BACKGROUND OF THE INVENTION
[0001] This invention relates to a method of tank cleaning and a tractor for use therein.
The method and tractor of specific embodiments are especially concerned with cleaning
and maintaining oil storage tanks.
[0002] Routine maintenance and cleaning of crude oil storage tanks includes several labour
intensive operations. Crude oil storage tanks develop a sediment accumulation which
must be removed prior to cleaning. Sediment deposits can vary in depth from 100 mm
up to one metre. The sediment consistency can vary from a viscous grease/paraffin
residue to a relative solidified bituminous/asphalt residue. Following sediment removal,
the tank must be cleaned and degreased for inspection and repair work. During cleaning,
personnel remove the remaining sediment from the tank bottom and they remove hard
and encrusted sediments from the tank walls and floors. Degreasing requires removal
of hydrocarbons from tank walls and floors to permit complete inspection of the tank
and any necessary repair work. Following the repair work, the tank walls and bottom
must be sandblasted to leave a white metal surface finish prior to application of
a tank coating. During these operations, gases need to be exhausted from the tank.
[0003] Hitherto cleaning and degreasing operations have usually been performed using manual
labour and the simplest of tools. Sediment removal is currently done by manually digging
out the material, transporting it across the tank in wheel barrows and dumping it
outside the tank through a hole in the tank wall. A typical tank can require up to
4000 manhours to remove material. Traditional cleaning and degreasing is done using
fire hoses and squeegees. This also is manual work and can require up to 1000 manhours
per tank. Sandblasting is done using conventional sandblast equipment with the typical
rates associated with this work. Manual labour is required to remove all of the spent
sand from the tank and to vacuum down the walls and tank bottom prior to painting.
This step can require an additional 1000 manhours.
[0004] There has been a long-felt need for a method and apparatus for tank cleaning, for
example for cleaning crude oil storage tanks, which facilitates cleaning in less time
and with less manual labour than are required by traditional methods.
[0005] According to the present invention there is provided an in-tank tractor for use in
cleaning the interior of storage tanks, the tractor comprising
a chassis,
a body means mounted on the chassis, the body means having a top and bottom,
wheels mounted to the chassis,
motor means for rotating the wheels,
boom means rotatably mounted to the top of the body means, the boom means having
inlet means for receiving hose means which convey power fluid to the tractor including
power fluid for the motor means, one end of the boom means extending beyond the chassis
and beyond the body means, and
conduit means for conveying power fluid from the boom means to the motor means.
[0006] According to the present invention there is also provided a method for cleaning sludge
from a storage tank, the method including the steps of
emplacing sludge removal means partially within the tank said sludge removal means
having an inlet within the tank and an outlet outside the tank,
passing the components of an in-tank tractor through an opening in the tank,
assembling the in-tank tractor within the tank, and
using the tractor to push the sludge to the inlet of the sludge removal means.
[0007] In embodiments the system for crude oil storage tank cleaning and maintenance includes
methods and apparatus for degassing, sediment removal, cleaning, and coating the interior
surfaces of a tank. The equipment used for sediment and sludge removal includes: an
in-tank tractor unit; a sediment transfer unit; a sediment removal pump; a power unit;
and a water blasting device. The equipment used for cleaning, degreasing, and sandblasting
includes: the in-tank tractor unit; the water blasting device; cleaning and surface
preparation accessories; the sediment transfer unit; and the power unit. In a preferred
embodiment this equipment is constructed to allow for easy entry into tanks through
a manway 750 mm in diameter. Tanks that have manways of smaller than 750 mm rarely
have diameters in excess of 10-15 m and are more efficiently cleaned using less automated
in-tank equipment. Equipment required for cleaning smaller tanks is designed to pass
through 500 mm diameter manways. Gas exhaust equipment may be used in tanks in which
dangerous gases are present.
[0008] The in-tank mobile tractor has a variety of uses. It can be used to partially emulsify
sediments; to break up solidified sediment; and to push sediment to a sediment transfer
unit. The tractor can be constructed completely of aluminium and brass to eliminate
sparking and combustion and it can be comprised of elements small enough so that it
can be passed through a 750 mm wide manway. The tractor can be made so that it is
completely hydraulically operable for its mechanical functions and it may have pneumatically
powered lights. A solid blade disposed preferably on the front of the tractor can
be used to push material and it can be raised as needed. By employing a swivel boom
for supporting the tractor's hydraulic power hoses and other lines such as compressed
air lines, the tractor can turn on its own axis without becoming entangled in the
hoses or damaging them. The tractor can support and transport the water and sand blasting
equipment within the tank.
[0009] The tractor's components can be passed through the tank's manway and reassembled
inside the tank. Each component can be a maximum weight of 100 kilograms making it
possible for two persons to lift and manipulate each component. A hydraulic motor
can be provided for each of the four wheels to facilitate the driving of the tractor
and to enhance its ability to drive in sludge or sediment.
[0010] The tractor can be steered by differential speed of the driving wheels. The tractor
operator sits on the tractor for visibility and safety. The operator's controls include
forward and reverse motion and steering controls. A forward/reverse selector can be
employed which requires that the operator maintain a constant force on it so that
the tractor's motion will cease when the selector is released by the operator. The
tractor's speed is controlled by a flow control valve. Communication equipment can
be used to link the tractor operator to personnel outside the tank.
[0011] The sediment transfer unit is useful for the emulsifying and breaking up of sludge
or sediment and for transferring it outside the tank. The unit has an auger-type conveyor
and is mounted on a trailer. Part of the unit is insertable through a 750 mm manway
in a tank. An hydraulic power unit is used with the sediment transfer unit. Pumps
can be used to pump sludge or sediment from the sediment transfer unit to a container,
to a sludge pit, or to a vacuum tanker; or sediment can be conveyed from the end of
the sediment transfer unit outside of the tank into a container or hopper.
[0012] The water blasting unit is useful for supplying liquid to break up sediment and for
partially emulsifying sediment. Also, it is useful for cleaning and descaling the
walls and floor of a tank. A non-foaming degreaser or surfactant can be injected into
blast water to assist in degreasing. Sand can be injected with water to sand blast
surfaces. A rust inhibitor can be injected with blast water. Water, other components,
and freed material and sediment can be vacuumed up and transferred to a storage container
or vacuum tank. Water blasting devices in both horizontal and vertical configurations
can be employed on the in-tank tractor.
[0013] When one area of a tank has been cleaned or has had a certain amount of sludge removed
from it, that area can be isolated with barriers (e.g., sand bags, boards, planks,
etc.). Further operations can be carried on in the isolated area while initial sludge
or sediment removal (or some other operation) is done in other areas of the tank.
[0014] Conventional power units, hoses, pumps, high pressure water generating systems, blowers,
air compressors, suction tanks, trucks, corrosion inhibitors, hydraulic fluids, couplings,
and fittings, can be used in combination with the various units described above.
[0015] The present invention seeks to provide, at least in preferred embodiments, novel
and efficient apparatuses and methods for cleaning and maintaining storage tanks,
e.g., crude oil storage tanks.
[0016] The present invention seeks to provide in an embodiment a system for cleaning crude
oil storage tanks in which the system components used inside the tank can be passed
through an opening 750 mm in diameter.
[0017] The present invention further seeks to provide in embodiments a system which can
be used to remove sediment or sludge from a tank and to clean or degrease the tank's
interior.
[0018] The present invention seeks to provide an embodiment of such a system which can deal
with sediment or sludge varying in depth from one hundred millimetres to one metre
and which can work effectively with viscous residues as well as solidified residues.
[0019] The present invention further seeks to provide an embodiment of a tractor which can
be used with: vertical or horizontal water or sand blasting units; pneumatically powered
lights; individual power drives for each wheel; a swivel boom for keeping power and
control lines out of the way of the tractor; and a blade for pushing sediment. Tractor
components can be made of non-sparking material.
[0020] The present invention seeks to provide embodiments of a tank cleaning system which
significantly reduces the amount of manual labour required to clean a tank.
[0021] The present invention seeks to provide embodiments of such a system which permits
certain operations (e.g., the cleaning of a specific area or zone) within portions
of a tank and provides barriers for demarcating and separating different zones or
areas within the tank.
[0022] Embodiments of the invention will now be described, by way of example only, with
reference to the accompanying drawings, in which:-
Fig. 1 shows a side view of an in-tank tractor according to an embodiment;
Fig. 2 shows in a side view, and partially in cross-section, a sediment transfer unit
partially in a tank;
Fig. 3 shows a side view of an in-tank tractor;
Fig. 4 shows a perspective view of the front portion and controls of the tractor of
Fig. 3;
Fig. 5 shows a top plan schematic view of a tank sediment removal system;
Fig. 6 shows a top plan schematic view of a tank cleaning system;
Fig. 7 shows a top plan schematic view of a tank cleaning system;
Fig. 8 shows a top plan schematic view of a tank wall cleaning system;
Fig. 9 shows a top plan schematic view of a tank preparation system; and
Fig. 10 shows a top plan schematic view of a tank coating system.
[0023] As shown in Fig. 5, a tank sediment removal system 2 for removing sediment from a
tank 111 includes a sediment transfer unit 15, a gas exhaust device 75, an hydraulic
power unit 14, air compressors 76 and 77, an in-tank tractor 54, and high pressure
water generating apparatuses 78. In this embodiment five water generating apparatuses
78a-78e are connected in series and each is capable of delivering water at the rate
of 1.26 l/s (20 gallons per minute) and collectively they are able to deliver 6.3
l/s (100 gallons per minute). A hand-held spray gun 79, which is supplied with high
pressure water through hose 82, can be used within the tank 111. Barriers 80 and 81,
e.g., formed of sand bags, are positioned to isolate an area in which the tractor
54 operates. Tractor 54 is provided with a front-mounted blade 55 which blade 55 is
used to push sediment or sludge to the sediment transfer unit 15. An air filter 83
can be used to provide filtered air as needed to various apparatuses or operators.
[0024] As shown in Fig. 2, the sediment transfer unit has an inlet portion 21 formed by
conduits 25c to f and extending within the tank 111 and an outlet portion 22 formed
by conduits 25a to w, which is exterior to the tank 111. One inlet conduit 25f is
formed with side recess 23 into which sludge or sediment can be pushed or inserted.
An auger 24 conveys material, which has been inserted into the side recess 23, through
the conduits 25 to the outlet portion 22 of the unit 15. The auger 24 extends within
the conduits 25a to f from the side recess 23 to an outlet channel 26 in the outlet
portion 22 at conduit 25a. A removable cover 27 is emplaced on conduit 25c within
the tank 111 for permitting access to a hanger bearing (not shown in Fig. 2) located
within the conduit 25c. This hanger bearing holds and supports the auger 24 so that
it does not rub against the interior of the conduit 25c. Likewise, hanger bearings
(not shown) are used in each conduit section 25a to f to support the auger 24. The
portion of the auger 24 in the conduit 25d has a U-joint connection in order to accommodate
the bend between conduits 25c and 25d and 25e. Thus, the conduit 25 is composed of
inlet conduit 25f, bottom conduits 25e, bend conduit 25d, bearing conduit 25c, exterior
conduits 25b, and outlet conduit 25a. Any number of conduits can be used so as to
extend or reduce in length either the exterior or interior portion of the conduit.
Segments can also be added to the auger 24. In this way, the auger 24 can access any
part of the tank 111.
[0025] A manway 28 in the embodiment shown in Fig. 2 is 750 mm (30 inches) wide. Of course,
the system herein described, is not restricted to use in a tank 111 with manways 28
of any particular size. However, it is a preferred feature herein that the components
of the system (or easily disassembleable parts thereof) be passable through a 750
mm wide manway.
[0026] The sludge or sediment dumped through the outlet channel 26 is introduced into a
hopper 29. A slide valve 30 disposed at the bottom of the hopper 29. By opening this
valve 30, material is introduced into the pumping unit 31. The material is pumped
through a pipe 107 (Fig. 6) to suction tankers such as the tank 13 shown in Fig. 6
or to other containers.
[0027] As shown in Fig. 1, a tractor 54 has a solid blade 55 (made of metal, e.g., aluminium)
movably mounted to the front of the tractor 54. A wear strip 55a ("squeegee"), which
is preferably made of a material such as neoprene, is mounted to the blade 55. An
hydraulic cylinder 56 is rotatably mounted to the tractor 54 at the pivot point 57
and to a blade support member 58 at the pivot point 59. Activation of cylinder 56
effects the raising of the blade 55 by causing a support member 58 to pivot upwardly
about a farther pivot point 60. The support member 58 is rotatably mounted at the
pivot point 60 to a top member 61 which itself is connected to the tractor 54.
[0028] The tractor 54 is comprised of components such as structural members 85, tyres 86,
and a boom 88. Boom 88 is swivelly mounted for swivel movement on the top of the tractor
54 by means of a swivel 89. In this embodiment of an in-tank tractor, a sand distribution
system 87 is provided which conveys sand to a blast unit (not shown) mounted on the
tractor. A suction hose 90 is used to suck water, sand, and blasted material from
such a blast unit. (A connecting hose which is not shown will connect the hose 90
to a blast unit mounted to the tractor). It is preferred that all of these components
(or easily disassembleable parts thereof) be able to be passed through a 750 mm manway
and that each part weight no more than 100 kilograms.
[0029] As shown in Fig. 6, both hydraulic and pneumatic power lines 104, 105 and 106 are
coupled to the tractor 54. As indicated in Fig. 1, a separate hydraulic motor is provided
for each wheel 92. In this manner the tractor 54 is adapted to make very sharp turns.
In use, if it is necessary, the tractor 54 is able to turn about its own vertical
axis. The hydraulic power fluid is conveyed through hoses 104, 150 from the hydraulic
power unit 14. At the tractor 54 these hoses are coupled to the hydraulic inlets 93,
94 on a boom 88. Within the tractor structure, conventional hydraulic fluid conduits
(not shown) are used to convey the fluid to hydraulically operable equipment on the
tractor 54. The compressed air from compressors 76 and 77 is conveyed through hoses
106 and is received by the tractor 54 at the air inlets 95, 96 on the boom 88. On
the tractor 54, the compressed air is then conducted to pneumatically operable equipment
on the tractor 54 through conventional conduits.
[0030] Breatheable air can be conveyed from either inlet 95 or 96 via a suitable conduit
to outlets 97, 98, 99 and 100 for use by the tractor operator and by tank cleaning
personnel with suitable umbilical hoses. Each of such personnel can also carry a small
supply of air so that in the event of an emergency each will have sufficient air to
exit from a tank.
[0031] The rotatable boom 88 keeps the hoses (pneumatic and hydraulic) out of the way of
the tractor 54 during cleaning operations. (Of course for environments in which he
use of electricity is permitted, electrical power may be used with the tractor).
[0032] In Fig. 3 a tractor 12 comprises components such as structural members 32, tyres
33, and vacuum tank 34 all of which, when disassembled, are able to be passes through
a 750 mm wide manway. Also, it is a preferred feature of the embodiment that the components
not exceed about 100 kilograms in weight so that two persons can handle, lift, and
manipulate them easily.
[0033] This tractor 12 is hydraulically powered via hydraulic power lines (not shown) each
of which is connected to a hydraulic line input 35 which communicates with the additional
hydraulic means and motors on the tractor 12. An air inlet 36 is provided for receiving
a compressed air hose (not shown) and for conveying compressed air to the various
means and apparatuses of the tractor 12 which require compressed air for operation.
[0034] A rotatable boom 37 is rotatably mounted to a top beam 38 of the tractor 12. The
inlets 35 and 36 are disposed on this boom 37 so that the tractor's motion is not
impeded by the air hose, hydraulic power line, or other members connected to the inlets.
When a separate hydraulic motor is used for each of the tractor's four wheels 33,
the tractor can turn on its own central vertical axis or otherwise manoeuvre within
a very small area, since the boom 37 keeps the power lines and air hoses out of the
tractor's way.
[0035] A pneumatically operated light (or lights) such as the light 39 can be mounted to
the tractor 12 as shown in Fig. 3. These lights 39 may be employed for cleaning operations
in the darkened interior of a storage tank or other vessel which has no light or is
poorly lit.
[0036] A water blasting device 40 is mounted in a horizontal configuration to the front
of the tractor 12. A shroud 41 has one or more blast nozzles 42 disposed therethrough.
Hose 43 is connected to nozzles 42 and conveys water under pressure thereto. Hose
44 conveys air or air with abrasive particles such as sand to the nozzle 42. A suction
or vacuum hose 45 sucks up the liquid, abrasives, and/or blasted material from a blasting
zone defined by the shroud 41 and conveys them to a suction tank 34. Alternatively
the hose 45 may be extended to a receptacle at the exterior of the tank 111. As shown
in Fig. 3, the water blasting device 40 is mounted for cleaning the floor of a tank.
It is also possible to mount the water blasting device 40 to the tractor 12 in a position
in which device 40 is arranged at an angle or vertically for cleaning the walls of
a tank. An hydraulic cylinder 46 is provided which, when actuated, is adapted to pivot
the device 40 upwardly about a pivot point 47. This actuation of cylinder 46 is employed
to displace the device 40 from its position adjacent a tank floor. A venturi 48 provides
a suction in the suction tank 35 and a silencer 49 silences the venturi noise. Material
is conveyed from the tank 34 through a pipe 51, a connection 52 and a hose 50. A check
valve 53 prevents backflow.
[0037] Controls 101 for an in-tank tractor such as tractor 12 (Fig. 3) or tractor 54 (Fig.
5) are shown in Fig. 4. A control lever 62 controls the hydraulic motors on the two
left wheels and a control lever 63 controls the hydraulic motors on the two right
wheels. By pulling back on both levers 62 and 63, the tractor will go in reverse.
Conversely, by pushing forward on both levers 62 and 63, the tractor will go forward.
A control lever 65 controls the hydraulic cylinder (either cylinder 46 or cylinder
56) which raises and lowers a member (either blasting device 40 or blade 55, respectively)
mounted on the front of the tractor. Additional levers 66, 67, and 68 can be used
to control other items on the tractor. A centre speed control lever 64 is used to
control the distribution of hydraulic power between the wheel motors and other functions.
When the lever 64 is in the vertical position, substantially all of the hydraulic
power flows to the function controls; but when the lever 64 is in the horizontal position,
substantially all power is directed to the wheel motors 91 (Fig. 5). An intermediate
position permits power fluid to flow both to the wheel motors and to the other functions.
[0038] In Fig. 6 a tank cleaning system is being used to clean a tank 111 by removing the
sludge and/or sediment in the tank 111. Thereafter the tank 111 may be inspected for
the purpose of detecting holes or breaks which may require welding or other repair.
A degassing blower/exhauster 75 is connected to tank manway 103 and is for removing
gases and fumes from the interior of the tank 111. Various ingoing power lines and
outgoing suction lines pass through a manway 102. Hydraulic power lines 104, 105 extend
from the hydraulic power unit 14, through the manway 102, and to the in-tank tractor
12. A compressed air line 106 extends from the air compressor 76 to the tractor 12
and a suction line 107 extends from the tractor 12 to the suction tank 13. The water
blaster high pressure water generators 78a-e are manifolded at the manifold 108 and
high pressure water is conveyed through the hose 109 to the tractor 12.
[0039] In Figs. 7 and 8, the preparation of the walls and floor of the tank 111 for painting
or coating is illustrated. Sand in a compressed air stream is fed from a sand distribution
device 110 ("sand pot"), through a hose 112 which passes through the manway 102 and
to the blast device 40 in the tractor 12 within the tank 111. Of course if the tractor
54 is used (Fig. 1), there is no need for a sand pot outside of the tank. As shown
in Fig. 8 the blast device 40 is mounted vertically on the tractor for cleaning the
tank walls.
[0040] Fig. 9 illustrates the use of a hand-held high pressure water gun 113, a foot-operated
hand-held gun 114, and a manually manoeuvrable water blaster 115 for treating any
sludge or sediment missed by the in-tank tractor. These devices are operated manually.
The water blaster 115 may be of the type known as "grate blaster", which is very useful
for the operation depicted in Fig. 9 and which has multiple nozzles for water blasting.
In such a grate blaster the nozzles are disposed within a blast shroud and traverse
from one side to the other within the shroud.
[0041] As shown in Fig. 10, once the interior of a tank has been cleaned and degreased to
a desired finish, the walls and floor of the tank can be painted or coated as needed.
The coating system 116 shown in Fig. 10 includes a pneumatically powered automatic
coating unit 117. Unit 117 is a pneumatically powered unit which includes a small
tractor having two rear mounted downwardly directed nozzles for coating the tank floor,
which nozzles can be re-oriented to coat the tank walls. Other coating units including
manual coating systems can be used, although not as efficiently as an automatic coating
unit.
[0042] A cleaning system as described herein is adapted to accomplish the following operations:
1. Cleaning and Descaling
[0043] --Remove sludge or sediment from the tank bottom.
--Remove all hard and encrusted sediments from the tank walls and floors.
2. Degreasing
[0044] --Removal of hydrocarbons from tank walls and floors to permit complete inspection
of the tank and any necessary repair work.
3. Abrasive Water Blasting
[0045] --Remove rust and scale up to an ISO surface preparation grade between SA2 to
2 1/2.
4. Coating
[0046] --Apply a reasonably uniform 150 micron coating to tank floor and walls.
[0047] A cleaning system according to the preferred embodiments is designed to achieve the
following production rates:
Sediment Removal
[0048]
1. Removal rate: up to approximately 75 m³/hr.
2. Removal to a depth of 3 cm.
3. Actual hours required to remove sludge will depend on quantity of sediment and
amount of water required to emulsify the material.
Cleaning and Degreasing
[0049]
1. Rate for cleaning and degreasing: up to approximately 250 m²/hr; cleaning path
1.2 metres wide; horizontal or vertical.
2. Cleaning and degreasing occur in same operation.
3. Degreasing is adequate to permit inspection and repair.
4. Actual hours required for an 80 m wide tank estimated to be 48 hours.
Sandblasting
[0050]
1. Rate for surface preparation prior to coating: up to approximately 250 m²/hr.
2. Surface preparation including removal of rust and scale up to an ISO Standard 2
to 2 1/2 finish.
3. Actual hours required for an 80 m wide tank estimated to be 48 hours.
4. Cleaning operation automatically removes spent sand requiring only minimal clean
up prior to coating.
Degassing
[0051]
1. Replace volume of air in tank every five to six minutes during sludge removal and
initial cleaning.
2. Replacement rates in excess of eight minutes for inspection, surface preparation
or coating.
Coating
[0052]
1. A reasonably uniform 150 micron thick coating to tank floor and walls.
2. Coating unit remotely operable.
[0053] Further disclosure pertinent to, and illustrative of, the system described herein
is made in Applicants' co-pending Applications, the disclosures of which are incorporated
herein by reference as follows:- Title: PUMP HEAD (Case WEAA,017)
DUMP CONTROL AND VALVE (Case WEAA,018)
LIQUID BLASTING SYSTEM (Case WEAA,020)
GRATE BLASTER (Case WEAA
AUTOMATIC COATING UNIT (Case WEAA
1. An in-tank tractor for use in cleaning the interior of storage tanks, the tractor
comprising
a chassis (85),
a body means (85) mounted on the chassis (85), the body means (85) having a
top and bottom,
wheels (92) mounted to the chassis (85),
motor means (91) for rotating the wheels (92),
boom means (88) rotatably mounted to the top of the body means (85), the boom
means (88) having inlet means (93 to 96) for receiving hose means (104, 106) which
convey power fluid to the tractor (12 or 54) including power fluid for the motor means
(91), one end of the boom means (88) extending beyond the chassis (85) and beyond
the body means (85), and conduit means for conveying power fluid from the boom means
to the motor means.
2. A tractor as claimed in Claim 1, wherein individual motor means (91) are provided
for each wheel (92), and control means (62, 63) are provided for each wheel (92) so
that differential speeds can be imparted to the wheels (92) for turning and manoeuvring
the tractor (12 or 54).
3. A tractor as claimed in either of Claim 1 or Claim 2, wherein a blade (55) is secured
to the tractor (12 or 54) for pushing the material.
4. A tractor as claimed in either of Claim 1 or Claim 2, wherein a fluid blast unit
(40) is secured to the tractor (54) for blasting material from a wall, ceiling or
floor surface of a tank (111) with pressurized fluid.
5. A tractor as claimed in Claim 4, wherein the blast unit (40) has shroud means (41)
for enclosing a surface to be blasted and defining a blasting zone, and suction means
(46) communicating with the blasting zone defined by the shroud means (41) for removing
blasted material from within the blasting zone.
6. A tractor as claimed in any one of Claims 1 to 5, further comprising pneumatically
powered lighting means (39) mounted on the tractor (12 or 54).
7. A tractor as claimed in any one of Claims 1 to 6, wherein each component of the
tractor (12 or 54) weighs less than 100 kilograms and is adapted to be passed through
a circular opening (102, 103) of 750 millimetre diameter, or each component is disassembleable
into sub-components which each weighs less than 100 kilograms and is adapted to be
passed through a circular opening (102, 103) of 750 millimetre diameter.
8. A method for cleaning sludge from a storage tank, the method including the steps
of
emplacing sludge removal means (15) partially within the tank (111), said sludge
removal means (15) having an inlet (23) within the tank (111) and an outlet (26) outside
the tank (111),
passing the components of an in-tank tractor (12 or 54) through an opening (102)
in the tank (111),
assembling the in-tank tractor (12 or 54) within the tank (111), and
using the tractor (54) to push the sludge to the inlet (23) of the sludge removal
means (15).
9. A method according to Claim 8, including also the step of exhausting gases from
the interior of the tank (111).
10. A method according to either Claim 8 or Claim 9, including also the step of isolating
a particular area within the tank (111) for cleaning by employing barrier means (79,
80) about that area.
11. A method according to any one of Claims 8 to 10, further including the step of
fluid blasting an area of the tank from which sludge has been removed to further clean
that area.
12. A method according to any one of Claims 8 to 11, wherein breatheable air is supplied
to the tractor for breathing by a tractor operator.
13. A method according to any one of Claims 8 to 12, wherein the components of the
tractor (12 or 54) each weight 100 kilograms or less, and each component is adapted
to be passed through a circular opening (102) in the tank (111) of 750 millimetre
diameter.