A method for calcining mineral rocks in a regenerative co-current vertical shaft furnace.

Abstract

The present invention provides a method for calcining mineral rocks in a regenerative co-current vertical shaft furnace that, without altering the cycle operation of the PFRK-type furnace or making little to no changes to its structure, at least partially improves the problem of significant CO2 emissions into the atmosphere and enables the recovery of CO2 present in the gaseous waste emitted by the furnace. [Solution] A method for calcining mineral rock in a regenerative co-current vertical shaft furnace is provided, comprising: collecting a portion of the gaseous waste discharged from the furnace shaft in preheating mode 2 in a recirculation circuit 18; mixing the portion collected from the gaseous waste with high-concentration oxygen from an oxygen source 20 to form an oxidizing mixture; and ensuring the combustion of fuel in the presence of oxygen by inserting the oxidizing mixture into the top of the shaft 1 in calcination mode, wherein the gaseous waste discharged from the furnace has a high concentration of CO2.

Description

[Technical Field]

[0001] The present invention relates to a method for calcining carbonate mineral rocks in a regenerative co-current vertical shaft furnace and to a furnace used therein. [Background technology]

[0002] Regenerative co-current vertical shaft furnaces or co-current regenerative kilns (PFRKs) have an energy efficiency of 85%–90%. This is the highest in the lime sector, even within the energy-intensive cement, steel, and glass industries as a whole. In Europe, 60% of lime is produced in this type of furnace. This percentage is expected to increase in Europe and worldwide, given the roadmap for energy and ecological transitions.

[0003] The "PFRK" furnace is a vertical double-shaft furnace in which fuel is injected alternately through two shafts for approximately 10-15 minutes, with a 1-2 minute pause between cycles during which the air and fuel circuits are reversed. This pause is the "reversal" period. The two shafts are connected via a connecting furnace tube. During combustion in one shaft (calcination mode), high-temperature combustion fumes pass through the connecting furnace tube (gas transfer channel), transferring some of their heat to the mineral rock being calcined, thereby preheating the mineral rock in the other shaft during regeneration or preheating mode. The shafts of a PFRK furnace are cylindrical or rectangular. In some cases, there are three shafts, two in preheating mode and one in calcination mode. The problems and solutions outlined below are effective for all PFRK furnace configurations.

[0004] The methods used in these known furnaces, in production mode, Loading carbonate mineral rocks at the top of the furnace, Preheating the aforementioned rock, To obtain calcined material by calcining the aforementioned rock accompanied by decarboxylation, Cooling the baking material using cooling air, To remove the burnt material from the bottom of the shaft, Includes, Each shaft operates alternately in firing mode and preheating mode, with one shaft in firing mode for a predetermined period of time while at least one other shaft is in preheating mode (and vice versa). In firing mode, As described above, in the firing mode, carbonate mineral rock is loaded onto the top of the shaft, In the presence of the preheated carbonate mineral rock descending in this shaft, fuel is burned in the presence of oxygen, and in the calcination mode, combustion fumes are released in the form of a gaseous flow descending in the shaft, thereby calcining the rock and obtaining calcined material through its decarboxylation. The gas flow containing these combustion fumes moves from the firing mode shaft to the at least one shaft in the preheating mode by using the gas transfer channel. In preheating mode, As described above, the loaded carbonate mineral rock is preheated by heat exchange with a gas flow containing combustion fumes that flows back from the gas transport channel to the loaded carbonate mineral rock described above and rises in the at least one shaft in the preheating mode. Based on the gas flow containing combustion fumes, gaseous waste is discharged from the furnace at the top of the at least one shaft in the preheating mode.

[0005] In the sense of the present invention, carbonate mineral rocks mean, in particular, limestone, dolomite, and / or magnesite, which are converted to quicklime, calcined dolomite, and / or magnesia, respectively, by calcination. The formula for calcining limestone to lime is as follows: CaCO3 (solid) + heat ←→ CaO (solid) + CO2 (gas)

[0006] This is a reversible endothermic reaction, where lime recombines with CO2 on its first occasion below 900°C, but this is accompanied by an equilibrium state and exhibits a faster or slower reaction rate depending on the temperature and ambient concentration of CO2.

[0007] Therefore, in this process, a large amount of CO2 is released while the initial limestone or dolomite rock is converted into lime or dolomite by calcination. Furthermore, since high temperatures are required to carry out this calcination, fuel must be burned, which also results in the release of a large amount of CO2. Overall, the calcination method has the disadvantage of actively contributing to the greenhouse effect.

[0008] This common calcination method also has drawbacks, such as the fact that the fuel is burned with air and the calcination products are cooled by the air. As a result, the gaseous waste released at the top of the furnace has high levels of nitrogen, while CO2 is relatively low (approximately 20% to 27% by volume in dry gas), and recovery is costly due to the large proportion of nitrogen (dinitrogen) from the air used.

[0009] To recover this CO2, one possible method is to use chemical solvents called "amines" for removal. This is most widely used as a technique applied to furnace fumes at the end of the line, after the dust collection filter. However, the cycle characteristics of PFRK furnaces, which involve 1-2 minute furnace shutdowns every 10-15 minutes, are incompatible with this technique. Furthermore, it is extremely costly and requires solvents that are not sustainable from an environmental law perspective.

[0010] In order to recover CO2 emitted in a PFRK furnace, methods have already been proposed to replace all air used in the method (combustion air transporting solid fuel and cooling air) with recycled combustion fumes and to introduce pure oxygen into the shaft during the firing mode (see CN105000811). It is obvious to those skilled in the art that this process is not feasible because lime undergoes recarbonation during cooling. Thus, it is not possible to cool lime by recirculating CO2, as the lime immediately recombines with this CO2 to reconstruct CaCO3. On the other hand, using pure oxygen at the top of the furnace presents serious material compatibility issues, as this input does not provide a sufficient mass flow to effectively recover the heat accumulated in the regeneration area. The drawbacks and feasibility issues of this method have already been discussed in U.S. Patent Application Publication 2020 / 0048146.

[0011] Furthermore, it should be noted that, in contrast to rotary furnaces, the cooling air in PFRK furnaces does not directly affect, for example, the combustion in firing mode and the calcination process in the shaft. No impact on product quality is expected.

[0012] The production mode refers to the normal operating state in which the furnace continuously produces calcined material. Therefore, this mode does not apply to the furnace startup and shutdown phases, nor to maintenance in the event of a malfunction. [Overview of the project] [Problems that the invention aims to solve]

[0013] The present invention aims to at least partially improve the problem of significant CO2 emissions into the atmosphere without altering the cycle operation of a PFRK-type furnace or making little to no changes to its structure. It also aims to enable the recovery of CO2 present in the gaseous waste emitted by the furnace. [Means for solving the problem]

[0014] To solve this problem, the present invention is, as described at first, a method for calcining mineral rock in a regenerative co-current vertical shaft furnace, comprising: collecting a part of the gaseous waste discharged from the furnace; forming an oxidizing mixture by mixing the collected part of the gaseous waste discharged from the furnace with high-concentration oxygen (dioxygen); introducing this oxidizing mixture at the top of the shaft in the firing mode to ensure the combustion of the fuel in the presence of oxygen; including; providing a method in which the gaseous waste discharged from the furnace has a high concentration of CO2.

[0015] When fuel is burned in high-concentration oxygen, the flame temperature becomes too high for conventional furnace equipment. Also, according to the present invention, it is also possible to collect a part of the gaseous waste rich in CO2 and mix it with oxygen. Instead of the conventional oxidant formed by the O2+N2 mixture of air, an O2+CO2 mixture at an appropriate flame temperature is thus obtained.

[0016] When fuel is burned in oxygen, a gas stream containing combustion fumes is generated and the carbonate rock is calcined. As a result, CO2 mainly containing impurities present in trace amounts in the fuel and the material to be calcined, and oxygen remaining after the combustion of the fuel, is produced. Naturally, these combustion fumes also contain the CO2 supplied to the oxidizing mixture. As a result, obviously, the CO2 concentration of the gaseous waste discharged from the top of the furnace becomes significantly higher than that of the conventional method. According to the present invention, the high CO2 concentration of the gaseous waste means that the CO2 content in the dry gas is at least 35% by volume, preferably at least 45% by volume, more preferably at least 60% by volume, especially at least 80% by volume, and particularly preferably at least 90% by volume. And by using or recovering this CO2 under favorable conditions, the contribution of the furnace to the greenhouse effect can be dramatically reduced.

[0017] Using this method does not necessarily require any specific design of the furnace itself. The modifications to the furnace are limited to the exterior and consist of changing the waste circuitry from the furnace and providing at least one high-concentration oxygen source.

[0018] According to the present invention, high-concentration dioxygen (hereinafter referred to as oxygen) means a gas with an oxygen level exceeding 50 volume percent. This is preferably 90 volume percent or more, particularly 93 volume percent, and advantageously 98 to 100 volume percent. The high-concentration oxygen source may be, for example, an air separation unit that separates air into oxygen and nitrogen and operates in parallel with an oxygen tank installed in or next to the furnace. It is advantageous for the combustion of the fuel to occur in the presence of an excess of oxygen, preferably about 5 to 50 volume percent, particularly 10 to 30 volume percent, and advantageously 15 to 25 volume percent, relative to the stoichiometric combustion requirement.

[0019] According to the present invention, fuel means any solid, liquid, or gaseous fuel (for example, natural gas, hydrogen, biogas, heavy oil, oils, coal or coke powder, solid biomass such as sawdust, and solid recovered fuels such as plastics, paper, and cardboard). In the case of solid fuel, it is preferable that the introduction of the calcination mode into the shaft be carried out in granular or powdery form by using a portion of the collected gaseous waste discharged from the furnace as the conveying gas. Alternatively, CO2 from any other source may be provided as the conveying gas.

[0020] According to one embodiment of the present invention, cooling of the calcining material involves supplying cooling air at the bottom of each shaft, which flows back through the descending calcining material and is heated by contact with the calcining material, the heated cooling air mixing with a gas flow containing combustion fumes in the calcining mode shaft before moving through a gas transfer channel, and after moving with a gas flow in at least one of the shafts in a preheating mode, so that the CO2-rich gaseous waste discharged from the furnace contains combustion fumes and cooling air. In this case, only the combustion air of the conventional method is replaced by the CO2-rich gaseous waste and oxygen-based oxidizing mixture discharged from the furnace. Such a method makes it possible to increase the CO2 content of the gaseous waste discharged from a conventional PFRK furnace from 20-27 volume percent in dry gas to at least 35 volume percent, preferably at least 45 volume percent, and even up to 65 volume percent in dry gas in the furnace according to the present invention. For example, replacing the coke ovens currently used in soda ash plants with PFRK furnaces using this method is advantageous because it can provide fumes containing 40% CO2 by volume. Furthermore, PFRK is a "sustainable" and energy-efficient furnace that can solve all the environmental problems associated with coke ovens, particularly the significant emission of pollutants (CO, NH3, H2S, etc.).

[0021] According to a particular embodiment of the present invention, cooling air is supplied to the furnace in a total volume less than or equal to the thermodynamic minimum required to cool the calcined material to a reference temperature of 100°C. It is considered advantageous that the total volume of cooling air supplied to the furnace is approximately 40-60%, preferably 50%, of the aforementioned thermodynamic minimum. In this case, the unloaded product will be at a higher temperature than in normal operation. Therefore, the unloading equipment must be adapted to materials that can withstand this temperature.

[0022] Furthermore, it is considered convenient that the cooling of the calcined material includes supplying cooling air at the bottom of the sole shaft of the calcination mode, which flows back through the descending calcined material and is heated by contact with the calcined material. The heated cooling air mixes with the gas flow containing combustion fumes before moving through the gas transfer channel, and the high CO2 concentration gaseous waste discharged from the furnace contains combustion fumes and cooling air. In this case as well, the cooling air may be supplied to the furnace in a total volume less than the thermodynamic minimum required to cool the calcined material to a reference temperature of 100°C. Therefore, it is considered convenient that the total volume of cooling air supplied to the furnace is approximately 40-60%, preferably 50%, of the aforementioned thermodynamic minimum.

[0023] According to one particularly advantageous embodiment of the present invention, the cooling of the calcining material involves supplying cooling air that flows back through the descending calcining material and is heated by contact with the calcining material at the bottom of each shaft or the bottom of the single shaft in a calcination mode, the method further comprising removing the heated cooling air from the furnace, the gaseous waste discharged from the furnace containing at least 90 vol%, preferably at least 95 vol%, of CO2 in dry gas. In this case, the gaseous waste discharged from the furnace is formed almost entirely of combustion fumes. Such gases can be used or recovered in specific industries.

[0024] According to a particular embodiment of the present invention, the method further includes heat exchange between the heated cooling air removed from the furnace and the collected portion of the gaseous waste discharged from the furnace before or after mixing with high-concentration oxygen. This makes it possible to introduce heat recovery of the oxidizing mixture into the shaft of the calcination mode.

[0025] Further details and features of the method according to the present invention are described in the appended claims.

[0026] Furthermore, the present invention relates to a PFRK-type regenerative co-current vertical shaft furnace.

[0027] Such furnaces At least two shafts interconnected by a gas transfer channel, each in an on or off position, At least one fuel supply device, At least one oxygen-containing oxidant supply opening for fuel combustion, At the top of the shaft is an entrance for loading carbonate mineral rock, An outlet for unloading the burnt material generated at the bottom of the shaft, At least two shafts equipped with, A gaseous waste discharge duct at the top of the shaft connected to the chimney, A cooling air source for cooling the generated baking material, A system for reversing the operation of shafts, wherein each shaft operates alternately in firing mode and preheating mode in production mode, with one shaft in firing mode for a predetermined period while at least one other shaft is in preheating mode (and vice versa), and the system is configured to control the on and off positions. It is equipped with.

[0028] According to the present invention, this furnace is A recirculation circuit is located between the gaseous waste discharge duct of the shaft and the oxidant supply opening of the shaft, wherein the recirculation system controls the collection of at least a portion of the gaseous waste from the shaft in preheating mode. A high-concentration oxygen source that forms an oxidizing mixture by supplying high-concentration oxygen through connection to a recirculation circuit, and a high-concentration oxygen source that ensures fuel combustion by supplying the oxidant supply opening of the shaft in firing mode in the ON position via the inversion system, To further prepare.

[0029] As described above, the PFRK furnace operates in cycle mode, with each shaft operating in firing mode for a predetermined period, followed by a 1-2 minute reversal time before operating in preheating mode, and so on. During the reversal time, the reversal system synchronously controls all changes necessary for transitioning from one mode to the other, for example, by opening the nozzles of the fuel supply device in the shaft during firing mode and closing them when transitioning to preheating mode. Thus, the reversal system controls not only many valves and gates, but also the operation of loading and unloading equipment or various suction, pumping, or injection elements.

[0030] As described above, the furnace according to the present invention requires only minor structural modifications to the outside of the furnace. Therefore, the calcination method according to the present invention may be implemented using a simple configuration of an existing furnace.

[0031] According to one embodiment of the present invention, the shaft is a connecting furnace tube having a circular cross-section, wherein the gas transfer channels enable the movement of gas by connecting peripheral channels arranged around each shaft, and the shaft is provided with a collection ring below the connecting furnace tube that enables the removal of heated cooling air from the furnace by connecting to an exhaust element. The circular shaft is preferably further provided with a central collection element at the bottom below the connecting furnace tube that enables the removal of heated cooling air from the furnace by connecting to an exhaust element.

[0032] According to another embodiment of the furnace according to the present invention, the shafts have a rectangular cross-section, with a first surface of the shaft facing the first surface of an adjacent shaft, and each shaft having a second surface opposite to the surface facing each other, and the gas transfer channels are connecting furnace tubes that directly connect one shaft to the other via the first surfaces, and the first and second surfaces of the shafts are each provided with collection tunnels below the connecting furnace tubes that enable the removal of heated cooling air from the furnace by connection to an exhaust element.

[0033] According to one embodiment of the present invention, the furnace includes a unit that separates air into oxygen and nitrogen as an oxygen source for the recirculation circuit. An oxygen tank may also be provided. It is convenient to heat the aforementioned oxidizing mixture prior to supplying it to the shaft in the firing mode by incorporating the heated cooling air removed from the furnace into the recirculation circuit of a heat exchanger to which the air is supplied.

[0034] Further details and features of the furnace according to the present invention are described in the appended claims.

[0035] Other features of the present invention will become apparent from the following description, but this is not limiting; please refer to the attached drawings. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic diagram of a conventional PFRK reactor. [Figure 2] Figures 2a and 2b show digital models of the oxygen mass % concentration in the gas flow of a conventional PFRK furnace with a circular cross-section and a conventional PFRK furnace with a rectangular cross-section. [Figure 3] This figure schematically shows several embodiments of a circular cross-section furnace according to the present invention. [Figure 4] This figure schematically shows several embodiments of a circular cross-section furnace according to the present invention. [Figure 5] This figure partially shows one embodiment of a rectangular cross-section furnace according to the present invention. [Modes for carrying out the invention]

[0037] In the diagrams, the same reference numerals are used for identical or similar parts. Conventionally, the shaft shown on the left is in firing mode, and the shaft shown on the right is in preheating mode. Standard parts such as loading or unloading equipment are either not shown or are shown very schematically to avoid making the drawings cluttered.

[0038] As shown in Figure 1, the illustrated "PFRK" furnace is a vertical double-shaft furnace 1, 2 in which fuel is alternately injected into shaft 1 and a subsequent shaft 2 for approximately 12 minutes, with the circuit reversed during a 1-2 minute stop period between cycles. This stop period is the "reversal" period. Both shafts have a circular cross-section and are provided with peripheral channels 13 interconnected by connecting furnace tubes 3. The shaft is divided vertically into three areas: a preheating area A where the carbonate rock is preheated before calcination, a combustion area B where the carbonate rock is calcined, and a cooling area C where the calcined material is cooled.

[0039] When the shaft is in calcination mode (in this case, shaft 1), a fuel supply device in the form of a nozzle 4 injects fuel 9 into the shaft, which in the illustrated example is natural gas. The carbonate rock, loaded at the top of the shaft through an open inlet 5, gradually descends through the shaft. Combustion air is introduced at the top of the shaft through a supply opening 6, which enables combustion of the fuel at the outlet of nozzle 4 and decarboxylation of the carbonate rock calcination material 10. The gas flow 11 formed by combustion and decarboxylation flows forward and downward over the calcination material and moves to the connecting furnace tube 3 via a peripheral channel 13. Cooling air is introduced back into the calcination material at the bottom of the shaft through a supply duct 7 to cool it. The heated cooling air 12 mixes with the gas flow containing combustion fumes 11 and moves to the connecting furnace tube 3. The calcination material is unloaded through an outlet 8 to an unloading device 24.

[0040] When the shaft is in preheating mode (in this case, shaft 2), the fuel supply is closed, and nozzle 4 is turned off. The same applies to the carbonate rock inlet 5 and the opening 6 that supplies combustion air. However, the cooling air supply duct 7 and the calcination material outlet 8 are kept in the open position. After heat exchange with the descending calcination material 10, the heated cooling air mixes with the gas flow 11 that entered the shaft from the connecting furnace tube 3 through the peripheral channel 13. This gas flow 11 travels until it reaches the top of the shaft, is discharged from the furnace via the exhaust duct 14, and carried to the chimney 15. In shaft 1 in calcination mode, this exhaust duct 14 is closed.

[0041] Furthermore, the furnace is equipped with a schematic inversion system 16, which synchronously and directly or remotely controls the movement of the shafts during the inversion time. It also controls the on / off switching of all elements of the furnace so that, in production mode, each shaft operates alternately in firing mode and preheating mode.

[0042] In some cases, there are three shafts: two for preheating mode and one for combustion mode.

[0043] Figure 1 shows a furnace designed to produce 430 tons of lime per day. All gas flows described below are Nm of the lime produced. 3 Expressed in units of / t.

[0044] Due to the reaction with the gas injected into shaft 1 as fuel, 1120 Nm 3 By using combustion air at a rate of / t, an excess of 19% by weight of air is obtained relative to the stoichiometric requirement, and 100 Nm³ is produced during combustion. 3 It forms CO2 at a rate of / t. Since the inflowing gas is air, its oxygen mass concentration is 23%. The temperature reached thereafter far exceeds 900°C, causing decarboxylation of the limestone, reaching 380 Nm³. 3 / t of CO2 is released. To cool the generated lime to approximately 100°C, 290 Nm is injected through the bottom of both shafts. 3 Cooling air at / t is introduced, with a total of 580Nm3 It is / t. For chimneys, it is 480Nm 3 2250Nm³ containing CO2 / t 3 A certain amount of gaseous waste is obtained, but this gaseous waste has a CO2 content of 23% in dry gas form. Because it is difficult to use or recover CO2 with such a low content, all of the gaseous waste is released into the atmosphere.

[0045] Figure 2a is a digital model of a circular cross-section PFRK furnace, showing the routes according to the oxygen content of the gas. This only shows the combustion area B and cooling area C from the nozzle end, and the top of the shaft is not shown.

[0046] Area a: Cooling air (bottom) and combustion air (top, only above the nozzle end) in the shaft during firing mode, with an O2 content of 23% by weight.

[0047] Area b: Combustion fume jet released by the nozzle; there is little oxygen remaining, but unreacted O2 may remain between the jets.

[0048] Area c: Fumes gradually mix with the cooling air, penetrating deep into cooling area C. These push the gaseous mixture into the surrounding channels 13 and ultimately into the connecting furnace tube 3.

[0049] Area d: Cooling air in the shaft during preheating mode.

[0050] Area e: This is a mixture of gas flow from the peripheral channel 13 and cooling air. The closer to the center of the shaft, the higher the residual O2 content.

[0051] Figure 2b shows this digital model for a PFRK furnace with a rectangular shaft cross-section. Here, the gas flow distribution is no longer symmetrical as it was in the case of a circular shaft.

[0052] Figure 3 is a diagram of the furnace according to the present invention. In this case, there is no change in the structure of the furnace. A separation member 17 capable of collecting a part of the gaseous waste discharged from the furnace and introducing it into the recirculation circuit 18 is provided in the external discharge duct 14. In this circuit, it is convenient for a part of the collected gaseous waste to be processed in the processing unit 19, and for example, filtering and / or drying may be performed. The air separation unit 20 separates the air supplied by the duct 21 into N2 discharged through the duct 22 and O2 supplied to the recirculation circuit 18 through the supply duct 23. And this circuit 18 supplies an oxidizing mixture formed by a part of the recycled gaseous waste and high-concentration O2 to the top of each shaft at the supply opening 6.

[0053] The operation of the furnace in FIG. 3 is similar to that of a PFRK furnace. The separation member 17 is the same as the processing unit 19 and the air separation unit 20 even when continuously operating. As described above, the inversion system 16 closes the discharge duct 14 at the top of the shaft in the firing mode. However, at the top of this shaft, the introduction of the oxidizing mixture is enabled by the opening of the supply opening 6, but it is closed at the top of the shaft in the preheating mode.

[0054] The amount of carbonate rock used and the flow rates of the fuel and the cooling air are the same as those of the conventional furnace described above. 830 Nm 3 / t of gaseous waste discharged from the furnace is rich in CO2 and is collected through the recirculation duct 18. This recirculated waste is mixed with 160 Nm 3 / t of O2 to maintain the mass concentration of O2 in the thus formed oxidizing mixture at the same 23% and to obtain the same 19 wt% excess oxygen with respect to the stoichiometric requirement during combustion. As a result, the nitrogen N2 in the combustion air is replaced with CO2 corresponding to its mass. Since this is heavier than nitrogen (specific gravity 1.977 with respect to 1.25 g / Nm 3 ), the total amount of the furnace fumes is reduced, resulting in a 13% reduction in the pressure loss compared to the conventional furnace. In the chimney, 1240 Nm 3The gaseous waste produced is 43% by volume of CO2 in dry gas form. As explained above, this CO2 content makes industrial use possible, for example, in a soda ash plant.

[0055] As a modification of such a furnace according to the present invention, the flow of cooling air may be suppressed in order to further reduce the air input of this method. For example, this input may be suppressed by 50% to 290 Nm 3 The cooling air may be / t. This reduced volume may be introduced through the supply duct 7 of the single shaft in the calcination mode, or it may be introduced using the supply duct 7 of both shafts. This measure reduces the dilution of fumes by 50%. As a result, the degree of cooling of the calcined material discharged through the outlet 8 is reduced. Therefore, it is necessary to provide unloading equipment that can withstand temperatures higher than 100°C, such as a heat-resistant steel unloading table and a steel drag chain. Since the lime comes out at a high temperature, there is little heat recovery by the cooling air, but this is because the combustion is 120 Nm 3 This is compensated for by slightly increasing the fuel input so that CO2 of / t is formed. On the other hand, such an increase is compensated for by the 1730 Nm³ emitted from the reactor in the recirculation circuit. 3 Collection of gaseous waste at 865 Nm 3 Changed to / t, and this collected waste is 200Nm 3 By mixing with O2 at / t, it is necessary to maintain the same 23% mass concentration of O2 in the resulting oxidizing mixture, while also obtaining the same 19% by weight excess oxygen relative to the stoichiometric requirement during combustion. Therefore, in a chimney, where the CO2 content is high at 63% by volume in dry gas, 865Nm³ is required. 3 Only gaseous waste in units of / t can be obtained.

[0056] In practice, a chimney can specify a custom CO2 concentration of 40% to 65% by adjusting the amount of cooling air to 100% to 50% of the minimum thermodynamic volume required to cool the calcining material to a reference temperature of 100°C. Within the limits of the temperature compatibility of the lime with the high-temperature unloading and transfer system installed for this purpose, it may be possible to obtain higher CO2 concentrations by limiting the cooling air input to less than 50%.

[0057] Figure 4 shows an advantageous furnace according to the present invention. As described above, this embodiment includes the features of the embodiment shown in Figure 3, but also includes a slight modification to the external structure of the furnace.

[0058] In this case, the removal system extracts heated cooling air through contact with the calcining material. Shafts 1 and 2 are each provided with a collection ring 25 below the connecting furnace tube 3 and peripheral channel 13, which is capable of removing heated cooling air from the furnace by connecting to an exhaust element 26. Thus, some or all of the combustion air may be extracted as needed by extracting only a small portion of the combustion fumes. In practice, as shown in Figure 2a, the descending gas penetrates deep into the cooling area C, so the cooling air is pressed against the outer wall of the furnace where the collection ring is located. The shaft may optionally further include a central collection element 27 at the bottom below the connecting furnace tube 3, which enables central removal of heated cooling air by connecting to the exhaust element 26.

[0059] In the case of a rectangular furnace, the use of a lateral recovery area also allows for the extraction of cooling air without a collection ring. As shown in Figure 5, each shaft includes four faces. A face 28 of one shaft faces a face 29 of an adjacent shaft, and each shaft includes second faces 30 and 31 opposite to the face facing each other. The gas transfer channel is a connecting furnace tube 3 that directly connects one shaft to the other via its respective faces 28 and 29. Below the connecting furnace tube, faces 28 to 31 are provided with collection tunnels 32 to 35, respectively, which allow the cooling air heated by the connection to the exhaust element 26 to be removed from the furnace.

[0060] Due to the asymmetrical spread of the gas flow in the rectangular shaft furnace (see Figure 2b), the cooling air is pushed to only one side by the hot fumes. Furthermore, in the illustrated furnace where shaft 1 is in firing mode and shaft 2 is in preheating mode, the inversion system 16 opens only collection tunnels 32 and 34. In subsequent cycles, only collection tunnels 33 and 35 are opened.

[0061] In the furnace shown in Figure 4, the amount of carbonate rock used and the flow rate of cooling air are the same as in the conventional furnace described above. The heated cooling air is removed from the furnace via the exhaust element 26. In shaft 1, 105 Nm³ is generated during combustion. 3 Fuel introduction is carried out so that CO2 of / t is formed. At the top of shaft 2, 1330 Nm 3 / t of gaseous waste is emitted. Of this CO2-rich exhaust gaseous waste, 730Nm³ 3 / t is collected via the recirculation circuit 18. This recirculated waste is 220 Nm 3 By mixing with O2 at / t, the mass concentration of O2 in the thus formed oxidizing mixture is maintained at the same 23%, while obtaining the same 19% by weight excess oxygen relative to the stoichiometric requirement during combustion. Therefore, in the chimney, 600 Nm³ of dry gas with a CO2 content of 96% 3 Only gaseous waste in units of / t can be obtained.

[0062] In the furnace shown in Figure 4, in order to recover a portion of the energy of the high-temperature air removed by the exhaust element 26, a heat exchanger 36 may be used to perform heat exchange on a portion of the recirculated gaseous waste before or after mixing with high-concentration oxygen.

[0063] Furthermore, in the connecting furnace tube 3 and the surrounding channel 13, a very small portion of the collected gaseous waste discharged from the furnace may be injected by using the injection duct 37. Optionally, heat exchange may be performed beforehand between the heated cooling air removed from the furnace and the injected small portion by using a heat exchanger (e.g., heat exchanger 36). If heat exchanger 36 is not available, a heat exchanger (not shown) may be provided in the injection duct 37.

[0064] In yet another modification, the temperature of the furnace tube may be reduced by injecting water at select locations in the connecting furnace tube and / or surrounding ring. This additional water does not have the effect of diluting the CO2 concentration with dry gas.

[0065] Such a configuration, which recovers heat from the heated cooling air removed from the furnace, can naturally be provided in rectangular shaft furnaces as well as in rectangular shaft furnaces by using such CO2 or water injection devices in the connecting furnace tube, in addition to heat exchangers.

[0066] In a furnace design similar to the one shown in Figure 4, it is clear that cooling air may be injected only at the bottom of one of the two shafts.

[0067] Table 1 below shows the flow in a conventional furnace and various modified furnaces according to the present invention, and Table 2 shows the amounts of various gaseous elements at the furnace inlet.

[0068] In each example column, 1 represents a conventional PFRK furnace, 2 and 3 represent furnaces according to Figure 3 with variable cooling airflow, and 4 and 5 represent furnaces according to Figure 4 with and without a heat exchanger.

[0069] [Table 1]

[0070] [Table 2]

[0071] The present invention is not limited in any way to the embodiments described above and can be modified without departing from the scope of the appended claims.

[0072] For example, it would be convenient if air-cooled fuel injection nozzles could be replaced with heat-insulated nozzles.

Claims

1. A method for calcining mineral rocks in a regenerative co-current vertical shaft furnace, wherein at least two shafts are interconnected via gas transfer channels, and in the production mode, Loading carbonate mineral rock onto the top of the furnace, Preheating the aforementioned carbonate mineral rock, To obtain calcined material by calcining the carbonate mineral rock accompanied by decarboxylation, Cooling the aforementioned baking material with cooling air, The burning material is unloaded at the bottom of the shaft, Includes, Each shaft operates alternately in firing mode and preheating mode, with one shaft in firing mode for a predetermined period of time while at least one other shaft is in preheating mode (and vice versa). In firing mode, As described above, in the firing mode, carbonate mineral rock is loaded onto the top of the shaft, In the presence of the preheated carbonate mineral rock descending in the shaft, the fuel is burned in the presence of oxygen, thereby burning the rock in conjunction with the release of combustion fumes in the form of a gaseous flow descending in the shaft in the firing mode, and obtaining calcined material by its decarbonation. The gas flow containing the combustion fumes moves from the shaft in the firing mode to the at least one shaft in the preheating mode by using the gas transfer channel. In preheating mode, As described above, the carbonate mineral rock described above is preheated by heat exchange with the gas flow containing the combustion fumes that flow back from the gas transfer channel to the carbonate mineral rock described above and rise in the at least one shaft in the preheating mode. A method for discharging gaseous waste from the furnace at the top of the at least one shaft in a preheating mode, based on the gas flow containing the combustion fumes, The combustion of the aforementioned fuel occurs in the presence of an excess of oxygen relative to the stoichiometric requirement. Collecting a portion of the gaseous waste discharged from the furnace, By mixing a portion of the gaseous waste discharged from the furnace with high-concentration oxygen, an oxidizing mixture is formed. By introducing the oxidizing mixture at the top of the shaft in the firing mode, combustion of the fuel in the presence of oxygen is ensured, It further includes, CO2, a gaseous waste discharged from the furnace. ２ A method characterized by a high concentration.

2. The cooling of the calcining material includes supplying cooling air at the bottom of each shaft that flows back through the descending calcining material and is heated by contact with the calcining material, wherein the heated cooling air mixes with the gas flow containing the combustion fumes in the shaft in calcination mode before moving through the gas transfer channel, and after moving, mixes with the gas flow in at least one shaft in preheating mode, and CO2 is discharged from the furnace. ２ The method according to claim 1, characterized in that the highly concentrated gaseous waste includes the combustion fume and the cooling air.

3. The cooling of the calcining material includes supplying cooling air that flows back through the descending calcining material at the bottom of the sole shaft of the calcining mode and is heated by contact with the calcining material, wherein the heated cooling air mixes with the gas flow containing the combustion fumes before moving through the gas transfer channel, and CO is discharged from the furnace. ２ The method according to claim 1, characterized in that the highly concentrated gaseous waste includes the combustion fume and the cooling air.

4. The method according to claim 2 or 3, characterized in that the cooling air is supplied to the furnace in a total volume less than or equal to the thermodynamic minimum required to cool the calcining material to a reference temperature of 100°C.

5. The method according to claim 4, characterized in that the total volume of cooling air supplied to the furnace is approximately 40 to 60%, preferably 50%, of the thermodynamic minimum value.

6. The cooling of the calcined material includes supplying cooling air that flows back through the descending calcined material and is heated by contact with the calcined material at the bottom of each of the shafts or the bottom of the single shaft in the calcination mode, the method further includes removing the heated cooling air from the furnace, the gaseous waste discharged from the furnace being at least 90% by volume of CO2 in dry gas form ２ The method according to claim 1, characterized by containing a substance.

7. The method according to claim 6, further comprising heat exchange between the heated cooling air removed from the furnace and a portion of the gaseous waste discharged from the furnace before or after mixing with high-concentration oxygen.

8. The method according to claim 6 or 7, further comprising, in the gas transfer channel, injecting a portion of the collected portion of the gaseous waste discharged from the furnace, and optionally, before the injection, heat exchange between the heated cooling air removed from the furnace and the injected portion.

9. The method according to any one of claims 1 to 8, further comprising injecting water into the gas transport channel.

10. The combustion of the fuel includes introducing a gaseous, liquid, or solid fuel into the shaft of the firing mode, and in the case of a solid fuel, the introduction is a further portion of the collected portion of the gaseous waste discharged from the furnace or another CO2 as a carrier gas. ２ The method according to any one of claims 1 to 9, characterized in that it is performed using a power source.

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