Such flue gas conditioning devices are typically used in connection with industrial production systems and in practice always in connection with cement production sys- tems in which burning takes place in a kiln, and in which the flue gas with its content of particles generated by the burning subsequently has to be freed of at least part of these particles in a separator. For example electro- static precipitators or bag filters may be used in this connection. Such separators make special demands on the state of the flue gas on introduction into these. Thus, for reasons of material alone it is required both in bag filters and in electrostatic precipitators that the flue gas has a suitably low temperature, while ensuring that the flue gas is not wet. The low temperature moreover causes a reduction in the volume of the gas which is to be treated after the conditioning device, and the respec- tive separator may therefore be dimensioned correspond- ingly smaller. In connection with an electrostatic pre- cipitator it is of great importance that the resistivity of the flue gas particles is sufficiently low to avoid

reflection in the electrostatic precipitator, as such re- flection results in a state of operation in which the separation capacity is impaired considerably. In connec- tion with bag filters it is likewise of great importance that no wet flue gas is present, since such presence af- fects the efficiency of the filter and may cause damage to the bag. To adapt the state of the flue gas to the re- quirements made by the separator, the flue gas, before being introduced into these, is fed into a flue gas con- ditioning device, as described above.

In the generally known flue gas conditioning devices there is a marked tendency for the flue gas stream to be separated from the inner wall of the conditioning cham- ber. Usually, it cannot be predicted where this separa- tion of the flue gas stream from the wall face takes place, but the result of it is that, on average, the tem- perature is considerably lower in the area close to the wall than in the area further toward the centre of the conditioning chamber. This means that in this wall area there is a considerable risk that water drops may settle on the inner wall and here give rise to the formation of encrustations, or will find their way from there to the bottom of the conditioning device. The latter results in a wet bottom in the device, which is extremely undesir- able in connection with discharge and optional upstream reintroduction of dust which has settled in the condi- tioning device.

The above-mentioned problems are particularly pronounced in conditioning devices in which the inlet pipe has a course generating a considerable pressure gradient across the inlet cross-section, which-in the side concerned where the pressure is low-results in an increased ten- dency for the flue gas to be separated from the wall area with consequences as described above, but to an even more

pronounced degree. Such inlets are characterized in that over a distance of up to 5 inlet pipe diameters these do not have an axis in parallel with the central axis of the conditioning chamber. This structure is common for sev- eral reasons. For one thing, such a structure involves a great overall height, which is undesirable, and for an- other, it is generally not practically possible to pro- vide support for such a high pipe.

To overcome the separation phenomenon to some extent it is common that a grating is placed in such conditioning devices, upwardly in the device and in this connection preferably in the area at the diffuser. Such a grating serves to smoothen the flue gas stream so as to bring about a more uniform flue gas stream. Such a grating remedies the above-mentioned problems in part. Another attempt at remedying the problem comprises constructing the diffuser with a small apex angle and with a rela- tively great length. This measure will remedy the above- mentioned problems in part. However, only a poor flow stability is created in devices comprising a grating as well as in devices comprising a diffuser with a small apex angle, and the above-mentioned problems will still occur to a significant degree.

Known is also a flue gas conditioning device in which the flue gas delivery consists of a pipe which is tangent to the inlet pipe and is directed obliquely upwards. In this previously known device the flue gas stream is reflected against a closed end of the inlet pipe, which means that the flue gas stream becomes turbulent and therefore does not have a well-defined direction of motion. The problems described above also manifest themselves in this previ- ously known flue gas conditioning device.

Because of a poor stability and thereby poor possibility of controlled regulation of the flue gas stream in the previously known devices there is a need for an improved flue gas conditioning device.

Accordingly, the object of the present invention is to provide a method in connection with such a flue gas con- ditioning device, which method ensures a more stable flue gas stream and, to a greater degree, a high temperature in the area around the wall.

This is achieved by the method according to the invention in that the flue gas stream is caused to perform a rotary movement with respect to an axis extending through the conditioning chamber.

In such a method, a high temperature at the wall is ob- tained by virtue of the rotating momentum, which ensures to a greater degree than known before that no water drops occur on the wall.

Expediently, the flue gas is simultaneously caused to perform an axial movement, and the speed of rotation con- stitutes between 10 and 40% of the axial speed, prefer- ably about 20%. The axial momentum ensures that the ro- tating momentum is passed toward the outlet and is also stabilized. With the rotating flow having a speed of ro- tation of between 10 and 40% of the axial speed, it is moreover possible to obtain pressure conditions which re- sult in a secondary flow directed toward the centre of the rotation. Such a secondary flow will give the in- jected water drops a prolonged residence time in the con- ditioning chamber, as the drops are entrained by the flow inwards toward the centre of the rotation and upwards to be included in the rotating flow again, thereby contrib- uting to the efficiency of the conditioning device.

The invention also relates to a flue gas conditioning de- vice for performing the method, said device comprising an inlet, a diffuser in extension of the inlet, and an es- sentially cylindrical pipe area in extension of the dif- fuser, said pipe area being equipped with a bottom and an outlet opposite the diffuser, said diffuser and said cy- lindrical pipe area defining a conditioning chamber, means being provided in an area of the conditioning cham- ber near the inlet to introduce conditioning water into the flue gas.

This conditioning device is characterized according to the invention in that means are provided to impart a ro- tating momentum to the flue gas stream.

Such a device, like the method, provides a high tempera- ture at the wall by virtue of the rotating momentum, which ensures to a higher degree than known before that no water drops occur on the wall. The axial momentum en- sures that the rotating momentum is passed toward the outlet and is also stabilized. With the rotating flow it is moreover possible to obtain pressure conditions which result in a secondary flow directed toward the centre of the rotation. Such a secondary flow will give the in- jected water drops a prolonged residence time in the con- ditioning chamber, as the drops are entrained by the flow inwards toward the centre of the rotation and upwards to be included in the rotating flow again, thereby contrib- uting to the efficiency of the conditioning device.

Expediently, the device according to the invention also comprises means to impart to the rotating flue gas stream a moment in an axial direction.

Such a rotation and also an axial movement may e. g. be provided in that guide blades are arranged in the inlet, said guide blades extending radially from the centre of the inlet pipe. A further possibility comprises providing a first essentially axial inlet pipe and in association with this a second tangentially directed flue gas inlet pipe.

The invention moreover relates to a cement production system comprising a kiln, a mill, a flue gas conditioning device and a separator. This system is characterized ac- cording to the invention by comprising a conditioning de- vice as described in the foregoing. The device is par- ticularly expedient in such a system, since this presents particularly difficult conditions of operation.

The invention will be explained more fully below with reference to the drawing which shows a preferred embodi- ment of the flue gas conditioning device.

In the drawing: Figure 1 shows a flue gas conditioning device seen from the side, Figure 2 shows a previously known flue gas conditioning device seen in section and with flow lines, Figure 3 shows a previously known flue gas conditioning device seen from the side, Figure 4 shows a previously known flue gas conditioning device seen in section, Figure 5 shows a guide blade structure for mounting in the inlet, seen from above and in perspective,

Figure 6 shows a partial section through inlet and dif- fuser of a flue gas conditioning device in which guide blades are positioned, as shown in figure 5, Figure 7 shows a flue gas conditioning device seen in section in which the invention is implemented, flow lines being shown for this structure, Figure 8 shows a speed profile for the flue gas stream in a preferred embodiment of the means to ensure the rotat- ing flow, and Figure 9 shows a flue gas conditioning device in which a pipe system for axial and tangential introduction of flue gas is provided.

Figure 1 shows a conditioning device 1 comprising an in- let pipe 2, a diffuser 3, a vertical side wall 4, a base part 5, and an outlet 6. The diffuser 3 is peripherally provided with a number of holes 7 which serve to intro- duce lances (not shown) having nozzles for the injection of conditioning water. The lances are connected with a water supply. The diffuser may also consist of a single cone, several cones having different angles, or of sev- eral cylindrical lengths of pipe having different diame- ters.

It appears from figure 2, as shown by flow arrows 8, how a separation of the flow takes place at the side of the lowest pressure (right-hand side of figure 2) in a structure with a great pressure gradient across the inlet. This is inexpedient because it results in a poor efficiency, and because it moreover involves a risk of formation of encrustations.

An example of a previously known device is shown in fig- ure 3, in which a long diffuser 3 having a small angle is provided to avoid the flow shown in figure 2. Figure 4 shows a further example of a previously known device in which a grating 9 is provided in the area at the dif- fuser. These features, however, are not sufficient to provide the desired conditions in the conditioning de- vice.

Figure 5 shows a blade structure 10 for mounting in the inlet pipe. As will appear, the structure comprises six blades 11, each of which is formed by a single-curved plate. This gives a particularly simple structure.

It appears from figure 6, partially in section, how a blade structure 10, as shown in figure 5, is incorporated in a conditioning device to form such a device according to the invention.

Figure 7 shows a conditioning device in which e. g. blades, as shown in figure 6, are implemented, flow lines 12 after this implementation being shown. It appears that the separation indicated in figure 2 no longer occurs.

Also a secondary flow 13 directed toward the conditioning chamber is visible. This likewise appears from figure 8 which shows a speed profile through this upper area of the conditioning chamber. It appears that there is a relatively great speed close to the inner wall, which in- dicates that a hot gas flows here, and that there is thus little risk of water drop settlement. The secondary flow is shown as a negative speed. A water drop 14 is indi- cated as being entrained.

Figure 9 shows an alternative embodiment of the inven- tion, in which a tangential inlet 15 is provided in addi- tion to the axial inlet 2. Both a downward flow and a ro- tating flow are provided hereby.