Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURIZED DIRECT CONTACT HEAT EXCHANGE PROCESS.
1. Field of the invention
This invention relates to sources, which continuously produce hot pressurized
non-
condensable gases containing water vapor, and which in combination with a
pressurized
direct contact heat exchange (PDCHE) process, continuously convert the energy
in
these gases into a more useful form, such as steam / electricity.
2. Description of the Prior Art.
Applicant in two previous patents, i.e. US 3920505 and 4079585 failed to
adequately
disclose and claim the present invention.
Present processes release large volumes of hot non-condensable gases
containing
water vapor into the atmosphere resulting in a great loss of energy,
especially the latent
energy of the water vapor. In the case of the combustion of water laden
materials
wastes this results in low thermal efficiencies.
SUMMARY OF THE INVENTION.
A main objective of the present invention is to retain this water within the
process and
convert it to steam in a more reusable form, and thereby raise the thermal
efficiency to a
much higher level. This objective is attained by an application of Henry's Law
of partial
pressures. For example, if the pressure of the gases leaving the PDCHE is 250
psia
(and higher) and the gases are cooled to below 200 degrees F, the water
content in the
gases would approach 0.10 Ibs per Ib of dry gas, and the thermal efficiency of
the
process would approach 90%. The pressure of the steam from the flash
evaporator at
those gas pressures would approach 70 psia.
The basic embodiment of the invention comprises:
(a) providing a source which continuously produces hot pressurized non-
condensable
gases containing water vapor whose given pressure is commensurate with the
steam
pressure desired in the following flash evaporating step and with the desired
overall
thermal efficiency
(b) continuously bringing the hot gases into intimate contact with an aqueous
liquid in a
pressurized direct-contact heat exchanging process having a hot well, where
the gases
will flow counter-current to a flow of an aqueous cooler liquid and where
water vapor will
condense and the gases will become drier, said exchanging process being
capable of
being divided into at least three areas / sections; (i) the first is one where
the
evaporative and heating property of, and part of the condensing and heating
property of
the water vapor in, the hot gas will be utilized to heat the cooler liquid to
the highest
temperature it could have when in equilibrium with the hot gases at the given
pressure,
and thereby cool the hot gases; as well as allow heated liquid and condensed
water to
collect in the hot well within the area, while still maintaining the highest
possible hot well
temperature; (ii) the second is one where the gas and liquid will continue to
progressively exchange heat content and supply heated liquid to the hot well,
until the
gas approaches the temperature of the liquid coming from the following flash
CA 02419774 2003-02-25
evaporation step; (iii) and the third is one where the gas and liquid will
progressively
exchange heat content, until the gas as it cools approaches the temperature of
the cool
liquid entering at the top of area (iii) and the liquid as it heats,
approaches the
temperature of the liquid from the flash evaporator.
(c) continuously removing heated liquid from the hot well and flash
evaporating it in a
flash evaporator at a pressure lower than the pressure corresponding to the
equilibrium
or hot well temperature to thereby (1) convert some of the water in the liquid
into steam
and (2) cool the liquid to a temperature corresponding to the pressure of the
flashed
steam and allow it to collect in a sump in the evaporator.
(d) continuously removing cooled liquid from the flash evaporator and re-
introducing it to
the direct-contact heat exchange section; at a point in area (ii) where the
gas in the area
is at about the same temperature.
(e) continuously removing the flashed steam from the flash evaporator for
further use;
(f) continuously replenishing the cool liquid entering at the top of area
(iii) and
continuously removing excess liquid from the flash evaporator, at the
appropriate rate in
order to keep the liquid in the exchanger and evaporator in balance; as well
as for
further use;
(g) continuously removing the cooled gases from the top of zone (iii) for
further use.
Other embodiments are listed below
BRIEF DESCRIPTION OF THE DRAWINGS.
Symbols used are defined in the next section. While, for compactness, the
PDCHE is
sometimes shown as a single chamber, the various areas could, were desired, be
allotted separate chambers. See FIGS 9 & 10. For similar reasons, valuing and
other
obvious operations are not shown, or labeled e.g. exhaust steam from the ST
could go
to a condenser; the TC in Fig. 3 could be connected directly to the TE, along
with a M;
An "o" indicates a pump; particulate removers would be installed when they are
required,
etc.
The following drawings are schematic representations of the various
embodiments /
applications of the present invention
FIG. 1 represents the main embodiment described above in the Summary together
with
examples of further use for the flashed steam and cool gases.
FIG. 2 represents the situation where a known process (Source) is adapted to
produce
the gases required for the embodiment shown in FIG. 1
FIG. 3 represents where the gases from a known process (Source) are passed
through
a TC to produce the pressurized hot gases required for the embodiment shown in
FIG. 1
FIG. 4 represents where the liquid from the hot well is heated to a higher
temperature
indirectly before flashing it in the flash evaporator. The indirect heater
could be located
within the Source.
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FIG. 5 represents where the pressurized gas-steam mixture is heated prior to
going to
the PDCHE.
FIG. 6 represents where the non-condensable gas content is in the low range
and the
gases are further pressurized by using a high pressure pump which condenses
more of
the water vapor prior to going to a secondary PDCHE.
FIG. 7 represents where combustible material is burnt under the earth or sea
and the
gases processed above the site in the PDCHE.
FIG. 8 represents where gaseous material under the earth or sea can be brought
above
and processed in the PDCHE.
FIG. 9 represents where a number of the embodiments are involved in an overall
process, applicable to the Pulp & Paper Industry.
FIG. 10 involves the electrolysis of water under pressure to illustrate a
symbiotic
relationship with the invention. Combining it with that of the embodiment of
FIG. 9 would
illustrate a further symbiotic relationship, in that the Paper Machine Dryers
would also
contribute further oxygen and steam to the combustion step.
FIG. 11 represents where a PDCHE is combined with a PICHE, located within the
source process, to generate high pressure steam, in order to take advantage of
the
higher efficiency of high pressure, high temperature steam turbines.
FIG.12 represents where the invention produces greenhouse gases, such as
carbon
dioxide which can be recycled through its use to accelerate biomass growth. in
this
embodiment a PDCHE and pressurized combustion is combined with pressurized
electrolysis of water to generate pressurized oxygen for the combustion, and
hydrogen
as a by-product, as well as produce substantially pure carbon dioxide in the
flue / exit
gases.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
The following embodiments are process sequences that provide a wide range of
choice
to fit a wide variety of circumstances, applications and available
technologies. Because
of the wide range of process variables involved and technologies to choose
from. it is
nearly impossible to describe in any detail how a particular embodiment is
carried out. In
most cases computer simulation will be required to balance the various
variables such
as the rate of: recirculation of the hot well liquid; cool liquid supply and
excess liquid
removal.
The embodiments as illustrated and described is such as to obtain maximum
thermal
efficiency, noting that, the higher the pressure and the lower the temperature
of the gas
leaving the PDCHE the higher the thermal efficiency Embodiments involving
lower
efficiencies should not however, detract from the invention.
Referring to the accompaning drawings and the following text, the symbols used
have
the following meaning
G Generator for electricity GT Gas Turbine
TC Turbine Compressor TE Turbine Expander
PR Particulate Remover M Motor electric
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ST Steam Turbine C Condenser
P Pump PM Paper Machine
PDCHE Pressurized Direct Contact Heat Exchanger
PICDHE Pressurized Indirect Contact heat Exchanger
Thus the following embodiments:
A. Illustrate In FIG 1 that which is expressed in the Summary of the
Invention.
Examples of further use for the flashed steam and cool gases are also shown,
namely,
as process steam and/or as a source of energy for the production of
electricity using
steam turbines connected to a generator for the flashed steam, and as a source
of
energy for the production of electricity using a turbo-expander connected to a
generator
for the cool gases.
The steam and any excess liquid from the system could also be used to heat
large
living and business complexes especially in remote places. Further use for the
cool
gases are described below e.g. in Y and AA. Further use for any excess liquid
accumulating in the sump / the hot well is described in various embodiments
below e.g.
J, Q, S.
While the various areas or zones of the PDCHE are shown in one chamber, they
could
be located in separate chambers or sections Here the hot well is shown near
the top of
zone, (i) so as to illustrate that the area below it could be used to dry
solid materials.
Normally it would be near the bottom.
Various technologies are available in determining how the chambers are
constructed
and the best type of mixer to use, while maintaining maximum heat exchange and
minimum pressure drop, e.g. the Field gas scrubber; bubble columns; packed
towers;
turbo-gas absorber; cascades; collecting the cooler liquid at any point in the
PDCHE and
recycling it in the exchanger until its temperature approaches that of the
gas; etc. While
the cooling liquid introduced into areas (I) and (ii) is shown as entering at
one point,
depending on the mixing technology used, it could be introduced at various
points in
each area or section.
The whole chamber or any one of the separate chambers could be located within
the
confines of the Source depending on the process producing the hot gases and
other
factors. Further elaboration is given in embodiment Q below for this and other
embodiments.
Existing high pressure process sources include: pressurized combustion
projects in the
Clean Coal Technology Program sponsored by the US Department of Energy, where
pressures in the range of 200 psia are reached; high pressure char oxidation;
processing of wood in digesters; etc.
B. Illustrate In FIG 2, where the Source involves a known process which does
not provide the pressurized hot gases required of A, but can be adapted to
perform at a
substantially elevated pressure and, if feasible, higher temperature.
Examples:
(1) Combustion / incineration of materials that produce water vapor, e.g. wet
combustibles. While some emphasis is on biomass fuels, the process could have
application to the combustion of (a) solid I liquid fossils fuels; especially
those having
a high sulphur content such that the acidic sulphur gases produced during
combustion can be easily removed in the PDCHE (scrubber) step by making the
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circulating fluid alkaline (see L); (b) fuels intermediate between the two
i.e. lignite
(brown coal), peat, etc, where the high moisture content is a deterrent to
their use;
(c) diverse fuels, such as Tire Derived Fuel (TDF), and various sludges, etc.
where
pollutants can be removed in the PDCHE and concentrated.
(2) Processes that produce other gases such as Lurgi power gas etc;
(3) Processes operating in the lower pressure range, where the pressure could
be increased. e.g. thermomechanical pulping of wood chips; (see M)
(4) Diverse processes such the smelting of ores; wet oxidation; chemical and
metallurgical processes (blast furnaces), and intermediary operations such as:
drying; stripping, extraction; boiling and the like.
C. Illustrate in FIG 3 where the increase in pressure and temperature of the
source
process cannot be carried out, then the gases from the source process are
turbo-
compressed to the desired pressure, with the temperature increased by the
compression. Here where an M drives TC, in step (g), a TE could be used to
drive the
compressor. For example in the drying of pulp or paper, enormous quantities of
air and
steam are expelled to the atmosphere, here the air-steam mixture could be
turbo-
compressed and their heat content recovered in the PDCHE. See embodiments F. &
Q.
below.
D. is where the steps of, collecting other non-condensable gases containing
water
vapor (which are outside of the source) and turbo-compressing them to a
pressure
sufficient to introduce them into the source process= are added prior to step
(a).
For example, as shown in FIG 9, the air-steam mixture is added to a high
pressure
combustion process. Other such mixtures include naturally occurring ones such
as fog
banks, low clouds, mists, steam eruptions from the earth, etc.
E. Illustrate in FIG 4, where the liquid from the hot well is heated
indirectly to a higher
temperature to thereby increase the steam pressure in the flash evaporator.
For
example, by passing the liquid through a tube bank within the source process,
should it
be capable of heating the liquid.
F. Illustrate in FIG 5, where the pressurized gases are further heated prior
to going to a
PDCHE. For example, by burning oil or gas in the mixture, where it will
consume any
remaining oxygen or to which additional oxygen may be added. Alternatively,
the
pressurized gases could be further heated by passing the gases through a tube
bank in
a hotter zone within the source process.
G. is where the cool gases leaving the PDCHE are heated prior to the TE. For
example,
by burning oil or gas in the mixture, or by combining the operations of the
expander and
compressor and introducing inter-stage cooling and heating, as mentioned in
embodiment T.This may be necessary to avoid water condensing or freezing in
the TE, if
the pressure is very high and the temperature low.
H. is where, if the pressure and temperature of the hot gases from the source
process
are high enough, after removing any particulates, they are passed through a GT
connected to a G to produce electricity, before being sent to the PDCHE.
This is particularly advantageous for a combustion process where high gas
temperatures are achievable as illustrated in FIG 9 8~ 10. If acidic gases are
a problem,
they may be removed prior to the GT by passing them through a scrubbing
chamber
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using a lime or limestone slurry and particulates might be removed using steam
scrubbing and the heat content recovered in the PDCHE. It could be important
to dry
any wet fuels prior to combustion so as to obtain a maximum temperature. The
drying
could be done using the gases after leaving the gas turbine as shown in Fig 9.
I. is where oxygen, required in any of the embodiments, is supplied by a
source under a
pressure greater than the pressure required for the source of the pressurized
hot gases
This makes the process more efficient by eliminating the need for a TC. The
electrolysis
of water or steam is one such source, where it is more efficient at the higher
pressures,
with pressurized hydrogen as a valuable by-product This is illustrated in FIG
10 and
expanded in R below. Alternatively, the oxygen may be supplied in bulk or by
air
liquefaction with nitrogen as a by-product.
J. is where by using cool liquids, containing dissolved or suspended materials
as the
cooling liquid, the liquid can be concentrated by the recycling of the liquid
through the
PDCHE and flash evaporator. Once the concentration of the materials in the
circulating
liquor reaches the desired level, a portion can be removed at a rate that will
prevent
further concentration.
If appropriate, the liquid may be used in the source process, e.g. where that
process is
one of combustion and the material in the liquid is combustible. This is
illustrated in FIG
9 & 10. (see Q and R below) Other such liquids are effluents from many other
mills, as
well as from sewage treatment plants.
Other examples would be (a) the desalination of salt water, the liquor would
provide a
source of salt and the condensed steam a source of salt-free water suitable
for irrigation;
(b) concentration of dilute sugar sources, i.e. cane, beet and maple sugars,
where any
residues or forest biomass can be combusted under pressure to produce the hot
gases;
water associated with oil from the wells (producer water) when separated from
the oil
can serve as the cool liquid and when concentrated can be added to the oil and
burnt
and the noncombustible pollutants removed in the ash for proper disposal; etc.
K. Is where area (i) of step (b) in embodiment A, is used to dry materials.
Here all or a portion of the hot gases would be introduced into a chamber
containing the
material to be dried. and the drying done in a number of ways, such as flash
drying, a
fluidized bed, rotary tumble drier, etc, and the dry or partially dried
material removed
through a screw press or decompression chambers, etc or sent directly to the
Source.
Various bio-masses, such as peat, lignite, bark, leaves, branches, roots, and
many other
materials considered as waste can thus be dried or partially dried. The gases
after being
so used and before the saturation temperature has been reached, would be sent
to the
rest of the PDCHE.
If the dried material is still considered waste and is combustible and the
source process
is one of combustion then it can be sent there and consumed. This is
illustrated in FIGS
9 & 10.
L. is where undesirable solids and/or gases are present in the hot gases and
can be removed in the heat exchanger by maintaining the circulating liquid
alkaline for
acidic gases and acidic for alkaline gases.
The substances so formed can then be concentrated and removed from the flash
evaporator (see J above).
This could allow greater use of fossil fuels containing a high sulphur
content. If the solids
/ gases are very soluble in the water, they could be put through a scrubbing
chamber
prior to the PDCHE, were a minimum of liquid could reduce their concentration.
M. Illustrate in FIG 6 where the non-condensable gas content is in the low
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Range. Here the pressurized hot gases are sent to a primary PDCHE and
processed
through the first and second areas of step (b) in embodiment A; then they are
removed
from the exchanger at a temperature close to that of the temperature of the
flashed
liquid in the evaporator and fed to the suction side of the pump removing the
flashed
liquid from the flash evaporator, which is capable of pressurizing this
removed mixture to
a pressure which will condense most of the steam in this removed gas mixture,
this
pressurized liquid and gas mixture is then sent to a secondary PDCHE where the
liquid
and gases separate at a temperature corresponding to that of the pump
pressure, the
separated liquid in the secondary PDCHE is sent to the top of the primary
PDCHE at a
point where the removed gases exit, the heat content of the separated gases
containing
a low amount of steam can then be recovered as desired e.g. in a TE, connected
to a
G, etc.
In certain applications, it is desirable to minimize the presence of the non-
condensables
in the source process, e.g. in the pressurized thermomechanical pulping of
wood chips,
by presteaming the chips prior to their entering the refiner.
N. is where if the steam from the flash evaporator is unsuitable for a
particular use, or
cannot be cleaned by conventional means, it is passed through a reboiler for
further use.
O. Illustrate in Fig. 7, where the source process is a combustion process
carried out
under the earth ~r sea under pressure, where there is combustible material,
where the
combustion is supported by a pressurized gas containing oxygen and controlled
by
water piped to the combustion site from above the site. The pressurized hot
gases would
be piped to a PDCHE above the site and processed utilizing any of the other
embodiments that will give the desired result
P. Illustrate in Fig 8, where the source process is carried out below the
earth or sea
under pressure, where there is recoverable material, and where the process is
activated
by high pressure steam, preferably superheated steam, which allows the
material to flow
to a PDCHE above the site and processed as for any of the other embodiments.
As illustrated, high pressure super-heated steam could flow down an insulated
pipe to
melt the methane hydrate ice and allow it and steam to flow up another pipe to
the
PDCHE above the site to be dried as in FIG 1. Alternatively, the two pipes
could consist
of concentric inner and outer pipes, with the steam flowing down the inner
pipe to melt
the hydrate, which will flow up the outer concentric pipe which is wide enough
to trap the
methane and in which the pressure is less than that of the liberated methane.
Some of
the methane could be used in a conventional boiler to produce the steam and
the water
supplied from the hot well. The end product would be a pressurized,
substantially dry
methane gas.
This could also be applicable to number of fossil fuels, e.g. unmineable,
gassy coal beds
containing methane; wells of natural gases, volatile oils, etc after the wells
have been
somewhat depleted; where the steam will act as a sweep gas.
Q. FIG 9 illustrates how a number of the above embodiments can function within
the
one process, with particular application to the Pulp and Paper Industry where
it forms a
somewhat symbiotic relationship.
A collector receives air-steam emissions from the paper and pulp mill,
especially those
from the drier section of the paper machines (other sources not indicated
include those
from thermomechanical pulping processes). This air-steam mixture, monitored
for the
correct amount of air required for combustion, is passed through a TC where it
is
compressed to a pressure high enough for the process to generate a steam
pressure
suitable for the dryers of the papermachine, as well as operate a gas turbine
e.g. 250
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psia. and higher. The compressed air-steam mixture goes to the pressure
combustion
furnace where combustible wet fuels are burnt to produce hot flue gases.
Auxiliary fuel,
oil or gas, can be added to the hot gases and burnt to maintain uniform
combustion and
an optimum temperature for the gas turbine. (see F above)
These hot gases are passed through a PR and a GT and then through a first
section or
area (i) of the PDCHE, a drier, which dries biomass material, e.g. forest
waste and bark
including, liquid concentrate from the flash evaporator, to a moisture content
amenable
to combustion in the pressure combustion furnace. From the drier the flue
gases pass
to the main second section or area (ii) of the PDCHE, a scrubber, where they
come into
intimate contact with a liquid concentrate, containing dissolved and suspended
solids
from paper 8~ pulp effluents. In applications where only an effluent
concentrate is to be
combusted or the wet fuels are dry enough to combust, the drier would be
omitted and
the flue gases would pass directly to the PDCHE. The above concentrate would
be
generated in the initial start-up of the process as the dilute effluent is
concentrated in the
flash evaporator.
By continuously removing the heated concentrate and evaporating it in the
flash
evaporator at a pressure lower than that corresponding to the equilibrium or
hot well
temperature, so as to (a) convert some of the water in the concentrate into
steam, (b)
further concentrate the liquid, and (c) cool the concentrate to a temperature
lower than
the hot well temperature, and then returning the cooled concentrate from the
flash
evaporator to be reheated in the PDCHE; and removing the steam from the flash
evaporator, much of the heat content of the flue gases is converted into
process steam.
The saturated flue gases from the main PDCHE, after they are cooled to
approximately
the temperature of the liquid concentrate from the evaporator, are passed
through the
last section or area (iii) of the PDCHE to come into intimate contact with
cool dilute
effluent to further cool the flue gases and preheat the effluent;
Thus depending on the temperature of the entering effluent and the efficiency
of the
PDCHE heater, if the pressure of the flue gases is around 250 psia the water
content in
the flue gases could be approximately 0.10 Ibs per Ib of dry flue gas, which
is that of the
water content of most ambient air, and the thermal efficiency of the process
could
approach 90% depending on other factors.
Then by continuously removing some of the heated concentrate and adding the
required preheated dilute effluent, the proper liquid concentration and
balance in the
system can be maintained.
The cooled flue gases from the PDCHE heater are passed through a TE to recover
some of remaining enthalpy, which is used to compress the air-steam mixture.
If
necessary they can be put through a PR before going through the TE. Any make-
up
power for the compression can be supplied by a motor or, while not shown in
the
drawing, the cooled flue gases can be passed through a combustion chamber in
which
oil or gas can be burnt to heat the gases to the required temperature before
they pass
through a TE. (See embodiment G) Any excess power can used to generate
electrical
energy by arranging for the M to also act as a G.
To remove any acidic gases from the flue gases, alkaline substances can be
added to
the liquor circulating in the PDCHE. By a proper choice of substances these
will
reappear in the ash being removed from the furnace, a portion of which may
then be
extracted using hot dilute effluent and returned to the PDCHE
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The rest of the drawing illustrates how the water from effluents and the steam
in the
emissions from the paper and pulp mill is recycled back to mill. The steam
from the flash
evaporator if necessary is passed through a PR or a reboiler and then sent
back to the
PM dryers, or some used in the pulp mill. Any excess steam can be used to
generate
electrical energy using condensing steam turbines. The condensate from the
dryers is
used as clean make-up water at the wet end of the PM. This water reappears
again in
the white waters from the wet end which are sent to a fiber recovery system,
from which
they appear in the effluents from that system and are sent to the effluent
collector, where
they join effluents from the pulp mill. Condensate from the steam turbines can
be used
similarly in the paper & pulp mill where it will return via the effluents from
the mill.
R. FIG 10 further illustrates how flexible the invention is and that it can
even enter into
further symbiotic relationships with other processes. One such process is the
electrolysis
of water under pressure (mentioned in embodiment I above) Electrical energy
required
for the electrolysis is supplied directly by any G adapted to produce the
direct current, as
converting AC to DC is inefficient. If the pressurized hydrogen, so produced,
is not also
used in the source process e.g. where CO is produced and this is combined with
the H
to form methanol, it becomes a very valuable by-product. Alternatively, the
oxygen may
be supplied as described in I above. If the electrolysis unit is located where
further
oxygen is required e.g .for pulping and bleaching, this may be a further
advantage.
Depending on the choice of material being burnt the exit gas will be fairly
pure carbon
dioxide, another by-product of the process, which has a wide use e.g. for
urea,
methanol, enhanced oil recovery, refrigeration , etc.
S. This is an embodiment were energy can be removed from the PDCHE for various
purposes, and the resulting cooled liquid returned to the DCHE to be reheated.
For
example, a primary flash evaporator produces steam at the highest possible
pressure
level, the flashed liquid from the primary is then flashed in a secondary
flash evaporator
to produce steam at a lower level, if desired this sequence could be continued
or, at any
stage, the flashed liquid could be used to indirectly heat other media e.g.
hot water
heating of a building, with the final cooler liquid returned to the PDCHE for
re-heating.
Similarly, by subdividing the hot well liquid and liquid after flashing and
using several
independent circulating systems, the rates of circulation, which may depend on
the rate
of steam production, are not inflexibly tied in with rates and methods of
cooling the
combustion hot gases.
T. This is an embodiment were the cooled gases from the top of zone (iii) are
cooled
further, in order to reclaim further latent heat, by bringing them into
indirect contact with
the cooler gases between expansion stages in the gas expander. This is an
example of
how inter-stage-cooling and inter-stage-heating could be practiced in a
counter-current
or parallel arrangement.
U. This is an embodiment where those of H & I can be combined, wherein the
electricity
produced in H is one of direct current which is then fed directly to the
electrolysis of
water in I, thereby increasing the efficiency of the overall process. This can
also apply to
any electricity produced in steps (e) & (g). Similarly, in the case of the
electrolysis of
steam, the process can supply the direct current as well as the steam.
V. This embodiment where, like some of the above, advantages of other
operations can
be made use of in the PDCHE process.. For example, transportation of materials
by
pipeline can often be less expensive than that by land or air. Thus, after the
appropriate
comminution of the material and its suspension in water, it can be pumped to
the
CA 02419774 2003-02-25
primary site, where the wetted material is not a problem and the excess water
can be
used to cool the gases in PDCHE and any dissolved / suspended material in the
water
concentrated in the flash evaporator. This could be very useful for pressure
combustion
processes, where the combustible material (e.g. coal, peat, and various
biomasses) can
be transported to the combustion site by pipeline.
W. Figure 11 illustrates how the pressurized direct contact heat exchanger
(PDCHE) is
combined with a pressurized indirect contact heat exchanger (PICHE), by
generating
high pressure steam in order to take advantage of the higher efficiency of
high pressure,
high temperature steam turbines. While the PICHE is shown outside the source
(for
ease of illustration) it would usually be located within the source. While the
amount of
energy extracted by the PICHE will vary depending on the application, a
maximum
amount would require that enough energy be left in the hot gases in order to
operate the
PDCHE so the latent energy of the water vapor in the gases can be extracted in
the
flash evaporator.
While the PICHE is shown as a separate chamber outside of the SOURCE, it could
be
located within the confines of the SOURCE depending on the process producing
the hot
pressurized gases. Where the SOURCE is a combustion process, the PICHE could
consist of tube banks located within the combustion chamber.
A PICHE can be introduced into any one of the above embodiments depending on
the
desired outcome.
X. In certain circumstances it may be possible to maximize the thermal
efficiency further
by combining both gas and steam turbine technologies with the PDCHE Process,
by
extracting some of the energy first in a gas turbine, then further energy in a
PICHE using
high pressure steam turbines (as shown in W. above) and finally the remaining
energy in
a PDCHE using the steam generated there either as process and / or in lower
pressure
steam turbines. Where the generation of electrical energy is the prime
objective, this
embodiment could offer the highest thermal efficiency. This could be the case
for
generation of electricity from coal, especially high sulphur coils. (See
embodiment L)
Y. Another application involves coal bed methane and the sequestering of
carbon
dioxide, where unmineable, gassy coal beds are swept with pressurized gases
containing carbon dioxide which releases the methane and traps the carbon
dioxide.
The gases containing carbon dioxide are also effective in increasing oil
recovery, by
reducing its viscosity and providing a driving force towards the wells The
addition of
water / steam improves the sweep efficiency and the water can be recovered in
the
PCDHE.
In these applications, by using the already pressurized gases from the PDCHE
the cost
of the pressurization of the gases is avoided.
In this technology, while one objective is the removal of the polluting carbon
dioxide, in
other situations nitrogen is also used to sweep the methane from the coal., so
how this
application is used could depend on the proportion of carbon dioxide and
nitrogen in the
gases from the PDCHE as well as the use of the end product of this
application, which
will be pressurized gases containing methane, e.g. this methane can be used to
further
heat the hot gases as described in embodiment F.
Z. The present invention also has application to processes which produce gases
which
on combustion yield hot pressurized non-condensable gases containing water
vapor.
The following is an example: a pressurized fluidized-bed gasifier transforms
coal into a
coal gas containing hydrogen and methane (and carbon monoxide), which after
suitable
cleaning is combusted with a gas turbine to produce electricity, the hot gases
containing
CA 02419774 2003-02-25
water vapor exit the turbine at a pressure sufficient to operate the PDCHE and
produce
low pressure steam as well as operate a PICHE which can supply high pressure
steam
to the gasifier, as illustrated in embodiment W above, Whether or not the
PIGHE
produces steam for high pressure steam turbines is a separate consideration.
In present
systems, the hot gases from the turbine are sent to a conventional heat
recovery steam
generator, so that the energy in the water vapor is lost to the atmosphere.
AA. FIG. 12 illustrates a way to reduce greenhouse gases, where a pressurized
direct
contact heat exchanger (PDCHE) and pressurized combustion is combined with
pressurized electrolysis of water to generate pressurized oxygen for the
combustion,
and hydrogen as a by-product. This produces substantially pure carbon dioxide
in the
flue I exit gases, which is used to accelerate biomass growth in a confined or
enclosed
space (e.g. an inflated plastic covering, see "solar tower" below). how
pressure steam
from the flash evaporator can be to heat the enclosed space. Part of the
carbon dioxide
can also be combined with ammonia to make compounds such as urea, which can
also
be used to accelerate biomass growth as urea.
By creating a false ceiling below the canopy or covering over the enclosed
space, the
oxygen and water vapour, generated by the biomass , being lighter than the
carbon
dioxide, can be segregated and removed and used in the PCDCHE process (and the
carbon dioxide recycled to the enclosed space or "greenhouse ")
Some or all of the biomass can be used for combustion I human consumption and
any
waste from the latter use can be recycled through the combustion cycle.
If air liquefaction is used in place of or in addition to water electrolysis
to produce the
pressurized oxygen then the nitrogen from the liquefaction can be used along
with the
hydrogen (in case of the latter) to produce ammonia with can then be used to
produce
the urea.
A further symbiotic situation is where the above is combined with
EnviroMission 's
(Australian firm) "solar tower" (a vertical wind farm) where a chimney,
connected to and
surrounded by a shallow, circular, acrylic greenhouse, (7km in diameter) will
provide
sufficient draft for the hot air generated by the greenhouse, to power turbo-
generators to
produce electricity.
AB. A special B embodiment is as follows: A fuel cell takes in hydrogen and a
gas .
containing oxygen and generates electricity and expels hot gases laden with
water
vapour. By operating the fuel cell at elevated pressures and passing the hot
gases
through the PDCHE the efficiency of the cell is increased' If the gases are
not hot
enough, pressurized combustible gases / oil can be burnt within the gases to
increase
their temperature and consume any remaining oxygen or they can be heated by
any of
the methods described above.
The preceding description of the invention is merely exemplary and is not
intended to
limit the scope of the present invention in any way thereof.
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