PIPING, HEADER, AND TUBING ARRANGEMENTS FOR SOLAR BOILERS

Abstract

A header system for fluid circulation in a boiler includes a header configured to conduct fluid therethrough for circulating fluids in a boiler. A plurality of suction lines are connected in fluid communication with the header. Each suction line is configured and adapted to connect a respective pump in fluid communication with the header. A plurality of downcomers are connected in fluid communication with the header. Each downcomer is configured and adapted to connect the header in fluid communication with a steam drum. The header, suction lines, and downcomers are configured and adapted to draw substantially equal amounts of fluid from each of the downcomers even when flow is uneven among the suction lines. A plurality of cascaded headers can fluidly connect the circulation header to a steam generator. The plurality of cascaded headers is configured and adapted to provide a substantially equal flow to panels of the steam generator.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to solar power production, and more particularly to boilers for solar power production.

2. Description of Related Art

Solar power generation has been considered a viable source to help provide for energy needs in a time of increasing consciousness of the environmental aspects of power production. Solar energy production relies mainly on the ability to collect and convert energy freely available from the sun and can be produced with very little impact on the environment. Solar power can be utilized without creating radioactive waste as in nuclear power production, and without producing pollutant emissions including greenhouse gases as in fossil fuel power production. Solar power production is independent of fluctuating fuel costs and does not consume non-renewable resources.

Solar power generators generally employ fields of controlled mirrors, called heliostats, to gather and concentrate sunlight on a receiver to provide a heat source for power production. A solar receiver typically takes the form of a panel of tubes conveying a working fluid therethrough. Previous solar generators have used working fluids such as molten salt because it has the ability to store energy, allowing power generation when there is no solar radiation. The heated working fluids are typically conveyed to a heat exchanger where they release heat into a second working fluid such as air, water, or steam. Power is generated by driving heated air or steam through a turbine that drives an electrical generator.

More recently, it has been determined that solar power production can be increased and simplified by 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 lead to new challenges in handling the intense solar heat without damage to the system. In a solar boiler, heat transfer rates can reach levels around 2-3 times the heat transfer rate of a typical fossil fuel fired boiler. This high heat transfer rate intensifies problems related to maintaining even heating and flow distribution throughout known designs of boiler panels. The high heat transfer rate gives rise to high pressures and temperatures in the boiler tubing and related structures.

In typical forced circulation boilers, such as coal fired boilers, single or multiple circulation pumps are used to circulate water from the drum through the steam generator panels, and back into the drum as a mixture of saturated water and steam. Traditional boilers often use multiple circulation pumps operating in parallel for capacity and redundancy reasons. In a traditional configuration, a plurality of pumps are connected in parallel along the length of a horizontal header, each pump being connected to the header by way of a suction line. The horizontal header is in turn connected to the drum through a plurality of vertical downcomers. Each pump draws water primarily from a specific portion of the drum through the nearest downcomers. In the event of failure of one or more of the pumps, the functioning pump or pumps draw uneven amounts of water from the drum through the different downcomers, creating an unbalance of flow in the drum. Unbalance along the length of the drum can lead to varying drum water level along the length of the drum. Uneven water level in the drum can cause many problems including high carry-under (when saturated fluid enters the downcomers) to a false low water level alarm or low water level trip. Prolonged operation with large unbalances in drum water level can also lead to constant water level alarms, water level trips, long-term fatigue and metallurgical problems from overheating, and affect the life and performance of the circulation pump.

Another aspect of traditional boilers, such as coal fired boilers, is that there are typically downcomers from the drum that feed four waterwall headers, namely two sidewall headers, a front wall header, and a rear wall header. Each of these headers, in turn, feeds a portion of the steam generator. This header arrangement, when applied to solar boiler applications, can lead to uneven flow from panel to panel, which can give rise to panel failure due to the intense heating described above. This, together with the with the circulation header arrangement described above, can result in detrimental uneven flow throughout the boiler system, and causes a risk of emergency shutdown or even failure of key components.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for boilers in general, and in particular solar boilers, that allow for improved flow distribution between the drum and circulation pumps. There also remains a need in the art for such boilers with improved flow distribution to the boiler panels. The present invention provides solutions for these problems.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful header system for forced fluid circulation in a boiler. The system includes a header configured to conduct fluid therethrough for circulating fluids in a boiler. A plurality of suction lines are connected in fluid communication with the header. Each suction line is configured and adapted to connect a respective pump in fluid communication with the header. A plurality of downcomers are connected in fluid communication with the header. Each downcomer is configured and adapted to connect the header in fluid communication with a steam drum. The header, suction lines, and downcomers are configured and adapted to draw substantially equal amounts of fluid from each of the downcomers even when flow is uneven among the suction lines.

In accordance with certain embodiments, the header defines a longitudinal axis and has an inlet section and an opposed outlet section that is spaced apart from the inlet section along the longitudinal axis. The suction lines are all connected to the outlet section of the header, and the downcomers are all connected to the inlet section of the header.

In certain exemplary embodiments, there are four downcomers, wherein an inner two of the downcomers are inboard with respect to two outboard downcomers. Each inner downcomer is connected to the header at a first common axial position on the header. Each outer downcomer is connected to the header at a second common axial position on the header. The first and second axial positions can be spaced apart axially along the longitudinal axis of the header.

It is contemplated that the downcomers can be oriented perpendicular to the header where connected thereto, and can all be oriented parallel to one another at inlet ends thereof. Similarly, one or more of the suction lines can be oriented perpendicular to the header where connected thereto, and parallel to one another at outlet ends thereof. Two suction lines can be staggered axially or can be axially aligned with respect to one another where connected to the header. A third suction line can be connected to the header in axial alignment therewith.

The invention also provides a solar boiler for solar power production. The solar boiler includes a steam generator and a superheater each connected in fluid communication with a steam drum. A plurality of downcomers are connected in fluid communication with the steam drum. A vertically oriented circulation header is fluidly connected to the downcomers. A plurality of suction lines is in fluid communication with the circulation header. The suction lines are each configured and adapted to place a circulation pump in fluid communication with the circulation header. The circulation header, suction lines, and downcomers are configured and adapted to draw substantially equal amounts of fluid from each of the downcomers even when flow is uneven among the suction lines. It is contemplated that the circulation header can have axially spaced apart inlet and outlet sections as described above, wherein the inlet section is above the outlet section.

The invention also provides a boiler for power production having a plurality of cascaded headers fluidly connecting a circulation header to a steam generator. The circulation header is configured to circulate water from a steam drum into the steam generator. The plurality of cascaded headers is configured and adapted to provide a substantially equal flow to panels of the steam generator.

In certain embodiments, the plurality of cascaded headers includes a flow path that passes through a series of progressively smaller headers from the circulation header to the panels of the steam generator. There can be at least three header sizes and/or levels between the circulation header and individual tubes of the steam generator panels.

In accordance with certain aspects, a second plurality of cascaded headers can be provided to fluidly connect the steam generator to the steam drum to provide a saturated mixture of water and steam from the steam generator to the steam drum. The second plurality of cascaded headers can include a flow path that passes through a series of progressively larger headers from the panels of the steam generator to the steam drum. There can be at least two header sizes and/or levels between individual tubes of the steam generator panels and the steam drum.

These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

FIG. 1 is a front elevation view of an exemplary embodiment of a solar boiler constructed in accordance with the present invention, showing the solar boiler atop a solar receiver tower, with a cut-away portion showing the steam drum and piping within the interior boiler space;

FIG. 2 is an elevation view of a portion of an exemplary circulation header typical of the prior art, showing the horizontal header arrangement;

FIG. 3 is an elevation view of a portion of the solar boiler of FIG. 1, showing the circulation header in a vertical header arrangement with the inlets and outlets of the header spaced out axially along the length thereof;

FIG. 4 is an elevation view of another exemplary embodiment of a circulation header constructed in accordance with the present invention, showing two staggered suction lines connecting the header to two respective pumps; and

FIG. 5 is schematic view of a portion of the solar boiler of FIG. 1, showing a cascading header arrangement for circulating fluids through the boiler panels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a solar boiler in accordance with the invention is shown in FIG. 1 and is designated generally by reference character 100. Other embodiments of solar boilers in accordance with the invention, or aspects thereof, are provided in FIGS. 3-5, as will be described. The systems of the invention can be used improve circulation reliability and flow distribution within boilers, and particularly in solar boilers.

With reference now to FIG. 1, solar boiler 100 for solar power production is shown at the top of a solar receiver tower 102, which can be surrounded by a field of heliostats for focusing solar radiation on solar boiler 100. Solar boiler 100 includes a plurality of solar boiler panels 104 forming a perimeter surrounding a boiler interior space 106, which is visible through the cut-away portion in FIG. 1. A support structure 108 within boiler interior space 106 supports solar boiler panels 104. Boiler panels 104 include a steam generator 110 with a superheater 112 contiguous therewith on top of boiler 100, and with a reheater 114 contiguous with steam generator 110 on the bottom of boiler 100. Panels 104 for steam generator 110, superheater 112, and reheater 114 are described in commonly owned, co-pending U.S. patent application Ser. No. 12/552,724, filed Sep. 2, 2009, which is incorporated by reference herein in its entirety.

As can be seen in the cut-away portion of FIG. 1, a steam drum 116 is mounted to support structure 108 within boiler interior space 106. Boiler panels 104 define upper and lower extents of boiler interior space 106, and drum 116 is mounted below the upper extent of boiler interior space 106. More particularly, drum 116 is mounted in interior space 106 within the elevation of superheater 112.

Since boiler panels 104 form a substantially contiguous heat transfer surface configured to block solar radiation incident thereon from boiler interior space 106, drum 116 is protected by panels 104 from the intense thermal radiation incident on the solar receiver during operation. Solar boiler panels 104 form four boiler walls surrounding boiler interior space 106. Any other suitable number of walls can be used without departing from the spirit and scope of the invention. Four wall boiler configurations are described in greater detail in commonly owned, co-pending U.S. patent application Ser. Nos. 12/547,650 and 12/617,054, filed Aug. 26, 2009 and Nov. 12, 2009, respectively, each of which is incorporated by reference herein in its entirety. Downcomers 152a, 152b, 152c, and 152d connected to steam drum 116 are also supported by support structure 108.

Referring now to FIG. 2, an example of a traditional steam drum 16 and circulation header 50 are shown. Four downcomers 52a, 52b, 52c, and 52d connect steam drum 16 to circulation header 50, which is in turn connected to pumps 54a, 54b, and 54c by way of suction lines 56a, 56b, and 56c, respectively. Under normal operation, pumps 54a-54c circulate saturated water out from drum 16, through downcomers 52a-52d, header 50, suction lines 56a-56c, through the steam generator, and back into drum 16 as a mixture of saturated steam and water. However, if one or more of the pumps 54a-54c fails or otherwise loses capacity or reduces its flow rate, the fluid levels inside drum 16 will become uneven. For example, if pump 54a stops working, suction line 56a will effectively be rendered inoperative. Since suction line 56a is in closest proximity to downcomers 52a and 52b, the flow in those two downcomers 52a and 52b will be reduced much more than will the flow in the more distant downcomers 52c and 52d. The result is that portions of drum 16 proximate the openings into downcomers 52a and 52b will have a higher fluid level than portions proximate downcomers 52c and 52d, which may still provide suction at near-normal levels. The uneven fluid levels across drum 16 will create a flow unbalance in drum 16, which can cause high carry-under or a false low water level alarm or low water level trip. Prolonged operation with large unbalances in drum water level can also lead to long-term fatigue and metallurgical problems arising from overheating drum 16.

Referring now to FIG. 3, the header system for fluid circulation in boiler 100 provides for even flow in the downcomers even when flow in one or more of the suction lines is reduced. The system includes circulation header 150 configured to conduct fluid therethrough for circulating fluids in boiler 100. Three suction lines 156a, 156b, and 156c are connected in fluid communication with circulation header 150. Each suction line 156a, 156b, and 156c is configured and adapted to connect a respective pump 154a, 154b, and 154c in fluid communication with circulation header 150. Four downcomers 152a, 152b, 152c, and 152d are connected in fluid communication with circulation header 150. Each of the downcomers 152a-152d connects circulation header 150 in fluid communication with steam drum 116.

Header 150 defines a longitudinal axis A and has an inlet section 158 and an opposed outlet section 160. Outlet section 160 is spaced apart axially from inlet section 158 along the longitudinal axis A. The suction lines 156a-156c are all connected to outlet section 160, and the downcomers 152a-152d are all connected to inlet section 158. All of the fluid passing from inlet section 158 to outlet section 160 must pass through a common section 162 between the outlets of downcomers 152a-152d and the inlets of suction lines 156a-156c. Since all of the fluid must pass through common section 162, in the event flow through one or more of suction lines 156a-156c is reduced relative to the others, suction flow will be decreased for all of the downcomers 152a-152d substantially evenly. Header 150, suction lines 156a-156c, and downcomers 152a-152d are thus configured and adapted to draw substantially equal amounts of fluid from each of the downcomers 152a-152d even when flow is uneven among the suction lines 156a-156c during single or multiple pump operation. Flow rate can be completely or partially reduced in a given pump due to a system failure, or without any failure, for example if it is desired to operate at a lower overall mass flow rate. The overall flow in such events would decrease, but the balance of the flow would remain substantially uniform along drum 116 and through downcomers 152a-152d. The problem of flow unbalance from losing one or more pumps is eliminated, which means the boiler can continue operating after loss of one or more pumps. This configuration also reduces or eliminates ill effects from water level unbalance including metal fatigue, overheating, boiler trips, and control issues.

The inner two downcomers 152b and 152c are inboard with respect to the two outboard downcomers 152a and 152d. Each of the inner downcomers 152b and 152c is connected to header 150 at a first common axial position 164 on the header, i.e., downcomers 152b and 152c connect to header 150 at the same elevation along axis A. Each of the outer downcomers 152a and 152d is connected to header 150 at a second common axial position 166 on header, i.e., downcomers 152a and 152d connect to header 150 at a common elevation along axis A, which is lower than where inner headers 152b and 152c connect to header 150, as oriented in FIG. 3.

With continued reference to FIG. 3, downcomers 152a-152d are all oriented perpendicular to header 150 where connected thereto. All of the downcomers 152a-152d are oriented parallel to one another at inlet ends thereof, i.e., where they connect to drum 116. Similarly, suction lines 156a and 156c are oriented perpendicular to header 150 where connected thereto, and are parallel to one another at outlet ends thereof, i.e., where connected to the respective pumps 154a and 154c. The third suction line 156b is connected to header 150 in axial alignment therewith. All of the suction lines 156a-156c and downcomers 152a-152d are predominantly oriented parallel to circulation header 150 and perpendicular to drum 116.

Referring now to FIG. 4, another exemplary embodiment of a header system 200 constructed in accordance with the subject invention is shown. Header system 200 includes drum 216, downcomers, 252a, 252b, 252c, and 252d, circulation header 250 with longitudinal axis B, inlet section 258, outlet section 260, common section 262, pumps 254a and 254b similar to those described above with respect to FIG. 3. Header system 200 has two pumps 254a and 254b connected to circulation header 250 by way of two respective suction lines 256a and 256b. Rather than connecting to header 250 at a common elevation as do suction lines 156a and 156c in FIG. 3, suction lines 256a and 256b are staggered axially with respect to one another where connected to header 250. Since all the fluid must be pumped through common portion 262, even if one of the two pumps 254a and 254b loses power or s otherwise diminished or reduced in capacity or mass flow rate, flow through downcomers 252a-252d will remain substantially equal, and fluid levels in drum 216 will remain substantially even. Staggering inlets for suction lines 256a and 256b provides advantages such as prevention of a false low level alarm or low level trip, decreased carry-under, and increased pump performance.

Referring again to FIGS. 1 and 3, steam generator 110 and superheater 112 are each connected in fluid communication with steam drum 116. Downcomers 152a-152d are connected to the bottom of steam drum 116 where the fluid resides. Circulation header 150 is vertically oriented within boiler 100, as are downcomers 152a-152d, and suction lines 156a-156c. In this vertical header orientation, the inlet section 158 of header 150 is above outlet section 160. While described herein in the exemplary context of having a vertically oriented circulation header, those skilled in the art will readily appreciate that a circulation header can be oriented horizontally, or in any other suitable orientation and still achieve benefits, as long as the downcomers and suction lines connect to the header in such a way as to provide substantially even flow through the downcomers even when flow is unequal in the suction lines.

With reference now to FIG. 5, steam generator 110 of boiler 100 is shown schematically. Substantially equal flow rates to each solar receiver panel 104 of steam generator 110 are provided by the system of cascaded headers fluidly connecting circulation header 150 (not shown in FIG. 5, but see FIG. 3) to steam generator 110.

The circulation pumps, e.g., circulation pumps 154a-154c and 254a-254b, feed into primary headers 168, as indicated in FIG. 5 by the arrows pointing into each primary header 168. The exemplary configuration shown in FIG. 5 has two lines feeding each primary header 168, such as if two circulation pumps, e.g., 254a and 254b, each have two discharge nozzles/lines, with each pump feeding one line into each primary header 168. In the event of one pump losing power, the remaining pump can still feed the entire steam generator 110 through both primary headers 168. Those skilled in the art will readily appreciate that the number of pumps and/or lines feeding primary headers 168 can be varied without departing from the spirit and scope of the invention. For example, if three pumps are used, such as pumps 154a-154c, each pump can have two feed lines, one to each primary header 168 so each primary header 168 can be fed by all three pumps.

Each primary header 168 has four outlet lines, each connected to a respective secondary header 170, for a total of eight secondary headers 170. Each secondary header 170 has eight outlet lines, with two outlet lines feeding into each panel inlet header 172. In FIG. 5, the components are all shown laid flat for clarity. Dotted line C indicates where the feed lines between secondary headers 170 and panel inlet headers 172 actually change direction in the constructed boiler 100, starting downward from the exits of headers 170, then bending upward at line C and continuing upward into panel inlet headers 172. This arrangement causes the flow through each panel to be in the upward direction. The benefits of having all steam generator panels in an up-flow configuration is described in greater detail in commonly owned, co-pending U.S. patent application Ser. No. 12/547,650.

Having two lines feeding each panel inlet header 172 helps provide even flow through the tubes of the panels 104. Each panel 104 feeds into a respective panel outlet header 174. In FIG. 5, only one panel 104, one panel inlet header 172, and one panel outlet header 174 are labeled with reference characters for sake of clarity. Each panel outlet header 174 has two outlet lines that feed into an intermediate outlet header 176. Each intermediate outlet header 176 is fed by a pair of panels 104, and feeds into steam drum 116 through a single feed line. Steam drum 116 is not shown in FIG. 5, but the flow into drum 116 is indicated by arrows pointing out of the intermediate outlet headers 176.

The plurality of cascaded headers 168, 170, and 172 define a branching flow path that passes through a series of progressively smaller headers from the supply (e.g., circulation header 150) to panels 104 of steam generator 110. There are three header sizes and three levels (168, 170, 172) between the source (e.g., circulation header 150) and individual tubes of the panels 104 in steam generator 110. On the outlet side of panels 104, a second plurality of cascaded headers, i.e. headers 174 and 176, fluidly connect steam generator 110 to steam drum 116 to provide a saturated mixture of water and steam from steam generator 110 to steam drum 116. This second plurality of cascaded headers 174 and 176 defines a flow path that passes through a series of progressively larger headers from panels 104, through headers 174, into headers 176, and then into steam drum 116. There are two header sizes and levels between individual tubes of the panels 104 of steam generator 110 and steam drum 116. This arrangement of cascaded inlet and outlet headers provides a substantially balanced flow to the individual tubes of panels 104 in steam generator 110, since each header provides mixing and balancing. With multiple levels of mixing, balancing headers between relatively large components like circulation header 150 and relatively small components like the tubes of panels 104, there are multiple places for the working fluid flow to mix and balance. Another benefit of having multiple stages of headers is that it facilitates modularization during boiler construction, maintenance, repairs, and the like. A cascaded header configuration, with increased number of headers, allows for the headers to be smaller and therefore the headers can have thinner walls. Given that a solar boiler is typically cycled daily, going from a hot state to a cold state, minimal wall thickness is advantageous for reducing creep, fatigue, and high stresses.

While described herein in the exemplary context of having three levels of cascading inlet headers and two levels of cascaded outlet headers, those skilled in the art will readily appreciate that any suitable number of header levels can be used on the inlet and outlet sides of boiler panels. Moreover, any suitable number or size of headers and feed lines can be used on any level of a cascaded inlet or outlet header system without departing from the spirit and scope of the invention. The systems and methods described herein provide particular advantages when applied to solar boilers, however those skilled in the art will readily appreciate that the systems and methods described herein can be applied to any other suitable type of boiler 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, provide for boilers, and particularly solar boilers, with superior properties including improved flow distribution in circulation components and receiver panels. While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.

Claims

1. A header system for fluid circulation in a boiler comprising: a) a header configured to conduct fluid therethrough for circulating fluids in a boiler;b) a plurality of suction lines connected in fluid communication with the header, each suction line being configured and adapted to connect a respective pump in fluid communication with the header; andc) a plurality of downcomers connected in fluid communication with the header, wherein each downcomer is configured and adapted to connect the header in fluid communication with a steam drum, wherein the header, suction lines, and downcomers are configured and adapted to draw substantially equal amounts of fluid from each of the downcomers even when flow is uneven among the suction lines.

2. A header system as recited in claim 1, wherein the header defines a longitudinal axis and has an inlet section and an opposed outlet section that is spaced apart from the inlet section along the longitudinal axis, and wherein the suction lines are all connected to the outlet section of the header, and wherein the downcomers are all connected to the inlet section of the header.

3. A header system as recited in claim 2, wherein there are four downcomers, an inner two of the downcomers being inboard with respect to two outboard downcomers.

4. A header system as recited in claim 3, wherein each inner downcomer is connected to the header at a first common axial position on the header, and wherein each outer downcomer is connected to the header at a second common axial position on the header, and wherein the first and second axial positions are spaced apart axially along the longitudinal axis of the header.

5. A header system as recited in claim 2, wherein the downcomers are oriented perpendicular to the header where connected thereto.

6. A header system as recited in claim 5, wherein the downcomers are all oriented parallel to one another at inlet ends thereof.

7. A header system as recited in claim 2, wherein one or more of the suction lines are oriented perpendicular to the header where connected thereto.

8. A header system as recited in claim 7, wherein the suction lines are all oriented parallel to one another at outlet ends thereof.

9. A header system as recited in claim 7, wherein two suction lines are staggered axially with respect to one another where connected to the header.

10. A header system as recited in claim 7, wherein two suction lines are axially aligned with respect to one another where connected to the header.

11. A header system as recited in claim 7, wherein a third suction line is connected to the header in axial alignment therewith.

12. A header system as recited in claim 7, wherein two suction lines are axially aligned with respect to one another where connected to the header, and wherein a third suction line is connected to the header in axial alignment therewith.

13. A solar boiler for solar power production comprising: a) a steam generator and a superheater each connected in fluid communication with a steam drum;b) a plurality of downcomers connected in fluid communication with the steam drum;c) a vertically oriented circulation header fluidly connected to the downcomers; andd) a plurality of suction lines in fluid communication with the circulation header, the suction lines each being configured and adapted to place a circulation pump in fluid communication with the circulation header, wherein the circulation header, suction lines, and downcomers are configured and adapted to draw substantially equal amounts of fluid from each of the downcomers even when flow is uneven among the suction lines.

14. A solar boiler as recited in claim 13, wherein the circulation header defines a longitudinal axis and has an inlet section and an opposed outlet section that is spaced apart from the inlet section along the longitudinal axis, wherein the inlet section is above the outlet section, and wherein the suction lines are all connected to the outlet section of the header, and wherein the downcomers are all connected to the inlet section of the header.

15. A solar boiler as recited in claim 13, further comprising a plurality of cascaded headers fluidly connecting the circulation header to the steam generator, wherein the plurality of cascaded headers is configured and adapted to provide a substantially equal flow to panels of the steam generator.

16. A boiler for power production comprising: a) a steam generator and a superheater each connected in fluid communication with a steam drum;b) a circulation header in fluid communication with the steam drum and the steam generator for circulating water from the steam drum into the steam generator; andc) a plurality of cascaded headers fluidly connecting the circulation header to the steam generator, wherein the plurality of cascaded headers is configured and adapted to provide a substantially equal flow to panels of the steam generator.

17. A boiler as recited in claim 16, wherein the plurality of cascaded headers includes a flow path that passes through a series of progressively smaller headers from the circulation header to the panels of the steam generator.

18. A boiler as recited in claim 17, wherein there are at least three header sizes between the circulation header and individual tubes of the steam generator panels.

19. A boiler as recited in claim 16, wherein a second plurality of cascaded headers fluidly connects the steam generator to the steam drum to provide a saturated mixture of water and steam from the steam generator to the steam drum.

20. A boiler as recited in claim 19, wherein the second plurality of cascaded headers includes a flow path that passes through a series of progressively larger headers from the panels of the steam generator to the steam drum, wherein there are at least two header sizes between individual tubes of the steam generator panels and the steam drum.