Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR PROVIDING
PRESSURIZED HYDROGEN GAS
FIELD OF THE INVENTION
This invention relates to the production of hydrogen gas at a desired
pressure, particularly
hydrogen gas produced by an electrolyser or methanol reformer, and more
particularly in a
continuous manner.
BACKGROUND TO THE INVENTION
An electrochemical cell is used for electrochemical reactions and comprises
anode and
cathode electrodes immersed in an electrolyte with the current passed between
the electrodes
from an external power source. The rate of production is proportional to the
current flow in the
absence of parasitic reactions. For example, in a liquid alkaline water
electrolysis cell, the DC
current is passed between the two electrodes in an aqueous electrolyte to
split water, the reactant,
into component product gases, namely, hydrogen and oxygen where the product
gases evolve at
the surfaces of the respective electrodes.
Hydrogen generating units, sometimes called "thermal compressors", are known,
for
example in USP 4,402,187 (1983) and USP 4,505,120 (1985), which utilize
reversible metal
hydrides. These metal alloys possess the ability to absorb large volumes of
hydrogen gas at room
temperature and because the pressure/temperature relationship is exponential,
large pressure
increases can be created with only moderate temperature increases. In a
thermal compressor,
hydrogen is absorbed at low pressure and temperature, typically, in a water-
cooled hydride
container, which is subsequently heated with hot water and hydrogen is then
released at higher
pressure. To obtain even higher pressures, several stages of compression may
be connected in
series, each stage using a different hydride alloy selected for its higher
operating pressure at the
operating temperature.
Thermoelectric modules are small, solid state, heat pumps that cool, heat and
generate
power. In function, they are similar to conventional refrigerators in that
they move heat from one
area to another and, thus, create a temperature differential.
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A thermoelectric module is comprised of an array of semiconductor couples (P
and N
pellets) connected electrically in series and thermally in parallel,
sandwiched between metallized
ceramic substrates. In essence, if a thermoelectric module is connected to a
DC power source,
heat is absorbed at one end of the device to cool that end, while heat is
rejected at the other end,
where the temperature rises. This is known as the Peltier Effect. By reversing
the current flow,
the direction of the heat flow is reversed.
It is known that a thermoelectric element (TEE) or module may function as a
heat pump
that performs the same cooling function as Freon-based vapor compression or
absorption
refrigerators. The main difference between a TEE device and the conventional
vapor-cycle
device is that thermoelectric elements are totally solid state, while vapor-
cycle devices include
moving mechanical parts and require a working fluid. Also, unlike conventional
vapor
compressor systems, thermoelectric modules are, most generally, miniature
devices. A typical
module measures 2.5 cm x 2.5 cm x 4 mm, while the smallest sub-miniature
modules may
measure 3 mm x 3 mm x 2 mm. These small units are capable of reducing the
temperature to
I S well-below water-freezing temperatures.
Thermoelectric devices are very effective when system design criteria requires
specific
factors, such as high reliability, small size or capacity, low cost, low
weight, intrinsic safety for
hazardous electrical environments, and precise temperature control. Further,
these devices are
capable of refrigerating a solid or fluid object.
A bismuth telluride thermoelectric element consists of a quaternary alloy of
bismuth,
tellurium, selenium and antimony - doped and processed to yield oriented
polycrystalline
semiconductors with anisotropic thermoelectric properties. The bismuth
telluride is primarily
used as a semiconductor material, heavily doped to create either an excess (n-
type) or a
deficiency (p-type) of electrons. A plurality of these couples are connected
in series electrically
and in parallel thermally, and integrated into modules. The modules are
packaged between
metallized ceramic plates to afford optimum electrical insulation and thermal
conduction with
high mechanical compression strength. Typical modules contain from 3 to 127
thermocouples.
Modules can also be mounted in parallel to increase the heat transfer effect
or stacked in
multistage cascades to achieve high differential temperatures.
These TEE devices became of practical importance only recently with the new
developments of semiconductor thermocouple materials. The practical
application of such
modules required the development of semiconductors that are good conductors of
electricity, but
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poor conductors of heat to provide the perfect balance for TEE performance.
During operation,
when an applied DC current flows through the couple, this causes heat to be
transferred from one
side of the TEE to the other; and, thus, creating a cold heat sink side and
hot heat sink side. If the
current is reversed, the heat is moved in the opposite direction. A single-
stage TEE can achieve
temperature differences of up to 70°C, or can transfer heat at a rate
of 125 W. To achieve greater
temperature differences, i.e up to 131°C, a multistage, cascaded TEE
may be utilized.
A typical application exposes the cold side of the TEE to the object or
substance to be
cooled and the hot side to a heat sink, which dissipates the heat to the
environment. A heat
exchanger with forced air or liquid may be required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide apparatus and process for
the production
of hydrogen gas at a desired pressure.
Accordingly, in one aspect the invention provides a process for producing
hydrogen gas
at a desired pressure, said process comprising feeding a hydrogen gas at a
first temperature and
first pressure from a hydrogen source to heat transfer means comprising
cooling means and
heating means; cooling said hydrogen gas with said cooling means to provide
cooled hydrogen
gas; feeding said cooled hydrogen gas to a metal hydride generation means
containing said metal;
forming said metal hydride within said generation means; heating said formed
metal hydride to a
temperature Tp and desired pressure; and releasing said pressurized hydrogen
gas at said desired
pressure from said generation means and producing regenerated said metal.
The metal hydrides of use in the present invention are examples of materials
collectively
termed "hydridable material".
The term metal hydride generator as used in this specification includes
"thermal hydrogen
compressors" as described, for example, in USP 4,402,187 and USP 4,505,120 and
other
publications.
Most preferably, the heat generated in the heat transfer means is used to heat
the metal
hydride generator when it contains the metal hydride made from the metal and
hydrogen, in order
to provide released hydrogen under the desired pressure. A preferred heat
transfer means is a
"Peltier" thermoelectric module which operably provides a cooling surface for
cooling the source
hydrogen and concomitantly heating surface which is used to heat a transfer
liquid, such as, for
example, water and/or steam.
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In those cases where the source hydrogen contains moisture and/or other
condensable
components, such as from a water electrolyser or methanol reformer, these
components are
preferably condensed out at the cooling surface of the thermoelectric module,
and removed.
I have found that feeding the cooled hydrogen gas to the metal hydride
generator while
the metal her se is still well above ambient temperature after releasing
pressurized hydrogen gas
product, increases the rate of cooling of the metal and, thus, turnaround, in
the regeneration of
metal hydride.
Further, to favour thermal balances within the full process and enhance the
rate of heating
of the generator to the desired temperature and pressure of the metal hydride
generator to effect
pressurized hydrogen release, heat produced in the hydrogen source generation
process, may be
transferred to the generator at the appropriate time.
In a most preferred process according to the invention, the process utilizes a
plurality of
metal hydride generators suitably linked by hydrogen gas transfer conduits and
heat transfer
conduits to the hydrogen source, heat transfer means and metal hydride
generators.
Accordingly, in a further aspect the invention provides a process as
hereinabove defined
further comprising providing a plurality of said metal hydride generation
means; feeding suitable
portions of said cooled hydrogen gas to said plurality of said metal hydride
generation means in a
selective manner to effect continuous, effective utilization of said cooled
hydrogen gas produced
at said cooling means and respective production of said metal hydride.
In a yet further aspect the invention further comprises generating heat in
said heating
means and transferring suitable portions of said generated heat to said
plurality of said generation
means in a selective manner to effect continuous utilization of said generated
heat to effect
respective release of said pressurized hydrogen gas, therefrom.
In a further aspect, the invention provides apparatus for producing
pressurized hydrogen
gas at a desired pressure, comprising means for providing a hydrogen gas; heat
transfer means
comprising cooling means and heating means; means for feeding said hydrogen
gas to said
cooling means to produce a cooled hydrogen gas; metal hydride generation means
comprising
said metal; means for feeding said cooled hydrogen gas to said generation
means; means for
heating said generation means; and means for releasing said pressurized
hydrogen gas from said
generation means.
In a yet further aspect, the invention provides apparatus as hereinbefore
defined further
comprising a plurality of said metal hydride generation means and means for
feeding said cooled
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hydrogen gas to said plurality of generation means in a selective manner to
effect continuous,
effective utilization of said cooled hydrogen produced at said cooling means
and respective
synchronous production of said metal hydride.
In a most preferred aspect, the invention provides a central processing unit
(CPU),
suitably linked to thermometers, pressure gauges, valves and adjustment and
timing units to
enable the process, once at steady state, to be continuously self monitoring
and continuously
providing hydrogen gas at a desired selected pressure for subsequent real-time
use or storage.
Accordingly in a further aspect, the invention provides a process as
hereinbefore defined
further comprising measuring, controlling and adjusting process temperatures,
pressures and
hydrogen gas flow rates parameters, and subjecting said parameters to
algorithmic treatment to
enable said process to be continually self monitoring.
In yet a further aspect, the invention provides apparatus as hereinbefore
defined further
comprising process control means to measure, control and adjust process
parameters.
The process control means may comprise
a. computer algorithmic microprocessor means; and
b. temperature and pressure sensor and control means, hydrogen gas flow rate
measurement, adjustment and control means.
The algorithmic means enables the process to be continuously self monitoring,
preferably
when a steady-state of hydrogen gas output for, immediate, subsequent use in
real-time or storage
has been reached.
BRIEF DESCRIPTION ON THE DRAWINGS
In order that the invention may be better understood, a preferred embodiment
will now be
described by way of example only with reference to the accompanying drawing
wherein Fig. 1 is
a block diagram of the apparatus and process according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Fig. 1 shows generally as 10 apparatus and process for the production of
purified
hydrogen at a desired pressure PF comprising a hydrogen source 12 and
thermoelectric module
heat transfer unit 14 linked through suitable conduits as hereinafter
described to each of a
plurality of metal hydride generators (hydrogen compressors) 16 (three in the
embodiment
shown). Hydrogen source 12 is preferably a water electrolyser which generates
hydrogen gas,
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typically, at positive pressure, for example, up to 100 psi. The hydrogen when
produced is wet
and contains caustic and oxygen impurities. Hydrogen is passed through conduit
18 to the
cooling surface 20 of thermoelectric module 14 activated by a DC source 22. At
surface 20,
water contained in the gas is condensed and run-off through conduit 24.
Compressors 16 contain a metal, such as nickel in the form of powder, suitable
to react
with hydrogen to form metal hydride.
Cooled hydrogen gas from module surface 20 is sent through conduit 26 to each
of units
16a, 16b, 16c, etc. in a suitable selective manner to utilize the continuously
produced cooled
hydrogen. For example, when reactor 16a is hot and pressurized, hydrogen
therefrom is
controllably released through conduit 28a as the desired product at pressure
PF and subsequently
in a timely fashion out of 28b, 28c, etc. Since this stage does not require
cooled hydrogen
addition, the latter, from the module is used to fill 16b or 16c, etc. as
appropriate in their
respective cycles.
Once metal has been regenerated in 16a, and pressurized hydrogen removed, the
cold
hydrogen is preferably added to 16a to enhance the rate of cooling of the
metal while the metal is
still hot, and the cycle is repeated.
In an analogous manner, heat generated at the 'hot' end 30 of module 14 is
transferred
through water/steam conduits 32 at the appropriate stage of each unit 16a,
16b, 16c, etc. cycle, to
selectively raise, in turn, the temperature of each unit 16a, 16b, 16c, etc.
in order to continuously,
efficiently, effectively utilize the heat generated at module end 30.
In a further analogous manner, any surplus heat produced at electrolyser
hydrogen source
12 may, likewise, stepwise, selectively be utilized to reinforce the heat
provided by module end
to units 16a, 16b, 16c, etc., through conduit 32.
The continuous self monitoring aspect of the apparatus and process results
from the use
25 of an algorithmical software-loaded microprocessor control module 34
electronically linked as
shown by the dotted lines to electrolyser 12, Pettier thermoelectric module
14, temperature and
pressure monitors contained within units 38 and electrically-controlled
control valves 40. Power
is supplied by supply 36.
Thus, the aforesaid embodiment provides a method and apparatus for producing
30 pressurized hydrogen at a desired pressure in a continuous manner by means
of a plurality of
hydrogen compressors operating in stepwise fashion in association with a
thermoelectric module
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and electrolyser. Accordingly, favourable heat transfers and thermal main
balances can be
suitably effected.
In alternative embodiments, a methanol reformer or other hydrogen generating
process
may be used to provide the hydrogen gas to be satisfactorily pressurized.
Although this disclosure has described and illustrated certain preferred
embodiments of
the invention, it is to be understood that the invention is not restricted to
those particular
embodiments. Rather, the invention includes all embodiments which are
functional or
mechanical equivalence of the specific embodiments and features that have been
described and
illustrated.
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