Abstract:
A volumetric receiver vessel for heating a fluid with concentrated solar radiation which includes: an external housing having an aperture at the front end; an internal housing separating fluid entering the vessel from fluid exiting thereof; a window covering the aperture of the vessel, where the window closes and seals the aperture of said vessel against a non-metallic seal; and a radiation absorber, located inside the vessel and places to absorb radiation entering the vessel through said window on a radiation absorbing surface, where said surface include at least two zones with different radiation absorption coefficients.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119           to U.S. Provisional Patent Application Ser. No. 61/577,028, filed Dec. 18, 2011, and entitled “The Klein solar thermal receiver”; which is incorporated herein by reference in its entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a system using concentrated radiation as the mode of heating a fluid situated inside the vessel, and more particularly solar energy systems with solar receivers. 
       BACKGROUND OF THE INVENTION 
       [0003]    The following publications, the disclosures of which are hereby incorporated by reference, are believed to represent the current state of the art: 
         [0004]    U.S. Pat. Nos. 5,931,158; 5,947,114; 6,516,792 B2,
   Kribus, A., Zaibel, R., Carey, D. Segal, A., Karni, J. 1998, “A solar-driven combined cycle power plant”, Solar Energy 62(2):121-129.   Mills, D., 2004, “Advances in solar thermal electricity technology”, Solar Energy 76:19-31.   Woerner, A., and Tamme, R., 1998, “CO 2  reforming of methane in a solar driven volumetric receiver-reactor” Catalysis Today 46:165-174.   Berman, A., Karn, R. K., Epstein, M., 2005, “Kinetics of steam reforming of methane on Ru/Al 2 0 3  catalysts promoted with Mn oxides”. Applied catalysis A: General 282:73-83.   Gordon, J. M. and Ries, H, 1993 “Tailored edge-ray concentrators as ideal second stages for Fresnel reflectors”, Applied Optics 32(13):2243-2250   
 
         [0010]    The invention relates to radiation based energy systems, such as systems using concentrated solar radiation to produce heat, electricity or to drive chemical reactions. The concentrated solar radiation can be used to directly or indirectly, drive turbines for electricity production. Central to the energy system is the vessel converting the radiation to sensible heat. This vessel is often called a solar receiver. 
         [0011]    The invention relates to a kind of solar receiver commonly called a volumetric receiver. In this type of vessel, the working fluid entering the receiver, for the purpose of heating and possibly also for chemical conversion of the fluid, is directly exposed to concentrated solar radiation by allowing the radiation to enter the vessel through a window. The window prevents the working fluid from mixing with ambient air, and prevents loss of pressure and/or the loss of already acquired heat in the incoming fluid. 
         [0012]    One of the most challenging aspects of this type of vessel is maintaining the integrity of the window. Pressure stresses, thermal stresses and issues of differences of thermal expansion between the window and other material in direct contact with the window can cause the window to crack, break or shatter. It is an object of the present invention to provide a positioning and sealing mechanism for the window that will put the least stress on the window and a design for a radiation absorber that will contribute to the lowering of thermal stresses on the window. 
         [0013]    Another challenging aspect of this type of receiver is the integrity of the radiation absorber. Pressure stresses and thermal stresses and issues of differences of thermal expansion between the absorber and other material in direct contact with the absorber can cause the absorber to melt, crack, break, crumble or shatter. It is an object of the present invention to provide a solution for, this problem by applying different materials with different radiation absorbing properties in different parts of the absorber. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention seeks to provide improved vessels for heating a fluid with concentrated, radiation, preferably solar radiation. 
         [0015]    There is thus provided in accordance with a preferred embodiment of the present invention a vessel for heating a fluid with concentrated radiation, which includes: a housing with an aperture and an ingress and an egress for fluid; a window covering the aperture in said housing for admitting and passing into the vessel concentrated radiation; a flow guide separating the fluid from the ingress from the fluid from the egress; and a permeable radiation absorber. 
         [0016]    Preferably, the window is flat. 
         [0017]    Most preferably the window covering the aperture is concave with the center of the window being deeper inside the body of the radiation receiving vessel than the rim of said window. The concave shape preferably follows an axis symmetric shape such as the radius of a sphere, a parabola, cone, capped cone, a combination of the mentioned shapes and other concave possibilities. 
         [0018]    Preferably, the window is placed on a seal to seal the aperture from fluid exchange with the ambient air. 
         [0019]    Most preferably the window is kept in place on the seal in the absence of any mechanism other than weight, gravity and friction to keep it in place. No other material is in direct contact with the window than the seal. 
         [0020]    Preferably, the window flange is actively cooled. 
         [0021]    Preferably, the window is actively cooled. 
         [0022]    Most preferably, the window is actively cooled from the outside. 
         [0023]    Preferably, the radiation absorber has at least two different areas with different radiation absorptivity, accomplished by the use of different absorption materials or by applying different external coating on the radiation absorbing side of the radiation absorber. 
         [0024]    There is also provided in accordance with a different preferred embodiment of the present invention a system for heating fluid with concentrated, radiation, preferably solar radiation. The system includes: concentrating devices to concentrate radiation from a radiation source; a vessel in which the concentrated radiation heats a fluid and a utilizer of the stored energy in the fluid. 
         [0025]    Preferably, the fluid contains any, all or a subset of the compounds; oxygen, methane, hydrogen, carbon dioxide, carbon monoxide, nitrogen, H 2 O. 
         [0026]    Most preferably, the fluid is air. 
         [0027]    Preferably, the radiation is concentrated and directed to the radiation receiving vessel by a primary optical device such as; an optical lens, a heliostat field with mirrors directing solar radiation to a target or a parabolic mirror or any combination of these concepts. 
         [0028]    Preferably, the radiation from the primary optical device is further concentrated by a secondary optical device located in close proximity in front of or around the aperture of the radiation receiving vessel such as; additional lens or lenses, a compound parabolic concentrator, a concentrator following closely or approximately the mathematical shape of a truncated cone, tailor-edge-ray concentrator and a trumpet flow-line concentrator. 
         [0029]    Preferably, the secondary optical device is actively cooled by water or other liquid coolant. 
         [0030]    Preferably, the radiation receiving vessel is configured as described in paragraph [0015] to [0023] in the present description, to heat a fluid by incoming concentrated radiation. 
         [0031]    Preferably, the heated fluid is utilized to heat, directly or indirectly, all or part of the fluid to drive a turbine for electrical generation. 
         [0032]    Most preferably, the heated fluid is used to heat all or part of the fluid, directly or indirectly, to drive a gas turbine for electrical generation. 
         [0033]    Preferably, the heated fluid from the radiation receiving vessel, which does not have a sufficiently high temperature to, economically or practically, be applied to electricity generation can be used for heating purposes such as; heat pump, boiler, absorption chiller, hot water heater, space heater. 
         [0034]    Most preferably, the fluid from the radiation absorbing vessel is first used to drive a turbine for electrical generation and afterwards used for heating purposes as described in [0033]. 
         [0035]    There is also provided in accordance with a different preferred embodiment of the present invention a system for heating fluid with concentrated, radiation, preferably solar radiation and to provide sufficient heat to also chemically alter the composition of the fluid. The system includes: concentrating devices to concentrate radiation from a radiation source and funnel the concentrated radiation to a reaction vessel; a reaction vessel receiving the concentrated radiation to heat and chemically alter a fluid and a utilizer of the stored heat and chemical compounds in the fluid. 
         [0036]    Preferably, the incoming fluid to the reaction vessel contains any, all or a subset of the compounds; oxygen, methane, hydrogen, carbon dioxide, carbon monoxide, nitrogen, H 2 O. 
         [0037]    Preferably, the outgoing fluid from the reaction vessel contains any, all or a subset of the compounds; oxygen, methane, hydrogen, carbon dioxide, carbon monoxide, nitrogen, H 2 O. 
         [0038]    Preferably, the radiation is concentrated and directed to the radiation receiving vessel by a primary optical device such as; an optical lens, a heliostat field with mirrors directing solar radiation to a target or a parabolic mirror or any combination of these concepts. 
         [0039]    Preferably, the radiation from the primary optical device is further concentrated by a secondary optical device located in close proximity in front of or around the aperture of the radiation receiving vessel such as; additional lens or lenses, compound parabolic concentrator, a concentrator following closely or approximately the mathematical shape of a truncated cone, tailor-edge-ray concentrator and a trumpet flow-line concentrator. 
         [0040]    Preferably, the secondary optical device is actively cooled by water or other liquid coolant. 
         [0041]    Preferably, a reaction vessel for heating and chemically altering a fluid with concentrated, radiation, preferably solar radiation, is used. 
         [0042]    Preferably, this reaction vessel is a vessel, which includes; a housing with an ingress and an egress for fluid and an aperture, a window covering the aperture of the housing for admitting and passing into the vessel concentrated radiation, a flow guide separating the fluid from the ingress from the fluid from the egress, a permeable radiation absorber. 
         [0043]    Preferably, the window in the reaction vessel described in [0042] is flat. 
         [0044]    Most preferably the window covering the aperture of the reaction vessel described in [0042] is concave with the center of the window being deeper inside the body of the radiation receiving vessel than the rim of said window. The concave shape preferably follows an axis symmetric shape such as the radius of a sphere, a parabola, cone, capped cone, a combination of the mentioned shapes and other concave possibilities. 
         [0045]    Preferably, the window is placed on a seal to seal the aperture the reaction vessel described in [0042] from fluid exchange with the ambient. 
         [0046]    Most preferably the window of the reaction vessel described in [0042] is kept in place on the seal in the absence of any mechanism other than weight, gravity and friction to keep it in place. 
         [0047]    Preferably, the window flange of the reaction vessel described in [0042] is actively cooled. 
         [0048]    Preferably, the window of the reaction vessel described in [0042] is actively cooled. 
         [0049]    Most preferably, the window of the reaction vessel described in [0042] is actively cooled from the outside. 
         [0050]    Preferably, the radiation absorber of the reaction vessel described in [0042] is able to absorb the concentrated radiation and transfer the heat to the fluid. 
         [0051]    Most preferably, the radiation absorber of the reaction vessel described in [0042] has at least two different areas with different radiation absorptivity, ascertained by the use of different absorption materials or by applying different external coating on the radiation absorbing side of the radiation absorber. 
         [0052]    Preferably, the reaction vessel described in [0042] is equipped with a high surface area covered with catalyst material to enable chemical alterations of the fluid inside the vessel. 
         [0053]    Most preferably, the high surface area provided with catalyst material is integrated with the radiation absorbing surface. 
         [0054]    Preferably, the heated fluid exiting the reaction vessel described in [0042] is used to preheat the fluid entering the reaction vessel described in [0042]. 
         [0055]    Preferably, the fluid leaving the reaction vessel is used to perform chemical reactions such as; combustion of the fluid and conversion of the fluid to liquid fuel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0056]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0057]      FIG. 1  is a simplified partially block diagram, partially schematic illustration of a system for heating a fluid with concentrated radiation in a vessel, constructed and operative in accordance with a preferred embodiment of the present invention; and 
           [0058]      FIG. 2  is an enlarged view of area A of the vessel shown in  FIG. 1 . 
           [0059]      FIG. 3  is a schematic view of the radiation absorbing surface,  127 , shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0060]    Reference is now made to  FIG. 1 , which is a schematic illustration of a vessel for heating a fluid with concentrated solar radiation, constructed and operative in accordance with a preferred embodiment of the present invention. 
         [0061]    As seen in  FIG. 1 , the present invention provides a system  100  for heating a fluid with concentrated radiation including a fluid supply source  102 . Examples of fluids include: oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen, gaseous hydrocarbons, steam or a combination of the above mentioned fluids. 
         [0062]    A radiation receiving vessel  120 , such as a vessel described inter alia in the above-referenced US patents: U.S. Pat. No. 5,931,158, U.S. Pat. No. 5,947,114 and U.S. Pat. No. 6,516,792 B2, the disclosures of which are hereby incorporated by reference, receives the fluid from the fluid supply source  102 , preferably at a pressure of between 1-200 bar, and most preferably at a pressure of about 1.5-10 bars. 
         [0063]    Preferably, radiation is highly concentrated prior to impinging on the radiation receiving vessel  120 . 
         [0064]    Preferably, the highly concentrated radiation originates from the sun. 
         [0065]    Preferably, concentration of the solar radiation is provided by directing incoming solar radiation through a concentrator  125 . Concentrator  125  may have various possible configurations such as those described inter alia in the above-referenced publications of Kribus, A., Zaibel, R., Carey, D. Segal, A., Karni, J. 1998, “A solar-driven combined cycle power plant”, Solar Energy 62(2):121-129, and Mills, D., 2004, “Advances in solar thermal electricity technology”, Solar Energy 76:19-31, the disclosures of which are hereby incorporated by reference. Heliostat fields and parabolic dished are the most preferred primary concentrators for concentrator  125 . The concentrator  125  can, but is not forced to, consist of both primary and secondary optics, example of which are described inter alia in the above-referenced publications of Gordon, J. M. and Ries, H, 1993 “Tailored edge-ray concentrators as ideal second stages for Fresnel reflectors”, Applied Optics 32(13):2243-2250, the disclosures of which are hereby incorporated by reference. Compound parabolic concentrators and cone shaped concentrators are most preferred as practical secondary optics devices for concentrator  125 . The output of concentrator  125  is directed through a window  126  of the radiation receiving vessel  120  so as to impinge onto a radiation absorbing surface  127 , located on the permeable heat transfer wall  128 . Window  126  is preferably formed of quartz and may be of any suitable shape such as flat or curved. Solar reactors having concave windows, described in the above-referenced U.S. patents: U.S. Pat. No. 5,931,158, and U.S. Pat. No. 6,516,794 may be suitable for this purpose. As used herein, in specifications or in claims, the term “concave” incorporates all shapes, where the center of the shape is deeper inside vessel  120  than the perimeter of the same shape. 
         [0066]    Preferably, window  126  is placed on a seal  140 , as illustrated in  FIG. 2 , window  126  is kept in place on seal  140 , placed on aperture opening surface  142 , solely by the force of gravity acting on the weight of the window  126  and the friction between window  126 , the seal  140  and the aperture opening surface  142 . Preferably, the window is only in direct contact with the seal and with no other device. If the vessel is operating under pressure the pressure inside the vessel assists in fixing the window in location and to seal the aperture  144 , by forcing the window  126  towards the aperture opening surface  142 . Thermal stresses and difference in thermal expansion between the window and its holding devices have been known in prior art to cause breakage to windows in similar vessels. 
         [0067]    The permeable heat transfer wall  128  is preferably formed of silicon carbide, silicon nitrite, alumina, or metallic wire mesh or other metallic, high surface area configuration. 
         [0068]    The permeable heat transfer wall  128  may employ any suitable catalyst on surface  127  if the objective of system  100  is not only to heat the fluid from the fluid supply source  102 , but also to react the fluid. For high temperature reactions the most preferred catalysts are Ruthenium and Rhodium. A somewhat less preferred catalyst is Iridium and even less preferred catalysts are Nickel, Platinum and Palladium. These catalysts are preferably applied over a pigmented wash coat which is deposited on highly porous support structures such as ceramic matrices, preferably formed of silicon carbide or alumina, as described inter alia in the above-referenced publications of Woerner, A., and Tamme, R., 1998, “CO 2  reforming of methane in a solar driven volumetric receiver-reactor” Catalysis Today 46:165-174, Berman, A., Karn, R. K., Epstein, M., 2005, “Kinetics of steam reforming of methane on Ru/Al 2 0 3  catalysts promoted with Mn oxides”, Applied catalysis A: General 282:73-83, and U.S. Pat. No. 5,431,855, the disclosures of which are hereby incorporated by reference. The permeable heat transfer wall  128  can also be constructed of silicon nitride or on a metallic wire mesh or other metallic, high surface area configuration and coated with a catalyst appropriate for the desired reaction. As used herein, in specifications or in claims, the term “silicon carbide” incorporates all compounds, washcoats or other coatings and materials containing any silicon carbide (SiC) or silicon carbide (SiSiC). As used herein, in specification or in claims, the term “alumina” incorporates all compounds, washcoats or other coatings and materials containing any alumina (Al 2 O 3 ). As used herein, in specifications or in claims, the term “silicon nitride” incorporates all compounds, washcoats or other coatings and materials containing any silicon nitride (Si 3 N 4 ). 
         [0069]    The permeable heat transfer wall  128  may consist of several different materials in different axis symmetric zones as illustrated in  FIG. 3 . The material in each zone is chosen according to the concentration of radiation expected to impinge thereon. Zone I, illustrated in  FIG. 3 , may receive the lowest radiation flux and may therefore have the highest radiation absorptivity of the zones. Zone II illustrated in  FIG. 3 , may receive the highest radiation flux and preferably have a low radiation absorptivity to prevent overheating of the permeable heat transfer wall  128  and/or overheating of window  126  as a consequence of a high temperature of the permeable heat transfer wall  128 . Preferably, the shape of zone II is highly concave to prevent reflected radiation from the surface  127  on  128  to exit the receiver through window  126 . Zone II would in such cases be closer to the window in the outer regions than in the inner/central regions, 
         [0070]    The fluid from the fluid supply source  102 , supplied to vessel  120  via a supply conduit  121 , preferably is caused to impinge on surface  127  of the permeable heat transfer wall  128 . In a preferred embodiment, conduit  121  extends into the reactor  120  and into close proximity with surface  127  of the permeable heat transfer wall  128 . Alternatively, conduit  121  may not necessarily extend into the vessel  120 , and fluid from the fluid supply source  102 , supplied to vessel  120  via a supply conduit  121  may be caused to impinge on surface  127  of permeable heat transfer wall  128  by another suitable method. 
         [0071]    In accordance with a preferred embodiment of the present invention, window  126  can be cooled, as by a flow of cooling fluid, such as pressurized air from a nozzle  130  impinging on the outside surface  132  of window  126 . The cooling action prevents excessive heating of the window from radiation absorption inside the window. The cooling of window  126  additionally prevents or reduces condensation on an inside surface  134  of window  126  and resultant reduction in the transparency thereof to incoming solar radiation and consequent excessive heating of the window  126 . 
         [0072]    It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and sub-combinations of various feature of the invention and modifications thereof which may occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.