AT393970B - METHOD FOR COMBUSTION OF GASES LOADED WITH DUST - Google Patents

Description

AT 393 970 B

The invention relates to a process for the combustion of gases which are loaded with dusts, in particular pyrolysis gases from waste disposal plants, in a combustion chamber, the particles being kept in suspension, and a combustion chamber for use in these processes.

In the course of many industrial processes, including the generation of energy, dusts, ashes or sludges are also produced as by-products or waste products. These are mostly disposed of by landfill. Now, however, many of these waste products are contaminated with substances harmful to the environment and their health due to the process they produce.On the other hand, many substances that have been known for some time have recently been recognized as harmful, so that for these reasons, landfilling without extensive protective measures must no longer be considered acceptable . The dust, ashes or sludge could be released from the landfills by water or wind and water can also lead to leaching of the pollutants and their further spread. Finally, the safe handling of these waste materials is very cumbersome, technically complex and therefore relatively expensive due to their properties, such as mostly small to very small particle sizes with the resulting risk of easy escape.

As a special example of a process in which contaminated dust occurs, the BRAM (fuel from waste) combustion is mentioned. Due to the composition of the waste, the exhaust gases of such plants are particularly contaminated with organic compounds and especially with heavy metals, which preferably accumulate on the fine dust. These fine dusts are very harmful to health even without accumulation due to their ability to enter the lungs. With the usual combustion processes for gases, the use of such gases was only possible with great additional effort for cleaning the polluting substances. For example, elaborate cleaning systems had to be provided for the exhaust gas, and due to the dust pollution, there were always faults in the combustion chamber or in the downstream cleaning systems.

In addition, the properties of the dust contained in the gas have not been changed, so that it is still difficult to deposit and is very environmentally hazardous due to the exposure to harmful chemicals and heavy metals. However, the problem just mentioned is no longer limited to the BRAM gases, but rather occurs during the combustion of any gases loaded with dusts.

But also flue gases and slag from power plants and waste incineration plants, pyrolysis gases from waste disposal plants, sludges from sewage treatment plants and filter plants or the like fall under the group of substances to be disposed of, and they too are increasingly polluted with environmental toxins suitable, which, however, would be associated with great difficulties with regard to a previous cleaning or a cleaning of the exhaust gas due to the pollutant load using the conventional combustion methods.

In the field of the combustion of solid or liquid fuels, it is known to remove dust or particulate emissions from the exhaust gas by fusing these dusts or parts in a subsequent process step and then separating them. For example, DE-OS 35 06 102 describes a coal-fired energy system in which coal dust is conducted through air at high pressure in combustion furnaces and is released in a cyclone downstream of the furnaces like unmelted ash. However, this removal of the ashes is incomplete, so that a further precision dust removal device has to be connected downstream. This additional process step requires additional equipment and energy, which reduces the economy of the overall process.

DE-OS 33 07 011, WO 85/02454 and US Pat. No. 4,542,708 describe processes for cleaning the exhaust gases from combustion of solid or liquid fuels, in which process steps downstream in the combustion process involve the fly ash or additional equipment. particulate emissions are separated.

The object of the present invention was therefore to provide a method which allows the combustion of gases which are loaded with dusts. The method is intended to allow the combustion of gas which is difficult to combust due to the dust load, without requiring excessive effort for cleaning systems for the exhaust gas. In particular, the method should be used in connection with waste disposal plants.

Another task was to design the method so that dusts, ashes or sludges of any origin, also contaminated, can be moved into a form that allows safe landfilling

Finally, an additional object of the invention was the construction of a combustion chamber for use in the methods according to the invention.

The method for solving the first-mentioned object is characterized in that the temperature in the combustion chamber is kept above the pour point of the dust, the dust particles melting in the combustion chamber and being discharged from the combustion chamber in liquid or reconsolidated form in a manner known per se.

In this method, the gas is advantageously burned in one step to generate energy and at the same time is cleaned of the dusts contained therein. As a result of the fusion, the dusts are finally in a form in which they can be easily converted into glass-like granulate particles or moldings. 2-

AT 393 970 B can be performed so that it is no longer possible to wash out the toxins contained in the landfill. In addition, the resulting granules or molded articles are easier to handle than conventionally filtered dust due to the greater density and particle dimensions.

According to a further feature of the method according to the invention it is provided that dusts, ashes or sludges intended for conditioning prior to its combustion are introduced into the gas intended for combustion in finely divided form and are kept in suspension and the temperature in the combustion chamber is above the highest pour point Dusts, ashes or sludges are kept.

The particles of dusts, ashes or sludge, which are initially in suspension, are also combined here by melting to form larger and thus heavier agglomerates. These can no longer be carried by the gas flow and therefore fall under the influence of gravity to the lowest point of the device. From there, they can then easily be drawn off in liquid form as a melt and fed to further processing, preferably also granulation or the formation of moldings, such as pellets, etc.

Particles that are still left in the exhaust gas can be removed from the exhaust gas by conventional dust separators, for example fabric filters, which are particularly suitable for fine dust, or electrostatic precipitators and re-fed to the melting process, whereby particularly good efficiency can be achieved. The granulate particles or moldings ultimately produced are much easier and safer to handle than the original dusts, ashes or sludges and do not require such strict safety precautions even when they are landfilled. In addition, many pollutants are burned by the high temperatures required for melting 20, preferably between 1000-1500 ° C and thus rendered harmless. On the other hand, the pollutants are integrated into the granulate or shaped bodies by the melting together in such a way that they are safe against washing out or the like and are therefore kept safe from the environment.

The combustion chamber, which comprises at least one supply line for the gas containing the dusts, ashes or sludges, at least one supply line for the heating medium, and at least one outlet for the treated gas and a discharge device for the molten particles, is according to the invention characterized in that at least one of the feed lines is pivoted with respect to the radial direction with respect to the axis of the combustion chamber, preferably between 10 and 60 °, but is at most exactly perpendicular to the radial direction. 30 Further features, advantages and exemplary embodiments of the invention follow below and with reference to the accompanying drawings. 1 shows a section through a combustion chamber according to the invention in a schematic representation, FIGS. 2a and 2b each show a cross section along the line (aa) in FIG. 1 for two different embodiments of the combustion chamber, FIGS. 3a and 3b to FIG. 7a and 7b show sections through further variants of the combustion chamber according to the invention, FIG. 8 shows the insulated set-up variant, and FIG. 9 shows the integration of the combustion chamber in a heat recovery system.

Dusts, ashes or sludges must first be introduced into the flow of a gas at the beginning of one variant of the process. In principle, it does not matter where the gas is fed in. In the case of very large, heavy particles, it is of course advantageous to mix them in relatively close to where the melting process takes place, otherwise too much of the particles in the pipe system could settle and impede further flow. In order to keep the dust particles in suspension for transport to the melting point and then to ensure a favorable heating or combustion process »! To maintain distribution in the gas stream, the dusts, ashes or sludges must be supplied in finely divided form. This can be done by slowly trickling into the moving gas stream, by feeding by means of injectors or nozzles and, in particular for the moisture-containing sludge, by 45 atomizations. The gas stream is then passed on and finally enters via one or more supply lines into the area in which the combustion of the gas and thus the melting of the suspended particles follows

In the case of the method variant, in which only one dust-laden gas, in particular for energy generation, is to be used, the entire method step associated with the introduction of the particles is naturally omitted. So z. B. exhaust gases from BRAM plants or pyrolysis gases from waste disposal plants directly into the melting area.

Of course, in many cases it is possible to combine the two methods. That is, dusts to be disposed of etc. are introduced into a dust-laden gas to be burned, whereby both tasks are solved in one process step. 55 Furthermore, the introduction of dusts, ashes or sludges into a gas containing pollutants is another advantageous alternative. In addition, the gas is also conditioned by the thermal afterburning and freed of the pollutants it contains

The method is preferably carried out in a combustion chamber (1) (FIG. 1) specially designed for this. As has already emerged from what has been said so far, this has at least one supply line (2) for 60 the dust-containing gas stream.

For the purpose of better distribution of the gas and the dust particles in the combustion chamber (1), several entry points for the gas are provided along the circumference of the combustion chamber. They are all in the top, -3-

AT 393 970 B mostly cylindrical part (L ') thereof and, according to a further feature of the invention, at least one of the feed lines (2) is pivoted with respect to the radial direction with respect to the axis of the combustion chamber, but is at most exactly perpendicular to it (Fig. 2a, 2b). Preferably, an exactly perpendicular to the radial direction, i. H. for round combustion chambers exactly tangential gas supply lines (Fig. 2a), used in the case of combustion chambers with only one or two inlet openings, since the flow runs more evenly along the combustion chamber wall. With three or more junctions, the axes of the supply lines can form an acute angle with the tangential direction (Fig. 2b), which is preferably between 10 ° and 60 °. As a result, more gas and thus also suspended particles are in the central area Coming to the combustion chamber and so its volume and thermal energy can be better utilized. This feature results in a cylindrical, moving gas flow in which the dust particles are also kept in suspension in the combustion chamber until they increase in weight and size due to the melting together and fall into the lower part (1 ”) of the combustion chamber (1) . This is essentially tapered downwards, so that the melt formed from the accumulated melted agglomerates collects at the lowest point of the combustion chamber (1) and is drawn off from there through a discharge device (3) in the liquid state. The melt is then either granulated using conventional devices, not shown, for example a water bath into which the melt is introduced. The fused particles can also be cast to form essentially any shaped bodies.

According to a further variant of the method according to the invention, the fused particles are drawn off in re-solidified form. Both passive and active cooling of the particles with subsequent solidification is possible. Passive cooling can consist, for example, of letting the fused particles fall into ever cooler zones of the combustion chamber or devices connected to them during the fall, whereby heat is radiated and the temperature of the particles finally drops below the pour point of the dust. On the other hand, the temperature of the gas containing the molten particles or of the particles themselves can be actively reduced by measures known per se. For example, heat exchangers can be provided to cool the gas (cooling by heat removal), cooling media, such as water or the like, sprayed into the gas (mixture cooling) or preferably sprayed onto the molten particles, as a result of which the particles due to the evaporation of this medium Heat is removed. The treated gas, whether inert carrier gas or exhaust gas from industrial plants, exits through at least one exhaust (4) in the direction of the axis of the combustion chamber. Further treatment steps can follow for the gas leaving the combustion chamber (1) if this should be necessary due to its nature. In this way, the exhaust gas can be passed into a desulphurization, denitrification or similar system, and / or a conventional dedusting system can also be connected to remove residual dust remaining in the exhaust gas. The in such a system, for. B. tissue or electrostatic precipitator, separated dust is advantageously fed back to the combustion chamber (1) for melting

Often there will be a proportion of molten particles in the exhaust gas of the combustion chamber (1) which have not reached the necessary size and weight, as is necessary for the regular separation described above. These small and very small particles would lead to major problems in the further treatment or recycling of the gas, they would cool down in lines or devices downstream, solidify and adhere to the line walls or devices, so that their function would soon be impaired.

Therefore, in a similar manner as previously explained, the temperature of the exhaust gas of the combustion chamber (1) and thus of the fused particles after the heating by means of heat removal, for example by means of a heat exchanger, by injecting water or the like, or by adding cold gaseous media , for example cold air, so far lowered that the particles solidify and the gas can be supplied, for example, to heat recovery. They can now be easily separated in separation systems, such as fabric filters, etc., and the cleaned gas can, for example, be sent for further use or derived. The separated solidified particles are advantageously added to the gas again before the heating in order to melt them again and to be able to remove them regularly.

In order to introduce the dusts, ashes or sludges, an introduction device (5) is provided in at least one feed line (2) for the gas to be burned (FIG. 3a). According to a variant (FIG. 3b), as an alternative or in addition to this, at least one introduction device (5 ') opening directly into the combustion chamber (1) can also be provided. Depending on the material to be introduced and its properties such as grain size, moisture, flowability, etc., the introduction devices (5.5 ', 5') include, for example, injectors, cellular wheel dispensers, nozzles and the like. the like

In the latter embodiment (FIG. 3b), a construction is advantageous in which the direction of introduction, usually represented by the extension of the axis of the introduction line into the combustion chamber, and the imaginary extension of the gas supply line located next to one another intersect (intersection (p ) in Fig. 3b, see also Fig. 2b). As a result, the entire introduced material is caught by the gas flow, carried into the cylindrical flow and distributed well in it, thereby avoiding a rapid sinking to the bottom of the combustion chamber.

In addition to the return of the unmelted dust, the gas could also, if its own

AT 393 970 B shafts have not been adversely changed by the treatment, have been reintegrated into the process and used for the new dust transport.

Since the dust-containing gas is combustible, the energy required for heating can at best only be achieved by burning this gas itself. Of course, it must always be taken into account that relatively high temperatures must be achieved in order to melt down, preferably between 1000 ° and 1500 ° C. Therefore, the combustion chamber can also be heated by other types of heating, preferably direct firing.

The feasible variants range from the combustion of solid, liquid or gaseous fuels, such as coal dust, heating oil or fuel gases, to electric arc heating or the like. 10 All of the listed variants for heat supply are also suitable for the process with the introduction of dusts,

Ashes or sludges can be carried out.

Fig. 4a schematically shows an embodiment of a combustion chamber (1) according to the invention with feed lines (2) for a dust-containing gas and feed lines (6) for a heating medium, Fig. 4b shows a variant with feed lines (2 ') for lean gas, i. H. Fuel gas with a low calorific value or (2 ") for rich gas and 15 a feed line (6) for an oxygen-containing gas, preferably air, to improve the combustion of the fuels.

Some advantageous embodiments of the combustion chamber according to the invention are to be described below, some of which also allow further improvements of the method.

The high process temperatures of preferably 1000 to 1500 ° C place high demands on the heat resistance of the structural parts of the combustion chamber and its connected lines, parts etc. Therefore, instead of the simplest uncooled version, which is only provided with a fireproof lining (Fig. 5a) be equipped with cooling devices. In addition to structural designs, such as cooling fins or the like (not shown) on the outside of the chamber (1), the installation or attachment of a system (7) comprising the chamber (1) and through which coolant flows is mainly provided, such as, for. B. shown in Fig. 5b. This can go so far that the wall of the combustion chamber (1) is constructed from adjacent cooling tubes. This makes it easy to utilize the waste heat generated in the method according to the invention via heat exchangers for the said coolant. However, even with existing cooling systems, the temperature of the inner wall of the combustion chamber must not be below the flow temperature of the dust, ash or sludge particles so that they do not solidify when they come into contact with the wall and adhere to the wall. Finally, the thermal energy inherent in the exhaust gas or carrier gas after the treatment can also be used in a corresponding manner, so that the combustion chamber according to the invention is suitable for incorporation into a heat recovery system

The step of utilizing the thermal energy of the exhaust gas from the combustion chamber (1) leads to an advantageous reduction in its temperature. As already described, residual dust particles present in the exhaust gas are solidified and can still be separated from the gas stream. But also for the system downstream of the combustion chamber, e.g. B. residual dust filter or other exhaust gas conditioning devices, too high temperatures would be disadvantageous. For this reason, preferably if there is no temperature reduction of the exhaust gas due to a heat exchanger for heat recovery, the exhaust (4) of the combustion chamber (1) with radiant surfaces and / or other cooling internals (8), e.g. B. heat exchanger tubes, (Fig. 6a) provided 40.

6b, a swirl breaker is also identified by (8 '). These are guide plates which are distributed along the circumference of the trigger (4) and point towards the center. They ensure the formation of a rectilinear flow, which is more favorable for the passage through downstream systems than the spiral exhaust gas flow created in the combustion chamber. 45 As mentioned above, it may be necessary or desirable to provide exhaust gas conditioning. In addition to the possibility of carrying this out in the combustion chamber (1) and the fume cupboard (4), this conditioning can already take place, at least in part, in the combustion chamber (1) or when passing the fume cupboard (4). For this purpose, the combustion chamber (1) according to the invention is equipped with one or more feed lines (9) and devices (10) for introducing cooling and / or conditioning media, such as. B. air, cold gas, inert gas, sorbs for sulfur or nitrogen oxides, etc. provided (Fig. 7a). Said devices are located in or on the fume cupboard (4) or also directly in the combustion chamber (1), again preferably in the immediate vicinity of the fume cupboard opening. A further variant, shown in FIG. 7b, provides for the entire inner wall of the fume cupboard (4) to be designed for the introduction of the media, for example by installing an annular cylindrical hollow body (10 ') with a perforated inner wall connected to a feed line (9').

Of course, any combination of one or more of the process steps and the structural features of the combustion chamber are also possible within the scope of the invention and their specific implementation is left to the person skilled in the art depending on the specific requirements.

An embodiment of the combustion chamber (1) according to the invention as an isolated process apparatus, 60 only connected to the feed lines (2 or 6) and the exhaust (4), as well as a slag discharge (3) and a collecting container (14) for the slag is in the Fig. 8 shown.

According to a further feature of the invention, however, as shown schematically in FIG.

Claims (18)

AT 393 970 B chamber (1) can be integrated in a heat recovery system. Here, for example, one or more heating surfaces (12), heat exchangers, etc. are arranged downstream of the combustion chamber (1) and the fume hood (4), preferably also ash separators (13) or the like. PATENT CLAIMS 1. Process for the combustion of gases containing dust are loaded, in particular pyrolysis gases from waste disposal systems, in a combustion chamber, the particles being kept in suspension, characterized in that the temperature in the combustion chamber is kept above the pour point of the dust, the dust particles melting in the combustion chamber and in a manner known per se are discharged from the combustion chamber in liquid or solidified form. 2. The method according to claim 1, characterized in that in the gas intended for combustion prior to its combustion certain dusts, ashes or sludges are introduced in finely divided form and kept in suspension, and the temperature in the combustion chamber above the highest pour point of the dusts , Ashes or sludge is kept. 3. The method according to claim 2, characterized in that sludges are atomized into the gas sprayed. 4. The method according to claim 1 or 2, characterized in that the gas and the particles held therein in the floating state are additionally heated by direct firing, in particular by combustion of fuel gases, heating oil or coal dust, by arc heating or the like. 5. The method according to claim 2, characterized in that the dusts, ashes or sludges are at least partially introduced into a pollutant-containing gas, and in addition the gas is heated by thermal afterburning and freed from the pollutants contained therein. 6. The method according to claim 1 or 2, characterized in that the temperature of the exhaust gas and the fused particles after heating by heat removal, preferably by means of a heat exchanger, by injecting in particular water or addition of cold, gaseous media, preferably cold air, as far as lowered is that any fused particles remaining in the gas can solidify and be separated in separating systems, in particular fabric filters, and the cleaned gas is used for heat recovery, preferably a heat exchanger. 7. The method according to claim 6, characterized in that the separated solidified particles are added to the gas again before combustion, 8. The method according to claim 1, characterized in that the fused particles are passed into a water bath and granulated therein. 9. The method according to claim 1, characterized in that the fused particles are cast into shaped bodies. 10. The method according to claim 6, characterized in that the fused particles are solidified when removed by active or passive cooling. 11. Combustion chamber for use in the method according to claim 1, with at least one supply line for the gas containing the dusts, ashes or sludges, if necessary at least one supply line for the heating medium, and at least one extractor for the treated gas and a discharge device for the molten particles , characterized in that at least one of the supply lines (2) is pivoted with respect to the radial or tangential direction with respect to the axis of the combustion chamber, preferably between 10 ° and 60 ° with respect to the tangential, but is at most exactly perpendicular to the radial direction 12. Combustion chamber according to claim 11, characterized in that an insertion device (5), for example injectors, nozzles, for dust, ash or sludge is provided in at least one, preferably each feed line (2) at least for the carrier gas or the dust-laden gas. -6- AT 393 970 B 13. Combustion chamber according to claim 11 or 12, characterized in that at least one, directly into the combustion chamber (1) opening introduction device (5 ') is provided for dust, ash or sludge. 14. Combustion chamber according to claim 13, characterized in that the imaginary extension of the direction of introduction of the introduction device (5 ') and the imaginary extension of the nearest feed line (2) intersect. 15. Combustion chamber according to claim 11, characterized in that a cooling system (7) are provided in or on the wall of the combustion chamber (1). 16. Combustion chamber according to claim 11, characterized in that in the fume cupboard (4) for the treated gas jet surfaces and / or cooling devices (8), preferably heat exchangers, are provided for lowering the exhaust gas temperature. 17. Combustion chamber according to claim 11, characterized in that in the fume cupboard (4) for the treated gas swirl breaker (8 ’), (ie. Baffles for the gas flow) are provided. 18. Combustion chamber according to claim 11, characterized in that in the combustion chamber (1) or on or in the fume cupboard (4) for the treated gas at least one device (10, 10 ') for introducing cooling or conditioning media, such as in particular Air, cold gas, inert gas, sorbent are present. For this 2 sheets of drawings -7-