The present invention relates to a solar radiation receiver for being used for direct steam generation in a solar energy system comprising a plurality of mirrors arranged to reflect solar radiation onto the solar radiation receiver. It also relates to a solar energy system comprising such solar radiation receiver as well as the use of such solar radiation receiver in a solar energy system.

Background

Solar energy systems with a central solar radiation receiver placed on a tower and surrounded by movable mirrors controlled to reflect solar radiation onto the solar radiation receiver are well-known in the art. US patent application No. US 2013/047610 discloses such system where the solar radiation receiver comprises a cylindrical, vertical steam drum surrounded by a plurality of water-filled tubes arranged in a cylindrical shell around the steam drum for direct generation of steam from the reflected solar radiation. US patent application No. US 2010101564 discloses a corresponding system, where the water-filled tubes are arranged around the vertical steam drum in a square pattern. US patent application No. US 2012/199117 discloses yet another solar energy system for direct generation of steam comprising a horizontal steam drum.

Brief description of the invention

The present invention relates in a first aspect to a solar radiation receiver suitable for being used for direct steam generation, in particular of saturated steam, in a solar energy system comprising a plurality of mirrors arranged to reflect solar radiation onto the solar radiation receiver, the solar radiation receiver comprising a steam drum comprising a steam receiving cavity, a plurality of receiver tubes, also known as boiler riser pipes, each receiver tube extending in a longitudinal direction of the solar radiation receiver and being in fluid connection at an upper end of the receiver tube to the steam receiving cavity of the steam drum and in fluid connection at a lower end of the receiver tube to the steam receiving cavity of the steam drum, the receiver tubes being distributed along a periphery of the solar radiation receiver and surrounding a central enclosure of the solar radiation receiver, and a water level gauge glass arranged to measure a water level within the steam receiving cavity of the steam drum and having a lower fluid connection to the cavity of the steam drum and an upper fluid connection to the cavity of the steam drum, wherein the upper fluid connection is arranged at a position above the upper end of at least some of the plurality of receiver tubes, and wherein the water level gauge glass is arranged to measure a water level within the steam receiving cavity of the steam drum above the upper end of at least some of the plurality of receiver tubes.

The longitudinal direction of the solar radiation receiver is shown in Fig. 1 and equals the vertical direction of the solar radiation receiver in use.

The water level gauge glass is arranged to measure the normal water level of the steam receiving cavity and variations above and below that level.

By arranging at least the upper fluid connection at a position above the upper end of at least some of the plurality of receiver tubes, it is made possible to position the water level gauge glass closer to the steam drum. In case the upper fluid connection was positioned below the upper end of all of the receiver tubes, the water level gauge glass would have to be situated at a substantially larger distance perpendicularly to the longitudinal direction to avoid access issues for positioning and maintenance of the water level gauge glass with the receiver tubes.

It is preferred that the upper fluid connection of the water level gauge glass to the cavity of the steam drum is arranged at a position above the upper end of each of the plurality of receiver tubes, and it is also preferred that the lower fluid connection of the water level gauge glass to the cavity of the steam drum is arranged at a position above the upper end of at least some of the plurality of receiver tubes, such as at a position above the upper end of each of the plurality of receiver tubes.

In a further preferred embodiment, the solar radiation receiver further comprises a lower vessel, in some embodiments known as the mud, enclosing a separate cavity for water, wherein each receiver tubes being in fluid connection at a lower end of the receiver tube to the cavity of the lower vessel, and at least one downcomer pipe connecting the steam receiving cavity with the cavity of the lower vessel for supplying water to the cavity of the lower vessel during operation of the solar radiation receiver.

By arranging the receiver tubes to extend between separate entities, i.e. the steam drum and the lower vessel, it is achieved that the total amount of water present in the solar radiation receiver during operation thereof may be reduced, thereby reducing the mass and the structural requirements of the arrangement, typically a tower, that supports the solar radiation receiver. Furthermore, the amount of material, such as steel needed for manufacturing the steam drum is reduced, which also reduces the mass of the solar radiation receiver.

The minimal distance between the steam drum and the lower vessel is preferably more than 1.5 meter, such as more than 2.5 meter in the longitudinal direction of the solar radiation receiver.

The lower vessel is preferably provided with an internal through-opening in the longitudinal direction of the solar radiation receiver, in a preferred embodiment with a through-opening of a minimum width perpendicular to the longitudinal direction of the solar radiation receiver of at least 1 meter, such as at least 1.5 meter. Hereby, the mass of the lower vessel can be minimized, the amount of water present in the solar radiation receiver during operation may be minimized and access for personnel entering the central enclosure of the solar radiation receiver for inspection and possible maintenance thereof.

A steam outlet pipe arranged to guide generated steam away from the steam receiving cavity of the steam drum is in a preferred embodiment extending inside the downcomer pipe, so that the steam exits the solar radiation receiver at the bottom part thereof and is kept heated by the water streaming from the steam receiving cavity and into the lower vessel, which is at or very near the boiling temperature of the water.

The plurality of receiver tubes are substantially evenly distributed along a periphery of the solar radiation receiver, wherein the central enclosure of the solar radiation receiver preferably is substantially fully shielded by means of the plurality of receiver tubes from solar radiation reflected onto the solar radiation receiver during operation of the solar radiation receiver.

It is furthermore preferred that the steam drum extends partially into the central enclosure of the solar radiation receiver, i.e. that the steam drum is arranged as a vertical drum.

The cross-sectional extend of the solar radiation receiver perpendicularly to the longitudinal direction of the solar radiation receiver is preferably so that is allows the solar radiation receiver to fit into the longitudinal direction of a ISO standard freight container, i.e. a freight container in accordance with ISO 668, for transport of the solar radiation receiver.

The solar radiation receiver may further comprise a camera directed at the water level gauge glass for allowing for remote monitoring of the water level gauge glass.

According to a second aspect, the present invention relates to a solar radiation receiver for being used for direct steam generation in a solar energy system comprising a plurality of mirrors arranged to reflect solar radiation onto the solar radiation receiver, the solar radiation receiver comprising a steam drum comprising a steam receiving cavity, a plurality of receiver tubes, each receiver tube extending in a longitudinal direction of the solar radiation receiver and being in fluid connection at an upper end of the receiver tube to the steam receiving cavity of the steam drum, the receiver tubes being distributed along a periphery of the solar radiation receiver and surrounding a central enclosure of the solar radiation receiver, a lower vessel enclosing a separate cavity for water, wherein each receiver tubes being in fluid connection at a lower end of the receiver tube to the cavity of the lower vessel, and at least one downcomer pipe connecting the steam receiving cavity with the cavity of the lower vessel for supplying water to the cavity of the lower vessel during operation of the solar radiation receiver. By arranging the receiver tubes to extend between separate entities, i.e. the steam drum and the lower vessel, it is achieved that the total amount of water present in the solar radiation receiver during operation thereof may be reduced, thereby reducing the mass and the structural requirements of the arrangement, typically a tower, that supports the solar radiation receiver. Furthermore, the amount of material, such as steel needed for manufacturing the steam drum is reduced, which also reduces the mass of the solar radiation receiver.

The minimal distance between the steam drum and the lower vessel is preferably more than 1.5 meter, such as more than 2.5 meter in the longitudinal direction of the solar radiation receiver.

The lower vessel is preferably provided with an internal through-opening in the longitudinal direction of the solar radiation receiver, in a preferred embodiment with a through-opening of a minimum width perpendicular to the longitudinal direction of the solar radiation receiver of at least 1 meter, such as at least 1.5 meter. Hereby, the mass of the lower vessel can be minimized, the amount of water present in the solar radiation receiver during operation may be minimized and access for personnel entering the central enclosure of the solar radiation receiver for inspection and possible maintenance thereof.

A steam outlet pipe arranged to guide generated steam away from the steam receiving cavity of the steam drum is in a preferred embodiment extending inside the downcomer pipe, so that the steam exits the solar radiation receiver at the bottom part thereof and is kept heated by the water streaming from the steam receiving cavity and into the lower vessel, which is at or very near the boiling temperature of the water.

The plurality of receiver tubes are substantially evenly distributed along a periphery of the solar radiation receiver, wherein the central enclosure of the solar radiation receiver preferably is substantially fully shielded by means of the plurality of receiver tubes from solar radiation reflected onto the solar radiation receiver during operation of the solar radiation receiver. It is furthermore preferred that the steam drum extends partially into the central enclosure of the solar radiation receiver, i.e. that the steam drum is arranged as a vertical drum.

The cross-sectional extend of the solar radiation receiver perpendicularly to the longitudinal direction of the solar radiation receiver is preferably so that is allows the solar radiation receiver to fit into the longitudinal direction of a ISO standard freight container, i.e. a freight container in accordance with ISO 668, for transport of the solar radiation receiver.

The present invention furthermore relates to a solar energy system comprising a solar radiation receiver as disclosed herein and a plurality of mirrors arranged to reflect solar radiation onto the solar radiation receiver.

The present invention also relates to the use of a solar radiation receiver as disclosed herein for direct steam generation in a solar energy system comprising a plurality of mirrors arranged to reflect solar radiation onto the solar radiation receiver.

Brief description of the figures

The enclosed figures show an embodiment of the present invention, of which

Fig. 1 is a longitudinal section of a solar radiation receiver according to the present invention,

Fig. 2 is a side view of the upper party of the solar radiation receiver of Fig. 1 , and

Fig. 3 shows a solar energy system using a solar radiation receiver according to the present invention.

Detailed description of example

An example of a solar radiation receiver 1 according to the present invention is shown in Figs. 1 and 2, comprising a plurality of receiver tubes 6 arranged in a circular pattern at the periphery of the solar radiation receiver 1 , forming a central enclosure 9, which is substantially shielded off from the solar light reflected by the mirrors 22 of the solar energy system 21 as shown in Fig. 3 for which the solar radiation receiver is intended to be used.

The upper ends 7 of the receiver tubes 6 are connected to the internal steam receiving cavity 5 of the steam drum 2 by means of openings 3 in the steam drum 2 and the lower end 8 of the receiving tubes 6 are connected to a lower vessel 15, which in the present example has the shape of a doughnut, i.e. annular with a circular cross-section. The lower vessel 15 is thereby formed with an internal through-opening 20 of a width W of typically at least 1.5 meter so as to allow for personnel entering the central enclosure 9 of the solar radiation receiver 1 for inspection and possible maintenance. The lower vessel 15 is supplied with water from the lower part of the steam drum 2 by means of a central downcomer pipe 17 which by means of downcomer connections 18 is in fluid communication with the cavity for water 16 in the lower vessel 15. The steam drum 2 is equipped with a safety valve 4.

The receiver tubes 6 may in alternative embodiments be arranged e.g. in a square cross-section instead of the depicted circular cross-section.

The lower part of the steam drum 2 extends into the central enclosure 9 of the solar radiation receiver 1, whereas the upper part of the steam drum extends above the central enclosure 9. On top of the steam receiving cavity 5 inside the steam drum 2 is an outlet 4 for steam generated in the solar radiation receiver 1 and a feed water pipe 24 is arranged for supplying feed water to the steam drum 2 to replace the loss of water due to the steam generation. Two pressure differential transmitters (not shown) are arranged to determine the water level in the steam receiving cavity 5 hydrostatically and are arranged to measure a pressure difference inside the steam receiving cavity 5 between a position where the water is in a liquid phase, preferably near the bottom of the steam receiving cavity 5 and a position where the water is in a steam phase. Furthermore, a water level gauge glass 10 is arranged on the outside of the steam drum 2 with a lower fluid connection 12 to the steam receiving cavity 5 below the normal water level 14 of the steam drum 2 and an upper fluid connection 13 above the normal water level 14 of the steam drum 2. By means of the camera 11 arranged for viewing the reading of the water level gauge glass 10, a remote monitoring of the water level is enabled. Alternatively to the camera, a fibreoptic cable connection may be established for remote monitoring of the water level gauge glass 10.

In the embodiment shown in the figures, both the lower fluid connection 12 and the upper fluid connection 13 are situated on the steam drum 2 above the upper end 7 of each of the receiver tubes 6, in other embodiments, some of upper ends 7 of the receiver tubes 6 may extend above the lower fluid connection 12 and/or the upper fluid connection 13, but the water level gauge glass 10 is preferably arranged above at least some of the upper ends 7 of the receiver tubes 6.

The upper part of the solar radiation receiver 1 including the upper ends 7 of the receiver tubes 6, the water level gauge glass 10 and the camera 11 are shielded off from the reflected solar radiation by means of an isolation arrangement (not shown) in order to prevent excessive heating of those parts, which are not water cooled during operation of the solar radiation receiver 1. The exposed parts of the receiver tubes 6 are filled with water or a mixture of water and steam, and the internal phase change of the water will cool the receiver tubes 6.

In the shown embodiment of the invention, a separation distance D of at least 1.5 meters, such as at least 2.5 meter between the steam drum 2 and the lower vessel 15 is provided in the longitudinal direction L of the receiver 1. This separation provides two advantages to the solar radiation receiver 1. One is that the amount of water present in the solar radiation receiver 1 during operation is reduced as compared to a single drum extending throughout the whole of the central enclosure 9 as is known from the prior art, e.g. from US patent application No. US 2013/047610, another is that the amount of steel needed for manufacturing the drum and connection between the upper ends 7 and the lower ends 8 of the receiver tubes 6 is reduced, which together reduces the mass of the solar radiation receiver 1 during operation and thereby reduces the requirements of the tower 23 supporting the solar radiation receiver 1 while the reduced amount of steel reduces the manufacturing costs of the solar radiation receiver. A steam outlet pipe 19 is arranged from the steam receiving cavity 5 of the steam drum 2 extending inside the downcomer pipe (17, so that the generated steam exits the solar radiation receiver 1 at the bottom part thereof and is kept heated by the water streaming from the steam receiving cavity 5 and into the lower vessel 15, which is at or very near the boiling temperature of the water.

In operation of a solar energy system 21 for direct generation of steam including a solar radiation receiver 1 according to the present invention, the solar radiation receiver 1 is placed on top of a tower 23 as shown in Fig. 3 at typically approximately 30 meter above the ground. A plurality of motor controlled mirrors 22 on or near the ground are surrounding the tower 23 and the position of the mirrors 22 are controlled to reflect solar radiation onto the solar radiation receiver 1 from all sides, i.e. 360° around the tower 23. This type of solar energy systems 21 is well- known in the art, except for the solar radiation receiver 1 according to the present invention.

The solar radiation receiver 1 operates typically at a pressure of about 35 bar at which water has a boiling temperature of 242.5 °C. However, higher and lower pressures and corresponding boiling temperatures may be envisaged for solar radiation receivers 1 according to the present invention.

In use of the solar energy system 21 including a solar radiation receiver 1 according to the present invention, the steam drum 2 must be filled with water to the normal water level 14 of the steam drum 2 in order to ensure that the receiver tubes 2 are cooled by the phase change of the water. The water level is monitored hydrostatically by two separate pressure differential transmitters (not shown) in order to provide redundancy and the output is employed for controlling the inflow of feed water into the steam drum 2 via the feed water pipe 24. For safety, the water level gauge glass 10 is monitored by means of the camera 11 and an automated or operator-based remote monitoring of the operation of the solar energy system 21.

The solar radiation concentrated and reflected by the mirrors 22 onto all sides of the solar radiation receiver 1 heats the receiver tubes 6 and raises the temperature of the water inside of them to a point where a phase change takes place at the boiling temperature of the pressurized water. The steam will due to its buoyancy move upwards in the receiver tubes 6 and into the steam receiving cavity 5 of the steam drum 2, and water will by natural circulation be supplied into the lower end 8 of the receiver tubes 6 from the cavity 5 of the steam drum 2 via the downcomer pipe 17, the downcomer connection 18 and the lower vessel 15.

The saturated steam will be collected at the top of the steam receiving cavity 5, which may be equipped with an arrangement (not shown) for removing liquid droplets from the steam before it leaves the steam receiving cavity 5 by means of the steam outlet pipe 19.

List of reference numerals

1 Solar radiation receiver

2 Steam drum

3 Openings in steam drum

4 Safety valve

5 Steam receiving cavity

6 Receiver tube

7 Upper end of receiver tube

8 Lower end of receiver tube

9 Central enclosure

10 Water level gauge glass

11 Camera

12 Lower fluid connection

13 Upper fluid connection

14 Normal water level of steam drum

15 Lower vessel

16 Cavity for water

17 Downcomer pipe

18 Downcomer connection

19 Steam outlet pipe

20 Internal through-opening

21 Solar energy system

22 Mirrors

23 Tower

24 Feed water pipe

L Longitudinal direction of solar radiation receiver

D Minimal distance between steam drum and lower vessel

W Width of through-opening