GB2561154A

GB2561154A - Solar Energy Device

Info

Publication number: GB2561154A
Application number: GB1704652.5A
Authority: GB
Inventors: Kane Hugh; Rhodes Paul
Original assignee: Energy Services Renewables Ltd
Current assignee: Energy Services Renewables Ltd
Priority date: 2017-03-20
Filing date: 2017-03-24
Publication date: 2018-10-10
Also published as: GB201704652D0; GB201704372D0

Abstract

A tube assembly for a high temperature solar collector comprises a sealed tube 10, which may be of non-circular cross section, surrounding a heat exchanger pipe 1, the tube having a generally transparent upper surface 25, which may include lens 28 for focusing sunlight on the heat exchanger pipe, and a focusing reflector or mirror 20. The assembly may include a gas inlet for introducing pressurized gas into the tube to create a positive internal pressure to prevent ingress of dust particles. The tube may be rotatable about its longitudinal axis and supported from beneath by roller bearings 12. Heat loss may be reduced by applying thermal insulation to lower parts of the tube. The assembly may further feature a wash trough 16 which collects cleaning liquid applied to the tube.

Description

(71) Applicant(s):

Energy Services Renewables Limited 50 Stratford Gate, Potters Bar, Hertfordshire, EN6 1PN, United Kingdom (51) INT CL:

F24S 10/40 (2018.01) (56) Documents Cited:

WO 2009/041947 A1 CN 101377357 A US 4011855 A US 20120279554 A1 US 20090260620 A1 (58) Field of Search:

INT CL F24J Other: WPI, EPODOC

F24S 23/30 (2018.01)

WO 1996/011364 A1 US 8479724 B1 US 20140182579 A1 US 20100186733 A1 (72) Inventor(s):

Hugh Kane Paul Rhodes (74) Agent and/or Address for Service:

CSY Herts

Helios Court, 1 Bishop Square, Hatfield, HERTFORDSHIRE, AL10 9NE, United Kingdom (54) Title of the Invention: Solar Energy Device

Abstract Title: High temperature solar collector assembly comprising heat exchanger pipe surrounded by sealed tube with reflector (57) A tube assembly for a high temperature solar collector comprises a sealed tube 10, which may be of non-circular cross section, surrounding a heat exchanger pipe 1, the tube having a generally transparent upper surface 25, which may include lens 28 for focusing sunlight on the heat exchanger pipe, and a focusing reflector or mirror 20. The assembly may include a gas inlet for introducing pressurized gas into the tube to create a positive internal pressure to prevent ingress of dust particles. The tube may be rotatable about its longitudinal axis and supported from beneath by roller bearings 12. Heat loss may be reduced by applying thermal insulation to lower parts of the tube. The assembly may further feature a wash trough 16 which collects cleaning liquid applied to the tube.

Approx 3000

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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1406 18

Figure 6B

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Figure 2

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Figure 3

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Figure 4

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Figure 5

Solar Thermal Energy Device

This invention relates to a high temperature collector arrangement for solar energy collection.

Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy or electrical energy for use in industry, and in the residential and commercial sectors.

Solar thermal collectors are generally classified as low, medium, or high-temperature collectors. Low-temperature collectors are flat plates directed generally at a midday sun positon and incorporating a convoluted set of heat exchanger pipes with some form of backing substrate. These might for example be used to heat a swimming pool. Mediumtemperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. High temperature applications use some form of (Concentrated Solar Power) system and the temperature is increased by very large flat or parabolic mirror area arrays which in turn means a larger equipment footprint.

High-temperature collectors concentrate sunlight onto the heat exchanger elements, using mirrors or lenses and are generally used for fulfilling heat requirements up to 600 deg CI 20 bar pressure for industrial processes, and for electric power production. Two categories of high temperature collectors include Concentrated Solar Thermal (CST) for fulfilling heat requirements in industries, and Concentrated Solar Power (CSP) when the heat collected is used for power generation.

Figure 1 shows a typical prior art arrangement for a concentrated solar thermal collector using, a plurality of open trough, parabolic mirrors 2, which reflect and concentrate solar energy on to an absorber / steam pipe 4. This type of arrangement is also shown and described in US 2009/0173338 A1.

This arrangement is widely used around the world. However, there are some significant problems in operating and maintaining this arrangement. For example, the mirrors are exposed to wind which causes distortion and therefore reduced efficiency, the mirrors are exposed to dirt and dust which requires regular cleaning in order to maintain efficiency and the mirrors are exposed to abrasion from large dust particles which permanently reduces efficiency.

In practice, such arrangements require regular replacement of the mirrors and suffer from other problems which are explained below.

A prior art solution to this problem is to enclose the array of trough mirrors in a glass building “greenhouse”, which are highly inefficient at light/heat transmission and are subject to wind loading and sand erosion in themselves. Also, sand loading could prove catastrophic to the greenhouses in sandstorm conditions. In practice, prior art systems cannot operationally and in extreme cases, physically, survive extreme weather which is not unusual in the areas of operation such as deserts.

According to a first aspect, the invention provides a tube assembly for a high temperature solar collector comprising a sealed tube surrounding a heat exchanger pipe, the tube having a generally transparent upper surface and a focussing reflector inside the tube and located behind the pipe for focussing sunlight on the heat exchanger pipe.

Thus the invention advantageously takes the parabolic mirrors and absorber pipe components and fits them inside, sealed, steel and glass tubes. The tubes are individual units typically of 3 metre diameter and 4 metre length but may be sized according to heat requirement. The size quoted is the maximum size for easy handling but is not a maximum. The tubes, mirrors and pipe are supported on rigid steel pipe supports. The whole arrangement rotates to track the sun and constantly align the reflector.

Advantageously, the sealed tube does require cleaning after dust storms but the simple tube profile can be cleaned by standard auto-wash systems incorporating wash water collection and recycling.

Typically, as the tubes are produced as units, the system is scalable to meet the needs of a wide range of projects. Each Tube Unit is, for example, capable of producing steam approx. 37.21kW -126,961 BtuperTube.

For context, 600 tubes of 1 to 3.2 metres dia x 4.2 metres long, would produce approx.

150 tonnes Steam per day. Steam Injection into heavy oil fields is on the increase, with significant investments being made It is used to maximise oil recovery and extend the asset life of the oil field. Thus there is a commercial need for efficient ways of producing such steam.

Steam for many other high temperature to medium temperature industrial applications is required which is normally provided by heating via single, or a combination of, fossil fuel sources. This invention provides a solution to industries which neither have access to, or can afford long term supply and cost of fossil fuels.

The tubes of the present invention are very compact and they typically provide the highest Steam Production per unit of land, of all current Solar Thermal Designs.

Embodiments of the invention will now be described by way of example and with reference to the drawings in which :Figure 2 is an elevation of a single tube of an array;

Figure 3 is a section along line A-A of Figure 2, of a tube of a first embodiment Figure 4 is a schematic section of a tube;

Figure 5 is a section along line A-A of Figure 2, of a tube of a second embodiment;

Figure 6A is a schematic view of a prior art parabolic trough mirror array; and Figure 6B is a schematic view of a tube array.

With reference to Figures 2, 3 and 4, a first embodiment of a high temperature collector arrangement for solar energy collection comprises a plurality of metal (typically steel) transparent (typically glass) tubes 10, each typically 1 to 3.2 metre dia x 4.2 metres long, although other lengths and diameters will be envisaged by the skilled person and service requirements. These are arranged in an array in an area which will be exposed to sunlight.

Each tube 10 is fixed around a, continuous heat conductive (typically steel) pipe 1. The pipe 1 typically contains a medium such as oil, gas or feed water (in a gas and oil production context) which is heated by the solar energy to suit various applications or is turned into steam for industrial applications. The pipe 1 may be darkened or blackened on its exterior surface, to improve energy absorption, for example, by an anodising process.

Behind the pipe 1 a focussing mirror, or several such mirrors 20, is arranged to reflect sunlight entering the tube from above, back onto the pipe 1. This increases the energy density of the sunlight which impinges on the pipe.

The tube 10 is sealed to protect the internal parts from dirt and sand which can cause abrasion and thus lower the efficiency of energy capture. This represents an improved feature compared to conventional Trough Solar Concentration Systems which have to be cleaned on a regular basis and suffer deterioration of mirror quality.

The tubes 10 preferably have a pressurised clean gas (typically air) feed to their interior space, to create a small positive internal air pressure to prevent ingress of small dust particles. This further represents an improved feature compared to conventional trough solar concentration systems.

The tubes 10 are preferably supported well above ground level, for example at 3 metres high, to avoid large, abrasive, sand/dirt particles and sand build up, e.g., dunes which appear on the sides of conventional glasshouses. This not only helps keep the view of the sun clear but also avoids the risk of a glasshouse being damaged or destroyed during sandstorms as in the prior art. This represents an improved feature compared to conventional trough solar concentration Systems which are situated close to ground level and suffer abrasion of the mirrors. This is a recognised issue with open trough systems as replacement of mirrors and mirror maintenance is a huge maintenance cost rarely mentioned at project commencement.

The upper section of the tube 10 has transparent sections 25 extending substantially along the whole length of the tube 10. This allows sunlight to pass through and on to the steam pipe 1 and past the steam pipe onto the mirrors 20 and reflected and focussed back onto the pipe 1. This represents a unique system of using multiple enclosed parabolic mirrors to concentrate heat on to the black anodised pipe 1.

In the first embodiment, the parabolic mirror 20 is fixed in position in the tube.. Accordingly, the tube 10 is preferably mounted on rollers 12 so that the pipe can be rotate about is longitudinal axis to follow the sun. As the tube is rotated, this increases pipe life cycle by heating different parts of the pipe over its circumference, during the day cycle; prior art systems only heat one side of the pipe.

Figure 5 shows an alternative embodiment having a movable parabolic mirror arrangement 20’ which may be moved by a motor which may be power by a photovoltaic solar convertor. This means that the tube 10 does not need to be rotated to follow the sun but incurs greater installation and manufacturing costs in mirrors 20’. Where the fixed configuration of Figure 5 is adopted, rotation of the tube 10 is not necessary, and the tube might have a noncircular cross section e.g. of a triangular section to save manufacturing costs and material as suits the application, space and wind conditions etc.

The embodiment of Figure 5 also discloses the use of focusing lenses 28 in the upper surface of the tube 10. These may be used in combination with the focussing reflector 20 or 20’. As drawn in Figure 5, the lenses cover enough of the upper surface of the tube to accept light over substantially the whole arc of the sun. A narrower arc of lenses may be accommodated, without loss of efficiency, by rotation of the tube in the same way as shown and described in connection with Figure 4.

Preferably, the multiple tube assemblies 10 are fixed to the steam pipe 1. The whole assemblies, including the pipe, are then rotated to track the sun’s movement. This reduces the number of moving parts and reduces the cost of Capital and Maintenance. This is a unique feature as prior art systems rotate their mirrors only.

Preferably, the lower section of the tube 10 is thermally insulated which significantly reduces heat loss to the ambient environment. This insulation may be located between the back of the mirror 20 and the lower inner surface 22 of the tube 10 which helps support the mirror 20. Insulation may also be applied to pipework which interconnect the tubes 10 Heat retention allows the system to heat up faster and retain maximum heat throughout the daytime heating cycle and keep warm throughout the night speeding up the heating cycle when the sun rises. Existing solar concentration trough systems do not use Insulation at the reflectors.

Preferably, the tube shape is designed to minimise wind distortion. To achieve this, the tube 10 is designed close to symmetrical around the pipe horizontal axis to evenly deflect wind above and below the tube. This avoids any significant air pressure differential above and below the pipe during winds which otherwise might cause distortion and/or stress on the tube 10 and pipe 1.

The tube 10 is significantly more compact than mainstream mirror trough designs and hence can be much closer packed whilst avoiding shadow and reducing the overall project foot print. With reference to Figures 6A and 6B, conventional parabolic troughs are typically 6 metres or larger in diameter. When the sun is low in the sky, the rows of large mirrors cast shadow over the next row preventing solar energy capture and dictating wide spacing of the troughs.

The tube of the present invention can be as small as 1 metre in diameter where heat requirements and service are determined. Thus the tubes can be significantly closer spaced than in prior art arrangements and this will significantly reduce space requirements whilst allowing similar steam generating capacity and avoiding the shadowing problem of the prior art. This is important as thermal heat transfer efficiency as best currently Is 60% whereas 87% efficiency is attainable with the proposed system.

Typically, the tube arrangements incorporate ‘Composite’ (for example, glass reinforced plastic) materials for supports, Access Platforms etc. This significantly reduces maintenance costs.

The tube design is capable of operating with recycled steam water by being able to recycle/reroute steam to upstream inlet and flushing the water/steam pipe.

Preferably, the tube 10 is stiffened by frames, which are preferably also mirror coated and preferably internal, light, and steel.

The arrangement preferably also includes an automatic wash/dry system which cleans the tube 10, and sections 25 in particular, preferably multiple rows at a time, by providing outlets to flush water or other cleaning liquid, over the top of the tube 10. Cleaning is usually carried out at night but at any time following dust storms. The arrangement is sized to allow the whole solar tube layout to be cleaned within one night. Wash water is collected by a water trough 16 for filtering and recycling the water. The water trough 16 has hinged closer flaps 18 along each side to prevent dust ingress when not in use.

Claims

1. A tube assembly for a high temperature solar collector comprising a sealed tube surrounding a heat exchanger pipe, the tube having a generally transparent upper surface and a focussing reflector inside the tube and located behind the pipe for focussing sunlight on the heat exchanger pipe.

2. An assembly according to claim 1, further including a gas inlet for introducing pressurised gas into the tube.

3. An assembly according to claim 1 or claim 2, further including a support cradle which supports the tube above ground at a height of at least 3 metres and more preferably 3 metres .

4. An assembly according to any preceding claim including rotation means for causing the tube to rotate about its longitudinal axis.

5. An assembly according to claim 4 wherein the rotation means includes a plurality of longitudinal rollers which support the tube from beneath and act as roller bearings during tube rotation.

6. An assembly according to any preceding claim which has a generally symmetrical profile about a horizontal plane such that cross-winds generate substantially no pressure difference above and below the tube.

7. An assembly according to any preceding claim, further including thermal insulation applied to lower parts of the tube.

8. An assembly according to any preceding claim including a wash trough beneath the tube which collect cleaning liquid applied to the generally transparent upper surface as it runs down the sides of the tube and drips off the bottom of the tube.

9. An assembly according to any preceding claim including a focussing lens in the transparent upper surface arranged to focus sunlight on the heat exchanger pipe.

10. An assembly according to claim 9, wherein the lens covers enough of the upper surface to be in sunlight through a substantial part of daylight time, without moving the tube.

5

11. An assembly according to any preceding claim wherein the tube has a non-circular cross-section.

Intellectual

Property

Office

Application No: GB1704652.5 Examiner: Mr Alastair Cort