Furnace and method for burning carbonate rock

Description

[0001] The invention relates to a furnace and a method for firing and cooling material, such as carbonate rocks, using a PGR shaft furnace. The furnace is, for example, a cocurrent countercurrent regenerative shaft furnace (PGR shaft furnace) or a shaft furnace, in particular an annular shaft furnace.

[0002] The burning of carbonate rock in a shaft furnace or a PGR shaft furnace has been known for about 60 years. Such a PGR shaft furnace, known for example from WO 2011 / 072894 A1, has two vertical, parallel shafts that operate cyclically, with burning taking place only in one shaft, the respective combustion shaft, while the other shaft operates as a regenerative shaft. Oxidation gas is fed to the combustion shaft in cocurrent with the material and fuel. The resulting hot exhaust gases, together with the heated cooling air supplied from below, are channeled via the overflow duct into the exhaust gas shaft, where the exhaust gases are discharged upward in countercurrent to the material, preheating the material. The material is usually fed into the shaft from above together with the oxidation gas, with fuels being injected into the combustion zone.

[0003] In each shaft, the material to be burned usually passes through a preheating zone to preheat the material, a subsequent burning zone in which the material is burned and a subsequent cooling zone in which cooling air is supplied to the hot material.

[0004] To meet the quality requirements regarding high reactivity of the quicklime, as required, for example, in steelworks, temperatures in the firing zone must not exceed 1100°C, preferably 1000°C. Furthermore, the demand for environmentally friendly quicklime production is also increasing, so certain requirements regarding the CO2 content of the exhaust gas for subsequent post-treatment must be met. To increase the CO2 content in the exhaust gas, it is known to redirect at least a portion of the exhaust gas into one of the shafts. Such exhaust gas recirculation requires complex and cost-intensive treatment of the exhaust gas before it can be returned to the shaft.

[0005] Based on this, it is the object of the present invention to provide a furnace, such as a shaft furnace and / or a cost-effective and energy-efficient PGR shaft furnace and a method for burning carbonate rock with such a furnace, with which lime with a high reactivity is produced, while at the same time enabling CO 2 separation from the exhaust gas.

[0006] This object is achieved 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 further developments emerge from the dependent claims.

[0007] According to a first aspect, the invention comprises a method for burning material, such as carbonate rocks, in a co-current countercurrent regenerative shaft furnace having two shafts which are operated alternately as a combustion shaft and as a regenerative shaft and are connected to one another by means of a connecting channel, wherein the 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 to a material outlet, wherein a cooling gas is admitted into the cooling zone, wherein exhaust gas is discharged from a shaft of the furnace via an exhaust gas outlet arranged within or above the preheating zone, and wherein the exhaust gas discharged from the shaft via the exhaust gas outlet is branched 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 supplied to an upper region of the preheating zone via a first exhaust gas inlet.The second part of the exhaust gas discharged from the shaft is fed to the preheating zone via a second exhaust gas inlet downstream of the first exhaust gas inlet.

[0008] A supply of exhaust gas at two different positions within the preheating zone ensures optimal exhaust gas flow within the preheating zone, wherein in particular an excessively low temperature within the preheating zone is reliably prevented and condensation of the exhaust gas within the preheating zone is thus avoided. This also reduces the risk of corrosion in the components of the further exhaust gas treatment. The shaft preferably has a plurality of first exhaust gas inlets, which are arranged, for example, circumferentially around the shaft, in particular at the same height, and to which the first part of the exhaust gas is supplied. Preferably, the first exhaust gas inlets are each connected to a line, in particular a ring line, for conducting the first part of the exhaust gas. For example, the first exhaust gas inlets are arranged at equal distances from one another.The shaft preferably has a plurality of second exhaust gas inlets, which are arranged, for example, circumferentially around the shaft, in particular at the same height, and to which the second portion of the exhaust gas is supplied. Preferably, the second exhaust gas inlets are each connected to a line, in particular a ring line, for conducting the second portion of the exhaust gas. For example, the second exhaust gas inlets are arranged at equal spacing from one another.

[0009] The exhaust gas discharged from the shaft via the exhaust outlet is, for example, completely cooled in a cooling device and then heated in a heating device to a maximum temperature of 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C. This reduces the relative humidity of the exhaust gas. In particular, the risk of water condensing and leading to operating problems in the compressors is greatly reduced. It is also possible for only a portion of the exhaust gas to be fed to the cooling device and then to the heating device. The exhaust gas is, for example, cooled in the cooling device to a temperature of 10°C to 50°C, in particular 15°C to 40°C. This results in at least partial condensation of the water in the exhaust gas, thereby reducing the absolute humidity of the exhaust gas. The cooling device and / or the heating device are optionally designed as heat exchangers.This enables the utilization of waste heat, in particular the temperature difference of a fluid, at another position in the furnace process. For example, the exhaust gas is dedusted in a filter before being cooled in the cooling device. The filter is preferably arranged between the exhaust gas outlet and the cooling device. The filter is preferably a dust filter for filtering dust particles from the exhaust gas. The filter is operated, for example, under positive pressure or negative pressure with a fan arranged downstream. A compressor, in particular a fan, is preferably arranged upstream of the filter in the flow direction of the exhaust gas.

[0010] The material to be burned is preferably limestone or dolomite with a grain size of 10 to 200 mm, preferably 15 to 120 mm, most preferably 30 to 100 mm. The cooling gas is, for example, air. Methane or hydrogen is preferably supplied to the furnace as fuel. At the exhaust gas outlet, the exhaust gas preferably has a water content of approximately 5 vol% to 40 vol%, in particular 10 vol% to 25 vol%, with the temperature being, for example, approximately 80°C to 100°C, and in particular less than 80°C during start-up of the system.

[0011] The furnace is, for example, a cocurrent countercurrent regenerative shaft furnace with two parallel shafts or a shaft furnace with exactly one shaft. A cocurrent countercurrent regenerative shaft furnace has at least two shafts, which are preferably arranged parallel to one another and vertically. The shafts can be operated alternately as a combustion shaft and as a regenerative shaft, wherein each shaft has, in the direction of flow of the material, a preheating zone for preheating the material, a combustion zone for combustion of the material, and a cooling zone for cooling the material. Each shaft preferably has a material inlet for admitting material to be combustion into the shaft, wherein the material inlet is located in particular at the upper end of the respective shaft so that the material falls into the respective shaft due to gravity.The material inlet and / or the material outlet is / are designed in particular as a lock for admitting and / or discharging material into the shaft furnace. A material inlet designed as a lock is preferably configured such that only the raw material to be burned enters the shaft, but not the ambient air. The material lock also prevents gas from escaping from the shaft via the material inlet. The lock is preferably designed such that it creates an airtight seal between the shaft and the environment and allows solids, such as the material to be burned, to enter the shaft.

[0012] The connecting channel is designed to provide a gas connection between the two shafts and preferably connects the combustion zones of the shafts. During operation of the GGR shaft furnace, one of the shafts is operated as a combustion shaft and is active, while the other shaft is operated as a regenerative shaft and is passive. The GGR shaft furnace is operated cyclically, with the function of the shafts being swapped after the cycle time has elapsed. This process is repeated continuously. In the active shaft operated as a combustion shaft, a fuel is introduced into the combustion zone via the burner lances. The material to be burned is heated in the preheating zone of the combustion shaft, preferably to a temperature of approximately 700°C. In the shaft operated as a combustion shaft, the combustion zone is designed as a cocurrent combustion zone, with the material to be burned flowing parallel to the gas.The gas flows within the combustion shaft from the preheating zone to the combustion zone and then via the connecting channel into the combustion zone and preheating zone of the regenerative shaft. In the shaft operated as a regenerative shaft, the gas flows countercurrently to the material being burned in the preheating zone and combustion zone.

[0013] In both the combustion shaft and the regenerative shaft, cooling gas is passed through the cooling zone in countercurrent to the material to be cooled and is preferably completely discharged from the shaft via the cooling gas outlet of the cooling air extraction 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 arranged above the material column in a material-free region of the preheating zone. The exhaust gas is preferably discharged exclusively from one shaft, in particular the regenerative shaft. The discharged exhaust gas is preferably fed to the other shaft, in particular the combustion shaft or the regenerative shaft. Preferably, only a portion of the exhaust gas discharged from the regenerative shaft is returned to at least one shaft. A portion of the exhaust gas discharged from the regenerative shaft is, for example, removed from the PGR shaft furnace and fed, for example, to further treatment, such as sequestration. The exhaust gas preferably consists of CO2 and optionally H2O.

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

[0016] Each shaft preferably has a plurality of burner lances that extend at least partially through the preheating zone and, in particular, open into the combustion zone of the respective shaft and serve to conduct, for example, fuel and / or an oxidizing gas, such as air or oxygen-enriched air or pure oxygen. Preferably, the fuel gas outlet of the burner lances is 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] Recirculating the exhaust gas into at least one or both shafts enables the production of lime with high reactivity, while simultaneously producing process gas with a CO2 content of more than 90% based on dry gas. Such process exhaust gas can be liquefied and sequestered with less effort. For example, the liquefied process exhaust gas is fed to further process steps or stored. Alternatively, the PFR shaft kiln described above can also be used to produce exhaust gas with a lower CO2 content, for example, 45% for soda production, 35% for sugar production, or 30% for the production of precipitated calcium carbonate.

[0018] In particular, the exhaust gas is introduced into the preheating zone of the shaft operated as a combustion shaft and / or as a regenerative shaft. Preferably, each shaft has an exhaust gas inlet, in particular a combustion gas inlet, which is arranged in the upper region of the shaft in the preheating zone and serves to introduce the gas required for combustion.

[0019] The GGR shaft furnace preferably has a branch downstream of the exhaust gas outlet, which is designed and configured to branch the exhaust gas discharged from the exhaust gas outlet into a first portion of the exhaust gas and a second portion of the exhaust gas. The branch is preferably arranged downstream of a dust filter, the heating device, and / or the cooling device in the flow direction of the exhaust gas. The first portion of the exhaust gas is fed to an upper region of the preheating zone of the combustion shaft and / or the regenerative shaft via a first exhaust gas inlet, wherein the second portion of the exhaust gas is fed to the preheating zone of the combustion shaft and / or the regenerative shaft via a second exhaust gas inlet downstream of the first exhaust gas inlet. The preheating zone of the combustion shaft and the regenerative shaft preferably each has a first exhaust gas inlet and a second exhaust gas inlet arranged downstream of the first exhaust gas inlet in the flow direction of the material.

[0020] In particular, the amount of exhaust gas fed to the preheating zone of the shaft operated as a combustion shaft and / or the shaft operated as a regenerative shaft via the first and / or second exhaust gas inlet is adjustable. The PGR shaft furnace preferably has at least one control element, such as a flap or a valve. Preferably, a control element is connected upstream of each of the first and second exhaust gas inlets, so that the amount of the first part of the exhaust gas fed to the first exhaust gas inlet and / or the amount of the second part of the exhaust gas fed to the second exhaust gas inlet is adjustable. In particular, the amount of exhaust gas fed to the first and / or second exhaust gas inlet is adjusted as a function of the CO2 content of the exhaust gas.

[0021] According to a first embodiment, oxygen is supplied to the first and / or second portion of the exhaust gas before it is introduced into the preheating zone. Preferably, an exhaust gas line connected to the exhaust gas outlet is connected to an oxidant line for conducting oxygen, so that oxygen is introduced into the exhaust gas line. For example, air, an oxygen-rich 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, the PGR shaft furnace has at least two oxidant lines, each connected to an exhaust gas inlet for admitting exhaust gas into the preheating zone. In particular, oxygen is supplied to the first exhaust gas inlet and / or exclusively to the second exhaust gas inlet of the preheating zone of the shaft operated as a combustion shaft.

[0022] According to a further embodiment, the second part of the exhaust gas is compressed to approximately 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, in particular 500 mbar, before being introduced into the preheating zone of the combustion shaft. The PGR shaft furnace preferably has a compressor arranged between the exhaust gas outlet and the second exhaust gas inlet and designed to compress the second part of the exhaust gas to approximately 100 mbar to 600 mbar, preferably 200 mbar to 550 mbar, in particular 500 mbar. This counteracts a pressure loss within the GR shaft furnace. Preferably, the second part of the exhaust gas is compressed to approximately 50 mbar to 300 mbar, preferably 70 mbar to 200 mbar, in particular 150 mbar, before being introduced into the preheating zone of the regenerative shaft.When the second part of the exhaust gas is introduced into the second exhaust gas inlet in the regenerative shaft, the pressure loss within the PGR furnace is preferably lower than when it is introduced into the combustion shaft.

[0023] According to a further embodiment, the second part of the exhaust gas is introduced into the preheating zone at the lower end, in particular directly. In particular, the second part of the exhaust gas is introduced into the preheating zone upstream of the combustion zone, in particular upstream of a combustion gas outlet of a burner lance, in the direction of material flow. The second part of the exhaust gas is preferably introduced into the preheating zone via one or more second exhaust gas inlets formed as passages in the shaft wall above the combustion zone.

[0024] According to a further embodiment, the second part 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 part of the exhaust gas is heated at least partially or completely in a heat exchanger. This achieves optimal preheating of the material within the preheating zone.

[0025] According to a further embodiment, the second part of the exhaust gas is introduced into a region of the preheating zone which has a temperature corresponding to the temperature of the second part of the exhaust gas and / or a temperature of 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C. The preheating zone preferably has a gas temperature of 70°C to 800°C, wherein at the upper end of the preheating zone the gas has a temperature of approximately 70°C to 100°C and at the lower end the gas has a temperature of approximately 700°C to 900°C, preferably 800°C. The temperature of the gas preferably increases continuously in the flow direction of the material. The second exhaust gas inlet is preferably arranged at a height of the preheating zone at which a gas temperature of 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C, is set within the preheating zone.

[0026] According to a further embodiment, the preheating zone has a length extending in the flow direction of the material, wherein the second exhaust gas inlet for admitting exhaust gas into the preheating zone is spaced from the upper end of the combustion zone in the flow direction of the material at a distance from the upper end of the combustion zone, and wherein the ratio of the distance to the length is 0 to 0.5, in particular 0.2 to 0.3, preferably 0.25. Preferably, the preheating zone extends from the fill level of the material and / or from the material inlet to the combustion zone, in particular to a combustion gas outlet of a burner lance. Such a ratio provides optimal mixing of the gas flows within the preheating zone with an optimal capacity-flow ratio.

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

[0028] The cooling gas extraction device preferably has a material-free space within the cooling zone of the shaft. The material-free space of the cooling gas extraction device is designed, for example, as an inner cylinder, which extends, in particular, centrally and vertically through the cooling zone. In particular, the inner cylinder extends at least partially into the combustion zone or ends at a vertical distance from the combustion zone. The cooling gas outlet for discharging the cooling gas from the shaft is arranged in the inner cylinder. The inner cylinder preferably has a cooling gas inlet for admitting cooling gas from the cooling zones into the interior of the inner cylinder, wherein the cooling gas inlet is preferably 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 gas zone and then into the inner cylinder of the cooling gas extraction device. Within the inner cylinder, the cooling gas preferably flows downwards toward the cooling gas outlet and into the cooling gas extraction line. The cooling gas extraction device is preferably designed such that it discharges all of the cooling gas from the shaft, so that preferably no cooling gas enters the combustion zone or the connecting channel connecting the combustion zones of the shafts. In particular, the cooling gas extraction device is connected to a control element, such as a flap or a valve, for adjusting the amount of cooling gas to be extracted.

[0029] The invention also encompasses a cocurrent countercurrent regenerative shaft furnace for burning and cooling material, such as carbonate rocks, having two shafts which can be operated alternately as a burning shaft and as a regenerative shaft and which are connected to one another by means of a connecting channel, wherein each shaft has, in the direction of flow of the material, a preheating zone for preheating the material, a burning zone for burning the material and a cooling zone for cooling the material, wherein at least one shaft of the PGR shaft furnace has an exhaust gas outlet arranged within or above the preheating zone for discharging exhaust gas from the shaft and a first exhaust gas inlet for admitting exhaust gas, and wherein the exhaust gas outlet is connected to the first exhaust gas inlet for admitting a first portion of the exhaust gas into the preheating zone.Within the preheating zone, the shaft has a second exhaust gas inlet in the flow direction of the material behind the first exhaust gas inlet, which is connected to the exhaust gas outlet for admitting a second portion of the exhaust gas into the preheating zone.

[0030] The embodiments and advantages described with reference to the method for burning material, such as carbonate rocks, in a GGR shaft furnace also apply to the GGR shaft furnace in a device-related manner.

[0031] According to one embodiment, the shaft furnace has a control element which is arranged upstream of the first and / or the second exhaust gas inlet for controlling the quantity of exhaust gas which is supplied to the preheating zone of the shaft operated as a combustion shaft and / or the shaft operated as a regenerative shaft via the first and / or the second exhaust gas inlet.

[0032] According to a further embodiment, the shaft furnace 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, an oxygen-rich gas, or pure oxygen.

[0033] According to a further embodiment, a compressor is connected upstream of the second exhaust gas inlet, which is designed and configured 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 it is introduced into the second exhaust gas inlet of the combustion shaft. In particular, a compressor is connected upstream of the second exhaust gas inlet, which is designed and configured 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 it is introduced into the second exhaust gas inlet of the regenerative shaft.

[0034] According to a further embodiment, the second exhaust gas inlet is arranged at the lower end of the preheating zone.

[0035] According to a further embodiment, a heat exchanger is arranged between the exhaust gas outlet and the second exhaust gas inlet, which heat exchanger is designed and configured such that it heats 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.

[0036] According to a further embodiment, the preheating zone has a length A extending in the flow direction of the material, wherein the second exhaust gas inlet for admitting exhaust gas into the preheating zone 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.

[0037] According to a further embodiment, the cooling zone has a cooling gas inlet for admitting cooling gas into the cooling zone and a cooling gas discharge device for discharging cooling gas from the shaft, and wherein the cooling gas discharge device is connected to the heat exchanger for heating the second part of the exhaust gas, in particular in counterflow. Description of the drawings

[0038] The invention is explained in more detail below using several embodiments with reference to the accompanying figures. Fig. 1 shows a schematic representation of a GGR shaft furnace in a sectional view according to an embodiment. Fig. 2 shows a schematic representation of a section of a GGR shaft furnace according to the embodiment of the Fig. 1 in a sectional view.

[0039] Fig. 1shows a furnace, in particular a PGR shaft furnace 1, with two parallel and vertically aligned shafts 2. The shafts 2 of the PGR shaft furnace 1 are essentially identical in design, so that in Fig. 1Only one of the two shafts 2 is provided with a reference numeral and, for the sake of simplicity, only one of the two shafts 2 is described below. Each shaft 2 has a material inlet 3 for admitting material to be fired into the respective shaft 2 of the PGR shaft furnace 1. The material to be fired is, in particular, limestone and / or dolomite stone, preferably with a grain size of 10 to 200 mm, preferably 15 to 120 mm, most preferably 30 to 100 mm. The material inlets 3 are arranged, for example, at the upper end of the respective shaft 2, so that the material falls into the shaft 2 through the material inlet 3 due to gravity. The material inlet 3 is designed, for example, as an upper opening of the shaft 2 and, in particular, as a lock 3 and preferably extends over all or part of the cross-section of the shaft 2.A material inlet designed as a lock 3 is preferably configured such that only the raw material to be burned enters the shaft 2, but not the ambient air. The lock 3 is preferably designed such that it hermetically seals the shaft 2 from the environment and allows solids, such as the material to be burned, to enter the shaft.

[0040] Each shaft 2 further has a combustion gas inlet 12 at its upper end for admitting combustion gas for the combustion of fuels. The combustion gas inlet 12 is a first exhaust gas inlet 12, wherein each shaft 2 preferably has a second exhaust gas inlet 15, which is arranged downstream of the first exhaust gas inlet 12 in the flow direction of the material. For example, the shaft 2 has a plurality of first and second exhaust gas inlets that are circumferentially spaced, in particular, at the same height and / or evenly spaced from one another. The combustion gas is, for example, dedusted exhaust gas from at least one of the shafts 2, wherein the exhaust gas is preferably enriched with oxygen. Furthermore, each shaft 2 has an exhaust gas outlet 6 for discharging exhaust gases from the respective shaft 2. Each exhaust gas outlet 6 and exhaust gas inlet 12, 15 is assigned, for example, a control element.The amount of combustion gas, in particular exhaust gas, into the respective exhaust gas inlet 12, 15 and the amount of exhaust gas to be removed via the respective exhaust gas outlet 6 can preferably be adjusted via the control elements, such as a quantity-adjustable compressor 35. The first exhaust gas inlet 12 and the exhaust gas outlet 6 are arranged, for example, at the same height and in particular 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 an upper end region, in particular the material-free upper end of the preheating zone 21 of the respective shaft 2.

[0041] At the lower end of shaft 2, a material outlet 40 is arranged for removing the fired material. Material outlet 40 is, for example, a lock as described with reference to material inlet 3. The fired material is, for example, guided into an outlet funnel 25, which is connected to the material outlet 40 of shaft 2. Outlet funnel 25 is, for example, funnel-shaped. Outlet funnel 25 preferably has a cooling gas inlet 23 for admitting cooling gas into the respective shaft 2. The cooling gas is preferably fed into the cooling gas inlet by means of a compressor 33.

[0042] During operation of the PFR 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, countercurrent to the material, through the respective shaft 2. The furnace exhaust gas is discharged from the shaft 2 through the exhaust outlet 6.

[0043] Below the material inlet 3 and the first exhaust gas inlet 12, in the direction of material flow, is the preheating zone 21 of the respective shaft 2. 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 burned. 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 direction of material flow are surrounded, for example, by a refractory lining.

[0044] A plurality of burner lances 10 are optionally arranged in the preheating zone 21, each of which opens into the combustion zone 20 and serves as an inlet for fuel, such as a fuel gas, oil, or ground solid fuel. The PGR shaft furnace 1 has, for example, 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 around the shaft region in which the burner lances 10 are arranged. Cooling air for cooling the burner lances 10 preferably flows through the cooling air ring lines. The burner lances 10 are preferably cooled by means of the exhaust gas discharged via the exhaust gas outlet 6. The exhaust gas outlet 6 is preferably connected to the burner lances 10 for conducting exhaust gas to the burner lances 10.

[0045] 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 designed as a ring line that extends circumferentially around the respective shaft 2. Preferably, each shaft 2 has a fuel line associated with the burner lances 10 of the shaft 2, each of which, in particular, has a control element for adjusting the amount of fuel supplied to the burner lances 10.

[0046] The preheating zone 21 is followed by the combustion zone 20 in the direction of material flow. In the combustion zone 20, the fuel is combusted, and the preheated material is fired at a temperature of approximately 1000°C. The burner lances preferably each have fuel outlets at their ends, with the combustion zone 20 extending in particular from the fuel outlets of the burner lances 10 in the direction of material flow. The PFR shaft furnace 1 further comprises a connecting channel 19 for the gas connection of the two shafts 2. In particular, no material to be burned is present in the connecting channel 19.

[0047] The Fig. 1 shows an example of a PGR lime kiln 1 with a round shaft cross-section. However, the shaft cross-section can have a different geometric contour, such as round, semicircular, oval, square, or polygonal.

[0048] Adjacent to the combustion zone 20 in the direction of material flow in each shaft 2 is a cooling zone 22, which extends to the discharge device 41. The material is cooled within the cooling zone 22 to approximately 100°C in countercurrent to the cooling gas flowing through the material.

[0049] Each cooling zone 22 has a cooling air extraction 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 respective shaft 2 via the cooling gas outlet 29 of the cooling air extraction device 17.

[0050] Each cooling zone 22 has a cooling gas discharge device 17 comprising an inner cylinder 26 extending from the cooling zone 22 at least partially into the combustion zone 20 or to a height spaced from the combustion zone and having a cooling gas outlet 29 connected to the cooling gas discharge line 11.

[0051] The cooling zone 22 is formed, for example, in a shaft section having an approximately constant cross-section, wherein the shaft cross-section of the cooling zone 22 approximately corresponds to the shaft cross-section of the lower region of the combustion zone 20. For example, a material-free annular space is formed at the level of the connecting channel 19. Each shaft 2 of the PGR shaft furnace 1 preferably has an inner cylinder 26 which extends centrally in a vertical direction through the cooling zone 22. 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. To cool the inner cylinder 29, a plurality of cooling air channels are formed in its outer walls, which are connected to a cooling air line (not shown) for conducting cooling air.The heated cooling air is, for example, directed into the cooling gas exhaust line 11 and preferably fed into the heat exchanger 43 to heat the exhaust gas. For example, the heated cooling air is used as an energy source for other processes, such as drying biomass or limestone.

[0052] The inner cylinder 26 of the cooling gas extraction device 17 has a cooling gas outlet 29, which extends radially outward from the inner cylinder 26 through the shaft wall and serves to conduct cooling gas from the inner cylinder 26 into the cooling gas extraction line 11. The inner cylinder 26 further has a cooling gas inlet 30 for admitting 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 to 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 PGR 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 extraction device 17.Preferably, all of 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 arranged 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 downward to the cooling gas outlet 29.

[0053] 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 the material to pass laterally between the discharge table and the casing wall of the PFR shaft kiln. The discharge device 41 is preferably designed as a pusher or rotary table, or as a table with a pusher clearer. This enables a uniform throughput rate of the firing material through the shafts 2. The discharge device 41 further comprises, for example, the outlet hopper 25, which adjoins the discharge table and at whose lower end the material outlet 40 is attached.

[0054] During operation of the GGR shaft kiln 1, one of the shafts 2 is active at a time, while the other shaft 2 is passive. The active shaft 2 is referred to as the combustion shaft and the passive shaft 2 as the regenerative shaft. The GGR shaft kiln 1 is operated in particular cyclically, 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 swapped. This process is repeated continuously. Material such as limestone or dolomite stone is alternately fed into the shafts 2 via the material inlets 3. In the active shaft 2, operated as a combustion shaft, a fuel is introduced into the combustion shaft 2 via the burner lances 10. The material to be burned is heated in the preheating zone 21 of the combustion shaft to a temperature of approximately 700°C. In the exemplary embodiment of the Fig. 1the left shaft 2 is operated as a combustion shaft, while the right shaft 2 is operated as a regenerative shaft.

[0055] During operation of the PGR shaft furnace 1, the cooling gas flows in both the combustion shaft 2 and the regenerative shaft 2 in countercurrent 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.

[0056] Within shaft 2, which is operated as a combustion shaft, the combustion gas flows through the first exhaust gas inlet 12 into the combustion shaft and, in cocurrent with the material within the combustion zone 20, into the material-free space formed 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 regenerative shaft. Within the regenerative shaft, the gas flows from the connecting channel 19 and the material-free space 18 of the regenerative shaft in countercurrent to the material to be burned through the combustion zone 20 into the preheating zone 21 and exits the regenerative shaft through the exhaust gas outlet 6 of the regenerative shaft. The exhaust gas discharged from shaft 2 preferably has a temperature of 60°C to 160°C, preferably 100°C.

[0057] The exhaust gas is fed into an exhaust line 39 adjoining the exhaust gas outlet 6. The exhaust line 39 optionally has an exhaust gas filter 31 for filtering fine particles, in particular dust, from the exhaust gas downstream of the exhaust gas outlet 6 in the flow direction of the exhaust gas. Downstream of the exhaust gas filter 31, the exhaust line 39 has a branch, wherein a first portion of the exhaust gas is fed in a combustion gas line 4 to the first exhaust gas inlet 12. Downstream of the branch, in the flow direction of the first portion of the exhaust gas, the combustion gas line 4 has, for example, a control element, such as a throttle valve, and a compressor 35. The combustion gas line 4 is preferably connected to the first exhaust gas inlet 12 of the shafts 2, wherein 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 upstream of the first exhaust gas inlet 12.It is also conceivable that the exhaust gas from the combustion gas line 4 is fed exclusively to the regenerative shaft or to both shafts 2. The combustion gas line 4 is preferably connected to an oxidant line 14, so that an oxidant, preferably pure oxygen, is introduced into the combustion gas line 4 and then, together with the exhaust gas, into the shaft 2 via the first exhaust 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 oxidant.

[0058] 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 via the exhaust gas line 39 to a second exhaust gas inlet 15 in the preheating zone 21. Downstream of the branch of the combustion gas line 4 in the flow direction of the second portion of the exhaust gas, the exhaust gas line 39 preferably has a volume-adjustable compressor 36 and a heat exchanger 43. The heat exchanger 43 is designed, for example, as a recuperator, wherein the second portion of the exhaust gas is heated in countercurrent to the extracted cooling gas, and the cooling gas is simultaneously cooled. The heat exchanger 43 is connected, in particular via a cooling gas discharge line 11, to the cooling gas outlets 29 of both shafts 2, so that the second portion of the exhaust gas is heated in the heat exchanger 43 by means of the extracted cooling gas, preferably in countercurrent.Following the heat exchanger 43, the cooling gas discharge line 11 optionally has a control element for adjusting the amount of cooling gas to be discharged and a filter 16 for removing dust from the cooling gas. The second portion of the exhaust gas is heated in the heat exchanger 43, preferably to a temperature of approximately 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C.

[0059] Downstream of the heat exchanger 43 and upstream of the second exhaust gas inlet 15, the exhaust gas line 39 is preferably connected to an oxidant line 14 for introducing an oxidant, such as pure oxygen, air or an oxygen-rich gas, into the exhaust gas line 39.

[0060] Downstream of the exhaust gas filter 31, in particular, a cooling device 32 is arranged. The cooling device 32 is, for example, a heat exchanger, which is preferably operated in countercurrent with a coolant, such as water. Downstream of the cooling device 32, a heating device 47 for heating the cooled exhaust gas is preferably arranged. The heating device 47 is preferably designed such that it heats the exhaust gas to a maximum temperature of 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, which is connected to the cooling gas discharge line 11, so that the cooling gas withdrawn from the shaft 2 is fed to the heating device 47. The cooling gas filtered in the filter 16 is preferably fed to the heat exchanger 47.

[0061] Downstream of the heating device 47, a branch is arranged, through which at least a portion of the exhaust gas is discharged and a second portion is returned to one of the shafts 2 via the exhaust line 39. In particular, a partial flow of the second portion of the exhaust gas is discharged downstream of the branch of the combustion gas line 4. The exhaust line has, for example, a compressor 36, 37 before and after the branch of the exhaust gas to be discharged.

[0062] The preheating zone 21 has a second exhaust gas inlet 15 for admitting recirculated exhaust gas, in particular the second part of the exhaust gas, into the preheating zone 21. The gas inlet 15 is connected via the exhaust gas line 39 to the exhaust gas outlet 6 of the shaft 2, so that exhaust gas discharged from the shaft 2, dedusted and heated, is passed into the preheating zone 21. The second exhaust gas inlet 15 is arranged, for example, in a lower end region of the preheating zone 21, wherein the position of the gas inlet 15 in the Fig. 2 shown in detail. Preferably, the second exhaust gas inlet 15 is arranged downstream of the first exhaust gas inlet 12 in the direction of material flow.

[0063] The oxidant line 14 preferably has a control element, such as a valve or a flap, via which the amount of oxidant in the combustion gas line 4 can be adjusted. The control element is preferably connected to the control device, wherein a control device is particularly designed to control the amount of oxidant in the combustion gas line 4 depending on the oxygen and / or CO2 content of the exhaust gas.

[0064] The cooling gas discharge line 11 preferably has a control element, such as a valve or a flap, via which the amount of cooling gas to be discharged via the cooling gas discharge device 17 can be adjusted. The control element is preferably connected to the control device, wherein the control device is particularly designed such that it controls the amount of cooling gas discharged via the cooling gas discharge device 17 depending on the oxygen and / or CO2 content of the cooling gas.

[0065] The control system is designed in particular to ensure that the cooling gas is removed as completely as possible from the PGR shaft furnace 1 while at the same time keeping as little or preferably no CO2 in the cooling gas removal line 11.

[0066] The lime produced with the previously described PGR shaft kiln 1 exhibits high reactivity, while simultaneously producing process gas with a CO2 content of more than 90% based on dry gas. With such process off-gas, it is possible to liquefy and sequester it with less effort. For example, the liquefied process off-gas is fed to further process steps or stored. Alternatively, the previously described PGR shaft kiln can also produce off-gas with a lower CO2 content, for example, 45% for soda production, 35% for sugar production, or 30% for the production of precipitated calcium carbonate.

[0067] Fig. 2shows a detailed view of a section of the PGR furnace 1, in which the second exhaust gas inlet 15 for admitting exhaust gas into the preheating zone 21 is shown. The second exhaust gas inlet 15 has a vertical distance B to the upper end of the combustion zone 20, wherein the upper end of the combustion zone 20 is arranged at the height of the fuel gas outlet of the burner lances 10. By way of example, the shaft 2 has five burner lances 10, all of which end at the same height. It is also conceivable for the burner lances 10 to end at different heights, wherein the upper end of the combustion zone 20 begins at the uppermost fuel gas outlet of a burner lance 10. The preheating zone 21 has a length A that extends from the upper end of the preheating zone 21 to the upper end of the combustion zone 20. The upper end of the preheating zone 21 is arranged, for example, at the material inlet 3 or the material bed height.Preferably, the ratio B / A of the distance B to the length A is 0 to 0.5, in particular 0.2 to 3, preferably 0.25. A second exhaust gas inlet positioned at this length ratio provides an optimal introduction position for the exhaust gas.

[0068] Preferably, the temperature of the gas within the preheating zone 21 is approximately 80°C to 800°C, with the gas having a temperature of approximately 80°C to 100°C at the exhaust gas outlet 6 of the preheating zone 21 and approximately 800°C to 900°C at the end of the preheating zone 21, in particular the transition between the preheating zone 21 and the combustion zone 20. The temperature within the preheating zone 21 preferably increases continuously in the flow direction of the material. In particular, the second exhaust gas inlet 15 is arranged at a height within the preheating zone 21 at which a temperature of approximately 500°C to 700°C, preferably 550°C to 650°C, in particular 600°C, is set within the preheating zone.

[0069] The exhaust gas line 39 preferably has a compressor which is designed to compress the exhaust gas to approximately 100 mbar to 500 mbar before it enters the preheating zone 21. List of reference symbols

[0070] 1 Furnace 2 Shaft 3 Material inlet / lock 4 Combustion gas line 6 Exhaust outlet 8 Heating device 9 Fuel line 10 Burner lances 11 Cooling gas discharge line 12 Combustion gas inlet / first exhaust inlet 13 Combustion chamber levels 14 Oxidant line 15 Gas inlet / second exhaust inlet 16 Filter 17 Cooling gas discharge device 18 Annular channel / material-free space 19 Connecting channel 20 Combustion zone 21 Preheating zone 22 Cooling zone 23 Cooling gas inlet 25 Outlet funnel 26 Inner cylinder 29 Cooling gas outlet 30 Cooling gas inlet 31 Exhaust filter 32 Cooling device 33 - 37 Compressor 39 Exhaust line 40 Material outlet / lock 41 Discharge device 43 Heat exchanger / recuperator 47Heating device 48Cooling air line

Claims

1. Method for firing material, such as carbonate rocks, in a co-current counter-current regenerative shaft kiln (1) with two shafts (2) which are operated alternately as a firing shaft and as a regenerative shaft and are connected to one another 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 introduced into the cooling zone (22) wherein exhaust gas is discharged from a shaft (2) of the kiln via an exhaust gas outlet (6) arranged within or above the preheating zone (21), and wherein the exhaust gas discharged from the shaft (2) via the exhaust gas outlet (6) is branched 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), characterized in that the second part 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).

2. The method according to claim 1, wherein oxygen is supplied to the first and / or the second part of the exhaust gas before it is introduced into the preheating zone (21).

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

4. Method according to one of the preceding claims, wherein the second part of the exhaust gas is introduced into the preheating zone (21) at the lower end thereof.

5. Method according to one of the preceding claims, wherein the second part 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 (15).

6. Method according to one of the preceding claims, wherein the second part of the exhaust gas is introduced into a region of the preheating zone (21) which has a temperature corresponding to the temperature of the second part of the exhaust gas and / or has a temperature of 500°C to 800°C, in particular 550°C to 700°C, preferably 600°C.

7. Method according to one of the preceding claims, wherein the preheating zone (21) has a length (A) extending in the direction of flow of the material and wherein the second exhaust gas inlet (15) for admitting exhaust gas into the preheating zone (21) has a distance (B) from the upper end of the burning zone (20) in the direction of flow 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. Method according to 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 discharge device (17) and wherein the cooling gas discharged from the cooling zone (22) is fed to a heat exchanger (43) for heating the second part of the exhaust gas.

9. Co-current counter-current regenerative shaft kiln (1) for firing and cooling 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 one another by means of a connecting channel (19), wherein each shaft (2) has 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 in the direction of flow of the material, wherein at least one shaft (2) of the Co-current counter-current regenerative shaft kiln (1) has an exhaust gas outlet (6) arranged within or above the preheating zone (21) for discharging exhaust gas from the shaft (2) and a first exhaust gas inlet (12) for admitting exhaust gas, and wherein the exhaust gas outlet (6) is connected to the first exhaust gas inlet (12) for admitting a first portion of the exhaust gas into the preheating zone (21) characterized in that the shaft (2) within the preheating zone (21) has a second exhaust gas inlet (15) in the flow direction of the material downstream of the first exhaust gas inlet (12), which is connected to the exhaust gas outlet (6) for admitting a second portion of the exhaust gas into the preheating zone (21).

10. Co-current counter-current regenerative shaft kiln (1) according to claim 9, wherein the shaft kiln (1) has a regulating element which is connected upstream of the first and / or the second exhaust gas inlet (12, 15) for regulating the quantity of exhaust gas which is fed to the preheating zone (21) of the shaft (2) operated as a combustion shaft and / or of the shaft (2) operated as a regenerative shaft via the first and / or the second exhaust gas inlet (12, 15).

11. Co-current counter-current regenerative shaft kiln (1) according to any one of claims 9 to 10, wherein the shaft kiln (1) comprises at least one oxidizing agent line (14) connected to the first and / or the second exhaust gas inlet (12, 15) for introducing an oxidizing agent into the exhaust gas.

12. Co-current counter-current regenerative shaft kiln (1) according to one of claims 9 to 11, wherein a compressor is connected upstream of the second exhaust gas inlet (15), which compressor is designed and set up in such a way 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. Co-current counter-current regenerative shaft kiln (1) according to any one of claims 9 to 12, wherein the second exhaust gas inlet (15) is arranged at the lower end of the preheating zone (21).

14. Co-current counter-current regenerative shaft kiln (1) according to one of claims 9 to 13, wherein a heat exchanger (43) is arranged between the exhaust gas outlet (6) and the second exhaust gas inlet (15), which heat exchanger is designed and set up in such a way that it heats 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. Co-current counter-current regenerative shaft kiln (1) according to one of claims 9 to 14, wherein the preheating zone (21) has a length (A) extending in the direction of flow of the material and wherein the second exhaust gas inlet (15) for admitting exhaust gas into the preheating zone (21) has a distance (B) from the upper end of the firing zone (20) in the direction of flow 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. Co-current counter-current regenerative shaft kiln (1) according to claim 14, wherein the cooling zone (22) comprises a cooling gas inlet (23) for admitting cooling gas into the cooling zone (22) and a cooling gas exhaust device (17) for discharging cooling gas from the shaft (2), and wherein the cooling gas exhaust device (17) is connected to the heat exchanger (43) for heating the second part of the exhaust gas.