DK2719983T3

DK2719983T3 - Drying system for bulk material with an air inlet

Info

Publication number: DK2719983T3
Application number: DK12007103.0T
Authority: DK
Inventors: Thomas Christian Laxhuber; Christoph Höfler
Original assignee: Stela Laxhuber Gmbh
Priority date: 2012-10-12
Filing date: 2012-10-12
Publication date: 2017-08-21
Also published as: SI2719983T1; PT2719983T; HRP20171130T1; HUE035348T2; EP2719983A1; EP2719983B1; ES2635032T3; LT2719983T; RS56264B1; PL2719983T3

Description

DRYING SYSTEM FOR BULK MATERIAL WITH AN AIR INTAKE UNIT Background of the invention

The invention relates to a drying system for bulk material, in particular agricultural grains, having a plurality of drying zones through which bulk material to be dried is successively passed, and an air duct for passing air through the drying zones, wherein an air introduction device is provided for introducing fresh air from the surroundings of the drying system as supply air into a first part of the drying zones. Furthermore, the invention relates to a method of operating such a drying system for bulk material.

In drying systems of the above-mentioned type, agricultural products, in particular grains such as cereals and maize, but also rapeseed or sunflower, are dried with warm air. These drying processes have become established in the agricultural field, because a high-performance, high-quality and careful drying of the agricultural grains is possible. Also the capital and operating costs are low by comparison with other drying processes, such as freeze drying, vacuum drying or radiant drying. In general the so-called continuous flow dryer has become established, in which the drying zones are formed by a vertical drying tower or a drying column through which bulk material to be dried is passed downwards from the top.

The air passes transversely through this drying tower. Heated supply air flows in at one side of the drying tower and then flows through the bulk product there. In this case the product or bulk material warms up and releases its moisture content to the warm air sweeping past. The bulk material dries. In contrast, the air cools and is humidified. The moist air escapes as exhaust air at the other side of the drying tower. In this case the supply air and/or exhaust air is conveyed by motor-driven fans which are arranged in the air supply and/or the air extractor. A drying device for bulk material, such as grain, is known from DE-U-20 2004 018 492, in which a hot air generator and a plurality of drying levels arranged one above the other as well as air guide channels for supplying air at different temperatures to different drying levels are provided. At least two drying levels are each associated with their own hot air generator, wherein the hot air generators can be operated independently of one another. In this case the air is supplied by a common air supply shaft and is extracted by a respective fan on the side of a guide shaft for the bulk material opposite the hot air generator. Such air ducting is technically comparatively complex and not very energy-efficient. FR-A-0 454 569 discloses a grain dryer according to the preamble to claim 1 as well as a method according to the preamble to claim 6, wherein air is drawn through a plurality of drying sections by means of one single air suction device. In this case the air is supplied by two air introduction devices. One of the air introduction devices leads to a first air heater and into a central part of the drying sections. The second air introduction device guides supply air without air heating to two drying sections which serve for cooling of the dried grains. Furthermore the second air introduction device guides supply air to a further air heater. This supply air is guided into a lower part of the drying sections and also to a third air heater, through which this supply air is then admixed with the exhaust air from the central part of the drying sections, in order to guide it into an upper part of the drying sections. Furthermore, a part of the drying sections with a third air introduction device which serves for intermediate cooling of the grains is also provided between the upper part and the central part of the drying sections. FR-A-2 567 636 discloses a drying system for granular goods, in which heated air is drawn through an upper part of the drying sections by means of a first air suction device. For a lower part of the drying zones cold cooling air and likewise the heated air are supplied. For this purpose the hot air is supplied and heated by means of one single air heater. By means of a second air suction device exhaust air is drawn out of the lower part of the drying sections and this exhaust air is returned to the single air heater. This returned exhaust air which is reheated on the single air heater is then likewise guided into the lower part and the upper part of the drying zones.

Solution according to the invention

According to the invention a drying system for bulk material is created, in particular for agricultural grains, with a plurality of drying zones through which bulk material to be dried is successively passed. The drying system is provided with an air duct for passing air through the drying zones, wherein an air introduction device is provided for introducing fresh air from the surroundings of the drying system as supply air into a first part of the drying zones. Furthermore in the air duct an air forwarding device is provided for forwarding exhaust air from the first part of the drying zones as supply air into a second part of the drying zones. Furthermore, in the air duct of the drying system according to the invention for bulk material a further air introduction device is provided for introducing further fresh air from the surroundings of the drying system into the supply air to the second part of the drying zones or into the second part of the drying zones.

In the drying system according to the invention, as also in conventional systems, fresh air is introduced by a first air introduction device on the drying column into a first part of the drying zones there. This air exits again as exhaust air on the other side and is then forwarded as supply air to a second part of the drying zones. In this way the already slightly humidified air from the first part of the drying zones can be used again in the second part of the drying zones and can thereby be humidified. A high energy efficiency should be achieved with this forwarding of exhaust air as supply air into second drying zones.

At the same time, with this forwarding of exhaust air from one part as supply air into another part of the drying zones the problem arises that the forwarded air is comparatively cold and in order to absorb further moisture its humidity level must be improved, and in particular must be heated. This heating could be achieved by passing the forwarded air through an air heater. However, with such heating of the air which has already been passed through drying zones the problem arises that this air is laden with dust and suspended matter from the bulk material from the first part of the drying zones. This dust or suspended matter is very highly flammable, so that in known drying systems with such processes fires occur repeatedly. In order to at least reduce the fire risk, in the known drying systems the forwarded air is often subjected to dust extraction.

According to the invention, on the other hand, the forwarded exhaust air from one part of the drying zones is improved with regard to its humidity level in that further fresh air from the surroundings of the drying system is supplied or added to this exhaust air. The added fresh air has a lower humidity level and thus also reduces the humidity level of the resulting air mixture.

Furthermore, with the forwarding of exhaust air according to the invention with simultaneous admixture of fresh air into the second part of the drying zones a particularly efficient dust reduction is produced. The exhaust air from the first part of the drying zones according to the invention can be more heavily dust-laden than in known drying systems, since the above-mentioned fire risk does not exist. The drying system according to the invention can be operated so that in the first part of the drying zones it is hotter than in conventional drying systems. Whilst in conventional drying systems it is usual to operate this first part of the drying zones at a temperature of 80 °C to 125 °C, the drying system according to the invention can advantageously be operated at a temperature of 130 °C to 160 °C, particularly preferably 140 °C to 150 °C, in the first part the drying zones. Since the entire exhaust air from the first part of the drying zones is reused in the second part of the drying zones, the stronger heating in the first part does not result in any energy loss but, rather, it improves the drying of the material there. This results in an advantageous configuration, since the dryer a material is, the more it can tolerate high temperatures. Thus the principle according to the invention produces higher throughputs than conventional principles.

In the drying system according to the invention this comparatively high dust contamination in the second part of the drying zones can then be returned to the material to be dried there. This is a further advantage of the concept according to the invention in addition to the saving of energy.

According to the invention, for the above-mentioned reasons this further supply of fresh air is itself also heated, wherein the heating takes place independently of the forwarded exhaust air from the first part of the drying zones. For this purpose in the drying system according to the invention an air heater is provided for heating the first fresh air supplied by the air introduction device and a further, second air heater is provided for heating the further, second fresh air supplied by the further air introduction device.

In this case it is particularly preferred that with the further air introduction device and the further air heater, an air mixture of exhaust air from the first part of the drying zones and further fresh air from the surroundings of the drying system is adjustable 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 supply of further, heated fresh air according to the invention for heating exhaust air from a first part of the drying zones with regard to the total energy balance of such a drying system.

For conveying the air on the drying system according to the invention an air suction device or fan is provided according to the invention for drawing exhaust air from the second part of the drying zones and additionally a further air suction device is provided for drawing the exhaust air from the first part of the drying zones. With the two air suction devices in each case a suction is produced by the first part of the drying zones and a further suction is produced by the second part of the drying zones. In this case the two air suction devices can be controlled independently of one another with regard to their suction capacity, so that the extraction of the exhaust air and the admixing of further fresh air can be optimally adapted to one another. With the air suction device the exhaust air is conveyed in the direction of the second part of the drying zones, in order to be drawn in there as supply air together with the further fresh air. With the suction of the further or second air suction device the amount of further fresh air to be drawn in can be determined at the same time. In this connection it is advantageous to provide a throttle valve or regulating valve on the further or second air introduction device, with which the air resistance for the air streams of forwarded exhaust air and supplied further fresh air can be influenced.

Furthermore, for a high energy yield the drying system according to the invention is preferably an air recycling system or an air recirculation system for returning exhaust air from the first part of the drying zones back as supply air into the first part of the drying zones. A third air introduction device is preferably provided on this air recirculation system for introducing fresh air from the surroundings of the drying system into a third part of the drying zones. This third part of the drying zones is preferably the lowermost portion of the drying column through which the bulk material flows last and which is used as the so-called cooling region for the bulk material.

On the drying column the lower portion, before or above the cooling region in the flow direction of the bulk material, is preferably provided as the first part of the drying zones. The second part of the drying zones is then the upper region of the drying column arranged above this first part.

Furthermore, in the drying system according to the invention an air recycling system is advantageously provided for returning exhaust air from the third part of the drying zones as supply air into the first part of the drying zones. This type of air recycling system forms a component of the above-mentioned air recycling system, which is advantageous in terms of energy, in the last portion of the drying column.

Furthermore, according to the invention a method for operating a drying system for bulk material is created, in particular for agricultural grains, in which bulk material to be dried is passed successively through a plurality of drying zones and air is guided through the drying zones. In this case fresh air from the surroundings of the drying system is introduced as supply air into a first part of the drying zones. On an air forwarding device exhaust air is forwarded from the first part of the drying zones as supply air into a second part of the drying zones. Furthermore, on a further air introduction device further fresh air from the surroundings of the drying system is introduced into the supply air to the second part of the drying zones or into the second part of the drying zones.

According to the invention, in such a method for operating a drying system corresponding to the above-mentioned design the fresh air supplied by the air introduction device is heated on an air heater and the further fresh air supplied by the further air introduction device is heated on a further air heater.

Particularly preferably, with the further air introduction device and the further air heater an air mixture of exhaust air from the first part of the drying zones and further fresh air from the surroundings of the drying system is set to a temperature between 100 °C and 145 °C, in particular between 110 °C and 125 °C.

Brief description of the drawings

An exemplary embodiment of the solution according to the invention is explained in greater detail with reference to the appended schematic drawings. In the drawings:

Figure 1 shows a simplified longitudinal section through a drying system for agricultural grains according to the prior art;

Figure 2 shows a simplified longitudinal section of a first embodiment of a drying system for agricultural grains according to the prior art;

Figure 3 shows a simplified longitudinal section of a second embodiment of a drying system for agricultural grains according to the invention and

Figure 4 shows a simplified longitudinal section of a third embodiment of a drying system for agricultural grains according to the invention.

Detailed description of the exemplary embodiments A drying system 10 for agricultural grains comprises as essential components a drying column 12 with drying zones T16 to Tl, an air supply 14 as well as an air discharge 16.

On the upper side of the drying column 12 is located a filling opening 18 for bulk material 20 to be dried, in this case maize grains. Due to the gravity acting on it, the bulk material 20 passes successively through the drying zones T16 to Tl of the drying column 12 from the top to the bottom. In this case the bulk material 20 trickles through roof-shaped air shafts which are each open at the bottom (not shown in greater detail).

The air supply 14 is designed with a first air introduction device 22 which is formed as an air supply shaft at the lower end region of the drying system 10, on the left of Figure 1. Fresh air 24 from the surroundings of the drying system 10 passes through the third air introduction device 22 into a first part 26 of the drying zones T16 to Tl, namely into the drying zones T8 to T3. This fresh air 24 at the air introduction device 22 is heated in a first air heater 28. The heated fresh air 24 is drawn in as supply air through the first part 26 of the drying zones T16 to Tl. It absorbs moisture from the bulk material 20 there and is discharged again as humidified exhaust air 30 from the drying column 12 at the right-hand side of these drying zones T8 to T3.

This exhaust air 30 is guided by an air forwarding device 32 in the form of a fan (in particular an axial fan or a radial fan) or air suction device 34 vertical upwards on the left-hand side of the drying zones T16 to T9 which form a second part 36 of the drying zones T16 to Tl. A second air heater 38 by which the exhaust air 30, which is passed through the air suction device 34 and is cooled in the meantime, is heated again to a temperature of approximately 140 °C, is associated with the air forwarding device 32 located after or downstream of the air suction device 34 in the flow direction. With such heating of the exhaust air 30 by means of the air heater 38, there is a high risk of ignition and fire, because the exhaust air 30 in the drying zones T8 to T1 has been enriched not only with moisture but also with dust and suspended matter.

The exhaust air 30 which is heated again then passes through the second part 36 of the drying zones T16 to T1 and flows off as exhaust air 40 through the air discharge 16. For this purpose the air discharge 16 has an air suction device 42 in the form of an axial fan or a radial fan, by which the exhaust air 40 is drawn off from the drying zones T16 to T9.

Figures 2 to 4 show solutions according to the invention for a drying system 10 in which the air forwarding device 32 is configured differently. The air forwarding device 32 according to Figure 2 has an air suction device 34 by which exhaust air 30 from the drying zones T8 to T1 is conveyed to the drying zones T16 to T9 without this exhaust air 30 being heated in the process. In order to improve the humidity level of the supply air to be fed into the drying zones T16 to T9 by comparison with the high humidity level of the exhaust air 30, further fresh air 46 from the surroundings of the drying system 12 is introduced by means of a further air introduction device 44 into an air guide channel 48 above the air suction device 34. In this air guide channel 48 is located a second air heater 50 according to the invention, by means of which the further fresh air 46 supplied by the further air introduction device 44 is heated. Since this fresh air 46 is not laden with dust or suspended matter, there is no fire risk during such heating of further fresh air 46. In the air guide channel 46 the heated further fresh air 46 is mixed with the exhaust air 30 in such a way that overall a temperature of the air mixture of approximately 110 °C to 125 °C is set. Then, similar to the drying system 10 according to Figure 1, the air mixture is conveyed by means of an air suction device 42 and possibly by means of a dust extractor (not shown) on the air discharge 16 through the drying zones T16 to T9 and outwards into the surroundings of the drying system 10.

Such a design with a further air introduction device 44 for further fresh air 46 as well as an associated air guide channel 48 with a second air heater 50 arranged therein is also provided in the drying systems 10 according to Figures 3 and 4.

The drying zones T2 and T1 of the drying column 12 according to Figure 2 are designed as a third part 52 of the drying zones T16 to T1 or as a so-called cooling region with individual cooling zones into which fresh air 54 can be supplied directly from the exterior by means of a third air introduction device 56. In the drying systems 10 according to Figures 1 and 2 this fresh air 54 passes through the drying zones T2 and T1 and then enters the air suction device 34 as exhaust air 30.

Figure 3 shows an embodiment of a drying system 10 in which the fresh air 54 is supplied to the drying zones T2 and T1 by the third air introduction device 56 from the exterior on the other side of the drying column 12. After this the resulting exhaust air is guided out of the drying zones T2 and T1 into a further air guide channel 60 on the side of the air supply 14. In this case the further air guide channel 60 is located above or downstream of the first air heater 28, so that the exhaust air from the drying zones T2 and T1 is admixed directly with the already heated fresh air 24 and is then supplied to the drying zones T8 to T3 as supply air.

The exhaust air 30 from the drying zones T8 to T3 then passes as explained above into the air forwarding device 32, in order subsequently to supply this air with heated further fresh air 46 and to convey it to the drying zones T16 to T9.

Figure 4 shows an embodiment of a drying system 10, in which the fresh air 54 passed through the drying zones T2 and T1 and also the exhaust air 30 from the drying zones T4 and T3 is used as recirculating air. For this purpose an air recycling system 58 is provided, by means of which this exhaust air from the drying zones T4 to T1 is returned to the air supply side of the drying zones T8 to T3.

In conclusion, it may be remarked that all the features which are mentioned in the application documents and in particular in the dependent claims, in spite of the formal reference back to one or more specific claims, are also entitled to independent protection individually or in any combination.

List of reference signs 10 drying system 12 drying column 14 air supply 16 air discharge 18 filling opening 20 bulk material 22 air introduction device 24 fresh air 26 first part the drying zones (T8 to T3) 28 air heater 30 exhaust air from the lower drying zones 32 air forwarding device 34 air suction device 36 second part the drying zones (T16 to T9) 38 further air heater according to the prior art 40 exhaust air from the drying zones T16 to T9 42 air suction device 44 further, second air introduction device 46 further fresh air 48 air guide channel above the air suction device 50 further air heater according to the invention 52 third part of the drying zones (T2 and Tl) 54 fresh air 56 third air introduction device 58 air recycling system 60 air guide channel above the first air heater T16-T1 drying zones

Claims

1. Bulk drying apparatus (10), in particular agricultural grains, having a plurality of drying zones (T16 - TI) through which bulk material (20) is to be successively dried, and an air duct for passing air through the drying zones (T16-T1), wherein an air inlet (22) for introducing fresh air (24) from the surroundings of the dryer (10) as supply air to a first portion (26) of the drying zones (T16 -TI) is provided, wherein an air inlet (32) for supplying exhaust air ( 30) from the first portion (26) of the wipe zones (T16 - TI) to a second portion (36) of the wipe zones (T16 - TI) are provided and wherein an additional air inlet (44) for introducing additional fresh air (46) from the surrounding wiper system (10) to the second portion (36) of the wipe zones (T16 -TI) are provided, whereby an air heater (28) for heating the fresh air (24) supplied by the air inlet (22) is provided, where an additional air heater (50) is provided. to heat the additional fresh air (46) t provided by the additional air inlet (44) is provided and wherein an air suction (42) for sucking exhaust air (40) from the second part (36) of the drying zones (T16 - TI) is provided, characterized in that an additional air cleaner (34) is provided. ) to extract exhaust air (30) from the first portion (26) of the drying zones (T16 - TI) is provided.

Drying system according to claim 1, wherein, with the additional air inlet (44) and the additional air heater (50), an air mixture of exhaust air (30) from the first part (26) of the drying zones (T16 - TI) and additional fresh air (46) ) from the surroundings the wiper system is adjustable to a temperature between 100 ° C and 145 ° C, in particular between 110 ° C and 125 ° C.

Drying system according to claim 1 or 2, wherein an air return (58) for returning exhaust air (30) from the first part (26) of the drying zones (T16 - TI) as supply air to the first part (26) of the drying zones (T16 - TI) ) is provided.

Drying system according to one of claims 1 to 3, wherein a third air inlet (56) for introducing fresh air (54) from the surroundings of the drying system (10) to a third part (52) of the drying zones (T16 - TI) is provided.

Drying system according to one of claims 1 to 4, wherein an air return (58) for returning exhaust air from the third part (52) of the drying zones (T16 - TI) as supply air to the first part (26) of the drying zones (T16 - TI) is provided.

A method of operating a bulk material drying plant (10), in particular agricultural grain, wherein bulk material (20) to be dried is passed successively through a plurality of drying zones (T16 - TI) and air (24) passing through the drying zones (T16-T1). ) where fresh air (24) from the surroundings of the wiper system (10) introduces fresh air (24) as supply air to a first part (26) of the wiping zones (T16 - TI), where, in the case of an air feeder (32), exhaust air (30) from the the first part (26) of the wiping zones (T16 - TI) is fed to a second part (36) of the wiping zones (T16 - TI), whereby further fresh air (46) from the surroundings of the wiping system (10) is introduced into the wiper zone (10). the second part (36) of the drying zones (T16 - TI), where, by an air heater (28), the fresh air (24) provided by the air introducer (22) is heated, and by an additional air heater (50) the additional fresh air (46) is provided of the additional air inlet (44) is heated, where by hj the exhaust air (40) is extracted from the second part (36) of the drying zones (T16 - TI) by means of an air cleaner (42), characterized in that exhaust air (30) is sucked from the first part (26) by means of an additional air cleaner (34). the wipe zones (T16 - TI).

A method of operating a drying system according to claim 6, wherein, with the additional air inlet (44) and the additional air heater (50), an air mixture of exhaust air (30) from the first part (26) of the drying zones (T16 - TI) and additional fresh air (46) from the surrounding wiper system (10) is adjusted to a temperature between 100 ° C and 145 ° C, in particular between 110 ° C and 125 ° C.