Abstract:
The present invention is directed to a solar energy system including a tower having a solar radiation receiver, the solar radiation receiver including a plurality of tubes carrying a heat-transfer medium and a drum, the drum in thermal communication with the tubes, and one or more mirrors configured to reflect solar radiation onto the receiver, wherein the receiver receives the reflected solar radiation from the mirrors, thereby heating the heat transfer medium and vaporizing the heat transfer medium.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to systems for collecting heat flux in the form of concentrated solar radiation. More particularly, the present invention relates to a power tower system for collecting concentrated solar radiation and having a curved receiver, where the components of the receiver are self-contained. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Concentrating solar power (CSP) offers a clean, endless, and reliable source of energy with potentially unlimited capacity. CSP plants have many advantages over other types of power plants, one of the most notable being that CSP plants produce little to no carbon dioxide emissions. As a result, many countries, including the United States, have begun integrating CSP into their national supply grids through large-scale commercial plants. 
     CSP plants produce power by concentrating sunlight to heat water and produce steam. The steam then rotates a turbine connected to a generator, or other conventional device, thereby producing electricity. Currently, there are four types of CSP technologies, including: parabolic troughs, dish/engine systems, linear Fresnel reflectors, and power towers. Parabolic trough technology uses parabolic mirrors to concentrate sunlight onto a linear receiver pipe positioned along the mirrors&#39; focal line. Because this technology was the first CSP technology, it is the most developed and commonly used technology. Dish/engine systems use a parabolic mirror to focus sunlight on a receiver placed at the mirror&#39;s focal point. These systems are smaller and may be used to generate power for smaller applications, such as for a single building. Linear Fresnel reflector technology is similar to parabolic trough technology, except that it uses flat mirrors that reflect sunlight onto water-filled pipes that generate steam. This technology often has a cost advantage over parabolic trough technology because flat mirrors are usually less expensive to produce than parabolic mirrors. Finally, power tower systems typically use flat mirrors to reflect the sun&#39;s rays onto a receiver located at the top of a central tower, often three to five hundred feet tall. 
     A problem with existing CSP technology is the complex array of components that must be assembled for the system to operate. Typically, the assembly of the system must be accomplished in the field. In the case of power tower technology, existing systems consist of a receiver mounted on top of a structural steel tower having box sections, diagonal bracing, etc. Many of the towers have as many as three to four thousand pieces of steel that must be assembled in the field. In addition, the rest of the system generally requires a single tube or pipe, or an assembly of pipes in the form of a piped manifold. The pipes are interconnected with receiver panels and a drum. These must be field erected using a significant number of piping components to be installed atop the large structural steel tower. Such a project often requires thousands of hours of labor or more and is very expensive. 
     In view of the problems noted above, there is a need for improved CSP systems that may require less in-field assembly and that may also efficiently collect solar radiation. The present invention addresses these needs and more. 
     The present invention provides a solar energy system that includes a tower having a solar radiation receiver, the solar radiation receiver including a plurality of tubes carrying a heat-transfer medium and a drum, where the drum is in thermal communication with the tubes. The solar energy apparatus further includes one or more mirrors configured to reflect solar radiation onto the receiver. The receiver receives the reflected solar radiation from the mirrors, thereby heating the heat transfer medium and vaporizes the heat transfer medium. 
     The present invention further provides a method of generating power from sunlight using the above described system, the method including focusing sunlight on a convex solar radiation receiver attached to a tower, the receiver being in the al communication with a heat transfer medium such that focused sunlight heats and vaporizes the heat transfer medium, and employing the vaporized heat transfer medium in a turbine generator to produce power. 
     The present invention also provides a solar energy system that includes a tower having a substantially convex solar radiation receiver attached thereto, and a plurality of mirrors arranged circumferentially around the tower and configured to focus sunlight onto the receiver, wherein the receiver includes a plurality of tubes carrying a heat transfer medium, the tubes configured to accept radiation from the sunlight reflected on the receiver and heat the heat transfer medium and vaporize the heat transfer medium within the receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
         FIG. 1  is a schematic perspective view of a system for collecting concentrated solar radiation; 
         FIG. 2  is a side view of a receiver for receiving focused sunlight; 
         FIG. 3  is a transparent side view of the receiver of  FIG. 2  where the internal components are made visible; 
         FIG. 4  is a transparent side view of the receiver of  FIGS. 2 and 3  where the internal components are made visible and showing the external tubes of the receiver; 
         FIG. 5  is a schematic view of a portion of a receiver of  FIGS. 2 and 3  showing the interface between the external tubes and the drum; 
         FIG. 6  is a side cross-sectional view of a receiver of  FIGS. 2-4  taken along line  5 - 5  of  FIG. 2 ; and 
         FIG. 7  is aside view of the tower having a receiver attached to the top. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing aspects, features, and advantages of the present invention will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing embodiments of the invention illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms used, and it is to be understood that each specific term may include equivalents that operate in a similar manner to accomplish a similar purpose. 
     Referring now to the drawings,  FIG. 1  shows a schematic perspective view of a system  10  for collecting heat flux in the form of solar radiation according to one possible embodiment of the present invention. The system  10  includes a tower  12  that has a receiver  14 . The receiver is preferably, but not necessarily, positioned at or near the top of the tower  12 . The system further includes a plurality of mirrors  16  that may preferably be positioned circumferentially around the tower  12 . The mirrors  16  may surround the tower  12  on all sides, as shown in  FIG. 1 . Alternatively, the mirrors  16  may surround only a portion of the tower  12 . 
     In practice, the mirrors  16  are oriented so that they receive sunlight  18  and reflect the sunlight to a focal point located at the receiver  14 . As discussed below, the receiver  14  is configured to absorb radiant heat associated with the focused sunlight and to use at least a portion of that heat to generate vapor. The vapor, in turn, may be used in any convenient process, such as to produce electricity or power. Because the mirrors  16  are positioned circumferentially around the tower  12 , the sunlight  18  may advantageously be focused onto the receiver  14  from many different directions. Thus, in order to maximize the amount of radiant heat absorbed, the receiver  14  is often configured to receive sunlight from many different directions. In one preferred embodiment, the receiver  14  has a convex shape allowing it to surround at least a portion of the tower  12  and receive focused sunlight from more than one direction. In another preferred embodiment, the receiver is cylindrical and receives focused sunlight from every direction 360 degrees around the tower. 
     Referring now to  FIG. 2 , there is shown a side view of a receiver  14  according to an embodiment of the present invention. The receiver  14  may preferably have a drum  20  and a plurality of external tubes  22  that carry a heat transfer medium. The heat transfer medium may be any fluid that has the critical pressure, critical temperature, thermal stability, and resistance to degradation or dissociation required to properly vaporize within the receiver. For example, the heat transfer medium may be water, methanol, single component hydrocarbon, single component refrigerant, etc. Preferred temperatures and pressures for the heat transfer medium vary depending on the fluid. For example, for water the preferred pressures may be between about 250 psia and about 2500 psia, and the temperature between about 400° F. and about 670° F. In the case of methanol, the preferred pressures may be between about 600 psia and about 1050 psia, and the temperature between about 400° F. and about 460° F. For hydrocarbons, the preferred pressure may be between about 150 psia and about 1100 psia, and the temperature between about 400° F. and about 1100° F. 
     As the receive  14  receives the focused sunlight  18 , the radiant heat of the sunlight heats the heat transfer medium in the external tubes  22 . The heat transfer medium then at least partially vaporizes within the tubes. This vaporization reduces the density of the heat transfer medium, and the heat transfer medium then circulates through the tubes  22  by natural convection. The vapor/water mixture is then returned to the drum  20  where it is transferred out of the receiver  14 . 
       FIG. 3  shows a transparent side view of the receiver  14  according to an embodiment of the present invention using water as the heat transfer medium and depicting some of the internal components of the drum  20  as well as the annular piping for the feed stream entering the drum and the vapor leaving the drum. In particular,  FIG. 3  shows a feed stream line  26  entering the bottom of the drum  20 , a feed stream impingement baffle  28 , and a feed stream storage area  30 . The feed stream storage area  30  may be surrounded by a shroud  46 .  FIG. 3  also depicts a vapor line  32 , a vapor baffle  34 , a vapor discharge area  36 , and a separator  38  dividing the feed stream storage area  30  from the vapor discharge area  36 .  FIG. 4  is similar to  FIG. 3 , but includes the external tubes  22  that carry the heat transfer medium.  FIG. 5  shows the interface between the external tubes  22  and the drum  20  in greater detail. 
     During use, feed stream enters the receiver  14  through the feed stream line  26 . Once inside the receiver  14 , the feed stream is directed into the feed stream storage area  30  by the feed stream impingement baffle  28 . One purpose of the feed stream impingement baffle  28  is to prevent incoming feed stream from impinging on internal components of the receiver  14 . In one preferred embodiment, the ends  40  of the external tubes  22  (shown in  FIGS. 4 and 5 ) are connected to the feed stream storage area  30  so that feed stream can be supplied to the tubes  22  as needed to maintain a sufficient amount of heat transfer medium in the tubes. As the receiver  14  receives solar radiation, the heat transfer medium within the tubes is heated until it at least partially vaporizes. The vapor mixture is then directed back into the drum  20  where the vapor accumulates in the vapor discharge area  36  and any unvaporized heat transfer medium rejoins the feed stream in the feed stream storage area  30 . From the vapor discharge area, the vapor is channeled through the steam line  32  out of the receiver  14 . Preferably, the vapor baffle  34  is positioned to prevent the outgoing vapor from carrying unwanted heat transfer medium out of the receiver  14  and directs the flow of the vapor from the appropriate locations within the receiver  14 . Further preferably, the separator  38  divides the feed stream storage area  30  from the vapor discharge area  36 . It is anticipated that the heat transfer medium could be water or any other suitable material. 
     In an alternative embodiment, the heat transfer fluid is fed into the external tubes  22 . As the heat transfer medium is heated by solar radiation, it transfers heat through the outer walls of the drum  20  and into the heat transfer medium stored in the feed stream storage area  30 . Thereafter, the heat transfer medium in the feed stream storage area  30  vaporizes and travels upward to the steam discharge area  36  where it is channeled into the steam line  32  and out of the receiver  14 . 
     In one embodiment, after the vapor exits the receiver  14  it is preferably provided to a power generation device (not shown). For example, the vapor may be utilized to generate power by expansion in a turbine, turbogenerator, or similar device as would be known to one of ordinary skill in the art. 
     There is shown in  FIG. 6  a side cross-sectional view of the receiver  14  according to an embodiment of the present invention without showing the external tubes, including additional drain and instrument level connections. As in  FIGS. 3 and 4  above,  FIG. 6  shows the drum  20 , a feed stream line  26 , a feed stream impingement baffle  28 , a feed stream storage area  30 , a vapor line  32 , a vapor baffle  34 , a vapor discharge area  36 , and a separator  38 . In addition,  FIG. 6  shows a level bridle  42  with one end in the feed stream storage area  30  of the drum and the other end outside the drum. The level bridle is positioned so that feed stream will communicate through the bridle to level measure instrumentation outside of the drum. Thus, the feed stream storage area will not usually be inadvertently overfilled or underfilled. In addition,  FIG. 3  shows drains  44  in the bottom of the drum  20  that may be opened to drain fluid from the bottom of the drum as necessary. In a preferred embodiment, there is a manway  24  at the top of the drum  20  to provide access to the internal components of the receiver  14 . Access to the internal components of the drum may be desired for a number of reasons, including, for example, servicing or replacing internal components of the drum. 
       FIG. 7  shows the tower  12  according to a preferred embodiment of the present invention. As can be seen, the tower  12  is preferably an annular pipe that is configured for attachment to the receiver  14  at the top thereof. Advantageously, the tower  12  may be prefabricated in sections at any convenient location and then transferred to a power plant site. In one preferred embodiment, the sections are 50 to 80 feet long. Once on site in the field, the sections of the tower  12  are assembled, such as, for example, by welding, on the ground and the receiver  14  is attached to the top thereof. Thereafter, the assembled tower  12  and receiver  14  may be lifted to a vertical position by a crane. Alternatively, the tower  12  may be lifted prior to installation of the receiver  14 , in which case the receiver  14  could be attached after the tower  12  is in a vertical position. 
     An advantage of the present invention over the prior art is the fact that all of the components of the receiver may be self contained in one unit and the tower may be prefabricated in transportable sections. Such an arrangement allows the receiver and tower to be fabricated and assembled in the shop if desired. Then, only minor field erection may be required to assemble the tower, attach the receiver thereto, and connect the receiver to a power generating device such as a steam generator. This arrangement is often more cost and/or labor efficient than prior art systems that usually require complicated assembly and/or erection of many different components in the field. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention.