Direct current / countercurrent regenerative shaft furnace and process for burning carbonate rock

Abstract

The invention comprises a method for burning material, such as carbonate rocks, in a co-current counter-current regenerative shaft furnace (1) with two shafts (2) which are operated alternately as a burning shaft and as a regenerative shaft and are connected to each other by means of a connecting channel (19), wherein the material flows through a material inlet (3) into 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 to a material outlet (40), wherein a cooling gas is admitted into the cooling zone, wherein exhaust gas is discharged from one of the shafts (2) via an exhaust gas outlet (6), wherein a fuel and oxygen are supplied to a first part of the exhaust gas discharged from the shaft (2) via the exhaust gas outlet (6) before being introduced into the shaft (2).

Description

The invention relates to a direct-current counter-current regenerative shaft furnace (DGR shaft furnace) and a method for firing and cooling material, such as carbonate rocks, with a DGR shaft furnace. The firing of carbonate rock in a GGR shaft kiln has been known for about 60 years. Such a GGR shaft kiln, known, for example, from WO 2011 / 072894 A1, has two vertical, parallel shafts that operate cyclically. Firing takes place in only one shaft at a time, the firing shaft, while the other shaft serves as a regeneration shaft. Oxide gas is fed into the firing shaft in co-current flow with the material and fuel. The resulting hot exhaust gases, together with the heated cooling air supplied from below, are routed via the overflow channel into the exhaust gas shaft. There, the exhaust gases are directed upwards in counter-current flow to the material, preheating it in the process. The material is typically fed into the shaft from above along with the oxidizer gas, with fuel being introduced into the firing zone. The material to be burned typically passes through a preheating zone in each shaft, followed by a combustion zone where the material is burned, and then a cooling zone where cooling air is supplied to the hot material. During operation of the GGR shaft furnace, fuel is fed into the combustion zone of the shaft via burner lances and preferably combusted within the combustion zone as it exits the burner lances. However, incomplete combustion of the fuel at the burner lances is common, leading to backflow or, in the worst case, blockage of the burner lances. Starting from this, the object of the present invention is to provide a GGR shaft furnace and a method for burning carbonate rock with a GGR shaft furnace, with which sufficient combustion of the fuel in the vicinity of the burner lances is ensured. This problem is solved according to the invention by a device having the features of independent method claim 1 and by a method having the features of independent device claim 10. Advantageous embodiments are described in the dependent claims. According to a first aspect, the invention comprises a method for firing and, in particular, subsequently cooling material, such as carbonate rocks, in a shaft kiln with only one shaft or in a co-current counter-current regenerative shaft kiln with two shafts, which are operated alternately as firing shafts and as regenerative shafts and are connected to each other by means of a connecting channel. In the co-current regenerative shaft kiln, the material flows through a material inlet into a preheating zone for preheating the material, a firing zone for firing the material, and a cooling zone for cooling the material to a material outlet, with a cooling gas being introduced into the cooling zone. The exhaust gas is discharged from one of the shafts via an exhaust gas outlet, with the exhaust gas discharged from the shaft via the exhaust gas outlet being at least partially introduced into at least one of the shafts.The exhaust gas is introduced, for example, directly into one of the shafts or indirectly via the connecting duct. Preferably, a fuel and oxygen are supplied to a first portion of the exhaust gas discharged from the shaft via the exhaust gas outlet before it is introduced into the shaft. In particular, the exhaust gas is routed through a fuel line connecting the exhaust gas outlet and the exhaust gas inlet into the shaft and mixed with the fuel and oxygen. Preferably, the exhaust gas inlet into the shaft is an inlet to a plurality of burner lances. The mixture of exhaust gas and oxygen preferably serves as a carrier gas for the fuel and ensures optimal combustion of the fuel, especially directly below the outlets of the burner lances in the combustion zone of the shaft. The fuel is, for example, a ground solid fuel such as coal or biomass. The material to be burned is preferably limestone or dolomite with a grain size of 10 to 200 mm, preferably 15 to 120 mm, and most preferably 30 to 100 mm. The cooling gas is, for example, air. The shaft kiln with only one shaft is preferably designed as an annular shaft kiln with an inner cylinder extending from the cooling zone to the firing zone and preferably into the preheating zone. The co-current counter-current regenerative shaft kiln has at least two shafts, which are preferably arranged parallel to each other and vertically. The shafts can be operated alternately as a firing shaft and as a regenerative shaft, with each shaft having, in the direction of material flow, a preheating zone for preheating the material, a firing zone for firing the material, and a cooling zone for cooling the material. Each shaft preferably has a material inlet for introducing material to be fired into the shaft, the material inlet being located, in particular, at the upper end of the respective shaft so that the material falls into the respective shaft by gravity.The material inlet and / or outlet is / are designed, in particular, as an airlock for introducing and / or discharging material into the shaft furnace. A material inlet designed as an airlock is preferably configured such that only the raw material to be burned enters the shaft, but not the ambient air. The airlock also prevents gas from escaping the shaft via the material inlet. Preferably, the airlock is designed to seal the shaft airtight against the environment while allowing solids, such as the material to be burned, to enter the shaft. The connecting channel is designed for the gas connection between the two shafts and preferably connects the combustion zones of the shafts. During operation of the GGR shaft kiln, one of the shafts is operated as the combustion shaft and is active, while the other shaft is operated as the regenerative shaft and is passive. The GGR shaft kiln is operated cyclically, with the function of the shafts being exchanged after the cycle time has elapsed. This process is repeated continuously. In the active shaft operated as the combustion shaft, fuel is introduced into the combustion zone via the burner lances. The material to be burned is preferably heated to a temperature of approximately 700°C in the preheating zone of the combustion shaft. In the shaft operated as the combustion shaft, the combustion zone is designed as a co-current combustion zone, with the material to be burned flowing parallel to the gas.Within the combustion shaft, the gas flows from the preheating zone into the combustion zone and then via the connecting channel into the combustion zone and the preheating zone of the regeneration shaft. In the shaft operated as a regeneration shaft, the gas flows counter-currently to the material being burned in the preheating zone and the combustion zone. In both the combustion chamber and the regeneration chamber, cooling gas is passed through the cooling zone in counterflow to the material to be cooled and preferably completely discharged from the chamber via the cooling gas outlet of the cooling air exhaust device, so that preferably no cooling gas flows from the cooling zone into the combustion zone. Each shaft preferably has at least one exhaust gas outlet, for example, at the upper end of the shaft within the preheating zone. Preferably, the exhaust gas outlet is located above the material column in a material-free area of ​​the preheating zone. The exhaust gas is preferably discharged exclusively from one shaft, in particular the regeneration shaft. The discharged exhaust gas is preferably fed to the other shaft, in particular the combustion shaft, and / or to the regeneration shaft via the connecting channel. Preferably, only a portion of the exhaust gas discharged from the regeneration shaft is fed back into at least one shaft. A portion of the exhaust gas discharged from the regeneration shaft is, for example, removed from the GGR shaft furnace and, for example, subjected to further treatment, such as sequestration. The exhaust gas preferably consists of CO2 and optionally H2O. Fuel is preferably supplied to the combustion zone and / or preheating zone of the shaft operated as a combustion shaft via a fuel line. Preferably, the fuel is supplied to burner lances arranged in the combustion zone and / or preheating zone. In the combustion zone, the material is preferably heated to a temperature of approximately 1100°C. Each shaft preferably has a plurality of burner lances that extend at least partially through the preheating zone and in particular lead into the combustion zone of the respective shaft and serve to convey, for example, fuel and / or an oxidizing gas, such as air or oxygen-enriched air or pure oxygen. Recirculating the exhaust gas into at least one shaft enables the production of highly reactive lime, while simultaneously generating process gas with a CO2 content exceeding 90% of dry gas. Such process gas can be liquefied and sequestered with less effort. For example, the liquefied process gas can be fed into further process steps or stored. Alternatively, the GGR shaft furnace described above can also be used to produce exhaust gas with a lower CO2 content, such as 45% for soda production, 35% for sugar production, or 30% for the production of precipitated calcium carbonate. According to a first embodiment, each shaft has a plurality of burner lances in the combustion zone and / or the preheating zone, wherein the first part of the exhaust gas is fed into the burner lances together with the fuel and the oxygen. In particular, the GGR shaft furnace has a plurality of fuel lines, wherein the number of fuel lines preferably corresponds to the number of burner lances, and in particular, each burner lance is connected to a respective fuel line for supplying fuel to the burner lance. Preferably, the first part of the exhaust gas is mixed uniformly with the ground fuel and the oxygen and introduced into the burner lances. In particular, the fuel line is connected to an oxidizer line for supplying the oxygen, in particular oxygen-containing gas. The oxygen-containing gas preferably has an oxygen content of at least 70 to 95 vol%, preferably 90 vol%.The oxidizing agent line is preferably connected to an oxygen source, such as a tank or the ambient air. According to a further embodiment, the first part of the exhaust gas is mixed with oxygen and then with the fuel. The oxygen is preferably added to the first part of the exhaust gas before the fuel is injected, i.e., upstream of the fuel injection point. According to a further embodiment, a second portion of the exhaust gas discharged from the shaft via the exhaust gas outlet is introduced into the preheating zone and / or the combustion zone of the shaft operated as a combustion shaft. Preferably, the second portion of the exhaust gas is routed separately to the first portion of the exhaust gas, which is mixed with fuel and oxygen, in a combustion gas line and, in particular, is not fed to the burner lances. Preferably, each shaft has a gas inlet, in particular a combustion gas inlet, which is arranged in the upper region of the shaft in the preheating zone, the connecting channel, or the combustion zone and also serves as the inlet for the gas required for combustion. The second portion of the exhaust gas is preferably routed, at least partially, to the gas inlet. Preferably, the gas inlet is arranged above the material column in a material-free space within the preheating zone.A control device, such as a valve or a variable-flow compressor, is preferably installed upstream of the gas inlet, allowing the amount of exhaust gas and / or oxidizer entering the shaft to be adjusted. The exhaust gas discharged from the shaft preferably has a temperature of approximately 60°C to 160°C, particularly 100°C. Preferably, only a portion of the exhaust gas is introduced into the preheating zone of the combustion chamber. Recirculating the exhaust gases into the preheating zone allows for an increase in the gas volume in the shaft, while simultaneously ensuring a high CO2 concentration in the exhaust gas. For example, the first and / or the second part of the exhaust gas is heated to a temperature of 600°C to 1100°C, preferably 1000°C, in a heat exchanger before being introduced into the shaft, in particular into the gas inlet. The coolant gas heated in the cooling zone is preferably discharged from the cooling zone of the shaft via a coolant gas discharge device. Specifically, the coolant gas introduced into the cooling zone is completely discharged from the respective shaft via the coolant gas discharge device. The coolant gas is preferably introduced into the cooling zone from below via a coolant gas inlet located in the lower part of the cooling zone. The coolant gas discharge device preferably has a coolant gas outlet for releasing the coolant gas from the shaft. The coolant gas outlet is preferably connected to a coolant gas discharge line for conveying the discharged coolant gas. Specifically, the coolant gas discharged from the cooling zone is fed to a heat exchanger to heat the exhaust gas. The exhaust gas discharged via the exhaust gas outlet is preferably heated in counterflow by the discharged coolant gas before being introduced into the connecting channel and / or the preheating zone of the regeneration shaft and / or combustion shaft.Preferably, the exhaust gas is heated to a temperature of 400°C to 800°C, in particular 600°C, by means of the heat exchanger. The cooling gas exhaust line preferably includes a control element, such as a valve or a flap, by which the amount of cooling gas to be discharged via the cooling gas exhaust device can be adjusted. The cooling zone preferably includes a cooling gas inlet for introducing cooling gas into the cooling zone and a cooling gas exhaust device for removing cooling gas from the shaft. The cooling gas exhaust device, for example, has a material-free space within the cooling zone of the shaft. In particular, the material-free space is designed as an outer annular space that extends circumferentially around, preferably, the upper region of the cooling zone adjacent to the combustion zone. The cooling gas outlet is located, in particular, within this material-free annular space. The material-free space of the cooling gas exhaust device is, for example, designed as an inner cylinder that extends, in particular, centrally and vertically through the cooling zone. In particular, the inner cylinder extends at least partially into the combustion zone. The cooling gas outlet for releasing the cooling gas from the shaft is located within the inner cylinder.The inner cylinder preferably has a cooling gas inlet for introducing cooling gas from the cooling zones into the interior of the inner cylinder, the cooling gas inlet preferably being arranged above the cooling gas outlet in the inner cylinder. 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 zone and then into the inner cylinder of the cooling gas extraction device. Within the inner cylinder, the cooling gas preferably flows downwards towards the cooling gas outlet and into the cooling gas extraction line. A cooling gas extraction device designed as an inner cylinder allows for a low overall height of the cooling zone and a comparatively simple retrofit of known GGR shaft furnaces. The cooling gas exhaust device is preferably designed to release all the cooling gas from the shaft, so that preferably no cooling gas enters the combustion zone or the connecting channel for linking the combustion zones of the shafts. In particular, the cooling gas exhaust device is connected to a control element, such as a flap or a valve, for adjusting the amount of cooling gas to be extracted. According to a further embodiment, the amount of oxygen supplied to the first and second parts of the exhaust gas is adjusted. Preferably, the total amount of oxygen supplied to the first and second parts of the exhaust gas is constant during operation of the GGR shaft furnace, preferably disregarding the switching process. According to a further embodiment, the amount of oxygen introduced into the first part of the exhaust gas is adjusted depending on the amount of fuel introduced into the first part of the exhaust gas, the particle size of the fuel, and / or the calorific value of the fuel introduced into the first part of the exhaust gas. This ensures optimal combustion of the fuel below the burner lances and in the combustion zone of the combustion chamber, thus preventing the burner lances from becoming clogged with unburned fuel. According to a further embodiment, the method comprises a switching process for switching the shaft operated as a combustion shaft to the shaft operated as a regeneration shaft, wherein the switching process comprises the following successive steps: - switching off the fuel supply to the first part of the exhaust gas; - introducing the mixture of the first part of the exhaust gas and oxygen into the burner lances over a burnout interval; - after the burnout interval, switching off the supply of oxygen to the first part of the exhaust gas. The oxygen supply to the burner lances is thus switched off with a delay during the changeover process. During the burnout interval, all remaining fuel in the burner lances is combusted, preventing clogging. Preferably, the oxygen supply to the first part of the exhaust gas, particularly to the fuel line, is stopped immediately after the burnout interval. Specifically, the first part of the exhaust gas continues to be routed to the burner lances after the burnout interval without additional oxygen or fuel. According to a further embodiment, the oxygen supply to the first part of the exhaust gas is increased during the burn-off period. Preferably, the oxygen supply to the second part of the exhaust gas is reduced or stopped during the burn-off period. This ensures that a larger quantity of oxygen is introduced into the first part of the exhaust gas, which is directed to the burner lances, thus guaranteeing rapid and complete combustion of the remaining fuel below the burner lances. According to another embodiment, the burnout time interval is 20 seconds to 2 minutes, and in particular less than 1 minute. By supplying additional oxygen during the burnout interval, this interval can be significantly reduced, thus considerably shortening the switching process and enabling more efficient operation of the GGR shaft furnace. According to one embodiment, the first part of the exhaust gas is dried in a drying device before the fuel is introduced into the first part of the exhaust gas. Preferably, the exhaust gas is dried so that it has a moisture content of a maximum of 5 to 10 vol%, and in particular a maximum of 7 vol%. A dried exhaust gas with a very low moisture content of, for example, a maximum of 7 vol% H₂O reliably prevents the fuel from clumping within the fuel line. The invention also includes a shaft kiln with only one shaft or a co-current counter-current regenerative shaft kiln for firing and cooling materials such as carbonate rocks. The embodiments and advantages described with regard to the method for firing materials such as carbonate rocks in a co-current counter-current regenerative shaft kiln also apply to the GGR shaft kiln in a correspondingly adapted form. The GGR shaft kiln comprises two shafts, which are operated alternately as a firing shaft and a regeneration shaft and are connected to each other by a connecting channel. Each shaft has, in the direction of material flow, a preheating zone for preheating the material, a firing zone for firing the material, and a cooling zone for cooling the material. Each shaft also has an exhaust gas outlet for venting exhaust gas from the shaft. The at least one exhaust gas outlet is connected to a gas inlet for introducing gas into at least one shaft. Preferably, the GGR shaft kiln has a plurality of gas inlets for introducing exhaust gas drawn from at least one of the shafts.The exhaust gas outlet is connected via a fuel line to a plurality of burner lances, the fuel line being connected to a first oxidizer line for supplying oxidizer to the fuel line and to a fuel supply device for supplying fuel to the fuel line. According to one embodiment, the exhaust gas outlet is connected via a combustion gas line to a combustion gas inlet in the preheating zone and / or a gas inlet in the preheating zone or the combustion zone of the shaft operated as a combustion shaft, wherein the combustion gas line is connected to a second oxidizer line for supplying oxidizer to the combustion gas line. According to one embodiment, the GGR shaft furnace has a control device which is connected to the first and / or the second oxidizer line in such a way that the amount of oxidizer in the fuel line and / or the combustion gas line can be adjusted by means of the control device. The oxidizer lines preferably each have a control element, such as a valve or a flap, by which the amount of oxidizer in the respective oxidizer line can be adjusted. The control element is preferably connected to the control device, which is particularly designed to adjust, in particular control or regulate, the amount of oxidizer in the oxidizer line depending on the amount of fuel introduced into the first part of the exhaust gas, the particle size of the fuel, and / or the calorific value of the fuel introduced into the first part of the exhaust gas. The control system serves in particular to ensure complete combustion of the fuel that is supplied to the burner lances via the fuel line. According to a further embodiment, the fuel line is connected to a gas dryer for drying the gas flowing in the fuel line. The fuel line is preferably connected to a fuel supply device for feeding fuel into the fuel line. The fuel supply device preferably comprises a fuel storage unit and a feeding device, such as a rotary valve, a control slide, a valve, or a metering element, such as a metering scale. The gas dryer for drying the first part of the exhaust gas is preferably arranged upstream of the fuel supply device. The gas dryer is preferably designed to cool and then heat the gas. The gas dryer is preferably arranged upstream of the fuel supply device so that the first part of the exhaust gas is dried in the gas dryer and the fuel is then introduced into the fuel line. The regulation serves in particular to ensure the most complete possible extraction of the cooling gas from the GGR shaft furnace while simultaneously minimizing or preferably eliminating CO2 in the cooling gas extraction line. According to one embodiment, the gas inlet is arranged in the preheating zone of the shaft operated as a combustion chamber. The gas inlet in the preheating zone of the combustion chamber is preferably a combustion gas inlet, through which, in addition to the exhaust gas, an oxidizing agent is preferably introduced into the preheating zone. The gas inlet is preferably arranged at the upper end of the preheating zone. According to a further embodiment, the gas inlet is arranged in the connecting channel for the gas connection of the combustion zones of the shafts and / or in the combustion zone of the shaft, in particular the regeneration shaft, and / or in a material-free space within the shaft. In particular, the material-free space is designed as an outer annular space that extends circumferentially around, preferably, the upper region of the cooling zone adjacent to the combustion zone. According to a further embodiment, a heat exchanger and / or a heating device, in particular an electric heating device, a solar heating device, or a combustion reactor, is arranged between the exhaust gas outlet and the gas inlet in the connecting channel for the gas connection of the combustion zones of the shafts and / or in the combustion zone for heating the exhaust gas. For example, the heat exchanger is arranged upstream of the heating device in the direction of exhaust gas flow. It is also conceivable that only a heat exchanger or a heating device is present for heating the exhaust gas. According to a further embodiment, each shaft has a combustion gas inlet for introducing combustion gas into the preheating zone and / or the combustion zone, wherein the combustion gas inlet is connected to an oxidizer line for introducing an oxidizer into the shaft. The combustion gas inlet is preferably connected to the exhaust gas outlet for directing the exhaust gas into the shaft. Description of the drawings The invention is explained in more detail below with reference to several exemplary embodiments and the accompanying figures. Fig. 1 shows a schematic representation of a GGR shaft furnace in a sectional view according to one exemplary embodiment. Figs. 2 and 3 each show a schematic representation of a section of a GGR shaft furnace in a cross-sectional view at the level of the burner lances according to one exemplary embodiment. Fig. 1 shows a GGR shaft kiln 1 with two parallel and vertically oriented shafts 2. The shafts 2 of the GGR shaft kiln 1 are essentially identical, so that in Fig. 1 only one of the two shafts 2 is labelled and, for the sake of simplicity, only one of the two shafts 2 will be described below. Each shaft 2 has a material inlet 3 for introducing material to be fired into the respective shaft 2 of the GGR shaft kiln 1. The material to be fired is, in particular, limestone and / or dolomite, preferably with a grain size of 10 to 200 mm, more preferably 15 to 120 mm, and most preferably 30 to 100 mm. The material inlets 3 are, by way of example, arranged at the upper end of the respective shaft 2, so that the material falls into the shaft 2 through the material inlet 3 by gravity.The material inlet 3 is designed, for example, as the upper opening of the shaft 2 and, in particular, as an airlock 3, and preferably extends over the entire or a part of the cross-section of the shaft 2. A material inlet designed as an airlock 3 is preferably configured such that only the raw material to be burned enters the shaft 2, but not the ambient air. Preferably, the airlock 3 is designed such that it seals the shaft 2 airtight against the environment and allows the entry of solids, such as the material to be burned, into the shaft. Each shaft 2 has a combustion gas inlet 12 at its upper end for introducing combustion gas for the combustion of fuels. The combustion gas is, for example, dedusted exhaust gas from at least one of the shafts 2, the exhaust gas preferably being enriched with oxygen. Furthermore, each shaft 2 has an exhaust gas outlet 6 for releasing exhaust gases from the respective shaft 2. Each exhaust gas outlet 6 and combustion gas inlet 12 is optionally assigned a control element. The amount of combustion gas entering the respective combustion gas inlet 12 and the amount of exhaust gas to be discharged via the respective exhaust gas outlet 6 can preferably be adjusted by means of the control elements, such as a variable-flow compressor 35. The combustion gas inlet 12 and the exhaust gas outlet are optionally arranged at the same height and, in particular, within the preheating zone 21 of the respective shaft 2. At the lower end of shaft 2, a material outlet 40 is arranged for discharging the calcined material. The material outlet 40 is, for example, a lock as described with reference to the material inlet 3. The calcined material is directed, for example, into an outlet hopper 25, to which the material outlet 40 of shaft 2 is connected. The outlet hopper 25 is, for example, funnel-shaped. The outlet hopper 25 preferably has a cooling gas inlet 23 for introducing cooling gas into the respective shaft 2. The cooling gas is preferably directed into the cooling gas inlet by means of a compressor 33. During operation of the GGR shaft furnace 1, the material to be burned flows from top to bottom through the respective shaft 2, while the cooling air flows from bottom to top, counter-current to the material, through the respective shaft 2. The furnace exhaust gas is discharged from the shaft 2 through the exhaust gas outlet 6. Below the material inlet 3 and the combustion gas inlet 12, the preheating zone 21 of the respective shaft 2 adjoins the material flow. In the preheating zone 21, the material and the combustion gas are preferably preheated to approximately 700°C. Preferably, the respective shaft 2 is filled with material to be incinerated. The material is preferably fed into the respective shaft 2 above the preheating zone 21. At least a portion of the preheating zone 21 and the portion of the respective shaft 2 adjoining it in the material flow direction are, for example, surrounded by a refractory lining. In the preheating zone 21, a plurality of burner lances 10 are optionally arranged, each serving as an inlet for fuel, such as a fuel gas, oil, or ground solid fuel. The GGR shaft furnace 1, for example, has a cooling device for cooling the burner lances 10. The cooling device comprises, for example, a plurality of cooling air ring lines that extend in a ring shape around the shaft area in which the burner lances 10 are arranged. Cooling air or, preferably, exhaust gas, which is extracted and compressed after the cooling device 32, flows through the cooling air ring lines to cool the burner lances 10 at the regeneration shaft. Preferably, a plurality, for example twelve or more, of burner lances 10 are arranged in each shaft 2 at substantially uniform intervals. In particular, the GGR shaft furnace 1 has a plurality of fuel lines 9, the number of fuel lines preferably corresponding to the number of burner lances 10. In particular, each burner lance is connected to a respective fuel line 9 for supplying fuel to the burner lance 10. The burner lances 10 are, for example, L-shaped and preferably extend horizontally into the respective shaft 2 and vertically within the shaft 2, particularly in the direction of material flow. The ends of the burner lances 10 of a shaft 2 are preferably all arranged at the same level. Preferably, the plane on which the lance ends are arranged is the lower end of the respective preheating zone 21.The burner lances 10 are preferably connected to a fuel line 9 for supplying fuel to the burner lances 10. The fuel line 9 is, for example, at least partially configured as a ring line extending circumferentially around the respective shaft 2. Preferably, a gas mixture consisting of a portion of the exhaust gas discharged via the exhaust gas outlet, oxygen, and a fuel flows in the fuel line. Preferably, each shaft 2 has a fuel line 9 assigned to the burner lances 10 of the shaft 2, each of which includes a control element for adjusting the amount of fuel, particularly the amount of gas, supplied to the burner lances 10. The combustion zone 20 adjoins the preheating zone 21 in the direction of material flow. In the combustion zone 20, the fuel is burned and the preheated material is fired at a temperature of approximately 1000°C. The GGR shaft furnace 1 also has a connecting channel 19 for gas-technical connection of the two shafts 2. In particular, no material to be fired is present in the connecting channel 19. Fig. 1 shows an example of a GGR lime kiln 1 with round shaft cross-sections. However, the shaft cross-section can have a different geometric contour, such as round, semicircular, oval, square, or polygonal. The combustion zone 20 extends, by way of example, in a shaft section with a cross-section that is essentially constant or increases slightly towards the bottom. In the direction of material flow in each shaft 2, a cooling zone 22 adjoins the combustion zone 20 and extends to the discharge device 41. The combustion zone 20, in particular the shaft section of the combustion zone 20, extends with its lower portion into the upper portion of the cooling zone 22, in particular the shaft section of the cooling zone 22, so that an annular channel 18 is formed between the two shaft sections. The annular channel 18 forms a material-free space in which no material to be burned is located. The second shaft section of the cooling zone 22 has, by way of example, a larger cross-section in its upper portion than the shaft section of the combustion zone 20. The annular channel 18 preferably extends circumferentially around the lower portion of the shaft section of the combustion zone 20. The shafts 2 of Fig. 1 each have, for example, an annular channel 18, which is connected to the connecting channel 19. Cooling zone 22 is located in a shaft section with a cross-section that is essentially constant or decreases downwards. Within cooling zone 22, the material is cooled to approximately 100°C in counterflow to the cooling gas flowing through it. Each cooling zone 22 has a cooling gas exhaust device 17, each with a 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 cooling gas outlet 29 of the cooling gas exhaust device 17 and out of the respective shaft 2. The cooling gas exhaust device 17 comprises an inner cylinder 26 that extends at least partially from the cooling zone 22 into the combustion zone 20 and has a cooling gas outlet 29 that is connected to the cooling gas exhaust line 11. Each shaft 2 of the GGR shaft furnace 1 has, for example, an inner cylinder 26 that extends vertically through the cooling zone 22 in the center. For example, the inner cylinder 26 extends from the discharge device 41 through the cooling zone 22 into the combustion zone 20 up to the level of the connecting channel 19. The inner cylinder 26 of the cooling gas exhaust device 17 has a cooling gas outlet 29 that extends radially outwards from the inner cylinder 26 through the shaft wall and serves to direct cooling gas from the inner cylinder into the cooling gas exhaust line 11. The inner cylinder 26 also has a cooling gas inlet 30 for introducing cooling gas from the cooling zone 22 into the inner cylinder 26. The cooling gas inlet 30 extends through the inner cylinder wall into the cooling zone 22 and connects the interior of the inner cylinder 26 with the cooling zone 22. The cooling gas inlet 30 is preferably arranged above the cooling gas outlet 29 in the cooling zone 22. During operation of the GGR shaft furnace 1, the cooling gas flows from bottom to top through the cooling zone 22 and into the cooling gas inlet 30 in the inner cylinder 26 of the cooling gas exhaust device 17.Preferably, all the cooling gas introduced into the cooling zone 22 flows through the cooling gas inlets 30 into the cooling gas exhaust device 17, so that no cooling gas enters the combustion zone 20. The cooling air outlet 29 of the inner cylinder 26 is preferably located in the lower region of the cooling zone 22. The cooling gas flows, in particular, from the cooling gas inlet 30 in the inner cylinder 26 downwards to the cooling gas outlet 29. A discharge device 41 is preferably arranged at the material outlet end of each shaft 2. The discharge devices 41 comprise, for example, horizontal plates, preferably a discharge table, which allow lateral passage of the material between the discharge table and the inner housing wall of the GGR shaft furnace. The discharge device 41 is preferably designed as a push or rotary table or as a table with a push scraper. This enables a uniform throughput rate of the material being processed through the shafts 2. The discharge device 41 further comprises, for example, the discharge hopper 25, which connects to the discharge table and at the lower end of which the material outlet 40 is located. In the operation of the GGR shaft kiln 1, one of the shafts 2 is active at any given time, while the other shaft 2 is passive. The active shaft 2 is referred to as the firing shaft, and the passive shaft 2 as the regeneration shaft. The GGR shaft kiln 1 is operated primarily in cycles, with a typical number of cycles being, for example, 75 to 150 cycles per day. After the cycle time has elapsed, the function of the shafts 2 is reversed. This process is repeated continuously. Material such as limestone or dolomite is alternately fed into the shafts 2 via the material inlets 3. In the active shaft 2, which is operating as the firing shaft, fuel is introduced into the firing shaft 2 via the burner lances 10. The material to be fired is heated to a temperature of approximately 700°C in the preheating zone 21 of the firing shaft. In the embodiment shown in Fig. 1, the left shaft 2 is operated as a combustion shaft, while the right shaft 2 is operated as a regeneration shaft. During operation of the GGR shaft furnace 1, the cooling gas flows in counterflow to the material to be cooled through the cooling zone 22 in both the combustion shaft 2 and the regeneration shaft 2 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. Within shaft 2, which is operated as a combustion shaft, the combustion gas flows through the combustion gas inlet 12 into the combustion shaft and, in cocurrent flow with the material within the combustion zone 20, into the material-free space designed as an annular channel 18. From the material-free space 18, the gas flows via the connecting channel 19 into shaft 2, which is operated as a regeneration shaft. Within the regeneration shaft, the gas flows from the connecting channel 19 and the material-free space 18 of the regeneration shaft in countercurrent flow to the material to be burned, through the combustion zone 20 into the preheating zone 21 and exits the regeneration shaft through the exhaust gas outlet 6 of the regeneration shaft. Preferably, the exhaust gas discharged from shaft 2 has a temperature of 60°C to 160°C, preferably 100°C. The exhaust gas is directed into an exhaust gas line 39 connected to the exhaust gas outlet 6. Downstream of the exhaust gas outlet 6, the exhaust gas line 39 optionally includes an exhaust gas filter 31 for filtering fine particles, especially dust, from the exhaust gas. Downstream of the exhaust gas filter 31, a cooling device 32 is arranged, for example, to cool the exhaust gas. The cooling device 32 is, for example, a heat exchanger, which is preferably operated in counterflow with a coolant such as water. Downstream of the cooling device 32, a portion of the exhaust gas is diverted and preferably discharged for CO2 liquefaction. A further portion of the exhaust gas is recirculated to the combustion process. For example, a first portion of the exhaust gas discharged from shaft 2 via exhaust gas outlet 6 is fed to the burner lances 10 via fuel line 9, specifically into the burner lances 10. A second portion of the exhaust gas discharged from shaft 2 via exhaust gas outlet 6 is preferably fed to the preheating zone 21 and the combustion zone 20 of shaft 2 via a combustion gas line 4. Preferably, the combustion gas line 4 is connected to the combustion gas inlet 12, so that the second portion of the exhaust gas is at least partially directed to the combustion gas inlet 12. Preferably, the combustion gas line 4 is connected to a gas inlet 15 in the preheating zone 21 or the combustion zone 20, so that the second portion of the exhaust gas is at least partially directed to the gas inlet 15.The fuel line 9 is, by way of example, connected to a first oxidizing agent line 14a for supplying an oxidizing agent, such as oxygen-rich gas, to the fuel line 9. The oxidizing agent is preferably pure oxygen or an oxygen-rich gas with an oxygen content of at least 70 to 95%, preferably 90%. Preferably, the combustion gas line 4 has a branch for connecting the combustion gas line 4 to the gas inlet 15 and the combustion gas inlet 12. The fuel line 9 is preferably connected to a fuel supply device 27 for feeding fuel into the fuel line 9. The fuel supply device 27 preferably comprises a fuel storage unit and a feeding device, such as a rotary valve, a control slide, a valve, or a metering element, such as a metering scale. Upstream of the fuel supply device 27, a gas dryer for drying the first part of the exhaust gas is preferably arranged. The gas dryer is preferably designed to cool the gas and then heat it. Downstream of the branch, the combustion gas line 4, in the direction of exhaust gas flow, includes, for example, a compressor 35. A control element is preferably installed upstream of the combustion gas inlet 12, so that exhaust gas is supplied only to the combustion gas inlet 12 of the shaft 2, which is operated as a combustion chamber. The combustion gas line 4 is preferably connected to a second oxidizer line 14b, so that an oxidizer, preferably pure oxygen, is introduced into the combustion gas line 4 and subsequently, together with the exhaust gas, into the shaft 2 via the combustion gas inlet 12. It is also conceivable that an oxygen-rich gas with an oxygen content of at least 70 to 95%, preferably 90%, is introduced into the combustion gas line 4 as the oxidizer. The portion of the exhaust gas that is not returned to the combustion gas inlet 12 is fed in the combustion gas line 4 to the gas inlet 15, which is exemplified as being located in the preheating zone 21, the combustion zone 20, or the connecting channel 19. Downstream of the branch point in the direction of exhaust gas flow, the combustion gas line 4 preferably has a flow-controllable compressor 36 and a heat exchanger 43 for heating the exhaust gas. The heat exchanger 43 is exemplified as a recuperator, in which the exhaust gas is heated in counterflow to the extracted cooling gas, and the cooling gas is simultaneously cooled. The heat exchanger 43 is, in particular, connected to the cooling gas outlets 29 of both shafts 2 via a cooling gas discharge line 11, so that the exhaust gas is heated in the heat exchanger 43 by means of the extracted cooling gas, preferably in counterflow.Downstream of the heat exchanger 43, the cooling gas exhaust line 11 optionally includes a control device for adjusting the amount of cooling gas to be extracted and a filter 16 for removing dust from the cooling gas. The exhaust gas is preferably heated in the heat exchanger 43 to a temperature of approximately 500°C to 700°C, particularly 600°C. The GGR shaft furnace 1 comprises, in particular, two gas analysis devices (not shown) configured to determine the oxygen and / or CO2 content of the respective gas. One gas analysis device is, by way of example, arranged in the exhaust gas line 39 downstream of the branch of the combustion gas line 4 and is designed to determine the oxygen and / or CO2 content of the exhaust gas, in particular the second part of the exhaust gas. The gas analysis device is, in particular, connected to a control device (not shown) for transmitting the determined oxygen and / or CO2 content of the exhaust gas.The first and second oxidizer lines 14a,b preferably each have a control element, such as a valve or a flap, by which the amount of oxidizer in the combustion gas line 4 or the fuel line 9 can be adjusted. The control element is preferably connected to the control device, the control device being configured in particular to regulate the amount of oxidizer in the combustion gas line 4 or the fuel line 9 depending on the oxygen and / or CO2 content of the exhaust gas determined by the gas analysis device. Preferably, the amount of oxidizer in the fuel line 9 is adjusted, in particular controlled or regulated, depending on the amount of fuel introduced into the fuel line, the particle size of the fuel, and / or the calorific value of the fuel.Preferably, the amount of oxidizer in the combustion gas line 4 is adjusted, and in particular controlled or regulated, depending on the amount of oxygen introduced into the fuel line 9. Preferably, the first and second oxidizer lines 14a,b are each connected to an oxidizer source, such as an oxygen tank. The control system primarily serves to ensure complete combustion of the fuel, which is supplied to the GGR shaft furnace 1 via fuel line 9. This prevents an undesirably high oxygen content in the exhaust gas line 39. The CO2 content in the exhaust gas line 39 is also measured to monitor the desired CO2 level. A switching process for changing the shaft operated as a combustion shaft to the shaft operated as a regeneration shaft preferably comprises the following steps: - Switching off the fuel supply to the first part of the exhaust gas - Introducing the mixture of the first part of the exhaust gas and oxygen into the burner lances over a burn-off time interval, - Switching off the supply of oxygen to the first part of the exhaust gas after the burn-off time interval Preferably, the control device is connected to the first oxidizer line 14a and configured to increase the oxygen supply to the fuel line during the burn-off interval. In particular, the control device is connected to the second oxidizer line 14b and configured to decrease or stop the oxygen supply to the combustion gas inlet 12 during the burn-off interval. The burn-off interval is, for example, 20 seconds to 2 minutes, and in particular less than 1 minute. The lime produced using the previously described GGR shaft kiln 1 exhibits high reactivity, while simultaneously generating process gas with a CO2 content exceeding 90% based on dry gas. Such process gas can be liquefied and sequestered with less effort. For example, the liquefied process gas can be fed into further process steps or stored. Alternatively, the previously described GGR shaft kiln can also produce gas with a lower CO2 content, such as 45% for soda production, 35% for sugar production, or 30% for the production of precipitated calcium carbonate. Fig. 2 shows a detailed view of a section of the burner lances 10 within the shaft 2 according to the prior art. Fig. 3 shows a cross-section of the shaft 2 at the level of the burner lances 10. The burner lances 10 are arranged, by way of example, at essentially uniform intervals within the preheating zone 21 and / or the combustion zone 20. Fig. 2 shows insufficient combustion of the fuel 28 in a GGR shaft furnace known, for example, from the prior art, where the flame 42, supplied by the combustion gas flowing in the shaft 2, is insufficient to burn the fuel 28 quickly and sufficiently to reliably prevent clogging of the burner lances 10. The embodiment of the GGR shaft furnace 1 described with reference to Fig. 1 reliably prevents such clogging of the burner lances 10. Reference symbol list 1 GGR shaft furnace 2 Shaft 3 Material inlet / airlock 4 Combustion gas line 6 Exhaust gas outlet 8 Heating unit 9 Fuel line 10 Burner lances 11 Cooling gas discharge line 12 Combustion gas inlet 14 First oxidizer line 15 Gas inlet 16 Filter 17 Material-free space / Cooling gas discharge unit 18 Ring channel / Material-free space 19 Connecting channel 20 Combustion zone 21 Preheating zone 22 Cooling zone 23 Cooling gas inlet 24 Further connecting channel of the cooling zones 25 Outlet hopper 26 Inner cylinder 27 Fuel supply unit 28 Fuel 29 Cooling gas outlet 30 Cooling gas inlet 31 Exhaust gas filter 32 Cooling unit 33 - 38 Compressor 39 Exhaust gas line 40 Material outlet / airlock 41 Discharge unit 42 Flame 43 Heat exchanger / recuperator QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature WO 2011 / 072894 A1

[0002]

Claims

Method for burning material, such as carbonate rocks, in a shaft kiln (1) with only one shaft (2) or in a co-current counter-current regenerative shaft kiln (1) with two shafts (2) which are operated alternately as a burning shaft and as a regenerative shaft and are connected to each other by means of a connecting channel (19), wherein the material flows through a material inlet (3) into a preheating zone (21) for preheating the material, a firing zone (20) for firing the material and a cooling zone (22) for cooling the material to a material outlet (40), wherein a cooling gas is admitted into the cooling zone, wherein exhaust gas is discharged from one of the shafts (2) via an exhaust gas outlet (6) and the exhaust gas discharged from the shaft (2) via the exhaust gas outlet (6) is at least partially introduced into at least one of the shafts (2), characterized in thatthat a fuel and oxygen are supplied to a first part of the exhaust gas released from the shaft (2) via the exhaust gas outlet (6) before being introduced into the shaft (2). Method according to claim 1, wherein each shaft (2) has a plurality of burner lances (10) in the combustion zone (20) and / or the preheating zone (21) and wherein the first part of the exhaust gas is directed into the burner lances (10) together with the fuel and the oxygen. Method according to one of the preceding claims, wherein the first part of the exhaust gas is mixed with the oxygen and the fuel. Method according to one of the preceding claims, wherein a second part of the exhaust gas discharged from the shaft (2) via the exhaust gas outlet (6) is introduced into the preheating zone (21) and / or the combustion zone (20) of the shaft (2) operated as a combustion shaft. Method according to claim 4, wherein the second part of the exhaust gas is mixed with oxygen before being introduced into the preheating zone (21) and / or the combustion zone (20). Method according to one of the preceding claims, wherein the amount of oxygen in the first and second part of the exhaust gas is adjustable. Method according to one of the preceding claims, wherein the amount of oxygen introduced into the first part of the exhaust gas is adjusted depending on the amount of fuel introduced into the first part of the exhaust gas, the particle size of the fuel and / or the calorific value of the fuel introduced into the first part of the exhaust gas. A method according to one of the preceding claims, wherein the method comprises a switching process for switching the shaft operated as a combustion shaft to the shaft operated as a regenerative shaft, and wherein the switching process comprises the following steps: - shutting off the fuel supply to the first part of the exhaust gas; - introducing the mixture of the first part of the exhaust gas and oxygen into the burner lances over a burnout time interval; - shutting off the supply of oxygen to the first part of the exhaust gas. Method according to claim 8, wherein the oxygen supply to the first part of the exhaust gas is increased during the burn-off time. Method according to claim 8 or 9, wherein during the burn-off time the oxygen supply to the second part of the exhaust gas is reduced, in particular stopped. Method according to any one of claims 8 to 10, wherein the burnout time interval comprises 20 seconds to 2 minutes, in particular less than 1 minute. Method according to one of the preceding claims, wherein the first part of the exhaust gas is dried in a drying device before the fuel is introduced into the first part of the exhaust gas. Shaft kiln (1) with a shaft (2) or co-current counter-current regenerative shaft kiln (1) for firing material, such as carbonate rocks, with two shafts (2) which can be operated alternately as a firing shaft and as a regenerative shaft and are connected to each other by means of a connecting channel (2), wherein each shaft (2) has, in the direction of flow of the material, a preheating zone (21) for preheating the material, a firing zone (20) for firing the material and a cooling zone (22) for cooling the material, wherein each shaft (2) has an exhaust gas outlet (6) for releasing exhaust gas from the shaft (2), at least one exhaust gas outlet (6) is connected to at least one shaft (2) for introducing gas into the shaft (2), characterized in this respect.that the exhaust gas outlet (6) is connected via a fuel line (9) to a plurality of burner lances (10) and wherein the fuel line (9) is connected to a first oxidizer line (14a) for supplying oxidizer to the fuel line (9) and to a fuel supply device (27) for supplying fuel to the fuel line (9). Shaft furnace (1) or co-current counter-current regenerative shaft furnace (1) according to claim 13, wherein the exhaust gas outlet (6) is connected via a combustion gas line (4) to a combustion gas inlet (12) in the preheating zone (21) and / or a gas inlet (15) in the preheating zone (21) or the combustion zone (20) of the shaft (2) operated as a combustion shaft, and wherein the combustion gas line (4) is connected to a second oxidizer line (14b) for supplying oxidizer to the combustion gas line (4). Shaft furnace (1) or co-current counter-current regenerative shaft furnace (1) according to claim 13 or 14, wherein the GGR shaft furnace (1) has a control device which is connected to the first and / or the second oxidizing agent line (14a,b) in such a way that the amount of oxidizing agent in the fuel line (9) and / or the combustion gas line (4) can be adjusted by means of the control device. Shaft furnace (1) or co-current counter-current regenerative shaft furnace (1) according to one of claims 13 to 15, wherein the fuel line (9) is connected to a gas dryer for drying the gas flowing in the fuel line (9).

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