Note: Descriptions are shown in the official language in which they were submitted.
3'7~11
RECOVERY OF HEA~Y HYDROCARBONS FROM OIL SLUDGE
. .
This invention relates to the recovery of heavy
hydrocarbons rom the sludge which forms when oil, either
crude or partly re~ined, is left standiny in a container.
Crude or partly refined oil is usually stored in
storage tanks and it is well known that the higher or
lighter oil fractions form layers above the heavier
fractions. In the course of time these heavier
fractions become more and more viscous and form a sludge.
Similarly sludges are ormed in other containers, such
as oil-filled pipelines where the oil is left standing
for a long time. These sludges play no useful part in
the oil-refining and processing plant and in fact reduce
the available storage capacit~ and processing rate.
Where the sludge is formed in an oil tank its presence
may affect the repeated measurements which are taken of
the stored volume of crude or partly processed oil
resulting in financial penalties being paid by the
proprietor. Furthermore if the tank is of the 10ating
roof type the sludge may form an uneven upper surface
resulting in harmful stresses on the floating roof
structure when the latter is resting on its legs.
Hitherto known methods of sludge removal include:
1) Removal of the readily pumpable li~uid oil fractions
followed by manual excavation of the sludge mass using
hand tools.
2) Circulation of hot higher-fraction oils and solvents
to dissolve at least the lighter sludge fractions.
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These known methods have not provecl satisfackory.
The first method is extremely time-consuming, the
operatives are required to work in an unhealthy and
dangerous environment and large volumes of waste are
excavated requiring careful and costly disposal. The
second method is also time-consuming, highly energy
intensive, ineffective as regards removal of the
heaviest of the sludge fractions, and can only be
practised with safety in installations specifically
designed for such extreme thermal stressing.
We have noted that the problem of dispersing oil in
water has recaived increased attention in recent years
due to the requirement to disperse oil spillages in sea
water, one effective method of achieving such dispersal
being by the use of dispersant chemicals such as are
described in U.K. Patent Specification No. 1459104~
We have attempted sludge removal from an oil tan~ by
circulating such dispersant chemicals over the sludge
bod~ but we have not ~ound it to be satisfactory. We
believe this to be because the dispersant is not brought
into intimate contact with the heaviest of the fractions
in the sludge body.
We have however surprisingly discovered that by
penetrating tubular lances into the sludge body and then
pumping such dispersant chemicals borne by a water jet
through the lances into the sludge body and by continu-
ously drawing off and recirculating the emulsified oil
37~31
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fractions under pressure, the sludge body can be broken
down both physically and chemically so as to form a
pumpable mass which can be drained from the container in
which the sludge body was formed.
Accordingly the present invention provides a method
of fluidising the non-pumpable hydrocarbonaceous sludge
body deposited by an oil haviny a substantial heavy
hydrocarbonaceous content when such oil is left standing
in a bulk-storage container, said method comprising the
steps of penetrating one or more substantially rigid
tubular lances into the sludge body, physically and
chemically breaking down the sludge body by pumping into
the sludge body by way of the tubular lances dispersant
chemical borne by a water jet so as to form emulsified
hydrocarbonaceous fractions on the surface of the sludge
~ody, the dispersant chemical being emulsifiable in
water, continuously drawing off the emulsified hydro-
carbonaceous fractions from the surface of the sludge
body and recirculating these fractions under pressure by
way of the tubular lances into the sludge body.
Pre~erably the dispersant chemical contains alkyd
resin and conveniently is prepared in the manner describ-
ed in any one of the examples recited in U.K. Patent
Specification No. 1459104.
Conveniently the drawn off emulsified hydro-
carbonaceous fractions are subjected to a mechanical
process (for example by being pumped through a wire mesh)
11~3~79~
to reduce the size of the solids con-tent prior to being
recirculated under pressure throucJh the -tubular lance~
The recirculated material may also be subjected to a
controlled amount of heating. Because the heated
material is recirculated into the sludye body the heat
is dissipated therein relatively quickly and the
installation is not subjected to extreme thermal
stressing.
Conveniently prior to the dispersant chemical being
pumped into the sludge body the higher fractions of the
sludge body are removed by washing with crude or gas
oil.
The present invention also provides a method of
recovery of heavy hydrocarbons from the sludge which
forms when oil is left standing in a container, comprising
emulsifying the sludge body by the use of water and
dispersant chemicals which are emulsifiable in water
as described above, mixing the emulsified fluid with a
larger volume of oil so as to allow dispersion of the
hydrocarbonaceous content of the emulsified fluid as a
suspension in the oil volume, allowi~g the water to
settle out of the mixture, and thereafter drawing off
the settled water layer.
Preferably the volume of oil with which the
emulsified fluid is mixed is contained in a container
into which the emulsified fluid is pumped to achieve
said mixing. Conveniently the oi.l is crude oil or gas
~9~
oil.
Conveniently the dispersant chemical is one oE the
formulations recited in U.K. Patent Specification No.
1459104.
An embodiment of the present invention will now be
described by way of example with reEerence to -the
accompanying drawings, in which:
Fig. L is a plan view of a storage tank with sludge
recovery apparatus connected thereto;
Fig. 2 is an elevational cross-section of the tank
of Fig. 1,
Fig. 3 illustxates a glanded plate used in Fig. l;
Fig. 4 is a sectional view of the plate of Fig. 3
showing the glanded nozzles in greater detail; and
Fig. 5 is a sectional view of an alternatlve form
of noz~le arrangement.
In Figs. 1 and 2 of the drawings an oil storage
tank 10 is formed by a peripheral wall 11 and a floating
roof 12 which has legs 13~ Within the tank 10 adherent
to the floor 14 thereof is a slugde body 15 which is to
be removed~ For this purpose the maximum volume of
pumpable oil within the tank is removed by pumping so
that the roof 12 assumes the position shown in Fig. 2.
By means of access through the roo~ 12, conveniently at
the legs 13, the profile of the sludge surface 16 is
determined and samples of the sludge are withdrawn for
chemical analysis. With the profile of the sludge
~1~3~791
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surface 16 determined several access points 17 in the
wall 11 of the tank 10 are selected at which there are
existing openings with externally removable cover plakes.
These openings may be manh~esor, as in Fiy. 2, a
mounting for a conventional equipment such as an agitator
or mixer. The existing cover plates are removed by
releasing the bolts securing these plates in position and
are replaced by special plates 18 (Fig. 3) containing a
plurality of glanded nozzles 19. Removal of the
existing plates is possible either because they lie above
the surace 16 of the sludge body 15 or if the~ lie
below the surface 16 a temporary cover plate is slipped
between the skirt of the floating roof 12 and the inner
surface of the wall 11 so that there is minimal spillage
from the tank 10 during this procedure. The plates 18
are positioned around the wall 11 of tank 10 in spaced
locations and permit entry of tubular lances ~0 of
relatively narrow bore into the tank 10 within the body
15 o~ sludge as indicated diagrammatically in Fig. 2 so
that the ends of the lances 20 lie in the vicinity o~
the peak of the surface 16. Conveniently the lances 20
are made of a non-corrosive plastics material such as ABS
formed in sections so that the length of each lance can
be increased or decreased as desired. For example each
lance section may be internally screw-threaded at one end
and external.ly screw-threaded at the other end, the
outer diameter of the lance throughout its length being
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substantially constant so that the lance is a fluid-
tight fit in the pertaining glanded nozzle 19.
A relatively large-diameter suction pipe ~1 is
entered through the pertaining glanded nozzle 19 in each
plate 18 and is directed through -the sludge body lS to
draw off pumpable fluids gathering on -the surface 16.
At each plate 18 the lances 20 and the suction pipe 21
are connected to a pump 22, via valved pipework 23, as
is a tank 24 containing dispersal chemical and a water
supply pipe 25.
The glanded nozzle 19 which accommodates the suction
pipe 21 is formed by a stand-off pipe 26 (Fig. 4) welded
at one end to the plate 18 and at the other end to a
flange 27. The suction pipe 21 is of fixed length
terminating at the plate 18 in a metal section which
includes a bend or elbow which incorporates a flange 28
which can be bolted to flange 27 in any one of a number
of orientations in order that the orientation of pipe 21
within the tank can be varied in steps to locate the
end of suction pipe 21 in a desired position. The space
formed between pipe 21 and the stand~off pipe 26 includes
packing (not shown) so that the pipe 21 is retained in
the nozzle 19 in a fluid-tight manner. In order to
provide for continuous positional ad]ustment of the end
o~ suction pipe 21 within the oil tank the flange 28 may
be mounted on the pipe 21 by means of screw threads 29
(Fig. 5) and a locking ring 30. Thus the flange 28 may
1~3791
be permanently secured to nozzle flange 27 and adjust-
ment of thc pipe 21 provided by releasing the engagement
of the locking ring 30 with the flanye 28 and therea~ter
rotating the pipe 21 to the required posi-tion.
The composition of the dtspersal chemical is
determined from the previously taken sample of the sludge
and is suited to the composition and physical character-
istics of the sludge and the down-stream oil-processing
plant in which the emulsified sludge will ultimately be
used.
By way of example the dispersal chemical may be
formulated as follows:
An alkyd resin (A) is prepared from pentaerythritol,
glycerol, polyethylene glycol (molecular weight Mn 600),
trimellitic anhydride and coconut fatty acids in a molar
ratio of 0.6:0.6:1.2:1.2:3.0 respectively so as to give
a polyethylene glycol content of 40% by wt. The resin
had an acid value of 18 to 22 mg KOH/g, and a (POH PA)e
value of l.O.
A second alkyd resin (B) was prepared in the same
manner replacing the coconut oil fatty acids by soyabean
fatty acids and in this instance the polyethylene glycol
content was 50% by wt.
Using resins A and B, the following formulation was
blended:-
l) Resin A 6 parts by wt (as a 75~ solids
solution in white spirit)
79~
2) Resin B 4 parts by wt (as a 95~ solids
solution in whi-te spirit)
3)*Teefroth AN (reaction product of propylene oxide
and methanol, containing an average of
3.7 molecules of propylene oxide per
molecule of methanol) 20 parts by wt.
4) NP6 (6 mole ethylene oxide alkoxide deriv-
ative of nonyl phenol) 10 parts by wt.
5) Heavy aromatic hydrocarbons 60 parts bv wt.
* Registered trademark of Imperial Chemical Industries.
To ef~ect removal of the sludge body 15 from the
tank 10 the dispersal chemical is pumped into the body
15 through lances 20 borne on a water jet resulting in
partial emulsification of the body 15. The emulsified
liquids gather on the surface 16 where they are
collected by suction pipe 21 ancl recirculated along the
lances 20 under the pressure imposed by the pump 22.
This process is repeated continuously utilising a pre-
determined volume of dispersal chemical for the
estimated volume of the sludge body 15 and thereafter
water is added to the recirculating fluids, the re-
circulation being continuous until such time as the
entire body 15 is emul.sified and is in the form of a
pumpable fluid, as determined by intermittent tests
made by dipping through one of the access points in the
roof 12.
By way of example it is estimated that for 2,000
lo l~L~79~
tons (tonnes) of sludge about 50 tons (tonnes) of
dispersal chemical and 7,000 tons (tonnes) of water is
re~uired using a pump with an output pressure of abou-t
50 psi g. (3.5 bar). Conveniently -the suction pipe 21
is about 6 inches (lS cm) diameter and there are Eour
lances 20 each about 4 inches (10 cm) in diameter, the
lance outlets being of reduced diameter, for example 2
inches (5 cm) in diameter. The wall thickness of the
suction pipe and of the lances conveniently is about
0.5 inches (1 cm) and each lance outlet incornorates a
non-return valve mechanism to prevent ingestion of sludge
as the lance is entered into the sludge body 15. The
suction inlet to the pump 22 may incorporate a device for
reducing the size of solids transmitted through the pump
and a heater may be connected to the pipework 23 to raise
the temperature of the recirculated fluids to ahout 30C.
When the sludge body 15 is completely emulsified
the emulsified fluid is pumped by way of an existing
outlet in the tank 10 to be mixed with a larger volume of
oil stored in another storage tank (not shown) as a
result of which the hydrocarbonaceous content of the
emulsion is dispersed in the stored oil and retained in
suspension therein whilst the water content of the
emulsion settles out and can be drawn off and disposed
of as clean effluent. The stored oil containing the
emulsified sludge and chemical in suspension is then
available for use as raw material in the down stream oil
3791
processing plant. During the pumping out of -the
cleaned tank it is desirable to maintain the pumps 22
in operation in order to prevent the sludge settling out
of the emulsified fluid.
It will be understood that various modifications
may be made to the embodiment within the broader concepts
of the invention. For example the invention may be
practised where the stored oil is contained in a lagoon
or underground cavern the boundary being defined by
natural rather than man-made formations. In this case
it is clearly not practical to enter the lances through
the side wall of the container but the invention may be
practised by directing the lances into the sludge body
from any direction - conveniently from above. Further~
more the sludge need not be formed from crude mineral
oil since other oils, such as heavy fuel oil and fish
oil, give rise to sludges which can be treated similarly.
The dispersant chemical may be any one or a mixture of
pol~meric surfactants in an oxygenated alyphatic solvent~
Where the invention is practised on a sludge body
within a closed oil storage tank the entire recovery
process can be carried out without the need for operat-
ing personnel to enter the tank; a gas-free atmosphere
within the tank can be provided on completion of the
process; spillages of hydrocarbonaceous material in
the vicinity of the tank is minimal; and the effluent
water after completion of the process is sufficiently
l~L~379~
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clean for disposal -through -the normal refinery eEEluent
treatment system. The water used in the recovery
process may be either fresh or sal-t water and because
the process is water-based the fire risk arising Erom
the invention is minimal. Economically, the inven-tion
permits recovery of the sludge body in a form which is
usable in the oil-processing plant and the down-time of
the tank being cleaned is only one third or one quarter
that required of the prior art manual method.
We have used the term 'emulsifiable' herein in
relation to the dispersability in water of the dispersant
chemical to indicate that the dispersant chemical is
substantially uniformly dispersable in the water in the
form of a colloidal suspension or a solution.
