Patent Publication Number: US-2023150871-A1

Title: Method and device for the production of cement clinker

Description:
The invention relates to a process and to an apparatus for production of cement clinker, wherein a bypass gas is branched off and dedusted. 
     The prior art discloses introduction of oxygenous gas into the rotary furnace or the calciner of a cement production plant for combustion of fuel. For reduction of the amount of offgas and in order to be able to dispense with complex purification methods, DE 10 2018 206 673 A1, for example, discloses using a combustion gas with a maximum oxygen level, such that the CO2 content in the offgas is high. DE 10 2018 206 673 A1 discloses the introducing of an oxygenous gas into the cooler inlet region for preheating of the gas and cooling of the clinker. 
     Especially when substitute fuels are used in the furnace of the cement production plant, cleaning of the furnace offgases in a substream of the offgas in the form of a bypass is necessary in order to separate pollutants out of the bypass gas. The bypass gas recycled into the cement production process frequently has too low an oxygen and CO2 concentration and too high a concentration of further offgas components, for example nitrogen, such that, for example, the formation of nitrogen oxides is favored. 
     Proceeding from this, it is an object of the present invention to provide an apparatus and a process for producing cement clinker, wherein a high CO2 concentration in the offgas and cost-optimized utilization of the oxygen concentration of the process gases within the cement production plant is ensured. 
     This object is achieved in accordance with the invention by an apparatus having the features of independent process claim  1  and by a process having the features of independent apparatus claim  9 . Advantageous developments will be apparent from the dependent claims. 
     In a first aspect, a process for producing cement clinker comprises the following, preferably successive, steps:
         preheating raw meal in a preheater,   calcining the preheated raw meal in a calciner,   burning the preheated and calcined raw meal in a furnace to give cement clinker,   cooling the cement clinker in a cooler,   branching off a portion of the furnace offgases flowing out of the furnace as bypass gas,   cooling the bypass gas in a mixing chamber with a cooling gas, and   separating out dust present in the bypass gas,       

     The cooling gas is formed partly or completely from the bypass gas and/or the calciner offgas and/or the preheater offgas. The calciner offgas is understood to mean the offgas emerging from the calciner. The calciner offgas preferably flows through the preheater. The preheater offgas therefore comprises the calciner offgas or consists, for example, entirely of the calciner offgas. For example, a portion of the preheater offgas is branched off and used as cooling gas. It is likewise conceivable that a portion of the cooling gas is formed from the bypass gas and/or the calciner offgas and, for example, a further portion of the cooling gas is formed from a gas stream that has not been taken from the cement process. This may, for example, be blast furnace offgas. The gas stream preferably has a low concentration of nitrogen, argon and/or other uncondensable gases. The uncondensable gases such as nitrogen and argon preferably comprise a proportion of not more than 20%, preferably less than 5%, in the gas stream. 
     A cement production plant preferably comprises, in flow direction of the material, a preheater, a calciner, a furnace and a cooler. In a cement production plant, the raw meal to be treated is introduced into a preheater and preheated. The preheater comprises a multitude of cyclone stages for separation of the raw meal from the gas stream. The gas stream flowing through the preheater in countercurrent to the raw meal serves to preheat the raw meal before it enters the calciner and the furnace, with formation of the gas stream from the furnace offgas and the calciner offgas. The raw meal preheated in the preheater is passed into the calciner between the last and second-from-last cyclone stage in flow direction of the material and calcined there. Thereafter, the calcined raw meal is guided into the last cyclone stage and thence into the furnace. The furnace offgas flows first through the calciner, then the preheater, and leaves the preheater preferably beyond the first cyclone stage in flow direction of the offgas as preheater offgas. 
     The furnace is preferably a rotary furnace with a rotary tube which is rotatable about its longitudinal axis and is preferably slightly inclined in conveying direction of the material to be burnt, such that the material is moved in conveying direction by virtue of the rotation of the rotary tube and gravity. The furnace preferably has, at one end, a material inlet for introduction of preheated raw meal and, at its opposite end from the material inlet, a material outlet for discharging the burnt clinker into the cooler. At the material outlet end of the furnace is preferably disposed the furnace head that has the burner for burning the material and preferably a fuel inlet for introduction of fuel into the furnace, preferably to the burner. The furnace preferably has a sintering zone in which the material is at least partly melted and especially has a temperature of 1500° C. to 1800° C., preferably 1450° C. to 1700° C. The sintering zone comprises, for example, the furnace head, preferably the last third or the last two thirds of the furnace in conveying direction of the material. 
     The combustion gas is, for example, partly or completely introduced directly into the furnace head, in which case the furnace head has, for example, a combustion gas inlet. The combustion gas is preferably introduced partly or completely into the furnace via the material outlet thereof. 
     The material outlet of the furnace is preferably connected to the cooler for cooling the cement clinker. The cooler preferably has a cooling gas space through which a cooling gas stream for cooling of the bulk material can flow 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 with a second cooling gas stream that follows on in conveying direction of the clinker, and wherein the combustion gas fed to the furnace is formed completely or partly by the first cooling gas stream. 
     The cooler has a conveying device for conveying the bulk material in conveying direction through the cooling gas space. The cooling gas space comprises a first cooling gas space section with a first cooling gas stream and a second cooling gas space section which adjoins the latter in conveying direction of the bulk material and has a second cooling gas stream. The cooling gas space is preferably bounded at the top by a cooling gas space roof and at the bottom by a dynamic and/or static grid, preferably the bulk material lying thereon. The cooling gas space is especially the entire cooler space through which cooling gas flows above the bulk material. The cooling gas stream flows through the dynamic and/or static grid, especially through the conveying device, through the bulk material and into the cooling gas space. The first cooling gas space section is preferably disposed directly beyond the cooler inlet, especially the material outlet from the furnace, in flow direction of the bulk material to be cooled. The clinker preferably falls out of the furnace into the first cooling gas space section. 
     The first cooling space section preferably has a static grid and/or dynamic grid disposed beneath the material outlet from the furnace, such that the clinker exiting from the furnace falls onto the static grid under gravity. The static grid is, for example, a grid set at an angle to the horizontal of 10° to 35°, preferably 12° to 33°, especially 13° to 21°, through which the first cooling gas stream flows from beneath. What flows into the first cooling gas space section is preferably exclusively the first cooling gas stream, which is accelerated, for example, by means of a ventilator. The second cooling gas space section adjoins the first cooling gas space section in conveying direction of the bulk material and is preferably separated for gas purposes from the first cooling gas space section by means of a dividing apparatus. What flows into the second cooling gas space section is preferably exclusively the second cooling gas stream, which is accelerated, for example, by means of a ventilator. 
     The second cooling gas space section preferably has a dynamic grid for conveying of the bulk material through the cooling gas space. The dynamic grid comprises a conveying unit for transport of the material in conveying direction, with the conveying unit having, for example, a ventilated floor through which cooling gas can flow and which has a multitude of flow openings for introduction of cooling gas. The cooling gas is provided, for example, by ventilators disposed beneath the ventilated floor, such that a cooling gas, for example cooling air, flows through the bulk material to be cooled in a transverse flow to the conveying direction. The ventilated floor preferably forms a plane on which the bulk material lies. The conveying unit additionally has a multitude of conveying elements that are movable in conveying direction and counter to conveying direction. The ventilated floor is preferably formed partly or fully by conveying elements which, arranged alongside one another, form a plane for accommodation of the bulk material. 
     The first cooling gas stream flowing through the first cooling gas space section is, for example, pure oxygen or a gas having a proportion of less than 35% by volume, especially less than 21% by volume, preferably 15% by volume or less, of nitrogen and/or argon and/or an oxygen content of more than 20.5%, especially more than 30%, preferably more than 95%. The first cooling gas section preferably directly adjoins the material outlet from the furnace, preferably the furnace head of the furnace, such that the cooling gas is heated in the cooler and then flows into the rotary furnace and is used as combustion gas. The second cooling gas stream is, for example, air. 
     The cooler preferably has a dividing apparatus for separation of the cooling gas sections from one another for gas purposes. 
     For cooling of the bypass gas, the mixing chamber has, for example, a gas inlet for introduction of bypass gas branched off from the furnace offgas or the calciner offgas. In addition, the mixing chamber has a further gas inlet for introduction of cooling gas. The cooling gas and the bypass gas are mixed in the mixing chamber, such that the bypass gas is cooled down, for example, to a temperature of 200-600° C., especially 400° C. to 500° C. It is likewise conceivable to connect a cooling apparatus upstream or downstream of the mixing chamber within the bypass system, such that the bypass gas is cooled down to the aforementioned temperature within the mixing chamber or in a cooling apparatus downstream of the mixing chamber. 
     A cooling gas formed from the bypass gas and/or the preheater offgas offers the advantage that the cooling gas has a high proportion of CO2 and/or a low proportion of uncondensable gases, and, therefore, the bypass gas, even after cooling in the mixing chamber, can be fed to the cement production process, especially to the calciner, without significantly lowering the CO2 content of the offgas or increasing the proportion of uncondensable gases. A high CO2 content in the offgas enables efficient and simple cleaning of the offgas, which is likewise usable in downstream processes, for example the drying of material for grinding. 
     In a first embodiment, the cooling gas is formed partly or completely from a portion of the dedusted and cooled bypass gas, wherein any portion of the bypass gas not fed to the mixing chamber is fed to the calciner, the furnace and/or the cooler. For example, the dedusted bypass gas is fed to the furnace head or to the first cooling gas space section. The dedusted bypass gas is an at least partly dedusted gas stream. Preferably, the cooling gas is formed from a proportion of 0% to 70%, especially 20% to 50%, of the dedusted and cooled bypass gas. The bypass gas is divided, preferably beyond the mixing chamber and the dust separator downstream of the mixing chamber, into a cooling gas stream and a calciner gas stream, wherein the cooling gas stream is preferably cooled and fed to the mixing chamber, and the calciner gas stream is fed to the calciner. The dust separator is, for example, a hot gas filter, an electrostatic filter or a separating cyclone. 
     In a further embodiment, the bypass gas is branched off between the furnace and the calciner or downstream of the calciner. The bypass gas branched off between the furnace and the calciner is preferably at a temperature of 1070° C., with the gas stream branched off downstream of the calciner at a temperature of preferably 920° C. 
     In a further embodiment, the cooling gas is cooled prior to entry into the mixing chamber. On entry into the mixing chamber, the cooling gas is at a temperature, for example, of 100° C. to 200°, especially 100-120° C. The cooler upstream of the mixing chamber, in a further embodiment, is an evaporative cooler or a gas-gas heat exchanger. 
     The cooling gas is introduced into the mixing chamber in a ratio of 2 to 10:1, especially 3 to 8:1, preferably 5:1, relative to the bypass gas. This enables reliable cooling of the bypass gas, such that the separation of dust that follows the mixing chamber is possible. 
     At least a portion of the cooled and dedusted bypass gas, in a further embodiment, is fed to the calciner, the furnace and/or the cooler. For example, the bypass gas, after cooling and the dusting, is fed completely to the calciner, furnace and/or cooler. In this case, the cooling gas is formed, for example, completely from the calciner offgas, especially the preheater offgas. The cooling gas is preferably branched off from the preheater offgas and, for example, cooled in the cooler before it enters the mixing chamber. 
     In a further embodiment, the furnace and the calciner are supplied with a combustion gas having an oxygen content of more than 20.5%, especially more than 30%, preferably more than 95%. The combustion gas consists, for example, entirely of pure oxygen, wherein the oxygen content of the combustion gas is 100%. 
     The invention also encompasses a cement production plant having
         a preheater ( 12 ) for preheating raw meal,   a calciner ( 14 ) for calcining the preheated raw meal,   a furnace ( 16 ) for burning the raw meal to give cement clinker,   a cooler ( 18 ) for cooling the cement clinker, and   a bypass system having
           a bypass conduit which is connected downstream of the furnace in flow direction of the furnace offgas for branching off a portion of the furnace offgases as bypass gas,   a mixing chamber for cooling the bypass gas with a cooling gas, and   a dust separator for separating out dust present in the bypass gas.   
               

     The dust separator and/or the preheater and/or the calciner is/are connected to the mixing chamber for introduction of cooling gas into the mixing chamber. The details and advantages described in relation to the process for producing cement clinker are also applicable to the cement production plant in a corresponding manner for apparatus purposes. The mixing chamber is designed such that the cooling gas is introduced into the mixing chamber in a ratio of 2-10:1 relative to the bypass gas. In particular, the mixing chamber has a control device designed to adjust the volume of cooling gas into the mixing chamber, especially under open-loop and/or closed-loop control. For example, the mixing chamber has a metering device, such as a valve, by means of which the volume of cooling gas is adjustable and which is preferably connected to the control device. 
     The bypass system, in one embodiment, has a branch for branching off a portion of the bypass gas which is downstream of the dust separator and is connected to the mixing chamber for guiding of a portion of the bypass gas and to the calciner, the furnace and/or the cooler for guiding of another portion of the bypass gas. 
     In a further embodiment, the bypass conduit is disposed between the furnace and the calciner or downstream of the calciner. 
     The bypass system, in a further embodiment, has a cooler upstream of the mixing chamber. In a further embodiment, the cooler is an evaporative cooler or a gas-gas heat exchanger. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention is elucidated in detail hereinafter by multiple working examples with reference to the appended figures. 
         FIG.  1    shows a schematic diagram of a cement production plant with a bypass system according to a working example. 
         FIG.  2    shows a schematic diagram of a cement production plant with a bypass system according to a further working example. 
         FIG.  3    shows a schematic diagram of a cement production plant with a bypass system. 
     
    
    
       FIG.  1    shows a cement production plant  10  with a preheater  12  for preheating of raw meal, a calciner  14  for calcining of the raw meal, a furnace  16 , especially a rotary furnace, for burning of the raw meal to give clinker, and a cooler  18  for cooling the clinker burnt in the furnace  16 . 
     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 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 burner 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 for introducing fuel into the riser. The calciner  14  also has a combustion gas inlet for introducing combustion gas into the riser of the calciner  14 . The combustion gas is, for example, 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 last cyclone stage, and leaves the preheater  12  beyond the uppermost cyclone stage as preheater offgas  22 . 
     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 furnace gas outlet  24 , especially material inlet, 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, 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 being heated, for example, in the first third of the rotary tube and burnt, especially sintered, in the downstream region of the rotary tube. The region within the rotary tube in which the raw meal is sintered, especially melted, is referred to 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 in material flow direction, especially the rear two thirds of the rotary tube. 
     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 . 
     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. 
     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. 
     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 furnace offgas consisting essentially of CO2, oxygen and water vapor. 
     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. 
     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. 
     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. 
     The cement production plant  10  of  FIG.  1    additionally has a bypass system  56 . The bypass system  56  comprises a bypass conduit  58  for branching off a portion of the furnace offgases flowing to the calciner as bypass gas. The bypass conduit  58  is connected to the furnace offgas outlet  24 , such that a portion of the offgas discharged from the furnace  24  is guided into the calciner  14  and another portion is guided into the bypass conduit  58 . In addition, the bypass system comprises a cooling device  60  for cooling of the bypass gas with a cooling gas. The cooling device  60  is directly connected to the furnace offgas outlet  24  via the bypass conduit  58 . The cooling device  60  is, for example, a mixing chamber. For example, the cooling device  60  has a cooling gas inlet for introducing cooling gas into the cooling device  60 , and a bypass gas outlet for discharging the cooled bypass gas from the cooling device  60 . The cooled bypass gas leaving the cooling device  60  has, for example, a temperature of 200° C. to 600° C., especially 400-500° C., and is guided into a dust separator  62  downstream of the cooling device  60 . The dust separator has a solids outlet for discharging the separated dust  64 , and a gas outlet for discharging the dedusted and cooled bypass gas. Following on from the dust separator  62  is a fan for accelerating the cooled and dedusted bypass gas. The bypass system  56  additionally has, downstream of the fan, a branch  68  for branching off a portion of the dedusted and cooled bypass gas, which is connected to the calciner  14  and a cooler  70 , such that a portion of the dedusted and cooled bypass gas is guided into the calciner  14  and the other portion into the cooler  70 . The cooler is, for example, an evaporative cooler or a gas-gas heat exchanger. The dedusted and cooled bypass gas fed to the calciner  14  is at a temperature, for example, of 200° C. to 600° C., especially 400-500° C. The cooler  10  is connected to the cooling device  60 , which is in the form of a mixing chamber by way of example. The branched-off, cooled and dedusted bypass gas leaves the cooler  70  as cooling gas  72  and is fed to the cooling device  60  for cooling of the bypass gas branched off from the furnace offgas outlet  24 . The cooling gas  72  is at a temperature, for example, of 100° C. to 200° C., especially 100-120° C. 
     In the working example of  FIG.  1   , the cooling gas for cooling of the bypass gas in the cooling device  60  is formed by the in flow direction of the bypass gas beyond the cooling device  60  and the separator  62  bypass gas, which is additionally cooled further by means of a cooler  70 . Thus, the additional introduction of cooling air into the cooling device  60  is dispensed with, such that the proportion of uncondensable gases in the bypass gas does not rise and, for example, the CO2 content of the bypass gas recycled into the calciner remains constant and high. 
       FIG.  2    shows a further embodiment of the cement production plant  10  that corresponds essentially to the cement production plant shown in  FIG.  1   . Identical elements are given the same reference numerals. By contrast with  FIG.  1   ,  FIG.  2    shows a cement production plant  10  with a bypass conduit  58  connected to the preheater  12 . In particular, the bypass conduit  58 , in flow direction of the furnace offgas, is disposed beyond the lowermost cyclone stage, preferably between the calciner  14  and the second-from-last cyclone stage. The offgas flowing through the preheater at this point is preferably at a temperature of 920° C. It is likewise conceivable to dispose the bypass conduit  58  at another position within the preheater  12 , preferably upstream of the uppermost cyclone stage. 
       FIG.  3    shows a further embodiment of the cement production plant  10 , which corresponds essentially to the cement production plant shown in  FIG.  1   . Identical elements are given the same reference numerals. By contrast with  FIG.  1   ,  FIG.  3    shows a cement production plant  10 , wherein the cooling gas  72  flowing into the cooling device  60  is formed by a from the preheater offgas  22  gas stream. The branch  68 , by contrast with  FIG.  1   , is disposed upstream of the preheater  12  for branching-off of a portion of the preheater offgas  22 . The branched-off preheater offgas is guided into the cooler  70  of the bypass system  56  and preferably cooled to a temperature of 100° C. to 200° C., especially 100 to 120° C. Subsequently, it is introduced into the cooling device  60  designed as a mixing chamber for cooling of the bypass gas branched off from the furnace offgas outlet. 
     Optionally, the cooled and dedusted bypass gas, in  FIGS.  1  to  3   , in addition to being fed to the calciner  14 , is fed partly to the furnace  16  and/or the cooler  18 . For sake of clarity, the corresponding conduits are not shown in  FIGS.  1  to  3   . The cooled and dedusted bypass gas is fed, for example, to the first cooling gas space section  36  and at least partly forms the first cooling gas stream  42 . It is likewise conceivable to feed a portion of the cooled and dedusted bypass gas to the furnace  16 , preferably to the furnace head and/or to the sintering zone  32 . 
     LIST OF REFERENCE NUMERALS 
       10  cement production plant 
       12  preheater 
       14  calciner 
       16  furnace 
       18  cooler 
       20  cyclone 
       22  preheater offgas 
       24  furnace offgas outlet 
       28  furnace burner 
       30  furnace fuel outlet 
       32  sintering zone 
       34  cooling gas space 
       36  first cooling gas space section 
       38  second cooling gas space section 
       40  static grid 
       42  first cooling gas stream 
       44  dynamic grid 
       46  second cooling gas stream 
       48  comminuting device 
       50  dynamic grid 
       52  cold clinker 
       54  cooler output air 
       56  bypass system 
       58  bypass conduit 
       60  mixing chamber 
       62  dust separator 
       64  separated dust 
       66  fan 
       68  branch 
       70  cooler 
       72  cooling gas