GB1604797A

GB1604797A - Method and a device for roasting fine grain to dust fine material more particularly raw cement powder

Info

Publication number: GB1604797A
Application number: GB2574978A
Authority: GB
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1977-11-21
Filing date: 1978-05-31
Publication date: 1981-12-16
Also published as: DE2751876A1

Description

(54) A METHOD AND A DEVICE FOR ROASTING FINE GRAIN TO DUST FINE MATERIAL MORE PARTICULARLY RAW CEMENT POWDER (71) We, KLocKNER-HuMsoLDT-DEuTz AKTIENGESELLSCHAFT of Deutz-Mulheimer Strasse 111, 5 Koln 80, Federal Republic of Germany, a German Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method and apparatus for roasting fine grain to dust fine material and is an improvement in or modification of our copending Application No. 22926/78 Serial No. 1601349.

In our copending application there is described and claimed a method of roasting fine grain to dust-fine material comprising passing preheated material into two sequential reaction stages prior to feeding it into a roasting stage, supplying heat separately to each reaction stage and separating the material from the hot gases prior to its passage into the second reaction stage.

Our copending application also describes and claims a device suitable for carrying out this method.

For example it is known when manufacturing cement to carry out decarbonation of the raw cement powder in the heat exchanger system almost completely by means of an additional burning device in the gas line between a baking kiln and the related heat exchanger system, so that, in effect, only the formation of clinker, i.e.

final roasting of the material needs to be carried out in the rotary kiln.

Thus, from German Offenlegungsschrift No. 2 361 427, for calcining the raw cement powder, a particularly constructed calcining chamber is provided between a suspension gas heat exchanger system and a rotary tube kiln in which chamber the gas material suspension while forming eddy currents is used to obtain an extended residence time in the hot roasting gases in order to achieve the most complete calcining possible. In this type of plant the economic disadvantage in the additional investment on the calcining chamber is justifled. The technological disadvantage in terms of method lies in that the residence times of the material in the chamber cannot be adjusted and there is the danger of overcalcining the material.

In accordance with the method according to the main application, an improvement in the known roasting methods is achieved by subdividing the calcining stage in the heat exchanger system into at least two calcining regions in the direction of passage of the treatment material. Heat is supplied separately to each of these reaction regions and the treatment material is separated from the hot gases before being fed into the next reaction region respectively.

As a result, a long residence time of the material in the temperature region required for calcination is achieved and this reaction can be controlled by control of the heat supply. With very good utilization of fuel, the time required for optimum calcining reactions in the material is achieved and over-roasting of particles of material can be completely avoided.

The present invention seeks to further refine and improve the roasting method according to the main application.

According to a first aspect of the invention, there is provided a method of roasting fine grain to dust fine material comprising thermally treating the material in a preheating stage, calcining the material in two stages in series, feeding fuel into the latter of the two stages both in the region of a material feed point and a gas separation point and roasting the material from the calcining stages in a kiln.

Preferably, heat is supplied separately to each of these reaction regions, and where in the treatment material in the calcining region is separated from the hot gases before being fed into the next reaction region respectively.

In this way optimum utilization of the fuel heat introduced into the lowermost calcining region is achieved and the calcining reaction of the already substantially calcined material in the reaction region connected therebefore can be exactly controlled in this way until complete calcining has been achieved, whereby any over-roasting of the particles of material is safely avoided. Thus among other things it is possible to introduce calcining of the material by means of appropriate control of the fuel heat sup plied in the lowermost reaction region, whereby the roasting stage connected thereafter only needs to take over safe roasting of the material.A further advantage of this measure lies in the fact that by appropriate control of the fuel heat introduced into the respective reaction regions, more particularly by means of appropriate control of the fuel heat added in the lowermost reaction region, this reaction region can take over complete baking of the material as a roasting machine.

Provision may be made for the fuel heat to be supplied by a lesser quality fuel which at the same time is a component of the material being treated. This is particularly advantageous if this lesser quality fuel is supplied to the lowermost reaction region at the point where the treatment material is separated from the hot gases of this reaction region. The lesser quality fuel introduced at this point and present in fine grain form meetts the kiln waste gases which still contain oxygen and have a temperature of 800 to 1000 C and is ignited whereby the temperature of the proportions of ash contained in the lesser quality fuel is brought directly to the temperature level of the other components of the material already substantially precalcined in the reaction regions connected therebefore.Thus burning off the lesser quality fuel components depends on the proportion of volatile components and on the proportion of solid carbon. The quantity of heat released by combustion of the lesser quality fuel in the oxygen-containing waste gases of the lowermost reaction is utilized for further decarbonation of the raw powder.

Provision may be made for the fuel heat to be supplied from coal having a grain spectrum of between 5 and 35mm, whereby the latter has a moisture content of between 5 and 15%. Burning off the carbon in the oxygencontaining gas of the lowermost reaction region is only incompletely executed in some circumstances. The unburnt fine grain carbon particles are present in the reaction region connected up stream in the direction of material flow, together with the waste gases from the lowermost reaction region and there they give off their heat to less calcined material so as to burn out. Material and fuel are therefore already in permanent contact in the reaction regions connected up stream and as a result the reaction time necessary for optimum calcining in the material are reached.The coarse grain coal parts also only burn out partially and arrive in the roasting stage together with the raw powder where burn out of this fuel takes place and the raw powder is either completely decarbonated there or the fuel heat is utilized at least for the purpose of partial baking of the raw powder.

In further refinement of the invention provision is also made for the fuel to be mixed into the hot treatment material after separation from the hot gases. This is particularly advantageous if unbroken coarse grain coal is used as a fuel said coal having a relatively high moisture content or still being moist from the mine. By mixing this type of coal into the raw material which is approximately 1000 C the coal is exploded by the impact of vaporization of the water bonded in it and is then finally distributed and mixed uniformly into the raw powder. Uniform burn out of the material takes place owing to this measure in the oxygencontaining atmosphere of the kiln and in this roasting stage either uniform residual calcining of the material can be carried out or baking of the material can be introduced.Expensive crushing devices for the solid fuel are thus economized.

The invention also relates to a device for thermal treatment of fine grain to dust fine material with the aid of the method in accordance with the invention, in which in the lowermost partial calcining path as seen in the direction of passage of the material at least one burner device is ar- ranged in the waste gas line running between the rotary tube kiln and the suspension gas heat exchanger and at least one further burning device is arranged in the device following the waste gas line for separating the material from the hot gases.

With this refinement the lowermost partial roasting path is given one more stage whereby the fuel is introduced into the heat exchanger system without any additional expenditure on plant and without any additional machines, and is introduced more particularly into the lowermost reaction region exactly where the best conditions for reaction of the fuel in an oxygencontaining atmosphere are present with intimate mixing with the preheated raw powder. Thus it is advisable if the device for separating material is a separating cyclone which is provided with a device for supplying fuel from fine grain coarse pieces.

In refinement of the device in accordance with the invention provision is made for the supply device for the fuel to be arranged in the material extraction region of the separating cyclone. Thus in particular there is the advantage of intimate mixing with the hot raw powder.

The invention will be described in greater detail together with an embodiment from which further advantages and features of the invention can be gathered.

The entire plant for roasting fine grain to dust fine material, more particularly for roasting raw cement powder comprises a rotary kiln 1, a suspension gas heat exchanger system 2 comprising at least three separating cyclones connected one after the other, being connected upstream of said rotary kiln 1 at the waste gas end. The separating cyclones 12 are connected one after the other by means of waste gas lines 5. The fine grain to dust fine material to be treated thermally, preferably raw cement powder, is introduced into the waste gas line at 4 via a supply device not shown in greater detail and thus arrives in the rotary tube kiln 1 gradually contrary to the direction of flow of the waste gases out of the rotary tube kiln 1 through the cyclones 12 and the waste gas lines 5 and the material extraction line 6.The material finally roasted and passing out of the rotary tube kiln is extracted via a material cooler 7.

The rotary tube kiln is provided with a burner lance 14 in the normal manner at its material extraction end said lance 14 only supplying as much heat as is necessary for roasting the raw powders completely decarbonated in the suspension gas heat exchanger system 2 or preheated therein in the device in accordance with the invention..

Each suspension gas heat exchanger has two calcining stages 10, 11 lying one behind the other as seen in the direction of passage of the raw cement powder, whereby heat is supplied separately to each of these reaction regions. A burner device or fuel supply 9 indicated only schematically is arranged in the gas line 5 leading from the lowermost cyclone 12.1 to the cyclone 12.2, said supply 9 representing a first calcining stage 11 in cooperation with the cyclone 12.2. The following calcining stage path 10 is formed by the waste gas line 3 and by the lowermost cyclone 12.1 whereby a burner device or fuel supply 8 also only indicated schematically is arranged in the waste gas line 3 and a further burner device 15 is arranged on the lowermost cyclone 12.1.

In operation of the cement roasting plant the raw cement powder passed at 4 into the gas line 5 is carried along by the rising hot gases, is separated from the hot gases in the uppermost cyclone 12.5 and gradually treated finally arrives in the waste gas line 5 via the extraction line 16. Heat from fuels of any type is introduced into this waste gas line via the burner device 9; this can be a high-quality or a lesser quality fuel of solid gaseous or liquid type.

The raw powder already preheated before this reaction region to a high degree is intimately mixed with the fuel introduced into the waste gas line 5. In addition hot cooler waste air is introduced via the air line 13. The fuel burns there in an oxygenenriched atmosphere without any flame and passes its heat directly to the raw cement powder for calcining. In the cyclone 12.2 the raw cement powder already partially calcined is separated from the hot gases and introduced into the subsequent calcining stage 10 and in fact into the waste gas line 3.

Heat from fuels of any type is also supplied into this waste gas line 3 of the lowermost partial calcining stage 10 via the burner device 8. In intimate mixing with the oxygen-containing kiln waste gases and cooler waste air, a further reaction takes place between the hot gases and the partially calcined raw cement powder. The now substantially calcined raw cement powder is separated in the lowermost cyclone 12.1 from the hot gases. At the same time an exactly predetermined quantity of heat is added in this cyclone via the burner device 15 which quantity is necessary for complete calcining of the raw cement powder or even for starting to roast the same.

The raw cement powder particles completely calcined and separated in the cyclone 12.1 are introduced into the rotary tube kiln 1 via the extraction line 6 and are roasted therein with the aid of the quantity of heat introduced via the burner lance 14.

The finally roasted material is guided into the material cooler 7 from the rotary tube kiln 1 and there is cooled off to the further processing temperature by means of air and is extracted from the cooler.

For the case where coal over the range from fine grain to coarse grain is introduced into the cyclone 12.1 of the lowermost partial roasting path 10 with the aid of the burner device 15 a substantial part of the fine grain coal will burn off directly in the cyclone and will give off heat to the raw cement powder. The fine grain and incompletely burnt out coal is carried along by the hot gases and introduced as a heat carrier into the calcining stage 11 so that only a small quantity of heat still needs to be supplied via the burner device 9 to this partial roasting path 11. The coarse grain coal which is also only par tially burnt out is mixed with the hot raw cement powder and extracted from the cyclone 12.1 into the rotary kiln 1 via the material extraction line 6 so that the coal burning out in the oxygen-rich kiln atmosphere brings about residual decarbonation of the raw cement powder or introduces baking of the raw cement powder so that as a result the use of a short rotary kiln is facilitated.

WHAT WE CLAIM IS: 1. A method of roasting fine grain to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the invention can be gathered. The entire plant for roasting fine grain to dust fine material, more particularly for roasting raw cement powder comprises a rotary kiln 1, a suspension gas heat exchanger system 2 comprising at least three separating cyclones connected one after the other, being connected upstream of said rotary kiln 1 at the waste gas end. The separating cyclones 12 are connected one after the other by means of waste gas lines 5. The fine grain to dust fine material to be treated thermally, preferably raw cement powder, is introduced into the waste gas line at 4 via a supply device not shown in greater detail and thus arrives in the rotary tube kiln 1 gradually contrary to the direction of flow of the waste gases out of the rotary tube kiln 1 through the cyclones 12 and the waste gas lines 5 and the material extraction line 6.The material finally roasted and passing out of the rotary tube kiln is extracted via a material cooler 7. The rotary tube kiln is provided with a burner lance 14 in the normal manner at its material extraction end said lance 14 only supplying as much heat as is necessary for roasting the raw powders completely decarbonated in the suspension gas heat exchanger system 2 or preheated therein in the device in accordance with the invention.. Each suspension gas heat exchanger has two calcining stages 10, 11 lying one behind the other as seen in the direction of passage of the raw cement powder, whereby heat is supplied separately to each of these reaction regions. A burner device or fuel supply 9 indicated only schematically is arranged in the gas line 5 leading from the lowermost cyclone 12.1 to the cyclone 12.2, said supply 9 representing a first calcining stage 11 in cooperation with the cyclone 12.2. The following calcining stage path 10 is formed by the waste gas line 3 and by the lowermost cyclone 12.1 whereby a burner device or fuel supply 8 also only indicated schematically is arranged in the waste gas line 3 and a further burner device 15 is arranged on the lowermost cyclone 12.1. In operation of the cement roasting plant the raw cement powder passed at 4 into the gas line 5 is carried along by the rising hot gases, is separated from the hot gases in the uppermost cyclone 12.5 and gradually treated finally arrives in the waste gas line 5 via the extraction line 16. Heat from fuels of any type is introduced into this waste gas line via the burner device 9; this can be a high-quality or a lesser quality fuel of solid gaseous or liquid type. The raw powder already preheated before this reaction region to a high degree is intimately mixed with the fuel introduced into the waste gas line 5. In addition hot cooler waste air is introduced via the air line 13. The fuel burns there in an oxygenenriched atmosphere without any flame and passes its heat directly to the raw cement powder for calcining. In the cyclone 12.2 the raw cement powder already partially calcined is separated from the hot gases and introduced into the subsequent calcining stage 10 and in fact into the waste gas line 3. Heat from fuels of any type is also supplied into this waste gas line 3 of the lowermost partial calcining stage 10 via the burner device 8. In intimate mixing with the oxygen-containing kiln waste gases and cooler waste air, a further reaction takes place between the hot gases and the partially calcined raw cement powder. The now substantially calcined raw cement powder is separated in the lowermost cyclone 12.1 from the hot gases. At the same time an exactly predetermined quantity of heat is added in this cyclone via the burner device 15 which quantity is necessary for complete calcining of the raw cement powder or even for starting to roast the same. The raw cement powder particles completely calcined and separated in the cyclone 12.1 are introduced into the rotary tube kiln 1 via the extraction line 6 and are roasted therein with the aid of the quantity of heat introduced via the burner lance 14. The finally roasted material is guided into the material cooler 7 from the rotary tube kiln 1 and there is cooled off to the further processing temperature by means of air and is extracted from the cooler. For the case where coal over the range from fine grain to coarse grain is introduced into the cyclone 12.1 of the lowermost partial roasting path 10 with the aid of the burner device 15 a substantial part of the fine grain coal will burn off directly in the cyclone and will give off heat to the raw cement powder. The fine grain and incompletely burnt out coal is carried along by the hot gases and introduced as a heat carrier into the calcining stage 11 so that only a small quantity of heat still needs to be supplied via the burner device 9 to this partial roasting path 11.The coarse grain coal which is also only par tially burnt out is mixed with the hot raw cement powder and extracted from the cyclone 12.1 into the rotary kiln 1 via the material extraction line 6 so that the coal burning out in the oxygen-rich kiln atmosphere brings about residual decarbonation of the raw cement powder or introduces baking of the raw cement powder so that as a result the use of a short rotary kiln is facilitated. WHAT WE CLAIM IS:

1. A method of roasting fine grain to

dust fine material comprising thermally treating the material in a preheating stage, calcining the material in two stages in series, feeding fuel into the later of the two stages both in the region of a material feed point and a gas separation point and roasting the material from the calcining stages in a kiln.

2. A method according to claim 1, wherein heat is supplied separately to each of these reaction regions, and wherein the treatment material in the calcining region is separated from the hot gases before being ded into the next reaction region respectively.

3. A method according to Claim 1 or 2, wherein so much heat is supplied during separation of the material from the hot gas as is necessary for complete calcining and/or baking of the treatment material.

4. A method according to Claim 1, 2 or 3, wherein the fuel heat is supplied from a lesser quality fuel which at the same time is a component of the material.

5. A method according to any one of claims 1 to 4, wherein the lesser value fuel is supplied in the lowermost reaction region in the region of the point where the treatment material is separated again from the hot gases.

6. A method according to any one of claims 1 to 5, wherein the fuel heat is supplied from preferably unbroken coal having a grain spectrum of between 5 and 35 mm whereby the same has a moisture of between 5 and 15%.

7. A method according to any one of the preceding claims, wherein the fuel is mixed into the hot treatment material directly after separating from the hot gases.

8. A method according to any one of the preceding claims, wherein, in addition, hot cooler waste air from the cooler is introduced into each of the reaction region.

9. A method according to any one of the preceding claims, wherein the treatment material is lime, magnesite, dolomite aluminium hydrate, phosphate or ores.

10. Apparatus for roasting fine grain to dust fine material comprising a preheating stage, two successive calcining stages, fed by the preheating stage, gas separation means for separating the material from hot gases in the second calcining stage, means for feeding fuel into the second calcining stage in the region in which the material is fed in and in the region of the gas separation means and a kiln for roasting the material from the second calcining stage.

11. Apparatus according to claim 10 wherein each calcining stage has a separate fuel supply, and means are provided for separating the treatmtnt material in the calcining regions from the hot gases before being fed into the next respective region.

12. A device according to claim 11 wherein the separating means comprises a separating cyclone which is provided with a device for supplying preferably fine grain fuel in coarse pieces.

13. A device according to claim 11 or 12, wherein the supply device for the fuel is arranged in the material extraction region of the separating cyclone.

14. A device according to claims 11, 12 or 13 wherein a supply device for hot waste air from the cooler is arranged in each of the two successive calcining stages.

15. A method of roasting fine grain to dust fine material substantially as described herein with reference to the drawing.

16. Apparatus for roasting fine grain to dust fine material substantially as described herein with reference to the drawing.