Method of oil coagulation utilizing entrained gas

The present invention proposes the utilization of a bed of finely divided, naturally occurring, strongly hydrophilic, strongly oleophobic materials for the coalescent removal of oil from water-oil mixtures containing appreciable amounts of entrained gas, such as crude oil. Preferably, the bed materials have a water wetting-to-oil wetting ratio greater than about three and are of a particle size ranging from about 20 mesh to about 60 mesh. Specifically utilized materials include fruit pit shells and nut shells such as apricot pit shells, peach pit shells, walnut shells and the like. The method consists of flowing a water-oil mixture containing entrained gas through a deep bed of fine particles and coalescing the oil internally of the bed into globules of a size incapable of passing through the interstices of the bed. The oil-free water effluent is recovered from the bed during coalescing of the oil and the oil is periodically recovered and removed from the bed by decanting or backwashing, the oil globules being readily released from the strongly oleophobic particles of the bed for flotation from the bed. Oil removal efficiencies in excess of 90% during a single passage through the bed are readily attained with the aid of the entrained gases, which materially increase the efficiency of oil-water separation, particularly in light oils or crude oil.

BACKGROUND OF THE INVENTION 
The removal of oil from admixture with water has posed a problem in many 
industries for many years. For example, an immediate problem exists in oil 
fields where water has to be separated from oil in order for the oil to be 
usable. This is particularly a vital problem where water or steam is 
injected into the well to aid in the oil extraction process. Also, 
previously known processes could not effectively separate light oils, such 
as kerosene, from admixture with water. 
Attempts have been made to remove water from oil-water emulsions or 
mixtures by the utilization of sand filters. It has been discovered that 
sand filters fail after a short period of operation and the sand media has 
to be replaced, due to the building of "mud balls" or mixtures of dirt, 
oil and water in the sand. These mud balls do not float out or break-up 
during the normal backwash of the filters, and the sand cannot be reused. 
It has now been determined that sand, although normally considered a 
highly hydrophilic and highly oleophobic filter medium, does not reject 
entrapped oil from the sand surface to a sufficient extent to accommodate 
effective backwashing. There exists a need for a filter medium which can 
reject accumulated oil more easily and more completely than does sand. 
In my earlier U.S. Pat. Nos. 3,780,861 and 3,992,291, I have proposed the 
specific utilization of a filter bed composed of granulated shells of 
black walnuts (Juglans Nigra L.) as a filter medium for removing solid 
contaminents or oil from liquids. 
As disclosed in my earlier patents, the filter bed preferably was cleaned 
-by violently and turbulently backwashing over a perforated element with 
at least a portion of the contaminents being withdrawn through the 
perforated element as the filter medium together with the contaminents 
were flowed thereover, all as described in my earlier U.S. Pat. No. 
3,550,774. For use in such cleaning processes, the particles must be on 
the order of 20-30 mesh to avoid clogging or by-passing of the perforate 
element. 
BRIEF DESCRIPTION OF THE INVENTION 
It has been found that water-oil mixtures or emulsions containing 
appreciable amounts of entrained gas can be separated by coalescing the 
oil in a filter bed of appreciable depth and composed of finely divided 
granular materials which are more highly oleophobic than sand. It has been 
found specifically that fruit pit shells and nut shells alone or in a 
mixture are more strongly hydrophilic and oleophobic than sand and, thus, 
make possible the separation of such water-oil gas containing mixtures on 
a continuous, renewable basis. Coaslescing beds comprising such materials 
are readily cleansed of the oil entrapped in the interstices of the bed by 
simple backwashing and/or decanting techniques, because the highly 
oleophobic materials readily reject the oil upon backwashing. It has been 
found that the presence of the entrained gases in the oil-water mixture 
facilitates the separation of the mixture components. 
The present invention thus proposes the removal of oil from water-oil 
mixtures containing appreciable amounts of entrained gases by flowing the 
mixture through a deep bed of highly hydrophilic and highly oleophobic 
materials with the oil being coalesced or agglomerated interiorly of the 
bed into aggregated or agglomerated globules of a size such that they 
cannot pass through the bed, and then removing the oil from the bed by 
decanting, preferably following backwashing.

DETAILED DESCRIPTION OF THE INVENTION 
It has been found that effective separation of water-oil mixtures 
containing appreciable amounts of entrained gases can be obtained by 
flowing the mixture through a deep bed filter in which the bed is of 
appreciable depth, generally in excess of about 12 inches, the bed 
consisting essentially of individual media particles which are highly 
hydrophilic and highly oleophobic. Exemplary media materials having the 
requisite strength and abrasion resistance when finely divided include 
fruit pit shells, such as apricot pit shells, peach pit shells and the 
like, and nut shells such as English walnut shells, black walnut shells, 
pecan shells, almond shells, coconut shells and the like. The materials 
can be used in mixtures with one another, if desired. 
When compared to sand, the materials are far less retentive of oil and far 
more retentive of water. The relative water and oil retention values are 
expressed herein in terms of a "water wetting-to-oil wetting ratio." To 
determine this ratio, the finely divided material is weighed, then surface 
wetted with water, and weighed again. The material is then dried, weighed 
again, surface wetted with oil, and then weighed a fourth time. The water 
wetting-to-oil wetting ratio is determined by the following formula: 
##EQU1## 
From actual tests, the following results were obtained: 
TABLE I 
______________________________________ 
Water Oil 
Grams/Grams Grams/Grams Ratio 
Media Media Media W/O 
______________________________________ 
Sand .162 .073 2.2 
Black Walnut 
.326 .085 3.8 
Shells 
English Walnut 
.357 .090 4.0 
Shells 
Apricot Pit 
.344 .091 3.8 
Shells 
______________________________________ 
It will be seen that uniformly the water wetting-to-oil wetting ratio of 
the nut shells and fruit pit shells is greater than that for sand and, for 
such shells, the ratio exceeds three. This means that the naturally 
occurring materials of the present invention each has a greater preference 
for water and a less preference for oil than does sand. Such shells, in 
the presence of both oil and water, will be wet by the water rather than 
by the oil. 
To demonstrate the effect of air upon the oil removal efficiency of the 
naturally occurring fruit pit shells and nut shells of the present 
invention, oil and water mixtures containing 150 parts per million oil of 
two types were flowed through an 18 inch deep bed of apricot pit shells, 
and the concentration of the oil in the effluent water was measured. The 
flow rate was eight gallons per minute per square foot of exposed upper 
area of the bed, the shells ranged in particle size from 20 to 50 mesh. 
The first runs were made without any preparation of the mixture other than 
uniformly mixing the oil in the water. Additional runs were made with each 
type of oil wherein the oil-water mixtures were violently whipped in a 
blender in the open air to entrain appreciable amount of air into the 
mixture. The test results were as follows from Tables II and III: 
TABLE II 
______________________________________ 
100 S.S.U. OIL 
Without Air With Air 
Oil Oil 
Gallons 
Effluent Removal Effluent Removal 
Filtered 
PPM Oil Efficiency 
PPM Oil Efficiency 
______________________________________ 
50 9.2 93.9% 9.2 93.9% 
100 8.7 94.2% 8.6 94.5% 
250 7.4 95.1% 7.4 95.1% 
500 5.3 96.5% 5.0 96.7% 
750 6.0 96.0% 5.5 96.5% 
1000 6.4 95.7% 5.4 96.6% 
1500 7.8 94.8% 5.1 96.7% 
______________________________________ 
TABLE III 
______________________________________ 
KEROSENE 
Without Air With Air 
Oil Oil 
Gallons 
Effluent Removal Effluent Removal 
Filtered 
PPM Oil Efficiency 
PPM Oil Efficiency 
______________________________________ 
50 45 70.0% 15 90.0% 
100 38 74.5% 12 92.5% 
250 36 75.7% 12 92.5% 
500 37 75.5% 12 92.5% 
750 34 78.0% 11 93.0% 
1000 37 75.5% 13 91.0% 
1500 40 73.5% 14 90.5% 
______________________________________ 
The gaseous component of the oil-water-gas mixture is entrained in the oil 
component or the water component or both. The gas can be introduced 
specifically to aid in coalescence as shown in Tables II or III, or the 
gas may naturally occur in the mixture, as in the case of crude petroleum 
or oil containing water and gases, such as hydrogen sulfide, methane, 
carbon disulfide, or the like, as the mixture is extracted from the earth. 
The gas can either be physically entrapped in the other mixture components 
or dissolved in either or both of the other components. For example, air 
can be entrapped into the mixture simply by spraying the oil-water mixture 
into the ambient atmosphere or, alternatively, the air or other gas can be 
dissolved into the other components by injection under pressure. The term 
entrained gas, as herein utilized, is intended to cover both entrapped and 
dissolved gases, either added or naturally occurring. 
The naturally occurring filter media of the present invention is preferably 
very fine, on the order of 20 to 60 mesh. In use, one or more of these 
finely divided, highly hydrophilic, highly oleophobic, naturally occurring 
nut shell or fruit pit shell materials are formed into a deep bed filter 
interiorly of a pressure vessel of known design. Of course, the depth of 
the bed is dependent upon the filtration pressure and generally is twelve 
inches or more in depth. The water-oil mixture is flowed in a first 
direction through the bed, preferably downwardly. 
Although it is not certain how the bed of the present invention operates, 
the highly hydrophilic media particles are preferentially wetted with 
water in the above defined ratio of at least 3-to-1. It appears that the 
oil is repelled from the water-wetted surfaces and, thus, does not adhere 
to the media. The finely divided media forms a myriad of interstices 
through which the mixture must flow during its passage through the bed. 
Since the bed is of appreciable depth, generally in excess of one foot, 
each globule of oil in the mixture is subjected to innumerable contacts 
with other oil globules during its passage through the bed. Statistically, 
each individual oil globule will be brought into contact with many other 
such globules many times throughout the depth of the bed, and such contact 
causes the coalescence of the oil into larger globules. These larger 
globules merge and coalesce, in turn, with one another on contact to form 
progressively larger globules which increase in size until they can no 
longer pass through the interstices of the bed. 
After appreciable flow of the mixture has occurred, the pressure drop 
across the bed will increase as the bed becomes clogged or internally 
"blinded off" by agglomerated or coalesced large oil globules filling the 
interstices of the bed. When the pressure drop increases beyond a 
predetermined desired value, the oil is removed by floatation from the 
bed. The influx of the mixture is halted, the system becomes quiescent, 
and the oil, which is lighter than the water of the bed particles, floats 
to the top of the bed. The oil can then be removed by decanting from the 
surface, with the level of the oil being elevated by the introduction of 
additional liquid; if desired. To aid in floatation of the oil from the 
bed, the bed may be agitated. 
Alternatively, the bed may be backwashed by introducing a countercurrent 
flow of water, i.e. a flow through the bed in the direction opposite to 
the initial filtration flow of the mixture. Also, the bed preferably is 
agitated during backwash. The cleansing flow of water expands and agitates 
the bed, and the hydraulic shear forces of the water will aid in freeing 
the bed of the coalesced oil globules. Due to the highly oleophobic 
character of the bed materials, the oil will be readily released from the 
bed granules and will flow to the top of the container for later removal 
or may be carried out of the container in the backwash liquid. Since the 
particles have a specific gravity ranging from about 1.3 to 1.5, the bed 
particles readily separate gravitationally from the agglomerated oil 
globules and will not be carried out of the container, so that separation 
of the oil from the bed particles will be readily obtained. If desired, 
the bed may also be agitated mechanically or by the introduction of air or 
other gas under pressure to aid in the expansion of the bed and the 
release of the oil globules. Further, backwashing may be repeated several 
times if necessary to effect complete oil removal. 
After backwashing has been accomplished, the flow of backwash liquid is 
terminated, the bed is allowed to settle to its original position within 
the filtration vessel, the oil on top of the backwash water is withdrawn, 
and the flow of the water-oil mixture into the vessel is reinitiated to 
start the filtration cycle again. 
As shown on the drawings, FIG. 1 illustrates one form of apparatus of the 
present invention capable of carrying out the method of the present 
invention. 
Essentially, the apparatus 10 comprises an open topped tank 11 containing, 
from the bottom, a first layer of uniformly sized gravel 12 within which 
is embedded an effluent drain 13 which is perforate and which communicates 
through a valve V-1 with a clean water conduit 14 discharging into a clean 
water tank 15. 
Superimposed on the layer 12 of gravel is a layer 16 of sand having 
embedded therein a backwash header 17 having a plurality of upwardly 
directed nozzles 18. The backwash header 17 receives backwash liquid, such 
as clean water, from a backwash liquid conduit 19 having a valve V-2 
therein. 
Superimposed on the layer 16 of sand is a bed 20 of filter media composed 
of fruit pit shells or nut shells, as hereinbefore described. This bed 20 
is of appreciable depth, at least 12 inches, preferably 18 inches or more. 
It will be noted that the superimposed or stacked layers 12, 16 and the 
bed 20 are of a combined depth substantially less than the vertical extent 
of the tank 11, for a purpose hereinafter to be more fully described. 
Located over the bed 20 and in spaced relation thereto is an inlet header 
25 having upwardly directed spray nozzles 26 and communicating with an 
inlet conduit 27 which is connected to a source of oil-water mixture to be 
separated by operation of the apparatus 10. A valve V-3 is interposed in 
the line 27 to control the flow of incoming liquid through the conduit. An 
upwardly opening decanting trough 28 is located in the tank 11 adjacent to 
top of the tank, substantially above the upper level of the bed 20 and 
above the inlet header 25. This trough communicates with an oil removal 
line 29 for carrying oil from the trough 28 to an oil receptacle 30. 
Embedded within the bed 20 is a propeller or agitator 31 having its drive 
shaft 32 projecting upwardly from the bed to an actuatable drive motor 33 
mounted, as by bracket 34, on the tank 11 at the upper extremity thereof. 
In the operation of the apparatus of FIG. 1 to carry out the method of the 
present invention, the layers 12, 16 and 20 are constituted and located as 
shown in FIG. 1, the valve V-3 is opened to introduce the oil and water 
mixture to be separated, and the valve V-1 is opened to accommodate the 
flow of effluent water through the drain 13 and the line 14 to the clean 
water receptacle 15. 
The oil and water mixture entering the line 27 is sprayed into the ambient 
atmosphere through the upwardly directed nozzles 26, this spray entraining 
air into the mixture, with the spray gravitationally falling into the pool 
35 overlying the bed 20. This pool 25 thus comprises a mixture of water 
and oil having air entrained therein. 
Although not specifically shown in the drawings, other methods of 
entrainment of air or other gases may be utilized. For example, air, 
nitrogen, or other gas can be injected under pressure into the liquid 
prior to its introduction into the conduit 27, or the top of the tank 11 
could be closed and air or other gas under pressure introduced into the 
tank over the level of the pool 35 to increase the efficiency of gas 
entrainment into the mixture sprayed from the nozzles 26. Other means of 
agitating the oil-water mixture in the presence of air or other gas to 
entrain appreciable amounts of gas into the mixture can be employed. 
As shown in FIG. 1, the oil and water mixture with the gas entrained 
therein flows downwardly through the bed 20 which is composed of a myriad 
of finely divided media particles of fruit pit shells or nut shells as 
hereinbefore described, and the oil coalesceses within the interstices of 
the bed, also as hereinbefore described. As the coalsecence proceeds, the 
bed 20 becomes clogged with coalesced oil globules, and the pressure drop 
across the bed increases. This increase in pressure drop may be measured 
by an increase in the height of the pool 35, by the decreased flow of 
clean water through the line 14, or by any other means. After the pressure 
drop has reached a predetermined maximum, it is necessary to reconstitute 
the bed, and this can be accomplished in several different ways. 
The simplest way of reconstituting the bed is to simply close the valve 
V-3, thereby stopping the introduction of oil and gas mixture through the 
header 25 and the nozzles 26, while also closing the valve V-1 to stop the 
flow of effluent. Next, the motor 33 is started to drive the agitator 31, 
thus mixing the bed 20 with the pool of liquid 35 over the bed. The bed 20 
is thereby expanded and agitated so that the oil globules are readily 
released from the bed. The oil, being lighter than both the bed 
constituents and the water, rises to the top of the expanded bed. Next, 
the agitator motor 33 is shut off, and the bed 20 is allowed to settle 
back to its position upon the lower sand bed 16. Due to the substantial 
differences in density between the particles of the bed 20 and the sand of 
the lower layer 16, there is very little intermixing of the two beds, and 
the bed 20 readily reconstitutes itself. 
At this state, the pool 35 now comprises a layer of oil at the surface from 
the bed 20 overlying the oil and water mixture which formed the original 
pool 35. Now the valve V-2 is opened and backwash fluid, preferably clean 
water, is introduced through the line 19 and the backwash header 17 to 
raise the level of the pool 35 to the level of the skimmer trough 28. The 
oil at the upper surface of the pool 35 simply flows into the trough 28 
and exits through the line 29 into the oil receptacle 30. The introduction 
of liquid through line 19 is continued until the level of the pool 35 has 
been elevated so that all or most of the oil on the surface has overflowed 
the edge of the trough and then collected in the receptacle 30. After this 
has occurred, the valve V-1 is reopened and the level of liquid in the 
receptacle 11 drops to the normal illustrated level of the pool 35 by the 
downward flow of liquid through the bed 20, the sand layer 16 and the 
gravel layer 12. When a desired level of the pool 35 is reestablished, the 
valve V-3 is opened and normal separating action of the apparatus 10 is 
reinitiated. 
If a more vigorous scrubbing action is required or desired during operation 
of the agitator 31 and the initial expansion of the bed 20, the valve V-2 
is opened during the period of agitation, and expansion backwash liquid is 
introduced through the spray nozzles 18. After the period of agitation and 
expansion of the bed 20 is completed, the valve V-2 is closed to allow the 
pool to become quiescent and the oil to flow to the surface thereof as 
before, although the level of the pool 30 will be higher than that 
illustrated in FIG. 1 due to the introduction of the additional backwash 
liquid. After gravitational separation of the oil has occurred, the valve 
V-2 is reopened and the liquid level is raised to decant the oil through 
the trough 28, as earlier described. 
In that embodiment of the invention illustrated in FIG. 2 of the drawings, 
a different form of apparatus is provided which is particularly adapted 
for the separation of crude oil or petroleum from water and/or the gases 
present in the oil as it is pumped from the earth. 
In this version of the invention, the receptacle 40 is in the form of a 
pressure vessel containing a lower bed 41 of coarse stone having embedded 
therein a backwash conduit 42 with a plurality of upwardly directed 
nozzles 43 and communicating through a valve V-4 and a conduit 44 with a 
source of backwash liquid, preferably clean water. Superimposed on the 
layer 41 of stone is a second layer 45 which comprises a finer grade of 
stone or coarse sand. Embedded within the layer 45 is a perforate drain 46 
for clean liquid or water communicating through a valve V-5 to a clean 
water conduit 47. Superimposed upon the layer 45 is a bed 50 of filter 
media as herein disclosed and preferably comprising fruit pit shells or 
nut shells or mixtures thereof. Projecting vertically through the pressure 
vessel 40 axially thereof is an agitator shaft 51 carrying an agitator 
blades 52 located within the confines of the bed 50, the shaft being 
journaled at axial extremities of the vessel 40 in sealed bearings 53. 
Surmounting the shaft 51 and serving to rotate the shaft and the agitator 
blades 52 is a driving motor 54. 
The mixture of water and crude oil or petroleum to be separated is 
introduced into the pressure receptacle 40 through conduit 60 and valve 
V-6, the liquid being introduced completely filling the pressure vessel 40 
for flow downwardly through the bed 50 and the lower level 45 to exit 
through the drain 46, the valve V-5 and the conduit 47 into the receptacle 
48. 
The crude oil or petroleum in the oil-water mixture normally contains gases 
entrained therein, such as methane, hydrogen sulfide, carbon disulfide, or 
the like. In the event that such gases evolve during the separation of the 
oil from the mixture, a check valve V-7 is supplied at the upper extremity 
of the pressure tank 40, this valve being installed in a vent conduit 61 
with a second openable and closeable valve V-8 being installed in series 
with the check valve. This valve V-7 is of the type through which gas, but 
not liquid, can flow. 
It also is necessary, in some instances, that the crude oil or petroleum 
not be exposed to oxygen or the ambient atmosphere which contains oxygen, 
since the oil contains iron and sulfur compounds which tend to precipitate 
out if exposed to oxygen. This condition not only dictates the use of a 
closed vessel 40, but it also requires a facility for providing a 
non-oxidizing atmosphere internally of the pressure tank 40, and such 
atmosphere can be provided by means of a conduit 65 connected to a source 
of non-oxidizing gas, such as nitrogen, and a valve V-9 in the conduit 65 
for controlling the gas flow. 
The vessel 40 is provided with an oil drain line 68 located adjacent to the 
upper regions of the vessel and communicating through a valve V-10 with an 
oil receptacle 69. 
In the operation of the apparatus of FIG. 2 to carry out the method of the 
present invention, the crude oil or petroleum and water mixture is 
introduced through line 60 and the open valve V-6 to completely fill the 
receptacle 40. The valve V-8 also is open at this time, so that any gases 
evolved from the mixture will be vented through the check valve V-7 
without permitting the flow of liquid through the line 61 and without 
allowing the entry of atmospheric air. 
The body of liquid over the bed 50 then flows downwardly through the bed 50 
where the oil is coagulated and retained as hereinbefore disclosed, with 
the water effluent flowing through the drain 46, the open valve V-5 and 
the line 47 into the receptacle 48. During the introduction of the 
oil-water mixture and the flow of the mixture through the bed, at least 
some of the gas dissolved in the oil will be evolved to pass upwardly 
through the bed. This gas will be vented from the tank through the valve 
V-7. 
As above explained, the pressure drop across bed 50 increases as 
coagulation proceeds, and as the collection of oil in the bed 50 
increases. This pressure drop can be measured in any number of ways, for 
example by a pressure probe into the receptacle space above the bed 50, by 
the pressure required to introduce the mixture through the line 60, by the 
amount of liquid flowing through the drain line 47, or the like. 
When the pressure drop exceeds a predetermined maximum desired value, the 
valves V-6 and V-5 are closed, the agitator motor 54 is actuated, and the 
bed is expanded, as heretofore explained. If desired, gas under pressure 
can be introduced through the line 65 by opening the valve V-9 prior to 
closing of valve V-5 to drain liquid from the upper portions of the casing 
40. The gas which is introduced under pressure may be an inert gas, such 
as nitrogen, in the event that exposure of the mixture to oxygen would be 
harmful. Alternatively, the valve V-5 can be left open after closure of 
the valve V-6 to allow the level of liquid above the bed 40 to drop, with 
the vessel merely being vented to the air, in the event that atmospheric 
air is not harmful to the vessel content. 
Preferably, the level inside the vessel 40 is lowered to below the level of 
the drain line 68 prior to expansion of the bed and the release of the oil 
which has been previously coagulated in the bed. This may not be required 
in the event that the amount of oil accumulating in the bed is so great as 
to extend from the top of vessel down to the level of the drain line 68. 
Assuming that the level of the liquid was initially dropped below the level 
of the drain line 68, the oil, being lighter than the water of the 
remaining, non-separated oil-water mixture or the bed particles rises 
gravitationally within the vessel to collect on top of the body of liquid 
remaining in the vessel. 
Next, the valve V-4 is opened and backwash liquid is introduced through the 
line 42 to raise the level of the liquid in the vessel, so that the oil 
flows outwardly through the drain line 68 into the receptacle 69 when the 
valve V-10 is opened. 
Alternatively, as hereinbefore discussed, backwash liquid can be introduced 
into the vessel during agitation and expansion of the bed. Preferably, the 
valve V-8 is closed at any time the valve V-9 is open to prevent the mere 
venting of pressured gas introduced through the line 65. 
Once the oil has been removed through the line 68 and into the receptacle 
69, the valves V-10 and V-4 are closed, and the valve V-5 is opened as is 
valve V-6, to reinstitute separating operation of the apparatus.