Heat transfer passes for solar boilers

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of the patent application

10 US No. 12 / 620,109 filed on November 17, 2009. This application is also a continuation in part of US patent application No. 12 / 547,650 filed on August 26, 2009. Each of US patent applications No. 12 / 620.109 and No. 12 / 547,650 claims priority over provisional application US No. 61 / 151,984, filed on February 12, 2009, to provisional application

fifteen US No. 61 / 152,011, filed on February 12, 2009, to provisional application US No. 61 / 152,035, filed on February 12, 2009, to provisional application US No. 61 / 152,049, filed on February 12, 2009, to provisional application US No. 61 / 152,077, filed on February 12, 2009, to provisional application US No. 61 / 152,114, filed on February 12, 2009, and to provisional application

twenty No. 61 / 152,286, filed on February 13, 2009. Each of the aforementioned applications is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

one. Field of the Invention

The present invention relates to a solar power production, and more particularly, to solar receiver panels for use in solar boilers. 30

2. Description of the related technique

Solar power generation has been considered a viable source to help meet energy needs at a time of increasing awareness of environmental aspects of power production. The production of solar energy depends mainly on the ability to capture and convert the available energy free of the sun and can occur with very little impact on

5 environment. Solar power can be produced without creating radioactive waste as in the production of nuclear power, and without producing polluting emissions that include greenhouse gases as in the production of power from fossil fuels. The production of solar power is independent of the fluctuation of fuel costs and does not consume non-renewable resources.

10 Solar power generators generally use controlled mirror fields, called heliostats, to collect and concentrate sunlight on a receiver to provide a source of heat for power production. A solar receiver normally takes the form of a panel of tubes that carry a working fluid through them. Previous solar generators have used fluids from

fifteen work such as molten salt because it has the ability to store energy, allowing the generation of power when there is no or little solar radiation. Hot work fluids are normally transported to a heat exchanger in which they release heat in a second work fluid such as air, water, or steam. Power is generated by moving hot air or steam through a turbine

twenty that drives an electric generator. More recently, it has been determined that solar production can be increased and simplified using water / steam as the only working fluid in a receiver that is a boiler. This can eliminate the need for an inefficient heat exchanger between two different working fluids. This development has led

25 new challenges in the processing of intense solar heat without damaging the system. In a solar boiler, heat transfer rates can reach levels of approximately 2-3 times the heat transfer rate of a typical fossil fuel ignition boiler. This high heat transfer rate intensifies problems related to heating maintenance and

30 Uniform flow distribution through known boiler panel designs. If the flow through a part of a receiver panel is insufficient when water / steam is used as a working fluid, overheating may occur for that part of the panel. Such overheating can result in damage or breakdown of the panel and the tubes that constitute them if

allow temperatures to be high. Compared to typical fuel ignition boilers, the

solar boilers have very variable heat inputs due to changes in the

5 incident solar radiation. In a typical boiler the combustion gas around any given tube section is at almost the same temperature, which means that the tubes absorb relatively similar amounts of energy regardless of their location. Solar boilers, however, have heat input that can vary up to 50% in a relatively small area.

10 In solar boilers consisting of only a few tubes that bend around the entire structure, as in traditional fuel-ignition boilers, the fluid in the tubes leaves at very different temperatures that create metal temperatures and problematic steam temperatures. This problem increases with the size of the boiler, that is, the larger the boiler,

fifteen The greater the temperature imbalance. This is especially so on a solar boiler panel or passage that is very wide or has a larger area, because the heat flow is very uneven and can create large temperature differences in the tubes. Although known solar power production systems have been

twenty generally considered satisfactory for the purposes for which they are intended, there is still a need in the art for solar receivers that can improve the distribution of heat and fluid flow. There is also a need in the art of solar receivers that are easy to manufacture and use. The present invention provides a solution to these problems.

SUMMARY OF THE INVENTION

The subject invention relates to a new and useful boiler for a solar receiver. A plurality of boiler walls arranged end to end surrounds an interior boiler space. Each wall includes a plurality of solar receiver panels next to each other. The panels are fluidly connected to each other by means of a steam circuit. The boiler also includes a plurality of ducts that each form a part of the steam circuit that connects

fluidic way the panels. The panels and ducts form a plurality of steps

of heat transfer in the steam circuit. In certain embodiments, the steam circuit includes between two and

Ten steps, inclusive. The steam circuit can include four steps and each

5 step may include a pair of parallel panels, in which the panels of each pair of parallel panels are substantially coplanar. It is also contemplated that each step may include four parallel panels or any other suitable number of parallel panels. The steam circuit may include six steps and each step may include a pair of parallel panels, in which at least some of the pairs of

10 Parallel panels include panels that are substantially coplanar, and at least some of the pairs of parallel panels include panels that are oriented at an angle to each other to form a boiler wall corner. It is also contemplated that the steam circuit may include eight steps.

fifteen According to certain embodiments, a first part of the panels are fluidically connected to each other by means of a first steam circuit

or subcircuit, and a second part of the panels are fluidically connected to each other by means of a second steam circuit or subcircuit. The boiler includes a first plurality of ducts that each form a part of the first steam circuit 20 that fluidly connects the panels of the first steam circuit, in which the panels and ducts of the first steam circuit form a plurality of passages of heat transfer in the first steam circuit. The boiler also includes a second plurality of ducts that each form a part of the second steam circuit that fluidly connects the panels of the second

25 steam circuit, in which the panels and ducts of the second steam circuit form a plurality of heat transfer passages in the second steam circuit. It is contemplated that in certain embodiments, at least one of the ducts is a crossover duct that forms a part of the steam circuit and that

30 fluidically connects the panels in a first of the boiler walls to panels in a second of the boiler walls opposite the first of the boiler walls. The steam circuit may include four passages of solar receiver panels with a first connector conduit that fluidly connects a first panel passage with a second panel passage, with a second connector conduit that fluidly connects a third step of panels with a fourth passage of panels, and with the crossing conduit that fluidly connects the second passage of panels with the third passage of panels. The first and fourth steps of

5 panels can be in boiler walls opposite each other, and the second and third steps of panels can be in boiler walls opposite each other. It is also contemplated that each panel passage may be in a separate boiler wall.

These and other features of the systems and methods of the subject invention will be more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments by making

Reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

fifteen In order for those skilled in the art to which the subject invention relates to easily understand how to manufacture and use the devices and methods of the subject invention without undue experimentation, their preferred embodiments thereof will be described in detail herein by making reference to certain figures, in which:

twenty Figure 1 is a side elevational view of an exemplary solar boiler panel constructed according to the present invention, showing the flat configuration of the boiler tubes; Figure 2 is an internal elevation view of the solar boiler panel of Figure 1, showing the flat configuration of the boiler tubes;

25 Figure 3 is a partial plan view of an exemplary embodiment of a solar boiler constructed according to the present invention, showing four boiler walls each presenting eight solar boiler panels such as those shown in the figures 1 and 2, arranged next to each other; Figure 4 is a schematic view of the solar boiler of Figure 3, which

30 schematically shows two steam subcircuits with eight steps each, as well as the placement of several spray stations for use to control the temperatures of the receiver panels; Figure 5 is a schematic cross-sectional plan view of the

solar boiler of Figure 3, showing the locations of the eight passages in one of the two steam subcircuits, and showing components in the interior boiler space;

Figure 6 is a partial schematic view of another embodiment by way of

5 an example of a solar boiler constructed according to the present invention, which schematically shows a four-cross panel layout of two subcircuits in a steam circuit;

Figure 7 is a schematic cross-sectional plan view of the solar boiler of Figure 6, showing the locations of the four passages of the first subcircuit of the steam circuit;

Figure 8 is a schematic cross-sectional plan view of the

solar boiler of figure 7, which shows the locations of the four steps of the

second subcircuit of the steam circuit;

Figure 9 is a partial plan view of another embodiment

fifteen Example of a solar boiler constructed according to the present invention, which shows the panels of two steam subcircuits, each having six steps; and Figure 10 is a schematic perspective view of an exemplary embodiment of a solar boiler constructed according to the present invention,

twenty which shows the stacking configuration of a steam generator section, a superheater section, and a reheater section in which four boiler walls surround an interior boiler space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

25 Reference will now be made to the drawings in which similar reference numbers identify similar structural features or aspects of the subject invention. By way of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a boiler is shown in Figure 1

30 according to the invention and is generally designated by reference number 100. Other embodiments of solar boilers according to the invention, or aspects thereof, are provided in Figures 2 to 10, as will be described. The systems and methods of the invention can be used to improve the control of the

steam temperature of the boiler, for example in the generation of solar power.

Fuel ignition boilers generally have the phases

separated from superheaters and / or reheaters, usually referred to as

"low temperature" and "high temperature" phases. Each phase, or step, presents

5 relatively uniform fluid conditions. That is, each boiler tube that constitutes a passage has fluid at the same temperature and pressure (without considering small variations due to temperature and flow imbalance).

A typical fuel ignition boiler is segregated in steps for several reasons. First, mixing the fluid at the end of each step allows mixing any temperature imbalance and creating a uniform temperature. This is important because each tube in one step does not have the same length and does not heat the same, so some tubes in one step may end up hotter or colder than the design specifications. Another reason for separating the sections is to allow tempering of the entire steam flow between sections, which allows

fifteen control of the steam temperature with respect to an established condition. Only a few phases are necessary in a typical fuel ignition boiler because the heating in each step is relatively uniform, and the tubes can be bent many times to allow the appropriate amount of heating surface. This is possible because most of

twenty the tubes in a typical fuel ignition boiler transfer heat by convection. The hot molecules that make up the combustion gas move from the combustion zone, the hottest area of ​​the boiler, and transport energy through the boiler around the tubes of the convective heat transfer passages. Convective heat transfer works around the entire

25 tube circumference, therefore making the entire surface of the tube an effective heat transfer area, because combustion gas flows easily through the spaces between and around the tubes. This means that many pipes can be arranged aligned between each other, filling the three-dimensional boiler space with tubes, and it can still be effective in transferring heat from the flue gas to the

30 vapor contained within the tubes. In a solar boiler, however, the mechanism of heat transfer is through solar radiation. In order to transfer heat by radiation, the surface of the tube has to be exposed directly to the heat source. In order for a tube

If the solar boiler is effective in transferring heat, the tubes must be directly exposed, for example, presenting a line of sight, to electromagnetic radiation from the sun. The heliostat mirrors surrounding a solar boiler serve to capture the incident radiation of a large area and make it converge to the heat transfer tubes. Only the part of the tube that is exposed to this reflected sunlight constitutes an effective heat transfer surface, therefore in a solar boiler only about half of each tube is effective because the inactive part remains in the shadow of the boiler tube itself . The actual effective area is normally just less than half of each tube due to the

10 shading effects of nearby tubes. Another important distinction of solar boilers is that there can only be one active row of tubes, since the additional rows of tubes in line behind the active row would be blocked or in the shade of the active row of tubes and therefore would be ineffective. This means that in order to increase heat transfer

fifteen beneficial, the solar boiler tubes must form a plane, instead of bending to have the traditional outstanding shape of the fuel ignition boiler tubes.

Referring to Figures 1 and 2, side and inner elevation views, respectively, of a solar boiler panel 102 of a solar boiler 100 20 constructed in accordance with the present invention are shown. The boiler panel 102 has a plurality of tubes that fluidly connect an inlet manifold 113 to an outlet manifold 104. The boiler panel tubes 102 form a flat solar receiver surface 107 and an opposite inner surface 108. The outer receiver surface 107 receives solar energy, for example, from a field of 25 heliostats, as indicated by the arrow in Figure 1. As shown in Figure 3, in boiler 100, eight panels 102 are arranged end to end to form each boiler wall, and four boiler walls are arranged to enclose an interior space 110 of the boiler 100. Since the walls and panels are located very close to each other, the radiation

30 solar is blocked and cannot reach the interior space 110. With this flat configuration, of a single row of solar boiler tubes, the boiler should be very high and the tubes long enough in order to transfer enough heat to a single row of tubes to reach the temperatures of

Steam needed in a single phase such as a superheater or one-step superheater. In boiler 100, the tubes within each phase are further advantageously divided into multiple steps.

Referring below to Figure 4, the connections between the

5 panels 102 are shown schematically. The panels 102 are fluidly connected to each other by means of a steam circuit that runs from the drum 106 to an outlet duct 108, which leads, for example, to a steam turbine for power production. A plurality of ducts 112, each forming a part of the steam circuit, are fluidly connected between

10 the respective panels 102, so that the panels 102 and the ducts 112 form eight heat transfer passages in the steam circuit. Each step includes two parallel panels 102. The steam circuit includes two subcircuits, namely the east subcircuit 114, which is the upper subcircuit as directed in Figure 4, and the west subcircuit 116, which is the lower subcircuit as oriented.

fifteen in Figure 4. Figure 5 shows the arrangement of the panels 102 surrounding the interior space 110 with ducts 112 and other components therein. Those skilled in the art will readily appreciate that the cardinal points provided above and in Figure 4 are exemplifying only, and that any suitable orientation can be used without departing from the spirit and

twenty scope of the invention. It is advantageous to present the first steps after drum 106, which receive relatively cold steam, oriented north if the location is in the northern hemisphere, since heliostats north of the boiler 100 will provide more direct radiation from the southern sun than heliostats south of boiler 100, which heat the last steps that present the hottest steam.

25 Four spray tempering stations 110a, 110b, 110c, and 110d are provided in four respective ducts 112 to keep temperatures controlled in the fifth to eighth steps of each subcircuit.

Referring now to Figure 6, another exemplary embodiment of a solar boiler 200 according to the invention is schematically shown. The boiler 200 includes a steam circuit that runs from a drum 206 through the panels 202 to an outlet duct 208 that leads to a turbine, for example, and which has spray tempering stations 210a, 210b, 210c, and 210d similar to that described above. The steam circuit includes two subcircuits, each subcircuit including four steps each having four coplanar panels, parallel 202. The first and second steps of each subcircuit are connected in series by a respective conduit 212, such as the third and fourth steps of Each subcircuit. The second and third passages of each subcircuit 5 are connected in series by a respective crossing duct 250, 252 that leads to opposite sides of the boiler 200 so that each circuit includes a passage on each of the four sides of the boiler 200 , for example, a first step in the north, a step in the west, a step in the east, and a fourth step in the south. Figure 7 shows the locations of the first step 230, the second step 232, the third step 234, and the fourth step 236 of the first subcircuit. Figure 8 shows the locations of the first step 240, the second step 242, the third step 244, and the fourth step 246 of the second subcircuit. An advantage of this crossover configuration is that each subcircuit receives substantially equal heat regardless of the location of the sun in the sky (that is, before or after noon), since each

fifteen subcircuit includes panels on all four sides of the boiler 200. Referring now to Figure 9, the panel part of another exemplary embodiment of a solar boiler 300 according to the invention is shown in which the steam circuit includes two subcircuits each presenting six steps. Boiler 300 includes four panel walls 302 surrounding a

twenty boiler interior space 310, similar to that described above. Each of the four walls includes six panels 302. Each step includes two parallel panels 302, and for the first, third, fourth and sixth steps of each subcircuit, the two panels 302 of each step are arranged coplanar to each other. As shown in Figure 9, the two panels 302 of the second and fifth steps of each subcircuit

25 they are perpendicular to each other to form a corner of the boiler 300. The exemplary embodiments described above have four, six, or eight steps in two subcircuits. Those skilled in the art will readily appreciate that any suitable number of subcircuits and steps can be used without departing from the spirit and scope of the invention. It is contemplated that the advantages

30 described herein can be achieved using between two and ten steps, inclusive, depending on the specific application. Considerations when selecting an adequate number of steps include the pressure drop, the total steam temperature increase (i.e. the steam temperature beginning at least the drum temperature, where more steps are appropriate for greater temperature increases), and heat flow distribution. The use of multiple heat transfer steps reduces temperature imbalance, provides appropriate steam temperatures, and achieves desirable levels of pressure drop. Yes

5 large variations in the steam temperature occur in the boiler panel tubes, the short interval between the steps allows mixing that matches the temperatures.

Referring to Figure 10, the multi-step configurations described above can also be used in phases. For example, solar boiler 10 100 includes a one-step steam generator 162, an eight-step superheater 160 configured as shown in Figure 3 to supply a high-pressure turbine phase, and an eight-step superheater 164 , configured similarly to superheater 160, to supply a low / intermediate pressure turbine phase. The superheater 164, the steam generator 162, and the superheater 15 160 are stacked and aligned as shown in Figure 10 with the superheater 164 at the bottom, the steam generator 162 in the middle, and the superheater 160 in the top With the individual solar boiler panels 102 (not identified in Figure 10, but see Figure 3) in close alignment with each other both horizontally and vertically, the collective surfaces of the panels 20 create four substantially solid receiver surfaces to receive solar radiation from heliostats on all four sides of boiler 100. The walls may be arranged facing north, east, south and west respectively, for example, and the boiler 100 may be placed on top of a central receiver tower in a heliostat field. With such a receiver configuration, a

25 Heliostat field can surround the boiler 100 from all cardinal points to provide radiation to heat the working fluid. Some or all of the remaining components of the system 100 may be protected from heliostats within the interior space 110 of the solar boiler 100, or may be located elsewhere in the solar boiler tower or on the ground.

30 The methods and systems of the present invention, as described above and as shown in the drawings provide solar boilers with steam circuits having multiple passages. This provides an improved ability to control the boiler panel and steam temperature within safe and effective limits. This also reduces the temperature imbalance, provides appropriate steam temperatures, and achieves desirable levels of pressure drop. Although the apparatus and methods of the subject invention have been shown and described with reference to the preferred embodiments, those skilled in the art will readily appreciate that changes and / or modifications can be made thereto without departing from the spirit and scope of the invention.