FI90884C - Electrolyser for hydrogen production - Google Patents

Description

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Electrolysis equipment for hydrogen production Elektrolysapparat for framstållning av våte

The invention relates to an electrolysis apparatus for producing hydrogen by decomposing water into hydrogen and oxygen by means of an electric current.

It is known to carry out the decomposition of water into hydrogen and oxygen in electrolytic cells which operate under pressure and thus produce hydrogen directly under pressure and no separate compression is required. However, the disadvantage of pressurizing the electrolytic cell is the increase in leakage.

It is also known to place the electrolytic cell sisaån separate pressure shell, whereby the pressure differential of the electrolytic cell 15 sisåpuolen and outside of the electoral law is substantially reduced and the leakage våhenevåt. Thus, for example, in the apparatus according to FR2466515, the pressure shell is pressurized by means of nitrogen gas and the apparatus includes means for keeping the pressure inside the electrolytic cell lower than the pressure in the pressure shell. However, the use of a separate pressurizing gas requires the preservation of pressurizing gases and the need for replenishing gas-20, and the system described in the patent is therefore not suitable, for example, for automatic power plants in solar areas.

It is known from GB patent 1518234 to place electrolytic plates inside a pressure shell, whereby a pressure of hydrogen gas prevails inside the pressure shell. However, the structure according to the patent does not have a closed electrolysis cell placed inside the pressure shell, but the electrodes used for the decomposition of the electrolyte liquid (HCl) are arranged to hang directly inside the pressure shell. The equipment presented in the patent is a plant for large-scale hydrogen production, the power demand of which is very high, the structure is complicated and expensive due to e.g. purification equipment and is not intended for oxygen recovery.

30

Finnish patent application FI923904 discloses an electrolysis apparatus for producing hydrogen from water, in which apparatus the electrolytic cell is placed in a liquid-filled pressure shell which is kept pressurized by the pressure of the gas generated in the electrolysis. The liquid in the pressure shell is selected e.g. on the basis of the corrosion properties of the jacket, the low electrical conductivity 2 and the mutual suitability of the liquid and the pressurized gas used for the supply.

The liquid-filled interior of the pressure shell can be connected, for example, by a pipe to a gas source 5 formed by a pressurized hydrogen or oxygen gas generated in the electrolytic cell. Thus, the pressure shell can be connected to any point in the piping between the gas tanks and the electrolytic cell. Preferably, the pressure shell is connected via a pipe to the upper part of a water separator used for degassing. The amount of pressurizing liquid is preferably used such that the liquid surface rises at least somewhat in the pipe transmitting the pressure-10 shell and the gas pressure.

A problem with such a system may be the evaporation or other migration of the pressurizing liquid into the liquid circuit of the gas used in the pressurization and through it into the electrolysis cell. Since the pressurizing fluid is often an oil, its entry into the electrolytic cell 15 causes a decrease in cell performance over time.

The present invention relates to an electrolysis apparatus in which this drawback has been eliminated. Thus, the invention relates to an electrolysis apparatus for producing hydrogen by decomposing an aqueous liquid by means of an electric current into an electrolytic cell pressurized with hydrogen and oxygen, such that the electrolytic cell is placed in a pressure shell filled with liquid. The invention is characterized in that the apparatus is provided with means for conducting the pressure of the gas generated by electrolysis to the pressure jacket, said members comprising a flow channel from the source of electrolysis gas the pressure of said gas source and the pressure of said pressure shell is applied to the discharge side.

The apparatus according to the invention thus prevents the liquid in the pressure shell from entering the gas circuits of the apparatus in liquid or vapor form and at the same time ensures that the pressure in the pressure shell 30 can drop in the event that the gas source pressure drops. In addition, the invention achieves variable pressure pressurization without the need for a separate shielding gas for pressurization and its production. The amount of gas required for pressurization is very small. In particular, it should be noted that in the apparatus according to the invention, 90884 3 can be used as a pressurizing gas, except for the hydrogen generated in the electrolytic cell, but also without the risk of corrosion.

In the most common embodiment of the invention, the electrolytic cell is placed inside a pressure-resistant pressure shell 5 and the pressure shell is filled with a liquid. In addition, the pressure shell is connected via a flow channel, for example a pipe, to a source of compressed gas formed by the gas generated in the electrolytic cell. Naturally, either oxygen or hydrogen can be used as the pressurizing gas. The pressure shell is preferably completely filled with liquid, thus avoiding the slowness of the yield due to the compressibility of the gas, which could occur if, for example, the pressure-10 shell contained some gas. Preferably, the pressurizing liquid is used in such an amount that the liquid surface rises at least to some extent in the pressure-transmitting flow channel or pipe.

According to the invention, a non-return valve or other device is arranged in the flow channel 15 between the pressure shell and the source of the gas generated in the electrolysis, which allows flow only to the end of the pressure shell. This prevents the pressurization fluid and any steam that may form from it from flowing out of the pressure shell and into the gas circuits of the equipment and through it into the electrolysis cell.

20 However, the non-return valve prevents the pressure in the pressure shell from dropping in the event that the pressure at the gas source drops lower or disappears completely, for example due to gas consumption, pipe damage or maintenance. In this case, the pressure difference between the interior and the exterior of the electrolytic cell may become too large. Therefore, according to the invention, an overflow valve is added in parallel with the non-return valve, which takes care of lowering the pressure automatically. A normal overflow valve comprises a diaphragm housed in a suitable housing which, under the pressure of a spring placed below it, presses against the outlet of the gas or liquid, closing it. Only when the pressure of the gas or liquid is exceeded can the flow of spring pressure pass through the outlet. According to the invention, the overflow valve is connected to a point in the pressure-transmitting flow channel between the non-return valve and the pressure shell. In addition, pressure is applied to the spring side of the overflow valve 30 from a gas source or from a point in the flow channel on the other side of said non-return valve.

The spring pressure of the overflow valve is suitably selected so that the pressure in the pressure shell remains somewhat lower than the pressure of the gas generated in the electrolysis. Generally, a suitable pressure is in the order of a few bar at most. When the pressure of the gas source decreases and the difference between the pressures of the gas source and the pressure housing falls below the spring pressure of the overflow valve from the flow channel between the non-return valve and the pressure shell, 5 air can escape.

The invention can be applied regardless of whether oxygen or hydrogen is used to pressurize the pressure shell. Even when using hydrogen, lowering the pressure in the casing to the outside air does not cause any inconvenience or danger, because the amounts of gas released are in any case very small.

Any liquid that is electrically non-conductive, inert to hydrogen or oxygen, and that can withstand the materials used and can withstand the operating temperature conditions can be used in the pressure shell. Price and non-toxicity are also important considerations.

15

Thus, in the apparatus according to the invention, e.g. silicone oils or fats, fluorinated oils, oil-based or synthetic lubricants, and even distilled or deionized water. The problem with the latter, however, is poor frost resistance and the fact that it can cause electrochemical corrosion, especially in contact with oxygen. Ordinary oils can also not be used in conjunction with oxygen.

Examples of suitable pressurizing fluids are, in particular, silicone oils and greases, such as "Dow Corning 200 Fluid" manufactured by Dow Coming or "Rhodosil" oil produced by Rhone-Poulenc.

25

The invention will be described in more detail below with reference to the accompanying figure.

The figure shows a variable pressure electrolysis cell 10 provided with an electrolysis liquid inlet connection 11, a hydrogen gas outlet connection 12 and an oxygen gas (hap-30 pi / water mixture) outlet connection 13, as well as power supply lines 14. In the embodiment according to the figure and oxygen gas, respectively.

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The electrolyte is fed to the electrolytic cell 10 via the water line 17, the pump 18 and the water line 19 to the oxygen gas water separator 16 and from there through the water supply line 20, the non-return valve 21 and the electrolyte liquid inlet 11 to the electrolytic cell 10. through the oxygen outlet line 22 to the oxygen water separator 16. The water entrained with the oxygen gas separates in the water separator 16 and returns to the electrolysis cell 10 via the line 20.

The hydrogen gas generated in the electrolysis cell 10 is led through the hydrogen outlet connection 12 and 10 through the hydrogen outlet line 23 to the hydrogen gas water separator 15. In the water separator 15, the water separated from the gas is discharged through the pipe 24 and the valve 25.

The electrolytic cell 10 is housed in a pressure shell 26 filled with an inert liquid, and pressurization is preferably accomplished by passing a tube 27 from the oxygen gas water separator 16 to the pressure shell 26. Thus, the oxygen shell pressure is substantially present in the pressure shell 26.

The hydrogen gas from the water separator 15 is further led through a line 28 and a non-return valve 29 to the hydrogen reservoir 30. The line 28 is additionally provided with a pipe 31 and a valve 32 for lowering the hydrogen pressure, for example for the maintenance of the electrolysis plant.

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Oxygen gas is led from the oxygen gas water separator 16 via line 33 to an overflow valve 34. The overflow valve 34 comprises a housing 35 divided by two membranes into two compartments 37 and 38. The compartment 37 includes a seat 39 with an opening 40 and a passage through the seat 39 flows through line 33 to compartment 37 of overflow valve 25 34 and further through orifice 40 and passage 41 to oxygen outlet pipe 42. Second compartment 38 of overflow valve 34 includes a spring 43 supported at one end at the end of the housing 35 and flowing from the other end into the membrane 36. 40 and through the channel 41 to the oxygen outlet pipe 42 only in the event that its pressure exceeds a certain value. In addition, the operation of the overflow valve 34 is essential 30, so that the compartment 38 containing the spring 43 is also connected to the hydrogen pressure, i.e. to the line 28, via a pipe 44.

In the apparatus according to the figure, the pressure recovery operates as follows. The diaphragm 36 of the overflow valve 34 6 is subjected on one side to the pressure in the hydrogen line 28 and in addition to the pressure caused by the spring 43, which presses the diaphragm 36 against the opening 40 in the seat 39. Thus, oxygen can flow into the outlet pipe 42 only when the oxygen pressure in line 33 is greater than the sum of the hydrogen line pressure and the spring pressure. As the oxygen flows, the pressure in the oxygen line 5 decreases until it is at most a spring pressure higher than the pressure in line 44 and 28, whereby the diaphragm 36 closes the opening 40. Thus the oxygen pressure automatically follows the pressure in line 28, always higher than line 28.

As described above, the pressure shell 26 is kept pressurized by the pressure of the gas generated in the electrolysis, in this case via a pipe 27 leading from the oxygen gas water separator 16 to the pressure shell 27. The amount of liquid added to the pressure shell 26 is preferably such that the liquid level rises at least some distance up the pipe 27. According to the invention, a non-return valve 45 is arranged in the pipe 27, which allows gas flow 15 only to the pressure shell 26. Thus, the oxygen gas pressure prevailing in the water separator 16 is transmitted through the pipe 27 and the non-return valve 45 to the pressure shell 26 and the liquid therein.

If it is desired to relieve the pressure from the electrolysis equipment, for example for maintenance, the valve 32 in the pipe 31 is opened 20 and the hydrogen is allowed to flow out. Thereafter, the pressure in the pipe 44 decreases and the membrane 36 allows oxygen to flow into the outlet pipe 42, whereby the oxygen pressure follows the decrease of the hydrogen pressure. The non-return valve 29 prevents the flow of hydrogen gas into the outlet pipe 31.

In this case, however, the non-return valve 45 in the pipe 27 prevents the pressure 25 from escaping from the pressure jacket 26. Accordingly, according to the invention, an overflow valve 46

As the pressure begins to drop in the water separator 16 and at the same time on the spring side of the overflow valve 46, the pressure in the pressure shell 26 initially remains unchanged. At a certain point the pressure of the pressure shell 26, however, ylittåå formed by the spring pressure of the overflow valve-side pressure and the spring pressure, whereby gas starts to flow out of the ylivirtausventtiilistå 46 through 49 of the tube.

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Although it is shown in the embodiment of the figure that the pressure shell 26 is kept pressurized by the oxygen pressure coming from the oxygen gas water separator through the pipe 27, it should be noted that the pressurization can be taken from anywhere else where the oxygen generated in the electrolysis cell is pressurized. The pipes 27 could thus be led, for example, from the pipe 33 or even from the pipe 22, although the latter method is not recommended because water is present in the oxygen gas passing through the pipe 22. It is also clear that the pressurization of the pressure shell can equally well be carried out by means of hydrogen pressure, in which case the pipe 27 can be led, for example, from a hydrogen gas water separator 15 or a hydrogen line 28.

The above embodiments are intended only to illustrate and not to limit the invention.

Claims (5)

8 An electrolysis apparatus for producing hydrogen by decomposing an aqueous liquid by means of an electric current in an electrolytic cell (10) pressurized to hydrogen and oxygen so that the electrolytic cell (10) is placed in a liquid-filled pressure shell (26), characterized in that the apparatus is provided with a non-return valve (45) located in the pressure shell (26), said members including a flow channel (27) from a source (16,33) of gas generated in the electrolysis of the flow channel (27), a non-return valve (45) located in the flow channel (27) allowing gas flow only upstream of the pressure shell (26) 46), on the spring side of which the pressure of said gas source (16,33) is applied and on the discharge side the pressure of said pressure shell (26) is applied. Apparatus according to claim 1, characterized in that oxygen pressure prevails in said flow channel (27). 15 Apparatus according to claim 1, characterized in that hydrogen pressure prevails in said flow channel (27). Apparatus according to any one of the preceding claims, characterized in that said means 20 comprise a pipe (47) leading from said flow channel (27) to the spring side of the overflow valve (46) and a pipe (48) leading from the flow channel (27) to the overflow valve (46) paast5puolelle. Apparatus according to claim 4, characterized in that the pipe (48) communicates with the outside air via a pipe (50) and a non-return valve (51) to prevent any vacuum in the pipe (27) between the non-return valve (45) and the pressure shell (26). 90884 9