Kiln and method for combusting carbonate rocks

Abstract

The invention relates to a method for combusting a material, such as carbonate rocks, in a parallel flow regenerative shaft kiln (1) having two shafts (2) which operate alternately as a combustion shaft and a regenerative shaft and which are connected to one another by means of a connecting line (19), the material flows through a material inlet (3) into a preheating zone (21) for preheating the material, into a combustion zone (20) for combusting the material, and into a cooling zone (22) for cooling the material, to a material outlet (40), in which cooling gas is fed into the cooling zone (22), in which exhaust gas is discharged from a shaft (2) of the kiln via an exhaust gas outlet (6) arranged in or above the preheating zone (21), and in which the exhaust gas is discharged from the shaft (2) of the kiln via an exhaust gas outlet (6) arranged in or above the preheating zone (21). The exhaust gas discharged from the shaft (2) via an exhaust gas outlet (6) branches into a first part of the exhaust gas and a second part of the exhaust gas, and wherein the first part of the exhaust gas is fed to an upper region of the preheating zone (21) via a first exhaust gas inlet (12), a second portion of the exhaust gas discharged from the shaft (2) is fed to the preheating zone (21) via a second exhaust gas inlet (15) downstream of the first exhaust gas inlet (12).

Description

[0001] The present invention relates to a kiln and a method for burning and cooling a material such as carbonate rock by means of a PFR shaft kiln. The kiln is for example a parallel flow regenerative shaft kiln (PFR shaft kiln) or a shaft kiln, in particular an annular shaft kiln.

[0002] The combustion of carbonate rock in shaft kilns, or PFR shaft kilns, has been known for approximately 60 years. Such a PFR shaft kiln, for example, as described in WO 2011 / 072894 A1, has two vertically parallel shafts operating in a circular pattern. Combustion occurs only in one shaft (the combustion shaft), while the other shaft functions as a regeneration shaft. The combustion shaft is supplied with oxidizing gas flowing co-currently with the material and fuel. The resulting hot exhaust gas, along with heated cooling air supplied from below, is introduced via a cross-duct into the exhaust gas shaft, where it is directed upwards counter-currently to the material, preheating it. The material is typically fed into the shaft from above along with the oxidizing gas, while fuel is injected into the combustion zone.

[0003] In each shaft, the material to be combusted typically passes through a preheating zone for preheating the material, a downstream combustion zone for combusting the material, and a downstream cooling zone for supplying cooling air to the hot material.

[0004] To meet the high reactivity quality requirements of burnt lime, such as those in steel mills, the temperature in the combustion zone must not exceed 1100°C, preferably 1000°C. Furthermore, the demand for environmentally friendly burnt lime production is increasing, necessitating certain requirements for the CO₂ content of the waste gas in subsequent post-treatment. A known method for increasing the CO₂ content in the waste gas is to recirculate at least a portion of the waste gas back into one of the shafts. This waste gas recirculation requires complex and expensive treatment before the waste gas is returned to the shaft.

[0005] Starting from this starting point, the object of the present invention is to provide a kiln, such as a shaft kiln and / or a PFR shaft kiln, which is inexpensive and energy-efficient, and a method for burning carbonate rocks in such a kiln, by which lime with high reactivity is produced while simultaneously separating CO2 from the exhaust gases.

[0006] According to the invention, this object is achieved by an apparatus having the features of the independent apparatus claim 1 and by a method having the features of the independent method claim 10. Advantageous developments result from the dependent claims.

[0007] In a first aspect, the present invention relates to a method for burning material, such as carbonate rock, in a parallel flow regenerative shaft kiln having two shafts, the two shafts being operated alternately as a combustion shaft and a regeneration shaft and being connected to one another by a connecting pipe, wherein material flows through a material inlet into a preheating zone for preheating the material, a combustion zone for burning the material, and a cooling zone for cooling the material, and flows to a material outlet, wherein cooling gas is fed into the cooling zone, wherein exhaust gas is discharged from one shaft of the kiln via an exhaust gas outlet arranged in or above the preheating zone, wherein the exhaust gas discharged from the shaft via the exhaust gas outlet branches into a first exhaust gas portion and a second exhaust gas portion, wherein the first exhaust gas portion is fed to an upper region of the preheating zone via a first exhaust gas inlet, and the second exhaust gas portion discharged from the shaft is fed to the preheating zone via a second exhaust gas inlet downstream of the first exhaust gas inlet.

[0008] Feeding the exhaust gas at two different locations within the preheating zone ensures an optimal exhaust gas flow within the preheating zone and, in particular, reliably prevents excessively low temperatures within the preheating zone, thereby avoiding condensation of the exhaust gas within the preheating zone. This further reduces the risk of corrosion of components involved in further exhaust gas treatment. The shaft preferably has a plurality of first exhaust gas inlets, which are arranged circumferentially around the shaft, for example, in particular at the same height, and are supplied with the first portion of the exhaust gas. The first exhaust gas inlets are preferably each connected to a pipeline, in particular an annular pipeline, for conducting the first portion of the exhaust gas. For example, the first exhaust gas inlets are arranged at regular intervals. The shaft preferably has a plurality of second exhaust gas inlets, which are arranged circumferentially around the shaft, for example, in particular at the same height, and are supplied with the second portion of the exhaust gas. The second exhaust gas inlets are preferably each connected to a pipeline, in particular annular pipeline, for conducting the second portion of the exhaust gas. For example, the second exhaust gas inlets are arranged at regular intervals.

[0009] For example, the exhaust gas discharged from the shaft through the exhaust gas outlet is completely cooled in a cooling device and then heated in a heating device to a temperature not exceeding 200°C, particularly between 50°C and 160°C, preferably between 70°C and 120°C. This results in a lower relative water content in the exhaust gas. In particular, the risk of water condensing and causing compressor operational problems is significantly reduced. Alternatively, only a portion of the exhaust gas can be fed to the cooling device and then to the heating device. For example, the exhaust gas can be cooled in the cooling device to a temperature between 10°C and 50°C, particularly between 15°C and 40°C. This at least partially condenses water in the exhaust gas, thereby reducing its absolute water content. The cooling device and / or heating device can optionally be designed as a heat exchanger. This allows for the utilization of waste heat, particularly temperature differences in a fluid at another location in the kiln process. For example, before cooling in the cooling device, the exhaust gas is dust-removed in a filter. The filter is preferably located between the exhaust gas outlet and the cooling device. The filter is preferably a dust filter for filtering dust particles from the exhaust gas. For example, the filter operates under positive or negative pressure, with a fan installed downstream. Preferably, a compressor, in particular a fan, is arranged upstream of the filter in the flow direction of the exhaust gas.

[0010] The material to be combusted is preferably limestone or dolomite with a particle size of 10 to 200 mm, preferably 15 to 120 mm, and most preferably 30 to 100 mm. For example, the cooling gas is air. The fuel supplied to the kiln is preferably methane or hydrogen. At the exhaust gas outlet, the water content of the exhaust gas is preferably approximately 5 to 40% by volume, in particular 10 to 25% by volume, while the temperature is, for example, approximately 80°C to 100°C, in particular below 80°C during system startup.

[0011] For example, the kiln can be a parallel-flow regenerative shaft kiln with two parallel shafts, or a shaft kiln with exactly one shaft. A parallel-flow regenerative shaft kiln has at least two shafts, preferably arranged vertically parallel to one another. The shafts can be operated alternately as a combustion shaft and a regeneration shaft, with each shaft comprising, in the direction of material flow, a preheating zone for preheating the material, a combustion zone for burning the material, and a cooling zone for cooling the material. Each shaft preferably has a material inlet for feeding the material to be combusted into the shaft, with the material inlet being located, in particular, at the upper end of the respective shaft so that the material falls into the respective shaft under the action of gravity. The material inlet and / or material outlet are preferably in the form of sluices for feeding and / or discharging material into the shaft kiln. The sluice-shaped material inlet is preferably designed so that only the raw material to be combusted enters the shaft, not ambient air. The material sluice also prevents gases from escaping the shaft via the material inlet. The sluice is preferably designed to hermetically seal the shaft from the surrounding environment while allowing solids (such as the material to be combusted) to enter the shaft.

[0012] The connecting pipe is designed to connect the gas flows of the two shafts and preferably connects the combustion zones of the shafts to each other. During operation of the PFR shaft kiln, one shaft at a time operates as the active combustion shaft, while the corresponding shaft operates as the passive regeneration shaft. PFR shaft kilns typically operate in a cyclical manner, switching the kiln function after the cycle time has elapsed. This process is repeated continuously. In the active shaft operating as the combustion shaft, fuel is introduced into the combustion zone via burner lances. The material to be combusted is heated in the preheating zone of the combustion shaft to a temperature of preferably approximately 700°C. In the shaft operating as the combustion shaft, the combustion zone is a co-current combustion zone, with the material to be combusted flowing parallel to the gas flow. Gas flows from the preheating zone into the combustion zone and then, via the connecting pipe, into the combustion and preheating zones of the regeneration shaft. In the shaft operating as the regeneration shaft, the gas flows in the preheating and combustion zones in countercurrent to the material to be combusted.

[0013] In both the combustion shaft and the regeneration shaft, the cooling gas flows countercurrently to the material to be cooled through the cooling zone and is preferably completely discharged from the shaft via the cooling gas outlet of the cooling air removal device, so that preferably no cooling gas flows from the cooling zone into the combustion zone.

[0014] Each shaft preferably has at least one exhaust gas outlet, for example at the upper end of the shaft within the preheating zone. The exhaust gas outlet is preferably located above the material column in the material-free area of ​​the preheating zone. Exhaust gas is preferably discharged from only one shaft, in particular the regeneration shaft. The discharged exhaust gas is preferably fed to a corresponding other shaft, in particular the combustion shaft or the regeneration shaft. Preferably, only a portion of the exhaust gas discharged from the regeneration shaft is fed back to at least one of the shafts. For example, a portion of the exhaust gas discharged from the regeneration shaft is discharged from the PFR shaft kiln and fed, for example, for further treatment, such as storage. The exhaust gas preferably consists of CO2 and optionally H2O.

[0015] The fuel is preferably fed via a fuel line to the combustion zone and / or preheating zone of a shaft operated as a combustion shaft. The fuel is preferably fed to burner lances arranged in the combustion zone and / or preheating zone. The fuel is, for example, a fuel gas such as blast furnace gas, methane, hydrogen, or natural gas, or pulverized coal, biomass, or a liquid fuel. The material is preferably heated to a temperature of approximately 1100° C. in the combustion zone.

[0016] Each shaft preferably has a plurality of burner lances which extend at least partially through the preheating zone, in particular into the combustion zone of the respective shaft, and are used to conduct, for example, fuel and / or oxidizing gas, such as air or oxygen-enriched air or pure oxygen. Preferably, the fuel gas outlets of the burner lances are arranged at the upper end of the combustion zone, so that the preheating zone extends to the fuel gas outlet of at least one burner lance.

[0017] Returning the waste gas to at least one or both shafts produces highly reactive lime and a process gas with a CO₂ content exceeding 90% on a dry gas basis. This process waste gas can be liquefied and stored with relatively low complexity. For example, the liquefied process waste gas can be fed to further process steps or stored. Alternatively, the PFR shaft kiln can be used to produce waste gas with a low CO₂ content, for example, 45% for soda ash production, 35% for sugar production, or 30% for precipitated calcium carbonate production.

[0018] In particular, the exhaust gas is introduced into the preheating zone of the shaft operating as a combustion shaft and / or regeneration shaft. Each shaft preferably has an exhaust gas inlet, in particular a firing gas inlet, which is arranged in the upper region of the preheating zone of the shaft to feed the gas required for firing.

[0019] The PFR shaft kiln preferably has a branch downstream of the exhaust gas outlet. This branch is designed and arranged to divide the exhaust gas discharged from the exhaust gas outlet into a first portion and a second portion of exhaust gas. The branch is preferably arranged in the direction of exhaust gas flow, past the dust filter, heating device, and / or cooling device. The first portion of the exhaust gas is supplied to the upper region of the preheating zone of the combustion shaft and / or regeneration shaft via a first exhaust gas inlet, while the second portion of the exhaust gas is supplied to the preheating zone of the combustion shaft and / or regeneration shaft via a second exhaust gas inlet downstream of the first exhaust gas inlet. Preferably, the preheating zones of both the combustion shaft and the regeneration shaft have a first exhaust gas inlet and a second exhaust gas inlet arranged past the latter in the direction of material flow.

[0020] In particular, the amount of waste gas supplied to the preheating zone of the shaft operating as a combustion shaft and / or as a regeneration shaft via the first and / or second waste gas inlet is adjustable. The PFR shaft kiln preferably has at least one control element, such as a flap or a valve. Preferably, a control element is located upstream of each of the first and second waste gas inlets, such that the amount of the first portion of waste gas flowing to the first waste gas inlet and / or the amount of the second portion of waste gas flowing to the second waste gas inlet is adjustable. In particular, the amount of waste gas entering the first and / or second waste gas inlet is adjusted depending on the CO2 content of the waste gas.

[0021] In a first embodiment, oxygen is fed to the first and / or second portion of the exhaust gas prior to introduction into the preheating zone. Preferably, the exhaust gas line connected to the exhaust gas outlet is connected to an oxidant line for introducing oxygen, thereby introducing oxygen into the exhaust gas line. For example, air, oxygen-enriched gas, or pure oxygen is supplied to the first and / or second portion of the exhaust gas. The oxidant line is preferably connected to an oxygen source. For example, a PFR shaft kiln has at least two oxidant lines, each connected to an exhaust gas inlet for introducing the exhaust gas into the preheating zone. In particular, oxygen is supplied to the first exhaust gas inlet and / or only to the second exhaust gas inlet of the preheating zone of a shaft operating as a combustion shaft.

[0022] In another embodiment, the second portion of the offgas is compressed to approximately 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, and in particular 500 mbar, before being introduced into the preheating zone of the combustion shaft. The PFR shaft kiln preferably has a compressor arranged between the offgas outlet and the second offgas inlet, which is designed to compress the second portion of the offgas to approximately 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, and in particular 500 mbar. This counteracts any pressure drop within the PFR shaft kiln. Preferably, the second portion of the offgas is compressed to approximately 50 mbar to 300 mbar, preferably 70 mbar to 200 mbar, and in particular 150 mbar, before being introduced into the preheating zone of the regeneration shaft. When the second portion of the offgas is introduced into the second offgas inlet in the regeneration shaft, the pressure drop within the PFR kiln is preferably lower than when it is introduced into the combustion shaft.

[0023] In another embodiment, the second portion of the exhaust gas is introduced into the preheating zone at its lower end, in particular directly. In particular, the second portion of the exhaust gas is introduced into the preheating zone upstream of the combustion zone, in particular upstream of the firing gas outlet of the burner lances, in the direction of material flow. The second portion of the exhaust gas is preferably introduced into the preheating zone via one or more exhaust gas inlets formed as passages in the shaft wall above the combustion zone.

[0024] In another embodiment, the second portion of the exhaust gas is heated to a temperature of 500° C. to 800° C., in particular 550° C. to 700° C., preferably 600° C., before being introduced into the second exhaust gas inlet. Preferably, the second portion of the exhaust gas is at least partially or completely heated in a heat exchanger. This ensures optimal preheating of the material in the preheating zone.

[0025] In another embodiment, the second portion of the exhaust gas is introduced into a region of the preheating zone whose temperature corresponds to the temperature of the second portion of the exhaust gas and / or to a temperature of 500°C to 800°C, in particular 550°C to 700°C, and preferably 600°C. Preferably, the gas temperature in the preheating zone is 70°C to 800°C, with the gas temperature at the upper end of the preheating zone being approximately 70°C to 100°C and the gas temperature at the lower end being 700°C to 900°C, preferably 800°C. The gas temperature preferably increases continuously in the direction of material flow. The second exhaust gas inlet is preferably located at a height of the preheating zone at which the gas temperature in the preheating zone is 500°C to 800°C, in particular 550°C to 700°C, and preferably 600°C.

[0026] In another embodiment, the preheating zone has a length extending in the direction of material flow, wherein a second exhaust gas inlet for introducing exhaust gas into the preheating zone is located at a distance from the upper end of the combustion zone in the direction of material flow, and wherein the ratio of distance to length is 0 to 0.5, particularly 0.2 to 0.3, and preferably 0.25. The preheating zone preferably extends from the material filling level and / or from the material inlet to the combustion zone, particularly to the fuel gas outlet of the burner lance. This ratio allows for optimal mixing of the gas flow in the preheating zone at an optimal volume flow ratio.

[0027] In another embodiment, the cooling gas heated in the cooling zone is discharged from the cooling zone of the shaft via a cooling gas removal device and fed to a heat exchanger for heating the second portion of the exhaust gas, in particular in countercurrent heating. The cooling gas heated in the cooling zone is preferably discharged from the cooling zone of the shaft via the cooling gas removal device. In particular, the cooling gas fed to the cooling zone is completely discharged from the respective shaft via the cooling gas removal device.

[0028] The cooling gas removal device preferably has a material-free space within the cooling zone of the shaft. The material-free space in the cooling gas removal device takes the form of, for example, an inner barrel that extends, in particular centrally and vertically, through the cooling zone. In particular, the inner barrel extends at least partially into the combustion zone or terminates at a vertical distance from the combustion zone. A cooling gas outlet for discharging cooling gas from the shaft is arranged within the inner barrel. The inner barrel preferably has a cooling gas inlet for conveying cooling gas from the cooling zone into the interior of the inner barrel, and the cooling gas inlet is preferably arranged above the cooling gas outlet in the inner barrel. In particular, the cooling gas inlet is arranged at the upper end of the cooling zone so that the cooling gas preferably flows through the entire cooling gas zone before flowing into the inner barrel of the cooling gas removal device. Within the inner barrel, the cooling gas preferably flows downward in the direction of the cooling gas outlet and enters the cooling gas removal line. The cooling gas removal device is preferably designed to discharge all cooling gas from the shaft, so that preferably no cooling gas enters the combustion zone or the connecting line for connecting the combustion zone of the shaft. In particular, the cooling gas removal device is connected to a control element, such as a flap or a valve, in order to regulate the amount of cooling gas to be removed.

[0029] The present invention also relates to a parallel-flow regenerative shaft kiln for burning and cooling materials such as carbonate rock, comprising two shafts that can be operated alternately as a combustion shaft and a regeneration shaft and are connected to each other via a connecting pipe. Each shaft comprises, in the material flow direction, a preheating zone for preheating the material, a combustion zone for burning the material, and a cooling zone for cooling the material. At least one shaft of the PFR shaft kiln comprises an exhaust gas outlet disposed within or above the preheating zone for discharging exhaust gas from the shaft, and a first exhaust gas inlet for introducing exhaust gas, the exhaust gas outlet being connected to the first exhaust gas inlet for introducing a first portion of the exhaust gas into the preheating zone. The shaft comprises a second exhaust gas inlet within the preheating zone, the second exhaust gas inlet being connected to the exhaust gas outlet in the material flow direction and being disposed beyond the first exhaust gas inlet for introducing a second portion of the exhaust gas into the preheating zone.

[0030] The embodiments and advantages described with respect to the method for burning materials (such as carbonate rocks) in a PFR shaft kiln are also applicable to the apparatus for a PFR shaft kiln.

[0031] In one embodiment, the shaft kiln has a control element upstream of the first and / or second exhaust gas inlet for controlling the exhaust gas quantity fed via the first and / or second exhaust gas inlet to the preheating zone of the shaft operated as a combustion shaft and / or the shaft operated as a regeneration shaft.

[0032] In another embodiment, the shaft kiln has at least one oxidant line connected to the first and / or second exhaust gas inlet for introducing an oxidant into the exhaust gas. The oxidant is, for example, air, oxygen-enriched gas, or pure oxygen.

[0033] In another embodiment, the compressor connected upstream of the second exhaust gas inlet is designed and arranged to compress the exhaust gas to a pressure of 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, in particular 500 mbar, before introduction into the second exhaust gas inlet of the combustion shaft. In particular, the compressor connected upstream of the second exhaust gas inlet is designed and arranged to compress the exhaust gas to a pressure of 50 mbar to 300 mbar, preferably 70 mbar to 200 mbar, in particular 150 mbar, before introduction into the second exhaust gas inlet of the regeneration shaft.

[0034] In another embodiment, the second exhaust gas inlet is provided at the lower end of the preheating zone.

[0035] In another embodiment, the heat exchanger arranged between the exhaust gas outlet and the second exhaust gas inlet is designed and arranged to heat the second part of the exhaust gas to a temperature of 500 to 800°C, in particular 550 to 700°C, preferably 600°C.

[0036] In another embodiment, the preheating zone has a length A extending in the flow direction of the material, wherein the second exhaust gas inlet for introducing exhaust gas into the preheating zone is at a distance B from the upper end of the combustion zone 20 in the flow direction of the material, and wherein the ratio B / A of the distance B to the length A is 0 to 0.5, in particular 0.2 to 0.3, preferably 0.25.

[0037] In another embodiment, the cooling zone has a cooling gas inlet for introducing cooling gas into the cooling zone and a cooling gas removal device for discharging cooling gas from the shaft, and wherein the cooling gas removal device is connected to a heat exchanger for heating the second part of the exhaust gas, in particular countercurrent heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be described in detail below through a number of working examples with reference to the accompanying drawings.

[0039] Figure 1 A schematic diagram of a PFR shaft kiln in a working example is shown in cross-section.

[0040] Figure 2 Shown in cross-section Figure 1 Schematic diagram of details of a PFR shaft kiln in an example.

[0041] Figure 1 A kiln is shown, more particularly a PFR shaft kiln 1 having two parallel and vertically oriented shafts 2. The shafts 2 of the PFR shaft kilns 1 have essentially the same structure, so that Figure 1 Only one of the two shafts 2 is given a reference number, and for simplicity, only one of these two shafts will be described below. Each shaft 2 has a corresponding material inlet 3 for feeding the material to be combusted into the corresponding shaft 2 of the PFR shaft kiln 1. The material to be combusted is, in particular, limestone and / or dolomite, preferably having a particle size of 10 to 200 mm, preferably 15 to 120 mm, and most preferably 30 to 100 mm. For example, the material inlet 3 is disposed at the upper end of the corresponding shaft 2 so that the material falls through the material inlet 3 into the shaft 2 under the action of gravity. The material inlet 3 takes the form of, for example, an upper opening in the shaft 2, in particular a sluice 3, and preferably extends across the entire or partial cross-section of the shaft 2. The material inlet, in the form of a sluice 3, is preferably configured so that only the raw material to be combusted enters the shaft 2, and not the outside air. The sluice 3 is preferably configured so that it seals the shaft 2 from the surroundings in an airtight manner while allowing solids (such as the material to be combusted) to enter the shaft.

[0042] Each shaft 2 also has a firing gas inlet 12 at its upper end for introducing firing gas to burn the fuel. The firing gas inlet 12 is a first exhaust gas inlet 12, with each shaft 2 preferably having a second exhaust gas inlet 15 located beyond the first exhaust gas inlet 12 in the direction of material flow. For example, the shaft 2 may have multiple first and second exhaust gas inlets, particularly at the same height and / or equidistant from one another around the circumference. The firing gas is, for example, dust-collected exhaust gas from at least one shaft 2, preferably oxygen-enriched. Furthermore, each shaft 2 has an exhaust gas outlet 6 for discharging exhaust gas from the respective shaft 2. For example, each exhaust gas outlet 6 and exhaust gas inlets 12, 15 is assigned a control element. The control element, such as a volume-controlled compressor 35, can preferably be used to regulate the firing gas, particularly the amount of exhaust gas, in the respective exhaust gas inlets 12, 15, as well as the amount of exhaust gas removed through the respective exhaust gas outlet 6. The first exhaust gas inlet 12 and the exhaust gas outlet 6 are, for example, located at the same height level, particularly within the preheating zone 21 of the respective shaft 2. For example, the first exhaust gas inlet 12 and the exhaust gas outlet 6 are arranged in the upper end region, in particular the material-free upper end of the preheating zone 21 of the respective shaft 2 .

[0043] A material outlet 40 for discharging the burned material is provided at the lower end of the shaft 2. The material outlet 40 is, for example, the gate described with reference to the material inlet 3.

[0044] For example, the burning material is directed to an outlet hopper 25 adjacent to the material outlet 40 of the shaft 2. The outlet hopper 25 is, for example, funnel-shaped. The outlet hopper 25 preferably has a cooling gas inlet 23 for feeding cooling gas into the corresponding shaft 2. The cooling gas is preferably directed to the cooling gas inlet by a compressor 33.

[0045] When the PFR shaft kiln 1 is in operation, the material to be combusted flows downward from the top through the corresponding shaft 2, while cooling air flows upward from the bottom, countercurrently with the material, through the corresponding shaft 2. Kiln exhaust gas is discharged from the shaft 2 through the exhaust gas outlet 6.

[0046] The bottom ends of the material inlet 3 and the first exhaust gas inlet 12 are adjacent to the preheating zone 21 of the corresponding shaft 2 in the direction of material flow. The material and firing gases are preferably preheated to approximately 700°C in the preheating zone 21. The corresponding shaft 2 is preferably filled with the material to be combusted. The material is preferably fed into the corresponding shaft 2 above the preheating zone 21. At least a portion of the preheating zone 21 and the portion of the corresponding shaft 2 adjacent thereto in the direction of material flow are surrounded by, for example, a refractory lining.

[0047] A plurality of burner lances 10, each opening into a combustion zone 20, are optionally disposed in the preheating zone 21 and each serving as an inlet for fuel, such as fuel gas, oil, or ground solid fuel. The PFR shaft kiln 1, for example, includes a cooling device for cooling the burner lances 10. The cooling device comprises, for example, a plurality of annular cooling air ducts extending annularly around the shaft region in which the burner lances 10 are disposed. The cooling air for cooling the burner lances 10 preferably flows through the annular cooling air ducts. The burner lances 10 are preferably cooled by exhaust gases discharged through an exhaust gas outlet 6. The exhaust gas outlet 6 is preferably connected to the burner lances 10 to direct the exhaust gases thereto.

[0048] The burner lances 10 are preferably connected to a fuel line 9 for conducting fuel to the burner lances 10. For example, the fuel line 9 is at least partially in the form of an annular line that extends circumferentially around the respective shaft 2. Preferably, each shaft 2 has a fuel line that is respectively assigned to the burner lances 10 of the shaft 2 and, in particular, has corresponding control elements for regulating the amount of fuel to the burner lances 10.

[0049] The preheating zone 21 is adjacent to the combustion zone 20 in the direction of material flow. In the combustion zone 20, fuel is fired, and the preheated material is burned at a temperature of approximately 1000°C. Each burner lance preferably has a fuel outlet at its end, with the combustion zone 20 extending in particular from the fuel outlet of the burner lance 10 in the direction of material flow. The PFR shaft kiln 1 also has a connecting pipe 19 for gaseous connection of the two shafts 2. In particular, no material to be burned is contained in the connecting pipe 19.

[0050] As an example, Figure 1 A PFR lime kiln 1 with a circular shaft cross section is shown. However, the shaft cross section may have a different geometrical profile, such as circular, semicircular, oval, square or polygonal.

[0051] The combustion zone 20 is adjacent to a cooling zone 22 in the direction of flow of the material in each shaft 2, which extends to the discharge device 41. The material is cooled in the cooling zone 22 to approximately 100° C. in countercurrent with a cooling gas flowing through the material.

[0052] Each cooling zone 22 has a respective cooling air removal device 17 with a respective cooling gas outlet 29. The cooling gas flowing into the cooling zone 22 via the cooling gas inlet 23 preferably flows completely out of the respective shaft 2 via the cooling gas outlet 29 of the cooling air removal device 17.

[0053] Each cooling zone 22 has a cooling gas removal device 17 comprising an inner barrel 26 extending from the cooling zone 22 at least partially into the combustion zone 20 or to a level spaced apart therefrom and having a cooling gas outlet 29 connected to the cooling gas removal line 11 .

[0054] The cooling zone 22 is formed, for example, in a shaft profile having a substantially constant cross-section, wherein the shaft profile of the cooling zone 22 corresponds approximately to the shaft profile of the lower region of the combustion zone 20. For example, a material-free annular space is formed at the level of the connecting duct 19. Each shaft 2 of the PFR shaft kiln 1 preferably has an inner barrel 26 that extends vertically and centrally through the cooling zone 22. For example, the inner barrel 26 extends from the discharge device 41 through the cooling zone 22 into the combustion zone 20 to the level of the connecting duct 19. The inner barrel 29 is cooled by a plurality of cooling air channels formed in its outer wall, which are connected to a cooling air line (not shown) for conducting cooling air. For example, the heated cooling air is introduced into the cooling gas removal line 11 and preferably into a heat exchanger 43 to heat the exhaust gases. For example, the heated cooling air is used as an energy source for other processes, such as drying biomass or limestone.

[0055] The inner barrel 26 of the cooling gas removal device 17 has a cooling gas outlet 29 extending radially outward from the inner barrel 26 through the shaft wall to direct cooling gas from the inner barrel 26 into the cooling gas removal line 11. The inner barrel 26 also has a cooling gas inlet 30 for introducing cooling gas from the cooling zone 22 into the inner barrel 26. The cooling gas inlet 30 extends through the inner barrel wall into the cooling zone 22 and connects the interior of the inner barrel 26 to the cooling zone 22. The cooling gas inlet 30 is preferably located above the cooling gas outlet 29 in the cooling zone 22. During operation of the PFR shaft kiln 1, cooling gas flows upward from the bottom through the cooling zone 22 and into the cooling gas inlet 30, entering the inner barrel 26 of the cooling gas removal device 17. Preferably, all cooling gas introduced into the cooling zone 22 flows into the cooling gas removal device 17 through the cooling gas inlet 30, so that no cooling gas enters the combustion zone 20. The cooling gas outlet 29 of the inner barrel 26 is preferably located in the lower region of the cooling zone 22. In particular, cooling gas flows downwardly from a cooling gas inlet 30 in the inner barrel 26 to a cooling gas outlet 29 .

[0056] A discharge device 41 is preferably provided at the material outlet end of each shaft 2. The discharge device 41 comprises, for example, a horizontal plate, preferably a discharge table, which allows the material to pass laterally between the discharge table and the shell wall of the PFR shaft kiln. The discharge device 41 is preferably designed as a sliding table or a rotating table, or as a table with pushable scrapers. This ensures a uniform flow rate of the material to be combusted through the shaft 2. For example, the discharge device 41 further comprises an outlet hopper 25 adjacent to the discharge table and having a material outlet 40 mounted at its lower end.

[0057] During operation of the PFR shaft kiln 1, one of the shafts 2 is active at any one time, while the other shaft 2 is passive. The active shaft 2 is called the combustion shaft and the passive shaft 2 is called the regeneration shaft. The PFR shaft kiln 1 is operated in particular in cycles, for example with a typical number of cycles of 75 to 150 cycles per day. After the cycle time has elapsed, the function of the shaft 2 is switched. This process is repeated continuously. Material, such as limestone or dolomite, is fed alternately to the shaft 2 via the material inlet 3. In the active shaft 2 operated as a combustion shaft, the fuel is introduced into the combustion shaft 2 via the burner lances 10. The material to be combusted is heated to a temperature of approximately 700°C in the preheating zone 21 of the combustion shaft. Figure 1 In the working example of FIG, the left shaft 2 is operated as a combustion shaft and the right shaft 2 is operated as a regeneration shaft.

[0058] During operation of the PFR shaft kiln 1 , both in the combustion shaft 2 and in the regeneration shaft 2 , the cooling gas flows countercurrently to the material to be cooled through the cooling zone 22 and is preferably completely discharged from the shaft 2 via the cooling gas outlet 29 , so that preferably no cooling gas flows from the cooling zone 22 into the combustion zone 20 .

[0059] In the shaft 2, which operates as a combustion shaft, the combustion gas flows into the combustion shaft through the first exhaust gas inlet 12 and flows into the material-free space in the form of an annular duct 18, co-currently with the material in the combustion zone 20. From the material-free space 18, the gas flows via a connecting duct 19 into the shaft 2, which operates as a regeneration shaft. In the regeneration shaft, the gas flows from the connecting duct 19 and the material-free space 18 of the regeneration shaft, counter-currently with the material to be burned, through the combustion zone 20 into the preheating zone 21, and leaves the regeneration shaft through the exhaust gas outlet 6 of the regeneration shaft. The exhaust gas discharged from the shaft 2 preferably has a temperature of 60°C to 160°C, preferably 100°C.

[0060] The exhaust gas is introduced into an exhaust gas line 39 adjacent to the exhaust gas outlet 6. The exhaust gas line 39 optionally has an exhaust gas filter 31 downstream of the exhaust gas outlet 6 in the direction of exhaust gas flow to filter out fine particles, in particular dust, from the exhaust gas. Downstream of the exhaust gas filter 31, the exhaust gas line 39 has a branch, in which a first part of the exhaust gas is guided in the firing gas line 4 to the first exhaust gas inlet 12. Downstream of the branch, the firing gas line 4 has, for example, a control element, such as a butterfly valve and a compressor 35, in the flow direction of the first part of the exhaust gas. The firing gas line 4 is preferably connected to the first exhaust gas inlet 12 of the shaft 2, and the exhaust gas is preferably fed only to the first exhaust gas inlet 12 of the shaft 2 operated as a combustion shaft via a control element connected upstream in the first exhaust gas inlet 12. It is also conceivable that the exhaust gas from the firing gas line 4 is fed only to the regeneration shaft or to both shafts 2. The firing gas line 4 is preferably connected to the oxidant line 14 so that an oxidant, preferably pure oxygen, is introduced into the firing gas line 4 and then, together with the waste gas, into the shaft 2 via the first waste gas inlet 12. It is also conceivable that the oxidant introduced into the firing gas line 4 is an oxygen-rich gas having an oxygen content of at least 70% to 95%, preferably 90%.

[0061] The portion of the exhaust gas that is not returned to the first exhaust gas inlet 12 is referred to as the second portion of the exhaust gas and is fed in the exhaust gas line 39 to the second exhaust gas inlet 15 in the preheating zone 21. In the flow direction of the second portion of the exhaust gas, downstream of the branch of the firing gas line 4, the exhaust gas line 39 preferably has a compressor 36 of controllable volume and a heat exchanger 43. For example, the heat exchanger 43 is in the form of a recuperator, in which the second portion of the exhaust gas is heated in countercurrent to the removed cooling gas, while the cooling gas is cooled. In particular, the heat exchanger 43 is connected to the cooling gas outlet 29 of the two shafts 2 via the cooling gas removal line 11, so that the second portion of the exhaust gas is heated in the heat exchanger 43, preferably in countercurrent to the removed cooling gas. Downstream of the heat exchanger 43, the cooling gas removal line 11 optionally has a control element for regulating the amount of cooling gas to be removed and a filter 16 for removing dust from the cooling gas. The second part of the exhaust gas is preferably heated in the heat exchanger 43 to a temperature of approximately 500° C. to 800° C., in particular 550° C. to 700° C., preferably 600° C.

[0062] Downstream of the heat exchanger 43 and upstream of the second exhaust gas inlet 15 , the exhaust gas line 39 is preferably connected to the oxidant line 14 to introduce an oxidant, such as pure oxygen, air, or oxygen-enriched gas, into the exhaust gas line 39 .

[0063] In particular, a cooling device 32 is provided downstream of the exhaust gas filter 31. The cooling device 32 is, for example, a heat exchanger, which preferably operates in countercurrent with a coolant (e.g., water). Downstream of the cooling device 32 is preferably a heating device 47 for heating the cooling exhaust gas. The heating device 47 is preferably designed to heat the exhaust gas to a temperature of no more than 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C. The heating device 47 is preferably designed as a heat exchanger and is connected to the cooling gas removal line 11 so that the cooling gas removed from the shaft 2 is supplied to the heating device 47. The cooling gas filtered in the filter 16 is preferably fed to the heat exchanger 47.

[0064] A branch is provided downstream of the heating device 47, through which at least a portion of the exhaust gas is discharged, and a second portion of the exhaust gas is returned to one of the shafts 2 via an exhaust gas line 39. In particular, a partial flow of the second portion of the exhaust gas is discharged downstream of the branch of the firing gas line 4. The exhaust gas line has, for example, a compressor 36, 37 upstream and downstream of the branch of the exhaust gas to be discharged.

[0065] The preheating zone 21 has a second exhaust gas inlet 15 for introducing recirculated exhaust gas (particularly the second portion of the exhaust gas) into the preheating zone 21. The gas inlet 15 is connected to the exhaust gas outlet 6 of the shaft 2 via an exhaust gas line 39, so that the dust-removed and heated exhaust gas discharged from the shaft 2 is guided to the preheating zone 21. For example, the second exhaust gas inlet 15 is arranged in the lower end region of the preheating zone 21. The position of the gas inlet 15 is Figure 2 Preferably, the second exhaust gas inlet 15 is arranged downstream of the first exhaust gas inlet 12 in the flow direction of the material.

[0066] The oxidant line 14 preferably has a control element, such as a valve or a flap, by means of which the amount of oxidant entering the firing gas line 4 can be adjusted. The control element is preferably connected to a control device which is particularly designed to control the amount of oxidant in the firing gas line 4 as a function of the oxygen content and / or CO2 content of the exhaust gas.

[0067] The cooling gas removal line 11 preferably has a control element, such as a valve or a flap, which can be used to adjust the amount of cooling gas discharged via the cooling gas removal device 17. The control element is preferably connected to a control device, wherein the control device is designed in particular such that the amount of cooling gas discharged via the cooling gas removal device 17 is controlled as a function of the oxygen and / or CO2 content of the cooling gas.

[0068] The control mechanism is particularly intended for very substantial removal of cooling gas from the PFR shaft kiln 1 , with minimal or preferably zero CO 2 in the cooling gas removal line 11 .

[0069] The lime produced in the PFR shaft kiln 1 described above is highly reactive and produces a process gas with a CO2 content exceeding 90% on a dry basis. This process waste gas can be liquefied and stored with relatively low complexity. For example, the liquefied process waste gas can be fed to further process steps or stored. Alternatively, the PFR shaft kiln can be used to produce waste gas with a low CO2 content, for example, 45% for soda ash production, 35% for sugar production, or 30% for precipitated calcium carbonate production.

[0070] Figure 2 A detail of a cross section of a PFR kiln 1 is shown, illustrating the second flue gas inlet 15 for introducing flue gas into the preheating zone 21. The second flue gas inlet 15 is located at a vertical distance B from the upper end of the combustion zone 20, which is located at the level of the combustion gas outlets of the burner lances 10. For example, the shaft 2 may have five burner lances 10, all terminating at the same height. It is also conceivable that the burner lances 10 terminate at different heights, in which case the upper end of the combustion zone 20 begins at the uppermost flue gas outlet of the burner lance 10. The preheating zone 21 has a length A extending from the upper end of the preheating zone 21 downward to the upper end of the combustion zone 20. The upper end of the preheating zone 21 is located, for example, at the level of the material inlet 3 or the material bed. Preferably, the ratio B / A (distance B to length A) is 0 to 0.5, particularly 0.2 to 3, and preferably 0.25. Positioning the second flue gas inlet at this length ratio provides an optimal location for flue gas introduction.

[0071] Preferably, the gas temperature within the preheating zone 21 is approximately 80°C to 800°C, while the gas temperature at the exhaust gas outlet 6 of the preheating zone 21 is approximately 80°C to 100°C. At the end of the preheating zone 21, particularly at the transition between the preheating zone 21 and the combustion zone 20, the temperature is approximately 800°C to 900°C. The temperature within the preheating zone 21 preferably increases continuously in the direction of material flow. In particular, the second exhaust gas inlet 15 is positioned at a level within the preheating zone 21 at which the temperature within the preheating zone is approximately 500°C to 700°C, preferably 550°C to 650°C, and particularly 600°C.

[0072] The exhaust gas line 39 preferably has a compressor designed to compress the exhaust gas to approximately 100 mbar to 500 mbar upstream of the inlet into the preheating zone 21 .

[0073] Reference Signs

[0074] 1 Kiln

[0075] 2 Shaft

[0076] 3 Material entrance / gate

[0077] 4 Firing gas pipeline

[0078] 6 Exhaust gas outlet

[0079] 8 Heating device

[0080] 9 Fuel lines

[0081] 10 Burner gun

[0082] 11 Cooling gas removal line

[0083] 12 Firing gas inlet / first exhaust gas inlet

[0084] 13 Firing Room Level

[0085] 14 Oxidant pipeline

[0086] 15 Gas inlet / second exhaust gas inlet

[0087] 16 filters

[0088] 17 Cooling gas removal device

[0089] 18 Annular pipe / no material space

[0090] 19 Connecting pipes

[0091] 20 Burning Zone

[0092] 21 Preheating Zone

[0093] 22 Cooling Zone

[0094] 23 Cooling gas inlet

[0095] 25 outlet funnel

[0096] 26 inner cylinder

[0097] 29 Cooling gas outlet

[0098] 30 Cooling gas inlet

[0099] 31 Exhaust filter

[0100] 32 Cooling device

[0101] 33-37 Compressor

[0102] 39 Exhaust pipe

[0103] 40 Material outlet / gate

[0104] 41 Discharge device

[0105] 43 Heat exchanger / regenerator

[0106] 47 Heating device

[0107] 48 Cooling air lines.

Claims

1. A method for burning materials, such as carbonate rocks, in a parallel flow regenerative shaft kiln (1), the shaft kiln (1) having two shafts (2), which are operated alternately as a combustion shaft and a regeneration shaft and are connected to one another via a connecting pipe (19), wherein: The material flows through the material inlet (3) to the material outlet (40), enters the preheating zone (21) for preheating the material, the combustion zone (20) for burning the material, and the cooling zone (22) for cooling the material. wherein cooling gas is fed into the cooling zone (22), wherein the exhaust gas is discharged from a shaft (2) of the kiln via an exhaust gas outlet (6) arranged in or above the preheating zone (21), and wherein the exhaust gas discharged from the shaft (2) through the exhaust gas outlet (6) is divided into a first portion of exhaust gas and a second portion of exhaust gas, and wherein a first portion of the exhaust gas is fed to the upper region of the preheating zone (21) via a first exhaust gas inlet (12), It is characterized by: A second portion of the exhaust gas discharged from the shaft (2) is fed via a second exhaust gas inlet (15) to the preheating zone (21) downstream of the first exhaust gas inlet (12).

2. The method according to claim 1, wherein Oxygen is fed to the first and / or second portion of the exhaust gas before being introduced into the preheating zone (21).

3. A method according to any one of the preceding claims, wherein Before being introduced into the preheating zone (21) of the combustion shaft, the second portion of the exhaust gas is compressed to approximately 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, in particular 500 mbar.

4. A method according to any one of the preceding claims, wherein A second portion of the exhaust gas is introduced into the preheating zone (21) at the lower end of the preheating zone (21).

5. A method according to any one of the preceding claims, wherein Before being introduced into the second exhaust gas inlet (15), the second portion of the exhaust gas is heated to a temperature of 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C.

6. A method according to any one of the preceding claims, wherein The second portion of the exhaust gas is introduced into a region of the preheating zone (21) at a temperature corresponding to the temperature of the second portion of the exhaust gas and / or at a temperature of 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C.

7. A method according to any one of the preceding claims, wherein The preheating zone (21) has a length (A) extending in the flow direction of the material, and wherein the second exhaust gas inlet (15) for introducing exhaust gas into the preheating zone (21) is at a distance (B) from the upper end of the combustion zone (20) in the flow direction of the material, and wherein the ratio (B / A) of the distance (B) to the length (A) is 0 to 0.5, in particular 0.2 to 0.3, preferably 0.

25.

8. A method according to any one of the preceding claims, wherein The cooling gas heated in the cooling zone (22) is discharged from the cooling zone (22) of the shaft (2) via a cooling gas removal device (17), and wherein the cooling gas discharged from the cooling zone (22) is fed to a heat exchanger (43) for heating a second portion of the exhaust gas.

9. A parallel flow regenerative shaft kiln (1) for burning and cooling materials such as carbonate rocks, comprising two shafts (2) which can be operated alternately as a combustion shaft and a regeneration shaft and are connected to one another via a connecting pipe (19). in, Each shaft (2) has a preheating zone (21) for preheating the material, a combustion zone (20) for burning the material, and a cooling zone (22) for cooling the material in the flow direction of the material. wherein at least one shaft (2) of the PFR shaft kiln (1) has an exhaust gas outlet (6) arranged in or above the preheating zone (21) for discharging exhaust gas from the shaft (2) and a first exhaust gas inlet (12) for introducing exhaust gas, and wherein the exhaust gas outlet (6) is connected to the first exhaust gas inlet (12) to introduce a first portion of the exhaust gas into the preheating zone (21), It is characterized by: The shaft (2) has a second exhaust gas inlet (15) in the preheating zone (21), which passes the first exhaust gas inlet (12) in the flow direction of the material and is connected to the exhaust gas outlet (6) to introduce a second part of the exhaust gas into the preheating zone (21).

10. The PFR shaft kiln (1) according to claim 9, wherein: The shaft kiln (1) has a control element upstream of the first exhaust gas inlet and / or the second exhaust gas inlet (12, 15) for controlling the amount of exhaust gas fed via the first exhaust gas inlet or the second exhaust gas inlet (12, 15) to the preheating zone (21) of the shaft (2) operated as a combustion shaft and / or the shaft (2) operated as a regeneration shaft.

11. The PFR shaft kiln (1) according to any one of claims 9 and 10, wherein The shaft kiln (1) has at least one oxidant line (14) connected to the first and second exhaust gas inlets and / or the second exhaust gas inlet (12, 15) for introducing an oxidant into the exhaust gas.

12. The PFR shaft kiln (1) according to any one of claims 9 to 11, wherein The compressor connected upstream of the second exhaust gas inlet (15) is designed and arranged such that it compresses the exhaust gas to a pressure of 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, in particular 500 mbar, before it is introduced into the second exhaust gas inlet (15) of the combustion shaft.

13. The PFR shaft kiln (1) according to any one of claims 9 to 12, wherein: The second exhaust gas inlet (15) is provided at the lower end of the preheating zone (21).

14. The PFR shaft kiln (1) according to any one of claims 9 to 13, wherein The heat exchanger (43) arranged between the exhaust gas outlet (6) and the second exhaust gas inlet (15) is designed and arranged to heat the second part of the exhaust gas to a temperature of 500° C. to 800° C., in particular 550° C. to 700° C., preferably 600° C.

15. The PFR shaft kiln (1) according to any one of claims 9 to 14, wherein The preheating zone (21) has a length (A) extending in the flow direction of the material, and wherein the second exhaust gas inlet (15) for introducing the exhaust gas into the preheating zone (21) has a distance (B) from the upper end of the combustion zone (20) in the flow direction of the material, and wherein the ratio (B / A) of the distance (B) to the length (A) is 0 to 0.5, in particular 0.2 to 0.3, preferably 0.

25.

16. The kiln (1) according to claim 14, wherein The cooling zone (22) has a cooling gas inlet (23) for introducing cooling gas into the cooling zone (22) and a cooling gas removal device (17) for discharging cooling gas from the shaft (2), and wherein the cooling gas removal device (17) is connected to the heat exchanger (43) to heat a second portion of the exhaust gas.

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