Drying tower for bulk material

Abstract

The invention relates to a drying tower for bulk goods, in particular agricultural grains, with at least one drying zone through which the bulk goods to be dried pass from top to bottom, and at least one air duct for passing air through the at least one drying zone, wherein at least one air inlet is provided for introducing fresh air from the vicinity of the drying tower as supply air into the at least one drying zone, wherein at least one air outlet is provided for removing exhaust air from the at least one drying zone, and wherein at least one heat exchanger is provided for transferring heat from the exhaust air to the fresh air, and at least one air return line for exhaust air is connected to the at least one air outlet and the at least one heat exchanger, and at least one air supply line for fresh air is connected to the at least one heat exchanger and the air inlet.

Description

Background of the invention

[0001] The invention relates to a drying tower for bulk material, in particular agricultural grains, comprising at least one drying zone through which the bulk material to be dried passes from top to bottom, and an air duct for passing air through the at least one drying zone. At least one air inlet is provided for introducing fresh air from the surroundings of the drying tower into the at least one drying zone as supply air, and at least one air outlet is provided for discharging exhaust air from the at least one drying zone. Furthermore, the invention relates to a method for operating such a drying tower for bulk material.

[0002] In drying towers of the above-mentioned type, which are also known as column dryers, agricultural products, especially grains such as cereals and corn, but also rapeseed or sunflowers, are dried with warm air. These drying processes have become established in the agricultural sector because they enable efficient, high-quality, and gentle drying of agricultural grains. The investment and operating costs are also low compared to other drying processes, such as freeze, vacuum, or radiation drying. The so-called roof-and-shaft dryer has generally prevailed, in which the drying zones are arranged consecutively in a vertical drying column and the bulk material to be dried passes through them from top to bottom.

[0003] The air flow initially passes across the drying column. Heated supply air flows in at one side of the drying column and then flows through the product bed there. This heats the product or bulk material and releases its moisture into the passing warm air. The bulk material dries. In turn, the air cools and becomes humidified. The moist air escapes as exhaust air at the other side of the drying column. The supply air and / or exhaust air are conveyed by motor-driven fans located in the air supply and / or air exhaust.

[0004] Such a drying tower is known from DE 20 2004 018 492 U1. It comprises a warm air generator and several stacked drying levels, as well as air ducts for supplying air at different temperatures to different drying levels. At least two drying levels are each assigned their own warm air generators, which can be operated independently of each other. The air is supplied through a common supply air duct and extracted by a fan on the side of a guide duct for the bulk material opposite the warm air generators. This type of air duct is technically comparatively complex and not very energy-efficient.

[0005] The invention is based on the object of reducing the energy consumption of a drying tower of this type as much as possible. Inventive solution

[0006] According to the invention, a drying tower for bulk material is created, in particular for agricultural grains, with at least one drying zone through which the bulk material to be dried must pass from top to bottom. The drying tower is provided with an air duct for passing air through the at least one drying zone, in which at least one air inlet is provided for introducing fresh air from the surroundings of the drying tower as supply air into the at least one drying zone. According to the invention, heat recovery from the exhaust air of the at least one drying zone is provided. For this purpose, at least one heat exchanger is provided for transferring heat from the exhaust air to the fresh air, as well as at least one air return duct for exhaust air, which is connected to the at least one air outlet and the at least one heat exchanger, and at least one air supply duct for fresh air, which is connected to the heat exchanger and the air inlet.Thus, according to the invention, the exhaust air is supplied to and passed through the heat exchanger via the air return pipe and the fresh air is supplied to the air inlet via the air supply pipe after the fresh air has passed through the heat exchanger.

[0007] According to the invention, by means of such heat recovery, a preheating of the fresh air supplied to the air inlet by approximately 20 Kelvin[k1] is achieved, whereby the energy required for this comes from the exhaust air itself and can thus be achieved without an additional energy input.

[0008] Advantageously, the at least one heat exchanger of the heat recovery system according to the invention is dimensioned such that moisture from the exhaust air condenses on it. Moisture condenses when the relative humidity of the relevant air reaches 100% (in words: one hundred percent). The relative humidity in air increases when the air, such as the warm exhaust air in this case, cools down. The condensation desired according to the invention is preferably achieved by the moisture condensing on a separating surface of the at least one heat exchanger. For this purpose, the exhaust air releases so much thermal energy at the separating surface that the relative humidity in the exhaust air reaches 100%. The at least one heat exchanger according to the invention thus advantageously has four functions. The first function is to dehumidify the exhaust air that flows through the at least one heat exchanger.The second function is to heat the supplied fresh air, which is passed through at least one heat exchanger. The third function is to reduce the relative humidity of the supplied fresh air by heating this fresh air. The fourth function is to dedust the exhaust air in the heat exchanger through condensation and the associated adhesion of dust to the moist surfaces of the heat exchanger.

[0009] Particularly preferably, the supplied fresh air is also further heated as such. For this purpose, the drying tower according to the invention preferably includes an air heater for heating the fresh air supplied through the air inlet.

[0010] In this case, the fresh air from the surroundings of the drying tower, preheated in at least one heat exchanger, is particularly preferably further adjusted to a temperature between 100 °C and 145 °C, in particular between 110 °C and 125 °C. These temperature ranges are particularly advantageous with regard to the overall energy balance of such a drying tower.

[0011] For the air guidance on the drying tower according to the invention, a first air extractor or blower is preferably provided for sucking exhaust air from the at least one drying zone. The air extractor creates a suction through the at least one drying zone. Furthermore, a second air extractor is preferably provided for sucking fresh air from the at least one heat exchanger to the air inlet. Thus, the exhaust air return and / or the fresh air supply are preferably each provided with a suction device by means of which the air to be conveyed is first sucked through the material to be dried and then returned or discharged. By conveying the air in this way by suction and not by blowing, a negative pressure can be generated within the material and the aforementioned sections, which prevents dust from escaping from these areas.

[0012] Preferably, the at least one drying zone comprises a plurality of drying zones, wherein a first part of the drying zones, preferably the lower section of a drying column, is provided upstream of or above a cooling zone in the flow direction of the bulk material. A second part of the drying zones is then the upper region of the drying column arranged above this first part.

[0013] In addition, for an even higher energy yield in the drying tower according to the invention, an air return or recirculation system can preferably be provided for returning at least part of the exhaust air from the first part of the drying zones as supply air back into the first part of the drying zones.

[0014] Particularly preferably, the drying tower according to the invention comprises a washing device associated with the at least one heat exchanger for washing out condensate and dust from the exhaust air passed through the at least one heat exchanger. The washing device is particularly preferably located above the at least one heat exchanger, so that wash water is particularly preferably fed from above onto the at least one heat exchanger, which in turn is particularly preferably flowed through by the exhaust air from below. This creates a countercurrent of wash water and exhaust air, which leads to particularly effective washing out of condensate and dust from the exhaust air.

[0015] Furthermore, according to the invention, a separation device can preferably be assigned to the at least one heat exchanger for separating condensate and dust from the exhaust air passing through the heat exchanger. The separation device is particularly preferably designed as a belt filter. The separation device can be arranged below the at least one heat exchanger and thus also collect the wash water from the washing device and filter out condensate and dust there. Instead of the belt filter, the use of a radial separator as the separation device is also conceivable according to the invention.

[0016] The condensate and dust from the exhaust air can then be removed from the separation device, collected and possibly further recycled.

[0017] According to the invention, a method for operating a drying tower for bulk material, in particular for agricultural grains, is further provided, in which at least one drying zone is passed through by bulk material to be dried from top to bottom and air is passed through the drying zone. In this case, fresh air from the surroundings of the drying tower is introduced into the at least one drying zone as supply air at an air inlet. According to the invention, heat is transferred from the exhaust air to the fresh air using at least one heat exchanger. Thus, according to the invention, the exhaust air is fed via the air return line to the [k2] heat exchanger and passed through the heat exchanger, and according to the invention, the fresh air is fed via the air supply line to the air inlet after the fresh air has passed through the heat exchanger.

[0018] Preferably, in such a method for operating a drying tower in accordance with the above-mentioned construction, the fresh air supplied through the air inlet is heated on an air heater.

[0019] The air heater is particularly preferably used to adjust fresh air from the surroundings of the drying tower to a temperature between 100 °C and 145 °C, in particular between 110 °C and 125 °C. Brief description of the drawings

[0020] In the following, exemplary embodiments of the inventive solution are explained in more detail with reference to the attached schematic drawings. It shows: Fig. 1 a schematic, mainly sectional side view of a drying tower for agricultural grains with a heat recovery device according to the invention, Fig. 2 a schematic, partially sectioned side view of the drying tower according to Fig.1 , Fig. 3a flow diagram of a first embodiment of a method according to the invention, Fig. 4 a flow diagram of a second embodiment of a method according to the invention, Fig. 5 a flow diagram of a third embodiment of a method according to the invention, Fig. 6 a flow diagram of a fourth embodiment of a method according to the invention and Fig. 7 a flow diagram of a fifth embodiment of a method according to the invention. Detailed description of the implementation examples

[0021] A drying tower 10 for agricultural grains comprises as essential components a drying column 12 with at least one drying zone T16 to T1, an air supply 14 and an air discharge 16.

[0022] At the top of the drying column 12 is a filling opening 18 for the bulk material 20 to be dried, in this case corn kernels. Due to the force of gravity acting on it, the bulk material 20 moves downwards from above through at least one drying zone T16 to T1 of the drying column 12. The bulk material 20 trickles down over roof-shaped air shafts (not shown in detail), each open at the bottom.

[0023] The air supply 14 is designed with an air inlet 22, which acts as an air supply shaft at the lower, relative to Fig. 1left end region of the drying tower 10. Fresh air 24 from the surroundings of the drying tower 10 passes through the air inlet 22 into a first part 26 of the drying zones T16 to T1, namely into the drying zones T8 to T3. This fresh air 24 is heated at the air inlet 22 in an air heater 28. The heated fresh air 24 is sucked as supply air through the first part 26 of the drying zones T16 to T1. It becomes enriched with moisture from the bulk material 20 there and is discharged from the drying column 12 again on the right side of these drying zones T8 to T3 as humidified exhaust air 30, which can also be referred to as intermediate air.

[0024] This exhaust air 30 or intermediate air is directed vertically upwards to the right side of the drying zones T16 to T9 by an air distributor 32 in the form of a fan (in particular an axial fan or a radial fan) or air extractor, forming a second part 36 of the drying zones T16 to T1. The exhaust air 30 or intermediate air there is heated to a higher temperature level by means of a hot air stream from an additional air heater 38.

[0025] The exhaust air 30 or intermediate air then passes through the second part 36 of the drying zones T16 to T1 and flows out as exhaust air 30 through an air outlet 34.

[0026] Downstream of the air outlet 34, at least one heat exchanger 40 is provided for transferring heat from the exhaust air 30 to the fresh air 24. An air return line 50 for the exhaust air 30 is connected to the at least one air outlet 34 and the at least one heat exchanger 40 (see Fig. 1 ). At least one air supply line 52 for the fresh air 24 is also connected to the at least one heat exchanger 40 on the one hand and the air inlet 22 on the other hand (see Fig. 2 ). Furthermore, a first air suction device 42 for sucking the exhaust air 30 from the at least one drying zone T16 to T1 (see Fig. 1 ) and a second air suction device 44 for sucking fresh air 24 from the at least one heat exchanger 40 to the air inlet 22 (see Fig. 2 ) is provided.

[0027] As in Fig. 1 As can be clearly seen, a washing device 54 is provided above the at least one heat exchanger 40, with several, in particular rotatable nozzles for spraying with washing water and for removing and washing out condensate or dust from the exhaust air 30 guided through the heat exchanger.

[0028] Additionally, a separation device 56 designed as a belt filter is arranged below the at least one heat exchanger 40 to separate dust from the condensate discharged from the heat exchanger. Alternatively, another type of separation device, such as a centrifuge, may also be provided.

[0029] The exhaust air is ultimately discharged further upwards from the drying tower 10 via an air discharge 16.

[0030] In the Fig. 3The basic principle of the solution according to the invention is specifically illustrated again: The drying tower 10 comprises a drying column 12 with at least one drying zone through which bulk material 20 passes from top to bottom and which further has a cooling zone 58, particularly at its lower end. Fresh air 24 is supplied to the drying column 12 through the heat exchanger 40. The thus preheated fresh air 24 is guided to the air heater 28, by which it is further heated. At the same time, fresh air is guided through the cooling zone 58 in order to cool the completely dried bulk material 20 there. This cooling air 60 is combined with the air heated by the air heater 22 and then guided into the drying column 12. By means of the air forwarder 32, the resulting exhaust air 30 is discharged again through the heat exchanger 40, preheating the fresh air 24.

[0031] The Fig. 4shows an embodiment of the inventive solution, in which the drying column 12 is divided into a first part 26 of drying zones and a second part 36 of drying zones. Here, the fresh air 24 is first passed through a preheater 62 and then through the heat exchanger 40. The fresh air 24 then reaches a first collection point 64, to which the fresh air 60 from the cooling zone 58 is also supplied. The fresh air 24 and fresh air 60 are then passed from the first collection point 64 to a second collection point 66.

[0032] In the first part 26 of the drying zones, the exhaust air 30 is circulated by means of an air extractor 68 and passed through the heat exchanger 40. A portion of the exhaust air 30 is discharged downstream of the drying zones by means of the air diverter 32 and passed through a heat exchanger 70. This partial air 72 is fed back into the recirculated air flow at the first part 26 of the drying zones. Further fresh air 74 is also passed through the heat exchanger 70, which is then preheated and passed past the second collection point 66 to the additional air heater 38, from which it is discharged into the second part 36 of the drying zones and through it to the outside by means of an air extractor 76.

[0033] The embodiment according to Fig. 5 is basically similar to that in Fig. 4shown. There is merely an additional heat exchanger 78 in the exhaust air stream behind the air extractor 76, through which the fresh air 24 is passed to the preheater 62.

[0034] The Fig. 6 also shows a Fig. 4 based embodiment, in which the only difference is that the additional air heater 38 is not connected directly into the supply air flow to the second part 36 of the drying zones, but instead preheats additional fresh air 80, which is then introduced into the said supply air flow at a third collection point 82.

[0035] The Fig. 7 Finally, shows an example of implementation that is basically based on Fig. 4 based and in which otherwise the arrangement of the heat exchanger 78 according to Fig. 5 with the arrangement of the additional air heater 38 according to Fig. 6 is combined.

[0036] Finally, it should be noted that all features mentioned in the application documents and in particular in the dependent claims, despite the formal reference to one or more specific claims, are intended to be granted independent protection, even individually or in any combination. List of reference symbols

[0037] 10 Drying tower 12 Drying column 14 Air supply 16 Air discharge 18 Filling opening 20 Bulk material 22 Air inlet 24 Fresh air 26 First part of the drying zones (T8 to T3) 28 Air heater 30 Exhaust air 32 Air forwarder 34 Air discharge 36 Second part of the drying zones (T16 to T9) 38 Additional air heater 40 Heat exchanger 42 First air extractor 44 Second air extractor 50 Air return conductor 52 Air supply conductor 54 Washing device 56 Separation device 58 Cooling zone 60 Cooling air 62 Pre-heater 64 First collection point 66 Second collection point 68 Air extractor 70 Heat exchanger 72 Partial air 74 Additional fresh air 76 Air extractor 78 Additional Heat exchanger 80 further fresh air 82 third collection point

Claims

1. Drying tower (10) for bulk material, in particular agricultural grains, with at least one drying zone (T16 to T1) through which the bulk material (20) to be dried passes from top to bottom, and at least one air duct for passing air through the at least one drying zone (T16 to T1), wherein at least one air inlet (22) is provided for introducing fresh air (24) from the surroundings of the drying tower (10) as supply air into the at least one drying zone (T16 to T1), and wherein at least one air outlet (34) is provided for discharging exhaust air (30) from the at least one drying zone (T16 to T1), characterized in thatat least one heat exchanger (40) is provided for dissipating heat from the exhaust air (30) to the fresh air (24), and at least one air return conductor (50) for exhaust air (30) is connected to the at least one air outlet (34) and the at least one heat exchanger (40), and at least one air supply conductor (52) for fresh air (24) is connected to the at least one heat exchanger (40) and the air inlet (22).

2. Drying tower according to claim 1, characterized in that at least one air heater (28) is provided for heating the fresh air (24) supplied through the air inlet (22).

3. Drying tower according to claim 2, characterized in that the air heater (28) can adjust the fresh air (24) from the surroundings of the drying tower to a temperature between 100 °C and 145 °C, in particular between 110 °C and 125 °C.

4. Drying tower according to one of claims 1 to 3, characterized in thata first air suction device (42) is provided for sucking exhaust air (30) from the at least one drying zone (T16 to T1) and a second air suction device (44) is provided for sucking fresh air (24) from the at least one heat exchanger (40) to the air inlet (22).

5. Drying tower according to one of claims 1 to 4, characterized in that a washing device (54) is assigned to the at least one heat exchanger (40) for washing out condensate and dust from the exhaust air (30) passed through the heat exchanger.

6. Drying tower according to one of claims 1 to 5, characterized in that a separation device (56) is assigned to the at least one heat exchanger (40) for separating condensate and dust from the exhaust air (30) passed through the heat exchanger.

7. Drying tower according to claim 6, characterized in that the separation device (56) is designed as a belt filter.

8. A method for operating a drying tower (10) for bulk material, in particular agricultural grains, in which at least one drying zone (T16 to T1) is passed through by bulk material (20) to be dried from top to bottom and air [k3] is passed through the at least one drying zone (T16 to T1), in which fresh air (24) from the environment of the drying tower (10) is introduced as supply air into the at least one drying zone (T16 to T1) at an air inlet (22), characterized in that Exhaust air (30) from the at least one drying zone (T16 to T1) is passed into at least one heat exchanger (40) and furthermore in the at least one heat exchanger (40) heat is released from the exhaust air (30) to the fresh air (24).

9. A method for operating a drying tower according to claim 8, characterized in that the fresh air (24) supplied through the air inlet (22) is heated on an air heater (28).

10. A method for operating a drying tower according to claim 9, characterized in that the air heater (28) is used to adjust the fresh air (24) from the surroundings of the drying tower (10) to a temperature between 100 °C and 145 °C, in particular between 110 °C and 125 °C.

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