PARALLEL-FLOW REGENERATIVE SHAFT KILN AND METHOD FOR CALCINING CARBONATE ROCK

Abstract

A method for calcining and cooling material such as carbonate rocks may be employed in a parallel-flow regenerative shaft kiln that has two shafts, which are operated alternately as a calcining shaft and as a regenerative shaft. Material flows through a preheating zone, a calcining zone, and a cooling zone to a product outlet. At least one gas flow is compressed by a high-pressure fan and introduced into the parallel-flow regenerative shaft kiln. The high-pressure fan is configured as an axial fan or as a radial fan, having an impeller through which flow takes place axially or radially. A parallel-flow regenerative shaft kiln may also be utilized to perform such methods.

Claims

1.-17. (canceled)

18. A method for calcining and cooling material in a parallel-flow regenerative shaft kiln that has two shafts that are operated alternately as a calcining shaft and as a regenerative shaft, the method comprising: causing the material to flow through a preheating zone, a calcining zone, and a cooling zone to a product outlet; and compressing a gas flow with a high-pressure fan and introducing the gas flow into the parallel-flow regenerative shaft kiln, wherein the high-pressure fan is an axial fan or a radial fan that has an impeller through which flow takes place axially or radially.

19. The method of claim 18 wherein the gas flow comprises: a cooling air flow that is introduced into the cooling zone; a combustion air flow that is introduced into the preheating zone and/or the calcining zone; and/or a fuel gas flow that is introduced into the preheating zone and/or the calcining zone.

20. The method of claim 18 wherein for switchover between the operation of a first shaft as the calcining shaft and as the regenerative shaft, the method comprises: ending feeding of fuel into the first shaft operated as the calcining shaft; reducing a gas quantity to the high-pressure fan with a swirl regulator disposed in the high-pressure fan; closing a shutoff facility between the high-pressure fan and the first shaft so that less of or none of the gas flow compressed by the high-pressure fan enters the first shaft; opening a drain valve disposed downstream of the high-pressure fan to let gas compressed by the high-pressure fan out of a conduit; and feeding fuel into the a second of the two shafts.

21. The method of claim 18 wherein for switchover between the operation of a first shaft as the calcining shaft and as the regenerative shaft, the method comprises: ending feeding of fuel into the first shaft operated as the calcining shaft; reducing a speed of the high-pressure fan by not more than 50% to 65% and/or closing a shutoff facility between the high-pressure fan and the first shaft so that less of or none of the gas flow compressed by the high-pressure fan enters the first shaft; and feeding fuel into a second of the two shafts.

22. The method of claim 21 wherein simultaneously with or following the step whereby less or none of the gas flow compressed by the high-pressure fan enters the first shaft, the method comprises increasing a speed of an off-gas fan for conveying off-gas out of the parallel-flow regenerative shaft kiln.

23. The method of claim 21 wherein following the step whereby less or none of the gas flow compressed by the high-pressure fan enters the first shaft, the method comprises opening an off-gas shutoff facility in an off-gas conduit to conduct off-gases out of the first shaft operated as the calcining shaft.

24. The method of claim 18 comprising discharging calcined material from the parallel-flow regenerative shaft kiln with a discharge system, wherein the discharge system includes the product outlet and, downstream of the product outlet, a buffer store with a second product outlet, wherein the calcined material is discharged continuously from the parallel-flow regenerative shaft kiln during operation of a shaft as the calcining shaft, wherein there is no discharge of calcined material from the parallel-flow regenerative shaft kiln during switchover between the operation of a first shaft as the calcining shaft and the operation of the first shaft as the regenerative shaft.

25. The method of claim 18 comprising ascertaining a pressure within a first shaft of the two shafts, wherein the product outlet for letting calcined material out of the first shaft operated as calcining shaft is opened if the pressure falls below a predetermined limit.

26. A parallel-flow regenerative shaft kiln for calcining and cooling material, comprising: two shafts that are operated alternately as a calcining shaft and as a regenerative shaft, wherein each shaft in a flow direction of material has a preheating zone for preheating material, a calcining zone for calcining material, and a cooling zone for cooling material; and a high-pressure fan that is configured and disposed for compressing a gas stream introduced into the parallel-flow regenerative shaft kiln, wherein the high-pressure fan is configured as an axial fan or as a radial fan and includes an impeller through which flow can take place axially or radially.

27. The parallel-flow regenerative shaft kiln of claim 26 comprising: a combustion air inlet for letting combustion air and/or a fuel gas into the preheating zone and/or the calcining zone; and a cooling air inlet for letting cooling air into the cooling zone, wherein the combustion air inlet and/or the cooling air inlet is connected to the high-pressure fan or, respectively, to high-pressure fans.

28. The parallel-flow regenerative shaft kiln of claim 26 comprising an open-loop/closed-loop controller that is connected to a fuel inlet for letting in fuel gas and is configured to provide for an operating state for switchover between operation of a first shaft of the two shafts as the calcining shaft and operation of the first shaft as the regenerative shaft, wherein the open-loop/closed-loop controller is configured to stop feeding fuel gas through the fuel inlet during the switchover.

29. The parallel-flow regenerative shaft kiln of claim 28 wherein the open-loop/closed-loop controller is connected to the high-pressure fan and is configured to during the switchover reduce a speed of the high-pressure fan by not more than 50% to 65%.

30. The parallel-flow regenerative shaft kiln of claim 28 wherein each of the two shafts has an off-gas outlet for letting off-gases out of the respective shaft, wherein each off-gas outlet is connected to a fan, wherein the open-loop/closed-loop controller is configured to increase a speed of the fan during the switchover.

31. The parallel-flow regenerative shaft kiln of claim 30 wherein each off-gas outlet is connected via an off-gas conduit to the fan, wherein at least one off-gas shutoff facility is disposed in the off-gas conduit and is connected to the open-loop/closed-loop controller, wherein the open-loop/closed-loop controller is configured such that during the switchover the open-loop/closed-loop controller opens the off-gas shutoff facility following the increase of the speed of the fan.

32. The parallel-flow regenerative shaft kiln of claim 28 wherein each shaft of the two shafts has a product outlet for letting calcined material out of the respective shaft and has a pressure-measuring facility for ascertaining a pressure within the respective shaft, wherein the open-loop/closed-loop controller is connected to the product outlet and to the pressure-measuring facility of each shaft and is configured to open the respective product outlet if the pressure falls below a predetermined limit.

33. The parallel-flow regenerative shaft kiln of claim 26 wherein each shaft has a discharge system with a first product outlet for letting calcined material out of the respective shaft, a buffer store downstream of the first product outlet, and a second product outlet.

34. The parallel-flow regenerative shaft kiln of claim 28 wherein the high-pressure fan is a first high-pressure fan, the parallel-flow regenerative shaft kiln comprising a second high-pressure fan, wherein each high-pressure fan is assigned a shutoff facility that in a closed position prevents a flow of gas from the respective high-pressure fan into the shaft, wherein the open-loop/closed-loop controller is connected to the shutoff facility and is configured to move the shutoff facility into the closed position during the switchover.

Description

DESCRIPTION OF THE DRAWINGS

[0068] The invention is elucidated in more detail below by means of a number of exemplary embodiments with reference to the appended figures.

[0069] FIG. 1 shows a schematic representation of a PFR shaft kiln in a sectional view according to one exemplary embodiment.

[0070] FIG. 1a shows a schematic representation of the detail A of FIG. 1 according to one exemplary embodiment.

[0071] FIG. 2 shows a schematic representation of a PFR shaft kiln in sectional view according to a further exemplary embodiment.

[0072] FIG. 1 shows a PFR shaft kiln 10 having two parallel and vertically oriented shafts 12. The shafts 12 of the PFR shaft kiln 10 are substantially identical in construction, and accordingly in FIG. 1 only one of the two shafts 12 is provided with reference symbols and, for the sake of simplicity, only one of the two shafts is described hereinafter. Each shaft 12 has a respective materials inlet 14 for letting material for calcining into the respective shaft 12 of the PFR shaft kiln. The material for calcining is more particularly limestone. The materials inlets 14 are disposed, illustratively, at the upper end of the respective shaft 12, and so the material falls through the materials inlet 14 by gravity into the shaft 12.

[0073] Each shaft 12 at its upper end also has a combustion air inlet 16 for letting combustion air or fuel gas in. The combustion air is, for example, air, oxygen-enriched air or pure oxygen. The fuel gas is, for example, blast-furnace gas or another fuel gas having a calorific value of less than 6.6 MJ/Nm.sup.3. Furthermore, each shaft 12 has an off-gas outlet 18 for letting kiln off-gases out of the respective shaft 12.

[0074] At the lower end of each shaft 12 there is a product outlet 20 for letting out the material calcined in the respective shaft 12. The product outlet 20 comprises, for example, flaps, which can be opened and closed automatically in particular. The calcined material is conducted for example into a bunker 22 which follows on from the product outlets 20 of the shafts 12. The bunker 22 is configured illustratively in the form of a hopper and has, illustratively, a bunker outlet 24 for letting the material out of the bunker 22. The bunker, furthermore, has an outgoing-air outlet 23 for letting outgoing air out of the bunker 22. The outgoing-air outlet 23 is followed by an outgoing-air filter 25 and a low-pressure fan 27 for dedusting the off-gas.

[0075] Each shaft 12 at its lower end has a cooling air inlet 26 for letting cooling air into the respective shaft 12. In the operation of the PFR shaft kiln 10, the material for calcining flows from top to bottom through the respective shaft 12, with the cooling air flowing through the respective shaft 12 from bottom to top, in countercurrent flow to the material. The kiln off-gas is removed from the shaft 12 through the off-gas outlet 18.

[0076] The materials inlet 14 and the combustion air inlet 16 are followed below them, in the flow direction of the material, by the preheating zone 28 of the respective shaft 12. In the preheating zone 28, the material and the combustion air or, optionally, the material and the fuel gas are preheated preferably to about 700° C. The respective shaft 12 is preferably filled with material for calcining up to the upper boundary face 30 of the preheating zone 28. The material and optionally the fuel, more particularly the fuel gas, are charged into the respective shaft 12 preferably above the preheating zone 28. At least part of the preheating zone 28, and the part of the respective shaft 12 that follows it in the flow direction of the material, are surrounded, for example with a refractory lining.

[0077] Disposed optionally in the preheating zone 28 are a plurality of burner lances 32, serving in each case as an inlet for fuel, such as a fuel gas, oil or ground solid fuel, for example. The PFR shaft kiln 10 preferably has a cooling facility 33 for cooling the burner lances. The cooling facility comprises a plurality of cooling-air circuit lines 35, which extend annularly around the shaft region in which the burner lances 32 are disposed. Cooling air for cooling the burner lances 32 flows through the cooling-air circuit lines 35.

[0078] In each shaft 12 there are preferably a plurality of—for example, twelve—burner lances 32, which are disposed at substantially uniform distances from one another. The burner lances 32 have an L shape, for example, and extend preferably in the horizontal direction into the respective shaft 12 and in a vertical direction within the shaft 12, more particularly in the flow direction of the material. The ends of the burner lances 32 of one shaft 12 are preferably all disposed at the same height level. The plane on which the ends of the lances 32 are disposed is preferably in each case the lower boundary face 34 of the respective preheating zone 32, 34. Alternatively or additionally to the burner lances 32, slits in the shaft wall may also form inlets for letting combustion air into the shaft.

[0079] The preheating zone 28 is followed in the flow direction of the material by the calcining zone 36. In the calcining zone 36, the fuel is burned and the preheated material is calcined at a temperature of about 1000° C. The PFR shaft kiln 10 additionally has an overflow duct 38 for providing a gas connection between the two shafts 12. FIGS. 1 and 2 show, illustratively, a PFR lime kiln having round shaft cross sections. The shaft cross section may, however, have a different geometrical contour. Depending on the cross-sectional shape used for the shafts, there are gas collector ducts 50 which are connected to the overflow duct 38. Also possible are shaft cross sections for which there is no need for the additional gas collector ducts 50. Disposed at the upper height level of the overflow duct 38, preferably, is the lower boundary face 40 of the calcining zone 36, more particularly the end of the calcining zone 36. The calcining zone 36 is followed in the flow direction of the material in each shaft 12 by a cooling zone 42, which extends down to the product outlet 20 or to the discharge facility of the respective shaft. The material is cooled within the cooling zone 42 to about 100° C.

[0080] At the product outlet end of each shaft 12 there is preferably a discharge facility 44 disposed. The discharge facilities 44 comprise, for example, horizontal plates, preferably a discharge table 46, which allow the material to pass through laterally between the discharge table 46 and the housing wall of the PFR shaft kiln. The discharge facility 44 is implemented preferably as a push table or rotary table or as a table with push-type scraper means. This enables a uniform throughput rate of the calcination material through the shafts 12. The discharge facility 44 further comprises, illustratively, a discharge hopper 48, which follows the discharge table and has the product outlet 20 mounted on its lower end.

[0081] In the operation of the PFR shaft kiln 10, one of the shafts 12 is active in each case, with the respective other shaft 12 being passive. The active shaft 12 is referred to as the calcining shaft, and the passive shaft 12 as the regenerative shaft. The PFR shaft kiln 10 is operated cyclically; a typical number of cycles is, for example, 75 to 150 cycles per day. After the cycle time has expired, the function of the shafts 12 is swapped. This procedure is repeated continuously.

[0082] Material such as limestone or dolomite rock is charged into the shafts 12 in alternation via the materials inlets 14. In the shaft 12 operated as calcining shaft, a fuel or an oxidizing gas such as, for example, air, oxygen-enriched air or pure oxygen is introduced into the calcining shaft via the burner lances 32. The material for calcining is heated in the preheating zone 28 of the calcining shaft to a temperature of about 700° C.

[0083] The PFR shaft kiln 10 has, for example, a round, oval, rectangular or polygonal cross section. Furthermore, the PFR shaft kiln 10 optionally has a gas collector duct 50 in the form of an annular space. The gas collector duct 50 extends preferably circumferentially around the lower region of the calcining zone 36, more particularly below the burner lances 32. Each shaft 12 may have a respective gas collector duct 50, with the gas collector ducts 50 being disposed at the height level of the overflow duct 38 for connection of the two shafts 12. The gas collector ducts 50 of the two shafts 12 have a gas connection to one another by way in particular of the overflow duct 38. In particular, the gas collector duct 50 has a gas connection to the cooling zone 42, and so the cooling gas flows at least partly into the gas collector duct 50.

[0084] This construction leads advantageously to a more uniform distribution of gas and of temperature in the shafts 12 and hence to better product quality and lower pollutant emissions. Another advantage of this construction is that any unburned fuel gases which flow out of the preheating zone 28 into the overflow channel 38, together with the cooling air fed to the calcining shaft, undergo afterburning there more effectively, because the gas duct volume is substantially greater.

[0085] The PFR shaft kiln further comprises, preferably, a cooling facility 51 for cooling the shaft region which includes the calcining zone 36. In particular, the region of the calcining zone 36 that projects into the cooling zone 42 is cooled by means of the cooling facility 51. The cooling facility 51 preferably comprises a plurality of circuit lines 52, which extend externally around the calcining zone of the shaft 12 and through which cooling air flows. Illustratively, the circuit lines 52 are mounted only around the lower region—the region adjacent to the cooling zone 42—of the calcining zone 36.

[0086] The combustion air inlet 16, the cooling air inlet 26, the burner lances 32, and the cooling-air circuit lines 35, 52 are each connected via conduits to a fan 55a,b, more particularly a high-pressure fan 54a-c. The high-pressure fans 54a-c serve to compress the respective process gases and are preferably configured in such a way that they each generate a pressure of about 300 mbar to 500 mbar, more particularly about 400 mbar. Each fan 55a-c, and each high-pressure fan 54a-c, is preferably assigned a shutoff facility 57a-e. The shutoff facility is, for example, a flap or a valve and is preferably configured in such a way that in a closed position it prevents a flow of gas from the respective fan 54a-c, 55a-c, more particularly from the high-pressure fan 54a-c, into the shaft 12. The combustion air conduit 62 and the cooling air conduits 56, 60, 68 preferably each have a shutoff facility 57a-e which is downstream of the respective fan 54a-c, 55a-c. In the closed position of the shutoff facility 57, there is preferably no possibility of a flow of gas from the respective conduit 56, 60, 62, 68 into the surroundings.

[0087] The cooling air inlet 26, for letting cooling air into the cooling zone 42, is connected more particularly to a high-pressure fan 54a via a cooling air conduit 56. The cooling air conduit 56 comprises a depressurization facility 58, such as a valve or a flap, for example, which can be brought, preferably steplessly, from an open position, in which cooling air flows from the cooling air conduit 56 into the surroundings, into a closed position, in which no cooling air emerges from the cooling air conduit 56.

[0088] The cooling facility 51 for cooling the shaft region which includes the calcining zone is connected, preferably via a cooling air conduit 60, to a fan 55a and optionally to a further fan 55b. The fans 55a, b are configured for example as medium-pressure or high-pressure fans, and so they generate in particular a pressure of about 50 mbar to 150 mbar, preferably 80 mbar to 120 mbar, more particularly 100 mbar.

[0089] The combustion air inlet 16, for letting combustion air into the preheating zone 28, is connected more particularly to a high-pressure fan 54b via a combustion air conduit 62. The combustion air conduit 62 comprises a depressurization facility 64, such as a valve or a flap, for example, which can be brought preferably steplessly from an open position, in which combustion air flows from the combustion air conduit 62 into the surroundings, into a closed position, in which no combustion air emerges from the combustion air conduit 62. Combustion air conduit 62 further preferably comprises a distributor facility 66, such as, for example, a gas diverter or a flap for conducting the combustion air to the respective shaft 12 operated as calcining shaft. The configuration of the distributor facility 66 is preferably such that it can be operated in at least two position: in a first position, combustion air is able to flow exclusively into the combustion air inlet 16 of the first shaft 12, and, in a second position, combustion air is able to flow exclusively into the combustion air inlet 16 of the second shaft 12.

[0090] The cooling facility 33 for cooling the burner lances 32, more particularly the cooling-air circuit line 35, is connected preferably via a cooling air conduit 68 to a high-pressure fan 54c.

[0091] The off-gas outlet 18 for letting the kiln off-gases out of the PFR shaft kiln is connected to a fan 55c preferably via an off-gas conduit 70. The fan 55c is configured, for example, for medium pressure, and so it generates in particular a pressure of about 20 mbar to 60 mbar, preferably 25 mbar to 50 mbar, more particularly 35 mbar. Furthermore, the off-gas outlet 18 is connected preferably to an off-gas filter 72 disposed upstream of the fan 55c. The off-gas conduit 70 additionally has, illustratively, two off-gas shutoff facilities 71, more particularly valves or flaps. In the flow direction of the off-gas, downstream of each off-gas outlet 18, there is preferably a respective off-gas shutoff facility 71 disposed, and so each off-gas outlet is preferably assigned an off-gas shutoff facility 71. The off-gas shutoff facility 71 can be moved between a closed position, in which no off-gas can flow from the shaft 12 through the off-gas conduit 70, and an open position, in which off-gas can flow through the off-gas conduit 70.

[0092] Optionally it is conceivable to charge the fuel, more particularly the fuel gas, into the calcining shaft of the PFR shaft kiln 10 by way of the combustion air inlet 16. In this embodiment of the PFR shaft kiln, the fuel gas is more particularly blast-furnace gas, having for example a calorific value of less than 6.6 MJ/Nm.sup.3. The fuel gas 63, more particularly the blast-furnace gas, is introduced in this embodiment into the combustion air conduit 62, and the combustion air is guided in particular through the burner lances into the shaft 12. The combustion air is, for example, oxygen-containing air, more particularly oxygen-enriched air, or a gas having an oxygen fraction of about 80%, or virtually pure oxygen.

[0093] This method reduces the quantities of gas which flow through the calcining zone 36 and through the preheating zone 28 of the regenerative shaft considerably; the gases flowing through the preheating zone 28 of the regenerative shaft contain no excess heat and preferably have an off-gas temperature of around 100° C. Owing to the smaller quantities of gas there is a considerable reduction in the pressure loss of the kiln as a whole, leading to a considerable saving in terms of electrical energy at the process gas compressors.

[0094] FIG. 1a shows the detail A marked in FIG. 1. The detail A shows, illustratively, the high-pressure fan 54a; the connection system represented can be employed for all other high-pressure fans 54a-c. Upstream of the high-pressure fan 54a in the flow direction of the gas is a flow rate-measuring facility 47 for ascertaining the quantity of gas, more particularly air, that flows per unit time through the conduit into the high-pressure fan 54a. The high-pressure fan 54a has a swirl regulator 53 which is configured to regulate the swirl of the flow of gas and is disposed at the gas inlet of the high-pressure fan 54a. The swirl regulator 53 comprises, for example, a plurality of guide vanes through which the gas flow flows. The work angles of the guide vanes are preferably adjustable, and so the swirl of the flow of gas entering the high-pressure fan 54a can be adjusted by means of a change to the work angle of the guide vanes.

[0095] FIG. 1a additionally shows a pressure-measuring facility 45 which is disposed downstream of the high-pressure fan 54a and is configured for determining the pressure within the conduit downstream of the high-pressure fan 54a. Mounted downstream of the high-pressure fan 54a, illustratively, is a drain valve 49, which in an open position enables a flow of gas from the conduit, for example, into the surroundings, and in a closed position does not allow any flow of gas from the conduit. The drain valve 49 is disposed, illustratively, upstream of the pressure-measuring facility. Downstream of the pressure-measuring facility 45 in the flow direction of the gas there is a shutoff facility 57a disposed, which has already been described above.

[0096] FIG. 2 represents a further embodiment of the PFR shaft kiln, which corresponds substantially to the PFR shaft kiln 10 of FIG. 1, with the difference that the calcined material is discharged in stages. The PFR shaft kiln 10 of FIG. 2 has a discharge system 73 which includes a product outlet 20, as described with reference to FIG. 1. In addition, the product outlet 20 is followed, and the bunker 22 preceded, by a buffer store 74 having a further product outlet 76 for letting the material out of the buffer store 74 into the bunker 22. The product outlet 76 is identical in configuration, for example, to the above-described product outlet 20. The materials discharge system 75 of FIG. 2 enables the discharge of material from the PFR shaft kiln 10 while a positive pressure is prevailing in the calcining shaft. As a result there is no need for a complete reduction of pressure in the switchover procedure wherein the function of the calcining shaft and of the regenerative shaft is swapped.

[0097] The PFR shaft kiln 10 of FIGS. 1 and 2 preferably also has an open-loop/closed-loop controller 78, which is connected preferably to the high-pressure fans 54a-c and the fans 55a-c for the open-loop/closed-loop control of the speed. The open-loop/closed-loop controller 78 is preferably further connected to a pressure-measuring facility, not represented in the figures, and so the pressure-measuring facility disposed in the shaft 12 transmits the ascertained pressure within the shaft 12 to the open-loop/closed-loop controller 78. The open-loop/closed-loop controller 78 is connected, furthermore, in particular to at least one or all of the shutoff facilities 57a-e, which accordingly can be opened and closed by means of the open-loop/closed-loop controller 78. The open-loop/closed-loop controller 78 is connected preferably to the product outlet 20, 76 in such a way that said outlet opens or closes depending, for example, on the pressure ascertained within the shaft 12, more particularly within the calcining shaft.

[0098] In the operation of the PFR shaft kiln 10 represented in FIGS. 1 and 2, for the switchover between the operation of a shaft 12 as calcining shaft and the operation of the shaft 12 as regenerative shaft, at least the following method steps are carried out: [0099] a. ending the feeding of fuel into the shaft 12 operated as calcining shaft, [0100] b. reducing the speed of the high-pressure fan 54a-c by not more than 50% to 65%, and/or closing a shutoff facility 57a-e between the high-pressure fan 54a-c and the shaft 12, and so no gas flow compressed by means of the respective high-pressure fan enters the shaft 12, and [0101] c. when a residual positive pressure of, for example, less than 200 mbar has been reached, opening the off-gas shutoff facility 71 on the kiln shaft which has just been the calcining shaft, in order to drain off the residual positive pressure in the kiln in the direction of the off-gas filter, and [0102] d. opening and closing the product outlet 20 to let material out of the kiln, and subsequently [0103] e. changing over the distributor facility 66 in order to feed the oxidizing gas or the fuel gas to the shaft which is subsequently operated as calcining shaft, and [0104] f. closing the off-gas shutoff facility 71 on the kiln shaft which is operated subsequently as the calcining shaft, and subsequently [0105] g. opening the shutoff facilities 57a-e between the high-pressure fans and the kiln and increasing the speed of the high-pressure fans 54a-c, so that the gases required for combustion and cooling are again available in the correct quantity, and subsequently [0106] h. engaging the fuel on the calcining shaft 12.

[0107] The open-loop/closed-loop controller 78 is preferably configured to provide open-loop/closed-loop control of the method steps described above.

[0108] In the case of a connection system of the high-pressure fans 57a-c as represented in FIG. 1a, the following steps preferably take place: [0109] a. ending the feeding of fuel into the shaft 12 operated as calcining shaft, [0110] b. reducing the quantity of gas to the high-pressure fan 54a-c by means of the swirl regulator 53 of the respective high-pressure fan 54a-c, [0111] c. closing a shutoff facility 57a-e between the high-pressure fan 54a-c and the shaft 12, so that there is no gas flow compressed by means of the respective high-pressure fan 54a-c into the shaft 12, [0112] d. opening the drain valve 49 to let the gas compressed by means of the high-pressure fan 54a-c out of the conduit, [0113] c. when a residual positive pressure within the kiln shaft of, for example, less than 200 mbar has been reached, opening the off-gas shutoff facility 71 on the kiln shaft which has just been the calcining shaft, in order to drain off the residual positive pressure in the kiln in the direction of the off-gas filter, and [0114] d. opening and closing the product outlet 20 to let material out of the kiln, and subsequently [0115] e. changing over the distributor facility 66 in order to feed the oxidizing gas or the fuel gas to the shaft which is subsequently operated as calcining shaft, and [0116] f. closing the off-gas shutoff facility 71 on the kiln shaft which is operated subsequently as the calcining shaft, and subsequently [0117] g. opening the shutoff facilities 57a-e between the high-pressure fans and the kiln and also increasing the quantity of gas to the high-pressure fan 54a-c by means of the swirl regulator 53 of the respective high-pressure fan 54a-c, so that the gases needed for combustion and cooling are available again in the amount necessary for operation of the kiln, and subsequently [0118] h. engaging the fuel on the calcining shaft 12.

[0119] In step b the quantity of gas is reduced by—for example—at least 50% to 65%. The quantity of gas is reduced by means of the swirl regulator 53, more particularly by way of a change to the work angles of the guide vanes of the swirl regulator 53. During the switchover procedure, the speed of the high-pressure fan 54a-c is preferably kept substantially constant or is reduced only slightly, more particularly by not more than 10% to 30%.

[0120] The quantity of gas which flows through the conduit into the high-pressure fan 54a-c is preferably ascertained by means of the flow rate-measuring facility 47. The opening width of the drain valve 49 is preferably steplessly adjustable. The opening width of the drain valve 49 and/or the swirl regulator 53 are/is preferably adjusted as a function of the quantity of gas ascertained by means of the flow rate-measuring facility 47. A target value for the quantity of gas is preferably determined beforehand.

[0121] If the figure ascertained for the quantity of gas exceeds the predetermined target value, then for example the swirl regulator 53 is adjusted, and more particularly the work angle of the guide vanes is adjusted, in such a way that the quantity of gas entering the high-pressure fan 54a-c is reduced. If the value ascertained for the quantity of gas falls below the predetermined target value, then for example the swirl regulator 53, and more particularly the work angle of the guide vanes, is adjusted in such a way that the quantity of gas entering the high-pressure fan 54a-c is increased.

[0122] If the value ascertained for the quantity of gas exceeds the predetermined target value, the opening width of the drain valve 49 is preferably increased. If the value ascertained for the quantity of gas falls below the predetermined target value, the opening width of the drain valve 49 is reduced.

[0123] The connection system represented in FIG. 1 offers the advantage that there is no need to reduce the speed of the high-pressure fan 54a-c. Instead, the quantity of air to the high-pressure fan 54a-c is reduced, and is preferably reduced to a minimum. A substantially constant speed of the high-pressure fan reliably prevents speed-fluctuation-related mechanical loads on the high-pressure fan.

LIST OF REFERENCE SYMBOLS

[0124] 10 PFR shaft kiln [0125] 12 shaft [0126] 14 materials inlet for letting in limestone [0127] 16 combustion air inlet [0128] 18 off-gas outlet [0129] 20 product outlet [0130] 22 bunker [0131] 23 outgoing-air outlet [0132] 24 bunker outlet [0133] 25 outgoing-air filter [0134] 26 cooling air inlet [0135] 27 low-pressure fan [0136] 28 preheating zone [0137] 30 upper boundary face of the preheating zone [0138] 32 burner lances [0139] 33 cooling facility [0140] 34 lower boundary face of the preheating zone/upper boundary face of the calcining zone [0141] 35 cooling-air circuit lines [0142] 36 calcining zone [0143] 38 overflow duct [0144] 40 lower boundary face of the calcining zone/upper boundary face of the cooling zone [0145] 42 cooling zone [0146] 44 discharge facility [0147] 45 pressure-measuring facility [0148] 46 discharge table [0149] 47 flow rate-measuring facility [0150] 48 discharge hopper [0151] 49 drain valve [0152] 50 gas collector duct [0153] 51 cooling facility [0154] 52 cooling-air circuit lines [0155] 53 swirl regulator [0156] 54a-c high-pressure fan [0157] 55a-c fan [0158] 56 cooling air conduit [0159] 57a-e shutoff facility [0160] 58 depressurization facility [0161] 60 cooling air conduit [0162] 62 combustion air conduit [0163] 63 fuel gas [0164] 64 depressurization facility [0165] 66 distributor facility [0166] 68 cooling air conduit [0167] 70 off-gas conduit [0168] 71 off-gas shutoff facility [0169] 72 off-gas filter [0170] 74 buffer store [0171] 75 discharge system [0172] 76 product outlet [0173] 78 open-loop/closed-loop controller