METHOD AND DEVICE FOR PURIFYING GASES

Abstract: Method for decomposing thermally decomposable components which are present in gases, whereby these gases are led through a heat exchange medium consisting of particles which resist the decomposition temperature, and whereby these gases are heated in said heat exchange medium up to the decomposition temperature of the decomposable components, characterized in that the heat exchange medium is continuously carried around and consequently carried away from a first zone (30) in which this heat exchange medium heats the gases and is again carried to a second zone (31) in which the heat exchange medium is heated, at least partly by the waste gases of the combustion of the decomposable components and/or of the decomposition products thereof and by the remainder of the gases which were further heated by this combustion, which combustion mainly takes place in a combustion zone (32) situated between these zones (30 and 31).

Description: Method and device for purifying σases. The present invention concerns a method for purifying gases which contain thermally decomposable components, whereby these thermally decomposable components are thermally decomposed. By thermally decomposable components are mainly understood volatile organic components which usually give off an unpleasant smell. Such components are for example aromatic or aliphatic compounds. Due to the decomposition, these decomposable components are decomposed in harmless end products . In particular, the invention concerns a method for decomposing thermally decomposable components, in particular volatile organic components which are present in gases, whereby these gases are led through a heat exchange medium consisting of particles which resist the decomposition temperature, and whereby these gases are heated in said heat exchange medium up to the decomposition temperature of the decomposable components . The gases may be derived from the drying and/or burning of organic waste and may largely consist of steam. In a known method of the above-mentioned type, the gases are carried downward by means of a stationary heat exchange medium consisting of ceramic rings, in which is erected an electrical heat resistor. In this known method, the heat exchange medium is polluted relatively fast, so that it has to be replaced relatively quickly. This known method cannot be used for damp gases. The invention aims a method for decomposing thermally decomposable components which are present in gases, with an excellent heat exchange, whereby the heat exchanging mass has to be replaced less quickly and whereby this method can also be used for damp gases. This aim is reached according to the invention in that the heat exchange medium is continuously carried around and consequently carried away from a first zone in which this heat exchange medium heats the gases and is again carried towards a second zone in which the heat exchange medium is heated, at least partly by the waste gases of the combustion of the decomposable components and/or of the decomposition products thereof and by the remainder of the gases which were further heated by this combustion, which combustion mainly takes place in a combustion zone situated between these zones. The carrying around of a heat exchange medium through which gases flow is known from US-A-2.636.575, but the heat exchange medium is an adsorbent which is mainly use for drying air in a topmost zone, whereas in a bottommost zone, the adsorbent is dried by other air which is heate by a burner. It is mentioned that the adsorbent can be a catalyst, whereby a catalytic reaction in this case takes place in the topmost zone and whereby the catalyst is purified of adsorbed reagents and products in the bottommost zone. According to a particular embodiment of the invention, external calorific value is supplied to the combustion zone. In the first and the second zone, the heat exchange medium is for example moved down through due to gravitation. The gases are preferably lead in a zigzag manner over the heat exchange medium, in such a manner that they cross said heat exchange medium several times . A suitable heat exchange medium is a granulated mass. The invention also concerns a device which is particularly suitable to carry out the method according to any of the above-described embodiments. Thus, the invention concerns a device for thermally decomposing thermally decomposable components which are present in gases, characterized in that it contains a tower with an inner casing provided with openings which is closed at the bottom and at the top; a second casing erected around this inner casing; a heat exchange medium between the two casings which consists of particles; means to collect this heat exchange medium at the bottom of the tower and to supply it back between said casings at the top of the tower; and means to introduce the gases at the bottom through the second casing and to discharge the gases at the top through the second casing. According to a special embodiment of the invention, the second casing is also provided with openings and the tower contains an outer casing which surrounds this second casing, whereby walls are provided in the space between the second casing and the outer casing which divide this space in chambers situated on top of one another, whereby these latter open into the space between the second casing and the inner casing via openings in the second casing and whereby the means to introduce the gases and to discharge them contain an inlet which opens into a chamber situated at the bottom and an exhaust which opens into a chamber situated at the top. Practically, the device contains means to supply calorific value from outside to the gases between the inlet and the exhaust, either in the shape of hot gases or in the shape of injected fuel. In order to better explain the characteristics of the invention, the following preferred embodiment of a method and device according to the invention for decomposing thermally decomposable components which are present .in gases is described as an example only without being limitative in any way, with reference to the accompanying drawings, in which: figure 1 schematically shows a section of a device for decomposing thermally decomposable components according to the invention; figure 2 shows a section according to line II-II in figure 1; figure 3 shows the detail which is indicated by F3 in figure 1 to a larger scale. As represented in the figures, the device for decomposing thermally decomposable components which are present in gases contains a tower 1 which mainly consists of three coaxial standing casings 2, 3 and 4 which form cylinders which are conically tapered on both ends. The inner casing 2 is closed at the top and at the bottom and is provided with openings 5 in its cylindrical part. The space inside this casing 2 is divided by partitions 6 in a top chamber 7 and a bottom chamber 8. As represented in detail in figure 3, this casing 2 can be made of hollow flame-resistant stones 9 which are provided with windows 10 in their bent walls which form the above-mentioned openings 5 together with the cavity 11 in the stones. The second, in other words the middlemost casing 3 is also provided with openings 12 in its cylindrical part and can be made of similar flame-resistant stones 9 in the same manner as the inner casing 2. The outer casing 4 is a solid wall of for example gas concrete. The conically tapered outer parts of these casings 3 and 4 are open at their end, such that at the top and at the bottom of the tower 1, they respectively form an inlet 13 and an exhaust 14 which open into the space 15 which is formed between the inner casing 2 and the second casing 3. The space between the second casing 3 and the outer casing 4 is divided by ring-shaped walls 16 in three ring-shaped chambers situated on top of one another, namely a bottom chamber 17, a middlemost chamber 18 and a topmost chamber 19. In case the second chamber 3 is formed of hollow stones 9 at the place of a ring-shaped wall 16, the hollow stone 9 is replaced by a solid stone in order to prevent that the chambers 17, 18 and 19 are directly connected to one another via the casing 3. The space between the inner casing 2 and the second casing 3 is not interrupted but filled with a heat exchange medium in the shape of a granulated mass consisting of particles which resist the temperatures required to dissolve the volatile organic components in the gases and which in particular resist temperatures of 800 to 900"C. For clarity's sake, this granulated mass is not represented in figure 3. Suitable particles are particles which easily absorb and give off heat such as burnt clay, aluminate, for example calcium aluminate or a composition containing aluminate. Not only can these particles ensure a good heat transfer, but possibly they can also have a catalytic action. The gases, which are derived from the drying and/or burning of organic waste, for example which are derived from a waste treatment unit, and which mainly consist of steam with volatile, thermally decomposable organic components which are usually harmful, can be supplied via an inlet 20 which opens into the bottom chamber 17 through the outer casing 4 by means of a fan 21 mounted in this inlet. To this inlet 20 is connected a pipe 22 for supplying hot air to the gases . The gases are discharged from the top chamber 19 via an exhaust 23 which extends through the outer casing 4 and in which is also mounted a fan 21. Calorific value or heat can be supplied to the granulated mass by means of a ring-shaped gas pipe 24 which is erected in the middlemost chamber 18, which is provided with openings and is connected to an external burner 25 which is erected outside the outer casing 4. The outer casing 4 is further surrounded by a housing 26 through which the above-mentioned inlets 13 and 20 and the exhausts 14 and 23 extend. Under the exhaust 14 for the granulated mass is erected a discharge screw 27 and above the inlet 13 for this granulated mass is erected a supply screw 28. In order to carry the granulated mass from one screw to the other, an elevator 29 is provided between the discharge screw 27 and the supply screw 28. A quantity of hot air, preferably up to 10 vol %, is added to the gases via the pipe 22 to supply a sufficient amount of oxygen for the combustion of the thermally decomposable components and/or decomposition products thereof as well as air for the possible combustion of the gases injected via the gas pipe 24. This air preferably has a temperature of over 650°C, which also provides for a pre-heating of the gases, and, if these gases contain steam, lowers the saturation temperature of this steam and in this manner prevents condensation. The principle of the gas purification, or in other words the decomposition of the decomposable components into harmless end products, consists in making the granulated mass circulate and leading the gases in counterflow in relation to a downward flow of this granulated mass, whereby the gases cross the flow of the granulated mass several times. This crossing becomes possible as the inner casing 2 and the second casing 3 are provided with openings 5, 12 respectively. At a normal regime, the gases are heated in a first, bottommost zone 30 of the granulate mass by the latter, whereas in a second, topmost zone 31 this granulated mass is heated by the waste gases of the combustion .or pyrolysis of the volatile organic components -and/or decomposition products thereof on the one hand, and by the waste gases of the external burner 25 which are introduced in the combustion zone 32 situated between the zones 30 and 31 via the gas pipe 24. The gases, at a temperature between 150 and 200°C, are blown in the bottommost zone 31 via the inlet 20 and the bottommost chamber 17 and through the second casing 3. As indicated by the arrows, the main part of these gases flows through the granulated mass and through the inner casing 2 in the bottommost chamber 8, whereby these gases are heated. The gases are stopped by a partition 6 and as a result again flow right through the zone 31 up to the middlemost chamber 18 between the casings 3 and 4, whereby they are further heated by the granulated mass. During said heating of the gases, at least a part of the decomposable components usually already start to decompose into gaseous decomposition products which can be further thermally decomposed or burnt. In this middlemost chamber 18 and the part of the granulated mass connected to it via openings 12 in the second casing 3 is formed the combustion zone 32. In this combustion zone 32, the further decomposition of the decomposable components and/or decomposition products thereof takes place, and especially the combustion of the gaseous decomposition products into harmless end products, in particular CO,, H, and N,. In this combustion zone 32, also the waste gases of the external burner 25 are possibly further burnt. The temperature of the gases rises in this combustion zone 32 with over 100°C, up to 800 to 900°C or even more. According to a variant, either ordinary heated gases or pure, for example gaseous fuel can be supplied via the gas pipe 24 instead of waste gases. Due to the injection of gases via the gas pipe 24 in the combustion zone 32, an excess pressure of less than 5% in relation to the atmospheric pressure is created, and these gases are spread in the other gases. Thus, the formation of nitrogen oxides is prevented. On top of the middlemost chamber 18, the hot gases again radially flow through the granulated mass, namely the topmost zone 31 thereof, into the chamber 7, whereby the gases heat the granulated mass. Thanks to the fan 21 in the exhaust 23 for the gases and because the chamber 7 is closed at the top, the predominantly purified gases flow, opposite the exhaust 23, radially outward from the chamber 7 through the granulated mass, such that they further heat this granulated mass . These gases are discharged via the topmost chamber 19 and the exhaust 23 and leave the tower 1 at a temperature of over 150°C. During this circulation of the gases, the granulated mass is carried around. This mass continuously descends in the space 15 between the inner casing 2 and the second casing 3 due to gravitation. At the bottom, cooled granulated mass is collected on the discharge screw 27. This mass is carried via the elevator 29 on the supply screw 28 and carried to the top of the space 15 by this supply screw. The heat exchange between the granulated mass and the gases is excellent and the purification of the gases by means of decomposition or combustion of the thermally decomposable components can be carried out in a very economic manner. Although the granulated mass is self-cleaning to a large extent, it can be further cleaned outside the tower 1 during the circulation. During the purification, this granulated mass can be replaced in part or as a whole by new mass . In the tower 1, the granulated mass can operate as a filter which stops the solid particles which may possibly be present in the gas flow, which preferably flows at a speed which is lower than 1.5 m/sec. During the cleaning of the granulated mass, these solid particles can then be removed via the discharge screw 27. Components such as metals which have been released during the purification, in particular copper, can precipitate on the particles of the granulated mass when it cools off. Thanks to the mutual friction of the particles as the granulated mass moves, this precipitation of the particles is removed. The method can be applied to damp gases, but these gases must .not necessarily consist mainly of steam. The circulation of the granulated mass must not necessarily take place by means of an elevator. It can for example also take place by means of screws or such. Also the flow of the gases must not necessarily be caused by means of two fans. It can also be done with a single fan or with one or more extractors. Calorific value from outside the combustion zone is added as required. It is not excluded that, once the starting up is over, such addition is no longer required as the decomposition or combustion of the organic components in the gases provides sufficient heat to keep the decomposition going. The present invention is by no means limited to the above-described embodiments represented in the accompanying drawings; on the contrary, such a method and device can be made in all sorts of variants while still remaining within the scope of the invention as described in the following claims.

Claims: Claims . 1. Method for decomposing thermally decomposable components which are present in gases, whereby these gases are led through a heat exchange medium consisting of particles which resist the decomposition temperature, and whereby these gases are heated in said heat exchange medium up to the decomposition temperature of the decomposable components, characterized in that the heat exchange medium is continuously carried around and consequently carried away from a first zone (30) in which this heat exchange medium heats the gases and is again carried to a second zone (31) in which the heat exchange medium is heated, at least partly by the waste gases of the combustion 'of the decomposable components and/or of the decomposition produces thereof and by the remainder of the gases which were further heated by this combustion, which combustion mainly takes place in a combustion zone (32) situated between these zones (30 and 31) . 2. Method according to claim 1, characterized in that the thermally decomposable components in the gases are volatile organic components and in that the gases in the combustion zone (32) are heated up to 800°C or more. 3. Method according to any of claims 1 and 2, characterized in that before the gases reach the combustion zone (32) , air is supplied to these gases. 4. Method according to claim 3, characterized in that air at a temperature of over 650"C is supplied. 5. Method according to claim 3 or 4, characterized in that up to 10 volume % of air is added to the gases. 6. Method according to any of the preceding claims, characterized in that calorific value from outside is added to the combustion zone (32) . 7. Method according to any of the preceding claims, characterized in that an excess pressure of less than 5% in relation to the atmospheric pressure is created in the combustion zone. 8. Method according to any of the preceding claims, characterized in that in the first and second zone (30 and 31; , the heat exchange medium is moved downward due to gravitation,, and the gases are lead in a zigzag manner over the heat exchange medium, such that they cross said heat exchange medium several times. 9. Method according to- any of the preceding claims, characterized in that a granulated mass is used as heat exchange medium. 10. Method according to the preceding claim, characterized in that one of the following materials is used as granulated mass: clay, aluminate and a composition containing aluminate. 11. Device for thermally decomposing thermally decomposable components which are present in gases, characterized in that it contains a tower (1) with an inner casing (2) provided with openings (5) which is closed at the bottom and at the top; a second casing (3) erected around this inner casing (2); a heat exchange medium between the two casings (2 and 3) which consists of particles; means (27-28-29) to collect this heat exchange medium at the bottom of the tower (1) and to supply it back to the top of the tower (1) between these casings (2 and 3); and means (20-21-23) to introduce the gases at the bottom through the second casing (3) and to discharge the gases at the top through the second casing (3) . 12. Device according to claim 11, characterized in that the second casing (3) is also provided with openings (12) and in that the tower (1) contains an outer casing (4) which surrounds this second casing (3) , whereby walls (16) are provided in the space (15) between the second casing (3) and the outer casing (4) which divide this space (15) in chambers (17-18-19) situated on top of one another which open into the space (15) between the second casing (3) and the inner casing (2) via openings (12) in the second casing (3) and whereby the means (20-21-23) to introduce the gases ' and to discharge them contain an inlet (20) for the gases which opens into a chamber (17) situated at the bottom and an exhaust (23) for the gases which opens into a chamber (19) situated at the top. 13. Device according to claim 12, characterized in that the space inside the inner casing (2) is divided in a top chamber (7) and a bottom chamber (8) by at least one partition (6) . 14. Device according to any of claims 10 to 13, characterized in that it contains means (24-25) to supply calorific value from outside to the gases between the inlet (20) and the exhaust (23) for the gases. 15. Device according to any of claims 12 and 14, characterized in that the means (24-25) to add calorific value to the gases contain a gas pipe (24) which is erected in a middlemost chamber (18) formed between the second casing (3) and the outer casing (4).

Inventors: MUYNCK JOSE OMER ARNOLD DE, DE MUYNCK, JOSE, OMER, ARNOLD
Applicants: DRUWEL NORBERT, GROEP DANIS NV, MUYNCK JOSE OMER ARNOLD DE, DE MUYNCK, JOSE, OMER, ARNOLD, DRUWEL, NORBERT, GROEP DANIS
Application year: 1996
Main classification: B01J8
IPC codes: B01D53, B01J8