WO2023079282A1

WO2023079282A1 - Solar heating system and process

Info

Publication number: WO2023079282A1
Application number: PCT/GB2022/052768
Authority: WO
Inventors: Gediz KARACA
Original assignee: Odqa Renewable Energy Technologies Ltd
Priority date: 2021-11-03
Filing date: 2022-11-03
Publication date: 2023-05-11
Also published as: GB202115825D0

Abstract

A process and associated system for providing thermal energy to a product using a working fluid. The process includes directing solar radiation onto a solar receiver to form a heated solar receiver; transferring heat from the heated solar receiver to the working fluid to form a solar-heated working fluid; passing the solar-heated working fluid to a rotary dryer or rotary kiln housing a product; and heating the product housed in the rotary dryer or rotary kiln using the solar-heated working fluid. The process may be carried out during periods of available sunlight.

Description

SOLAR HEATING SYSTEM AND PROCESS

INTRODUCTION

[0001 ] The present invention relates to solar dryers, solar kilns and methods of heating products in rotary heating systems such as dryers and/or kilns via solar radiation. More particularly, the present invention relates to processes for heating rotary dryers and/or rotary kilns using solar radiation.

[0002] Dryers and kilns are traditionally used to heat products to a desired temperature to instigate a change in said products. Dryers are generally used to drive water, moisture, or other volatile species from products residing in the dryer. Kilns typically operate at higher temperatures than dryers and so may initiate thermally induced chemical reactions in the products inside the kiln while also driving off water, moisture, and volatile species in the manner of a dryer. The chemical reactions carried out in a kiln usually result in a chemical or physiochemical modification to the product. Examples of processes that may be carried out in kilns, and some dryers, include drying, hardening, sintering, calcining, annealing, ageing, and the like.

[0003] Rotary dryers and kilns are used in industry and usually include a rotating hollow structure through which products or material flow. The rotating nature of the structure often serves to drive or direct the flow of products or material passing through the structure. The rotating structure may be heated directly to provide the drying or kilning effect. Additionally, or alternatively, heated gas may be passed through the rotating structure to heat the product. The heated gas may pass through a portion of the rotating structure which houses the product or material such that the heated gas is in direct contact with the product or material. Some dryer and kiln designs may pass heated gas through passages or conduits in the shell of the rotating structure to heat the shell to a desired temperature.

[0004] Traditionally, the thermal energy or heat energy required for dryer and kiln processes has been derived from combustion of fuel stocks such as natural gas, coal, wood, hydrocarbon-based fuels, or similar energy rich materials. Natural gas burner technology is the dominant source of thermal energy in industrial scale commercial rotary dryer and kiln systems with many systems using a burner that fires directly into the hollow portion of the rotary system through which the products or material to be heated are passed. The use of combustion techniques involving hydrocarbonaceous fuels is increasingly undesirable for a number of reasons. Firstly, the combustion of traditional fuels is not considered environmentally responsible due to the production of CO2, particulates, and other by-products as a result of the combustion process. Similarly, the production and transportation of such fuels also carries an environmental cost. On a more practical level, industrial processes reliant on such fuels require the necessary infrastructure in proximity to the drying or kilning process in order to maintain steady operation. This may limit the viable locations for industrial drying or kilning processes or necessitate a complex logistics network to bring fuel and/or the raw product materials from distant areas to the dryer or kiln. There is therefore a desire for alternative dryers, kilns, and associated processes that address the shortcomings of some traditional dryer and kiln systems. The inventors of the present invention have appreciated that high energy solar technology may be utilised to provide the thermal energy required to operate a rotary dryer or kiln to advantageous effect.

[0005] According to one aspect of the invention, there is provided a process for providing thermal energy to a product using a working fluid. The process includes: (i) directing solar radiation onto a solar receiver to form a heated solar receiver; (ii) transferring heat from the heated solar receiver to the working fluid to form a solar- heated working fluid; (iii) passing the solar-heated working fluid to a rotary heating system such as a rotary dryer or rotary kiln housing a product; and (iv) heating the product housed in the rotary heating system using the solar-heated working fluid. Steps (i), (ii), (iii) and (iv) are carried out during periods of available sunlight. The process may further include: (I) passing the solar-heated working fluid to a thermal storage system; and (II) transferring heat from the solar-heated working fluid to the thermal storage system to form a heated thermal storage system. The process may further include: (III) transferring heat from the heated thermal storage system to the working fluid to form a storage-heated working fluid; (IV) passing the storage-heated working fluid to the rotary heating system housing the product; and (V) heating the product housed in the rotary heating system using the storage-heated working fluid. The process may further include: (a) using a burner to heat the working fluid to form a burner-heated working fluid; (b) passing the burner-heated working fluid through the rotary heating system housing the product; and (c) heating the product housed in the rotary heating system using the burner-heated working fluid. Steps (a), (b), and (c) may be carried out during periods of low or no sunlight. Steps (III), (IV), and (V) may be carried out during periods of low or no sunlight. The working fluid may be a gas. The working fluid may be air. Transferring heat from the heated solar receiver to the working fluid to form a solar-heated working fluid may increase the temperature of the solar-heated working fluid to 100 °C to 1500 °C. The temperature of the solar-heated working fluid may be increased to under 600°C. The temperature of the solar-heated working fluid may be increased to over 600°C. Transferring heat from the heated thermal storage system to the working fluid to form a storage-heated working fluid may increase the temperature of the storage-heated working fluid to 100 °C to 1500 °C. The temperature of the storage-heated working fluid may be increased to under 600°C. The temperature of the storage-heated working fluid may be increased to over 600°C. Using a burner to heat the working fluid to form a burner-heated working fluid may increase the temperature of the burner-heated working fluid to 100 °C to 1500 °C. The temperature of the burner-heated working fluid may be increased to under 600°C. The temperature of the burner-heated working fluid may be increased to over 600°C. Heating the product may include increasing the temperature of the product to over 100 °C. The temperature of the product may be increased to a temperature of, or a temperature in excess of 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, or 1500 °C. Heating the product may include drying the product and/or initiating a chemical and/or physiochemical reaction in the product to form a reacted product. The burner, where present, may combust a fuel. The fuel may include natural gas. The fuel may include hydrogen gas. The process may include removing water and/or a volatile substance from the working fluid. The product may be a powder, granular product, dust, particulate, pulverant, or any combination thereof.

[0006] According to another aspect of the invention, there is provided a solar thermal system for heating one or more products using the processes as descried herein. The system includes a solar receiver configured to: convert incident solar radiation to heat energy; and heat working fluid using the heat energy. The system further includes a rotary heating system, and a working fluid system configured to flow heated working fluid from the solar receiver to the rotary heating system. The rotary heating system may be a rotary dryer; or a rotary kiln. The solar thermal system may include a thermal storage system. The working fluid system may be configured to flow working fluid from the solar receiver and/or the rotary heating system to the thermal storage system. The rotary heating system may be substantially cylindrical in shape. The rotary heating system may include a hollow inner compartment through which product flows when the solar thermal system is in use. The rotary heating system may include one or more louvres, slates, bars, beams, or regions of elevated topography configured to drive the product through the rotary heating system when the system is in use. The rotary heating system may include a hollow shell configured to provide a flow passage for working fluid through the shell when the rotary heating system is in use. The solar thermal system may include an optical system configured to direct incident sunlight onto the solar receiver. The optical system may include one or more heliostats.

[0007] According to a further aspect of the invention, there is provided a process for heating a product in a rotary dryer or rotary kiln. The process includes:(i) directing solar radiation at a concentration of 2000 or more onto a solar receiver to form a heated solar receiver; (ii) transferring heat from the heated solar receiver to air as a working fluid to form a solar-heated working fluid at a temperature of 600°C or more; (iii) passing the solar-heated working fluid to a rotary dryer or rotary kiln; and (iv) heating the product housed in the rotary dryer or rotary kiln to a temperature of 550°C or more using the solar-heated working fluid. In any aspect of the invention described herein, the solar receiver may be a stationary solar receiver. In any aspect of the invention described here, the solar receiver may include a rotor.

[0008] These and other aspects of the present invention will be apparent to one skilled in the art with the benefit of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be described with reference to the following drawings, in which: Figure 1A shows a schematic representation of a solar thermal system including a rotary heating system;

Figure 1 B shows a schematic representation of an alternative solar thermal system;

Figure 2 shows a schematic representation of a solar thermal system including a burner;

Figure 3 shows a schematic representation of a solar thermal system including a thermal storage system;

Figure 4 shows a process for providing thermal energy to a product using a working fluid;

Figure 5 shows an example of a solar rotor that may be used as part of a solar receiver in the solar thermal systems described herein; and

Figure 6 shows an example of another solar rotor that may be used as part of a solar receiver in the solar thermal systems described herein.

DETAILED DESCRIPTION

[0010] Many products and materials require heating during manufacturing or processing. The heating of a product or material requires energy that will ultimately be provided to the product or material in the form of heat. A solar thermal system is one system by which energy may be harnessed and used to heat one or more products using a rotary heating system. The solar thermal systems described herein generally include a solar receiver, a rotary heating system and a working fluid system. The solar thermal systems described herein may derive the majority of, or all of, the thermal energy or heat energy used to heat the rotary heating system and/or products passing therethrough from solar radiation, at least during times of sunlight. The terms heat energy and thermal energy are used interchangeably throughout and should be considered to be analogous terms. The detailed description which follows will discuss the use of solar thermal systems in the heating and drying of various products. However, the person skilled in the art will, with the benefit of this disclosure, appreciate that the systems and processes described herein are equally applicable to the production of other products or the processing of other materials not explicitly recited.

[0011 ] The solar thermal systems as described herein generally include a solar receiver. The solar receiver may form part of a concentrated solar system. In operation, solar radiation is directed, focussed, and/or concentrated upon the solar receiver to convert solar radiation into heat energy at the solar receiver. When the solar receiver is part of a concentrated solar system, the concentrated solar system may use a series of reflectors such as heliostats including mirrors and/or lenses to concentrate the sunlight incident on large surface areas onto the smaller area of the solar receiver from which the energy may be harnessed. Multiple heliostats may be present and formed into cooperative grouped arrangements known as ‘banks’. The banks of heliostats may be positioned in proximity to a tower or mast supporting the solar receiver. The tower or mast may be any suitable height suffice that the heliostats have an uninterrupted view of the solar receiver to allow incident solar radiation to be directed from the heliostat to the solar receiver. The solar tower or mast may be freestanding, that is distinct and separate from other structures, buildings, or the like. Alternatively, the solar tower or mast may be incorporated into, or form part of, another structure or building such that the solar receiver is positioned towards the top of the building or structure. The tower or mast may be 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, or more in height. The heliostats may be positioned such that they will reflect incident solar radiation towards the solar receiver which, in turn, absorbs the energy as heat energy. The heat energy may then be transferred to a working fluid in contact or in proximity to the solar receiver for further use. The solar receiver may heat the working fluid to a temperature of over 100 °C. For example, the solar receiver may increase the temperature of the working fluid to a temperature of 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, or 1500 °C. The working fluid may be heated to within a temperature range of about 150 °C to about 1500 °C, about 200 °C to about 1500 °C, about 250 °C to about 1500 °C, about 300 °C to about 1500 °C, about 350 °C to about 1500 °C, about 400 °C to about 1500 °C, about 450 °C to about 1500 °C, about 500 °C to about 1500 °C, about 600 °C to about 1500 °C, about 700 °C to about 1500 °C, about 800 °C to about 1500 °C, about 800 °C to about 1500 °C, about 900 °C to about 1500 °C, about 1000 °C to about 1500 °C, about 1100 °C to about 1500 °C, about 1200 °C to about 1500 °C, about 1300 °C to about 1500 °C, or about 1400 °C to about 1500 °C. The working fluid may be heated to a temperature equal to, or in excess of, about 150 °C, about 200 °C, about 250 °C, about 300 °C, about 350 °C, about 400 °C, about 450 °C, about 500 °C, about 600 °C, about 650 °C, about 700 °C, about 750 °C, about 800 °C, about 850 °C, about 900 °C, about 950 °C, about 1000 °C, about 1050 °C, about 1100 °C, about 1150 °C, about 1200 °C, about 1250 °C, about 1300 °C, about 1350 °C, about 1400 °C, about 1450 °C, about 1500 °C, or more than 1500 °C. In some examples, the working fluid may be heated solely by the heated solar receiver. In other examples, the working fluid may be heated by the heated solar receiver and by directing the concentrated solar radiation onto and/or through the working fluid before it is absorbed by a portion of the solar receiver. In examples where the working fluid is heated solely by the solar receiver, the working fluid may not be heated by any other means prior to the working fluid being passed to a rotary heating system as described herein. However, in some examples, additional heating means may be used to heat the working fluid such as a burner, heater, radiator, or the like. The heliostats directing solar radiation onto the solar receiver may be fitted with a tracking system that allows them to adjust alignment relative to the position of the sun to ensure that the incident light continues to be directed towards the solar receiver throughout the day.

[0012] The solar receiver may be distinct and/or separate from other components of the solar thermal system. For example, the solar receiver may be distinct and/or separate from the rotary heating system such that the solar receiver and rotary heating system are separated by a distance. In an example, the solar receiver may not abut, not form part of, or not be integral to the rotary heating system. The use of a distinct or separate solar receiver may be advantageous as it allows the portion of the system upon which solar energy is concentrated to be set apart from other portions of the system that may not have a high tolerance to heat or light energy. Solar radiation and light focussed upon the solar receiver may therefore be directed via heliostats, optical arrangements, or the like such that the focussed or concentrated light is not directed towards the rotary heating system directly. In this manner, the exterior of the rotary heating system, the interior of the rotary heating system, and/or any product present in or flowing through the rotary heating system may not receive concentrated solar radiation when the solar thermal system is in use.

[0013] The concentration of incident solar radiation upon the solar receiver is referred to as the light concentration factor, c. The light concentration factor is defined as the thermal flux (W/m²) that is incident on at least a portion of the solar receiver, divided by the corresponding thermal flux arriving at the concentrated solar system from the sun (also known as the ‘insolation’). The concentration factor has a direct effect on the efficiency of energy collection and it is a sensible intent for a designer to try to maximise c. Greater values of c represent increased energy density which in turn represents a greater potential energy resource that may be harnessed by the solar receiver. The value of c in a concentrated solar system is influenced by the total surface area of the heliostats and/or optical elements which direct incident solar radiation to the solar receiver. Increasing the c value of a concentrated solar system will induce higher temperatures in the receiver medium. The maximum value of c at which a receiver can operate is thus limited by the thermal tolerances of the receiver and its materials. For example, temperatures in excess of 1000°C may be achieved as the value of c increases. The solar receiver used in the solar thermal system may be configured to operate at a c value of 50 or more. The solar receiver used in the solar thermal system may therefore be configured to operate at a c value of 75 or more, 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, 600 or more, 700 or more, 800 or more, 900 or more, 1000 or more, 1100 or more, 1200 or more, 1300 or more, 1400 or more, 1500 or more, 1600 or more, 1700 or more, 1800 or more, 1900 or more, 2000 or more, 2100 or more, 2200 or more, 2300 or more, 2400 or more, 2500 or more, 2600 or more, 2700 or more, 2800 or more, 2900 or more,

3000 or more, 3100 or more, 3200 or more, 3300 or more, 3400 or more, 3500 or more, 3600 or more, 3700 or more, 3800 or more, 3900 or more, 4000 or more, 4500 or more, 5000 or more, 5500 or more, 6000 or more, 6500 or more, 7000 or more,

7500 or more, 8000 or more, 8500 or more, 9000 or more, 9500 or more, 10000 or more, 10500 or more, 11000 or more, 11500 or more, 12000 or more, 12500 or more, 13000 or more, 13500 or more, 14000 or more, 14500 or more, 15000 or more, 15500 or more, 16000 or more, 16500 or more, 17000 or more, 17500 or more, 18000 or more, 18500 or more, 19000 or more, 19500 or more, or 20000 or more.

[0014] The solar receiver may be a solid, liquid or gas type receiver depending upon the solar radiation-absorbing medium of the receiver. The solar receiver will store heat energy in the solid, liquid, or gas of the receiver and transfer the heat energy to a working fluid. The solar receiver may transfer heat energy to a working fluid via conduction and/or convection. In liquid or gas solar receivers, the fluid receiving the solar radiation may also be utilised as the working fluid. The absorbing surface of the receiver may have a high absorptance to enable absorption of as great a proportion of the incident solar radiation as possible. To allow the solar receiver to operate at high values of c, the solar receiver may be at least partially formed from, and/or at least partly coated with, a high temperature refractive material. The properties of such a material may include a high refractive index, high solar absorptance, high thermal tolerance, and high strength resistance. For example, it may be advantageous to utilise a material with a solar absorptance in excess of 0.5. Preferably the material may have a solar absorptance in excess of 0.5 such as 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90 or 0.95. The material may have a solar absorptance in excess of 0.95. Suitable materials for use in the solar receiver include ceramics, cermets, zirconia, zirconium species, tantalum species, borosilicates, silicon species, carbon-based materials, metals, metal oxides, alloys, and any other suitable material alone or in combination. Materials which may be used to at least partly coat the solar receiver include Pyromark 2500™ (available from Tempil® Corporation); zirconium bromide; zirconium oxide, and/or its zirconium cermet; chromium oxide, and/or its nickel or chromium cermets; aluminium oxide, and/or its nickel, molybdenum and tungsten cermets; aluminium nitride, and/or its titanium cermet; silicon carbide; or any combination thereof.

[0015] The solar receiver may be any suitable type of solar receiver. For example, the solar receiver may be a stationary solar receiver. A stationary solar receiver is one in which the absorber does not move, or substantially move, during operation. In other examples, the solar receiver may include a solid rotor. In an example, the absorber of the solar receiver may optionally consist of one or more solid rotors. In such examples, the solar receiver may not include solar absorbers that are not rotors or absorbers which to not at least partially rotate during steady-state operation. The use of a solid rotor in a solar receiver may allow higher values of c to be employed by the solar thermal system as rotation of the rotor may prevent any particular portion of the solar rotor from becoming overly hot to the point of failure when high concentrations of solar radiation are focussed upon the rotor. Where the solar receiver includes a rotor, the rotor may be configured to rotate at speeds of between 0.1 revolutions per minute (rpm) and 20,000 rpm. Preferably, the rotor may be configured to rotate at speeds of between 25 rpm and 10,000 rpm. More preferably, the rotor may be configured to rotate at between speeds of 60 rpm and 6,000 rpm. The rotor movement and/or rotation of the rotor may be driven by any suitable driving means such as a motor, drive belt and/or drive wheel arrangement. In practice, the rotor may move from a first position to a second positon, and may move in a circuit, a closed loop, rotate fully through 360° or rotate partly through rotation less than 360°. The movement or rotational direction of the rotor may be constant, or alternatively, the rotor may change movement or rotational direction. As such, the rotor may move or rotate back and forward to rock between two end positions that may be around a rotational axis. The rotor may move and/or rotate in a single two dimensional plane, or may move and/or rotate through multiple planes in the course of movement and/or rotation. It may be advantageous to rotate the rotor in a constant direction through 360 degree rotation in a single two dimensional plane. In operation, the speed of movement of the rotor may be manually adjustable by an operator. Advantageously, the movement speed of the rotor may additionally, or independently, be controlled automatically in response to measurements of incident energy, system temperature or any other suitable measurement. For example, the rotational speed of a rotor may be increased in response to an increased density of solar energy incident upon the rotor and decreased in response to a decreased density of solar energy incident upon the rotor, for example, to maintain an approximately constant maximum temperature experienced by any part of the rotor. Alternatively, or additionally, the rotational speed of the rotor may be increased or decreased in response to an increase or decrease in temperature of one or more components of the solar receiver or concentrated solar system. In practice, the speed of the rotor may be adjusted in response to one or more measurements made by one or more sensors communicably coupled to a control system. Movement of the rotor at high speeds reduces the duration of time across which any particular portion of the rotor is exposed to high concentrations of solar radiation and allows management of temperature and limitation of the material’s thermal degradation, as required. Automatic adjustment of the speed of the rotor may be achieved using a computer communicably coupled to one or more sensors.

[0016] In solar thermal systems where the solar receiver is a solar rotor, a movement device at least partly rotates the rotor. It may be advantageous to move the rotor such that it does not move, or does not substantially move, along the axis of rotation. In such examples, the movement device does not move, or does not substantially move the rotor in a direction along the axis of rotation. Therefore, in some implementations, the rotor will rotate without movement along the axis of rotation. Movement of the rotor in a solely rotational manner may be advantageous due to the comparable mechanical simplicity of the motion when compared to motion involving rotation and translation along both directions of the rotational axis. Rotating the rotor while also translating the rotor along the axis may limit the maximum speed at which the rotor can be rotated and/or may impart additional or increased mechanical stresses upon the rotor, the solar receiver, and/or its associated systems. Were the rotational speed of the rotor to be limited in this manner, the solar receiver’s ability to carry heat away from the area of incident solar radiation would be subsequently reduced. This reduction may, in turn, cause the rotor to increase in maximum operating temperature which may reduce the lifespan of the materials and increases the risk that the device fails under high concentrations of solar radiation. Movement of the rotor in a solely or substantially solely rotational manner may therefore allow for the use of greater rotational speeds and increased concentrations of solar radiation.

[0017] The portion of the solar receiver that absorbs solar radiation when the solar receiver is in use may be any suitable size depending upon the intended application. A solar tower in a high temperature and high throughput solar kilning process will require a larger solar receiver than a comparable receiver to be employed on a small localised drying system. In practice, the size of the absorbing portion of the solar receiver is determined by the capacity requirement of the installation in which it is housed and the capability of the working fluid and heat transfer system by which it is accompanied. In examples where the solar receiver is a solid rotor, the rotor may have a diameter, width, length or dimension of between 1 cm and 10000 cm. Preferably, the rotor may have a diameter and/or length of between 50 cm and 2000 cm. In other preferable examples, the rotor may have a diameter and/or length of between 2 cm and 500 cm. In additional preferable examples, the rotor may have a diameter and/or length of between 5 cm and 300 cm. In one particular example where the solar receiver includes a rotor in a kilning system, the solar receiver may operate at a solar radiation concentration value of 10,000 c using a cylindrical rotor of approximately 35 cm in height and up to 200 cm in diameter.

[0018] In systems where a solar rotor is used, any suitable rotor design may be employed in the solar receiver suffice that light may be directed to one or more surfaces of the rotor such that the rotor becomes heated, and that the rotor may move or rotate such that the heated portion of the rotor may be cooled by exchanging heat between the rotor surface and a suitable working fluid. Consequently, many alternative rotor designs are envisaged. The rotor may be any suitable shape including, but not limited to, cylindrical, discoidal, conical, frustoconical, a shape of irregular crosssection, or any other suitable shape. The rotor may include, be formed from, or formed in part from a plurality of absorbing elements. Absorbing elements may be solid structures with no internal hollows or cavities, may be hollow solid structures such as conduits that allow flow of fluid therethrough, or any other suitable solid element capable of absorbing incident solar radiation in the form of heat. In use, at least a part of each of the plurality of absorbing elements may, where present, absorb incident solar radiation. In an example, the plurality of absorbing elements may include one or more conduits. In this example, at least a portion of the outer surface of the conduits are exposed to incident solar radiation such that the conduits become heated. Working fluid flowing through the interior of the conduit will become heated due to transfer of heat from the internal surface of the conduit to the working fluid. In this example, the fluid system of the solar receiver flows the working fluid through one or more flowpaths in each of the plurality of conduits and the heated working fluid is carried away to be utilised. In another example, the plurality of absorbing elements include one or more solid absorbers with no internal cavities, void space or hollow portions that allow flow of working fluid therethrough. In this example, at least a portion of the outer surface of the absorbers are exposed to incident solar radiation such that the absorber becomes heated. The fluid system flows working fluid across the heated outer surface of each of the plurality of solid absorbers such that heat is transferred from the absorber to the working fluid. The heated working fluid is then carried away to be utilised.

[0019] The solar receivers that may be used in the solar thermal systems described herein may include a single absorbing element or a plurality of absorbing elements. In systems where the solar receiver includes a plurality of absorbing elements, at least a part of each of the plurality of absorbing elements may absorb incident solar radiation in use. The absorbing elements may be arranged such that a first absorbing element of the plurality of absorbing elements at least partially occludes a second absorbing element of the plurality of absorbing elements such that the at least partially occluded portion of the second absorbing element is not exposed to incident solar radiation when the solar receiver is in use. The absorbing elements may be arranged such that a primary absorbing element of the plurality of absorbing elements is exposed to a greater time-averaged flux of solar radiation than a secondary absorbing element of the plurality of absorbing elements. The plurality of absorbing elements may include a near absorbing element and a distal absorbing element, wherein the near absorbing element is positioned proximate to an axis of movement of the solar receiver, where the solar receiver includes such an axis, and the distal absorbing element is positioned distant from the axis of movement of the solar receiver. The plurality of absorbing elements may be arranged such that at least a portion of solar radiation incident upon at least one of the plurality of absorbing elements is reflected or directed towards an absorbing surface of one or more further absorbing elements. At least one of the plurality of the absorbing elements may be formed from a plurality of materials such that the absorbing surface of the at least one of the plurality of absorbing elements has different solar absorption and/or reflection properties across a surface area upon which solar radiation is incident in use. The surface of at least two of the plurality of absorbing elements that absorb incident solar radiation may be formed from materials with different solar absorption and/or reflection properties respectively. At least one of the plurality of absorbing elements may have a surface topography, morphology, or texture different from the surface topography, morphology, or texture of another of the plurality of absorbing elements such that the absorbing elements have different solar absorption and/or reflection properties. The at least a portion of the solar receiver heated by incident solar radiation may include a selective absorption material that selectively absorbs part of the wavelength spectrum of incident solar radiation. A cross-section of at least one of the absorbing elements may be configured to promote transfer of heat to the working fluid from the heated portions of the at least one of the absorbing elements, promote reflection of reflected incident solar radiation reflected from the at least one of the absorbing elements to another absorbing element, and/or promote absorption of incident solar radiation as heat when the solar receiver is in use. The cross-section may be defined as the perimeter shape of a cross-section of at least one of the absorbing elements in a plane coincident, in use, with incident solar radiation. The ratio of a first dimension of the cross-section and a second dimension of the cross-section of the at least one absorbing element may be selected to promote transfer of heat to the working fluid from the heated portions of the at least one of the absorbing elements, promote reflection of reflected incident solar radiation reflected from the at least one of the absorbing elements to another absorbing element, and/or promote absorption of incident solar radiation as heat when the solar receiver is in use. The cross-section of at least one of the absorbing elements may be elliptical in shape, tear-shaped, bullet-shaped, irregular in shape, or any other suitable shape.

[0020] The solar thermal system uses a heated working fluid to heat the products to be processed in the rotary heating system such as a rotary dryer or kiln. The solar thermal system may therefore be configured such that concentrated solar radiation is not used to directly heat the product itself. The use of a solar receiver to heat working fluid in preference to the direct heating of a product with concentrated solar radiation may be advantageous as the temperature to which a product is heated may be better controlled to avoid damage of unintended degradation of the product. In some examples, concentrated solar radiation may not be directed onto the product in the rotary heating system. In some examples, concentrated solar radiation may not be directed onto any portion of the rotary heating system itself. The heat energy collected by the solar receiver is transferred to the working fluid, unless the absorbing medium of the solar receiver is itself the working fluid in which case it may be used directly. The working fluid may be heated by conduction and/or convection by passing over, across, through, or around at least part of the solar receiver which has stored solar radiation as heat energy. The heat energy may be transferred using one or more heat exchangers forming part of the solar receiver and/or working fluid system. Where the solar receiver is a rotor and/or is heated unevenly, the working fluid may flow over, across, through, or around the solar receiver in a counter-current direction. The working fluid may be a liquid or gas. Preferably, the working fluid is a gas. An example of a suitable working fluid is air. In an example, the working fluid may consist of a gas. More particularly, in such an example, heat is transferred from the solar receiver to the rotary heating system via a gaseous working fluid only. In such examples, the working fluid does not include a liquid. In such examples, the working fluid may consist of air. Where the working fluid is a gas, the working fluid may not include a flowable solid such as a power or particulate medium.

[0021 ] The solar thermal system includes a working fluid system configured to flow working fluid from the solar receiver to the rotary heating system to heat products therein. In this manner, working fluid heated by the solar receiver is transferred to the parts of the process, such as the rotary heating system, where its energy may be utilised. The solar receiver may be a distinct and separate component of the solar thermal system. For example, the rotary heating system may be distinct and separate from the rotary heating system such that working fluid heated in the solar receiver must be transferred to the portions of the system where it may be used. The working fluid system may include one or more conduits, pipes, channels, ducts, or similar pathway to direct the working fluid to the desired parts of the solar thermal system. For example, where the working fluid system includes conduits, pipes, channels, ducts, or similar fluid pathways, the working fluid system may provide a means through which heated working fluid can flow from the solar receiver to the rotary heating system. The working fluid system may include a means for driving, flowing, directing, or otherwise moving the working fluid through the working fluid system. The means for driving the working fluid may include one or more fans, compressors, pumps, impellers, any other suitable driving means, or any combination thereof. In one example, the solar thermal system and/or working fluid system may not include a compressor. It may be preferable to avoid the use of compressors to drive working fluid flow due to the general inefficiency of driving fluid via compressor. Where the working fluid system includes a fan, the fan may be on the ‘cold’ side of the process working fluid system. The ‘cold’ side of the working fluid system may be a portion of the working fluid system where the working fluid flowing therethrough is towards the lower end of the range of temperatures experienced by the working fluid during operation. In general, the ‘cold’ side of the process will be the part of the working fluid system prior, or immediately prior to the working fluid reaching the solar receiver. The ‘cold’ side of the process may additionally, or alternatively, be the portion of the working fluid system into which the working fluid flows after it has been used in the process in the rotary heating system such as a rotary dryer or rotary kiln to process one or more products. Positioning the fan in the ‘cold’ side of the working fluid system may extend the life of the fan and prevent thermal distortion, damage, or degradation of the fan materials. The fan may be formed, at least in part, from a thermally resistant material such as ceramic. The working fluid system may be configured such that working fluid flows in an open-loop manner. Additionally, or alternatively, the working fluid may, at times, flow in a closed- loop or circuit. For example, working fluid heated at, or in proximity to, the solar receiver may be directed to heat a product in a rotary heating system before being directed back towards the solar receiver for subsequent re-heating. In this manner, working fluid may be reused and/or recycled throughout the solar thermal system with any residual heat energy present in the working fluid retained after use for heating the product and/or rotary heating system. The working fluid system may operate as a substantially closed-loop system only part of the time. For example, the working fluid system may operate as a substantially closed loop system for a first period of time before opening the system to introduce additional working fluid into the system. In such examples, the working fluid system may be switched between open and substantially closed-loop operation as desired by a user. The working fluid system may include means to remove working fluid from the working fluid system such as a vent, drain, or the like. However, the recycling and/or re-use of working fluid may not be suitable in all applications if impurities or substances carried from the rotary heating system are unsuitable for introduction into conduits, piping, or other components of the system such as the solar receiver. The skilled person, with the benefit of this disclosure, will be able to determine whether working fluid should flow in a closed- or open-loop manner. The working fluid system may include means to introduce working fluid into the working fluid system. Such working fluid may be drawn into the system directly or stored isolated from the working fluid system and then introduced when needed using a control system such as a valve. Where the working fluid is air, additional working fluid may be introduced by drawing air into the system from the atmosphere.

[0022] The solar thermal system includes a rotary heating system. The rotary heating system may be a rotary dryer or rotary kiln. A rotary dryer is a rotating device intended to heat a product in the rotary dryer to a temperature sufficient to drive off water, moisture, and/or volatile substances present in a product. A rotary kiln system is intended to heat a product in the rotary kiln to a temperature sufficient to initiate a chemical or physiochemical reaction in the product present in the rotary kiln. For the avoidance of doubt, a rotary kiln may also drive off water, moisture, and/or volatile substances by heating the product and any water, moisture, or volatile substances to a temperature at which they evaporate or volatilise and leave the product in the form of a gas. Similarly, where a chemical or physiochemical reaction occurs at a low temperature, a rotary dryer may initiate a chemical or physiochemical reaction at a temperature intended primarily for the drying of a product, the removal of volatile substances, or the like. Rotary dryers, rotary kilns, and the like are generally in the form of a cylindrical or substantially drum or tube that rotates around an axis. Although cylindrical rotary heating systems will be described in the examples herein, for the avoidance of doubt, the rotary heating system may be any suitable shape or of any suitable cross section. For example, the rotary heating system may be of square cross section, triangular cross section, irregular cross section, or any other suitable cross section suffice that the rotary heating system may be rotated as described herein. The axis of rotation generally runs through the centre point of the circular cross-section of the cylindrical drum and the axis will typically be aligned horizontally or substantially horizontally relative to the ground or wider apparatus in which the rotary heating system is mounted. A rotary heating system such as a rotary dryer or kiln system may therefore have the appearance of a cylinder that is on its side and rotating in an axis perpendicular or substantially perpendicular to the direction of gravity. Rotary heating systems such as rotary dryer or kiln systems usually include a hollow inner cavity through which product or material flows. The rotating nature of the rotary heating system serves to drive or direct the flow of products or material passing through the structure in a particular direction. Some rotary heating systems are angled relative to the ground to promote additional flow of product or material through the heating system. The residence time of a product or material in the rotary heating system will depend upon the size of the rotary heating system, the speed of rotation of the system, the angle of the rotary heating system relative to the direction of gravity, and the rate at which product is introduced to the hollow cavity of the rotary heating system. For example, a larger rotary heating system will generally promote a longer product residence time when compared to a smaller rotary heating system. Similarly, a greater speed of rotation will generally reduce the residence time of a product in the rotary heating system when compared to a rotary heating system with a lesser speed of rotation. In some configurations, introducing additional product or material into the rotary heating system may ‘push’ or drive product already present in the rotary heating system out of the hollow cavity and so a greater rate of introduction of product or material may reduce the residence time of a product in the rotary heating system when compared to a system with a lesser rate of introduction of product or material.

[0023] A working fluid flows through the rotary heating system in a direction. Typically, the working fluid will flow from one end of the cylinder of the rotary heating system to the other. The working fluid may flow along, or substantially along, the axis of rotation of the rotary heating system. The working fluid may flow through the rotary heating system in a counter-current manner relative to the direction of flow of the product or material flowing through the rotary heating system. Alternatively, the working fluid may flow through the rotary heating system in a co-current manner relative to the direction of flow of the product or material flowing through the rotary heating system. In some examples, the working fluid flows through the hollow cavity of the rotary heating system in which the product or material is flowing. In this configuration, the working fluid may directly contact the product or material in the rotary heating system as it flows through the hollow cavity of the rotary heating system. Additionally, or alternatively, the rotary heating system may include a hollow shell configured to allow working fluid to flow through the shell or the rotary heating system. In this configuration, the heated working fluid may heat the outer shell of the rotary heating system which, in turn, heats the product or material flowing through the rotary heating system. In some configurations, heated working fluid is introduced to the hollow cavity of the rotary heating system and simultaneously flows through at least a portion of a hollow outer shell of the rotary heating system. Working fluid flowing through the hollow outer shell of the rotary heating system may then flow into the hollow cavity of the rotary heating system through one or more apertures, vents, nozzles, outlets, or the like. By flowing from the hollow outer shell of the rotary heating system and into the hollow inner cavity, the heated working fluid may flow through at least a portion of the bed of product or material flowing through the rotary heating system. Flowing working material through the bed of product or material may increase the efficiency with which heat energy is transferred from the working fluid to the product or material.

[0024] The rotary heating system may be of any suitable dimensions. For example, where the rotary heating system may be up to or equal to 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m, 60 m, 65 m, 70 m, 75 m, 80 m, 85 m, 90 m, 95 m, 100 m, 105 m, 110 m, 115 m, 120 m, 125 m, 130 m, 135 m, 140 m, 145 m, 150 m, 155 m, 160 m, 165 m, 170 m, 175 m, 180 m, 185 m, 190 m ,195 m, 200 m, 205 m, 210 m, 215 m, 220 m, 225 m, 230 m in length, or any other suitable length. Where the rotary heating system is cylindrical, or substantially cylindrical in shape, the diameter of the cylinder may be up to or equal to 0.5 m, 1.0 m, 1 .5 m, 2.0 m, 2.5 m, 3.0 m, 3.5 m, 4.0 m, 4.5 m, 5.0 m, 5.5 m, 6.0 m, or any other suitable diameter. The rotary heating system may be formed from any suitable material or materials capable of withstanding the temperatures at which the rotary heating system operates for sufficient time to allow a product or material to be processed. For example, the rotary heating system may be formed from a material with a melting point in excess of 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, 1500 °C, 1550 °C, 1600 °C, or any other suitable temperature. Examples of suitable material may include steel and/or titanium. The rotary heating system may be formed, at least in part, from refractory materials.

[0025] The rotary heating system may be any suitable scale or capacity depending upon the application and technical field in which the rotary heating system is to be used. In an example, the rotary heating system may operate in a range of 0.5 MWTh to 50 MWTh. The rotary heating system may therefore operate at, or be rated at, 0.5 MWth, 1 MWTh, 2 MWTh, 3 MWTh, 4 MWTh, 5 MWTh, 6 MWTh, 7 MWTh, 8 MWTh, 9 MWth, 10 MWTh, 15 MWTh, 20 MWTh, 25 MWTh, 30 MWTh, 35 MWTh, 40 MwTh, 45 MWTh, or 50MWTh. The thermal energy passed to the rotary heating system may be managed through use of a solar receiver capable of providing sufficient heat energy. For example, where the rotary heating system is intended to operate at higher values of MWTh then a solar receiver that operates at higher temperatures with a larger bank of heliostats may be required. In particular, the concentration of solar radiation, and the efficiency of energy capture and heat transfer to the working fluid at the solar receiver may be configured and/or scaled to provide the desired thermal energy to the rotary heating system via the working fluid system. The skilled person, with the benefit of this disclosure, will be able to determine a suitable solar receiver and associated apparatus to provide a desired thermal input to the rotary heating system for a given application.

[0026] The rotary heating system may be rotated by means of one or more roller systems. For example, the rotary heating system may include one or more rollers, riding rings, or tyres forming part of the rotary heating system itself. Additionally, or alternatively, the rotary heating system may rest upon one or more rollers, wheels, or the like to facilitate rotation of the structure. Rotation of the rotary heating system may be driven by one or more driving gears, girth gears, or the like. [0027] The product or material to be heated using the rotary heating system may be any suitable product that may benefit from increased temperature for a period of time. The product may be a raw material, an intermediate product, a finished product, or any other suitable category of product. Typically, the material or product to be introduced to the rotary heating system will be at least partially solid in nature. The solid material may be capable of at least partly flowing through the rotary heating system. The product may be a powder, granular product, dust, particulate, pulverant, or any combination thereof. In other examples, the product may be a mixture of one or more solids and one or more liquids such as a slurry. Particular examples of products that may be heated using the solar thermal systems described herein include, but are not limited to, cements, aggregates, minerals, ores, stones, limes, clays, kaolins, activated carbon, grains, agricultural products, biomass, or any other suitable material. The product may form a fluidised bed in the rotary heating system. The product or material may at least partially mix as it flows through the rotary heating system. In operation, the rotary heating system may move the product up one of the sides of the hollow inner cavity of the rotary heating system such that the product falls, tumbles, and/or cascades back into the bulk bed of the product or material. The rotary heating system may include one or more louvres, slates, bars, beams, or regions of elevated topography configured to drive the product through the rotary heating system when in use and/or to promote mixing of the product or material.

[0028] The rotary heating system may optionally include a burner. The burner may be present in, or in proximity to, the hollow cavity of the rotary heating system such that the burner flame directly enters the hollow cavity of the rotary heating system in which the product or material is flowing. Alternatively, the burner may be exterior to the rotary heating system or removed such that the burner flame does not contact or reside in the vicinity of the product or material in the rotary heating system. The burner may heat the working fluid as an alternative to, or in addition to, the solar receiver. The burner may allow the rotary heating system to operate in periods of low or no light such as night-time or cloudy weather. The solar receiver and the burner may be used in combination to elevate the temperature of the working fluid. In an example, in a period of low light there may be insufficient incident solar radiation to increase the temperature of the working fluid to a desired level. In this situation, the burner may be used to make up for the shortfall in energy to raise the temperature of the working fluid to the desired level. The burner, where present, will generally consume a fuel. The burner may consume the fuel by combusting the fuel. The fuel may be natural gas, hydrogen, ammonia, or any combination thereof. A hydrogen burner system may be preferable to a natural gas burner system due to the environmental impact of a natural gas burner. Using the solar receiver and the burner in combination in this manner may be advantageous as the fuel consumed by the burner will be reduced in comparison to a process that solely utilises the burner to increase the temperature of the working fluid. The solar thermal system may, in some examples, not include a means of heating the working fluid other than the solar receiver and burner, where present. For example, the solar thermal system may include only a solar receiver and a burner as a means of heating the working fluid. In other examples, further means of heating the working fluid may be including in the system alongside the solar receiver and burner, where present. An example of such further heating means may include an electric heater.

[0029] The solar thermal systems described herein are described with reference to a single rotary heating system. However, the system may include two or more rotary heating systems. Where the solar thermal system includes a plurality of rotary heating systems, each rotary heating system may be the same as at least one other rotary heating system of the solar thermal system. Alternatively, each rotary heating system may be different from at least one other rotary heating system of the solar thermal system. Where a plurality of rotary heating systems are present, they may be arranged in any suitable configuration. For example, the rotary heating systems may be arranged in series such that products of material flowing through the system flows through two or more rotary heating systems. In an example of such a system, a product may be processed in a rotary kiln at high temperature before being passed to a washing process. Following the washing process, the product may be passed to a rotary dryer system to drive the moisture from the washed product. In other example, the rotary drying systems may be arranged in parallel. The use of rotary heating systems in parallel may allow increased throughput of product and material. In examples where a plurality of rotary heating systems are used, the plurality of rotary heating systems may form part of a solar thermal system including a single solar receiver or a number of solar receivers less than the number of rotary heating systems. In this manner, a single solar receiver may be used to provide heated working fluid to two or more rotary heating systems. In systems including a burner, each of a plurality of rotary heating systems may include a burner. In other examples a single burner, or a number of burners less than the number of rotary heating systems may be used to heat the plurality of rotary heating systems, where present.

[0030] The solar thermal system may include one or more thermal storage systems. The thermal storage system may be any system capable of capturing and storing thermal energy from the working fluid. The thermal storage system may be a solid thermal storage system such as a rock bed. In solid thermal storage systems, heated working fluid is passed across or through solid material to thereby transfer heat to the solid material. When the heat stored in the solid working material is later to be used, cool working fluid may be passed across the heated solid thermal storage materials to heat the cool working fluid. Other examples of solid thermal storage systems include concrete absorbers, or other materials with a high heat capacity. Other thermal storage systems include molten systems where heat is stored by material that is initially solid but then melts as its temperature increases. Examples of molten thermal storage systems include salt-based systems and silicon systems. Heat is transferred into and out of the molten systems in a similar manner to the solid systems whereby hot working fluid is directed across or in proximity to the solid or molten material to heat the thermal storage material. Cool working fluid is later passed across or in proximity to the molten material to generate heated working fluid. The thermal storage system may be heated using hot working fluid sourced from the solar receiver or burner, where present. It may be advantageous to heat the thermal storage system using solely the solar receiver to ensure that energy is sourced primarily, or solely, from renewable energy sources. Additionally, or alternatively, working fluid with residual heat that is exiting the rotary heating system may be passed to the thermal storage system to allow recover of any remaining heat present in the working fluid once the working fluid has been used in the heating of a material or product in the rotary heating system. The thermal storage system may include one or more heat exchangers to facilitate transfer of heat to, and/or from, the working fluid and/or the thermal storage system. The thermal storage system may allow the generation of heated working fluid in periods of low or no incident sunlight. The thermal storage system may therefore be utilised in conjunction with the solar receiver to operate a process 24 hours a day using energy primarily derived from the solar receiver alone, where desired. [0031 ] The burner system and the thermal storage system described herein are not mutually exclusive and may be used in combination. For example, the solar receiver may heat the working fluid during daylight periods where solar radiation is available. A portion of the working fluid heated by the solar receiver may be passed to a thermal storage system during periods in which the solar receiver is operational. When a period of low light such as night-time occurs, working fluid may initially be heated using the thermal energy stored in the thermal energy storage system to allow the process to continue operating using energy originally sourced from the solar receiver. If the energy stored in the energy storage system is insufficient to allow operation of the rotary heating system throughout the entirety of the low light period, the burner may be used to heat the working fluid for the remaining period until there is again sufficient incident solar radiation to allow the process to operate using the solar receiver. In this manner, the solar receiver, thermal storage system, and burner may be used synergistically to provide a solar thermal system capable of operation 24 hours a day.

[0032] The solar thermal system may include one or more components for removing one or more species from the working fluid. For example, the solar thermal system may include an apparatus for removing water, contaminants, particulates, or other species from the working fluid. In examples, the solar thermal system may include one or more filters, pressure drop chambers, cyclones, scrubbers, venturi system, weir arrangements, condensers, any other suitable apparatus, or any combination thereof. The components for removing species from the working fluid may form part of, or be attached to, the working fluid system. The components for removing species from the working fluid may be present in any suitable part of the system. For example, the components for removing species from the working fluid may remove species from the working fluid prior to it arriving at the solar receiver. In a particular example, a condenser may be used to remove moisture from air drawn into the process prior to the heating of the air using the solar receiver. In other examples, the components for removing species from the working fluid may be positioned to remove components from the working fluid leaving the rotary heating system.

[0033] The solar thermal systems described herein may be operated by any suitable process that allows incident solar radiation to be captured by the solar receiver as thermal energy prior to the thermal energy being used to heat products or material in the rotary heating system. Such a process generally includes directing solar radiation onto a solar receiver to form a heated solar receiver; transferring heat from the heated solar receiver to the working fluid to form a solar-heated working fluid; passing the solar-heated working fluid to a rotary heating system housing a product; and heating the product housed in the rotary heating system using the solar-heated working fluid. Collection of energy at the solar receiver and the subsequent transfer of the collected energy to the product in the rotary heating system may be carried during periods of available sunlight. As previously described, the rotary heating system may be a rotary dryer or rotary kiln.

[0034] A burner may be used to heat working fluid in addition to, or as an alternative to, the solar receiver. A process including the use of a burner may include using the burner to heat the working fluid to form a burner-heated working fluid; passing the burner-heated working fluid through the rotary heating system housing the product; and heating the product housed in the rotary heating system using the burner-heated working fluid. Where the burner is used in conjunction with the solar receiver, the working fluid may be heated by both the solar receiver and the burner. In an example, the solar receiver may heat the working fluid to form a solar-heated working fluid. The solar-heated working fluid may then flow to rotary heating system via a flow path that directs the solar-heated working fluid past or across the burner. The burner may then heat the solar-heated working fluid to form a working fluid heated by both solar and burner means. Such a process may be used when the amount of incident solar radiation is insufficient to allow the solar receiver to heat the working fluid to a desired temperature without the additional contribution of the burner. In processes where the solar receiver and the burner are not used together, the burner may be used during periods of low or no light. In one example, the burner may be used at night-time. In another example, the burner may be used during periods of substantial cloud coverage. Use of the burner to heat the working fluid during periods of low or no light allows the process to operate to heat product or materials in the rotary heating system in all conditions and at all times of day. The burner may combust a fuel and the fuel may include natural gas, hydrogen gas, or any combination thereof. It may be advantageous to combust a fuel with a high hydrogen gas content to avoid the generation of undesired combustion by-products. [0035] Where the solar thermal system includes a thermal storage system, the process may include passing the solar-heated working fluid to a thermal storage system and transferring heat from the solar-heated working fluid to the thermal storage system to form a heated thermal storage system. Heated working fluid may be sent to the thermal storage system from any suitable source or from any portion of the process where the working fluid contains heat energy. Solar-heated working fluid, or a portion thereof, may be passed to the thermal storage system directly from the solar receiver. Where the process includes heating the working fluid using a burner, burner-heated working fluid, or a portion thereof, may be passed to the thermal storage system directly from the burner. Where the working fluid is being heated by both the solar receiver and a burner, a portion of working fluid heated by the solar receiver, heated by the burner, or heated by both the solar receiver and the burner may be passed to the thermal storage system. Working fluid that has been used to heat the product or material in the rotary heating system may additionally, or alternatively, be passed to the thermal storage system. In these examples, the working fluid exiting the rotary heating system may contain residual heat energy which may be recovered by the thermal storage system. The heated thermal storage system may be used to provide thermal energy to one or more processes. The heated thermal storage system may be used in a process including transferring heat from the heated thermal storage system to the working fluid to form a storage-heated working fluid, passing the storage-heated working fluid to the rotary heating system housing the product; and heating the product housed in the rotary heating system using the storage-heated working fluid. In this manner, the energy stored in the thermal storage system may be used to heat the working fluid which subsequently heats the product. The working fluid may be heated by the thermal storage system in combination with any other means of heating the working fluid. More particularly, the working fluid may be heated using the thermal storage system, the solar receiver, the burner, or any combination thereof. It may be advantageous to heat the working fluid using the thermal storage system during periods where the solar receiver is unable to heat the working fluid to a desired temperature such as periods of low or no light. The use of the thermal storage system may be preferable to the use of the burner in situations where the working fluid is required to be heated using means other than, or in addition to, the solar receiver as the use of the thermal storage system may avoid the need to consume burner fuel. Where the process stores energy in the thermal storage system, the energy in the thermal storage system may be used in one or more additional applications. For example, working fluid may be passed through the energy storage system to form storage-heated working fluid, and the storage heated-working fluid may be used in a process other than the heating of the product or material in the rotary heating system.

[0036] The processes described herein may increase the temperature of the working fluid to any desired temperature suffice that the solar receiver, or other heating means where present, are sufficient to impart the desired heat energy to the working fluid. The heat transferred from the heated solar receiver to the working fluid to form a solar- heated working fluid may increase the temperature of the solar-heated working fluid to a temperature of from and including 100 °C to 1500 °C. In a particular example, the processes described herein may increase the temperature of the solar-heated working fluid to under 600°C. In another example, the processes described herein may increase the temperature of the solar-heated working fluid to over 600°C. A drying process may operate at temperatures of under 600°C, whereas a kilning process may operate at temperatures of over 600°C. Similarly, the heat transferred from the burner, where present, to the working fluid to form a burner-heated working fluid may increase the temperature of the burner-heated working fluid to a temperature of from and including 100 °C to 1500 °C. In a particular example, the processes described herein may increase the temperature of the burner-heated working fluid to under 600°C. In another example, the processes described herein may increase the temperature of the burner-heated working fluid to over 600°C. Furthermore, the heat transferred from the heated thermal storage system to the working fluid to form a storage-heated working fluid may increase the temperature of the storage-heated working fluid to a temperature of from and including 100 °C to 1500 °C. In a particular example, the processes described herein may increase the temperature of the storage-heated working fluid to under 600°C. In another example, the processes described herein may increase the temperature of the storage-heated working fluid to over 600°C. The heated working fluid when used to heat a product or material in the rotary heating system may therefore increase the temperature of the product to over 100 °C. In particular examples, the heated working fluid may increase the temperature of the product to a temperature equal to, or greater than 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, or 1500 °C. Heating the product to such temperatures may therefore include drying the product and/or initiating a chemical and/or physiochemical reaction in the product to form a reacted product, depending upon the particular temperature to which the product is heated and the nature of said product. Heating the product in this manner may therefore remove water, one or more volatile substances, or any combination thereof from the product.

[0037] The processes described herein and the steps thereof may be carried out in any sequence or combination as desired by a user. Some process steps may be repeated or performed multiple times if desired. For example, a product or material may be heated multiple times. In another example, a particular working fluid may be passed over a product or material several times. The skilled person, with the benefit if this disclosure, will be able to determine suitable sequences and repetitions of processes or individual process steps as described herein. The processes described herein may further include one or more additional process steps. The processes may further include one or more additional drying, kilning, purification, separation, crushing, grinding, washing, sorting, screening, filtering, processing, or any other suitable process carried out upon the product or material heated in the rotary heating system. Such processes may be performed prior to and/or following the heating of the product in the rotary heating system.

[0038] Figure 1 A shows a schematic representation of an example of a solar thermal system 100 including a rotary heating system 106. The system 100 includes a bank of heliostats 101 positioned to direct solar radiation 102 towards a solar receiver 103 residing atop a tower structure 104. The rotary heating system 106 is located inside a facility 105 which may be a building, factory, warehouse, or similar structure. Working fluid 107 flows in a direction 108 from the solar receiver 103, where it is heated, to the rotary heating system 106. The working fluid 107 heats a product or material (not shown) residing in the rotary heating system 106 before exiting the rotary heating system 106 via flow conduit 109. Figure 1 B shows a schematic representation of an alternative example of a solar thermal system 150. In contrast to the system of Figure 1A, the system shown in Figure 1 B positions the solar receiver 153 atop the facility 155 and not atop a tower. In the system of Figure 1 B, a bank of heliostats 151 directs solar radiation 152 towards a solar receiver 153 mounted atop a facility structure 155 upon mounting 154. Working fluid 157 flows through a working fluid system in direction 158 from the solar receiver 153 to the rotary heating system 156 located in facility 155. The working fluid heats the product or material (not shown) present in the rotary heating system 156 before exiting the rotary heating system via exhaust passage 159.

[0039] Figure 2 shows a schematic representation of a solar thermal system 200 including a burner. The system 200 of Figure 2 is similar to that of Figure 1A in that a bank of heliostats 201 is positioned and configured to direct solar radiation 202 towards solar receiver 203 positioned atop a tower structure 204. Heated working fluid 207 from the solar receiver 203 flows in direction 208 towards the rotary heating system 206 located in facility structure 205. In contrast to the system 100 of Figure 1A, the system 200 of Figure 2 includes a burner 210. The burner 210 is located inside the rotary heating system 206 such that the burner 210 may be used to directly heat working fluid inside, or flowing through, the rotary heating system 206. The burner is connected to a fuel source 211 that provides the burner 210 with fuel during use. The fuel may be a natural gas and/or hydrogen gas based fuel. Although Figure 2 shows the fuel source 211 as present inside the facility 205, the fuel source 211 may be positioned exterior to the facility 205. For example, the fuel source 211 may be a gas tank or reservoir. In another example, the fuel source 211 may include a pipeline to supply fuel to the burner from a distant location. Working fluid 207 flows out of the rotary heating system 206 via flow passage 209.

[0040] Figure 3 shows a schematic representation of a solar thermal system 300 including a thermal storage system. The system 300 of Figure 3 is similar to system 100 of Figure 1 A except that system 300 of Figure 3 include a thermal storage system 310. System 300 includes a bank of heliostats 301 positioned and configured to direct solar radiation 302 incident upon the bank of heliostats towards the solar receiver 303. Solar receiver 303 is located upon tower structure 304 to provide a point upon which the heliostats 301 may focus the solar radiation 302. Working fluid 307 is heated by the solar receiver and flows in direction 308 from the solar receiver 303 to the rotary heating system 306 located within facility 305. The working fluid 307 heats product or material (not shown) resident in the rotary heating system 306 before exiting the rotary heating system via flow passage 309. The working fluid 307 flows through thermal storage system 310 where a portion of the heat energy in the working fluid 307 may be stored. When desired, the energy stored in the thermal storage system 310 may be recovered by passing cold working fluid through the thermal storage system 310. The working fluid thus heated by its passage through the thermal storage system 310 may then be used to heat a product or material in the rotary heating system 306.

[0041 ] Figure 4 shows a process 400 for providing thermal energy to a product using a working fluid. The process 400 includes directing 401 solar radiation onto a solar receiver to form a heated solar receiver. The process 400 further includes transferring 402 heat from the heated solar receiver to the working fluid to form a solar-heated working fluid. The process 400 also includes passing 403 the solar-heated working fluid to a rotary dryer or rotary kiln housing a product. The process 400 yet further includes heating 404 the product housed in the rotary heating system using the solar- heated working fluid. The directing 401 , transferring 402, passing 403, and heating 404 may be carried out during periods of available sunlight.

[0042] Figure 5 shows a cross-sectional schematic representation of a solar rotor type solar receiver 500 that may be used with the solar thermal systems described herein. The rotor 500 is formed from two body portions 501 ,502 which are substantially discoidal in shape. In practice, the body portions may be any suitable shape although it may be advantageous to utilise discoidal-shaped body portions in some implementations to facilitate ease of rotation. The body portions 501 , 502 are substantially hollow such that working fluid may flow into the first body portion 501 via inlet 503 in the first body portion and out of outlet 504 in the second body portion 502. Positioned between the first body portion 501 and the second body portion 502 are a plurality of conduits 505 which represent the absorbing elements of the rotor 500. The conduits may be any suitable shape including, but not limited to square or rectangular in cross section, tubular with a circular or oval cross section, or more complex cross sectional shapes as desired. The conduits are arranged around the outer circumferential periphery of the circular faces of the discoidal body portions 501 , 502, such that the conduits 505 connect the first body portion 501 to the second body portion 502. The resulting configuration approximates the shape of a cylindrical cage with the inlet 503 and the outlet 504 extending out from the respective first and second body portions 502, 503 on the opposite side of each body portion from the side to which the conduits 505 are connected. The conduits 505 are substantially hollow and are in fluid communication with the hollow region of each of the first and second body portions 501 , 502. In use, working fluid may therefore flow into the rotor via the inlet 503 into the hollow part of the first body portion 501 , through the plurality of conduits

505 into the hollow part of the second body portion 502 and then out through the outlet 504. Solar radiation 506 may be directed towards the surface of one or more of the plurality of conduits 505 via one or more optical arrangements. In an example, the solar radiation may be directed from one or more optical arrangements to pass through a slot in an outer housing (not shown) in which the rotor resides such that the light incident upon the rotor 500 is directed towards a surface area greater than, equivalent to, or less than, the surface area of one side of a single conduit 505. Solar radiation

506 incident upon the surface of a conduit 505 will cause the surface of the conduit to become heated. In use, rotor 500 rotates in a direction 507 such that each of the plurality of conduits 505 will periodically become exposed to the solar radiation, and thus heated, in turn. Working fluid is passed through the rotor 510 and over the heated internal surfaces of the plurality of conduits 505 such that heat is transferred from the rotor surfaces to the working fluid cooling the rotor and heating the working fluid. Once cooled, each of the plurality of conduits 505 will eventually be carried back to a position at which it is subjected to further heating via the incident solar radiation 506 due to the rotational movement of the rotor 500. The conduits may be positioned in any suitable arrangement around the periphery of the rotor body. In an example, the conduits may be positioned such that when the rotor is rotating and the incident solar radiation passes between two conduits on the near side of the rotor, a further conduit will be exposed to the solar radiation on the far side of the rotor due to the solar radiation passing through the gap between the two conduits nearest the source of the solar radiation.

[0043] Figure 6 shows a further configuration of a solar receiver that may be used in the solar thermal systems described herein. The solar receiver of Figure 6 is a frustoconical, or substantially conical, shaped rotor. The receiver comprises a heat exchanger cowl 620, a shaft 662, a rotor 661 , slot 653, inlet 623 and outlet 624. The rotor 661 and cowl 620 are positioned on and around shaft 662, configured such at least rotor 661 may rotate freely around the shaft 662. At least one portion of cowl 620 is absent to form slot 653 which exposes one or more surfaces of the rotor 661 beneath. In operation, solar radiation 601 is focussed towards the exposed portion of the rotor 661 within the slot 653. The exposed portion of rotor 661 absorbs the solar radiation 601 and stores it as heat energy. The frustoconical shape of the receiver allows light to be more easily directed towards the inner surface of the rotor. The rotor

661 rotates via bearing arrangements 663, the rotation driven by a motor and drive belt arrangement (not shown) that cause rotor 661 to rotate while the heat exchanger cowl 620 remains stationary. Cowl 620 is affixed to shaft 662 by any suitable fixing means such as screws or bolts. Working fluid enters the heat exchanger cowl 620 via inlet 623 inside the shaft 662. The working fluid circulates around the heat exchanger cowl 620 across the surface of the rotor 661 before leaving the solar receiver via outlet 624 positioned internal to the shaft 662. The cowl 620 and/or rotor 661 may be at least partially lined with insulating or refractory material. The heat exchanger cowl may further comprise one or more sealing lips to prevent loss of working fluid through residual gaps formed between the rotor 661 and cowl 620. An additional sealing lip may also be present at the base of the cone/bowl arrangement in proximity to the shaft

662 to prevent further loss of heat.

[0044] In an example, in use, the solar thermal system described herein will collect incident solar radiation from the sun using one or more heliostats. The heliostats will generally be positioned and configured to direct incident solar radiation on to one or more absorbing surfaces of a solar receiver which may be a rotor. The total surface area of the heliostats will typically be greater than the surface area of the absorbing portion of the solar receiver such that solar radiation is concentrated upon the solar receiver. The solar receiver will absorb the incident solar radiation from the heliostats in the form of heat. The heat energy in the solar receiver will then be transferred to a working fluid flowing in, around, and/or through the solar receiver to heat the working fluid to a temperature suitable for use in a rotary heating system such as a rotary dryer or rotary kiln. The heated working fluid will then be passed to the rotary heating system and used to heat a product or material flowing through the rotary heating system. In periods of low or no light, a burner may be used to heat the working fluid to allow the process to continue when the solar receiver is unable to provide a working fluid with the necessary thermal energy. A thermal storage system may store thermal energy from the working fluid for later use, in periods where the solar receiver is unable to provide sufficiently hot working fluid for use in the rotary heating system. [0045] The solar thermal systems and associated processes are therefore well placed to impart the benefits and advantages as described herein. The person skilled in the art will appreciate that the solar thermal systems and processes described herein may be modified without departing from the scope of the invention as defined by the appended claims. In particular, while the Figures and specific examples provided herein show particular implementations of the solar thermal systems and associated processes, the skilled person will appreciate that the features of such exemplified systems, process, and Figures are not necessarily limited to the sole examples in which they are described and that such features may be combined in any technically appropriate manner consistent with this disclosure.

Claims

33 CLAIMS

1 . A process comprising:

(i) directing solar radiation onto a solar receiver to form a heated solar receiver;

(ii) transferring heat from the heated solar receiver to the working fluid to form a solar-heated working fluid;

(iii) passing the solar-heated working fluid to a rotary heating system housing a product, optionally wherein the rotary heating system is a rotary dryer or rotary kiln; and

(iv) heating the product housed in the rotary heating system using the solar- heated working fluid; wherein (i), (ii), (iii) and (iv) are carried out during periods of available sunlight.

2. A process according to claim 1 , the process further comprising:

(I) passing the solar-heated working fluid to a thermal storage system; and

(II) transferring heat from the solar-heated working fluid to the thermal storage system to form a heated thermal storage system.

3. A process according to claim 2, the process further comprising:

(III) transferring heat from the heated thermal storage system to the working fluid to form a storage-heated working fluid;

(IV) passing the storage-heated working fluid to the rotary heating system housing the product; and

(V) heating the product housed in the rotary heating system using the storage-heated working fluid.

4. A process according to claim 3, wherein (III), (IV), and (V) are carried out during periods of low or no sunlight.

5. A process according to any preceding claim, the process further comprising:

(a) using a burner to heat the working fluid to form a burner-heated working fluid;

(b) passing the burner-heated working fluid through the rotary heating system housing the product; and

(c) heating the product housed in the rotary heating system using the burner-heated working fluid.

6. A process according to claim 5, wherein (a), (b), and (c) are carried out during periods of low or no sunlight.

7. A process according to any preceding claim, wherein the working fluid is a gas, optionally wherein the working fluid is air. 34

8. A process according to any preceding claim, wherein transferring heat from the heated solar receiver to the working fluid to form a solar-heated working fluid increases the temperature of the solar-heated working fluid to 100 °C to 1500 °C, optionally wherein: the temperature of the solar-heated working fluid is increased to under 600°C; or the temperature of the solar-heated working fluid is increased to over 600°C.

9. A process according to any of claims 3 to 8, wherein transferring heat from the heated thermal storage system to the working fluid to form a storage-heated working fluid increases the temperature of the storage-heated working fluid to 100 °C to 1500 °C, optionally wherein: the temperature of the storage-heated working fluid is increased to under 600°C; or the temperature of the storage-heated working fluid is increased to over 600°C.

10. A process according to claim 5 or 6, wherein using a burner to heat the working fluid to form a burner-heated working fluid increases the temperature of the burner- heated working fluid to 100 °C to 1500 °C, optionally wherein: the temperature of the burner-heated working fluid is increased to under 600°C; or the temperature of the burner-heated working fluid is increased to over 600°C.

11. A process according to any preceding claim, wherein heating the product comprises increasing the temperature of the product to 100 °C or more, optionally wherein the temperature of the product is increased to a temperature equal to or greater than 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C, or 1500 °C.

12. A process according to any preceding claim, wherein heating the product comprises: drying the product; and/or initiating a chemical and/or physiochemical reaction in the product to form a reacted product.

13. A process according to claim 5, 6 or 10, wherein the burner combusts a fuel, wherein: the fuel comprises natural gas; and/or the fuel comprises hydrogen gas.

14. A process according to any preceding claim, the process further comprising removing water and/or a volatile substance from the working fluid.

15. A process according to any preceding claim, wherein the product is a powder, granular product, dust, particulate, pulverant, or any combination thereof.

16. A solar thermal system for heating one or more products using the process of any preceding claim, the system comprising: a solar receiver configured to: convert incident solar radiation to heat energy; and heat working fluid using the heat energy; a rotary heating system; and a working fluid system configured to pass heated working fluid from the solar receiver to the rotary heating system.

17. A solar thermal system according to claim 16, wherein the rotary heating system is: a rotary dryer; or a rotary kiln.

18. A solar thermal system according to claim 16 or 17, wherein the solar thermal system comprises a thermal storage system.

19. A solar thermal system according to claim 18, wherein the working fluid system is further configured to flow working fluid from the solar receiver and/or the rotary heating system to the thermal storage system.

20. A solar thermal system according to any of claims 16 to 19, wherein the rotary heating system is substantially cylindrical in shape and comprises a hollow inner compartment through which product flows when the solar thermal system is in use.

21. A solar thermal system according to claim 20, wherein the rotary heating system comprises: one or more louvres, slates, bars, beams, or regions of elevated topography configured to drive the product through the rotary heating system when the system is in use; and/or a hollow shell configured to provide a flow passage for working fluid through the shell when the rotary heating system is in use.

22. A solar thermal system according to any of claims 16 to 21 , further comprising an optical system configured to direct incident sunlight onto the solar receiver.

23. A solar thermal system according to claim 22, wherein the optical system comprises one or more heliostats.

24. A process for heating a product in a rotary dryer or rotary kiln, the process comprising:

(i) directing solar radiation at a concentration of 2000 or more onto a solar receiver to form a heated solar receiver;

(ii) transferring heat from the heated solar receiver to air as a working fluid to form a solar-heated working fluid at a temperature of 600°C or more;

(iii) passing the solar-heated working fluid to a rotary dryer or rotary kiln; and

(iv) heating the product housed in the rotary dryer or rotary kiln to a temperature of 550°C or more using the solar-heated working fluid.

25. A process or solar thermal system according to any preceding claim, wherein the solar receiver is a stationary solar receiver.

26. A process or solar thermal system according to any of claims 1 to 24, wherein the solar receiver is a rotor.