Modular solar receiver panels and solar boilers with modular receiver panels

Solar boiler

Cross reference with related requests

The present application is, in part, a continuation of US Patent Application No. 13 / 007,262, filed on January 14, 2011, which is, in part, a continuation of each of US Patent Application No. 12 /620.109 filed November 17, 2009 and US Patent Application No. 12 / 547,650 filed on August 26, 2009. This application is also, in part, a continuation of US Patent Application No. 12 / 552,724, filed on September 2, 2009.

Each of said US patent applications No. 12 / 547,650, 12 / 552,724 and 12 / 620,109 claim priority over provisional application US No. 61 / 151,984, filed on February 12, 2009, over provisional application US No. 61 /152.011, filed on February 12, 2009, on provisional application US No. 61 / 152,035, filed on February 12, 2009, on provisional application US No. 61 / 152,049, filed on February 12, 2009, on provisional application US No. 61 / 152.077, filed on February 12, 2009, on provisional application US No. 61 / 152,114, filed on February 12, 2009, and on provisional application US No. 61 / 152,286, filed on February 13, 2009. Each of The above patent applications are incorporated in their entirety, by reference, herein.

Background of the invention

<dl><dt>1. </dt><dd>Field of the Invention </dd></dl>

The present invention relates to the production of solar energy and, more particularly, to solar boilers and solar receiver panels for solar boilers.

<dl><dt>2. </dt><dd>Description of the related technique </dd></dl>

Solar power generation has been considered as a viable source to help meet energy needs at a time of growing awareness of the environmental aspects of energy production. Solar energy production is based primarily on the ability to collect and convert freely available energy from the sun and can be produced with very little impact on the environment. Solar energy can be used without creating radioactive waste, such as in the production of nuclear energy, and without producing polluting emissions, including greenhouse gases as in the production of energy using fossil fuels. Solar energy production is independent of fluctuating fuel costs and does not consume non-renewable resources.

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Generally, solar power generators use controlled mirror fields, called heliostats, to collect and concentrate sunlight on a receiver to provide a source of heat for energy production. Typically, a solar receiver takes the form of a panel of tubes that carry a working fluid through it. Previous solar generators have used work fluids such as molten salt, since it has the ability to store energy, which allows the generation of energy when there is no solar radiation. Typically, heated work fluids are transported to a heat exchanger where they release heat in a second work fluid, such as air, water or water vapor. The energy is generated by passing the hot air or steam through a turbine that drives an electric generator.

More recently, it has been determined that solar energy production can be increased and simplified by the use of water / water vapor 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 to new challenges in handling 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 fueled boiler. This high heat transfer rate intensifies problems related to maintaining uniform heating and flow distribution along known boiler panel designs. The high rate of heat transfer results in high pressures and temperatures in the boiler tubes and related structures. In addition, in solar boilers, only one side of each boiler tube is heated, while the opposite side is in the shade, which results in stresses related to gradients in thermal expansion / contraction. In addition, because the sun rises and sets every day, solar boilers must undergo a daily cycle of thermal expansion / contraction, which can lead to increased creep and fatigue damage due to the stresses caused by the cycles

In typical boilers, for example coal boilers, heat transfer surfaces, namely the superheater, reheater and evaporator, are separated from the physical location, as well as from the heat transfer mode, for example, convection against dominant radiation. The separation of heat transfer surfaces is important since each different section contains fluid with different physical properties, including temperature, pressure and quality. This separation allows the different heat transfer surfaces to be individually supported and allows different rates of thermal expansion on each of the different heat transfer surfaces. For example, the evaporation section in a typical boiler takes the form of a quadrilateral, with rigid supports on the center line of each wall and fixed welds in each corner. This is possible because each side of the boiler will expand at a constant and equal rate, since each side has the same steam conditions and experiences a similar heat flow. When the boiler is heated and expanded, the evaporation section, in the shape of a quadrilateral, expands without adding additional stress on the evaporation panels.

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In contrast, solar boilers frequently have heat transfer surfaces that are integral, contiguous, or stacked on top of each other, which means that heat transfer surfaces are very close, one to the other. In addition, each individual heat transfer surface can have extremely different heat flux, steam temperatures and metal temperatures, due to the non-homogeneous distribution of solar energy. If a traditional panel support procedure is used, such as in traditional coal boilers, for example, the large variation in thermal expansion would cause the panels to separate.

While known solar energy production systems have generally been considered satisfactory for their intended purposes, there is still a need in the technique of solar boilers and solar boiler panels that can better accommodate heat and tension related to solar energy production. . There is also still a need in the art for such solar boilers and solar boiler panels that are easy to manufacture and use. The present invention provides a solution to these problems.

Summary of the invention

The present invention is directed to new and useful modular panels for solar boilers. According to an exemplary embodiment, the panel includes an inlet manifold, an outlet manifold and a plurality of tubes that fluidly connect the inlet manifold to the outlet manifold. The tubes are substantially coplanar, with each other, forming a solar receiving surface and an opposite internal surface.

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In certain embodiments, each tube has an outside diameter in a range that includes approximately 5.08 cm (2 inches) and lower values. Each tube can have an outside diameter in a range that includes approximately 3.81 cm (1.5 inches) and lower values, approximately 2.54 cm (1 inch) and lower values, or approximately 1.27 cm (0.5 inches).

According to certain embodiments, the tubes have a pressure drop in a range that includes from about 1.34 kg / cm2 to about 19.34 kg / cm2 (from about 19 psi to about 275 psi). The tubes may have a pressure drop in a range that includes from about 1.76 kg / cm2 to about 5.27 kg / cm2 (from about 25 psi to about 75 psi). Each of the tubes can have a thickness, from its inner diameter to its outer diameter, in a range of about 3,429 mm (0.135 inches) to about 5,588 mm (0.220 inches). The number of tubes in the panel can be in a range of about 50 to about 200, or about 100 to about 150.

The invention also provides a solar boiler. The solar boiler includes a plurality of modular panels as described above, in which the tubes have a thermal conductivity in a range of approximately 5.78 W / (mK) and higher values, which may be approximately 8.67 W / (mK) or higher values. In certain embodiments, the tubes include a T91 alloy. The tubes may include any other suitable alloy or alloys, for example, 178C, 192, 21 OA1, 210C, T1, T2, T11, T12, T22, T9, 304H, 310H, 316H, 321 H and / or 347H. The manifolds can include any suitable type of steel or other suitable material. It is also contemplated that the solar heater may include a drum for distributing steam from a steam generating part of the modular panels to a superheater part of the modular panels, and tubes that fluidly connect the drum to the steam generator and the superheater parts of the modular panels.

The invention also includes a solar boiler, which includes a steam generator having a plurality of steam generating panels and a superheater having a plurality of superheater panels, the panels being in fluid communication with a boiler fluid circuit. Each of the steam generator and superheater panels is a separate modular panel, as described above. The tubes of the superheater panels have a smaller diameter than the tubes of the steam generating panels. According to certain embodiments, the superheater has a pressure drop in a range that includes approximately 14.06 kg / cm2 (200 psi) and lower values. It is also contemplated that the superheater may be configured to have a pressure drop in a range that includes approximately 19.34 kg / cm 2 (275 psi) and lower values, approximately 12.31 kg / cm2 (175 psi) and lower values , approximately 10.55 kg / cm2 (150 psi) and lower values, approximately 8.79 kg / cm2 (125 psi) and lower values, approximately 7.03 kg / cm2 (100 psi) and lower values, or approximately 3, 52 kg / cm 2 (50 psi) and lower values.

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These and other features of the systems and procedures of the present invention will be more apparent to persons with knowledge in the art from the following detailed description of the preferred embodiments, along with the drawings.

Brief description of the drawings

In order that persons with knowledge in the subject to which the present invention pertains easily understand how to manufacture and use the devices and methods of the present invention without undue experimentation, then the preferred embodiments thereof will be described in detail with reference to certain figures, in which:

Fig. 1 is a side elevational view of an exemplary embodiment of a modular solar boiler panel constructed according to the present invention, showing the input and output collectors, with the solar receiving surface of an adjacent panel covering the input manifold ;

Fig. 2 is a side elevational view of manifold parts of exemplary embodiments of generator of the vertically contiguous steam generator, superheater and reheater panels, constructed according to the present invention, showing vertical separation to accommodate expansion and expansion. thermal contraction of the panels;

Fig. 3 is a perspective view of a part of the modular solar boiler panel of Fig. 1, showing the collector and collectors of adjacent panels arranged to accommodate thermal expansion and contraction in the panels;

Fig. 4 is an internal elevational view of a plurality of panels of Fig. 1, showing the panels when mounted in a solar boiler to form a wall thereof, with the panels arranged side by side with a separation to accommodate thermal expansion and contraction in the horizontal direction;

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Fig. 5 is a plan view of the solar boiler of Fig. 4, showing four boiler walls surrounding an interior space of the boiler; Y

Fig. 6 is an exploded, schematic cross-sectional view of an exemplary boiler tube constructed in accordance with the present invention, which schematically shows the circumferential tension.

Detailed description of the preferred embodiments

Reference will now be made to the drawings, in which similar reference numbers identify similar structural aspects or characteristics of the present invention. For explanatory and illustrative and non-limiting purposes, a partial view of an exemplary embodiment of a modular solar boiler panel according to the invention is shown in Fig. 1 and is designated, in general, by the reference character 100. Other embodiments of solar boilers according to the invention, or aspects thereof, are provided in Figs. 2-6, as will be described. The systems and methods of the invention can be used to better accommodate and / or reduce thermally induced stresses in the solar boiler panels.

According to the present invention, the heat transfer or receiving surfaces of solar boilers are divided into smaller segments as modular receiver panels, which can expand and contract independently, relieving thermally induced stresses and thereby relieving the problems in traditional solar boiler pipes, described above. With reference now to Fig. 1, it shows the characteristics of a solar boiler 100 constructed according to the present invention. The boiler 100 for a solar receiver includes a first boiler panel 102 (the bottom panel in Fig. 1, which is only partially shown) having a plurality of substantially coplanar tubes that fluidly connect an inlet manifold 113 of the first collector panel (not shown in Fig. 1, but see Fig. 2) to an outlet manifold 104 of the first boiler panel 102. The tubes of the first boiler panel 102 form a first solar receiving surface 106 and a first inner surface 108, opposite the first solar receiving surface 106. The outer receiving surface 106 receives solar energy, for example, from a heliostat field, as indicated by the arrows in Fig. 1. People skilled in the art will readily appreciate that the fact that the tubes are coplanar is advantageous for heating each tube evenly, but non-coplanar arrangements can also be used without departing from the spirit and scope of the invention.

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A second boiler panel 110 (the upper panel shown in Fig. 1) similarly includes a plurality of tubes that fluidly connect an inlet manifold 112 of the panel 110 to an outlet manifold 114 of the panel 110. The tubes of the panel 110 form a second solar receiving surface 116 and a second inner surface 118, opposite the second solar receiving surface 116, (i.e. the outer and inner surfaces, as indicated in Fig. 1) . Like the receiver surface 106, the outer receiving surface 116 receives solar energy, for example, from a heliostat field, as indicated by the arrows in Fig. 2.

The first panel 102 and the second panel 110 of the boiler are adjacent to an upper end portion 120 of the panel 102 AND the corresponding end portion of the surface 106 superimposed on a lower end 122 of the panel 110 to reduce or prevent solar radiation from passing between the first surface 106 and the second surface 116 of the solar receiver to the interior space of the boiler 100. The inner surfaces 108 and 118 have a layer of insulating material 124 to protect the interior space of the boiler 100 and the components therein from the high temperatures at the back of the pipes.

As indicated by the arrows in Fig. 1, the region of overlap between panels 102 and 110 allows the thermal expansion and contraction of the panels. There is a gap 121 between the end part 120 of the panel 102 and the end part 122 of the panel 110. As can be seen in Fig. 1, the hole 121 is labyrinthine and, in this way, any leakage of solar radiation is absorbed by the boiler tubes, for example, at an extreme part 122, and is not allowed to penetrate into the interior space of the boiler 100 . Because the end 120 of the panel 102 and the end 122 of the panel 110 are separated from each other, the panels 102 and 110 can move, relative to each other, during the thermal expansion and contraction resulting, for example, from the daily cycle of solar radiation incident on the boiler reception area 100. Thus, although the gap 121 accommodates thermal expansion and contraction, in terms of solar radiation leakage there is virtually no gap between panels 102 and 110.

Referring now to Fig. 2, panel 102 is a steam generator panel and panel 110 is a superheater panel. Boiler 100 also includes 140 reheater panels. Each reheater panel 140 includes a plurality of tubes that fluidly connect an inlet manifold 117 to an outlet manifold 115, in a manner similar to that described above with respect to panels 102 and 110. Panel 140 overlaps panel 102 in the same manner as panel 102 overlaps panel 110, as described above. It should be understood that boiler 100 includes multiple parallel panels of each type, as indicated in Figs. 3-5. Multiple sets of overlapping panels 102, 110 and 140 may be arranged close to each other to form a boiler wall, as shown in Fig. 4. As shown in Fig. 5, multiple boiler walls can be joined, for example, to form a four-sided or multi-sided boiler capable of receiving concentrated solar energy from the heliostats surrounding the base of the boiler. Although described herein in the context of a three-stage boiler, persons skilled in the art will readily appreciate that any suitable number of stages can be used, and can be arranged in any suitable manner without departing from spirit and scope. of the invention.

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Previously, Figs. 1 and 2 showing how boiler panels 102, 110 accommodate thermal expansion and contraction in the vertical direction. Referring now to Fig. 3, the panels 102, 110 of the boiler are also configured to accommodate thermal expansion and contraction in the horizontal direction due to their modular configuration. The modular configuration of the panels 102, 110 gives them a relatively small width with respect to the entire solar boiler 100. There are two or three end tubes 191 at each end of the manifolds 112 and 104. The end tubes 191 bend inwardly to reduce the total length of the respective manifolds 112 and 104, and the same applies to the manifolds 113,114,115 and 117 , which are not shown in Fig. 3, but see Fig. 2. Fig. 4 shows a set of boiler panels 102, in which eight boiler panels 102 are placed close to each other, such as when the superheater part of a solar boiler wall is formed. Fig. 5 shows four of said walls from above, with the four walls surrounding an interior space of the boiler. Each of Figs. 3-5 shows vertical gaps 103 between the panels 102, which allows the individual panels 102 of the boiler to expand and contract independently with respect to the neighboring panels. It is advantageous that the openings 103 close completely or almost completely as the panels 102 expand during operation, in order to make the best use of the solar radiation supplied to the reception area, and to protect the interior space of the boiler, as described above.

As indicated in Fig. 3, each panel 102 of the boiler includes 52 tubes. However, it is contemplated that any suitable number of tubes can be used for a given application without departing from the spirit and scope of the invention. For example, the number of panel tubes may vary in a range of 50 to 200, or for a superheater panel, for example, in a range of 100 to 150. The use of smaller tube sizes allows a greater number of tubes in a panel of a given width, and / or allows smaller panel widths with a certain number of tubes. The size of the tubes is described in more detail below.

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A limited number of tubes allows a limited cell width. In addition, using multiple passes, and accommodating thermal expansion / contraction in the vertical direction, as described above, the panels may have a limited height. The configurations of solar boilers with multiple passes are described in more detail in the US patent application No. 13 / 007.262, of shared ownership, processed together with this, filed on January 14, 2011, which is incorporated by reference, to the present memory, in its entirety. Limiting the height and width of the panels is key to manufacturing the modular panels and to achieve the advantages described herein. For example, if the width of the panel is less than 233.68 cm (7 feet, 8 inches), it is possible to ship these panels in a standard transport container that has an interior width of 233.68 cm (7 feet, 8 inches) ).

Particularly high heat fluxes and heating characteristics of solar energy production, and the high voltage values ​​generated, together with the fact that the boiler cycles daily, present a unique challenge in the design of the transfer tube of heat The materials and configuration described herein are capable of reducing the amount of tension present within a given tube, while also minimizing the effect of creep and damage due to creep / fatigue. Boiler tubes 100 use specific materials that are resistant to creep and damage due to creep / fatigue, such as chromomolibdenum steels. Exemplary creep resistant materials for this application include chromium-molybdenum alloys, such as T11, T12, T22, T9 and T91, as well as austenitic stainless steel alloys, such as 304H, 310H, 316H, 321H and 347H.

Another important factor in reducing the thermally induced stresses in the tubes and other components of the boiler 100 is the use of materials that have a high thermal conductivity. The general opinion regarding the selection of the boiler tube material dictates that in a typical boiler design (for example, fossil fuel plants), tube materials are selected only based on their strength. However, it has been determined according to the present invention that, due to the high heat flux of the solar boiler application, a special consideration in the selection of the tube material is advantageous not only considering the strength of the material, but taking into account It also counts the thermal conductivity of the material. The thermal conductivity, which can be expressed in W / (mK), where 1 W / (mK) = 0.578 BTU / (hr.ft.F), is the property of a material that indicates its ability to conduct heat. The higher the thermal conductivity, the higher the rate of heat flow through the material. In a solar boiler, heat flow is applied only to the part of the tube exposed to concentrated solar radiation, that is, the surface facing outwards. The shaded part of the tube, that is, the inwardly oriented surface, receives no intense solar radiation. This creates a tendency for the tubes to be hot on the exposed side and relatively cold inside. This large thermal gradient results in thermally induced stress within the tubes, since thermal expansion is a function of temperature. An increase in thermal conductivity allows the tube to more easily conduct heat from the exposed side to the cold side, even helping to homogenize the thermal gradient through the tube and thus reducing thermally induced stresses.

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An advantageous balance is achieved between resistance and thermal conductivity, according to the invention. This contradicts the general opinion in the art, in which the tube material is selected according to the criterion that the most resistant is the best since, in general, the most resistant materials have lower thermal conductivities. Because heat must be conducted through the tube wall, it is advantageous to select a tube material that has a relatively high thermal conductivity (i.e., low thermal resistance). This is especially true for the superheater and superheater that have a relatively low internal heat transfer coefficient compared to the steam generator. It has been determined, according to the present invention, that in order to effectively transfer heat through the wall of a tube, the thermal conductivity should be at least 5.78 W / (mK), and preferably at least 8 , 67 W / (mK). Therefore, the tubes in the panels 102 have a thermal conductivity of approximately 8.67 W / (mK) or greater. Exemplary tube materials with resistance and thermal conductivity suitable for the present application include chromium-molybdenum steels, such as those indicated above, low carbon steel (e.g. 178C), medium carbon steel (e.g. 192, 210A1 And 210C), and molybdenum and carbon alloy steel (for example, T1 and T2), for example.

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Advantageously, the tubes of the panels 102 have a low coefficient of thermal expansion. This is beneficial since the intensity of the incident solar radiation on the tubes during operation can potentially cause large temperature differences in the structure of the tubes. The low coefficient of thermal expansion reduces the amount of thermal expansion and contraction that the tubes experience, thus reducing thermal stress, fatigue and related effects. Exemplary materials with adequately low thermal expansion coefficients include low carbon steel, medium carbon steel, molybdenum alloy and carbon steel and chromium molybdenum steel, for example.

The manifolds may include a material such as any type of steel or other suitable material. The solar boiler 100 includes a drum for distributing the steam from a steam generating part of the modular panels (for example, a plurality of panels 102 as in Fig. 2) to a superheater part of the modular panels (for example, a plurality of panels 110 as in Fig. 2), And tubes that fluidly connect the drum to the steam generator and the superheater parts of the modular panels. Suitable drum and tube configurations are shown and described in more detail in US Patent Application Publication No. 2010-0199974, jointly processed, together with this, and US Patent Application Publication No. 2010-0199976 , of shared ownership, processed together with this, each of which is incorporated in its entirety herein, by reference.

Taking into account all the considerations explained above, including considerations that go against the general opinion of the technique, the superheater, superheater and steam generating tubes of the boiler 100 are manufactured in T91 steel. T91 steel is an unconventional material for boiler tubes, due, at least in part, to the availability of materials that are easier to work, that is, welding, folding, etc. But according to the invention, T91 steel provides an advantageous thermal conductivity and high strength. T91 steel has a relatively low thermal expansion coefficient compared to stainless steel, for example, which would be a selected material if the opinion accepted in the art is followed. However, persons skilled in the art will readily appreciate that T91 steel is exemplary and that any of the other materials described above, or any other suitable material may be used according to the above considerations, without departing from the spirit and scope of the invention.

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Another important way to reduce the thermally induced stresses in the solar boiler tubes is by using tube diameters and wall thicknesses that respond better to the thermal gradients and the pressures involved. The use of tube wall thicknesses that are thinner than in typical boilers, for example, coal boilers, helps distribute heat more evenly through the tube. This is due to the fact that there is less mass to conduct heat in tubes with thinner walls. This is important, since in solar boiler applications all solar energy is focused on the outer diameter of the tube and must be conducted through the wall of the metal tube to the working fluid. A thicker wall tube equals higher thermal resistance and worse heat transfer. The use of a thin-walled tube is advantageous to cool the tube and heat the working fluid efficiently. In order to maintain sufficient strength to maintain the pressures and temperatures present inside a solar boiler, however, a minimum wall thickness of the tube must be maintained.

Now, reference is made to Fig. 6, which schematically represents the circumferential tension in an exemplary tube 150 of one of the panels (for example, panels 102, 110, 140 of the boiler). An advantageous way to reduce the thickness of the wall is to reduce the outer radius (r) of the tube itself. By reducing the outer radius (r) of the tube, the circumferential tension (Oh), indicated by the small arrows in the cross-sectional cut in Fig. 6, is reduced. The circumferential tension (Oh) is caused by the force of the internal pressure (P) that pushes outwards on the inner surface of the tube, as indicated by the large arrows in Fig. 6. Because the force is the product of the pressure and the area, reducing the radius (r) of the tube reduces the amount of surface area on which the pressure (P) can act and, therefore, reduces the circumferential tension (Oh) in the inside of the tube

Smaller circumferential stresses (Oh) mean that a tube can have a thinner wall thickness (t) and can still accommodate the pressure (P). The smaller tube thickness (t) also means that each tube uses less material. Because there is less material for heat to be conducted through a thinner tube, heat is distributed more evenly than it would be in thicker-walled tubes. In this way, reducing the diameter of the tube also reduces thermal gradients and thermally induced stresses.

The smaller tube diameter is an advantage in terms of stress and thermal factors;

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however, the advantages must be weighed against the fact that the pressure drop increases as the tube diameter decreases and, in particular, the interior diameter decreases. Smaller tubes, with smaller cross-sectional flow areas, create higher pressure drops than larger diameter tubes. A balance must be struck between pressure drop and thermally induced stress. To balance these conflicting properties, the boiler 100 uses a tube diameter that is in the range of 1.27 cm to 5.08 cm (~ inch to 2 inches) outside diameter, with a corresponding wall thickness sufficiently Great to maintain the required strength. A suitable range for the wall thickness is from about 3,429 mm to about 5,588 mm (from about 0.135 inches to about 0.220 inches). This range of tube diameters and tube wall thicknesses provides ideal conditions for stress reduction, heat transfer and pressure drop. The pressure drop with these tube sizes is maintained between 3.52 and 19.34 kg / cm2 (50 and 275 psi). The diameter of the tube, the thickness and the corresponding pressure drop can be varied from one application to another, depending on elements such as pipe lengths, the number of passes and the like. For example, for a superheater with panels such as panel 110, which has tubes with an outside diameter of 1.905 cm (0.75 inches) and a wall thickness of 3,429 mm (0.135 inches), the pressure drop is approximately 8.79 kg / cm2 (125 psi). As another example, for a superheater that has tubes with an outside diameter of 1.905 cm (0.75 inches) and a wall thickness of 3.81 mm (0.155 inches), the pressure drop is approximately 12.31 kg / cm2 (175 psi). In another example, for a superheater that has tubes with an outside diameter of 1.905 cm (0.75 inches) and a wall thickness of 5,588 mm (0.220 inches), the pressure drop is approximately 19.34 kg / cm2 ( 275 psi). These examples provide a pressure drop in the superheater as a whole, based on an exemplary superheater system that has panel lengths of 723.9 cm (23 feet, 9 inches), four passes, eight panels per pass and interconnect tubes .

The opinion accepted in the boiler technique dictates that larger tubes, typically larger than 6.35 cm (2.5 inches), should be used in the superheater, reheater and evaporator, specifically to increase the flow area to reduce The pressure drop. In addition, the opinion accepted in the art also dictates that the superheater tubes should have a larger diameter than the steam generator tubes due to the lower density of water vapor at sub-critical pressures. For example, WO 2008/154599, published on December 18, 2008, indicates that steam generating tubes should be 1.27 cm (0.5 inches) in diameter while superheater tubes should be 2 , 54 cm (1.0 inch) in diameter.

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Contrary to the opinion accepted in the art, according to the present invention, the tubes of the panels 102 of the steam generator, sometimes referred to as evaporator or water walls, have an outside diameter in the range of about 2.54 cm to about 3 , 81 cm (from about 1.0 to about 1.5 inches), and the tubes of the superheater panels 110 have a smaller diameter than the evaporator tubes, with an outside diameter of approximately 2.54 cm (1.0 inch). The tubes of the panels 140 of the superheater have a diameter greater than the tubes of the evaporator, with an outside diameter greater than or equal to approximately 3.81 cm (1.5 inches). The typical heat flux for solar boiler panels is 2-3 times greater than that of a conventional boiler (fossil fuels). According to the invention, it has been determined that heat transfer, namely the heating of the fluids and the cooling of the tubes, takes priority over the reduction of the pressure drop. The superheater tubes, of reduced diameter, increase the heat transfer coefficient by convection inside the tubes, which translates into additional cooling of the tube. The greater capacity of heat transfer allows a general reduction of the size of the boiler, which allows a certain level of energy production with a smaller number of necessary heliostats mirrors.

The systems and procedures of the present invention are described herein in the exemplary context of a sub-critical solar boiler. It is also contemplated that the systems and methods of the invention can be implemented in supercritical boilers without departing from the spirit and scope of the invention.

The methods and systems of the present invention, as described above and shown in the drawings, allow solar boilers and solar boiler panels with superior properties, including better accommodation of thermally induced stresses, ease of construction and maintenance. , and better heat distribution. An additional benefit of a smaller or modular construction for the solar panels of the boiler is the ease of transport and the ease of construction of the sub-assemblies. It also allows less construction effort and easy replacement of only certain panels, or all panels, as necessary.

Although the apparatus and methods of the present invention have been shown and described with reference to the preferred embodiments, persons 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 present invention.

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