EP0040690B1 - Device for the combustion of oxidizable components in waste gases - Google Patents

Abstract

1. Combustion apparatus for the combustion of oxidizable substances in waste gases, with a burner (13) and a mixing device (1a), with a high-velocity tube (1) adjoined thereto, with a swirl chamber (4) situated at its free end and designed as a combustion space, the high-velocity tube (1) projecting concentrically into the swirl chamber (4), and also with a heat exchanger (5) which is in communication with the swirl chamber (4) via an afterburning space (9), which concentrically surrounds this latter and in which the individual tubes of the tube assembly extending parallel to the longitudinal axis are fitted at one end into the end wall of the waste-gas inlet annular space (12), and a burner projection (14) arranged about the longitudinal axis of the combustion apparatus is of such a diameter that an annular gap is formed between the edge of the burner projection (14) and the inflow cone (7), characterised in that the individual tubes of the heat exchanger (5) are bent over at their other ends inwards towards the longitudinal axis of the combustion apparatus, the bent-over ends being fitted into a drum (6) concentrically surrounding the burner projection (14) and the individual tubes of the heat exchanger (5) being so arranged on circular rings concentric with the longitudinal axis that the flow passes around them at approximately uniform air velocity.

Description

The present invention relates to a combustion device for the combustion of oxidizable substances in exhaust gases, but in particular the design of the heat exchanger and the design of an inflow space into which a burner axially fires.

Combustion devices of this type are becoming increasingly important in the context of environmental protection, in particular in those cases in which small quantities of oxidizable substances have to be removed from large amounts of exhaust air because the legal provisions so require.

Such a combustion device is known from US-A-3607118 and from DE-B2-2352204. In the known devices, the gases are fed through a recuperative heat exchanger to a burner firing in the direction of the longitudinal axis of the combustion device into a flame tube and, after leaving an actual combustion chamber, serve as heating gases for the heat exchanger.

In the combustion device known from DE-B2-2352204, the heat exchanger is designed as a tube bundle of straight tubes that extends concentrically to the longitudinal axis within the combustion device, the ends of which are welded into perforated plates.

However, this constructive design of the heat exchanger can prove to be disadvantageous if the combustion device is only operated temporarily. In the heating and cooling phases and in fluctuating operating conditions, the individual tubes of the heat exchanger bundle receive different temperatures, and this results in different expansion, which inevitably leads to stresses on the end plates, so that individual tubes can tear or cracking on the end plates. In addition, the flow conditions of the exhaust gases to the burner are still in need of improvement.

The object of the present invention was to provide a combustion device in which the heat exchanger is designed such that temperature-related different expansions of individual pipes do not generate any thermal stresses on the end plates of the heat exchanger and that one end of the heat exchanger is formed at the same time in such a way that the inflow conditions of the burner can be improved.

This object is achieved by a combustion device for burning oxidizable substances in exhaust gases with a burner and a mixing device, an adjoining high-speed pipe, a swirl chamber located at its free end and designed as a combustion chamber, the high-speed pipe projecting concentrically into the swirl chamber, and one with the Whirl chamber via a post-combustion chamber connected to this concentrically surrounding heat exchanger, in which the individual tubes of the tube bundle extending parallel to the longitudinal axis are inserted at one end into the end wall of the exhaust gas inlet annular space, and a burner stem arranged around the longitudinal axis of the combustion device has such a diameter, that an annular gap is created between the edge of the burner stem and the inflow cone. The characteristic of the invention is that the individual tubes of the heat exchanger are bent at their other ends inwards onto the longitudinal axis of the combustion device, the bent ends being inserted in a drum concentrically surrounding the burner stem and the individual tubes of the heat exchanger concentrating on the longitudinal axis Circular rings are arranged so that the air flows around them at approximately the same speed.

Preferred embodiments of the invention are described in the subclaims.

Due to the bending of the individual tubes of the heat exchanger in the direction of the axis of the combustion device and the penetration of the tube ends into a preferably cylindrical or conical perforated drum arranged concentrically around the longitudinal axis, this end of the heat exchanger is no longer directly flown by the hot flue gases, but rather these are deflected and deflected by a connecting wall so that they strike a section of the pipe that has not yet been bent. As a result, the thermal load on the connection points between the pipe ends and the drum becomes more uniform. By bending at angles between 45 ° and 120 °, preferably approximately 90 ° concentrically inwards, forces which act on the pipes in the longitudinal direction due to thermal expansion are canceled and deflected, so that there are no mechanical stresses on both ends of the pipes of the heat exchanger build up more and safely and reliably prevents the pipes from tearing out of the end plate or the perforated drum or cracking on the end plate. The formation of one end of the heat exchanger as a concentrically arranged, preferably cylindrical or conical drum creates an inflow space in its interior for the actual flame formed by the burner. It has now been found that this constructive design of the end of the heat exchanger not only reliably avoids thermal stresses within the heat exchanger, but that this design of an inflow space also enables particularly favorable mixing of the exhaust gas with the fuel.

In the combustion device is within the inflow space at a distance from the stream mel the burner stem designed so that an annular gap is formed between the end of the burner stem with the inflow cone. The burner stem is provided with gas passage openings of such a size that their overall cross-section brings about a division of the gas flow emerging from the heat exchanger into the inflow space. One partial gas flow enters the high-speed tube through the annular gap, and the other partial flow passes through the openings directly into the interior of the burner stem, in which the actual fuel flame is generated. In this way, a particularly intensive mixture of the exhaust air with the fuel is achieved and the oxygen required for burning is extracted from the exhaust air.

In order to be able to adapt the cross-section of the annular gap between the edge of the burner stem and the inflow cone to the operational requirements, in a particular embodiment of the invention the burner stem is designed to be displaceable in the direction of the longitudinal axis, and / or the end of the burner stem facing the mixing chamber has an adjustable, attached aperture ring. This aperture ring has devices that allow adjustment from the outside without interruptions in operation. By changing the annular gap cross-section, the size of this outlet area changes in comparison to the area of the openings on the surface of the burner stem and thus the ratio of the amount of exhaust air directly supplied to the flame to the amount of exhaust air that only enters the mixing room and is only mixed in there to participate in the combustion .

In a further embodiment of the invention, the diameter of the burner stem and drum are dimensioned such that the inflow space that arises between them is sufficiently large to be able to accommodate an annular injection device for further substances. If, in this embodiment of the invention, an injection device is present in the inflow space, there is the possibility of further optimizing the mode of operation of the combustion device according to the invention by introducing liquid or gaseous substances such as water, waste liquids and the like. The evaporation of the injected liquid products takes place on the basis of the existing radiation energy of the burner.

The cross section of the flame tube or high-speed tube is very narrow, so that flow velocities of 40 to 60 m / sec can be achieved. The end of the flame tube facing the burner stem is conical as a Venturi tube, the interior of which serves as an additional mixing zone for the exhaust air with the burner gases. The other end of the high-speed tube extends into the main combustion chamber.

The inventive design of the heat exchanger end and the inflow chamber achieves such an intensive premixing of the exhaust gas with the fuel that, at the high flow velocities in the flame tube, the contaminants contained in the exhaust gases are largely or completely burned off at temperatures of 720 ° in the combustion chamber. The separation of the heat exchanger part and the combustion chamber part in the combustion device has the particular advantage that the length and size of the actual combustion chamber on the tube can be varied depending on the requirements of the actual combustion process, but the heat exchanger part and the head part of the combustion device do not have to be changed. This, however, enables inexpensive series production of these parts in several basic sizes, while the high-speed pipe and combustion chamber can be adapted to the specific conditions.

The inventive design of the combustion device allows systems for an exhaust air throughput of 5000 m ³ , but also of 20 000 m ^{3 to be carried out} in a particularly compact design and with these systems, impurity levels in the exhaust air from 100 mg to several grams per m ³ safely and can be reliably eliminated and in this way comply with the statutory provisions on the permissible limit values in exhaust air.

The particular advantage of the combustion device according to the invention, however, is that it permits production-related interruptions in operation, without thermal voltages being able to build up during heating and cooling, in particular in the area of the heat exchanger, which can lead to damage in the device.

• Fig. 1 zeigt eine Ausführungsform der erfindungsgemässen Verbrennungseinrichtung im Längsschnitt.
• Fig. 1a zeigt einen Querschnitt längs der Linie A-B von Fig. 1.
• Fig. 2 zeigt eine Ausführungsform, bei der im Ausströmraum eine ringförmige Eindüsvorrichtung angeordnet und der verstellbare Blendenring vorhanden ist.

The invention will now be explained in more detail with reference to a drawing and a description of the method. The same reference numbers refer to the same parts.

• Fig. 1 shows an embodiment of the combustion device according to the invention in longitudinal section.
• FIG. 1 a shows a cross section along the line AB from FIG. 1.
• 2 shows an embodiment in which an annular injection device is arranged in the outflow space and the adjustable diaphragm ring is present.

The combustion device shown in FIG. 1 consists of a high-speed tube 1 which is variable in length and narrow in cross section, the rear end of which projects into the actual combustion chamber 4. The high-speed pipe 1 preferably extends far into the combustion chamber, so that an annular space is created between the end thereof and the end wall of the combustion device, which results in a transition into the actual combustion chamber 4. This configuration creates an intense turbulence of the gas flow in the actual combustion chamber 4 in order to prevent the deposition of solid particles contained in the exhaust gases Avoid walls of the vortex chamber 4 and to allow such particles to burn almost completely. In the swirl chamber 4, therefore, internals (not shown) can also be present in order to give the gas flow an additional swirl and to increase the turbulence. This also increases the residence time of solid particles in the swirl chamber 4, so that the combustion of the particles improves.

The opposite end 1 of the high-speed or flame tube (HGR) 1 is designed as a Venturi tube and serves as a mixing device or additional mixing space. The annular space 9, which partially surrounds the HGR 1, serves as an afterburning space and connects to the combustion space 4. A burner stem 14 adjoins the venturi part 1a of the HGR 1 axially in such a way that an annular gap 2 is formed between the inflow cone 7 and the burner stem 14, through which part of the exhaust gas can enter the HGR 1.

The burner designated by number 13 is understood to mean any type of conventional industrial burner, including so-called surface burners, which are designed either as primary or as secondary air burners. The essential parts of the burner 13 can be attached outside the overall system and concentrically to the system axis on the front side of the combustion device.

The burner stem 14 has holes through which a partial flow of the exhaust gas from the inflow space 15 can reach the flame 3.

The burner stem 14 is surrounded concentrically at a distance by a cylindrical or conical perforated drum 6. One end of the drum 6 is connected by the flow cone 7 to the end of the mixing device 1a a of the high-speed tube 1. The other end face of the drum 6 is connected to the outer wall of the combustion device via the partition 8 and thus closes off the inflow space 15 from the outer space 17. This partition is preferably designed as a movable membrane or has corrugated expansion joints.

The drum 6 has a cylindrical or conical shape and the wall is perforated to receive the ends of the individual tubes of the tube bundle of the heat exchanger 5. These tubes are welded or rolled into the holes in the drum to produce a gas-tight connection. In the figure, the individual tubes of the heat exchanger tube bundle 5 are not shown as such, but only as a block. The individual tubes are arranged on circular rings concentric to the longitudinal axis. The distance and the arrangement are chosen so that the flow velocity of the gases on the surface of the tubes is the same. The flow rate is preferably 8-18 m / sec. This tube bundle extends from the drum 6 initially in the direction of the outer wall of the combustion device and then bends in a direction parallel to the longitudinal axis of the combustion device and runs through the outer space of the heat exchanger 17 and ends at the end wall to the exhaust gas inlet annular chamber 17. Also at this end are the individual pipes of the Tube bundle welded or rolled into the wall. This configuration of the tube bundle 5 in the outer space 17 creates a recuperative heat exchanger in which the cold gases flow in the tubes and these tubes are surrounded by the hot combustion gases outside in the so-called outer space 17, so that the exhaust gas supplied to the combustion device is heated by the hot combustion gases is preheated. The outer space of the heat exchanger 17 has a combustion outlet connection 11 at the end adjoining the inlet annular chamber 12. The tube bundle 5 is held within the outer space 17 by spacers 5a, which are arranged and designed such that the gases get a swirl and move spirally through the space 17 with the tube bundle 5 arranged therein, so that a good heat transfer from the hot combustion gases to the initially cooler exhaust gases.

FIG. 1 a, a section along the line A-B of FIG. 1, shows the ends of the tubes of the heat exchanger tube bundle 5, which are inserted in the drum 6 and are bent inwards towards the longitudinal axis of the combustion device. The space created between the burner stem 14 and the drum 6 is the inflow space 15.

FIG. 2 shows the embodiment in which an injection device 18 is additionally arranged in the inflow space 15 in order to be able to introduce further substances into the combustion device. In order to enable a uniform distribution, an annular injection device is preferred, but this is not mandatory. Other shapes are possible and suitable. In addition, an adjustable aperture ring 19 is available.

For a better understanding of the combustion device according to the invention, the following example shows how this device works.

20,000 Nm 3 of exhaust gas from a process in which different types of solvents are used flow through the exhaust gas inlet stub 10 into the exhaust gas inlet ring chamber 12 in front of the heat exchanger 5 of the combustion device in the middle from above or tangentially from above, for example at 100 ° C. The exhaust gas is distributed evenly over the entire number of individual tubes of the heat exchanger 5, flows through them and is heated to 550 ° C. in the process. The preheated exhaust gas leaves the heat exchanger 5 through the openings in the drum 6 and arrives in the inflow space 15. From there it partly reaches the actual flame 3 through the openings in the burner stem 14, while another partial flow through the ring gap 2 enters the Venturi part 1 (mixing device) of the flame tube 1 directly. The partial flow, which reaches the flame 3 through the burner stem 14, supplies the flame with the oxygen required and mixes intensively with the fuel due to the inflow. The exhaust gas flow entering through the annular gap 2 is mixed in the mixing device 1 a with the fuel already mixed with the exhaust gas. By guiding the preheated exhaust gas flow in the inflow space 15, a particularly intensive mixing of the exhaust gas flow with the fuel is achieved from the start.

In order to be able to adapt the mixing process to the special needs in individual cases, an embodiment is provided which enables the cross-section of the annular gap 2 to be adjusted. This can be done either by an adjustable aperture ring 19 placed on the end of the burner stem 14 or by the burner stem which is designed to be displaceable in the direction of the longitudinal axis of the combustion device. By changing the cross-section of the annular gap 2, its area can vary in relation to the open area of the burner stem 14, and thus the division of the gas flow can be controlled.

The burner 13 fires in the direction of the high-speed tube 1 along the axis of the combustion device. In the vicinity of the burner 13 is the high-speed tube 1 surrounded by the afterburning chamber 9, which represents the smaller part of the total combustion volume. In this flame tube 1, which is small in diameter and at least protrudes in length beyond the length of the heat exchanger, there is further mixing of the exhaust gases and the flame smoke gases as well as heating thereof by approximately 80 ° C. to approximately 630 ° C. At the end of the flame tube 1, the mixed exhaust gases are swirled and diverted, if necessary, by additional swirl devices, thereby reaching the actual combustion or swirl chamber 4, where they heat up by a further 120 ° C. to approximately 750 ° C. (natural heat due to exothermic reaction). At the front of the combustion device, i.e. the actual combustion chamber, the exhaust gases are in turn deflected by 180 ° and thereby moved through the combustion chamber 4 in the direction of the afterburning chamber 9, with an additional swirling of the exhaust gases being brought about. At the end of the afterburning chamber 9, the gases on the connecting wall between the flame tube and the cylindrical drum are deflected and deflected into the outer chamber 17 of the heat exchanger. In one or more deflections, the oxidized hot flue gas flows through the ring bundle (tube or pocket bundle) of the heat exchanger 5, the flue gas flowing around the tube bundle from the inside to the outside or from the outside to the inside. As a result, the hot flue gases are cooled to approximately 315 ° C. and leave the combustion device through the outlet connection 11.

If the concentration of the contaminants in the exhaust gas drops for technical reasons of the upstream process, the burner 13 is automatically regulated to a higher output, so that an almost constant temperature of 720 to 750 ° C. in the combustion chamber is made possible.

In the opposite case, i.e. when the concentration of the contaminants in the exhaust gas rises, unburned exhaust gas can be injected directly into the flame tube via a passage connecting the inlet annular space 12 and the flame tube, which is then not shown in the illustration, and which is then opened without this part of the Exhaust gas has previously been heated in the heat exchanger.

The combustion device, which is made of all-steel or masonry or in combinations, also has a manhole on the end face, which is arranged concentrically with the axis of the overall system and is not shown in the figure, which allows the flame tube 1 to be walked on. Observation flaps for direct observation of the flame and temperature measuring devices can also be arranged on this end face adjoining the actual combustion chamber 4.

Claims (6)

1. Combustion apparatus for the combustion of oxidizable substances in waste gases, with a burner (13) and a mixing device (1a), with a high-velocity tube (1) adjoined thereto, with a swirl chamber (4) situated at its free end and designed as a combustion space, the high-velocity tube (1) projecting concentrically into the swirl chamber (4), and also with a heat exchanger (5) which is in communication with the swirl chamber (4) via an afterburning space (9), which concentrically surrounds this latter and in which the individual tubes of the tube assembly extending parallel to the longitudinal axis are fitted at one end into the end wall of the waste-gas inlet annular space (12), and a burner projection (14) arranged about the longitudinal axis of the combustion apparatus is of such a diameter that an annular gap is formed between the edge of the burner projection (14) and the inflow cone (7), characterised in that the individual tubes of the heat exchanger (5) are bent over at their other ends inwards towards the longitudinal axis of the combustion apparatus, the bent-over ends being fitted into a drum (6) concentrically surrounding the burner projection (14) and the individual tubes of the heat exchanger (5) being so arranged on circular rings concentric with the longitudinal axis that the flow passes around them at approximately uniform air velocity.

2. Combustion apparatus according to Claim 1, characterised in that the drum (6) is cylindrical or conical design, and at one end is connected by an inflow cone (7) to the mixing device (1 a) and to the adjoining high-velocity tube (1) and from its other end a movable dividing wall (8) extends up to the outer wall of the combustion apparatus.

3. Combustion apparatus according to Claims 1 and 2, characterised in that the individual tubes of the heat exchanger tube assembly (5) are bent over approximately at right angles inwards towards the longitudinal axis of the combustion apparatus.

4. Combustion apparatus according to Claims 1 to 3, characterised in that the individual tubes of the heat exchanger tube assembly are bent over approximately at right angles inwards towards the conical drum (6).

5. Combustion apparatus according to Claims 1 to 4, characterised in that the burner projection (14) is designed to be displaceable in the direction of the longitudinal axis of the combustion apparatus and an adjustable aperture ring (19) is arranged at the end of the burner projection (14) nearest the mixing device (1 a).

6. Combustion apparatus acording to Claims 1 to 5, characterised in that the inflow space (15), formed between the drum (6) surrounding the burner projection (14) and the burner projection (14), is so dimensioned that an annular single-jet device (18) can be disposed therein.

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