METHOD AND DEVICE FOR REMOVING ONE OR MORE CONTAMINATIONS FROM A BULK MATERIAL

Abstract: A method for removing one or more contaminations from a bulk material, the bulk material being fed to a treating chamber (1), exposed herein to a temperature treatment and discharged. According to the invention the bulk material is exposed to a vacuum treatment during temperature treatment. An apparatus according to the invention for the implementation of the method comprises a treating chamber (1) for treating contaminated bulk material herein, feeding means (2) for feeding the bulk material to the treating chamber (1), discharging means (9) for discharging the bulk material from the treating chamber and heating means (19) for heating the bulk material in the treating chamber and also comprises a vacuum forming means (16) for forming a vacuum in the treating chamber.

Description: Method and device for removing one or more contaminations from a bulk material The invention relates to a method for removing one or more contaminations from a bulk material, the bulk material being fed to a treating chamber, subjected the¬ rein to a temperature treatment and discharged. The inven¬ tion relates furthermore to an apparatus for the implemen¬ tation of the method. With increased attention being paid to the environment in recent years, a great demand for a cheap, efficient method of purifying contaminated bulk material has arisen. This material can, for example, be waste contaminated by mercury, earth polluted by mercury or silt containing mercury. A known method consists of feeding a heating oven with a specific quantity of the contaminated bulk material, heating being used to evaporate contamination from the bulk material. Drawbacks of this known method are, among other things, that a very high temperature is necessary for contaminations to evaporate and that the amount of combus¬ tion gas which has to be subjected to a follow-up treat¬ ment is large, so that the risk of still posing a threat SUBSTITUTE SHEET to the environment as a result of too high an emission level from the contamination in question, is considerable. The required high temperature does not only give rise to high energy consumption, but also logically has the effect that each time the quantity of bulk material which has been introduced, has first of all to be heated to a high temperature, which makes the treatment lengthy and unsuit¬ able for processing large quantities of bulk material per unit of time. According to another well-known technique bulk material is subjected to a chemical treatment to immobilze contaminations in the bulk material. It is obvious that here contamination is not removed. Moreover, the weight and volume of the bulk material increase as a result of this treatment. This bulkmaterial should be subsequently disposed of as waste. In practice, this often results in opting for direct disposal of the contaminated bulk material in places especially intended for that purpose, often abroad. One of the aims of the invention is to provide a method and apparatus for removing one or more contaminati¬ ons from a bulk material, ensuring that a high removal yield is achieved in an efficient way with no, or at any rate a low hazard to the environment. For this purpose, in accordance with the inven¬ tion a method of the kind mentioned in the preamble is provided, characterized in that during temperature treat¬ ment the bulk material is subjected to a vacuum treatment. The vacuum treatment of the bulk material has an important advantage, particularly by the formation of a vacuum in the treating chamber, in that the vapour pressu¬ re and therefore also the boiling point of the contamina¬ tions is lowered, so that the contaminations can easily escape from the bulk material. By doing so contaminations containing heavy metals, such as cadmium or less volatile hydrocarbon compounds, such as insecticides, pesticides and PCB's are also removed. Besides, the closed vacuum system reduces leakage of vapours to an absolute minimum. Apart from that, the absence of air in the treating cham¬ ber prevents the formation of dioxines and other environ¬ mentally hazardous substances formed by oxidization. As the quantity of combustion gases is very small, the fol¬ low-up treatment of the extracted vapours can take place more efficiently. A low heating temperature being possible, a practical technical implementation of the method is ena- bled, whereby the bulk material is treated continuously. Tests have shown that a high removal yield is achieved, even when the length of treatment is short, to such an extent that the residue concentration of one or more contaminations in the bulk material is far below the maxi- mum level permitted by the authorities. Preferably the bulk material is conveyed to the treating chamber, whilst undergoing temperature treatment, essentially in a direction from an entrance of the trea¬ ting chamber to an exit of the• treating chamber. During continuous operation polluted bulk material can, for that reason, be fed through the entrance of the treating cham¬ ber, be moved therein to the exit and discharged from there. What is more, regular feeding and discharging is promoted, if this takes place proportionately. According to a further development of the me¬ thod, feeding and/or discharging of the bulk material occur in each case through at least two passages, which are alternately released. In this way, it can easily be arranged that the underpressure in the treating chamber is also retained during feeding and/or discharging of the bulk material, so that treatment in the chamber need not be interrupted. In order to attain as high a removal yield as possible, the bulk material in the treating chamber can, moreover, be moved in a direction essentially diagonal to the direction of conveyance. Apart from that, by doing this, the length of stay of the bulk material in the treating chamber can be decreased or the processing capa¬ city of the latter can be enlarged at the same machine speed, and because of this the bulk material is mixed together in such a way that each time other bulk material comes to the surface, which furthers the removal of conta¬ minations. The contaminated bulk material can contain any contaminated substance, for example waste, which is pollu¬ ted by one or more vaporizable substances such as mercury, lead, antimony or hydrocarbon. Favourable results have been shown, especially with mercury polluted fluorescent powder originating from gas-discharge lamps. In the case of the treatment of bulk material which contains a sizeable amount of liquid, such as silt, it is preferred if the bulk material undergoes a, prefera¬ bly fased, pre-drying treatment before feeding it to the treating chamber. A further increase in removal yield is achieved by adding at least one rinsing agent, such as air, nitro- gen or water to the bulk material during treatment. In this way the evaporated substances are expelled from the treating chamber not only by having been extracted by the vacuum formation but also by the rinsing agent. Preference is given to the formation of a vacuum in the treating chamber to a pressure lower than 3 mbar, preferably 0,5 to 1 mbar. So that all contaminations in the bulk material are removed, the temperature of the bulk material in the treating chamber at the prevailing pressure can be round about the highest boiling point of the contaminations to be removed. In accordance with the invention an apparatus for implementing the method is also provided, which com¬ prises a treating chamber for the treatment therein of contaminated bulk material, feeding means for feeding the bulk material to the treating chamber, discharging means for discharging the bulk material from the treating cham- ber, and heating means for heating the bulk material in the treating chamber and is characterized in that vacuum means are provided for forming a vacuum in the treating chamber. The treating chamber can be formed by a rotata- ble container which is provided with at least one entrance and at least one exit. By rotating the container, the bulk material can easily be conveyed from the entrance to the exit of the treating room, the bulk material being also subjected to a displacement in an essentially diagonal direction . to the conveying direction so that the bulk material is suitably mixed for the sake of achieving a high removal yield. Preferably, the container is essentially cylin- drical, the ends of which are provided with coupling means for coupling the feeding means and the discharging means respectively. A good heating insulation is attained hereby if the coupling means comprise flange connections in which at least one heat insulating packing is fitted. In accordance with a further development of the apparatus according to the invention, the feeding and dis¬ charging means each time comprise a rotatable, essentially helical body arranged coaxially with regard to the contai¬ ner. In a preferred embodiment of the apparatus according to the invention, at least one helical body is mounted on a hollow axle, the axle cavity being connected on the one hand with vacuum forming means and, on the other hand, forming an open connection to the treating chamber. The axle cavity of the other helical body can thereby be in contact with a rinsing agent source for supplying the treating chamber with a rinsing agent, preferably air, nitrogen and/or water. A beneficial embodiment is achieved if the helical bodies are connected to the cylindrical container and the axles of the feeding and discharging means are placed in sliding ring seals. The cylindrical container is preferably a drum, the casing of which contains an electrically conductive material and the heating means comprise an electrical induction means placed around the drum. This embodiment is particularly suited for use in surroundings where there is risk of explosion and where the use of gas burners is undesirable. The cylindrical container consists preferably of mutually coupling sections, so as to facilitate the adap- tation of the volume of the treating chamber, depending on the desired capacity and/or the processing speed, as well as on the bulk material which is to be purified. For additional mixing of the bulk material in the container, the latter can be provided on the inside with one or more baffles. The invention will be explained in the following among other things on the basis of a preferred embodiment of the apparatus of the invention, referring to the figu¬ res, in which: fig. 1 shows a block diagram in explanation of the method and apparatus according to the invention, and fig. 2 shows a diagram of a preferred embodiment of the apparatus according to the invention. In fig. 1 the continuous double lines indicate the path of the bulk material, the arrows showing the direction of conveyance. The continuous single lines represent connecting or control pipes which, depending on the function, can for instance be electric, pneumatic or hydraulic pipes. Contaminated bulk material is fed from a feeding means 2 to a treating chamber 1, which then in turn is fed to feeding means 2 from stock buffers 3 and 4, the inlets and outlets of which are regulated in this case by valves 5 to 8. In treating chamber 1 treated bulk material is discharged through a discharging means 9 to two storage buffers 10 and 11, the inlets and outlets of which are regulated by valves 12 to 15. In chamber 1 a vaccuum is formed by a vacuum forming means 16, which is coupled by means of a vacuum pipe 17 to chamber 1 , a vapour treating means 18 being provided in the pipe for treating the expelled vapours. The means 18 can contain condensers, active carbon fil¬ ters, catalysts, agents for a wet gas washing and so on. Moreover, a heating means 19 is shown in diagram form in fig. 1 for heating the bulk material in the cham¬ ber 1, a feeding means for a rinsing agent 20 for feeding a rinsing agent by means of a feeding pipe 21 to the cham¬ ber, and driving means 22, 23, 24 for driving chamber 1 and the feeding and discharging means 2 and 9 respective¬ ly, in order to ensure a regular, continual conveyance of the bulk material. In the diagram shown the valves 5 to 8, 12 to 15, the heating means 19, the feeding means for the rin¬ sing agent 20 and the driving means 22 to 24 are represen¬ ted as being controlled from a centre point by a control means 25 which can, for example, be a computer. Fig. 2 shows a preferred embodiment of the appa¬ ratus according to the invention in diagram form. Here the parts which correspond to those according to fig. 1 are provided with the same reference numbers. In this embodiment the treating chamber 1 is formed by a cylindrical container, in particular a drum, which is rotatably supported by rollers 26 mounted on a frame 27 adjustable in height and in the angle of inclina¬ tion. The ends of the drum, which determine an entrance and an exit of the drum respectively, are closed by head flanges 28, 29 provided with collars 30, 31, in which in each case between drum 1 and the flanges 28, 29 one packing - not shown - is disposed, preferably in the form of a metal seal made of annealed copper or titanium, these materials being highly resistant to high operating tempe- ratures. At lower operating temperatures, for example up to 500°C, packings made of an elastomer or asbestos are used. The flange connections allow for an easy dismantling of the drum 1, for example for maintenance purposes, and also facilitate the requested lengthening of the drum by linking various sections to one another, each section being, for example, one meter long with a diameter of 30 centimeters. The collars 30, 31 are inserted into the feeding means 2 and the discharge means 9 respectively and are supported by sliding ring seals 32, 33 respectively. Besides that, the sliding ring seals can be subjected externally to underpressure to prevent lubricants escaping from the seals. A hollow axle 34 extends through the feeding means 2 up to a central part of the drum 1. The axle 34 is supported by sliding rings seals 32, 35 and 36. The axle cavity is connected by means of a coupling section 37 to a vacuum pump - not shown - for forming a vacuum in the drum 1. A hollow axle 38 which is inserted in the drum 1 extends through the discharging means 9 and is supported by sliding ring seals 33 and 39. By means of a coupling section 40 nitrogen, water and/or air is blown into the the drum 1 in order to disperse vapours which have escaped from the bulk material. The sliding ring seals 32, 33, 35, 36 and 39 can, for instance, be made of silicon carbide, stainless steel, carbon or nylon, depending on the locally prevai¬ ling temperature. On each of the axles 34, 38 a screw 41, 42 respectively is mounted, connected firmly on the circum- ference to the collar 30, 31 respectively. The screws 41, 42 thus each form a screw conveyor so that the bulk mate¬ rial is conveyed into and out of the drum 1 respectively. The drum 1 and the screws 41, 42 are jointly driven by means of the single driving means 22 which can be a echa- nical transmission. In order to discharge the bulk materi¬ al proportionately from the drum, a baffle or scoop 43 is provided in the vicinity of the headflange 29 to carry along a measured quantity of bulk material to the screw 42 after each revolution. The carrying velocity through the drum 1 is determined not only by the physical qualities of the material and the rotation velocity of the drum, but also by the angle of inclination of the drum and can also be influenced by other baffles disposed on the inside of the drum, for example, a helical baffle which extends along the length of the drum. The speed of revolution of the drum is essentially determined by the nature of the bulk material and can vary from, for instance, 0,5 revo¬ lutions per minute for powdered bulk material to 500 revo¬ lutions per minute for silt-free sand. The drive through the driving means 22 preferably occurs stepless by means of a hydraulic motor. Drum 1 is heated inductively by an induction coil 19, for which purpose the casing of the drum is made of an electrically conductive material such as steel. The head flanges 28, 29 are, on the other hand, not electri¬ cally conductive, in order to restrict a transfer of warmth from the drum to the feeding means 2 and the dis¬ charge means 9 as much as possible. The operating temperature in the drum at the prevailing pressure is in the main determined by the boiling point of the contaminations to be removed and can for instance be 500° to 600° C. Heavy metals such as cadmium require a higher temperature, for example in the region of 1200°C to 1300°C at one millibar. During operation the buffers 3, 4, and 10, 11 respectively are released in turn. In fig. 2 the situation is shown whereby the buffers 4 and 10 are released. In this position the other buffers, in figure 3 and 11, are being filled or emptied respectively by opening the valve 5, 15 respectively, in the course of which, after the closure of these valves, the buffers 3 and 11 are pre- evacuated, prior to opening valves 6 and 4, after closure of the valves 8 and 12, so that a current of air from the buffers is prevented from entering the treating chamber through the screws 41, 42. It is plain that if a suitable control of the valves 6, 8, 12 and 14 rather than a conti¬ nuous feeding and discharging is selected, then loading and unloading the drum in a "batch 11 fashion can be achie- ved. In the case of silt-type bulk material the buffers 3 and 4 can be preceded by a pre-drying installa¬ tion for a phased pre-drying of the bulk material. For an expert it will be evident that many modifications in the above described preferred embodiment of the apparatus according to the invention can be intro¬ duced without, however, having to abandon the framework of the invention. For instance, instead of inductive heating, the bulk material can be heated by high frequency irradi- ation or by gas burners. Instead of using a screw convey¬ or, feeding can also be done by extrusion, particularly in the case of silt-type bulk material.

Claims: Claims 1. Method for removing one or more contaminations from bulk material, the bulk material being fed to a treating chamber, subjected therein to temperature treatment and discharged, characterized in that during temperature treatment the bulk material is subjected to a vacuum treatment. 2. Method according to claim 1, characterized in that the bulk material is transported to the treating chamber during temperature treatment, in a direction essentially from an entrance to the treating chamber to an exit from the treating chamber. 3. Method according to claim 1 or 2, characterized in that the feed and the discharge takes place proportionately. 4. Method according to claims 1 - 3 characterized in that the feed and/or discharge of the bulk material takes place in each case by means of at least two passages, which are alternately released. 5. Method according to any one of claims 2 - 4, characte¬ rized in that the bulk material in the treating chamber is moreover removed in an essentially diagonal direction to the transport direction. 6. Method according to claims 1 - 5, characterized in that the bulk material is a material contaminated by one or more vaporizable materials, for example a waste material. 7. Method according to claim 6, characterized in that the bulkmaterial is a fluorescent powder polluted by mercury. 8. Method according to any one of the previous claims, characterized in that the bulk material is subjected preferably to a phased pre-drying treatment. 9. Method according to any one of the previous claims, characterized in that at least one rinsing agent, prefera¬ bly air, nitrogen and/or water is fed to the treating chamber during the treatment of the bulk material. 10. Method according to any one of the previous claims, characterized in that in the treating chamber a vacuum is formed up to a pressure lower than 3 mbar, preferably 0.5 to 1 mbar. 11. Method according to any one of the previous claims, characterized in that the temperature of the bulk material in the treating chamber is brought to a level which, at the prevailing pressure, is approximately that of the highest boiling point of the contaminations to be removed. 12. Apparatus for the implementation of the method accor¬ ding to any one of the previous claims, comprising a treating chamber for the treatment therein of contaminated bulk material, feeding means for feeding the bulk material to the treating chamber, discharging means for discharging the bulk material from the treating chamber and heating means for heating the bulk material in the treating cham¬ ber, characterized in that vacuum means are provided for forming a vacuum in the treating chamber. 13. Apparatus according to claim 12, characterized in that the treating chamber is formed by a rotatable container provided with at least one entrance and one exit. 14. Apparatus according to claim 13, characterized in that the container is substantially cylindrical, the ends of which are provided with coupling means for coupling the feed means and the discharge means respectively to the container. 15. Apparatus according to claim 14, characterized in that the coupling means comprise flange connections in which at least one heat insulating packing is fitted. 16. Apparatus according to any one of the previous claims 13 - 15, characterized in that the feeding and discharging means each comprise a rotatable, essentially helical body, arranged coaxially with regard to the container. 17. Apparatus according to claim 16, characterized in that at least one helical body comprises a hollow axle, the axle cavity being connected on the one hand to the vacuum forming means and forming on the other hand an open con¬ nection to the treating.chamber. 18. Apparatus according to claim 17, characterized in that the axle cavity of another helical body is in contact with a rinsing agent source for supplying the treating chamber with a rinsing agent, preferably air, nitrogen and/or water. 19. Apparatus according to any one of the claims 16 - 18, characterized in that the helical bodies are securely connected to the cylindrical container. 20. Apparatus according to any one of the claims 17 - 19, characterized in that the axle of the helical body is placed in sliding ring seals. 21. Apparatus according to any one of the claims 13 - 20, characterized in that the container is a drum of which the casing contains an electrically conductive material, and that the heating means comprises an electrical induc¬ tion means arranged around the drum. 22. Apparatus according to any one of the claims 13 to 21, characterized in that the container consists of mutually coupling sections. 23. Apparatus according to any one of the claims 13 - 22, characterized in that the container is internally provided with one or more baffles.

Inventors: BLONK DIRK JAN, BLONK, DIRK, JAN
Applicants: J M C MANAGEMENT BEHEER B V, RECYCLING NEDERLAND B V, J.M.C. MANAGEMENT BEHEER B.V., RECYCLING NEDERLAND B.V.
Application year: 1992
Main classification: B01J3
IPC codes: B01J3, B01J8, B09B3, B09C1, C02F1, C02F9, C22B5, C22B9, C22B43, F26B11, F27B7, F27D3, F27D23