WO2021148266A1

WO2021148266A1 - Device and method for producing cement clinker

Info

Publication number: WO2021148266A1
Application number: PCT/EP2021/050369
Authority: WO
Inventors: Andreas Hoppe; Rodrigo GOMEZ; Jürgen Schneberger
Original assignee: Thyssenkrupp Industrial Solutions Ag; Thyssenkrupp Ag
Priority date: 2020-01-20
Filing date: 2021-01-11
Publication date: 2021-07-29
Also published as: EP4094029A1

Abstract

The present invention relates to a device for the production of cement clinker, said device comprising a preheater (50), a calciner (60) and a cooler (70). Said device also comprises a feed for cement raw material, characterized in that a mechanical fluidized bed reactor (30) is arranged between the feed for cement raw material and the preheater (50), the calciner (60) being directly connected to the cooler (70).

Description

Apparatus and method for the production of cement clinker

The invention relates to a method and a device for producing cement clinker.

From DE 2726 138 A1 a method and a device for the production of cement clinker from moist agglomerated cement raw material is known. The device has a preheating zone, a deacidification zone and a sintering zone.

DE 102017202824 A1 discloses a plant for the production of cement, in particular cement clinker, with a preheater which has a plurality of cyclones, a calciner for deacidification and a rotary kiln.

In the cement process, the mineral raw material is first ground, then preheated in the preheater, deacidified in the calciner and finally heated in the furnace. The material coming out of the furnace is cooled down in the subsequent cooler.

A common problem is that there is material build-up in the area of the preheater. These material deposits are created in particular by dust, very fine-grained material that is created when the mineral starting material is ground. In order to remove these material deposits, the affected system parts must be cleaned under sometimes dangerous working conditions. To do this, the furnace must be stopped.

A method for drying granulated material is known from EP 3476812 A1.

From EP 0500561 B1 a device for mixing and thermal treatment of solid particles with a substantially horizontally arranged container is known. From DE 1 051 250 a method and a device for mixing powdery or fine-grained masses with liquids are known. DE 2729477 C2 discloses a ploughshare-like mixing tool for such devices famous. A similar mixing tool for such devices is also known from DE 197 06 364 C2. Corresponding mixing devices are offered by the company Gebrüder Lödige Maschinenbau GmbH under the name ploughshare mixer and generate a mechanical fluidized bed inside.

A method for reducing the content of exhaust gases when producing cement clinker is known from WO 2008/074048.

From DE 37 05 037 A1 a system for the production of cement liner by the semi-wet process is known.

From CN 106 630 707 A a method for burning silicate clinker is known.

From CN 106 904 848 A a method for sintering belite at low temperatures is known.

From CN 107 352 819 A a process for the production of calcium fluoroaluminate clinker is known.

The object of the invention is to provide a cement process and a device for this purpose, which enables novel product qualities.

This object is achieved by the method with the features specified in claim 1 and by the device with the features specified in claim 9. Advantageous further developments result from the subclaims, the following description and the drawings.

The device according to the invention for the production of cement clinker has a preheater, a calciner and a cooler as well as a feed for cement raw material. The device is particularly preferably used to carry out the method according to the invention. According to the invention, a mixer, for example and preferably a mechanical fluidized bed reactor, is arranged between the feed for cement raw material and the preheater. Furthermore, in a preferred embodiment, the calciner is connected directly to the cooler. In a further alternative embodiment, the calciner is connected to the cooler via a furnace, in particular a rotary kiln.

The mixer and the preheater are connected to one another via a continuous flow of material. This means that there is in particular no storage between these steps. Storage could have a negative effect on the particle size and thus change the product quality.

By using the mechanical fluidized bed reactor, it has been found that extremely uniform agglomeration of the starting material is achieved. This leads to the fact that, in addition to the excellent, non-sticking passage through the preheater and the calciner, there is also extremely good and above all uniform heating and thus conversion of the starting material. In a preferred embodiment, the calciner is connected directly to the cooler without an intermediate furnace. It has been shown that the starting material has already been converted into cement clinker after it has passed through the calciner. The device is preferred for producing clinker based on dicalcium silicate, in particular clinker based on β-Ca2 [SiO4], also called belite. The advantage over the production of clinker based on alite, in particular, for which an additional furnace is required, is the lower energy requirement, slightly less CO2 emissions, as well as the shorter dwell time and the lower investment, which leads to a cheaper product. This results in savings both in the construction of the system and, above all, in its operation.

While gases are used in a normal fluidized bed reactor to mix a solid with the gas space and thus fluidize and transport it, in a mechanical fluidized bed reactor this is achieved purely mechanically with the help of a mixing tool. It has been shown that the effect of the mechanical fluidized bed reactor is that the very fine particles that arise during grinding agglomerate. This avoids the formation of dust in the following process steps, since particularly small particles in particular can be reduced very significantly. As a result, there is also significantly less material sticking in areas of increasing temperature, for example and in particular on the walls of the preheater.

The preheater can be designed as a direct current preheater. Here, gas and solid are transported in the same direction, while the heat is transferred from the gas to the solid. An example of this are cyclones connected in series. The heat transfer takes place in the connections between the cyclones in cocurrent, the cyclones then serve to separate gas and solids.

Alternatively, the preheater can be designed as a countercurrent preheater. A corresponding preheater is known for example and in particular from DE 383 42 15 A1.

In a further embodiment, a furnace, in particular a rotary kiln, can be arranged between the calciner and the cooler. However, this embodiment does not lead to belite as a product and is therefore only preferred for other products.

In a further embodiment of the invention, the mechanical fluidized bed reactor has an essentially horizontally arranged container. A shaft is arranged centrally along the longitudinal axis of the container, with mixing tools being arranged radially on the shaft. In the simplest case, these mixing tools can be arranged in the form of a rod and vertically on the shaft. The mixing tools are particularly preferably designed in the shape of a ploughshare. Examples of ploughshare-shaped mixing tools can be found in DE 27 29 477 C2 or DE 197 06 364 C2, for example.

In a further embodiment of the invention, the mechanical fluidized bed reactor has at least one fluid supply. Further fluid feeds can also be used, in particular along the transport direction of the material, be arranged. The fluid supply is particularly preferably used to supply water. Water supports the agglomeration and thus leads to more uniform particles. The reduction in the dust content prevents material from sticking in the preheater in a particularly efficient manner.

In a further embodiment of the invention, a fluid feed is arranged upstream of the mechanical fluidized bed reactor. This can be present in addition or as an alternative to a fluid supply in the mechanical fluidized bed reactor.

In a further embodiment of the invention, the mechanical fluidized bed reactor has a fuel feed. Alternatively or additionally, fuel can also be fed in upstream of the mechanical fluidized bed reactor. As a result, the fuel can be incorporated into the particles formed by agglomeration in the mechanical fluidized bed reactor. This fuel ignites in a later process after its ignition temperature is exceeded, for example in the calciner, and thus leads to a much more targeted heating of the raw material.

In a further embodiment of the invention, a first riser tube dryer is arranged between the mechanical fluidized bed reactor and the preheater. The riser dryer has two advantages. On the one hand, in particular water, which is used in the agglomeration in the mechanical fluidized bed reactor, can be expelled. On the other hand, the material can be transported to the entrance height of the preheater. The riser dryer can also be used to adjust the particle size. Particles that are too large can in particular be separated off via the gas velocity and, if necessary, via a separating cyclone or sifter at the upper end of the riser dryer and, in particular, returned to the grinding stage for regrinding or to the ploughshare mixer. It is preferably returned for regrinding in the grinding stage.

In a further embodiment of the invention, the feed for cement raw material has a grinding stage. In a further embodiment of the invention with a riser dryer and a grinding stage, the device has a return for coarse material from the underside of the riser dryer to the grinding stage. In this way, particles which are either not sufficiently finely ground or have agglomerated to form large particles in the mechanical fluidized bed reactor can be removed and returned to the grinding stage or the fluidized bed reactor.

In a further embodiment of the invention, the cooler consists of one to eight cyclones. Cyclones allow the cement clinker to cool down quickly and efficiently. At the same time, the process gas is heated in countercurrent. For example, cooling to below 600 ° C. can also be carried out in the absence of oxygen, for example by means of water-cooled cooling screws.

The preheater and the cooler are preferably constructed from cyclones. As a result, a similar material throughput can be achieved both when the material is heated and when it is cooled, thus realizing a uniform flow of material.

In a further embodiment of the invention, a homogenization stage is arranged between the grinding stage and the feed for cement raw material to the mechanical fluidized bed reactor. The homogenization stage is preferably a mixing silo. In a mixing silo, in particular, the starting materials produced by milling in the milling stage can be made uniform over time. For example, and in particular, several silos can also be used, which are filled one after the other and later emptied together, so that the feed streams from the different silos mix and thereby a more uniformity is achieved.

In a further aspect, the invention relates to the use of a device according to the invention for the production of belite, also dicalcium silicate, C2S or 2 CaO S1O2.

In contrast to alite, or tricalcium silicate, C3S or 3 CaO S1O2, lower firing temperatures, for example of 1300 ° C instead of the conventional 1450 ° C, are sufficient for producing the cement clinker. At the same time, due to the rapid cooling in the device according to the invention, a recrystallize and so does the Formation of Y-Ca2 [Si04] (gamma belite, calcio-olivine) prevented. Thus, the setting of the particles in the size of 200 gm and 5 mm and the associated rapid heating, deacidification and in particular also the rapid cooling, especially at 1000 ° C per minute, is the prerequisite for producing Belit on an industrial scale and with sufficient product quality in particular hydraulic reactivity.

Since other additives, such as iron oxide or aluminum oxide, are usually added as starting materials, no pure alite or belite is usually produced as cement clinker, which is also not desired. For the purposes of the invention, it is understood that belite is proportionately the most frequent phase of the product, that is to say no other phase has a higher proportion in% by mass. For example and preferably, the proportion of belite is at least 50% by mass.

In a further embodiment, the calciner is designed to be solar thermal. This means that the sunlight is focused in such a concentrated manner on the area through which the particles in the calciner flow through the sun, in particular via mirrors, that the necessary temperatures, possibly also ignition of a fuel located in the particles, is reached. This is possible because the particulate form and thus the good flow behavior as well as the short reaction time required make such a construction possible.

In a further aspect, the invention relates to a method for producing cement clinker, the method having the following steps: a) grinding the cement raw material in one grinding stage, b) preheating in a preheater, c) deacidification in a calciner, d) cooling in one Cooler.

The cement raw material goes through these steps in chronological order and is processed into cement clinker. In purely practical terms, these processes usually run parallel to one another in a continuous process, so that each material is in the various process steps, but each material individually goes through the steps sequentially in this order. According to the invention, step d) directly follows step c). The following step is also carried out between step a) and step b): e) Agglomeration of the ground material, so that 90% of all particles have a particle size between 200 μm and 5 mm.

Particles with a diameter of more than 5 mm become too heavy and have poorer properties in the entrained flow. Furthermore, the particles should be heated up quickly during firing, and carbon dioxide in particular must escape from the particles during firing. Both processes are slowed down and made more difficult if the particles become too large. According to the invention, the upper limit of 5 mm has therefore proven to be usable for technical production. Furthermore, a particle that is too large can burst due to the released CO2 and thereby form a great deal of small, dusty material, which is disadvantageous. All these effects further increase the risk that calcium carbonate will not be converted into calcium oxide and thus deteriorate the product quality. In addition, after firing, the product is cooled at a rate of 1000 C per minute in order to achieve optimum quality. This leaves only a few seconds for the heat transfer to cool the product sufficiently quickly. If the particles become larger, the heat transport during cooling is limited and the interior of the particles can no longer be cooled down quickly enough.

Particles or even flour or dust with a size smaller than 200 gm, often even smaller than 100 gm can be heated and cooled very easily, carbon dioxide can escape very well and a homogeneous product property is due to the small distance between the interior of the particles and the environment easier to get to. In return, the flow properties in a calciner are disadvantageous. Small material is swirled more strongly, the flow is therefore more irregular, whereas particles larger than 200 gm (up to 5 mm) have good flow properties, as known from trickling sand. As a result, a uniform flow and a very uniform residence time and thus a very uniform reaction time are achieved. A very homogeneous product can thus be obtained. Another advantage of the particle size between 200 gm and 5 mm is that more fuel can be fed to the process than is required for the process, which creates hotter exhaust gases that are then used for other processes, especially in a network or to generate electricity be able. If the particles were smaller, the amount of material carried away as dust from the exhaust gas with hotter exhaust gases would be comparatively large.

The starting material should advantageously be ground very finely. The finer the materials are ground, the more homogeneous the mixture in the agglomerates is. This is beneficial for the process and product quality.

In a further embodiment of the invention, step e) is carried out in a mechanical fluidized bed reactor. A fluidized bed reactor is particularly well suited to obtain the desired size of the particles between 200 μm and 5 mm. In particular, the particles can be used directly without further processing, possibly with the exception of drying, due to the suitable size distribution. Direct use without further storage also prevents the particle size from increasing unintentionally due to further clumping or from decreasing again due to mechanical stress, for example when sieving.

In a further alternative embodiment of the invention, step e) is carried out with a granulating plate. A combination of a mechanical fluidized bed and a pelletizing plate is also conceivable.

In a further alternative embodiment of the invention, step e) is carried out with a material bed roller mill.

In a further alternative embodiment of the invention, step e) is carried out with a bricket press.

In a further embodiment of the invention, the material is transferred directly or exclusively via drying after agglomeration in step e) for preheating in step b). In particular, there is no storage in which the Particles can continue to agglomerate or change in other ways. Likewise, fractions are preferably not separated, for example by sieving. On the one hand, the selection of a fraction of 200 gm and 5 mm by sieving on an industrial scale is extremely difficult. It is therefore advantageous if the agglomeration already produces the particle size necessary for the freezing of the product.

For the production of cement clinker, it is unusual for the cement clinker obtained to be cooled directly in a calciner immediately after deacidification. Usually, the actual burning of the starting product to the finished cement clinker takes place in a rotary kiln, which is connected to the calciner. This embodiment is preferred if belite is to be produced as the main component of the cement clinker and an oven is not used in the process.

The method is particularly preferably used for the production of cement clinker, the main component of which is belite.

In a further embodiment of the invention, the following step is carried out between step e) and step b): f) drying in a first ascending tube dryer.

In a further embodiment of the invention, the following step is carried out between step c) and step d): g) firing in a furnace

In a further embodiment of the invention, the cement raw material is ground in step a) to sizes smaller than 200 μm, preferably smaller than 50 μm, particularly preferably smaller than 10 μm. Fine grindings of this kind have so far been unusual because these fine particles lead to massive problems in the process, for example due to the formation of dust. On the other hand, such a fine grind enables a much better homogenization and thus leads to a better product quality. This advantage can be used through the subsequent agglomeration in step e) without causing problems in the process. In a further embodiment of the invention, a fluid, in particular water, is added before and / or in step e). This can support the agglomeration in the mechanical fluidized bed reactor.

In a further embodiment of the invention, a fuel, in particular a fuel with an ignition temperature of 500.degree. C. to 650.degree. C., is added before and / or in step e). For example, the fuel is coal, coal dust, cellulose or fluff. The ignition in the temperature range 500 ° C to 650 ° causes local heating in the calciner. This achieves an extremely fast and evident conversion of the raw materials into cement clinker. Preferably, 2% by weight to 15% by weight, particularly preferably 5% by weight to 10% by weight, of fuel are added. This has two advantages. On the one hand, the heat is generated directly in the material, so no heat transfer is necessary, heating is much faster. On the other hand, there is a direct reduction in which carbon is reacted with calcium carbonate to form calcium oxide and carbon monoxide, which further accelerates the deacidification. The carbon monoxide is then further oxidized to carbon dioxide with the release of heat in the air stream. This second effect has another benefit. This creates a reducing atmosphere in the particle which, for example, either reduces iron-containing constituents to iron (II) or prevents oxidation to iron (III). The addition of a fuel to the particles therefore also leads to an optimization of the color.

In a further embodiment of the invention, wet grinding takes place in step a) and subsequent agglomeration in step e) without prior drying.

In a further embodiment of the invention carried out in such a way that the nitrogen content of the gas phase in the preheater is less than 30% by volume, preferably less than 15% by volume, particularly preferably less than 5% by volume. This is preferably achieved by carrying out the combustion with oxygen-enriched air. The advantage is that, due to the significantly reduced amount of gas, a subsequent separation of the carbon dioxide formed from the gas phase is facilitated. This is advantageous with the agglomeration of the starting material, since dusts interfere with the deposition of the carbon dioxide. Dusts are, however, particularly greatly reduced by the method according to the invention. The separation of the carbon dioxide serves to avoid the emission of climate-damaging gases. Another advantage is that by using oxygen-enriched air, the calciner can be operated in particular 50 ° C to 100 ° C hotter. The increased tendency of the material to build up is avoided by using agglomerated material.

The device according to the invention and the method are explained in more detail below with reference to the exemplary embodiments shown in the drawings.

Fig. 1 First device for the production of cement clinker without a furnace. Fig. 2 Second device for the production of cement clinker without a furnace. Fig. 3 Third device for the production of cement clinker with a furnace

In Fig. 1, a first device according to the invention for the production of cement clinker is shown schematically. The starting material is ground in a grinding stage 10. The various starting materials are mixed in a homogenization stage 20 and fed to the mechanical fluidized bed reactor 30. The material is then conveyed in a rising tube dryer 40. From there, the material passes into the preheater 50 and then into the calciner 60. The calciner 60 is heated by means of the burner 80. The finished cement clinker passes from the calciner 60 into the cooler 70. Both the preheater 50 and the cooler 70 are particularly preferably designed as a cascade of 2 to 8 cyclones.

The second device shown in FIG. 2 differs from the first embodiment shown in FIG. 1 only in that, for structural reasons, the cooler 70 is divided into a first partial cooler 72 and a second partial cooler 74, the material between the first partial cooler 72 and the second partial cooler 74 is conveyed by means of a riser pipe 90. In particular, the first partial cooler 72 consists of a cyclone and the second partial cooler 74 consists of one to eight cyclones. A third device with a rotary kiln 100 is shown in FIG. 3. The material reaches the mechanical fluidized bed reactor 30 via a grinding stage 10. Optionally, a homogenization stage 20 can also be arranged in between. After the mechanical fluidized bed reactor 30, the material is dried and raised in a riser dryer 40 and reaches the preheater 50. From the preheater 50, the material passes via a calciner 60 into the rotary kiln 100 and then into the cooler 100.

Reference number 10 grinding stage

20 homogenization stage 30 mechanical fluidized bed reactor 40 riser dryer 50 preheater 60 calciner

70 cooler 72 first partial cooler 74 second partial cooler 80 burner 90 riser pipe

100 rotary kiln

Claims

1. A method for producing cement clinker, the method comprising the following steps: a) grinding the cement raw material in a grinding stage (10), b) preheating in a preheater (50), c) deacidification in a calciner (60), d) Cooling in a cooler (70), characterized in that step d) directly follows step c), the following step being carried out between step a) and step b): e) agglomerating the ground material so that 90% of all Particles have a particle size between 200 gm and 5 mm.

2. The method according to claim 1, characterized in that the agglomeration in step e) of material is carried out in a mechanical fluidized bed reactor (20).

3. The method according to any one of claims 1 to 2, characterized in that the following step is carried out between step e) and step b): f) drying and classifying in a first ascending tube dryer (40).

4. The method according to any one of claims 1 to 3, characterized in that the following step is carried out between step c) and step d): g) firing in a furnace.

5. The method according to any one of claims 1 to 4, characterized in that a fluid, in particular water, is added before and / or in step e).

6. The method according to any one of claims 1 to 5, characterized in that before and / or in step e) a fuel, in particular a fuel with an ignition temperature of 500 ° C to 650 ° C, is added.

7. The method according to claim 6, characterized in that 2 wt .-% to 15 wt .-%, particularly preferably 5 wt .-% to 10 wt .-%, fuel are added.

8. The method according to any one of claims 1 to 7, characterized in that oxygen-enriched air is supplied in step c).

9. Device for the production of cement clinker, the device having a preheater (50), a calciner (60) and a cooler (70), the device having a feed for cement raw material, characterized in that between the feed for cement raw material and the Preheater (50) a mixer is arranged, wherein the calciner (60) is directly connected to the cooler (70).

10. The device according to claim 9, characterized in that a first riser tube dryer (40) is arranged between the mixer and the preheater (50).

11. The device according to claim 10, characterized in that the feed for cement raw material has a grinding stage (10), the device having a return for coarse material from the underside of the first riser dryer (40) to the grinding stage (10).

12. Device according to one of the preceding claims, characterized in that the mixer is a mechanical fluidized bed reactor (30).

13. The device according to claim 12, characterized in that the mechanical fluidized bed reactor (30) has a fluid supply.

14. Device according to one of claims 12 to 13, characterized in that the mechanical fluidized bed reactor (30) has a substantially horizontally arranged container, a shaft being arranged centrally along the longitudinal axis of the container, with mixing tools being arranged radially on the shaft.

15. The device according to claim 14, characterized in that the mixing tools are designed in the shape of a ploughshare.

16. Device according to one of claims 9 to 15, characterized in that a homogenization stage (20) is arranged between the feed for cement raw material and the mechanical fluidized bed reactor (30).

17. Use of a device according to one of claims 9 to 16 for the production of belite.