Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Descri~tion
Process for operating a
pressure electrolysis apparatus
The invention concerns a process for operating a pressure
electrolysis apparatus for electrolyzing water by electric energy
to generate hydrogen and nxy~en , whereby the electrolytic cell
block contained in a pressure-resistant casing is surrounded by a
fluid under pressure.
German application DE-OS 38 37 354 describes a process for
operating a pressure electrolysis system. In that application,
the electrolytic cell block, also called the reduction pot, is
contained in a pressure casing and surrounded by a fluid under
pressure. The fluid is always maintained at a higher pressure
than the internal pressure of the reduction pot. This allows the
construction design to be simplified relative to conventional
pressure reduction pots, since uncontrolled escape of gases from
the electrolytic cells can be effectively prevented.
A disadvantage of this process is nevertheless that the
electrolytic cell block continues to be operated under a pressure
differential. This limits the design to the use of materials
impervious to pressure.
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Objective of the present invention is to provide a process for
the operation of pressure electrolysis equipment which avoids the
disadvantages of the known state of the technology.
The invention resolves this task by having the electrolytic eell
block surrounded by a non-conductive fluid which is maintained at
the working pressure of the electrolytic process.
Analogous to the known state of the teehnology, the invention
employs a pressure casing to contain the electrolytic eell bloek.
However, in contrast to the known process, the fluid surrounding
the eleetrolytie eell bloek is maintained at the same pressure as
within the actual reduction pot. By working under a pressure
equilibrium, the invention obviates the electrolytic cell block
having to withstand a pressure differential. Mechanical stress
thus results only from the construction, such as in reduction
pots of the filter press design. To prevent eseape of gases from
the reduction pot, it is furthermore entirely sufficient to
maintain a pressure equilibrium.
As a further development of the invention, it is proposed to use
feed water or hydrogen as non-eonduetive fluids. When using
hydrogen as fluid, the hydrogen produeed by the hydrogen
electrolysis should preferably be utilized.
Under the invention, any electrically non-conductive and inert
fluid is suitable, provided it requires no special measures to
be taken concerning its corrosion behaviour relative to the
reduction pot and/or the pressure-resistant casing. However,
for hydrogen electrolysis it is nevertheless
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especially advantageous to use feed water (totally desalinated
water). The feed water is pumped up to the pressure in the
electrolytic cell block and fed through the pressure tank before
being mixed with the electrolytes separated from the product
gases and routed to the water separation. Since this provides for
a constant flow of feed water through the pressure-resistant
casing, the reduction pot can be efficiently cooled. Additional
cooling can be provided by cooling water in a heat exchanger
installed in the pressure tank.
As a development of the invention, the pressure of the
electrically non-conductive fluid is controlled via the pressure
of one or both product gases.
The hydrogen and oxygen resulting as product gases from the
hydrogen electrolysis are separated by the entrained electrolytes
and are available at the working pressure of the hydrogen
electrolysis. The pressure of the electrically non-conductive
fluid can therefore be effectively controlled directly or
indirectly via the product gas pressure. If e.g. feed water is
used as fluid, the fluid level will be detected in one of the
product gas/electrolyte separators, serving as a control signal
for the fluid. If hydrogen is used as fluid, control is
simplified by the fact that the interior space of the pressure
tank is in direct contact with the hydrogen product. In this
invention variant, pressure fluctuations in the reduction pot,
which transmit as pressure fluctuations in the product gas
separator, result in prompt and direct pressure equalization in
the pressure tank.
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While, in accordance with the invention, direct pressure
adjustment by means of the product hydrogen is very advantageous,
one additional advantage results from the use of feed water as
fluid. In the invented process, the feed water can be used as
heat carrier medium.
As a development of the invention, heating the electrically non-
conductive fluid for the start-up phase of the pressure
electrolysis equipment can be accomplished by heating inside the
pressure-resistant casing.
Raised temperature facilitates the electrolysis of water under
pressure. To bring the electrolytic cell block to the start-up
temperature required for the reaction, the feed water is heated
directly within the pressure-resistant casing.
During steady-state operation of the electrolysis equipment, the
feed water is preferably cooled within the casing by a heat
exchanger. Cooling the feed water has a direct cooling effect on
the reduction pot and avoids an unacceptable increase in its
operating temperature.
The invented process here described is especially suited to the
use of electrolytic cell blocks in the so-called filter press
design which uses electrolytic cell frames made of non-pressure
resistant materials. These materials which, although not
impervious to pressure, are suitable for the construction of
electrolytic cell blocks include ceramic materials and non-
conductive synthetics.
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The invented process is described and exemplified below in the
schematic figures 1 and 2.
Figure 1 shows the invention variant using feed water as
electrically non-conductive fluid. An electrolytic cell block 1,
which reduces water to hydrogen and oxygen under pressure, is
contained in a pressure tank 2, surrounded by an electrically
non-conductive fluid 3. The resulting product gases are captured
separately in the reduction pot and evacuated via conduits 4 and
5. In the separators Al and A2, entrained electrolyte is
separated from the product gases. From separator Al, product
hydrogen is drawn off through conduit 6 by means of a pressure-
controlled valve. The oxygen generated is drawn off via
separator A2 through conduit 7 by means of a level-controlled
valve. The two separators are connected on the side of the
separated fluid by communicating pipes. Leading from these pipes
is conduit 9 through which separated electrolyte is returned to
the electrolytic cell block, displaced by feed water for
separation. For the purpose, the fluid is pumped up to the
electrolytic working pressure and fed to the electrolytic cell
block 1 via conduit 9'. The feed water for separation by the
electrolysis is carried via conduit 10 and pumped up to the
electrolytic working pressure by means of pump P2. Thereafter it
surrounds the electrolytic cell block 1 as fluid 3 in the
pressure-resistant casing 2. To equalize pressure fluctuations
relative to the reduction pot working pressure, the product gas
pressure as measured in the hydrogen separator Al is used to
effect the pressure control. The fluid level in the hydrogen
separator Al is provided to the pump P2 as control signal. After
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the feed water has surrounded the reduction pot, it is evacuated
from the pressure-resistant casing 2 via conduit 8 and mixed with
the electrolytes in the ~xygen separator A2. At start-up, the
heater E is used to heat the water to the operating temperature.
During steady-state operation, cooling is obtained by means of
the heat exchanger W in order to evacuate heat released during
electrolysis.
Figure 2 shows the invention variant using product hydrogen as
electrically non-conductive fluid. The equipment design is herc
similar to that in Figure 1, wherefore structural components have
been assigned the same reference numbers. As fluid 3, product
hydrogen is used. The interior of the pressure tank 2 is
accordingly connected with the product gas conduit 6 via the
feeder line 6a. Since pressure fluctuations in the reduction pot
1 lead to corresponding pressure fluctuations in the product gas,
no indirect control is required. Cooling of the reduction pot 1
is here obtained by means of the heat exchangers W1 and W1 in the
electrolyte/product gas separators A1 and A1.
