METHOD FOR BURNING CARBON-CONTAINING MATERIAL IN A PFR SHAFT FURNACE

Abstract

A method can be used to burn and cool material in a parallel flow-counter flow regenerative shaft kiln having two shafts that are operated alternately as a burning shaft and a regenerative shaft. The material flows through a preheating zone, a burning zone, and a cooling zone to a material outlet. Fuel is supplied in or above the preheating zone, and thus fuel is heated in the preheating zone prior to entering the burning zone. Further, a parallel flow-counter flow regenerative shaft kiln for burning and cooling material may have two shafts that can be operated alternately as a burning shaft and a regenerative shaft. Each shaft has, in a flow direction, a preheating zone for preheating material, a burning zone for burning material, and a cooling zone for cooling material. A fuel inlet that admits fuel into each shaft is arranged above or inside the preheating zone.

Claims

1.-15. (canceled)

16. A method for burning and cooling material in a parallel flow-counter flow regenerative shaft kiln that includes two shafts that are operated alternately as a burning shaft and as a regenerative shaft, wherein the material flows through a preheating zone, a burning zone, and a cooling zone to a material outlet, wherein fuel is supplied inside or above the preheating zone such that the fuel is heated in the preheating zone prior to the fuel entering into the burning zone.

17. The method of claim 16 comprising supplying oxidation gas into the burning zone.

18. The method of claim 16 wherein the fuel has a calorific value of 1 MJ/Nm.sup.3 to 7 MJ/Nm.sup.3.

19. The method of claim 16 comprising introducing oxidation gas into the burning zone via a multiplicity of lances or slots in a shaft wall.

20. The method of claim 16 wherein arranged at a transition between the preheating zone and the burning zone is a flow resistance for generating a volume region without material to be burned, wherein oxidation gas is introduced into the volume region.

21. The method of claim 16 comprising introducing oxidation gas into an annular space arranged around a transition between the preheating zone and the burning zone.

22. The method of claim 16 wherein one of the two shafts is operated as the burning shaft over a length of time of a burning cycle, wherein the method comprises the following steps during the burning cycle: a) supplying the fuel through a fuel inlet into the burning shaft over a time interval of a fuel supply time; b) supplying an inert gas through the fuel inlet into the burning shaft over a preliminary flushing time; c) supplying a low-oxygen gas through the fuel inlet into the burning shaft over a subsequent flushing time; and d) reversing the kiln operation by reversing functions of the burning shaft and of the regenerative shaft.

23. The method of claim 22 wherein, during the preliminary flushing time and/or the subsequent flushing time, the method comprises introducing an oxidation gas into the burning shaft via lances and/or slots in a shaft wall.

24. A parallel flow-counter flow regenerative shaft kiln for burning and cooling material, the parallel flow-counter flow regenerative shaft kiln including two shafts that are each configured to be operated alternately as a burning shaft and as a regenerative shaft, wherein each of the two shafts includes, in a direction of flow of the material, a preheating zone for preheating the material, a burning zone for burning the material, and a cooling zone for cooling the material, wherein a fuel inlet for admitting fuel into each shaft is arranged above or inside the preheating zone.

25. The parallel flow-counter flow regenerative shaft kiln of claim 24 wherein a multiplicity of lances or slots in a shaft wall for introducing oxidation gas are arranged inside the burning zone.

26. The parallel flow-counter flow regenerative shaft kiln of claim 24 wherein a multiplicity of gas lances for introducing oxidation gas are arranged inside the burning zone, inside the cooling zone, and/or inside a gas channel for connection of the two shafts.

27. The parallel flow-counter flow regenerative shaft kiln of claim 24 wherein arranged at a transition between the preheating zone and the burning zone is a flow resistance for generating a volume region without material to be burned.

28. The parallel flow-counter flow regenerative shaft kiln of claim 24 wherein an annular space is formed around a transition between the preheating zone and the burning zone, wherein a volume region without material to be burned is formed inside the annular space.

29. The parallel flow-counter flow regenerative shaft kiln of claim 28 wherein means are arranged for introducing oxidation gas into the volume region without material to be burned.

30. The parallel flow-counter flow regenerative shaft kiln of claim 24 wherein each shaft includes a respective gas collection channel that is configured as an annular space, wherein the gas collection channels of the two shafts are connected to one another in terms of gas technology via a gas channel.

Description

DESCRIPTION OF THE DRAWINGS

[0037] The invention is explained in more detail in the following text on the basis of a number of exemplary embodiments with reference to the attached figures.

[0038] FIG. 1 shows a schematic illustration of a PFR shaft kiln in a longitudinal and cross-sectional view according to one exemplary embodiment.

[0039] FIG. 2 shows a schematic illustration of a PFR shaft kiln in a longitudinal and cross-sectional view according to a further exemplary embodiment.

[0040] FIG. 3 shows a schematic illustration of a PFR shaft kiln in a longitudinal and cross-sectional view according to a further exemplary embodiment.

[0041] FIG. 4 shows a schematic illustration of a PFR shaft kiln in a longitudinal sectional view according to a further exemplary embodiment.

[0042] FIG. 5 shows a schematic illustration of the temporal sequences inside the shaft operated as a burning shaft over a burning cycle according to one exemplary embodiment.

[0043] FIG. 1 shows a PFR shaft kiln 10 having two parallel and vertically oriented shafts 12, 14. Each shaft 12, 14 has a respective material inlet 16, 18 for admission of material to be burned into the respective shaft 12, 14 of the PFR shaft kiln. By way of example, the material inlets 16, 18 are arranged at the upper end of the respective shaft 12, 14, and therefore the material falls though the material inlet 16, 18 into the shaft 12, 14 due to gravity.

[0044] Each shaft 12, 14 furthermore has, at its upper end, a fuel inlet 20, 22 for admission of fuel gases. By way of example, the fuel inlets 20, 22 are arranged at the same height level as the material inlets 16, 18.

[0045] At the lower end of each shaft 12, 14, there is a material outlet 24, 26 for letting out the material which has been burned in the respective shaft 12, 14. Each shaft 12, 14 has, at its lower end, a cooling air inlet 28, 30 for admission of cooling air into the respective shaft 12, 14. During operation of the PFR shaft kiln 10, the material to be burned flows from the top to the bottom through the respective shaft 12, 14, wherein the cooling air flows from the bottom to the top, in counter flow to the material, through the respective shaft. The kiln exhaust gas is conducted away, for example, through the material inlet 16, 18 or through the fuel inlet 20, 22 or a gas outlet separate therefrom out of the respective shaft 12, 14.

[0046] The preheating zone 32, 34 of the respective shaft 12, 14 adjoins in the direction of flow of the material below the material inlets 16, 18 and the fuel inlets 20, 22. In the preheating zone 32, 34, the material and the fuel are preferably preheated to approximately 700° C. Preferably, the respective shaft 12 is filled with material to be burned as far as the upper boundary surface 36, 38 of the preheating zone 32, 34. The material and the fuel, in particular the fuel gas, are preferably supplied above the preheating zone 32, 34 into the respective shaft. At least a part of the preheating zone 32, 34 and that part of the respective shaft 12, 14 which adjoins it in the direction of flow of the material are surrounded with a refractory lining 44, for example.

[0047] A multiplicity of lances 40, 42 are optionally arranged in the preheating zone 32, 34 and serve in each case as an inlet for an oxidation gas, such as, for example, oxygen-containing air, in particular oxygen-enriched air or a gas with a proportion of oxygen of approximately 80% or virtually pure oxygen. FIG. 1 likewise shows a cross-sectional view of the PFR shaft kiln 10 at the height level of the lances 40, 42. By way of example, twelve lances 40, 42 are arranged in each shaft 12, 14 at a substantially uniform spacing from one another. By way of example, the lances 40, 42 have an L shape and preferably extend in a horizontal direction into the respective shaft 12, 14 and in a vertical direction, in particular in the direction of flow of the material, inside the shaft 12, 14. The ends of the lances 40, 42 of a shaft 12, 14 are preferably arranged at the same height level. Preferably, the plane on which the lance ends 40, 42 are arranged is in each case the lower boundary surfaces 46, 48 of the respective preheating zone 32, 34. As an alternative to or in addition to the lances 40, 42, it is also possible for slots in the shaft wall to form inlets for admission of oxidation air into the shaft.

[0048] The burning zone 50, 52 adjoins the preheating zone 32, 34 in the direction of flow of the material. In the burning zone, the fuel is combusted and the preheated material is burned at a temperature of approximately 1000° C. The oxidation gas which is introduced through the lances 40, 42 into the burning zone 50, 52 permits the combustion of the fuel in the burning zone 50, 52. A multiplicity of gas lances 64, 66 are optionally provided inside the burning zone 50, 52 and/or the cooling zone 60, 62, said gas lances extending into the burning zone 50, 52 and/or the cooling zone 60, 62 at a position downstream of the above-described lances 40, 42 in the direction of flow of the material and serving for the admission of oxidation gas into the burning zone 50, 52 and/or the cooling zone 60, 62. The gas lances 64, 66 are for example arranged in a lower region of the burning zone close to the lower boundary surface 56, 58 of the burning zone 50 and/or in the upper region of the cooling zone 60, 62 close to the lower boundary of the burning zone 50, 52. It is likewise conceivable for the gas lances 64, 66, as illustrated in FIG. 1, to be provided inside the cooling zone 60, 62.

[0049] The PFR shaft kiln 10 furthermore has a gas channel 54 for the gas-technological connection of the two shafts 12, 14 to one another. The lower boundary surface 56, 58 of the burning zone 50, 52, in particular the end of the burning zone 50, 52, is preferably arranged at the upper height level of the gas channel 54. The burning zone 50, 52 is adjoined in the direction of flow of the material in each shaft 12, 14 by a cooling zone 60, 62 which extends as far as the material outlet 24, 26 or the discharge device 68, 70 of the respective shaft. The material is cooled inside the cooling zone 60, 62 to approximately 100° C.

[0050] A discharge device 68, 70 is arranged at the material-outlet-side end of each shaft 12, 14. The discharge devices 68, 70 for example comprise horizontal plates which allow the material to pass through laterally between the discharge devices 68, 70 and the housing wall of the PFR shaft kiln. The discharge device 68, 70 is preferably embodied as a push table or rotary table or as a table with push-type scraper means. This permits a uniform throughput speed of the material to be burned through the kiln shafts 12, 14.

[0051] During operation of the PFR shaft kiln 10, a respective one of the shafts 12, 14 is active, with the respectively other shaft 12, 14 being passive. The active shaft 12, 14 is referred to as burning shaft and the passive shaft 12, 14 is referred to as regenerative shaft. The PFR shaft kiln 10 is operated in cycles; a typical number of cycles being 75 to 150 cycles per day. After the cycle time has expired, the function of the shafts 12, 14 is swapped. This operation is continuously repeated. Material such as limestone or dolomite rock is supplied into the shaft 12, 14 which is in each case operated as a burning shaft in an alternating manner via the material inlets 16, 18. In the shaft 12, 14 which is operated as a burning shaft, a fuel gas, such as, for example, blast furnace gas, is introduced into the burning shaft via the fuel inlet 20, 22, wherein the fuel inlet 20, 22 serves as an exhaust gas outlet in the regenerative shaft. The fuel gas is heated in the preheating zone 32, 34 of the burning shaft to a temperature of approximately 700° C.

[0052] By way of the lances 40, 42, an oxidation gas, for example air, oxygen-enriched air or oxygen, but preferably an oxidation gas with a high oxygen content, most preferably an oxidation gas with an oxygen content of more than 80% by volume, is supplied in the burning shaft. As a result of this method, the amounts of gas which flow through the burning zone 50, 52 and through the preheating zone 32, 34 of the regenerative shaft are reduced considerably, wherein the gases flowing through the preheating zone 32, 34 of the regenerative shaft contain no surplus heat and preferably have an exhaust gas temperature of about 100° C. Owing to the relatively small amounts of gas, the pressure loss of the entire kiln is reduced considerably, which leads to considerable savings in terms of electrical energy at the process gas compressors.

[0053] FIG. 2 shows a further exemplary embodiment of a PFR shaft kiln 10 having two parallel shafts 12, 14, wherein the PFR shaft kiln corresponds substantially to the PFR shaft kiln 10 of FIG. 1. Some of the reference designations which have been explained already in FIG. 1 have been omitted for the sake of clarity. In contrast to the PFR shaft kiln 10 of FIG. 1, the PFR shaft kiln 10 of FIG. 2 has a round cross section. However, all cross-sectional shapes such as round, oval, rectangular or polygonal are conceivable. Furthermore, the PFR shaft kiln 10 of FIG. 2 has a gas collection channel 82, 84, which is configured in the form of an annular space. The gas collection channel preferably extends in a circumferential manner around the lower region of the burning zone 50, 52, in particular below the gas lances 64, 66. Each shaft 12, 14 has a respective gas collection channel 82, 84, wherein the gas collection channels 82, 84 are arranged at the height level of the gas channel 54 for connection of the two shafts 12, 14. The gas collection channels 82, 84 of the two shafts 12, 14 are in particular connected to one another in terms of gas technology via the gas channel 54. In particular, the gas collection channel 82 is connected in terms of gas technology to the cooling zone 60, 62, with the result that the cooling gas flows at least partially into the gas collection channel 82.

[0054] This construction advantageously leads to a more uniform distribution of gas and temperature in the shafts 12, 14 and, as a result, to better product quality and to lower harmful emissions. A further advantage of this construction is that, if necessary, non-combusted fuel gases, which flow out of the preheating zone 32, 34 into the gas channel 54, together with the cooling air which is supplied to the burning shaft, are subsequently combusted there in a better manner since the gas channel volume is substantially greater.

[0055] FIG. 3 shows a further exemplary embodiment of a PFR shaft kiln 10 having two parallel shafts 12, 14, wherein the PFR shaft kiln corresponds substantially to the PFR shaft kiln 10 of FIG. 1. Some of the reference designations which have been explained already in FIG. 1 have been omitted for the sake of clarity. In contrast to the PFR shaft kiln 10 of FIG. 1, the PFR shaft kiln 10 of FIG. 3 has no lances 40, 42. Merely the gas lances 64, 66 inside the burning zone 50, 52 and/or the cooling zone 60, 62 are provided. Furthermore, the PFR shaft kiln 10 of FIG. 3 has, in each preheating zone 32, 34, a flow resistance which is oriented transversely with respect to the material flow direction, in particular a bar 86, 88. Oxidation gas, such as, for example, air, oxygen-enriched air, oxygen or an oxidation gas with a proportion of oxygen of at least 80%, is introduced below the bar 86, 88.

[0056] FIG. 4 shows a further exemplary embodiment of a PFR shaft kiln 10 having two parallel shafts 12, 14, wherein the PFR shaft kiln corresponds substantially to the PFR shaft kiln 10 of FIG. 2. Some of the reference designations which have been explained already in FIG. 2 have been omitted for the sake of clarity. In contrast to the PFR shaft kiln 10 of FIG. 2, the PFR shaft kiln 10 of FIG. 4 has no lances 40, 42. The PFR shaft kiln 10 of FIG. 4 has a further annular space 90, 92 which extends around the lower region of a respective preheating zone 32, 34. The annular space 90, 92 is connected in terms of gas technology to the burning zone and for example represents a region in which no material to be burned is present. An oxidation gas, for example air or oxygen-enriched air or oxygen, but preferably an oxidation gas with a high oxygen content, most preferably an oxidation gas with an oxygen content of more than 80% by volume, is preferably supplied inside the annular space 90, 92.

[0057] By way of example, the PFR shaft kilns of FIGS. 1 to 4 each have two shafts 12, 14. It is likewise conceivable for three or more interconnected shafts to be provided in a PFR shaft kiln. The gas lances 64, 66 illustrated in FIGS. 1 to 4 can for example be arranged, in addition to or as an alternative to the illustrated gas lances, inside the gas channel 54, such that oxidation gas is introduced directly into the gas channel.

[0058] Each of the shafts 12, 14 of the PFR shaft kiln 10 is operated as a burning shaft over a burning cycle time and subsequently as a regeneration shaft over a regeneration cycle time.

[0059] The temporal sequences within a burning cycle are illustrated in FIG. 5. The burning cycle time 72 is divided into the fuel supply time 74, the preliminary flushing time 76, the subsequent flushing time 78 and the reversal time 80. In the preliminary flushing time 76, directly after the supply of fuel has been turned off, an inert gas, such as, for example, nitrogen or carbon dioxide, is supplied to the fuel inlets 20, 22 on the burning shaft and, as a result, the fuel gas is preferably pushed downwards in the direction of flow of the material. At the end of the preliminary flushing time 76, there is preferably no longer any ignitable gas mixture inside or above the preheating zone 32, 34 of the burning shaft. The subsequent flushing time 78 temporally follows the preliminary flushing time 76, wherein a low-oxygen gas, such as, for example, kiln exhaust gas, is introduced into the burning shaft at the fuel inlets 20, 22 of the burning shaft, as a result of which the already diluted fuel gas is preferably pushed, in the direction of flow of the material, further downwards inside the burning shaft. At the end of the subsequent flushing time 78, the concentration of environmentally harmful gases inside and above the preheating zone 32, 34 of the burning shaft is preferably so low that the reversal with respect to the other shaft 12, 14, operated as a regeneration shaft, can be initiated. Preferably, during the preliminary flushing time 76 and the subsequent flushing time 78, an oxidation gas is introduced into the burning shaft in particular in a continuous manner via the lances 40, 42, with the result that the combustible gases which flow from above into the burning zone 50, 52 during the preliminary and subsequent flushing times are completely combusted.

[0060] The above-described method for operating the PFR shaft kiln 10 affords the advantage that the fuel gas which has not yet been combusted upon reversal of the mode of operation, or at the end of a cycle, wherein the operation of the shafts 12, 14 as burning shaft or regeneration shaft is swapped, is preferably completely combusted inside the burning zone 50, 52 of the burning shaft before the function of the kiln shafts is swapped, in order to minimize the risk of explosion and to prevent impermissible emissions into the atmosphere.

[0061] It is likewise possible for the above-described PFR shaft kiln 10, in particular in the start-up phase, to be operated in such a way that oxidation gas is supplied through the fuel inlets 20, 22 into the respective shaft 12, 14, wherein the fuel, in particular the fuel gas, is supplied into the transition between the preheating zone 32, 34 and the burning zone 50, 52 via the lances 40, 42.

LIST OF REFERENCE DESIGNATIONS

[0062] 10 PFR shaft kiln [0063] 12, 14 Shaft [0064] 16, 18 Material inlet [0065] 20, 22 Fuel inlet [0066] 24, 26 Material outlet [0067] 28, 30 Cooling air inlet [0068] 32, 34 Preheating zone [0069] 36, 38 Upper boundary surface of the preheating zone [0070] 40, 42 Lances [0071] 44 Refractory lining [0072] 46, 48 Lower boundary surface of the preheating zone/upper boundary surface of the burning zone [0073] 50, 52 Burning zone [0074] 54 Gas channel [0075] 56, 58 Lower boundary surface of the burning zone/upper boundary surface of the cooling zone [0076] 60, 62 Cooling zone [0077] 64, 66 Gas lances [0078] 68, 70 Discharge device [0079] 72 Burning cycle time [0080] 74 Fuel supply time [0081] 76 Preliminary flushing time [0082] 78 Subsequent flushing time [0083] 80 Reversal time [0084] 82, 84 Gas collection channel [0085] 86, 88 Bar [0086] 90, 92 Annular space