Method and apparatus for producing cement clinker

Abstract

The invention relates to a method for producing cement clinker (50), comprising the steps of preheating raw materials (20) in a preheater (12), calcining the preheated raw materials (26) in a calciner (14), burning the preheated and precalcined raw meal (32) in a kiln (16) to form cement clinker (38), wherein the kiln (16) is supplied with combustion gases (42) having an oxygen content of more than 20% by volume, in particular more than 40% by volume, preferably more than 60% by volume, and cooling the cement clinker (38) in a cooler (18), wherein the cooler (18) has a first cooling zone (18a) and a second cooling zone (18b) in the conveying direction of the cement clinker (38), and wherein the exhaust gases from the first cooling zone (18a) form the combustion gases (42), wherein the exhaust gases (24) from the second cooling zone (18b) are supplied to the calciner (14) and have an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing cement clinker. BACKGROUND

[0002] It is known from the prior art to introduce an oxygen-containing gas for burning fuel into a rotary kiln furnace or calciner of a cement production plant. In order to reduce the amount of exhaust gas and in order to be able to dispense with complex cleaning processes, it is known, for example from DE 10 2018 206 673 A1, to use a combustion gas which is as rich in oxygen as possible, so that the CO2 content in the exhaust gas is high. DE 10 2018 206 673 A1 discloses the introduction of oxygen-rich gas into the cooling inlet region in order to preheat the gas and cool the clinker.

[0003] DE 198 44 038 A1 discloses a method for producing white cement.

[0004] In such operating modes, for example in a calciner, very high temperatures and high solids loads of the gas occur, for example. This leads to material deposition in the calciner, which in the worst case leads to clogging and damage to the inner wall of the calciner. SUMMARY

[0005] Starting from this, it is an object of the present invention to provide a method and a plant for producing cement clinker which overcome the above-mentioned disadvantages and at the same time enable a simple separation of CO2 from the exhaust gas.

[0006] According to the invention, this object is achieved by a method and a cement production plant according to the invention.

[0007] According to a first aspect, a method for producing cement clinker, comprising the following steps:

[0008] preheating raw meal in a preheater,

[0009] calcining the preheated raw meal in a calciner,

[0010] combusting the preheated and precalcined raw meal in a kiln to form cement clinker, wherein the kiln is supplied with a combustion gas having an oxygen content of more than 50% by volume, in particular more than 80% by volume, preferably more than 95% by volume, and

[0011] cooling the cement clinker in a cooler, wherein the cooler has a first cooling zone and a second cooling zone in the conveying direction of the cement clinker, and wherein the exhaust gas from the first cooling zone forms the combustion gas supplied to the kiln.

[0012] The offgas from the second cooling zone is fed to the calciner and has an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume. The offgas from the second cooling zone preferably has a CO2 content of more than 75% by volume. Preferably, the offgas from the second cooling zone is fed completely or partially to the calciner, the amount of offgas fed to the calciner being preferably adjustable.

[0013] The fluid fed to the second cooling zone has an inert fraction of at least 60% by volume, in particular at least 80% by volume, preferably at least 90% by volume. The inert fraction of the fluid consists of water, carbon dioxide or water and carbon dioxide. The fluid fed to the second cooling zone can comprise further components. For example, in order to ensure complete combustion, a residual oxygen content of 1% to 5% by volume is usually present. Furthermore, for example, argon can be present as a further inert gas. Furthermore, nitrogen can also be present as a further inert gas. Nitrogen oxides and / or sulphur oxides can in particular also be present, preferably only in trace amounts.

[0014] In contrast to the prior art, in which air or nitrogen is fed at this point, the use of a fluid having water and / or carbon dioxide as an inert fraction ensures that this gas increases the carrying capacity of the raw materials without introducing any additional gases into the system which would cause damage in the subsequent separation. If the aim is to separate off the carbon dioxide at the end, the purer the preheater offgas, in particular the lower the nitrogen content, the easier this is. Avoiding nitrogen as a carrier gas for the process thus makes the CO2 easier to separate throughout the process.

[0015] The offgas from the second cooling zone is preferably used as a carrier gas in the calciner and ensures an increase in the amount of gas within the calciner and / or the preheater. This prevents the calciner from overheating and reduces the solids load in the calciner gas, so that material deposits within the calciner are avoided.

[0016] The combustion gas fed to the kiln has an oxygen content of, for example, more than 50% by volume, in particular more than 80% by volume, preferably more than 95% by volume. The combustion gas consists, for example, entirely of pure oxygen, wherein the oxygen content of the combustion gas is 100% by volume.

[0017] The oxygen content and the CO2 content are preferably percentages by volume, in particular based on dry gas.

[0018] The kiln is preferably a rotary kiln with a rotary tube which can be rotated about its longitudinal axis and which is preferably slightly inclined in the conveying direction of the material to be combusted, so that the material moves in the conveying direction due to the rotation of the rotary tube and the force of gravity. The kiln preferably has a material inlet at one end for receiving raw material which is preheated and precalcined, and a material outlet at its end opposite the material inlet for discharging the combusted clinker into a cooler. The kiln head is preferably arranged at the material outlet end of the kiln and comprises a burner for combusting the material, and preferably a fuel inlet for receiving fuel into the kiln, preferably into the burner. The kiln preferably has a sintering zone in which the material is at least partially melted, and in particular has a temperature of 1500°C to 1800°C, preferably 1450°C to 1700°C.

[0019] The cooler for cooling cement clinker is preferably adjacent to the material outlet of the kiln. Within the cooler, the cement clinker to be cooled is conveyed in the conveying direction via a conveying device towards the outlet of the cooler. In the conveying direction, the cooler preferably has at least two, preferably three cooling zones. The first cooling zone upstream in the conveying direction is in particular directly adjacent to the kiln and is preferably arranged such that the cement clinker combusted in the kiln preferably falls due to the force of gravity from the material outlet of the kiln into the first cooling zone. The first cooling zone has for example a static or dynamic grid. Preferably, a first cooling gas and a second cooling gas are supplied to the cooler. In particular, the first cooling gas is supplied to the first cooling zone. The first cooling zone in particular has a cooling gas inlet below the static or dynamic grid, through which the first cooling gas is introduced and flows from below through the static or dynamic grid and the cement clinker to be cooled located thereon. The first cooling zone preferably has a waste gas outlet for discharging the first cooling gas, which is connected to the kiln, in particular to the kiln head, so that the waste gas is conducted to the kiln and preferably completely forms the combustion gas of the kiln.

[0020] In particular, a second cooling gas is supplied to the second cooling zone. The second cooling zone preferably has a dynamic grid for conveying the cement clinker to be cooled, in particular a cooling gas inlet is arranged below the dynamic grid, through which the second cooling gas is introduced and flows from below through the dynamic grid and the cement clinker to be cooled located thereon. The second cooling zone preferably has a waste gas outlet for discharging the second cooling gas. The second cooling zone is preferably directly adjacent to the first cooling zone in the conveying direction of the cement clinker and in particular is separated from the first cooling zone in terms of gas, so that the first cooling gas only flows through the first cooling zone and not into the second cooling zone. The second cooling gas preferably only flows through the second cooling zone and not into the first cooling zone. In order to separate the first cooling zone and the second cooling zone in terms of gas, the cooler preferably has a separating device, such as a flap, a curtain or a gas distributor. The separating device is for example a pressure difference between the first cooling zone and the second cooling zone, by means of which the separation of the cooling gases within the cooling zones is achieved.

[0021] In particular, a second cooling gas is supplied to the second cooling zone. The second cooling zone preferably has a dynamic grid for conveying the cement clinker to be cooled, in particular a cooling gas inlet is arranged below the dynamic grid, through which the second cooling gas is introduced and flows from below through the dynamic grid and the cement clinker to be cooled located thereon. The second cooling zone preferably has a waste gas outlet for discharging the second cooling gas. The second cooling zone is preferably directly adjacent to the first cooling zone in the conveying direction of the cement clinker and in particular is separated from the first cooling zone in terms of gas, so that the first cooling gas only flows through the first cooling zone and not into the second cooling zone. The second cooling gas preferably only flows through the second cooling zone and not into the first cooling zone. In order to separate the first cooling zone and the second cooling zone in terms of gas, the cooler preferably has a separating device, such as a flap, a curtain or a gas distributor. The separating device is for example a pressure difference between the first cooling zone and the second cooling zone, by means of which the separation of the cooling gases within the cooling zones is achieved.

[0022] The above-described method results in a lower CO2 partial pressure in the kiln, as a result of which residual calcination of incompletely calcined material is achieved, which only requires a small amount of thermal energy to be consumed. Due to the increased CO2 partial pressure, the CO2 concentration based on the moist exhaust gas is preferably less than 40% by volume, and the effort for cleaning so-called deposits is reduced. Deposits are considered to be a solid phase, which is usually a mineral phase and forms from temperatures above 850°C. The mineral phase can be for example xonotlite or a dicalcium silicate phase. In order to keep the cleaning effort within reasonable limits, the precalcination degree can be reduced by operating the calciner at a precalcination degree of less than 90% by volume or at a lower temperature. Due to the lower CO2 partial pressure, the residual calcination proceeds more quickly in the kiln at the same temperatures as with the above-described method, and for example the calcination of the raw materials can also proceed spontaneously.

[0023] According to a first embodiment, the cooling gas is supplied to the first cooling zone and to the second cooling zone separately, wherein the cooling gas supplied to the second cooling zone has an oxygen content of at most 15% by volume, in particular 10% by volume, preferably 5% by volume. The second cooling gas supplied to the second cooling zone preferably has a CO2 content of at least 75% by volume, in particular at least 80% by volume, preferably at least 90% by volume. Oxygen is preferably supplied to the second cooling gas and / or the exhaust gas from the second cooling zone, such that the oxygen content of the exhaust gas before entering the calciner is at most 15% by volume, in particular 10% by volume, preferably 5% by volume.

[0024] According to a further embodiment, the oxygen concentration of the calciner exhaust gas is determined downstream of the calciner, and the oxygen concentration of the exhaust gas from the second cooling zone supplied to the calciner is adjusted on the basis of the determined oxygen concentration.

[0025] Preferably, the oxygen content of the calciner exhaust gas is determined by means of a measuring device, and the amount and / or the oxygen content of the exhaust gas from the second cooling zone is adjusted, in particular increased or decreased, on the basis of the determined oxygen content. In particular, the volume flow of the exhaust gas from the second cooling zone is kept constant. The determined oxygen content is preferably compared with a predetermined limit value, and in the event of a deviation from this limit value, the amount of exhaust gas from the second cooling zone supplied to the calciner and / or the oxygen content of the exhaust gas is increased or decreased. If the limit value for the oxygen content is exceeded, the amount of exhaust gas from the second cooling zone supplied to the calciner and / or the oxygen content of the exhaust gas is preferably decreased. If the limit value for the oxygen content is undershot, the amount of exhaust gas from the second cooling zone supplied to the calciner and / or the oxygen content of the exhaust gas is preferably increased.

[0026] The exhaust gas from the second cooling zone is fed to the calciner and forms, for example, partly the combustion gas of the calciner. The exhaust gas from the kiln also forms, at least partly or completely, the combustion gas of the calciner. Preferably, a predetermined amount of oxygen is fed to the kiln and the calciner, wherein the respective proportion of oxygen to the kiln and the calciner is preferably adjustable. The oxygen content of the combustion air fed to the kiln is preferably adjusted based on the oxygen content of the exhaust gas from the second cooling zone fed to the calciner. A high oxygen concentration in the combustion gas to the kiln, in particular in the sintering zone of the kiln, improves the combustion kinetics, simplifies the handling of the fuel. Furthermore, the complexity and the operating costs of the kiln burner are reduced. The grinding process, which is optionally connected upstream, is also simplified or requires lower operating costs. It is also conceivable to use a high proportion of alternative fuels. The high oxygen concentration within the kiln ensures a high sintering zone temperature, which results in a clinker with a higher content of tricalcium silicate, which enables a reduction of the clinker content in the cement. For example, the clinker is replaced by materials with a lower CO2 density, such as limestone, fly ash, calcined clay, etc., resulting in a lower CO2 emission of the cement and the subsequent products at the same strength values. The high sintering zone temperature also enables a reduction of the residence time of the solids in the kiln, since the formation of the clinker phase is faster. This enables the kiln to be operated with a higher clinker output.

[0027] According to a further embodiment, at least a part of the exhaust gas from the second cooling zone is fed to the preheater. The amount of exhaust gas from the second cooling zone to the calciner and the preheater is preferably adjustable. In particular, a metering element, such as a valve or a flap, is arranged in the pipeline between the second cooling zone and the preheater or the calciner. The conduction of the exhaust gas at least partly to the preheater enables an optimization of the combustion conditions in the calciner.

[0028] According to a further embodiment, the exhaust gas from the preheater is fed to a conditioning device. The conditioning device is, for example, a filter, a heat exchanger, a gas mixer, a condenser or a jet column. Preferably, the conditioning device is arranged downstream of the preheater in the flow direction of the gas and, in particular, is connected to the second cooling zone or the third cooling zone, so that the exhaust gas from the conditioning device forms the first cooling gas or the second cooling gas. The gas is preferably dehumidified and / or cleaned in the conditioning device.

[0029] According to a further embodiment, after the conditioning device, the gas is fed to the second cooling zone. Preferably, the exhaust gas from the preheater treated by the conditioning device at least partly or completely forms the second cooling gas.

[0030] According to a further embodiment, after the conditioning device, the gas is fed to the third cooling zone. Preferably, the exhaust gas from the preheater treated by the conditioning device at least partly or completely forms the third cooling gas.

[0031] According to another embodiment, the exhaust gas from the third cooling region is fed to the second cooling region. Preferably, water is fed to the third cooling region, whereby the water content of the exhaust gas from the third cooler region is preferably adjusted. The exhaust gas from the third cooling region is preferably dedusted and / or cooled before entering the second cooling region.

[0032] According to another embodiment, water is fed to the second cooling region. The water is preferably fed to the second cooling region via a humidification device. The humidification device preferably comprises a plurality of nozzles for spraying water into the second cooling region. In particular, water is injected into the second cooling region separately from the second cooling gas. Preferably, a water content of more than 10% by volume, in particular more than 20% by volume, preferably more than 30% by volume is set in the second cooling region by the humidification device. Accordingly, a corresponding moisture content is also set in the calciner. This leads to a reduced CO2 partial pressure in the calciner. Water in the exhaust gas, in particular in the preheater exhaust gas, can easily condense out, which increases the CO2 partial pressure in the exhaust gas and thus simplifies the subsequent CO2 separation.

[0033] Preferably, the temperature and / or the volume flow of the exhaust gas from the second cooling region is determined by a measuring device, and the amount of water introduced into the second cooler region via the humidification device is adjusted, in particular increased or decreased, depending on the determined temperature and / or volume flow. In particular, the volume flow of the exhaust gas remains constant. The determined volume flow and / or the determined temperature are preferably compared with a corresponding predetermined limit value, and in the event of a deviation from this limit value, the amount of water into the second cooling region is increased or decreased. If a limit value for the volume flow and / or the temperature is exceeded, the amount of water into the second cooling region is preferably increased. If a limit value for the volume flow and / or the temperature is undershot, the amount of water into the second cooling region is preferably decreased.

[0034] According to another embodiment, the cooling gas fed to the second cooling region has a water content of more than 10% by volume, in particular more than 20% by volume, preferably more than 30% by volume. Preferably, the exhaust gas from the second cooling region has a water content of more than 10% by volume, in particular more than 20% by volume, preferably more than 30% by volume.

[0035] According to another embodiment, the fluid fed to the second cooling region is taken from the preheater exhaust gas. This enables a circulation of the carrier gas, so that no additional gas, in particular no additional nitrogen gas, is fed which then has to be laboriously separated again.

[0036] According to another embodiment, the gas stream of the preheater exhaust gas is split and a substream of the preheater exhaust gas is fed to the second cooling region.

[0037] According to another embodiment, the gas stream of the preheater offgas is dehumidified and at least a part of the water separated in liquid form is fed to the second cooling zone. This feeding is particularly preferably effected by spraying, so that the heat of evaporation is also used for cooling the product.

[0038] According to another embodiment, the gas stream of the preheater offgas is divided and a substream of the preheater offgas is fed to the second cooling zone. The gas stream of the preheater offgas is additionally dehumidified and at least a part of the water separated in liquid form is fed to the second cooling zone.

[0039] The invention also comprises a cement production plant having

[0040] - a preheater for preheating raw meal,

[0041] - a calciner for calcining the preheated raw meal,

[0042] - a kiln for burning the raw meal to form cement clinker, and

[0043] - a cooler for cooling the cement clinker, wherein the cooler has a first cooling zone and a second cooling zone in the conveying direction of the clinker, and wherein the first cooling zone is connected in terms of gas to the kiln, so that offgas from the first cooling zone can be fed to the kiln as combustion gas.

[0044] The second cooling zone is connected in terms of gas to the calciner, so that offgas from the second cooling zone can be fed to the calciner and optionally additionally to the preheater.

[0045] The second cooling zone is connected to the preheater offgas 30, so that a part of the preheater offgas stream is conducted to the second cooling zone. In contrast to the prior art, in which air or nitrogen is fed at this point, the use of preheater offgas ensures that this circulating gas increases the carrying capacity of the raw materials, but does not introduce any additional gas into the system. If the aim is to separate carbon dioxide at the end, the purer the preheater offgas, in particular the lower the nitrogen content, the easier this is. Nitrogen is avoided as a carrier gas for this method, so that CO2 is more easily separated in the overall method.

[0046] The advantages and configurations described with reference to the method of producing cement clinker are also applied in a corresponding manner to the cement production plant in terms of the plant.

[0047] Preferably, the second cooling zone is connected to the calciner via a duct for conducting the gas, in particular extending from a cooling gas outlet of the second cooling zone to a gas inlet of the calciner. The second cooling zone is optionally connected to the preheater via a duct for conducting the gas. The calciner preferably has a riser duct through which the exhaust gas from the kiln and the raw material to be calcined at least partially flow co-currently. Furthermore, the calciner preferably has a combustion chamber or burner connected to the riser duct for combusting fuel within the calciner.

[0048] According to one embodiment, the conditioning device for treating the exhaust gas from the preheater is arranged downstream of the preheater in the direction of the gas flow.

[0049] According to another embodiment, the cooler has a third cooling zone adjoining the second cooling zone, and wherein the conditioning device is connected in terms of gas to the second cooling zone or to the third cooling zone.

[0050] According to another embodiment, the third cooling zone is connected to the second cooling zone for recirculating exhaust gas from the third cooling zone into the second cooling zone.

[0051] According to another embodiment, the cooler has a humidification device for humidifying the cooling gas within the cooler.

[0052] According to another embodiment, the second cooling zone is directly connected in a gas-conducting manner to the preheater exhaust gas. Thus, a subflow of the preheater exhaust gas can be directly guided into the second cooling zone.

[0053] According to another embodiment, the preheater exhaust gas is guided through a dehumidifier. The dehumidifier is connected in a liquid-conducting manner to the second cooling zone. In particular, liquid water separated in the dehumidifier is introduced into the second cooling zone by means of a spraying device. BRIEF DESCRIPTION OF DRAWINGS

[0054] The application is described in more detail below on the basis of a plurality of exemplary embodiments with reference to the drawings.

[0055] Figure 1 A schematic diagram of a cement production plant according to one exemplary embodiment is shown in a flow chart.

[0056] Figure 2 A schematic diagram of a cement production plant according to another exemplary embodiment is shown in a flow chart.

[0057] Figure 3 A schematic diagram of a cement production plant according to one exemplary embodiment is shown in a flow chart.

[0058] Figure 4 A schematic diagram of a cement production plant according to another exemplary embodiment is shown in a flow chart. DETAILED DESCRIPTION

[0059] Figure 1 A cement production plant 10 is shown, which has, for example, a single strand preheater 12 for preheating raw meal, a calciner 14 for calcining raw meal, a kiln 16, in particular a rotary kiln, for burning raw meal to form clinker, and a cooler 18 for cooling clinker burned in the kiln 16.

[0060] The preheater 12 preferably comprises a plurality of cyclones for separating raw meal from a raw meal gas stream. For example, the preheater 12 has five cyclones arranged one above the other in four cyclone stages. The preheater 12 in particular has a material inlet for raw material 20, in particular raw meal, to enter the uppermost cyclone stage of the preheater 12, preferably. The raw material 20 flows continuously through the cyclones of the cyclone stages of the preheater 12 counter-current to the kiln and / or calciner exhaust gas and is thereby heated to obtain hot meal 26. For example, the calciner 14 is arranged between the last cyclone stage and the penultimate cyclone stage. The calciner 14 preferably has a riser tube with at least one combustion location for heating the raw meal 26 heated in the preheater, so that the raw meal is calcined in the calciner 14. Furthermore, the calciner 14 has a fuel inlet for introducing fuel 22 into the riser tube of the calciner 14. The calciner 14 preferably also has a gas inlet for admitting gas, in particular carrier gas 24, into the riser tube of the calciner 14. Calciner exhaust gas 28 is introduced into the preheater 12, preferably into the penultimate cyclone stage, and leaves the preheater 12 downstream of the uppermost cyclone stage as preheater exhaust gas 30.

[0061] Connected downstream of the preheater 12 in the flow direction of the raw meal is the kiln 16, so that raw material 32 preheated in the preheater 12 and calcined in the calciner 14 flows into the kiln 16. The material inlet of the kiln 16 is preferably directly connected to the riser tube of the calciner 14, so that kiln exhaust gas 34 flows into the calciner 14 and subsequently into the preheater 12. The kiln 16 is, for example, a rotary kiln with a rotary tube that can be rotated about its longitudinal axis, which is arranged at a slightly inclined angle. At the material outlet end within the rotary tube, the kiln 16 preferably has a burner and an associated fuel inlet for admitting fuel 36 into the kiln 16. The material outlet of the kiln 16 is arranged at the end of the rotary tube opposite the material inlet, so that the raw material 32 is conveyed within the rotary tube in the direction of the burner and the material outlet by rotation of the rotary tube. The raw material 32 is burned in the kiln 16 to form cement clinker 38. Preferably, the temperature within the kiln 16, in particular the temperature within the sintering zone of the kiln 16, is approximately 1450°C to 1800°C, preferably 1500°C to 1700°C.

[0062] A cooler 18 for cooling the clinker is adjacent to the material outlet of the kiln 16. The clinker is conveyed through the cooler 18 in the conveying direction F. The cooler 18 has a first cooling zone 18a in the conveying direction F of the clinker 38 to be cooled and a second cooling zone 18b adjacent to the first cooling zone 18a in the conveying direction F. Furthermore, the cooler 18 has a third cooling zone 18c adjacent to the second cooling zone 18b in the conveying direction F. The kiln 16 is connected to the cooler 18 via the material outlet of the kiln 16, so that the clinker 38 combusted in the kiln 16 falls into the cooler 18.

[0063] The first cooling zone 18a is preferably arranged below the material outlet of the kiln 16, so that the cement clinker 38 falls from the kiln 16 into the first cooling zone 18a. The first cooling zone 18a constitutes an intake zone of the cooler 18 and preferably has a static grid that receives the clinker 38 leaving the kiln 16. The static grid is in particular arranged completely within the first cooling zone 18a of the cooler 18. Preferably, the clinker falls directly from the kiln 16 onto the static grid. The static grid 40 preferably extends in such a way that the clinker slides along the static grid in the conveying direction F. The first cooling zone 18a has, for example, in addition to or only a dynamic grid for conveying the clinker through the cooler 18 in the conveying direction F.

[0064] The first cooling zone 18a is adjacent to the second cooling zone 18b of the cooler 18, into which the hot clinker 46 cooled in the first cooling zone 18a is fed. In the first cooling zone 18a of the cooler 18, the clinker is in particular cooled to a temperature of less than 1100°C, the cooling taking place in such a way that the liquid phase present in the clinker is completely solidified into a solid phase. When leaving the first cooling zone 18a of the cooler 18, the hot clinker 46 is preferably completely present in the solid phase and has a temperature of at most 1100°C, in particular at most 1000°C. In the second cooling zone 18b of the cooler 18, the hot clinker 48 is further cooled, preferably to a temperature of less than 700°C. In the third cooling zone 18c, the clinker is in particular cooled to a temperature of approximately 100°C or less and leaves the cooler 18 as cold clinker 50. Preferably, the second cooling gas stream can be divided into a plurality of gas substreams having different temperatures.

[0065] The static or dynamic grid of the first cooling zone 18a has, for example, passages through which the first cooling gas 40 enters the first cooling zone 18a. The first cooling gas 40 preferably flows through the static or dynamic grid from below into the first cooling zone 18a. The first cooling gas stream 40 is, for example, pure oxygen or a gas having a nitrogen content of 15% by volume or less and an oxygen content of 50% by volume or more. The first cooling gas 40 flows over the clinker and then into the kiln 16. The first cooling gas 40, in particular the exhaust gas from the first cooling zone 18a, forms, for example, partly or completely, the combustion gas 42 of the kiln 16. The high proportion of oxygen in the combustion gas 42 results in a preheater exhaust gas 30 which consists essentially of CO2and water vapor and has the advantage that complex downstream cleaning methods for exhaust gas cleaning can be omitted. Furthermore, the amount of process gas is reduced, as a result of which the plant can be given a comparatively small size.

[0066] The first cooling zone 18a and the second cooling zone 18b are preferably separated from one another in terms of gas via a separation device, so that the first cooling gas 40 flows only into the first cooling zone 18a and leaves it as exhaust gas 42, in particular as combustion gas 42 for the kiln 16. The first cooling gas 40 preferably does not enter the second cooling zone 18b or the third cooling zone 18c. The second cooling gas 44 preferably flows only into the second cooling zone 18b and leaves it as exhaust gas 24, in particular as combustion gas 24 for the calciner 14. The third cooling gas 52 preferably flows only into the third cooling zone 18c and leaves it as the cooler exhaust gas 54. It is alternatively conceivable that the first cooling zone 18a and the second cooling zone 18b are not separated from one another in terms of gas, which means that the cooling gases 40 and 44 flow into the first cooling zone 18a and the second cooling zone 18b.

[0067] Preferably arranged between the first cooling zone 18a and the second cooling zone 18c and optionally between the second cooling zone 18b and the third cooling zone 18c is a separation device for separating the cooling zones in terms of gas. The separation device is, for example, a mechanical separation device, such as a flap or a curtain. The separation device can also comprise a gas distributor in which a separation gas, such as CO2, is supplied between the cooler sections 18a-18c. The separation device can also be a pressure difference set between the first cooling zone and the second cooling zone. Such a pressure difference leads to a controlled separation of the gases of the cooling zones.

[0068] Within the cooler 18, the clinker to be cooled is moved along a conveying direction F. The second cooling gas region 18b preferably has a dynamic, in particular movable, grid which adjoins the first cooling region 18b along the conveying direction F. The dynamic grid in particular has a conveying unit which conveys the clinker along the conveying direction F. The conveying unit is for example a sliding floor conveyor which has a plurality of conveying elements for conveying bulk material. In the case of a sliding floor conveyor, the conveying elements are a plurality of plates which form a ventilated floor, preferably a grid plate. The conveying elements are arranged next to one another and are movable along and against the conveying direction F. The cooling gas can flow through the conveying elements in the form of conveying plates or grid plates which are arranged over the entire length of the second cooling region 18b of the cooler 18 and form the surface on which the clinker is deposited. The conveying unit can also be a pusher conveyor in which the conveying unit comprises a stationary ventilated floor through which the cooling gas flow is able to flow and a plurality of conveying elements which are movable relative to the ventilated floor. The conveying elements of the pusher conveyor are preferably arranged above the ventilated floor and have entrainment elements which run transversely to the conveying direction. In order to convey the clinker along the ventilated floor, the conveying elements are movable along and against the conveying direction F. The conveying elements of the pusher conveyor and the sliding floor conveyor can be moved in accordance with the "walking floor principle", in which the conveying elements are all moved along the conveying direction simultaneously and against the conveying direction non-simultaneously. As an alternative thereto, other conveying principles used in bulk material technology are also conceivable.

[0069] A plurality of fans are optionally arranged below the dynamic grid through which the second cooling gas 44 is blown through the dynamic grid from below. The second cooling gas 44 is preferably an oxygen-depleted gas which has an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume. The oxygen content is in particular the oxygen in percent by volume based on the dry gas. In particular, the second cooling gas 44 comprises a mixture of CO2 and water. The offgas 24 of the second cooling region 18b is preferably fed completely or partially to the calciner 14 and preferably forms the carrier gas within the calciner 14. The carrier gas 24 introduced into the calciner 14 preferably has an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume. In order to achieve such an oxygen content, the cooling gas preferably has such an oxygen content or the offgas 24 from the second cooling region 18b is enriched with oxygen before it enters the calciner in order to establish an oxygen content of at most 15% by volume in the offgas 24. The carrier gas 24, in particular the offgas from the second cooling region 18b, preferably has a CO2 content of at least 75% by volume based on the dry gas. The carrier gas 24 ensures improved conveying of the solids within the calciner 14 while the gas quantity within the calciner 14 is increased. The low oxygen content and the high CO2 content in the carrier gas enable simple separation of the CO2 in the preheater offgas 30, for example using a cryogenic method.

[0070] The amount of carrier gas 24 conducted into the calciner 14 is preferably adjustable. In particular, the amount of carrier gas 24 and / or the oxygen content in the carrier gas 24 is adjusted. Preferably, the oxygen content of the calciner offgas 28 is determined by a measuring device, and based on the determined oxygen content, the amount of carrier gas and / or the oxygen content in the carrier gas 24 is adjusted, in particular increased or decreased. In particular, the volume flow of the offgas 24 is kept constant. The determined oxygen content is preferably compared to a predetermined limit value, and in the event of a deviation from the limit value, the amount of carrier gas 24 and / or the oxygen content in the carrier gas 24 is increased or decreased. If the limit value for the oxygen content is exceeded, the amount of carrier gas 24 and / or the oxygen content in the carrier gas 24 is preferably reduced. If the limit value for the oxygen content is not sufficient, the amount of carrier gas 24 and / or the oxygen content in the carrier gas 24 is preferably increased.

[0071] The second cooling zone 18b is, for example, adjoined by a third cooling zone 18c, which, for example, has a dynamic grid as described above to transport the hot clinker 48 in the conveying direction F. A third cooling gas 52 is preferably supplied to the third cooling zone 18c and, after cooling the hot clinker 48 in the third cooling zone 18c, is thereby discharged as cooler exhaust gas 52 from the cooler 18. The third cooling gas 52 is, for example, air.

[0072] Figure 2 A cement production plant 10 is shown, which essentially corresponds to the cement production plant 10 shown in Figure 1 . Identical elements have the same reference signs. In contrast to the cement production plant shown in Figure 1 , in the cement production plant shown in Figure 2 , the offgas 24 from the second cooling zone is separated into two gas partial streams, a first gas partial stream 24a being conducted to the calciner 14 as carrier gas, and a second gas partial stream 24 being conducted to the preheater 12. The amount of the gas partial streams based on the offgas 24 can preferably be adjusted. Thus, the amount of gas to the calciner 14 and to the preheater 12 can be adjusted, so that an optimum fuel consumption in the calciner 14 can be achieved.

[0073] Figure 3 A cement production plant 10 is shown, which essentially corresponds to the cement production plant 10 shown in Figure 1 . Identical elements have the same reference signs. In contrast to the cement production plant shown in Figure 1In contrast, the cement production plant 10 has a conditioning device 56 to which the preheater offgas 30 is at least partially fed. The conditioning device 56 is, for example, a filter, a heat exchanger, a gas mixer, a condenser or a spray tower. The conditioning device 56 is preferably configured such that it processes the preheater offgas, in particular cools it, filters dust or coarser particles from the preheater gas and / or increases or reduces the water content of the preheater offgas. The conditioning device 56 is preferably configured such that it processes the preheater offgas such that it has an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume, and preferably comprises a mixture of CO2 and water, in particular has a CO2 content of preferably at least 75% by volume, when leaving the conditioning device 56. The preheater offgas processed in the conditioning device 56 preferably forms the second cooling gas 44 completely or partially and is introduced into the second cooling zone 18b.

[0074] Unlike the cement production plant of Figure 1 , Figure 3 the cement production plant 10 has a humidification device 58 which is configured and arranged to introduce, in particular inject, water into the second cooling zone 18b. Preferably, a water content of more than 10% by volume, in particular more than 20% by volume, preferably more than 30% by volume, is set in the second cooling zone 18b by means of the humidification device 58. Accordingly, a corresponding moisture content is also set in the calciner 14. The calciner offgas 28 and the preheater offgas 30 preferably have a corresponding moisture content. This leads to an increase in the CO2 partial pressure in the offgas, in particular the preheater offgas 30, preferably after condensation of the moisture present in the offgas, for example in a condenser or a gas scrubber, which enables a subsequent separation of CO2 with lower electrical energy consumption.

[0075] Preferably, the temperature and / or the volume flow of the offgas 24 from the second cooling zone 18b is determined by means of a measuring device, and the amount of water introduced into the second cooler zone 18b via the humidification device 58 is adjusted, in particular increased or reduced, depending on the determined temperature and / or volume flow. In particular, the volume flow of the offgas 24 is kept constant. The determined volume flow and / or the determined temperature are preferably compared with a corresponding predetermined limit value, and in the event of a deviation from this limit value, the amount of water introduced into the second cooling zone 18b is increased or reduced. If the limit value for the volume flow and / or the temperature is exceeded, the amount of water introduced into the second cooling zone 18b is preferably increased.

[0076] Preferably, a substream of the preheater offgas 30 is fed to the conditioning device 56, the remaining substream 30 of the preheater offgas being discharged. It is also conceivable that the preheater offgas 30 is completely fed to the conditioning device 56, and that only one substream forms the second cooling gas 44 after the conditioning device 56 and the remaining substream is discharged from the cement production plant 10.

[0077] Figure 4 A cement production plant 10 is shown, which essentially corresponds to the cement production plant 10 shown in Figure 3 . Identical elements have identical reference numerals. In contrast to Figure 3 , in the exemplary embodiment of Figure 4 , the preheater offgas 30 treated by the conditioning device 56 is fed to the third cooling zone 18c and forms, partially or completely, the third cooling gas 52. The offgas 54 from the third cooling zone 18c is preferably fed, completely or partially, to the second cooling zone 18b and forms the second cooling gas 44. The third cooling zone 18c has, for example, a further humidification device 58 which is configured to introduce water into the third cooling zone 18c.

[0078] Preferably, arranged between the second cooling zone 18b and the third cooling zone 18c is a further conditioning device which is not shown in Figure 4 and which is configured to treat the offgas from the third cooling zone 18c such that, upon leaving the conditioning device 56, it has an oxygen content of at most 15% by volume, in particular at most 10% by volume, preferably at most 5% by volume, and preferably comprises a mixture of CO2 and water, in particular having a CO2 content of preferably at least 75% by volume. The preheater offgas treated in the further conditioning device preferably forms, completely or partially, the second cooling gas 44 and is introduced into the second cooling zone 18b. This makes it possible to reduce the amount of offgas from the cooler 18.

[0079] The exemplary embodiment differs from the exemplary embodiment shown in Figure 3 in that an additional dehumidifier 60 dehumidifies the preheater offgas 30, for example, prior to the separation of the carbon dioxide. The water separated in the dehumidifier 60 is fed to the second cooling zone 18b via a fluid flow 62 and in particular sprayed into the latter.

[0080] List of reference signs

[0081] 10 cement production plant

[0082] 12 preheater

[0083] 14 calciner

[0084] 16 kiln

[0085] 18 cooler

[0086] 18a first cooling zone

[0087] 18b second cooling zone

[0088] 18c third cooling zone

[0089] 20 raw material

[0090] 22 fuel

[0091] 24 exhaust gas from second cooling zone / carrier gas to calciner

[0092] 26 hot material / heated raw material

[0093] 28 calciner exhaust gas

[0094] 30 preheater exhaust gas

[0095] 32 calcined raw material

[0096] 34 kiln exhaust gas

[0097] 36 fuel

[0098] 38 hot cement clinker

[0099] 40 first cooling gas

[0100] 42 exhaust gas from first cooling zone / combustion gas to kiln

[0101] 44 second cooling gas

[0102] 46 hot clinker

[0103] 48 hot clinker

[0104] 50 cold clinker

[0105] 52 third cooling gas

[0106] 54 cooler exhaust gas

[0107] 56 conditioning device

[0108] 58 humidification device

[0109] 60 dehumidifier

[0110] 62 fluid flow

[0111] F direction of transport of clinker in cooler 18

Claims

1. A method for producing cement clinker, comprising the steps of: preheating raw materials (20) in a preheater (12), calcining the preheated raw materials (26) in a calciner (14), combusting the preheated and calcined raw materials (32) in a kiln (16) to form cement clinker (38), wherein a combustion gas (42) having an oxygen content of more than 50% by volume is supplied to the kiln (16), and cooling the cement clinker (38) in a cooler (18), wherein the cooler (18) has a first cooling zone (18a) and a second cooling zone (18b) in the conveying direction of the cement clinker (38), and wherein exhaust gas from the first cooling zone (18a) forms the combustion gas (42), characterized in that exhaust gas (24) from the second cooling zone (18b) is supplied to the calciner (14) and has an oxygen content of at most 15% by volume, wherein a fluid supplied to the second cooling zone (18b) has an inert portion of at least 60% by volume, wherein the inert portion of the fluid consists of water, consists of carbon dioxide or consists of water and carbon dioxide.

2. The method of claim 1, wherein, a first cooling gas (40) and a second cooling gas (44) are supplied separately to the first cooling zone (18a) and the second cooling zone (18b), respectively, and wherein the second cooling gas (44) supplied to the second cooling zone (18b) has an oxygen content of at most 15% by volume.

3. The method according to any of the preceding claims 1 - 2, characterized in that, The oxygen concentration of the gas (28) is determined downstream of the calciner (14), and the oxygen concentration of the exhaust gas (24) from the second cooling zone (18b) supplied to the calciner (14) is adjusted based on the determined oxygen concentration.

4. The method according to any of the preceding claims 1 - 2, characterized in that, At least a portion of the exhaust gas (24) from the second cooling zone (18b) is supplied to the preheater (12).

5. The method according to any of the preceding claims 1 - 2, characterized in that, Preheater exhaust gas (30) is supplied to a conditioning device (56) for treatment.

6. The method according to the preceding claim 5, characterized in that, Preheater exhaust gas (30) is supplied to a conditioning device (56) for thermal treatment, humidification and / or cleaning.

7. The method of claim 5, wherein, After the conditioning device (56), the preheater exhaust gas (30) is supplied to the second cooling zone (18b).

8. The method of claim 5, wherein, The cooler (18) has a third cooling zone (18c) adjoining the second cooling zone (18b), and wherein, after the conditioning device (56), the preheater exhaust gas (30) is supplied to the third cooling zone (18c).

9. The method of claim 8, wherein, Exhaust gas (54) from the third cooling zone (18c) is supplied to the second cooling zone (18b).

10. The method according to any of the preceding claims 1 - 2, characterized in that, Water is supplied to the second cooling zone (18b).

11. The method according to any of the preceding claims 1-2, characterized in that, The second cooling gas (44) supplied to the second cooling zone (18b) has a water content of more than 10% by volume.

12. The method according to the preceding claim 11, characterized in that, The second cooling gas (44) supplied to the second cooling zone (18b) has a water content of more than 20% by volume.

13. The method according to the preceding claim 12, characterized in that, The second cooling gas (44) supplied to the second cooling zone (18b) has a water content of more than 30% by volume.

14. The method according to any of the preceding claims 1-2, characterized in that, The kiln (16) is supplied with combustion gas (42) having an oxygen content of more than 80% by volume.

15. The method according to the preceding claim 14, characterized in that, The kiln (16) is supplied with combustion gas (42) having an oxygen content of more than 90% by volume.

16. The method according to any of the preceding claims 1-2, characterized in that, The exhaust gas (24) from the second cooling zone (18b) has an oxygen content of at most 10% by volume.

17. The method according to any of the preceding claims 1-2, characterized in that, The exhaust gas (24) from the second cooling zone (18b) has an oxygen content of at most 5% by volume.

18. The method according to any of the preceding claims 1-2, characterized by, The fluid supplied to the second cooling zone (18b) has an inert fraction of at least 80% by volume.

19. The method according to the preceding claim 18, characterized in that, The fluid supplied to the second cooling zone (18b) has an inert fraction of at least 90% by volume.

20. The method of the immediately preceding claim, wherein, The second cooling gas (44) supplied to the second cooling zone (18b) has an oxygen content of at most 10% by volume.

21. The method according to the preceding claim 20, characterized in that, The second cooling gas (44) supplied to the second cooling zone (18b) has an oxygen content of at most 5% by volume.

22. A cement production plant (10) having - a preheater (12) for preheating raw material (20), - a calciner (14) for calcining preheated raw material (26), - a kiln (16) for burning calcined raw material (32) to form cement clinker (38), and - a cooler (18) for cooling the cement clinker (38), wherein The cooler (18) has a first cooling zone (18a) and a second cooling zone (18b) in the conveying direction (F) of the cement clinker (38), and wherein the first cooling zone (18a) is connected in terms of gas to the kiln (16) such that combustion gas (42) from the first cooling zone (18a) can be supplied as combustion gas to the kiln (16), characterized in that the second cooling zone (18b) is connected in terms of gas to the calciner (14) such that exhaust gas (24) from the second cooling zone (18b) can be supplied to the calciner (14) and has an oxygen content of at most 15% by volume, wherein the second cooling zone (18b) is connected to preheater exhaust gas (30) such that a portion of the preheater exhaust gas (30) is conducted to the second cooling zone (18b).

23. Cement production plant (10) according to claim 22, characterized in that A conditioning device (56) for treating the preheater exhaust gas (30) is arranged downstream of the preheater (12) in the gas flow direction.

24. Cement production plant (10) according to claim 22 or 23, characterized in that The cooler (18) has a third cooling zone (18c) adjoining the second cooling zone (18b), and wherein the conditioning device (56) is connected in terms of gas to the second cooling zone (18b) or to the third cooling zone (18c).

25. Cement production plant (10) according to claim 24, characterized in that The third cooling zone (18c) is connected to the second cooling zone (18b) to recirculate exhaust gas (54) from the third cooling zone (18c) into the second cooling zone (18b).

26. Cement production plant (10) according to any one of claims 22 to 23, characterized in that The cooler (18) has a humidification device (58) for humidifying the cooling gas within the cooler (18).

27. Cement production plant (10) according to any one of claims 22 to 23, characterized in that The second cooling zone (18b) is directly connected in terms of gas conduction to the preheater exhaust gas (30).

28. Cement production plant (10) according to any one of claims 22 to 23, characterized in that The preheater offgas (30) is guided through a dehumidifier (60), wherein the dehumidifier (60) is connected in liquid conducting manner to the second cooling zone (18b).

29. Cement production plant (10) according to any one of claims 22 to 23, characterized in that The offgas (24) from the second cooling zone (18b) has an oxygen content of at most 10% by volume.

30. The cement production plant (10) according to any one of claims 22 to 23, the offgas (24) from the second cooling zone (18b) has an oxygen content of at most 5% by volume.

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