US3374158A - High pressure electrolysis system and process for hydrogen-oxygen generation - Google Patents

Description

March 19, 1968 A. M. LORD rarAL 3,374,158

HIGH PRESSURE ELECTROLYSIS SYSTEM AND PROCESS FOR HYDROGENOXYGEN GENERATION Filed April 1, 1964 RNE YS United States Patent O HIGH PRESSURE ELECTRLYSIS SYSTEM AND PRCESS FR HYDRQGEN-OXYGEN GENERATIN Albert M. Lord, Lakewood, and Thomas H. Hacha,

Willoughby, Ohio, assignors to TRW Inc., a corporation of Ohio Filed Apr. 1, 1964, Ser. No. 356,470 9 Claims. (Cl. 204--129) ABSTRACT F THE DSCLDSURE Electrolysis system for hydrogen-oxygen generation wherein a portion of one of the product gases is humidified and returned to a porous electrode in the electrolysis cell to replenish the water used up during electrolysis.

This invention generally relates to a high-pressure elecrolysis system and more particularly relates to au improved high--pressure electrolysis system.

For exemplary purpose only, our invention will be described in conjunction with a water electrolysis system wherein water is decomposed to produce hydrogen and oxygen gases. Water decomposition in the system decreases the water content of the electrolyte therein and produces heat that is absorbed by the electrolyte. In order to avoid the detrimental aspects of replenishing the electrolyte water content by the direct addition of water to the electrolyte in the electrolytic cells, known electrolysis systems provide for constant recirculation of the electrolyte wherein the electrolyte was replenished with water and cooled outside of the electrolytic cell. This arrangement required auxiliary equipment which made water electrolysis systems undesirably large and heavy for effective use for fuel cells utilized in aircrafts and for other purposes where weight and size are prime factors. The present invention provides an improved high-pressure electrolysis system having a plurality of electrolytic cells, by maintaining the electrolyte in each electrolytic cell and recirculating a portion of the gases produced to cool the cells and replenish the electrolyte thereof by vapor diffusion.

Therefore, it is an object of the present invention to provide a high-pressure electrolysis system that replenishes the electrolyte of the electrolytic cell 'by vapor diffusion.

It is another object of the present invention to provide a method of controlling the electrolyte concentration and temperature by vapor diffusion.

it is still further another object of the present invention to provide an electrolysis system having a plurality of electrolytic cells and electrolyte concentration and temperature control by vapor diffusion within each electrolytic cell.

It is still another object of the present invention to provide a high-pressure water electrolysis system having electrolyte concentration and temperature control by circulating, cooling, and humidifying a portion of the hydrogen gas produced.

Still another object of the present invention is to provide a high-pressure water electrolysis system utilizing a plurality of electrolytic cells having electrolyte concentration and temperature control by cooling and humiditying a` portion of the hydrogen gas produced in each cell and then returning the cooled and humidiied hydrogen to the cathode portion of each cell at such a temperature and humidity that heat is removed and water vapor is condensed on the electrolyte.

Other objects, features and advantages of the present invention will become apparent after considering the fol- 3,374,158 Patented Mar. 19, 1968 lowing description taken in conjunction with the drawings wherein like reference numerals refer to like and corresponding parts.

In the drawings:

FIGURE l is a partial schematic view illustrating the high-pressure electrolysis system of the present invention; and

FIGURE 2 is a temperature graph illustrating the temperature .profiles of the high-pressure water electrolysis system of the present invention.

As shown in the drawings:

The electrolysis system of the present invention is concerned with a compact high-pressure electrolysis system utilizing a plurality of electrolytic cells. The electrolytic cells have their electrodes electrically connected and provide electrolyte cooling and replenishing by circulating a portion of the gases evolved in each cell through a cooling means, an electrolyte saturation means and then returning the electrolyte containing gases to the electrode from which it was evolved to replenish the electrolyte by vapor diffusion and cool the electrolytic cells by sensible heat transfer.

Referring to FIGURE 1 there is illustrated a highpressure water electrolysis system 11 having a plurality of electrolytic cells 12. Each electrolytic cell 12 has a pair of electrodes 13 and 14 dividing the cell into two gas chambers 16 and 17 and an electrolytic chamber 19. The electrolyte chamber is filled with an aqueous electrolyte 18 such as an impervious asbestos matrix impregnated with an aqueous electrolyte solution of potassium hydroxide, sodium hydroxide, phosphoric acid, or sulfuric acid.

The electrodes 13 and 14 are sintered nickel porous plates varying from 0.004 to 0.020 inch thick, nickel screen of 0.003 inch wire with wires per inch, nickel screen with a coating of platinum black, silver and tantalum screens, or porous carbon plates. The electrical current may be delivered to the electrodes by metal screens i.e. nickel or copper, which are positioned adjacent and in contact with the electrodes.

A hydrogen outlet manifold 21 is connected to each gas chamber 1d by outlet conduits 22 and an oxygen outlet manifold 23 is connected to each gas chamber 17 by outlet conduits 24. The hydrogen manifold 21 has a relief valve 2.6 connected thereto and the oxygen manifold 23 has a relief valve 27 connected thereto. The relief valves 26 and 27 are preferably interconnected respectively by lines 28 and 29 to a control means 31 such that the cathodic and anodic compartments 16 and 17 of the electrode assemblies do not experience a pressure difference greater than 1.0 p.s.i.a. Varied and substantial pres sure differentials in the compartments 16 and 1'7 will interfere with accurate system controls and input vapor pressure levels in the system.

The hydrogen and oxygen gases passing through the manifolds 21 and 23 in the direction of the arrows 25 may be delivered to a suitable fuel cell or other suitable means such as oxygen or hydrogen tired engines.

A recirculating conduit 32 is connected to the manifold 21 and a radiator 33 to tap `and deliver a portion of the hydrogen evolved in the hydrogen chamber 16 to the radiator. The radiator 33 cools the hydrogen by circulating conduits and cooling tins (not shown). A fan means 37 Iblows ambient air over the radiator tins to thereby allow one radiator to cool the gases passing therethrough. A conduit 38 interconnects the radiator 33 with a spray vapor pressure increasing or humidifying chamber 39 to deliver cool hydrogen gas thereto. A heat exchanger by-pass conduit 34 interconnects the manifold 21, through the conduit 32, to the conduit 38 to deliver hot hydrogen gas thereto. A normally closed temperature sensitive valve 36 is n) mounted on the conduit 34 and is set to open at a predetermined temperature to control the sensible heat removed from the tapped hydrogen gas by the heat exchanger or radiator 33.

The spray chamber 39 has a spray nozzle 41 mounted therein which is adapted to spray water into the spray chamber 39 to increase the humidity of lthe hydrogen gas passing therethrough.

A wate-r pump 44 is connected to a water supply 46 by conduit 47 and delivers water under pressure to the nozzle 41 by conduit means 48. The nozzle 41 sprays water 40 into the chamber 39 to humidity the hydrogen gas passing therethrough. The water spray rate is controlled by a gas temperature depression sensor 45 suitably connected to the spray chamber 39 and a water control valve 45a by line 45h so that saturated hydrogen is delivered to spray chamber outlet conduit 42. The spray chamber outlet conduit 42 connects the spray chamber 39 with a blower 43 that delivers the saturated hydrogen gas to a hydrogen inlet manifold 49 `by a conduit 51 connected to the hydrogen blower outlet. A plurality of inlet conduits 52 interconnect the hydrogen chambers 16 with the manifold 49.

The electrolytic cells 12, as illustrated in FIGURE l, have their electrodes connected in electrical series. That is, the anodes 14 are connected to the cathodes 13 of adjacent cells by suitable line means 53 with the end cells having their free anode or cathode, as the case may be, connected to an electrical supply means (not shown) such as for example the very fuel -cell to which the oxygen and hydrogen is supplied by the electrolysis system since only a very small amount of electrical input energy is needed. However, the cells 12 may be connected in electrical parallel if desired. That is, the anodes of each cell are connected to each other and the cathodes of each cell connected to each other with one end cell having its anode and cathode connected to the electrical current supply means.

In operation, the electrolytic cells have their electrolyte, an inert asbestos matrix impregnated with suitable aqueous electrolyte solution, positioned between the cathode and anode thereof. Hydrogen ions a-re reduced at the cathodes 13 to produce hydrogen gas in the hydrogen cavities or chambers 16, and hydroxyl ions are oxidized at the anodes 14 to produce oxygen gas in the oxygen cavities or chambers 17. The production of hydrogen and oxygen gases is such that the gases pass through the valves 26 and 27 are at pressures as great as 4500 p.s.i.a. The oxygen gas is delivered to the oxygen outlet manifold 23 by oxygen outlet conduits 24 communicating with the oxygen chambers 17 and the hydrogen gas is delivered to the manifold 21 by the outlet conduits 22 communicating with hydrogen chambers 16. The hydrogen and oxygen manifolds 21 and 23 respectively deliver the gases through their respective valves 26 and 27 to operate means such as a fuel cell (not shown). A portion of the hydrogen is tapped by the conduit 32 and therefrom delivered to the heat exchanger 33. The heat exchanger -by-pass conduit 34 controls the sensible heat removal of the heat exchanger 33 by selectively allowing hot hydrogen gas to by-pass the heat exchanger and to mix with hydrogen gas exiting from the heat exchanger. The cooled hydrogen gas is then preferably saturated in spray chamber 39 by water spray 40 which is controlled to allow saturated hydrogen to enter the hydrogen chambers 16, th-rough the inlet conduits 52, at a temperature of between room temperature and 440 F. The dry bulb hydrogen temperature is higher than the electrolyte saturation temperature and the hydrogen vapor pressure is greater than the electrolyte vapor pressure. Therefore, the hydrogen removes heat from the electrolytic cells by sensible cooilng and the water vapor in hydrogen gas diffuses through the cathode electrode and condenses thereon to wet the electrolyte and thereby replace the electrolyte water that has decomposed to form hydrogen and oxygen gases.

Referring to FIGURE 2, there is illustrated the graph showing the temperature profiles of one electrolytic cell with the left-hand portion of the graph illustrating the admission of saturated hydrogen to the cell and the righthand portion indicating the exit of the hydrogen gas from the cell. The vapor pressure ofthe electrolyte, as indicated by the Dew Point above electrolyte line is less than the vapor -pressure of the saturated hydrogen, as indicated by the Hydrogen Dew Point line and therefore, water vapor is transferred from the hydrogen to the electrolyte.

In an assembly utilizing cells for electrolyzing l0 pounds per hourof water and wherein hydrogen and oxygen gases are delivered at 4500 p.s.i.a. through the outlet valves 26 and 27, the power consumption is 45 kilowatts at 300 volts. The cells operate at 300 F., with 6 N KOH impregnated asbestos electrolytes. The entire assembly consisting of 100 cells and all the temperature and water feed controls may be contained in a pressurized cylinder 2l inches in diameter and 60 inches long with the cylinder having external tins for cooling. The saturated or humidied hydrogen is delivered to the cell through conduits 52 at 277 F. The system was tested with sintered nickel electrodes with the polarization data for gases being delivered to the valves 26 and 27 at 4500 p.s.i.a., calculated as follows:

`Current density Volts: (amps/ft2) 2.13 50 2.75 100 2.96

In each cell, the hydrogen removes heat therefrom by sensi-ble cooling. The dry 'bulb hydrogen temperature is higher than the electrolyte saturation temperature, as is shown in FIGURE l. The slopes of the sensible and latent temperatures are adjusted to satisfy the cooling heat flux and water addition requirements of a 3-Volt cell. The average electrolyte saturation temperature depression in this case corresponds to an average concentration slightly higher than 6 N. The concentration will be lower at the air gas inlet side than at the outlet with the dilerence between the concentration being reduced by increasing the hydrogen recirculation dow rate.

Another high-pressure electrolysis assembly has 100 electrolytic cells and a power consumption of 30 kilowatts at 200 volts for electrolyzing l0 pounds per hour of water with its module being 2l inches in diameter and 48 inches long. The cells operate at 300 F. with a 6 N KOH impregnated fiber electrolyte to decompose water and deliver hydrogen and oxygen gases at pressures as high as 4500 p.s.i.a. ri`his compact assembly was tested with the sinteredA nickel electrodes having a platinum catalyst to produce polarization data calculated for carrying out the electrolysis at 4500 p.s.i.a. as follows:

Current density (amps/ft2) 100 The humidified hydrogen was fed to the electrolytic cells at 277 F., and the relief valves 26 and 27 are controlled so that the gas chambers 16 and 17 do not experience a pressure difference greater than 1.0 p.s.i.a.

It is of course understood that although the above system and electrolysis method was described in conjunction with water electrolysis, wherein a portion of the hydrogen gas evolved is tapped, cooled, humidied and recirculated to the hydrogen chamber it is not intended that the above invention bev limited to such. For instance, a similar embodiment within the concepts of the present invention would provide for the recirculation and humidication of the hydrogen gas and/or the oxygen gas wherein conditions are controlled such that the vapor pressure of the oxygen gas is increased such that it is higher than the vapor pressure of the electrolyte. Likewise, .another embodiment applicable to other electrolytic systems will replenish their electrolytes by vapor diifusion Volts:

by recirculating a portion of the gases produced in the system and spraying the desired electrolyte solution into the recirculated gases to increase the electrolyte vapor pressure of the gases and controlling conditions such that the electrolyte vapor pressure of the recirculated gas is higher than the electrolyte vapor pressure in the electrolytic cells. It is understood that other modifications and variations may also be effected without departing from the true spirit and scope of the novel concepts of the present invention as defined by the following claims.

We claim as our invention:

1. A method of controlling the water concentration of a hydrogen-oxygen producing electrolysis system having an electrolytic cell with an aqueous electrolyte therein, comprising:

passing an electric current through the electrolyte to form hydrogen and oxygen gases,

tapping a portion of the gas produced,

humidifying the tapped gas,

controlling the humidication of the tapped gas to provide the tapped gas with a vapor pressure greater than the vapor pressure of the electrolyte in the electrolytic cell, and

delivering the humidified gas to the electrolytic cell whereby the water vapor of the humidified gas diffuses and condenses in the electrolytic cell to replenish the water content thereof.

2. The method of claim 1 in which the hydrogen.

3. The method of claim =1 in which said electrolysis system is operated under substantial super-atmospheric pressure.

l4. The method of claim 1 in which said humidifying is accomplished by spraying water into said tapped gas.

5. The method of claim 1 in which a portion of the tapped portion is cooled and recombined with the untapped gas isJ 6. A Water electrolysis system comprising:

an electrolytic cell,

said electrolytic cell having a hydrogen chamber having a porous cathode,

a hydrogen outlet means connected to the electrolytic cell hydrogen chamber to receive hydrogen gas therefrom,

cooled remainder of the tapped .portion before humidityfirst conduit means connected to the hydrogen outlet means to tap a portion of the hydrogen gas therein,

a humidifying chamber,

said first conduit means connected to said humidifying chamber to deliver hydrogen gas thereto,

means to humidity the hydrogen gas in said humiditying chamber to provide the hydrogen gas with a vapor pressure greater than the vapor pressure of the electrolyte in the electrolytic cell, and

a hydrogen inlet means connected to the humidifying chamber and the hydrogen chamber of the electrolytic cell to deliver the hydrogen gas thereto, whereby the humidied hydrogen gas entering the hydrogen chamber of the electrolytic cell has a portion of its water vapor diffuse through the cathode of the electrolytic cell and condenses on'said cathode to mix with the electrolyte and thereby replenish the Water content of said electrolyte.

7. The system of claim 6 in which said humidifying chamber includes means for spraying water into the hydrogen gas.

8. The system of claim 6 which includes a heat exchange means in said first conduit means for cooling the hydrogen gas Ibeing delivered to said humidifying chamber.

9. The system of claim S which includes by-pass means about said heat exchange means for directing a portion of the hydrogen gas directly into said humidifying chamber.

References Cited UNITED STATES PATENTS 2,816,067 12/1957 Keidel 204-130 3,062,732 11/1962 Keidel 204--130 3,180,813 5/1965 Wasp et al 204-106 OTHER REFERENCES Websters Seventh New Collegiate Dictionary, G. & C. Merriam Co., 1965, Springfield, Mass., p. 266, col. 2, lines 92 to 95.

HOWARD S. WILLIAMS, Primary Examiner. JOHN H. MACK, Examiner. H. M. FLOURNOY, Assistant Examiner.

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