U.S. patent application number 12/592927 was filed with the patent office on 2010-06-10 for treatment for produced and flowback waters from wells.
Invention is credited to Robert L. Sloan.
Application Number | 20100140107 12/592927 |
Document ID | / |
Family ID | 42229877 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100140107 |
Kind Code |
A1 |
Sloan; Robert L. |
June 10, 2010 |
Treatment for produced and flowback waters from wells
Abstract
Produced and flowback fluids, and other fluids emanating from
oil, mining, and mineral extraction operations, are treated to
remove heavy metals by introducing an oxidizing agent and passing
the fluid through an electrocoagulator. A cavitation device is used
to intensify the oxidation reactions. Coalesced bodies made in the
electrocoagulator, including heavy metals such as iron rendered
insoluble by elevation of their oxidation states, are separated
from the fluids so they may be reused.
Inventors: |
Sloan; Robert L.; (Katy,
TX) |
Correspondence
Address: |
William L. Krayer;Attorney at Law
1771 Helen Drive
Pittsburgh
PA
15216
US
|
Family ID: |
42229877 |
Appl. No.: |
12/592927 |
Filed: |
December 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61201105 |
Dec 5, 2008 |
|
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61200968 |
Dec 5, 2008 |
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Current U.S.
Class: |
205/751 ;
204/514 |
Current CPC
Class: |
C02F 2103/10 20130101;
C02F 9/00 20130101; C02F 1/72 20130101; C02F 9/00 20130101; C02F
1/34 20130101; C25B 1/26 20130101; C02F 2101/20 20130101; C02F
1/461 20130101; C02F 1/34 20130101; C02F 1/72 20130101; C02F 1/461
20130101 |
Class at
Publication: |
205/751 ;
204/514 |
International
Class: |
C25B 15/08 20060101
C25B015/08; C25B 3/02 20060101 C25B003/02 |
Claims
1. Method of treating an aqueous fluid emanating from the earth in
an oilfield, mining, or mineral extraction operation to remove
soluble heavy metals contained therein in preparation for reuse
comprising (a) introducing an oxidizing agent to said fluid to
elevate the oxidation state of at least some of said soluble heavy
metals, thereby converting said at least some soluble heavy metals
to insoluble heavy metals, (b) passing said fluid through a
cavitation device to mix and heat said fluid containing said
oxidizing agent, thereby enhancing the rate of conversion of said
soluble heavy metals to insoluble heavy metals, (c) passing said
fluid into an electrocoagulator to coalesce at least some of said
insoluble heavy metals into coagulant bodies, and (d) separating
said coagulant bodies from said fluid.
2. Method of claim 1 wherein step (d) is performed at least partly
by a filter.
3. Method of claim 1 wherein step (d) is accomplished at least
partly by adding a coagulant or flocculating agent, followed by
settling.
4. Method of claim 1 including, between step (c) and step (d),
passing said fluid through a second cavitation device to further
mix and heat said fluid, thereby causing further coalescence of
said insoluble heavy metals.
5. Method of claim 1 wherein said aqueous fluid comprises acid mine
drainage.
6. Method of claim 1 wherein said aqueous fluid comprises produced
and flowback fluid in an oilfield operation, followed by the step
of reusing said fluid in an oilfield operation.
7. Method of claim 1 wherein said aqueous fluid comprises produced
and flowback fluid contain alkali metal chlorides, and including
the steps of (i) generating alkali metal hypochlorite by
electrolysis of said fluid and (ii) utilizing said alkali metal
hypochlorite as the oxidizing agent of step (a).
8. Method of treating an aqueous fluid emanating from the earth in
an oilfield, mining, or mineral extraction operation to remove
soluble heavy metals contained therein and to prepare said fluid
for reuse comprising (a) introducing an oxidizing agent to said
fluid to elevate the oxidation state of at least some of said
soluble heavy metals, thereby converting said at least some soluble
heavy metals to insoluble heavy metals, (b) passing said fluid into
an electrocoagulator to coalesce at least some of said insoluble
heavy metals into coagulant bodies, (c) passing said fluid through
a cavitation device to mix and heat said fluid, thereby enhancing
the rate of conversion of said soluble heavy metals to insoluble
heavy metals, thereby forming additional coagulant bodies, and (d)
separating said coagulant bodies from said fluid.
9. Method of claim 8 wherein step (d) is performed at least partly
by a filter.
10. Method of claim 8 wherein step (d) at least partly comprises
flocculation and settling.
11. Method of claim 8 wherein said aqueous fluid comprises acid
mine drainage.
12 Method of claim 8 wherein said aqueous fluid comprises produced
and flowback fluid in an oilfield operation.
13. Method of claim 12 wherein said produced and flowback fluid
contain alkali metal chlorides, and including the steps of (i)
generating alkali metal hypochlorite by electrolysis of said fluid
and (ii) utilizing said alkali metal hypochlorite as the oxidizing
agent of step (a).
14. Method of treating aqueous oilfield chloride-containing
produced and flowback fluid containing heavy metal components
comprising (a) electrolytically generating hypochlorite in a side
stream or portion of said fluid, (b) injecting said side stream or
portion containing hypochlorite into said fluid, (c) passing said
fluid containing said hypochlorite through an electrocoagulator,
thereby at least partially oxidizing said heavy metal components,
and (d) separating said at least partially oxidized heavy metal
components from said fluid.
15. Method of claim 14 wherein step (d) comprises filtering said
fluid.
16. Method of claim 14 wherein step (d) comprises collecting said
heavy metal components in a settling tank.
17. Method of claim 14 wherein said electrocoagulator is capable of
handling at least 200 gallons per minute of fluid with at least 200
amperes current.
18. Method of claim 14 wherein said electrocoagulator comprises
sacrificial anodes.
19. Method of claim 14 followed by reusing said fluid in an
oilfield operation.
20. Method of claim 14 including, between step (b) and step (d),
passing said fluid through a cavitation device.
Description
RELATED APPLICATIONS
[0001] This application claims the full benefit of Provisional
Applications 61/201,105 and 61/200,968, both filed Dec. 5,
2008.
TECHNICAL FIELD
[0002] An oxidizing agent is introduced to produced and
recirculated ("flowback") aqueous fluids from wells before
processing in an electrocoagulator. Hypochlorite may be generated
on site from a portion of the treatment fluid to be used as the
oxidizing agent for introduction to the main stream before passing
to the electrocoagulator. Efficiency of the process is enhanced by
passing the fluid through a cavitation device, which improves
mixing, accelerates oxidation of metals, kills bacteria, and
promotes precipitation and other reactions, thereby enabling the
electrocoagulator to handle better the large quantities of fluid
presented in the hydrocarbon recovery process. The process may also
be used to reclaim usable water from acid mine drainage.
BACKGROUND OF THE INVENTION
[0003] In the drilling of wells and the recovery of hydrocarbons
from them, aqueous drilling fluids and other aqueous fluids are
circulated to the bottom of the well to recover the drillings, and
to treat the well for various purposes. Returning to the surface,
the fluid commonly brings with it "produced fluid," such as connate
fluid and other materials picked up from the well. Such additional
fluids may or may not originate with the drilling rig. I use the
term "flowback fluid" to mean the original drilling fluid,
completion fluid, workover or other fluid injected into the well by
the operator and returned to the surface. My invention is
applicable to either type of fluid if it is delivered to the
earth's surface separately, but most frequently the produced fluid
becomes mixed with the flowback fluid.
[0004] Heavy metals, typically and especially iron, scale-forming
materials such as calcium, solid particles such as bits of shale or
rock (sediment or silt), lighter solids, and oil can be detrimental
to the reuse of produced and flowback fluids. The calcium is
generally dissolved from the earth formation.
[0005] The fluid will commonly contain a high concentration of
alkali metal halides, mainly sodium chloride, but also potassium
chloride or bromide, and sodium bromide. Frequently these materials
are desirable for reuse; the heavier ones likely were placed in the
fluid to adjust its specific gravity to provide buoyancy for the
drill cuttings.
[0006] Thus the need is for an efficient system for removing the
contaminants in produced and flowback waters in the hydrocarbon
recovery industry. Brine-forming components are not incompatible
with reuse and in fact are usually beneficial; thus the objective
is to remove the heavy metals, the solids, and the scale-forming
materials so that the fluid can be reused rather than having to
prepare additional treatment fluids while disposing of the used
fluid without causing environmental problems.
SUMMARY OF THE INVENTION
[0007] My invention combines the use of an electrocoagulator with a
cavitation device for treating aqueous fluids emanating from the
earth in an oilfield, mining, or mineral extraction operation, such
as produced and flowback fluids, which may arrive at the treatment
site in large quantities and high flow rates. My invention further
includes generating hypochlorite on site from the
chloride-containing produced and flowback fluid, and using the
hypochlorite so generated to oxidize heavy metsls and other
materials in the electrocoagulator, further enhanced by the
cavitation device. After the fluid is treated by my process, it may
be recycled or used in another operation or process involving the
use of water in the earth.
[0008] My invention is particularly adapted to treat the wide
variety of such mixed fluids encountered in hydrocarbon production.
It may also be used to treat acid mine drainage, which has long
been a problem for coal and other types of mines The ability to
process such diverse fluids so the water can be reused has
excellent environmental and economic benefits. When I generate the
oxidizing agent sodium (or other alkali metal or acidic)
hypochlorite from the processed fluid, it must contain a minimum
amount of chloride ion. Therefore I call the subject of my
treatment "chloride-containing produced and flowback fluid."
[0009] The principle of the electrocoagulator is well known--a
plurality of electrodes, usually steel or aluminum, are placed in a
vessel suitable for handling electrolysis, and a direct current is
applied to the solution or dilute slurry within it. Usually the
electrodes are disposed as alternate anodes and cathodes, As the
aqueous fluid flows through, the current causes ionic charges to be
applied to the particles, colloids, heavy metal components, and the
like (I sometimes refer to these materials as "coagulant bodies"),
which facilitates oxidation, precipitation, flocculation, and other
events tending to cause a separation of the contaminants from the
aqueous carrier. As is known in the art of electrolysis, a certain
level of electrolyte concentration is necessary for optimum
operation of an electrolytic cell, and a similar principle is true
of the electrocoagulator. An electrocoagulator is typically
followed by one or more devices for collecting precipitants and the
like; such devices include settling vessels, filters, and further
chemical treatment vessels. I have found, however, that the
electrocoagulator is generally not able to prepare produced and
flowback fluids for reuse by itself. Passing the fluid from the
electrocoagulator to a cavitation device prior to any collection
devices greatly enhances the treatment results. Filtration is also
helpful before treatment in the electrocoagulator, to minimize
fouling. In my flow scheme, the electrocoagulator may be preceded
by filtration, addition of a flocculant or coagulant, or a pH
adjustment.
[0010] An electrocoagulation device described in 1982 U.S. Pat. No.
4,329,211 to Plantes et al is said to have accomplished the
oxidation of iron to form insoluble compounds in waste water,
rendering them more amenable to agglomeration and removal. The
electrocoagulator of the '211 patent is said to be an improvement
on an earlier design. This patent, U.S. Pat. No. 4,329,211 to
Plantes et al is hereby specifically incorporated herein, in its
entirety, by reference.
[0011] U.S. Pat. No. 6,488,835 describes an electrocoagulator and
method of electrocoagulation wherein the electrode plates are
consumed (sacrificial), providing a procedure for replacing them.
This U.S. Pat. No. 6,488,835 to Powell is also specifically
incorporated herein, in its entirety, by reference.
[0012] In Stephenson et al U.S. Pat. No. 6,346,197, a basic
electrocoagulator unit is illustrated relatively simply in FIGS. 2
and 3. Conductive plates are alternatingly connected to oppositely
charged electrodes, providing an equal amount of anode and cathode
conductive plates. In this construction, the plates are large in
area and few in number, permitting lower pressure and voltage
drops. They are preferably aluminum but may be made of various
other metals and alloys. They are arranged to define a serpentine
flow path. This U.S. Pat. No. 6,346,197 to Stephenson et al is also
specifically incorporated herein by reference in its entirety.
[0013] In the U.S. Pat. No. 6,719,894 to Gavrel et al, an
electrocoagulator vessel is described including parallel
electrolytic plates therein; fluid in the vessel is subject to
pressure manipulation to enhance solids removal. This patent U.S.
Pat. No. 6,719,894 to Gavrel et al is also specifically
incorporated herein by reference in its entirety.
[0014] FIG. 3 in particular of Robinson U.S. Pat. No. 6,800,206
also presents the basic principles of an electrocoagulator. The
anodes are sacrificial, providing ions to assist In treating the
fluid passing through, and the number of anodes actually passing
current may be controlled as a function of the conductivity of the
fluid. This U.S. Pat. No. 6,800,206 to Robinson is also hereby
specifically incorporated herein by reference in its entirety.
[0015] A tubular configuration is shown for an electrocoagulator in
FIG. 2 of Bradley U.S. Pat. No. 6,960,301. As mentioned therein
(col. 6, lines 56-60) factors influencing the rate of coagulation
include the residence time of the fluid in the device, the applied
current and voltage, turbulent flow characteristics of the fluid,
temperature, electrode surface area, and concentrations of various
contaminants in the fluid. As with other electrocoagulators, the
Bradley device is said to be effective in removing bacteria as well
as metals from arsenic to zinc, organic solids and anionic species
amenable to coagulation: column 5, lines 9-22. The Bradley U.S.
Pat. No. 6,960,301 is also incorporated herein specifically in its
entirety.
[0016] The above references to various designs and types of
electrocoagulators are not intended to be limiting, but rather to
illustrate that any workable design for an electrocoagulator may be
used in my invention; any of the above may be used as well as any
commercial electrocoagulator on the market having an appropriate
capacity and the abilities described herein.
[0017] Electrocoagulators are particularly well adapted to oxidize
heavy metals such as iron. When an oxidizing agent is introduced
ahead of the electrocoagulator, the oxidizing reaction is
accelerated in the electrocoagulator, but the oxidation reaction
will generally require a residence time for completion which may
not be practical for the electrocoagulator alone. This appears to
be the reason it has not found use in oilfield fluid
reclamation.
[0018] The electrocoagulator in my invention is adapted to handle
the high flow rates containing a variety of contaminants. Generally
it should be able to handle a flow rate of 100 to 400 gallons per
minute. For a typical flow rate of 200 gallons per minute (gpm), a
generator or power source on site should be able to deliver 480 V
and 400 amps. To prevent scale build up and to evenly wear the
plates, the charge should be alternated every few minutes. When the
phase changes, there is a surge, thus the 400 amp is needed. Steady
state treatment of 200 gpm normally requires 200 amperes. I do not
intend to be limited to electrocoagulators having the capabilities
or specifications just mentioned; they can of course be somewhat
smaller and considerably larger, depending on the expected flow
rates and other conditions; the principle of operation remains
substantially the same.
[0019] An oxidizing agent is added to the fluid prior to its
introduction to the electrocoagulator. While there may be air, and
hence oxygen, entering the fluid through pumps, valves and the like
as well as the electrocoagulator itself, the oxygen not
deliberately dissolved in the fluid will not be enough to oxidize
the iron frequently found in the fluids I treat and elevate its
valence state to achieve an insoluble form. Moreover, other metals
will commonly be found in the fluid, and these may consume some of
the oxygen provided by aeration. In addition, an added oxidizing
agent is desirable to kill or coagulate bacteria. It should be kept
in mind that it is an important object of the invention to prepare
produced and flowback fluids for recirculation to a well, to
minimize the usage of new water; treatment of acid mine drainage
also permits practical use of an otherwise contaminated water in a
way that first removes many of its worst ingredients.
[0020] After treatment in the electrocoagulator, the fluid may be
sent to the cavitation device, which functions as a simultaneous
heater and intimate mixer. It is particularly good at promoting the
oxidation reaction of heavy metals present in the fluid. The
oxidation of heavy metals such as iron produces heavy metal oxides
which will settle out under the proper conditions, given the high
volume and flow rates of the fluid, but it is generally impossible
to achieve the residence time in the EC necessary to complete the
oxidation reaction. In the cavitation device, the increased
temperature and the intimate mixing assure completion of the
reaction.
[0021] Almost all used clear completion fluids, and also many
drilling fluids, and thus usually the produced and flowback fluids
I treat, contain iron, which has historically been extremely
difficult to remove in the process of cleaning and preserving the
fluids for reuse. Iron is generally in the form of FeO, which is
soluble in the low pH common in completion fluids. Dissolved iron
in the form of FeO cannot be filtered unless it is oxidized to a
higher oxidative state. Raising the pH should be considered only
while recognizing the counterproductive possibility of
precipitating out some useful zinc or even bromide salts. The fluid
frequently incorporates dissolved oxygen from the air with normal
pumping and handling; this may convert some of the iron to
Fe.sub.2O.sub.3 in the form of a 0.5 micron colloidal suspension,
but the quantity of oxygen dissolved in this manner is seldom
anywhere near enough. Iron is a pervasive component of acid mine
drainage fluids and can be removed by my invention in a manner
similar to that by which I treat produced and flowback fluids.
[0022] As indicated above, a small amount of oxygen or air can
always be expected to be dissolved in the treated fluid, and this
oxygen is available to oxidize heavy metals under the appropriate
conditions. Oxidation is enhanced by the injection of an oxidizing
agent ahead of the electrocoagulator. Generally, up to about 100
ppm O.sub.2 or equivalent will be used, but the amount will depend
on operator's knowledge of iron content and other prevelant
conditions. Ozone and other convenient oxidizing agents, such as
hydrogen peroxide, may also be used. The performance of hydrogen
peroxide may be enhanced by the addition of ferric chloride. And,
the oxidation reaction may be enhanced by the use of a cavitation
device between the oxidizer addition and the electrocoagulator.
[0023] Where the treated fluid has a significant chlorine content,
which is common in produced and flowback fluids where, for example,
a drilling fluid contains high concentrations of alkali metal
chlorides) alkali metal hypochlorites may be made in situ by a
hypochlorite electrolytic cell or other device. The manufacture of
alkali metal hypochlorite, particularly sodium hypochlorite, is
also well known. See, for example, Langeland et al U.S. Pat. No.
4,783,246 showing the use of flat, platelike bipolar electrodes in
an electrolytic cell. See also Bennett et al U.S. Pat. No.
3,849,281. The constructions and methods of these patents are
illustrative of the basic art of using electrolysis to make sodium
or potassium hypochlorite (cesium may be present in some oilfield
brines as well), but I do not intend to be limited to the
temperatures, concentrations of chloride, and pH ranges recited in
them. Nevertheless, both the Langeland et al patent U.S. Pat. No.
4,783,246 and the Bennet et al U.S. Pat. No. 3,849,281 are hereby
specifically incorporated herein by reference in their entireties.
Any commercially available hypochlorite generator having a capacity
suitable for the flow rates and volumes necessitated by the flow
and volume of the produced and flowback fluids treated herein may
be used.
[0024] Preferably the cavitation device is one manufactured and
sold by Hydro Dynamics, Inc., of Rome, Ga., most preferably the
device described in U.S. Pat. Nos. 5,385,298, 5,957,122 6,627,784
and particularly 5,188,090, all of which are incorporated herein by
reference in their entireties.
[0025] Definition: I use the term "cavitation device" to mean and
include any device which will cause bubbles or pockets of partial
vacuum to form within the liquid it processes. The bubbles or
pockets of partial vacuum have also been described as areas within
the liquid which have reached the vapor pressure of the liquid. The
turbulence and/or impact, which may be called a shock wave, caused
by the implosion imparts thermal energy to the liquid. The bubbles
or pockets of partial vacuum are typically created by flowing the
liquid through narrow passages which present side depressions,
cavities, pockets, apertures, or dead-end holes to the flowing
liquid; hence the term "cavitation effect" is frequently applied,
and devices known as "cavitation pumps" or "cavitation
regenerators" are included in my definition. Steam generated in the
cavitation device can be separated from the remaining, now
concentrated, water and/or other liquid which frequently will
include significant quantities of solids small enough to pass
through the reactor. Cavitation devices can be used to heat fluids,
but in my invention I use them as excellent intimate mixing
devices. I therefore rely mainly on the shearing stress and
turbulence imparted to the liquid as it passes through the narrow
passages between the rotor and the concentric housing surface. The
term "cavitation device" includes not only all the devices
described in the above itemized patents U.S. Pat. No. 5,385,298,
5,957,122 6,627,784 and 5,188,090 but also any of the devices
described by Sajewski in U.S. Pat. Nos. 5,183,513, 5,184,576, and
5,239,948, Wyszomirski in U.S. Pat. No. 3,198,191, Selivanov in
U.S. Pat. No. 6,016,798, Thoma in U.S. Pat. Nos. 7,089,886,
6,976,486, 6,959,669, 6,910,448, and 6,823,820, Crosta et al in
U.S. Pat. No. 6,595,759, Giebeler et al in U.S. Pat. Nos. 5,931,153
and 6,164,274, Huffman in U.S. Pat. No. 5,419,306, Archibald et al
in U.S. Pat. No. 6,596,178 and other similar devices which employ a
shearing effect between two close surfaces, at least one of which
is moving, such as a rotor, and at least one of which will normally
have cavities of various designs in its surface as explained above,
but for the intimate mixing purposes of my invention, a cavitation
effect is not essential and therefore the term cavitation device as
used herein should be read to include other devices which will
generate shear between two close surfaces, one of which is
moving.
[0026] An additional benefit for my invention from the presence of
copious amounts of chlorides is that I can generate hypochlorite
directly from the fluid on site and use it to oxidize heavy metals
and other materials in the fluid.
[0027] The cavitation device also facilitates the removal of
calcium and other scale-forming materials by intimately mixing the
fluid with sodium bicarbonate injected between the
electrocoagulator and the cavitation device, thus assuring
completion of the reaction to form calcium carbonate, which can be
removed in later separation steps. The efficiency of any inorganic
or organic coagulant or flucculant, including polymers, will be
enhanced by the intimate mixing afforded by the cavitation
device.
[0028] Zinc, aluminum, nickel, manganese, magnesium, cadmium and
copper may be found in acid mine drainage as well as iron. Some of
these metal forms are toxic, and significant amounts of sulfuric
acid are typical of acid mine drainage compositions. Accordingly
acid mine drainage is a challenging problem for remediation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIGS. 1a and 1b illustrate a cavitation device useful in my
invention.
[0030] FIG. 2 shows the disposition of the electrodes in an
electrocoagulator useful in my invention.
[0031] FIG. 3 is a flow sheet showing the placement of the
hypochlorite generator, the EC, and the cavitation device.
DETAILED DESCRIPTION OF THE INVENTION
[0032] FIGS. 1a and 1b show two slightly different variations, and
views, of a cavitation device.
[0033] FIGS. 1a and 1b are taken from FIGS. 1 and 2 of Griggs U.S.
Pat. No. 5,188,090, which is incorporated herein by reference along
with related US patents U.S. Pat. Nos. 5,385,298, 5,957,122, and
6,627,784.
[0034] A housing 10 in FIGS. 1a and 1b encloses cylindrical rotor
11 leaving only a small clearance 12 around its curved surface and
clearance 13 at the ends. The rotor 11 is mounted on a shaft 14
turned by motor 15. Cavities 17 are drilled or otherwise cut into
the surface of rotor 11. As explained in the Griggs patents, other
irregularities, such as shallow lips around the cavities 17, may be
placed on the surface of the rotor 11. Some of the cavities 17 may
be drilled at an angle other than perpendicular to the surface of
rotor 11--for example, at a 15 degree angle. Liquid (fluid)--in the
case of the present invention, the produced and/or backflow
fluid,--is introduced through port 16 under pressure and enters
clearances 13 and 12. As the fluid passes from port 16 to clearance
13 to clearance 12 and out exit 18 while the rotor 11 is turning,
areas of vacuum are generated within the fluid from its own
turbulence, expansion and compression. As explained at column 2
lines 61 et seq in the U.S. Pat. No. 5,188,090 patent, "(T)he
depth, diameter and orientation of (the cavities) may be adjusted
in dimension to optimize efficiency and effectiveness of (the
cavitation device) for heating various fluids, and to optimize
operation, efficiency, and effectiveness . . . with respect to
particular fluid temperatures, pressures and flow rates, as they
relate to rotational speed of (the rotor 11)." Smaller or larger
clearances may be provided (col. 3, lines 9-14) to adjust shear.
Also the interior surface of the housing 10 may be smooth with no
irregularities or may be serrated, feature holes or bores or other
irregularities as desired to increase efficiency and effectiveness
for particular fluids, flow rates and rotational speeds of the
rotor 11. (col. 3, lines 23-29) Rotational velocity may be on the
order of 5000 rpm (col 4 line 13). The diameter of the exhaust
ports 18 may be varied also depending on the fluid treated. Note
that the position of exit port 18 is somewhat different in FIGS. 1a
and 1b; likewise the position of entrance port 16 differs in the
two versions and may also be varied to achieve different effects in
the flow pattern within the cavitation device.
[0035] Another variation which can lend versatility to the
cavitation device is to design the opposing surfaces of housing 10
and rotor 11 to be somewhat conical, and to provide a means for
adjusting the position of the rotor within the housing so as to
increase or decrease the width of the clearance 12 to adjust shear.
This can allow for different sizes of solids present in the fluid,
to reduce the shearing effect if desired (by increasing the width
of clearance 12), to vary the velocity of the rotor as a function
of the fluid's viscosity, or for any other reason.
[0036] Operation of the cavitation device is as follows. A shearing
stress is created in the solution as it passes into the narrow
clearance 12 between the rotor 11 and the housing 10. The solution
quickly encounters the cavities 17 in the rotor 11, and tends to
fill the cavities, but the centrifugal force of the rotation tends
to throw the liquid back out of the cavity. Small bubbles, some of
them microscopic, are formed. Where no gas is present, the small
bubbles are imploded.
[0037] FIG. 2 shows the disposition of the electrodes in an
electrocoagulator useful in my invention.
[0038] FIG. 2 depicts the disposition of the electrodes in an
electrocoagulator of a type suitable for my invention. The vessel
or housing is not shown; nor is the fluid to be treated. The vessel
or housing should have a suitable entrance and a suitable exit for
the fluid, and should be able to accommodate the rather high flow
rates contemplated by the process. Parallel electrodes 30 and 31
are desirably, but need not be, completely submerged in the fluid,
and are given alternate positive and negative functions under
direct current Here it is seen that the electrodes 30 are
positively charged and electrodes 31 are negatively charged. When
made of steel, iron and other metals, the anodes will tend to erode
as sacrificial anodes. In order to balance this effect, the current
is reversed periodically, typically every few minutes; reversing
the current will also minimize scale formation on the
electrodes.
[0039] Desirably the gaps between the electrodes will be adjustable
so the operator can obtain optimum benefit for different
compositions of fluid. As indicated above, the power requirements
(current) will surge each time the phase is changed, and
accordingly assumptions about steady state may not suffice when
designing the electrocoagulator. The operator will wish to avoid
conditions likely to generate chlorine gas.
[0040] FIG. 3 is a flow sheet showing the placement of the
hypochlorite generator, the electrocoagulator and the cavitation
device. Produced water and/or flowback water (or other fluid as
described herein, including acid mine drainage) is moved through
conduit 41 from tank 40 or other source such as a pipe into the
electrocoagulator 42 ("EC unit"). A portion of the fluid is
directed in line 48 to hypochlorite generator 47, which is an
electrolytic cell adapted to generate hypochlorite from the
chloride-containing fluid. The hypochlorite generated in the
hypochlorite generator 47 is injected through line 50 into conduit
41 upstream of the electrocoagulator 42. In the EC unit 42, the
fluid is subjected to a direct current as described with respect to
FIG. 2, bringing about oxidation and other reactions in the
components of the fluid. The fluid is then passed through conduit
43 to the cavitation device 44 where it is subjected to shear,
moderate temperature elevation, and intimate mixing, facilitating
efficient contact of the reactants on the molecular level. I call
this intensifying the reactions. Various copolymers and/or anionic
or cationic polymers can be injected into the fluid in conduit 43
from feeders 51, and this is an excellent point at which to inject
a bicarbonate compound to react with calcium and other
scale-forming polyvalent metals, as indicated by bicarbonate source
45. The cavitation device will enhance the precipitation of calcium
carbonate as well as enhance the oxidation of FeO to a higher
oxidative state such as Fe.sub.2O.sub.3, which is more readily
coagulated and more readily filterable.
[0041] The fluid proceeds in line 46 as indicated in FIG. 3, to a
solids/liquid separation section, where polymeric flocculants
and/or inorganic coagulants may enhance the separation of solids
and other materials by filtration, settling or other means.
Possible separation devices indicated by reference numbers 52 and
53 include lamella gravity settlers, tube settlers, and various
filters. Scale inhibitors and biocides may be added to the cleaned
fluid from source 54 prior to use in a well or for other
purposes.
[0042] Hypochlorite generator 47 is basically an electrolytic cell
having one or more anodes and one or more cathodes, operated under
conditions to generate hypochlorite from the chloride-containing
fluid. After the process is begun, the hypochlorite generator 47
may be fed additionally or alternatively by a slip stream from the
fluid at a point downstream from the cavitation device, such as
through line 49, in order to minimize fouling in the hypochlorite
generator 47. Any suitable electrodes may be used in the
hypochlorite generator. Where the chloride content of the fluid is
insufficient, simple injection of an oxidizing agent such as
oxygen, air, or hydrogen peroxide may be substituted. It is to be
understood that oxidizing agents such as hydrogen peroxide and
alkali metal hypochlorite may be expected to perform very well as
bactericides, and the operator should keep this in mind
particularly where sulfate-reducing bacteria are present.
[0043] A cavitation device may be interposed between oxidizing
agent introduction and the electrocoagulator; the cavitation device
will intensify the oxidation reaction by increasing the temperature
of the fluid and intimately and violently mixing the contents of
the fluid prior to entering the electrocoagulator. In this case,
the operator may decide not to use a device positioned as
cavitation device 44, but the process would benefit from cavitation
devices at both locations. Use of a single cavitation device at
either location is within my invention.
[0044] Thus it is seen that my invention includes a method of
treating an aqueous fluid emanating from the earth in an oilfield,
mining, or mineral extraction operation to remove soluble heavy
metals contained therein in preparation for reuse comprising (a)
introducing an oxidizing agent to the fluid to elevate the
oxidation state of at least some of the soluble heavy metals,
thereby converting the at least some soluble heavy metals to
insoluble heavy metals, (b) passing the fluid through a cavitation
device to mix and heat the fluid containing the oxidizing agent,
thereby enhancing the rate of conversion of the soluble heavy
metals to insoluble heavy metals, (c) passing the fluid into an
electrocoagulator to coalesce at least some of the insoluble heavy
metals into coagulant bodies, and (d) separating the coagulant
bodies from the fluid.
[0045] My invention also includes a method of treating an aqueous
fluid emanating from the earth in an oilfield, mining, or mineral
extraction operation to remove soluble heavy metals contained
therein and to prepare the fluid for reuse comprising (a)
introducing an oxidizing agent to the fluid to elevate the
oxidation state of at least some of the soluble heavy metals,
thereby converting the at least some soluble heavy metals to
insoluble heavy metals, (b) passing the fluid into an
electrocoagulator to coalesce at least some of the insoluble heavy
metals into coagulant bodies, (c) passing the fluid through a
cavitation device to mix and heat the fluid, thereby enhancing the
rate of conversion of the soluble heavy metals to insoluble heavy
metals, thereby forming additional coagulant bodies, and (d)
separating the coagulant bodies from said
[0046] And, my invention includes a method of treating aqueous
oilfield chloride-containing produced and flowback fluid containing
heavy metal components comprising (a) electrolytically generating
hypochlorite in a side stream or portion of the fluid, (b)
injecting the side stream or portion containing hypochlorite into
the fluid, (c) passing the fluid containing the hypochlorite
through an electrocoagulator, thereby at least partially oxidizing
the heavy metal components, and (d) separating the at least
partially oxidized heavy metal components from said fluid.
* * * * *