WO2010057257A1

WO2010057257A1 - An apparatus and method for producing hydrogen gas

Info

Publication number: WO2010057257A1
Application number: PCT/AU2009/001508
Authority: WO
Inventors: John Beavis Lasich
Original assignee: Solar Systems Pty Ltd
Priority date: 2008-11-19
Filing date: 2009-11-19
Publication date: 2010-05-27

Abstract

The present invention relates to an electrolyser for producing hydrogen gas. The electrolyser comprises electrolysis cells in communication with a distributor of steam and one or more energy guides disposed within the electrolyser for directing radiant energy to irradiate the plurality of electrolysis cells so the electrolysis cells absorb thermal energy to facilitate electrolysis in the electrolysis cells. The electrolyser also comprises a hydrogen gas collector for collecting hydrogen gas generated by the electrolysis cells. The invention also relates to an apparatus and a method for generating hydrogen gas, hydrogen gas produced by the apparatus and a method of generating electricity from hydrogen gas collected from the electrolyser.

Description

AN APPARATUS AND METHOD FOR PRODUCING HYDROGEN GAS

Field of the Invention

The invention relates to an apparatus and a method for producing hydrogen gas and in particular for producing hydrogen gas in an electrolysis cell using radiation, for example solar radiation, as a source of energy for the cell.

Background to the Invention

Fossil fuel energy sources, such as petroleum- based products, coal and natural gas, are increasingly viewed as having a negative environmental impact. Alternative fuel sources are being sought to replace fossil fuels.

One alternative fuel source is hydrogen. The use of hydrogen as a carrier of energy, particularly in the context as a fuel, has the following significant technical advantages over other energy sources .

1. Supply side considerations - hydrogen derived from solar energy & water is inexhaustible, storable, transportable, and has a high energy density per unit mass compared with other chemical fuels.

2. Demand side considerations - hydrogen is non-polluting, more versatile than electricity, more efficient than petrol, and convertible directly to heat and electricity for both mobile and stationary applications .

However, notwithstanding the above technical advantages of hydrogen as an energy vector (or carrier) the cost of production of solar hydrogen from clean renewable sources has been too high hitherto for widespread use as a fuel. In the case of the production of hydrogen by electrolysis of water, a major factor in the high cost of production has been the cost of electricity to operate electrolysis cells .

In addressing this problem, International patent publication WO94/12843 (Lasich) proposes to carry out electrolysis with a source of electrical and thermal energy derived from solar energy.

Lasich also proposes to carry out electrolysis at high temperature to improve overall energy efficiency. Specifically, Lasich recognises that when the electrolysis process is run at high temperature (e.g. 1000⁰C) the electrical voltage required to maintain a given output of hydrogen can be reduced provided there is a complementary increase in thermal energy input.

Lasich also recognises that a significant improvement in efficiency of energy utilisation over and above a conventional electrolysis cell that is operated solely by electrical energy generated from solar radiation by a photovoltaic cell (or by thermal electrical generation methods) can be achieved by using the thermal energy produced in the generation of electrical energy. The thermal energy would otherwise be regarded as a waste low temperature heat (with a cost of disposal) .

Accordingly, Lasich discloses a method for producing hydrogen that comprises separating solar radiation into a shorter wavelength component and a longer wavelength component, and converting the shorter wavelength component into electrical energy and converting the longer wavelength component into thermal energy. For transferring thermal energy to the electrolysis cell to assist electrolysis and to heat steam to around 1000⁰C, Lasich discloses a simple arrangement with a single cell, which was suitable for demonstration purposes but lacks a practical method of delivering the thermal energy for electrolysis in a compact large scale electrolyser having a substantial surface area in a small volume .

It is an object of the invention to provide an apparatus and method for practical generation of hydrogen gas with improved energy efficiency.

Summary of the Invention Thermal energy, produced from radiant energy such as solar energy, can only be used to advantage in electrolysis , in terms of efficiency of energy utilisation, if that thermal energy can be transferred efficiently to the electrolysis cell and produce the high temperatures necessary to operate the electrolysis cell.

Accordingly, the applicant recognises that any thermal energy losses or unevenness resulting from transferring the thermal energy to the electrolysis cell result in a commensurate reduction in overall energy efficiency.

Accordingly, a first aspect of the invention provides an electrolyser for generating hydrogen gas by electrolysis of steam, the electrolyser comprising:

(a) a plurality of electrolysis cells in communication with a distributor of steam;

(b) one or more energy guides disposed within the electrolyser for directing radiant energy to irradiate the plurality of electrolysis cells so the electrolysis cells absorb thermal energy to facilitate electrolysis in the electrolysis cells; and

(c) a hydrogen gas collector for collecting hydrogen gas generated by the electrolysis cells .

The invention is based on the realisation that a practical system is obtained by providing a compact multi- cell electrolyser and irradiating the multiple electrolysis cells with guided radiant energy that would otherwise not irradiate the cells sufficiently evenly for high efficiency.

In a second aspect of the invention there is provided an apparatus for generating hydrogen gas electrolysis of water or steam, the apparatus comprising:

(a) an electrolyser having:

(i) a plurality of electrolysis cells in communication with a distributor of steam;

(ii) one or more energy guides disposed within the electrolyser for directing radiant energy to irradiate the plurality of electrolysis cells so that the electrolysis cells absorb thermal energy to facilitate electrolysis in the electrolysis cells ; and

(iϋ) a. hydrogen gas collector for collecting hydrogen gas generated by the electrolysis cells ; and

(b) an energy concentrator for collecting and concentrating radiant energy from a source for use in the electrolyser as an energy source . Some embodiments of the apparatus further comprise:

(c) a convertor that converts incident radiant energy into electrical energy and that is electrically linked to the plurality of electrolysis cells to supply electricity to the electrolysis cells ; and

(d) a separator that is interposed between the energy concentrator and the convertor for receiving and separating the concentrated radiant energy into a first band of short wavelength radiation and a second band of long wavelength radiation and directing the first band to the convertor and directing the second band to the one or more energy guides.

In one embodiment, the energy guides are located in close proximity to surfaces of the respective electrolysis cells .

In one embodiment, the electrolysis cells are generally elongate and the energy guides are generally elongate and disposed generally parallel to the electrolysis cells .

In one embodiment, the energy guides have a textured surface that disperses at least some incident radiant energy from within the energy guide to externally of the energy guide, whereby the dispersed radiation impinges upon the one or more electrolysis cells and heats the electrolysis cells .

Light entering an energy guide is transmitted along the length of the energy guide by internal reflection. However, a portion of the light is dispersed through the surface, by virtue of the surface roughness, and falls incident on an electrolysis cell where the radiant energy is converted to heat energy, thus heating the electrolysis cell.

Furthermore, light scattering events occurring at the textured surface will result in heating of the energy guide such that the energy guides will radiate thermal energy. The radiated thermal energy assists with heating the electrolysis cells .

In one embodiment, the textured surface has a surface roughness in the range of lum to a few millimetres , and more preferably in the range of lum to 500um.

In one embodiment, the textured surface comprises a surface formed by sand-blasting or acid etching.

In one embodiment, the energy guide comprises quartz, crystal or an amorphous glass-product .

In one embodiment, the electrolysis cells are arranged in a hexagonal array about each energy guide .

In one embodiment, the energy guides collectively define a light-receiving surface on which radiant energy is directed for transmitting radiant energy through the energy guides for direction onto the electrolysis cells .

In one embodiment, each energy guide has an end portion with a dove-tail longitudinal profile for collecting radiant energy in the energy guide.

In one embodiment, each energy guide has a section profile for forming the light-receiving surface in combination with other energy guides. In one form, the section profile is hexagonal and the energy guides are formed as rods .

In an alternative form, the section profile is rectangular and the energy guides are formed as panels .

In one embodiment, the light-receiving surface is generally continuous .

In an alternative form, the energy guide comprises a surface layer formed on each electrolysis cell and having selected reflective properties to reflect part of the incident radiant energy and to transmit part of the incident radiant energy onto the electrolysis cell, thereby heating the electrolysis cell.

The reflective properties of the surface layer may be selected to control the level of reflected and transmitted radiant energy, and particularly in view of geometrical dimensions and relative arrangement of electrolysis cells .

In one embodiment, energy density transmitted to the electrolysis cell is controlled with regard to the concentration of radiant energy, energy guide reflective properties and total surface area of electrolysis cells .

In one embodiment, the energy density is controlled to be in the range of 0.1 to 2 W/cm² on the surface of electrolysis cells, preferably 0.5 to 2 W/ cm² and, more preferably, about 1 W/cm².

In one embodiment, the one or more energy guides facilitate electrolysis in the electrolysis cells at a temperature of greater than 700⁰C, preferably about 1000⁰C. In embodiments of either form, a window may also be provided facing the radiant energy and enclosing the electrolyser cells and energy guides , to trap infrared radiation within the electrolyser.

In a third aspect, the invention provides a method of generating hydrogen gas from steam, the method comprising:

(a) passing steam through a plurality of electrolysis cells and electrolysing the steam to produce hydrogen gas; and

(b) directing radiant energy within the electrolyser to irradiate the plurality of electrolysis cells with the radiant energy, and thereby heating the electrolysis cells to facilitate electrolysis of the steam.

In one embodiment, the method includes operating the electrolysis cells with electrical energy converted from radiant energy.

In one embodiment, the method involves dividing solar energy into a first band of short wavelength radiation and a second band of long wavelength radiation and converting the first band of short wavelength radiation into electrical energy and supplying steam and the electrical energy to the plurality of electrolysis cells to electrolyse the steam.

In one embodiment, step (b) involves directing the second band of long wavelength radiation through one or more energy guides to disperse the long wavelength radiation to irradiate the electrolysis cells. In one embodiment, the method involves controlling the energy density of long wavelength radiation that irradiates the electrolysis cells by selecting a concentration of the solar radiation, a reflectivity of the one or more energy guides and a total surface area of the electrolysis cells .

In one embodiment, the method involved controlling the energy density to be in the range of 0.1 to 2 W/cm² on the surface of electrolysis cells, preferably 0.5 to 2 W/cm² and more preferably about 1 W/cm².

In one embodiment, step (b) involves directing the radiant energy to irradiate and heat the plurality of electrolysis cell to a temperature of greater than 700⁰C, preferably about 1000⁰C.

In a fourth aspect, the invention provides hydrogen gas produced by a method according to the third aspect of the invention.

In a fifth aspect, the invention provides a method of producing electricity for solar radiation using the apparatus according to the second aspect and having a converter and separator as described above, the method comprising using the collected hydrogen gas to produce electricity in a fuel cell or turbine generator to supplement the electricity produced directly from the converter .

Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings , in which : Figure 1 is a schematic representation of an apparatus for generating hydrogen gas in accordance with an embodiment of the invention.

Figure 2 is cut-away perspective view of an electrolyser in accordance with an embodiment of the present invention for use in the apparatus in Figure 1.

Figure 3A is a perspective view of an end of the electrolyser in Figure 2.

Figure 3B is a schematic cross-section of energy guides and electrolysis cells at the end of the electrolyser in Figure 3A.

Figure 4A is a cross-section of an alternative embodiment of an electrolyser for use in the apparatus in Figure 1.

Figure 4B is a schematic perspective view of energy guides and electrolysis cells of the electrolyser in Figure 4A.

Figure 5 is a schematic view of two electrolysis cells in accordance with a further alternative embodiment of the present invention.

Detailed Description of Embodiments

With reference to Figure 1, an electrolysis apparatus 10 is shown. The electrolysis apparatus 10 has a solar energy input in the form of the sun 12.

Solar energy from the sun 12 falls incident on solar concentrators in the form of a heliostat array 14 which reflect and concentrate the solar energy onto a separator in the form of a wavelength separator 16. The concentration of solar energy at the separator is approximately 500 times the incident solar energy.

The wavelength separator 16 separates the solar energy into a short wavelength component 18 that is directed onto an array of photovoltaic cells 22 for converting the solar energy into electrical energy. The electrical energy is transferred by a conduit to a junction box 24 that controls transmission of electrical power to various end uses. At least part of the electrical power received at the junction box 24 is transferred to an electrolyser 30 for electrolysing of water or steam, thereby generating hydrogen gas and oxygen gas.

With reference to Figure 2, 3A and 3B, steam is directed internally through the electrolysis cells 38 and is split into hydrogen gas and oxygen ions at the inner surface forming the cathode 40. The oxygen ions migrate through the porous wall of the electrolysis cells and combine with electrons at the outer surface anode 42 to form oxygen gas. The oxygen gas percolating out of the outer surfaces of the electrolysis cells 42 into the space between the electrolysis cells 38 and the energy guides 44 is collected at an oxygen gas outlet 36 (Figure 2) of the electrolyser 30 for subsequent processing and use.

The electrolysis process is enhanced by operating the electrolyser 30 at high temperature, namely at least 700°C and up to 1000°C.

Heat input to the electrolyser is provided by a separated long wavelength component 20 of the solar radiation which is reflected from the wavelength separator 16 to fall incident upon an end of the electrolyser 33 shown in Figure 3A. The end 33 of the electrolyser may also comprise a quartz window facing the radiant energy and enclosing the electrolyser cells and energy guides , to trap infrared radiation within the electrolyser

The electrolyser 30 comprises an array of energy guides in the form of light rods 44 that are formed of quartz. Surrounding the light rods 44 are a plurality of electrolysis cells 38 configured in a hexagonal array. The electrolysis cells 38 are formed as elongate porous zirconia tubes with an inner surface of the tube coated with a conductive medium to form a cathode 40 (Figure 3B) and an outer surface coated with a further conductive medium to form an anode 42.

The electrolysis cells communicate with an inlet manifold 33 for conveying steam externally of the electrolyser 30 through the electrolysis cells 38. At rear end of the electrolyser 30 , a collection manifold 35 communicates with the opposite end of the electrolysis cells 38 to collect hydrogen gas and water in the form of steam. The collection manifold 35 is linked to an outlet 34 for conveying the hydrogen gas and steam away from the electrolyser 30 for subsequent processing, such as separation and storage of the hydrogen gas. The separation may be performed by condensing the steam by bubbling through water, or by membrane separation techniques.

In other embodiments , the inlet and collection manifolds may both be provided at the rear end, distal from the radiation facing surface, and the steam may be delivered to the radiation facing end by tubes internal to the electrolysis cells travelling the length of the cells and terminating near the radiation facing surface .

The light rods 44 have a generally circular profile and are arranged generally parallel to the electrolysis cells 38 and extend within the electrolyser 30 the same distance as the electrolysis cells . The light rods 44 include a fluted end portion 46 that collects the long wave length component 20 of solar radiation reflected onto the electrolyser from the wave length separator 16. The fluted end portion assists to reflect the incident light into the light rod 44 by total internal reflection.

The surface of the light rods that coincides with electrolysis cells 38 is roughened such that a portion of the long wavelength component 20 that enters the light rods 44 and that is incident on the side wall is reflected back into the light rod 44 to travel further along the light rod 44. Another portion of the long wavelength component 20 is transmitted through the surface to fall incident upon a nearby electrolysis cells . This portion is converted from light energy to thermal energy at a surface of the electrolysis cells 38 to heat the electrolysis cells 38 to a temperature in the range of 700 to 1000°C. In this way the radiant energy is efficiently delivered throughout the length of the electrolysis surfaces.

Additionally, a portion of the light incident upon the surface of the light guide 44 is converted to heat energy which radiates from the surface of the light guide 44 and contributes to heating of nearby outer electrolysis cells 38.

Internal reflection of light along the length of the light guides combined with controlled release by the surface roughening ensures a generally even dispersion of solar radiation falling incident upon the length of the electrolysis cells 38. Accordingly, there is generally even thermal heating along the length of the electrolysis cells 38.

The use of the light rods 44 improves overall energy efficiency of the electrolyser 30 by providing a generally even distribution of solar energy on the surfaces of the electrolysis cells 38 so there is generally even heating of the electrolysis cells 38 along their length. This ensures that the electrolysis cells 38 have a generally consistent electrolysis process efficiency due to improved utilisation of the surface area of the electrolysis cells 38 for electrolysis .

In an alternative form shown in Figures 4A and 4B, the light rods 44 are replaced with light panels 48 that are interleaved with generally rectangular panel- shaped electrolysis cells 38. Operation of an electrolyser 30 based on the light panel 48 and electrolysis cell 38 configuration shown in Figures 4A and 4B is the same as that described above in respect of the electrolyser 30 disclosed in Figures 2, 3A and 3B.

The surface roughness of the light rods 44 and the light panels 48 is selected to cause a portion of incident light to impinge upon the surface of adjacent electrolysis cells to provide a thermal energy density of 0.5 to 2 W/cm² on the electrolysis cells 38 surface. Other factors influencing the thermal energy density are the concentration of incident light in the long wavelength component 20 and the total area of the electrolysis cell

38 surface. These factors are controllable to provide a desirable energy density of 1 W/cm².

In an alternative form shown in Figure 5, electrolysis cells 50, similar to those of Fig 3A and 3B, have a tubular structure with an internal passage for conveying steam and/or hydrogen gas and with electrodes formed on the surface of the internal passage and on the outer surface of the electrolysis cell 50. Instead of light rods 44, the electrolysis cell 50 further has a partially reflective coating 54 and a reflective end cap 52. The end cap 52 directs light incident on the electrolyser 30 between adjacent electrolysis cells 50. The light is directed onto the reflective surface 54 where a portion of the incident light is reflected onto adjacent electrolysis cells 50 and a portion of the light is transmitted to the surface of the electrolysis cell 50 and converted to thermal energy to heat the electrolysis cell 50.

The heat energy provided to the electrolysis cells 38 and 50 may be recycled by heat exchange from the hydrogen gas and/or heated steam or additionally oxygen gas leaving the electrolyser 30, to water or steam supplied to the electrolyser 30 for electrolysis . In this manner the water or steam may be pre-heated to a temperature of about 600°C before entering the electrolyser. This improves use of available energy.

The above-described embodiment of the invention is in the context of using radiant energy in the form of solar energy as a source of energy for use in the electrolyser 30. However, it is anticipated that other forms of radiant energy may be utilised. For example, the radiant energy may be in the form of nuclear radiation from a nuclear reactor and the energy guides may be formed of suitable materials for directing the nuclear energy within the electrolyser 30 to fall incident on the electrolysis cells 38.

Persons skilled in the art will appreciate that the drawings are schematic in nature and additional features for implementing the embodiment are not shown for clarity of exposition.

Further many variations may be made without departing from the scope of the invention. In particular, features of the above embodiments may be employed together to form further embodiments . In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as

"comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, the reference to any prior art publications herein does not constitute an admission that the publication forms a part of the common general knowledge in the art.

Claims

CLAIMS :

1. An electrolyser for generating hydrogen gas by electrolysis of steam, the electrolyser comprising: (a) a plurality of electrolysis cells in communication with a distributor of steam;

(b) one or more energy guides disposed within the electrolyser for directing radiant energy to irradiate the plurality of electrolysis cells so the electrolysis cells absorb thermal energy to facilitate electrolysis in the electrolysis cells ; and

2. An electrolyser as claimed in claim 1, wherein the energy guides are located in close proximity to surfaces of the respective electrolysis cells .

3. An electrolyser as claimed in claim 1 or claim 2 , wherein the electrolysis cells are generally elongate and the energy guides are generally elongate and disposed generally parallel to the electrolysis cells .

4. An electrolyser as claimed in any one of the preceding claims, wherein the energy guides have a textured surface that disperses at least some incident radiation from within the energy guide to externally of the energy guide, whereby the dispersed radiation falls incident upon the one or more electrolysis cells and heats the electrolysis cells.

5. An electrolyser as claimed in claim 4 , wherein the textured surface has a surface roughness in the range of lum to a few millimetres .

6. An electrolyser as claimed in claim 4 , wherein the textured surface has a surface roughness in the range of lum to 500um.

7. An electrolyser as claimed in claim 4 , wherein the textured surface comprises a surface formed by sandblasting or acid etching.

8. An electrolyser as claimed in any one of the preceding claims, wherein each energy guide comprises quartz, crystal or an amorphous glass-product .

9. An electrolyser as claimed in any one of the preceding claims, wherein the electrolysis cells are arranged in a hexagonal array about each energy guide.

10. An electrolyser as claimed in any one of the preceding claims , wherein the energy guides collectively define a light-receiving surface on which radiation is directed for transmitting radiant energy through the energy guides for direction onto the electrolysis cells .

11. An electrolyser as claimed in claim 10, wherein each energy guide has an end portion with a dove-tail longitudinal profile for collecting radiant energy into the energy guide .

12. An electrolyser as claimed in claim 10, wherein each energy guide has a section profile for forming the light-receiving surface in combination with other energy guides .

13. An electrolyser as claimed in claim 12 , wherein the section profile is hexagonal and the energy guides are formed as rods.

14. An electrolyser as claimed in claim 12, wherein the section profile is rectangular and the energy guides are formed as panels .

15. An electrolyser as claimed in any one of claims 10 to 14, wherein the light-receiving surface is generally continuous .

16. An electrolyser as claimed in claim 1, wherein the energy guide comprises a surface layer formed on each electrolysis cell and having selected reflective properties to reflect part of the incident radiant energy and to transmit part of the incident radiant energy onto the electrolysis cells, thereby heating the electrolysis cells.

17. An electrolyser as claimed in claim 16, wherein the reflective properties of the surface layer may be selected to control the level of reflected and transmitted radiant energy, and particularly in view of geometrical dimensions and relative arrangement of electrolysis cells .

18. An electrolyser as claimed in any one of the preceding claims , wherein an energy density transmitted to the electrolysis cells is controlled with regard to the concentration of the radiant energy, energy guide reflective properties and total surface area of the electrolysis cells .

19. An electrolyser as claimed in claim 18, wherein the energy density is controlled to be in the range of 0.1 to 2 W/cm² on the surface of electrolysis cells .

20. An electrolyser as claimed in claim 18, wherein the energy density is controlled to be about 1 W/cm².

21. An electrolyser as claimed in any one of the preceding claims , wherein the one or more energy guides facilitate electrolysis in the electrolysis cells at a temperature of greater than 700⁰C.

22. An apparatus for generating hydrogen gas electrolysis of water or steam, the apparatus comprising:

(a) an electrolyser having:

(iii) a hydrogen gas collector for collecting hydrogen gas generated by the electrolysis cells ; and

(b) an energy concentrator for collecting and concentrating radiant energy from a source for use in the electrolyser as an energy source.

23. An apparatus as claimed in claim 22 , wherein the apparatus further comprises:

(c) a convertor that converts the radiant energy into electrical energy and that is electrically linked to the plurality of electrolysis cells to supply the electrical energy to the electrolysis cells; and (d) a separator that is interposed between the energy concentrator and the convertor for receiving and separating the concentrated radiant energy into a first band of short wavelength radiation and a second band of long wavelength radiation and directing the first band to the convertor and directing the second band to the one or more energy guides .

24. A method of generating hydrogen gas from steam, the method comprising:

(a) passing steam through a plurality of electrolysis cells located within an electrolyser and electrolysing the steam to produce hydrogen gas; and

25. The method claimed in claim 24, wherein the method involves operating the electrolysis cells with electrical energy converted from the radiant energy.

26. The method claimed in claim 25, wherein the method involves dividing the radiant energy into a first band of short wavelength radiation and a second band of long wavelength radiation and converting the first band of short wavelength radiation into electrical energy and supplying steam and the electrical energy to the plurality of electrolysis cells to electrolyse the steam.

27. The method claimed in claim 26, wherein the step (b) involves directing the second band of long wavelength radiation through one or more energy guides to disperse the long wavelength radiation to irradiate the electrolysis cells.

28. The method claimed in claim 27, wherein the method involves controlling the energy density of long wavelength radiation that irradiates the electrolysis cells by selecting a concentration of the radiant energy, a reflectivity of the one or more energy guides and a total surface area of the electrolysis cells .

29. The method claimed in claim 28, wherein the method involves controlling the energy density to be in the range of 0.1 to 2 W/cm² on the surface of electrolysis cells.

30. The method claimed in claim 28, wherein the method involves controlling the energy density to be about 1 W/cm².

31. The method claimed in claim 24, wherein step (b) involves directing the radiant energy to irradiate and heat the plurality of electrolysis cell to a temperature of about 1000⁰C.

32. Hydrogen gas produced by the method claimed in claim 24.

33. A method of producing electricity from solar radiation using the apparatus of claim 22 , comprising using the collected hydrogen gas to produce electricity in a fuel cell or turbine generator to supplement the electricity produced directly from the converter.