INTRODUCTION

[0001] The present invention relates to solar kilns and methods of heating intermediate, or unfinished, products in kilns via solar radiation. More particularly, the present invention relates to processes for firing clay and ceramic products using solar kilns.

[0002] Kilns are traditionally used to heat products to a desired temperature to instigate a change in said products. Examples of processes commonly carried out in kilns include drying, hardening, sintering, calcining, annealing, ageing, and the like. Kilns are often used in the process of producing pottery, ceramics, earthenware, stoneware, and similar products which require exposure to elevated temperatures for periods of hours or more in order to form a finished product. In particular, kilns are used on industrial scales in the production of ceramic products including bricks and tiles.

[0003] The industrial process for producing pottery and ceramic products including bricks and tiles generally involves four stages. The products are first moulded into a desired shape from clay or other suitable raw materials. The shaped products are then dried across a period of several hours to remove moisture on the surface or trapped within the pore structure of the raw materials. The dried products are then gradually exposed to incrementally elevated temperatures to perform what is referred to as mineral dehydroxylation whereby hydroxyl groups bound to the products, the water of crystallisation, and/or molecular water trapped within the structure of the product are removed or driven off. Once shaped, and prior to sintering and/or calcination, the products may be referred to as intermediate, or unfinished. Finally, the products are sintered and/or calcined at high temperatures to produce the finished product such as a brick or tile. The majority of these process steps involve exposing the unfinished product to elevated temperatures which makes such processes thermally intensive.

[0004] Traditionally, the thermal energy or heat energy required for kiln processes has been derived from combustion of fuel stocks such as natural gas, coal, wood, hydrocarbon-based fuels, or similar energy rich materials. The use of combustion techniques 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 process in order to maintain steady operation. This may limit the viable locations for industrial kilning processes or necessitate a complex logistics network to bring fuel and/or the raw product materials from distant areas to the kiln. There is therefore a desire for alternative kilns and kiln processes that address the shortcomings of some traditional kilns. The inventors of the present invention have appreciated that high energy solar technology may be utilised in the production of pottery and ceramics such as bricks and tiles to advantageous effect.

[0005] According to one aspect of the invention, there is provided a process for manufacturing ceramic products. The process includes directing solar radiation on to a solar receiver to form a heated solar receiver, transferring heat from the heated solar receiver to a working fluid to form a first heated working fluid, passing the first heated working fluid to a ceramic product manufacturing station; and heating one or more unfinished ceramic products using the first heated working fluid.

[0006] The working fluid may be a gas. Optionally the working fluid is air, or the working fluid may be a purified or manufactured gas, for example nitrogen, or defined mixture of gases so that the working fluid composition can be controlled to be, for example less chemically active. Heating the one or more unfinished ceramic products, or intermediate products, may include drying the one or more ceramic products to remove surface and/or pore-bound moisture. Heating the one or more unfinished ceramic products may include mineral dehydroxylation. Mineral dehydroxylation may include removing bound hydroxyl groups, the water of crystallisation, molecular water, and/or internal water from the one or more unfinished clay products. The first heated working fluid may be at a temperature of 100 °C to 1500 °C. Heating the one or more unfinished ceramic products may include increasing the temperature of the one or more unfinished ceramic products to over 400 °C, optionally wherein the one or more unfinished ceramic products are heated to a temperature of over 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, or 1500 °C. Heating the one or more unfinished ceramic products may include increasing the temperature of the one or more unfinished ceramic products at a rate of less than or equal to 80 °C per hour, optionally wherein the temperature of the one or more unfinished ceramic products is increased at a rate of less than or equal to 60 °C per hour, 50 °C per hour, 40 °C per hour, 30 °C per hour, or 20 °C per hour. Heating the one or more unfinished ceramic products may be carried out solely using the first heated working fluid and the first heated working fluid is heated solely using heat from the solar receiver. Heating the one or more unfinished ceramic products may include sintering and/or calcining the one or more unfinished ceramic products to form one or more hot ceramic products. The directing of solar radiation and heating of one or more unfinished ceramic products may be carried out during periods in which the sun is shining. Sintering and/or calcining the one or more unfinished ceramic products using the first heated working fluid may cool the first heated working fluid so that it becomes a second heated working fluid at a lower temperature than the first heated working fluid. The process may further include using the second heated working fluid to: dry one or more unfinished ceramic products to remove surface and/or pore bound moisture; and/or induce mineral dehydroxylation in the one or more unfinished ceramic products, optionally wherein mineral dehydroxylation removes bound hydroxyl groups, water of crystallisation, molecular water, and/or internal water from one or more unfinished ceramic products.

[0007] In some examples a ceramic product manufacturing station may comprise a substantially enclosed chamber within which unfinished, or intermediate, products can be located, for example via a door or port. The working fluid can be passed through an interior of the chamber to heat the unfinished, or intermediate, products therein. Once heating, and any further processing, has concluded the products can be removed from the chamber and a new set of unfinished, or intermediate, products can be arranged in the chamber. This is an example of a batch type manufacturing process.

[0008] The enclosed chambers may be uncoupled from, and coupled to, a working fluid distribution system in a plurality of different locations. This allows the enclosed chambers to be movable so that, in some locations, products within the chamber can be heated by working fluid while, in other locations, products within the chamber can be used to heat working fluid. The working fluid distribution system may be configured to be able to re-route working fluid as required and this could reduce, or avoid, the need to move chambers. It may be beneficial to have a consistent ‘highest temperature’ working area and movable chambers may allow this to be achieved while allowing products in a single chamber to be heated by a working fluid and to heat a working fluid at a different stage in the process.

[0009] In some examples a ceramic product manufacturing station may comprise a region of a track on which unfinished, or intermediate, products are located. The track may move relative to the region being heated, or the region of the track being heated may move relative to the track, so that it is possible for products to continuously enter the ceramic product manufacturing station and be heated, while other products leave the ceramic product manufacturing station. This is an example of a continuous type manufacturing process.

[0010] The manufacturing process may be on an industrial scale, For example, the number of unfinished products in a station may be at least 25, at least 50, at least 100, at least 150, at least 300, at least 600, at least 1200, at least 2400, at least 5000, at least 10000, or at least 30000.

[0011] The process may further include heating a working fluid by passing the working fluid across one or more hot ceramic products to form a third heated working fluid. The process may further include using the third heated working fluid to: dry one or more unfinished ceramic products to remove surface and/or pore bound moisture; and/or to induce mineral dehydroxylation in the one or more unfinished ceramic products, optionally wherein mineral dehydroxylation removes bound hydroxyl groups, water of crystallisation, molecular water, and/or internal water from one or more unfinished ceramic products. Using the third heating working fluid may be carried out during periods of no or limited sunshine. The working fluid, first heated working fluid, second heated working fluid, and/or third heated working fluid may flow in a substantially closed-loop flow path. [0012] The process may further include removing water from the working fluid, first heated working fluid, second heated working fluid, and/or third heated working fluid. The removal of water from a working fluid may be achieved by any suitable device for example a heat exchanger or condenser. An example of a suitable device has been identified as a rotary heat exchanger having a condensation wheel, for example that available from Hoval™. It is noted that there may be in excess of 100 litres of water to be removed from every ton of brick being fired. This means that removing water from the working fluid may be helpful, particularly if working fluid is to be reused.

[0013] According to another aspect of the invention, there is provided a solar kiln system for manufacturing one or more ceramic products using the processes described 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 one or more ceramic product manufacturing stations and a working fluid system configured to flow heated working fluid from the solar receiver to the one or more ceramic product manufacturing stations. The working fluid system may be configured to flow working fluid from the one or more ceramic product manufacturing stations to the solar receiver. The working fluid system may include one or more fans and one or more conduits configured to cause flow of working fluid between the solar receiver and the one or more ceramic product manufacturing stations, optionally wherein the working fluid system does not comprise a compressor. The one or more ceramic product manufacturing stations may include a first ceramic product manufacturing station, the first ceramic product manufacturing station including a first chamber housing one or more unfinished ceramic products, the one or more unfinished ceramic products including surface and/or pore-bound moisture.

[0014] The one or more ceramic product manufacturing stations may include a second ceramic product manufacturing station, the second ceramic product manufacturing station may include a second chamber housing one or more unfinished ceramic products, the one or more unfinished ceramic products including bound hydroxyl groups, water of crystallisation, molecular water, and/or internal water but substantially no surface and/or pore-bound moisture. The one or more ceramic product manufacturing stations may include a third ceramic product manufacturing station, the third ceramic product manufacturing station including a chamber housing one or more unfinished ceramic products, the one or more unfinished ceramic products including substantially no water. The one or more ceramic product manufacturing stations may include any combination of the first ceramic product manufacturing station, the second product manufacturing station, and the third product manufacturing station.

[0015] The working fluid system may be configured to flow a first portion of the heated working fluid across the one or more unfinished ceramic products of the third chamber prior to flowing the first portion of the heated working fluid across the one or more unfinished ceramic products of the second chamber. The working fluid system may configured to flow a second portion of the heated working fluid across the one or more unfinished ceramic products of the second chamber prior to flowing the second portion of the heated working fluid across the one or more unfinished ceramic products of the first chamber. The first portion of working fluid and the second portion of working fluid may be substantially the same portion of working fluid.

[0016] According to a further aspect of the invention, there is provided a process for manufacturing ceramic products. The process includes heating one or more unfinished ceramic products at a first ceramic product manufacturing station using a heated working fluid. The process further includes transferring the heated working fluid from the first ceramic product manufacturing station to a second ceramic product manufacturing station; and heating one or more unfinished ceramic products at the second ceramic product manufacturing station using the heated working fluid. The process may further include transferring the heated working fluid from the second ceramic product manufacturing station to a third ceramic product manufacturing station, and heating one or more unfinished ceramic products at the third ceramic product manufacturing station using the heated working fluid. For the avoidance of doubt, the scope of the invention is defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be described with reference to the following drawings, in which:

Figure 1A shows a schematic representation of a solar kiln system;

Figure 1 B shows a schematic representation of an alternative solar kiln system; Figure 2 shows a process for manufacturing a ceramic product;

Figure 3 shows a schematic process view of a part of a solar kiln system operating in a period of incident solar radiation;

Figure 4 shows a schematic process view of a part of a solar kiln system operating in a period of low or no incident solar radiation;

Figure 5 shows a process for manufacturing a ceramic product; and Figure 6 shows a schematic representation of another solar kiln system

DETAILED DESCRIPTION

[0018] A solar kiln is defined as a kiln that derives the majority or substantial majority of thermal energy or heat energy used therein from solar radiation. 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 kilns in the production ceramic products including bricks and tiles. 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 pottery, ceramics, earthenware, stoneware, and the like.

[0019] The solar kiln as described herein generally includes 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 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. The banks of heliostats may be positioned in proximity to a tower or mast supporting the solar receiver. 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 heliostats 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.

[0020] 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/m ² ) 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 kiln may be configured to operate at a c value of 50 or more. The solar receiver used in the solar kiln 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, 750 or more, or 1000 or more.

[0021] 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 0.8. 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.

[0022] The solar receiver may include a solid rotor. The use of a solid rotor in a solar receiver may allow higher values of c to be employed by the solar kiln. Where 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. 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 a higher density of incident solar energy upon the rotor and decreased in response to a decrease in 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.

[0023] The solar kiln uses a heated working fluid to heat the products to be processed therein. 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.

[0024] The solar kiln includes a working fluid system configured to flow working fluid from the solar receiver to the intermediate products to be heated by the working fluid. In this manner, working fluid heated by the solar receiver is transferred to the parts of the process where its energy may be utilised. 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 kiln. 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 kiln 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 of drying one or more intermediate products. Positioning the fan in the ‘cold’ side or portion 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 a substantially closed-loop or closed circuit. For example, working fluid heated at, or in proximity to, the solar receiver may be directed to heat an intermediate product 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 kiln. The working fluid system may include means to introduce additional working fluid into the working fluid system. Such additional working fluid may be 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. 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.

[0025] The solar kiln includes at least one product processing station. A product processing station may be a ceramic product manufacturing station. Where the product is a brick or a tile, the at least one product manufacturing station is at least one brick or tile manufacturing station. The one or more product manufacturing stations are the parts of the product manufacturing process where the intermediate product is processed in some manner to progress the intermediate product further towards the finished product. A product manufacturing station such as a brick or tile manufacturing station used in the solar kilns described herein may be an oven, a kiln, a roaster, heating station, or the like configured to utilise working fluid as a means of heating an intermediate product. As previously described, the formation of a ceramic product such as a brick or tile involves at least three stages of thermal treatment including: (i) drying the moulded product to remove moisture on the surface or trapped within the pore structure of the raw materials; (ii) gradually exposing the intermediate product to incrementally elevated temperatures to induce mineral dehydroxylation; and (iii) sintering and/or calcining the intermediate product that is substantially free of water at high temperatures to produce the finished product such as a brick or tile. The product manufacturing stations are configured such that heated working fluid from the solar receiver may flow through at least part of the product manufacturing station to directly or indirectly heat the intermediate product residing or housed in the product manufacturing station. In some examples, the working fluid will directly heat the intermediate product by flowing around, across, through, and/or over the intermediate product itself. In such examples, the product manufacturing stations may not include a heat exchanger. More particularly, in such examples, there may be no heat exchanger present to promote transfer of heat energy from the working fluid to the one or more unfinished products resident in the product manufacturing station. Where the working fluid is air, the air may flow directly across, around, and/or through the intermediate products so that heat energy in the air working fluid is transferred directly to the intermediate product.

[0026] For a given product, the drying, mineral dehydroxylation, and sintering/calcining stages of the process may be carried out in a single product manufacturing station. In these examples, working fluid of gradually increasing temperature may be introduced to the product manufacturing station to first dry the product, then induce mineral dehydroxylation, and then sintered and/or calcine the product. In these examples, the unfinished product may be transported into a product manufacturing station prior to drying and then transported out of the product manufacturing station once the sintering and/or calcination process is complete. In other examples, the one or more product manufacturing stations of the solar kiln may include a first chamber housing one or more intermediate products, the one or more intermediate products with surface and/or pore bound moisture. Where the one or more product manufacturing stations include the first chamber, the working fluid may flow through the first chamber to heat the intermediate product resident in the chamber to dry and remove surface moisture and pore-bound moisture from the intermediate product. The one or more product manufacturing stations of the solar kiln may include a second chamber housing one or more intermediate products, the one or more intermediate products including bound hydroxyl groups, water of crystallisation, molecular water, and/or internal water but substantially no surface and/or pore bound moisture. Where the one or more product manufacturing stations include the second chamber, the working fluid may flow through the second chamber to induce mineral dehydroxylation in the intermediate product resident in the second chamber by heating the intermediate product resident in the second chamber. The one or more product manufacturing stations may include a third chamber housing one or more intermediate products, the one or more intermediate products including substantially no water. Where the one or more product manufacturing stations includes the third chamber, the working fluid may flow through the third chamber to heat the intermediate product to sinter and/or calcine the intermediate product to form finished ceramic product such as a brick or tile. The solar kiln may include at least three product manufacturing manufacturing stations. Each of the at least three product manufacturing stations may include the first chamber or the second chamber or the third chamber. The solar kiln may include a first product manufacturing station including a first chamber, a second product manufacturing station including a second chamber, and a third product manufacturing station including a third chamber. In other examples, a product manufacturing station may include the first chamber, the second chamber, and the third chamber. The first chamber, second chamber, and third chamber may be different chambers and/or the same chambers.

[0027] In other examples, the one or more product manufacturing stations of the solar kiln may comprise regions of a track containing one or more intermediate products instead of defined chambers. As noted above, the track may move relative to the region being heated, or the region of the track being heated may move relative to the track. In this way it is possible for products to continuously enter a product manufacturing station and be heated, while other products leave the ceramic product manufacturing station. In some examples the products in a first region of the track that have been heated may be used to heat a working fluid to a first temperature suitable for heating products in a second region of the track, or second manufacturing station, that are currently at a temperature below the first temperature. For example the first region of the track may contain products that have undergone a calcination process may be used to heat a working fluid that is to be used to heat products in a second region to remove surface and/or pore bound moisture.

[0028] To reduce the distance travelled by the working fluid between the first region and second region the track may be configured to include bends, curves or corners so that the first and second regions may be arranged proximal to one another. For example the track may include a hairpin bend in the region of the manufacturing station in which a calcination step takes place. This means that the heated products leaving the calcination manufacturing station can be cooled by heating a working fluid that can be used to pre-heat products in manufacturing stations in which products have not yet reached the calcination manufacturing station.

[0029] Where the solar kiln includes a plurality of product manufacturing stations such as brick or tile manufacturing stations, the working fluid system may be configured to direct working fluid from one product manufacturing station to another. For example, where an intermediate product is sintered and/or calcined in a product manufacturing station including a third chamber as described above, working fluid used to heat the intermediate product to a temperature suitable for sintering and/or calcining may be passed to another product manufacturing station including the second chamber where the intermediate product is heated to induce mineral dehydroxylation. In this manner, a given portion of working fluid may be used to heat multiple stages in the product manufacturing process without further heating or re-heating via the solar receiver. Similarly, working fluid used in the sintering and/or calcining process in the third chamber may be directed to dry the intermediate product of surface and/or pore-bound moisture in a product manufacturing station including a first chamber. Similarly, working fluid used to induce mineral dehydroxylation in a product or tile manufacturing station including a second chamber may be directed to a product or tile manufacturing station including a first chamber for the purposes of drying the surface and/or pore- bound moisture of an intermediate product therein. As will be described below in relation to solar kiln processes, the working fluid used in a process at a first temperature may be subsequently used in a process at a lower second temperature to efficiently utilise the heat transferred to the working fluid by the solar receiver or other means. [0030] As described herein, the solar kiln may include a product manufacturing station in which a given unfinished product may be dried, subjected to mineral dehydroxylation, and subsequently calcined in a single chamber of the product manufacturing station. In such examples, the temperature of the working fluid may be controlled using the solar receiver to prevent premature overheating of the unfinished product. Controlling the temperature of the working fluid may include reducing the maximum temperature of working fluid heated by the solar receiver by occluding, or partly occluding portions of the solar receiver such that a reduced concentration of solar radiation is incident upon the solar receiver, deactivating one or more heliostats to reduce to the c value upon the receiver, increasing the rotational speed of the solar receiver where the solar receiver is a rotor, actively cooling the heated working fluid, or any other suitable process for reducing the maximum energy imparted to the working fluid. When high temperature working fluid is required, such processes may be operated in reverse and the intensity of incident solar radiation increased, and/or the maximum temperature of the solar receiver increased such that a greater maximum energy may be imparted to working fluid by the solar receiver.

[0031] In general, the process for producing a product using a solar kiln includes directing solar radiation on to at least a portion of a solar receiver to form a heated solar receiver, transferring heat from at least a portion of the heated solar receiver to a working fluid to form a heated working fluid; passing the heated working fluid to a product manufacturing station, and heating one or more intermediate products using the heated working fluid. The product may be a brick or a tile and the intermediate products may be any unfinished, mid-production, pre-production, intermediate, or work in progress product such as a bricks or tiles that have not yet been ‘fired’ via sintering and/or calcination. In general, an intermediate product will not yet have been processed to become a finished product by, for example, sintering and/or calcining the intermediate product.

[0032] As previously discussed, the process of producing pottery, ceramics, earthenware, stoneware, and similar products includes processes stages where the intermediate product is heated in at least three stages. These three stages include drying the product, inducing mineral dehydroxylation, and then sintering and/or calcining the product. The drying stage typically takes place at temperature of between 80 °C and 300 °C. The mineral dehydroxylation stage typically takes place at a temperature of between 400 °C and 800 °C. The sintering and/or calcining stage typically takes place at between 700 °C and 1400 °C. One or more additional thermally induced processes may be included in the production process including, but not limited to, combustion of organic matter, alpha-beta silicon dioxide inversion, carbonate decomposition, densification, glass transition, eta-alpha silicon dioxide inversion. The calcining and/or sintering stage of the process is typically followed by a densification of the product. The process of producing a brick or tile from initial wet raw material generally consumes in excess of 700 kilojoules of heat per kilogram of final product produced. It is therefore important that the solar kiln collects sufficient energy via the solar receiver such that working fluid heated by the solar receiver may impart sufficient energy to the intermediate product to allow the production process to continue to completion.

[0033] The process includes the directing of solar radiation on to at least a portion of a solar receiver to form a heated solar receiver. The solar receiver collects the incident solar radiation as heat and then transfers this heat a working fluid that subsequently provides heat for the production of pottery, ceramics, earthenware, stoneware, and similar products including bricks and tiles. The process may use a gaseous working fluid. The gaseous working fluid may be air. The use of air as a working fluid may be advantageous as air is abundant, cheap, and safe. Incident solar radiation may be directed towards the solar receiver from one or more optical elements of sufficient surface area to provide a c value of greater than or equal to 75 or more, 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, 750 or more, or 1000 or more. It may be advantageous to concentrate incident solar radiation upon the solar receiver at a c value of 400 or more as this c value is believed to impart sufficient energy under most configurations to complete the thermal stages of the manufacturing cycle of pottery, ceramics, earthenware, stoneware, bricks, tiles, and the like. More particularly, a c value of 400 or more is believed to be sufficient to provide above 700 kilojoules of heat per kilogram of finished produced to be produced via the processes described herein.

[0034] Without being bound by theory, the raw materials suitable for the production of pottery, ceramics, earthenware, stoneware, and similar products including bricks and tiles includes minerals and predominantly inorganic materials that typically harden or set when exposed to sufficient heat. Such materials include, but are not limited to those composed of 50% or more silica by weight, those composed of 10% or more alumina by weight, and those including ferric oxide, titania, quicklime, magnesia, potassium oxide, sodium oxide and/or any combination thereof. The proportion of each component in a raw material will vary depending on the intended product and the person skilled in the art, with the benefit of this disclosure, will be able to identify suitable raw materials for use in the manufacturing or products using the processes and solar kilns described herein. During the sintering and/or calcining process, the raw materials typically undergo physicochemical changes induced by thermal energy. For example, ceramic materials consume energy to undergo transformation to quartz, haematite, anorthite, wollastonite, enstatite, diopside, gehlenite, mullite, potassium feldspar, albite, lllite or muscovite mica, akermanite, periclase, other suitable minerals, and/or any combination thereof.

[0035] The process of manufacturing of pottery, ceramics, earthenware, stoneware, and similar products including bricks and tiles may require several hours from start to finish. The drying stage of the process may take between 1 hour and 5 hours or more. For example the drying stage of the process may take 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or more than 5 hours. The mineral dehydroxylation step of the process may require between 4 hours and 12 hours or more. For example, the mineral dehydroxylation step may require 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or more than 12 hours to carry out the process in a satisfactory manner. The mineral dehydroxylation stage of the process may include endothermic reactions and so heat energy may be absorbed by the process which in turn lowers the temperature of the working fluid used to heat the products. Consequently, this stage of the process may involve the highest energy burden among the common steps in the production lifecycle. During both the drying and the mineral dehydroxylation steps of the process it is generally not possible to heat the unfinished product rapidly as water driven from the material at too high a rate may result in cracking, void formation, shattering, or similar damage to the unfinished product. In these stages the temperature of the product is therefore increased gradually either by exposure of the unfinished product to working fluid of gradually increasing temperature, or by managing the flow of working fluid and carried thermal energy to which the unfinished product is exposed. Unfinished material in the drying and/or mineral dehydroxylation stage may therefore be heated at a rate of between 30 °C and 400 °C per hour. For example, the unfinished product may be heated at a rate of 400 °C per hour, 350 °C per hour, 300 °C per hour, 250 °C per hour, 200 °C per hour, 150 °C per hour, 100 °C per hour, 80 °C per hour, 60 °C per hour, 50°C per hour, 40°C per hour, 30 ^oC per hour, or 20 ^oC per hour. The optimal rate of hearing will be dependent upon the nature of the product being heated, the desired speed of production, and the rate required to prevent an unacceptable proportion of product failure. The sintering and/or calcination stage of the process may be carried out at temperatures of 700 °C to 1400 °C. In other examples, the sintering and/or calcination stage may be carried out at temperatures of 400 °C to 1200 °C. The sintering and/or calcination process may involve heating the unfinished product at a rate of between 100 °C per hour to 400 °C per hour for a period of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or more than 6 hours. The high temperatures required to satisfactorily operate the sintering and/or calcination process require a working fluid with the greatest energy burden of any stage in the process. It may therefore be advantageous to utilised heated working fluid heated via the solar receiver directly in the sintering and/or calcination process without further processing and with the minimum possible loss of energy from the working fluid. The drying, mineral dehydroxylation, and/or sintering/calcining processes may require a peak energy consumption in the range of 100 to 600 Watts per kilogram of unfinished product. However, towards the end if the sintering and/or calcination stage of the process the energy consumed by the unfinished product may be reduced, requiring only 150 to 300 Watts of energy per kilogram of unfinished product.

[0036] In the processes described herein, heating the one or more unfinished products such as a work in progress or intermediate brick or tile may include drying the unfinished product to remove surface and/or pore bound moisture, heating the unfinished product to induce mineral dehydroxylation whereby water of crystallisation, molecular water, and/or internal water is removed from the unfinished product, and heating the unfinished product to induce sintering and/or calcination. The temperature of the working fluid required during each heating step of the process may be higher than the temperature to which the unfinished product is to be heated. For example, if a sintering and/or calcination process requires the heating of an unfinished product to 1200 °C, the working fluid heated by the solar received may, in use, require to be heated to a temperature of 1250 °C, 1300 °C, 1350 °C, 1400 °C or more. Heating the the one or more unfinished products may include increasing the temperature of the one or more unfinished products to over 400 °C such as to temperatures of 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, or 1500 °C. Heating the one or more unfinished products may be carried out solely using the heated working fluid with the heating working fluid being heated substantially only using heat energy imparted from the solar receiver and exothermic reactions occurring within the manufacturing process. In an example, the process may include no significant input of heat energy other than from the solar receiver.

[0037] In general the sintering process is performed at a higher temperature than the mineral dehydroxilation process, which in turn is performed at a higher temperature than the initial drying process. Working fluid initially used to heat the unfinished product in the sintering and/or calcination process may therefore be used in the mineral dehydroxylation process once its temperature has decreased, or its energy has diminished to the point where it is of a suitable temperature or energy to not increase the temperature of the unfinished product at an undesirable rate. Similarly, working fluid used to induce the mineral dehydroxylation may be used in the drying process once its temperature has decreased, or its energy has diminished to the point where it is of a suitable temperature or energy to not increase the temperature of the unfinished product at an undesirable rate. Working fluid used in the sintering and/or calcination process may be subsequently used in the mineral dehydroxylation process and/or the drying process. Working fluid used in the mineral dehydroxylation process may therefore be used in the drying process. In this manner, heat energy initially provided by the solar receiver and exothermic reactions occurring within the manufacturing process, and optionally provided substantially only by the solar receiver and exothermic reactions occurring within the manufacturing process, may be used, re-used, and/or recycled throughout the manufacturing process. Sintering and/or calcining one or more intermediate products using the working heated by the solar receiver may form an intermediate working fluid, wherein the intermediate working fluid is a lower temperature than the heated working fluid. The intermediate working fluid may be used to dry one or more intermediate bricks to remove surface and/or pore bound moisture; and/or to induce mineral dehydroxylation to remove bound hydroxyl groups, water of crystallisation, molecular water, and/or internal water from one or more unfinished products.

[0038] In practice, solar radiation is available only during hours of daylight. For example, daylight may be available for a period of approximately 8 hours. The solar receiver may therefore only heat the working fluid during periods of daylight in which sufficient incident solar radiation can be focussed upon the solar receiver. In periods where no or little solar radiation is incident upon the solar receiver, it may not be possible to maintain working fluid at a sufficient temperature to carry out the sintering and/or calcination step of the manufacturing process. In such periods, such as during the night, working fluid may be passed across product which has recently undergone sintering and/or calcination and therefore possesses a high residual temperature and associated heat energy. While it may not be possible use such working fluid for the purposes of sintering and/or calcination, this working fluid may yet be used in the mineral dehydroxylation process and/or the drying process in the manner previous described. Manufacturing processes may therefore be scheduled such that unfinished products such as unfinished bricks and unfinished tiles are sintered and/or calcined during periods of daylight and the residual energy in the then finished products is captured and used in the mineral dehydroxylation and/or drying processes which are performed at lower temperature ranges. The finished products formed following the sintering and/or calcining step may be hot products and working fluid may be passed across, over, around, or through one or more hot products to form a warm working fluid, wherein the warm working fluid is a higher temperature than the working fluid. The warm working fluid may then be used to dry one or more intermediate bricks to remove surface and/or pore bound moisture, and/or to induce mineral dehydroxylation. The warm working fluid may be used in this manner during night-time and/or periods of low incident solar radiation. In periods of night-time or low incident solar radiation, the working fluid heated via the hot product may be flow throughout the process in a substantially closed-loop flow path. For the avoidance of doubt, the use of working fluid in this manner is not limited to periods of night-time or low incident solar radiation. However, it may be optimal to use working fluid in this manner at such times. In general, working fluid may also be used in this manner to cool a finished product that has been sintered and/or calcined, and/or unfinished products that have been heated during drying or mineral dehydroxylation processes. The use of working fluid to cool the finished or unfinished product may allow the working fluid to pick up additional heat energy which may then be used elsewhere in the process by cycling the working fluid back to a process step where it may be used.

[0039] The drying process and/or the mineral dehydroxylation processes described herein will generally release water from the unfinished product which will be picked up in, carried by, or form part of the working fluid stream. Over time, the moisture content of the working fluid may increase to undesirable levels. The process may therefore include a means to remove water from the working fluid. The removal of water may be carried out by a dehumidifier, a condenser, or the like. Additionally, or alternatively, at least a portion of the working fluid may be continuously or intermittently removed from the process and replaced with a working fluid with a lower or negligible water content. These processes may be used together or in isolation to maintain desired levels of moisture in the working fluid. In processes where working fluid is removed from the process intermittently, the working fluid may flow in a closed loop or circuit at times when working fluid is not being removed and/or exchanged.

[0040] In general, the solar kiln and associated processes described herein operate as follows. Incident solar radiation is directed to a solar receiver via one or more optical arrangements which may include one or more heliostats. The solar radiation absorbed by the solar receiver as heat energy is then transferred to a working fluid to heat the working fluid. The heated working fluid is then directed to a product manufacturing station where an unfinished product such as pottery, ceramics, earthenware, stoneware, or similar product is to be heated to sinter and/or calcine the unfinished product, to induce mineral dehydroxylation in the unfinished product, and/or to dry surface and/or pore-bound moisture from the unfinished product. In one example, the heated working fluid from the solar receiver is used to sinter and/or calcine a first unfinished product at a maximum temperature of 1000 °C or more. The working fluid, once used in the sintering and/or calcination process, is then used to induce mineral dehydroxylation in a second unfinished product. The working fluid used to induce mineral dehydroxylation in a second unfinished product may then be used to dry a third unfinished product. When incident solar radiation is unavailable, the solar receiver is unable to provide additional energy to the working fluid, and so working fluid may be passed across hot finished products to collect sufficient energy to induce mineral dehydroxylation or the drying or unfinished products. In a similar manner, working fluid may be passed across hot dehydroxylated product to collect sufficient energy to dry other unfinished products.

[0041] The solar kiln processes may be scheduled to efficiently process raw materials while also optimising the use of heat energy throughout the process. The manufacturing processes may be scheduled such that the sintering and/or calcination, mineral dehydroxylation, and or drying processes are carried out in the same product manufacturing station when solar radiation is available. In this example, unfinished product may be moved into, and subsequently out of, a product manufacturing station such that, in a given product manufacturing station, a first unfinished product is sintered and/or calcined followed by the mineral dehydroxylation of a second unfinished product followed by the drying of a third unfinished product. In this example, working fluid remains resident in a particular product manufacturing station for multiple manufacturing processes. However, this is merely one option for operation of the system and working fluid may instead be passed between product manufacturing stations in which different processes take place upon different unfinished products.

[0042] When it can be predicted that incident solar radiation is unavailable, such as in periods of night-time or obfuscation of the sun, the sintering and/or calcination may be scheduled to complete around the time that incident solar radiation becomes unavailable. At such times, cooling processes may be scheduled to start for a batch of product that previously, or more recently, completed the sintering and densification stage, thus providing the opportunity for heat emitted by the batch to be reused and/or recycled as described herein. Radiative heat transfer occurs in the product manufacturing stations. In one example, working fluid used to cool previously sintered and/or calcined product may have a temperature difference of 500 to 1000 °C between the working fluid and the hot sintered/calcined product. Radiative heat transfer from the hot sintered/calcined product to the working fluid may potentially reach 50 to 200 kilowatt per square meter of product surface area.

[0043] When it can be predicted that incident solar radiation will become available again during periods of available sunlight, the batch which previously completed the sintering and/or calcination stage may be transported out of the product manufacturing station for further cooling. The product manufacturing station, now available, may be used for sintering and/or calcining of further product and material that had previously been subject to mineral dehydroxylation may now be sintered and/or calcined in the product manufacturing station as working fluid may once again be heated to a sufficient temperature for sintering and/or calcination due to the solar radiation incident upon the solar receiver. These product manufacturing cycles may be continued on a daily schedule or as required by a user depending at least in part upon the availability of sunlight.

[0044] Figure 1A shows a schematic view of an example of a solar kiln system 100 as described herein. The solar kiln system includes a heliostat field 101 configured to direct solar radiation 102 towards solar receiver 103 mounted atop a support tower 104. The support tower is positioned apart from ceramic manufacturing facility 105 which houses a first ceramic manufacturing station 106, a second ceramic manufacturing station 107, and a third ceramic manufacturing station 108. A series of conduits carrying working fluid 109 fluidly couple the solar receiver 103, the first ceramic manufacturing station 106, the second ceramic manufacturing station 107, and the third ceramic manufacturing station 108 such that working fluid can flow from the solar receiver 103 to the first, second, and then third manufacturing stations 106, 107, 108 and then back to the solar receiver 103 in a flow direction 110. The solar radiation from the heliostat field 101 heats the solar receiver 103 atop the support tower 104 which in turn heats the working fluid 109 flowing through the conduits in proximity and/or in fluid communication with the solar receiver 103. The heated working fluid is then passed to the first manufacturing station 106 where it is used to heat a first unfinished ceramic product. In an example the first manufacturing station is used to sinter and/or calcine the first unfinished ceramic product. The working fluid is then passed to the second manufacturing station 107 where it is used to heat a second unfinished ceramic product. In an example, the second manufacturing station is used to induce mineral dehydroxylation in the second unfinished ceramic product. The working fluid is then passed to a third ceramic manufacturing station where the working fluid is used to heat a third unfinished ceramic product. In an example, the third unfinished ceramic product is dried in the third manufacturing station. In the examples of Figure 1A, the first, second and third unfinished ceramic products may be unfinished bricks and/or tiles. [0045] Figure 1 B shows an alternative example of a solar kiln system 150. The solar kiln system 150 of Figure 2 operates in a similar manner to solar kiln system 100 of Figure 1 . Solar kiln system 150 includes a heliostat field 151 configured to direct solar radiation 152 towards solar receiver 153 mounted atop a support structure 154. In contrast to the system 100 of Figure 1 , the solar receiver 153 is not mounted on a support tower distinct from the ceramic manufacturing facility 155 and is instead mounted directly upon the manufacturing facility 155 itself via support structure 154. As demonstrated, the solar receivers of the solar kiln systems described herein may therefore be part of, and/or integrated with a manufacturing facility without being positioned distant from the facility that they heat. The manufacturing facility 155 of Figure 1 B includes a first ceramic manufacturing station 156, a second ceramic manufacturing station 157, and a third ceramic manufacturing station 158. A series of conduits carrying working fluid 159 fluidly couple the solar receiver 153, the first ceramic manufacturing station 156, the second ceramic manufacturing station 157, and the third ceramic manufacturing station 158 such that working fluid can flow from the solar receiver 153 to the first, second, and then third manufacturing stations 156, 157, 158 and then back to the solar receiver 153 in a flow direction 160 in the manner described in respect of system 100 of Figure 1 .

[0046] Figure 2 shows a process flow diagram of a process 200 for manufacturing ceramic products as described herein. The process 200 includes directing 201 solar radiation on to a solar receiver to form a heated solar receiver and transferring 202 heat from the heated solar receiver to a working fluid to form a first heated working fluid. The process further includes passing 203 the first heated working fluid to a ceramic product manufacturing station, and heating 204 one or more unfinished ceramic products using the first heated working fluid. The process 200 may include one or more additional process steps as substantially described herein such as cooling one or more unfinished ceramic products.

[0047] Figure 3 shows a schematic view of at least part of a solar kiln system 300 as described herein. The solar kiln system 300 includes a solar receiver 301 , a product manufacturing station 302, a fan 303, a series of conduits configured to allow working fluid 304 to flow around the solar kiln system in a flow direction 305. The solar kiln system 300 of Figure 3 may be operated during periods of incident solar radiation such as when the sun is shining. Incident solar radiation 306 is directed towards the solar receiver 301 which heats the working fluid 304 flowing in flow direction 305. The fan 303 provides the means through which working fluid is directed throughout the solar kiln system 300. An unfinished ceramic product housed in product manufacturing station 302 is heated by flowing the working fluid 304 heated by the solar receiver 301 through the product manufacturing station 302. Once the working fluid 304 has imparted sufficient heat to the unfinished product in product manufacturing station 302 the working fluid flows via the action of the fan 303 back to the solar receiver 301 where it is heated once again. In an example, the working fluid leaving the solar receiver may be at a temperature of 1200 °C or more. The working fluid flowing between the product manufacturing station 302 and the solar receiver via the fan 303 may be at a temperature of 600 °C ± 100 °C.

[0048] Figure 4 shows a schematic view of at least part of a solar kiln system 400 as described herein. The solar kiln system 400 includes a first product manufacturing station 401 and a second product manufacturing station 402. A series of conduits containing working fluid 404 connects the first product manufacturing station 401 and the second product manufacturing station 402. The working fluid 404 flows through the conduits in a flow direction 405 through the action of a fan 403. A hot finished or unfinished ceramic product may reside in the second product manufacturing station 402. The hot finished or unfinished ceramic product may be at a temperature of between 1200 °C and 200 °C depending upon the heating process to which it was most recently subjected. Working fluid directed by fan 403 passes through the second product manufacturing station 402 where it acquires heat energy radiated from the hot finished or unfinished product. The heated working fluid 404 then flows through the conduits to the first product manufacturing station 401 where the heat energy in the working fluid 404 may be used to heat an unfinished ceramic product in the first product manufacturing station 401 . The unfinished ceramic product in the first product manufacturing station may be at a temperature of between 25 °C and 700 °C depending on the stage of manufacturing to be carried out in the first product manufacturing station 401. The solar kiln system 400 shown in Figure 4 may be used in periods where there is limited or no incident solar radiation which prevents the heating of working fluid using a solar receiver. A solar kiln system may comprise both the systems 300 and 400 shown in Figures 3 and 4 such that the solar kiln can use one or more of the modes of operation depicted in the Figures interchangeably or as desired in response to changes in incident solar radiation or the presence or lack of incident solar radiation. It should also be understood that the product manufacturing stations 401 , 402, and 302 of the systems 300 and 400 may be movable chambers so that the heated chamber 302 of Figure 3 can be removed from the system 300 and inserted into the system 400 of Figure 4 to provide the product manufacturing station 402.

[0049] Figure 5 shows a process flow diagram of a process 500 for manufacturing ceramic products as described herein. The process 500 includes heating 501 one or more unfinished ceramic products at a first ceramic product manufacturing station using a heated working fluid. The process further includes transferring 502 the heated working fluid from the first ceramic product manufacturing station to a second ceramic product manufacturing station. The process yet further includes heating 503 one or more unfinished ceramic products at the second ceramic product manufacturing station using the heated working fluid.

[0050] Figure 6 shows a schematic diagram of another solar kiln system 600. As with the previous solar kilns described, the solar kiln system 600 includes a heliostat field 601 configured to direct solar radiation 602 towards solar receiver 603 mounted in a suitable location. The solar kiln system includes a track 604 along which unfinished ceramic products are transported. As the unfinished ceramic products are transported along the track they pass through a plurality of product manufacturing stations 605, 606 and 607, and cooling stations 608 and 609.

[0051] The hottest product manufacturing station is product manufacturing station 607, in this example the middle station, which is heated using a working fluid heated in the solar receiver 603 as described elsewhere. The products leaving product manufacturing station 607 pass into cooling station 608 where the hot products are used to heat a working fluid which can be used to heat the products in product manufacturing station 606 which is just before they enter product manufacturing station 607. The, now cooler, products exiting cooling station 608 are still warm enough in cooling station 609 to heat a working fluid which can be used to heat products in product manufacturing station 605, which is the first product manufacturing station encountered by the products in this example. In this way products moving along the track are heated by the residual heat of the products heated in the hottest product manufacturing station 607. The track 604 includes a hairpin bend 610 within product manufacturing station 606 so that cooling station 608 and product manufacturing station 606, and cooling station 609 and product manufacturing station 605 are located close to one another.

[0052] The solar kiln 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 kiln and processes described herein may be modified without departing from the scope of the invention as defined by the appended claims.