U.S. patent application number 12/879724 was filed with the patent office on 2011-03-24 for mercury removal from water.
This patent application is currently assigned to ConocoPhillips Company. Invention is credited to Joseph B. Cross, Sally A. Thomas, Erin E. Tullos.
Application Number | 20110068046 12/879724 |
Document ID | / |
Family ID | 43755715 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110068046 |
Kind Code |
A1 |
Tullos; Erin E. ; et
al. |
March 24, 2011 |
MERCURY REMOVAL FROM WATER
Abstract
Methods and apparatus relate to removal of mercury from water.
The removal relies on transferring mercury from an aqueous stream
to a natural gas stream upon contacting the aqueous stream with the
natural gas stream. Processing of the natural gas stream after used
to strip the mercury from the aqueous stream removes the mercury
from the natural gas stream.
Inventors: |
Tullos; Erin E.;
(Bartlesville, OK) ; Cross; Joseph B.;
(Bartlesville, OK) ; Thomas; Sally A.;
(Bartlesville, OK) |
Assignee: |
ConocoPhillips Company
Houston
TX
|
Family ID: |
43755715 |
Appl. No.: |
12/879724 |
Filed: |
September 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61243879 |
Sep 18, 2009 |
|
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|
Current U.S.
Class: |
208/187 |
Current CPC
Class: |
C02F 2103/365 20130101;
C10G 2300/1025 20130101; C10G 2300/205 20130101; C02F 2103/18
20130101; C02F 1/70 20130101; C10G 31/00 20130101; E21B 43/34
20130101; C02F 1/001 20130101; C10G 2300/805 20130101; B01D
2257/602 20130101; C02F 2101/20 20130101; C10G 33/00 20130101 |
Class at
Publication: |
208/187 |
International
Class: |
C10G 33/00 20060101
C10G033/00 |
Claims
1. A method, comprising: separating crude production into a gaseous
hydrocarbon stream, a liquid hydrocarbon stream and an aqueous
stream, wherein water forms a majority of the aqueous stream;
removing mercury from a contaminated gas stream including the
gaseous hydrocarbon stream to provide a treated gas stream; and
contacting the treated gas stream with the aqueous stream to
transfer mercury from the aqueous stream to the treated gas stream
such that mercury removal from the aqueous stream is independent
from the liquid hydrocarbon stream.
2. The method according to claim 1, further comprising adding a
reducing agent to the aqueous stream such that mercury-containing
compounds in the aqueous stream are converted to form elemental
mercury.
3. The method according to claim 1, further comprising adding
stannous chloride to the aqueous stream.
4. The method according to claim 1, further comprising filtering
the aqueous stream that has been contacted with the treated gas
stream, wherein the filtering removes particles that include
residual mercury.
5. The method according to claim 1, further comprising adding a
reducing agent to the aqueous stream and filtering the aqueous
stream that has been contacted with the treated gas stream.
6. The method according to claim 1, wherein the contaminated gas
stream further includes a recycle stream formed of vapor effluent
from the contacting of the treated gas stream with the aqueous
stream.
7. The method according to claim 1, further comprising contacting
the treated gas stream with the liquid hydrocarbon stream to
transfer mercury from the liquid hydrocarbon stream to the treated
gas stream.
8. The method according to claim 1, further comprising transferring
mercury from a mixture of the liquid hydrocarbon stream and the
aqueous stream to the treated gas stream, wherein the transferring
is separate from and prior to the contacting of the treated gas
stream with the aqueous stream.
9. The method according to claim 1, wherein removing mercury from
the contaminated gas stream comprises introducing the contaminated
gas stream into a mercury-sorbent based removal unit.
10. The method according to claim 1, further comprising removing
mercury within vapor effluent from the contacting of the treated
gas stream with the aqueous stream.
11. The method according to claim 1, wherein clean water discharge
formed of liquid effluent from the contacting of the treated gas
stream with the aqueous stream contains less than 10 weight percent
of elemental mercury contained in the aqueous stream.
12. A method, comprising: adding a reducing agent to an aqueous
stream such that mercury-containing compounds in the aqueous stream
are converted to form elemental mercury; transferring the elemental
mercury from the aqueous stream to a methane-containing gas stream,
wherein the transferring occurs upon contacting the gas stream with
the aqueous stream combined with the reducing agent; and removing
the elemental mercury from the gas stream.
13. The method according to claim 12, wherein the reducing agent is
at least one of stannous chloride, sodium borohydride, and
hydrazine.
14. The method according to claim 12, wherein the reducing agent
comprises stannous chloride.
15. The method according to claim 12, further comprising separating
crude production into the aqueous stream and vapors that form at
least part of the gas stream upon being treated to remove
mercury.
16. The method according to claim 12, further comprising filtering
the aqueous stream that has been contacted with the gas stream,
wherein the filtering removes particles that include residual
mercury.
17. A method, comprising: separating crude production into a
gaseous hydrocarbon stream, a liquid hydrocarbon stream and an
aqueous stream, wherein water forms a majority of the aqueous
stream; transferring mercury from the liquid hydrocarbon stream to
a first portion of a treated gas stream by contacting the first
portion of the treated gas stream with the liquid hydrocarbon
stream; transferring mercury from the aqueous stream to a second
portion of the treated gas stream by contacting the second portion
of the treated gas stream with the aqueous stream independent of
the first portion of the treated gas stream being contacted with
the liquid hydrocarbon stream; and forming the treated gas stream
by removing mercury from the gaseous hydrocarbon stream mixed with
the first and second portions of the treated gas stream recycled
after the contacting with the liquid hydrocarbon and aqueous
streams.
18. The method according to claim 17, further comprising adding a
reducing agent to the aqueous stream such that mercury-containing
compounds in the aqueous stream are converted to form elemental
mercury.
19. The method according to claim 17, further comprising filtering
the aqueous stream that has been contacted with the second portion
of the treated gas stream, wherein the filtering removes particles
that include residual mercury.
20. The method according to claim 17, wherein the transferring
mercury from the liquid hydrocarbon stream to the first portion of
the treated gas stream occurs while the liquid hydrocarbon stream
and the aqueous stream are mixed together.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims benefit under 35 USC .sctn.119(e) to U.S. Provisional
Application Ser. No. 61/243,879 filed Sep. 18, 2009, entitled
"MERCURY REMOVAL FROM WATER," which is incorporated herein in its
entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None
FIELD OF THE INVENTION
[0003] Embodiments of the invention relate to methods and systems
for removing mercury from water.
BACKGROUND OF THE INVENTION
[0004] Recovered fluids from wells drilled into hydrocarbon
reservoirs often include water. Separators remove the water from
oil and gas products also produced. However, the water from some
reservoirs contains mercury. The mercury in the water presents
environmental and safety concerns and may prevent ability to
discharge the water without first being treated.
[0005] Techniques utilizing solid absorbents for mercury removal
from the produced water tend to result in fouling of mercury
removal beds. Other factors limiting applicability of prior
approaches to remove mercury include expense and size requirements
given limited space available when used at platforms. Due to
mercury solubility in the water, effectiveness problems arise with
some of the prior approaches since the mercury contaminating the
water tends to be part of inorganic compounds or a mixture of the
inorganic compounds and elemental mercury.
[0006] Therefore, a need exists for improved methods and systems
for removing mercury from water.
SUMMARY OF THE INVENTION
[0007] In one embodiment, a process of removing mercury from water
includes separating crude production into a gaseous hydrocarbon
stream, a liquid hydrocarbon stream and an aqueous stream. Water
forms a majority of the aqueous stream. Removing mercury from a
contaminated gas stream including the gaseous hydrocarbon stream
provides a treated gas stream. Further, contacting the treated gas
stream with the aqueous stream transfers mercury from the aqueous
stream to the treated gas stream such that mercury removal from the
aqueous stream is independent from the liquid hydrocarbon
stream.
[0008] According to one embodiment, a method of removing mercury
from water includes adding a reducing agent to an aqueous stream
such that mercury-containing compounds in the aqueous stream are
converted to form elemental mercury. The method further includes
transferring the elemental mercury from the aqueous stream to a
methane-containing gas stream. The transferring occurs upon
contacting the gas stream with the aqueous stream combined with the
reducing agent. In addition, the method includes removing the
elemental mercury from the gas stream.
[0009] For one embodiment, a process of removing mercury from water
includes separating crude production into a gaseous hydrocarbon
stream, a liquid hydrocarbon stream and an aqueous stream. Water
forms a majority of the aqueous stream. Transferring mercury from
the liquid hydrocarbon stream to a first portion of a treated gas
stream occurs by contacting the first portion of the treated gas
stream with the liquid hydrocarbon stream. Furthermore,
transferring mercury from the aqueous stream to a second portion of
the treated gas stream by contacting the second portion of the
treated gas stream with the aqueous stream is independent of the
first portion of the treated gas stream being contacted with the
liquid hydrocarbon stream. The treated gas stream forms by removing
mercury from the gaseous hydrocarbon stream mixed with the first
and second portions of the treated gas stream recycled after the
contacting with the liquid hydrocarbon and aqueous streams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings.
[0011] FIG. 1 is a schematic of a production system for mercury
removal from water, according to one embodiment of the
invention.
[0012] FIG. 2 is a schematic of a production system having elements
shown in FIG. 1 with a subunit for removing mercury from a
hydrocarbon liquid stream, according to one embodiment of the
invention.
[0013] FIG. 3 is a schematic of a production system having elements
shown in FIG. 1 with a subunit for initial removal of mercury from
a hydrocarbon and water mixture, according to one embodiment of the
invention.
[0014] FIG. 4 is a graph showing mercury concentration in water
before and after being contacted with a stream of hydrocarbon gas,
according to one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Embodiments of the invention relate to removal of mercury
from water. The removal relies on transferring mercury from an
aqueous stream to a natural gas stream upon contacting the aqueous
stream with the natural gas stream. Processing of the natural gas
stream after used to strip the mercury from the aqueous stream
removes the mercury from the natural gas stream.
[0016] In some embodiments, the water comes from crude production
and is thus recovered from reservoirs along with hydrocarbons that
may be liquid and gaseous. Mercury concentrations in the water that
is produced often prevent outputting the water as waste due to
environmental issues and regulations. The removal of the mercury
from the water thereby enables discharge of the water separated
from the hydrocarbons. As used herein, "mercury" refers to mercury
within or from compounds, such as mercuric chloride, mercury oxide
and combinations thereof, containing mercury and at least one other
element and/or elemental mercury. Location for removing the mercury
depends on application and can be performed onsite at offshore
platforms with limited space and facilities.
[0017] FIG. 1 illustrates a system in which crude production
removed from a well defines an input stream 100 introduced into a
separator 102 for separation into a hydrocarbon gas stream 104, a
hydrocarbon liquid "HC(L)" stream 108, and an aqueous stream 106
that are each individually removed from the separator 102. Water
forms a majority of the aqueous stream 106. Mercury-containing gas,
including in part at least a portion of the hydrocarbon gas stream
104, feeds into a mercury removal unit (MRU) 118 for removal of
mercury from the mercury-containing gas, thereby forming a treated
gas stream 122 output from the MRU 118. The treated gas stream 122
includes hydrocarbon gas "HC(G)," such as methane, and may provide
a supply for natural gas usable in part for sales or as fuel.
[0018] Part of the treated gas stream 122 forms a recycle gas
stream 120, which is introduced into a water-gas contactor 112 for
contact with at least a portion of the aqueous stream 106 that also
enters the water-gas contactor 112. Through such contacting, at
least a portion of the mercury contained in the aqueous stream 106
transfers to the recycle gas stream 120, thereby forming a
water-passed gas stream 116 output from the water-gas contactor 112
and a treated water "H2O" stream 114 output from the water-gas
contactor 112. The water-passed gas stream 116 hence includes
hydrocarbon gas and mercury "HC(G)+HG." For some embodiments, the
water-passed gas stream 116 mixes with the hydrocarbon gas stream
104 and provides a portion of the mercury-containing gas that feeds
into the MRU 118.
[0019] In some embodiments, an optional chemical additive stream
110 mixes with the aqueous stream 106 to introduce a reducing agent
into the aqueous stream 106 upstream from passing of the recycle
gas stream 120 in contact with the aqueous stream 106. The reducing
agent breaks molecular bonds between mercury atoms and other
elements in mercury-containing compounds. As used herein, the
reducing agent may be provided as a liquid and includes any
substance that forms a compound with such released non-mercury
elements to prevent recombination with elemental mercury. Examples
of the reducing agent include stannous chloride (SnCl.sub.2;
"SNCL2"), sodium borohydride, and hydrazine. Amount of the reducing
agent introduced via the additive stream depends on concentration
of mercury in the aqueous stream 106 and may be sufficient to
establish an excess mole ratio of the reducing agent relative to
the mercury.
[0020] The reducing agent supplied through the additive stream 110
may facilitate effectiveness of sparging within the water-gas
contactor 112 since mercury removal ability via the sparging is
higher for elemental mercury relative to when not in elemental
form. Reducing inorganic compounds, such as mercury oxide or
mercuric chloride, in the aqueous stream 106 tends to promote the
mercury removal. Even though the mercury in the aqueous stream 106
can tend to remain in elemental form while at elevated formation
temperatures, the elemental mercury may convert into mixed element
compounds due to cooling of the aqueous stream 106 and temperature
influence on solubility of the elemental mercury. In operation, the
aqueous stream 106 may cool upon coming out of the well making
introduction of the additive stream 110 desirable to reduce the
inorganic compounds to the elemental mercury.
[0021] For some embodiments, the treated water stream 114 passes
through an optional filtration system 124 to remove suspended
particulates from the treated water stream 114. The filtration
system 124 operates based on size exclusion to trap or retain
particles above a certain size, such as about 0.2 micron or about
0.4 micron. The cooling that is inevitable after the input stream
100 comes out of the well promotes adherence of the mercury to the
particulates. Generation of a filtered water stream 126 flowing out
of the filtration system 124 thus results in further mercury
removal .since residual mercury still within the treated water
stream 114 is associated with the particulates.
[0022] In some embodiments, the water-gas contactor 112 includes
multiple (e.g., 2, 4, 6 or more) theoretical stages of separation
between vapor and liquid phases. Either trays or packing material
of the water-gas contactor 112 may form the theoretical stages by
being in a flow path of fluids described herein passing through the
water-gas contactor 112. For example, the packing material making
up an internal part of the water-gas contactor 112 may include
random oriented objects or a shaped structure and may be made of
metallic, ceramic, plastic or other solid material. For some
embodiments, amount of the packing material utilized depends on a
desired number of the stages provided by the packing material.
[0023] The MRU 118 defines a fixed bed including any mercury
sorbent material capable of removing mercury from gases. In some
embodiments, the treated gas stream 122 includes less than about 20
weight percent (wt. %) of the mercury within the mercury-containing
gas, less than about 10 wt. % of the mercury within the
mercury-containing gas, or less than about 1 wt. % of the mercury
within the mercury-containing gas. The treated water stream 114 or
the filtered water stream 126 may contain less than about 50 wt. %,
10 wt. %, or 1 wt. % of the mercury contained in the aqueous stream
106. The aqueous stream 106 for some embodiments contains at least
about 5 parts-per-billion (ppb), 100 ppb or 500 ppb mercury.
[0024] For some embodiments, the recycle gas stream 120 contacts
the aqueous stream 106 at ambient temperature, such as about
21.degree. C., or from about 0.degree. C. to about 300.degree. C.;
a pressure in the range of from about 0.1 Bars to about 15 Bars,
from about 0.5 Bars to about 10 Bars, or from about 1 Bar to about
5 Bars; and a gas to liquid ratio in the range of from about 50 to
about 300 standard cubic feet of gas/barrel of liquid (SCF/bbl) or
from about 100 to about 200 SCF/bbl.
[0025] FIG. 2 illustrates a schematic of a production system that
includes a subunit for removing mercury from the hydrocarbon liquid
stream 108. The system incorporates an oil-gas contactor 200 of the
subunit with elements already described herein with respect to FIG.
1 and identified by common reference numbers. A first portion 220
of the treated gas stream 122 enters the water-gas contactor 112 to
generate the treated water stream 114. A second portion 221 of the
treated gas stream 122 flows into the oil-gas contactor 200 and is
introduced into the hydrocarbon liquid stream 108 also input into
the oil-gas contactor 200. Such contacting transfers mercury from
the hydrocarbon liquid stream 108 to the second portion 221 of the
treated gas stream 122 and occurs subsequent to separation of the
hydrocarbon liquid stream 108 from the aqueous stream 106.
Resulting effluent from the oil-gas contactor 200 includes
hydrocarbon liquids forming a treated oil stream 208 and
hydrocarbon gases contaminated with mercury forming an oil-passed
gas stream 216. The oil-passed gas stream 216 also passes through
the mercury removal unit 118 and is thereby regenerated to make up
part of the treated gas stream 122.
[0026] FIG. 3 shows a schematic of a production system with an
exemplary alternative configuration such that a subunit provides
initial removal of mercury from a hydrocarbon and water liquid
mixture. U.S. patent application Ser. No. 12/538,606, which is
herein incorporated by reference in its entirety, further describes
such exemplary techniques depicted by the subunits in FIGS. 2 and 3
for liquid hydrocarbon processing to remove mercury. Similar to
other embodiments, the water-gas contactor 112 generates the
treated water stream 114 utilizing a first portion 320 of the
treated gas stream 122. In addition to elements already described
herein having like reference numbers, the system further
incorporates an emulsion-gas contactor 300 of the subunit. The
separator 102 may only provide separation for two phases leaving
water in the hydrocarbon liquid stream 108 that feeds into the
emulsion-gas contactor 300. A second portion 321 of the treated gas
stream 122 flows into the emulsion-gas contactor 300 where
introduced into the hydrocarbon liquid stream 108. Such contacting
transfers mercury from the hydrocarbon liquid stream 108 to the
second portion 321 of the treated gas stream 122 and occurs prior
to separation of the aqueous stream 106 out of the hydrocarbon
liquid stream 108. Three individual resulting effluents from the
oil-gas contactor 200 include hydrocarbon liquids forming a treated
oil stream 308, hydrocarbon gases contaminated with mercury forming
an emulsion-passed gas stream 316, and the aqueous stream 106,
which then feeds to the water-gas contactor 112 for further water
treatment as set forth herein. The emulsion-passed gas stream 316
passes through the mercury removal unit 118 and is thereby
regenerated to make up part of the treated gas stream 122.
[0027] Independence with respect to removing mercury from the
aqueous stream enables mercury to be removed from the water alone
or tailoring amount of mercury to be removed from each of the water
and the hydrocarbon liquids as desired. Referring to FIGS. 2 and 3,
the oil-gas contactor 200 and the emulsion-gas contactor 300 enable
reducing mercury concentration in the hydrocarbon liquid stream 108
independent of utilizing the water-gas contactor 112 to remove the
mercury from the aqueous stream 106. Thresholds for mercury
concentrations in the hydrocarbon liquids depend on economics and
marketability to refineries. However, mercury concentration in the
water may need to meet separate set requirements necessitating
individual treatment of the aqueous stream 106. Furthermore,
independent processing of the aqueous stream 106 to remove mercury
makes possible optional addition of the reducing agent, optional
use of the filtration system 124, and conducting treatment without
having to ensure certain temperatures of the aqueous stream 106
during the contacting to remove the mercury.
[0028] FIG. 4 depicts a graph showing mercury concentration in
water before and after being contacted with a stream of hydrocarbon
gas. Prior to being sparged with the gas, the water contained 489
micrograms per liter (.mu.g/l) of total mercury and 1.4 82 g/l of
dissolved mercury. The water after being sparged with the gas for
20 minutes contained no dissolved mercury and had only 10 .mu.g/l
of the total mercury remaining. Since the 10 .mu.g/l of the total
mercury remaining was associated with suspended particles greater
than 0.45 microns in size, filtering provided an option for
removing residual mercury from the water following the sparging.
Results thus demonstrated effectiveness of such techniques for
removing mercury from actual produced water.
[0029] The preferred embodiment of the present invention has been
disclosed and illustrated. However, the invention is intended to be
as broad as defined in the claims below. Those skilled in the art
may be able to study the preferred embodiments and identify other
ways to practice the invention that are not exactly as described
herein. It is the intent of the inventors that variations and
equivalents of the invention are within the scope of the claims
below and the description, abstract and drawings are not to be used
to limit the scope of the invention.
* * * * *