Abstract:
A solar receiver  10  is coated by erecting the solar receiver, coating the erected solar receiver with a curable energy-absorptive coating; and concentrating solar energy  15  on the coated erected solar receiver  10  to cure the energy-absorptive coating.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/057,262 filed May 30, 2008, the contents of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates generally to a method of coating a solar receiver, and more particularly to a method of coating a solar receiver situated to receive solar radiant energy from a solar energy concentrator system, e.g., a field of mirrors or heliostats. 
       BACKGROUND 
       [0003]    A solar boiler is a type of solar receiver which is used to absorb concentrated solar radiant energy to heat a transfer fluid and to produce a flow of steam from the fluid. The steam, in effect, contains the absorbed energy. The product steam, typically at high temperature and pressure, is then directed to drive a turbine of a steam turbine generator, thus converting the solar energy to electricity. 
         [0004]    The surfaces of some solar receivers are coated with a material that exhibits a high solar spectrum absorption. Paint-like, commercial energy-absorptive coatings are available which will fulfill this function, e.g., PYROMARK 2500 (Pyromark is a registered trademark of Illinois Tool Works, Inc., Glenview, Ill. USA). Such coatings require a thermal curing cycle with various stages with temperature up to about 1,000° F. (538° C.) and the use of curing ovens. The painting/curing processes are carried out in a factory environment during fabrication of the solar receiver. 
       SUMMARY OF THE INVENTION 
       [0005]    According to aspects disclosed herein, there is provided a method of coating a solar receiver and/or components thereof, in situ. The method includes, subsequent to erecting the solar receiver, coating the solar receiver and/or portion thereof with a curable energy-absorptive coating. During operation of the solar receiver, solar energy is concentrated on the coated portion of the solar receiver, thereby curing the energy-absorptive coating. 
         [0006]    According to other aspects disclosed herein, there is provided a method of repairing a damaged solar receiver and/or components in situ. This is accomplished by applying the curable energy-absorptive coating onto the damaged portion of the solar receiver, and during operation of the solar receiver, solar energy is concentrated on the portions of the solar receiver where the energy absorptive coating was applied, thereby curing it. 
         [0007]    According to other aspects disclosed herein, there is provided a method of curing a curable energy absorptive material, in which curable energy-absorptive material is applied to the surface of a substrate to provide a curable energy-absorptive coating; and solar radiant energy is concentrated onto the curable energy-absorptive coating using a solar energy concentrator system, to cure the curable energy-absorptive coating. 
         [0008]    The above described and other features are illustrated by the following figures and detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike: 
           [0010]      FIG. 1  is a schematic block diagram of a solar steam generation system including a solar receiver in accordance with one embodiment; 
           [0011]      FIG. 1A  is a plane view of a panel of the solar receiver of  FIG. 1  formed of an array of tubes; and 
           [0012]      FIG. 2  is a schematic block diagram of a solar steam generation system including a solar receiver in accordance with another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]    As shown in  FIG. 1 , a solar receiver  10  is erected on a tower  12  disposed near a solar energy concentrator system indicated generally at  14 . The solar energy concentrator system  14  directs solar energy or solar radiation  15  from the sun  16  to the solar receiver  10 . In the illustrated embodiment, the solar energy concentrator system  14  may comprise a plurality of solar collectors  18 , such as mirrors or heliostats. In one embodiment, each solar collector  18  can be independently adjustable to track the relative position of the sun  16 . For example, the solar collectors  18  can be arranged in arrays, whereby the solar collectors in each array are controlled separately or in combination with the other solar collectors of the array by one or more control devices (not shown) configured to detect and track the relative position of the sun  16 . Thus, the solar collectors can periodically adjust according to the position of the sun  16  to reflect solar energy onto the solar receiver  10 . This in turn results in heat being transferred to a transfer fluid  21  flowing through the solar receiver  10 . The solar receiver  10  receives, via inlet conduit  20 , the transfer fluid  21  to be heated, and the heated fluid  21  (or combination fluid, vapor or steam) is emitted from the solar receiver  10  via an outlet conduit  22 . 
         [0014]    In one embodiment, the solar receiver  10  includes at least one solar panel  60  comprising a plurality of tubes  62  attached to a first header  64  (e.g., an upper header/output manifold) and a second header  66  (e.g. a lower header/inlet manifold), shown in greater detail in  FIG. 1A . The plurality of tubes  62  are coupled to the inlet conduit  20  to receive the transfer fluid  21  and to the outlet conduit  22  to pass the heated fluid  21  (fluid, vapor or steam) from the solar receiver  10  by the headers  66  and  64 , respectively. It should be appreciated that the solar receiver  10  may include a plurality of the solar panels  60 . A portion  60   a  of the panel  60  includes an energy-absorptive coating  60   b  applied in an uncured form after the panel  60  and/or the receiver  10  is assembled and erected on the tower  12 . The uncured energy-absorptive coating  60   b  may be sprayed or otherwise painted onto the portion  60   a  of the panel  60  (e.g., an exterior surface of the tubes  62 ) and then cured in place by the application of solar energy  15  provided by the solar energy concentrator system  14  appropriately controlled to provide a heat curing cycle as may be specified by the energy-absorptive coating manufacturer. In one embodiment, the silicone-based energy-absorptive coating  60   b  can have a solar absorptivity of about 0.95. One such coating having particular utility in the above-described system is referred to as Pyromark 2500, but the invention is not limited in this regard, and in other embodiments, any other suitable energy-absorptive coating may be used. In one embodiment, the heat curing cycle may comprise heating the coating to about 1,000° F. (538° C.). Regarding the above-described Pyromark 2500 material, the manufacturer recommends that following application, the material be allowed to air dry overnight and then be cured for two hours at 480° F. For maximum resistance to heat shock, slowly bring the material to 1,000° F. over a one hour period. The energy-absorptive coating  60   b  applied as described herein may be the first energy-absorptive coating applied to the portion  60   a  of the panel  60 , or it may be a remedial energy-absorptive coating applied over an energy-absorptive coating that was previously applied in a factory according to the prior art and that was damaged during erection of the solar receiver  10  and/or installation of the panel  60 . Alternatively, a remedial energy-absorptive coating may be applied over a previously applied energy-absorptive coating that has deteriorated over time and/or during use of the solar receiver  10 . 
         [0015]    In one embodiment, the solar receiver  10  is part of a solar-powered electricity generation system indicated generally at  24 , wherein the fluid  21  heated by the solar receiver  10  is water and the solar receiver  10  is a boiler that produces high energy steam for a steam turbine generator  26  in fluid communication (via the outlet conduit  22 ) with the receiver  10 . The steam turbine generator  26  includes a steam turbine  28  that is driven by the steam passed from the outlet conduit  22  to turn an outlet shaft  29  which powers a generator  30  to produce electricity  32 . Water returns from the steam turbine generator  26  to the solar receiver  10  via the inlet piping  20 . In one embodiment, a pump  31  drives the water/transfer fluid back to the solar receiver  10  via the inlet conduit  20 . 
         [0016]    In another embodiment, a solar receiver  34  shown in  FIG. 2  is erected on the tower  12  to be part of a solar-powered electricity generation system indicated generally at  36 . The solar-powered electricity generation system  36  includes a solar energy concentrator system  14  which reflects the solar radiant energy  15  of the sun  16  onto the solar receiver  34 . The solar receiver  34  includes serpentine tubes (e.g., one or more panels  60 ) that receive a heat transfer fluid (e.g., fluid  21 ) therethrough. The solar receiver  34  (e.g., the panel  60 ) is coated with an uncured energy-absorptive coating after being erected on the tower  12 , and the uncured energy-absorptive coating is cured using the solar energy concentrator system  14  as described herein. The heat transfer fluid  21  is delivered from the tower  12  to a steam generator  38 , in which thermal energy is exchanged from the heat transfer fluid  21  to water circulating in a separate fluid circuit  40 . The heat transfer fluid  21  is thereby cooled in the steam generator  38  and can then be recirculated back to the solar receiver  34  for reheating. Pumps  42  can be used to circulate the heat transfer fluid  21 , and tanks  44 ,  46  can be used to store the heat transfer fluid before and after heating by the solar receiver  34 . Various types of heat transfer fluids can be used with the solar-powered electricity generation system  36 . In one embodiment, for example, the heat transfer fluid  21  may be a molten salt such as a nitrate salt including about 60% sodium nitrate and about 40% potassium nitrate. Such a nitrate salt is generally useful in a temperature range of about 450° F. to 1100° F. (233° C. to about 593° C.), within which the nitrate salt generally exists as a single phase, i.e., a liquid, such that density of the fluid is substantially uniform throughout the operation of the electricity generation system  36 . Alternative heat transfer fluids  21  include other liquid salts as well as oils and other fluids. The heat transfer fluids can be selected according to the desired and anticipated temperature variation of the fluid in the electricity generation system  36 . 
         [0017]    The water heated in the steam generator  38  forms steam that is circulated to the steam turbine which powers the generator  30  to produce electricity  32 . As shown in  FIG. 2 , the steam can be passed through a condenser  48  that, in conjunction with a cooling tower  50 , condenses the steam to form hot water that is heated in a preheater  52  and is circulated back to the steam generator  38  by a pump  54 . 
         [0018]    As described herein, a curable energy-absorption coating is applied onto a solar receiver and/or components thereof, for example, a solar boiler, after the solar receiver is erected. As a result, the factory assembly process for the solar receiver and/or components is simplified and the operation of the solar receiver can be maintained more easily. Moreover, the curable energy-absorption coating may be applied or periodically reapplied to supplement or replace damaged or deteriorated coating on the solar receiver and components. Once reapplied, the coating is cured in place, as described herein. In another aspect, the invention is not limited to the use of solar radiant energy for curing a curable energy-absorptive coating on a solar receiver and/or components, and in other embodiments, the curable energy-absorptive coating may be applied onto any other substrate for which an energy-absorptive surface is desired, and the coating may be cured thereon by the use of solar radiant energy as described herein. 
         [0019]    While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.