EP0300297B1 - Process and plant for treating recovered granular material used on wintry roads - Google Patents

Abstract

The impure granular material which is fed to a feeder bin (4) is metered through a take-off device (5). An adjoining coarse-grain separator (13) is used to remove the coarse-grain impurities by screening. The remaining granular material is introduced to a drier (16), where the granular material is dried and the fine-grained impurities are separated by pneumatic sifting. The purified granular material is passed to a grit silo (31), from where it can be removed. By treating the used granular material and reusing it, environmental pollution is reduced, while, at the same time, less energy is required since the treatment is carried out without the addition of wash water. <IMAGE>

Description

The invention relates to a method for the preparation of grit used for winter service on walked and driven, at least partially icy and / or snow-covered traffic areas for the protection of people and vehicles against gliding, in particular of grit, which when used is contaminated by foreign materials and melt water and other liquids are moistened, the grit collected after use being cleaned and dehumidified from coarse-grained contaminants by sieving and then from fine-grained contaminants by air separation.

So far, road salt has been used extensively in winter service as a grit, with which it is possible with relatively little effort to reach non-slip traffic areas for people and vehicles. However, the road salt used in large quantities creates a considerable environmental impact, which has been objected to considerably since ecological aspects have been more closely considered. Since then, the use of grit, which is understood to mean broken, angular natural rock of different grain compositions, as a spreading agent that protects against sliding, has increased significantly in winter maintenance.

Experience has shown that around 2/3 of the amount of chippings used in winter maintenance remains until spring and is then picked up by the street sweepers. Also at Problems occur with the use of grit, especially if much larger quantities of grit are used than before. The scattered chippings are also not available in unlimited quantities, since their dismantling causes damage to the landscape. For this reason, considerations have been made as to how the grit collected after its use could be processed for further use. It must be taken into account here that the used grit contains environmentally harmful contaminants, such as heavy metals, salts, oils and fats. On the other hand, the storage of large quantities of used grit in landfills is problematic.

Despite these problems with the exclusive use of unused grit, i.e. new chippings, the processing of used grit, i.e. that is, old chippings, so far not able to enforce. The reason for this is the relatively high cost of reprocessing at central locations using the wet process common in the gravel industry. In this process, the wash water must be passed through a sewage treatment plant. Because of the danger of groundwater contamination from toxins contained in the washing water, it can in no case be allowed to seep away in open sedimentation areas. In addition, after washing the grit must be dried again with a correspondingly high expenditure of energy so that it remains free-flowing even at low temperatures.

From FR-A 2578454 a method for separating a composite mixture of different particles is generally known. For this purpose, an oscillating device is used, the mixture being conveyed over a first plateau to the edge of a discharge opening and then being carried upwards by air flow with air. Depending on the density and / or dimensions, the particles of the mixture describe one corresponding parabolic trajectory and land either on a second plateau, on a corresponding landing area or on the floor pan of a channel. However, this vibrating device is not suitable for separating dust-like contaminants from a moist grit.

US-A 4523988 describes a method for processing the abrasive grain of a blasting sand. In this process, coarse impurities are first separated out and then the material is dried and then air sifted by separating dust. However, the drying takes place in a drying drum, in which the material is rubbed against one another very strongly and is thus crushed to an undesirable extent in the manner of sand. This also means that part of the goods are discharged as abraded dust during the wind sifting.

The object of the present invention is to obtain high-quality grit by processing old grit, with as little old grit as possible being lost. Furthermore, the entire preparation process should be quick and inexpensive.

To achieve this object, a vibrating fluid bed is provided for drying and air separation to separate fine-grained impurities, which has a drying zone and an air separation zone, both zones being exposed to hot air.

Drying in a vibrating fluid bed can be carried out much more gently. The material to be dried is only subjected to a micro-throwing motion on a vibrating fluid bed, abrasion of the material being substantially reduced. Furthermore, since the heating medium, both in the drying zone and in the wind classification zone, directly through the one to be dried Is well conducted, there is an intensive heat exchange, so that the drying is accelerated.

By processing in the dry process, i.e. Without the addition of wash water, the costs for wastewater treatment are not incurred and the costs for chippings drying are also greatly reduced.

If the wet process is used, the washed and pre-dewatered old chippings still contain 15-20% by weight of water which has to be evaporated in the dryer, while in the process according to the invention with old chippings which are moist in the landfill, this only has a moisture content of between 5-7% by weight. This means a 60-70% reduction in energy consumption when drying.

The collected grit is cleaned of coarse-grained contaminants by sieving and fine-grained grit by air sifting, while at the same time as the air sifting, the grit is dehumidified to a final moisture level suitable for use in winter service.

The invention also includes a system, the task of which is to be able to carry out the method optimally. This object is achieved according to the invention in that the drying and the air separation for separating the fine-grained contaminants from the scattering material is provided in a vibrating fluid bed, which is preceded by a vibrating sieve for separating the coarse-grained contaminants.

The vibrating fluid bed has a drying zone and a separation zone, both zones being exposed to hot air. Here, the vibrating fluid bed can be a control device be assigned, which uses the exhaust air temperature of the separation zone as a reference variable.

Fig. 1

eine schematisch dargestellte Anlage für die Aufbereitung von Altsplitt und

Fig. 2

eine schematische Darstellung eines Gerätes zum Trocknen des Altsplitts und der Abtrennung der feinkörnigen Verunreinigen nach der Trocknung durch Windsichtung.

An exemplary embodiment of a system for processing used chippings used in winter service is shown in the drawing and is described below. Show it:

Fig. 1

a schematically illustrated plant for the processing of old chippings and

Fig. 2

a schematic representation of a device for drying the old chippings and the separation of the fine-grained contaminants after drying by air separation.

In Fig. 1, the arrow 1 shows the transport of the used and collected old chippings, which is delivered to an intermediate landfill 2. The delivery takes place here with transport vehicles or directly from the street sweepers. The old chippings are conveyed from the intermediate landfill 2 into a feed bunker 4 by means of a conveying device 3, for example a charger. This is expediently dimensioned such that it can hold approximately a material supply with which the system can be operated for approximately 30-60 minutes. The old chippings are removed from the feed bunker 4 by a suitable, controllable extraction device 5, which is designed, for example, as a vibration conveyor suitable for the bunker extraction. By means of the extraction device 5, the old chippings are fed to a separator 13 for the separation of coarse-grained impurities in the old chippings by a conveying member 12. This feeding can take place directly or, as shown in FIG. 1, by means of the conveying element 12, for example an inclined conveyor.

The old grit usually contains about 5-7% by weight of coarse-grained impurities. The separator 13 has the task of this Eliminate foreign bodies and grit particles with a grain size above the grit size of the spreading material of preferably 8-10 mm from the old grit. Separators 13 in the form of vibrating sieves are particularly suitable for this purpose. The coarse-grained contaminants are supplied by a suitable transport device 15, for example a chute, to a container 23, for example a trough container.

The old chippings cleaned of coarse-grained impurities then reach a dryer 16 via a feed chute 14. The dryer 16 has the task of conveying the landfill-moist old chippings with a moisture content of usually 4-7% by weight to a final moisture content of maximum 0.5% by weight dry so that the processed chippings remain free-flowing even at low temperatures. Suitable dryer types can be used for drying bulk goods. For several reasons, dryers designed as vibrating fluid bed dryers are particularly advantageous for this, since the wind sifting can be integrated into the construction of the dryer 16 in order to separate the fine-grained impurities. In addition, a vibrating fluid bed dryer is comparatively small in its outer dimensions and can therefore be very easily accommodated even in confined spaces, for example on a vehicle.

Vibratory fluid bed dryers differ from stationary fluid bed dryers in that they are set in a directional vibration by a vibration exciter. In this way, the items to be dried are also fluidized by the oscillating movement, in addition to the air flow generated in the dryer, so that even items that are difficult to fluidize, such as moist chippings, can be dried.

Scattered chippings should not contain more than 2% fine-grained or dust-like impurities, otherwise this material is scattered Inadmissible dust pollution can occur. For this reason, the dryer 16 is provided with an air separation zone 17 integrated therein, as will be explained in detail with reference to FIG. 2. The wind sifting zone 17 is located at the end of a drying zone 18 designed as a drying section, since it is only here that the fine-grained impurities are released from the grit. The wind sifting zone 17 differs from the drying zone 18 essentially in that the air velocity corresponds to at least 1.5 times the sinking velocity of the largest particles to be removed and the exhaust air duct is designed such that the detached fine-grained impurities are entrained by the air flow into an exhaust air line 19 will. For this reason, the wind classification zone 17 is equipped with its own exhaust air line 19 for the removal of the dust-laden air classifier exhaust air. The drying zone also has its own exhaust air duct 20. The old chippings cleaned in this way contain a maximum of 0.5-2.0% dust-like impurities.

At the end of the wind classification zone 17 there is an outlet 21 from which the cleaned, processed scattered chippings are transferred to a conveyor device 30 and conveyed into a split silo 31. The split silo 31 has a removal device 32, via which the grit can be removed for further distribution.

The dryer 16 is supplied by a hot gas generator 22 with drying air at a temperature between 200 and 300 ° C. The hot gas generator 22 consists of a combustion chamber 23 ', a total air blower 25, a primary air blower 26, a reservoir 24 and actuators 27, 28 which are required for the operation of the hot gas generator 22. The hot gas generator 22 can be operated with either liquid, gaseous or solid fuels.

The dust-laden exhaust air emerging from the wind classification zone 17 and the drying zone 18 of the dryer 16 is conducted via a line 29 into a dedusting system 6. An exhaust air fan 7 is connected on the clean gas side of the dedusting system 6 in order to prevent wear on the fan components or at least to keep them low. The cleaned exhaust air is blown out into the atmosphere through a line 8. The dust separated in the dedusting system 6 is discharged from the dedusting system 6 via a conveying element 9, for example a collecting screw, and introduced into a closed container 10, for example a closed trough container.

From Fig. 2 it can also be seen that the two exhaust air lines 19, 20 open into a cyclone 33, where the heavier parts of the dust-like impurities are retained and are returned to the drying zone via a conveying element 34, for example a dust chute. The other fine-grained impurities leave the cyclone 33 and are fed via line 29 into the dedusting system 6.

At the end of the dryer 16 which is above the wind sifting zone 17 there is an inlet opening 35 through which the contaminated, collected old chippings are introduced into the drying zone 18.

The dryer 16 has a vibration isolation frame 36, which is supported on spring elements 37 on a fixed bottom surface 39. The machine parts of the wind classification zone 17 and the drying zone 18 form a counterweight to the mass of the vibration isolation frame 36 and are connected to the vibration isolation frame 36 by flexible coupling members 40. A vibration exciter 41, for example with rotating unbalances, is fastened to the vibration isolation frame 36 and is driven by a drive 42. Between An air chamber 43 for the drying zone 18 and a further air chamber 44 for the air separation zone are formed in the two zones 17, 18 and the vibration isolation frame 36, from which two chambers the air passes through a floor 45 into the drying zone 18 and through a further floor 46 into the Wind classification zone 17 flows.

The interim storage of the old chippings 1 in the open landfill 2 has the consequence that the moisture of the same is constantly subject to strong fluctuations during the dismantling from the landfill 2. Special control measures are required to ensure smooth operation. For this purpose, it is provided that, in addition to the drying air temperature, the amounts of chippings that are passed through are controlled by automatic control devices 47, 48, 49. These control devices are connected to the control valves 27, 28 and to the controllable bunker discharge device 5. The regulation of the amount of old chippings implemented has the task of compensating for longer-term fluctuations in the feed moisture, while the regulation of the drying air temperature compensates for the shorter-term fluctuations. The dehumidification of the old chippings is not suitable as a guide variable because it is difficult to measure continuously. However, it has been shown that the exhaust air temperature of the air visibility zone 17 is very well suited as a substitute guide variable.

As already mentioned, the system described can be used in a transportable version. In Fig. 1, the system is shown on two vehicles 11, 38, which can be carried out with motor drives or as a trailer or semi-trailer. Another possibility is the arrangement on a so-called swap body. The swap body is easily detachably connected to the chassis, so that the chassis and the system can be removed at the place of use can be operated alone on the swap body. Since the mobile system can also work in the vicinity of residential areas, all system components can be designed with low noise emissions or can be equipped with additional noise protection devices.

Claims (4)

1. A method for preparing grit used on traffic areas which are passed or travelled on in winter, at least areas which are partially covered with ice or snow, said grit being for the protection of persons and vehicles against skidding, in particular scattering chippings, which when used is polluted with foreign materials and moistened by melted snow and other liquids, whereby the grit collected after application, is separated from coarse-grained impurities by filtering-off and then from fine-grained impurities by air sifting and dehumidifying, characterised in that for drying and air sifting for separating fine-grained impurities an oscillating fluidized bed is provided, which has a drying zone (18) and an air sifting zone (17), wherein both zones are acted upon with hot air.

2. A method according to claim 1, characterised in that the cleaning of the collected grit is able to be transported and carried to changing places of use.

3. A unit for carrying out the method according to claim 1, characterised in that for drying and air sifting for separating the fine-grained impurities in the collected grit there is provided a dryer (16) with an oscillating fluidized bed, in which one after the other a drying zone (18) and an air sifting zone (17) are arranged, wherein for separating the coarse-grained impurities of the collected grit an oscillatory sieve (13) is connected before the dryer (16).

4. A unit according to claim 3, characterised in that for dosing the collected grit in the dryer (16), a delivery device (5) is provided and for the dryer (16) there is provided a hot gas generator (22), wherein the delivery device (5), the dryer (16) and the hot gas generator (22) are allocated regulating devices (47, 48, 49), such that the grit throughput quantity is regulated in dependence on the exhaust air temperature at the dryer (16).

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