USOO709.

4341B2

(12) United States Patent (10) Patent No.: US 7,094,341 B2

Max (45) Date of Patent: Aug. 22, 2006
(54) HYDRATE-BASED 4,453,959 A 6, 1984 Bishkin
DESALINATIONAPURIFICATION USING 4,678,583 A 7/1987 Willson, III et al.
PERMEABLE SUPPORT MEMBER 4,776, 177 A 10, 1988 Jancic et al.
5,630,865 A 5, 1997 Price
5,964,923 A 10, 1999 Lokhandwala
(75) Inventor: Michael David Max, St. Pete Beach, 6,028,234. A 2/2000 Heinemann et al.
FL (US) 6,145,340 A 11/2000 Stepanski et al.
6,158,239 A 12/2000 Max et al.
(73) Assignee: Marine Desalination Systems, L.L.C., 6,158,242 A 12, 2000 Lu
Washington, DC (US) 6,350,928 B1 2/2002 Waycuilis et al.
6,395,138 B1* 5/2002 Darredeau et al. .......... 202,158
(*) Notice: Subject to any disclaimer, the term of this 6,502.404 B1* 1/2003 Arman et al. ..... 62.3.1
patent is extended or adjusted under 35 6,562,234 B1* 5/2003 Max ........................... 210, 170
U.S.C. 154(b) by 0 days. 6,673,249 B1 1/2004 Max ........................... 21Of 747
6,703,534 B1 3/2004 Waycuilis et al.
(21) Appl. No.: 11/089,369
(Continued)
(22) Filed: Mar. 25, 2005 FOREIGN PATENT DOCUMENTS
(65) Prior Publication Data JP 11 319805 11, 1999
US 2005/O1942.99 A1 Sep. 8, 2005
(Continued)
Related U.S. Application Data Primary Examiner Peter A. Hruskoci
(62) Division of application No. 10/429,765, filed on May (74) Attorney, Agent, or Firm—Kenneth M. Fagin, Esq.
6, 2003. (57) ABSTRACT
(60) Provisional application No. 60/378,368, filed on May
8, 2002. Processes and apparatus are disclosed for separating and
purifying aqueous solutions such as seawater by causing a
(51) Int. Cl. Substantially impermeable mat of gas hydrate to form on a
CO2F I/02 (2006.01) porous restraint. Once the mat of gas hydrate has formed on
(52) U.S. Cl. ........................... 210/170; 62/3.2; 62/123; the porous restraint, the portion of the mat of gas hydrate
62/238.5: 210/177: 210/181; 210/182; 210/202; adjacent to the restraint is caused to dissociate and flow
210/205 through the restraint, e.g., by lowering the pressure in a
(58) Field of Classification Search ............... 62/238.5; collection region on the opposite side of the restraint. The
210/177, 180 purified or desalinated water may then be recovered from the
See application file for complete search history. collection region. The process may be used for marine
(56) References Cited desalination as well as for drying wet gas and hydrocarbon
Solutions. If conditions in the solution are not conductive to
U.S. PATENT DOCUMENTS forming hydrate, a heated or refrigerated porous restraint
may be used to create hydrate-forming conditions near the
1,727,504 A * 9, 1929 Gibson ....................... 210,180 restraint, thereby causing gas hydrates to form directly on
2.475,255 A 7, 1949 Rollman the surface of the restraint.
2.990,691 A 7/1961 Glasgow
3,132,096 A * 5, 1964 Walton ....................... 210,711
4,162,617 A * 7/1979 Schmidt et al. ............... 62.123 69 Claims, 14 Drawing Sheets
100

20
 US 7,094,341 B2
Page 2

U.S. PATENT DOCUMENTS FOREIGN PATENT DOCUMENTS

6,767.388 B1 7/2004 Lecomte et al. WO WO 01/010541 A1 2, 2001
6,774,246 B1 8, 2004 Reuter et al. WO WO O2/OO553 A2 1, 2002
6,830,682 B1 12/2004 Max ........................... 210, 170
6,866,750 B1* 3/2005 Gougel et al. ................ 203/10
6,946,017 B1 9/2005 Leppen * cited by examiner
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U.S. Patent Aug. 22, 2006 Sheet 12 of 14 US 7,094,341 B2
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 US 7,094,341 B2
1. 2
HYDRATE-BASED fluid still enters the region of hydrate dissociation, which
DESALINATIONAPURIFICATION USING increases the Salinity in the dissociation region and thus
PERMEABLE SUPPORT MEMBER reduces the “purity” of the product water.
In addition to research on using hydrates for desalination/
CROSS-REFERENCE TO RELATED purification, much of the hydrate research to date has been
APPLICATIONS conducted by energy companies concerned with inhibiting
hydrate formation and growth in hydrocarbon pipelines
This is a divisional of application Ser. No. 10/429,765 because hydrate-caused flow constrictions in Such pipelines
filed May 6, 2003, the entire contents of which are incor can be extremely costly. Moreover, even if hydrate does not
porated by reference. This application claims the benefit of 10 cause a flow constriction, Small crystals of hydrate may form
provisional U.S. patent application Ser. No. 60/378,368 filed in petroleum, which crystals act as abrasive crystals in the
May 8, 2002, the contents of which are incorporated by moving fluid. Therefore, it is desirable to remove hydrate
reference. from pipelines and other hydrocarbon-containing vessels,
even if the hydrate occurs only in Small quantities.
GOVERNMENTAL SUPPORTAND INTEREST 15
Prior energy industry research efforts have yielded a
number of methods for inhibiting hydrate growth or for
This invention was made with Government support under removing unwanted hydrate from piping. However, existing
Contract No. NBCHC 010003 dated Jan. 29, 2001 and methods involve high capital costs, high energy demands,
issued by the Department of the Interior National Business and in some cases, the use of chemicals (such as alcohols)
Center (DARPA). The Government has certain rights in the which absorb the water from petroleums but which create
invention. their own separation problems. If drying of petroleums is
BACKGROUND AND FIELD OF THE carried out on the seafloor in deep water, costs are magnified.
INVENTION
SUMMARY OF THE INVENTION
25
In general, the invention relates to gas hydrate-based
desalination and/or water purification. In particular, the The invention provides various methods and apparatuses
invention significantly reduces the amount of residual brine for extracting fresh water from saline or otherwise polluted
that mixes with the product water, thereby greatly enhancing water with greatly increased purity of the final, product
the purity of the product water. 30 water that is obtained. The invention entails forming a
Purified water may be obtained from saline or polluted Substantially solid, compacted mat of gas hydrate (or other
water by forming and then dissociating crystalline hydrate. clathrate, if fluid other than water is used) on or against a
Such a process for obtaining purified water from Saline or porous, fluid-permeable restraint. Residual saline interstitial
polluted water is disclosed in, for example, U.S. Pat. Nos. fluid is expelled from the mat of hydrate by the forces
5,873,262 and 3,027.320. According to those patents, a gas 35 governing hydrate crystallization. Hydrate within the por
or mixture of gases is brought into contact with saline or tions of the mat that are closest to or adjacent to the restraint
polluted water under appropriate conditions of pressure and are caused or allowed to dissociate, e.g., by lowering system
temperature and forms hydrate. The hydrate is then brought pressure on the side of the restraint that is opposite to the mat
to a region of higher temperature and lower pressure, where of hydrate. That reduced pressure or "suction' acts on the
it dissociates to release fresh water and the hydrate-forming 40 hydrate through the pores in the restraint. Purified water (or
gas or gases. other fluid if the process is used to form clathrates of fluid
When the hydrate is formed in saltwater to desalinate it, other than water) and the hydrate-forming gas (or clathrate
highly saline brines typically remain in the interstices of the forming gas) pass through the restraint via the pores in the
hydrate as it forms a slurry. These brines may also contain restraint and are collected from the side of the restraint
dissolved or Suspended Solids. 45 opposite the mat of hydrate. Because the residual fluids
One of the principal problems that has inhibited the remaining after the hydrate has been formed (e.g., the highly
Successful development of hydrate-based desalination on a saline residual brines) have been expelled from the mat, the
commercial scale has been the difficulty of removing Such product water (or other product fluid) passing through the
residual, interstitial brines from the hydrate slurry or a restraint is substantially free of salts, other dissolved mate
hydrate-brine mixture. In particular, it has proven difficult to 50 rials, or contaminants. Thus, purity of the product water is
develop a successful process for thoroughly washing an significantly increased as compared to the prior art.
essentially static mixture of hydrate and interstitial brines, in Under steady state conditions, operation of the system is
which process the saline interstitial fluid is removed (and controlled such that hydrate forms and accumulates on one
perhaps replaced by less Saline interstitial water). Surface of the mat of hydrate at the same rate as it dissociates
According to the two patents noted above, the hydrate, 55 from the opposite Surface of the mat, adjacent to the
which is positively buoyant, simply floats upward from restraint. Thus, a substantially uniform mat of hydrate of
where it forms (a region of highly saline water) into a region essentially constant thickness can be maintained, and the
of less saline water. The hydrate dissociates in the region of process of the invention can be run on a continuous basis.
less Saline water, while residual brine remains in or sinks The gas hydrate used in the process may be any gas
toward the region of highly saline water. The region of less 60 hydrate formed under typical hydrate-forming pressure and
saline water may be maintained at the reduced salinity levels temperature conditions, as known in the art. Moreover, in the
by introducing fresh water released upon dissociation of the context of the invention, “fresh' water is water that is
hydrate. Such moving of hydrate, or allowing of hydrate to Substantially less Saline and contains substantially fewer
move, into a region of less Saline water minimizes undesir dissolved chemical species than the water from which the
able mixing of “purified’ water with interstitial water and is 65 gas hydrate was formed, for example, water that contains
particularly well suited to large-scale production of fresh less than 500 TDS (total dissolved solids). Such fresh water
water. However, variable amounts of highly saline residual may be either pure or potable.
 US 7,094,341 B2
3 4
The porous and permeable restraint can be made from, for FIG. 7 is a diagrammatic section view illustrating appa
example, a highly thermally conducting, relatively stiff ratus using a contoured hydrate asymmetric restraint to
metal, plastic, ceramic, or synthetic material. Examples of desalinate or purify water using negatively buoyant hydrate
suitable materials from which the porous, permeable according to the invention;
restraint can be made include steel plate, a Supported metal FIG. 8 is a diagrammatic section view of a shaft-based
or plastic screen, or a composite material having hydropho installation for desalinating or purifying water using a
bic and hydrophilic areas such that hydrate adheres to the hydrate asymmetric restraint like that shown in FIGS. 1 and
material but water can readily pass through the material. The 2 and using positively buoyant hydrate according to the
porous and permeable restraint, also referred to herein as a invention;
“hydrate asymmetric restraint’ or simply “restraint, is 10 FIG. 9 is a diagrammatic section view of an apparatus
configured such that it allows fluid and gas to pass through used to purify or desalinate seawater using positively buoy
it. (The term “asymmetric' in “hydrate asymmetric ant hydrate, which apparatus is submerged in an open-ocean
restraint” refers to the different (i.e., “asymmetric) pressure environment according to the invention;
conditions that exist on either side of the restraint when a FIG. 10 is a diagrammatic section view of an apparatus
system according to the invention is operating at steady 15 for desalinating or purifying water in a Submerged, open
state.) ocean environment according to the invention, which appa
Additionally, the restraint also may have a series of ratus has a contoured hydrate asymmetric restraint like that
conduits (e.g., internal, extending between the pores of the shown in FIG. 6 and an open-ended configuration like that
restraint) or cavities (e.g., formed in its Surface) through shown in FIG. 9;
which cooling and/or heating fluids circulate or in which FIG. 11 is a diagrammatic perspective view of a ther
cooling or heating apparatus can be installed. Cooling and/or mally-assisted hydrate asymmetric restraint according to the
heating facilitate hydrate formation (e.g., during system invention;
startup) or dissociation (i.e., by providing Sufficient heat FIG. 12 is a diagrammatic perspective view of a pipe
required for the hydrate to dissociate by “compensating for based hydrate asymmetric restraint according to the inven
heat of exothermic formation of the hydrate that has been 25 tion;
carried away from the system, e.g., by residual brines. FIG. 13 is a diagrammatic perspective view of apparatus
The restraint can be formed in a number of different configured to remove hydrate from hydrocarbon pipelines
configurations, depending, for example, on whether it is according to the invention; and
desired to operate using positively or negatively buoyant FIG. 14 is a detailed diagrammatic perspective view of a
hydrate. Systems using a hydrate asymmetric restraint can 30 hydrate asymmetric restraint used in the embodiment of
FIG. 13.
be mechanically or “artificially” pressurized in order to
generate pressures necessary for hydrate to form. Alterna DETAILED DESCRIPTION OF EMBODIMENTS
tively, apparatus using an asymmetric restraint can be Sub OF THE INVENTION
merged, e.g., at the bottom of a shaft of depth sufficient for 35
the weight of the column of water above the restraint to As shown in FIG. 1, general apparatus 100 according to
generate appropriate operating pressures or in an open-ocean the invention and having a hydrate asymmetric restraint 102
marine environment.
includes a vessel 104, the walls of which contain the hydrate
BRIEF DESCRIPTION OF THE DRAWINGS
and the fluid from which it is formed. The vessel 104 may
40 be a conventional pressure vessel Such as a steel or alumi
num tank, or any other vessel capable of withstanding
These and other features of the invention will become typical hydrate-forming temperatures and pressures.
clearer in view of the following description and the figures, Hydrate-forming temperatures and pressures are known
in which: in the art and generally range from about 1° C. to about 30°
FIG. 1 is a generalized, diagrammatic section view illus 45 C., with pressures ranging from ambient pressure (about 0.1
trating a hydrate asymmetric restraint for practicing methods MPa) to about 10 MPa, depending on the particular hydrate
of the present invention; forming gas being used. (Processes and apparatuses accord
FIG. 2 is a detailed perspective view, partially in section, ing to the invention may be adapted to use any available
of a portion of the hydrate, asymmetric restraint illustrated hydrate-forming gas or mixture of hydrate-forming gases.)
in FIG. 1; 50 As is known in the art, forming hydrate at higher tempera
FIG. 3 is a diagrammatic section view illustrating appa tures generally requires the use of higher pressures. Many
ratus for desalinating or purifying water using a hydrate types of hydrate-forming gases are known in the art, includ
asymmetric restraint like that shown in FIGS. 1 and 2 and ing but not limited to low molecular weight hydrocarbon
using positively buoyant hydrate according to the invention; gases (e.g., methane, ethane, and propane), carbon dioxide,
55 Sulfur trioxide, nitrogen, halogens, noble gases, and Sulfur
FIG. 4 is a diagrammatic section view illustrating appa hexafluoride.
ratus for desalinating or purifying water using a hydrate The vessel 104 has appropriate inlet and outlet ports (not
asymmetric restraint like that shown in FIGS. 1 and 2 and shown) for introducing and removing gas and water. Addi
using negatively buoyant hydrate according to the invention; tionally, the vessel 104 may have suitably reinforced, trans
FIG. 5 is a diagrammatic section view of a contoured 60 parent observation ports, also not shown, by means of which
hydrate asymmetric restraint which can be used to practice operation of the vessel can be visually monitored. The size
methods of the present invention; and relative dimensions of the vessel 104 are determined
FIG. 6 is a diagrammatic section view illustrating appa largely by the physico-chemical characteristics of the par
ratus using a contoured hydrate asymmetric restraint similar ticular hydrate-forming gas or gas mixture as well as the
to that illustrated in FIG. 5 and configured to desalinate or 65 volume output of fresh water to be produced.
purify water using positively buoyant hydrate according to The hydrate asymmetric restraint 102 illustrated in FIGS.
the invention; 1 and 2 is a porous, stainless steel plate or other Suitably
 US 7,094,341 B2
5 6
strong, non-corrosive material. The restraint 102 has a compacts into the generally solid mat 114, residual, highly
porosity of about 80%, with an average pore size of about saline interstitial brines will be expelled or displaced (down
2.5 mm. In other embodiments, the porosity of the restraint ward in the embodiment illustrated in FIG. 1), thus produc
102 may be between about 75% and about 95%, with a pore ing a mat 114 that is Substantially pure hydrate, i.e., free of
size between about 1 mm and about 5 mm. The pore size brines or other contaminants.
may be varied depending on the thickness of the hydrate Portions of the mat of hydrate 114 that are adjacent to the
layer that is to be formed in the restraint, with smaller pores restraint 102 (i.e., on the side of the mat 114 opposite to that
used when a thinner layer of hydrate is to be formed on the where hydrate accumulates) will dissociate under the influ
restraint and larger pores used when a thicker layer of ence of lower pressure conditions established in the fresh
hydrate is to be formed on the restraint. 10 water collection region 108. In particular, those portions of
The pores 120 in the restraint 102 may be cylindrical, or the mat of hydrate 114 will be subjected to the lower
they may have some other shape. For example, as shown in pressure of the fresh water collection region 108 through the
FIG. 2, the pores 120 in the restraint 102 may have a conical pores of the restraint 102, and the lower pressure is such that
cross-sectional shape, with the pores decreasing in diameter the hydrate in those low-pressure-exposed portions of the
from the high-pressure, hydrate formation side 121 toward 15 mat 114 no longer remain stable. Therefore, it will dissoci
the low-pressure-exposed side 122. Such diminishing-diam ate.
eter configuration helps prevent Solid fragments of hydrate As the hydrate in the portions of the mat 114 adjacent the
from “blowing through the restraint 102, i.e., from moving restraint 102 dissociates, the constituent fresh water F and
from the high-pressure or “upstream” side of the restraint hydrate-forming gas G are released from the hydrate and
121 to the low-pressure or “downstream” side of the flow through the pores 120 of the restraint 102 and into the
restraint 122. fresh water collection region 108, while the interstitial,
The restraint 102 is securely connected to the walls of the highly saline residual brines are Substantially (i.e., virtually
vessel 104 by means of fasteners (e.g., bolts, screws, or entirely) left behind in the hydrate formation region 106
rivets), a weldment, or any other conventional connecting because they have been expelled by compaction of the
means. Alternatively, depending on the size and character 25 granular layer 116 into the mat 114. Thus, far purer product
istics of the vessel 104, the restraint 102 may be molded or water (or other fluid from which clathrate can be formed)
cast as an integral part of the vessel 104. In other embodi can be produced by means of the present invention than has
ments, other materials may be used for the restraint 102 and been produced by means of prior art methodologies.
vessel 104. Such other materials including aluminum, brass, Under steady state operating conditions, new hydrate 112
plastics, and composites. The material of the restraint 102 30 joins the granular layer 116 at the same rate that hydrate
and vessel 104 should be chosen such that the components dissociates from the opposite surface of the mat of hydrate
do not corrode with extended exposure to a saline environ 114, thereby maintaining the existence and integrity of the
ment. The restraint 102 is constructed with sufficient size sealing or barrier layer 118 and thus the pressure seal created
and thickness to resist stresses of approximately 150–300 by it. Therefore, hydrate formation region 106 can be
pounds per square inch without failure. 35 maintained at a higher pressure than the fresh water collec
The restraint 102 separates a relatively high-salinity, tion region 108; alternatively stated, the fresh water collec
hydrate formation region 106 from a fresh water collection tion region 108 can be maintained at a lower pressure than
region 108 of lower salinity. Hydrate-forming gas G is the hydrate formation region 106. The pressure differential
supplied to the hydrate formation region 108 and, because between the hydrate formation region 106 and the fresh
pressure and temperature conditions within the hydrate 40 water collection region 108 is controlled so as to cause as
formation region 106 are conducive to forming hydrate, free much fresh water as possible to flow into the fresh water
hydrate (generally indicated as 112 when newly formed) collection region 108 under steady state conditions without
spontaneously forms. causing the pressure sealing layer 118 or the restraint 102 to
Apparatus 100 is configured for use with positively buoy fracture or otherwise fail mechanically.
ant hydrate. Thus, the newly formed hydrate 112 may be 45 Although as a whole the mat of hydrate 114 is substan
either naturally positively buoyant per se or, alternatively, tially solid in the steady state, the hydrate itself is usually
formed in a manner Such that there is enough trapped initially deposited (e.g., during system start-up) on the
hydrate-forming gas so as to be positively buoyant in toto restraint 102 in an incomplete manner Such that the deposits
even though the hydrate, per se, is negatively buoyant. As of hydrate on the restraint 102 are not completely solid
illustrated by arrows H, the newly formed hydrate 112 floats 50 hydrate; rather, they are able to change shape without
upward toward the restraint 102, where it accumulates and recrystallizing. If all of the hydrate 112 in the mat were solid
compacts. and therefore unable to change shape without recrystalliz
The apparatus 100 is illustrated in FIG. 1 as operating ing, Small holes might form in the hydrate mat through
under steady state conditions after a mat of hydrate 114 has which residual saline water from the hydrate formation
formed on the restraint 102. Under steady state conditions, 55 region 106 could pass. However, hydrate formation that
a substantially solid mat of hydrate 114 will be “clotted prevents gas from coming into contact with water will
against the restraint 102. Just beneath the substantially solid generally yield Substantially complete sealing of the restraint
mat of hydrate 114, a generally granular Zone or layer of 102.
hydrate 116, the porosity of which decreases toward the In particular, hydrate shells commonly form around
solid mat of hydrate 114, is formed. Together, the substan 60 bubbles of hydrate-forming gas, which prevents all of the
tially solid mat of hydrate 114 and granular Zone or layer of hydrate-forming gas in the bubble from forming hydrate.
hydrate 116 form a pressure-sealing barrier layer 118 that Thus, the bubbles tend to be “soft” in that they change shape
substantially seals the pores of the restraint 102. Newly and flatten somewhat when they come into contact with the
formed hydrate 112 rises into contact with and joins the restraint 102. When these hydrate-shelled gas bubbles
granular layer of hydrate 116, and the generally granular 65 (which often become encrusted with acicular and tabular
layer of hydrate 116 slowly becomes compacted into the crystals of hydrate that grow both outward from the shells
generally solid mat of hydrate 114. As the granular hydrate into the Surrounding water and into the gas bubbles) are
 US 7,094,341 B2
7 8
strained sufficiently, they fracture, thereby releasing gas into In the forming mat of hydrate 114, the axis of maximum
the Surrounding water as well as allowing water to enter the strain typically will be approximately normal to the restraint
existing hydrate-shell. Both events cause more hydrate to 102 because of the different pressures on either side of the
form spontaneously, which Substantially reduces the remain restraint 102, and the axes of minimum and intermediate
ing porosity of the hydrate mat and causes residual water to strain will lie in a plane approximately parallel with the
move away from Such secondarily formed hydrate. restraint 102. Therefore, compressive strains will arise in a
Thus, the original, “soft' bubbles carry hydrate-forming plane approximately normal to the plane of the restraint 102.
gas and hydrate into the immediate vicinity of the restraint and extensive strains will arise in a plane approximately
102, and interstitial residual water fluid is gradually dis parallel to the restraint 102. Such a strain field will cause
placed away from the restraint 102, first by the hydrate 10 differential stresses on the individual grains of hydrate
shelled gas bubbles deforming as they press into the open within the mat of hydrate 114, and such differential stresses
pores of the restraint 102 and then by the “secondary will cause the mat of hydrate 114 to compress even further
formation of more hydrate as the shells fracture. As this against the clotted restraint 102, thereby displacing addi
process continues, the pores of the restraint 102 gradually tional interstitial fluid away from the restraint 102. (It is
will become blocked or clogged. While some of the pores in 15 believed that this effect is attributable to annealing recrys
the restraint 102 are still unblocked, residual water will be tallization and grain boundary minimalization that accom
expelled away from the restraint 102 as the growing or pany recrystallization of polycrystalline accumulations
thickening mat of hydrate (which is growing towards the under conditions of anisotropic Strain.) Typically, the
hydrate formation region 106) pushes the residual water hydrate will tend to recrystallize in a lateral direction, away
towards the hydrate formation region 106. Eventually, all (or from the axis of maximum strain and along the plane in
almost all) of the pores in the asymmetric restraint facing the which the axes of minimum and intermediate Strain lie.
hydrate formation region 106 will become clogged or clotted The strain couple within the hydrate immediately proxi
with hydrate such that the mat of hydrate 114 and the mate to the surface of the restraint 102 (i.e., where the
restraint 102 form a pressure seal or pressure barrier hydrate is dissociating) will be different from that within the
between the hydrate formation region 106 and the fresh 25 region of the mat of hydrate 114 where hydrate is deforming
water collection region 108. and recrystallizing. Because the hydrate dissociates only at
Forming hydrate shells around gas bubbles also has the the surface of the mat of hydrate 114 (or in small fissures that
benefit of increasing the buoyancy of hydrate which, perse, extend from the surface into the interior of the mat 114), it
is positively buoyant so that it will exert more force against is believed that there will be little or no accompanying
the restraint 102 when it comes into contact with the 30 recrystallization of the hydrate under the new strain field.
restraint, thus increasing the tendency to "squeeze out” pore However, even if there were some recrystallization within
space. Similarly, when gas bubbles are formed or trapped the new strain field, the relative degree of salinity of the
within hydrate which, per se, is negatively buoyant so as to water produced from that recrystallized hydrate would likely
form a “soft’ hydrate bubble that will deform against an be unaffected because porosity and permeability of the solid
asymmetric restraint, the hydrate mat, in toto, will be 35 hydrate mat are essentially eliminated in the early stages of
positively buoyant. Although the buoyancy of the resultant formation of the hydrate mat 114.
gas/hydrate mixture in a bubble of hydrate which, per se, is When gas inclusions remain within the mat of hydrate
negatively buoyant is not as great as that of a gas/hydrate 114, the gas typically will pass through the restraint 102
mixture formed from positively buoyant hydrate (for similar when the hydrate around it dissociates (along with fresh
volumes of included gas), such bubbles will, nonetheless, 40 water produced when the hydrate dissociates). As individual
join the solid mat of hydrate 114 and be held there by grains or bubbles of hydrate are subjected to the low
intergrowth with other hydrate already present in the mat of pressure proximate to the surface of the restraint 102 (as well
hydrate 114. The mat of hydrate 114 will be held against the as the high pressure in the hydrate formation region 106,
restraint 102 by virtue of the pressure differential across it acting through the hydrate mat 114), the grains of hydrate
(as well as by virtue of the hydrate’s buoyancy where the 45 will tend to crush, and gas will tend to escape through the
hydrate, per se, is positively buoyant). restraint 102. This may have a slight effect on the overall
In addition to the formation of hydrate within the hydrate efficiency of the process because additional gas may need to
formation region 106 and, secondarily, at the face of the be delivered to the hydrate formation region 106 to replace
restraint 102, more dynamic recrystallization will occur that which has escaped. The relative efficiency of the pro
within the mat of hydrate 114 as a result of forces created 50 cess, however, will have little (if any) effect on the salinity
within the hydrate by the significant pressure differential of water produced by the process.
across the mat of hydrate 114. For example, when the As noted above, under steady state operating conditions,
pressure in the hydrate forming region 106 is about 1.7 MPa hydrate will accumulate on one surface of the mat of hydrate
(about 17 bar) with a water temperature of 8.5° C., and a 114 at the same rate as hydrate dissociates from the opposite
mixed hydrate-forming gas comprising methane with about 55 surface of the mat 114 (i.e., from the surface adjacent the
5% propane is used to form the hydrate, the pressure in the restraint 102), and this rate balance maintains the integrity of
fresh water collection region 108 may be maintained at the pressure sealing layer 118 formed by the clotted restraint
between about 1 MPa and about 1.2 MPa (10 to 12 bar). The 102 and the mat of hydrate 114. Once the pressure sealing
actual pressures in the hydrate forming region 106 and fresh layer 118 has been formed completely (i.e., at the end of the
water collection region 108 will vary depending on the 60 start-up phase of operation), the pressure in the fresh water
particular type of hydrate-forming gas being used and the collection region 106 (i.e., on the downstream side 122 of
temperature of the input water, and the pressure on the the restraint 102) can be lowered.
dissociation side will depend on the desired rate of disso When the pressure initially is lowered on the downstream
ciation for a particular apparatus and for particular operating side 122 of the restraint 102, a thermodynamic hydrate
conditions. Irrespective of the actual pressures employed, 65 stability boundary (not illustrated) will arise between the
however, the strain induced in the mat of hydrate 114 is hydrate formation region 106 and the fresh water collection
likely to be strongly asymmetric. region 108. Along this stability boundary, the mat of hydrate
 US 7,094,341 B2
10
114 will be exposed to pressure and temperature conditions thermodynamic conditions of the restraint 102. If solid state
that cause the hydrate in the mat 114 closest to the stability Pelletier thermoelectric effect or magnetocaloric devices are
boundary to dissociate. The thermodynamic stability bound used to heat and/or cool the restraint 102, the tubes 112 may
ary may be located somewhere within the mat of hydrate be formed as relatively shallow grooves or channels into
114, at the surface of the restraint 102 against which the which a number of the devices are installed. Alternatively,
hydrate bears, or somewhere within the restraint 102 (the depending on the material from which the restraint 102 is
latter situation occurring particularly in cases where hydrate made, it may be desirable to “print’ or microfabricate the
has penetrated into the pores of the restraint 102 during heating/cooling devices in a layer at or near either or both
formation of the mat of hydrate 114). Under normal oper surfaces of the restraint 102. A plurality of Pelletier or
ating conditions, the stability boundary will be located 10 magnetocaloric devices may be activated selectively so as to
somewhere within the mat of hydrate 114 near the restraint cause localized heating and/or cooling of the restraint 102.
102. In other words, the vessel 104, restraint 102, and More specific apparatus 200 for practicing the present
temperature and pressure conditions within the apparatus invention is illustrated in FIG. 3. The apparatus 200 is
100 are configured and set such that the hydrate will be configured to produce fresh water on a large scale using
stable within the hydrate formation region 106 and will 15 positively buoyant hydrate to do so. The apparatus 200
become unstable (and hence tend to dissociate) at a location includes many components that are the same as or similar to
somewhere within the mat of hydrate 114. (Hydrate that is those shown in apparatus 100, including a vessel 204 that is
not located at the stability boundary may also be unstable, divided into a hydrate formation region 206 and a fresh
but it generally will dissociate only if it is located at the free water collection region 208 by means of a porous and
edges of the pressure-sealing layer 118.) permeable hydrate asymmetric restraint 202. The apparatus
The “formation side' of the mat of hydrate 114 will tend 200 is shown in FIG. 3 in steady state operation, i.e., with
to be warm because hydrate formation is exothermic. Con a pressure-sealing layer of hydrate 218 completely formed
versely, the hydrate that is dissociating on the opposite side on the restraint 202.
of the mat 114 will consume heat because hydrate dissocia Gas G is injected into the vessel 204 through gas Supply
tion is endothermic. The amount of heat produced when the 25 pipeline 235. The pipeline 235 may include a manual,
hydrate forms and the amount of heat required for the automatic, or remotely controlled valve or valve assembly.
hydrate to dissociate are about equal, but of opposite sign. Input water to be treated W (i.e., purified) is supplied to the
Thus, dissociation of the hydrate will absorb heat and cool vessel 204 through input water pipeline 240, and hydrate 112
the mat of hydrate and the warm hydrate produced in the forms upon mixing of the gas G and the input water W.
hydrate formation region 106. 30 Residual water or brine is removed from the vessel through
However, because heat will be transported away from the drain line 239. A separator 242 (e.g., a screen) is connected
system in the warmed residual brines “left over from to the drain line 239 to prevent hydrate from being removed
hydrate formation as they are removed from the system (not from the apparatus 200.
illustrated), as well as in the water and gas evolved during As described above in the context of FIGS. 1 and 2,
dissociation, the overall vessel 104 may act as a heat sink, 35 hydrate will accumulate against the restraint 202 and form a
especially in the immediate vicinity of the gas hydrate. hydrate mat which, upon reduction of pressure in the region
Therefore, the demand for heat required to drive hydrate 208, will dissociate into freshwater and the hydrate-forming
dissociation may exceed the rate at which heat can be gas, both of which pass through the restraint into region 208.
provided by the exothermic formation of solid hydrate and Fresh product water PW is withdrawn through fresh water
the rate at which it will be available in the hydrate formation 40 drain line 261, and gas G is removed through gas line 263.
region 106. Thus, it may be necessary to heat the restraint The recovered gas may be processed (for example, by drying
102 to a certain extent to ensure that water ice does not form and recompressing) before it is used in another cycle of
and clog the restraint. This may be particularly true when hydrate formation or before it is passed on to another user
dissociation rates (i.e., heat consumption rates) are fast. for other purposes.
Conversely, it may be necessary to cool the restraint 102 to 45 The gas typically is dried before re-use to prevent gas
encourage hydrate growth (especially, for example, during hydrates from forming in the gas lines. However, if the gas
system start-up). is compressed and injected back into the apparatus 200
Heating and/or cooling may be provided by circulating a immediately, drying the gas may not be necessary because,
heating or cooling fluid in tubes 126 integral with the since the gas is heated during recompression, hydrate will
restraint 102 or in tubes (not shown) attached to the restraint, 50 not likely form in the short period of time that it takes to
or by any other conventional heating means such as resis re-inject the gas into the vessel 204. (If so desired, the
tance heating or heating/cooling using Pelletier thermoelec compression process may be specifically designed to heat
tric effect or magnetocaloric devices. As illustrated in FIG. the gas to a specific temperature at which hydrates will not
2, tubes 126 are provided in the restraint 102 to provide form.) Alternatively, if the gas is not to be re-injected into
passages for heating and/or cooling fluids to flow through or 55 the vessel immediately, the gas lines 263 may be provided
for the installation of heating/cooling devices. The tubes 126 with any sort of conventional Supplemental warming appa
are disposed between the pores 120 in the restraint 102. The ratuS.
tubes 126 are arranged such that they cover a substantial Another embodiment 300 of an apparatus for practicing
portion of the surface area of the restraint 102. The tubes 126 the invention is illustrated in FIG. 4. Apparatus 300 is
may be provided as a single, closed-loop circuit traversing 60 configured to produce fresh water on a large scale using
substantially the entirety of the restraint 102, or they may be negatively buoyant hydrate to do so. The apparatus 300
provided as multiple sets of tubes 126 arranged in a number includes many components that are the same as or similar to
of shorter heating/cooling loops such that each of the shorter those shown in apparatus 100 or 200, including a vessel 304
loops traverses only a portion of the restraint 102. If mul that is divided into a hydrate formation region 306 and a
tiple, shorter heating/cooling loops are employed, they may 65 fresh water collection region 308 by means of a porous and
be selectively activated to cause portions of the restraint 102 permeable hydrate asymmetric restraint 302. The apparatus
to be selectively heated or cooled depending on localized 300 is shown in FIG. 4 in steady state operation, i.e., with
 US 7,094,341 B2
11 12
a pressure-sealing layer of hydrate 318 completely formed asymmetric restraint 402 may increase the efficiency or
on the restraint 302. In contrast to apparatus 200, however, throughput of a water purification (or other liquid separa
in apparatus 300, the hydrate formation region 306 is located tion) process. Additionally, using a larger restraint facilitates
at the top of the vessel 304, and negatively buoyant hydrate heat transfer and may reduce the need to balance the heat
sinks downward onto the restraint 302. Thus, the pressure demand of dissociation.
sealing layer 318 is formed on top of the restraint 302 in this A more specific water purification system 500 which uses
embodiment of the invention. Hydrate will dissociate from a contoured hydrate asymmetric restraint 502 and hydrate
the bottom of the hydrate mat, with fresh water and gas that is less dense than the saltwater from which it forms (i.e.,
flowing or being drawn (by reduced pressure) down through which is positively buoyant) is illustrated in FIG. 6. The
the restraint; consequently, fresh water collection region 308 10 restraint 502 is generally U-shaped in cross-section and is
is located at the bottom of the vessel 304. Fresh product immersed in a vessel 504 such that the restraint 502 is
water PW is removed via drain line 361, and gas G is positioned substantially in the center of the vessel 504. The
removed via gas line 363. restraint 502 includes a non-porous endcap portion 550,
In apparatus 300, gas G is injected into the vessel 304 which constitutes the portion of the restraint 502 having the
through gas pipeline 335. The gas pipeline 335 may include 15 most significant curvature. The curvature of the endcap
a manual, automatic, or remotely-controlled valve or valve portion 550 may affect the strain field in a mat of hydrate that
assembly. Input water to be treated W (i.e., purified) is forms on it and thus may change the manner in which that
supplied to the vessel 304 through input water pipeline 340, mat of hydrate forms and dissociates. However, because
and hydrate 112 spontaneously forms upon mixing of the gas endcap portion 550 is non-porous, and therefore fresh water
G and the input water W. Residual waters or brines are and gas do not pass through it, any localized differences in
removed from the vessel through drain line 339. A separator hydrate formation and dissociation on the endcap portion
342 (e.g., a screen) is connected to the drain line 339 to 550 will not affect the overall desalination or separation
prevent solid hydrate from being removed from the appa process. Therefore, if hydrate forms on the endcap portion
ratus 300. 550, it may simply be allowed to accumulate.
In the embodiments 100, 200, and 300 illustrated in FIGS. 25 A centrally located water injection pipe 506 supplies
1–4, the freshwater collection regions 106, 206, and 306 and water to be treated into the vessel 504, which water to be
hydrate formation regions 108, 208, and 308 are depicted as treated exits the water injection pipe 506 via injectors 508
being substantially the same size. However, in other embodi that are located away from the center of the vessel 504. As
ments, the fresh water collection regions 106, 206, and 306 illustrated, the water injection pipe 506 extends through the
may be smaller than the hydrate formation regions 108, 208, 30 interior compartment or lumen 516 of the contoured restraint
and 308, respectively. 502. The injectors 508 may be nozzles designed to provide
A hydrate asymmetric restraint according to the invention a specific water velocity and direction that will form a
may also be contoured and may be used without a vessel, hydrocyclone (i.e., a high-speed, rotating watermass that
e.g., by being immersed in an aqueous Saline environment as introduces centrifugal forces), or they may simply be
illustrated, for example, in FIG. 5. In particular, the restraint 35 unmodified ends of the water injection pipe 506.
402 in this embodiment 400 is shaped (for example, Gas supply apparatuses 510 line the walls of the vessel
U-shaped in cross-section) so as to form an interior lumen or 504. The gas supply apparatuses 510 include panels 513
compartment 404 in which low-pressure hydrate dissocia which each have a plurality of nozzles or slots 514 through
tion conditions can be established. The restraint 402 is which hydrate-forming gas G is Supplied to the interior of
constructed from any of the materials noted above and may 40 the vessel 512. The angles of the gas nozzles 514 are set to
have the internal pore and tube configuration shown in FIG. optimize the amount of flow turbulence for hydrate forma
2. Hydrate (not shown) is caused to form in the body of fluid tion. In apparatus 500, formation of hydrate on the restraint
in which the contoured restraint is immersed by injecting 502 is facilitated by rotating the water to be treated using a
hydrate-forming gas into the body of fluid under pressure hydrocyclone or other conventional mechanical rotating
and temperature conditions conductive to forming hydrate 45 means (not shown). In this embodiment, the water injectors
So as to cause hydrate to form generally in the vicinity of the 508 are used to create a hydrocyclone, but another set of jets
contoured restraint. A pressure-sealing mat of hydrate 406 is (not shown) may also or alternatively be provided for this
induced to form on the exterior surface 408 of the restraint purpose. Rotating the water (e.g., by creating a hydrocy
402; pressure inside the compartment 404 is lowered; and clone) creates centipetal acceleration, which, because the
hydrate adjacent to the exterior surface 408 of the restraint 50 hydrate is less dense than the input saltwater, causes formed
402 dissociates, thereby allowing gas and fresh water hydrate to migrate radially inward toward the restraint 502,
released by the dissociating hydrate to flow (or be drawn by i.e., away from the walls of the vessel 504 where it might
the reduced pressure) into the compartment 404, i.e., in the otherwise encrust the apparatus. Unwanted residual brines in
direction indicated by arrows F. the apparatus 500, which brines remain after the hydrate
The open end of the compartment 404 is sealed by a plate 55 forms and extracts fresh water from the saline water to be
412 or other structure, and fresh water and gas are drawn out treated, are removed from the apparatus 500 at exit points
through pipe 414 connected to the plate 412. The extracted 520, and dissociated gas and fresh water are collected from
fresh water and gas are then transferred to a vessel down the top of the interior compartment 516.
stream (not shown), where they are separated. As in the The design and placement of the water injection pipe 506
embodiments 100, 200, and 300 described above, the 60 provides certain thermodynamic advantages. As noted above
restraint 402 may be heated or cooled to induce hydrate with respect to other embodiments, fresh water released as
formation or to maintain the rates of hydrate formation and the hydrate dissociates, which flows through the restraint
dissociation at desired levels. 502 and into the interior compartment 516, will be cold
Advantageously, a contoured restraint Such as restraint because dissociation is an endothermic process. Because the
402 provides a larger Surface area on which hydrate accu 65 water injection pipe 506 passes through the interior com
mulates and dissociates than a Substantially flat restraint of partment 516 and is exposed to the cold fresh water, the
similar widthwise dimensions. Therefore, using a contoured water injection pipe 506 functions as a heat exchanger to
 US 7,094,341 B2
13 14
cool the water to be treated as it flows through the water in a free-standing tower extending above the ground—where
injection pipe 506 and out through the injectors 508. That is the weight of the water column generates Sufficient pressure
advantageous because cooling the water to be treated facili for hydrate to form. An example of such an embodiment 800
tates hydrate formation and provides a natural density gra that is suitable for shaft installation and that is configured to
dient. Conversely, the cool, fresh, product water within the 5 be used with positively buoyant hydrate (either perse or in
interior compartment 516 will absorb heat from the warmer toto) is illustrated in FIG. 8.
water flowing through the water injection pipe 506 which, in The apparatus 800 is constructed in a shaft 803 extending
turn, helps warm the restraint 502 and encourages hydrate down into the ground 805. The shaft is deep enough for the
encrusted on the restraint to dissociate. Although illustrated weight of a column of water of depth equal to the depth of
as a Substantially straight pipe in FIG. 6, the water injection 10 the shaft to generate water pressure Sufficient to cause
pipe may be coiled or contoured to increase its Surface area hydrate to form spontaneously when hydrate-forming gas is
and, consequently, its effectiveness as a heat exchanger. injected into the water to be treated (assuming the water to
Another embodiment 600 of an apparatus for practicing be treated is at sufficiently low temperature).
the invention is illustrated in FIG. 7. In this apparatus 600, The shaft 803 has a generally conical solid partition 828
which is configured for use with negatively buoyant hydrate 15 extending across it, and the solid partition 828 divides the
(i.e., hydrate that is more dense than the saline input water shaft into a lower shaft portion 802 and an upper shaft
to be treated), a substantially tubular hydrate asymmetric portion 808. The lower shaft portion 802 has a hydrate
restraint 602 is positioned within a vessel 604, with the asymmetric restraint 804 extending across it, and the hydrate
restraint 602 being arranged generally concentrically with asymmetric restraint 804 is constructed from any of the
the vessel and sized such that it lies generally proximate to 20 materials identified above in connection with the hydrate
the walls of the vessel but with space therebetween as asymmetric restraint 102 in FIG. 1. Preferably, the hydrate
illustrated. Fresh water collection region 616 is defined asymmetric restraint has an internal pore and tube configu
between the exterior surface 618 of the restraint 602 and the ration like that shown in FIG. 2 in connection with the
interior wall of the vessel 604. Hydrate-forming gas and hydrate asymmetric restraint 102 shown in FIG. 1. The
water to be treated are injected into the center of the vessel 25 restraint 804 divides the lower shaft portion 802 into a
604 by means of central distribution piping 606, which hydrate formation region 806 and a fresh water and gas
includes gas distribution piping 608 and water distribution collection region 824. A bypass pipe 810 extends from the
piping 610. (Gas may also be delivered via gas nozzles (not upper shaft portion 808 to the lower shaft portion 802 (in
shown) that extend from the walls of the vessel 604 through particular, the hydrate formation region 806) and establishes
the restraint 602.) Water to be treated W and gas G enter the 30 open fluid communication between the upper shaft portion
interior compartment 608 bounded by the restraint 602, and 808 and the lower shaft portion 802 (hydrate formation
hydrate forms and accumulates on the interior surface 614 of region 806).
the restraint 602. Fresh water and gas released upon disso Water input pipe 840 delivers input water to be treated to
ciation of the hydrate pass radially outward through the the installation 800 from a source of water to be treated (not
restraint 602 and into the fresh water collection region 616. 35 shown). Preferably, the apparatus 800 is located relatively
Gas removal piping 620 and fresh water removal piping 622 close to the body of water from which the water to be treated
transport the dissociated gas and fresh water away from the is extracted, as that should reduce pumping costs for obtain
water collection region 616, and brine removal pipe 624 ing the water to be treated. It is also advantageous if the top
transports unwanted residual brines from the vessel. of the apparatus 800 (e.g., ground level 805) is at a level that
Similar to apparatus 500, apparatus 600 uses a hydrocy- 40 is at or below the surface of the body of water from which
clone or other mechanical rotating means (not shown) to the input water to be treated is obtained. That, too, can
force the forming hydrate outward, towards the interior reduce pumping costs (e.g., by effectively creating a siphon
surface 614 of the restraint 602. In this embodiment 600, to help draw water from the body of water from which water
however, the hydrate migrates radially outward as the water to be treated is obtained and to deliver it to the installation
rotates because it is more dense than the saline input water 45 800).
to be treated. Jets of water from the water distribution piping The water input pipe 840 fills the upper shaft portion 808
610 may drive the hydrocyclone, or another set of jets (not with water to be treated, which water to be treated flows
shown) may do so. Because the embodiment 600 is config through bypass pipe 810 and into the hydrate formation
ured for use with negatively buoyant hydrate, the gas region 806. (Although the water input pipe 840 could pass
distribution piping 608 should be configured to inject the 50 directly into the bypass pipe 810 and the upper shaft portion
hydrate-forming gas G in small bubbles such that there is 808 could be left unfilled (“dry”), it is easier to control
little residual gas in the formed hydrates. That is because, as system operation (e.g., water input and hydrate formation
explained above, large amounts of residual gas in the rates) when a “reservoir from which water to be treated can
hydrate could cause the overall hydrate masses to be posi be drawn and passed to the hydrate formation region, i.e., by
tively buoyant instead of negatively buoyant. Gas should 55 filling the upper shaft portion 808.) Because the bypass pipe
also be injected as close to the hydrate formation region as 810 establishes open fluid communication between the
possible to prevent gas from “pooling around the gas upper shaft portion 808 and the hydrate formation region
distribution piping 608. 806, and because the upper shaft portion 808 is not pressure
In the embodiments described above, the required sealed and therefore is in pressure balance with atmospheric
hydrate-forming water pressures are mechanically generated 60 pressure at its upper end, water pressure within the hydrate
within the vessels, e.g., by parametric pumping (not shown) formation region 806 will be equal to that generated by the
or by any other form of mechanically-generated compres weight of a column of water of depth equal to that of the
sion (not shown). However, water purification apparatus hydrate formation region 806 (assuming the upper shaft
utilizing a hydrate asymmetric restraint may be installed in portion 808 is completely filled to ground level with water
an environment which provides a column of water—either 65 to be treated).
free or unbounded, as in the open ocean, or bounded or In operation, input water to be treated W is supplied to the
restrained, as in a shaft extending down into the ground or apparatus 800 via input water pipe 840, as noted above; fills
 US 7,094,341 B2
15 16
the upper shaft portion 808; flows through bypass pipe 810; collection region 824 will be at a pressure that is lower than
and fills the hydrate formation region 806. Hydrate-forming the pressure of the input water to be treated at the same level
gas is Supplied to the apparatus 800 via gas input pipe 822. within the bypass pipe 810. Accordingly, the level of fresh
Gas pump/directional control unit 824a directs incoming water in the fresh water extraction pipe 848 will not auto
hydrate-forming gas G received from gas input pipe 822 matically equilibrate with the level of water in the upper
downward to be injected into the hydrate formation region shaft portion 808. Therefore, pumps 850 are provided along
806. There, it mixes with the water to be treated under the length of fresh water extraction pipe 848 in order to help
temperature and pressure conditions (established by the remove fresh water from the fresh water collection region
weight of the water column above the hydrate formation 824.
region) appropriate for hydrate H to form spontaneously, as 10
Hydrate-forming gas which has been released upon dis
indicated in FIG. 8.
Because the hydrate is positively buoyant—either sociation of the hydrate, on the other hand, will bubble up to
because the hydrate, perse, is positively buoyant or because the vertex of the conical solid partition 828 and rise through
the hydrate, perse, is negatively buoyant but is formed in an gas removal pipe 820. Gas pump? directional control assem
incomplete manner Such that gas bubbles trapped within 15
bly 824b controls the flow of gas that has been released from
hydrate shells are, in toto, positively buoyant it will rise the hydrate and that has risen through gas pipe 820. In
particular, control assembly 824b directs some or all of the
within the hydrate formation region 806 and accumulate gas to a downstream application (e.g., to a gas-fired power
along the undersurface of the hydrate asymmetric restraint station or fuel cell assembly) via gas line 830 and/or some
804 in the same manner as described above with respect to or all of the gas to gas recycling unit 852, which reprocesses
the embodiments shown in FIGS. 1 and 3. Highly saline the gas by drying and/or repressurizing it for reuse in further
residual brines remaining after the hydrate forms are hydrate formation cycles.
removed from the apparatus 800 via brine removal pipe 832, As indicated above, the hydrate asymmetric restraint 804
also removing a portion of heat generated during the exo
thermic formation of the hydrate with it. (and, therefore, the solid mat of hydrate 818) is located
As is understood in the art, for a given temperature, 25
significantly below the hydrate stability pressure boundary
hydrate will remain stable over a range of pressures or, in the 826. Therefore, it is necessary to reduce pressure in the fresh
context of water weight-induced pressures, over a range of water collection region 824; depending on the vertical
distance between the level of the restraint 804 and the
depths. Preferably, in a shaft-based embodiment such as that hydrate stability pressure boundary 826, the amount by
illustrated in FIG. 8, the hydrate asymmetric restraint 804 is which the pressure in the fresh water collection region 824
positioned well below the shallowest depth at which hydrate 30
will remain stable for any given hydrate-forming gas needs to be reduced can be substantial. The pumps 850 in the
expected to be used in the apparatus, i.e., significantly fresh water extraction line 848 can create suction for pres
deeper than the hydrate stability pressure boundary 826. If sure reduction within the fresh water collection region 824,
desired, however, the lower shaft portion 802 and the and one or more pumps located in-line in the gas recovery
restraint 804 may be configured so that the depth of the 35 pipe 820 will also help lower pressure within the fresh water
restraint 804 can be adjusted either up or down, e.g., by collection region 824.
sliding or by removal and repositioning. That allows the Finally, with respect to the embodiment 800 illustrated in
depth of the restraint 804 to be changed as necessary to keep FIG. 8, while the conical configuration of the solid partition
hydrate at a pressure-depth at which gas hydrate will form 828, with the vertex located at the top of the partition, helps
and remain stable for any given hydrate-forming gas or gas 40 direct the released gas into the gas pipe 820 to be removed
mixture that is used with the apparatus. Preferably, the from the apparatus, that configuration also helps Support the
restraint 804 is located sufficiently below the hydrate sta weight of the input water in the upper shaft portion 808. As
bility boundary 826 for hydrate to form relatively rapidly. explained above, the pressure within the fresh water collec
(AS is known in the art, for a given temperature, the rate at tion region 824 will be lower than that within the bypass
which hydrate forms tends to decrease as the pressure depth 45 pipe 810 at the same depth level, which is generally the same
of the region where hydrate is formed approaches the as the pressure at the bottom of the upper shaft portion 808.
pressure-depth of the hydrate stability pressure boundary Therefore, there will be a pressure differential across the
826.) Solid partition acting in the downward direction, and the
The embodiment 800 is illustrated in FIG. 8 under steady upwardly oriented conical shape of the solid partition 828
state operating conditions. Therefore, it is illustrated with a 50 helps the solid partition withstand that pressure differential.
solid mat of hydrate 818 having accumulated over the lower (Conversely, the weight of the water in the upper shaft
surface of the restraint 805 to form a pressure seal or barrier portion 808 counteracts pressure forces that the fresh water
extending across the entire cross-sectional area of the lower in fresh water collection region 824 exerts on the partition
shaft portion 802. Under steady state operating conditions, 824; that pressure counteraction is another benefit of filling
hydrate will dissociate from the portions of the mat of 55 the upper shaft portion 808 instead of leaving it dry.)
hydrate 818 adjacent to the restraint 804. Purified water and As noted above, apparatus 800 is specifically configured
gas released upon dissociation of the hydrate pass through to utilize positively buoyant hydrates. However, a shaft
the porous, permeable restraint 804 and into the fresh water based apparatus may be configured with a centrifugal force
collection region 824 located above the hydrate asymmetric type device, as shown and described with respect to FIGS.
restraint 804 and freshwater is removed from the freshwater 60 6 and 7, such that either positively buoyant or negatively
collection region 824 via fresh water extraction pipe 848. buoyant hydrates may be used and formed on a contoured
Because the solid mat of hydrate 818 and the hydrate restraint. In that case, the contoured restraint would likely
asymmetric restraint 804 together effectively form a pres have significantly more surface area than the restraint 804
Sure seal or barrier across the cross-sectional area of the shown in FIG. 8. Such a configuration would also allow for
lower shaft portion 802, and because the restraint 804 is a 65 a smaller hydrate formation region 812. In either case (i.e.,
flow restrictor and, as such, causes a pressure drop as water apparatus configured for use with either positively buoyant
and gas flow through it, the fresh water in the fresh water or negatively buoyant hydrate), the restraint would be heated
 US 7,094,341 B2
17 18
or cooled to facilitate hydrate formation, and may have the 1004. The vents 1004 are relatively small in size and allow
heat-exchanging tube configuration shown in restraint 102 in the residual brines to leave the apparatus 1000 at a relatively
FIG 2. slow rate. This relatively slow rate of residual brine expul
Another embodiment of the invention 900 is illustrated in sion allows a stable hydrocyclone to be maintained. Once
FIG. 9. Apparatus 900 is submerged in a marine environ- 5 the brines are expelled, the natural difference in the buoy
ment, at a pressure depth at which gas hydrates form ancy of the residual brines (which is greater after tempera
spontaneously. Preferably, a number of apparatuses 900 are ture equilibration) and the temperature of the residual brines
Suspended from a frame that is attached to a ship or a (which is initially higher than that of the surrounding water)
semi-submersible platform. That way, the depth of each will cause the residual brines to flow away from the appa
apparatus 900 may be individual set to provide for optimum 10 ratus, even in very low-current conditions.
hydrate-forming conditions. It should be noted that the “residual brines' created as a
The apparatus 900 is formed of a rigid material such as result of the processes described above need not be highly
heavy plastic that has an anti-fouling coating. A restraint 904 concentrated. In fact, the processes described above are
is secured to the interior walls of apparatus 900, and capable of recovering significant amounts of fresh water
apparatus 900 is illustrated as operating under steady-state 15 from seawater while producing a brine that, without mixing,
conditions, i.e., with a pressure sealing layer of hydrate 906 has a Salinity and Suspended Solids content that is within or
formed on the underside of the restraint 904.
The restraint 904 and pressure sealing layer of hydrate very close to the ranges acceptable to marine life. (Because
of the relatively low cost and high efficiency of processes
906 divide the apparatus 900 into a hydrate formation region according to the invention as compared to conventional
908 and a fresh water and gas collection region 910. The 20
hydrate formation region 908 is open to the surrounding sea desalination
available
processes, there is no need to extract all of the
fresh water from a given volume of seawater.)
at its lower end. Therefore, opening 912 allows seawater (or Therefore, an apparatus
other input water to be treated in which the apparatus 900 is employed even in areasaccording where
to the invention may be
marine parks and other
submerged) to enter the hydrate formation region 908. protected marine wildlife areas exist.
Hydrate formation region 908 may be laterally extended to 25
allow residual brines remaining after hydrate forms to Embodiments of the invention may be used in non-marine
equilibrate in temperature with respect to the Surrounding environments, e.g., to separate water from other dissolved or
seawater, which will increase the density of the residual Suspendeda materials in environments that would not usually
brines and cause them to sink out through opening 912 and provide favorable environment for hydrate formation.
into the Sea. 30 More specifically, a thermally assisted or refrigerated
A piping system (not shown in detail) similar to that used restraint
suitable
may be configured and adapted to create conditions
for hydrate formation and can be used to perform
in apparatus 800 may be used to supply hydrate-forming gas
to the apparatus 900 and to remove dissociated gas and using desalination or separation processes. Hydrate formation
product water from apparatus 900. Piping to remove disso slightlya from thermally assisted asymmetric restraint differs
the method of hydrate formation using the
ciated gas and product water (again, not shown) will be 35 previously described, non-assisted restraints. In particular,
connected to port 914, and the water removal pipe will whereas with the hydrate
extend further into the fresh water and gas collection region above hydrate is formed inasymmetric restraints described
910 than the gas collection pipe. Fresh water and gas rounding the restraint and Subsequently isenvironment
the aqueous Sur
deposited on or
collection region 910 may be extended laterally to allow the
collected fresh product water and gas to equilibrate in 40 accumulates on the restraint, with a thermally assisted
temperature with the surrounding seawater. Collected fresh restraint,
from an
hydrate is induced to form directly on the restraint
aqueous, non-aqueous, or gaseous environment
product water and gas may be pumped directly to the Surface
or, if a number of apparatuses 900 are used simultaneously, Such as wet gas.
the fresh water and gas may be collected in a number of FIG. 11 illustrates one embodiment 700 of a refrigerated
Smaller riser pipes before passing to the Surface. 45 or thermally assisted restraint. One or more such thermally
Another embodiment of the invention 1000 for marine assisted restraints 700 may be placed in an environment such
applications is illustrated in FIG. 10. The embodiment 1000 as an aqueous environment that is maintained at appropriate
“combines' features of embodiment 500 (FIG. 6) with the hydrate-forming pressures, including in pressurized vessels,
open-ended features of embodiment 900 (FIG. 9). Like shafts, towers, or marine installations, with the number of
embodiment 500, embodiment 1000 uses a hydrocyclone or 50 restraints 700 used depending on the environmental condi
other form of rotational water movement to facilitate hydrate tions and desired throughput of the process.
formation and accumulation on the restraint 502. Unlike the Thermally assisted restraint 700 includes a formation
free-standing embodiment 500, however, embodiment 1000 portion 702, which is a contoured, porous restraint, and the
is Submerged at a pressure depth at which hydrate forms general configuration of formation portion 702 is similar to
spontaneously. The components of embodiment 1000 that 55 that of restraint 502 of embodiment 500. Formation portion
are used to Supply hydrate-forming gas are essentially the 702 has an interior structure similar to that illustrated in FIG.
same as those shown in FIG. 5. (For clarity, the top of 2 and, in particular, includes internal tubes which are used to
apparatus 1000 is not shown in FIG. 10.) cool the formation portion 702 to an appropriate hydrate
Input water to be treated enters the hydrate-forming forming temperature. Depending on whether a conventional
region of the apparatus from the Surrounding environment 60 refrigeration system, thermoelectric, or magnetocaloric
through aperture 1012 and is caused to rotate to generate a cooling system is used, the tubes may be filled with a
hydrocyclone. Hydrate that is less dense than the seawater circulating coolant fluid or they may serve as cavities into
(i.e., that is positively buoyant) forms and accumulates on which thermoelectric or magnetocaloric devices may be
the restraint 502, and residual brines move centrifugally installed. A connecting pipe assembly 704 is connected to
toward the walls of apparatus 500. In contrast to embodi- 65 the interior compartment of the formation portion 702, and
ment 500, in embodiment 1000, the residual brines are the connecting pipe assembly 704 is coupled to a port in the
expelled back into the marine environment through vents walls of the containing vessel 706 such that, in operation,
 US 7,094,341 B2
19 20
fresh water and dissociated gas may be removed from the it. Additionally, a thermally assisted restraint 700 may be
compartment in the formation portion 702. used for processes such as sewage treatment in which
When a thermally assisted restraint 700 is used to extract removing excess water is a typical or desired first treatment
water from an aqueous environment, hydrate-forming gas is step.
dissolved in the aqueous medium in which the restraint is 5 When the aqueous solution to be treated is a relatively
immersed to Saturated or Super-saturated conditions, and dense slurry, the slurry should be agitated, thereby causing
hydrate is induced to form directly on the thermally assisted it to pass over the restraint 700 in bulk so as to prevent the
restraint 700 by refrigerating the restraint 700. A shroud or slurry from dewatering near the restraint 700 and creating a
simple water duct may be used to control the flow of water barrier to further water movement. Moreover, if a gas
across the restraint 700, or the restraint 700 may be specifi- 10 containing material Such as sewage is used with the ther
cally contoured to optimize water flow across its surface in mally assisted restraint 700, the gas contained in the material
a particular environment or vessel. itself may be used, at least in part, as the hydrate-forming
The presence of large amounts of hydrate-forming gas in gas, either with or without the use of additional gas.
the region where hydrate formation is induced promotes the Alternatively, a thermally assisted restraint 700 may be
growth of solid gas hydrate on the surface of the hydrate- 15 used in a primarily gaseous or non-aqueous environment in
forming portion 702 with few inclusions, and solubility which water is to be extracted from the non-aqueous or
gradients will cause the dissolved hydrate-forming gas to gaseous medium. One example of Such a gaseous or non
migrate toward the region in which hydrate is forming. aqueous environment where water often needs to be
Further, hydrate-forming gas is added into the aqueous removed is in a hydrocarbon well. As is known, extracts
medium at a location where temperatures are too high or 20 from hydrocarbon wells may be warm or hot before or
pressures are too low for the formation of hydrate, and the immediately following extraction, and in many cases may
dissolved (to saturated or supersaturated levels) hydrate have a temperature in excess of 100° C. After the extracted
forming gas migrates toward the thermally assisted restraint hydrocarbons are cooled by heat exchange with the Sur
700, where it crystallizes. Additional hydrate-forming gas rounding environment (e.g., seawater in the case of Subsea
may be added as necessary. 25 wells), the resultant “wet’ hydrocarbons, which may still be
The thermally assisted restraint 700 may be combined at a relatively warm temperature and in either a liquid
with a localized heating apparatus in an environment where (non-aqueous) or gaseous state depending on pressure and
“plugs” of hydrate or water ice form at unwanted locations. temperature conditions, can be dewatered by exposing them
If a localized heating apparatus is used in combination with to a thermally assisted restraint 700. (As will be appreciated
a thermally assisted restraint 700, the heating apparatus is 30 by those having skill in the art, the water to be removed will
used to melt the “plugs” of hydrate or water ice so that be in either a liquid or gaseous state, depending on pressure
hydrate formation can be limited or restricted to the forma and temperature conditions. In this regard, "dewater” is a
tion portion 702 of the restraint 700. term that will be understood by those having skill in the art
Once hydrate has formed on the surface of the formation as referring generically to removing H2O from a medium,
portion 702, pressure in the interior of the formation portion 35 regardless of whether the HO is in a liquid orgaseous state.)
702 is lowered by an appropriate pump (not shown) that is Localized cooling at the surface of restraint 700 will cause
coupled to the connecting pipe assembly 702. Hydrate that hydrate to form on the formation portion 702 of the restraint
is closest to the surface of the formation portion 702 is thus 700. This restraint-based dewatering process substantially
caused to dissociate, and the resultant fresh water and gas prevents hydrate formation and provides flow assurance in
are drawn through the restraint and into the interior of it. 40 high-pressure pipelines and other hydrocarbon apparatus.
They are then withdrawn from the formation portion 702 In certain applications where a thermally assisted restraint
through the connecting pipe assembly 704. The fresh water 700 is used, it may be desirable for hydrate formed on the
should be withdrawn at a moderate rate such that brines of restraint actually not to dissociate. For example, in a hydro
extremely high Salinity or mineral content do not form carbon dewatering process like the process described above,
around the restraint 700. 45 simply forming hydrate on the restraint 700 may be suffi
Advantageously, with a thermally-assisted restraint 700, cient to remove water from the Surrounding medium, i.e.,
there is no need to cool an entire volume of water (when the there may be no need to cause the hydrate to dissociate. In
thermally assisted restraint 700 is used in an aqueous other separation or dewatering applications in which the
environment) in order to form hydrate. Instead, it is only water content in the Solution or Suspension is relatively low,
necessary to cool the volume of water that is to form hydrate, 50 the dissociation process may be initiated at intervals (e.g.,
i.e., the volume of water immediately near the surface of the every few minutes or hours) in order to allow enough time
formation portion 702. This may result in significant cost for a sufficiently thick mat of hydrate to accumulate on the
savings. Additionally, hydrate is induced to crystallize on the restraint 700 before initiating dissociation.
formation portion 702 of the restraint 700 such that it Another example of a situation where either no dissocia
contains essentially no included Saline water, and this results 55 tion or “delayed dissociation is preferable is when it is
in product water with very low salinity. desired to fill a vessel as completely as possible with hydrate
The thermally assisted restraint 700 may also be used for in a relatively short period of time. In this situation, heat may
other applications in which it is desired to remove water or be removed from the vessel as a whole most effectively by
moisture from the environment in which the restraint 700 is installing within the vessel a number of thermally assisted
immersed besides other than desalination. For example, a 60 surfaces upon which the hydrate is crystallized. This will
thermally assisted restraint 700 may be used to concentrate allow the water or air courses between the thermally assisted
and remove dissolved or Suspended solids such as metals surfaces to remain open until the vessel is nearly full of
from an aqueous solution (e.g., a metaliferous brine) if the hydrate and will provide optimal circulation within the
water in the solution is used to form hydrate on the restraint vessel as a whole during the hydrate forming event. Yet
700 and is subsequently caused to dissociate through the 65 another example is a situation where a sample of Solid
restraint 700. In other words, the restraint is used to “draw hydrate that forms naturally upon a refrigerated Surface is
moisture out of the solution by using hydrate to “sequester required to be obtained. For example, samples of hydrate
 US 7,094,341 B2
21 22
may be used for carrying out thermodynamic, chemical, hydrate removal apparatus 1300 shown in FIG. 13 consists
and/or crystallographic analyses, among other uses, which of a series of segments of flexible piping 1306 with a
are not possible to conduct within the vessel (which may be thermally assisted restraint assembly 1312 positioned on one
a pipeline or other apparatus in which hydrate naturally end or, as shown, with other restraint assembly segments
forms). 1312 along its length. The apparatus 1300 may also include
Where dissociation is later desired or required, it may be a number of high-frequency acoustic sources 1320 of the
accomplished in the manner previously described using same or different frequencies. Once the apparatus 1300 has
apparatus such as that described above, e.g., a contoured, been inserted into a hydrocarbon pipeline (not shown), the
thermally assisted restraint 700 as described above, or acoustic sources 1320 allow the apparatus 1300 to be located
within the vessel as a whole, in which case separation of the 10 within the pipeline using known hydrophone or microphone
hydrate-forming material and the water will take place triangulation techniques.
immiscibly, allowing each to be removed into separate One end of the apparatus 1300 is shown in greater detail
containers. Where, on the other hand, dissociation is not in FIG. 14. A restraint assembly 1312 is mounted on the
desired (e.g., where it is necessary or desirable to collect the outer surface of a segment of flexible pipe 1306. The
hydrate as such), simplified apparatus can be used. In 15 restraint assembly 1312 is constructed such that hydrate can
particular, pooling plates or panels that have a refrigeration form on an end face 1314 of the restraint 1312 and can then
system to cool the plates and remove heat—for example, but dissociate into an interior cavity of the restraint (not illus
not limited to, a series of internal tubes or conduits, as trated). The interior cavity of the restraint communicates
illustrated in and described above in connection with FIG. with the flexible piping 1306 such that dissociated water can
2—can be provided for the hydrate to form on. Such cooling be removed through the flexible piping 1306.
plates or panels may be configured to look generally like the When hydrate has formed in a pipeline or other vessel
thermally assisted restraint 700 shown in FIG. 11, but they from which it is desired to be removed, the apparatus 1300
need not be (and preferably are not) porous, and they is inserted into the pipeline or other vessel. In order to
preferably are not contoured (i.e., they preferably do not remove a hydrate “plug from a pipeline or other vessel, it
have an interior lumen, chamber, or cavity). 25 is usually necessary to melt the hydrate in situ. Therefore,
Further embodiments of a thermally assisted restraint may apparatus 1300 includes at least one heater element 1310 to
be contoured and adapted for installation in specific loca melt such unwanted hydrate “plugs.” The heater 1310 may
tions. For example, a contoured, thermally assisted restraint be any type of conventional heater Such as a resistance
assembly 1100 which is installed within a pipe 1102 is element heater, thermoelectric heater, or convection-type
illustrated in FIG. 12. The assembly 1100 includes a sub 30 heating element. However, it is preferable that the heater
stantially cylindrical, thermally assisted restraint 1104 1310 be activated in a controlled or directional manner so as
mounted concentrically within the pipe 1102. The diameter to conserve energy and to avoid heating the medium unnec
of the restraint 1104 relative to that of the pipe 1102 may essarily. Accordingly, one particularly advantageous type of
vary with the particular installation, although for purposes of heater 1310 is a focused microwave heater tuned specifically
illustration, the diameter of the restraint 1104 is shown as 35 to provide power output at a frequency Suitable for heating
relatively large with respect to that of the pipe 1102. water molecules.
The restraint 1104 divides the pipe 1102 into a radially Apparatus 1300 may be used in combination with a
outer compartment 1106, defined between the outer surface remotely operated vehicle (ROV) which is either tethered or
of the restraint 1104 and the inner surface of the pipe 1102, autonomous. The ROV would include at least one apparatus
and a radially inner compartment 1108, which is located in 40 1300, as well as pumps for maintaining the pressure in the
the interior of the restraint 1104. dissociation regions of the restraints 1316, power Supplies
With the apparatus 1100, either the outer compartment for the heater 1310, and tanks to store dissociated water. The
1106 or the inner compartment 1108 can function as the ROV would also include an appropriate propulsion system
hydrate formation region. However, it is advantageous for and, preferably, a sensing and visualization system. The
hydrate to be formed on the outer surface of the restraint 45 sensing and visualization system of the ROV may be visual,
1104, i.e., the surface bounding the outer compartment 1106, acoustic, or infrared, depending on the medium and the
because, with Such arrangement, the pressure-sealing layer particular ROV that is used. An ROV equipped with an
of hydrate (not shown) naturally crushes inward toward the apparatus 1300 could be inserted into a vessel or a pipeline
inner compartment 1108, which helps to maintain the pres to autonomously or semi-autonomously remove hydrate
Sure seal. 50 deposits within the pipeline or vessel and could be removed
In operation, relatively high temperature water is pumped from the pipeline or vessel from time to time to allow its
through the outer compartment 1106. Hydrate-forming gas tanks to be drained and other systems to be maintained.
is injected into the apparatus by gas injection assembly 1110. Finally, asymmetric restraint-based separation and puri
which is mounted on an exterior surface of the pipe 1102, fication processes and apparatuses may also be used with
and the thermally assisted restraint 1104 is cooled, thereby 55 other clathrates, many types of which are known. (Gas
causing hydrate to form and accumulate on the restraint hydrates are simply a particular class or species of clathrate,
1104 in the outer compartment. Pressure in the inner com in which water acts as the “host molecule and the hydrate
partment 1108 is subsequently lowered, thereby causing forming gas acts as the 'guest molecule.) For example,
inner portions of the hydrate on the restraint 1104 to disso phenol will form clathrates with many types of guest mol
ciate and the resulting water and gas to enter the inner 60 ecules, including hydrogen Sulfide, Sulfur dioxide, carbon
compartment 1108. The dissociated water and gas flow dioxide, carbon disulfide, hydrogen chloride, hydrogen bro
within the inner compartment 1108 and may be removed at mide, methylene chloride, vinyl chloride, and xenon. Urea
appropriate collection points along the pipe 1102 (not shown will form clathrates with a variety of linear organic com
in FIG. 12). pounds. Thiourea will form clathrates with linear and
In addition to desalination or other water purification 65 branched organic compounds.
applications, embodiments of the invention may also be If other clathrates are used with asymmetric restraints, the
used to remove hydrate from pipelines. For example, process temperatures may be higher than the process tem
 US 7,094,341 B2
23 24
peratures for gas hydrates. For example, phenol, urea, and an outlet for collecting said host molecules and an outlet
thiourea are solids at ambient temperature with melting for collecting said guest molecules from said collection
points of 40° C., 133° C., and 182° C., respectively. There region.
fore, using one of these compounds as the clathrate host 2. The apparatus of claim 1, wherein said means for
molecule, the process temperature would bee maintained at 5 inducing comprises means for heating the side of said
a temperature higher than the melting point of the host permeable restraint on which or against which said layer of
molecule such that the host molecule dissociates from the clathrate has formed or accumulated.
guest molecule and flows through the restraint. A thermally 3. The apparatus of claim 2, wherein said means for
assisted restraint such as restraint 700 may be used to heat heating comprises a series of heating passages disposed
or cool the host/guest mixture to induce a clathrate to form 10 within or on said permeable restraint.
on its surface; alternatively, the clathrate could be formed 4. The apparatus of claim 2, wherein said means for
away from the restraint and Subsequently caused to be heating comprises resistance heaters.
deposited on one of its Surfaces. 5. The apparatus of claim 2, wherein said means for
In a non-aqueous clathrate process, the clathrate may be heating comprises Pelletier thermoelectric effect heaters.
formed in one of several ways. If the host molecule is in 15
6. The apparatus of claim 2, wherein said means for
solid solution or solid form and is soluble in a solution of the heating comprises magnetocaloric devices.
guest molecule, the host molecule or a solid Solution con 7. The apparatus of claim 1, wherein said permeable
taining the host molecule may be dissolved in the guest restraint has a plurality of pores extending through it from
molecule solution, thereby causing clathrate to form. In said one side thereof to said opposite side thereof.
other cases, the mixture of host and guest molecules may be 8. The apparatus of claim 7, wherein said pores are
heated while the host molecule is dissolving in the guest conical, with the diameter of said pores decreasing from said
molecule solution. Alternatively, a solid host may be dis one side of said permeable restraint to said opposite side of
Solved in a solvent and mixed with the guest molecule. said permeable restraint.
While the invention has been described with respect to 9. The apparatus of claim 7, wherein said means for
certain embodiments, modifications and variations may be 25
inducing comprises means for reducing pressure within said
made by one of ordinary skill in the art. All such modifi collection region during operation of said apparatus, the
cations to and departures from the disclosed embodiments reduced pressure within said collection region acting on said
are deemed to be within the scope of the following claims. layer of hydrate through said pores.
The invention claimed is: 30
10. The apparatus of claim 9, wherein said means for
1. Apparatus for separating components of a fluid system, reducing pressure comprises one or more pressure-reducing
said fluid system being 1) a solution comprising a solute pumps.
dissolved in a solvent, 2) a Suspension comprising Solid 11. The apparatus of claim 9, wherein said means for
material Suspended within a suspension Suspending fluid, or reducing pressure comprises one or more pumps disposed in
3) an emulsion comprising liquid material Suspended within 35 fluid communication with said collection region via said
an emulsion Suspending fluid, said apparatus being config outlet for collecting said host molecules.
ured to use clathrate having a crystalline structure compris 12. The apparatus of claim 9, wherein said means for
ing one or more guest molecules disposed within a cage reducing pressure comprises one or more pumps disposed in
structure formed from a plurality of host molecules to fluid communication with said collection region via said
separate said components of said fluid system, said appara 40 outlet for collecting said guest molecules.
tus comprising: 13. The apparatus of claim 1, wherein said permeable
a containment vessel; restraint comprises a cooling system.
a permeable restraint disposed within said containment 14. The apparatus of claim 13, wherein said cooling
vessel and dividing said containment vessel into a system comprises a plurality of cooling passages extending
clathrate formation and/or accumulation region on one 45 through said permeable restraint.
side of said permeable restraint and a collection region 15. The apparatus of claim 14, wherein said cooling
on an opposite side of said permeable restraint, said passages circulate cooling fluid therein.
permeable restraint being sufficiently permeable that 16. The apparatus of claim 14, wherein said cooling
said host molecules and said guest molecules are able passages contain Pelletier thermoelectric effect cooling
to pass through it, from said clathrate formation and/or 50 members.
accumulation region and into said collection region, 17. The apparatus of claim 14, wherein said cooling
upon dissociation of clathrate against said permeable passages contain magnetocaloric effect cooling devices.
restraint; 18. The apparatus of claim 1, wherein said permeable
an inlet for introducing said fluid system into said clath restraint has a plurality of pores extending through it from
rate formation and/or accumulation region; 55 said one side thereof to said opposite side thereof and
an outlet for removing residual fluid remaining in said wherein said permeable restraint comprises a cooling system
clathrate formation and/or accumulation region after comprising a plurality of cooling passages extending
clathrate has formed therein and/or accumulated through said restraint, said cooling passages being arranged
against said permeable restraint; So as to extend in between said plurality of pores and
means for inducing a layer of clathrate that, during 60 generally parallel with the sides of said permeable restraint.
operation of said apparatus, has formed on or accumu 19. The apparatus of claim 1, wherein said permeable
lated against a side of said permeable restraint facing restraint comprises a heating system.
said clathrate formation and/or accumulation region to 20. The apparatus of claim 19, wherein said heating
dissociate into said host molecules and said guest system comprises a plurality of heating passages extending
molecules Such that said host molecules and said guest 65 through said permeable restraint.
molecules can pass through said permeable restraint 21. The apparatus of claim 20, wherein said heating
and into said collection region; and passages circulate heating fluid therein.
 US 7,094,341 B2
25 26
22. The apparatus of claim 20, wherein said heating fluid system to migrate radially outwardly and said clathrate
passages have resistance heaters disposed therein. to migrate radially inwardly toward said permeable restraint.
23. The apparatus of claim 20, wherein said heating 34. The apparatus of claim 1, wherein said permeable
passages have Pelletier thermoelectric effect heaters dis restraint is a contoured restraint which has a lumen or
posed therein. compartment formed therein and wherein during operation
24. The apparatus of claim 20, wherein said heating of the apparatus, said permeable restraint Surrounds said
passages have magnetocaloric heaters disposed therein. fluid system with said lumen or compartment forming said
25. The apparatus of claim 1, wherein said permeable clathrate formation and/or accumulation region and the
restraint has a plurality of pores extending through it from region of space exterior to said permeable restraint and
said one side thereof to said opposite side thereof and 10 bounded at least in part by walls of said containment vessel
wherein said permeable restraint comprises a heating system forming said collection region.
comprising a plurality of heating passages extending 35. The apparatus of claim 34, wherein said lumen or
through said restraint, said heating passages being arranged compartment, and hence said clathrate formation and/or
So as to extend in between said plurality of pores and accumulation region, is generally cylindrical and said per
generally parallel with the sides of said permeable restraint. 15 meable restraint is generally radially outwardly and coaxi
26. The apparatus of claim 1, wherein said apparatus is ally disposed within said containment vessel.
configured such that said clathrate formation and/or accu 36. The apparatus of claim 34, further comprising a
mulation region and said collection region are vertically conduit extending into the interior lumen or compartment of
disposed relative to each other. said permeable restraint and having one or more fluid system
27. The apparatus of claim 26, wherein said permeable outlets disposed interiorly to said permeable restraint,
restraint is generally planar and horizontally oriented and wherein said inlet for introducing said fluid system into said
wherein said permeable restraint extends across said con clathrate formation and/or accumulation region comprises
tainment vessel to divide said containment vessel into said said one or more fluid system outlets.
clathrate formation and/or accumulation region and said 37. The apparatus of claim 36, wherein said one or more
collection region. 25 fluid system outlets is or are configured to cause fluid system
28. The apparatus of claim 26, wherein said clathrate disposed within said clathrate formation and/or accumula
formation and/or accumulation region is disposed above said tion region to rotate within said clathrate formation and/or
collection region and wherein said apparatus is configured accumulation region during operation of said apparatus, said
for use with negatively buoyant clathrate which sinks or apparatus being configured for use with clathrate that is
settles toward said permeable restraint to form said layer of 30 negatively buoyant relative to said fluid system Such that as
clathrate. said fluid system rotates within said clathrate formation
29. The apparatus of claim 26, wherein said clathrate and/or accumulation region, centrifugal forces cause said
formation and/or accumulation region is disposed below fluid system to migrate radially inwardly and said clathrate
said collection region and wherein said apparatus is config to migrate radially outwardly toward said permeable
ured for use with positively buoyant clathrate which rises 35 restraint.
toward said permeable restraint to form said layer of clath 38. The apparatus of claim 1, wherein said containment
rate. vessel comprises a pressure vessel which is pressurizeable to
30. The apparatus of claim 1, wherein said permeable pressure conditions within said clathrate formation and/or
restraint is a contoured restraint which has an interior lumen accumulation region that are conducive to formation of and
or compartment formed therein and wherein during opera 40 or to maintenance of stability of clathrate within said clath
tion of the apparatus, said permeable restraint is immersed rate formation and/or accumulation region.
in and surrounded by said fluid system 1) with the region of 39. The apparatus of claim 1, wherein said containment
space exterior to said permeable restraint and bounded at vessel is disposed at a lower region of a shaft, said shaft
least in part by walls of said containment vessel forming said having a length sufficient for the weight of a column of said
clathrate formation and/or accumulation region; and 2) with 45 fluid system of the same length as said shaft to generate
said interior lumen or compartment forming said collection pressure conditions within said clathrate formation and/or
region. accumulation region that are conducive to formation of
31. The apparatus of claim 30, wherein said clathrate and/or maintenance of stability of clathrate within said
formation and/or accumulation region is generally cylindri clathrate formation and/or accumulation region.
cal and said permeable restraint is generally centrally and 50 40. The apparatus of claim 39, wherein said shaft extends
coaxially disposed within said containment vessel. down into the ground.
32. The apparatus of claim 30, further comprising a 41. The apparatus of claim 39, wherein said shaft has a
conduit extending through the interior lumen or compart Solid, Sealing partition extending across it and said contain
ment of said permeable restraint and having one or more ment vessel is defined between said solid, Sealing partition
fluid system outlets disposed exteriorly to said permeable 55 and a bottom portion of said shaft.
restraint, wherein said inlet for introducing said fluid system 42. The apparatus of claim 41, wherein said collection
into said clathrate formation and/or accumulation region region is disposed between said solid, sealing partition and
comprises said one or more fluid system outlets. said permeable restraint and said clathrate formation and/or
33. The apparatus of claim 32, wherein said one or more accumulation region is disposed between said permeable
fluid system outlets is or are configured to cause fluid system 60 restraint and said bottom portion of said shaft, said apparatus
disposed within said clathrate formation and/or accumula being configured for use with clathrate that is positively
tion region to rotate within said clathrate formation and/or buoyant relative to said fluid system and that rises toward
accumulation region during operation of said apparatus, said and accumulates along a lower Surface of said permeable
apparatus being configured for use with clathrate that is restraint.
positively buoyant relative to said fluid system such that as 65 43. The apparatus of claim 41, wherein said clathrate
said fluid system rotates within said clathrate formation formation and/or accumulation region is disposed between
and/or accumulation region, centrifugal forces cause said said Solid, sealing partition and said permeable restraint and
 US 7,094,341 B2
27 28
said collection region is disposed between said permeable 52. The apparatus of claim 51, wherein said means for
restraint and said bottom portion of said shaft, said apparatus reducing pressure comprises one or more pressure-reducing
being configured for use with clathrate that is negatively pumps.
buoyant relative to said fluid system and that settles or sinks 53. Apparatus for separating components of a fluid system
toward and accumulates on an upper Surface of said perme in which said apparatus is immersed, said fluid system being
able restraint. 1) a Solution comprising a solute dissolved in a solvent, 2)
44. The apparatus of claim 41, wherein a portion of said a Suspension comprising Solid material Suspended within a
shaft above said solid, sealing partition forms a reservoir Suspension Suspending fluid, 3) an emulsion comprising
portion of said shaft in which said fluid system can be held liquid material Suspended within an emulsion Suspending
before being introduced into said clathrate formation and/or 10 fluid, or 4) a gaseous or non-aqueous medium with water
accumulation region, said apparatus further comprising a contained therein, said apparatus being configured to use
bypass pipe establishing fluid communication between said clathrate having a crystalline structure comprising one or
reservoir portion and said clathrate formation and/or accu more guest molecules disposed within a cage structure
mulation region Such that said fluid system can pass from formed from a plurality of host molecules to separate said
said reservoir portion into said clathrate formation and/or 15 components of said fluid system, said apparatus comprising:
accumulation region. a contoured, thermally assisted permeable restraint con
45. The apparatus of claim 1, wherein said apparatus is figured to form a generally enclosed interior lumen or
configured to be submerged in a naturally occurring body of compartment therein which comprises a collection
said fluid system at a depth sufficient for the weight of a region, said contoured, thermally assisted permeable
column of said fluid system above said apparatus to generate restraint having a plurality of pores extending through
pressure conditions that are conducive to formation of it from one Surface bounding said interior lumen or
and/or maintenance of stability of clathrate within said compartment to an opposite, exterior-facing Surface
clathrate formation and/or accumulation region. thereof, said contoured, thermally assisted permeable
46. The apparatus of claim 45, wherein said clathrate restraint further having a cooling system configured to
formation and/or accumulation region is open to said natu 25 cool at least said opposite, exterior-facing Surface so as
rally occurring body of said fluid system such that said fluid to cool portions of said fluid system in contact with or
system naturally enters said clathrate formation and/or accu in proximity to said opposite, exterior-facing Surface to
mulation region. form a generally solid layer of clathrate thereon, said
47. The apparatus of claim 45, wherein said clathrate contoured, thermally assisted permeable restraint being
formation and/or accumulation region is open to said natu 30 Sufficiently permeable that said guest molecules and
rally occurring body of said fluid system and is configured said host molecules are able to pass through it and into
such that residual fluids remaining after clathrate is formed said interior lumen or compartment upon dissociation
in said fluid system contained within said clathrate forma of clathrate from portions of said layer of clathrate that
tion and/or accumulation region sink or settle naturally out are in contact with or adjacent to said exterior-facing
of said apparatus and into said naturally occurring body of Surface of said contoured, thermally assisted permeable
said fluid system. restraint;
48. The apparatus of claim 45, wherein said clathrate means for inducing said portions of said layer of clathrate
formation and/or accumulation region is disposed at a lower that are in contact with or adjacent to said exterior
portion of said apparatus and is open at a lower end thereof facing Surface of said contoured, thermally assisted
to said naturally occurring body of fluid system such that
40 permeable restraint to dissociate into said host mol
said fluid system naturally enters said clathrate formation ecules and said guest molecules such that said host
and/or accumulation region through the open lower end molecules and said guest molecules can pass through
thereof and such that residual fluids remaining after clathrate said permeable restraint and into said collection region;
and
is formed in said fluid system contained within said clathrate 45 a conduit configured and disposed to convey said guest
formation and/or accumulation region sink or settle naturally molecules out of said interior lumen or compartment
out of said apparatus through the open lower end of said and a conduit configured and disposed to convey said
clathrate formation and/or accumulation region and into said host molecules out of said interior lumen or compart
naturally occurring body of said fluid system. ment after said guest molecules and said host molecules
49. The apparatus of claim 1, wherein said outlet for 50 have passed through said contoured, thermally assisted
collecting said host molecules and said outlet for collecting permeable restraint and into said collection region.
said guest molecules from said collection region comprise a 54. The apparatus of claim 53, wherein said cooling
single, unitary outlet by means of which both said guest system comprises a plurality of cooling passages extending
molecules and said host molecules are collected. through said permeable restraint, said cooling passages
50. The apparatus of claim 1, said apparatus further 55 being arranged so as to extend in between said plurality of
comprising a clathrate-forming-Substance introducing sys pores and generally parallel with the sides of said permeable
tem, said clathrate-forming-Substance introducing system restraint.
comprising one or more conduits configured and disposed to 55. The apparatus of claim 54, wherein said cooling
introduce a clathrate-forming Substance into said clathrate passages circulate cooling fluid therein.
formation and/or accumulation region, which clathrate 60 56. The apparatus of claim 54, wherein said cooling
forming Substance combines with said solvent, said Suspen passages contain Pelletier thermoelectric effect cooling
sion Suspending fluid, or said emulsion Suspending fluid members.
during operation of said apparatus to form said clathrate 57. The apparatus of claim 54, wherein said cooling
under Suitable conditions of temperature and pressure. passages contain magnetocaloric effect cooling devices.
51. The apparatus of claim 1, wherein said means for 65 58. The apparatus of claim 53, wherein said pores are
inducing comprises means for reducing pressure within said conical, with the diameter of said pores decreasing from the
collection region. exterior-facing Surface of said contoured, thermally assisted
 US 7,094,341 B2
29 30
permeable restraint to said one surface bounding said inte fluid communication with said conduit configured and dis
rior lumen or compartment of said contoured, thermally posed to convey said guest molecules out of said interior
assisted permeable restraint. lumen or compartment.
59. The apparatus of claim 53, wherein said means for 67. The apparatus of claim 64, wherein said means for
inducing comprises means for heating said exterior-facing reducing pressure comprises one or more pumps disposed in
Surface of said contoured, thermally assisted permeable
restraint. fluid communication with said conduit configured and dis
60. The apparatus of claim 59, wherein said means for posed to convey said host molecules out of said interior
heating comprises a series of heating passages disposed lumen or compartment.
within or on said contoured, thermally assisted permeable 10 68. The apparatus of claim 53, wherein said conduit
restraint, said heating passages being arranged so as to configured and disposed to convey said guest molecules out
extend in between said plurality of pores and generally of said interior lumen or compartment and said conduit
parallel with the sides of said permeable restraint. configured and disposed to convey said host molecules out
61. The apparatus of claim 59, wherein said means for of said interior lumen or compartment comprise a single,
heating comprises resistance heaters. 15
unitary conduit.
62. The apparatus of claim 59, wherein said means for
heating comprises Pelletier thermoelectric effect heaters. 69. Apparatus for forming hydrate or other clathrate,
63. The apparatus of claim 59, wherein said means for comprising:
heating comprises magnetocaloric devices. a vessel in which components of said hydrate or clathrate
64. The apparatus of claim 53, wherein said means for can be located; and
inducing comprises means for reducing pressure within said a permeable hydrate-formation or clathrate-formation
collection region, the reduced pressure within said collection Support member disposed within said vessel, said Sup
region acting on said portions of said layer of clathrate that port member having a plurality of pores of diminishing
are in contact with or adjacent to said exterior-facing Surface cross-sectional configuration formed through the thick
of said contoured, thermally assisted permeable restraint 25
ness thereof and said Support member having a cooling
through said pores.
65. The apparatus of claim 64, wherein said means for system by means of which said Support member is
reducing pressure comprises one or more pressure-reducing cooled so as to facilitate formation of hydrate or
pumps. clathrate on a surface thereof.
66. The apparatus of claim 64, wherein said means for 30
reducing pressure comprises one or more pumps disposed in