Hydrogen permeable pipe

A solar thermal power plant is provided. The solar thermal power plant includes a solar collection system configured for utilizing incident solar radiation to heat a heat transfer fluid (HTF) and a power block configured for utilizing the heated HTF to generate power. The solar collection system includes a plurality of pipes for carrying HTF characterized by a first degree of permeability to hydrogen, at least some of the pipes including portions exposed to the atmosphere, and including a membrane made of a material being characterized by a second degree of permeability to hydrogen, the second degree of permeability being higher than the first degree of permeability to hydrogen.

FIELD OF THE INVENTION

This invention relates to solar thermal power plants, and in particular to arrangements for removing dissociated hydrogen therefrom.

BACKGROUND OF THE INVENTION

Amid concerns over global warming, and forecasts of both the depletion of non-renewable energy sources and rising power demand, suppliers of energy are: increasingly seeking alternative primary sources of energy. One such source of energy is solar energy, and one way of utilizing solar energy is with a solar thermal power plant.

One type of solar power plant utilizes a “radiation concentrator collector” which concentrates the solar radiation by focusing it onto a smaller area, e.g., using mirrored surfaces or lenses. In this system, a reflector, which is typically parabolic, receives and reflects (focuses) incoming solar radiation onto a radiation absorber, which is formed as a tube. The tube radiation absorber is concentrically surrounded by a treated glass enclosure tube to limit the loss of heat. The collector system further includes means to track the sun.

The tube radiation absorber is made of metal with a coating having a high solar radiation absorption coefficient to maximize the energy transfer imparted by the solar radiation reflecting off the reflector. A heat transfer fluid (HTF), which is typically a liquid such as oil, flows within the tube radiation absorber.

The thermal energy is transported by the HTF to power, e.g., a thermalelectric power plant to drive one or more power-generation systems thereof, in order to generate electricity in a conventional way, e.g., by coupling the axle of each of the turbines to an electric generator. One such example of a thermal-electric power plant is a steam-electric power plant, which uses thermal energy provided thereto to produce steam to drive turbines thereof, which in turn drive a generator, thus generating electricity.

Portions of the tube radiation absorbers are typically surrounded with a glass envelope, with the volume therebetween evacuated in order to limit heat loss due to convection. However, hydrogen may be released within the HTF, either by dissociation therefrom or as a product of a cathodic reaction with the interior of the tube radiation absorber, which escapes via the wall of the tube radiation absorber and enters the evacuated volume. In order to maintain high efficiency of the solar power plant, as much of this hydrogen should be removed.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a pipe for carrying heat transfer fluid (HTF) within a solar thermal power plant, the plant comprising a solar collection system configured for utilizing incident solar radiation to heat the HTF, and a power block configured for utilizing the heated HTF to generate power; the pipe, which may be made of stainless steel, is characterized by a first degree of permeability to hydrogen thereacross (i.e., between a surface which faces the: ulterior of the pipe and a surface which faces the exterior of the pipe) and comprising at least one portion configured for being exposed to the atmosphere during use arid comprising a hydrogen-passage being characterized by a second degree of permeability to hydrogen, being higher than the first degree of permeability to hydrogen, thereacross.

The hydrogen-passage may compose a membrane comprising palladium, and it may further comprise up to about 30% silver.

The hydrogen-passage may further comprise a covering mechanically secured to the pipe, which may be made of porous steel, being characterized by a permeability to hydrogen which is at least as high as that of the membrane. As hydrogen and The covering may be securingly connected to an area of the pipe surrounding the membrane.

The portion may be formed as a chamber comprising an enclosed volume open to the interior of the pipe and filled with an inert gas, such as nitrogen. The enclosed volume may be disposed such that substantially all of the inert gas remains therein during operation of the plant.

A section of the pipe adjacent the portion may be surrounded by a solid envelope, for example made of a glass or stainless steel material, spaced therefrom, the volume between the envelope and the pipe being evacuated.

The HTF may be selected from a group comprising thermal oil and water/steam.

The solar collection system may comprise a plurality of concentrators, such as parabolic reflectors, configured for concentrating incident sunlight on the, pipes.

According to another aspect of the present invention, there is provided a solar thermal power plant comprising a solar collection system configured for utilizing incident solar radiation to heat an HTF, and a power block configured for utilizing the heated HTF to generate power; the solar collection system comprising a plurality of pipes as described above.

According to a further aspect of the present invention, there is provided a pipe, which may be made of stainless steel, for carrying; heat transfer fluid (HTF) within a solar thermal power plant, die plant comprising a solar collection system configured for utilizing incident solar radiation to heat the HTF, arid a power block configured for utilizing the heated HTF to generate power; the pipe being surrounded by one or more solid envelopes, which may be made of a glass or a stainless steel material, spaced therefrom, a volume defined between each envelope and its respective pipe being evacuated; the pipe comprising:at least one chamber associated with arid in fluid communication with at least one of the volumes; at least a portion of a wall defining the chamber and exposed to the atmosphere comprising a membrane having a high permeability to hydrogen; the chamber containing a getter material adapted to absorb hydrogen gas and to release it when the getter material is at or above a discharge temperature;valve configured to selectively isolate the chamber from the volume when closed, and bring the chamber and the volume into fluid communication with one another when open; anda heating element configured to bring; the getter material to a temperature no less than the discharge temperature.

The pipe may further comprise a control system configured to regulate elements of the plant, and to operate in one of:a hydrogen release mode, wherein it ensures that the valve is closed and the heating element is on; anda hydrogen storage mode, wherein it ensures that the valve is open and the heating element is off.

The plant may further comprise a temperature sensor in communication with the control system and disposed so as to measure the temperature within the chamber, the control system being further configured to ensure that the valve is closed when the temperature within the chamber is at or above a predetermined temperature. The predeteimined temperature may be equal to the discharge temperature, or it may be a fixed amount above the ambient temperature, for example approximately 25° C. above the ambient temperature.

The pipe may further comprise a pressure sensor in communication with the control system and disposed so as to measure the pressure within the chamber, the control system being further configured to ensure that the valve is closed when the pressure within the chamber is at or above a predetermined pressure.

The pipe may be a header pipe configured for carrying HTF between the power block and heat collecting elements of said solar collection system.

The chamber may be associated with more than one volume. For example, at least one of the pipes may be surrounded by two transparent solid envelopes spaced axiallyfrom one another and denning separate volumes, the chamber being in fluid communication with both volumes.

The HTF may be selected from a group comprising thermal oil mid water/steam.

The solar collection system may comprise a plurality of concentrators, such as parabolic reflectors, configured for concentrating incident sunlight on the pipes.

According to a still further aspect of the present invention, there is provided a solar thermal power plant comprising a solar collection system configured for utilizing incident solar radiation to heat a heat transfer fluid (HTF), and a power block configured for utilizing the heated HTF to generate power; the solar collection system comprising at least one pipe as described in the above aspect.

DETAILED DESCRIPTION OF EMBODIMENTS

As illustrated inFIG. 1, there is provided a solar thermal power plant, generally indicated at10. The plant10comprises a power block12, such as a thermal-electric power plant, which utilizes heat to drive its operation to produce electricity, and a solar, collection system14for providing the heat therefor. The solar thermal power plant may be designed m accordance with that described in PCT/IL2009/000899, filed on Sep. 15, 2009, to the present applicant, the disclosure of which is incorporated herein by reference.

The power block12comprises elements which are typically found within a power plant and which are well-known, such as one or more turbines, a condenser, feedwater heaters, pumps, etc. (individual elements of the power block are not illustrated). The turbines are coupled to an electrical generator for generating electricity, as is well known in the art. The power block12may be designed in accordance with that described in WO2009/034577, filed on Sep. 11, 2008, to the present applicant, the disclosure of which is incorporated herein by reference.

The power block12further comprises a steam generation system16comprising a steam generation train having three heat exchangers, a pre-heater18, an evaporator20, and a super-heater22. The steam generation train is configured to transfer heat from an outside source (in this case, the solar collection system14) to working fluid of the power block12, so that it can reach the elevated temperature and pressure required to optimally drive the turbines thereof The steam generation train may further comprise an optional reheater (not illustrated).

The solar collection system14comprises one or more solar fields24, which are configured to capture heat from sunlight impinging thereon and transfer it to the steam generation system14of the power block12for driving its operation. For this purpose, the solar fields24comprise one or more tube radiation absorbers26, which may be made out of stainless steel, and a plurality of trough collectors28, such as single-axis parabolic reflectors. As illustrated inFIG. 2, portions of the tube radiation absorbers26which are within the collectors28are surrounded by a glass envelope30spaced therefrom, thus defining a volume32between the tube radiation absorber26and the glass envelope which is evacuated in order to limit heat loss. Alternatively, any suitable means for concentrating solar radiation, such as Fresnel collectors, may be provided. The tube radiation absorbers26carry a heat transfer fluid (HTF) therein, such as a thermal oil (phenyls) which is commercially available, such as under the trade name Therminol® VP-1, Dowtherm™, etc. Alternatively, the HTTP may also be one of steam/water, in which case the plant10may operate using direct steam, i.e., the HTF is used as the working fluid for the turbines of the power block12, and thus the steam generation system16may be excluded. The HTF, according to any of the embodiments, is heated within the tube, radiation absorbers26upon their exposure to direct solar radiation and solar radiation concentrated by the trough collectors28. Thus, the HTF is heated as it flows through the tube radiation absorbers26. Solar collection systems of this type are provided, inter alia by Solel Solar Systems, Ltd. (Israel).

It will be appreciated that while the solar collection system24is illustrated inFIG. 1as comprising two solar fields, any suitable number of fields may be provided without departing from the spirit and scope of the present invention, mutatis mutandis.

Each of the tube radiation absorbers26constitutes a loop, which carries HTF through a solar field24for heating. Each loop is connected, at an upstream end thereof, to a local return header pipe34, which is configured to carry thermally depleted HTF from the power block12to the solar field24, and, at a downstream end thereof, to a local supply header pipe36, which is configured for carrying heated HTF from the solar collection system14. The solar collection system14further comprises a main return header pipe38, which is configured for carrying thermally depleted HTF from the power block12thereto via the local return header pipe34, and a main supply header pipe40, which is configured for carrying heated HTF from the solar collection system to die power block for driving its operation. The direction of now of HTF through each of the tube radiation absorbers26, local return header pipes34, local supply header pipes36, main return header pipe38, and main supply header pipe40is indicated by arrows inFIG. 1.

A middle portion42of each loop is typically not exposed to concentrated solar radiation from the trough collectors28. This portion42may exposed to the atmosphere, i.e., not being surrounded by an envelope and thus having no evacuated volume therearound. /Is illustrated inFIG. 3A, a radially extending chamber44may be provided on the middle portion42of the loop, which may be made as an extension of the tube radiation absorber26. The chamber defines an enclosed volume which is open at one end to tile interior of the tube radiation absorber26(the line inFIG. 3between the middle portion42of the loop and the ulterior of the chamber44indicates the surface of the HTF, and is not a structural separation between the two). A portion of the chamber44consumes a hydrogen passage45, being made of a material with a high permeability to hydrogen, such as comprising or being constituted by a thin (e.g., on the order of 0.1 mm) membrane46of palladium, which may contain silver, for example up to about 20%-30%. As the membrane46is typically very thin, it may be subject to rupture or detachment from the rest of the chamber44. Therefore, the hydrogen passage45may further comprise a covering48over the membrane46, on the outer side of the chamber44, in order to prevent the relatively high pressure of the HTF during operation to eject the membrane46from its place. The covering48may comprise a high strength, highly permeable material, such as porous stainless steel, for example formed as a disk. The covering48may be connected to an area of the chamber surrounding the membrane46, for example by welding or by pressing thereon with high pressure. The covering48maintains the membrane46in place, while not interfering with gas transfer thereacross.

As illustrated inFIG. 3B, the middle portion42may be enclosed surrounded by an envelope30a, which may be glass, stainless steel, or any other suitable material. The volume32abetween the envelope30band the middle portion42may be evacuated. The volume32amay be in fluid communication with the volume32between the tube radiation absorber26and its associated glass envelope30, or it may be isolated therefrom.

It will be appreciated that while the chamber44is described as being located at a middle portion42of a loop (i.e., a portion thereof not exposed to concentrated solar radiation from the trough collectors28), it may be provided at any portion of the loop, for example on a portion of a tube radiation absorber26which is exposed to concentrated solar radiation.

It will be appreciated that while reference is made to a middle portion42of the loop, the chamber44may be provided at any appropriate portion thereof, or on a pipe or tube carrying HTF which does riot constitute a portion of one of the loops, for example on one of the header pipes34,36,38,40.

The interior of the chamber44is filled with an inert gas, such as nitrogen (N2). The chamber is maintained above the HTF, in order to keep the inert gas therein, and thus prevent HTF from collecting therein.

During operation, the HTF is heated. In a case where the HTF is provided as a thermal oil, hydrogen is released by dissociation therefrom. In a case where the HTF is provided as water/steam, i.e., when the plant10operates using direct steam as described above, corrosion of the tube radiation absorber may be associated with a cathodic reaction in which hydrogen is released. In either case, as hydrogen is a relatively small molecule, the material of the tube radiation absorber26exhibits a degree of permeability thereto; thus, some of it escapes the tube radiation absorber and enters the evacuated volume32between it arid the glass envelope30. The presence of this hydrogen hi the volume32allows for conductive heat flow between the, tube radiation absorber26and the atmosphere, thus resulting in heat losses, as is well known in the art, getters (not illustrated) maybe provided within the evacuated volume32to sequester this hydrogen, and thus limit the heat loss.

In addition, a portion of the released hydrogen enters the chambers44, wherein it rises through the inert gas therein and exits via the membrane46. As the permeability of the membrane to hydrogen is relatively high, and in any event higher than that of the material of the tube radiation absorber26, a significant amount of hydrogen is released to the atmosphere thereby. Thus, the number of getters necessary within the enclosed volume32may be reduced.

Alternatively, as illustrated inFIG. 4, part of the middle portion42of the loop may be foamed containing the membrane46, without provided a chamber as described above. A covering48is provided, for example as described above, or wrapped around the portion42and covering the membrane.

As illustrated inFIG. 5, one or more of the header pipes34,36,38,40(in the ensuing discussion and corresponding figures, reference number50will be used to refer to header pipe, which may be any header pipe; it will be appreciated that the example described below, while making specific reference to a header pipe, may be provided for any pipe in the plant10, such as tube radiation absorbers26, mutatis mutandis) is surrounded by an envelope52spaced therefrom, thus defining a volume54between the header pipe50and the envelope which is evacuated in order to limit heat loss.

A chamber56associated with the header pipe50is provided, for example in a location which is shielded from incident solar radiation, in order to maintain a low temperature thereof. The chamber56may be made of any material, for example of the same material as that of me envelope52. However, at least one portion of the wall of the chamber56is formed as a membrane58having a high degree of permeability to hydrogen. It may be made of, e.g., palladium, which may contain silver, for example up to about 20%-30%. In addition, getters60(e.g., pellet, or other elements made of a getter material) are provided within the chamber56.

One or more tubes62are provided, which are disposed so as to bring the interior of the chamber56into fluid communication with die volume54defined between the header pipe50and die envelope52surrounding it. A valve64is provided so as to selectively close the tube62, thus isolating the interior of the chamber56from the volume54.

As illustrated inFIG. 6A, one tube62may be formed so as to bring two otherwise isolated volumes54a,54binto fluid communication with the interior of the chamber56, for example by providing a T-junction66therein. The valve64may be placed at a location so as to isolate the two volumes541a,54bfrom the chamber. Alternatively, as illustrated inFIG. 6B, each volume54a,54b, may be provided with its own corresponding valve64a,64b, so that each may be isolated from the interior of the chamber56individually. In addition, the tube62may be provided with valves as per bothFIGS. 6A and 6B(not illustrated).

In addition, each chamber is associated with a heating element68, which is configured to heat the getters to a temperature at which hydrogen sequestered therein is released.

A control system (not illustrated) may be further provided in order to regulate operation of elements described above. A temperature sensor70may be provided, for example oil the outer surface of the envelope52, in order to measure the temperature of the volume54(placement of the temperature sensor on the exterior surface of the envelope is for convenience; it will be appreciated that the temperature sensor may be placed at any other convenient location). In addition, a pressure sensor72may be provided within the chamber56. The temperature and pressure sensors70,72are in communication with the control system, in order to transmit information thereto regarding conditions within the chamber.

During operation, as heated HTF flows through the header50, hydrogen is released therethrough into the evacuated volume54. As discussed above, the source of the hydrogen is either by dissociation therefrom from the HTF, in a case where it is provided as a thermal oil, or from corrosion of the header pipe50may be associated with a cathodic reaction in which hydrogen is released. The presence of this hydrogen in the volume54allows for conductive heat flow between the header pipe50and the atmosphere, thus resulting in heat losses. By absorbing hydrogen, the getters60function as a chemical pump, drawing the released hydrogen into the chamber56and sequestering it mere, thus helping to maintain the vacuum in the volume.

At a time determined by the control system, for example at night or during an off-peak period of power production, the control system operates in a hydrogen release mode, it closes the valve64(thus isolating the interior of the chamber56from the volume54), and turns on the heating element68to a temperature above which the getters release the sequestered hydrogen, for example to 400-450° C. The partial pressure of the hydrogen within the chamber56rises due to the release of hydrogen from the getters, exceeding that of the atmosphere (which is close to zero). The differential in the partial pressures of hydrogen between the chamber56and the atmosphere cause the release of hydrogen to exit the chamber via the membrane58. At a time determined by the control system, it operates in a hydrogen storage mode, in which it turns off the heating element68and opens the valve64(thus bringing the ulterior of the chamber56into fluid communication with the volume54). The control system may open the valve64only after a delay, during which the getters60are allowed to return to a temperature at which they sequester hydrogen.

The determination by the control system as to when to operate in its hydrogen release mode may be based on any one or more of the following:

The temperature within the chamber56(for example as measured at the outer surface of the envelope52) is determined to be a fixed amount (for example, about 25° C.) above the ambient temperature. This may indicate that there is a buildup of hydrogen within the chamber, for example due to the getters inability to sequester hydrogen either due to an elevated temperature thereof, or their having reached their hydrogen storage capacity. The pressure within the chamber56may rise above a predetermined pressure. This may indicate that the getters60are not storing hydrogen, arid that it must be released therefrom immediately.
A predeteimined amount of time has passed since the last time the controller operated in hydrogen release mode.

In addition, the control system may be configured to only operate in its hydrogen release mode at a certain time of the day, for example at night or at another time when the power demand on plant10are relatively low.

In addition, the control system may operate to close the valve64if the temperature of the interior of the chamber56(for example as measured at the outer surface of the envelope52) rises above a predetermined value, for example that at which the getters60release hydrogen, in order to allow the released hydrogen to exit via the membrane68.

While the arrangement described above with reference toFIGS. 5 through 6Bmay be suitable for any pipe carrying HTF within the plant10, it is particularly suited for a header pipe50, as it enables them to be insulated by being surrounded by an evacuated space by providing a system for removing the large amounts of hydrogen therefrom, which are released to the relatively large amount of HTF flowing therethrough, without requiring a large amount of getters. In addition, by removing released hydrogen from the HTF flowing through the header pipe50, the number of getters necessary within the enclosed volumes of the loops may be reduced.

Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis.