fluid, drilled cuttings, debris, etc.), the vibratory separator having a basket for holding screening apparatus; vibrating apparatus for vibrating the screening apparatus; screening apparatus mounted in the basket, the screening apparatus having at least a first portion and a second portion, the first portion lower in the basket than the second portion, and receptacle apparatus below the screening apparatus for receiving material components flowing through the screening apparatus.
With a vibratory separat
Crabbe Mark D
Grichar Charles N.
Schulte David L.
McClung Guy
Rodriguez Joseph C
Varco I/P Inc.
Walsh Donald P.
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