GB1575312A

GB1575312A - Vibratory sifting machines

Info

Publication number: GB1575312A
Application number: GB4979576A
Authority: GB
Original assignee: Thule United Ltd
Current assignee: Thule United Ltd
Priority date: 1976-11-30
Filing date: 1976-11-30
Publication date: 1980-09-17
Also published as: DE2753160A1; JPS6224979U; FR2371973A1; JPS6310845Y2; JPS5395369A

Description

(54) VIBRATORY SHIFTING MACHINES (71) We, THULE UNITED LIMITED, a British company of South College Street, Aberdeen, Great Britain, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to vibratory sifting machines for use in the oil industry at drilling sites. Such sifting machines are used to separate silt and cuttings to enable reusable drilling fluid to be recovered for reconstitution into mud. Such sifting machines hitherto available have a limited performance owing to deficiencies in available vibratory drives, which this invention seeks to overcome.

In this connection, it is explained that, as is wéll known, the flow characteristics of the drilling mud changes frequently, due especially to changes in viscosity, and, as vibratory shifting machines hitherto available can be operated only at one and the same speed, the screen has to be changed to one of a different mesh size to compensate for the changed viscosity. In some such machines, an alternative course is to change the vibration-inducing weight and thus change the amplitude of vibration. In either event, it is necessary to stop the machine, with a consequent loss of working time.

According to the present invention there is provided a vibratory sifting machine having a frame; a sifting basket resiliently mounted on said frame for vibratory movement in a substantially oscillatory manner in vertical planes. The sifting basket having opposed side walls, and a base formed by a screen;and a vibratory drive unit comprising a rotatable shaft extending between said side walls and having opposed end portions projecting respectively through the side walls and journalled in bearing elements; eccentric weights secured respectively to said end portions of the shaft; a motor supported on one of said die walls coaxially with the shaft, and in driving connection with one of said end portions of the shaft; and a control device by which the speed of the motor can be steplessly varied.

An embodiment of the invention will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 is an end elevational view of a sifting machine according to the invention; Figure 2 is a side elevation corresponding to Figure 1; Figure 2A diagrammatically illustrates orbital motion to which a sieve element of the machine is subjected during operation; and Figure 3 is a cross sectional view corresponding to Figure 1, with certain parts omitted.

As is well known, drilling mud is circulated through a bore hole during drilling, and mud leaving the bore hole is contaminated with silt and cuttings. It is desired to be able to separate the silt and cuttings from the fluid, for re-use of the latter. Barite, insoluble barium sulphate, is commonly added to drilling mud for adjusting the density. thereof to a predetermined level, and it is desired to recover the barite for re-use. The equipment illustrated in the drawings enables waste, namely silt and cuttings, to be separated from re-usable constituents of the drilling mud.

The equipment comprises a vibratorytype separating or sifting machine 10 and a power unit 11. The heart of the machine 10 is a sifting element which comprises a so-called sifting basket 12 and a sieve mesh screen 13, the latter having a mesh size e.g.

6 to 600 mesh or any combination thereof such that silt and cuttings are unable to pass therethrough, while fluid and barite particles can do so. The basket 12 is coupled to a vibratory drive unit 14 which is energised by operation of the power unit 11. The drive unit 14 functions to shake the basket 12 so that the basket vibrates elliptically in vertical planes, the elliptical vibratory or shaking motion being sketched in Figure 2A. The basket 12 is mounted on the frame 15 of the machine by way of rubber pads 16, although steel coil springs could be used instead, as shown in Figure 3.

Referring to Figure 3, it will be seen that the so-called basket 12 has opposed side walls 12A and an end wall 12B. The basket is open at the top and bottom, and the base of the basket is formed by the screen 13. As shown in Figure 3, the screen 13 is formed by two screen elements 13A which are located side-by-side and are removably clamped in position. The basket 12, at its bottom end, is reinforced by spaced cross bars 12C or by an open frame, which, in either case, may be formed integrally with the side walls and end wall.

In use, contaminated mud from a bore hole is fed under pressure of around 40 p.s.i.

and at a flow rate of 400 to 1600 gallons per minute into two inlet ducts 20 of the machine 10. The ducts are each closed at one end 21 and mud forced into the ducts 20 exits therefrom via side pipes 22 into several desilter cones 23. Sixteen such cones are included'in the illustrated machine 10. It is arranged that the pressurized mud enters the cones 23 generally tangentially via pipes 22 so that a swirling action is generated within the cones. Owing to centrifugal force, the denser constituents of the contaminated mud, including barite, silt and cuttings, tend to segregate towards the bottoms of the cones 23, while the lighter constituents tend to flow upwardly towards the tops of the cones. The lighter constituents comprise principally the fluid. Fluid rising to the tops of the cones 23 enters discharge pipes 24 and flows from the machine via one of two discharge ducts 25.

The fluid leaving ducts 25 is essentially free of silt and cuttings and can be re-formed into mud for recycling to a bore hole being drilled. Approximately 80% of the fluid content of the contaminated mud is separated by the desilter cones 23 from the barite, silt and cuttings for re-use.

The remainder of the mud, comprising about 20% of the originally-present fluid, barite, silt and cuttings is discharged from the bottoms of the cones on to an inclined tray or chute 27. The tray 27 serves to deliver the mud to an upstream end 28 of the basket 12. With the basket vibrating or shaking, fluid and barite in the mud are encouraged to pass through the screen 13 to fall into a collector 30 whence they are removed through an outlet or outlets 31 for reconstitution into drilling mud. Silt and cuttings stay behind on the screen 13 and, due to the vibratory motion, are gradually conveyed to a downstream end 32 of the basket. Upon reaching end 32, the silt and cuttings move on to a discharge lip or chute 33 and fall into a receptacle, not shown. The material accumulating in the receptacle is periodically discarded.

Conveyance of silt and cuttings along the screen 13 towards the downstream end 32 of the-basket 12 is found to be enhanced if the downstream end of the screen is slightly higher than the opposite end thereof. A satisfactory height difference is 1/4 inch or so. The screen 13 can be tilted most conveniently at the rubber pad mountings or springs 16. As shown, the pads or springs 16 extend between bearer plates 35 on the side walls of the basket 12 and co-operating supports 36 on the machine frame 15, the pads or springs 16 being sandwiched between the plates 35 and the supports 36. The rubber pads or springs 16 form the only connections between the basket 12 and the machine frame 15, and permit the basket 12 to execute the elliptical vibratory motion sketched in Figure 2A.The major axis 40 of the elliptical motion is normal to the major dimension of the drive unit 14 and is aligned with the general direction along which silt and cuttings move upon the screen. The minor axis 41 of the elliptical motion is substantially vertical. As shown, the major axis is tilted slightly with respect to the horizontal 42.

The mesh size of the screen elements may range from 6 to 600 per inch dependent upon the average size of the particles to be retained thereby.

The vibratory drive unit 14 is shown in more detail in Figure 3 and basically comprises a hydraulic motor 50 directly coupled to drive an eccentrically-loaded rotatable mass 51. The motor is thus free to vibrate with the basket 12, as distinct from an arrangement in which the motor is secured for example to the base 15 or other fixture, and the mass 51 is driven by a belt from the motor. The motor may alternatively be an electric motor or a pneumatic motor. Hydraulic fluid under pressure is fed to the motor 50 by high pressure flexible hoses 52 from the power unit 11. The latter is a pumping system driven by an electric motor 53. For safety, since the equipment will be used at a drilling site, such as an offshore drilling rig where inflammable gases or liquids may be present, steps are taken to guard against sparking.

The rotatable mass 51 is in the form of a shaft which extends across the basket 12 and has end portions 51A, 51B which project through holes in the opposed side walls 12A of the basket. The shaft 51 is spaced above the screens 13A and below the tray 27, and passes through substantially the centre of gravity of the basket.

The main portion of the shaft 51 is housed within a tubular casing 52, which, at its ends fits into the holes in the walls 12A and is welded to the walls 12A. Seals 53s are provided between the shaft 51 and the casing 52. The motor 50 is axially aligned with the shaft 51, and the drive shaft 50A of the motor is connected to the end portion 51A of the shaft 51, preferably by a disc coupling 53C, as shown. The motor 50 is secured by bolts to the outer face of the end wall 54 of a cylindrical casing 55. The latter houses the coupling 53C, an eccentric weight 56, and a bearing 57 on the shaft portion 51A. The bearing is located within a bush 58 which is bolted to an annular plate 59 welded to the adjacent wall 12A of the basket. Axial displacement of the shaft 51 is prevented by a locknut 60 located between the bearing 57 and a retaining plate 61 bolted to the bush 58.The casing 55 consists of axially spaced inner and outer rings 62 and 63, the ring 62 having a flange bolted to the plate 59, and the ring 63 being welded to the end wall 54. The rings 62, 63 are connected by rods 64, and the gap between the rings is closed by a removable clamping ring 65. The weight 56 is locked in position by a screw-threaded pin 66 engaging in a keyway in the shaft 51.

At the other side of the basket 12, the arrangement is somewhat similar to that above described. Thus, there is a cylindrical casing 55A which is secured to an annular base plate 59A on the adjacent side wall 12A of the basket and is closed at its outer end by a wall 54A. Also, the casing 55A houses an eccentric weight 56A on the end portion 51B of the shaft 51, a bearing 57A between the shaft portion 51B and a bush 58A, and a retaining plate 61A. The outer end wall 54A has bolted to it a weight 67 for counter balancing the weight of the motor 50. The weights 56, 56A are identical in mass and shape and are mutually aligned, and are preferably substantially sectorshaped. In order to minimise the radial length of the weights 56, 56A, both faces of each is axially outwardly stepped, as shown.

Each weight may range from 2 to 20 kilogrammes approximately.

When rotated, the shaft 51 vibrates and executes an orbital motion which is transmitted to the bearings 57, 57A, and hence to the basket via the bushes 58, 58A, and the base plates 59, 59A. The vibratory motion of the basket 12 with the screen 13 is constrained to be elliptical as aforesaid, due to the pads or springs 16 allowing greater freedom of vibratory movement to the basket in the horizontal plane than in the vertical plane.

The speed of the motor 50 may be steplessly adjusted from 0 to 3000 r.p.m. by adjustment of a speed control device with which the unit 11 is equipped, and satisfactory operation can be obtained when driven at 800 to 2000 r.p.m.. In this connection, it will be understood that the speed of the motor is adjusted to increase or decrease the vibrational speed of the screen to compensate for changes in the flow characteristics of the mud being sifted, so that it is no longer necessary to change the screen or the eccentric weights.

The construction which has been described imparts an extremely uniform oscillatory motion to the screen 13, which results in a very even distribution of silt and cuttings across its surface. Localised accumulations of matter on the screen are avoided, so that a highly efficient separation of fluid and barite particles from the silt and cuttings is achieved, and can be maintained during continuous operation of the machine. Highly improved results are attained over those obtainable by an arrangement in which an eccentricallyloaded shaft is driven by a belt-and-pulley drive from a motor secured to the base of the machine or other fixture.With the latter arrangement, the drive belt is repetitively tensioned and relaxed alternately, as the shaft executes its orbital motion, and, as the drive is applied to only one end of the shaft, and thus the basket, to skew, that is to say, turn laterally about a vertical axis, and/or to cant about a fore-and-aft horizontal axis.

This results in non-uniform feed of material along the screen, localised accumulation of matter on the screen, and also causes excessive wear on the drive belt and on the shaft and motor bearings.

It will be recognised that the weights 56, 56A need not be sector shaped, but may consist of parallel-sided bars, for instance.

The mass and shape of the weights may be varied to vary the amplitudes of the horizontal and vertical components of the vibration at the screen 13.

The drive unit 14 may have an overall length of 78" approximately. The shaft 51 may have a length of 63" between the bearings 57, 57A and a diameter of 3". The shaft is made of steel, and each of the sector-shaped weights 56, 56A is also made of steel, and may weigh 14 lb and be approximately 2.2" thick. The length of the arcuate face of the weight may be 5.5" and the vertical distance between the centre of the shaft and the arcuate face may be 1.97".

The vertical height of the weight may be 5.1", measured between its lowermost end, as seen in Figure 3 and a chord joining the ends of the arc of the arcuate face. The peripheral length of the weight measured between the said ends of the arc and around the said apex may be 14.50".

Claims

WHAT WE CLAIM IS:

1. A vibratory shifting machine having a frame; a sifting basket resiliently mounted on said frame for vibratory movement in a substantially oscillatory manner in vertical planes, the sifting basket having opposed side walls, and a base formed by a screen; and a vibratory drive unit comprising a rotatable shaft extending between said side walls and having opposed end portions projecting respectively through the side walls and journalled in bearing elements; eccentric weights secured respectively to said end portions of the shaft; a motor supported on one of said side walls coaxially with the shaft, and in driving connection with one of said end portions of the shaft; and a control device by which the speed of the motor can be steplessly varied.

2. A vibratory sifting machine as claimed in Claim 1, in which the end portions of the shaft are housed together with the weights within casings secured to the side walls respectively, the motor being secured to an axially outer end wall of one of the casings, and a weight counterbalancing the weight of the motor being secured to an axially outer end wall of the other of the casings.

3. A vibratory sifting machine as claimed in Claim 2, in which each of the bearing elements is located within a bush bolted to an annular plate secured to the adjacent side wall of the basket, and by a lock nut located between the bearing element and a retaining plate bolted to said bush.

4. A vibratory sifting machine as claimed in any one of the preceding Claims, in which the drive shaft of the motor is connected to said rotatable shaft by a disc coupling.

5. A vibratory sifting machine as claimed in any of the preceding Claims, in which said motor is a fluid-operated motor driven by a power unit including said control device.

6. A vibratory sifting machine as claimed in any one of the preceding Claims in which a chute is provided for feeding material to be sifted to one end of the screen, the chute being located above and extending across said rotatable shaft.

7. A vibratory sifting machine as claimed in Claim 6, in which a plurality of cyclone separators is provided for discharging material to be sifted on to said chute.

8. A vibratory sifting machine as claimed in any of the preceding claims, in which the portion of the shaft extending between the side walls of the sifting basket is housed within a tubular casing which is secured at its ends to said side walls.

9. A vibratory sifting machine as claimed in Claim 1 substantially as hereinbefore described with reference to the accompanying drawings.