Method and device for mixing fluid flows

The present invention relates to a method for mixing at least two separate fluid flows (2, 3), in particular for a burner of a power plant.To improve the mixing, a plurality of swirl flows (7, 8), which are annular and concentric with respect to a longitudinal center line (6), are generated from the fluid flows (2, 3), in such a manner that radially adjacent swirl flows (7, 8) have opposite directions of rotation.

FIELD OF THE INVENTION

The present invention relates to a method and a device for mixing at least two separate fluid flows, in particular for a burner of a power plant.

A range of applications require thorough mixing of separate gas flows. One such application is, for example, catalytic combustion for generating hot gas for operation of a gas turbine, in which a gaseous fuel, generally natural gas, and a gaseous oxidant, generally air, have to be intensively mixed before this fuel-oxidant mixture enters the respective catalyst. Conventional lean-mix premix burners also require the fuel-oxidant mixture supplied to be mixed as homogeneously as possible. Inadequate mixing may lead to a lack of uniformity in the combustion process, in which relatively extensive temperature differences may be determined, with increased levels of undesirable NOxforming in zones which are at particularly high temperatures.

U.S. Pat. No. 5,202,203 and U.S. Pat. No. 5,328,359 show catalysts which are constructed from corrugated or folded plate material. The folds or corrugations of the plate material form a multiplicity of channels through which medium can flow. As it flows through a catalyst of this type, some of a fuel-oxidant mixture is burnt. To prevent a catalyst of this type from overheating, the combustion has to be restricted to only part of the mixture flowing through the catalyst. For this purpose, only some of the channels are made catalytically active, for example by a suitable coating, whereas the other channels are catalytically inactive. As the medium flows through the catalyst, combustion takes place only within the catalytically active channels, whereas the flow through the catalytically inactive channels cools the catalyst. In the known catalysts, the corrugations or folds are, moreover, repeatedly inclined in zigzag fashion with respect to a main through flow direction. The layered arrangement is then such that the inclinations of adjacent layers are offset with respect to one another, in such a way that the folds or corrugations of one layer cannot penetrate into the folds or corrugations of the adjacent layer. The channels which are formed on one side of the respective plate material by the corrugations or folds of the latter are open toward those channels which are formed on the facing side of the adjacent plate material by the corrugations or folds of the latter. This means that the flow of fluid can constantly alternate between the channels which are open toward one another by passing between adjacent plate materials, with the result that the gas flow does not have a defined outflow direction at the outlet of the respective catalyst.

SUMMARY OF THE INVENTION

The invention seeks to remedy this problem. The invention as characterized in the claims deals with the problem of demonstrating an advantageous way of mixing at least two separate fluid flows.

According to the invention, this problem is solved by the subject matters of the independent claims. Advantageous embodiments form the subject matter of the dependent claims.

The present invention is based on the general idea of effecting mixing with the aid of a plurality of opposite swirl flows which are arranged helically or annularly and concentrically with respect to an axial longitudinal center line extending in the main direction of flow. The formation of the largest possible number of swirl flows which rotate in opposite directions and are arranged concentrically inside one another leads to the formation of a correspondingly large number of concentric and likewise annular shearing layers, which effect intimate fluid mixing. The quality of mixing which can be achieved depends on the number of shearing layers that are formed; the more shearing layers are formed, the better the mixing becomes.

In a particularly advantageous refinement, it is possible to provide for an annular, concentric and swirl-free axial flow to be generated at least between two radially adjacent swirl flows. This too gives rise to shearing layers which contribute to intimate mixing. At the same time, the axial flow effects axial orientation of the swirl flows during the mixing. Therefore, the mixing flow can be homogenized in terms of flow velocity and flow direction with the aid of this measure.

Further features and advantages of the present invention will emerge from the subclaims, from the drawings and from the associated description of figures with reference to the drawings.

WAYS OF CARRYING OUT THE INVENTION

FIG. 1shows a portion of a channel1into which at least two separate fluid flows2and3are introduced. It is preferable for the channel portion1to lead to a burner (not shown here) or to a combustor for heating a gas turbine of a power plant. The fluid flows are then preferably a fuel flow2and an oxidant flow3, the fuel used preferably being natural gas and the oxidant used expediently being air.

To achieve intensive mixing of the two fluid flows2,3, a device4according to the invention is arranged in the channel portion1. The device4comprises a swirl generating structure5, which is designed in such a way that when medium flows through it a plurality of annular swirl flows7,8which are arranged concentrically with respect to an axial longitudinal center line6, are generated, in such a manner that radially adjacent swirl flows7,8each have an opposite direction of rotation. Therefore, to illustrate this, inFIG. 1the first swirl flows7are illustrated by solid lines, while the oppositely directed other swirl flows8are indicated by dashed lines.

In accordance withFIG. 2, the swirl generating structure5of the device4is preferably produced by helically winding a plurality of plates9,10made from corrugated or folded first plate material9and flat or smooth second plate material10. Therefore, the first plate material9has corrugations or folds11, which by virtue of the special layered arrangement form a multiplicity of channels12through which medium can flow through the swirl generating structure5. On account of the design selected for the swirl generating structure5, the channels12are arranged in concentric annuli or concentric coils with respect to the longitudinal center line6.

The visible, outermost first plate material9is oriented with its folds or corrugations11such that the channels12which are thereby formed are inclined in a first direction13, represented by an arrow, in the circumferential direction with respect to the longitudinal center line6. This inclination results in an angle α between the respective channel12or the respective corrugation or fold11and an axis14which runs through the respective channel12and parallel to the longitudinal center line6. The corrugations or folds11of the first plate material9which adjoins it on the radially inner side are oriented in the opposite direction, so that the channels12which are thereby formed are inclined in a second direction15, which is represented by an arrow and extends in the opposite direction to the first direction13, in the circumferential direction with respect to the longitudinal center line6. Accordingly, there is an opposite angle −α, the magnitude of which is approximately equal to that of the angle in the adjacent plate material9, between the folds or corrugations11indicated by dashed lines or the channels12which they form and the axis14, which is correspondingly offset in the radially inward direction. The alternating orientation of the channels12then continues in the radial direction.

In this context, it may be expedient for the angles α and −α to decrease continuously in magnitude from the radially outer side and to deviate little if at all from a value of zero in the vicinity of the longitudinal center line6.

Furthermore, in an advantageous development which is explained in more detail below, further first plate materials9may be present, these materials being oriented in such a way within the swirl generating structure5that their folds or corrugations11or the channels12which they form run parallel to the longitudinal center line6, so that the angle α has a value of zero.

In the embodiment described here, the plate materials9,10in the swirl generating structure5are arranged in such a way that individual annuli or coils are formed, and when medium flows through these annuli or coils in each case a left-hand swirl flow or a right-hand swirl flow or a swirl-free axial flow is generated. It will be clear that in another embodiment the material plates9,10may also be arranged in such a way that in each case at least two annuli or coils, which generate identically directed flows in medium flowing through them, are combined to form a group, in which case groups which generate left-hand swirl flows or right-hand swirl flows or swirl-free axial flows then alternate in the radial direction. In the present context, the term coil is to be understood as meaning a winding arrangement around the winding axis6which extends through at least 360° in the circumferential direction.

In accordance withFIG. 3, the layered arrangement of the folded or corrugated first plate material9and of the flat or smooth second plate material10is made so as to be concentric and annular or helical with respect to the longitudinal center line6. As a result, the channels12form first annuli or coils16and second annuli or coils17, which are indicated by curly brackets inFIG. 3.

In the first annuli or coils16, the associated channels12are inclined in the first direction13in the circumferential direction with respect to the longitudinal center line6. The inclination and orientation of the channels12of the first annuli or coils16is in this case selected in such a way that when medium flows through them the annular swirl flow7rotating in the first direction13results for each first annulus16or for each first coil16, as symbolized by corresponding arrows inFIG. 3.

By contrast, the channels12in the second annuli or coils17are inclined in the second direction15in the circumferential direction with respect to the longitudinal center line6. Accordingly, the channels12of the second annuli or coils17, when medium flows through them, generate the annular swirl flow8which rotates in the second direction15for each second annulus17or for each second coil17, which is once again symbolized by corresponding arrows inFIG. 3.

In this context, it is important that according toFIG. 3the first annuli or coils16and the second annuli or coils17alternate in the radial direction with respect to the longitudinal center line6. In this way, the swirl generating structure5, when medium flows through it, generates a multiplicity of annular swirl flows7,8, i.e. annulus swirl flows7,8, which, as seen in the radial direction, alternately rotate in the first direction13and the second direction15.

A complex flow system of this type made up of concentric, opposite annulus swirl flows7,8has a correspondingly large number of tangential shearing layers, which are in each case formed between mutually adjacent flows with different flow velocities and/or flow directions. The adjacent flows are intimately mixed in shearing layers of this type, and consequently a large number of shearing layers is associated with a correspondingly intensive flow mixing. The result of this is that in the flow mixing according to the invention the fluid flows2,3which have been supplied to the device4are intensively mixed after only a relatively short mixing section.

To impart as homogeneous an axial orientation as possible to the mixed flow, in an advantageous refinement it is possible for at least one or preferably a plurality of annular, as far as possible swirl-free axial flows, which are likewise arranged concentrically with respect to the longitudinal center line6, to be formed in addition to the swirl flows7,8which rotate in opposite directions. In this case, the axial flows are each arranged radially between two adjacent swirl flows7,8rotating in opposite directions. These axial flows are represented by rectilinear, dotted arrows18inFIG. 1.

FIG. 4shows an excerpt from the swirl generating structure5, with the aid of which, as medium flows through it, the axial flows18are generated as well as the swirl flows7,8. For this purpose, a third annulus19or a third coil19is arranged in each case between a first annulus16or a first coil16and a second annulus17or a second coil17. For the third annuli or coils19, the corrugated or folded first plate material9which is in each case used is oriented in such a way that its folds or corrugations11or the channels12which they form run parallel to the longitudinal center line6of the swirl generating structure5. As medium flows through them, the third annuli or coils19generate an annular axial flow18for each third annulus19or for each coil19, symbolized by arrow tips designated18inFIG. 4.

A tangential shearing layer which contributes to intimate mixing is likewise formed between an annular axial flow18of this type and the respectively adjacent swirl flow7or8. At the same time, the respective swirl flow7or8is diverted in axial direction. Therefore, the mixture flow can be axially oriented with the aid of these additional axial flows18. An axial orientation of this nature may be advantageous for certain applications, for example if a fuel-oxidant mixture is to be introduced into a catalyst, a burner or a combustion chamber.

In accordance withFIG. 1, the device4may have a straightener structure21, which axially orients the mixed flow which is supplied and flows through it, at the end of a mixing zone20downstream of the swirl generating structure5.

In accordance withFIG. 5, the straightener structure21may expediently comprise a multiplicity of channels22which run parallel to the longitudinal center line6and effect the desired axial orientation of the mixed flow passing through them. It is preferable for the straightener structure21also to be constructed from a layered arrangement of corrugated or folded first plate materials9and flat or smooth second plate materials10. In this case too, the individual corrugations or folds11form the parallel channels22. The axially oriented mixture flow is in each case denoted by23inFIGS. 1 and 5and symbolized by arrows (FIG. 1) or by arrow tips (FIG. 5).

To obtain the lowest possible pressure drop during flow through the straightener structure21, the channels22of the straightener structure21are relatively short, in particular shorter than the channels12of the swirl generating structure5. Moreover, the channels22of the straightener structure21may have relatively large cross-sectional areas; in particular, their cross-sectional areas are larger than those of the channels12of the swirl generating structure5.

It is expedient for the cross-sectional areas of the channels12to be relatively small, so that the swirl generating structure5at the same time forms an effective protection against flashback. By way of example, the channels12have a diameter of from 0.5 mm to 5 mm.

In a refinement, the function of a catalyst may be integrated in the swirl generating structure5. This is expediently realized by some of the channels12being designed to be catalytically active, while the other channels12are catalytically inactive. Catalytically active channels12can be realized, for example, by catalytically active surfaces in the respective channels12. In this context, a configuration in which catalytically active channels12and catalytically inactive channels12alternate would be expedient, so that the flow through the catalytically inactive channels12serves to cool the swirl generating structure5.

The mixing of the separate fluid flows2and3supplied can also be improved by adjacent channels12of the swirl generating structure5being in communication with one another in a portion which is at a distance from the outlet end of the swirl generating structure5. The communicating connection in this gas-permeable portion may be made possible, for example, by through openings, bores, porosity or gas-permeable plate materials9,10or gas-permeable structures, such as grid or mesh structures. Moreover, this communicating connection may be arranged and/or configured in such a way that channels which are adjacent within the same annulus16,17,19or within the same coil16,17,19are in communication with one another. As an alternative or in addition, the communicating connection may be arranged and/or configured in such a way that channels12which adjoin one another in adjacent annuli or coils16,17,19are in communication with one another. What is important is that all the channels12be separate from one another and have medium flowing through them independently of one another at least at the outlet end of the swirl generating structure5.

According to another refinement, it is possible for channels12which are arranged radially further inward to have a different magnitude of inclination with respect to the longitudinal center line6than channels12arranged radially further outward. It is preferable for the inclination of the channels12with respect to the longitudinal center line6to increase at increasing distance from the longitudinal center line6.

The mixing according to the invention functions as follows, in accordance withFIG. 1:

The two separate fluid flows2,3are fed to the swirl generating structure5. During flow through the swirl generating structure5, the abovementioned, opposite swirl flows7,8are generated from the two fluid flows2,3, which swirl flows7,8are arranged concentrically with respect to the longitudinal center line6and rotate into one another. Then, intensive mixing of the flow and in particular tangential widening of the flow are effected in the mixing zone20.

Given a corresponding design, the swirl generating structure5may also produce annular axial flows18which are introduced concentrically into the flow system of the opposite swirl flows7,8.

In addition, the straightener structure21may be provided at the end of the mixing zone20, so as to additionally axially orient the mixed flow as it flows through it. Ultimately, a more or less axially oriented flow23leaves the device4.

InFIGS. 3,4and5, the individual plates of the plate materials9,10are illustrated as being flat, for the sake of simplicity. It will be clear that the individual plates of the plate materials9,10are in each case curved about the longitudinal center line (not shown), specifically in accordance with their respective radial distance from the longitudinal center line6.

The swirl generating structure5having the design shown inFIG. 3can expediently be produced in the following way:

A first plate9Imade from the corrugated or folded first plate material9is positioned in such a way that its corrugations or folds11are inclined in the first direction13with respect to a winding axis, which coincides with the subsequent longitudinal center line6of the swirl generating structure5. Then, a second plate10IImade from the smooth or flat second plate material10is placed onto this first plate9I. Then, a third plate9IIImade from the first plate material9is placed onto the second plate10II, in such a manner that its corrugations or folds11are inclined in the opposite, second direction15with respect to the winding axis (longitudinal center line6). Then, a fourth plate10IV, which again consists of the smooth or flat second plate material10, can be placed onto the third plate9III. Then, the layered arrangement of plates9I,10II,9III,10IVformed in this way is wound helically around the winding axis (longitudinal center line6). As a result of the winding, a first plate9, in turn comes to bear on the fourth plate10IV, so that the layer structure is repeated in the radial direction. It will be clear that the layered arrangement may, of course, also be started with a smooth or flat second plate material10rather than a corrugated or folded first plate material9, in order to arrive at the swirl generating structure5after the winding operation.

Alternatively, the swirl generating structure5having the design illustrated inFIG. 3can also be produced in the following way:

In accordance withFIG. 6, a modified first plate9, is produced, comprising a plurality of individual portions of the first plate material9arranged next to one another in a row, with the inclinations of the corrugations or folds11of successive portions9′a,9′bbeing oriented in opposite directions with respect to the winding axis6. This modified first plate9′ is then placed, as indicated by arrows25, onto a second plate10′ made from the planar second plate material10and is wound together with the latter around the winding axis or longitudinal center line6. Depending on the length of the individual portions9′a,9′bwith the same fold or corrugation inclination, this results in one or more helical windings (annuli or coils), in which the channels12have in each case substantially the same inclination. Since the portions9′a,9′bwith corrugations or folds11oriented in the same direction alternate in a winding direction24symbolized by an arrow, the result of winding in the radial direction is a layered arrangement, in which oppositely oriented annuli or coils16,17or oppositely oriented groups of annuli or coils16,17alternate. With this procedure, only two plates9′,10′ which have been placed on top of one another have to be wound, which facilitates the winding operation, since the inclination of the corrugations or folds11with respect to the winding axis6in the case of the first plate material9or9′ impedes the winding operation. The more layers or strata of the corrugated or folded first plate material9have to be wound simultaneously, the more difficult the winding operation becomes.

The swirl generating structure5shown inFIG. 4can, for example, be produced in the following way:

First of all, once again a first plate9Imade from the corrugated or folded first plate material9is positioned in such a way that an inclination in the first direction13with respect to the winding axis6is produced for the associated channels12. Then, a second plate10II, which consists of the smooth or flat second plate material10, is placed onto the first plate9I.

Then, a third plate9IIImade from the first plate material9is placed onto the second plate10II, with its folds or corrugations11oriented in such a way that the channels12that are formed as a result run parallel to the winding axis6. Then, a fourth plate10IVmade from the second plate material10is placed onto the third plate9III. Then, a fifth plate9Vonce again made from the first plate material9is placed onto the fourth plate10IV, with the orientation of the folds or corrugations11in this case being selected in such a way that the channels12which are formed as a result are inclined in the second direction15with respect to the winding axis6. Then, a sixth plate10VI, once again made from the second plate material10, is placed onto the fifth plate9V, and a seventh plate9VIImade from the first plate material9is placed onto the sixth plate10VI. The orientation of the folds or corrugations11of the seventh plate9VIIare once again selected in such a way that the channels12which are formed as a result run parallel to the winding axis6. Finally, an eighth plate10VIIImade from the second plate material10is placed onto the seventh plate9VII. Only then is the layer structure finished, so that the plates which have been layered on top of one another can be wound helically around the winding axis6. The winding operation then in turn causes a first plate9Ito come to bear on the eighth plate10VIII. Here too, it will be clear that the first plate may in principle be formed from the second plate material10rather than from the first plate material9, in order to achieve the desired design of the swirl generating structure5.

There is also an alternative procedure for the production of the swirl generating structure5shown inFIG. 4, and this alternative procedure will be explained briefly below with reference toFIG. 7.

First of all, in this case too a modified first plate9″ is produced from corrugated or folded first plate material9, with the first plate9″ being assembled from a plurality of portions9″a,9″b,9″c, which are placed against one another in the winding direction24. The individual portions9″a,9″b,9″cdiffer from one another by having a different orientation of their folds or corrugations11with respect to the winding axis6. In the case of portions9″aand9″c, the corrugations or folds11are oriented such that they are inclined at between 0° and 90° with respect to the winding axis6, whereas in the case of the angle portion9″barranged between them they are oriented substantially parallel to the winding axis6. Furthermore, the corrugations or folds11of the two portions9″aand9″care inclined in opposite directions to one another with respect to the winding axis6.

This modified first plate9″ is then placed onto a second plate10″ made from the planar or smooth second plate material10. Then, this assembly is wound around the winding axis6. The dimensions of the individual portions9″a,9″b,9″cof the modified first plate9″ in the winding direction24are such that the winding results in the radial direction in a structure in which first annuli or coils16, third annuli or coils19, second annuli or coils17and third annuli or coils19again alternate more or less regularly.

It is relatively simple to produce the straigtener structure21as shown inFIG. 5. For this purpose, in accordance withFIG. 8, a first plate9′″ made from corrugated or folded first plate material9is provided, with the folds or corrugations11oriented parallel to the winding axis6. This first plate9′″ is placed onto a second plate10′″ made from smooth or planar second plate material10and together with the latter is wound up about the winding axis6. This results in the structure shown inFIG. 5. It is also possible, prior to the winding operation, for a plurality of pairs of first plates9′″ made from first plate material9and second plates10′″ made from second plate material10to be layered on top of one another and then to be jointly wound around the winding axis6.

LIST OF DESIGNATIONS