Drying system for bulk materials

Abstract

The present invention describes a solar drying system for bulk materials comprising a transport device, a drive device, an air inlet and an air outlet, as well as a bulk material feed and a bulk material discharge, characterized in that the drying system has a substantially horizontal first tube and a substantially vertical second tube, wherein the first tube and the second tube are in an air-conducting connection, wherein material to be dried, in particular bulk material, and drying air are passed through the first tube and only air, in particular only drying air, is passed through the second tube, and wherein the drying air is heated by solar energy.

Description

[0001] The present invention relates to a drying plant for bulk materials.

[0002] Drying systems for bulk materials are well known in the art. For example, bulk materials are dried in drum dryers, which are fed with heated air for drying.

[0003] The drying air is heated, for example, by flue gas from a solid fuel furnace, by gas burners, by hot gas from a gas turbine or a gas engine, or the like.

[0004] In a drum dryer, the product to be dried is placed into a rotating drum or tube. The product then trickles through the directly or indirectly heated drum and heats up. Any water contained in the product evaporates and is absorbed by the drying air. At the end of the drum, the dried product is separated in a discharge housing and discharged. Rotary tube dryers are suitable for high throughputs. The moist material is mixed by the rotating movement of the tube. Internal components inside the tube, such as lifting vanes, lift the product to be dried and ensure intensive contact with the drying gas, which flows through the tube in cocurrent or countercurrent flow. Exhaust gas from burners with very high temperatures is often used as the drying gas (direct-fired dryers).

[0005] There are many other state-of-the-art options for drying bulk materials. However, the common feature of state-of-the-art dryers is that they use varying amounts of energy to complete the drying process in the shortest possible time. These processes therefore generally require a high level of control to keep energy consumption as low as possible. Conventional drying systems are therefore usually highly complex and require a high level of material and, in turn, energy input during their construction.

[0006] Solar, energy-efficient drying has so far been limited to simply dumping and shifting bulk material on covered, well-ventilated areas. The air for drying is either heated by actively induced heat buildup or heated air is obtained, for example, using special thermal collectors. This type of process is also referred to as discontinuous. A limited amount of material is fed into the process system as a whole and removed from it as a whole after the drying process is completed.

[0007] The disadvantage here is that storage areas must be provided both for the supply of new material and for the storage of dried material. The material to be dried remains stationary during the discontinuous process, which makes drying increasingly difficult in the interior of the pile. Rearranging the material, for example, with wheel loaders, is complex and difficult to control.

[0008] The object of the present invention is to provide a drying system for bulk materials with the lowest possible primary energy requirement, while minimizing control effort. At the same time, the use of embodied energy should be minimized.

[0009] The grey energy of a product is the total energy required for its production, transport, storage, sale and disposal.

[0010] The aim of the present invention is, in the preferred case, to combine decommissioned machine or plant components with solar energy input in such a way that the grey energy in the machine and plant components is used and the primary energy consumption during operation is reduced to as little as possible.

[0011] This problem is solved by a solar drying system for bulk materials having the features of patent claim 1.

[0012] Advantageous embodiments and variants of the invention emerge from the dependent claims and the following description. The features listed individually in the dependent claims can be combined with each other in any technically reasonable manner, as well as with the features explained in more detail in the following description, and represent other advantageous embodiments of the invention.

[0013] A solar drying system for bulk materials according to the invention comprises a transport device, a drive device, an air inlet and an air outlet as well as a bulk material feed and a bulk material discharge, wherein the drying system comprises a first substantially horizontal tube and a second substantially vertical tube, wherein the first tube and the second tube are in air-conducting communication, bulk material and drying air are passed through the first tube and only air, in particular only drying air, is passed through the second tube, and wherein the drying air is solar-heated.

[0014] A solar drying system designed in this way combines several advantages. Firstly, it enables a continuous drying process thanks to the transport device for conveying the bulk material. This allows a continuous supply of bulk material to be dried and a continuous removal of dried bulk material, unlike batchwise or batch-wise drying. This makes it possible to stabilize upstream and downstream processes and thus ensure continuous machine utilization. The transport device can be designed separately or, preferably, integrally with the first tube. A separately designed transport device can be designed, for example, as a belt conveyor or as a screw conveyor. However, a design in which the bulk material is transported by a rotation of the first tube is preferred.For this purpose, a surface line can have a gradient at the lowest point of the tube, so that the end of the first tube facing the bulk material inlet is higher than the end of the first tube facing the bulk material outlet. In this case, the bulk material is transported by the gradient as the tube rotates around its longitudinal axis, and is simultaneously circulated and aerated by the rotation. Aeration can be promoted by additional fittings, such as scoops or flights.

[0015] Secondly, the two tubes, which are connected by air conduction, create a continuous airflow through solar radiation, heating the first horizontal tube and natural convection. This airflow rises through the second tube, which acts as a chimney, and draws additional air into the first tube. Thus, a continuous airflow prevails in the first tube for drying the bulk material.

[0016] The fact that only air is passed through the second tube means in particular that the second tube is not flowed through by the bulk material, but only by air from the first tube, ie the drying air and possibly other air.

[0017] The effect achieved by solar heating and convection can be further enhanced if the first tube has a solar enclosure, whereby the solar enclosure has a roof, preferably also walls, made of a translucent and, if necessary, heat-insulating material.

[0018] A solar enclosure can significantly increase the heating of the first tube and the air surrounding it through the resulting greenhouse effect. The increased heating of the air results in greater convection, resulting in a stronger airflow. Furthermore, the more heated air can also absorb more moisture from the bulk material being dried. This significantly increases the overall drying capacity of the system.

[0019] In a preferred embodiment, the solar drying system is designed according to the countercurrent principle. In a drying system based on the countercurrent principle, the material to be dried and the drying air move in opposite directions. This also means that the drying air with the highest temperature and the lowest water vapor content hits the material to be dried shortly before the discharge and is then passed over the remaining material in the first tube before entering the second tube. This has the advantage of ensuring that the material is dried before the discharge with the most heated drying air with the highest moisture absorption capacity, thus achieving complete drying of the material to be dried.

[0020] In principle, it is conceivable that the drying air could be heated by additional heating devices, such as gas burners, electric heaters, or the like, in addition to solar heating. This design can ensure weather-independent operation of the drying system.

[0021] As part of sector coupling, it is also conceivable that surplus electricity from renewable energies, particularly wind power, hydropower, or photovoltaics, could be used for drying. For example, the surplus energy in the grid can be converted into heat for drying using a heater, into movement of the first tube, and / or into an air stream using a fan, and thus utilized.

[0022] However, a preferred embodiment of the solar drying system is one in which the drying air generation is solar-autonomous.

[0023] In this context, solar self-sufficient means that the drying air is heated exclusively by solar energy. Due to the previously described design of this drying system, the solar heating of the air simultaneously induces convection, which creates an air flow in the opposite direction to the material flow. Therefore, no additional air circulation is required.

[0024] To further increase the efficiency of solar heating of the drying air, it is advantageous if surfaces within the solar enclosure and / or the vertical tower have a surface with increased light absorption, particularly if they are coated with a coating with increased light absorption. This can be achieved particularly easily if these surfaces are coated black.

[0025] A particularly important surface within the solar enclosure is the surface of the first tube. A surface with increased light absorption enables both improved heating of the air within the solar enclosure, which then flows through the first tube, and direct heating of the first tube, which heats and thus improves the drying of the dry material contained within.

[0026] In a further development of the drying system, the connection between the first and second tubes has an adjustable effective cross-section. By adjusting this cross-section, the air flow velocity can be regulated. This allows the contact time between the bulk material and the drying air to be adjusted.

[0027] An updraft turbine for generating electricity can be installed in the second tube. The air flow caused by convection drives the updraft turbine and can thus contribute to the drying system's completely energy-independent operation. The generated electrical energy can, for example, be used to rotate the first tube, thus circulating and conveying the bulk material to be dried.

[0028] If, due to strong solar radiation, there is too much thermal energy available that is not needed for drying the material, in one embodiment the updraft turbine can also be supplied with heated air that was not passed through the first tube via a bypass, thus generating electrical energy.

[0029] In a preferred embodiment, the first tube and / or the second tube is conical, in particular a diameter of the first tube can increase with increasing distance from the second tube.

[0030] In the design with conical tubes, the air flows from one end with a large cross-section to one end with a smaller cross-section in the first tube. Due to the decreasing cross-section in the direction of flow in the first tube, the air flow velocity increases with the decreasing cross-section.

[0031] As already explained above, the first tube is preferably arranged such that a bottom surface of the first tube slopes downwards from an end facing the second tube, i.e., a surface line at a lowest point of the tube slopes downwards, so that the end of the first tube facing the bulk material inlet is higher than the end of the first tube facing the bulk material outlet. In this case, the bulk material is transported by the slope as the tube rotates about its longitudinal axis, and is simultaneously circulated and aerated by the rotation.

[0032] To ensure the most energy-efficient construction of the drying system, it is advantageous to use a dismantled wind turbine tower as the first and / or second tube. Such tubes are available in large numbers from the repowering of wind turbines, as they generally cannot be reused during repowering.

[0033] Further savings in required energy consumption can be achieved if the first tower is mounted on used truck axles, preferably used ones. Used truck axles are also available in large quantities, allowing for optimal reuse.

[0034] By using dismantled towers from the repowering of wind turbines and used truck axles, the energy required to construct the drying plant can be minimized. The embodied energy previously used to construct the wind turbines and truck axles can thus be reused for the drying plant.

[0035] The first tube preferably has a length of at least 5 m. The length of the first tube and the residence time of the material in the first tube are preferably coordinated such that drying of the material is achieved at a predetermined duration and intensity of solar radiation.

[0036] The second tube preferably has a length of at least 10 m, preferably at least 15 m or more. From such a length, a sufficient chimney effect is achieved, ensuring a sufficient air flow velocity.

[0037] The present invention will be explained in detail below using exemplary embodiments with reference to the accompanying figures. They show: Figure 1 shows an embodiment of a solar drying system.

[0038] In the figures, unless otherwise stated, the same reference symbols designate the same or corresponding components with the same function.

[0039] Figure 1 shows an embodiment of a solar drying system 100 according to the present application.

[0040] The solar drying system 100 shown is essentially constructed from recycled components. In this case, the tower of a decommissioned wind turbine was used. Such towers are tapered steel tubes composed of several segments, in this case four.

[0041] A first tube 1, consisting of upper segments of the tower, is arranged horizontally and supported on used truck axles 7. A second tube 3, consisting of lower segments of the tower, is mounted vertically with the foundation ring used for the wind turbine and connected to the first tube 1 in an air-conducting manner.

[0042] In a preferred case, the solar drying system 100 is constructed at the site of the reused wind turbine, continuing to utilize the existing foundation. This then does not require the laborious removal of the foundation, as is usually the case. The entire tower of the wind turbine can also be used as the second tube 3. The first tube 1 can also originate from another wind turbine.

[0043] Such towers can weigh up to 100 tons, but due to their original purpose, they are so rigid that great lengths can be used. Truck axles 7 are sufficiently resilient, technically simple, and available in large quantities.

[0044] The first tube 1 is arranged such that a first end 11 of the first tube 1, with a smaller cross-section, points towards the second tube 3, and a second end 12 of the first tube 1 is arranged pointing away from the second tube 3. A surface line at a lowest point of the first tube 1 has a gradient starting from the first end 11, so that material M to be dried, which is fed in at the first end 11, is automatically transported towards the second end 12 by the gradient when the first tube 1 rotates about its longitudinal axis.

[0045] In order to improve aeration and mixing of the material M to be dried, blades or carriers pointing inwards and suitably aligned for transporting the material M are arranged in the first tube 1, which lift the material M when the first tube 1 rotates, so that it is turned over as it falls and is thus mixed and aerated.

[0046] The truck axles 7 are arranged and aligned such that the first tube 1 rests on them at the previously described gradient. Depending on the length and weight of the first tube, one or more of the truck axles 7 can be equipped with a drive designed to rotate the first tube 1. In the present embodiment, an electric motor is used as the drive 13, which is arranged on the middle of three truck axles 7 and drives them.

[0047] The raw material is thus conveyed evenly toward the second end 12 and gently circulated and evenly heated by the rotation of the first tube 1. This prevents clumping. A low speed prevents breakage, abrasion, and the stirring up of the material to be dried.

[0048] At the first end 11 of the first tube 1, it has a bulk material feed 15, which in the present embodiment is designed as a lock for the material feed.

[0049] The bulk material is evenly fed into the higher first end 11 and moves slowly towards the lower second end 12 due to the rotational movement of the first pipe 1.

[0050] The first tube 1 is connected to the second tube 3 in an air-conducting manner, so that air flowing through the first tube 1 can pass into the second tube 3. A transition 14 from the first tube 1 to the second tube 3 has a variable effective cross-section, so that the amount of air flowing from the first tube 1 into the second tube 3 is adjustable.

[0051] The second tube 3 is coated on the outside with light-absorbing paint. A wind turbine 9 for generating electrical energy is arranged inside the second tube 3, between an upper end of the second tube 3 and the transition 14. The wind turbine 9 is arranged and designed such that, when the solar drying system 100 is in operation, it generates sufficient energy to operate the drying system 100. If additional electrical energy is required to operate the drying system, the wind turbine 9 can be supported by photovoltaic modules, allowing the drying system 100 to operate independently of its energy supply.

[0052] To enhance solar heating of the first tube 1 and the air L flowing through it, the first tube 1 has a solar enclosure 5 along its entire length, which in this case is designed as a glasshouse similar to a greenhouse. The solar enclosure 5 accordingly has a translucent roof and translucent side walls, which, in the preferred case, are also thermally insulating. The greenhouse effect desired for heating the first tube 1 and the air L surrounding it can be achieved, for example, with transparent glass or plastic panels.

[0053] The solar housing 5 is dimensioned in such a way that an air space of appropriate size is created between the solar housing 5 and the first tube 1, depending on the application.

[0054] In this room, as many surfaces as possible, including the outer surface of the first tube 1, are coated with light-absorbing paint.

[0055] Outside air flows in at one end of the greenhouse in a controlled manner and is heated as much as possible by solar radiation S.

[0056] The solar housing 5 has an air inlet at one end facing the second tube 3, which Figure 1 is marked with an arrow and the reference symbol L. Since the air L heated in the second tube 3 has a lower density due to the higher temperature, it rises upwards in the second tube 3 and heated air is sucked in from the first tube 1 and the solar enclosure 5, which then flows through the first tube 1 and over the material M to be dried. The air flow thus generated drives the wind turbine 9 and generates electrical energy, which feeds the drive 13 and thus sets the first tube 1 in rotation, so that the material M to be dried is circulated and transported.

[0057] A further rotating pipe can be installed inside the first pipe 1 in order to reduce the internal volume of the first pipe and increase the flow velocity of the air.

[0058] For highly dusty bulk materials, an additional solar enclosure 5 can be installed behind the second end 12 of the first tube 1 to settle the dust. This enclosure can be equipped with a large filter surface, if necessary. This allows for the generation of additional warm air for operation.

[0059] Heated air L not required in the dryer can be fed directly to the second tube 3 via a bypass and used to produce energy by means of the wind turbine.

[0060] With the exception of wind turbine 9, all mechanical movements will be very slow due to the size of the turbine. This means simple, low-maintenance components with minimal wear. Likewise, the effort required for control and accident prevention will be kept to a minimum.

[0061] Nevertheless, all process steps are measured and the system components are precisely controlled to optimize performance.

[0062] In the preferred case, all system components are used and can be reused unchanged after the system has been dismantled.

[0063] In the preferred case, no fixed foundations are necessary (except for the vertical tower). Mobile elements such as concrete "Legos" or concrete road slabs are used.

[0064] This solar drying system 100 is primarily designed for drying clay for clay plasters and clay adhesives. These natural products can further reduce their carbon footprint with CO2-neutral drying.

[0065] The reduction in the plant's production output that this usually entails will not be a problem for many bulk materials, even thanks to the cost savings achieved in this way.

[0066] The system's drying performance will fluctuate greatly depending on the time of day and the season. By using as many heavy heat-storing components as possible, such as the greenhouse base, limited operation at night will be possible.

[0067] The economic efficiency results from operation without external energy supply.

[0068] In the preferred case, a wind turbine tower or its lower segments are used at the original site. This allows the large amounts of embodied energy contained in the foundations to be utilized.

[0069] Constantly rising primary energy costs provide further incentive for investing in solar drying technology. List of reference symbols

[0070] 1First tube 3Second tube 5Solar enclosure 7Truck axle 9Wind turbine 11First end 12Second end 13Drive 14Transition 15Bulk material feed 100Drying plant MMaterial LAir SSun radiation

Claims

1. Solar drying plant (100) for bulk materials comprising a transport device, a drive device, an air inlet and an air outlet as well as a bulk material feed (15) and a bulk material discharge, characterized in that the drying system (100) has a substantially horizontal first tube (1) and a substantially vertical second tube (3), wherein the first tube (1) and the second tube (3) are in air-conducting communication, wherein material M to be dried, in particular bulk material, and drying air are passed through the first tube (1) and only air L, in particular only drying air, is passed through the second tube (3), and wherein the drying air is solar-heated.

2. Solar drying system (100) according to claim 1, characterized in that the first tube (1) has a solar housing (5), wherein the solar housing (5) has a roof, preferably also walls, made of a translucent and preferably heat-insulating material.

3. Solar drying system (100) according to one of the preceding claims, characterized in that the system (100) is designed according to the countercurrent principle.

4. Solar drying system (100) according to one of the preceding claims, characterized in that a drying air generation system is solar-autonomous.

5. Solar drying system (100) according to one of claims 1 to 3, characterized in that drying air extraction has external support.

6. Solar drying system (100) according to one of the preceding claims, characterized in that Surfaces within the solar enclosure (5) and / or vertical tower are provided with a surface with increased light absorption, in particular with a coating with increased light absorption, in particular that they are coated black.

7. Solar drying system (100) according to one of the preceding claims, characterized in thatthe connection between the first tube (1) and the second tube (3) has an adjustable effective cross-section.

8. Solar drying system (100) according to one of the preceding claims, characterized in that in the second tube (3) an updraft turbine (9) is arranged for generating electricity.

9. Solar drying system (100) according to one of the preceding claims, characterized in that the first tube (1) and / or the second tube (3) are conical.

10. Solar drying system (100) according to claim 9, characterized in that a diameter of the first tube (1) increases with increasing distance from the second tube (3).

11. Solar drying system (100) according to claim 10, characterized in that the first tube (1) is arranged such that a bottom surface of the first tube (1) has a gradient starting from an end facing the second tube (3).

12. Solar drying system (100) according to one of the preceding claims, characterized in that a dismantled tower of a wind turbine is used as the first and / or second tube (1, 3).

13. Solar drying system (100) according to one of the preceding claims, characterized in that the first tower is mounted on preferably used truck axles (7).

14. Solar drying system (100) according to one of the preceding claims, characterized in that the first tube (1) has a length of at least 3 m.

15. Solar drying system (100) according to one of the preceding claims, characterized in that the second tube (3) has a length of at least 5 m.

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