Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR CLEANING OIL
STORAGE TANKS
FIELD OF THE INVENTION
The present invention relates to a method of cleaning a crude oil
storage tank and more particularly to the apparatus used for cleaning the oil
storage
tank.
BACKGROUND
When storing crude oil in an oil storage tank the oil is known to be
separated into layers including a layer of settled sand at a bottom of the
tank, an
intermediate layer of produced water from the crude oil, and an upper layer of
separated oil. The sand which settles on the bottom of the tank forms
deposits, the
removal of which require periodic cleaning of the tank. It is also desirable
for some
of the produced water in the tank to be removed in conventional cleaning
operations.
Various devices have been designed specifically for cleaning oil storage
tanks.
Examples of these are found in the following Untied States patents: 6,142,160
to
Winslow et al, 6,125,865 to Bacon Cochrane et al, 5,582,652 to Robertson et
al,
5,561,883 to Landry et al, 5,421,903 to Manabe et al, 5,293,887 to Thibodeaux,
4,859,323 to Rolfvondenbaumen and 4,770,711 to Deal, III et al. None of these
devices however are particularly suited for being readily transported from
site to site
in an efficient and low cost manner.
SUMMARY
According to one aspect of the present invention there is provided an
apparatus for cleaning an oil storage tank, the apparatus comprising:
a portable collection tank;
an injector nozzle for injecting fluid into the oil storage tank adjacent a
bottom of the oil storage tank;
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a pump having an inlet for receiving produced water from the oil
storage tank and an outlet for communication with the injector, the pump inlet
being
arranged to be coupled to a standard valve on the storage tank spaced above a
floor
of the storage tank; and
a suction line for connection between the collection tank and the oil
storage tank adjacent the bottom thereof.
The portable tank and recirculating pump can be supported on a single
vehicle for transport from site to site while enabling the use of produced
water as a
fluidising agent in a storage tank cleaning operation. This eliminates the
requirement of a second pressure truck having a supply of fluidising agent as
in
conventional cleaning operations.
The collection tank and pump are preferably supported on a single
vehicle such as a trailer unit which can be used on site.
The pump of the apparatus may be operable within a range of output
pressures between 40 and 250 psi, however an ideal output pressure is between
60
and 80 psi.
The pump inlet is preferably arranged to be coupled to a standard
valve on storage tank spaced above a floor of the storage tank and in
alignment with
the layer of produced water in the tank.
The pump may comprise a gear pump or in alternate arrangements, a
progressive cavity pump.
In the preferred embodiment, the collection tank comprises a vacuum
tank.
According to a second aspect of the present invention there is provided
a method of cleaning an oil storage tank comprising:
providing a portable collection tank;
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providing an injector nozzle for injecting fluid into the oil storage tank;
providing a recirculating pump;
coupling the inlet of the recirculating pump to a standard valve on the
storage tank at a location spaced above a floor of the storage tank;
coupling an outlet of the recirculating pump for communication with the
injector;
providing a suction line;
connecting the suction line in communication between a bottom of the
oil storage tank and the collection tank;
locating the injector nozzle adjacent the bottom of the oil storage tank;
operating the recirculating pump to draw produced water from the oil
storage tank and to inject the produced water back into the oil storage tank
through
the injector nozzle;
operating the suction line to draw a slurry from the bottom of the oil
storage tank into the collection tank.
The method preferably includes coupling the inlet of the recirculating
pump to a lowermost standard valve on the storage tank at a location spaced
above
the floor of the storage tank which is in alignment with a layer of produced
water in
the storage tank.
Operation of the recirculating pump may cease when a level of
produced water in the storage tank falls below the standard valve on the
storage
tank, when sufficient sand has been removed from the storage tank or when the
collection tank is full.
An external water supply may be provided when there is insufficient
produced water in the storage tank.
The method preferably includes allowing the slurry in the collection
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tank to settle and pumping the produced water from which the sand in the
slurry has
settled back into the storage tank.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary
embodiment of the present invention:
Figure 1 is an isometric view of the apparatus shown coupled to a
crude oil storage tank.
Figure 2 is a schematic view of the apparatus according to Figure 1 as
shown coupled to a crude oil storage tank.
Figure 3 is a partly sectional view of the manifold coupling the suction
line and the injector of the apparatus of Figure 1 to the bottom valve of a
storage
tank.
DETAILED DESCRIPTION
Referring to the accompanying drawings, there is illustrated a tank
cleaning apparatus generally indicated by reference numeral 10. The apparatus
10
is generally arranged for cleaning crude oil storage tanks 12 for storing
crude oil
therein.
When the crude oil is permitted to separate, various layers are formed
within the tank including a layer of oil sands 14 at a bottom 16 of the tank,
an
intermediate layer of produced water 18 and an upper layer of separated oil 20
above the produced water. Typical storage tanks 12 include a bottom valve 22
located in a side wall of the tank adjacent the floor thereof for
communication with
the sand 14 in the tank. One or more intermediate valves 24 are also provided
in
the side wall of the tank at various positions spaced above the floor of the
tank. A
common reference height of typical intermediate valves is 3 feet from the
floor of the
tank for communication with the produced water 18 in the tank, however various
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other intermediate valves may be located at 4, 5 or 7 feet as examples.
The apparatus 10 is arranged to be supported on a trailer 30 so that
the apparatus is portable from site to site when towed by a suitable truck 32
for on
sight use of the apparatus. The trailer 30 includes a conventional collection
tank 34
supported thereon which is suitably sealed for permitting a vacuum pressure to
be
contained therein. A vacuum pump 36 is supported on the trailer 30 in
communication with the collection tank 34 adjacent a top end of the tank for
creating
the vacuum pressure within the tank as in conventional vacuum tank trailers.
The apparatus 10 also includes a recirculating pump 38 which is
arranged to be supported on the trailer 30 along side one of the fenders of
the trailer
or adjacent a cab of the truck 32. The recirculating pump 38 is a gear pump
having
an inlet which is arranged to be connected to one of the intermediate valves
24 of
the storage tank 12 by suitable flexible hoses 42. The inlet 40 of the
recirculating
pump can be connected to an external supply of fluidizing agent, however in
the
illustrated embodiment the inlet 40 is arranged to draw produced water 18 from
the
storage tank 12 for recirculation back into the storage tank 12 adjacent the
bottom
end thereof through bottom valve 22. This is accomplished by connecting the
outlet
44 of the recirculating pump 38 to a rigid injector wand 46 by suitable
flexible hoses
42.
A manifold 48 is provided for coupling the injector wand 46 to the
bottom valve 22 of the storage tank. The manifold 48 generally comprises an
outer
pipe 50 which couples a T-shaped fitting 52 thereon such that a main portion
of the
T-shaped fitting extends generally radially outwardly from a side wall of the
storage
tank 12. The injector wand 46 is substantially smaller in diameter than an
inner
diameter of the outer pipe 50 and the T-shaped fitting 52 so as to permit the
injector
wand 46 to be slidably displaced concentrically therein while being spaced
from the
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walls of the pipe. An outer end 54 of the main portion of the T-shaped fitting
52
includes a seal mounted between the injector wand 46 and the fitting 52 for
sealing
therebetween while permitting the injector wand 46 to remain slidable relative
to the
T-shaped fitting.
The injector wand is an elongate rigid pipe in the order of 18 feet in
length which is arranged to be extended into the storage tank 12 through the
bottom
valve 22 by the manifold 48 so that a free end 56 of the injector wand 46 is
movable
across a bottom of the storage tank 12. The outer end 58 of the injector wand
46 is
coupled by the flexible hose 42 to the pump 38 such that produced water from
the
storage tank is pumped through the wand and into the sands 14 at a bottom of
the
tank by suitable nozzles 60 supported on the wand 46. The nozzles 60 may be
positioned at various directions for injecting the produced water into the
sands 14 so
that the sands may be stirred up and removed from the tank. The nozzles 60 are
located adjacent the free end of the wand 46 so as not to interfere with
sliding
movement of the wand through the manifold 48.
A branched portion of the T-shaped fitting 52 is coupled to a suction
line 62 which connects the manifold 48 to the collection tank 34 at a location
within
the tank spaced below a top end of the collection tank. The suction line 62 is
a
suitable flexible hose arranged to pump a slurry of produced water and sand 14
therethrough. The slung is drawn through the suction line 62 and into the
collection
tank 34 due to vacuum pressure in the collection tank as maintained by the
vacuum
pump 36. The slung is drawn into the suction line 62 through the bottom valve
22 in
the side wall of the tank in the annular space defined between the injector
wand 46
and the surrounding outer pipe 50 of the manifold 48.
The apparatus 10 is thus arranged to support all equipment required
for cleaning sand from a crude oil storage tank on a single trailer or
vehicle.
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Because produced water from the storage tank itself is used for stirring up
the sands
an extra pressure truck having its own supply of fluidizing agent is not
required. The
use of a recirculating pump supported directly on the same trailer as the
collection
tank 34 is sufficient for stirring up the sands in the storage tank even when
operated
at low pressures. The apparatus 10 and the recirculating pump thereof, remain
effective when operated in a range of 40 to 250 psi however an ideal range
appears
to be in the range of 60 to 80 psi at an outlet of the recirculating pump 38.
The
flexible hoses 42 which are arranged to maintain pressure therein can easily
handle
this range of pressure which is considerably safer than pressures in the order
of
2000 psi which are known to be used with the plunger pumps of pressure trucks
normally required for oil storage tank cleaning operations.
In order to use the apparatus 10 the various flexible hoses 42 must be
connected between the recirculating pump 38, the collection tank 34 and the
oil
storage tank 12. This includes connecting the suction line 62 between the
manifold
48 at the bottom valve 22 and the collection tank 34. An inlet flexible hose
42 is
connected between the inlet 40 of the recirculating pump 38 and a selected
intermediate valve 24 of the storage tank 12 which is in alignment with a
level of
produced water 18 within the tank. An outlet flexible hose 42 is then coupled
between the outlet 44 of the recirculating pump 38 and the outer end of the
injector
wand 46 which is positioned in a sealing configuration within the manifold 48
to
extend into the storage tank 12.
The cleaning operation begins by operating the vacuum pump 36 to
maintain a vacuum pressure within the collection tank 34. A valve 66 coupled
between the suction line 62 and the collection tank 34 is then opened so that
the
suction line 62 is exposed to the vacuum pressure of the collection tank 34.
Opening the intermediate valve 24 to which the inlet flexible hose 42 is
coupled then
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permits produced water to be introduced to the inlet of the recirculating pump
38
which is then put into operation for dispensing pressurized produced water
through
the injector wand 46. Opening the bottom valve 22 to which the manifold 48 is
connected permits the injector wand 46 to be introduced into the storage tank
12 so
that the pressurized produced water from the recirculating pump 38 is injected
into
the sands 14 across a bottom of the storage tank. Displacement of the free end
of
the injector wand 46 back and forth across the tank stirs the sand 14 at the
bottom of
the tank into a slurry which is then sucked into the suction line 62 via the
space
between the injector wand and the outer walls of the manifold 48 at the bottom
valve
22. The slurry is drawn through the suction line 62 into the collection tank
34 to
remove the sands from the oil storage tank 12. The operation ceases by
discontinuing operation of the pumps and disconnecting all of the flexible
hoses
once the appropriate valves have been closed. The cleaning operation
terminates
when the collection tank 34 has been filled to a desired amount of sand in a
slurry of
produced water. The slurry is then permitted to settle within the collection
tank 34 so
that the water in the collection tank from which the sand has settled out of
can be
pumped back into the oil storage tank for later use in a further cleaning
operation.
The water may be pumped back by reconnecting the inlet of the recirculating
pump
38 to the collection tank 34 at an intermediate location above the settled
sand in the
tank. In an alternate arrangement the water in the collection tank 34 can be
returned
to the storage tank by pressurising the collection tank with the suction line
62 being
connected at one end to the valve 66 on the collection tank above the level of
settled
sand spaced above a bottom end of the tank and at the other end to the
intermediate valve 24 on the storage tank. Opening valves 66 and 24 with the
collection tank 34 being pressurised thus forces the water back into the
storage tank.
More sand can then be removed from the oil storage tank 12 by reconnecting the
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inlet of the recirculating pump 38 to a suitable intermediate valve 24 of the
oil
storage tank in alignment with produced water within the tank or by
reconnecting the
suction line 62 as described above. The vacuum pump 36 can again be operated
with the cleaning operation steps being repeated so that a further slurry of
sand and
produced water is introduced into the collection tank 34. If more sand is
desired to
be removed from the oil storage tank 12 various cycles of permitting sand to
settle
within the collection tank 34 for reuse of the produced water can be
performed,
however if it is desirable to remove both the sand 14 and a portion of the
produced
water 18 from the storage tank 12 the apparatus 10 may cease the cleaning
operation and hall away the water and sand at any moment.
In this arrangement only a single unit is required for cleaning an oil
storage tank as opposed to a collection vehicle and a pressure vehicle for
supplying
a fluidizing agent as is required in conventional cleaning operations. In this
arrangement no water or oil is transferred to or from the collection tank 34
other than
washed sand 14 and a portion of the produced water 18 which carries the sand
into
the tank in a slurry. The recycled use of produced water using a recirculating
pump
38 as described also permits operation under much lower pressures than
conventional cleaning operations for reducing occurrences of injury and costly
damage due to accidental hose rupturing and the like.
When using the cleaning operation as described herein for the first
time in some instances, there may be insufficient produced water within the
storage
tank 12. In this instance some water may initially be added to the storage
tank 12
prior to cleaning, however if the produced water and sand slurry removed from
the
storage tank 12 are permitted to settle in the collection tank 34 with the
produced
water being returned to the storage tank 12, further water is typically not
required to
be added in further cleaning operations. Furthermore additional produced water
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results when it is separated from crude oil added to the storage tank 12 and
separated therein.
In further embodiments of the present invention, other forms of trailers
30 may be suitable without using a vacuum collection tank 34. Any suitable
container may be used when suitable pumps are provided in communication with
the
suction line 62 for pumping the slurry from the bottom valve 22 of the storage
tank
12 to the container on the alternate trailer. A vacuum collection tank 34 on a
trailer
30 as described herein however is preferred as the vacuum pump 36 generally
has
a longer life than slurry pumps and is able to provide constant suction to the
suction
line 62.
In other embodiments the recirculating pump 38 may comprise a
progressive cavity pump for example in place of a gear pump as described
above. A
gear pump is generally preferred as it is cheaper and lighter so as to permit
the
pump to be readily supported on the trailer 30. While the gear pump may not be
able to handle as much debris being pumped therethrough as a progressive
cavity
pump, progressive cavity pumps are considerably more expensive.
While one embodiment of the present invention has been described in
the foregoing, it is to be understood that other embodiments are possible
within the
scope of the invention. The invention is to be considered limited solely by
the scope
of the appended claims.
