METHOD FOR THE PRODUCTION OF CEMENT CLINKER

Abstract

A process for producing cement clinker, may involve preheating raw meal in a preheater, calcining the preheated raw meal in a calciner, and burning the preheated and calcined raw meal in a furnace to give cement clinker. The furnace may be supplied with a combustion gas having an oxygen content, and the temperature within the furnace is ascertained. The process may involve cooling the cement clinker in a cooler. The oxygen supply to the furnace is under closed-loop control as a function of the temperature ascertained within the furnace. The temperature ascertained is compared with a target value and, in the event of any variance of the temperature ascertained from the target value, the oxygen supply to the furnace and/or to the calciner is increased or decreased. The target value is adjusted depending on a particle size distribution and/or a lime standard.

Claims

1.-13. (canceled)

14. A process for producing cement clinker, the process comprising: preheating raw meal in a preheater; calcining in a calciner the raw meal that has been preheated; burning in a furnace the raw meal that has been preheated and calcined to give cement clinker; supplying the furnace with a combustion gas having an oxygen content; ascertaining a temperature within the furnace, wherein the supply of oxygen to the furnace is under closed-loop control as a function of the temperature ascertained within the furnace; cooling the cement clinker in a cooler; comparing the temperature with a target value and increasing or reducing the supply of oxygen to the furnace based on a variance of the temperature from the target value; and adjusting the target value based on a particle size distribution and/or a lime standard.

15. The process of claim 14 wherein the temperature within the furnace is ascertained directly with a temperature measurement device or indirectly by way of process parameters that include at least one of a nitrogen oxide content in the furnace, a power consumption of the furnace, an oxygen content in the furnace, a fuel supply to the furnace, an outside temperature of a furnace wall, or a supply of raw meal to the preheater.

16. The process of claim 14 comprising adjusting the supply of oxygen to the furnace and to the calciner such that there is superstoichiometric combustion in the calciner and the furnace.

17. The process of claim 14 comprising supplying the furnace with a fuel, wherein the supply of fuel to the furnace is under closed-loop control as a function of the temperature ascertained within the furnace.

18. The process of claim 14 wherein the cooler has a cooling gas space through which a cooling gas stream for cooling bulk material flows in crossflow, wherein the cooling gas space comprises a first cooling gas space section with a first cooling gas stream and a second cooling gas space section that adjoins the latter in a conveying direction of the cement clinker and has a second cooling gas stream, wherein the combustion gas supplied to the furnace is formed by the first cooling gas stream, wherein the supply of the combustion gas is under closed-loop control as a function of the temperature ascertained within the furnace.

19. The process of claim 14 comprising introducing the combustion gas into the furnace through combustion gas inlets in the furnace, wherein the supply of the combustion gas to the respective combustion gas inlets is controlled in each case depending on the temperature ascertained within the furnace.

20. The process of claim 14 comprising ascertaining values of an amount of fuel applied to the furnace and the calciner, a proportion of nitrogen oxides in a furnace offgas, a proportion of oxygen in the furnace offgas, and an amount of raw meal applied to the preheater, wherein the oxygen supply to at least one of the furnace or the calciner is under closed-loop control as a function of at least one of the values ascertained.

21. The process of claim 14 wherein ascertaining the temperature within the furnace and/or a temperature at a material inlet to the furnace comprises ascertaining a temperature contactlessly of at least one of a gas phase, an inner wall surface, or the cement clinker within a sintering zone.

22. A cement production plant comprising: a preheater configured to preheat raw meal; a calciner configured to calcine the raw meal that has been preheated; a furnace configured to burn the raw meal to give cement clinker, wherein the furnace includes: a temperature measurement device for ascertaining a temperature within the furnace, and a combustion gas inlet for introducing a combustion gas with an oxygen content into the furnace; a cooler configured to cool the cement clinker; a control device connected to the temperature measurement device and the combustion gas inlet and configured to control the supply of oxygen to the furnace depending on the temperature ascertained within the furnace, wherein the control device is configured to compare the temperature ascertained in the furnace with a target value and increase or decrease the supply of oxygen to at least one of the furnace or the calciner if the temperature that is ascertained varies from the target value, wherein the cement production plant is configured such that the target value is adjusted depending on at least one of a particle size distribution and/or a lime standard.

23. The cement production plant of claim 22 wherein the preheater includes an oxygen measurement device, which is connected to the control device, for ascertaining an oxygen content of a gas flowing through the preheater, wherein the control device is configured to control the oxygen supply to the calciner and the furnace such that stoichiometric combustion is effected in the furnace and the calciner.

24. The cement production plant of claim 22 wherein the preheater includes an oxygen measurement device, which is connected to the control device, for ascertaining an oxygen content of a gas flowing through the preheater, wherein the control device is configured to control the oxygen supply to the calciner and the furnace such that superstoichiometric combustion is effected in the furnace and the calciner.

25. The cement production plant of claim 22 wherein the calciner and the furnace each have means for supplying fuel, respectively, to the furnace and to the calciner, wherein the control device is connected to the means for supplying fuel and configured to control the supply of fuel to the calciner and/or the furnace depending on the temperature ascertained within the furnace.

26. The cement production plant of claim 22 wherein the furnace has combustion gas inlets through which the combustion gas can be introduced into the furnace, wherein the control device is configured to control the supply of combustion gas to each of the respective combustion gas inlets depending on the temperature ascertained within the furnace.

27. The cement production plant of claim 22 wherein the temperature measurement device is configured to perform contactless temperature measurement on the cement clinker within a sintering zone.

28. The cement production plant of claim 22 wherein the temperature measurement device is configured to perform contactless temperature measurement on an inner surface of a furnace wall within a sintering zone.

Description

DESCRIPTION OF THE DRAWINGS

[0056] The invention is elucidated in detail hereinafter by multiple working examples with reference to the appended figures.

[0057] FIG. 1 shows a schematic diagram of a cement production plant with a control device according to one working example.

[0058] FIG. 2 shows a schematic diagram of a cement production plant with a control device according to a further working example.

[0059] FIG. 1 shows a production plant 10 with a single-strand preheater 12 for preheating of raw meal, a calciner 14 for calcining the raw meal, a furnace 16, especially a rotary furnace for combusting the raw meal to clinker, and a cooler 18 for cooling the clinker burnt in the furnace 16.

[0060] The preheater 12 comprises a multitude of cyclones 20 for separation of the raw meal out of the raw meal gas stream. By way of example, the preheater 12 has five cyclones 20 arranged in four cyclone stages one below another. The preheater 12 has a material inlet (not shown) for introduction of the raw meal into the uppermost cyclone stage of the preheater 12 that comprises two cyclones 20. The raw meal flows successively through the cyclones 20 of the cyclone stages in countercurrent to the furnace offgas and/or calciner offgas and is heated as a result. The calciner 14 is disposed between the last and penultimate cyclone stages. The calciner 14 has a riser with at least one combustion site for heating of the raw meal, such that the raw meal is calcined in the calciner 14. In addition, the calciner 14 has a fuel inlet 24 for introducing fuel into the riser. The calciner 14 also has a combustion gas inlet 26 for introducing combustion gas into the riser of the calciner 14. The combustion gas is, for example, air, oxygen-enriched air, pure oxygen or a gas having an oxygen content of at least 85%. The calciner offgas is introduced into the preheater 12, preferably into the penultimate cyclone stage, and leaves the preheater 12 beyond the uppermost cyclone stage as preheater offgas 22.

[0061] Connected downstream of the preheater 12 in flow direction of the raw meal is the furnace 16, such that the raw meal preheated in the preheater 12 and calcined in the calciner 14 flows into the furnace 16. The material inlet 25 of the furnace 16 is connected directly to the riser of the calciner 14, such that the furnace offgas flows into the calciner 14 and subsequently into the preheater 12. The furnace 16 is, by way of example, a rotary furnace having a rotary tube rotatable about its longitudinal axis, arranged at a slightly declining angle. The furnace 12 has a burner 28 and a corresponding fuel inlet 30 at the material outlet end within the rotary tube. The material outlet from the furnace 16 is disposed at the opposite end of the rotary tube from the material inlet 25, such that the raw meal is conveyed within the rotary tube by the rotation of the rotary tube in the direction of the burner 28 and of the material outlet. The raw meal is burnt within the furnace 16 to give cement clinker, with the raw meal essentially undergoing the phases of clinker formation in the rotary tube and being formed in about the last third of the furnace C3S in meal flow direction. This permanently forms, in the last third of the furnace, a layer of hard crust of thickness about 250 mm which, in chemical/mineralogical terms, corresponds to cement clinker. The region of the furnace 16 in which C3S is formed is referred to hereinafter as sintering zone 32. The sintering zone 32 comprises the far region of the rotary tube on the material outlet side, preferably the rear third material flow direction, especially the rear two thirds of the rotary tube. The sintering zone 32 is preferably the region of the furnace 16 in which the temperature is about 1450° C. to 1800° C., preferably 1500° C. to 1700° C.

[0062] Following on from the material outlet of the furnace 16 is the cooler 18 for cooling of the clinker. The cooler 18 has a cooling gas space 34 in which the clinker is cooled by a cooling gas stream. The clinker is conveyed in conveying direction F through the cooling gas space 34. The cooling gas space 34 has a first cooling gas space section 36, and a second cooling gas space section 38 which follows on in conveying direction F from the first cooling gas space section 36. The furnace 16 is connected to the cooler 18 via the material outlet of the furnace 16, such that the clinker burnt in the rotary furnace 20 falls into the cooler 18.

[0063] The first cooling gas space section 36 is disposed beneath the material outlet of the furnace 16, such that the clinker falls from the furnace 16 into the first cooling gas space section 36. The first cooling gas space section 36 constitutes an intake region for the cooler 18 and preferably has a static grid 40 that receives the clinker exiting from the furnace 16. The static grid 40 is especially disposed entirely within the first cooling gas space section 36 of the cooler 10. The clinker preferably falls out of the furnace 16 directly onto the static grid 40. The static grid 40 extends preferably completely at an angle of 10° to 35°, preferably 14° to 33°, especially 21 to 25, to the horizontal, such that the clinker slides along the static grid 40 in conveying direction.

[0064] Following on from the first cooling gas space section 36 is the second cooling gas space section 38 of the cooler 18. In the first cooling gas space section 36 of the cooler 18, the clinker is especially cooled to a temperature of less than 1100° C., the cooling being effected in such a way that liquid phases present in the clinker are fully solidified to solid phases. When it leaves the first cooling gas space section 36 of the cooler 18, the clinker is preferably completely in the solid phase and at a temperature of not more than 1100° C. In the second cooling gas space section 38 of the cooler 18, the clinker is cooled down further, preferably to a temperature of less than 100° C. The second cooling gas stream can preferably be divided into multiple gas substreams having different temperatures.

[0065] The static grid of the first cooling gas space section 36 has, for example, passages through which a cooling gas enters the cooler 18 and the clinker. The cooling gas is generated, for example, by means of at least one ventilator disposed beneath the static grid 40, such that a first cooling gas stream 42 flows from below through the static grid into the first cooling gas space section 36. The first cooling gas stream 42 is, for example, pure oxygen or a gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen. The first cooling gas stream 42 flows through the clinker and then flows into the furnace 16. The first cooling gas stream forms, for example, a portion or the entirety of the combustion gas for the furnace 16. The high proportion of oxygen in the combustion gas leads to a preheater offgas consisting essentially of CO2 and water vapor, and has the advantage that it is possible to dispense with complex downstream purification methods for offgas cleaning. Also achieved is a reduction in the volumes of process gas, such that the plant can have considerably smaller dimensions.

[0066] Within the cooler 18, the clinker to be cooled is moved in conveying direction F. The second cooling gas section 38 preferably has a dynamic, especially movable, grid 44 which follows on from the static grid 40 in conveying direction F. The dynamic grid 44 especially has a conveying unit that transports the clinker in conveying direction F. The conveying unit is, for example, a moving floor conveyor having a multitude of conveying elements for transport of the bulk material. The conveying elements in a moving floor conveyor are a multitude of planks, preferably grid planks, that form a ventilated floor. The conveying elements are disposed alongside one another and are movable in conveying direction F and counter to conveying direction F. It is preferably possible for cooling gas stream to flow through the conveying elements in the form of conveying planks or grid planks, and these are disposed over the entire length of the second cooling gas section 38 of the cooler 18 and form the surface on which the clinker lies. The conveying unit may also be a moving conveyor, in which case the conveying unit has a stationary ventilated floor through which cooling gas stream can flow and a multitude of conveying elements movable relative to the ventilated floor. The conveying elements of the moving conveyor are preferably disposed above the ventilated floor and have entrainers that run transverse to conveying direction. For transport of the clinker along the ventilated floor, the conveying elements are movable in conveying direction F and counter to conveying direction F. The conveying elements of the moving conveyor and of the moving floor conveyor may be movable by the “walking floor principle”, wherein the conveying elements are all moved simultaneously in conveying direction and non-simultaneously counter to conveying direction. Alternatively, other conveying principles from bulk material technology are also conceivable.

[0067] Beneath the dynamic grid 44 are disposed, by way of example, a multitude of ventilators by means of which the second cooling gas stream 46 is blown from below through the dynamic grid 44. The second cooling gas stream 46 is, for example, air.

[0068] Following on from the dynamic grid 44 of the second cooling gas space section 38 in FIG. 1, by way of example, is a comminuting device 48. The comminuting device 48 is, for example, a crusher having at least two crusher rolls that are rotatable in opposing directions and a crusher nip formed between them, in which the comminution of the material takes place. Following on from the comminuting device 48 is a further dynamic grid 50 beneath the comminuting device 48. The cold clinker 52 on departure from the cooler 18 is preferably at a temperature of 100° C. or less.

[0069] For example, cooler output air 54 is removed from the second cooling gas space section 38 and guided into a separator 56, for example a cyclone, for separation of solids. The solids are fed back to the cooler 18 by way of example. Connected downstream of the separator 56 is an air-air heat exchanger 58, such that the cooling output air preheats air within the heat exchanger 58, and this is fed, for example, to a raw mill.

[0070] Within the furnace 16, preferably within the sintering zone 32 of the furnace 16, is disposed a temperature measurement device 60 for ascertaining the temperature of the gas and/or the clinker within the furnace 16. The temperature measurement device 60 is connected to a control device 62, such that the temperature data ascertained are transmitted to the control device 62. The control device 62 is connected to the combustion gas inlet 26 of the calciner 14 for control of the amount of combustion gas that flows into the calciner 14. The control device 62 is preferably designed such that it controls the amount of the first cooling gas stream 42 entering the first cooling gas space section 36 of the cooler 18. The control device 62 is especially designed such that it controls the amount of combustion air into the furnace and/or the amount of combustion air into the calciner, preferably as a function of the temperature ascertained within the furnace 16, especially within the sintering zone 32. In particular, the control device 62 is set up such that it controls the amount of oxygen which is fed to the calciner 14 and/or the furnace 16. The amount of oxygen to the calciner 14 or the furnace 16 is adjusted, for example, via the amount of combustion gas or the oxygen content in the combustion gas. The control device 62 is preferably connected to one ventilator or a multitude of ventilators for acceleration of the combustion gas from the furnace 16 and/or the calciner 14, such that the control device controls the speed of the ventilator, for example.

[0071] It is likewise conceivable that the control device 62 is connected to a respective inlet for introduction of combustion gas into the calciner 14 or the furnace 16, in such a way that it controls the opening size of the respective inlet. It is likewise conceivable that the control device 62 is connected to an oxygen conduit for guiding oxygen into the combustion gas and controls the amount of oxygen flowing into the combustion gas via the conduit. The oxygen is preferably provided either in gaseous or liquid form from a pressure vessel. The gas is guided, for example, from a liquid oxygen source into an evaporator, where it is converted to liquid phase. In the case of gaseous provision either from the evaporator or a gaseous source under pressure, preference is given to generating a supply pressure, such that only a low level of compression/acceleration work has to be generated by a ventilator or compressor. Preferably, the conduit to the respective inlets in the furnace is adjusted by one or more valves. For example, means of measuring the flow of oxygen are provided in the section of pipeline.

[0072] The control device 62 is preferably designed such that it compares the temperature ascertained within the sintering zone 32 of the furnace 16 with a predetermined target value and, in the event of any variance of the temperature ascertained from the target value, increases or reduces the amount of combustion gas, especially the amount of oxygen, that flows into the furnace 16 and/or the calciner 14. For example, the control device 62 is designed such that it increases the amount of combustion gas, especially the amount of oxygen in the combustion gas, in the event that the target value is exceeded by the temperature ascertained. The control device 62 is preferably set up such that it reduces the amount of combustion gas, especially amount of oxygen in the combustion gas, in the event that the temperature ascertained goes below the target value. The inventors have found that an excess amount of combustion gas causes the temperature within the furnace 16 to fall, since the interior of the furnace is cooled by the excess combustion gas which is not converted in the combustion process. In principle, superstoichiometric combustion can be assumed here.

[0073] Such control of the furnace temperature enables the production of a clinker having a desired proportion of alite in a simple manner.

[0074] The predetermined target value for the temperature within the furnace, especially within the sintering zone 32, permits the establishment of a high lime standard in the raw meal, and consequently in the cement clinker, and is thus crucial for the product quality. In spite of a high lime standard of, for example, more than 100-105, the higher sintering zone temperatures than usual can result in complete or virtually complete reaction of belite with calcium oxide to give alite. The resulting cement clinker has a proportion of alite of at least 65%, especially more than 75%, but preferably of 85%, while the proportions of belite and unconverted calcium oxide (free lime) approach zero.

[0075] For a CEM I with 95-100% clinker content according to DIN EN 197-1, even in the case of low cement finenesses of less than 600 m.sup.2/kg according to Blaine, but preferably less than 500 m.sup.2/kg according to Blaine, this results in 2-day initial strengths of well above 30 MPa, especially above 40 MPa, but preferably above 50 MPa, and 28-day standard strengths of well above 50 MPa, especially above 60 MPa, but preferably above 70 MPa.

[0076] Superstoichiometric combustion is established by adjusting the entire oxygen supply to the combustion processes, especially the oxygen supply to the calciner 14 and the oxygen supply to the furnace 16. There is preferably a measurement device for ascertaining the oxygen content in the preheater 12, preferably in the preheater gas, disposed beyond the second cyclone stage in gas flow direction, with the first cyclone stage being the uppermost cyclone stage. The amount of oxygen which is supplied overall to the combustion processes within the calciner 14 and the furnace 16 is controlled as a function of the oxygen content ascertained downstream of the second cyclone stage, the amount of fuel which is supplied to the combustion processes and preferably the amount of raw meal which is introduced into the preheater, such that there is superstoichiometric combustion within the calciner 14 and the furnace 16.

[0077] The total amount of oxygen ascertained is divided between the furnace 16 and the calciner 14 as a function of the temperature ascertained within the furnace 16, especially within the sintering zone 32. The control device 62 is designed such that it divides the amount of oxygen that flows into the furnace 16 and/or the calciner 14 in such a way that the sum total corresponds to the total amount of oxygen needed for superstoichiometric combustion.

[0078] FIG. 2 shows a further working example of a cement production plant, which corresponds for the most part to the working example of FIG. 1, and wherein identical elements are given the same reference numerals. By contrast with the working example of FIG. 1, the temperature measurement device 60 is disposed by way of example in the material inlet 25 of the furnace 16. The temperature measurement device 60 is preferably designed such that it ascertains the temperature of the material entering the furnace 16. The temperature ascertained is transmitted to the control device 62 and serve especially for closed-loop control of the supply of oxygen to the furnace and/or the calciner, as described above with reference to FIG. 1. It is likewise conceivable that the temperature measurement device 60 is designed such that it both ascertains the temperature in the material inlet 25 and the sintering zone 32 of the furnace 16 and transmits it to the control device 62.

[0079] In addition to the temperature in the sintering zone 32 and/or the material inlet 25 of the furnace 16, it is likewise conceivable that further parameters, for example the fuel supply to the calciner 14 and/or the furnace 16, the raw meal supply to the preheater 12 or the proportion of nitrogen oxides in the furnace offgas, the calciner offgas or the preheater offgas, are ascertained and transmitted to the control device 62. The oxygen supply to the furnace 16 and/or the calciner is controlled, for example, as a function of the aforementioned parameters.

[0080] For example, the power consumption of the furnace 16 is additionally ascertained and transmitted to the control device. This gives an indication of the furnace operation and the need for a control intervention. For example, the oxygen supply to the furnace is additionally under closed-loop control as a function of the power consumption of the furnace 16 by the control device 62.

LIST OF REFERENCE NUMERALS

[0081] 10 cement production plant

[0082] 12 preheater

[0083] 14 calciner

[0084] 16 furnace

[0085] 18 cooler

[0086] 20 cyclone

[0087] 22 preheater offgas

[0088] 24 fuel inlet of the calciner

[0089] 25 material inlet into the furnace

[0090] 26 combustion gas inlet of the calciner

[0091] 28 burner of the furnace

[0092] 30 fuel inlet of the furnace

[0093] 32 sintering zone

[0094] 34 cooling gas space

[0095] 36 first cooling gas space section

[0096] 38 second cooling gas space section

[0097] 40 static grid

[0098] 42 first cooling gas stream

[0099] 44 dynamic grid

[0100] 46 second cooling gas stream

[0101] 48 comminution device

[0102] 50 dynamic grid 50

[0103] 52 cold clinker

[0104] 54 cooler output air

[0105] 56 separator

[0106] 58 heat exchanger

[0107] 60 temperature measurement device

[0108] 62 control device