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1. (WO2005068369) AGENCEMENT DE DISTILLATION DANS UN CONVOYEUR DE DISTILLATION
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

Distillation arrangement comprising a distillation conveyor

TECHNICAL FIELD

The present arrangement refers to a distillation arrangement comprising a distillation conveyor for transporting distillation material, and a heating arrangement arranged to heat distillation material in the distillation conveyor.

TECHNICAL BACKGROUND

Arrangements with dry distillation are used for example to separate mercury from waste. Known art comprises so-called batch distillation, at which a container is filled with waste and placed in a distillation device, whereupon the container after distillation is removed and emptied of its content. It is also known to use retort fur- naces, but these are open arrangements, which can lead to a risk of leakage, e.g. in the event of a power failure.

US 4 087 276 shows a distillation design for removing mercury from waste, whereby the waste is transported through a horizontal heatable cylinder by means of a screw arranged in the cylinder, and provided with a shaft. Similar designs are shown in US 4 235 676, WO 0013811 and US 6 416 567 Bl. In the design of US 4 087 276, the evaporated mercury is mixed with air between the blades of the screw, whereby the air is transported mainly at the same rate as the waste. This, in turn, can result in the air being saturated with mercury gas, since the flow of air is not suffi- cient for diverting the gaseous mercury at a rate corresponding to the rate of the mercury being secreted from the waste.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the distillation process by distillation with continuous or stepwise feeding.

This object is achieved by a distillation arrangement of the type initially mentioned, in which the distillation conveyor is arranged so that a gas can flow in the distillation conveyor between at least two points located at a distance from each other, which flow is independent of the movement of the distillation conveyor, and the dis-filiation conveyor is arranged so that the gas can be in contact with the distillation material in the distillation conveyor.

The gas, which for example could be air, is used as a "carrier" of gaseous substances, e.g. gaseous mercury, which are separated from the distillation material dur-ing distillation. The invention makes it possible for the flow of the "carrier gas" to be independent of the transportation speed of the distillation material. This means that the gas flow can be adapted to an optimal distillation process at which the gas flow is adapted to an optimal reception and diversion of the gaseous substances formed during the distillation. In one embodiment, the distillation arrangement is arranged so that the gas flow can be controlled.

Preferably the distillation conveyor comprises a fixed part and at least one part which extends in a screw-shaped manner in the fixed part and is rotatable, at which a central space, located radially inside of the screw-shaped part, is open so that the gas can flow in the longitudinal direction of the screw-shaped part. Thereby, a large space can be provided for an effective flow of the gas through the area of the distillation arrangement where the distillation material is heated.

Preferably the screw-shaped part is made from one piece of a material with suitable heat resistance, rigidity and strength, and is, for its rotation, in one end connected to a driving arrangement. The design of the screw-shaped part results in a simplified manufacture of the arrangement and makes it a durable construction.

Preferably a screw- shaped space, formed due to the pitch or rise of the screw-shaped part between consecutive turns of the screw-shaped part in its longitudinal direction, communicates with the central space. As a result, the distillation material in the screw-shaped space can be exposed to the gas, flowing through the central space, so that gaseous substances formed during heating can effectively be absorbed by the flowing gas.

Preferably the distillation arrangement comprises means, in turn comprising e.g. a non-return valve, for preventing the gas from flowing in a direction opposite to the transportation direction of the distillation conveyor. This considerably reduces the risk of leakage of hazardous waste caused by gas flowing in the wrong direction in the arrangement, something which can otherwise occur e.g. during clogging, i.e. choking of a filter for reception of particles in the distillation gases. This improves the safety when distilling environmentally hazardous waste.

Preferably the distillation arrangement comprises means, in turn comprising e.g. a feeding conveyor, for controlling the flow of distillation material to the distillation conveyor. This means that the feeding of distillation material can be adapted to different parameters, such as the speed of the distillation conveyor, and the type of distillation material, which, among other things, makes it possible to control the amount of distillation material in the heating arrangement at a certain point of time.

Preferably the distillation arrangement comprises means for selectively feeding distillation material from one or more of at least two containers. This offers a possibility, when a container during a distillation process in progress is emptied, to change the feeding so that it takes place from another container, which means that the feed-ing will not have to be interrupted when a container is emptied. This embodiment also offers the possibility to prepare distillation of different types of material provided in different containers.

Preferably the distillation arrangement comprises means for measuring the gas flow. Thereby, a reduction of the gas flow, potentially harmful to the distillation process, for example due to clogging of conduits or components in the arrangement, can be detected. Such a detection can also offer a possibility to take measures for preventing a gas flow in the opposite direction in the arrangement to occur, which could lead to a discharge of substances that are harmful to the environment and/or to the human health.

Preferably the distillation arrangement is arranged to alert at least one operator of the distillation arrangement if the gas flow should be lower than a predetermined value. Thereby, the operator can be made aware of a potentially harmful decrease of the gas flow.

Preferably the distillation arrangement is arranged to reduce or stop the flow of distillation material to the distillation conveyor if the gas flow should be lower than a predetermined value. Thereby is secured that the secretion in the distillation con-veyor of substances, which could be harmful to the environment and/or to the human health, will be reduced or terminated in the event of the gas flow being reduced or occurring in the opposite direction.

Preferably the distillation arrangement comprises means for selectively feeding dis-filiation material from the heating arrangement to one or more of at least two containers. Thereby, an opportunity is given, when a container during a distillation process in progress has been filled, to change the feeding so that it takes place to another container, which means that the feeding will not have to be interrupted when a container is full.

Preferably the distillation arrangement comprises at least one electrostatic filter located downstream of the distillation conveyor. Many materials which are to be distilled comprise powder and dust. During dry distillation for which this invention is especially suited, substantially all moisture is removed, whereby powder and dust could follow the gas flow. The powder and dust can then gather in conduits and components downstream of the distillation conveyor. When the accumulations are sufficiently large, the gas flow can be restrained, reduced or even stopped. Further, re-condensation of distilled material, such as mercury, can occur. A way of avoiding this problem is to provide a plurality of condensers arranged successively, which, however, is complicated and expensive. The electrostatic filter removes powder and dust effectively from the gas flowing from the distillation conveyor. Furthermore, an electrostatic filter is well suited for the task of removing dust and powder from the warm gas from the heating arrangement, since it is able to withstand much higher temperatures compared to other types of filters. The gas temperature in this part of the arrangement can be 600-700°C. Further, the electrostatic filter does not substantially affect the gas flow, as distinguished from other types of filters.

Preferably the electrostatic filter is located upstream of a condensation arrangement. Thereby, powder and dust can be removed before it reaches the condensation ar-rangement so that harmful deposition in the latter can be prevented.

Preferably the electrostatic filter is located above the distillation conveyor. Thereby powder and dust having been filtered can be fed by means of gravity back to the distillation conveyor so that it thereafter can be fed out together with other solid mate-rials.

DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with the aid of the enclosed drawings, in which - Fig. 1 shows a diagram of a distillation arrangement according to a preferred embodiment of the invention,
- Fig. 2 shows a partly sectioned view of a portion of the distillation arrangement according to Fig. 1,
- Fig. 3 shows a cross-sectional view with the section oriented along the line III-III in Fig. 2, and
- Fig. 4 shows a diagram of a portion of the distillation arrangement in Fig. 1.

DETAILED DESCRIPTION

Fig. 1 shows a diagram of a distillation arrangement 1, in which distillation material, i.e. material to be dry-distilled, e.g. for separating mercury therein, is fed from one or both of two containers 2, via vibration feeder 3 to means 4 for controlling the flow of distillation material to a distillation conveyor 5, described closer below. In Fig. 1, intended transport directions for materials and fluids through the distillation arrangement 1 are indicated with arrows A. The means 4 for controlling the flow of distillation material to the distillation conveyor comprises a feeding conveyor 4, which in this example is a screw conveyor driven by a motor 6, the rotational speed of which can be controlled.

By means 7 for selectively feeding distillation material from one or both of the containers, including valves 7, the feeding from the containers 2 to the feeding conveyor 4 can be controlled. Of course, more than two containers 2 can be arranged at the feeding conveyor 4.

From the feeding conveyor 4, the distillation material is fed to the distillation conveyor 5. The distillation arrangement 1 comprises a heating arrangement 8, in turn comprising four units 8a, 8b, 8c, 8d for heating, which can be controlled individually. Of course, other numbers of heating units can be used, e.g. only one or more than four. The units 8a, 8b, 8c, 8d enclose the distillation conveyor 5 in radial direction and are arranged to heat distillation material in the distillation conveyor 5.

The distillation conveyor 5 is arranged so that a gas, e.g. air, can flow in the distilla-tion conveyor between a gas inlet 9 and a gas outlet 10, located at a distance from each other in the transport direction. Of course, the gas can be adapted to the circumstances of the distillation process, e.g. the type of material to be distilled. For example, if one wishes to exclude oxygen in the process, the gas can be an inert gas, e.g. nitrogen gas N2. If, on the other hand, one wishes gas with a rich content of oxygen, oxygen 02 can be added. As described closer below, the gas flow is independent of the movement of the distillation conveyor 5, and the distillation conveyor 5 is arranged so that gases can be in contact with distillation material in the distillation conveyor 5.

As can be seen in Fig. 2, the distillation conveyor 5 comprises a fixed part 11 in the form of a tube 11. The distillation conveyor 5 further comprises a part 12 extending in a screw-shaped manner in the tube 11 and being rotatable. As can be seen in Fig.

I, the screw-shaped part 12 in one end is connected to a driving arrangement 13 for its rotation, in the form of a motor 13 the rotational speed of which can be con-trolled. Preferably the screw-shaped part 12 is made from one piece and arranged essentially concentrically in the tube 11.

As can be seen in Fig. 3, a central space 14, located radially inside of the screw-shaped part 12, is open so that the gas from the gas inlet 9 can flow in the longitudi-nal direction of the screw-shaped part 12, towards the gas outlet 10 (see Fig. 1).

As can be seen in Fig. 2, distillation material 15 is located in a lower part of the tube

I I, where it can be transported by means of the rotation of the screw-shaped part. A screw-shaped space 16 communicates with the central space 14. The screw-shaped space 16 is delimited radially outwards by the inner wall of the tube 11 and radially inwards by an imaginary surface, located at the same radial distance from the central line of the tube 11 as the inner limitation of the screw-shaped part. The intersection between the inner limitation of the screw-shaped space 16 and a vertical plane through the centreline of the tube 11 is partly indicated in Fig. 2 by a broken line 16a. Thus, the screw-shaped space 16 is formed due to the rise of the screw-shaped part 12 between consecutive turns of the screw-shaped part 12 in the longitudinal direction of the screw-shaped part 12.

Preferably the screw-shaped part 12 is made from a steel which has suitable features for the environment in the distillation conveyor. Apart from the advantages pointed out above, the design of the screw-shaped part 12 has the advantage of having a relatively large resilience, especially in its longitudinal direction but also in that individual turns on/of the screw can bend in relation to other turns. As a result, the screw-shaped part 12 can, when needed, change its form. For example, in a situation where a relatively large continuous piece of the distillation material is wedged between the tube 11 and the screw-shaped part 12, whereby the latter can be subjected to an elastic deformation so that the piece can be released, or at least transported further. This reduces the risk of a stoppage in the distillation conveyor 5.

In the distillation process the distillation material 15 in the distillation conveyor 5 is heated by the heating arrangement 8, which distillation material can be waste in solid form, whereby part thereof, containing e.g. mercury, is vaporized. The vaporized part of the distillation material 15 is mixed with the gas in the central space 14 and the screw-shaped space 16 and led with the gas via the gas outlet 10 (see Fig. 1) through a conduit 17 to a condensation arrangement 18. The condensation arrangement 18 cooperates with a cooling arrangement 19, and the vaporized part of the distillation material 15 is transformed in the condensation arrangement 18 into liquid foπΗ, whereafter it can be taken care of via a drain valve 18a. The remaining gas is led via a filter arrangement 20 to an evacuation conduit 21.

With reference to Fig. 1 the distillation material 15 can, through suitable control of the motor 13, be continuously fed (Fig. 2) through the distillation conveyor 5 at a suitable speed or stepwise, so that a certain selectable time of residence at the heating arrangement 8 is accomplished, or so that the distillation material 15 is stepwise transported through the different parts 8a, 8b, 8c, 8d of the heating arrangement 8.

The non- vaporized part of the distillation material 15, which in most applications would appear in solid form, is diverted from the distillation conveyor 5 to a collecting arrangement 22. The collecting arrangement 22 comprises means 23, 24, 25 for selectively feeding the distillation material 15 from the heating arrangement 8 to any of two containers 26, which means comprises a diverting conveyor 23, in this example in the form of a screw conveyor. The diverting conveyor 23 is driven by a motor 24, the rotational speed of which can be controlled, and which can drive the diverting conveyor 23 in both directions. By suitable control of the motor 24 and the valves 25, located downstream of the diverting conveyor 23 and upstream of the containers 26, the flow of material 15 can be guided to any of the containers 26. Of course, the collecting arrangement 22 can be arranged so that more than two containers 26 can be coupled to it.

The collecting arrangement 22 also comprises a cooling arrangement 27 for cooling the distillation material 15, which cooling arrangement cooperates with the cooling arrangement 19 for condensation arrangement 18 and comprises cooling conduits enclosing the diverting conveyor 23.

The distillation arrangement comprises an electrostatic filter 17a, located downstream of the distillation conveyor 5 for removing dust and powder from the gas flowing from the distillation conveyor 5. Alternatively, the distillation arrangement can comprise more than one electrostatic filter. The electrostatic filter 17a is of a conventional type and comprises a unit for static charge 17b. The electrostatic filter 17a is located upstream of a condensation arrangement 18. Further, the electrostatic filter 17a is located above the distillation conveyor 5 and includes a cyclone wall 17c formed as an inverted frusto-cone, which is connected to the conduit 10 from the distillation conveyor 5. Thereby dust and powder having been separated from the gas can be fed under the influence of gravity via the cyclone wall 17c and through the conduit 10 back to the distillation conveyor 5, so that it can be fed with the non- vaporized part of the distillation material 15 to the collecting arrangement 22.

Here reference is made to Fig. 4, showing a gas inlet arrangement 28 comprising the above mentioned gas inlet 9 to the distillation conveyor 5. The gas inlet arrangement 28 comprises means 29 in the form of a non-return valve 29 for preventing the gas from flowing in a direction which is opposite to the transport direction of the distillation conveyor 5. The gas inlet arrangement 28 also comprises an adjustable valve 30 for control of the gas supply.

With reference to Fig. 4, the distillation arrangement comprises means 31 for measuring the gas flow at the gas inlet 9. This means can be provided in the form of a gas flow meter and can alternatively be provided so that it measures the gas flow in some other part of the distillation arrangement, for example in the conduit 17 which leads gas from the distillation conveyor 5.

The means 31 for measuring the gas flow can be arranged to send signals corresponding to values of the gas flow to a central control unit (not shown) for the distillation arrangement. The control unit can in turn be arranged to activate a warning or alarm signal, which can be detected by an operator of the distillation arrangement if the gas flow is lower than a predetermined value. The distillation arrangement can also be provided with means, e.g. in the form of a display device, for showing among other things values of the gas flow during operation of the arrangement. The control unit can also, or alternatively, be arranged to control the vibration feeders 3 and/or the feeding conveyor 4, so that the flow of distillation material to the distilla- tion conveyor is reduced or stopped if the gas flow should be lower than a predetermined value. Preferably the predetermined gas flow value for reducing or stopping the feeding of distillation material is lower than the predetermined gas flow value for activating the warning or alarm signal.

The distillation arrangement 1 described above constitutes a closed system, wherein the distillation material, vaporized material and condensed material, as well as transport gases are separated from the surrounding atmosphere throughout the entire distillation process. Thus, the process material is kept in an enclosed manner and transported from the containers 2 upstream of the distillation conveyor 5, through the vibration feeders 3, the feeding conveyor 4 and the distillation conveyor 5, as well as through the gas outlet 10, the conduit 17, the condensation arrangement 18, the drain valve 18a, the filter arrangement 20 and the evacuation conduit 21, as well as through the collecting arrangement 22 with the diverting conveyor 23, and the containers 26. This closed system will substantially reduce the risk of leakage, e.g. in the event of a power failure.