Note: Descriptions are shown in the official language in which they were submitted.
CA 02676576 2009-09-09
System and Process for Converting Non-Fresh Water to
Fresh Water
FIELD OF THE INVENTION
The present invention relates to the conversion of non-fresh water and in
particular seawater, waste water, brackish water, polluted water and the like,
to fresh
water.
BACKGROUND
Water is one of the most vital natural resources for all life on Earth. The
availability and quality of water has always played an important part in
determining
not only where people can live, but also their quality of life. Domestic use
includes
water that is used in the home every day such as for drinking, food
preparation,
bathing, washing clothes and dishes, flushing toilets, and watering lawns and
gardens. Commercial water use includes fresh water for motels, hotels,
restaurants,
office buildings, other commercial facilities, and civilian and military
institutions.
Industrial water use is a valuable resource to a nation's industries for such
purposes
as processing, cleaning, transportation, dilution, and cooling in
manufacturing
facilities. Major water-using industries include steel, chemical, paper, and
petroleum
refining. Water is used in the production of electricity in thermoelectric
power plants
that are fueled by fossil fuels, nuclear fission, or geothermal. Irrigation
water use is
water artificially applied to farm, orchard, pasture, and horticultural crops,
as well as
water used to irrigate pastures, for frost and freeze protection, chemical
application,
crop cooling, and harvesting. Livestock water use includes water for stock
animals,
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feed lots, dairies, fish farms, and other nonfarm needs. Water is needed for
the
production of red meat, poultry, eggs, milk, and wool, and for horses,
rabbits, and
pets.
The planet's water reserves are estimated at 1,304,100 teratons (1 teraton is
1012 tons) of which freshwater reserves only account for 2.82% of this figure.
Agriculture consumes 70% of the world's freshwater, industry 20% and
households
10%. Between 1900 and 1995, drinking water demand grew twice as fast as the
world population. By 2025, this demand should grow another 40%. In fifty
years, the
Canadian Agency for International Development has predicted that some forty
countries could lack adequate drinking water. This will inevitably lead to
conflict,
even wars, as local areas, provinces and countries will go to any length to
defend
their fresh water resources.
Almost all conventional power plants, including coal, oil, natural gas, and
nuclear facilities, employ water cycles in the generation of electricity.
Recently
available data from the U.S. Geologic Survey shows that thermoelectric power
plants,
in the U.S.A., use more than 195 billion gallons of water per day. Such
immense
water needs produce equally immense concerns given the likelihood of future
droughts and shortages, especially during the summer months. The addition of
new
conventional power plants therefore, has inherent water-related risks that may
result
in electric utilities no longer able to construct them.
In Canada, there are vast oil sand resources estimate at 1.7 trillion barrels
(270x109 m) of bitumen. Water is required to convert bitumen into synthetic
crude
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oil. A recent report by the Pembina Institute shows that it requires about 2-
4.5 m3 of
water to produce one cubic metre (m) of synthetic crude. The need for
industrial
water use will increase with population growth and global warming as the
demand for
fuel and electricity increases.
According to recent numbers by UNICEF and the World Health Organization,
there are an estimated 884 million people without adequate drinking water, and
a
correlating 2.5 billion without adequate water for sanitation (e.g. wastewater
disposal). Also, cross-contamination of drinking water by untreated sewage is
the
chief adverse outcome of inadequate safe water supply. Consequently, disease
and
significant deaths arise from people using contaminated water supplies; these
effects
are particularly pronounced for children in underdeveloped countries, where
3900
children per day die of diarrhea alone. The greatest irony is that 97% of the
water
exists as seawater which is unfit for human consumption. Consequently, as the
world population grows it is increasingly important to find ways to produce
fresh water
such as by converting no n-fresh water and in particular seawater, waste
water,
brackish water and polluted waters to fresh water. "Fresh water" as used
herein is
potable water.
Seawater contains about 3% salts and minerals, with 97% of the seawater
being water. Brackish water contains more than 500 ppm of salts but less than
sea
water, which has between 34,000 to 36,000 ppm of salt. Desalination refers to
any of
several processes that convert seawater to fresh water. Sometimes the process
produces table salt as a by-product. It is also used on many seagoing ships
and
submarines.
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DESCRIPTION OF PRIOR ART
The two most popular desalination technologies are Multi Stage Flash
Distillation (MSF) and Reverse Osmosis (RO), or some variations of them, which
account for about 90% of the technologies that desalinate seawater across the
globe.
Most desalination plants convert only about 30% - 60% of the seawater to fresh
water.
Multi-stage flash distillation ("MSF") is a desalination process that distills
sea
water by flashing a portion of the water into steam in multiple stages of what
are
essentially regenerative heat exchangers. Seawater is first heated in a
container
known as a brine heater. This is usually achieved by condensing steam on a
bank of
tubes carrying sea water through the brine heater. Heated water is passed to
another container known as a "stage", where the surrounding pressure is lower
than
that in the brine heater. It is the sudden introduction of this water into a
lower
pressure "stage" that causes it to boil so rapidly as to flash into steam. As
a rule,
only a small percentage of this water is converted into steam. Consequently,
it is
normally the case that the remaining water will be sent through a series of
additional
stages, each possessing a lower ambient pressure than the previous "stage." As
steam is generated, it is condensed on tubes of heat exchangers that run
through
each stage. MSF distillation plants, especially large ones, are paired with
power
plants in a cogeneration configuration where the waste heat from the power
plant is
used to heat the seawater rather than generate electricity or be used in an
industrial/chemical process. The power plants consume large amounts of fossil
fuels
thereby contributing significantly to global warming. The world's largest MSF
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desalination plant is the Jebel Ali Desalination Plant located in the United
Arab
Emirates and is capable of producing 820,000 cubic meters (215 million
gallons/day)
of fresh water per day.
Reverse Osmosis ("RO") is a filtration process typically used for water. It
works by using pressure to force a solution through a membrane, retaining the
solute
on one side and allowing the pure solvent to pass to the other side. This is
the
reverse of the normal osmosis process, which is the natural movement of
solvent
from an area of low solute concentration, through a membrane, to an area of
high
solute concentration when no external pressure is applied. The largest Sea
Water
Reverse Osmosis (SWRO) installation is built in Ashkelon, Israel capable of
producing 320,000 cubic meters of fresh water per day. The Ashkelon plant has
a
dedicated 80 MW gas turbine to supply the required electrical need. The Tampa
Bay
plant (the largest in North America) takes 44 million gallons of seawater and
converts
it to 25 million gallons (95,000 cubic meters) of fresh water every day (a
56.8%
conversion rate).
Electrolysis of water is the decomposition of water (H20) into oxygen (02) gas
and hydrogen (H2) gas due to an electric current being passed through the
water. An
electrical power source is connected to two electrodes, or two plates,
(typically made
from some inert metal such as platinum or stainless steel) which are placed in
the
water. Hydrogen will appear at the cathode (the negatively charged electrode,
where
electrons are pumped into the water), and oxygen will appear at the anode (the
positively charged electrode). The generated amount of hydrogen is twice the
amount of oxygen, and both are proportional to the total electrical charge
that was
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sent through the water. Electrolysis of pure water is very slow, and can only
occur
due to the self-ionization of water. Pure water has an electrical conductivity
about
one millionth that of seawater. It is sped up dramatically by adding an
electrolyte
(such as a salt, an acid or a base). Electrolysis at normal conditions (25 C
and 1
atm) is completely impractical for electrolyzing water for anything but a
small lab
experiment.
High-temperature electrolysis ("HTE"), also known as steam electrolysis, is
the
same concept as electrolysis except that it occurs at high temperatures. High
temperature electrolysis is more efficient economically than traditional room-
temperature electrolysis because some of the energy is supplied as heat, which
commercially is generally less expensive to supply than electricity, and
because the
electrolysis reaction is more efficient at higher temperatures.
As the temperature increases, the efficiency of the electrical conversion of
water to hydrogen increases. In fact, at thermolysis (about 3200 C),
electrical input
is unnecessary because water breaks down to hydrogen and oxygen. The
efficiency
improvement of high-temperature electrolysis is best appreciated by assuming
that
the electricity used comes from a heat engine, and then considering the amount
of
heat energy necessary to produce one kg hydrogen (141.86 mega joules), both in
the
HTE process itself and also in producing the electricity used. At 100 C, 350
mega
joules of thermal energy are required (41% efficient). At 850 C, 225 mega
joules are
required (64% efficient).
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As we go to higher temperatures, the energy necessary for electrolysis comes
from heat (thermal energy) rather than electricity. It is known that at around
1000 C,
about 70% of the energy requirement comes from electricity and about 30% can
come from heat. This increases the efficiency and reduces the cost
significantly.
Thermal decomposition, also called thermolysis, is defined as a chemical
reaction when a chemical substance breaks up into at least two chemical
substances
when heated. The reaction is usually endothermic as heat is required to break
chemical bonds in the compound undergoing decomposition. The decomposition
temperature of a substance is the temperature at which the substance
decomposes
into smaller substances or into its constituent atoms. As explained
previously, water
will decompose to its elements at temperatures around 3200 C. In this case the
entire required energy for hydrogen and oxygen production is completely
provided by
heat and no electricity is necessary.
As discussed above, fresh water scarcity is a growing problem in many parts
of the world. However, in parts of the world where fresh water is more
abundant, the
fresh water supply can also be threatened, not by scarcity, but rather by
contamination. For example, an investigation by the Associated Press has
revealed
that the drinking water of at least 41 million people in the United States is
contaminated with pharmaceutical drugs. It has long been known that drugs are
not
wholly absorbed or broken down by the human body. Significant amounts of any
medication taken eventually pass out of the body, primarily through the urine.
While
sewage is treated before being released back into the environment and water
from
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reservoirs or rivers is also treated before being funneled back into the
drinking water
supply, none of these treatments are able to remove all traces of medications.
Medications for animals are also contaminating the water supply. Drugs given
to animals are also entering the water supply. One study found that 10 percent
of the
steroids given to cattle pass directly through their bodies. Another study
found that
steroid concentrations in the water downstream of a Nebraska feedlot were four
times as high as the water upstream. Male fish downstream of the feedlot were
found to have depressed levels of testosterone and smaller than normal heads,
most
likely due to the pharmaceutical contamination in their water.
In most modern cities, rivers and lakes, within their vicinity have become the
focal point of business, resulting in heavy development and commercialization
of
these primary natural resources. The Seine River in Paris, the Singapore River
in the
Lion City, the Chao Phraya in Bangkok and the Thames in London, to name just a
few famous ones, have all been turned into tourist destinations with massive
commercial development around them. In all these cities, businesses flourish
along
their river corridors and the aesthetic values the rivers offer to the city
denizens such
as scenic beauty, solitude, natural environment cannot be described with words
but
need to be experienced. But, there is a heavy price to pay for the massive
economic
development and the booming commercial activities along these rivers and
within
their vicinity. These rivers are slowly being killed by the unrestrained
development
which is often accompanied by massive pollution and other ecological damage.
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Conventional desalination methods (most notably Multi-Stage Flashing and
Reverse Osmosis) can help to close the gap between the supply and demand of
fresh water. However, these desalination methods require a lot of capital
expenditures and consume an enormous amount of fossil fuels. The sad reality
is
that the countries that need the fresh water most are the developing countries
(and in
many cases the poorest countries) who do not have the required capital and can
not
afford to purchase the enormous annual amount of fossil fuel that is required
to
operate these plants.
In the last decade, there has been much discussion about using nuclear
energy to provide the required energy for the desalination plants. While
nuclear
plants may offer some solutions, they also create many other problems. Nuclear
plants require significant capital, take a long time to be put in place
(permitting,
construction etc.) and require the availability of highly trained staff to run
the plants.
Unfortunately, this option will not be available to most developing countries
and in
particular the poorest countries. In the world of instability, the last thing
that the world
need is the proliferation of nuclear plants that may lead to a nuclear race in
many
unstable regions of the world. Moreover, it is impractical to have a nuclear
plant in
every province much less in every village where fresh water is often needed
most.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to the conversion of seawater to
fresh water using high temperature electrolysis to dissociate water to
hydrogen and
oxygen and to separate the minerals, and then combusting the generated
hydrogen
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and oxygen at elevated pressure to form high pressure high temperature
superheated steam wherein a closed loop heat recovery system is utilized to
recycle
the heat generated by the combustion process to the high temperature
electrolysis
unit for the dissociation of the seawater. The extraction of heat from the
superheated
steam by the heat recovery system condenses the superheated steam to produce
fresh water. This total process of generating fresh water by this invention
has been
given the name of "The Rosenbaum-Weisz Process" by the inventor. The reference
to Rosenbaum and Weisz is in honour of the invento-'s parents.
In another aspect, the present invention relates to the Rosenbaum-Weisz
Process which utilizes high temperature electrolysis of seawater to produce
fresh
water. The required heat for high temperature electrolysis is obtained by
capturing
and utilizing heat that is generated by the combustion of hydrogen and oxygen.
When hydrogen and oxygen are combusted, the resulting product is heat and
superheated steam. The combustion temperature is around 3200 C (same as
thermolysis). The heat generated by the combustion of hydrogen and oxygen is
extracted by a heat exchanger system and recycled to be used in the high
temperature electrolysis process. The extraction of the heat by the heat
exchanger
system condenses the superheated steam into fresh water. The overall process
includes the following steps: seawater treatment; evaporation of the treated
seawater, high temperature electrolysis; hydrogen and oxygen production;
hydrogen
and oxygen storage; combustion of hydrogen and oxygen; heat exchanger recovery
system; and the condensing of the superheated steam into fresh water.
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The heat for the high temperature electrolysis can come from different
sources. One way to create on-site heat is by burning fossil fuels such as
natural gas
to produce the required heat. Another way is to capture waste heat from a
nearby
cogeneration plant. The typical temperature of the waste heat from a
cogeneration
plant is between 800 C and 1000 C. Yet another way is to locate a HTE facility
near
a nuclear plant thereby utilizing the heat from the nuclear plant. For HTE
occurring at
around 1500 C, the energy contribution can be approximately 50% from the
electrical
input and 50% from the heat and at around 2000 C, the energy contribution can
be
approximately 25% from the electrical input and 75% from the heat. At even
higher
temperatures, thermal decomposition occurs. It will be understood by persons
of
ordinary skill in the art that the ratio of electricity to thermal energy used
as input
energy for the HTE process can be varied according to the conditions under
which
the HTE operates. In general, if more heat energy is used, less electricity is
required
and vice versa.
If seawater is to be converted to fresh-water, the seawater is preferably
pretreated to remove organics, algae, and fine particles if brackish water is
used.
Conventional processes can be used for the pretreatment.
If waste water or polluted water is to be converted to fresh water,
pretreatment
to remove waste material is preferred and conventional processes can be used
for
such pretreatment. The treated water is then subjected to high temperature
electrolysis.
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An HTE system according to aspect of the present invention can operate at
temperatures ranging from about 100 C to about 850 C, a typical known range
for
HTE. At higher temperatures, more of the energy is derived from the heat thus
requiring less electricity for the electrolysis. An HTE system according to
another
aspect of the present invention can operate at temperatures ranging from 850 C
to
just below the thermolysis temperature (thermolysis temperature is about 3200
C).
An HTE system according to another aspect of the present invention can operate
at
temperature ranging from 1000 C to just below the thermolysis temperature. An
HTE
system according to a still further aspect of the present invention can
operate at
temperature ranging from 100 C to just below the thermolysis temperature.
Operating the system at just below the thermolysis temperature, the energy
required for hydrogen and oxygen production comes mainly (can be as high as
99%)
from heat generated by the combustion of hydrogen and oxygen (in a later stage
of
the system) and the remaining 1% from electricity. In this way, the hydrogen
and
oxygen production is mostly through heat, and electricity is used primarily to
separate
produced hydrogen and oxygen and avoid their recombination.
In one aspect, the present invention relates to converting almost all of the
input seawater to fresh water where the Rosenbaum-Weisz Process has the
potential
of converting 97% seawater and 3% salts/mineral into 97% fresh water and 3%
salts/minerals thereby providing fresh water for humans, industries, livestock
and
agriculture.
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In another aspect, the present invention relates to a desalination system
where the high temperature electrolysis units are operated at pressures
greater than
1 atms. Such higher or elevated pressure reduces the volume required for the
HTE
and thus the volume of the electrolysis units and in turn the number of high
temperature electrolysis units needed.
In a further aspect, the present invention provides to a system and method
where the energy required for the HTE process is provided by harnessing the
heat
that is generated by the combustion of the hydrogen and oxygen (a green and
renewable energy process) rather than burning fossil fuels, which are known to
cause
global warming.
In a still further aspect, the present invention relates to a system and
method
where fresh drinking water is provided from polluted waters by increasing
water
temperature thereby rejuvenating polluted rivers and stream, eliminating drugs
and
other deadly bacteria in waste treatment plants. The standard requirement for
eliminating hazardous material in typical incineration process is by keeping
the
material at 2000 C for 2 seconds. The present system in one embodiment
provides
such conditions for polluted and waste water.
In other embodiments of the present invention, a system using the
Rosenbaum-Weisz Process can be installed in existing MSF desalination plants
as
well as SWRO desalination plants. Thus, the extensive non-renewable energy
that
contributes significantly to global warming, that is currently being consumed
can be
replaced by the implementation of the Rosenbaum-Weisz Process. In the case of
the
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MSF desalination process, the waste heat from the adjacent cogeneration plants
can
be used to produce electricity or be used in an industrial/chemical process,
since they
will not be closed down.
In another embodiment of the present invention, a new plant using the
Rosenbaum-Weisz Process does not require massive investments in the
construction
of an adjacent cogeneration power plant. Consequently, plants employing the
Rosenbaum-Weisz Process can be located anywhere in the world since they are
dependant on having a cogeneration power plant beside them to supply the
required
energy. Plants employing the Rosenbaum-Weisz Process can be located in a small
village in Africa that has a small plant to convert seawater, brackish or
polluted water
to fresh water or in a large metropolitan city that has large plant
converting, seawater,
brackish or polluted water to fresh water since they are not depended on being
located near a cogeneration power plant.
In a further embodiment of the present invention, dedicated plants employing
the Rosenbaum-Weisz Process can be set up to provide vast amounts of water
that
are required for industrial use and for power plants.
In still further embodiment of the present invention, the Rosenbaum-Weisz
Process can provide fresh water from many non-fresh water sources and does not
require the consumption of large amounts of non-renewable fossil fuels.
Consequently, the Rosenbaum-Weisz Process can be a major contributor to the
slowing down of the consumption of non-renewable fossil fuel and thus
significantly
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contributing to the slowing down of global warming and thereby extending the
life of
non-renewable fossil fuel reserves.
The Rosenbaum-Weisz Process can be utilized by both rich and poor nations
across the world since it requires very little purchase of external energy to
operate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates processes in high temperature electrolysis of seawater
producing fresh water according to certain embodiments of the invention.
FIG. 2 illustrates a high temperature electrolysis unit according to one
embodiment of the present invention.
FIG. 3 illustrates a hydrogen and oxygen combustor according to one
embodiment of the present invention.
FIG. 4 illustrates one embodiment of a heat exchanger used for extracting
heat from a combustion of hydrogen and oxygen to produce superheated steam
according to one embodiment of the present invention.
FIG. 5 illustrates one embodiment of the present process that is utilizing
part
of hydrogen and oxygen produced for external use and sale according to one
embodiment of the present invention.
FIG. 6 illustrates one embodiment of the present process that is utilizing
part
of the heat extracted from superheated steam to generate electricity according
to one
embodiment of the present invention.
FIG. 7 illustrates one embodiment of the present process that is utilizing
part
of hydrogen and oxygen produced for external use and sale and utilizing part
of heat
extracted from superheated steam to generate electricity according to one
embodiment of the present invention.
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FIG. 8 illustrates one embodiment of the present process where hydrogen and
oxygen are provided from other source(s) and/or process(es), in addition to
hydrogen
and oxygen generated by the high temperature electrolysis. The combined
generated and provided hydrogen and oxygen are combusted to produce
superheated steam and heat. The heat extracted from the superheated steam can
be used to compensate for the heat losses in the system, to generate
electricity
and/or be used in an industrial/chemical process according to one embodiment
of the
present invention.
FIG 9 illustrates the impact of temperature on the contribution of heat and
electricity according to one embodiment of the present invention.
FIG. 10 illustrates a system according to one embodiment of the present
invention where an evaporator and an electrolysis unit are separate.
FIG. 11 illustrates a system according to one embodiment of the present
invention which includes a mixing station to reduce scaling.
FIG. 12 illustrates a system according to one embodiment of the present
invention which includes utilizing heat from cooling and compression of
hydrogen and
oxygen gases.
FIG. 13 illustrates a system according to one embodiment of the present
invention where a high temperature electrolysis unit also includes a combustor
and a
water pipe. This embodiment does not require the use of a high temperature
heat
exchanger system.
FIG. 14 illustrates a system according to one embodiment of the present
invention that details a high temperature electrolysis unit that includes a
combustor
and a water pipe.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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Referring initially to FIG. 1, in one embodiment, of the present invention all
of
the hydrogen and oxygen that is generated by the high temperature electrolysis
process is combusted at elevated pressure to produce high pressure high
temperature superheated steam. The heat generated through the combustion of
hydrogen and oxygen is then extracted by the heat exchanger system and is
recycled to be used in the high temperature electrolysis process. The
extraction of
the heat by the heat exchanger system condenses the superheated steam to
produce fresh water.
The process can be summarized as follows:
HTE
H20+HEAT=>H2+'/202 (1)
Non-Fresh
Water
Combustion
H2+'/202=>H20+HEAT (2)
Fresh
Water
As shown in equation (1), non-fresh water is heated to create supersaturated
steam and using the high temperature electrolysis process the supersaturated
steam
is separated into hydrogen and oxygen. The generated hydrogen and oxygen is
then
combusted to create supersaturated steam and heat as shown in equation (2).
The
heat generated by the process of combustion of hydrogen and oxygen is then
recovered to be used for the required heat in the high temperature
electrolysis
process.
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Seawater 1 is first taken to a treatment station 2. Seawater is treated to
remove organics, algae and particulate such as sand. Fine particles are
removed if
brackish water is used as the input water. Waste material is removed if waste
or
polluted water is used as the input water. Conventional processes can be used
for
such removal as will be understood by those of ordinary skill in the art.
Salts and minerals can cause scaling issues as the treated seawater is
heated thereby evaporating a portion of the seawater. The scaling issue
becomes
more acute as the treated seawater is evaporated thereby increasing the
relative
concentration of salts and minerals in the remaining seawater. In another
embodiment of the present invention as shown in FIG. 11 in order to minimize
the
scaling caused by the evaporation of the treated seawater, the relative
concentration
of the salts and minerals in the treated seawater is diluted by mixing the
treated
seawater with fresh water, as provided by loop 4, in the mixing station 2A
prior to the
high temperature electrolysis ("HTE") unit 5. The amount of fresh water that
is used
to dilution can be substantially greater than the amount of original treated
seawater.
The resulting increased combined treated seawater is then directed to the HTE
unit.
The resulting increased quantity of hydrogen and oxygen that is produced by
the
HTE process will generate increased quantities of heat and fresh water by the
combustion of hydrogen and oxygen in the combustion chamber. A portion of the
fresh water that is produced at the end of the water pipe is diverted back to
mixing
station 2A by loop 4 while the remaining part will be the net output of fresh
water
produced by the Rosenbaum-Weisz Process. It should be noted that the mixing
station 2A and this looping back process is not necessary where scaling is not
an
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issue. It will be understood by those skilled in the art that any number of
suitable
types of collection vessels (referred to generally as a "collector") can be
used in place
of a water pipe for condensing steam and the present invention is not limited
to the
use of a water pipe.
The next step in the process is the high temperature electrolysis process 5.
In
this stage, the treated seawater is electrolyzed into hydrogen and oxygen. The
electrolysis process is through high temperature electrolysis, in which the
treated
seawater is heated to extreme temperature operation just below the thermolysis
temperature. Electrolysis at a temperature of 3150 C can be used for example.
Consequently, only a relatively small amount of electricity is required to
cause the
hydrogen and oxygen to separate and flow in different channels after
decomposition.
The required heat for the high temperature electrolysis is provided from the
combustion of hydrogen and oxygen at elevated pressure in a later stage of the
process. The required electricity for the electrolysis process, whose only
purpose is
to separate hydrogen and oxygen, can be purchased from an outside source or
may
even be produced by utilizing the excess heat produced at various stages of
the
present method. Alternatively, the excess heat can be used as an energy input
for
an electricity generator such as a steam turbine and the energy produced can
be
sold. High temperature electrolysis process is an established process and
consequently, the selection of electrodes and the construction of HTE unit are
within
the knowledge of a person of ordinary skill in the art. There are several
methods of
constructing high temperature electrolysis systems. One method is described by
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Jensen, Larsen and Mogensen, the details of which are incorporated herein by
reference (International Journal of Hydrogen Energy, 32 (2007) 3253-3257.
FIG 1 illustrates, heat from combustion, the addition of heat 3 (if required),
and
electricity 4 are provided to the high temperature electrolysis unit 5. The
high
temperature electrolysis unit contains two sections, the evaporation chamber
and the
high temperature electrolysis section. Additional heat from outside sources
may be
required so as to compensate for any heat losses in the system such as heat
exchanger inefficiencies. Electricity, whose sole purpose will be to separate
the
hydrogen and oxygen, will be negligible and may be purchased from outside
sources
or generated by capturing the lost heat at various stages in the plant.
External
sources, such as energy from wind, solar, fossil fuel, nuclear and geothermal
sources
can be used to compensate for the heat losses and/or supply the minimal
electrical
need to separate the hydrogen and oxygen.
The treated seawater is taken into the evaporation chamber section where the
treated seawater is turned into steam by the addition of some of the recycled
heat
(carried by suitable piping) from the combustion of hydrogen and oxygen at
elevated
pressure in a later stage of the process. The purpose of the separate
evaporation
chamber section is to pre-heat the treated seawater thereby separating the
water
from the salts, mineral and other contaminants by evaporating the water
component
of the treated seawater into steam and then subjecting the steam to extreme
temperatures, just below the thermolysis temperature in the high temperature
electrolysis section.
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Consequently, the steam in the evaporation chamber section will be
substantially pure and will not contain salts, minerals or other contaminants.
As a
result of thermal expansion the steam then flows into the high temperature
electrolysis section where additional heat, the balance of the recycled heat
from the
combustion of hydrogen and oxygen at elevated pressure, is added. Salt,
minerals
and other contaminants at the bottom 6 of the HTE unit are removed, preferably
continuously. The salts/minerals can be removed from the evaporator chamber
and/or evaporator by ensuring that not all of the seawater is evaporated thus
enabling the slurry to be easily removed and with the assistance of gravity.
As shown in FIG. 2, treated seawater enters the evaporation chamber section
of the HTE unit at 51. Some heat is diverted from the recycled combustion heat
at 52
and it heats up the treated seawater to create steam. The remaining salts and
minerals are removed, preferably continuously from the evaporation chamber at
53.
The recovered salts and minerals can be sold thereby providing an additional
source
of revenue. As a result of thermal expansion, the steam in the evaporator
chamber
section will then flow into the high temperature electrolysis section of the
HTE unit 5
where additional heat from the recycled combustion heat is added to the steam
through a heat exchanging system 55 and 54. Most of the heat needed for this
process is generated internally 54 through loop 1 that recycles the heat that
is
provided by the combustion of the hydrogen and oxygen at elevated pressure in
a
later stage of the process. Any additional heat, if needed, comes from
external
sources 55 through loop 2. Two electrodes, cathode 56 and anode 57 located
inside
the HTE unit 5 act to separate the oxygen 58 and hydrogen 59. The minimal
amount
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of electricity that is required for the high temperature electrolysis process
is supplied
to the electrodes by the AC/DC converter unit 4.
In an alternate embodiment of the present invention as shown in FIG. 10, the
evaporation chamber section and the high temperature electrolysis section can
be
two separate equipment units rather than two sections within the same unit.
In an alternate embodiment of the present invention, the evaporation chamber
section in the HTE unit may not be employed. In this situation all of the
heating and
the removal of the salts and minerals occur in the high temperature
electrolysis
section.
Preferably, the evaporator section (whether part of the HTE unit or separated)
and the high temperature electrolysis section of the HTE unit 5, the combustor
9 and
the high temperature heat exchanger 11 are insulated so as to minimize heat
loss
and maximize their efficiencies. The selection of insulating materials is
within the
knowledge of a person of ordinary skill in the art.
Preferably, the evaporator section (whether part of the HTE unit or separated)
and the high temperature electrolysis section of the HTE unit 5 and the mixing
station 2A are made of material suitable to withstand the presence of the
salts and
minerals so that to minimize corrosion. The selection of the appropriate
material is
within the knowledge of a person of ordinary skill in the art.
Once hydrogen and oxygen are generated and separated by the HTE unit 5,
they are compressed and stored in different storage tanks under pressure.
Elevated
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pressure is used so as to minimize the amount of the required storage. A
compressor 7A is used to compress and move the oxygen into a storage tank 7B,
and a compressor 8A is used to compress and move hydrogen into a storage tank
8B. The hydrogen and oxygen gases leaving the HTE unit will be at elevated
temperature. The hydrogen and oxygen gases will be cooled by their respective
compressor operating at elevated pressure (i.e. greater than 1 atmosphere). A
compression pressure of 2 atmospheres can be used for example. Cooling of the
hydrogen and oxygen gases will reduce their volatility and will reduce the
required
storage space.
Another embodiment of the present invention as shown in FIG. 12, the heat
from the heated hydrogen and oxygen is extracted by way of one or more heat
exchangers 18 and by the compression of the gases. The extracted heat can be
used in the evaporation chamber and/or the evaporator unit, generate
electricity, or in
the drying of the salts/minerals which are extracted or in other parts of the
process. If
the extracted heat is used to generate electricity then the generated
electricity can be
used for internal use (thereby reducing the plant's external electrical
purchase) or be
sold to an external source resulting in a revenue stream.
As shown in FIG. 3, hydrogen at elevated pressure 91 and oxygen at elevated
pressure 92 are then injected into a combustor 9 to generate superheated steam
93.
The pressurized hydrogen and oxygen ensures that the combustion will occur
under
high pressure thus preventing air from entering the combustor thereby
preventing the
creation of nitrous oxide ("NOX"). The combustion pressure will exceed 1
atmosphere so as to exclude the air from entering the combustor. A combustion
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pressure of 2 atmospheres can be used for example. The combustion chamber is
designed to withstand high combustion temperatures without significant heat
loss.
The combustion chamber is preferably constructed of refractory materials or
has high
temperature ceramic surface coatings 9 4. Another means for carrying out high
temperature combustion is described in U.S. Patent No. 7,128,005, details of
which
are incorporated herein by reference. The combustion process produces
superheated steam at high pressure and high temperature. The heat from the
superheated steam is extracted through a high temperature heat exchanger
system
11. The material in the system is chosen from material that is suitable for
high
temperature operation. Current technology has the capacity to deal with heat
in
excess of 3200 C. For example, there are ceramics that can withstand the heat
and
thus could line the surface of the combustor, the appropriate selection of
which is
within the knowledge of a person of ordinary skill in the art.
As shown in FIG 4, the superheated steam 101 so produced is at a
combustion temperature of about 3200 C. This high temperature superheated
steam
then flows through a water pipe 10, transferring heat to a high temperature
heat
exchanger system 11. The returned heat exchanger fluid enters the heat
exchanger
system at 102. The heat energy extracted by the heat exchanger system from the
high pressure high temperature superheated steam is then returned to the high
temperature electrolysis unit 103 to heat the treated seawater through loop 1.
The
superheated steam produced by the high pressure combustion process is cooled
by
the extraction of the heat by the high temperature heat exchanger system to
produce
fresh water stored in a fresh water tank 12. The water pipe 104 serves the
purpose
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of containing the superheated steam isolated so that no impurities are
introduced into
the process of fresh water creation. The water pipe and the combustor are
hermetically sealed thereby ensuring that no air or contaminants will enter
the
process. The superheated steam exiting from the combustor to the water pipe is
also
under high pressure thus ensuring that no air will enter the water pipe.
The wall thickness of the water pipe can be tapered as the temperature
gradient reduces along the water pipe due to heat extraction. The tapered wall
reduces the cost of the water pipe. Heat is extracted from the water pipe by
way of
suitable high temperature heat exchanger system. The combustor and the water
pipe containing high pressure high temperature superheated steam and are made
of
material that can stand high pressure and high temperatures. The heat
exchanger
fluid is not in direct contact with the super saturated steam which is
contained in the
water pipe. Many known industries such as nuclear plants, foundries, rockets
etc.
operate at very high temperatures and consequently, the selection of
appropriate
heat exchanger and heat exchanger fluids suitable for the Rosenbaum-Weisz
Process is within the knowledge of a person of ordinary skill in the art.
In another embodiment of the present invention as illustrated in FIG. 13,
where
the HTE unit also contains, the combustor and the water pipe. This
configuration
does not require the high temperature heat exchanger system thereby reducing
the
capital cost and significantly reducing the system heat loss. Unlike previous
embodiments, in this embodiment the water pipe is in direct contact with the
HTE
unit.
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In another embodiment of the present invention as illustrated in FIG. 14
illustrates the details of the HTE unit that also has the combustor and the
water pipe.
The wall that the water pipe and combustor share in common is covered by
ceramic
tiles so as to prevent heat transfer between them so as to eliminate heat
losses.
Conversely, the wall that the water pipe and the HTE unit share in common is
not
covered by ceramic tile so that there is maximum heat transfer from the water
pipe to
the high temperature electrolysis section. The higher the amount of heat
transfer to
the high temperature electrolysis section the lower the amount of electricity
that is
required for electrolysis. This embodiment may be furthered refined by
excluding the
evaporation section from the HTE unit. The selection of the ceramics that can
withstand the heat and thus could line the surface of the combustor and the
water
pipe is within the knowledge of a person of ordinary skill in the art. The
selection of
appropriate materials suitable for the water pipe is within the knowledge of a
person
of ordinary skill in the art. This is the only situation in which part of the
surface of the
water pipe is covered by ceramic tiles so as to prevent heat transfer. In all
other
embodiments the contain heat exchanger system none of the water pipe surface
is
covered by ceramic so as to maximize the heat transfer from the water pipe to
the
heat exchanger system.
In another embodiment of the present invention as illustrated in FIG. 5, some
of the hydrogen and oxygen is sold rather than be used to generate heat. Some
of
the oxygen and hydrogen are extracted from the storage tanks 7B and 8B for
external use. Thus, this process can be used to generate hydrogen for the
hydrogen
economy. The selling of some of the hydrogen and oxygen implies that less
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hydrogen and oxygen is combusted in the combustor. The extraction of hydrogen
and oxygen results in reducing the amount of heat available to the HTE process
from
the combustion of hydrogen and oxygen. Thus, the reduction of the heat from
the
combustion can be made up by increasing the amount of heat and or electricity
that
would be required to be purchased from outside sources. This is an arbitrage
situation. The amount of hydrogen that can be sold is a function of the
difference in
the sum of the cost of purchasing heat and/or electricity and the reduction of
fresh
water revenue versus the revenue that could be generated by the sale of
hydrogen
and oxygen.
Another embodiment of the present invention is illustrated in FIG. 6, where
some of the heat that is generated by the combustion of hydrogen and oxygen
can
be diverted to a steam generator to be converted by a steam turbine into
electricity.
All of the hydrogen and oxygen are used for combustion. There is no sale of
hydrogen or oxygen. Part of the combustion heat is captured through another
heat
exchanger 12 and carried through loop 3 to a steam generator 14. The generated
steam is then taken to a steam turbine 15 to generate electricity 16. The
extraction of
the heat to generate electricity will result in reducing the amount of heat
available to
the HTE process from the combustion of hydrogen and oxygen. Thus, the
reduction
of the heat from the combustion can be made up by increasing the amount of
heat
and/or electricity that would be required to be purchased from outside
sources. One
reason that one would do this is because some of the generated electricity may
be
classified as "green electricity" thereby enabling the plant to get a high
premium price
for the generated electricity. This is an arbitrage situation. Typically,
however, the
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capital cost required for the generation of electricity would make it
uneconomical to
generate and sell electricity unless there was a premium paid for the
generated
electricity.
Another embodiment of the present invention as shown in FIG. 7 is a
combination of extraction of hydrogen and oxygen as well as producing
electricity.
Another embodiment of the present invention as shown in FIG. 8 illustrates a
process where hydrogen and oxygen are provided from other source(s) and/or
process(es) and the hydrogen and oxygen that is produced by the high
temperature
electrolysis are combined to be combusted at elevated pressure to produce
superheated steam at high pressure and high temperature. The heat extracted
from
the superheated steam can be used to compensate for the heat losses in the
system,
generate electricity and/or be used in an industrial/chemical process. This
may be
done where the cost of the additional hydrogen and oxygen is less than the
purchase
of heat from other sources to compensate for the heat losses in the system.
Another
reason for doing this is if the revenue from electricity produced exceeds the
cost of
the additional hydrogen and oxygen.
To demonstrate the ability of this method to minimize the electricity usage
for
hydrogen and oxygen production two sample cases have been considered. FIG. 9
(taken from an article published in the International Journal of Hydrogen
Energy 32
(2007) 3253-3257 by Soren H. Jensen, Peter H. Larsen, Mogens Mogensen of the
Riso National Laboratory) illustrates the relationship between the
contribution of heat
and electricity as a function of temperature. The temperature range is
consistent with
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the typical temperature of the waste heat from a cogeneration plant.
Extrapolating
the relationship, for electrolysis occurring at 1500 C, it is estimated that
50% of the
required energy will come from heat and 50% from electricity (Case A). If the
electrolysis occurs at 2000 C then it is estimated that 75% of the required
energy
comes from heat and 25% from electricity (Case B). It should be noted that
heat
usage can go much higher to 99% if the electrolysis is at around 3200 C.
The above cases clearly demonstrate that electricity purchases are
significantly reduced even in the cases where only 75% of the energy
requirement
comes from heat. For the proposed invention where approximately 99% energy
will
be provided from the heat generated by the combustion of hydrogen and oxygen.
It
can be easily predicted that electricity purchase, whose sole purpose will be
to
separate the hydrogen and oxygen, will be negligible.
In an alternate embodiment, the system and process of the present invention
with appropriate modification can be used with a sewage treatment plant to
eliminate
impurities and hazardous materials in the non-fresh water being processed.
Current
process to elimination hazardous material requires the incineration of such
materials
at 2000 C for 2 seconds which is very expensive. Using the Rosenbaum-Weisz
Process results in an electrolysis temperature around 3200 C thereby
eliminating all
of the hazardous material as part of the process.
It will be understood by those skilled in the art that the process of the
present
invention can be used on a variety of scales such as from a small plant that
purifies
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water in a small village to large desalination plant providing fresh water to
a major
metropolitan city.
It will be further understood by those skilled in the art that the system of
the
present invention can be configured in a number of ways. For example, in
certain
embodiments, multiple units can be used such as, but not limited to, two HTE
units,
three combustors, and four heat exchangers. The mixing station 2A, loop 4 and
heat
exchanger 18 can likewise be optionally included in systems according to the
invention as needed.
While preferred processes are described, various modifications, alterations,
and changes may be made without departing from the spirit and scope of the
process
according to the present invention as defined in the appended claims. Many
other
configurations of the described processes may be useable by one skilled in the
art.
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