EP0455624A2 - Method for burning dust-laden gases as well as a combustion chamber for use in such a process - Google Patents

Abstract

Process for the combustion of gases which are loaded with dusts, the particles in the gas, possibly also the dusts, ashes or sludges introduced therein in finely divided form, being heated above their pour point, thereby fused and subsequently removed. The fused particles can be drawn off in the liquid state and, for example, passed into a water bath for granulation, or solidified by pulling them off by active or passive cooling and removed in solidified form. The combustion chamber for use in the method has at least one supply line 2 for the gas containing the dusts, ashes or sludges, at least one supply line for the heating medium, as well as at least one exhaust 3 for the treated gas and a discharge device for the molten particles. wherein at least one of the feed 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.

Description

The invention relates to a method 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 this method.

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 that are harmful to the environment and health due to the process they produce. On the other hand, the harmfulness of many substances which have been known for a long time has also recently been recognized, so that for these reasons, landfilling without extensive protective measures must no longer be regarded as 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 preferentially 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 bisland gas combustion processes customary up to now, the use of such gases was only possible with great additional effort for cleaning the polluting substances. For example, elaborate cleaning systems for the exhaust gas had to be provided and due to the dust pollution, there were always disturbances 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 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. The substances mentioned would often be suitable for the renewed generation of energy by combustion, 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 when 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 combustion involve additional fly equipment or particulate emissions be deposited.

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 process so that dusts, ashes or sludges of any origin, also contaminated, can be converted into a form that allows safe disposal.

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 thus advantageously burned in one step to generate energy and at the same time cleaned of the dusts contained therein. As a result of the fusion, the dusts are finally in a form in which they can be converted into glass-like granulate particles or shaped bodies in a simple manner, so that when the landfill is deposited, the toxins contained are washed out is no longer possible. 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, the process according to the invention provides that finely divided dusts, ashes or sludges are introduced into the gas intended for combustion before being burned for conditioning and kept in suspension and the temperature in the combustion chamber is above the highest pour point of the dusts , Ashes or sludge is 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 cannot be carried further by the gas flow and therefore fall to the lowest point of the device under the influence of gravity. 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 fed back into the melting process, whereby particularly good efficiency can be achieved. The granulate particles or moldings ultimately produced are much simpler 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, preferably between 1000-1500 ° C and thus rendered harmless. On the other hand, the pollutants are integrated into the granules or shaped bodies by the melting together, so that they counteract Wash out or the like are safe and therefore safe from the environment.

The combustion chamber, which comprises 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, as well as at least one outlet for the treated gas and a discharge device for the molten particles, is characterized according to the invention in that at least one of the supply 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.

• Dabei zeigt Fig. 1 einen Schnitt durch eine erfindungsgemäße Brennkammer in schematischer Darstellung,
• Fig. 2a und 2b je einen Querschnitt entlang der Linie a-a in Fig. 1 für zwei verschiedene Ausführungsformen der Brennkammer,
• Fig. 3a und 3b bis Fig. 7a und 7 b zeigen Schnitte durch weitere Varianten der erfindungsgemäßen Brennkammer,
• Fig. 8 stellt die isolierte Aufstellungsvariante dar, und
• Fig. 9 zeigt die Einbindung der Brennkammer in ein Wärmerückgewinnungssystem.

Further features, advantages and exemplary embodiments of the invention are explained in more detail below and with reference to the accompanying drawings.

• 1 shows a section through a combustion chamber according to the invention in a schematic representation,
• 2a and 2b each a cross section along the line aa in Fig. 1 for two different embodiments of the combustion chamber,
• 3a and 3b to 7a and 7b show sections through further variants of the combustion chamber according to the invention,
• Fig. 8 shows the isolated installation 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 at which point of the gas supply this introduction takes place. In the case of very large, heavy particles it is of course advantageous to mix them in relatively close to the point at which the melting process takes place, since otherwise too much of the particles could settle in the pipe system and hinder the further flow. In order to keep the dust particles in suspension for transport to the melting point and then in a, a favorable heating or. In order to maintain the distribution in the gas stream that ensures the combustion process, 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 supplying it with injectors or nozzles and, in particular for the moisture-containing sludge, also by atomizing. The gas flow is then passed on and finally enters via one or more feed lines into the area in which the combustion of the gas and thus the melting of the suspended particles takes place.

In the case of the process variant in which only one dust-laden gas is to be used, in particular for energy generation, the entire process step associated with the introduction of the particles is naturally omitted. Thus, e.g. Exhaust gases from BRAM plants or pyrolysis gases from waste disposal plants are fed directly into the melting area.

Of course, in many cases it is possible to combine the two methods. This means that 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.

In addition, the introduction of the 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 been stated above, this has at least one feed line 2 for the dust-containing gas stream.

For the purpose of better distribution of the gas and 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 upper, mostly cylindrical part 1 '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 it is at most exactly perpendicular to it (Fig. 2a ,2 B). Preferably, a gas supply line that is exactly perpendicular to the radial direction, that is to say tangential for round combustion chambers (FIG. 2a), is used in the case of combustion chambers with only one or two inlet openings, since the flow runs more uniformly along the combustion chamber wall. With three or more junctions, the axes of the feed lines can form an acute angle with the tangential direction (FIG. 2b), which is preferably between 10 ° and 60 °. The result of this is that more gas and thus also suspended particles get into the central area of the combustion chamber and their volume and thermal energy are thus better utilized. This feature results in a cylindrical, moving gas flow in which the dust particles are 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 by 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. For this purpose, both passive and active cooling of the particles with subsequent solidification is possible. Passive cooling can consist, for example, of allowing the fused particles to fall into ever cooler zones of the combustion chamber or the 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. E.g. Heat exchangers can be provided to cool the gas (cooling by heat extraction), 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 heat is removed from the particles due to the evaporation of this medium. 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. For the gas leaving the combustion chamber 1, further treatment steps can follow if this should be necessary due to its nature. In this way, the exhaust gas can be passed to a desulfurization, 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, e.g. Tissue or electrostatic precipitators, separated dust is advantageously returned 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 tiny and tiny particles would under certain circumstances lead to major problems in the further treatment or recycling of the gas, they would cool down in downstream lines or apparatus, solidify and adhere to the line walls or apparatus, so that their function would soon be impaired.

Therefore, in a similar manner as explained above, 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 addition of cold gaseous media, for example cold air, so far lowered that the particles solidify and the gas can be fed, for example, to heat recovery. Now they can be separated without problems in separation plants, such as fabric filters, etc., and the cleaned gas can, for example, be sent for further utilization or can be discharged. 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 supply 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 insertion devices 5.5 ', 5˝ include, for example, injectors, cellular wheel distributors, 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 closest one The supply line for the gas intersect (intersection S 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 be reintroduced into the process and used to transport the dust again if its properties have not adversely affected by the treatment.

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 for melting, 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.

All of the listed variants for the supply of heat can also be carried out for the process with the introduction of dusts, ashes or sludges.

Fig. 4a schematically shows an embodiment of a combustion chamber 1 according to the invention with supply lines 2 for a dust-containing gas and supply lines 6 for a heating medium, Fig. 4b shows a variant with supply lines 2 'for poor gas, ie fuel gas with a low calorific value, or 2˝ for Rich gas and 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 their connected lines, parts, etc. Therefore, instead of the simplest uncooled version, which is only provided with a fireproof lining (Fig.5a) Cooling devices to be equipped. 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 through which coolant flows and which comprises the chamber 1 is mainly provided, e.g. 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 of the combustion chamber 1 leads to an advantageous lowering of its temperature. As already described, residual dust components in the exhaust gas are thus solidified and can still be separated from the gas stream. But also for that of the combustion chamber Downstream system, e.g. 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 can be provided with jet surfaces and / or other cooling internals 8, for example heat exchanger tubes (FIG. 6a).

In Fig. 6b is also marked with 8 'a swirl breaker. 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.

As previously mentioned, it may be necessary or desirable to additionally provide exhaust gas conditioning. In addition to the possibility of carrying this out downstream 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 e.g. Provide air, cold gas, inert gas, sorbents for sulfur or nitrogen oxides, etc. (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. Another variant, shown in Fig. 7b, provides to design the entire inner wall of the trigger 4 for introducing the media, for example by installing an annular cylindrical hollow body 10 'connected to a feed line 9' with a perforated inner wall.

Of course, any combination of one or more of the method steps and the structural features of the combustion chamber are also possible within the scope of the invention and their specific ones Realization left to the specialist depending on the specific requirements.

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

According to a further feature of the invention, however, as shown schematically in FIG. 9, the combustion chamber 1 can also 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 extractor 4, preferably also ash separators 13 or the like.

Claims (18)

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, characterized in that the temperature in the combustion chamber is kept above the pour point of the dust, the dust particles in merge the combustion chamber and be discharged from the combustion chamber in a known manner in liquid or solidified form. A method according to claim 1, characterized in that dusts, ashes or sludges intended for conditioning are introduced into the gas intended for combustion in finely divided form and conditioned and kept in suspension, and the temperature in the combustion chamber is above the highest pour point of the dusts, ashes or sludge is kept. A method according to claim 2, characterized in that sludges are sprayed into the gas in a finely atomized manner. A 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. A method according to claim 2, characterized in that the dusts, ashes or sludges are at least partially introduced into a gas containing pollutants, and in addition the gas is heated by thermal afterburning and freed from the pollutants contained therein. A method according to claim 1 or 2, characterized in that the temperature of the exhaust gas and the fused particles after the Heating by means of heat extraction, preferably by means of a heat exchanger, by injecting in particular water or the addition of cold, gaseous media, preferably cold air, so far that it is lowered so that fused particles remaining in the gas solidify and can be separated in separating plants, in particular fabric filters, and the cleaned Gas for heat recovery, preferably a heat exchanger, is supplied. Method according to Claim 6, characterized in that the solidified particles which have separated out are added again to the gas before the combustion. A method according to claim 1, characterized in that the fused particles are passed into a water bath and granulated therein. Method according to claim 1, characterized in that the fused particles are cast into shaped bodies. Method according to claim 6, characterized in that the fused particles are solidified by being removed by active or passive cooling. 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 exhaust (3) for the treated gas and a discharge device for the molten Particles, characterized in that at least one of the feed 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. Combustion chamber according to Claim 11, characterized in that an introduction 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. Combustion chamber according to claim 11 or 12, characterized in that at least one introduction device (5 ′) which opens directly into the combustion chamber (1) is provided for dust, ashes or sludge. 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 closest feed line (2) intersect. Combustion chamber according to claim 11, characterized in that a cooling system (7) is provided in or on the wall of the combustion chamber (1). Combustion chamber according to claim 11, characterized in that jet surfaces and / or cooling devices (8), preferably heat exchangers, are provided in the fume cupboard (4) for lowering the exhaust gas temperature. Combustion chamber according to Claim 11, characterized in that swirl breakers (8 ′), (i.e. baffles for the gas flow) are provided in the exhaust (4) for the treated gas. Combustion chamber according to Claim 11, characterized in that at least one device (10, 10 ′) for introducing cooling or conditioning media, such as in particular air, for the treated gas in the combustion chamber (1) or on or in its exhaust (4) , Cold gas, inert gas, sorbent are present.

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