U.S. patent application number 10/833175 was filed with the patent office on 2004-10-07 for hydrate-based reduction of fluid inventories and concentration of aqueous and other water-containing products.
This patent application is currently assigned to Marine Desalination Systems, L.L.C.. Invention is credited to Max, Michael D., Osegovic, John P..
Application Number | 20040195160 10/833175 |
Document ID | / |
Family ID | 33102405 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040195160 |
Kind Code |
A1 |
Max, Michael D. ; et
al. |
October 7, 2004 |
Hydrate-based reduction of fluid inventories and concentration of
aqueous and other water-containing products
Abstract
Toxic waste waters polluted with high levels of chemical
byproducts of various industrial processes (e.g., waste water held
in industrial holding ponds) are treated using gas hydrate to
extract and remove fresh water from the polluted water, thus
reducing the volume of toxic waste water inventories. Extracting
fresh water by forming and removing the hydrate raises the
concentration of dissolved materials in the residual concentrated
brines to levels at which the residual fluid is suitable for use as
an industrial feedstock. Furthermore, so raising the concentration
of the residual brine will cause certain mineral species to
precipitate out of solution, which mineral species are separated
from the fluid and may be put to other uses, as appropriate. Food
products are also advantageously concentrated by means of gas
hydrates.
Inventors: |
Max, Michael D.; (St. Pete
Beach, FL) ; Osegovic, John P.; (Tampa, FL) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
Marine Desalination Systems,
L.L.C.
Washington
DC
|
Family ID: |
33102405 |
Appl. No.: |
10/833175 |
Filed: |
April 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10833175 |
Apr 28, 2004 |
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10266258 |
Oct 8, 2002 |
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6733667 |
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10266258 |
Oct 8, 2002 |
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09397500 |
Sep 17, 1999 |
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6497794 |
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09397500 |
Sep 17, 1999 |
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09375410 |
Aug 17, 1999 |
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6531034 |
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09375410 |
Aug 17, 1999 |
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09350906 |
Jul 12, 1999 |
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6565715 |
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Current U.S.
Class: |
210/177 ;
203/10 |
Current CPC
Class: |
A23L 2/08 20130101; C01F
11/46 20130101; C02F 2103/32 20130101; B01D 53/62 20130101; Y02A
20/132 20180101; C02F 1/26 20130101; Y10S 210/906 20130101; C02F
1/20 20130101; Y02A 20/124 20180101; C02F 2101/105 20130101; B01D
2257/504 20130101; C02F 1/5236 20130101; Y02C 10/04 20130101; C02F
2103/18 20130101; C02F 2101/101 20130101; C02F 1/22 20130101; C02F
1/265 20130101; Y02C 20/40 20200801; Y02P 20/152 20151101; Y02P
20/151 20151101 |
Class at
Publication: |
210/177 ;
203/010 |
International
Class: |
C02F 001/02 |
Goverment Interests
[0002] This invention was made with Government support under
Contract No. NBCHC 010003 dated Jan. 29, 2001 and issued by the
Department of the Interior--National Business Center (DARPA). The
Government has certain rights in the invention.
Claims
What is claimed is:
1. A method for treating a highly polluted or otherwise
contaminated solution comprising water and one or more solutes
dissolved therein, the solution being a byproduct of an industrial
process, said method comprising: mixing a hydrate-forming substance
with the solution under pressure and temperature conditions
suitable for hydrate to form, whereby hydrate of said
hydrate-forming substance forms and removes water from said
solution to produce residual fluid having higher concentration of
said one or more solutes than said solution; removing said hydrate
from said residual fluid; and providing said residual fluid to said
industrial process as an industrial feedstock of said one or more
solutes.
2. The method of claim 1, further comprising dissociating said
hydrate to release water and hydrate-forming substance
therefrom.
3. The method of claim 2, further comprising returning water
released from said hydrate to said contaminated solution.
4. The method of claim 2, further comprising releasing water
released from said hydrate to surface waters.
5. The method of claim 2, further comprising reusing
hydrate-forming substance released from said hydrate in additional
cycles of hydrate formation.
6. A method for treating a highly polluted or otherwise
contaminated solution comprising water and one or more solutes
dissolved therein, the solution being a byproduct of an industrial
process, said method comprising: mixing a hydrate-forming substance
with the solution under pressure and temperature conditions
suitable for hydrate to form, whereby hydrate of said
hydrate-forming substance forms and removes water from said
solution to produce residual fluid having higher concentration of
said one or more solutes than said solution; and removing said
hydrate from said residual fluid; wherein sufficient amounts of
water is removed from said solution via said hydrate to raise the
concentration of said one or more solutes in said residual fluid to
saturation levels, whereby at least one of said one or more solutes
precipitates out of said residual fluid; said method further
comprising collecting said precipitated solute material.
7. The method of claim 6, further comprising dissociating said
hydrate to release water and hydrate-forming substance
therefrom.
8. The method of claim 7, further comprising returning water
released from said hydrate to said contaminated solution.
9. The method of claim 7, further comprising releasing water
released from said hydrate to surface waters.
10. The method of claim 7, further comprising reusing
hydrate-forming substance released from said hydrate in additional
cycles of hydrate formation.
11. A method of concentrating a food material fluid containing
water, said method comprising: introducing said food material fluid
into a hydrate formation apparatus; mixing said food material fluid
with hydrate-forming substance in said hydrate formation apparatus
under pressure conditions and temperature conditions suitable for
hydrate of said hydrate-forming substance to form, thereby causing
hydrate of said hydrate-forming substance to form; and removing
said hydrate from said hydrate formation apparatus, thereby
yielding a food material concentrate.
12. The method of claim 11, further comprising melting said hydrate
to release water and hydrate-forming substance.
13. The method of claim 12, further comprising re-using said
released hydrate-forming substance in further cycles of hydrate
formation.
14. The method of claim 11, further comprising using said food
material concentrate as a feedstock in further food process
manufacturing.
15. The method of claim 11, further comprising packaging said food
material concentrate as a final, concentrated consumer food
product.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending
U.S. application Ser. No. 10/266,258 filed Oct. 8, 2002. That
application is a divisional of U.S. application Ser. No. 09/397,500
filed Sep. 17, 1999 (issued Dec. 24, 2002 as U.S. Pat. No.
6,497,794), which is a continuation-in-part of U.S. application
Ser. No. 09/375,410 filed Aug. 17, 1999 (issued Mar. 11, 2003 as
U.S. Pat. No. 6,531,034), which is a continuation-in-part of U.S.
application Ser. No. 09/350,906 filed on Jul. 12, 1999 (issued May
20, 2003 as U.S. Pat. No. 6,565,715).
FIELD OF THE INVENTION
[0003] The invention relates to reducing fluid inventories and
concentrating aqueous and other water-containing products using
hydrates to extract fresh water from the fluid inventories or from
the material being concentrated, respectively.
BACKGROUND OF THE INVENTION
[0004] In general, desalination and purification of saline or
polluted water using gas hydrates is known in the art. See, for
example, the above-referenced issued patents to which this
application is related, the contents of each of which are
incorporated by reference and replicated below. According to those
patents, a hydrate-forming gas, liquid, or mixture of gases or
liquids is combined with water to be treated under pressure and
temperature conditions at which hydrate spontaneously forms, i.e.,
conditions within the hydrate pressure/temperature stability zone
for the particular hydrate-forming substance used. The hydrate is
then naturally or mechanically separated from the residual brine
("brine" being used herein to refer to either residual saltwater or
residual polluted water, depending on the particular context) and
allowed or caused to dissociate (melt), thereby releasing fresh
water (e.g., for drinking) and the hydrate-forming substance.
Alternatively, as taught in co-pending application Ser. No.
10/429,765 filed May 6, 2003 (published Nov. 13, 2003 as
Publication Number 2003/0209492), the contents of which are
incorporated by reference, hydrate may be caused to form on or
collect against a permeable support member, then be caused to
dissociate against the support member (e.g., by lowering pressure
on the side of the support member opposite to the hydrate), with
the released hydrate-forming substance (e.g., gas) and pure water
passing through the permeable support member to be collected on the
opposite side.
[0005] It is also known to conduct hydrate-based desalination in an
open-ocean installation, as disclosed, for example, in U.S. Pat.
Nos. 5,873,262 and 3,027,320.
[0006] According to the referenced patents and published
application, the hydrate may be formed in a hydrate-formation
region at the bottom of a body of water (either formed in land or
in an open-ocean environment), where the pressure is naturally high
enough for hydrate to form. Alternatively, the hydrate may be
formed in a pressurized hydrate formation vessel. In either case,
the residual brine will have somewhat elevated concentrations of
salt (NaCl) or other chemical pollutants, solute(s), or suspended
particulate matter.
[0007] Where the primary reason for forming hydrate in seawater or
polluted water is to obtain water for potable, agricultural, or
industrial use, low conversion rates--i.e., relatively small
percentage removal of water--are often desirable to maintain the
environmental quality of the residual water, which may be returned
to its source.
[0008] On the other hand, there are certain cases of naturally
occurring, highly acidified bodies of water the salinities of which
are in the brackish to seawater range and which are toxic to
aquatic life. For certain other bodies of water, where the salinity
of each of the various dissolved chemical species is much higher
than naturally occurring water--the term "salinity" being used here
and throughout this application in the broadest sense, as
appropriate--and where the pH of the water is dramatically
different from naturally occurring water, the environmental
concerns associated with them and the water treatment processes
typically employed with them may be substantially different from
those associated with and used for treating natural seawater or
brackish water. These bodies of water are not generally naturally
occurring, but are commonly the residue of industrial processes and
are commonly referred to as "toxic wastes." In contrast to the case
for seawater or brackish water, where total salinity and the amount
of suspended matter is naturally occurring and of such compositions
and concentrations as to be tolerable for a wide variety of life
forms, toxic wastes are inhospitable to a wide variety of life
forms and may comprise dangerous biotoxins. Therefore, in these
cases, it may be desirable to reduce as much as possible the volume
of water that has been made toxic by the presence of dissolved
chemical substances.
[0009] In that regard, there is a general need in many industries
that produce large volumes of toxic waste water to reduce the
volumes of such fluids, which may be held in large ponds. For
instance, the wet process manufacture of phosphoric acid as
practiced in Florida and many other parts of the world requires a
large volume of process water that is used as a water source for
the phosphoric acid; for gas scrubbing; to slurry the phosphogypsum
produced and transport it to storage; to operate barometric
condensers; and for a multitude of other uses in the chemical
complex. A major portion of the heat released in the process ends
up in the process water and is discharged to the atmosphere by
evaporative cooling. The process water is stored in holding ponds
that provide the large surface area needed for evaporation and
cooling of the water. (Other industries, such as the
micro-electronics industry, mining, coal beneficiation, and metal
coatings industries, can also produce waste water inventories that
are held in such holding ponds.)
[0010] Such pond water is extremely acidic (pH=1 to 2). (For
reference, most fish are killed when the water reaches a pH of 5.6,
and entire lakes or other bodies of water are considered to be
incapable of supporting normal aquatic life at pH 4.1). Therefore
the pond water is a strong biotoxin, which if released can strongly
pollute surface and ground waters, surface water including lakes,
rivers, and all water that flows on the land surface and ground
water being water that has sunken into the ground and resides in or
moves through groundwater aquifers. Such pond water contains high
dissolved salt, mineral acid, and flourinated compounds
concentrations, as identified in Table 1. The dissolved materials
include ammonium, fluorosilicic acid (H.sub.2SiF.sub.6),
hydrofluoric acid, fluorine, and sulfur tetrafluoride.
1TABLE 1 Phosphoric Acid Process Water Research Background
Information. From the Florida Institute of Phosphate Research
website <http://www.fipr.state.fl.us/> Untreated Process
Parameter Water Density (MDS) 1.03-1.05 Lab pH 2.1 Conductivity
(.mu.mhos/cm) 22,100 Turbidity (NTU), 24 hours -- Turbidity (NTU),
72 hours -- Lab Turbidity (NTU) 0.9 Color (Pt/Co units) 300
Calcium, Ca (mg/l) 538 Magnesium, Mg (mg/l) 223 Sodium, Na (mg/l)
2260 Potassium, K (mg/l) 210 Iron, Fe (mg/l) 59 Manganese, Mn
(mg/l) 15 Total Chloride, Cl (mg/l) 140 Total Fluoride, F (mg/l)
4120 Sulfate, SO4 (mg/l) 6200 Total Phosphorus, P (mg/l) 6600
Ammonia Nitrogen, N (mg/l) 1240 Acidity, CaCO3 (mg/l) --
Alkalinity, CaCO3 (mg/l) -- Solids, Total Dissolved (mg/l) 39,800
Solids, Total Suspended (mg/l) 22
[0011] In Florida, the average yearly rainfall and the pond
evaporation rate are approximately equal, according to Florida
Institute of Phosphate Research, and it is normally possible to
operate an industrial chemical complex with a negative water
balance by strict control of the water inputs to the ponds.
However, in a year where rainfall is significantly above average or
where water management practices fail to sufficiently reduce water
inventory, it may become necessary to treat the surplus water and
release it to the surface waters in order to avoid an uncontrolled
discharge of the untreated process water.
[0012] Present treatment practice is to "lime" the water (i.e., add
lime to it) to obtain a pH of approximately 4.5; remove the solids
formed; lime the water again to a pH of approximately 11; remove
the solids formed; air strip the water to remove ammonia; and add
sulfuric acid to reduce the pH to approximately 6.5. Although the
water will still contain dissolved solids and have a conductivity
above discharge standards, under emergency situations it can be
discharged to the surface waters under an emergency permit from the
Florida Department of Environmental Protection. Unfortunately, the
residual dissolved salts in industrial pond water present hazards
to public health and the environment, and a significant release of
pond water can easily destroy most aquatic organisms. Although a
significant emergency release of treated water may not have such
severe results, it can still cause significant biodegradation and
environmental impact.
[0013] Thus, there is significant need to control total volume of
such industrial pond waters.
[0014] In addition to the double-liming technique explained above,
two other techniques typically are used to reduce pond water volume
along with methods for adjusting the pH of the pond water (double
liming).
[0015] (1) Evaporation. This is a natural method for reducing the
water inventory. Evaporation is widely used in the phosphate
industry. Where ponds have a very large surface area, considerable
evaporation may occur. Spray techniques can be used to increase
evaporation by increasing the surface area of the water. The rate
of evaporation is related to the surface area of liquid exposed,
the temperature of the liquid, and the relative humidity. In
addition, the vapor pressure of pond water is lowered significantly
due to elevated dissolved salt concentrations. The lower pond water
vapor pressure lowers the rate of evaporation. Further, high
humidity, as often exists in Florida, lowers the rate of
evaporation; when humidity approaches 100%, little evaporation
takes place at all.
[0016] Artificial evaporation desalination techniques, such as
multi-stage flash techniques, have substantial associated energy
costs for heating the pond water (to make the process more
efficient in terms of the percentage of water that can be
evaporated from a particular volume of water). In addition, because
the untreated pond water may be at or close to saturation,
evaporation will lead to the formation of large amounts of
crystallized scale, which can clog the installation apparatus and
render the process less efficient. Thus, application of artificial
evaporation desalination techniques appears to be impractical,
without prior treatment to lower the pH by causing substantial
precipitation of dissolved and suspended matter.
[0017] (2) Conventional desalination, Reverse Osmosis (RO). This
method is also being used in at least one trial installation to
reduce pond water inventory. Osmosis is a natural phenomenon in
which a liquid--water, in this case--passes through a
semi-permeable membrane from a relatively dilute solution toward a
more concentrated solution. This flow produces a measurable
pressure, called osmotic pressure. If pressure is applied to the
more concentrated solution, and if that pressure exceeds the
osmotic pressure, water flows through the membrane from the more
concentrated solution toward the dilute solution. This process,
called reverse osmosis (RO), removes up to 98% of dissolved solids,
and virtually 100% of colloidal and suspended matter.
[0018] The membrane must be physically strong to stand up to high
osmotic pressure--in the case of seawater, about 2500 kg/m2. After
filtration to remove suspended particles, incoming water is
pressurized to 200-400 psi (1380-2760 kPa), which exceeds the
water's osmotic pressure. As a result, a portion of the water (the
permeate) diffuses through the membrane, leaving dissolved salts
and other contaminants behind with the remaining water with which
they are sent to drain as waste (the concentrate).
[0019] RO has a number of well-known limitations, especially in
highly saline water and with dissolved solids at or near their
saturation limit. A significant limitation with RO treatment of
highly saline or highly chemically saturated water is membrane
fouling from suspended particulates and scaling. Pond water is a
saturated or nearly saturated solution of many salts. Cooling the
water or raising the concentration by removing water initiates
precipitation of dissolved materials, and scaling of the RO
membranes will result. Therefore, RO treatment of the highly
saturated pond water requires pretreatment to prevent scaling.
[0020] In addition, the little-used desalination method of freezing
has been suggested for treating waste pond water. However, this
method is very energy-intensive, especially if rapid freezing and
subsequent melting is required, in part because the high volume of
dissolved solids lowers the freezing point substantially. Also,
rapid freezing causes poor rejection of dissolved solids, which can
be accommodated within the hexagonal crystal structure of ice.
Additionally, residual brines can be overgrown and trapped between
ice crystals. Furthermore, in a hot and humid region such as
Florida, pond water freezing would be prohibitively expensive.
[0021] There is thus strong need for a more versatile,
cost-effective technique to decontaminate and reduce industrial
pond waste water inventories. Furthermore, there are numerous other
processes in which significant volumes of water need to be removed
from aqueous or other water-containing products. For example,
drying and concentration of food products intended for human or
animal consumption is an important part of many industrial
processes. Many types of food products such as orange juice,
condensed milk, evaporated skim milk, powdered milk, powdered whey,
amongst other food products, are concentrated by evaporation, in
which considerable amounts of heat must be applied to drive off
water.
[0022] In the case of dairy and other food products, heat is
commonly applied under partial vacuum conditions to lower the
boiling point; otherwise, the food will be spoiled, which would
require its disposal, or it will have an undesirable cooked flavor.
In the case of milk, the temperature must be controlled accurately.
Milk is commonly heated under a vacuum that is deep enough to cause
the milk to boil at between 40-45.degree. C., and the milk is
concentrated to approximately 30% solids concentration under
essentially fluid conditions. This concentrated milk is either
removed as a relatively viscous fluid, for packaging or other
processing that does not involve further concentration, or it is
further dried. Alternatively, dry powdered mild is produced through
spray evaporation at 200.degree. C. in a chamber filled with hot
gas that causes the milk to form small, non-aggregated particles.
The powdered milk has less than 5% water content.
[0023] Concentrated orange juice and other citrus, fruit, and
vegetable concentrates are also produced by evaporation. Sometimes,
but not always, the evaporation process also uses reduced pressure
evaporators. However, fruit and vegetable juices are more resistant
to spoiling when temperatures are raised for evaporative processes.
Thus, if reduced pressure is used, the vacuum need not be so deep,
and hence as expensive to produce, but the amount of heat that has
to be applied is greater. Throughout the process of evaporation,
the rate of evaporation slows as the material becomes more
concentrated. Lowering of vapor pressure effect is a colligative
property that acts broadly throughout the fluid because of the
distribution of hydraulic pressure. As concentration increases, the
vapor pressure of the water in the fruit or vegetable juice lowers
linearly, and more heat must be applied to drive the evaporation
process and remove more water. Evaporation thus becomes less
efficient under conditions of increasing concentration.
[0024] Because of the requirement to apply considerable heat over
short periods of time, and often under conditions where vacuum
pumping must be carried out continuously, present concentration
processes add significant cost to the concentrated food production
process. Moreover, the efficiency of the process can decrease
significantly with increasing concentration, as noted above.
Accordingly, a process for concentrating aqueous or other
water-containing food products that does not require such levels of
heat input, and that generally remains efficient, is desirable.
BRIEF SUMMARY OF THE INVENTION
[0025] In one regard, the invention provides an efficient,
cost-effective technique for reducing the volume of industrial
waste waters, e.g., water held in industrial holding ponds. In
particular, according to the invention, hydrate is formed in the
waste water (either directly in the pond itself or in a separate
facility or installation) and is then removed. The hydrate extracts
fresh water from the waste water, so removing the hydrate reduces
the volume of the waste water. Fresh water released when the
hydrate dissociates (melts) may be pure enough to release to
ordinary surface waters, either directly or after minor
post-processing (e.g., chemical polishing or RO), and the residual
brine will be of significantly elevated concentration of dissolved
materials. The elevated concentration of the residual brine is
sufficient to permit the residual brine to be used as an industrial
feedstock for the basic, underlying process in connection with
which the waste water was produced. Thus, cost savings can be
realized by returning significant amounts of one or more of the
original reagents to the industrial process in the residual
brine.
[0026] Additionally, elevating the concentration(s) of any of the
various dissolved species in the residual fluid to saturation
levels by removing water from the solution causes the dissolved
materials to precipitate out of the solution. For example, in the
embodiment of the invention described below (that specific
embodiment being for illustrative purposes and not intended to be
limiting in nature), in the case of phosphate ponds, the material
that crystallizes out of solution will be gypsum and phosphogypsum
(PCaSO.sub.4). This precipitated material is collected and stored
on site or used for other suitable purposes. For example,
precipitated gypsum and phosphogyspum can be used in roadbeds or
for the manufacture of gypsum wallboard. Thus, controlled
production of solid precipitate optimizes or makes more profitable
the overall manufacturing process.
[0027] Thus, according to a first aspect, the invention features a
method of treating a highly polluted or otherwise contaminated
solution including water and one or more solutes dissolved therein,
where the solution is a byproduct of an industrial process. The
method includes mixing a hydrate-forming substance with the
solution under pressure and temperature conditions suitable for
hydrate to form, so that hydrate of the hydrate-forming substance
forms and removes water from the solution. This produces a residual
fluid having higher concentration of the various solutes than the
solution being treated. The hydrate is removed from the residual
fluid, and the elevated concentration residual fluid is provided
back to the industrial process as an industrial feedstock to
provide the various solutes back to the industrial process.
[0028] In another aspect, the invention features method of treating
a highly polluted or otherwise contaminated solution including
water and one or more solutes dissolved therein, where the solution
is a byproduct of an industrial process. The method includes mixing
a hydrate-forming substance with the solution under pressure and
temperature conditions suitable for hydrate to form, so that
hydrate of the hydrate-forming substance forms and removes water
from the solution. This produces residual fluid having higher
concentration of the various solutes than the solution being
treated. The hydrate is removed from the residual fluid.
Additionally, sufficient amounts of water is removed from the
solution via the hydrate to raise the concentration of the various
solutes in the residual fluid to saturation levels. As a result at
least one of the various solutes precipitates out of the residual
fluid, and the precipitated solute(s) can be collected and put to
other uses, as desired.
[0029] In either case, the hydrate may be dissociated to release
relatively pure water and the hydrate-forming substance. The water
may be released to surface waters or returned to the solution being
treated, as appropriate, and the hydrate-forming recaptured for
further cycles of the hydrate-forming process.
[0030] In another regard, the invention provides an efficient
technique for concentrating aqueous and other water-containing food
products, such as (but not limited to) milk and fruit or vegetable
juices. According to this aspect of the invention, a food product
in relatively liquid or fluid form is mixed with hydrate-forming
material under pressure and temperature conditions suitable for
hydrate to form, and the hydrate extracts water from the food
product. Hydrate is removed and melted to release water (which may
be used as potable water) and the hydrate-forming substance, and
the concentrated food product is then packaged for sale where so
desired (e.g., condensed milk) or used for further food
manufacturing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The invention will now be described in greater detail in
connection with the drawings, in which:
[0032] FIG. 1 is a generalized, diagrammatic depiction of a
land-based treatment installation;
[0033] FIG. 2 is a diagrammatic, side elevation view of an
embodiment of a hydrate fractionation column which utilizes
positively buoyant hydrate and which may be employed in the
installation shown in FIG. 1;
[0034] FIGS. 3 and 4 are diagrammatic, side elevation views showing
two alternative heat extraction portions of a desalination
fractionation column employed in the installation shown in FIG.
1;
[0035] FIG. 5 is a diagrammatic, side elevation view of another
embodiment of a hydrate fractionation column which utilizes
positively buoyant hydrate and which may be employed in the
installation shown in FIG. 1;
[0036] FIG. 6 is a diagrammatic, side elevation view showing
overlapping water vents used in the hydrate fractionation column
shown in FIG. 5;
[0037] FIG. 7 is a diagrammatic, side elevation view of yet another
embodiment of a buoyant hydrate-based fractionation column employed
in the installation shown in FIG. 1, which embodiment is similar to
that shown in FIG. 5.
[0038] FIG. 8 is a diagrammatic, side elevation view of an
embodiment of a hydrate fractionation column which permits the
utilization of negatively buoyant hydrate and which may be employed
in the installation shown in FIG. 1;
[0039] FIGS. 9 and 10 are schematic, isometric and end views,
respectively, of the dissociation and heat exchange portion of the
hydrate fractionation column shown in FIG. 8;
[0040] FIG. 11 is a Pressure/Temperature diagram depicting regions
of CO.sub.2 hydrate stability, the CO.sub.2 liquidus, and the
operating envelope for a negatively buoyant, CO.sub.2 hydrate-based
desalination system;
[0041] FIG. 12. is a diagrammatic, side elevation view of a
residual fluid replacement section designed to facilitate washing
of the hydrate slurry;
[0042] FIG. 13 is a diagrammatic, side elevation view of another
embodiment of a hydrate fractionation column which permits the
utilization of a negatively buoyant hydrate, which embodiment
facilitates separation of residual brines from the negatively
buoyant hydrate;
[0043] FIG. 14 is a diagrammatic, side elevation view of a
slurry-holding, fluid separation apparatus used in the installation
of FIG. 13;
[0044] FIG. 15 is a diagrammatic, side elevation view of an
embodiment of a hydrate fractionation column configured to maintain
the hydrate-forming gas at elevated pressure;
[0045] FIG. 16 is a diagrammatic, side elevation view of an
embodiment of a mechanically pressurized fluid treatment system
configured to use positively buoyant hydrate;
[0046] FIG. 17 is a diagrammatic, side elevation view of an
embodiment of a mechanically pressurized fluid treatment system
which is similar to that shown in FIG. 16 but which is configured
to use negatively buoyant hydrate;
[0047] FIG. 18. is a diagrammatic, side elevation view of an
embodiment of a mechanically pressurized fluid treatment system
configured to use either positively or negatively buoyant
hydrate;
[0048] FIG. 19 is a process flow diagram illustrating hydrate-based
treatment of and material reclamation from a highly contaminated
body of water;
[0049] FIG. 20 is a simplified hydrogen sulfide hydrate stability
diagram; and
[0050] FIG. 21 is a process flow diagram illustrating hydrate-based
treatment of and material concentration of food product.
DETAILED DESCRIPTION
[0051] Hydrate-Based Desalination/Fluid Treatment, Generally
[0052] A land-based installation for desalination or other fluid
treatment as per the above-referenced patents is shown
schematically in FIG. 1, in generalized fashion. The installation
may be divided roughly into three sections or regions: an intake
portion 10; a water purification portion 12; and post-processing
and downstream usage section 14.
[0053] In the context of desalinating seawater to produce potable
water, the intake portion 10 consists essentially of the apparatus
and various subinstallations necessary to extract seawater from the
ocean 16 and transport it to the desalination/purification
installation at region 12, including subaquatic water intake piping
18 and pumping means (not shown) to draw the water from the ocean
and pump it to shore for subsequent processing. Large volume
installations can be located relatively close to the sea to reduce
the piping distance of the input water to a minimum, and
establishing the installation as close to sea level as possible
will reduce the cost of pumping against pressure head.
[0054] The intake pipeline 18 preferably extends sufficiently out
to sea that it draws deep water, e.g., from the slope 20 of the
continental shelf because deep water is more pure and colder than
shallow water. Alternatively, water may be drawn from locations
closer to land, e.g., from areas on the continental shelf 22 where
the distance across the shallow water is too great for practice.
The precise depth from which water is drawn will ultimately be
determined by a number of factors, including primarily the specific
embodiment of the desalination fractionation column which is
employed, as described below. Ideally, the desalination
installation, per se, is located so that the highest part of the
fluid-handling system is at or below sea-level to reduce the costs
of intake pumping.
[0055] Additionally, the water may be pretreated at a pretreatment
station 24. Pretreatment consists mainly of de-aeration, filtering
to remove particulate matter and degassing, consistent with the
requirement that material necessary for hydrate nucleation and
growth not be removed from the water.
[0056] One embodiment of the purification installation 30, per se,
is illustrated in FIGS. 2, 3, and 4, which embodiment utilizes
positively buoyant hydrate to extract fresh water from seawater.
Seawater is pumped into the installation 130 at water input 32 and
is pumped down to the lower, hydrate formation section 34 of the
installation. The bottom of the hydrate formation section is no
more than about 800 meters deep, and perhaps even shallower (again
depending on the particular gas or gas mixture being used). A
suitable, positively buoyant hydrate-forming gas (or liquid) is
injected into the hydrate formation section at 36, and positively
buoyant hydrate 38 spontaneously forms and begins to rise through
the water column, as is known in the art.
[0057] The hydrate-forming gas can be pumped using sequential,
in-line, intermediate pressure pumps, with the gas conduit
extending either down through the fractionation column, per se, or
down through the input water line so that gas line pressure is
counteracted by ambient water pressure. As a result, it is not
necessary to use expensive, high pressure gas pumps located on the
surface. Alternatively, once a gas has been liquefied, it can be
pumped to greater depths without further significant
compression.
[0058] Hydrate formation (crystallization) is an exothermic
process. Accordingly, as the positively buoyant hydrate forms and
rises automatically through the water column--forming a hydrate
"slurry" as hydrate crystals continue to nucleate and grow as they
rise, until the hydrate-forming gas is used up--the surrounding
water, which will increasingly become a concentrated saline
"residue," will be heated by the heat energy released during
crystallization of the hydrate.
[0059] Below a certain salinity, the heated residual seawater will
have a relatively decreased density and will rise in the column
along with the hydrate 38. When the salinity of the residual
seawater rises high enough due to the extraction of fresh water
from it, however, the highly saline residual seawater will sink to
the bottom of the water column. This highly saline residual
seawater is collected in sump 40 at the bottom of the fractionation
column and is removed.
[0060] As the slurry of hydrate and heated residual seawater rises
in the fractionation column, heated residual seawater is removed
from the system in heat extraction portion 44 of the fractionation
column at one or more points 46. The heat extraction section 44 is
shown in greater detail in FIG. 3. As illustrated in FIG. 3, for
one mode of separation of hydrate and slurry, water is pumped from
the system as part of the vertical fractionation process. This is
accomplished through a two-stage process. An internal sleeve 45
allows a primary separation to take place, as a water trap 49 is
formed below the top of the sleeve. Hydrate continues to rise,
while water floods the entire section 44. Water is pumped from
below the level at which hydrate exits from the top of the sleeve
through fine conical screens 47. These are designed to obstruct the
passage of particulate hydrate. (The screens can be heated
periodically to clear them of hydrate when flow restriction exceeds
design limits.) Residual water is drawn off at a slow enough rate
that any hydrate that may reside within water drawn toward the
screen has a greater tendency to rise buoyantly than the tendency
toward downwards or sideways movement associated with the force of
suction of the drawn-off water. Very buoyant gas rises and stays
within the column.
[0061] An alternative configuration 44' of the heat extraction zone
is shown in FIG. 4. In this configuration, a centrifuge is used to
allow a separate, mechanically-driven density fractionation system
to operate. In this configuration, a segment 51 of the column is
made mobile and capable of rotary movement. The mobile, rotary
centrifuge column segment is carried by bearings 53 at the base 55
and at intervals along its height to keep it in vertical alignment
with the entirety of the column, and to allow it to rotate with
respect to the portions 57, 59 of the column above and below it.
This section is motor-driven, using a hydraulic system 61 driven
from the surface. Vanes 63 within the centrifuge section will cause
the water column to rotate, which vanes are designed based on
turbine vane design to cause the hydrate-residual water in the
section to rotate without turbulence and with increasing velocity
toward the top of the section where residual water is extracted.
Gravity "settling" or fractionation works here in a horizontal
plane, where the heavier residual water "settles" toward the sides
of the column while the lighter, more buoyant hydrate "settles"
toward the center of the column. The hydrate continues to rise
buoyantly and concentrates in the center of the centrifuge section.
It will be appreciated that more than one such centrifuge section
may be employed.
[0062] As the hydrate rises into the upper, dissociation and heat
exchange region 50 of the desalination fractionation column, the
depth-related pressures which forced or drove formation of the
hydrate dissipate; accordingly, the hydrate, which is substantially
in the form of a slurry, will be driven to dissociate back into the
hydrate-forming gas (or mixture of gases) and fresh water. However,
regardless of the particular method used to extract the warmed
residual seawater, heat energy in the surrounding seawater which
ordinarily (i.e., in the prior art) would be absorbed by the
hydrate as it dissociates is no longer available to the hydrate.
Therefore, because heat has been removed from the system by
extracting warmed residual seawater in the heat extraction portion
44 of the apparatus, a net or overall cooling bias is created in
the upper, dissociation and heat exchange portion 50 of the
installation.
[0063] This cooling bias is capitalized upon to significant
advantage. In particular, as indicated schematically in FIG. 2,
water being pumped into the system (at 32 ) is passed in
heat-exchanging relationship through the regions of dissociating
hydrate. For example, it is contemplated that the dissociation and
heat exchange portion 50 may be constructed as one or more large,
individual enclosures on the order of one hundred meters across.
The input water will pass via a series of conduits through the
regions of dissociating hydrate and will be cooled significantly as
it does so. In fact, although some initial refrigeration will be
required at start-up of the process, which initial refrigeration
may be provided by heat exchange means 52, the installation
eventually will attain a steady-state condition in which the amount
of heat energy transferred from the input water to the dissociating
hydrate is sufficient to cool the input water to temperatures
appropriate for spontaneous formation of hydrate at the particular
depth of the dissociation column.
[0064] Ideally, the input water is stabilized at 4.degree. C. or
below. This is because below that temperature, the density of the
water increases, which enhances separation of the hydrate-water
slurry formed by injections of the gas. Additionally, at a given
pressure, hydrate nucleation proceeds faster at colder water
temperatures. During the start-up period, the system is run in a
mode of maximum warm fluid extraction (to create a state of induced
thermal bias) before equilibrium or steady-state is reached;
although the duration of this start-up period will vary depending
on the particular installation parameters, the design goal is that
once steady-state is reached, the system can be run for extremely
long operating periods without being shut down, i.e., periods on
the order of years. Controlling residue water (brine) extraction,
and thus heat removal, maintains a steady-state condition so that
the apparatus does not keep cooling to below steady-state operating
conditions.
[0065] Once the hydrate has dissociated into its constituent fresh
water and gas or gases, the fresh water is pumped off, e.g. as at
54, and the gas is captured and recycled. (Provisions may be made
for liquefying certain gases where this is desired.) Additionally,
a portion of the water in the dissociation and heat exchange region
50 will be "gray water," which is fresh water containing some small
portion of salts that have been removed from the hydrate by washing
of the hydrate with water. The distinction between the "gray" or
mixed water and pure fresh water is indicated schematically by
dashed line 56. The gray water may be suitable for drinking,
depending on the salt concentration, or for agricultural or
industrial use without further processing. The cold, gray water may
be recycled back into the fractionation column, either by pumping
it back down to the hydrate formation section 34, as indicated at
58; or it may be injected back into the concentrated hydrate slurry
at a region of the fractionation column located above the heat
extraction portion 44, as indicated at 60, to increase the fluid
nature of the hydrate slurry and to aid in controlling overall
thermal balance of the system. Furthermore, providing gray water at
62 to dilute residual interstitial fluid allows for
pre-dissociation washing.
[0066] As further shown in FIG. 1, in the post-processing and
downstream usage section 14, the fresh water preferably is treated
by secondary treatment means 64. The secondary treatment means may
include, for example, fine filtering, gas extraction, aeration, and
other processing required to bring the water to drinking water
standard.
[0067] Moreover, it is extremely significant that depending on
operating parameters such as temperature of the source water, the
amount of residual seawater extracted in the heat extraction
section 44, dimensions of the installation, and other parameters
such as viscosities of fluids within the system; buoyancy of the
hydrate relative to all fluids within the system; salinity and
temperature of residual water; the design output requirements of
fresh water; salinity and temperature of input water; design
cooling requirements; system inefficiencies affecting thermal
balance; etc., the fresh water produced will be significantly
cooled. This cooled water can be used to absorb heat from other
applications or locations such as the insides of buildings, and
hence can be used to provide refrigeration or provide for
air-conditioning.
[0068] Finally, once the seawater has been cycled through the
desalination fractionation column and downstream processing
applications a desired number of times, the residual, concentrated
seawater (which may be highly saline in nature) is simply pumped
back to sea. Alternatively, it may be retained for those who desire
it.
[0069] With respect to overall design, engineering, and
construction considerations for the system, it is contemplated that
the desalination fractionation column 130 will be on the order of
15 to 20 meters in diameter, or even larger. Conventional
excavation and shaft-lining methodologies common to the mining and
tunneling industry can be used in the construction of the column
130. Overall dimensions will be determined based on the total
desired fresh water production desired and relevant thermodynamic
considerations. For example, one cubic meter of methane hydrate has
the capacity to warm about 90 to 100 cubic meters of water by about
1.degree. C. as it forms, and that same cubic meter of hydrate has
the capacity to cool about 90 to 100 cubic meters of water by about
1.degree. C. as it dissociates. (Mixes of suitable gases have
higher heats of fusion, which makes the process more efficient.)
Required cooling therefore will, in part, determine hydrate
production rates, and hence dimensions of the system and the choice
of gas or gases to meet those production rates.
[0070] Preferably, the diameter of the residual fluid removal
column segment is larger. This facilitates buoyant, upward movement
of the hydrate through the water column while first allowing
separation of residue water from the hydrate in the heat extraction
region 44, and then dissociation and heat exchange in the
dissociation and heat exchange region 50.
[0071] The dissociation and heat exchange region 50 may be
constituted not just by a single dissociation "pool," as shown
schematically in FIG. 2, but rather may consist of a number of
linked, heat-exchanging devices in a number of different water
treatment ponds or pools. The actual depth, size, throughput, etc.
will depend on the production rate, which will depend, in turn, on
the temperature of the input water, the particular gas or gas
mixture used to form the hydrate, the rate at which heat can be
removed from the system, etc.
[0072] The input of water into the base of the fractionation column
can be controlled by a device (not shown) that alters the input
throat diameter so as to facilitate mixing of the gas and water,
thereby promoting more rapid and complete hydrate formation.
Alternatively or additionally, hydrate formation can be enhanced by
creating flow turbulence in the input water, just below or within
the base of the hydrate forming gas injection port 36. It may
further be desirable to vary the diameter of the desalination
fraction column in a manner to slow the buoyant descent of the
hydrate slurry, thereby enhancing hydrate formation.
[0073] The dissociation and heat exchange region 50 will be
significantly wider and larger than the lower portions of the
desalination column. This is because hydrate will be floating up
into it and dissociating into gas and fresh water at a rate that is
faster than that which could be accommodated in a pool that is the
diameter of the column itself. Moreover, the requirement for heat
will be great; if sufficient heat cannot be provided, water ice
will form and disrupt the desalination process. Provision for
physical constriction within a column will hold hydrate below the
level where it dissociates freely, thus providing for a control on
the amount of gas arriving at the surface. This is done for both
normal operational and safety reasons.
[0074] Because the positively buoyant hydrate used in this
embodiment of a hydrate-based fluid processing installation floats,
fresh water tends to be produced at the top of the section, thereby
minimizing mixing of fresh and saline water. To inhibit unwanted
dissociation, the heat exchanger apparatus may extend downward to
the top of the residual water removal section. The dissociation and
heat exchange pools do not need to be centered over the water
column; moreover, more than one desalination fractionation column
may feed upward into a given dissociation and heat exchange pool.
Similarly, groups of desalination fraction columns can be located
close together so as to be supported by common primary and
secondary water treatment facilities, thereby decreasing
installation costs and increasing economy.
[0075] In addition to large-scale installations, relatively
small-scale installations are also possible. For these
installations, smaller diameter desalination columns can be
constructed in locations where lower volumes of fresh water are
required. Although overall efficiency of such systems will be lower
than larger scale systems, the primary advantage of such
small-scale installations is that they can be implemented using
standard drilling methods. Furthermore, mass-produced,
prefabricated desalination apparatus sections can be installed in
the casings of drilled holes; this allows the installation to be
completed in a relatively short period of time. Capital cost of
such an installation also is reduced, as fabrication of the
components can be carried out on an industrialized basis using mass
production techniques. The various operating sections of a
smaller-scale installation might be replaced by extracting them
from their casing using conventional drilling and pipeline
maintenance techniques.
[0076] An alternate, slightly simplified embodiment 230 of a
hydrate-based fluid treatment (e.g., desalination) fractionation
column is shown in FIG. 5. In this embodiment, hydrate formation
occurs essentially within a thermal equilibration column 132. The
thermal equilibration column 132 has an open lower end 134 and is
suspended in shaft 136. In this embodiment, input water is injected
near the base of the desalination column 132, e.g. as at 138,
preferably after passing through heat exchange and dissociation
region 150 of the column 230 in similar fashion to the embodiment
shown in FIG. 2. Positively buoyant hydrate-forming gas is injected
into the lower portions of the thermal equilibration column 132, as
at 140, and hydrate will form and rise within the column 132 much
as in the previous embodiment.
[0077] The embodiment 230 is simplified in that heat of formation
of the hydrate is transferred to water surrounding the thermal
equilibration column 132 within a "water jacket" defined between
the walls of the column 132 and the shaft 136 in which the
desalination fractionation column is constructed. To this end, the
hydrate formation conduit preferably is made from fabricated (i.e.,
"sewn") artificial fiber material, which is ideal because of its
light weight and its potential for being used in an open weave that
greatly facilitates thermal equilibration between residual saline
water within the thermal equilibration column 132 and seawater
circulating within the water jacket.
[0078] As is the case with the embodiment shown in FIG. 2, warmed
water is pumped out of the system, this warmed water being water
which has circulated within the water jacket. In contrast to the
embodiment shown in FIG. 2, however, the intent of removing warmed
water from the water jacket is not to remove so much heat energy
that the input water is automatically cooled to temperatures
suitable for formation of the hydrate at the base of the column,
but rather it is simply to remove enough heat energy to prevent
water within the interior of the hydrate formation conduit from
becoming so warm that hydrate cannot form at all. Accordingly, the
rate at which warm water is removed from the water jacket may be
relatively small compared to the rate at which warm water is
removed from the heat extraction portion 44 of the embodiment shown
in FIG. 2. As a result, it is necessary to supplement the cooling
which takes place in the heat exchange and dissociation region 150
using supplemental "artificial" refrigeration means 152. Operation
is otherwise similar to that of the embodiment shown in FIG. 2:
fresh water is extracted from the upper portions of the heat
exchange and dissociation portion 150; "gray water" is extracted
from lower portions of the heat exchange and dissociation region
150, i.e., from below the line of separation 156; and concentrated
brine is removed from brine sump 141.
[0079] To facilitate "settling out" of residual fluid or brine
(e.g., salt brine) which is sufficiently dense to be negatively
buoyant due to concentration and/or cooling, and to facilitate heat
transfer and thermal equilibration, the equilibration column 132
preferably is constructed with overlapping joints, as shown in FIG.
6. This configuration permits the buoyant hydrate to rise
throughout the column, while cooled, more saline water can flow out
through the vents 142, as indicated schematically.
[0080] The hydrate fractionation column installation may be further
simplified by feeding the input water into the system without
passing it through the dissociation section 250 of the embodiment
330 shown in FIG. 7. If the input water is not sufficiently cold,
more artificial refrigeration will need to be provided by
refrigeration means 252, but operation is otherwise the same as
embodiment 230 shown in FIG. 5.
[0081] Whereas the embodiments described so far utilize gas or
mixtures of gas which form positively buoyant hydrates under
appropriate temperature and pressure conditions, the versatility of
hydrate-based desalination, purification, or other fluid treatment
can be expanded greatly by adapting the methods and apparatus
described above to accommodate negatively buoyant hydrates. An
embodiment 430 of a hydrate fractionation "column" configured to
permit the use of negatively buoyant hydrate for water purification
is shown in FIGS. 8-10. The major difference between this
embodiment 430 and the preceding embodiments of hydrate
fractionation columns is that the heat exchange and dissociation
portion 350 of the installation is laterally or horizontally
displaced or offset relative to the hydrate formation and heat
removal sections 336 and 346, respectively. The hydrate formation
and heat removal sections are similar to those in the embodiments
described above.
[0082] A number of different operating gases can be employed with
this configuration. Low molecular weight gases such as O.sub.2,
N.sub.2, H.sub.2S, Ar, Kr, Xe, CH.sub.4, and CO.sub.2 all form
hydrates under different pressure-temperature conditions. Each of
the different hydrate-forming gas systems will require special
design of the hydrate column, which is tailored to the particular
gas used in the installation, but the principles of hydrate
formation to extract fresh water will remain the same.
Additionally, adding small amounts of additive gas(es) to the
primary hydrate-forming gas may broaden the hydrate stability field
in the same way the methane hydrate stability field is expanded by
mixing higher density hydrocarbon gases with methane.
[0083] Although a number of different gases that form negatively
buoyant hydrate may be used for hydrate-based treatment (e.g.,
desalination), carbon dioxide and the desalination column in which
it is used are described herein to illustrate the design
requirements and considerations for a treatment system employing
hydrate that is naturally less buoyant than the fluid matrix (e.g.,
seawater). Carbon dioxide (or carbon dioxide-based gas mixtures,
referred to herein simply as "carbon dioxide" for simplicity) is an
ideal gas to use for a number of reasons: carbon dioxide does not
combust under the physical and thermal conditions encountered in
the hydrate desalination apparatus, and is thus virtually
hazard-free; carbon dioxide hydrate is stable at shallower depths
than methane hydrate (and about the same as mixed gas methane
hydrate); even if present dissolved in relatively high
concentrations, carbon dioxide is safe for human consumption--in
fact, fresh water produced using carbon dioxide can be made so as
to retain some quantity of the carbon dioxide, thereby providing
soda water that is similar to many popular brands but that is
different in at least one significant way: it will contain all the
naturally occurring minerals found in seawater in proportion to the
remaining salts not removed during the desalination process--and is
not offensive to either taste or smell (as would be the case of
H.sub.2S hydrate); carbon dioxide hydrate is, like methane,
tasteless and odorless; there is considerable recent experimental
information which demonstrate clearly the actual marine behavior of
the formation and behavior of carbon dioxide hydrate; and carbon
dioxide is very common and can be produced locally almost anywhere
and is also commonly available as an industrial waste product. (A
further advantage of using carbon dioxide as compared to methane or
methane mixes is that the higher heat of fusion of carbon dioxide
hydrate will heat the residual water more quickly than methane or
methane-mixed gases; thus, the induced thermal bias will be higher
and the system will operate more efficiently.)
[0084] Design and engineering of the hydrate fractionation column
will be determined in large measure based on the phase properties
of the particular gas being used. FIG. 11 shows, for example, the
carbon dioxide hydrate stability regions superimposed over the
carbon dioxide phase diagram. The shaded portion of the diagram
indicates that carbon dioxide hydrate (formed from carbon dioxide
gas) is stable at from an upper pressure limit of about 18
atmospheres, just above 0.degree. C., to about 40 atmospheres
pressure at just above about 8.degree. C. With respect to carbon
dioxide, per se, the liquidus extends from about 37 atmospheres
pressure at just above 0.degree. C., to about 40 atmospheres
pressure at just above 8.degree. C. Above the liquidus, carbon
dioxide exists as a gas; below the liquidus, carbon dioxide
spontaneously compresses to a liquid.
[0085] Accordingly, the system is constructed so that, assuming
carbon dioxide is used as the operating gas, the carbon dioxide is
injected into the hydrate formation portion of the column at
ambient temperature and pressure that is within the operating
region 450 that consists of the portion of the carbon dioxide
hydrate stability zone that lies above the carbon dioxide liquidus
and above the freezing point of water. The practical result of this
is that the range of water depths at which carbon dioxide may be
used as the operating gas is relatively small and is comparatively
shallow. Accordingly, a relatively shallow land apparatus can be
constructed, which will reduce construction complexity and
cost.
[0086] Similar to the embodiments described above, carbon dioxide
(or other negatively buoyant hydrate-forming gas, as desired) is
injected near the base of the hydrate formation section 336 (e.g.,
at 352) and mixed with supply or input seawater that has been
chilled by being passed through the heat exchange and dissociation
portion 350 and/or by "artificial" refrigeration, as at 354. The
carbon dioxide hydrate will float only if the formation of the
hydrate is incomplete such that a complex, hydrate-gas meshwork is
formed. This condition is met when the gas is injected rapidly and
in relatively large bubbles. The carbon dioxide hydrate isolates
carbon dioxide gas bubbles from the surrounding seawater, thereby
preventing further formation of hydrate. The combined gas/liquid
carbon dioxide and hydrate is positively buoyant, even though the
hydrate per se is negatively buoyant (i.e., has a greater specific
gravity than the seawater), and floats upward, as at 356.
Additionally, some of the bubbles will burst and new hydrate shells
will be formed; hydrate shells with gas bubbles predominantly form
new carbon dioxide hydrate rims, which are assisted upward by
carbon dioxide gas which tends to adhere to solid hydrate
particles.
[0087] The system is designed to produce as much hydrate as
possible, consistent with leaving enough warm, lower-density,
residual fluid to form a "flux" and to allow extraction of heat by
removing the residual seawater in the heat extraction section 346.
The system furthermore has the capacity for very rapid liquid or
gas injection, which may be in time-sequence bursts rather than
being continuous. It is intended that not all gas form hydrate, as
noted above, to ensure incomplete formation of hydrate. Thus,
larger quantities of gas are required for a negatively buoyant
hydrate-based system than for a complete hydrate-forming gas system
such as the positively buoyant hydrate-based systems described
above.
[0088] As in the case of positively buoyant hydrate-based
embodiments, formation of the negatively buoyant (assisted
buoyancy) hydrate is exothermic. Accordingly, heat which is given
off during hydrate formation warms the surrounding, residual brine,
e.g., seawater, which makes the residual seawater more buoyant than
the chilled seawater which is being input into the lower part of
the column. The residual seawater therefore moves buoyantly upward
along with the hydrate as new, denser input water is supplied to
the base of the fractionation column, as at 360.
[0089] The upward movement of the surrounding residual seawater,
along with the original upward movement of the assisted buoyancy
hydrate, has a certain momentum associated with it. This carries
the hydrate upward through the column until it reaches a lateral
deflection zone 362, where the hydrate/residual seawater slurry is
diverted horizontally or laterally relative to the hydrate
formation and heat removal sections 336 and 346 and into the
dissociation and heat removal section 350. Thus, even though some
of the hydrate "bubbles" will burst or crack, thereby releasing the
carbon dioxide gas contained therein and losing buoyancy, the
hydrate in large measure continues to move upward and over into the
heat exchange and dissociation region of the column 350 due to this
momentum. As the hydrate loses momentum within the heat exchange
and dissociation portion 350, it will settle and dissociate into
the gas and fresh water, which will separate from residual seawater
as described in greater detail below.
[0090] Some of the hydrate, however, will form solid masses without
entrapped gas and will sink to the lowermost, sump portion 364 of
the column. Concentrated brine will also sink to and settle in the
sump portion 364. The sunken hydrate and concentrated residual
brine are pumped out of the sump at 365 and separated by
appropriately configured separation means 366. The waste saline
water 368 is disposed of as appropriate, and a slurry consisting of
the sunken hydrate is pumped upwardly as indicated at 370 and is
discharged into the heat exchange and dissociation chamber 350,
e.g. at 372, where the hydrate dissociates into gas and fresh
water.
[0091] Within the dissociation and heat exchange chamber 350, the
hydrate, whether delivered or transported to the chamber via the
lateral deflection portion 362 of the column or pumped from the
sump of the desalination fractionation column 364, will dissociate
into fresh water and the hydrate-forming gas.
[0092] To facilitate separation of fresh water from saline water,
it is necessary to promote transfer of as much hydrate to the upper
part of the dissociation and heat exchange chamber 350 as possible;
to hold hydrate as high in the dissociation and heat exchange
chamber 350 as possible until dissociation of that volume of
hydrate is complete; and to keep mixing of the fresh water produced
by dissociation and the more saline residual water to a minimum.
The configuration of the dissociation and heat exchange chamber
shown in FIGS. 9 and 10 facilitates these objectives.
[0093] In particular, the assisted buoyancy hydrate slurry rising
through the desalination fractionation column enters the chamber as
at 360 after being diverted laterally at deflection portion 362, as
indicated schematically in FIG. 9. Additionally, hydrate slurry
being pumped from the sump is injected into the dissociation
chamber at 372, where it may be placed within special fluid
separation devices. The dissociation and heat exchange chamber is
constructed with a number of canted separator shelves 380 which
extend from one end of the chamber to the other, as well as from
one side of the chamber to the other. The canted nature of the
shelves allows the denser saline water to sink and the lighter
fresh water to rise within and between the shelves, thereby
minimizing turbidity and mixing of saline and fresh water. The
separator shelves 380 are canted in that they slope downward, both
from one end of the chamber to the other as well as from one side
of the chamber to the other. The separator shelves have
pass-through apertures 382 which allow the denser, saline water to
sink within the system and the less dense, fresh water to rise
within the system to the top of the chamber as the hydrate
dissociates into the fresh water and gas.
[0094] Fresh water, which is cooled due to the cooling bias created
by the removal of warm residual water as described above in
connection with the positively buoyant hydrate embodiments, is
removed as at 384 and may be used for cooling as well as for
potable water. "Gray" water and saline residue are removed from
lower portions of the heat exchange and dissociation chamber 350,
as at 386 and 388, and are handled as described above in the
context of the positively buoyant hydrate embodiments, e.g., gray
water may be used for drinking or industrial applications and the
saline residue may be recycled back as input into the base of the
desalination fractionation column.
[0095] As an alternative to gaseous carbon dioxide, liquid carbon
dioxide can be used to form assisted buoyancy hydrate. At the
relatively shallow depths appropriate to the formation of hydrate
for separation of fresh water, liquid carbon dioxide is more
buoyant than seawater (although not as buoyant as gaseous carbon
dioxide.) By injecting liquid carbon dioxide energetically into
seawater, a resultant meshwork of hydrate and liquid carbon dioxide
is formed which is positively buoyant. The meshwork mass will rise
spontaneously as a whole immediately upon forming and will behave
essentially the same as a hydrate meshwork formed from gaseous
carbon dioxide and carbon dioxide hydrate.
[0096] (Advantages of liquid carbon dioxide over gaseous carbon
dioxide stem from the fact that once the carbon dioxide is
compressed, it can be transported to deeper depths without further
compression. Thus, injecting liquid carbon dioxide at depths of
five hundred meters or more--well below the liquidus--is possible
without the need for deep, in-line pumps. Moreover, deeper (i.e.,
higher pressure) injection of liquid carbon dioxide will promote
very rapid crystallization and growth of the hydrate crystals.)
[0097] When liquid carbon dioxide is used to form assisted buoyancy
hydrate, dissociation is comparatively violent because the
unhydrated liquid carbon dioxide trapped within the meshwork
produces large volumes of carbon dioxide gas when the mixture rises
above the liquidus. Thus, in addition to the carbon dioxide gas
released by dissociation of the hydrate (which occurs above the
carbon dioxide liquidus), the extra gas produced by conversion of
the liquid carbon dioxide to gaseous carbon dioxide has the
potential to cause significant turbulence and mixing. Therefore,
flow of the hydrate should be controlled such that it enters the
dissociation section while still within the hydrate stability field
in order to preclude significant dissociation while residual
interstitial saline water remains in the slurry.
[0098] Additionally, where carbon dioxide liquid is used to form
assisted buoyancy hydrate, care should be taken to allow residual
fluid to alter its state to gas once the hydrate has risen above
the liquidus pressure depth, but while the hydrate remains stable.
This will reduce turbulence and mixing when the hydrate finally
dissociates.
[0099] Ideally, residual saline water should be replaced by fresh
water before the hydrate rises into the gas-stable zone and then
the dissociation area of the carbon dioxide hydrate phase diagram
(FIG. 11). This can be accomplished using multiple water injection
points alternatingly arranged between multiple residual or
interstitial water removal sections, as illustrated in FIG. 12. In
other words, the fluid removal section 44 (FIG. 2) is constructed
as an alternating sequence of fresh water injection subsections 412
and fluid removal subsections 414 constructed as shown in either
FIG. 3 or FIG. 4. The benefits of removing the interstitial saline
fluid include additional heat removal; washing of the slurry (i.e.,
removal of pollutants or adhering ions or particulate material from
the surface of the hydrate crystals) by fluid replacement; and
direct removal of saline interstitial water from the hydrate slurry
and dilution or replacement of the original saline interstitial
fluid produced by the process of hydrate formation.
[0100] Although washing of interstitial water is strongly
recommended for the slurry mixture of liquid carbon dioxide and
carbon dioxide hydrate so as to minimize turbulence and mixing
attributable to the liquid carbon dioxide converting to gaseous
carbon dioxide, washing the slurry and flushing saline interstitial
fluid therefrom would also provide benefits for any positively
buoyant hydrate-based or assisted buoyancy hydrate-based system. In
particular, injecting cold water (either fresh or gray) from the
dissociation section into the hydrate slurry will remove additional
heat from the hydrate at the same time that saline interstitial
water is flushed from the hydrate slurry. Moreover, multiple
residual water flushings will ensure greater fresh water
production.
[0101] Another embodiment 530 of a hydrate fractionation "column"
for hydrate-based fluid treatment (e.g., desalination) which is
configured to utilize negatively buoyant hydrate and which
facilitates separation of the hydrate and residual seawater is
illustrated in FIGS. 13 and 14. The "column" is configured as an
asymmetric, U-shaped installation, which consists primarily of a
seawater input conduit 432, a hydrate formation and catch sump
region 434, and a residue fluid riser conduit 436. As in previous
embodiments, the seawater input conduit passes through a
dissociation and heat exchange region 438 which, in this
embodiment, is configured especially as a hydrate "catch basin." As
in the previous embodiments, the input water is passed through the
dissociation/heat exchange catch basin 438 in heat exchanging
relationship with dissociating hydrate in order to chill the input
seawater.
[0102] The input seawater is pumped to the base 440 of the column,
where it turns and flows upward and laterally through elbow portion
442 before entering the hydrate formation and catch sump 434.
Negatively buoyant hydrate-forming liquid or gas is injected into
the input seawater in the hydrate formation and catch sump at 444.
(Means 945 for liquefying certain gases are provided; residual
fluid can be used in a heat exchanger 457 to provide cooling for
the liquefaction process.) Injection of the gas or liquid is
controlled such that hydrate formation is complete (in contrast to
incomplete, as in the case of the previously described, assisted
buoyancy embodiment), i.e., such that all gas is utilized to form
hydrate. The negatively buoyant hydrate settles to the bottom of
the catch sump 434. As the hydrate settles, it displaces the
residual seawater, which is warmed by the heat liberated during
hydrate formation. The residual seawater therefore rises buoyantly
through residue fluid riser conduit 436, and it is pumped out of
the system to remove heat and create a cooling bias in the system
as in the previously described embodiments.
[0103] The rate of formation and settling of the hydrate is
controlled such that it "packs" down to the point of being grain
supported. Mechanical apparatus such as a vibration tray is located
on the sloping floor 439 of the settling portion of the
hydrate-residual fluid chamber 434. This concentrates the hydrate
and minimizes residual fluid remaining so that the hydrate can be
pumped rapidly, as a slurry, from the base of the sump up into the
dissociation/heat exchange catch basin 438 via slurry pumping
conduit 446. The hydrate slurry is pumped to the dissociation/heat
exchange catch basin 438 at a rate that is generally faster than
the rate at which positively buoyant hydrates rises in the
previously described embodiments. Decreasing the time required to
transfer the hydrate from the formation region (where it is at its
maximum stability) to the dissociation region (where it is at its
minimum stability) ensures that a greater proportion of the hydrate
will dissociate relatively high in the catch basin. This reduces
the amount of mixing of fresh and residue water and increases the
relative proportion of fresh water that can be recovered.
[0104] Pumped hydrate slurry arrives in the dissociation/heat
exchange basin in a concentrated form with little more than
intergranular saline water present. Care is taken to allow the
saline water to separate downward and fresh water upward so that
there is a minimum of mixing. This is achieved by placing a slurry
holder and fluid separator tank in the upper part of the
dissociation/heat exchange chamber 438. This allows the negative
buoyancy hydrate dissociation to take place so that saline water is
delivered to and collects in the lower part of the dissociation
chamber 438, in which the slurry holder and fluid separator tank is
placed, without mixing with fresh water.
[0105] An embodiment of a slurry holder and fluid separator
consists of a fixed, wide-mouthed, upwardly open tank or tanks 450
(FIG. 14) that receive the hydrate slurry from above. Each tank
holds the negatively buoyant hydrate from the hydrate slurry
transfer system 446 and prevents it from sinking to toward the base
of the dissociation chamber 438. The hydrate slurry is delivered by
pipes 448 to a number of hydrate spreaders consisting of vanes or
rotating vanes designed to disperse the granular hydrate 468. The
negatively buoyant hydrate separates while falling to a screen
shelf 470 in the tank. This allows saline water to sink through the
screen shelf at the base of the circulating input water intercooler
system 474, which transfers heat from the input water to the
dissociating hydrate and feeds the cooled water downward to be
treated.
[0106] A number of residual water delivery pipes 475 extend
downward from the base of this slurry holding tank, which allows
heavier saline water to flow to the base of the vessel without
disturbing the water surrounding these pipes. Thus, even when the
fresh water-saline water interface is located in the vessel below
the slurry holding tank, no mixing occurs between the residue water
purged from each input of hydrate slurry because of a physical
separation. The main interface 477 (dashed line) between fresh and
saline water will be located somewhere the lower part of the
dissociation/heat exchange chamber 438, where saline water
naturally collects below fresh due to density differences. Saline
water is removed at the base of the chamber 480, and provision is
also made for gray water removal as at 482.
[0107] Multiple slurry holding tanks may be placed within a given
dissociation/heat exchange chamber so that the flow of hydrate
slurry can be rapid enough to prevent clogging or freezing up of
any one tank. Circulating input water may be passed first through
one slurry holding tank and then through another to minimize
temperature of the input water as it exits the dissociation/heat
exchange chamber.
[0108] All fluids will find their relative positions according to
natural buoyancy or through a process of fractionation. All
internal piping in the vessel can be fabricated from inexpensive
plastic or other material. This method of fluid separation may also
be installed in the dissociation/heat exchange section of the
assisted buoyancy and pumped sump embodiment shown in FIG. 8.
[0109] The slurry pumping conduit 446 may be constructed as a
variable volume pipe, in order to permit periodic pumping of
hydrate without allowing the hydrate to settle or move upward
slowly. Such a variable volume pipe can be fabricated relatively
easily by inserting a flexible sleeve within the slurry pumping
conduit 446 around which fluid can flood when the pressure within
the liner is reduced.
[0110] The injection point 444 of the hydrate-forming liquid or
gas, it will be noted, is positioned above the base of the column
440 so that in the event of incomplete hydrate formation (which
would result in the formation of assisted buoyancy hydrate), any
excess gas which does not form hydrate (along with assisted
buoyancy hydrate) will rise up the residue fluid riser conduit 436.
(Very little hydrate will escape with gas up the residue fluid
riser conduit 436, and any such hydrate will have dissociated prior
to arriving at the top of the residue riser section. Therefore, the
amount of fresh water "lost" by being transported by such hydrate
will be minimal; recovery of that fresh water is not feasible; and
accordingly no connection is provided between the output of the
residue fluid riser conduit 436 and the dissociation/heat exchange
catch basin 438.)
[0111] For proper operation of this embodiment, flow rate controls
such as constrictors should be used to keep the rate of flow of
fluid through the system low enough to keep solid hydrate from
being swept up the residue fluid riser conduit 436. Furthermore,
the design of the hydrate formation and catch sump 434, as well as
the lower portion of the residue fluid riser conduit, should be
designed to facilitate "clean" separation of the hydrate from the
residue fluid. Accordingly, the hydrate formation and catch sump
434 is designed to impart lateral movement to the residue fluid as
well as to permit upward movement thereof. This causes the
hydrate/residue fluid mixture to move initially with a relatively
small upward component, which facilitates settling out of the
hydrate and which is in contrast to the previously described
embodiments, which provide more vertically oriented fluid movement
that is comparatively turbid and which have poorer settling and
separation characteristics.
[0112] In the embodiments described thus far, the weight of the
column of water creates the pressures required for hydrate
formation. In these embodiments, the minimum pressure depth at
which hydrate is stable is far greater than at sea level, where the
pressure is one atmosphere. Accordingly, the hydrate begins to
dissociate at relatively elevated pressures.
[0113] Various ones of the embodiments described above may be
modified so as to collect the fresh water released from the hydrate
and to capture the released gas at the region of the fractionation
column where the dissociation takes place, rather than at the top
of the column (surface level; one atmosphere ambient pressure),
with certain resultant advantages. In particular, relatively large
volumes of hydrate-forming gases and gas mixtures are required to
desalinate large volumes of water. Therefore, if the gas is
captured, processed for re-injection, and stored while maintained
at elevated pressures (e.g., the pressure at which the hydrate
begins to dissociate), the volume of gas that must be handled will
be much smaller than would be the case if the gas were allowed to
expand fully as it rises to the surface and pressure drops to
atmospheric. Additionally, if the hydrate-forming gas is kept
pressurized, raising its pressure to the pressure required for
injection in the hydrate-forming section requires far less
recompression of the gas and hence is less costly.
[0114] An embodiment 600 in which dissociation and gas capture and
processing are controlled so as to be kept at elevated pressure is
illustrated in FIG. 15. In this embodiment, a physical barrier 610
extends across the fractionation column and blocks the upward
movement of the hydrate slurry. The location of the barrier 610
depends on the stability limits of the particular hydrate-forming
substance used, but will be above the region of hydrate stability
(i.e., at lesser pressure-depth). As the hydrate dissociates, the
released gas forms a pocket at trap 620 and enters a gas recovery
and processing system 626 while still at a pressure depth
considerably greater than one atmosphere surface pressure. (The gas
processing system 626 may contain means for liquefying certain
gases.) The gas is processed and re-injected into the hydrate
formation section 628 at 629 in the same manner as in the
previously described embodiments, except the gas system is
maintained at considerably higher pressure.
[0115] The hydrate dissociation section 630 extends downward to
some particular depth determined by the particular hydrate-forming
gas being used. Because the hydrate dissociates under "controlled,"
elevated pressure, the dissociation reaction will proceed generally
more slowly than in the above-described embodiments. Therefore, the
heat exchanger 632 present in the dissociation/heat exchanger
section (as described in connection with previous embodiments) is
designed to accommodate the particular, slower reaction rates.
Input water 634 is passed through the dissociation/heat exchange
section in heat exchanger 632 and is injected into the base of the
desalination fractionation column at 636, as in previously
described embodiments.
[0116] One or more fresh water bypass pipes 640 communicate with
the dissociation region at a point 641 located above the fresh
water/saline water interface 644 but below the upper boundary 648
of the hydrate stability field. The pipe(s) 640, which are screened
or otherwise configured to prevent hydrate from entering them,
deliver fresh water released from the hydrate to fresh water
accumulation region 666. A gray water return pipe 650 allows
denser, more saline gray water to flow back down into the saline
fluid below the fresh water/saline water interface 644. More highly
saline residual water and/or negatively buoyant hydrate is drawn
from the sump 654 and processed or removed as at 658, as in
previously described embodiments. Output fresh water, some of which
may be returned to the fluid removal section for purposes of
washing interstitial saline water as described above (not shown),
is drawn off at 660, near the top of the fresh water accumulation
region 666 and well above the physical barrier 610.
[0117] It is contemplated that the physical barrier 610, the fresh
water and gray water return pipes 640, 650, and the heat exchanger
in the dissociation/heat exchange section 630 may be configured
such that their positions can be varied, thereby permitting
different hydrate-forming liquids, gases, or gas mixtures to be
used in the same installation. The physical barrier 610 and heat
exchanger might be vertically adjustable, whereas a series of
bypass and return pipes 640, 650 having different inlet locations
can be provided and opened and closed remotely using suitable inlet
and outlet valves. In this manner, changing from one
hydrate-forming substance to another can be effected very quickly
and conveniently.
[0118] By holding and fully processing for re-injection the
hydrate-forming gas while it is still under pressure, considerable
economies of operation can be achieved. The variation in the
pressure of the liquid or gas, from that required for formation of
the hydrate down to that at which fresh water is released from the
hydrate, can be kept to a minimum. This, in turn, minimizes the
energy cost associated with pumping the captured hydrate-forming
gas from above the dissociation/heat exchange section back down to
the hydrate-forming section at the base of the apparatus,
particularly considering the fact that, percentagewise, the
greatest change of pressure in a hydraulic column (such as any of
the above-described embodiments) takes place in the upper portions
of the column. Moreover, the volume of the gas to be handled (and
accordingly the size of the gas handling equipment and facility)
will also be reduced significantly.
[0119] As an alternative (not shown) to the configuration shown in
FIG. 15, the upper part of the desalination fractionation column
can be sealed and pressurized by means of an associated hydraulic
standpipe, thereby causing pressures within the apparatus near the
surface to be equivalent to the pressure-height of the standpipe.
Where the standpipe is implemented in tall structures (such as
adjacent buildings near the desalination facility), relatively high
pressures can be created in the topmost part of the
dissociation/heat exchange section, which is at ground level.
[0120] In further embodiments of the a hydrate-based fluid
treatment installation, fluid to be treated may be desalinated or
purified in self-contained, mechanically pressurized vessels. Such
embodiments offer a number of distinct advantages, including the
fact that the installations can be of various sizes and shapes to
suit local conditions, containment constraints, and fresh water
requirements. Moreover, whereas the previously described
embodiments are relatively large-scale and therefore are of a
fixed, permanent nature, self-contained, pressurized embodiments
can be more temporary in nature in terms of their construction and
their location. Individual pressurized installations can occupy
relatively small spaces and produce fresh water efficiently, even
in low volumes. Such installations can be fabricated at central
manufacturing facilities and installed on site with a minimum of
local site construction, which site might be a building or even a
ship or other mobile platform.
[0121] A mechanically pressurized installation configured to use
positively buoyant hydrate to extract fresh water from, for
example, seawater is illustrated in FIG. 16. Input water is pumped
and pressurized from input pressure to the operating system
pressure by pump 704. The water enters the pressurized hydrate
formation and separation vessel 710 at water input 711, and a
suitable, positively buoyant hydrate-forming substance is injected
at injection point 712. (Means 713 for liquefying certain gases are
provided where this is advantageous to the desalination process.)
Positively buoyant hydrate 714 spontaneously forms and rises
through the residual water, as in previously described embodiments,
to the top of the vessel 710 where it accumulates and
concentrates.
[0122] The buoyant hydrate slurry is subsequently admitted into
transfer and washing section 720, and then into the
dissociation/heat exchange vessel 722. (Flow of the hydrate slurry
is regulated by valves 734.) While in the transfer and washing
section 720, the hydrate may be washed of the residual,
intergranular saline fluid using fresh water 726 tapped from the
fresh water output 728. More than one wash cycle may be used to
completely flush residual fluid, although the number of washings
will depend on the effectiveness of separation through
fractionation (which may vary for different gases and gas mixtures)
and the nature of the crystalline fraction of the slurry. In some
cases, no washing may be necessary.
[0123] Pressure is maintained in the hydrate formation and
separation vessel 710 and in the dissociation/heat exchange vessel
722 by pressure balance reservoir systems 732 (one for each
vessel), and movement of fluid from one vessel to the other is
controlled by varying pressure and using the in-line valves 734.
The systems 732 each have a pressure pump 733 and a diaphragm or
gas-fluid interface 736, which are used to raise and lower pressure
in each vessel. Pressure in the vessels is controlled so that the
hydrate remains stable as hydrate until it is finally collected and
concentrated at the top of the dissociation vessel 722. This is
because premature dissociation will release considerable amounts of
gas and therefore will cause undesired mixing. Moreover, pressure
conditions in the dissociation vessel should be controlled to
minimize turbulence in the fluid-gas mixture and to promote
efficient separation of saline and fresh water.
[0124] The dissociation and heat exchange vessel 722 may be
constituted by a number of linked, heat-exchanging devices in a
number of different water treatment chambers. The actual size,
throughput, etc. will depend on the overall system production rate
which, in turn, will depend on the temperature of the input water,
the particular liquid, gas, or gas mixture used to form the
hydrate, the rate at which heat can be removed from the system,
etc. Fractionation, concentration, separation, drying, and re-use
of the hydrate-forming gas takes place in the same manner as in the
previously described embodiments. Additionally, heat produced by
liquefying hydrate-forming gas can be absorbed and removed using
heat exchangers containing residue or saline fluids.
[0125] It will be appreciated that the mechanically pressurized
process is inherently less continuous than the previously described
embodiments and is essentially a batch process. Pressure in the
system is controlled so as to simulate the pressure variation in
the previously described embodiments: the fluid to be treated is
pressurized and injected into the apparatus, and then pressure is
raised and lowered to control the rate of the hydrate formation and
dissociation reactions.
[0126] Mechanically pressurized embodiments provide increased
versatility in that pressures may be controlled to provide the
optimum pressures for formation of hydrate and to control the rate
of dissociation. Moreover, different liquids, gases, and gas
mixtures can be used within the same apparatus, and the same water
can be processed more than once using different liquids, gases, and
gas mixtures.
[0127] A further mechanically pressurized embodiment 800, which
embodiment utilizes negatively buoyant hydrate to extract fresh
water from the fluid to be treated, is shown in FIG. 17. Input
water is pumped from input pressure up to the operating system
pressure and into the pressurized hydrate formation and separation
vessel 810 by pumps 804, and a suitable, negatively buoyant
hydrate-forming gas is injected at injection point 812. (Means 812
for liquefying certain gases may be provided.) Negatively buoyant
hydrate 814 spontaneously forms and sinks through the residual
water, as described in connection with previously described
negatively buoyant hydrate embodiments, and collects and
concentrates in gated sump isolation sections 816, which are opened
and closed to control passage of the hydrate therethrough.
[0128] As in the previously described mechanically pressurized
embodiment, pressure is maintained in the system by pressure
balance reservoir systems 832 (one for each vessel), and movement
of the fluid can be controlled by varying the pressure in the
system compartments. Pressure pumps 830 and diaphragms or gas-fluid
interfaces 836 are used to raise and lower pressure in each vessel
independently.
[0129] As the hydrate slurry passes through the transfer and
washing section 820 and into the dissociation/heat exchange vessel
822, it may be washed of the residual, intergranular saline fluid
with fresh water tapped from the fresh water output 828, which
removes salt from the hydrate slurry prior to dissociation.
[0130] Subsequently, the hydrate is permitted to flow downward from
the transfer and washing section 820, and into the hydrate
dissociation and heat exchange vessel 822, where is dissociates and
fresh, gray, and saline water are removed. Heat exchange between
the input water and the dissociating hydrate slurry occurs as
described in previous embodiments. Dissociation takes place under
controlled pressure conditions to minimize turbulence in the
fluid-gas mixture and to promote efficient separation of saline and
fresh water.
[0131] A slurry holder and fluid separator tank 860 may be provided
in the upper part of the dissociation/heat exchange vessel 822 and
is similar in construction to that described above and shown in
FIGS. 12 and 13. The tank 860 minimizes mixing of fresh and saline
water by providing a conduit for the residual saline water to sink
to the bottom of the vessel, which conduit isolates the saline
water from the lower density fresh water.
[0132] As in the case of the mechanically pressurized, positively
buoyant hydrate embodiment, the dissociation and heat exchange
vessel 822 may be constituted by a number of linked,
heat-exchanging devices in a number of different water treatment
chambers. The actual size, throughput, etc. will depend on the
production rate which, in turn, will depend on the temperature of
the input water, the particular liquid, gas, or gas mixture used to
form the hydrate, the rate at which heat can be removed from the
system, etc. Fractionation, concentration, separation, drying, and
re-use of the hydrate-forming substance takes place in the same
manner as in the previously described embodiments.
[0133] Another embodiment 900, which embodiment provides greater
versatility by using either positively or negatively buoyant
hydrate to treat fluid such as seawater or polluted water, is shown
in FIG. 18. Pumps P and in-line valves 914 are provided throughout
the system. Operation, depending on the particular hydrate-forming
substance used, is as described in the pressurized vessel
installations using either positively or negatively buoyant gas
hydrate.
[0134] This embodiment is particularly useful where the gas or gas
mixture supply is uncertain as a variety of gases may be used.
Embodiments of this type could be useful in disaster relief or in
expeditionary military activity, or at any place where a temporary
supply of fresh water is required without a significant
construction requirement. This embodiment contains all the
attributes of both the positive and negative buoyancy hydrate,
mechanically pressurized desalination fractionation embodiments,
including use of fresh water 926 from the fresh water output 928 to
flush residual saline water. Multiple liquid or gas injection
points 908 are provided, as well as provision for handling either
positively or negatively buoyant hydrate. In particular, multiple
pumping units P and fluid control valves 914 are provided to direct
the flow of fluids and hydrate slurries in fluid control and
washing units 916 and hydrate slurry control units 918. The gas
processing system 944 includes means for liquefying certain
recovered gases and gas mixtures.
[0135] As in the above-described embodiments in which the weight of
the column of water generates the requisite pressures, any of the
mechanically pressurized vessel installations may be simplified by
feeding the input water into the system without passing it through
the dissociation section for heat exchange. More artificial
refrigeration will need to be provided, but operation will
otherwise be the same as for the positive and negative buoyancy
hydrate embodiments shown in FIGS. 16 and 17 and the "combined"
pressurized apparatus as shown in FIG. 18.
[0136] Similar compact installations can be fabricated as
pre-packaged components that can be airlifted or easily flown and
trucked to a particular site--for instance, to a waste pond needing
decontamination or reduction in water volume--and assembled
rapidly. Where temporary or mobile installations are operated, more
compact versions of the intake, outfall, and gas processing
apparatus similar to that described for FIG. 1 are employed. These
can be specially designed for light weight, ease of deployability,
and ability to operate in a variety of conditions.
[0137] Hydrate-Based Treatment/Reclamation from a Highly
Contaminated Body of Water
[0138] As explained above, there is a pressing need for better,
more versatile, cost-effective techniques to decontaminate and
reduce the water volumes of industrial pond waste water inventories
and other highly saline or otherwise contaminated bodies of water.
Hydrate-based processing is a solution.
[0139] Any of the above-described methods for forming, collecting,
and dissociating (melting) the hydrate may be employed to do so.
Where the body of fluid (e.g., a waste water holding pond) is deep
enough to generate the necessary hydrate-forming pressures, an
in-land shaft approach as described above and in the referenced
patents may be used, with the pond itself constituting the shaft.
In that regard, a shaft, as that term is used above or in the
referenced patents, can have a width that is generally on the same
order of magnitude as its depth. In other words, the term "shaft"
does not imply any specific relationship between the width of the
body of water and its depth, so long as the shaft extends to some
depth into the ground in which the pond is located. However,
depending on the fluid being treated, the hydrate-forming substance
being employed, and the required hydrate-forming pressures, it may
be desirable or advantageous to construct a separate shaft, e.g.
adjacent to a waste water holding pond, extending considerably
further into the ground than the depth of the waste water holding
pond and to conduct hydrate formation and separation in that
separate shaft.
[0140] Alternatively, any pressurized vessel apparatus, e.g., as
described above, may be used to form, collect, and dissociate the
hydrate.
[0141] Still further, a hybrid, pressurized shaft installation may
be used, as described in co-pending U.S. patent application Ser.
No. 10/019,691 filed Jan. 2, 2002 (published Oct. 24, 2003 as
Publication Number 2002/0155047 and claiming priority to PCT
application number PCT/US01/19920 filed Jun. 25, 2001), the
contents of which are incorporated by reference.
[0142] In conducting hydrate-based treatment of waste ponds or
other highly saline/contaminated bodies of water, in order to
enhance hydrate formation and growth, it may be desirable to
pre-treat the fluid being treated with hydrate-forming substance to
some level at or below saturation. Techniques for doing so are
described in U.S. Pat. No. 6,673,249 and co-pending U.S.
application Ser. No. 10/402,940 filed Apr. 1, 2003, the contents of
both of which are incorporated by reference.
[0143] An embodiment of the invention, as applied in the exemplary
context of reducing waste water volumes produced by a phosphate
fertilizer factory and held in a waste pond 1008, is illustrated in
FIG. 19. The Hydrate Processing Facility 1010 can be any suitable
facility, as described above, or it can be a waste water pond
itself.
[0144] In general, crystallizing gas hydrate in a strongly
saturated, toxic waste pond-water solution of the sort found in
ponds 1008 associated with such a phosphate fertilizer factory
causes the nucleation and growth of solid crystalline material
(e.g., phosphogypsum, Ca(P)SO.sub.4, in which small amounts of
phosphate (PO.sub.4.sup.3-) substitute for sulfate
(SO.sub.4.sup.2-) in the gypsum crystals) as the concentrations of
the various solutes rise above saturation. Hydrate formation also
strongly rejects suspended particulate matter 1012, which will
settle to the bottom of the pond (if the hydrate
formation/de-watering process is being conducted in a holding pond)
or hydrate-forming installation (shaft or pressure vessel). The
material is then dredged (if in a pond) or otherwise removed from
the installation, and may simply be piled in large mounds adjacent
to the body of water/waste fluid being treated. Alternatively,
depending on relative densities of the fluid and the crystallized
and/or rejected particulate matter, or if the crystallized and/or
rejected particulate matter has fine bubbles of hydrate-forming gas
adhered to it, the solid material may "hang" suspended in the fluid
column or may rise to the surface on its own. In those instances,
the solid material can be removed by filtering or other appropriate
means that would be known to one of skill in the art (e.g.,
centrifugal separation).
[0145] Following separation and removal of the hydrate crystals
from the residual brines and suspended particulate matter, the
hydrate is disassociated (melted), either on a continuous or a
batch basis depending on the nature of the installation and
process. This produces a melt water stream 1014, and the gas (or
other hydrate-forming substance) 1016 and purified water 1014 are
separated and recovered. The gas can be reused for further cycles
of hydrate formation if desired, thereby reducing the amount of gas
required, or it can be disposed of through combustion or other
chemical reactions. The melt water 1014 produced from the
dissociating hydrate will, in some instances, be pure enough to
dispose of as released surface water, e.g., as at 1018. Where
slight chemical contamination remains, however, polishing or other
conventional purification technology (e.g., reverse osmosis) can be
used to economically polish or further process the water to very
high levels of purity, as at 1020.
[0146] Alternatively or additionally, it may be desirable in some
instances to return all or a portion of the melt stream water to
the waste water holding pond, as illustrated at 1024. It is noted
that the invention has as one of its main benefits the reduction of
total volume of the waste water holding ponds for reasons explained
above, along with the additional benefit of providing an industrial
feedstock stream via the concentrated residual fluid as explained
below. However, there may be times (e.g., during droughts) when, if
the melt water stream were not returned to the pond, the fluid
level of the waste water holding pond would decrease too far or too
fast, in which case steady production the enriched feedstock stream
of residual fluid (e.g., the phosphate-enriched stream being
returned to a phosphate fertilizer plant) would be adversely
affected. Additionally, solids would precipitate out at an
undesirably high rate and/or the concentration of the residual
fluid would be undesirably high.
[0147] Because water is being removed from the solution by the
hydrate, the concentration of dissolved solute in the solution
(e.g., phosphate, mainly in the form of phosphoric acid
H.sub.3PO.sub.4), dissolved in the pond water) will increase
significantly. In general, the concentration of all dissolved ionic
materials increases in proportion to the amount of hydrate formed
in any particular volume of the water. Thus, the concentration of
any particular dissolved chemical species (for example, phosphoric
acid) remaining in the concentrated, residual brine stream 1022
(which will also exist either on a continuous or a batch basis,
depending on the nature of the installation and process used) can
be controlled or regulated by controlling the amount of hydrate
produced and removed in the hydrate processing facility 1010, thus
achieving a desired level of one or more dissolved species (the
level being a desired concentration, total mass, or mass-flow
rate). Because the concentrate stream 1022 will have elevated
levels of dissolved chemical species, which chemical species will
have been used in the underlying or primary chemical process (e.g.,
producing phosphate fertilizer) and may be used again in the
primary chemical process, the residual concentrate or brine stream
1022 preferably is recycled back for further use in the primary
industrial or manufacturing chemical process, e.g., back to
fertilizer plant 1026. It may be necessary or desirable to polish
or otherwise process (chemically or mechanically) the concentrate
stream 1022, e.g., as at 1028.
[0148] In general, the temperature of the pond water will normally
be too high to support spontaneous formation of hydrate at low to
moderate pressures. Therefore, the pond water may need to be
cooled. Spray evaporation and other refrigeration techniques can be
employed as necessary to reach the desired temperatures.
[0149] Because crystallization of hydrate is exothermic, further
heat must be removed from the hydrate processing facility 1010. The
hydrate itself can provide a heat sink during its dissociation, as
dissociation is an endothermic process that consumes about the same
amount of heat as is liberated during hydrate formation. Various
methods to remove heat from the system and to exchange the heat of
formation with the heat of dissociation are described above and in
the various referenced patents and patent applications. In
addition, supplementary cooling of the water-to-be-treated can be
provided by heat exchange between the melt water stream and the
input water. The various sources of cooling provided are indicated
generally or schematically in FIG. 19 by the cooling system 1032,
and the double-headed arrow 1030 extending between the melt water
stream 1014 and the cooling system 1032 represents the contribution
to overall cooling provided by the melt water stream.
[0150] In contrast to extracting fresh water from seawater or
brackish water, extracting water from highly contaminated water
such as waste water ponds may be more constrained due to the large
concentration of chemicals already present in the water and because
a number of corrosive and poisonous chemical species may be present
at near-saturation levels. In addition to the salinities of each of
the particular chemical species common to most waste water ponds
(which can be quite high, e.g., on the order of 44,000 to 46,000
ppm), the various chemicals and their mixtures dissolved in the
water may vary considerably from waste pond to waste pond, because
different industrial processes each produce contaminated water
having different waste product compositions. Therefore, the
particular hydrate-forming gas or mixture of gases used will depend
on the particular chemical composition of the particular waste pond
or the particular industrial process in connection with which the
waste pond is used
[0151] For instance, in the case of phosphate-rich waste water
ponds used to support operation of a phosphate fertilizer factory,
which ponds have considerable H.sub.2S and SO.sub.2, mixing
chlorine with the solution as the hydrate-forming substance
produces sulfuric acid (H.sub.2SO.sub.4), hydrochloric acid (HCl),
and sulfur, depending on relative concentrations and as described
by equations 1-3.
SO.sub.2(aq)+Cl.sub.2(aq).fwdarw.SO.sub.2Cl.sub.2(aq) eq. 1
SO.sub.2Cl.sub.2(aq)+2H.sub.2O(l).fwdarw.3H.sup.+(aq)+2Cl.sup.-(aq)+HSO.su-
b.4.sup.-(aq) eq. 2
H.sub.2S(aq)+Cl.sub.2(aq).fwdarw.S(s)+2H.sup.+(aq)+2Cl.sup.-(aq)
eq. 3
[0152] Therefore, while chlorine might be used to reduce
phosphate-rich pond water inventory, certain secondary chemical
reactions can be anticipated with crystallization of hydrate, which
secondary chemical reactions and their byproducts can be
accommodated as appropriate using techniques that would be known to
and/or understood by one having skill in the art. Such
consideration to mixing limitations should be taken into account
for almost any toxic industrial waste pond water in which
hydrate-forming gas is to be added to remove water through hydrate
formation.
[0153] Furthermore, some industrial gases typically available at
chemical plants can be used as hydrate-forming gases. These gases
typically would not be used for gas hydrate desalination where the
object of the process is to provide potable drinking water.
However, because these gases are readily available and are already
the subject of safe handling practices at chemical plant
facilities, it may be desirable to use such gases in the context of
treating chemically toxic, polluted water. For example, some
hydrate-forming gases commonly available at phosphorous fertilizer
production installations (where large amounts of sulfuric acid may
also be made and used) include hydrogen sulfide (H.sub.2S), sulfur
dioxide (SO.sub.2), sulfur trioxide (SO.sub.3), and sulfur
hexafluoride (SF.sub.6). In addition, large amounts of chlorine are
commonly present at major industrial sites. Although many of these
gases can be toxic and dangerous, major industrial plants generally
handle large quantities of these and other such materials and have
safe handling procedures in place for their use. Therefore, these
materials may suitably be chosen for use as hydrate-forming
substances.
[0154] In this regard, it should be noted that one distinct
advantage of using such generally hazardous industrial gases for
the purpose of hydrate formation is that this group of gases
generally will form gas hydrate at relatively low pressures and
relatively high temperatures, which helps reduce process cost. For
example, H.sub.2S gas hydrate, the phase diagram for which is shown
in FIG. 20, forms below a temperature of 29.5 degrees C. at 325
PSIa, and those conditions are relatively easy to achieve.
[0155] Additional cooling will directly affect the concentration of
the concentrated phosphoric acid recycle stream, which is returned
to the industrial chemical plant for further use as an industrial
feedstock. By way of specific, non-limiting example at one
particular temperature point, production of and removal of H.sub.2S
gas hydrate from typical phosphate pond water at 18.degree. C. will
produce a phosphoric acid concentrate stream that is nine times as
concentrated as the normal input concentrations of phosphoric acid
to the fertilizer factory. Finally, when the concentration of
dissolved chemicals is increased to the point of saturation as
hydrate is formed and water is extracted from the fluid in the
process, crystal growth of various mineral species will occur. For
example, where average waste pond water from phosphate fertilizer
manufacture is processed according to the above invention, gypsum
and phosphogypsum are formed. These solids, which may be
individually very fine-grained, are typically considered waste
products that are produced during any water concentration process
but which advantageously are recovered and used in various
processes as described above (e.g., in road beds and
wallboard).
[0156] Furthermore, various other applications of hydrate-based
dewatering technique, in a process similar to that described above
for treating phosphate pond water, exist and involve removing water
from other toxic materials during industrial processing. For
instance, in the production of acids (e.g., sulfuric acid), thermal
evaporative processes are commonly used to remove water. Also,
controlled exposure of sulfur trioxide to water as a component of
the acid manufacturing process also produces heat that can drive
evaporation. Notably, these evaporative processes often involve
high temperatures that increase the risk of combustion or
explosion. Using hydrate to remove water content as described
above, on the other hand, involves carrying out the removal under
considerably lower pressures and moderate temperatures that lower
the overall risk of combustion or explosion. Accordingly,
hydrate-based dewatering is a highly advantageous alternative to
conventional dewatering processes in a diverse range of industrial
chemical processing operations.
[0157] Furthermore, the power of using hydrate to remove water,
with the attendant concentration of the residual matter, can be put
to advantageous use in other areas as well--particularly
concentrating food products, as illustrated in Figure. In
particular, a food material fluid 1110 such as milk or juice to be
concentrated, in liquid or fluid form, is introduced into
hydrate-forming apparatus, e.g., a pressure vessel, illustrated
schematically at 1112. The apparatus 1112 includes hydrate
separation apparatus such as described and illustrated above (e.g.,
centrifugal separation apparatus). The temperature and pressure
conditions in the hydrate-forming apparatus 1112 are controlled
such that gas hydrate will spontaneously form and grow when
hydrate-forming material 1114 (gas or liquid) is administered in a
controlled fashion to achieve nucleation and growth of the gas
hydrate. These conditions will usually be more gentle to the food
material, or easier and less expensive to obtain, than the
evaporation techniques that are currently employed. In addition,
these conditions are generally less likely to cause spoilage of
food products than are the higher-temperature evaporative processes
described above.
[0158] Gas hydrate forms within the food material fluid 1110 in the
hydrate processing and separation apparatus 1112, thereby
sequestering water into an easily removed solid phase and raising
the concentration of the food material fluid in the apparatus 1112.
The solid hydrate is removed from the process fluid and passed to
hydrate melter 1116, and residual, concentrated food material
product 1118 is removed for further processing and/or packaging.
The concentrate 1118, which is the more viscous residual fluid
remaining after the hydrate is removed, is removed to storage or
other apparatus and may be used as feedstock for another process
(e.g., concentrated whey) or as the final product itself (orange
juice concentrate, evaporated milk, etc.).
[0159] Once the hydrate is separated, it is decomposed in hydrate
melter 1116, thus producing relatively pure water with few
contaminants. Because these contaminants are all derived from the
food product, this water may be suitable for other food
processing-related uses with little or no treatment. The produced
water is removed for possible further treatment and may be used as
potable water 1122. The hydrate-forming material 1114, which is
usually gas but may be liquid (e.g., liquid carbon dioxide), may be
captured and reused in further cycles of hydrate formation; it may
added to the food product to achieve some purpose such as
carbonation or preservation; or it may simply be discarded.
[0160] Although particular and specific embodiments of the
invention have been disclosed in some detail, numerous
modifications will occur to those having skill in the art, which
modifications hold true to the spirit of this invention. Such
modifications are deemed to be within the scope of the following
claims.
* * * * *
References