Device and method for reducing hazardous materials in flue gases

Abstract

Device for reducing pollutants in flue gases, in which the flue gases exiting the combustion chamber (3) are dammed and swirled when passing through a tube (7) equipped with plates (8) and arranged after the combustion chamber (3), whereby CO and fine dust present in the flue gases are further oxidized to CO2 under excess air.

Description

[0001] The invention relates to a device for reducing pollutants in flue gases according to claim 1. A similar device is arranged in the combustion chamber according to US Pat. No. 4,161,917. Stoves for the combustion of wood and compressed biological combustion products, hereinafter generally referred to as "pellets," are enjoying increasing popularity due to the energy sources that mostly originate from renewable raw materials and the often lower operating costs compared to other forms of heat generation. While the emission of carbon dioxide (CO2) is desirable in this context as a product of complete combustion, since the released carbon dioxide is ideally rebound in renewable raw materials, the emission of carbon monoxide (CO) and particulate matter represents an undesirable side effect.These, along with carbon dioxide and other compounds, are discharged from the combustion chamber as flue gas and subsequently released into the environment. Due to the harmful effects of carbon monoxide and particulate matter on health, there is a desire to reduce these emissions as much as possible.

[0002] The aim and object of this invention is to achieve a reduction in the emission of carbon monoxide and particulate matter.

[0003] According to the invention, these objects are achieved by a device for damming and swirling flue gases, which has the features of claim 1. In other words, the flue gases emerging from the combustion chamber are dammed and swirled as they pass through a pipe equipped with platelets and arranged downstream of the combustion chamber, whereby CO and particulate matter contained in the flue gases are further oxidised to CO 2 in the presence of excess air.

[0004] The invention is explained in more detail below with reference to the drawings. the Fig. 1 the position of the device according to the invention in a combustion furnace, the Fig. 2 the device according to the invention in a perspective view from the side of the combustion chamber, the Fig. 3 the device according to the invention in a perspective view towards the combustion chamber and the Fig. 4 a sectional view of the device Fig. 3 .

[0005] The Fig. 1 shows a furnace 1 with a pellet burner 2 and a combustion chamber 3, which is closed at the top by the device 4 according to the invention and whose upper opening leads into a heat exchanger 5.

[0006] The Fig. 2shows the device 4 according to the invention, comprising a cover plate 6 which covers the combustion chamber 3 in the upper region, a pipe 7 for discharging the flue gas, plates 8, a fastening screw 9, a web 10 for securely centering the fastening screw 9 and locking devices 11 for preventing the plates 8 from rotating, in a perspective view from the viewpoint of the combustion chamber 3. The cover plate 6 sits as the upper end on the combustion chamber 3. In the center of the cover plate 6 are two openings which lead to the pipe 7 attached to the cover plate 6. The two openings are separated from one another by the web 10, with a hole in the center of the web 10 for centering the plates 8.

[0007] The Fig. 3shows the device 4 according to the invention in a perspective view from above the combustion chamber 3. The tube 7 is mounted on the cover plate 6. The plates 8 are arranged around the fastening screw 9. This assembly is housed as a whole in the tube 7 and secured against rotation by locking devices 11. A fastening bracket 12 is the counterpart to the web 10 and, like the latter, ensures that the fastening screw 9 remains centered.

[0008] The Fig. 4 shows a perspective section through the device 4 according to the invention analogous to Fig. 2 . Spacer sleeves 13 are visible around the fastening screw 9 for axial spacing and fixing of the plates 8, as well as a fastening nut 14 that axially fixes the plates 8 and spacer sleeves 13 on the fastening screw 9. In the middle of the tube 7, the central tube axis 15 runs through the fastening screw 9.

[0009] The device 4 according to the invention sits directly on the combustion chamber 3. To ensure the extraction of the flue gas from the combustion chamber 3 and its passage through the pipe 7, the illustrated embodiment uses an induced draft fan to extract the flue gas from the combustion chamber 3. During the passage of the flue gas through the pipe 7, the flue gas is dammed and swirled by the plates 8.

[0010] The thickness of the plates 8 depends on the heating output of the furnace. When using sheet steel and a heating output of up to 8 kW, the plates 8 preferably have a thickness of no more than 2 mm, and even more preferably, a thickness of 1 mm or less. For higher heating outputs, correspondingly thicker plates 8 must be used. The inclination of the plates 8 is between 0° and 50°, preferably between 25° and 35°, relative to a plane perpendicular to the central tube axis 15. Tests that lead to the optimal results for the respective application can be carried out quickly and easily by a specialist.

[0011] Heating begins as the air flows around the plates 8. The temperature of the flue gas upon exiting the combustion chamber 3, immediately before entering the tube 7, ranges between 470°C at a heating output of 4 kW and 730°C at a heating output of 8 kW. These temperatures, in conjunction with the turbulence of the gases, surprisingly achieve a measurable reduction in carbon monoxide and particulate matter. The table below shows examples of the pollutants measured at 8 kW, both with and without the device 4 according to the invention. average CO content based on 13% O2 ​​- with conventional draft deflection average CO content based on 13% O2 ​​- with new train deflection average dust content based on 13% 02 - with conventional draft deflection average dust content based on 13% 02 - with new train deflection 95 mg / Nm 3< to 110 mg / Nm 3< 16 mg / Nm 2< to 36 mg / Nm 3< 20 mg / Nm 3< to 45 mg / Nm 3< 4 mg / Nm 3< to 10 mg / Nm 3<

[0012] It is not clear what the exact cause of this reduction is. Based on experiments, however, it can be assumed that it is an effect that is partly due to the local flow at the edges of the 8-platelets, partly to their even heating, and partly to the longer residence time with simultaneous excess air. In this case, a continuous helical pitch would not produce the desired effect, or at least not to the same quality. It is also possible that the impact of fine dust and the associated local temperature increases contribute to the effect. In this case, under the same operating conditions, thinner thicknesses would have to be selected for 8-platelets made of ceramic than for corresponding 8-platelets made of metal. Experiments that lead to the optimal results for the respective application can be carried out quickly and easily by a specialist.

[0013] The locking devices 11 are used in designs in which the plates 8 are not firmly connected to the tube 7, as would be the case with welding or a one-piece casting. They can be connected to the tube 7 by any means known to those skilled in the art, for example by welding, casting, or 3D printing the locking device 11 and the tube 7 as one part, by positive connection by inserting a lug or recess of the locking device 11 into a recess provided for this purpose in the tube 7, by screwing, or by riveting. The locking device 11 itself consists of a rod or at least has rod-shaped sections that engage in complementary recesses of the plates 8 and thus fix them in the circumferential direction. The plates can also be fixed by axial pressure via the fixing screw 9, but a positive fastening is generally preferable to a force-fitting fastening due to the different thermal expansions.In addition to the locking device 11, the positive locking can also be achieved by means of opposing, interlocking recesses and noses in the plates 8 and spacer sleeves 13 in the circumferential direction.

[0014] In principle, all materials known from the state of the art for furnace construction and that meet the technical requirements are suitable for the individual components. For the platelets 8, in particular, all materials whose heat resistance allows their use are suitable, such as all types of steel and heat-resistant metals (cast iron, cast steel, titanium, tungsten, etc.) in rolled, forged, 3D-printed, cast, or sintered form, as well as any other manufacturing form known from the state of the art, depending on the possibilities for processing the materials. The platelets have a fan shape in a tube with a circular cross-section. In the context of this invention, a fan-shaped element is understood to mean a circular segment with an angle of less than 180°.If plate 8 is located in a pipe with a non-circular cross-section, the fan shape transitions from a circular segment to an analogous geometric pattern adapted to the pipe's cross-section, capable of covering the desired section of the pipe up to the wall. For a pipe with a polygenic, particularly quadrangular, cross-section, the deflection plate would, for example, transition from a circular segment to a deltoid, also known as a kite. The same applies analogously to all other possible cross-sectional shapes.

[0015] The illustrated socket is an exemplary embodiment, but the invention is not limited to this embodiment. Specifically, it is possible to provide multiple webs instead of the single web 10. Furthermore, instead of a structure comprising the plates 8 and the spacer sleeves 13, it is possible to use a single part manufactured using a method known from the prior art, e.g., by 3D printing, casting, or sintering.

[0016] Another possible embodiment is the direct fixation of the fan-shaped plates 8 to the pipe 7 by welding, or by casting or 3D printing in one piece. However, the invention does not require a seal between the plates 8 and the pipe 7, as can be achieved, for example, by welding. A gap that is small compared to the diameter of the pipe 7 - gaps up to 1 mm wide occurred in the tests carried out - had no negative effects in the tests carried out. This also makes it possible, for example, to hang an assembly of the plates 8, spacer sleeves 13 and fixing screw 9 from above into the pipe 7 on a suspension. If necessary, the maximum permissible width of this gap can be quickly and easily determined by a specialist through tests. The plates can also be designed with holes of different sizes. These lists are examples and are not exhaustive.The invention is therefore not limited to the illustrated and described embodiments, but can be modified in many ways. In particular, it is possible to combine and / or multiply partial aspects as desired.

[0017] In this context, flue gas refers to the totality of all substances produced by combustion and released into the environment in the gaseous phase (e.g., CO, CO2, water vapor, etc.) or suspended in this phase (e.g., fine dust particles, suspended embers, etc.). Similar terms for flue gas include combustion gas, combustion air, exhaust gas, or colloquially, "smoke."

[0018] Pellet burner 2 refers to the container in which the actual combustion of wood or pellets takes place with the aid of air. Therefore, it is not necessary to burn actual pellets; in principle, any form of solid fuel commonly used in stoves can be used. The term "pellet burner" is used for clarity.

[0019] Combustion chamber 3 is located above pellet burner 2. This is the space where the flames are visually visible. Combustion chamber 3 serves to heat the flue gases, but is often separated from the surroundings by a transparent pane, creating the visual effect of an open fireplace, but without the associated risks.

[0020] In the description and claims, "substantially" means a deviation of up to 10% of the stated value, if physically possible, both upwards and downwards, otherwise only in the reasonable direction; for degrees (angle and temperature) this means ± 10°.

[0021] The term "combination" or "combinations" means, unless otherwise stated, all types of combinations, from any two of the components in question to a plurality or all of such components; the term "containing" also means "consisting of".

[0022] The features and variants specified in the individual embodiments and examples can be freely combined with those of the other examples and embodiments and can be used, in particular, to characterise the innovation in the claims without necessarily including the other details of the respective embodiment or example. List of reference symbols: 1 Oven 9 Fixing screw 2 pellet burner 10 web 3 combustion chamber 11 Locks 4 Device according to the invention 12 Mounting bracket 5 heat exchanger 13 Spacer sleeves 6 cover plate 14 fastening nut 7 Pipe 15 central pipe axis 8 Platelets

Claims

1. Device for reducing pollutants in flue gases which are fed from a combustion chamber (3) into a tube (7) having a central tube axis (15), wherein platelets (8) are arranged inside the tube (7) at an angle to the central tube axis (15), the platelets (8) having a fan shape in the case of a circular tube cross-section and a shape adapted to the cross-section in the case of a polygonal shape of the tube cross-section, wherein the adapted shape enables contact between the platelets (8) and the wall of the tube (7), wherein the platelets (8) cover a tube section at an angle of less than 180°, wherein the inclination of the platelets (8) with respect to a plane perpendicular to a central tube axis (15) is between 0° and 50°, preferably between 25° and 35°, and wherein the platelets (8) are flat.

2. Device according to any one of claims 1 to 5, wherein the platelets (8) are perforated.

3. Device according to any one of claims 1 to 6, wherein the platelets (8) are made of a heat-resistant material, preferably of a metal.

4. Device according to any one of claims 1 to 7, wherein the platelets (8) have a thickness of at most 2 mm, preferably a thickness of 1 mm or less.

5. Method for reducing pollutants in flue gases, wherein flue gas at a temperature between 470°C and 730°C flows out of the combustion chamber (3) and into a device (4) according to one of claims 1 to 4 and is set into a turbulent flow by the platelets (8).

6. Furnace (1) for the combustion of solids, wherein the furnace (1) comprises a device (4) for the reduction of pollutants in flue gases according to one of the claims 1 to 4.

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