From PCT/EP98/00145 which is held by the applicant of the present application, and the content of which being regarded as comprised by the present application, a burner of the kind mentioned above is known.

When using burners of this type in, for example, a rotary kiln for manufacturing cement where a dust-laden kiln atmosphere is often encountered, it has shown that deposits tend to be formed quite frequently on the upper side of the outer pipe of the burner near its pointed end. Within a matter of hours, such deposits may develop into pyramidal mountains-rising to a height of several metres-which essentially consist of partially molten clinker dust. Such deposits may cause operational problems since they may partially block the air nozzle, thereby altering the shape and direction of the flame, which entails that under adverse circumstances the flame may impinge on the internal lining in the kiln, potentially leading to a substantial reduction of the service life of the lining. In case of extensive deposits, as noted above, the burner pipe may be subjected to excessive stress loads, which may cause the burner to break down.

It is a well-known fact that the mentioned problem can be solved on the basis of regular removal of deposits. Up to this point in time, it has been standard practice to remove the deposits manually using a long, tubular lance, equipped with a nozzle for injecting water at high pressure,

approximately 300 bar. The lance, which is normally inserted through one of the observation holes in the kiln hood, must be brought into close contact with the deposits. When the water jet impacts the deposits, the high temperature will cause a steam explosion to take place. It is this steam explosion which causes the deposits to disintegrate.

The above-mentioned method involves a number of disadvantages. The intensive steam explosions pose hazards in terms of injury to operating personnel. For this reason, it is an essential requirement that the operator is wearing the necessary protective outfit. Since the deposits are formed at the pointed end of the burner pipe, the length of which may typically be from eight to ten metres, it may not be an easy task to manoeuvre the long lance through the small observation hole. In many cases, two persons are needed to operate the lance. There is a distinct risk of damage to the refractory lining of the burner pipe due to the fact that the water jet may inadvertently impact the lining instead of the deposits. To ensure effectiveness of this method, the deposits must be removed frequently, quite often at intervals down to two or three hours, and this makes the method very time-consuming.

Another method which has been attempted involves permanent installation of the water lance inside the burner pipe. This will dispense with the hazardous and time-consuming manual operation. However, this method has turned out to be unsuitable as it appears that effective removal of the deposits can only be achieved if water jet impacting is applied over an extended area.

Finally, a third method has been described in DE-19628487- A1. The burner described in said publication comprises an additional, outer pipe which is equipped at its pointed end with a number of nozzle openings in the axial and radial

direction. The pipe is connected to a pneumatically operated air blaster, and the deposits can purportedly be removed by activating the air blaster at regular intervals. However, it is unlikely that this method will be able to remove all deposits, probably removing only deposits located in immediate proximity of the nozzle openings.

It is the objective of the present invention to provide a burner by means of which deposits can be removed without any of the aforementioned disadvantages.

According to the invention this is achieved by means of a burner of the kind mentioned in the introduction, and being characterized in that it comprises a turning means by means of which at least the outermost pipe can be rotated about the longitudinal axis of the burner.

It is hereby obtained that build-up of deposits on the upper side of the burner during operation can be avoided since any such dust deposits will be dislodged when the pipe is rotated. Another significant advantage of the method is that the abrasion and radiant heat arising from the product flow which will normally have a degrading effect on the lining on the lower side of the burner will be evenly distributed across the entire circumference of the burner because of the rotation of the pipe. This will prolong the service life of the burner, thus enhancing the run factor of the kiln.

The turning means may consist of any conceivable suitable type but preferably it should be of a mechanical design, for example in the form of a toothed gearing. The turning means may be operated manually or using a motor which may be remote-controlled.

In cases where the turning device is motorized, the motor should appropriately be set to give the pipe with a rotational speed within the range of 0.25 to 5 revolutions per hour, preferably at around 1 revolution per hour.

In its most basic design, the burner comprises only one pipe for conducting fuel and primary air. However, it is preferred that the burner comprises a burner pipe which incorporates one or several inner pipes located concentrically with the burner pipe, said pipes forming a number of annular ducts for separate conducting and injection of fuel and primary air. In such an embodiment of the burner according to the invention, it will be possible at least for the outermost pipe to rotate about the longitudinal axis of the burner, but the burner may also be configured to allow the entire burner to rotate about its longitudinal axis.

In a preferred embodiment the burner may comprise a jacket pipe which is arranged concentrically around the burner pipe, and in this embodiment at least the jacket pipe can be made to rotate about the longitudinal axis of the burner.

In cases where the burner comprises a jacket pipe it will be possible to direct a portion of the primary airflow through a gap provided between the burner pipe and the jacket pipe in order to cool off the jacket pipe. The airflow which is directed through the burner pipe and the jacket pipe may advantageously constitute between 2 and 4 per cent of the theoretically required combustion airflow.

Furthermore, the jacket pipe may be equipped with holes for diverting the incoming airflow which may contribute towards restricting the level of dust being deposited on the burner.

The burner may further comprise one or several burner lances for conducting and injecting liquid or gaseous fuel and one or several pipes for conducting and injecting supplementary solid fuels.

The invention will now be described in further details with reference to the drawing, being diagrammatical, and where Fig. 1 shows a partial sectional side view of a burner according to the invention, and Fig. 2 shows a sectional view of the front section of the same burner.

In Fig. 1 and 2 is shown a burner 1 which is intended for combined firing on oil and pulverized coal in a kiln, such as a rotary kiln for manufacturing cement clinker or similar products. The burner 1 is essentially of a known design and comprises a central protective pipe 2 in which a separate lance, not shown, may be fitted for conducting and atomizing the fuel oil.

Arranged concentrically around the protective pipe 2 are two pipes 3 and 4 which form between them an annular duct 6 for conducting and injecting a mixture of pulverized coal and air. In order to cool the not shown oil lance and to keep it free from dust a small amount of the total primary airflow may be conducted and injected through the gap between pipe 3 and the protective pipe 2. In addition to the protective pipe 2, it will be possible to insert in the pipe 3 one or several pipes for feeding supplementary alternative fuels.

Arranged concentrically around the pipe 4 is a burner pipe 7 which in conjunction with the pipe 4 forms an annular duct 9 for conducting the remaining part of the primary airflow.

Outermost the shown burner comprises a jacket pipe 11 which is externally equipped with a refractory lining 12 and being supported at its foremost end by spacers 13. Inside the jacket pipe there is a guide ring 15 which lies true against the spacers. The rear end of the pipe 11 is supported by rollers 19. The pipe 11 can be rotated by means of a tooth gearing 21. At the location where the jacket pipe is inserted through the kiln wall 23 there is a spring-loaded closing plate 25. The closing plate will prevent in-leakage of false air while allowing, at the same time, the jacket pipe 11 to rotate. Also, the spring loading of the closing plate 25 will ensure that the aforementioned guide ring 15 lies true against the spacers so that the jacket pipe is fixed in the axial direction regardless of thermal longitudinal expansion.

The burner pipe 7 has a number of drilled holes 31 through which a small portion of the primary airflow can be directed out into the gap 33 between the burner pipe and the jacket pipe for cooling. This cooling airflow which will normally constitute 2-4 per cent of the theoretical combustion airflow should essentially be directed backwards through the gap in order to minimize to practicable extent the inflow of cold air into the kiln. Alternatively, the jacket pipe 11 may be formed with a number of holes 35 for diverting the air through the refractory lining.

During operation formation of deposits on the jacket pipe can be avoided by rotating the pipe using the tooth gearing 21, either manually or using a built-on motor, not shown.

The applied rotational speed should be such that the pipe completes at least one full revolution per hour. Rotation may take place at a constant rotational speed or at a discontinuous speed.