Note: Descriptions are shown in the official language in which they were submitted.
1 17~769
This invention relates to the removal of one or more
organic constituents from particulate, inorganic-rich mineral
solids and more particularly to process and apparatus for
removing oil from oil-contaminated cuttings resulting from
5 oil well drilling.
So called "drilling muds" are fluids used to control
formation pressures, lubricate and cool the bit, flush drill
cuttings from the borehole, and form a consolidated wall cake
on the sides of the hole prior to casing. These muds, which
10 are highly viscous, are complex formulations and include such
finely divided materials as ground ilmenite, bentonite,
various clays, barite, lead ore, fibers, hulls, etc. in a
liquid medium which may be aqueous (e.g., water or brine) or
an oil (e.g., diesel oil). The latter, the so-called oil
15 muds, have been found to be particularly advantageous in
solving certain drilling problems, especially those
associated with shale drilling and those encountered in
offshore operations. Thus oil muds have been found to solve
such offshore drilling problems as hole instability, shale
20 sloughing, salt flow and excessive corrosion. The oil muds
are, moreover, particularly suited to high-temperature
conditions and they help reduce the wear of downhole drilling
motors.
There is, however, a serious problem inherent in the
25 use of drilling muds, particularly the oil muds, in offshore
drilling. This is the problem of disposing of the drill
cuttings which, after separation from the mud pumped up from
the well, carry oil on their surfaces and often within their
porous structure. In many instances the oil-contaminated
30 cuttings also carry surfactants and other mud additives.
Since environmental regulations prohibit the dumping
overboard of the oil-contaminated cuttings from an offshore
drilling rig, it is necessary to provide some way to clean
them or to otherwise dispose of them.
As pointed out in the article "Cuttings Can Meet
Offshore Environment Specifications," Oil and Gas Journal,
August 14, 197~, pp. 73-7~, the two general choices to
l ~777~9
--2--
achieve disposal of the cuttings have been the cleaning of
the cuttings on the rig or the relatively costly hauling of
the cuttings to onshore disposal sites. Cleaning has been
done either by washing using a suitable detergent; by burning
5Off the oil using high-intensity lamps to expose the cuttings
to about 2200C or by vacuum distillation. Solvent extraction
has also been suggested. Washing of the cuttings requires the
handling of large volumes of a wash solution; burning off the
oil raises the risk of fire as well as of the failure to
lOequally expose all the cuttings to the lamps; and vacuum
distillation requires large capital outlays. U.S. Patent
4,242,146, presents as an alternative to these generally used
techniques of oil removal the compacting of the
oil-contaminated cuttings and a special surfactant with an
l5oil-absorbent material to bind the oil followed by the
subsequent dumping overboard of the compacted material.
Although the compacted material will apparently sink to a
level depending upon its density, there seems to be present
the long-range possibility that the compacted material will
20disintegrate, rise to the surface and bring oil with it.
Moreover, this technique requires the continual supplying of
the expendable surfactant and absorbent material to the
offshore rig, a requirement which adds to the cost of the
drilling.
It is apparent that there is a real need for an
improved method and apparatus for cleaning drill cuttings so
that they may be disposed of without introducing any
pollution problems. Although this need is at present
particularly urgent in offshore drilling operations where it
30is highly desirable to be able to dump the cuttings overboard
off the rig, it may in time become equally important in
onshore drilling operations if and when regulations make it
no longer possible to provide disposal sites for the
oil-contaminated drillings.
Inasmuch as drilling muds contain such additives as
emulsifiers and surfactants it may be desirable or necessary
to periodically remove an excessive buildup of such materials
1 17~76;9
in recycled muds. It may also be desirable or necessary to
process oil-based muds which have become degraded to recover
the oil and dispose o the solid materials.
Particulate, inorganic-rich mineral solids other
than drill cuttings may require that they be separated from
oil. For example, oil may be physically mixed with mineral
solids, e.g., sand, either through a geological process or
through some inadvertent happening such as an oil spill. Such
physical mixtures of oil and particulate, inorganic-rich
mineral solids may be subjected to the method of this
invention to separate the two components.
Although the method and apparatus of this invention
will, for convenience, be described in terms of removing oil
from drill cuttings, it will be understood that they are
equally useful for removing organic constiutents from mineral
solids such as detailed above.
It is therefore a primary object of this invention
to provide a novel method for removing one or more organic
constituents from particulate, inorganic-rich mineral solids
wherein the organic material is not chemically bonded to the
mineral.
It is another primary object of this invention to
provide an improved method for treating drill cuttings to
remove oil and other additives from them. It is another
object of this invention to provide a method of the character
described which makes it possible to dispose of the treated
cuttings by dumping them overboard from an offshore rig
without polluting the water. A further object is to provide
such a method which is based on the use of a recycling
extractant and requires the supplying of only makeup
extractant. It is still another object to provide a method of
the character described which provides flexibility with
regard to such factors as the types of mud being used, the
character of the cuttings being brought up, and the degree to
which mud components can be recovered andJor recycled.
It is a further primary object of this invention to
provide improved apparatus and a system embodying it,
1 177769
suitable for onshore or offshore installation, for treating
drill cuttîngs or other particulate inorganic-rich mineral
solids to remove oil or other organic contaminants therefrom.
It is another object to provide apparatus of the character
described wnich achieves the removal of oil from cuttings to
a degree which permits the disposal of the cuttings without
creating pollution problems. Still another object is to
provide such apparatus which makes possible the recycling of
extractant, recovery of mud components and the efficient use
of th~ energy supplied to the system.
Other objects of the invention will in part be
obvious and will in part be apparent hereinafter.
The invention accordingly comprises the several
steps and the relation of one or more of such steps with
respect to each of the others, and the apparatus embodying
features of construction~ combinations of elements and
arrangement of parts which are adapted to effect such steps,
all as exemplified in the following detailed disclosure, and
the scope of the invention will be indicated in the claims.
According to one aspect of this invention there is
provided a method of removing contaminants including oil from
particulate, inorganic-rich mineral solids comprising the
steps of cont:acting such mineral solids with an extractant
comprising a gas maintained under conditions of pressure and
temperature to provide the extractant in a fluidic state and
render it a solvent for the organic contaminant; and
separating the extractant with the contaminant contained
therein from the mineral solids.
According to another aspect of this invention there
is provided a method of removing oil from particulate,
inorganic-rich mineral solids, comprising the steps of
contacting the mineral solids in a pressure vessel with an
extractant which is a gas under a pressure and at a
temperature to convert the gas to a fluidic oil-solvent state
thereby to dissolve the oil in the extractant and form an
effluent containing an extractant-oil solution; separating
the effluent from the resulting essentially oil-free mineral
7 6 9
solids; subjecting the effluent to sufficient
depressurization to render the extractant a nonsolvent for
the oil and form a two-phase depressurization product; and
separating the two-phase depressurization product into oil
and extractant for recycling.
According to yet another aspect of this invention
there is provided a system for removing organic contaminants
including oil from particulate, inorganic-rich, mineral
solids comprising, in combination pressure vessel means
arranged to effect contact between particulate,
inorganic-rich, mineral solids containing an organic
contaminant and an extractant for the contaminant which is a
gas maintained under conditions of pressure and temperature
to convert it to the fluidic solvent state for the
contaminant; means to circulate the extractant in the
fluidic solvent state through the pressure vessel means
thereby to orm an effluent containing the contaminant;
depressurizing means to depressurize the effluent to form two
phases comprising a vapor phase containing the extractant and
a liquid phase containing the contaminant; separating means
to separate the vapor and liquid phases; and means to
withdraw the essentially contaminant-free solids from the
pressure vessel means for disposal.
For a fuller understanding of the nature and objects
of the invention, reference should be had to the following
detailed description taken in connection with the
accompanying drawings in which
Fig. 1 is a diagram setting forth the basic steps of
the method of this invention;
Fig. 2 is a detailed flow diagram illustrating
exemplary apparatus for the system of this invention up to
the point of separating the extractant and the oil to recover
them;
Fig. 3 is a continuation of Fig. 2 illustrating one
embodiment of apparatus forming the means for separating the
extractant and oil and for recycling one or both; and
1 ~77769
E`ig. 4, which ls on ~he same shee~ a~ Fig. 1, is
a diagram of an apparatus used to evaluate various
extractants to remove oil from drill cuttings.
In the following detailed description the removal
of oil from drill cuttings carried in an oil-based mud will
be taken as exemplary of the method and apparatus of this
invention.
As shown diagramma-tically in E~ig. 1, the drilling
mud brought up from the borehole contains the cuttings from
which the oil must be removed. If the mud used is oil-based
then the oil on the cuttings is the oil in the mud or a
mixture of the oil in the mud and oil from -the well; if the
mud used is water-based, then contaminants on the cuttings
may be various organic additives added to the mud and/or any
oil from the well. Although it is generally preferable to
remove as much of the mud from the cuttings as possible
before treating them, it is possible to treat the cuttings
without separating them from the mud in which case the oil
in the mud is also extracted. Separation of the cuttings
from the mud is typically performed by a screening machine or
a "shale shaker" which comprises a screen of a suitable mesh
si~.e to ensure that the mud can fall through and the cuttings
be retained for further treatment. In the case of oil-based
mud, the cuttings resulting from the screening may have up to
about 50~ by cuttings weight of oil adhered to the surface as
well as within the pores if the cuttings are formed of a
porous material. Moreover, the cuttings may also have
adhered to thern such mud additives as surEactants, hydro-
phobic agents, emulsifying agents, chelating agents and the
like. There are at present restrictions on the maximum oil
content of any cuttings dumped overboard from offshore
drilling platforms and all indications are that such
restrictions may be made more stringent.
Once the oil-contaminated drill cuttings are
separated from the mud it may be desirable or necessary to
crush the separated cuttings to provide an optimum si~e range
of these cuttings commensurate with the operating
dm ~c - 6 -
1 1~7769
ch2racteristics of the remainins apparatus making up the
treating system and of the processing fluids employed. Such
an optimum size range is readily determined for any one
overall system; and it will depend upon such factors as the
level of residual oil which can be tolerated, the porosity of
the drill cuttings, and the like. It is preferable that they
be sized no larger than 10 Tyler mesh.
The oil-contaminated cuttings within a predetermined
size range are then conveyed to a pressure extraction column.
This conveying is preferably accomplished by forming the
cuttings into a pumpable slurry, using an oil or an aqueous
liquid to form the slurry, and pumping them into the column.
Diesel oil may be taken as exemplary of a slurry-forming oil;
and seawater or brine as exemplary of an aqueous liquid. It
will be appreciated that other oils and aqueous liquids,
including fresh water, may be used; however, in the following
detailed description it will be assumed for convenience that
either diesel fuel or seawater is used. It is, of course,
desirable to form a pumpable cuttings slurry having as high a
solids content as it is possible to handle with the pump or
pumps being used. Normally, a solids content of about 50% by
slurry weight represents such a maximum.
As previously noted, either a water-based mud or an
oil-based mud may be used in drilling. The use of these two
di~ferent muds along with the fact that the steps of
separating the cuttings from the mud and/or the step of
crushing the cuttings may be omitted give rise to a number of
possibilities both with regard to the steps taken prior to
slurrying and to the slurries formed for further processing.
Thus if the cuttings are brought from the well in a
water-based mud, they may contain oil and/or other organic
contaminants, e.g~, mud additives such as surfactants and the
like. Such water-based mud may be made directly into a
slurry; or, alternatively, the cuttings may be separated from
it, crushed if required, and then formed into an aqueous or
an oil slurry. If, however the cuttings are brought up in an
- ( -
1 177769
--8--
oil-based mud, they will be contaminated principally with
oil. This mud with cuttings may be formed directly into an
oil slurry; or the euttings may be separated from it, crushed
if required, and then formed into a water or preferably an
oil slurry.
The cuttings are conveyed to the extraction vessel
to be contacted by an extractant. If they are conveyed in a
slurry then excess slurrying oil or water is preferably
drained or forced from the slurry immediately prior to the
~^ extracting step.
The extractant used is a material which is in a
gaseous state at normal pressure and temperature and which
can be converted to a solvent fluidic state, e.g., a liquid
or supercritical fluid, by subjecting it to a combination of
pressure and temperature which changes its physical state~ It
is usually preferable to use as extractants gases having a
molecular weight no greater than about 20~. Among such
extractants suitable for this invention are carbon dioxide,
ethane, ethylene, propane, propylene, and other hydrocarbons,
and the gaseous halogenated hydrocarbons such as
dichlorodifluoromethane.
Preferred extractants for the method of this
invention are dichlorodifluoromethane (Tc 120.~C; Pc 40.6
atmospheres); propane (Tc, 95.6C; Pc, 43 atmospheres); and
carbon dioxide (Tc, 31.1C; Pc, 73 atmospheres). Carbon
dioxide, although requiring a higher pressure than propane,
may be a preferred extractant since it is inexpensive,
nonpolluting in itself and a relatively good solvent over
pressure and temperature ranges which do not place undue
requirements on the mechanical strength of the equipment
used. Carbon dioxide may be maintained in thè desired fluidic
state under pressures between about 5~ and 22~ atmospheres
and at temperatures between about 15C and about 150C.
Propane and dichlorodifluoromethane may be used over the same
temperature range and over pressure ranges of 8 to 220
atmosphere and 4.8 to 220 atmospheres, respectively.
I 1 ~7769
_9~
The ability of carbon dioxide as a liquid in its
near critical state and as a fluid in its supercritical state
to serve as an ex~racting solvent has been known for a number
of years. [See ~or example Francis, ~ ., J. Phys. Chem. 58,
1099 ~1954) and Ind. Eng. Chem. 47, 230 (1955).~ ~ear
critical and supercritical fluids, including carbon dioxide,
have been suggested as solventsfor a wide range of materials
including various oils (U.S. Patents 1,805,751, 2,130,147,
2,281,8~5); flavor components (U.S. Patent 3,477,856);
caffein in coffee (U.S. Patent 3,842,847); cocoa butter from
a cocoa mass (U.S. Patent 3,923,847); fats from grains and
the like (U.S. Patent 3,939,281); residual hexane from
de-fatted grain (U.S. Patent 3,966,981); and a variety of
materials such as paraffins, glycerol, oils and fats from a
variety of compositions (U.S. Patent 3,9~9l195). A very
detailed review of the general field of extraction with
supercritical gases is to be found in Angewandte Chemie --
International Edition in English, 17: 10, pp. 701-784
(october 1978).
The extracting step is carried out at a temperature
determined by the choice of temperature/pressure conditions
to render the extractant a solvent for the oil adhered to the
cuttings and any oil present in the slurry. Once the oil has
been transferred from the cuttings to the extractant by being
dissolved therein, the cleaned, oil-free cuttings are
separated from the oil-extractant solution and dumped
overboard from an offshore rig or taken from an onshore
drilling operation to a suitable disposal site.
The extractant is recovered by subjecting the
effluent from the extraction step to a change in physical
condition to render it a nonsolvent for the oil. Normally,
this may be accomplished by reducing the pressure on the
effluent, the extent to which the pressure is reduced to
convert the extractant to a nonsolvent state for the oil
being dependent upon the extractant used and upon the
temperature of the solution. The rendering of the extractant
1 177769
--10--
a nonsolvent for the oil results in the formation of a
two-phase system which is then separated into a phase
enriched in oil and a nonsolvent extractant phase. Adjusting
the pressure, and the temperature if required, reconverts the
extractant to a solvent condition for the oil and puts it in
condition for recycling. ~ssentially complete separation of
the oil and extractant in the effluent produces an oil of
such a quality that it may be added to the drilling mud,
reused ~o form a pumpable slurry or used in any other way
desired.
1. Fig. 2 presents a detailed flow diagram of a system
suitable for carrying out the method of this invention. The
mud with the drill cuttings is pumped out of the well at a
temperature which depends upon the location, depth of well,
etc. Although it is possible ~o transfer the mud from the
well to mud storage means before treating the cuttings, it is
preferable to treat the cuttings directly to eliminate the
need for storage volume. Thus, as shown in Fig. 2, the mud is
preferably transported directly from the well to a cuttings
separator 10, e.g., a shale shaker which has a screen ll of a
mesh size suitable to retain essentially all of the cuttings
above a predetermined size, e.g., greater than about 5~um
from which the cuttings have been removed, is then taken
through line 12 to a mud pit (not shown) for reuse.
If the cuttings are to be conveyed to the extraction
vessel as a slurry, the cuttings retained on screen ll are
taken by line 15 to a slurrying tank 16. If the cuttings are
to be reduced in size, such as by crushing, they are sent
through a crusher 17, e.g., a smooth roll crusher, in line
15. As indicated by dotted lines 18 and l9 a portion of the
mud from separator 10 or all of the mud from the well may be
sent to the slurrying tank. It may be desirable to
periodically process all of the mud from the well to reduce
the amount of particulate fines e.g., cuttings which pass
through screen ll. An excessive amount of such fines may
35 increase the viscosity of the mud beyond a level where it is
1 177~69
feasible to pump it into and out of the well.
As previously noted, the slurry-forming liquid may
be an oil, e.g~, one having a boiling range between about
175C and about 350C, or an aqueous liquid. Diesel oil is
5 particularly suited as a slurrying liquid. Liquid to ~orm the
slurry is pumped by pump 20 through valved-controlled line 21
from slurry liquid makeup tank 22 into slurrying tank 16.
Slurrying tank 16 is equipped with suitable stirring means 23
and a heater 24 controlled to bring the temperature of the
10 slurry up to that at which it is desired to operate the
extractor columns 30 and 31 which are preferably thermally
insulated. In the system diagrammed in Fig. 2, two extractor
columns are shown in parallel, an arrangement which permits
essentially continuous operation by using one for carrying
15 out the extracting step while depressurizing, dischargingl
refilling and repressurizing the other. It is, of course, to
be understood that one or more such extractor columns may be
used.
The slurry at the desired temperature is withdrawn
20 from slurrying tank 16 through line 35 and flow control valve
36, and it is then pumped by slurry pump 37 through line 38
to a slurry inlet line 39 having a branch line 40, controlled
by valve 41, into extractor column 30 and a branch line 42,
controlled by value 43, into extractor column 31.
Although Fig. 2 illustrates the conveying of the
drill cuttings, along with any mud, by forming a slurry and
pumping the slurry, the cuttings and mud rnay be transferred
to the extraction columns by mechanical means such as a screw
conveyor~ thus eliminating the need for slurrying tank 1~,
30 slurry makeup liquid tank 22, pumps 20 and 37 and the
attendant transfer lines.
~ hen a slurry is used to convey the cuttings to the
extractor columns 30 and 31 it is preferable first to drain
off as much of the slurry liquid as possible before
3~ contacting the contaminated chips with the extractant. To
this end, columns 30 and 31 are provided at the bottom end
1 ~77769
~12-
with screens of the desired mesh to retain the cuttings. The
slurry liquid passing through the screen is then drained or
forced from the columns through slurry drawoff lines, i.e.,
line 94, controlled by valve 45, for column 30, and line 46
controlled by valve 47 for column 31. These lines converge
into line 48 which leads back to slurry liquid makeup tank
22, thus making it possible to recycle the slurry-forming
liquid. ~ pump 49 may be provided to pump the liquid in line
48.
10Once the extractor column is filled to a
predetermined level with the drill cuttings to be treated,
the extractant at the desired temperature and pressure is
circulated through the extractor column until the oil on
and/or within the pores of the drill cuttings has been
removed to attained the desired contaminant level. In
circulating the extractant it is brought in through
extractant supply line 50 through a branch line 51,
controlled by valve 52, to column 30; and through branch line
~ 53, controlled by valve 54, to column 31. In cycling through
the columns, the extractant containing oil, i.e., the column
effluent, is withdrawn from column 30 through branch line 55,
controlled by valve 5h and from column 31 through branch line
57, controlled by valve 58, branch lines 55 and 57 feeding
into primary effluent discharge line 59. In order to remove
the extractant and any oil dissolved therein remaining in the
columns after conclusion of an extractant cycle, a water
piston is used to force the residual mixture from the
extractant columns to leave the cleaned cuttings. Thus there
are provided a branch line ~5, controlled by valve 5~, from
column 3~ and a branch line ~7, controlled by valve 58, from
column 31, which lead into secondary discharge line 69.
Primary and secondary discharge lines 59 and h9 converge and
form main effluent line 7~ which leads to the separation and
recovery portion of the systems as detailed in the
embodiments diagrammed in Fig. 3.
1 ~77769
-13-
The water needed to provide the water piston is
supplied from any suitable source, e.g., the sea for an
offshore rig operation, through main water line 75; and it is
pumped by a high-discharge-pressure water pump 76 through
5 line 77 controlled by valve 78, to branch line 73, controlled
by valve 80, into column 30 or through branch line 81,
controlled by valve 82, into column 31.
Once the residual effluent has been forced from the
extractant columns, clean water is pumped in at a rate
10 sufficient to carry out the cleaned, essentially oil-free
cuttings. This water is preferably drawn from main water line
75 by pump 84 through line 85, which is controlled by valve
86, and which is connected to branch line 87, controlled by
valve 88, leading into column 30 and to branch line 89,
15 controlled by valve 90, leading into column 31. The water
carrying the clean cuttings is withdrawn from column 30
through branch line 95, controlled by valve 96, and from
column 31 through branch line 97, controlled by valve 98,
lines 95 and 97 leading into main cuttings discharge line 99.
20 From line 99 the slurry may be discharged overboard through
line 10~, controlled by valve 101~ Alternatively, if any
quantity of mud was processed through the system, it may be
desirable to recover the solids content o~ the mud by running
the clean cuttings/water slurry through line 103, controlled
25 by valve 104, into a holding tank 105 from which the heavier
solids can periodically be discharged from the bottom through
line 106, controlled by valve 107, and the remaining liquid
with suspended clay particles, after stirring with stirrer
108, can be pumped by way of line 109 and pump 110 to a
30 suitable separation means (not shown). As an alternative to
discharging the cuttings directly into the oceanr it may be
desirable to compact them in a compactor to form bricks or
pellets which will sink readily beneath the surface.
The slurry drawoff lines 44, 46, and 48 are also
35 used to discharge the water formlng the water piston used in
forcing out residual oil/extractant effluent after extraction
is complete. Any makeup water for the slurry may be drawn
~ 177769
-14-
from main water line 75 by line 120, pump 121 and valve 122.
When water is not used to orm the slurry, then that which is
discharged through line 43 may be pumped overboard through
line 123, having valve 124; and line 120, pump 121 and valve
5 122 may be omitted. If the slurry is formed with oil, then
all or a portion of the oil recovered from the extractant may
be carried by line 125, from the oil recovery portion of the
system diagrammed in Fig. 3 to oil return line 126 and into
tank 22. Any makeup oil can be added through line 127.
Fig. 3 is a flow diagram of a preferred embodiment
of that section of the system in which the extractant and oil
are separated and recovered. As noted above in connection
with the description of Fig. 2, the effluent containing a
mixture of oil and extractant containing the oil along with
15 whatever mud additives may be dissolved in it, which resulted
from the cycling of the extractant through the extractor
columns, is withdrawn from the extractor columns 30 and 31
and brought to line 70 through line 59. That effluent
containing extractant with oil and additive which is forced
20 out by action of the water piston is withdrawn through line
69 to become part of the total effluent in line 70. This
effluent is then depressurized to render the extractant
essentially nonsolvent for the oil and also preferably for
any other mucl additives which may have been dissolved and
25 extracted. It is desirable first to lower the pressure only
to the extent that there is formed a separable, two-phase
system, i.e., an extractant phase and a phase enriched in
oil. In the apparatus illustrated in Fig. 3, this first
depressurization is accomplished in a suitable pressure
reducing valve 130 between lines 70 and 131; and the
resulting pressure in line 131 is monitored ~y a pressure
gage 132.
The two-phase fluid in line 131 is taken into a
separator shown as an evaporator 133 which has an upper
35 distillation zone 139 and a lower reboiler zone 135.
Extractant vapor from distillation zone 134 is withdrawn in
line 140 and compressed in compressor 141 to the pressure at
~ 177~69
-15-
which the extractant is to be cycled through the extractor
columns. The resulting heated compressed ex~ractant is then
taken by line 142 through a heat exchanger 143 within
reboiler zone 135 to provide the heat required in
5 d~stillation column 133 to boil off the extractant vapor. The
thus recovered extractant is then directed into extractant
supply line 50 in the extractant cycling loop. If any
adjustment in the temperature of the extractant is required
prior to its introduction into one of the extractor columns
30 or 31, this may be accomplished in a suitable indirect
heat exchanger 145 located in supply line 50. This may be
done by circu~ating a suitable heat transfer fluid through
coils 14~.
It may be desirable to achieve some refluxing of the
extractant vapor leaving evaporator 133 through line 140. To
this end there may be provided a reflux return line 147
incorporating a condenser 148 having cold water or any other
suitable cooling liquid circulating therethrough. Only a
portion of the extractant vapor is sent through this reflux
20 line, and condenser 149 is equipped with a pressure actuated
vent 149 which permits the escape of the noncondensables from
the system.
~ ithin the evaporator 133 the oil-containing bottoms
are circulated in reboiler zone 135 and they are discharged
therefrom through bottoms discharge line 150 which leads to a
pressure reducing valve 151 connecting line 150 with a line
152 which feeds into an intermediate-pressure flash tank 153
and in which the pressure is monitored by a pressure gage
154. Extractant vapor is discharged from flash tank 153
through line 155 and the liquid further enriched in oil is
withdrawn through line 156, there being between line 155 and
flash tank 153 a liquid level control system generally
indicated by the reference numeral 157 and incorporating a
pressure valve 158 in line 156.
The intermediate-pressure fluid from rlash tank 153
is then taken by line 156 through another pressure reducing
valve 159 and line 150, having pressure gage 161, to a
1 ~7769
-16-
low-pressure flash tank 162, preferably maintained slightly
above atmospheric pressure. Low-pressure flash tank 1~2 may
be equipped with a bottom heater 1~3 to ensure the boiling
off of any residual extractant vapor through line 170. The
finally recovered, essentially extractant-free oil is forced
out through line 171, having a pressure-actuable valve 1720
That portion of the recovered oil destined to be recycled is
directed through oil recycle line 125 to slurry liquid tank
22 (Fig. 2). Remaining recovered oil is carried through line
173 for any desired use such as makeup to the active mud
system.
The extractant vapor in line 170 is compressed in
compressor 174 to essentially that pressure obtaining in
intermediate-pressure flash tank 153 and taken by line 175 to
line 152. Extractant vapor from flash tank 153 is discharged
through line 180 into a line 181 leading from a makeup
extractant reservoir 182 to a compressor 183 from which the
extractant, compressed to essentially that pressure obtaining
in evaporator 133, is carried to line 131 for introduction
into evaporator 133.
The method and apparatus of this invention may be
described further in terms of an example of the operation of
the system of Fig. 2 and 3 and in terms of laboratory runs
using various extractants to remove oil from drill cuttings.
In describing the operation of the system it will be
assumed that diesel oil is used to form the slurry, the drill
cuttings are separated from the mud before cleaning, seawater
is used to wash out the cuttings and carbon dioxide is used
as the extractant. Further, for purposes of illustration, the
solvent state of the carbon dioxide extractant will be
defined as 150 atmospheres and about 50C. Finally, it will
also be assumed that two extractor columns 30 and 31 will be
used and that column 30 is in a condition to receive a charge
of the oil/drillings slurry.
Since the mud as it is brought up from the well may
be hot, e.g., between about 3sC and 50oC, the drill cuttings
will advantageously retain a large part of their heat,
1 1~7~69
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requiring only sufficient heat input into slurry tank 1~ to
bring the slurry temperature within the desired extraction
temperature range. In transferring the slurry to extractor
column 30 through lines ~8 and 40, valves 3~, 41 and 45
5 remain open and valves 52, h6, 96, 88, 11~, 80 and 56 remain
closed until column 30 is charged with the desired amount of
cuttings. Durin~ charging the slurry-forming oil drains out
through line 44. Once column 30 has been charged, valves 41
and 45 are closed and valve 52 is opened to deliver the
lO carbon dioxide into the column and pressurize it to 150
atmospheres and raise the temperature to about 50C. Under
these conditions, the carbon dioxide, in a fluidic state, is
a solvent for the oll and it thérefore extracts it from the
surface and pores of the cuttings in forming a carbon
15 dioxide/oil solution which is part of the effluent withdrawn
from column 30. Opening valves 56 directs the effluent
through lines 55, 59 and 70 into pressure reduction valve 130
in which the pressure is reduced to about 60 atmospheres
converting most of the carbon dioxide to a nonsolvent state
20 for the oil.
At the completion of the removal of the effluent
mixture of carbon dioxide and oil from column 30 through
lines 55 and 59, valve 56 is closed, valve ~6 is opened and
seawater is brought in through line 75 and pumped by
25 high-discharge-pressure water pump 7~ through lines 77 and 79
(valves 78 and 80 being open) into the botton of column 30.
Since evaporator 30 is now maintained at about ~0 atmospheres
the water introduced acts as a piston to force out residual
effluent made up of carbon dioxide and oil through lines ~5
30 and ~9 into line 70 through line ~9.
After the extraction cycle the initially
depressurized effluent in line 131 is introduced into
evaporator 134 from which carbon dioxide vapor is withdrawn
through line 14g. A m;nor amount of this vapor may be
35 condensed in condenser 148 and returned to distillation zone
134 as reflux liquid while most of it is compressed in
compressor 141 back up to lSO atmospheres. The heat of
1 1~7769
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compression is therefore available to effect the indirect
heating of the liquid in reboiler zone 135 to boil off the
carbon dioxide. The oil-containing bottoms from reboiler 135
are depressurized in valve 151 to about 2~ atmosphere to
flash off additional extractant vapor which is compressed in
compressor 183 to about 60 atmospheres prior to being
returned to evaporator 133. The 2~-atmosphere oil-rich
bottoms drawn off through line 156 from flash tank 153 are
then let down to about 1.3 atmospheres in valve 159 and taken
to flash tank 162 from which the extractant vapor is
withdrawn through line 170, recompressed in compressor 174
and returned to flash tank 153 through line 1750 The liquid
from flash tank 162, which is essentially extractant-free
diesel oil, is then withdrawn through line 171, a
predetermined amount being returned through line 125 as
slurry oil to slurry liquid tank 22 and the remainder being
sent to other destinations.
The extractant from heat exchanger 143 is in
condition to be recycled through line 50. It may, however, be
2~ necessary to effect some change in its temperature which can
be done in heat exchanger 145. Makeup extractant from
reservoir 182 is compressed to 60 atmospheres and cycled
through evaporator 133.
Subsequent to the discharge of the residual effluent
from the top of column 30 through the use of the water
piston, valve 66 is closed, and valve 116 is opened to
discharge the water through lines 115 and 119 into the ocean.
Seawater is then pumped through column 30 by pump 84 from
main water line 75 through lines 85, valve 86, line 87 and
valve 88 to carry the clean cutting out of column 33 through
lines 95 and 99 either for direct discharge by way of line
10~ or into hold tank 1~5. With the draining of residual
water from column 3g through lines 44 and 48, it is in
condition to begin the cycle again.
It will be appreciated that the same cycle is
carried out using extractor column 31, phasing the cycle so
that while extraction is being carried out in column 33, the
1 177769
--19--
steps of depressurizing, discharging, refill-ng and
repressurizing are being carried out in column 31.
A number of extraction runs were made to remove oil
from muds, from cuttings separated from muds and from sand
mixed with fuel oil to simulate a material which could result
from an oil spill or to simulate sands or other
inorganic-rich mineral solids laden with oil. Generally, the
muds as they came up from offshore wells were about 50~ by
weight cuttings. In some cases the cuttings after separation
from mud were hand crushed. These extraction runs were made
in the apparatus diagrammed in Fig. 4. Carbon dioxide was
supplied at about 57 atmospheres from a cylinder 185, propane
at about 8.5 atmospheres from a cylinder 186 and
dichlorodifluoromethane (Freon 1 ~) at about ~ atmospheres
from a cyliner 187. Valve controlled lines 188, 189 and 190
led from cylinders 185, 186 and 1~7, respectively, to a
compressor 191 which in turn was connected to a high-pressure
extractor 192 through line 193. A heat exchanger 194 was
interposed in line 193 and provided with coils l9S to
circulate a heat transfer fluid to adjust the temperature of
the high-pressure extractant to the desired level before
entering extractor 192. Extractor 192 was a length of
high-pressure stainless steel piping with fluid-tight
couplings 196 and 197 to seal it. The mud, cuttings or sand
from which the oil was to be extracted was placed ~n
extractor 192. The effluent from extractor 192 was discharged
into oil collector 198 through a high-pressure fluid
discharge line 199 in which there was a pressure reduction
valve 20~ designed to reduce the pressure to one atmosphere.
The extractant was then discharged through a volume meter 201
and a vent 202 and the character of the cuttings was noted
and the amount of oil removed was measured.
The results on nine such runs are tabulated in Table
1. In Examples 2, 3, 4, 5 and 7 the cuttings were separated
~5 from an oil-based mud and ground to pass a 2~-mesh Tyler
sieve. In the use of propane and Freon 1 ~, the extractants
were in a relatively incompressible state at the temperatures
I 177769
--20--
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~ ~77769
-21-
used and their pressures varied with the on/off cycling of
the compressor over the ranges given. In Examples 2 and 5,
for which ppm of hydrocarbons remaining on the cuttings are
given, the measurements were made in the ~ollowing manner.
5 The cuttings which were removed from high-pressure extractor
192 after extraction was then extracted with methylene
chloride, the methylene chloride extractant was dissolved in
carbon tetrachloride and the infrared absorbence of the
resulting mixture was compared with the infrared absorbence
10 of standards made up with measured concentrations of the
collected oil in carbon tetrachloride.
It will be seen from the data of Table 1 that the
three extractants used were capable of extracting oil from
the drill cuttings. Carbon dioxide, which poses no real
15 pollution or environmental problems, was particularly
effective in this role.
The method and apparatus of this invention make
possible the removal of oil from drill cuttings to a level
which permits the cuttings to be disposed of without creating
20 undesirable pollution problems. In offshore drilling, where
the use of oil-based drilling muds is highly desirable, this
means that the apparatus can be located on a drilling rig and
the cleaned drill cuttings can be dumped overboard. The
method and apparatus of this invention are also applicable to
25 the removal of oil and other organic contaminants from
particulate, inorganic rich mineral solids, for example the
removing oil from sands whether it was mixed with the sands
accidentally or by geological design. The method offers a
choice of extractant, operating conditions and manner of
30 handling the solids to be treated and the products of the
extraction.
It will thus be seen that the objects set forth
above, among those made apparent from the preceding
description, are efficiently attained and, since certain
35 changes may be made in carrying out the above method and in
the constructions set forth without departing from the scope
of the invention, it is intended that all matter contained in
1 177769
-22-
the above description or shown in the accompanying drawings
shall be interpreted as ill~strative and not in a limiting
sense.
