U.S. patent application number 15/201787 was filed with the patent office on 2016-10-27 for method and system for treating produced water.
The applicant listed for this patent is De Nora Water Technologies, Inc.. Invention is credited to Christopher Clark, Richard Dennis.
Application Number | 20160311701 15/201787 |
Document ID | / |
Family ID | 50273375 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160311701 |
Kind Code |
A1 |
Dennis; Richard ; et
al. |
October 27, 2016 |
Method and System for Treating Produced Water
Abstract
Embodiments of the present invention provide systems and methods
for purifying produced water. The system comprises: a closed loop
cation exchange unit, wherein the cation exchange unit comprises a
cation resin bed; a closed loop anion exchange unit, wherein the
anion exchange unit comprises an anion resin bed; an intermediate
degasifer, wherein the cation exchange unit and the anion exchange
unit are connected in series through the intermediate degasifier,
wherein each of the exchange units further comprises a plurality of
treatment zones, wherein the treatment zones comprise at least an
adsorption zone, a rinse zone, a regeneration zone and a pulsing
zone and a backwash zone; and a rinse tail outlet collector for
collecting and removing the rinse fluids from the rinse zone.
Inventors: |
Dennis; Richard; (Wesley
Chapel, FL) ; Clark; Christopher; (Madeira Beach,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
De Nora Water Technologies, Inc. |
Colmar |
PA |
US |
|
|
Family ID: |
50273375 |
Appl. No.: |
15/201787 |
Filed: |
July 5, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13621355 |
Sep 17, 2012 |
9403698 |
|
|
15201787 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 47/026 20130101;
C02F 2103/10 20130101; B01J 39/07 20170101; C02F 1/42 20130101;
B01J 39/07 20170101; B01J 41/07 20170101; B01J 49/57 20170101; C02F
2001/425 20130101; C02F 1/441 20130101; C02F 1/20 20130101; B01J
49/53 20170101; B01J 49/08 20170101; C02F 2101/10 20130101; B01J
39/05 20170101; C02F 2101/12 20130101; B01J 49/75 20170101; C02F
2303/16 20130101; B01J 39/046 20130101; B01J 41/046 20130101; C02F
2001/422 20130101; B01J 41/07 20170101 |
International
Class: |
C02F 1/42 20060101
C02F001/42; C02F 1/44 20060101 C02F001/44; C02F 1/20 20060101
C02F001/20 |
Claims
1. A system for purification of produced water, the system
comprising: a closed loop cation exchange unit, wherein the cation
exchange unit comprises a cation resin bed; a closed loop anion
exchange unit, wherein the anion exchange unit comprises an anion
resin bed; an intermediate degasifer, wherein the cation exchange
unit and the anion exchange unit are connected in series through
the intermediate degasifier, each of the exchange units further
comprises a plurality of treatment zones, and wherein the treatment
zones comprise at least an adsorption zone, a rinse zone, a
regeneration zone and a pulsing zone and a backwash zone; and a
rinse tail outlet collector for collecting and removing the rinse
fluids from the rinse zone, wherein the rinse tail outlet collector
is positioned within the rinse zone and above a caustic regenerant
inlet distributor to prevent dilution of the caustic regenerant
while the anion resin bed is rinsed, wherein the rinse tail outlet
collector and the caustic regenerant inlet distributor are located
in a portion of the closed loop anion exchange unit where the resin
moves upwardly, wherein the rinse zone is positioned between the
adsorption zone and the regeneration zone, wherein a volume of the
produced water is flowed through the adsorption zone of the cation
exchange unit to remove cations comprising Na+ from the produced
water and produce an acidic decationized effluent, wherein, in the
regeneration zone of the cation exchange unit, the cation resin bed
is regenerated by contacting it with an acid regenerant, wherein,
in the degasifier, carbon dioxide gas is released from the acidic
decationized effluent to produce an acidic degasified effluent,
wherein deionized treated water having a neutral pH is produced by
flowing a volume of the acidic degasified effluent through the
adsorption zone of the anion exchange unit, wherein, in the
regeneration zone of the anion exchange unit, the anion resin bed
is regenerated by contacting it with a caustic regenerant, wherein
the regenerated anion resin bed is rinsed in a two-stage process,
comprising: i) in a first stage, piping a slip stream flow of the
acidic degasified effluent through the rinse zone of the anion
exchange unit; and ii) in a second stage, passing a stream of the
deionized treated water through the rinse zone of the anion
exchange unit, and wherein after the anion resin bed is
regenerated, acidic degasified effluent and the deionized treated
water which were used in the anion resin rinsing zone are collected
and discharged through the rinse tail outlet collector as a rinse
tail stream.
2. The system according to claim 1, further comprising a feed tank,
wherein the acidic degasified effluent is recycled from the rinse
tail to the feed tank.
3. The system according to claim 1, wherein the cation resin bed is
regenerated by diverting a stream of the acidic degasified effluent
for preventing the evolution of carbon dioxide gas within the
cation resin bed.
4. The system according to claim 1, wherein the acid regenerant is
selected from the group consisting of HCl, H.sub.2SO.sub.4,
HNO.sub.3, H.sub.3PO.sub.4, and H.sub.2CO.sub.3, citric acid,
methane sulfonic acid acetic acid.
5. The system according to claim 1, wherein the cation resin bed
further comprises a strong acid cation resin bed.
6. The system according to claim 1, wherein the anion resin bed
further comprises a weak base anion resin bed.
7. The system according to claim 2, wherein upon the condition that
the produced water is pre-treated using reverse osmosis (RO) and a
RO concentrate is produced, the RO concentrate in the feed tank,
and wherein a sufficiently large volume of the deionized treated
water is recycled internally to the feed tank to dilute the RO
concentrate.
8. The system according to claim 7, wherein the RO concentrate is
diluted for mitigating an excessive evolution of carbon dioxide in
the cation exchange unit.
9. The system according to claim 1, wherein at least one of the
anion exchange unit and the cation exchange unit operates with
continuous counter-current flow.
10. The system according to claim 1, wherein the produced water
comprises elevated levels of total dissolved solids, Na+, carbonate
and Cl.sup.- ions.
11. The system according to claim 1, wherein calcium salt is added
to the deionized treated water to buffer it prior to discharge.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of and claims priority to
U.S. Ser. No. 13/621,355 filed Sep. 17, 2012, the contents of which
are incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to the purification of
produced water, and, more particularly, to the purification of
produced water utilizing continuous ion exchange.
BACKGROUND
[0003] Water trapped in underground geological formations, and
water injected into oil and gas reservoirs to achieve optimal
hydrocarbon recovery, may be produced and brought to the surface
during the hydrocarbon product recovery process. This produced
water may have variable physical and chemical properties. For
instance, depending on the geographic location of the reservoir and
the particular formation, the sodium content of produced water may
be extremely high and its discharge to the environment may be
harmful to both plant and animal life.
[0004] A primary contaminant in produced water is sodium
bicarbonate and/or sodium chloride. The high bicarbonate/carbonate
content and overall total dissolve solids (TDS) content adversely
affects the environment. A number of countries have enacted
regulations prohibiting the untreated discharge of produced water.
There is an unmet need for processes that expand options for
recycling and reusing produced water, and for creating useful
products from produced water.
SUMMARY
[0005] Embodiments of the present invention provide methods and
systems for purification of produced water.
[0006] One or more embodiments of the present invention provide
processes for purification of produced water, involving: providing
a closed loop cation exchange unit and a closed loop anion exchange
unit, the cation exchange unit and the anion exchange unit
connected in series through an intermediate degasifier. In one
aspect, the produced water may comprise elevated levels of total
dissolved solids, Na+, carbonate and C1.sup.-ions.
[0007] At least one of the anion exchange unit and the cation
exchange unit may operate with continuous counter-current flow.
[0008] The cation exchange unit may comprise a cation resin bed,
and the anion exchange unit may comprise an anion resin bed. The
cation resin bed may be a strong acid cation resin bed, and the
anion resin bed may be a weak base anion resin bed. Each of the
exchange units may further comprise a plurality of treatment zones,
the treatment zones comprising at least an adsorption zone, a rinse
zone, a regeneration zone, a pulsing zone and a backwash zone.
[0009] The process may further involve flowing a volume of the
produced water through the adsorption zone of the cation exchange
unit to remove cations comprising Na+ from the produced water and
produce an acidic decationized effluent.
[0010] In the regeneration zone of the cation exchange unit, the
cation exchange unit may regenerated by contacting it with an acid
regenerant. The acid regenerant may be selected from a group
consisting of: HCl, H.sub.2SO.sub.4, HNO.sub.3, H.sub.3PO.sub.4,
H.sub.2CO.sub.3, citric acid, methane sulfonic acid, and acetic
acid.
[0011] The acidic decationized effluent is passed through a
degasifier to strip or release carbon dioxide and thereby produce
an acidic degasified effluent.
[0012] Deionized treated water, having a neutral pH, may be
produced by flowing a volume of the acidic degasified effluent
through the adsorption zone of the anion exchange unit. Calcium
salt may be added to the deionized treated water to buffer it prior
to discharge.
[0013] In the regeneration zone of the anion exchange unit, the
anion resin bed may be regenerated by contacting the anion resin
with a caustic regenerant.
[0014] In one or more embodiments, the process may further involve
rinsing the regenerated anion resin bed in a two-stage process, the
process involving: in a first stage, piping a slip stream flow of
the acidic degasified effluent through the rinse zone of the anion
exchange unit; and, in a second stage, passing a stream of the
deionized treated water through the rinse zone of the anion
exchange unit.
[0015] In one or more embodiments, a residual portion of the acidic
degasified effluent and the deionized treated water may be
collected and removed through a rinse tail outlet collector in the
anion exchange unit. The rinse tail may be positioned within the
rinse zone and above a caustic regenerant inlet distributor. The
acidic degasified effluent may be recycled from the rinse tail to a
feed tank for the cation exchange unit.
[0016] In one or more embodiments, the process may further involve
an inline process for inhibiting biofouling within the regeneration
zone of the anion exchange unit and/or inhibiting biofouling and
treating biofoulants within the regeneration zone of the anion
exchange unit. The inline process may comprise scrubbing the anion
resin bed with a caustic brine solution.
[0017] In one or more embodiments, the process may further involve
regenerating the cation resin bed by diverting a stream of the
acidic degasified effluent, the acidic degasified effluent
controlling the evolution of carbon dioxide within the cation resin
bed.
[0018] In one or more embodiments, upon the condition that the
produced water is pre-treated using reverse osmosis (RO) and a RO
concentrate is produced, the RO concentrate may be stored in the
feed tank and a sufficiently large volume of the deionized treated
water may be recycled internally to a produced water feed tank to
dilute the RO concentrate. Diluting the RO concentrate may mitigate
an excessive evolution of carbon dioxide in the cation exchange
unit.
[0019] One or more embodiments of the present invention provide
systems for purifying produced water, comprising a closed loop
cation exchange unit, a closed loop anion exchange unit, and an
intermediate degasifier.
[0020] In one or more embodiments, the closed loop cation exchange
unit may comprise a cation resin bed, and a plurality of treatment
zones. The plurality of treatment zones may comprise a cation
adsorption zone, a cation rinse zone, a cation regeneration zone, a
cation pulse zone and a cation backwash zone.
[0021] In one or more embodiments, the closed loop anion exchange
unit may comprise an anion resin bed, and a plurality of treatment
zones. The plurality of treatment zones may comprise an anion
adsorption zone, an anion rinse zone, an anion regeneration zone,
an anion pulse zone and an anion backwash zone.
[0022] The closed loop anion exchange unit may further comprise a
rinse system, the rinse system having means for conveying a
plurality of rinse fluids to the anion rinse zone. The fluids may
comprise at least acidic degasified fluid and deionized treated
fluid. The rinse system may further have a rinse tail for
collecting and removing the rinse fluids from the rinse zone. The
rinse tail may be disposed above the anion regeneration zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a flow diagram illustrating systems and
processes in accordance with one or more embodiments of the present
invention.
[0024] FIG. 2 shows a flow diagram illustrating systems and
processes in accordance with one or more embodiments of the present
invention.
[0025] FIG. 3 shows a flow diagram illustrating systems and
processes in accordance with one or more embodiments of the present
invention.
[0026] FIG. 4 shows a flow diagram illustrating systems and
processes in accordance with one or more embodiments of the present
invention.
[0027] FIG. 5 shows a flow chart illustrating processes in
accordance with one or more embodiments of the present
invention.
DETAILED DESCRIPTION
[0028] Available options for produced water disposition include
infiltration and containment impoundment, land application
disposal, and reinjection. However, these options may not be viable
for water balance, environmental or economic reasons.
[0029] Reverse osmosis (RO), considered one of the best available
technologies for treatment of produced water. However, RO may
involve high energy costs which, combined with reinjection of high
volumes of concentrate wastewater rejected from the membranes,
makes it economic value doubtful.
[0030] Conventional adsorption or ion exchange processes may also
be used to treat produced waters. However, the combined chemical
costs and large spent regenerant waste volumes involved may make
these processes uneconomical.
[0031] Despite the deficiencies of conventional adsorption or ion
exchange processes, at least one type of adsorption/ion exchange
process has been determined sufficiently efficient at produced
water purification. Continuous ion exchange (CIX) technology,
specifically the Higgins Loop.TM.. Continuous Ion Exchange
Contactor, has been utilized commercially for several years for
produced water purification. In the context of purifying water
produced in the coal seam gas (CSG) production process (or oil and
gas or hydrocarbon recovery process), for example, this technology
utilizes cation resins to remove sodium from the produced water and
concentrate it into a very small brine stream for disposal. It also
reduces the water's bicarbonate content by evolving carbon dioxide
gas from the low sodium water under slightly acidic pH conditions.
The purified water is then neutralized with limestone, which
increases the purified water's calcium content and makes the water
more suitable for use in irrigation, human consumption, ranching,
and for aquatic life in rivers and creeks.
[0032] The systems and methods of the present invention involve the
treatment of produced water utilizing continuous ion exchange. U.S.
Pat. No. 7,273,555, discloses processes for continuous
countercurrent ion exchange comprising, among other things, piping
a contaminated feed stream into a closed-loop cation exchange
contactor. This and all other referenced patents and applications
are incorporated herein by reference in their entirety.
Furthermore, where a definition or use of a term in a reference
that is incorporated by reference herein is inconsistent or
contrary to the definition of that term provided herein, the
definition of that term provided herein applies and the definition
of that term in the reference does not apply.
[0033] Referring to FIG. 1, in accordance with one or more
embodiments of the present invention, a produced water purification
system 100 may comprise a closed-loop cation exchange unit 104 and
a closed-loop anion exchange unit 108. The cation exchange unit 104
may be connected in series to the anion exchange unit 108 via an
intermediate degasifier 112.
[0034] Produced water 116 to be treated by the produced water
purification system 100 may be stored in a feed tank (not shown).
The produced water 116 may be subject to pretreatment and controls
in the feed tank. For instance, the produced water 116 may be
filtered to remove organic contaminants and dissolved solids. The
produced water 116 may be flowed through the cation exchange unit
104 to remove cations present in the produced water 116. In one or
more embodiments, the cations present in the produced water 116 may
primarily comprise sodium (Na+). The produced water 116 may have
Na+ content of 600 to 2,400 mg/L Na, a Cl+ content of 300 to 2,000
mg/L Cl and carbonate of 1,000 to 2,800 mg/L CO.sub.3.
[0035] The Na+ ions in the produced water 116 may be exchanged for
hydrogen (H+) ions in a packed cation resin bed of the cation
exchange unit 104. The cation exchange unit 104 is described in
more detail below with reference to FIG. 2.
[0036] The decationized water 120, which may be slightly acidic
with a pH under 2.0, may be discharged from the cation exchange
unit 104. In one or more embodiments, the decationized water 120
may comprise anions, primarily bicarbonate and chloride ions. The
decationized water 120 may have an excess of hydrogen ions which
lowers the pH of the decationized water 120. The pH may be lowered
from about 7.5-8.5 to about 1.4 to 2.5. In the lowered pH range,
the bicarbonate ions in the decationized water may react with the
hydrogen ions and produce carbon dioxide gas, as illustrated by the
following equation:
H+HCO.sub.3.sup.-.fwdarw.H.sub.2O+CO.sub.2(Gas)CO.sub.2
PRODUCTION:
[0037] The discharged decationized water 120 may be flowed to an
intermediate degasifier 112. In one or more embodiments, the
degasifier 112 may be a forced draft gas stripper. The degasifier
112 may be used to release carbon dioxide gas from the discharged
decationized water 120, thereby reducing the dissolved solids
content of the decationized water 120. In one or more embodiments,
the released carbon dioxide may be beneficially recovered as a
purified carbonate salt byproduct using a combined gas
stripper/absorber system (not shown) thereby also reducing the
emission of deleterious greenhouse gases. In one embodiment, the
carbon dioxide that has been released may be passed through an
absorption unit (not shown) comprising soda lime to produce calcium
carbonate which may be used as a fertilizer.
[0038] The degasified water 124 may be discharged from the
degasifier 112 and flowed to the anion exchange unit 108 to remove
anions present in the degasified water 124. In one or more
embodiments, the anions present in the degasified water 124 may
primarily comprise chloride (Cl-) ions. The anion exchange unit 108
is described in more detail below with reference to FIG. 3.
[0039] Purified water 128, having a neutral pH and "deionized" of
both cations and anions, may be discharged from the anion exchange
unit 108. In one or more embodiments, the discharged purified water
128 may be subject to one or more further treatment steps (not
shown). The purified water 128 may have less than 50 mg/L Na+ and
50 mg/L Cl.sup.-.
[0040] In one or more embodiments, the produced water purification
system 100 may further comprise one or more recycle streams (e.g.,
recycle streams 132a-c). As described below with reference to FIGS.
2-4, it should be understood that the cation exchange unit 104 and
the anion exchange unit 108 may produce a plurality of effluents.
In other words, the produced water purification system 100 is not
limited to the discharged decationized water 120, degasified water
124, and purified water 128 effluents described above with
reference to FIG. 1. Moreover, any combination of one or more
influents and/or effluents may be used as slip streams (recycle
streams or otherwise) leading to any portion of the water
purification system 100 thus suitable to optimize, among other
desirable efficiency parameters, process, resource, environmental,
and/or economic efficiency.
[0041] Referring now to FIG. 2, in accordance with one or more
embodiments of the present invention, the cation exchange unit 104
may be a closed-loop continuous countercurrent exchange unit (e.g.,
a Higgins Loop.TM. closed-loop contactor), comprising an adsorption
zone 204, a rinse zone 208, a regeneration zone 212, a pulse zone
216, and a backwash zone 218.
[0042] The cation exchange unit 104 may further comprise internal
butterfly valves A-D, and external valves V102-V119.
[0043] The produced water 116 flowed to the cation exchange unit
104 may comprise any solution having ions that need to be removed
from the solution. For example, in one or more embodiments, the
produced water 116 may comprise water produced as a result of
extracting coal seam gas (CSG). The produced water 116 may comprise
a high content of sodium bicarbonate and/or sodium chloride, which,
if discharged to the environment, may harm plant and animal
life.
[0044] The produced water 116 may be flowed down through the
adsorption zone 204 of the cation exchange unit 104, which
comprises at least a portion of the packed bed of cation resin 220
in the cation exchange unit 104. In one or more embodiments, the
produced water 116 may flow down the adsorption zone 204 in a
counterclockwise direction with respect to the cation exchange unit
104.
[0045] Contact between the produced water 116 and the cation resin
220 as the produced water flows down the adsorption zone 204 may
cause an exchange of ions, resulting in the removal of cations,
primarily Na+, from the produced water 116. In one or more
embodiments, the cation resin bed 220 may comprise a strong acid
cation resin bed. The exchange of ions ("cation adsorption") may
occur between the Na+ ions in the produced water 116 for the H+
ions on the cation resin 220. The cation adsorption is illustrated
by the following chemical equation, where "R-" represents the resin
220:
R-H.sup.++Na.sup.+.fwdarw.R-Na.sup.++H.sup.+(Water)CATION
ADSORPTION:
[0046] Referring FIGS. 1-2, the decationized water 120 may be
discharged from the adsorption zone 204 and flowed to the
intermediate degasifier 112.
[0047] Cation adsorption may exhaust the cation resin 220 in the
adsorption zone 204, i.e., in time, at least a portion of the resin
220 may have diminished or no capacity to exchange ions with the
produced water 116 flowing through the adsorption zone 204. When
this happens, in one or more embodiments, a volume of fluid 224 is
pumped into the pulse zone 216 to advance the cation resin 220
below the adsorption zone 204 and replace the exhausted resin
220.
[0048] By pulsing fluid 224 such that it travels in a clockwise
direction (with respect to the cation exchange unit 104) through
the pulse zone 216, the fluid 224 may displace the cation resin 220
disposed downstream of the pulsed fluid 224, thereby replacing the
exhausted resin 220 with resin 220 advanced from below the
adsorption zone 204. As described in more detail below, cation
resin 220 may be regenerated in the regeneration zone 212.
[0049] In one or more embodiments, the fluid 224 may comprise
water. The fluid 224 may be stored in a tank 228. A pump 232 may be
used to pulse the fluid 224 from the tank 228 to, for example: the
pulse zone 216 via stream routes 10-to-25 and 10-to-26; the
produced water 116 entering the adsorption zone 204 via stream
route 10-to-12; and, for diluting acid supplied to the regeneration
zone 212, to a mixer via stream 15. The tank may receive pulsing
fluid from one or more of a variety of sources, such as, for
example, produced water 116 via stream route 12-to-10-to-28,
backwash 218 via stream 27, and spent pulsing fluid 224 via stream
routes 24-to-28 and 21-to-28.
[0050] In one or more embodiments, valves B, C, and D may be open
during the pulse stage, and valve A may be closed. During the
cation adsorption stage, all of valves A-D may be closed to avoid
cross-contamination between the zones.
[0051] Prior to advancement to the adsorption zone 204, exhausted
resin 220 residing in the regeneration zone 212 may be regenerated
for suitable ion exchange use in the adsorption zone 204. Within
the regeneration zone 212, a resin regeneration stream 17 may be
moved through the resin 220 in a counter-clockwise direction with
respect to the cation exchange unit 104 (as is the produced water
116 stream).
[0052] Cation resin bed performance may be detected by measuring
one or more physical properties of the fluids in the various zones
in the cation exchange unit 104. The measurements may be made with
any combination of location, frequency and duration. Any single
physical property, or combination of physical properties, of cation
exchange unit fluids may be measured including pH and
conductivity.
[0053] In one or more embodiments, the resin regeneration stream 17
may comprise an acid regenerant 240. The acid regenerant 240 may
comprise an acid selected from a group consisting of: HCl,
H.sub.2SO.sub.4, HNO.sub.3, H.sub.3PO.sub.4, and H.sub.2CO.sub.3,
citric acid, methane sulfonic acid and acetic acid. The acid
regenerant 240 may be stored in a storage tank (not shown) and may
be recycled back to the cation exchange unit 104. In one
embodiment, the acid regenerant 240 may be pumped out of the
storage tank and into a static mixer (not shown) that meters the
flow of acid regenerant into the cation exchange unit 104.
[0054] The acid regenerant 240 added to the resin 220 may restore
the hydrogen ion content of the resin 220, as illustrated by the
following chemical equation:
R-Na.sup.++H.sup.++Cl.sup.-(Acid).fwdarw.R-H.sup.++Na.sup.++Cl.sup.-(Br--
ine)REGENERATION:
[0055] The resulting brine/spent regenerant 244, may be piped out
of the cation exchange unit 104 via stream 20.
[0056] In one or more embodiments, with reference to FIGS. 1-2, the
degasified water 124, free of bicarbonate, may be recycled via
stream 136 to be used as strong acid hydrochloric acid regenerant
240, thereby minimizing or preventing carbon dioxide gas evolution
within the cation resin bed 220.
[0057] In one or more embodiments, the regenerated cation resin 220
may be rinsed to remove excess acid regenerant 240 therefrom prior
to advancement to the adsorption zone 204. The rinsing may occur in
a rinse zone 208 disposed between the adsorption zone 204 and the
regeneration zone 212. A stream 20 of the produced water 116 may be
diverted from stream 12 and used to rinse the regenerated cation
resin 220.
[0058] Referring to FIG. 3, in accordance with one or more
embodiments of the present invention, the anion exchange unit 108
may be a closed-loop continuous countercurrent exchange unit (e.g.,
a Higgins Loop.TM. closed-loop contactor), comprising an adsorption
zone 304, a rinse zone 308, a regeneration zone 312, a pulse zone
316, and a backwash zone 318.
[0059] As discussed above with reference to FIGS. 1-2, the
discharged decationized water 120 may be flowed to an intermediate
degasifier 112, which may be used to release carbon dioxide gas
(and beneficially recover it as a purified carbonate salt) from the
discharged decationized water 120, thereby reducing the
decationized water's 120 dissolved solids content.
[0060] The degasified water 124 may be discharged from the
degasifier 112 and flowed to the anion exchange unit 108 to remove
anions present in the degasified water 124. In one or more
embodiments, the anions present in the degasified water 124 may
primarily comprise bicarbonate and chloride.
[0061] The degasified water 124, still acidic, may be flowed down
through the adsorption zone 304 of the anion exchange unit 108,
which comprises at least a portion of the packed bed of anion resin
320 in the anion exchange unit 108. In one or more embodiments, the
degasified water 124 may flow down the adsorption zone 304 in a
counterclockwise direction with respect to the anion exchange unit
108.
[0062] Contact between the degasified water 124 and the anion resin
320 as the degasified water flows down the adsorption zone 304 may
cause an exchange of ions, resulting in the removal of anions,
primarily Cl-, from the degasified water 124. In one or more
embodiments, the anion resin bed 320 may comprise a weak base anion
resin bed. The exchange of ions ("anion adsorption") may occur
between the Cl- ions in the degasified water 124 for the H ions on
the anion resin 320. The anion adsorption is illustrated by the
following chemical equation, where "R-" represents the resin
320:
R-OH+HCl.fwdarw.R-Cl.sup.-+H.sub.2O(water)ANION ADSORPTION:
[0063] Purified water 128, having a neutral pH and "deionized" of
both cations and anions, may be discharged from the adsorption zone
304. In one or more embodiments, the discharged purified water 128
may be flowed to one or more further treatment steps (not
shown).
[0064] Anion adsorption may exhaust the anion resin 320 in the
adsorption zone 304. When this happens, in one or more embodiments,
the regeneration zone 312 and the pulse zone 316 are utilized to
advance regenerated anion resin 320 to the adsorption zone 304 in
processes similar to those described above with reference to the
corresponding regeneration zone 212 and pulse zone 216 of the
cation exchange unit 104. However, rather than using an acid
regenerant 240 as in the cation exchange unit 104, the anion
exchange unit 108 contacts the exhausted resin 320 with a
concentrated alkali (caustic) regenerant 340, for example, NaOH, as
illustrated by the following chemical equation:
R-Cl+NaOH(alkali).fwdarw.R-OH+NaCl(Brine)REGENERATION:
[0065] In some embodiments, the caustic regenerant may include
NaOH, soda ash, calcium carbonate, sodium bicarbonate, magnesium
hydroxide, lime (Ca(OH).sub.2) and any derivatives of the
aforementioned. The caustic may be NaOH of concentrated commercial
grade. In some embodiments, the caustic regenerant may be the
product of purification and conversion of either, or both of,
acidic and caustic brine discharged from the cation and anion
exchange units, respectively.
[0066] Anion resin bed performance may be detected by measuring one
or more physical properties of the fluids in the various zones in
the anion exchange unit 108. Any single, or combination of,
physical property or physical properties of anion exchange unit
fluids may be measured including pH and conductivity.
[0067] The resulting brine/spent regenerant 344, an alkaline
solution of sodium chloride which may be heavily concentrated with
Cl ions, may be piped out of the anion exchange unit 108 via stream
40. In one or more embodiments, this stream 40 may comprise a
volume less than about 1.0% of the purified water 120 volume.
[0068] In one or more embodiments, the regenerated anion resin 320
may be rinsed to remove excess caustic regenerant 340 therefrom
prior to advancement to the adsorption zone 304. The rinsing may
occur in a rinse zone 308 disposed between the adsorption zone 304
and the regeneration zone 312.
[0069] In one or more embodiments, rinsing the regenerated anion
resin 320 may comprise a two-stage rinsing system/process.
[0070] In a first stage, a slip stream 34a of the acidic degasified
water 124 may be flowed through the rinse zone 308 to rinse the
regenerated anion resin 320 of its caustic regenerant 340 by
displacing and neutralizing the residual caustic with the
degasified water's 124 free acidity.
[0071] In a second stage, a slip stream 34b of deionized purified
water 128 may be flowed through the rinse zone 308 to rinse the
residual acidic degasified water 124 from the regenerated anion
resin 320 to ensure that when to-be-treated degasified water 124
enters the adsorption zone 304, the discharged purified water 128
will be low in acidity.
[0072] In one or more embodiments, the rinse water may be
discharged from the rinse zone 308 through an outlet collector
called a "rinse tail" 348. The rinse tail 348 may be disposed above
the caustic regenerant 340 inlet 352 to prevent excessive dilution
of the spent caustic regenerant 344. The rinse tail 348 water may
contain some sodium and chloride, and may be recycled to the
produced water 116 stream entering the cation exchange unit
104.
[0073] Conventional ion exchange design typically uses a high
volume of rinse water to flush residual caustic from the resin bed.
The two-stage rinse processes of the present invention may reduce
rinse time and minimize the volume of rinse water by using the
acidic degasified water 124 to neutralize residual caustic. The
rinse tail 348 may provide a means of thorough rinsing while not
diluting the caustic regenerant 340 or adding to the waste volume
generated.
[0074] Referring to FIGS. 1-3, one or more embodiments of the
produced water purification system 100 may be used to treat a waste
stream or concentrate from a RO process. As described earlier, RO
may be used to treat produced water at some sites. However, the RO
concentrate needs to be further treated through the Higgins
Loop.TM. in order to convert the salt in the RO concentrate into a
beneficial byproduct. The RO concentrate may also be hazardous to
the environment because of its contaminants. For example, the RO
concentrate may have high levels of bicarbonate. The RO concentrate
may be stored in a feed tank (not shown). A large volume of the
discharged purified deionized water 128 may be recycled internally,
for example, via stream 132c, to the feed tank to dilute the RO
concentrate prior to flowing it to the cation exchange unit 104 for
further treatment. Diluting the RO concentrate in this manner may
mitigate excessive evolution of carbon dioxide (due to its high
levels of bicarbonate) in the cation exchange unit 104. Treatment
of the RO concentrate in the cation exchange unit 104 may further
produce a value added brine stream. The brine stream may be
suitable as a feedstock for either salt or chloro-alkali
production.
[0075] In one or more embodiments, the anion resin bed 320 may be
scrubbed with a caustic brine solution as an inline process. The
caustic brine solution may comprise the caustic regenerant 340. The
caustic brine solution may be collected in a storage tank and, as
needed, used to treat biofouling, by feeding it through a static
mixer and line and to the regeneration zone of the anion exchange
unit 108.
[0076] The internal scrubbing may preclude the necessity of
production downtime and resin removal to conduct an offline process
to rejuvenate the Cl-loaded resin 320 of organic contaminant
buildup, thereby, reducing biofouling within the regeneration zone
312 of the anion exchange unit 108.
[0077] Referring now to FIG. 4, in accordance with one or more
embodiments of the present invention, a produced water purification
system 400 may comprise a closed-loop cation exchange unit 104 and
a closed-loop anion exchange unit 108, and an intermediate
degasifier 112, as described above with reference to FIGS. 1-3.
[0078] In one or more embodiments, the produced water may comprise
elevated levels of total dissolved solids, Na+, carbonate, and
Cl.sup.- ions.
[0079] The brine/spent regenerant 244, 344 discharged from the
cation exchange unit 104 and the anion exchange unit 108 may be
combined into a solution and flowed via brine stream 404. The
dissolved solids in the pre-treated produced water are concentrated
into a combined 20% in the brine stream 404 having a volume of less
than 2- (and) 1/2% of the pre-treated produced water. The
concentrated brine stream 404 may be suitable as feedstock to
produce additional byproducts. The concentrated brine stream 404
may be sent to further processing 408, where it may be purified,
concentrated, and converted into acid and caustic. In some
embodiments, the conversion may be by electrolysis
[0080] The products resulting from the further processing 408 may
comprise NaOH, HCl, and/or H.sub.2. Produced acid may be recycled
via stream 412 to the cation exchange unit 104 to be used as acid
regenerant 240, and produced caustic may be recycled via stream 416
to the anion exchange unit 108 to be used as caustic regenerant
340.
[0081] The purified deionized water 128 may be flowed to further
processing 420, where it may be further treated with calcium salt
addition (either or both of lime and gypsum, for example) to buffer
it prior to discharge. In one or more embodiments, the purified
deionized water 128 may further be blended with untreated produced
water 424, producing treated water 428.
[0082] One or more embodiments of the produced water purification
system 100 may be fully automated and designed for unattended
operation. The produced water purification system 100 may comprise
in line instrumentation (not shown) to monitor and adjust feed
parameters and flow volumes. The produced water purification system
100 may be remotely controlled and monitored. Daily site visits may
be required to visually check on the components of the produced
water purification system 100.
[0083] Although the term "system" (and its plural form) may be used
in the above description with reference to FIGS. 1-4, these figures
(and their corresponding detailed descriptions) are to be
recognized as also illustrating and describing embodiments of the
processes of the present invention.
[0084] Notwithstanding the foregoing, FIG. 5 generally illustrates
processes in accordance with one or more embodiments of the present
invention.
[0085] In steps 504, 508, and 512, respectively, a cation exchange
unit, an intermediate degasifier, and an anion exchange unit are
provided.
[0086] In step 504a, the cation exchange unit may receive produced
water to be treated. The produced water may be flowed through the
adsorption zone of the cation exchange unit to remove cations
comprising Na+ from the produced water and produce an acidic
decationized effluent (step 504b).
[0087] In step 506, the acidic decationized effluent may be
discharged from the adsorption zone of the cation exchange unit and
flowed to the intermediate degasifier. The degasifier may, in steps
508a-508b, strip and release carbon dioxide gas from the acidic
decationized effluent, producing an acidic degasified effluent.
[0088] In step 510, the acidic degasified effluent may be
discharged from the intermediate degasifier and flowed to the anion
exchange unit. In step 512a, the acidic degasified effluent may be
received and flowed through the adsorption zone of the anion
exchange unit, producing deionized treated water (step 512b).
[0089] In the regeneration zone of the anion exchange unit, the
anion resin bed may be regenerated by contacting it with a caustic
regenerant. The regenerated anion resin bed may be rinsed in the
rinse zone using a two-stage process. The two-stage rinse process
involves: in a first stage, piping a slip stream flow of the acidic
degasified effluent through the rinse zone of the anion exchange
unit; and, in a second stage, passing a stream of the deionized
treated water through the rinse zone of the anion exchange
unit.
[0090] In or more embodiments of the invention, the produced water
feed streams and the various effluents and spent brine are sampled
and analyzed on a routine basis.
[0091] The one or more embodiments of the invention may provide
several economic and environmental benefits. There is a 50%
reduction in regenerant chemical usage in the countercurrent ion
exchange units of the invention as compared to chemical usage in
normal ion exchange units. The TDS content in pre-treated produced
water is reduced by over 30% by degasifying the decationized
produced water thereby reducing chemical usage and waste brine
volumes. The purified water is suitable for discharge into the
environment, for irrigation or livestock and for use as potable
drinking water.
[0092] While the foregoing describes various embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof. The scope
of the invention is determined by the claims that follow.
[0093] The invention is not limited to the described embodiments,
versions or examples, which are included to enable a person having
ordinary skill in the art to make and use the invention when
combined with information and knowledge available to the person
having ordinary skill in the art.
* * * * *