Note: Descriptions are shown in the official language in which they were submitted.
CA 02848738 2014-04-11
"A DESANDING APPARATUS AND A METHOD OF USING SAME"
2
3 FIELD OF THE DISCLOSURE
4 The present
disclosure generally relates to an apparatus and a
method for removing particulates from multiphase fluid streams, and in
particular,
6 relates to an
apparatus and a method for removing sands from multiphase fluid
7 streams
produced from an oil or gas well while minimizing the abrasion to the
8 equipment involved.
9
BACKGROUND
11 Production
from wells in the oil and gas industry often contains
12 particulates
such as sand. These particulates could be part of the formation from
13 which the
hydrocarbon is being produced, introduced from hydraulic fracturing, or
14 fluid loss
material from drilling mud or fracturing fluids, or from a phase change of
produced hydrocarbons caused by changing conditions at the wellbore (Asphalt
16 or wax
formation). As the particulates are produced, problems occur due to
17 abrasion and
plugging of production equipment. In a typical startup after
18 stimulating a
well by fracturing, the stimulated well may produce sand until the
19 well has
stabilized, often lasting for several months after production commences.
Other wells may produce sand for a much longer period of time.
21 Erosion of
the production equipment is severe enough to cause
22 catastrophic
failure. High fluid stream velocities are typical and are even
23 purposefully
designed for elutriating particles up the well and to the surface. An
24 erosive
failure of this nature can become a serious safety and environmental
issue for the well operator. A failure such as a breach of high pressure
piping or
CA 02848738 2014-04-11
1 equipment releases uncontrolled high velocity flow of fluid which is
hazardous to
2 service personnel. Releasing such fluid to the environment is damaging to
the
3 environment resulting in expensive cleanup and loss of production. Repair
costs
4 are also high.
In all cases, retention of particulates contaminates surface
6 equipment and the produced fluids and impairs the normal operation of the
oil
7 and gas gathering systems and process facilities. Therefore, desanding
devices
8 are required for removing sand from the fluid stream. Due to the nature
of the
9 gases handled, including pressure and toxicity, all vessels and pressure
piping in
desanding devices must be manufactured and approved by appropriate boiler
11 and pressure vessel safety authorities.
12 In one existing system, a pressurized tank ("P-Tank") is placed on
13 the wellsite and the well is allowed to produce fluid and particulates.
The fluid
14 stream is produced from a wellhead and into a P-Tank until sand
production
ceases. The large size of the P-Tank usually restricts the maximum operating
16 pressure of the vessel to something in the order of 1,000 ¨ 2,100 kPa.
In the
17 case of a gas well, this requires some pressure control to be placed on
the well to
18 protect the P-Tank. Further, for a gas well, a pressure reduction
usually is
19 associated with an increase in gas velocity which in turn makes sand-
laden
wellhead effluent much more abrasive and places the pressure controlling choke
21 at risk of failure. Another problem associated with this type of
desanding
22 technique is that it is only a temporary solution. If the well continues
to make
23 sand, the solution becomes prohibitively expensive. In most situations
with this
24 kind of temporary solution, the gas vapors are not conserved and sold as
a
commercial product.
2
CA 02848738 2015-08-07
1 Another known
system includes employing filters to remove
2 particulates.
A common design is to have a number of fiber-mesh filter bags
3 placed inside
a pressure vessel. The density of the filter bag fiber-mesh is
4 matched to the
anticipated size of the particulates. Filter bags are generally not
effective in the removal of particulates in a multiphase condition. Usually
6 multiphase
flow in the oil and gas operations is unstable. Large slugs of fluid
7 followed by a
gas mist are common. In these cases, the fiber bags become a
8 cause of
pressure drop and often fail due to the liquid flow therethrough. Due to
9 the high
chance of failure, filter bags may not be trusted to remove particulates in
critical applications or where the flow parameters of a well are unknown. An
11 additional
problem with filter bags in most jurisdictions, is the cost associated with
12 disposal. The
fiber-mesh filter bags are considered to be contaminated with
13 hydrocarbons
and must be disposed of in accordance to local environmental
14 regulation.
In Canadian Patent Number 2,433,741, issued February 3, 2004
16 and in
Canadian Patent Number 2,407,554, issued June 20, 2006, both assigned
17 to the
Applicant of the subject patent application, a desander is disclosed having
18 an elongate,
horizontal vessel with an inlet at one end and an outlet at the other
19 end. The
outlet separated from the inlet by a downcomer flow barrier, such as a
weir, adjacent the vessel's outlet or exit. The weir forms, and maintains, an
21 upper
freeboard portion having a cross-sectional area which is greater than that
22 of the field
piping from whence the fluid stream emanates for encouraging water
23 and
particulates to fall out of the freeboard portion. Water and particulates
24 accumulate
along a belly portion. The accumulation of particulates is along a
3
CA 02848738 2015-08-07
1 substantial
length of the elongate vessel increasing the difficulty of periodic
2 manual removal of such accumulation using scraper rods and the like.
3 While
Applicant has substantially maintained their elongated
4 horizontal
design virtually unchanged for years, there has been a desire to
improve the ease with which the vessel can be cleaned and further improvement
6 in separation
efficiency. Further, due to the nature of the gases handled,
7 including
pressure and toxicity, all vessels and pressure piping must be
8 manufactured
and approved by appropriate boiler and pressure vessel safety
9 authorities.
11 SUMMARY
12 Desanding
apparatus is provided which is placed adjacent to a
13 well's
wellhead for intercepting a fluid stream flow prior to entry to equipment
14 including
piping, separators, valves, chokes and downstream equipment. The
fluid stream can contain a variety of phases including liquid, gas and solids.
In
16 one
embodiment, a pressure vessel is inserted in the flowstream by insertion into
17 high velocity
field piping extending from the wellhead. The vessel contains an
18 upper
freeboard portion having a cross-sectional area which is greater than that
19 of the field
piping from whence the fluid stream emanates. As a result, fluid
stream velocity drops and particulates cannot be maintained in suspension. The
21 freeboard
portion is maintained through control of the angle of the desander,
22 obviating the
need for a downcomer of Applicant's own prior art horizontal
23 desanders.
24 In a broad
aspect, a desanding system receives a gas stream
containing entrained liquid and particulates. The system comprises a vessel,
4
CA 02848738 2014-04-11
1 elongated
along a longitudinal axis and inclined from a horizontal at a non-zero
2 inclination
angle. The vessel has a fluid inlet, adjacent an upper end for
3 discharging
the gas stream into the vessel at an inlet velocity, and a fluid outlet,
4 spaced along the longitudinal axis from, and lower than, the fluid inlet.
The vessel further has a gas/liquid interface at the fluid outlet, a
6 belly storage
portion formed below the interface, and a freeboard portion formed
7 adjacent an
upper portion of the vessel above the interface. The freeboard
8 portion has a
freeboard cross-sectional area which diminishes from the fluid inlet
9 to the fluid
outlet, wherein a freeboard velocity, adjacent the fluid inlet is less than
the inlet velocity, the freeboard velocity being such that the entrained
liquids and
11 particulates
fall out of the gas stream for collecting in the belly storage portion. A
12 desanded gas
stream flows out of the freeboard portion and out the fluid outlet,
13 being free of a substantial portion of the particulates.
14 More
preferably, a vessel of an embodiment of the present
invention is incorporated in a desanding system to replace existing prior
16 connective
piping for a wellhead, the vessel being supported using structure to
17 align the
vessel with the wellhead piping and downstream equipment. The
18 desander's
fluid inlet and fluid outlet, associated with the inclined world of the
19 desander, are
adapted to connect to the orthogonal world of the connective
piping.
21 In another
broad aspect, a method for desanding a fluid stream,
22 emanating from a wellhead and containing gas and entrained liquid and
23
particulates, comprises providing an elongated vessel having a longitudinal
axis
24 which is
inclined from the horizontal. The vessel has a fluid inlet adjacent an first
end of the vessel and a fluid outlet spaced along the longitudinal axis from
the
5
CA 02848738 2015-08-07
1 fluid inlet;
inclining the vessel at angle from a horizontal at a non-zero inclination
2 angle so that
the fluid outlet is lower that the fluid inlet for forming a freeboard
3 portion above
the fluid outlet. The fluid stream is discharging from the fluid inlet,
4 into the
vessel and substantially parallel to the longitudinal axis for establishing a
liquid interface in a belly portion of the vessel, the belly portion being
formed
6 below the
fluid outlet. Liquid and particulates are being directed along a
7 trajectory in
the freeboard portion of the vessel to intercept a substantial portion
8 of the
particulates at the liquid interface for storage in the belly portion. A
9 desanded gas
stream is recovered at the fluid outlet which is substantially free of
particulates.
11 The inlet can
be parallel or non-parallel with the longitudinal axis for
12 enabling a
trajectory to intercept the gas/liquid interface. The fluid stream can be
13 introduced
through a replaceable nozzle. The fluid inlet can be curved to align
14 the inlet from the inclined desander and orthogonal piping from a
wellhead.
In yet another broad aspect, there is provided a vessel having a
16 distal end and
a proximal end for removing particulates from a multiple-phase
17 fluid stream containing gas, entrained liquid and particulates, the vessel
18 comprising: a
volume having a diverging bounding wall, a distal base, and an
19 apex; the
diverging bounding wall having a top wall at a first inclination angle and
a bottom wall at a second inclination angle; the second inclination angle at a
21 greater angle
than the first inclination angle; a fluid inlet interface at the apex for
22 receiving said
fluid stream into the volume of the vessel; a fluid outlet on the top
23 of the top
wall, spaced from the fluid inlet interface; a horizontally extending
24 freeboard
interface separating a freeboard portion formed adjacent an upper
portion of the vessel above the interface and a belly portion therebelow, the
belly
6
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1 portion being bounded at its bottom by the bottom wall, the freeboard
portion
2 forming a freeboard cross-sectional area for a freeboard velocity of the
fluid
3 stream less than a fluid stream velocity at the fluid inlet interface;
and an
4 elongated flow path for receiving the fluid stream from the fluid inlet
interface and
directing the fluid stream to the fluid outlet; wherein said length of the
elongated
6 flow path and the freeboard velocity are such that an effective amount of
the
7 entrained liquid and particulates fall out of the fluid stream and
particulates settle
8 towards the bottom wall of the belly portion; and wherein a desanded gas
stream
9 flows out of the freeboard portion through the fluid outlet and is free of a
substantial portion of the particulates.
11 The second inclination angle may be greater than the angle of
12 repose of settled particulates. The top inclination angle may be
inclusively
13 between 2 and 20 degrees. The cross-sectional shape of the proximal base
may
14 be circular.
In some embodiments, the central axis may be perpendicular to the
16 plane of the distal base. In some other embodiments, the central axis
may be
17 oblique to the distal base.
18 Applicable in all instances, at steady state, once the belly
portion
19 fills with liquid and in cases where liquid removal from the belly
portion is less
than the rate of incoming liquid, a mass balance of liquid in and out can be
21 established in which case the incoming liquid co-exiting with the
desanded gas.
22 The vessel may further comprise a lower discharge from the
belly
23 portion for discharging liquid and collected particulates. The discharge
further
24 comprises: an inlet valve adjacent and fluidly connected to the
discharge; a
particulate accumulation chamber; and a discharge valve, wherein the
particulate
7
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1 accumulation
chamber is sandwiched between the inlet valve and the discharge
2 valve.
3 In some
embodiments, the fluid inlet interface has a discharge end,
4 and the
discharge end is oriented for discharging the gas stream into the
freeboard at an angle equal to the top inclination angle. The fluid inlet
interface
6 may further
comprise a replaceable nozzle having a discharge end oriented for
7 discharging
the gas stream into the freeboard. The replaceable nozzle may be
8 connected to the fluid inlet interface at a flange.
9 In some
embodiments, the desanding system receives a gas
stream emanating from a wellhead and the fluid inlet interface further
comprises
11 a receiving
end for receiving the gas stream, the receiving end being orthogonal
12 to the wellhead.
13 In some
embodiments, the top inclination angle is variable for
14 varying fluid stream conditions. In some other embodiments, the bottom
inclination angle is variable for particulate stream conditions.
16 According to
another broad aspect of this disclosure, there is
17 provided a
method for desanding a fluid stream emanating from a wellhead, the
18 fluid stream containing gas, entrained liquid and particulates, the method
19 comprising: providing an elongated vessel extending from a proximal end
downwardly towards a distal end and having a diverging bounding wall to define
21 a top
inclination angle and a bottom inclination angle larger than the top
22 inclination
angle; injecting, at a first fluid velocity, the fluid stream into the vessel
23 from the
proximal end at about the first inclination angle; directing, at a second
24 fluid
velocity slower than said first fluid velocity, said fluid stream along an
elongated flow path in the vessel from the proximal end towards the distal end
to
8
CA 02848738 2014-04-11
1 allow an effective amount of the entrained liquid and particulates fall
out of the
2 fluid stream and move into a belly portion; collecting desanded gas in a
freeboard
3 portion, said freeboard portion being above the belly portion and being
separated
4 therefrom by a gas/liquid interface; and discharging the desanded gas
from the
freeboard portion at the distal end; wherein said desanded gas is free of a
6 substantial portion of the particulates.
7 In some embodiments, the method further comprises collecting
8 desanded liquid from the belly portion and discharging, from the belly
portion, the
9 desanded liquid with the discharged gas at the distal end.
11 BRIEF DESCRIPTION OF THE DRAWINGS
12 Figure 1 is a cross-sectional side view of Applicant's prior art
13 elongated horizontal desander illustrating downcomer flow barrier, fluid
streams,
14 falling trajectory of particulates, and accumulations of separated liquid,
particulates and particulate-free fluid discharge;
16 Figure 2 is a cross-sectional view of an embodiment of a tilted or
17 inclined desander;
18 Figures 3A and 3B are perspective representations of the volumes
19 of the belly portion and freeboard portions of the inclined desander of
Fig. 2;
Figure 4 is a cross-sectional view of another embodiment of an
21 inclined desander having a greater inclination angle than that of Fig.
2;
22 Figure 5 is a cross sectional view of a curved fluid inlet, square
to
23 the desander, and having a long radius angular transition elbow between
24 orthogonal piping and the inclined desander;
9
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1 Figure 6 is a
representation of an inclined desander illustrating
2 parameters for an example 36 inch diameter desander having a horizontal
fluid
3 inlet; and
4 Figure 7 is a
cross-sectional view of a desander having a tilted
conical vessel, according to another embodiment.
6
7 DETAILED DESCRIPTION
8 A desander is
typically inserted between or as a replacement for
9 existing piping such as connecting piping between a wellhead and
downstream
equipment such as multiphase separators.
11 As shown in
Fig. 1, a prior art horizontal desander comprises a
12 cylindrical pressure vessel 11 having a substantially horizontal axis A,
a first fluid
13 inlet end 12 adapted for connection to the fluid stream F. The fluid
stream F
14 typically comprises a variety of phases including gas G, some liquid L
and
entrained particulates such as sand S. The fluid stream F containing sand S
16 enters through the inlet end 12 and is received by a freeboard portion
13. In the
17 illustrated prior art vessel, the freeboard area is set by a downcomer
flow barrier
18 14. Accordingly, the velocity of the fluid stream F slows to a point
below the
19 entrainment or elutriation velocity of at least a portion of the
particulates S in the
fluid stream. Given sufficient horizontal distance without interference,
the
21 particulates S eventually fall from the freeboard portion 13.
Particulates S and
22 liquids L accumulate over time in the belly portion 15 and are
periodically cleaned
23 out at sufficient intervals to ensure that the maximum accumulated depth
does
24 not encroach on the freeboard portion 13. The desanded fluid stream,
typically
liquid L and gas G, emanates from fluid outlet 16.
CA 02848738 2014-04-11
1 As shown in Figs. 2 through 7, embodiments of an inclined
2 desander 20 are free of the prior art flow barrier and, through tilting
or inclination
3 of the vessel, maximize freeboard upon entry of the flow stream, and
reduce
4 liquid flow rates for maximizing settling conditions therein and
retention of
captured particulates S. Variability of the inclination angle a enables a
measure
6 of variability between the respective freeboard and liquid-storing belly
portion for
7 adjusting performance.
8 As shown in Fig. 2, the desander 20 comprises a vessel 22 having
9 an axis A oriented at an acute angle a to the horizontal H. The desander
20 has
a fluid inlet 24 at an upper end 25 for receiving a fluid stream F typically
11 comprising a variety of phases including gas G, some liquid L and
entrained
12 particulates such as sand S. In this embodiment, the fluid inlet 24 is
oriented
13 parallel to a longitudinal axis A of the vessel 22. A fluid outlet 26 is
located along
14 a top 28 of the vessel 22, and spaced from the fluid inlet 24. In an
operating
state, a gas/liquid interface 32 forms extending horizontally from about the
fluid
16 outlet 26. A belly portion 40 is formed below the interface 32 for
containing liquid
17 L and particulates S. A freeboard portion 44 is formed above the
interface 32.
18 The fluid inlet 24 discharges into the freeboard 44. Particulate
trajectory can be
19 manipulated by positioning and orienting a discharge end 29 of the fluid
inlet 24.
In one embodiment, the discharge 29 of the inlet 24 can be aligned parallel to
the
21 vessel axis A. The inlet 24 or discharge 29 can be oriented in other
orientations
22 including above the inclined axis A, or below the axis A.
23 The
interface 32 is a generally obround, gas/liquid interface
24 between
the belly and freeboard portions 40, 44. The obround interface 32 has a
distal end 33 adjacent the fluid outlet 26 and a proximal end 34, the location
of
11
CA 02848738 2014-04-11
1 which is
intermediate the fluid outlet 26 and fluid inlet 24 and varies with liquid
2 level and
inclination angle a. As a result of the desander 20 inclination, the
3 trajectory of
the fluid stream F, from inlet 24, converges with the interface 32.
4 The trajectory
for dropping sand S and liquid L into the belly portion 40 is
foreshortened, reducing drop out time. The vessel 22 is long enough to space
6 the fluid
inlet 24 sufficiently from the interface 32 to minimize turbulence of the
7 liquid L in
the belly portion 40, that spacing being dependent upon various design
8 factors
including vessel inclination angle a, inlet fluid stream velocity and
9 characteristics.
At a steady state, the maximum level of the interface 32, is
11 controlled at
the distal end 33, set by eventual liquid entrainment and discharge
12 at the fluid
outlet 26. Gas G discharges at the fluid outlet 26. At steady state,
13 when the
liquid level reaches the fluid outlet 26, any oil and other liquids are re-
14 entrained with
the gas G exiting at fluid outlet 26. Particulates S continue to be
captured in the belly portion 40 until its volumetric capacity is reached.
16 Connective
piping 46, between conventional wellhead and
17 downstream
equipment, is typically in rectilinear or orthogonal arrangements.
18 Thus, the angle a of the desander 20 introduces coupling or connection
19 challenges.
The connective piping 46 is generally horizontal or vertical and
incorporation of the inclined desander 20 requires an adjustment made at the
21 fluid inlet 24
and fluid outlet 26. In many scenarios, with a small inclination angle
22 a, the fluid
outlet 26 can be fit to the top 28 of the vessel 22 at angle a, orienting
23 the outlet 26 vertically and thereby obviating the need for an angular
transition.
24 Turning to
Figs. 3A and 3B, the desander 20 is shown
diagrammatically split at the interface 32 for illustrating the incrementally
12
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1 increasing volume of the belly portion 40 below and the incrementally
decreasing
2 volume of freeboard portion 44, increasing and decreasing as referenced
to the
3 feed stream F. The freeboard portion 44 demonstrates a cross-sectional area
4 which diminishes from the fluid inlet 24 to the fluid outlet 26. As shown
in Figs. 2
and 4, a freeboard velocity at the fluid inlet 24 is such that the entrained
liquids L
6 and particulates S fall out of the fluid stream F and collect in the
storage belly
7 portion 40. The cross-sectional area of the freeboard portion 44,
adjacent the
8 fluid inlet 24, is at its greatest for achieving the lowest average inlet
velocity for
9 maximum drop out efficiency for particulates S and liquids L. As the
freeboard
cross-sectional area adjacent the fluid inlet 24 is large and relatively
unimpeded
11 by the belly portion 40, the velocity reduction upon discharge is
significantly
12 greater than that of Applicant's prior art horizontal desander.
Particulate removal
13 is accomplished while minimizing the portion of the vessel allocated to the
14 freeboard portion 44, maximizing the efficiency of that freeboard
portion for
particulate drop out, and resulting in a greater allocation of the overall
portion of
16 the vessel to the belly portion 40 for storage.
17 Velocity in the freeboard portion 44 increases after a substantial
18 portion of the particulates S have already deposited in the belly
portion 40. The
19 cross-sectional area of the belly portion 40 increases towards the fluid
outlet 26
and the velocity of liquids accumulating therein diminishes.
21 With reference again to Fig. 2 and to Fig. 4, in the belly portion,
22 particulates accumulate and flow downvessel at an angle of repose. The
23 accumulation of liquid L and particulates S establishes a downward flow
in the
24 belly portion, and as the particulates accumulate and limit the free
flow of the
13
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1 liquid L in the belly portion 40, the liquid velocity begins to increase,
drawing
2 more particulates S downvessel.
3 With reference to Fig. 4, the inclination angle a can be adjusted,
4 shown here as an increased angle over that of Fig. 2. At increasing
angles a the
trajectory of the feed stream impinges the interface 32 at less acute angle,
6 impinges the interface 32 sooner and enables selection of shorter vessels
22 and
7 greater particulate removal efficiency.
8 Inclination angles a can be adjusted, for a given length of vessel
22,
9 between fluid inlet 24 and fluid outlet 26, to accommodate gas G and
liquid L
content in the feed fluid stream F. Inclination angles a would generally be in
the
11 range of about 2 degrees to about 20 degrees. The shallowest operating
angle a
12 is limited by the minimum requirement for a minimum freeboard 44 cross-
13 sectional area adjacent the inlet 24 once the interface 32 builds to
about the fluid
14 outlet 26. The steepest operating angle a is limited by the requirement
for a
minimum storage capacity in the belly portion 40. The minimum inclination
angle
16 would be the condition where the inlet 24 is entirely in the gas phase
of the
17 freeboard portion 44 and the gas phase at the discharge is of zero
height. The
18 maximum inclination angle would be the condition where the inlet 24 is
well
19 above the gas/liquid interface allowing substantial freeboard to handle
slug flow.
Angles above 45 degrees limit the performance of desander considerably since
21 the residence time of the liquid phase in the belly portion 40 is
reduced.
22 With reference to Figs. 4 and 5, the fluid inlet 24, exposed to
23 entrained particulates S in the fluid stream, is subject to greatest
risk of erosion.
24 While the inlet 24 can be integrated with the vessel 22, one can also
provide an
inlet 24 or discharge 29 that is replaceable for ease of maintenance. Options
14
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1 include accepting eventual wear and shutdown of the desander 20 for
2 replacement of an integrated inlet 24; modifying the material or
configuration of
3 the inlet 24 to prolong service life, or using replaceable discharge of
nozzle for
4 minimizing turnaround time. As stated, one approach is to make the
discharge
29 replaceable including incorporating features of a replaceable nozzle as set
6 forth in Applicant's Patent CA 2,535,215 issued May 8, 2008. A replaceable
7 nozzle 50 can be fit to a compatible coupling at the upper end 25 of the
vessel
8 22. One form of replaceable nozzle 50 comprises the discharge 29, and a
9 threaded connection or nozzle flange 29i, for connection to a compatible
threaded connection or flange 24i at the inlet 24 of the vessel 22. The
orientation
11 of the discharge is dependent on the coupling 24i, 29i and arrangement
of the
12 discharge relative thereto. The replaceable nozzle 50 includes a connecting
13 piping coupling, such as a connective flange 47i for connecting to the
piping 47.
14 To maximize service life, the nozzle 50 can incorporate a curved
portion 51, such as a long radius elbow, transition between the orthogonal
world
16 of the connecting piping and the inclined axis A of the vessel 22. That
curved
17 portion 51 can be integrated with the inlet 24, nozzle 50 or located in
advance
18 thereof, such as in a transition pup joint.
19 In operation, various sizes are desanders are employed in the prior
art for differing operational conditions. Prior art desanders 10, such as that
21 described in US 6,983,852 to Applicant, for different feed fluid streams
F, might
22 include one typical standard vessel 11 having a nominal 0.3 m (12 inch)
diameter
23 by 3.048 m (10 feet) long and another vessel 11 having 0.3 m (12 inch)
diameter
24 by 6.096 m (20 feet) long, both of which are fitted with a downcomer
weir to set
the freeboard portion.
CA 02848738 2014-04-11
1 Herein, in the inclined desander 20, the prior art downcomer
flow
2 barrier, such as a weir, can be eliminated by providing similar 0.3 m (12
inch)
3 diameter vessels 22 and tilting the upper end 30 of the new desander 20
at about
4 twice the prior art weir height so as to form the interface 32 at the
fluid outlet 26.
To mimic the minimum operating performance of the 3.048 m (10 feet) and
6 6.096 m (20 feet) prior art desanders, a 20 foot long inclined vessel 22
would only
7 need to be inclined about 1/2 the angle a of the 10 foot long inclined
vessel 22.
8 Performance can be adjusted by varying the angle.
9 An example of an inclined desander 20 includes that sized to
receive a fluid stream F of 50 m3/d, bearing particulates S having an average
size
11 of 150 um. The fluid stream typically includes sufficient liquid to
accumulate in
12 the belly portion. The fluid stream F is discharged to vessel 22, having
a 0.3 m (1
13 foot) diameter and 3.048 m (10 feet) long. A typical pressure of the
fluid stream F
14 is about 7000 kPa (1015 psia). At an inclination angle a of 4.9 degrees,
the
freeboard volume is 0.10 m3 and the belly portion is 0.486 m3. The resulting
belly
16 portion capacity is about 502 kg of liquid and sand particulates.
17 As shown in Fig. 6, another embodiment of an inclined desander
20
18 illustrates some additional optional characteristics including a fluid
inlet 24
19 oriented horizontally, the inlet being directly connectable to
orthogonal connection
piping. The discharge 29 is oriented at an angle to the longitudinal axis A,
in this
21 case in a generally horizontal plane, which is angled upwardly from axis
A. The
22 initially horizontal trajectory of a substantial portion of the feed
stream falls off
23 before engaging the vessel 22. In part, the inlet 24 can be square to
the
24 connective pipe as, in this embodiment, the vessel 22 is of sufficient
diameter,
such as 36 inches, to permit inlet placement in the freeboard 44 while the
16
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1 trajectory is such that it minimizes or avoids vessel wall involvement.
As shown,
2 a horizontal spacing between the inlet 24 and inside wall of the vessel
22 is about
3 1.5 feet.
4 Removal of accumulated particulates is conducted periodically with
the vessel 22 shut in, adjacent the inlet 24 and outlet 26, and depressurized.
6 Conveniently, access can be through a pressure-rated access closure and
port at
7 the lower end 42, as the angle of repose and flow in the belly portion
carries
8 particulates thereto. A suitable closure is shown in Fig. 1 of the prior
art and in
9 Fig. 6 as adapted to the inclined desander 20. The vessel 22 is supported
sufficiently high of the ground or otherwise positioned for angular access
thereto,
11 such as with scrapers and the like. A pressure vessel, hemispherical
head-form
12 of closure 60 can be pivoted from the vessel 22 and counterweighted to
close
13 flush to the inclined cylindrical end of the vessel 22. A gantry 62
assists in
14 manipulation of the head for access to the belly portion 40.
Further, the illustrated vessel 22 includes an eccentric end 64 at the
16 lower end 42, to reduce the diameter of the vessel 22 downstream of the
fluid
17 outlet 26. Advantages of reducing the vessel diameter at the lower end
42
18 include adapting to a smaller, more easily manageable or standard form
of clean
19 out. As shown the cleanout is a pressure-rated closure 60 supported upon
gantry
62. In this embodiment, a 36 inch vessel, having 33 inch internal diameter, is
21 inclined at 4 degrees. The cylindrical portion of the vessel is about 20
feet long
22 with a 3 foot long eccentric portion, reducing the diameter from 3 to
about 18
23 inches for fitting an 18 inch clean out.
17
CA 02848738 2015-08-07
Conventional pressure safety valves and other gas phase related
2 devices and instrumentation, not shown, are reliably located in the
freeboard
3 portion 44 between the fluid outlet 26 and the upper end 25.
4 Fig. 7 shows a cross-sectional view of a desander 100, according to
an alternative embodiment. The desander 100 comprises a tilted vessel 102
6 coupled to a particulate collection structure 180. The desander 100 does
not
7 require a flow barrier. The vessel defines an elongate, enclosing volume
having
8 a surface or diverging bounding wall terminated at opposing ends; a
proximal end
9 accommodating a flow inlet, and a distal end. A portion of the bounding
wall is
oriented as a top wall and a portion of which is oriented as a bottom wall.
The
11 top wall is tilted downwardly in the direction of flow at a first angle
of inclination.
12 The bottom wall is also tiled downwardly in the direction of flow. The
slope of the
13 bottom wall is divergent from the top wall so as to have a second angle
of
14 inclination that is greater than that of the top wall.
Such volumes are accomplished by vessel geometries including a
16 conical shape. Generally a conical vessel can be a circular cone having
an axis
17 extending from the apex to the base and a surface thereabout, the axis
of which
18 is angled so that the top wall has the downward and first angle of
inclination. A
19 right conical vessel has a circular cross-section; however, non-circular
cross-
sections are contemplated including elliptical, obround and polygonal. One
21 skilled in the art would have to account for the use of non-conventional
shapes
22 when considering pressure boundaries or use a conventional pressure
boundary
23 with non-pressure bearing internals of the proposed shapes.
24 By exploiting a tilted or inclined vessel 102 with divergent top
and
bottom walls, the desander 100 maximizes the effectiveness of the freeboard
18
CA 02848738 2014-04-11
1 portion, and reduces liquid flow rates to optimize settling conditions
therein and
2 improve retention of captured particulates S. Herein, components
described as
3 proximal and distal as related to their proximity to the inlet.
4 In the context of a right conical shape vessel 102, a conical body
104 extending from a lower, distal end 106 tapering to an upper, proximal end
6 108 with a central axis 110 upwardly slanting from a horizontal line (not
shown).
7 In this embodiment, the vessel is a right circular conical frustum having
a circular
8 distal base 112 at the lower, distal end 106 perpendicular to the central
axis 110,
9 a geometric surface comprising a conical wall 114 shown axially
symmetrical to
the central axis 110, and an apex 116 at the upper, proximal end 108. For
11 accommodation of a flow inlet, apex 116 is truncated for installation of
connecting
12 hardware such as flanges.
13 The vessel 102 is characterized by a first, acute top inclination
14 angle a defined by a top wall 118 of the body 104 and a horizontal line
120, and a
second, bottom inclination angle 13 defined by the bottom wall 122 of the body
16 104 and a horizontal line 124. The top inclination angle a is selected
for forming
17 the freeboard portion of the vessel, and the bottom inclination angle 13
is selected
18 for forming a belly portion that minimizes sand deposition and instead
19 encourages a mobile sand dune for migration of settled particulates to a
sump at
the bottom of the vessel and subsequent transferring to a sand accumulator.
21 The relationship between the top and bottom inclination angles a
22 and 13, the diameter of the circular distal base 112, the diameter of
the circular
23 truncated apex 116 and the length (i.e., the distance between the distal
base 112
24 and the truncated apex 116) of the vessel 102 is:
13 = Arctan( (D_distal ¨ D_proximal) /2 / L) ) x 2 + a,
19
CA 02848738 2014-04-11
where Arctan() represents the arctangent function, D_distal represents the
2 diameter of the circular distal base 112, D_proximal represents the
diameter of
3 the circular truncated apex 116, and L represents the length of the
vessel 102
4 measured along the central axis 110. Therefore, the vessel 102 may be
customized in design by selecting a proper vessel length, diameter of the
circular
6 distal base 112, ratio of the diameter of the circular distal base 112 to
that of the
7 circular truncated apex 116, and top inclination angle a to meet a
process
8 performance requirement.
9 The vessel 102 comprises a fluid inlet interface 140 at the upper
proximal end 108 and a fluid outlet 142 located on the top side of the vessel
in
11 proximity with the distal end 106 and spaced from the fluid inlet
interface 140.
12 The fluid inlet interface 140 comprises a receiving end 144 outside the
vessel 102
13 for receiving a fluid stream F typically comprising a variety of phases
including
14 gas G, some liquid L and entrained particulates such as sand S, and a
discharge
end 146 inside the vessel 102 for discharging the received multiphase fluid
16 stream F into the vessel at an inlet velocity. The position and
orientation of the
17 discharge end 146 determine the particulate trajectory. In this
embodiment, the
18 discharge end 146 is oriented such that the received fluid F is injected
into the
19 vessel along a direction 148 parallel to the top wall 118. However, in
some other
embodiments, the discharge end 146 may alternatively be oriented in other
21 orientations, e.g., an angle smaller or larger than that of the top wall
118,
22 depending on the design.
23 In an operating state, a gas/liquid interface 160 forms extending
24 horizontally in the vessel 102 from about the fluid outlet 142. The
gas/liquid
interface 160 is a generally elliptic, gas and liquid interface having a
distal end
CA 02848738 2014-04-11
1 166 adjacent the fluid outlet 142 and a proximal end 168, the location of
which is
2 determined by the lower end of the fluid outlet 142 and the top
inclination angle a.
3 A freeboard portion 164 is formed above the gas/liquid interface 160. A
belly
4 portion 162 is formed below the gas/liquid interface 160 for containing
liquid L
and particulates S. The belly portion 162 has a large volume as the diameter
of
6 the vessel 102 increases towards the distal end 106.
7 A fluid stream discharged from the fluid inlet interface 140
travels
8 along an elongated flow path from the fluid inlet interface 140 to the
fluid outlet
9 142. As the freeboard portion 164 has a cross-sectional area greater than
that of
the fluid inlet interface 140, the fluid velocity in the freeboard portion
adjacent the
11 fluid inlet interface 140, is less than that in the inlet, and
particulates cannot be
12 maintained in suspension.
13 By properly selecting length of the vessel to be sufficiently long
and
14 the freeboard velocity to be sufficiently low, when a fluid stream is
discharged
from the fluid inlet interface 140 and travels along the flow path, an
effective
16 amount of the entrained liquid L and particulates S fall out of the
fluid stream and
17 collect in a belly portion 162 (described later). A desanded fluid
stream is
18 discharged from the vessel via the fluid outlet 142.
19 The trajectory of the fluid stream F, from inlet 140, converges
with
the gas/liquid interface 160. The trajectory for dropping sand S and liquid L
into
21 the belly portion 162 is foreshortened, reducing drop out time. The
vessel 102 is
22 of sufficient length to space the fluid inlet 140 sufficiently from the
gas/liquid
23 interface 160 to minimize turbulence of the liquid L in the belly
portion 162, that
24 spacing being dependent upon various design factors including vessel top
21
CA 02848738 2014-04-11
1 inclination
angle a, bottom inclination angle [3, inlet fluid stream velocity and
2 characteristics.
3 At a steady
state, the level of the gas/liquid interface 160 is
4 controlled by
the fluid outlet 142 in proximity with the distal end 106, set by
eventual liquid entrainment and discharge at the fluid outlet 142. At steady
state,
6 when the
liquid level reaches the fluid outlet 142, any oil and other liquid is re-
7 entrained with
the gas G exiting at fluid outlet 142. In this state, the fluid stream
8 discharged
from the fluid outlet 142 has about the same gas/liquid ratio as the
9 stream
received at the inlet 140. In other words a mass balance is established in
that discharged liquid matches incoming liquid.
11 Particulates S
continue to be captured in the belly portion 162,
12 creating an
unstable sand bank. In a steady state liquid filled environment, the
13 particulates
form a sand bank on the lower portion of the vessel 102. The bottom
14 inclination
angle f3 of the vessel 102 is selected to be steep enough, e.g., to be
about or larger than the angle of repose of a bank of wet particulates. Thus,
the
16 sand and
liquid migrate towards the bottom of the vessel 102 via a lower
17 discharge 172
into the particulate collection structure 180, and fall through the
18 open valves
182 into the sand accumulation chamber 184. In the embodiments
19 in which
particulates are periodically or continuously removed from the lower
discharge 172, the liquid discharged from the fluid outlet 142 will, on
occasion, be
21 less than that
in the incoming liquid by the amount removed with the particulates.
22 Having a lower
discharge 172, at least particulates are collected
23 and discharged
from the belly portion. Typically particulates and liquid are
24 collected in
the belly portion and are periodically or continuously discharged
22
CA 02848738 2014-04-11
1 therefrom.
With a gas/liquid interface formed, liquid is discharged with desanded
2 gas from the freeboard portion at the distal end at the fluid outlet 142.
3 When in use,
the fluid inlet 140 and the fluid outlet 142 are
4 connected to
the connective pipes of a conventional wellhead and downstream
equipment (not shown), respectively. The receiving end 144 of the fluid inlet
6 interface is
typically orthogonal to the wellhead. As the connecting pipes are
7 typically in
rectilinear or orthogonal arrangements, the fluid outlet 142 is
8 configured in
a vertical orientation and thereby obviates the need for an angular
9 transition.
As described above, the fluid inlet 140, being exposed to entrained
11 particulates S
in the fluid stream F, is subject to significant risk of erosion, and
12 has to be
properly designed to ensure the regular use of the desander 100.
13 Methods
described above, e.g., using appropriate material or configuration to
14 prolong its
service life, regularly replacing the worn-out fluid inlet, and/or using a
replaceable discharge of nozzle, may be used in various embodiments. In this
16 embodiment, a
replaceable nozzle as shown in Fig. 5 that has a discharge end
17 with an
inclination angle a and a horizontal receiving end is used for coupling to
18 the horizontal connective pipe (not shown).
19 Velocity in
the freeboard portion 164 increases after a substantial
portion of the particulates S have already deposited in the belly portion 162.
The
21 cross-
sectional area of the belly portion 162 increases towards the fluid outlet
22 142, and the velocity of liquids accumulating therein diminishes.
23 In the belly
portion 162, particulates accumulate and flow down the
24 vessel 102 at
an angle of repose. The accumulation of liquid L and particulates S
establishes a downward flow in the belly portion 162, and as the particulates
23
CA 02848738 2014-04-11
1 accumulate and limit the free flow of the liquid L in the belly portion
162, the liquid
2 velocity begins to increase, drawing more particulates S down vessel. As the
3 bottom inclination angle 13 is greater than the angle of repose of a bank
of wet
4 particulates, the sand will migrate towards the particulate collection
structure 180.
For a given length of vessel 102, or a given distance between the
6 fluid inlet 140 and the fluid outlet 142, the top inclination angle a may
be selected
7 to meet the requirement of accommodating gas G and liquid L content in
the feed
8 fluid stream F. The smallest top inclination angle a is limited by the
minimum
9 requirement for a minimum freeboard 164 cross-sectional area adjacent the
inlet
140 once the gas/liquid interface 160 builds to about the fluid outlet 142.
The
11 largest top inclination angle a is limited by the requirement for a
minimum
12 freeboard gas capacity to accommodate particulate removal of any sand S
in the
13 gaseous phase G of the incoming fluid stream F. In particular, the
minimum top
14 inclination angle a is the minimum inclination angle of the top wall 118
that
ensures the inlet 24 be entirely in the freeboard 164 when the gas/liquid
interface
16 160 reaches the bottom of the fluid outlet 142. The maximum top
inclination
17 angle a is the inclination angle of the top wall 118 at which the inlet
140 is well
18 above the gas/liquid interface 160 allowing substantial freeboard to
handle slug
19 flow. Moreover, if a greater top inclination angle a is used, the
trajectory of the
injected fluid stream F impinges the gas/liquid interface 160 at less acute
angle,
21 impinges the gas/liquid interface 160 sooner and allows the use of
shorter
22 vessels 102 and greater particulate removal efficiency. As increasing
the top
23 inclination angle a also increases the bottom inclination angle 13, a
larger top
24 inclination angle a thus reduces the need for a steeply tapered cone
shape of the
vessel 102.
24
CA 02848738 2014-04-11
In this embodiment, the top inclination angle a is preferably selected
2 from the range of about 2 degrees to about 20 degrees.
3 For a given length of vessel 102, the bottom inclination angle 13
may
4 be selected to be great than or equal to the estimated angle of repose of
a wet
sand bank to facilitate smooth particulates drop-off. Generally, the bottom
6 inclination angle 13 is larger than the top inclination angle a. The
conical shape
7 vessel 102 is determined after the length of the vessel 102, the top and
bottom
8 inclination angles a and 13 are selected.
9 In one example, a desander 100 comprises a conical shape vessel
102 having a circular distal base of diameter 0.91 meter (36 inches), a
circular
11 truncated apex of diameter 0.154 meter (i.e., 6 inches) and a length of
3.05
12 meters (i.e., 10 feet). The vessel is tilted such that the bottom
inclination angle 13
13 is 35 degree.
14 Referring again to Fig. 7, the vessel 102 comprises a lower
discharge 172 coupled to the particulate collection structure 180 to allow
16 particulates and liquid to migrate thereto. The particulate collection
structure 180
17 comprises a sand accumulation chamber 184 sandwiched between an inlet
valve
18 182 and a discharge valve 186. The inlet valve 182 is connected to the
vessel
19 102 on top thereof and to the sand accumulation chamber 184 therebelow,
and
the sand accumulation chamber 184 is in turn connected to the discharge valve
21 186 therebelow. The particulate collection structure 180 also comprises
a
22 particulate detector 188, e.g., an ultrasonic sand detector, to detect
particulate
23 accumulation in the sand accumulation chamber 184.
24 The inlet valve 182 may be set to the open position and the
discharge valve 186 set to the closed position in normal operation to allow
the
CA 02848738 2014-04-11
1 sand accumulation chamber 184 to collect particulates and liquid from the
vessel
2 102.
3 Unlike the
prior art desanders that require shutting down the
4 operation to depressurize the vessel 102 for removing accumulated
particulates,
the removal of accumulated particulates can be conducted periodically with the
6 vessel 102 being pressurized and in operation. For this purpose, the
valves 182
7 and 186 are controlled automatically by the particulate detector 188 to
8 periodically open and close. Typically, an interlock is used to prevent
the inlet and
9 discharge valves from being open at the same time. In particular, the
valve 182,
between the vessel 102 and the sand accumulation chamber 184 is normally
11 open except at the time of particulate removal, allowing particulates to
fall into the
12 accumulator. The discharge valve 186 is normally closed except at the
time of
13 particulate removal.
14 To remove
particulates while maintaining the desander 100 in
operation, the valve 182 is first closed. Valve 186 is then opened allowing
the
16 particulates contained in the sand accumulation chamber 184 to exit.
Usually,
17 valve 186 is opened only for a short period of time sufficient to allow
the volume
18 of the sand accumulation chamber 184 to be evacuated. After removing
19 particulates from the sand accumulation chamber 184, valve 186 is closed
and
valve 182 is then reopened to allow particulates in the particulate drop out
the
21 vessel 102 to migrate into the sand accumulation chamber 184. The belly
portion
22 162 of the
vessel has sufficient space to store particulates inside the vessel 102
23 during the particulates-removing process, and the volume of the sand
24 accumulation chamber 184 is sufficiently large to discharge enough
particulates
within a cleaning cycle so as not to cause a backup of particulates into valve
182
26
CA 02848738 2014-04-11
1 thereby preventing the valve to close. Both valves 182 and 186 are
required to
2 have service rated for abrasive slurries.
3 As an alternate, if line washing is desired and the downstream
4 piping is able to support the pressure, valve 182 can be left open. Valve
186 is
opened only for a short period of time, sufficient to allow the volume of the
sand
6 accumulation chamber 184 to be evacuated.
7 Conventional pressure safety valves and other gas phase related
8 devices and instrumentation, not shown, are reliably located in the
freeboard
9 portion 164.
Although not shown in the figures, the vessel 102 is supported by
11 supporting structure to maintain the vessel 102 in its vertical
orientation.
12 In an alternative embodiment, the top inclination angle of the
vessel
13 102 is adjustable at the time of installation. The fluid inlet 140 and
outlet 142 are
14 rendered orthogonal. After installation, the orientation of the vessel
102, the
receiving end 144 of the inlet 140, the fluid outlet 142 and the particulate
16 collection structure 180 is then fixed for operation.
17 In another embodiment, the support structure comprises an
18 inclination adjustment structure for adjusting the inclination angle of
the vessel
19 102 to adapt to fluid stream conditions and or particulate stream
conditions. For
example, the support structure may comprise a first support anchor pivotably
21 coupled to the vessel 102 at a position near the distal end thereof, and
a second
22 support anchor pivotably coupled to the vessel 102 at a position near
the
23 truncated apex thereof. The height of the first and/or second support
anchors is
24 adjustable such that the inclination angle of the vessel may be adjusted
by
adjusting the height of the first and/or second support anchors.
27
CA 02848738 2015-08-07
The fluid outlet 142 and the particulate collection structure 180,
2 each facilitated by a correcting insert or spool attached thereon, may be
pivotable
3 within a predefined range of angle to allow a generally orthogonal
orientation
4 under any suitable inclination angle of the vessel 102. The inlet 140 may
also be
pivotable within a predefined range of angle such that the orientation of the
6 receiving end 144 thereof may be adjusted to adapt to the orientation of the
7 vessel. In yet another embodiment, a set of inlets 140 are provided to
allow users
8 to choose an inlet 140 suitable for an orientation-adjusted vessel 102
and install it
9 thereon.
Persons skilled in the art appreciate that various alternative
11 embodiments are readily available. For example, although in above
embodiment,
12 a particulate detector 188 is used for detecting particulate
accumulation in the
13 sand accumulation chamber 184, in an alternative embodiment, a timer may
14 alternatively be used to periodically control valves 182 and 186 to
remove
particulates from the sand accumulation chamber 184. In another embodiment,
16 no particulate detector or timer is used, and the valves 182 and 186 are
manually
17 controlled to remove particulates from the sand accumulation chamber
184.
18 Although in above embodiments, the vessel 102 is a tilted, right
19 circular conical frustum, in some other embodiments, the vessel 102 may
be an
oblique circular frustum such that the circular distal base located at the
lower,
21 distal end of the vessel is not perpendicular to the central axis.
22 Although in above embodiments, the vessel 102 tapers from the
23 distal end to a smaller, truncated apex at the proximal end, in some
alternative
24 embodiments, the vessel 102 has a constant diameter from the distal end
to the
proximal end.
28
CA 02848738 2014-04-11
1 Those skilled in the art appreciate that the particulate
collection
2 structure 180 may alternatively comprise different components. For
example, in
3 some alternative embodiments, the particulate collection structure 180
may be a
4 simple sand sump having no valve.
As appreciated by persons skilled in the art, the desanding devices
6 in the embodiments described above are made of suitable material for the
7 environment, fluid and pressures, such as steel or the like, with
specifications
8 satisfying relevant safety code requirements.
9
29
