Note: Descriptions are shown in the official language in which they were submitted.
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BACKGE~OUND OF THE INVENTION
1. FIELD OF THE INVENTION: The invention relates to a
particle segregation apparatus for the selective segregation of
particles based upon particle size and density.
2. DESCRIPTION OF THE PRIOR ART: Various methods and
apparatus have been applied to the problems of segregating parti-
cles having varying characteristics. The segregation of particles
from each other and the separation of particles from fluid mediums
which may be serving as carriers for the particles must be accom-
plished in`numerous industries. Examples of applicable processes
are the treatment o~ gases and the treatment of liquids containing
various solid matter which require segregation according to
particle characteristics such as size and density. Fluids may
have suspended therein various liquid and solid particles which
require segregation from each other and separation from the gases
in which the particles are suspended. A mixture of fluids may
require segregation in accordance with the molecular weight of
the various par~icles which make up each of the gases comprising
the mixture.
A particularly important problem encountered in the petroleum
industry is the treatment of drilling fluids which involves the
processing of large quantities of liquid-solid mixtures containing
particles of solid matter which are to be retained in the drilling
fluid system and particles of solid matter which are picked up by
the fluid during drilling and are to be removed from the system.
The solids content of a drilling fluid must be carefully controlled
to insure that the drilling fluid will function properly in the
drilling operation. Control of viscosity and weight are condition~
which must be considered in the preparation and handling of
drilling fluids. The drilling fluid may be weighted with a
relatively high density powdered material, such as barite. The
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viscosity of the drilling fluid is controlled to a value consistent
with desirable low pumping energy requirements and within the
degree required for proper bore hole conditioning. During the
circulation of the drilling fluid through a bore hole, finely
divided cuttings accumulate in the fluid and the viscosity of the
fluid consequently increases, often times to a state of non-
pumpability. Such conditions present a need for both removing
some of the finely divided cuttings and re-establishing the
needed viscosity of the fluid. The viscosity can be reduced by
the addition of suspending medium, but in a closed circulating
system, withdrawal of an amount of fluid equivalent to that added
must be made. Without the employment of methods and apparatus to
segregate the unwanted cuttings from those which are to be retained,
the withdrawal of fluids in amounts equal to those added to
reduce the viscosity results in the loss of expensive weighting
materials which materially adds to the drilling costs.
One commonly employed apparatus for the separation of solid
particles from fluids has been the decanting centri~uge. In
operation, the centrifuge normally requires rotation of the
entire mass of material being treated. Also, the rotation of the
entire mass of material being treated results in a concentration
of material in the form of a sludge along the inner walls o~ the
rotating bowl of the centrifuge. Because of certain peculiar
characteristics of some drilling fluids, difficulties are encoun-
tered in the use of a centrifuge to carry out fluid and solid
separation processes. Drilling fluids containing solids are so
constituted that they tend to gel or set under static conditions.
These types of drilling fluids, when treated in a centrifuge
where the entire mass attains the annular velocity of the rotating
portions of the centrifuge, will tend to gel and thus reach a
consistency which will oppose the needed migration of the particles
to be separated.
An apparatus for effecting particle segregation utilizing a
permeable rotating annular member wherein it is unnecessary to
rotate the entire mass of material being treated at the speed of
the rotating member is disclosed in United States Letters Patent
No. 3,400,819, entitled ''Method And Apparatus For Particle Segre-
gation", issued September 10, 1~68~ The Particle separation perform-
ance of this apparatus is substantially dependent upon operationwithin its capacity limit and requires continued adjustment of
the flow volume rate which is split into underflow and overflow
(or effluent) streams. This apparatus may be employed within a
number of operation mode varieties for use in a drilling mud
system. For example, the apparatus may be modified to retain the
underflow and discard the overflow (or effluent). This programming
would be preferred when it is desired to weight up the drilling
fluid system. Alternatively, when it is desired to utilize a
lighter weight drilling fluid, the apparatus may be programmed
such that the overflow is retained while the underflow is discarded.
Moreover, the apparatus disclosed in U.S. Patent No. 3,400,819
requires the utilization of three separate pumping units, a
hydraulic system and a control panel to operate the pumps, as
well as other operational mechanical elements. In a preferred
operational mode, this apparatus has its input volume rate estab-
lished by setting and calibrating the revolutions per minute
cycling of one of the three pumps, i.e., the mud pump, which is
directly coupled to a second or water pump by means of a timing
belt or by means of a hydraulic control valve and hydraulic
motor. However, once the input volume rates are set, the separa-
tion or "cut" obtained depends on controlling the underflowlover-
flow volume flow rate. This is achieved by mounting onto the
unit a pump at the underflow exit and controlling its speed with
a hydraulic control valve and hydraulic motor. For each input
volume ~--low rate, each mud weight and each mud-water dilution
rate, there is an optirnum flow split, and the pump must be adjusted
accordingly.
Thus, if the apparatus is properly and continuously adjusted,
the apparatus will provide its designed separation or "cut". The
designed separation or "cut" is not always obtainable, inasmuch
as the pump rpm/gpm ratios may vary considerably. Additionally,
the multiplicity of control components requires considerable
training to assure proper machine operation, and increases main-
tenance costs.
It has been determined that the "cut" or separation obtained
with this apparatus is directly proportional to a ratio of under-
flow weight to drilling fluid input weight Moreover, it has
been discovered that a proper flow rate split between underflow
and overflow may be satisfactorily obtained by utilizing a choke
mechanism or flow regulator instead of the underflow pump. This
modification would result in the elimination of the underflow
pump, hydraulic controls, hydraulic reservoir and heat exchanger
on the apparatus
SUMMARY OF THE INVENTION
The present invention contemplates utilization of an apparatus
for effecting selective particle separation in a liquid mixture
containing solid particles o~ varying weights, the apparatus
comprising a vessel which is provided with a pressure-tight
closed chamber. A first conduit is secured to the vessel and is
utilized for introduction of the liquid-solid mixture into the
chamber. A hollow cylinder is rotatably supported within the
chamber, and a second conduit is provided for withdrawing the
overflow portion of the liquid-solid mixture which contains
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classified finer and solid particles from within the cylindrical
means. A third conduit is provided for withdrawing the underflow
portion of the liquid mixture which contains classified coarser
particles from the chamber outside of the cylindrical means. Prefer-
ably the cylindrical means within the vessel provldes an outer surface
which defines a plurality of openings thereacross, each of which
is a multiple of the cross-sectional area of the largest particles
in the liquid-solid mixture to prevent bridging of the particles
over the openings, the total area of the openings being ~etween
about 5 and about 30 percent of the cylindrical surface area of
the cylindrical means, with the cylindrical means having a length-
to-radius ratio of at least about 2.0, the radius of the diameter
of the openings to the diameter of the cylindrical means being
between about 0.01 and about 0.1. A full opening orifice choke
means communicates with at least one of the second and third
conduit means and provides selective regulation of the rate of
flow between the overflow of the liquid-solid mixture and the
underflow of the liquid-solid mixture, Means to support and
rotate the cylindrical means at a predetermined speed within the
chamber to effect selective separation of the solid particles
also is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow diagram showing a particle segregater
employed in a system for reducing the level of fine solid particles
recovering barite from contaminated drilling fluids.
Fig. 2 is a similar flow diagram illustrating usage of the
adjustable choke in an apparatus utilizing only one p~mping
mechanism.
Fig. 3A is a sectional view of the adjustable choke mechanism
of the present invention as illustrated in Figs. 1 and 2, the ad-
justable choke being shown in the fully open position.
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Fig. 3B is a sectional illustration similar to that shown in
Fig~ 3A, the adjustable choke being illustrated in partially com-
pressed position.
Fig. 4 is a schematic sectional view of the separation
chamber of the apparatus.
DESCRIPTION OF THE P~EFERRED EMBODIMENTS
.
Referring to Fig. 1, the apparatus is shown as incorporated
within a drilling fluid circulation system. Drilling fluid is
recovered from a bore hole and passed to a mud pit including a
settling tank 10 and a suction tank 11. The drilling fluid is
withdrawn from the settling tank through conduit 12 by means of a
mud pump 13, which is preferably a positive displacement pump,
and is introduced through inlet conduit 14 into a particle segre-
gater 15 which may be skid or trailer mounted. To provide
makeup liquid and to improve the capacity of the device, water
may be withdrawn from a water pit through line 16 by water pump
17 and introduced into inlet conduit 14 to dilute the feed to the
particle segregater. While it is prefered that the water dilute
the feed to the segregater, it is also apparent that the water
may be alternatively added elsewhere in the system.
Referring now to Fig. 4, the diluted liquid-solid drilling
fluid is pumped into a stationary barrel or particle segregater
15 in a tangential direction. The separation chamber 15 includes
an exterior stationary case 15A defining a hollow interior therein.
A perforated cylindrical member 15B is carried wlthin the case
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15A and is rotationally manipulated by means of a power unit and
transmission system manipulating a perforated rotor shaft 15C
which carries the perforated cylinder 15B around the exterior
thereof. The liquid-solids mixture must pass either through the
perforated cylinder 15B and exit through the perforated shaft 15C
or, alternatively, must pass between the perforated cylinder 15B
and exit through the underflow port. The performance of the
apparatus is, again, dependent upon control of the volume rate
adjustment between the overflow and the underflow. With proper
adjustment, the fine light clay particles exit in the overflow,
and the heavier barite particles exit through the underflow.
In order to obtain the proper flow rate split between over-
fLow and underflow, the present invention contemplates utilization
of an adjustable choke mechanism 100 (as shown in Figs. 3A and
3B) which, preferably, is placed immediate the particle segregater
and in communication with the underflow conduit extending from
the particle segregater to the suction tank. The adjustable
choke 100 provides a longitudinally extending body lOl having a
bore lOlA therein. The body 101 is connected by threads lOlB to
the underflow port of the particle segregater. A pressure indi-
cator of known construction 102 may be securely affixed through
the body 101 of the adjustable choke 100 for measuring pressure
through the adjustable choke 100, to assist in adjustment of the
choke 100, but is not critical to its operation. An enlarged
central body 103 is secured to the main body 101 by means of
threads 103A, an elastomeric 0-ring 104 carried within its bore
104A preventing ~luid communication between the bodies 101 and
103. A longitudinally extending elastomeric element 105 having a
bore lO5A extending therethrough and communicating with the bore
of the body l is carried within the enlarged body 103, the
inner end 1 _ on the body 101 and the inwardly extending shoulder
103B of the inner body 103 snugly securing the elastomer 105
within the enlarged body 103. A connecter 106 is secured by
threads 106A to the enlarged body 103 and provides the beginning
of a conduit for transmission of the underflow to the suction
tank.
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The adjustable choke 100 may be easily adjusted to permit
contraction of the orifice through the interior of the elastomer
lOS simply by rotating the central or enlarged body 103 with
respect to the body 101, the threads 103A permitting the body 103
to travel thereon. As the body 103 is manipulated, the adjustable
choke 100 will telescope to permit variation of the orifice
within the elastomer 105. For example, if the body 103 is mani-
pulated toward the body 101, the shoulders 103B of the inner body
103 and the end lOlC of the body 101 will cause the elastomer 105
to contract, as the result of the telescopic inner action of the
bodies 101 and 103. The positioning of the adjustable choke 100
in such a fashion is as shown in Fig. 3B.
Although the invention has been described in terms of speci-
fied embodiments which are set forth in detail, it shouLd be
understood that this is by illustration only and that the invention
is not necessarily limited thereto, since alternative embodiments
and operating techniques will become apparent to those skilled in
the art in view of the disclosure. Accordingly, modifications
are contemplated which can be made without departing from the
spirit of the described invention.
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