PULSED COMBUSTION REACTOR WITH PULSATING FLAME, IN PARTICULAR FOR THERMAL MATERIAL TREATMENT OR MATERIAL SYNTHESIS

Abstract

A method and a device for reliably preventing undesired flashback or excessive separation/extinction of a pulsating flame for use in pulsed combustion reactors or pulsation reactors for thermal material treatment or thermal material synthesis is disclosed. The invention makes it possible to operate pulsed combustion reactors or pulsation reactors with thermal material treatment at markedly greater amplitudes of an oscillation of a hot gas flow in the reactor, and to improve the properties of the thermally treated/thermally synthesized material, and to markedly increase the throughput rates of the reactor (reactor capacity), and thus to reduce production costs in comparison to other thermal methods/apparatus for material treatment, and hence to make the pulsed combustion reactor technology or pulsation reactor technology more competitive. According to the invention, the invention uses a swirl burner to generate a swirl-stabilized flame, an essentially conical diffuser being connected downstream of the burner.

Claims

1. A device for thermal treatment of a raw material in an oscillating hot gas stream of a pulsed combustion reactor, having a burner to which is supplied, via at least one line, a mass flow to form at least one pulsating flame which generates the oscillating hot gas stream, wherein the flame is arranged in a combustion chamber, wherein the burner is a swirl burner, and wherein a diffuser is connected downstream of a burner outlet of the burner.

2. The device as claimed in claim 1, wherein the pulsating flame is a swirl-stabilized flame and has an inner, central recirculation zone.

3. The device as claimed in claim 1, wherein the diffuser is conical in shape, with a cross-sectional area that increases in the axial direction.

4. The device as claimed in claim 1, wherein the diffuser has an opening half-angle in the range between 3 degrees and 45 degrees.

5. The device as claimed in claim 1, wherein the diffuser has an axial extent of between 0.5 times and 10 times the free diameter of the burner outlet.

6. A method for thermal treatment of a raw material in an oscillating hot gas stream of a pulsed combustion reactor, having a burner to which is supplied, via at least one line, a mass flow of fuel gas and air to form at least one pulsating flame which generates the oscillating hot gas stream, wherein the flame is arranged in a combustion chamber with an adjoining reaction space, wherein the fuel/air mixture flowing to the pulsating flame is guided through a swirl burner and a diffusor adjoining this burner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Other advantages and features of the invention emerge from the following description of an exemplary embodiment, in which:

[0050] FIG. 1 is a concept diagram of a swirl burner with diffuser;

[0051] FIG. 2 shows the concept diagram of a diffuser from FIG. 1 with a pulsating flame at two different positions.

DETAILED DESCRIPTION

[0052] FIG. 1 shows a swirl burner 1 to which are supplied either fuel and combustion air separately 2, or a premixed fuel/air mixture 2 via at least one line, not shown in greater detail here.

[0053] Fuel is to be understood for example as fuel gases such as natural gas, methane, hydrogen, or liquid fuels such as alcohol, etc. Within the context of the present invention, combustion air is to be understood in general terms as an oxidant which supplies the oxygen necessary for combustion. In addition to air, this for example also includes pure oxygen or oxygen-enriched air etc.

[0054] This combustion air stream or this fuel/air mixture is guided via a swirler 3 within the swirl burner 1 such that the mass flow 5 issuing from the burner outlet 4 has, in addition to movement in the axial direction, a rotational movement 6 in the circumferential direction (tangential velocity component or “swirl”).

[0055] With this rotational movement 6, the mass flow 5 flows into a diffuser 7. The walls of the diffuser have an essentially conical profile with an opening half-angle 8. This opening half-angle 8 is in a range between 3° and 45° and is measured with respect to the axial direction.

[0056] The burner outlet 4 has an essentially circular cross section and can have an axial extent 9 which is preferably, for example, in the range between 0 and 0.5 m.

[0057] The axial length 10 of the conical or frustoconical diffuser 7 can for example be between 0.1 and 1 m. It is therefore, relative to the dimensions of the burner outlet 4, between approximately 0.5 times and 10 times the free diameter of the burner outlet.

[0058] Toward the end 11 of the diffuser 7, a swirl flame 12 forms in the mass flow 5 of the issuing fuel/air mixture.

[0059] This swirl flame 12 is in particular also characterized by a central recirculation region 13, which is an important characteristic of a swirl-stabilized flame.

[0060] The flame 12 burns in a pulsating manner into a combustion chamber, not shown in greater detail here, fluidically connected to the diffuser 7, where it generates an oscillating hot gas flow. To this hot gas flow, a quantity of material for material treatment or material synthesis is to be added as required. Once treated or synthesized in the hot gas flow, this material is then separated out again, for example in a cyclone or a hot gas filter, which are also not represented.

[0061] The pulsation of the flame 12 is self-induced and, in the burner-flame-combustion chamber-reaction space-separation device system, feeds back on the inflowing mass flow 5.

[0062] Owing to the previously mentioned oscillation of the hot gas flow, the flame 12 pulsates and therefore oscillates the rotating mass flow 5 flowing into it, which in turn maintains the pulsation and so on and so forth (that is to say that the mass flow issuing from the burner has a time-dependent—generally approximately sinusoidal—time profile).

[0063] The oscillating mass flow 5 causes the velocity in the axial direction of the burner outlet flow (axial velocity component of the burner outflow) to change, while at the same time the flame speed 14 of the flame 12 that forms remains constant. In that context, the flame speed is the speed with which the flame 12 propagates in the fuel/air mixture flowing to it, counter to the outflow direction of this mixture.

[0064] This causes a shift in the axial position of the flame that forms: when the outflow velocity of the mass flow 5 drops, the flame 12 migrates into the diffuser 7, for example as far as “position 1” shown in FIG. 2. As the velocity of the mass flow 5 subsequently rises again, in the course of the pulsation, the flame is pushed back out of the diffuser 7 in the axial direction, for example as far as “position 2” shown in FIG. 2.

[0065] Now, however, the geometric extent of the flame 12 transversely to the outflow direction is essentially constant irrespective of its axial position. This is associated with the special properties of a swirl-stabilized flame, as already stated above.

[0066] The fact that the cross-sectional areas A.sub.l and A.sub.2 available for the flow in axial positions 1 and 2 are different in size in said positions, owing to the conical shape of the diffuser 7, causes a corresponding change, between positions 1 and 2, in the size of the annular areas 15 and 17 formed at those positions between the flame 12 (of constant geometric extent) and the wall 16 of the diffuser:

[0067] Since the cross section of the diffuser broadens conically in the flame propagation direction between the area A.sub.l and the area A.sub.2, the free annular area of the annular gap, that surrounds the flame 12 and lies between the flame 12 and the wall 16 of the diffuser 7, increases accordingly. In that context, the swirl-stabilized flame 12 acts like a solid body through which the mass flow 5 of issuing fuel/air mixture cannot flow, in part due to the central, inner recirculation zone 13 present therein.

[0068] In position 2, the free annular area 15 causes an axial velocity U.sub.2 with an axial impulse flow İ.sub.2. If the pulsating flame 12 now migrates as described within the pulsation period due to the time-dependent and initially decreasing burner outlet mass flow M.sub.zu(t) and thus the decreasing outlet velocity U, upstream in the direction of the burner 1, it will reach position 1 shown in FIG. 2.

[0069] In position 1, the free annular area 17 is, as stated, smaller than the free annular area 15 of position 2 owing to the conical shape of the diffuser 7. Thus, in position 1, when the area through which the flow cannot pass and which is taken up by the swirl-stabilized flame 12 characterized by the central recirculation zone is the same, the axial flow velocity U.sub.1 increases and thus the axial impulse flow İ.sub.1 also increases there. The axial impulse flow İ.sub.1 is therefore greater than the axial impulse flow İ.sub.2.

[0070] Owing to the axial flow velocity U.sub.1 rising as explained, the flame 12 is thus prevented from migrating further upstream into the diffuser 7 and thus into the burner 4. Rather, the flame 12 halts in approximately this position 1 until the burner outlet mass flow 5, rising again within the pulsation period and accordingly also having a burner outlet velocity which is increasing again, pushes the flame 12 back downstream into the original position 2, which is to be considered safe.

[0071] This ensures that the flame 12 cannot migrate as far as the burner 1 or as far as the swirler 3, and cannot establish itself therein in the event of a flashback.

[0072] It should also be noted, at this point, that the wall 16 of the diffuser 7 and the wall 18 of the burner outlet 4 can be either uncooled or, as shown on the left-hand side of FIG. 2, can be provided with a cooling system 19 which is for example effected by a flow 20 of air or water that is conveyed through the cooling system 19.

[0073] It is also possible to protect the walls 16 and 18 using a ceramic cladding.

[0074] The device described here, and the operation thereof, make it possible to set the pulse amplitude of a pulsed combustion reactor to high values even when the installation is idling (i.e. with no addition of material), without this implying the risk of a flashback into the burner, since such a flashback is reliably prevented by the diffuser provided, according to the invention, on the swirl burner used.

LIST OF REFERENCE SIGNS

[0075] 1 Swirl burner [0076] 2 Combustion air mass flow or fuel/air mixture mass flow [0077] 3 Swirler [0078] 4 Burner outlet [0079] 5 Mass flow [0080] 6 Rotation [0081] 7 Diffuser [0082] 8 Opening half-angle [0083] 9 Axial extent of the burner outlet [0084] 10 Axial extent of the diffuser [0085] 11 End of the diffuser [0086] 12 Swirl flame [0087] 13 Recirculation region [0088] 14 Flame speed [0089] 15 Annular area [0090] 16 Wall [0091] 17 Annular area [0092] 18 Wall [0093] 19 Cooling system [0094] 20 Flow of air or water