WO2000004325A1

WO2000004325A1 - Heat energy collection and conveying apparatus

Info

Publication number: WO2000004325A1
Application number: PCT/AU1999/000388
Authority: WO
Inventors: Allan James Yeomans
Original assignee: Allan James Yeomans
Priority date: 1998-07-13
Filing date: 1999-05-21
Publication date: 2000-01-27
Also published as: AUPP460298A0

Abstract

A heat transfer and delivery system (10) including an endothermic reactor (11) in which ammonia in the presence of a catalyst is converted or partly converted into nitrogen and hydrogen, an exothermic reactor (12) in which nitrogen and hydrogen are reconverted into ammonia and a conveying duct assembly (16) for conveying ammonia, nitrogen and hydrogen between the endothermic reactor (11) and endothermic reactor (12) and including an outer duct (14) for containing ammonia and an inner duct (15) for containing hydrogen and nitrogen located within the outer duct (14). The heat energy for the endothermic reactor (11) is provided by a solar energy concentrator which concentrates solar energy on a hollow energy collection element which contains a catalyst through which ammonia is passed for conversion or partial conversion into nitrogen and hydrogen.

Description

HEAT ENERGY COLLECTION AND CONVEYING APPARATUS Technical Field

This invention relates to heat energy collection and conveying apparatus and in particular to apparatus in which heat energy is collected and conveyed to a location remote from the collection location. A typical application is in radiant energy collecting apparatus for example solar energy collecting apparatus where collected heat energy is required to be conveyed to a remote location for use. Background Art

Solar energy collecting apparatus as used for power generation generally are steam based. For example, an energy transport medium such as oil is heated by the solar energy collecting apparatus and the collected and concentrated heat is used via the energy transport medium to convert water into steam for the driving of steam turbines and the generation of power. Such systems have a number of disadvantages. To reduce energy loss from the energy transport medium during its conveyance from the solar energy collecting apparatus to the power generation location, highly insulated ducting is required to be employed otherwise high energy loss occurs. Conversion of the heat energy into steam at the heat collection location results in high thermal losses from steam lines in conveyance to the power generation location, energy in the thermal mass of steam is lost periodically and start up problems are encountered associated with water filled steam lines due to steam condensation. To overcome the above disadvantages, a thermochemical system has been proposed wherein a gas such as ammonia is used for heat transfer and conversion. In such a system, ammonia constrained in a closed loop system is converted or partly converted into nitrogen and hydrogen in an endothermic reaction subject to the heat energy input of a solar concentrator and thereafter recombination of the nitrogen and hydrogen in an exothermic reaction generates heat for the conversion of water into steam for driving a steam turbine. Use of ammonia in such an application provides a number of advantages. Energy loss is low, no side reactions occur and standard catalysts can be used in the reactions. Furthermore, the energy generated in the endothermic reaction can be transported at ambient temperature. One disadvantage however is that hydrogen produced during the reactions is often lost through leakage. This occurs because of the small size of the hydrogen molecules. To overcome this problem it has been necessary to use accurately sealed pipes for conveying the hydrogen. Conventional joints and seals between pipes do not contain the hydrogen in the system. As a result, joints between pipes are required to be formed by electric welding. This leads to substantially increased costs for plant construction. Similar disadvantages occur where other gases such as methane are used. Summary of the Invention

The present invention aims to provide in one aspect, a heat transfer and delivery system using a gas which can be broken down into constituent gases in an endothermic reaction and recombined in an exothermic reaction where one of the constituent gases has a fine molecular structure. The present invention in a further aspect aims to provide a system which enables increased and more efficient separation of the constituent gases in the endothermic reaction. The present invention in a further aspect aims to provide a system which provides for more efficient gas dissociation in the endothermic reaction. The present invention in a further aspect aims to provide solar energy collecting apparatus incorporating the above heat transfer and delivery system. Other objects and advantages of the invention will become apparent from the following description.

The present invention thus provides in a first aspect a heat transfer and delivery system including endothermic reactor means in which a first gas in the presence of a catalyst is converted or partly converted into constituent gases, exothermic reactor means in which said constituent gases are reconverted into said first gas and means between said endothermic reactor and endothermic reactor for conveying said first gas and said constituent gases, said conveying means including first duct means for containing primarily said first gas and further duct means for containing said constituent gases, said further duct means being located within said first duct means.

The first gas may comprise ammonia in which case the constituent gases comprise nitrogen and hydrogen. Alternatively, the first gas may comprise methane which in the presence of carbon dioxide is converted into carbon monoxide and hydrogen in the endothermic reaction and which convert back into methane in the exothermic reaction. The first gas however may be any other gas which may be converted into -

constituent gases, one of which, such as hydrogen, has a fine molecular structure.

The heat energy for the endothermic reactor means suitably is supplied by a solar energy concentrator. The heat generated in the exothermic reactor may be used for the generation of power for example by converting water into steam for driving a steam turbine for driving electrical generators.

In a preferred aspect, the solar energy concentrator concentrates solar energy on a hollow energy collection element containing a suitable catalyst through which the first gas is passed for conversion or partial conversion in an endothermic reaction into the constituent gases. In a further aspect, the energy collection element includes a first inner duct portion containing a catalyst and defining an inlet duct for the first gas for disassociation or partial disassociation into the constituent gases, and a second outer duct portion coaxial with said first inner duct portion and communicating therewith, said first and second duct portions defining an outlet passage for the constituent gases and residual first gas. For more efficient disassociation of the first gas and separation of the one gas having a fine molecular structure from the first gas/constituent gas mix, the energy collection element may include a collection chamber for the one gas communicating via a membrane or material permeable to the one gas with at least the first inner duct portion and preferably also with the passage between the first and second duct portions. This permits the one gas disassociating from the first gas on one side of the membrane of permeable material in the endothermic reaction to be drawn off from the first gas and be collected in the collection chamber on the other side of the permeable membrane or material and as a result permit further dissociation of the first gas into the constituent gases. In a further aspect, the first and second duct portions of the energy collection element are located coaxially within a third outer duct which is subject to direct heating by the solar energy concentrator and the first and second duct portions have walls or wall sections formed of a material permeable to hydrogen. In this aspect, the space between the first and second duct portions defines the collection chamber for the one gas disassociating from the first gas in the first duct portion and from the first gas/constituent gas mix in the passage between the second duct portion and third duct. In this aspect, corresponding ends of the first duct portion and second duct portion are joined to form a collection chamber for the one gas.

A catalyst for converting the first gas into the constituent gases is provided at least between the first inner duct portion and first outer duct portion and preferably also within the inner duct.

In yet a further aspect, the first gas prior to supply to the energy collecting element is preheated in the presence of a catalyst. Heat for this purpose is provided by the hot constituent gases exiting the heat collection element. The first gas is thus partially dissociated through catalytic reaction prior to entry into the heat collection element. In addition, heat drawn from the hot gases in the catalytic reaction reduces the temperature of the gases towards ambient temperature.

For this purpose, a duct assembly including inner and outer tubes connects the energy collection element to a transfer network for the supply of gases to, and conveyance of gas from, the element. A catalyst may be provided in the space between the inner and outer tubes. Heat exchange occurs between the gases flowing out through the inner tube and gases flowing in through the space between the inner and outer tubes. In the inner tube, however, laminar flow of gases tends to occur resulting in inefficient heat exchange.

In yet a further aspect, the present invention provides solar energy coUecting apparatus including a heat transfer and delivery system of one of the types described above, the solar energy collecting apparatus including solar concentrating means for concentrating solar energy on said energy collecting element.

The duct portions of the energy collection element usually are connected to a manifold block by welding however after assembly, filling of the assembled tubes with a suitable catalyst which is of granular form proves difficult. If the catalyst is installed in the tubes prior to assembly by welding, damage to the catalyst can occur due to the heat generated during welding.

The present invention in yet a further aspect provides a heat energy collection assembly of an endothermic reactor using gases as a working fluid, said energy collection assembly including a manifold and a heat energy collection element arranged in use to be exposed to a heat source and including first and second coaxial tubes connected to said manifold, passage means in said manifold communicating with said element, a catalyst introduced into said element through one of said passage means and plug means insertable in said one passage means to retain said catalyst in said element.

The present invention in yet a further aspect provides a method for introducing a catalyst into the heat energy collection element, said method including the steps of passing catalyst into said element via said one passage means and thereafter securing said plug to said manifold.

Suitably the tubes are connected to the manifold by welding prior to introduction of the catalyst into the element. The plug is also suitably secured to the manifold by welding after introduction of the catalyst into the element. The plug includes a reduced portion extending into the one passage means permitting flow of gases therepast but restraining catalyst movement from the element.

The present invention provides in yet a further aspect, a connecting duct assembly for conveying gases to and from the heat collection element, said connecting duct assembly including coaxial inner and outer bes defining a first gas passage in said inner tube and a second gas passage between said inner and outer tubes whereby heat exchange may occur between gases flowing through said first and second passages and rod means within and coaxial with said inner tube defining an annular space in said inner tube for gas flow through said inner tube. In yet a further aspect, the present invention provides solar energy collecting apparatus including an energy collection assembly as described above, the solar energy collecting apparatus including solar concentrating means for concentrating solar energy on said energy collection element. The solar energy collecting apparatus may further include a connecting duct assembly connecting the energy collection element to a transfer network for supply of gas to and conveyance of gas from the element.

As stated above the gases used in the apparatus may comprise ammonia which is converted in the presence of a catalyst into hydrogen and nitrogen in the element.

The catalyst in such an arrangement may comprise haematite. An alternative gas combination may comprise methane and carbon dioxide which is converted into carbon monoxide and hydrogen in the element in the presence of a suitable catalyst. Brief Description of the Drawings

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein :- Fig. 1 illustrates schematically a heat transfer and delivery system according to one aspect of the invention;

Fig. 2 illustrates a typical solar energy collecting apparatus in which the system of the invention may be used;

Fig. 3 is a cross sectional view of the heat collection element and associated supply lines used in the solar energy collection apparatus of Fig. 2;

Fig. 4 is an enlarged sectional view along line A-A of Fig. 3; Fig. 5 is a cross sectional view similar to Fig. 3 showing a further form of heat collection element;

Fig. 6 is a enlarged sectional view along line B-B of Fig. 4. Fig. 7 illustrates in sectional view portion of an alternative embodiment of energy collection element and connecting duct assembly;

Fig. 8 is an end partly sectioned view of the element and supply duct assembly of Fig.7;

Fig. 9 is a sectional view along line C-C of Fig.7; and Fig. 10 illustrates the manner in which the catalyst is supplied to the energy collection element. Detailed Description of the Drawings

Referring to the drawings and firstly to Fig. 1, there is illustrated schematically a heat transfer and delivery system 10 in which in this case ammonia is converted or partly converted into nitrogen and hydrogen in an endothermic reactor 11 and in which the nitrogen and hydrogen are reconverted or partly reconverted into ammonia in an exothermic reactor 12. The heat input for the endothermic reactor 11 may be provided by any suitable heat source however in accordance with a preferred aspect of the invention, the heat source comprises a source of solar energy for example a suitable solar concentrator. Heat drawn off at the exothermic reactor 12 may be used for power generation for example by heating water for generating steam for driving a steam turbine. For transferring the ammonia, nitrogen and hydrogen between the exothermic reactor 11 and endothermic reactor 12, the transfer network shown schematically at 13 is provided. The network 13 includes an outer duct 14 and an inner duct 15 located within the outer duct 13 and extending therealong. The outer duct 14 is

5 used primarily for conveying ammonia between the reactors 11 and 12 whist the inner duct 15 is used primarily for the conveying of hydrogen and nitrogen separated from the ammonia together with non-dissociated ammonia.

Such an arrangement as described substantially reduces the cost and complexity of the transfer network in that the outer duct 14 may comprise any suitable

10 duct formed of any suitable material which will resist the pressure of ammonia within the system with joints 16 being of conventional form and using conventional sealing arrangements for example separate sealing elements. The inner duct 15 being located within the outer duct 14 may be constructed with conventional joints 17. For example, the duct 15 may comprise a plastics duct with conventional adhesively connected joining

15 sleeves 17. Any leakage of hydrogen duct 15 within the network 13 will thus be substantially contained having to escape both through the joints 15 and 16 to reach the atmosphere. It will of course be appreciated that the joints 17 may be any other type of pipe joint for example screw joints or bolted together joints.

Referring now to Fig. 2, there is illustrated solar concentrating assemblies

20 20 incorporating the present invention arranged on, or defining a platform assembly or base 21. The platform assembly 21 is in one embodiment formed of a buoyant material and is arranged for flotation on a body of water which acts as a bearing so that the platform assembly 21 may be rotated about a vertical axis to track movement of the sun. Such an arrangement is shown in my U.S. No. 5,309,893 issued May 10, 1994, the

25 contents of which are incorporated herein by reference. Actuating means are provided to cause rotation of the platform assembly 21 about a vertical axis to track movement of the sun, the actuating means being actuated in response to any suitable sun tracking means. In an alternative configuration, the array of solar assemblies 20 may be fixed and reflectors in the assembly may be moved so as to track the sun. Of course the solar assemblies may

30 comprise any number of concentrating assemblies to suit the particular application requirements. The base 21 is provided with or includes on or in its upper side, a plurality of angled planar surfaces 22 which define mounts for elongated strip reflectors 23 which are supported thereon, the surfaces 22 being arranged at an increasing inclination to the horizontal outwardly from the centre along parabolic curves and on opposite sides of the base 21 so that the reflectors 23 form a composite primary reflector 24 having substantially cylindrical parabolic reflector properties and having a principal axis or axes 25. Intersection of light rays from the reflectors 23 occurs at a focus line 26.

The reflectors 23 are arranged to concentrate solar energy onto or towards a secondary concentrating assembly 25 supported above the base 21 by means of pairs of opposite downwardly and outwardly inclined struts which are mounted at their lower ends to the base 21. A pair of opposite spaced apart planar reflectors 27 which have their reflective surfaces facing and which extend parallel to each other are arranged to be equidistant to, and on either side of the principal axis 25 or plane containing the principal axes of the primary reflector 24. The reflectors 27 are so placed that their lowest edges, that is their edges proximate to the primary reflector 24 are substantially at or aligned with the focus line 26 of the primary reflector 24.

Arranged between the planar reflectors 27 are a series of secondary concentrating cylindrical parabolic reflectors 28 which have their focus lines 29 extending substantially normal to the planar reflectors 27 and the principal axis 25 of the primary reflector 24.

The reflectors 28 are supported for limited rotation about an axis of rotation extending along their focus lines 29.

Extending along the focus line 29 of each reflector 28 is an energy collecting element 42 in the form of a tubular duct which passes through an opening in one of the side reflectors 26 as at 43 and which is closed at its outer free end 44.

The element 42 as shown in Figs. 3 and 4 includes in one embodiment an outer duct 50, a first coaxial inner duct 51 and a second duct 52 within the duct 51 and coaxial with the inner and outer ducts 50 and 51. The ducts 51 and 52 are formed of a material permeable to hydrogen. A typical material for this purpose may comprise a ceramic. The ducts 51 and 52 define therebetween an annular chamber 53. The outer end of the passage 53 is closed as at 54 by any suitable plug or sealing means. The inner duct 52 defines a passage 55 primarily for ammonia and the passage 55 contains a suitable catalyst 56 for the endothermic reaction. The annular space 57 between the duct 51 and duct 50 communicates around the end of the ducts 51 and 52 with the passage 55 and may also carry a suitable catalyst 56. The permeable nature of the ducts 51 and 52 enables hydrogen disassociating from the ammonia in the passages 55 and/or 57 through the endothermic conversion of the ammonia to permeate into the chamber 53 and thereby be separated from the ammonia. This allows for further disassociation of hydrogen from the ammonia in the passages 57 and/or 55 and thus more efficient dissociation or cracking of the ammonia. The element 42 is supported in a cantilever manner from an end manifold block 58 arranged externally of a side mirror 27, the block 58 including an inlet passage 59 which communicates with the passage 55. Outlet passages 60 and 61 communicate with the passages 53 and 57 for the outlet flow primarily of dissociated hydrogen and nitrogen. These two passages 60 and 61 are joined into a common outlet passage 62. An adjustable throttling valve 63 is associated with the passage 60 to control flow through the passage 60. This valve 63 primarily controls the nitrogen and non-disassociated ammonia flow from the passage 57 within the element 42 to maintain or control pressure drop across the permeable ducts 51 and 52 to thereby ensure efficient hydrogen collection in the chamber 53. The valve 63 may comprise any form of valve such as a screw-in throttle valve.

A connecting duct assembly 64 extends from the manifold block 58 to connect the element 42 to the transfer network 13 of the type described with reference to Fig. 1. The assembly 64 includes an outer duct 65 defining a passage 66 with which the inlet passage 59 communicates. The duct 65 is connected at its opposite end to the duct 14 to receive ammonia therefrom. A catalyst 56 is located within the duct 65. A further duct 67 is located coaxially within the duct 65 and communicates at one end with the passage 62 and at its opposite end with the duct 15 of the transfer network 13 through any suitable connection arrangement.

The duct assembly 64 serves a dual function in a heat exchanging operation. Hydrogen and nitrogen disassociated from the ammonia together with residual ammonia flowing into the passage 67 from the element 42 is hot. Ammonia flowing into the passage 66 and through the catalyst 56 therein is subject to the heat of the hot gases in the passage 67. This will cause preheating of the ammonia and cause a catalytic reaction in the passage 66 and thereby cracking or partial disassociation of the ammonia into nitrogen and hydrogen. At the same time, the catalytic reaction will draw heat from the hot gases flowing through the passage 67 so that the gases at the transfer network 13 are reduced substantially to ambient temperature.

In a further embodiment of the invention shown in Figs. 5 and 6, the energy collecting element 42 comprises an outer duct 50 and an inner duct 68 coaxial with the outer duct 50 defining an inner passage 69 within the inner duct 68 and an outer passage 70 between the inner and outer ducts 68 and 50. The inner duct 50 in this embodiment is not formed of a material permeable to hydrogen. At least the passage 70 and preferably both passages 69 and 70 contain a suitable catalyst. In this embodiment, ammonia passing down the inner passage 69 flows into the outer passage 70 where due to catalytic conversion under influence of heating of the duct 50 from concentration of the solar energy, it disassociates or partly disassociates into nitrogen and hydrogen. Some disassociation of the ammonia will also occur within the passage 69. The modified form of element 42 may be connected in a similar manner to Figs. 3 and 4 to a manifold block 58 and heat exchanger duct assembly 64. The hydrogen and nitrogen disassociating within the element 42 thus passes into the passage in the duct assembly 64 to be connected to the transfer network 13.

In yet a further embodiment of the invention, the energy collection element 42 may be of the form described in my Australian Patent No. 679598 with a divider separating the element 42 into a pair of passages each of which may contain the catalyst. In operation the array of solar collecting assemblies 20 are arranged so that the planes containing the principal axes 25 of the reflectors 24 contain the sun shown as S and maintain this relationship with the sun by rotating as the sun moves from sunrise to sunset. The incident angle of the sun's rays on the reflectors 23 varies in accordance with the time of day and with the season. The rotational position of the parabolic reflectors 28 is adjusted so that their principal axes are substantially parallel to the reflected rays from the primary reflectors 23. Rays striking the central region of the reflector assembly 24 are reflected directly to the parabolic reflectors 28 where they are concentrated on the element 42. Rays striking the reflector assembly 24 outwardly of the centre of the assembly 24 will because of the parabolic configuration of the reflector assembly 24 be directed inwardly towards the secondary concentrating assembly 25, the rays crossing at the focus line 18. Some rays will strike the parabolic reflector 28 and be directed onto the side reflector 27 and be concentrated on the element 42. Other rays will strike the opposite side reflectors 27 to be reflected onto the parabolic reflector 28 which concentrates the rays on the element 42. Other rays may be reflected from opposite side reflectors 27 before being concentrated on the element 42 by the parabolic reflector 28.

The element 42 thus is heated by the rays concentrated on the element 42. Ammonia flowing through the duct 14, and into the passage 66 will flow in the embodiment of Figs. 3 and 4 into the passage 55 so as to be at least partly converted into hydrogen and nitrogen. The hydrogen as described above is drawn through the permeable duct 52 into the chamber 53. This endothermic reaction will continue as the ammonia flows along the passage 55 and into the passage 57. The collected hydrogen in the chamber 53 passes into the passage 67 for flow into the duct 15. The nitrogen and residual ammonia passes into the passage 60 and then into the passage 67 for flow to the duct 15 with pressure being controlled by the valve 60. The heated gases flowing in the passage 67 preheat the ammonia passing through the passage 66 which is partially cracked due to the catalytic reaction with the catalyst 56 within the passage 66. The cooled and disassociated hydrogen and nitrogen and residual ammonia collecting in the duct 15 is delivered in the transfer network 13 in the manner described with reference to Fig. 1 for re-association in the exothermic reactor 12 to generate heat energy.

Whilst the invention has been described with reference to one particular form of solar concentrator, it will be appreciated that it may be used with other forms of solar concentrators such as parabolic or cylindrical parabolic concentrators.

Referring now to Fig. 7 there is illustrated schematically a further form of an energy collection element 80 typically for use in solar energy collecting apparatus of an endothermic reactor using gas as the working fluid with the heat source comprising solar energy for example a suitable solar concentrator. Gas supply to and from the energy collection element occurs through a connecting duct assembly 11.

The energy collecting element 80 and connecting duct assembly 81 are typically used in the solar energy collecting or concentrating apparatus 20 of the type shown in Fig. 2.

The energy collection element 80 as previously is positioned to extend along the focus line 29 of each reflector 17. The connecting duct assemblies 81 associated 5 with each element 80 are connected to a transfer network 13 through which the gases are conveyed to and from the element 80.

The energy collecting element 80 includes in this embodiment and as shown in Figs. 7, 8 and 9 an outer duct 91, and a coaxial inner duct 92 which define a first passage 93 between the inner and outer ducts or mbes 91 and 92 and an inner passage

10 94 within the inner duct 92. The outer duct 91 is closed by an end plug 95 secured in position for example by means of a welded joint. The end plug 95 as shown also in Fig. 9 includes an extending spigot 96 having an enlarged head 97 which is located within the end of the inner duct 92 so as to support the latter. The head 97 is of generally cylindrical form with one or more flats 98 on is side surface defining openings 99 allowing

15 communication between the passages 93 and 94.

The mbes 91 and 92 are supported in a cantilever manner from an end manifold block 100. The connecting duct assembly 81 also extends from the manifold block 100 to connect the element 80 to the transfer network 100.

The outer tube 91 of the energy collection element 80 is weldably

20 connected to the manifold block 100 at 101. Welded joints are preferred to prevent gas escape. The manifold block 100 also includes a hollow spigot 102 which extends into, to support, the inner tube 92 and is weldably connected thereto. The manifold block 100 includes a right angled gas supply passage 103 having a first section 104 which extends through the spigot 102 to communicate with the passage 94 within the tube 92 and a

25 second section 105 which opens through face 106 of the manifold block 100.

The manifold block 100 also includes a second right angled passage 107 which includes a section 108 communicating with the outer passage 93 of the element 80 and a section 109 which also opens through the face 106 of the manifold block 100. The section 108 also has an extension passage 110 which opens through a further face 111 of

30 the block 100 to define a catalyst filling opening. The passage 110 is arranged to receive a plug 112 of similar diameter to the passage 110, the plug 112 also including a reduced diameter tongue portion 113 which extends into the passage section 108 to thereby define an annular space 114 communicating with the passage section 109. The plug 112 is held in position by a welded connection at 115.

The catalyst 116. which is in the form of a fine granular material is required to be placed within the passage 93 and for this purpose, the element 80 may be oriented as in Fig. 10 and with the plug 112 removed, the catalyst 116 is supplied through the passage sections 110 and 108 until the required amount of catalyst within the passage 93 is achieved. The plug 112 is then inserted into the passage 110 and welded in position by the weld 115 to seal the passage 110. The tongue portion 113 protects into the passage section 108 and is of a diameter such as to allow gas to pass through the annular space 114 into the connection duct assembly 81 but retain the granular catalyst 116. Typically, the radial width of the annular space 114 is in the order of 0.5 mm where the catalyst 116 has a typical dimension of at least 1.00mm in diameter. The connecting duct assembly 81 also includes coaxial inner and outer tubes 121 and 122 which are weldably connected to the manifold block 100 so that the passage 123 between the inner and outer tubes 121 and 122 communicates with the passage 103 and the space 124 within the inner tube 121 communicates with the passage 107. To prevent laminar flow of gases in the passage 124, a solid rod 125 is located coaxiaUy within the tube 121. This constrains gases passing into the passage 124 in the annular space 126 between the rod 125 and tube 121 to thereby increase the heat exchange efficiency between gases flowing through the space 126 and gases flowing in the passage 123. This arrangement encourages turbulent flow equalising velocity distribution of the gases flowing through the passage 124. The apparatus of the invention may be used with ammonia gas which is cracked into nitrogen and hydrogen in an endothermic reaction and which recombines into ammonia in an exothermic reaction. An alternative gas combination is carbon dioxide and methane which is converted in the element 80 into carbon monoxide and hydrogen, the latter being reconverted into carbon dioxide and methane in an exothermic reactor. Any other gas which breaks down into constiment gases one of which is of fine molecular structure may be used. Where ammonia is the working fluid, it is supplied from the transfer network through the passage 123 of the connecting duct assembly 81 via the passage 103 in the manifold block 100 into the passage 94. The gas then flows via the openings 99 into the passage 93 so as to be converted, in the presence of the catalyst 116, at least partly converted into hydrogen and nitrogen under the influence of the heat applied to the element 80. These gases then pass into the passage 124.

The duct assembly 81 serves a dual function in a heat exchanging operation. Hydrogen and nitrogen disassociated from the ammonia together with residual ammonia flowing into the passage 124 from the element 80 is hot. Ammonia supplied to the passage 123 and through catalyst therein is subject to the heat of the hot gases passing through the space 123. This will cause preheating of the ammonia and cause a catalytic reaction in the passage 113 and thereby cracking or partial disassociation of the ammonia into nitrogen and hydrogen. At the same time, the catalytic reaction will draw heat from the hot gases flowing through the space 121 so that the gases at the transfer network 13 are reduced substantiaUy to ambient temperature.

In some arrangements it is desirable to have catalyst 116 within the tube passage 94 and for this purpose the end plug 95 may be truncated along the dotted line 127 shown in Fig. 7 and the end of the tube 92 supported in an alternative fashion for example by radial ribs extending between the tube 92 and tube 91. The passage 94 will then be supplied with catalyst 116 using the method described with reference to Fig. 10.

The manifold block 109 and the passages therein may be of configurations other than that shown provided that one of the passages can be extended through the block 100 to receive a plug. The tube 92 may in addition be directly secured to the block 100 by welding without the use of the spigot 102. The mbes of the element 80 and/or duct assembly 81 may be formed of any suitable metal with a particular suitable metal being incanel. A typical catalyst used in the above described embodiments is a granular haematite however any other catalyst suitable for the purpose may be employed.

Whilst the invention has been described with reference to one particular form of solar concentrator, it will be appreciated that it may be used with other forms of solar concentrators such as parabolic or cylindrical parabolic concentrators which concentrate solar energy directly on the element 10 or 80. The system may equally be used with other heat transfer and distribution arrangements where heat energy is required to be conveyed between different locations.

AU other modifications and variations to the invention as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as defined in the appended claims.

Claims

1. A heat transfer and delivery system including endothermic reactor means in which a first gas in the presence of a catalyst is converted or partly converted into constituent gases, exothermic reactor means in which said constiment gases are reconverted into said first gas and means for conveying said first gas and constiment gases between said endothermic reactor and endothermic reactor, said conveying means including first duct means for primarily containing said first gas and further duct means for containing said constituent gases, said further duct means being located within said first duct means.

2. A heat transfer and delivery system according to Claim 1 wherein heat energy for said endothermic reactor means is supplied by a solar energy concentrator.

3. A heat transfer and delivery system according to Claim 2 wherein said solar energy concentrator concentrates solar energy on a hoUow energy collection element containing a catalyst through which said first gas is passed for conversion or partial conversion in an endothermic reaction into said constituent gases.

4. A heat transfer and delivery system according to Claim 3 wherein said energy collection element includes a first inner duct portion containing a said catalyst and defining an inlet passage for said first gas for disassociation or partial disassociation into said constituent gases, and a second outer duct portion coaxial with said first inner duct portion and communicating therewith, said first and second duct portions defining an outlet passage for said constiment gases and said first gas.

5. A heat transfer and delivery system according to Claim 4 wherein said energy coUection element includes a coUection chamber for one gas of said consitunet gases communicating via a membrane or material permeable to said one gas with at least said first inner duct portion and optionally with the passage between the first and second duct portions.

6. A heat transfer and delivery system according to Claim 5 wherein said first and second duct portions of said energy coUection element are located coaxiaUy within a third outer duct which is subject to direct heating by said solar energy concentrator and wherein said first and second duct portions have walls or waU sections formed of a material permeable to said one gas.

7. A heat transfer and delivery system according to Claim 6 wherein the space between said first and second portions defines said coUection chamber for said one gas disassociating from said first gas in said first duct portion and from the first gas/constituent gas mix in the passage between said second duct portion and said third duct.

8. A heat transfer and delivery system according to Claim 7 wherein corresponding ends of said first duct portion and second duct portion are joined to form a collection chamber for said one gas.

9. A heat transfer and delivery system according to Claim 8 wherein said catalyst is provided at least between said first inner duct portion and said third outer duct and optionally within said first inner duct portion.

10. A heat transfer and delivery system according to Claim 9 and including a conveying duct assembly including inner and outer tubes connecting said energy coUection element to a transfer network for the supply of gases to and conveyance of gases from said element.

11. A heat transfer and delivery system according to Claim 10 and including a catalyst in the space between said inner and outer mbes.

12. A heat transfer and delivery system according to Claim 1 wherein said first gas comprises ammonia and said constiment gases comprise hydrogen and nitrogen.

13. Solar energy coUecting apparatus including a heat transfer and delivery system according to any one of the preceding claims.

14. A heat energy coUection assembly of an endothermic reactor using gases as a working fluid, said energy coUection assembly including a manifold and a heat energy coUection element arranged in use to be exposed to a heat source and including first and second coaxial tubes connected to said manifold, passage means in said manifold communicating with said element, and a catalyst introduced into said element through said passage means and plug means msertable in said passage means to retain said catalyst in said element.

15. A method for introducing a catalyst into a an energy coUection assembly of an endothermic reactor, said energy coUection assembly including a manifold and a heat energy collection element arranged in use to be exposed to a heat source and including first and second coaxial tubes connected to said manifold, passage means in said manifold communicating with said element, said method including the steps of passing catalyst into said element via said passage means and thereafter securing said plug to said manifold.

16. A method according to claim 15 wherein said mbes are connected to said manifold by welding prior to introduction of catalyst into said element.

17. A method according to Claim 16 wherein said plug is secured to said manifold by welding after introduction of the catalyst into said element.

18. A method according to Claim 17 wherein said plug includes a reduced portion extending into the one passage means permitting flow of gases therepast but restraining catalyst movement from said element.

19. A connecting duct assembly for conveying gases to and from an energy coUection assembly of an endothermic reactor, said connecting duct assembly including coaxial inner and outer mbes defining a first gas passage in said inner tube and a second gas passage between said inner and outer mbes whereby heat exchange may occur between gases flowing through said first and second passages and rod means within and coaxial with said inner mbe and defining an annular space in said inner tube for gas flow through said inner tube.

20. Solar energy collecting apparatus including an energy collection assembly as defined in claim 14 and including solar concentrating means for concentrating solar energy on said energy collection element.

21. Solar energy collecting apparatus according to claim 20 and including a connecting duct assembly as defined in claim 19 connecting said energy coUection assembly to a transfer network for supply of gas to and conveyance of gas from said energy coUection assembly.