Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR REMOVING PARTICLES FROM A LIOUID
This invention relates to apparatus for removing
particles from liquid such as a drilling fluid.
BACKGROUND TO THE INVENTION
When drilling for oil or gas, the drill is passed
down a well, which is lined with a casing in the form
of a steel tube. It is has now been found that, when a
well is apparently exhausted, further oil or gas may be
recovered by drilling off to the side of the well. In
order to be able to do this, it is necessary to cut or
mill a window in the side of the tube. This milling
generates swarf, which is floated up to the well head
using a drilling or cutting fluid such as a mud. The
swarf then has to be removed from the upflow of
drilling fluids, so that the fluids can be reused.
The applicant has proposed the use of a trommel, in the
form of rotating perforated drum, to remove swarf
and/or other particles from drilling fluid. However,
trommels have the disadvantage that they have rotating
parts which are subject to high loads and vibration.
In the hostile environment of a drilling rig or
platform these rotating parts have been subject to
excessive wear and premature failure. The present
invention therefore seeks to provide apparatus which
alleviates the disadvantages associated with
conventional trommels.
SUMMARY OF THE INVENTION
According to a first aspect of the present
invention, there is provided a trommel comprising a
rotatable drum supported on a roller, the roller being
rotatably supported on an axle fixed to a support
structure of the trommel, a tungsten carbide sleeve
being disposed between the roller and the axle.
According to a second aspect of the present
invention, there is provided a roller which is
rotatably supported on an axle, a tungsten carbide
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sleeve being disposed between the roller and the axle.
Preferably, the axle is formed from stainless
steel. It had been thought that a combination of a
tungsten carbide sleeve running on a stainless steel
axle would be unsatisfactory, since the axle would tend
to wear very rapidly. However it has been found that
this combination of materials has surprising benefits
in terms of longevity of the bearing, together with an
improved resistance to corrosion. Most preferably, the
axle is formed from 420 grade flame hardened stainless
steel.
Preferably a lubricating channel is formed in the
axle.
Preferably respective seals are provided at the
ends of the axle, the seals extending between the axle
and the roller. A vent hole may be provided through at
least one of the seals to allow the controlled escape
of lubricant.
Preferably, the tungsten carbide sleeve is a loose
sliding fit on the axle so that a film of lubricant can
be established between the sliding surfaces.
The tungsten carbide sleeve may be separate from
the axle of the roller or may be fixed to or form part
of the roller. Preferably, the roller is in the form
of a wheel.
Preferably a plurality of rollers are used to
support the rotatable drum.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present
invention, and to show how it may be brought into
effect, reference will now be made, by way of example,
to the accompanying drawings, in which:-
Figure 1 is a schematic partial cross-section
through apparatus in accordance with the invention;
Figure 2 is an end view on arrow A of the
apparatus shown in Figure 1;
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Figure 3 is a partial cross-section through a drum
support roller; and
Figure 4 is a partial cross-section through a tool
used to remove the axle from the roller of Figure 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
Figure 1 shows a drum 2 having an inlet pipe 4
through which mud and swarf from a wellbore are
supplied to the drum. The drum 2 is perforated with a
large number of through-holes 6 over the majority of
its length, but has a first non-perforated section 8 at
the end nearest the inlet pipe 4 and a second non-
perforated section 9 at the other end thereof. The
sizes of the perforations may be chosen in dependence
on the expected solid particle sizes.
The drum 2 is made of anti-magnetic material. As
a result, the swarf, which often has some magnetism
induced by the process of milling the steel tube, is
less likely to be retained on the drum.
The apparatus further includes a drive motor 10.
The drive motor preferably has a variable operating
speed. The motor causes the drum 2 to rotate by means
of a friction drive 12 which contacts the non-
perforated section 8 of the drum. It will be understood
that the drum may equally be driven by some other
mechanical means, for example a gear mechanism.
The axis of rotation 14 of the drum is inclined to
the horizontal at an angle 8, with the inlet end being
uppermost. This angle 8 is adjustable. At its lower
end, the drum 2 is supported by rollers 16 and a thrust
ring 18 which prevents it from sliding. The drum can
thus be rotated as shown by arrow B. The speed and
direction of rotation are preferably variable, but the
speed is preferably set at about 100 rpm.
Liquid, together with particles which are small
enough to pass through the perforations, fall through
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the perforations and then out of the drum into the
collection area 20, and out through an outlet 22. The
larger and most important swarf particles are collected
in a container 24.
The apparatus may be used in a process in which
swarf is generated, and needs to be removed from a
drilling fluid. When a window is milled in a side of a
steel tube, for example in a deviation drilling
process, some of the swarf is generated in the form of
large balls or entanglements, which present great
difficulties if one attempts to remove them using
conventional classifiers, because they tend to become
jammed in the perforations. However, using the present
invention, this problem is alleviated, because, if a
ball of swarf does become partly engaged in the
perforations of the inner drum, the rotation of the
drum will tend to allow the swarf to fall out. This is
a major, otherwise unforeseen, advantage of using a
rotating drum device of this type in this particular
process.
Clearly, the amount of swarf collected will depend
upon the size of the perforations 6 in the drum 2.
However, it is also possible to vary the rate at which
material is supplied via the inlet 4, the speed of
rotation of the drum, or the angle B of inclination of
the drum. Variation of any or all of these parameters
will affect the amount of swarf removed from the mud.
Figure 2 is a schematic end view of the drum 2,
showing the rollers 16. Figure 2 also shows a cutter
blade 26 (not shown in Figure 1). This blade is
mounted fixedly along the length of the drum at a
constant distance from the axis of rotation 14. Thus,
it removes protruding strands of swarf and prevents the
mechanism from becoming jammed.
Figure 3 is an enlarged partial cross-section
through one of the rollers 16 which supports the drum
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2. The roller 16 is rotatably supported in a support
structure 28 of the trommel by means of an axle 30. A
first end of the axle 30 is located in an opening 31
formed in the support structure 28, and a second end of
the axle 30 is located in a clamping bracket 32 which
is welded to the support structure 28. The axle 30 is
secured in the clamping bracket 32 by means of a
clamping bolt 34 which passes through an opening 36 in
the axle 30.
The roller 16 comprises a central steel bush 38 to
which is fitted a steel annulus 40 which is
substantially I-shaped in cross-section and defines a
pair of annular recesses on opposite sides of the
roller. The recesses are filled with polyurethane
material 42 and the radially outer surface of the
annulus 40 is fitted with a tyre 44.
Between the axle 30 and the bush 38 is disposed a
tungsten carbide sleeve 46. The tungsten carbide
sleeve 46 is a close fit within the bush 38, but is a
loose sliding fit on the axle 30. Consequently, the
roller 16 is free to rotate about the axle 30 at the
interface between the axle 30 and the tungsten carbide
sleeve 46.
Two thrust washers 47, 49 are provided between the
roller 16 and the support structure 28 to keep the
roller 16 disposed centrally on the axle 30.
Annular recesses 48, 50 are formed in the ends of
the bush 38. These recesses accommodate respective
lubricant seals 52, 54 which extend between the bush 38
and the axle 30.
The end of the axle 30 is provided with a grease
nipple 56 which provides access to a bore 58 which
extends along the central axis of the axle 30. The
bore 58 is continuous with a second bore 60 which
extends radially from the central axis of the axle 30
to the outside surface of the axle 30. Thus, there is
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a continuous lubricant flow passage extending from the
grease nipple 56 into the space between the axle 30 and
the tungsten carbide sleeve 46, so that by applying
lubricant under pressure to the grease nipple 56
lubricant is forced between the axle 30 and the
tungsten carbide sleeve 46.
To avoid damage to the lubricant seals 52, 54 if
too much lubricant is applied to the grease nipple, an
opening (not shown) is provided in at least one of the
seals 52, 54. Any excess lubricant can escape past the
seal through this opening.
Although the combination of a stainless steel axle
30 and tungsten carbide sleeve 46 greatly reduces the
wear on the sliding surfaces, it may still be necessary
to remove the axle 30 from the roller 16 for inspection
and/or replacement. To facilitate removal of the axle
30, a tool 66 has been developed which is illustrated
in Figure 4. The tool 66 comprises a threaded rod 68,
to the end of which is welded a nut 70. A jacking nut
72 is received on the threads of the threaded rod 68
and abuts a hollow spacer sleeve 74 which is free to
slide along the threaded rod 68.
In use, the threaded rod 68 is screwed into a
threaded bore 69 formed in an end of the axle 30 by
applying a spanner to the nut 70 and turning it in an
appropriate direction. The spacer sleeve is then slid
along the threaded rod 68 until it abuts against the
clamping bracket 31 or 32 and the jacking nut 72 is
screwed down against the spacer sleeve 74. The bolts
33, 34 are then loosened from their respective nuts, so
that the axle 30 can slide relative to the clamping
brackets 31, 32. Further turning of the jacking nut 72
against the spacer sleeve 74 causes the axle 30 to be
withdrawn from the roller 16. It will be appreciated
that, because the tool 66 can apply a high withdrawing
force to the axle 30, the axle 30 can still be
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withdrawn from the roller 16, even if considerable
damage has occurred to the outer surface of the axle 30
or the inside surface of the tungsten carbide sleeve 46
or if corrosion has occurred between the axle 30 and
the clamping brackets 31, 32.
