Furnace and process for firing 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 PFR shaft furnace has been known for approximately 60 years. Such a PFR 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 directed via the overflow channel into the exhaust gas shaft, where the exhaust gases are discharged upward in countercurrent to the material, thereby preheating the material. DE 10 2010 060 866 B3 discloses heating the recirculated exhaust gas in a heat exchanger to a temperature of 500°C in a single step.The material is usually fed into the shaft from above together with the oxidizing 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 quicklime, as required in steel mills, for example, 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.

[0005] Furthermore, the use of alternative fuels such as hydrogen or methane is being sought within the framework of the environmentally friendly production of quicklime.

[0006] Based on this, it is the object of the present invention to provide a furnace, such as a shaft furnace and / or a PGR shaft furnace and a method for burning carbonate rock with such a furnace, with which lime with a high reactivity is made possible with simultaneous CO2 separation from the exhaust gas and the use of alternative fuels.

[0007] 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.

[0008] According to a first aspect, the invention comprises a method for firing material, such as carbonate rocks, in a furnace with one or two shafts, wherein 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. A cooling gas is admitted into the cooling zone. Exhaust gas is discharged from a shaft of the furnace via an exhaust gas outlet arranged within or above the preheating zone. The exhaust gas discharged from the shaft via the exhaust gas outlet is at least partially introduced into at least one shaft of the furnace. Before being introduced into the shaft, the exhaust gas is at least partially cooled in a cooling device and subsequently heated in a heating device to a temperature of at most 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C.Following the heating device, the exhaust gas is heated in a heat exchanger to a temperature of 400°C to 800°C, in particular 600°C.

[0009] Cooling the exhaust gas in the cooling system and subsequent heating in the heating system reduces the relative humidity of the exhaust gas. In particular, the risk of water condensation and causing operational problems in the compressors is significantly reduced. This also reduces the risk of corrosion in the components of the downstream exhaust gas treatment system.

[0010] Preferably, the entire exhaust gas discharged from the shaft is cooled in the cooling device and subsequently heated in the heating device. It is also possible for only a portion of the exhaust gas to be fed to the cooling device and subsequently to the heating device.

[0011] 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. Preferably, methane or hydrogen is supplied to the furnace as fuel. At the exhaust gas outlet, the exhaust gas preferably has a water content of approximately 15 vol% to 40 vol%, in particular 25 vol% to 35 vol%, with the temperature being, for example, approximately 80°C to 100°C, and in particular less than 80°C at start-up of the system.

[0012] 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, with each shaft having, 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, with the material inlet being located in particular at the upper end of the respective shaft so that the material falls into the respective shaft 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 hermetically seals the shaft from the environment and allows solids, such as the material to be burned, to enter the shaft.

[0013] 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 PFR shaft furnace, 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 PFR 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 the 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 the 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 in the preheating zone and combustion zone in countercurrent to the material being burned.

[0014] 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.

[0015] 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, and / or via the connecting channel to 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 discharged, for example, from the PFR shaft furnace and fed, for example, to further treatment, such as sequestration. The exhaust gas preferably consists of CO2 and optionally H2O.

[0016] 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.

[0017] Each shaft preferably has a plurality of burner lances which 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.

[0018] Recirculating the exhaust gas into at least one shaft 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.

[0019] In particular, the exhaust gas is introduced into the preheating zone of the shaft operated as a combustion shaft. Each shaft preferably has a 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 inlet the gas required for combustion. For example, the exhaust gas is introduced into the connecting channel and / or into the combustion zone of the shaft operated as a regenerative shaft. Introducing the exhaust gas into the connecting channel enables uniform mixing of the exhaust gas with the gases in the combustion zone of the combustion shaft, since no material is present in the connecting channel. Preferably, only a portion of the exhaust gas is introduced into the connecting channel and / or into the combustion zone of the regenerative shaft.

[0020] According to a first embodiment, the exhaust gas is 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.

[0021] According to a further embodiment, the cooling device and / or the heating device are designed as heat exchangers. This allows the utilization of waste heat, in particular the temperature difference of a fluid at another position in the furnace process.

[0022] According to a further embodiment, the exhaust gas is dedusted in a filter before being cooled in the cooling device. The filter is preferably arranged between the exhaust outlet and the cooling device. The filter is preferably a dust filter for filtering dust particles from the exhaust gas. According to a further embodiment, the filter is operated under positive pressure. A compressor, in particular a fan, is preferably arranged upstream of the filter in the direction of flow of the exhaust gas.

[0023] 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 to the heating device designed as a heat exchanger for heating the exhaust gas cooled in the cooling device. The cooling gas heated in the cooling zone is preferably discharged from the cooling zone of the shaft via a 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.

[0024] The cooling gas extraction device preferably has a material-free space within the cooling zone of the shaft. In particular, the material-free space is designed as an external annular space that extends circumferentially around preferably the upper region of the cooling zone adjacent to the combustion zone. The cooling gas outlet, in particular, is arranged in the material-free annular space.

[0025] 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. 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, such 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 towards the cooling gas outlet and into the cooling gas extraction line.The cooling gas exhaust device is preferably designed to exhaust 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 exhaust device is connected to a control element, such as a flap or valve, for adjusting the amount of cooling gas to be exhausted.

[0026] In the direction of flow of the exhaust gas, the heating device is followed, in particular, by a heat exchanger for heating the exhaust gas. The heat exchanger is preferably connected to the cooling gas extraction device, so that at least a portion of the extracted cooling gas is fed to the heat exchanger. The heat exchanger is arranged separately from the heating device, with the exhaust gas being heated in the heating device and subsequently in the heat exchanger. The exhaust gas is preferably heated by the heat exchanger to a temperature of 400°C to 800°C, in particular 600°C.

[0027] Arranged in the flow direction of the extracted cooling gas is the heat exchanger for heating the exhaust gas to a temperature of 400°C to 800°C, in particular 600°C, and then, for example, the heating device designed as a heat exchanger for heating the exhaust gas to a temperature of 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C. The heating of the exhaust gas preferably takes place in two successive steps, each in a respective heat exchanger in counterflow to the extracted cooling gas.

[0028] For example, the exhaust gas is heated in a heating device to a temperature of 900°C to 1100°C, preferably 1000°C, after the heat exchanger and before being introduced into the shaft. The heating device is preferably designed for indirect heating or for direct heating, for example by means of an oxyfuel burner. The heating device comprises, for example, an electric heating device, an electric flow-through heater, a solar device, a combustion reactor and / or a heat exchanger and is in particular operable with renewable energy sources. The heating device is, for example, an electrically operated heating device. In particular, the heating device is operated using solar energy and preferably comprises a solar receiver, in particular a photovoltaic system for generating electrical energy using solar energy.The heating device comprises, for example, a solar thermal system, wherein, for example, a heat exchanger fluid is heated using solar energy and heats the recirculated exhaust gas in a heat exchanger, preferably in counterflow to the recirculated exhaust gas. For example, the heating device comprises a solar receiver which heats the recirculated exhaust gas, in particular directly. For this purpose, the solar receiver comprises, for example, part of the exhaust gas outlet line. The heating device has, for example, a combustion reactor which is preferably designed for the combustion of renewable energy sources, such as wood, wherein oxygen is preferably supplied instead of air in order to avoid the introduction of nitrogen. Preferably, the heating device comprises a heat exchanger for heating the exhaust gas in counterflow to a heat transfer fluid. The heat transfer fluid is heated, for example, using solar energy and / or the combustion reactor.

[0029] Preferably, a thermal treatment of the exhaust gas takes place in four successive steps, wherein in a first step the exhaust gas is cooled to a temperature of 10°C to 50°C, in particular 15°C to 40°C, in a second step the exhaust gas is heated to a temperature of at most 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C, in a third step the exhaust gas is heated to a temperature of 400°C to 800°C, in particular 600°C and in an optional fourth step the exhaust gas is heated to a temperature of 900°C to 1100°C, preferably 1000°C.

[0030] According to a further embodiment, the furnace comprises a cocurrent-countercurrent regenerative shaft furnace with two shafts that are operated alternately as a combustion shaft and as a regenerative shaft and are connected to one another by means of a connecting channel. A cocurrent combustion zone is formed in the shaft operated as a combustion shaft, and the exhaust gas discharged from the shaft is introduced into the preheating zone of the shaft operated as a combustion shaft and / or into the connecting channel and / or into the combustion zone of the shaft operated as a regenerative shaft. According to a further embodiment, the exhaust gas is heated downstream of the heating device and before being introduced into the connecting channel or into the combustion zone of the shaft operated as a regenerative shaft, in particular by means of the heating device, to a temperature of 900°C to 1100°C, preferably 1000°C.

[0031] According to a further embodiment, the furnace comprises a shaft furnace with exactly one shaft, with a cocurrent combustion zone formed within the combustion zone. The shaft furnace is preferably operated under positive pressure.

[0032] An oxidizing agent is preferably supplied to the shaft, particularly to the shaft of a PFR furnace operating as a combustion shaft. The oxidizing agent is, for example, pure oxygen or an oxygen-rich gas with an oxygen content of at least 70 to 95%, preferably 90%. The oxidizing agent is preferably introduced into the shaft together with the exhaust gas. It is also conceivable for the shaft in the preheating zone and / or the combustion zone to have a separate oxidizing agent inlet for admitting the oxidizing agent into the shaft separately from the exhaust gas.

[0033] The invention also encompasses a furnace for burning and cooling material, such as carbonate rocks, having one or two shafts, wherein a shaft of the furnace has, in the direction of flow of the material, a preheating zone for preheating the material, a combustion zone for burning the material, and a cooling zone for cooling the material. A shaft of the furnace has an exhaust gas outlet arranged within or above the preheating zone for discharging exhaust gas from the shaft, and wherein at least one exhaust gas outlet is connected to a gas inlet for admitting gas into a shaft of the furnace.The furnace has a cooling device and a heating device downstream of the exhaust gas outlet in the flow direction of the exhaust gas, wherein the heating device is arranged downstream of the cooling device and is designed such that it heats the exhaust gas to a temperature of at most 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C, wherein a heat exchanger is arranged downstream of the heating device and is designed such that it heats the exhaust gas to a temperature of 400°C to 800°C, in particular 600°C, wherein at least one exhaust gas outlet is connected to a gas inlet for admitting the heated exhaust gas into a shaft of the furnace.

[0034] The embodiments and advantages described with reference to the method for burning material, such as carbonate rocks, in a furnace also apply to the furnace in a device-related manner.

[0035] According to one embodiment, the cooling device is configured to cool the exhaust gas to a temperature of 10°C to 50°C, in particular 15°C to 40°C. According to another embodiment, the cooling device and / or the heating device is configured as a heat exchanger. According to another embodiment, a filter for removing dust from the exhaust gas is arranged upstream of the cooling device.

[0036] 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 exhaust device for discharging cooling gas from the shaft. The cooling gas exhaust device is connected to the heating device, designed as a heat exchanger, for heating the exhaust gas. According to a further embodiment, a compressor, in particular a blower or fan, is arranged upstream of the filter.

[0037] According to a further embodiment, the furnace comprises a cocurrent countercurrent regenerative shaft furnace with two shafts which can be operated alternately as a combustion shaft and as a regenerative shaft and are connected to one another by means of a connecting channel, wherein a cocurrent combustion zone is formed in the shaft operated as a combustion shaft, wherein each shaft has an exhaust gas outlet arranged within or above the preheating zone for discharging exhaust gas from the shaft, wherein at least one exhaust gas outlet is connected to a gas inlet for admitting gas into at least one shaft, wherein the gas inlet is arranged in the preheating zone of the shaft operated as a combustion shaft and / or in the connecting channel and / or the combustion zone of the shaft and / or a material-free space in the shaft.

[0038] According to a further embodiment, a heat exchanger and / or a heating device, in particular an electric heating device, a solar device or a combustion reactor, for heating the exhaust gas is arranged between the exhaust gas outlet and the gas inlet in the connecting channel and / or the combustion zone.

[0039] According to a further embodiment, the furnace comprises a shaft furnace with precisely one shaft, wherein the combustion zone is at least partially configured as a cocurrent combustion zone. Preferably, in a furnace configured as a shaft furnace with only one shaft, the exhaust gas is introduced into the combustion zone of the shaft. In particular, in a furnace configured as a PFR shaft furnace, the exhaust gas is introduced into the preheating zone and / or the combustion zone of the shaft operated as a combustion shaft and / or into the connecting channel and / or into the combustion zone of the shaft operated as a regenerative shaft. Description of the drawings

[0040] 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 PGR shaft furnace in a sectional view according to one embodiment. Fig. 2 shows a schematic representation of a shaft furnace for firing and / or calcining lumpy material, in a longitudinal section according to one embodiment.

[0041] Fig. 1 shows 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 configured 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.

[0042] 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 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 combustion gas inlet 12 is assigned, for example, a control element. Via the control elements, such as a quantity-adjustable compressor 35, the amount of combustion gas into the respective combustion gas inlet 12 and the amount of exhaust gas to be extracted via the respective exhaust gas outlet 6 can preferably be adjusted. The combustion 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.

[0043] At the lower end of shaft 2, a material outlet 40 is arranged for removing the fired material. The material outlet 40 is, for example, a lock as described with reference to the 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. The outlet funnel 25 is, for example, funnel-shaped. The 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.

[0044] 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.

[0045] Below the material inlet 3 and the combustion 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.

[0046] A plurality of burner lances 10 are optionally arranged in the preheating zone 21 and each serve as an inlet for fuel, such as a fuel gas, oil, or ground solid fuel. The PFR 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.

[0047] 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, 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.

[0048] 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 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.

[0049] The Fig. 1 shows an example of a PFR 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.

[0050] Adjacent to the combustion zone 20 in the direction of flow of the material in each shaft 2 is a cooling zone 22, which extends to the material outlet 40. The material is cooled within the cooling zone 22 to approximately 100°C in countercurrent to the cooling gas flowing through the material.

[0051] 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 cooling gas outlet 29 of the cooling air extraction device 17 from the respective shaft 2.

[0052] Cooling gas extraction device 17 comprising an inner cylinder 26 extending at least partially from the cooling zone 22 into the combustion zone 20 and having a cooling gas outlet 29 connected to the cooling gas extraction line 11.

[0053] 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 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 PFR 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 7 for conducting cooling air. The cooling air is preferably guided by means of a compressor 38 via the cooling air line 7 into the cooling air channels of the inner cylinder 26.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. The inner cylinders 26 each have a radially outwardly extending cooling air inlet 27 and a cooling air outlet 28, which are connected to the cooling air line 7.

[0054] 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 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 PFR 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. In particular, the cooling gas flows downward from the cooling gas inlet 30 in the inner cylinder 26 to the cooling gas outlet 29.

[0055] 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.

[0056] During operation of the PFR 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 PFR 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, which is 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.

[0057] During operation of the PFR 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.

[0058] 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 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.

[0059] The exhaust gas is directed into an exhaust line 39 adjoining the exhaust gas outlet 6. The exhaust line 39 optionally has an exhaust filter 31 for filtering fine particles, in particular dust, from the exhaust gas in the flow direction of the exhaust gas following the exhaust outlet 6. Downstream of the exhaust filter 31, the exhaust line 39 has a branch, wherein a portion of the exhaust gas is directed in a combustion gas line 4 to the combustion gas inlet 12. Downstream of the branch, in the flow direction 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 combustion gas inlets 12 of the shafts 2, wherein the exhaust gas is preferably fed only to the combustion gas inlet 12 of the shaft 2 operated as a combustion shaft via a control element upstream of the combustion gas inlet 12.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 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 oxidant.

[0060] The portion of the exhaust gas that is not returned to the combustion gas inlet 12 is fed in the exhaust line 39 to a gas inlet 15 in the connecting channel 19. Downstream of the branch of the combustion gas line 4 in the flow direction of the exhaust gas, the exhaust line 39 preferably has a volume-adjustable compressor 36, a heat exchanger 43, and optionally a heating device 8 for heating the exhaust gas. The heat exchanger 43 is designed, for example, as a recuperator, wherein the exhaust gas is heated in countercurrent to the extracted cooling gas and the cooling gas is cooled simultaneously. 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 exhaust gas is heated in the heat exchanger 43 by means of the extracted cooling gas, preferably in countercurrent.Following the heat exchanger, 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 exhaust gas is heated in the heat exchanger 43 and / or the heating device 8, preferably to a temperature of approximately 900°C to 1100°C, in particular 1000°C. It is also conceivable for the exhaust gas line 39 to have only a heat exchanger 43 or a heating device 8 for heating the exhaust gas. For example, the exhaust gas is heated in the heat exchanger 43 to a temperature of approximately 600°C and subsequently in the heating device 8 to a temperature of approximately 1000°C.

[0061] The heating device 8 is, for example, an electrically operated heating device. In particular, the heating device is powered by solar energy. It is also conceivable for the heating device 8 to comprise a heat exchanger, wherein the countercurrent flowing heat medium is heated by solar energy. The heating device 8 is preferably designed as a combustion reactor for the combustion of preferably renewable energy sources, such as wood, wherein the combustion preferably takes place such that the combustion gas has a high CO2 content of at least 90%.

[0062] 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.

[0063] Downstream of the heating device 47, a branch is arranged, via 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. The exhaust line has, for example, a compressor 34, 36, 37 before and after the branch of the exhaust gas to be discharged.

[0064] The connecting duct 19 has a gas inlet 15 for admitting recirculated exhaust gas into the connecting duct 19. The gas inlet 15 is connected to the exhaust outlet 6 of the shaft 2 via the exhaust line 39, so that the dust-free, and heated exhaust gas discharged from the shaft 2 is directed into the connecting duct 19. The gas inlet 15 is arranged, for example, centrally in the upper wall of the gas duct 15. It is also conceivable for the gas inlet 15 to be arranged at a different position in the wall of the connecting duct 19 or in the annular ducts 18. It is also conceivable for a plurality of gas inlets 15 to be arranged in the connecting duct 19 or in the annular ducts 18, each of which is connected to the exhaust line 39.

[0065] Fig. 1further shows, by way of example, two gas analysis devices 45, 46. The gas analysis devices 45, 46 are designed such that they each determine the oxygen and / or CO2 content of the respective gas. A gas analysis device 45 is arranged, for example, in the exhaust 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. The gas analysis device 45 is connected, in particular, to a control device (not shown) for transmitting the determined oxygen and / or CO2 content of the exhaust gas.

[0066] 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 the control device is particularly designed such that it controls the amount of oxidant in the combustion gas line 4 as a function of the oxygen and / or CO2 content of the exhaust gas determined by means of the gas analysis device 45.

[0067] The control system serves primarily to ensure complete combustion of the fuel supplied to the PFR shaft furnace 1 via the fuel line 9. This prevents an undesirably high oxygen content in the exhaust line 39. To control the desired CO2 content in the exhaust line 39, the CO2 content is also measured.

[0068] A gas analysis device 46 is arranged, for example, in the cooling gas discharge line 11, in particular downstream of the heat exchanger 43 and, for example, the filter 16, and is designed to determine the oxygen and / or CO2 content of the discharged cooling gas. The gas analysis device 46 is connected, in particular, to the control device (not shown) for transmitting the determined oxygen and / or CO2 content of the cooling gas.

[0069] 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 as a function of the oxygen and / or CO2 content of the cooling gas determined by the gas analysis device 46.

[0070] The control system is designed in particular to ensure that the cooling gas is removed as completely as possible from the PFR shaft furnace 1 while at the same time maintaining as little or preferably no CO2 in the cooling gas removal line 11.

[0071] 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. Such process off-gas can be liquefied and sequestered 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.

[0072] Fig. 2shows a further embodiment of a furnace 1, in particular a shaft furnace 1, such as an annular shaft furnace. The shaft furnace 1 comprises a shaft 2, which preferably extends in the vertical direction and, for example, has a substantially constant cross-section. For example, the shaft 2 has a round, in particular circular, or angular, in particular quadrangular cross-section. The shaft 2 is surrounded by a shaft wall, which is made, for example, of steel with an adjoining brick, refractory inner wall. The shaft 2 has a material inlet 3 at its upper end, which 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. The material inlet 3 serves to admit material to be fired into the shaft furnace 1.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 configured 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.

[0073] The shaft 2 has an exhaust gas outlet 6 in an upper region for discharging kiln exhaust gas from the shaft 2. The exhaust gas is guided from the exhaust gas outlet 6 into an exhaust gas line 39. For example, the exhaust gas is extracted via a material-free annular gap. Within the shaft 2, the material to be fired is conveyed by gravity from top to bottom through the shaft 2, wherein the shaft 2 has, in the conveying direction 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 fired material. The preheating zone 21 preferably extends from the material inlet 3 to the firing zone 20 and serves to preheat the material before firing. In the firing zone 20, in contrast to the preheating zone 21, firing, in particular calcination, preferably by deacidification, of the material takes place.

[0074] Combustion chamber levels 13 are preferably formed in the combustion zone 20 of the shaft 2, with at least one combustion chamber with at least one burner 10 being arranged in each combustion chamber level 13. The shaft furnace 1 further comprises a fuel line 9 for introducing fuel and an oxidant supply line 14 for introducing an oxidant into the combustion zone 20 of the shaft 2. The oxidant is, for example, air, oxygen-enriched air, pure oxygen, or a gas with an oxygen content of at least approximately 90%. The oxidant supply line 14 and the fuel line 9 are each connected, for example, to a fan, preferably a compressor, so that the oxidant and / or the fuel is forced towards the burners 10.

[0075] At the lower end of the shaft 2, a material outlet 40 is arranged for removing the fired material. The material outlet is, for example, a lock as described with reference to the material inlet 3. Adjacent to the cooling zone 22 in the material conveying direction is an outlet hopper 25, in particular a lower material bunker, which opens into the material outlet 40 for discharging the material from the shaft furnace 1. In the outlet hopper 25, for example, a discharge device 41 is arranged, which serves to discharge material from the cooling zone 22 of the shaft furnace 1 into the outlet hopper 25. The discharge device 41 is, for example, a turntable or push table. For example, a cooling air inlet is arranged in the shaft furnace 1, which introduces cooling air into the outlet hopper 25. Preferably, the cooling air is blown into the outlet funnel 25 at a pressure of up to 500 mbar by means of a cooling air compressor.

[0076] The shaft 12 further comprises a cooling gas extraction device 17 for removing at least a portion of the cooling air from the shaft 2. The cooling gas extraction device 17 is designed, for example, as an inner cylinder arranged concentrically to the shaft 2 and within the shaft. The cooling air flows through the shaft furnace 1, in particular the shaft 2, from bottom to top in a vertical direction and in countercurrent to the material and leaves the shaft 2 through the exhaust gas outlet line 39 of the exhaust gas outlet 6 and / or through the cooling gas extraction device 17. The cooling gas extraction device 29 extends, for example, centrally through the combustion zone 20 of the shaft 2. The combustion zone 20 of the shaft 2 is preferably designed at least partially or completely as an annular space arranged concentrically to the cooling gas extraction device 29.Optionally, the cooling gas extraction device 29 extends from the cooling zone 22 or the boundary between the combustion zone 20 and the cooling zone 22, through the combustion zone 20, for example, into the preheating zone 21, and through the shaft wall out of the shaft 2. The cooling gas extraction device 17 is provided with a gas outlet 29 for discharging the cooling air and, for example, exhaust gas from the shaft 2. The gas exiting the gas outlet 12 preferably flows into a cooling air extraction line 11. The cooling gas extraction device 17 extends through the shaft 2, for example, up to the gas outlet or beyond it. The gas outlet 29 is preferably arranged at the same height as the combustion zone 22.

[0077] To cool the cooling gas extraction device 17, the shaft 2 preferably has a cooling air inlet through which cooling air is introduced into a cooling air line 48 above the discharge device 41 by means of a cooling air compressor 33. The cooling air line 48 preferably extends along the cooling gas extraction device 17, in particular along the outer wall of the cylindrical cooling gas extraction device 17, and preferably opens into the cooling air extraction line 11. Optionally, the cooling air line 48 opens into the additional cooling air line 7 arranged for cooling the upper inner cylinder. The cooling air lines 7, 48 are preferably connected to the cooling air extraction line 11 via a control device, such as a flap or a valve, for the controlled supply of cooling air into the cooling air extraction line 11.

[0078] The shaft furnace 1 optionally further comprises an upper inner cylinder, which extends at least partially through the preheating zone 21 and is arranged above the cooling gas discharge device 29. The upper inner cylinder has an outlet for discharging gas from the shaft 2, wherein this outlet is preferably closed so that the gas entering the upper inner cylinder 6 cannot escape from the shaft 2. During operation of the shaft furnace 1, the upper inner cylinder serves to even out the material flow within the preheating zone 21. A cooling air inlet for cooling the upper inner cylinder is preferably arranged in the preheating zone 21. Cooling air, accelerated preferably by means of a fan 34, flows through the cooling air inlet into a ring line arranged around the preheating zone 21 and / or a cooling air line 7 arranged at least partially within the upper inner cylinder.

[0079] During operation of the shaft furnace 1, the material flows through the shaft 2 essentially due to gravity and is thermally treated in countercurrent or partly in cocurrent. Preferably, a countercurrent combustion zone is formed within the combustion zone 20, in which the material flows against the gas flow through the shaft 2. The countercurrent combustion zone is formed, for example, above the lower combustion chamber level 13. Preferably, a cocurrent combustion zone is also formed within the combustion zone 20, in which the gas flow runs in the same direction as the material flow through the shaft 2. The cocurrent combustion zone is formed, for example, below the lower combustion chamber level 13. The arrangement of the cocurrent combustion zone and the countercurrent combustion zone can vary depending on the flow velocity of the material and the gas flow, whereby the countercurrent combustion zone is preferably always formed above the cocurrent combustion zone.

[0080] Preferably, in the preheating zone 21, the material is preheated to a temperature of up to approximately 800°C, with the firing zone 22 having, for example, a temperature of 800°C to 1800°C, and in the cooling zone 22, the material is cooled again to approximately 100°C.

[0081] During operation of the shaft furnace 1, a column of material forms in the combustion zone 20 of the shaft 2, containing the material fed via the material feed 3. The material migrates downwards under gravity and is withdrawn in the area of ​​the cooling zone 22 via the material outlet 40 as a calcined product, for example, quicklime. The material preferably fills the combustion zone 20 over the entire, preferably circular, cross-section and the cooling zone 22. The cooling gas discharge device 29 is preferably free of material. The cooling gas flows through the material bed and enters the cooling gas discharge device 29. At least some of the exhaust gas from the combustion zone 24 preferably enters the cooling gas discharge device 17 in addition to the cooling gas.The cooling gas extraction device 17 is connected via the cooling air extraction line 11 to a control element in the form of, for example, a flap for regulating the amount of air flowing through the cooling gas extraction device 17, in particular the adjoining cooling air extraction line 11.

[0082] The exhaust gas outlet 6 for discharging the exhaust gas from the preheating zone 21 is preferably connected via the exhaust gas outlet line 39 to an exhaust gas filter 31 for dedusting the exhaust gas and optionally to a cooling device 32, in particular a heat exchanger, for cooling the hot exhaust gas. The exhaust gas from the combustion zone 20 is at least partially or completely discharged from the shaft 2 via the exhaust gas outlet line 39. The exhaust gas withdrawn from the shaft 2 via the exhaust gas outlet 6 and the exhaust gas outlet line 39 is dedusted, in particular, in the exhaust gas filter 31 and then discharged, for example, for further processing as dedusted exhaust gas by means of a fan 33. Optionally, the exhaust gas can be cooled downstream of the exhaust gas filter 31, in particular in a heat exchanger with water cooling, in a cooling device 32.The exhaust gas discharged before or after the cooling device 32 has a high CO2 content and can, for example, be fed to sequestration and / or further industrial utilization, such as the production of soda or precipitated calcium carbonate.

[0083] For example, a portion of the exhaust gas discharged via the exhaust gas outlet line 39 is introduced into the combustion zone 20, for example to supply heat to the combustion zone 20 and to adjust the combustion temperature.

[0084] 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.

[0085] In the flow direction of the exhaust gas, downstream of the heating device 47, for example, a heat exchanger 43 is arranged. The recirculated portion of the exhaust gas is preferably preheated to, in particular, 500°C in the heat exchanger 43, which is operated, for example, by the extracted cooling air. To prevent deposits from reducing heat transfer in the heat exchanger 43, it may be expedient for the cooling gas extracted via the cooling gas extraction device 17, which has, for example, a temperature of 900°C, to be cooled beforehand to below 700°C, preferably below 600°C. The cooling can be effected, for example, by mixing with air or in the cooling device 32. A fan 34 or compressor, in particular a high-pressure compressor, rotary piston compressor, or screw compressor, is preferably provided to accelerate the recirculated exhaust gas toward the oxidant ring lines 14.It is also conceivable that the recirculated exhaust gas is fed exclusively to a heat exchanger, namely the heat exchanger 43, before the exhaust gas is introduced into the combustion zone 20. The cooling device 32, designed as a heat exchanger, is preferably arranged in the flow direction of the exhaust gas after the branching of the exhaust gas to be discharged and, for example, upstream of the fan 33. The cooling air exhaust line 11 is optionally connected to a filter 16 so that the cooling air extracted via the cooling gas extraction device is cooled and dedusted. List of reference symbols

[0086] 1 Furnace 2 Shaft 3 Material inlet / lock 4 Combustion gas line 6 Exhaust gas outlet 7 Cooling air line 8 Heating device 9 Fuel line 10 Burner lances 11 Cooling gas discharge line 12 Combustion gas inlet 13 Combustion chamber levels 14 Oxidant line 15 Gas 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 27 Cooling air inlet 28 Cooling air outlet 29 Cooling gas outlet 30 Cooling gas inlet 31 Exhaust gas filter 32 Cooling device 33 - 38 Compressor 39 Exhaust gas line 40 Material outlet / lock 41 Discharge device 43Heat exchanger / recuperator 45, 46Gas analysis device 47Heating device 48Cooling air line

Claims

1. A method of firing material, such as carbonate rocks, in a kiln having one or two shafts, wherein the material flows through a material inlet (3) into a preheating zone (21) for preheating the material, a burning zone (20) for burning the material and a cooling zone (22) for cooling the material to a material outlet (40), whereby a cooling gas is introduced into the cooling zone, wherein exhaust gas is discharged from a shaft (2) of the furnace via an exhaust gas outlet (6) arranged within or above the preheating zone (21), and wherein the waste gas discharged from the shaft (2) via the waste gas outlet (6) is at least partially introduced into at least one shaft (2) of the kiln characterized in that the waste gas is at least partially cooled in a cooling device (32) before being introduced into the shaft (2) and then heated in a heating device (47) to a temperature of at most 200°C, in particular 50°C to 160°C, preferably 70°C to 120°C, and wherein the waste gas is heated to a temperature of 400°C to 800°C, in particular 600°C, in a heat exchanger (43) downstream of the heating device (47).

2. Method according to claim 1, wherein the exhaust gas is cooled in the cooling device (32) to a temperature of 10°C to 50°C, in particular 15°C to 40°C.

3. Method according to one of the preceding claims, wherein the cooling device (32) and / or the heating device (47) is a heat exchanger.

4. 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 the heating device (47), which is designed as a heat exchanger, for heating the exhaust gas cooled in the cooling device (32).

5. Method according to one of the preceding claims, wherein the exhaust gas is dedusted in a filter (31) before cooling in the cooling device (32) and wherein the filter (31) is operated at overpressure.

6. Method according to one of the preceding claims, wherein the kiln comprises 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 duct (19), wherein a co-current combustion zone is formed in the shaft (2) operated as a burning shaft, wherein the waste gas discharged from the shaft (2) is introduced into the preheating zone (21) of the shaft (2) operated as a burning shaft and / or into the connecting duct (19) and / or into the burning zone (20) of the shaft (2) operated as a regenerative shaft.

7. Method according to claim 6, wherein the exhaust gas is heated downstream of the heating device (47) and before being introduced into the connecting duct (19) or into the burning zone (20) of the shaft (2) operated as a regenerative shaft, in particular to a temperature of 900°C to 1100°C, preferably 1000°C.

8. The method according to any one of claims 1 to 5, wherein the kiln comprises a shaft kiln with exactly one shaft, wherein a co-current burning zone (24) is formed within the burning zone (20).

9. Kiln (1) for firing and cooling material, such as carbonate rocks, having one or two shafts (2), one shaft (2) of the kiln having, in the direction of flow of the material, a preheating zone (21) for preheating the material, a burning zone (20) for burning the material and a cooling zone (22) for cooling the material, wherein a shaft (2) of the kiln (1) has an exhaust gas outlet (6) arranged within or above the preheating zone (21) for discharging exhaust gas from the shaft (2), characterized in that the kiln (1) has a cooling device (32) and a heating device (47) downstream of the exhaust gas outlet in the direction of flow of the exhaust gas, the heating device (47) being arranged downstream of the cooling device (32) and being 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, wherein a heat exchanger (43) is arranged downstream of the heating device (47) and is designed such that it heats the exhaust gas to a temperature of 400°C to 800°C, in particular 600°C, wherein at least one exhaust gas outlet (6) is connected to a gas inlet (12, 15) for admitting the heated exhaust gas into a shaft (2) of the kiln (1).

10. Kiln (1) according to claim 9, wherein the cooling device (32) and / or the heating device (47) is a heat exchanger.

11. Kiln (1) according to one of claims 9 to 10, wherein the cooling zone (22) has a cooling gas inlet (23) for admitting cooling gas into the cooling zone (22) and a cooling gas discharge device (17) for discharging cooling gas from the shaft (2), and wherein the cooling gas discharge device (17) is connected to the heating device (47) designed as a heat exchanger for heating the exhaust gas.

12. Kiln (1) according to claim 11, wherein a filter (31) for dedusting the exhaust gas is arranged upstream of the cooling device (32) and wherein a compressor (34), in particular a blower or a fan, is arranged upstream of the filter (31).

13. Kiln (1) according to one of claims 9 to 12, wherein the furnace (1) comprises a co-current counter-current regenerative shaft furnace 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 duct (2), wherein a co-current burning zone is formed in the shaft operated as a burning shaft, wherein each shaft (2) has an exhaust gas outlet (6) arranged within or above the preheating zone (21) for discharging exhaust gas from the shaft (2), wherein at least one exhaust gas outlet (6) is connected to a gas inlet (12, 15) for admitting gas into at least one shaft (2), wherein the gas inlet (12, 15) is arranged in the preheating zone (21) of the shaft (2) operated as a burning shaft and / or in the connecting duct (19) and / or the burning zone (20) of the shaft (2) and / or a material-free space in the shaft (2).

14. Kiln (1) according to claim 13, wherein a heat exchanger (43) and / or a heating device (8), in particular an electrical heating device, a solar device or a combustion reactor, for heating the exhaust gas is arranged between the exhaust gas outlet (6) and the gas inlet (15) in the connecting duct (19) and / or the burning zone (20).

15. Kiln (1) according to any one of claims 9 to 12, wherein the kiln (1) comprises a shaft kiln with exactly one shaft, wherein the burning zone is at least partially designed as a co-current firing zone.