EP2908078B1 - Method and installation for the thermal processing of a material - Google Patents

Description

1. a) einen Drehrohrofen mit einer drehbaren Ofentrommel, deren Trommelwand einen beheizbaren Trommelraum begrenzt, durch den das Material von einem Trommeleingang zu einem Trommelausgang der Ofentrommel förderbar ist;
2. b) ein Heizsystem, mittels welchem der Trommelraum beheizbar ist.

Es gibt einige industrielle Prozesse, bei denen Materialen entstehen, die thermisch aufbereitet und hierdurch gegebenenfalls auch regeneriert werden können. Hierzu zählen beispielsweise Gießereialtsände, welche Reste an organischen und anorganischen Bindern, zum Beispiel Harze oder Bentonit, aufweisen können. Mit Hilfe einer thermischen Aufbereitung wird Bentonit beispielsweise kalziniert. Organische Binder werden dagegen oxidiert, wodurch der im Sand verbleibende Kohlenstoffanteil auf weniger als 0,8 Gew.% reduziert werden kann.The invention relates to a method for the thermal treatment of a material, in particular foundry sand or roadside material, in a rotary kiln with a rotatable kiln drum whose drum wall defines a heated drum space through which the material is conveyed from a drum inlet to a drum outlet of the kiln drum. CN 102 840 587 A relates to a rotary kiln with direct and indirect heating in which the heating gases are passed from the inlet to the outlet of the furnace on the outside of the drum. In addition, the invention relates to a plant for the thermal treatment of a material, in particular foundry sand or roadside material, which comprises

1. a) a rotary kiln with a rotatable kiln drum whose drum wall defines a heated drum space through which the material is conveyed from a drum inlet to a drum outlet of the kiln drum;
2. b) a heating system by means of which the drum space is heated.

There are some industrial processes that produce materials that can be thermally treated and, if necessary, also be regenerated. These include, for example, foundry sites which may have residues of organic and inorganic binders, for example resins or bentonite. For example, bentonite is calcined with the aid of thermal treatment. On the other hand, organic binders are oxidized, reducing the amount of carbon remaining in the sand to less than 0.8% by weight.

With regard to the thermal treatment of foundry stock in rotary kilns, it is particularly known to directly heat them with a gas burner by the flame has in the drum space and the hot gases generated are fed into the drum space, and also to operate in DC. This means that the material to be processed in the same direction is conveyed through the furnace drum, as the flow direction of the hot gases.

During thermal treatment, flue gases are produced. However, these have a relatively high carbon monoxide (CO) concentration in such a rotary kiln operation. The CO fraction can only be reduced by an afterburner, which increases the operating costs of the system.

In addition, the coming of the gas burner fuel gas must have a relatively high temperature in a DC operation, especially in the beginning of the rotary kiln, since the regenerated foundry sand must have a temperature of more than 700 ° C when leaving the rotary kiln. Since the drum atmosphere cools down in the conveying direction or flow direction, adequate starting temperature must be provided accordingly at the beginning. However, this leads in particular in the initial region of the furnace drum to high demands on the temperature resistance of the furnace material, which also leads to high costs.

Although there are approaches to operate a rotary kiln in countercurrent, in which the conveying direction of the material of the flow direction of the heating gas is opposite and the material exiting the furnace drum in the region of the burner flame. In this case, although the temperature at the burner flame may be lower than in a DC operation. However, then also the outlet temperature drops the flue gases, which cool when flowing through the furnace drum. This can lead to an undesired condensation of hydrocarbons in the flue gas lines.
In addition, in the case of a countercurrent operation, an afterburning of the flue gases is required because in addition to the vaporized hydrocarbons from the organic binder and dioxins can arise, which must be removed from the flue gases.

Similar problems arise in the thermal treatment of road breaking material. In particular, older roads were often built using a road surface using pitch (coal tar) as the binder. However, pitch contains a high proportion of environmentally harmful polycyclic aromatic hydrocarbons (PAHs) with the lead substance benzo (a) pyrene. The use or recycling of such road-breaking material is no longer permitted today.

Therefore, the immediate recycling of only mechanically treated, pitch-borne road-breaking material is ruled out and the split contained must be freed from the pitch-bearing binder before the split can then be used to make new asphalt.
It is therefore an object of the invention to provide a method and a system of the type mentioned, which take into account this idea.

This object is achieved by the method according to claim 1. According to the invention, it has been recognized that a uniform temperature profile in the furnace drum can be achieved by the combination of direct heating of the drum space, as is known, for example, using a gas burner, with indirect heating of the drum space via its drum wall. In particular, a cooling of the flue gases on the way through the kiln drum can be prevented. In addition, the temperature at the direct heater compared to a direct heating alone can be reduced, whereby the requirements for the furnace material are less high.
An afterburning of the flue gases is then not necessary because they have a sufficiently high temperature at the exit from the furnace drum.

By the heating gas is passed at the drum inlet of the furnace drum in the drum space, the rotary kiln can be operated based on direct heating on the DC principle.

With regard to the indirect heating, it is advantageous if the drum wall is heated by a heating medium is passed from the outside to the drum wall.

In this case, the heating medium is conducted in a direction from the drum outlet to the drum inlet of the furnace drum on the outside of the drum wall. Based on the conveying direction of the material through the furnace drum, the indirect heating thus takes place according to the countercurrent principle. Thus, the kiln drum in its longitudinal direction be heated with opposite temperature gradient, so that a total of a homogeneous temperature profile is constructed in the drum room.
So that the heating medium flows over the drum wall in a targeted manner, this is favorable when the heating medium is passed through an annular space surrounding the oven drum.
As explained above, the maximum temperature prevailing locally in the drum space, in particular in the area of direct heating, can be lowered. Advantageously, this makes it possible that an oven drum is used, of which at least the drum wall and / or a conveying structure on the inner lateral surface of the drum wall are made of steel. The steel used is selected depending on the temperatures reached in the drum room.

With regard to the system, the above-mentioned object is achieved by the device according to claim 5.

The advantages achieved by these measures correspond to the advantages explained above for the method.
If the direct heating device comprises a burner unit, which is arranged at the drum inlet of the furnace drum is, so that heating gas is conducted there in the drum space, established techniques for a direct firing of the drum space can be used.

It is favorable if the indirect heating device comprises a burner unit, by means of which a heating medium can be generated, and at least one line through which the heating medium can be conducted to the drum wall from the outside. Thus, also known for the indirect heater, based on the use of burners heating techniques can be used.

As explained above, it is favorable for a homogeneous temperature in the drum space when the indirect heater comprises a flow path through which the heating medium in the direction of the drum outlet on the drum inlet of the furnace drum outside the drum wall is guided along.

The flow path for the heating medium can advantageously be provided by the indirect heating device comprising a cladding tube with an inlet connection for heating medium and an outlet connection for heating medium, which is arranged coaxially with the oven drum such that an annular space surrounding the oven drum is formed, by which heating medium indirect heating device is conductive.

It is advantageous if a helical guide structure is arranged in the annular space so that the heating medium flows in a helical manner from the inlet connection to the outlet connection and around the oven drum. In this way it can be ensured that all areas of the furnace drum are uniformly and selectively overflowed by heating medium.

As explained above, at least the drum wall and / or a conveying structure on the inner lateral surface of the drum wall can be made of steel from the furnace drum.

Figur 1

eine schematische Layoutansicht eines Systems zum thermischen Aufbereiten eines Materials mit einem Drehrohrofen;

Figur 2

in teilweiser Durchsicht einen schematischen Schnitt des Drehrohrofens in größerem Maßstab.

An embodiment of the invention will be explained in more detail with reference to the drawings. Show it

FIG. 1

a schematic layout view of a system for thermally processing a material with a rotary kiln;

FIG. 2

in partial view a schematic section of the rotary kiln on a larger scale.

In FIG. 1 10 generally designates a system shown schematically for the thermal treatment of a material. As explained at the beginning, the material to be processed can be, for example, foundry sand or even road-breaking material. The system 10 has a rotary kiln 12, which initially based FIG. 2 is explained, which shows the rotary kiln in more detail, but also only schematically.

The rotary kiln 12 comprises a furnace drum 14, which is rotatably mounted about pivot bearings 16 about its longitudinal axis 18 is driven by means of a motor 20. The furnace drum 14 has a drum space 22, which is delimited by a drum wall 24 and is open at a front-side drum inlet 26 and a drum exit 28 opposite thereto. At the drum inlet 26, the furnace drum 14 opens into an inlet flange 30, which carries a feed pipe 32, can be introduced through the drum inlet 26 into the furnace drum 14 through the material to be processed. In FIG. 1 the supply nozzle 32 is illustrated as a dashed arrow.

In addition, a burner unit 34 in the form of a gas burner 36 is arranged on the input flange 30, which has a Fuel gas line 38 is supplied with fuel gas from a not specifically shown fuel gas source. Via an air line 40 the gas burner 36 is supplied for its operation required burner air.

The gas burner 36 generates in a manner known per se and heating gas, which is passed in a direction indicated by an arrow heating gas flow direction 42 in the drum chamber 22, flows through it and heated directly.

The furnace drum 14 opens at the drum outlet 28 into an outlet flange 44, which comprises a flue gas outlet 46 and a material outlet 48. In the thermal treatment of the material in the furnace drum 14 resulting flue gas flows from the drum chamber 22 into the output flange 44 and from there via the flue gas outlet 46 in a flue gas duct 50; This will be discussed again below.

On its inner circumferential surface, the drum wall 24 carries a conveyor structure 52, for example a continuous conveyor coil 54. As the oven drum 14 rotates, material entering the drum space 22 through the supply nozzle 32 is conveyed therethrough in a conveying direction 56 by the conveyor coil 54 Material outlet 28 of the furnace drum 14 promoted where it enters the output flange 44 and is discharged through the material outlet 48.

The conveyor coil 54 may still include parallel to the longitudinal axis 18 extending and radially inwardly projecting sheets, which are not shown here specifically. These sheets take the material with the rotation of the kiln drum 14 initially up with, until the material drops again when reaching a certain height from the sheets down. This is compared to a conveyor coil 18 without such additional sheets achieved an even better mixing of the material.

Relative to the heating gas flow direction 42 and the conveying direction 56 of the material to be processed, the rotary kiln 12 is consequently operated in the so-called DC process.

As FIG. 1 shows the flue gas is guided from the output flange 44 via the flue gas line 50 in a dust removal device 58. From there, the now dedusted flue gas passes into an adjustable distribution unit 60, by means of which a portion of the purified flue gas is directed into the air line 40 to the gas burner 36 and the remaining portion of the purified flue gas can be removed via a line 62.

With the help of the distribution unit 60 can also fresh air from a fresh air line 64 are passed with a fresh air blower 66 in the air line 40, so that the ratio of a mixture of purified flue gas and fresh air can be adjusted, which then passes as combustion air to the gas burner 36.

The combustion air can thus be provided by pure purified flue gas, pure fresh air or by a mixture of flue gas and fresh air in an adjustable ratio.

The burner unit 34 with the associated components is an exemplary embodiment of a first, direct heating device 68, by means of which the drum space 22 can be heated directly by generating a heating gas and can be conducted into the drum space 22. This heater 68 is part of a generally designated 70 heating system, by means of which the drum chamber 22 is heated.

In addition to the direct heater 68, this includes Heating system 70 still one in FIG. 1 illustrated second, indirect heating device 72, by means of which the drum space 22 is indirectly heated by the drum wall 24 is at least partially heated. For this purpose, the indirect heating device generates a heating medium.

The indirect heating device 72 in the present embodiment comprises a second burner unit 74 in the form of a second gas burner 76, which is supplied via a fuel gas line 78 with fuel gas from a fuel gas source not specifically shown. Via an air line 80 the burner gas required for the operation of the second gas burner 76 is supplied. Thus, the heating medium of the indirect heater 72 is also a heating gas.

This heating gas is passed via a Heizgasleitung 82 to the drum wall 24 of the furnace drum 14, where it can flow along the outside. Like back in FIG. 2 is shown, the furnace drum 14 is surrounded by an annular space 84, which is formed by that a cladding tube 86 is arranged coaxially with the furnace drum 14.

The cladding tube 86 includes an input port 88 and an output port 90 for heating medium so that the annulus 84 provides a flow path to the fuel gas of the second gas burner 76. The input port 88 is disposed at the end of the cladding tube 86, which faces toward the output flange 44 of the rotary kiln 12. The output port 90 is located at the end of the cladding tube 86 facing toward its input flange 30. The input port 88 is connected to the Heizgasleitung 82 of the second gas burner 76, so that the heating gas generated by this in a counter-flow direction 92 outside the drum wall 24 is guided along, which points from the drum outlet 26 to the drum inlet 28 of the furnace drum 14.

Based on the conveying direction 56 of the material to be processed and the flow direction 42 of the heating gas of the first gas burner 36 through the drum space 22, the indirect heating device 72 thus follows the countercurrent principle.

The output port 90 of the cladding tube 86 is connected to a return line 94 with a blower 96, which leads at the other end to a second adjustable distributor unit 98, which in FIG. 1 is shown and to which the heating gas of the second gas burner 76 passes after flowing through the annular space 84.

This can derive the used fuel gas completely or partially in the air line 80 for the second gas burner 76 or completely or partially dissipate via a line 100.

The second distributor unit 98 can supply the fresh air from a fresh air line 102 with a fresh air blower 104 to the air line 80, so that an adjustable mixture of used heating gas from the annular space 84 and fresh air passes through the air line 80 as combustion air to the second gas burner 76.

In addition, from the return line 94 for the spent fuel gas of the second gas burner 76 branches off a fuel gas line 106 from the gas burner 76, through which this fuel gas can be performed as fuel gas in the combustion chamber 76 a of the gas burner 76.

So that now the drum wall 22 of the furnace drum 14 can be uniformly flowed around by the heating gas of the second gas burner 76, a helical guide structure 108 is disposed in the annular space 84, so that the heating gas of the helically Input terminal 88 to the output port 90 and flows around the furnace drum 14 around. From the conductive structure 108 are in FIG. 2 sections lying behind the plane of the drawing are only partially indicated by dashed lines.

The heat input by the indirect heating device 72 in the drum chamber 22 on the one hand via the drum wall 24, on the other hand via the conveyor coil 54, which can absorb the heat from the drum wall 24 and deliver it to the material.

In order for the furnace drum 14 also to withstand abrasive materials, at least the drum wall 22 and / or the conveyor spiral 54 of the furnace drum 14 are made of steel. In the operating concept described herein, the rotary kiln 12 may be formed as a solid steel welded construction.

As explained above, in the rotary kiln 12, the operating temperature in the kiln drum 14 can be uniformly maintained at a moderate temperature. As a result, the volume flow of the flue gases produced remains relatively small, whereby their flow rate is lower.

It is possible to achieve material temperatures which are only 100 ° C. below the maximum heating gas temperature. Characterized in that in the drum chamber 22, a largely uniformly distributed temperature prevails, the material moves over a large conveyor section at the temperature at which the material is to leave the furnace drum 14.

The temperature in the drum space 22, the conveying speed and the associated residence time of the material in the drum space 22 as well as the excess of oxygen can also be easily adapted to the material to be processed be matched by the direct and indirect heaters 68 and 72 of the heating system 70.

Claims (9)

1. Method for the thermal processing of a material, in particular of used foundry sand or of road construction material, in a rotary kiln (12) with a rotatable kiln drum (14), the drum wall (24) of which delimits a heatable drum chamber (22), through which the material is conveyed from a drum inlet (26) to a drum outlet (28) of the kiln drum (14), wherein

   a) the drum chamber (22) is heated directly by conducting a heating gas into the drum chamber (22);

   b) the drum chamber (22) is also heated indirectly by warming the drum wall (24) at least in areas;

   c) the drum wall (24) is warmed by conducting a heating medium from outside onto the drum wall (24),
   characterized in that

   d) the heating medium is conducted along the outside of the drum wall (24) in a direction from the drum outlet (28) to the drum inlet (26) of the kiln drum (14).
2. Method according to claim 1, characterized in that the heating gas is conducted into the drum chamber (22) at the drum inlet (26) of the kiln drum (14).
3. Method according to claim 1 or 2, characterized in that the heating medium is conducted through an annular chamber (84) surrounding the kiln drum (14).
4. Method according to one of claims 1 to 3, characterized in that a kiln drum (14) is used of which at least the drum wall (24) and/or a conveying structure (52) on the inner shell surface of the drum wall (24) are made of steel.
5. Installation for the thermal processing of a material, in particular of used foundry sand or of road construction material, which comprises

   a) a rotary kiln (12) with a rotatable kiln drum (14), the drum wall (24) of which delimits a heatable drum chamber (22), through which the material is conveyable from a drum inlet (26) to a drum outlet (28) of the kiln drum (14);

   b) a heating system (70), by means of which the drum chamber (22) is heatable,
   wherein

   c) the heating system (70) comprises a first, direct heating device (68), by means of which the drum chamber (68) is directly heatable, in that a heating gas is generatable and conductable into the drum chamber (22);

   d) the heating system (70) comprises a second, indirect heating device (72), by means of which the drum chamber (22) is indirectly heatable, in that the drum wall (24) is warmable at least in areas;

   e) the indirect heating device (72) comprises a burner unit (74), by which a heating medium is generatable, and at least one conduit (82) through which the heating medium is conductable onto the drum wall (24) from outside,
   characterized in that

   f) the indirect heating device (72) comprises a flow path (84), through which the heating medium is conductable along the outside of the drum wall (24) in the direction from the drum outlet (28) to the drum inlet (26) of the kiln drum (12).
6. Installation according to claim 5, characterized in that the direct heating device (68) comprises a burner unit (34), which is arranged at the drum inlet of the kiln drum, so that heating gas is conducted into the drum chamber there.
7. Installation according to claim 5 or 6, characterized in that the indirect heating device (72) comprises a cladding tube (86) with an inlet connection (88) for heating medium and an outlet connection (90) for heating medium, which tube is arranged coaxially to the kiln drum (14) in such a way that an annular chamber (84) surrounding the kiln drum (14) is formed, through which the heating medium of the indirect heating device (72) is conductable.
8. Installation according to claim 7, characterized in that a helical conducting structure (108) is arranged in the annular chamber (84), so that the heating medium flows helically from the inlet connection (88) to the outlet connection (90) and around the kiln drum (14).
9. Installation according to one of claims 5 to 8, characterized in that of the kiln drum (14) at least the drum wall (24) and/or a conveying structure (52) on the inner shell surface of the drum wall (24) are made of steel.

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