Method for calcining mineral rock in a regenerative co-current vertical shaft furnace and furnace used

Abstract

The present invention relates to a method for calcining mineral rock in a regenerative co-current vertical shaft furnace, comprising collecting a portion of the gaseous waste discharged from the furnace shaft in a preheating mode (2) in a recirculation circuit (18), mixing the collected portion of the gaseous waste with a high concentration of oxygen from an oxygen source (20) to form an oxidizing mixture, and inserting the oxidizing mixture into the top of the shaft (1) in a calcining mode, thereby ensuring combustion of the fuel in the presence of oxygen, 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 rock in a regenerative co-current vertical shaft furnace and the furnace used. [Background technology]

[0002] Regenerative co-flow vertical shaft furnaces or co-flow regenerative kilns (PFRK) have an energy efficiency of 85% to 90%. This is the highest in the lime sector, even within the entire energy-intensive cement, steel, and glass industries. In Europe, 60% of lime is produced in this type of furnace. This proportion is expected to increase in Europe and worldwide, taking into account the roadmap for the energy and ecological transition.

[0003] A "PFRK" furnace is a vertical, double-shaft furnace in which fuel is injected alternately through two shafts for approximately 10 to 15 minutes, with the air and fuel circuits reversed during a 1 to 2 minute pause between cycles. This pause is called the "reversal" period. The two shafts are connected via a connecting flue. When one shaft is firing (calcination mode), hot combustion fumes pass through the connecting flue (gas transfer channel) and transfer some of their heat to the mineral rock being calcined, thereby preheating the mineral rock in the other shaft in regeneration or preheating mode. PFRK furnace shafts 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 valid for all PFRK furnace configurations.

[0004] The method used in these known furnaces is to: loading carbonate mineral rock at the top of the furnace; preheating the rock; Calcination of said rock with decarbonation to obtain a calcined material; cooling the calcined material with cooling air; unloading the calcined material at the bottom of the shaft; Including, each shaft alternately operates in a firing mode and a preheating mode, such that one shaft is in firing mode for a predetermined period of time while at least one other shaft is in preheating mode (or vice versa); In baking mode, As described above, in the firing mode, loading carbonate mineral rock at the top of the shaft; In the presence of the preheated carbonate mineral rock descending in the shaft, a fuel is burned in the presence of oxygen, thereby calcining the rock and obtaining a calcined material by decarbonation, with the release of combustion fumes in the form of a gas stream descending in the shaft in a calcination mode; the gas flow containing these combustion fumes is transferred from a shaft in a firing mode to the at least one shaft in a preheating mode by using the gas transfer channel; In preheat mode, preheating the loaded carbonate mineral rock by heat exchange with a gas stream containing combustion fumes flowing up through said at least one shaft in a preheating mode, counterflowing from a gas transfer channel to said loaded carbonate mineral rock, as described above; Based on the gas flow containing combustion fumes, gaseous waste is discharged from the furnace at the top of said at least one shaft in a preheating mode.

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

[0006] This is a reversible endothermic reaction, and lime will recombine with CO2 at the first opportunity below 900°C, but this involves an equilibrium state, with faster or slower reaction rates depending on the temperature and environmental concentration of CO2.

[0007] Therefore, in this process, a large amount of CO2 is released during the calcination of the initial limestone or dolomite rock into lime or dolomite. Furthermore, the high temperatures required to carry out this calcination require the burning of fuel, which 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 the disadvantage that the fuel is burned with air and the calcined product is cooled by air. As a result, the gaseous waste released at the top of the furnace has high levels of nitrogen, relatively low levels of CO2 (approximately 20%-27% volume concentration of dry gas), and a large proportion of nitrogen (dinitrogen) from the air used, which makes recovery costly.

[0009] To capture this CO2, chemical solvent removal methods known as "amines" are considered, but this is the most widespread technology applied to furnace fumes at the end of the line, after the dust collection filter. However, the cyclic nature of PFRK furnaces, which require shutdowns of 1-2 minutes every 10-15 minutes, makes this technology incompatible. Furthermore, it is very expensive and requires solvents that are not sustainable from an environmental law perspective.

[0010] To recover the CO2 emitted in a PFRK furnace, a method has already been proposed in which all air (combustion air carrying the solid fuel and cooling air) is replaced by recycled combustion fumes and pure oxygen is introduced into the shaft during calcination (see CN105000811). Those skilled in the art will appreciate that this process is not feasible, since lime recarbonates during cooling. Thus, cooling the lime by recirculating CO2 is not possible, since the lime would immediately recombine with this CO2 and reconstitute CaCO3. On the other hand, using pure oxygen at the top of the furnace presents serious problems in terms of material compatibility, and this input does not result in a sufficient mass flow to effectively recover the heat accumulated in the regeneration area. The drawbacks and feasibility of this method have already been discussed in U.S. Patent Application Publication No. 2020 / 0048146.

[0011] It should also be noted that the cooling air in the PFRK furnace, in contrast to rotary furnaces, does not have a direct effect on the combustion and calcination processes in the shaft, for example, in the firing mode. No influence on the quality of the product is to be expected.

[0012] Production mode means that the furnace is in normal operation, continuously producing calcined material. This mode therefore does not apply to the start-up and shutdown phases of the furnace, nor to maintenance in case of breakdowns. Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention aims to at least partially ameliorate the problem of significant CO2 emissions into the atmosphere without changing the cycle operation of the PFRK-type reactor and with little or no changes to its design, and to make it possible to recover the CO2 present in the gaseous waste emitted by the reactor. [Means for solving the problem]

[0014] To achieve this object, the present invention provides, as initially stated, a method for calcining mineral rock in a regenerative co-current vertical shaft furnace, comprising: collecting a portion of the gaseous waste emitted from the furnace; mixing a collected portion of the gaseous waste from the furnace with a high concentration of oxygen (dioxygen) to form an oxidizing mixture; introducing this oxidizing mixture at the top of the shaft in firing mode to ensure combustion of said fuel in the presence of oxygen; Including, The method provides that the gaseous waste product discharged from the furnace has a high concentration of CO2.

[0015] Combustion of fuel in an oxygen-rich atmosphere results in flame temperatures that are too high for conventional furnace equipment. According to the present invention, it is also possible to collect a portion of the CO2-rich gaseous waste and mix it with oxygen. Instead of the conventional oxidant formed by the O2 + N2 mixture of air, a mixture of O2 + CO2 is thus obtained at the appropriate flame temperature.

[0016] Combustion of fuel in oxygen produces a gas stream containing combustion fumes and calcines carbonate rock. This primarily produces CO2, which contains trace amounts of impurities present in the fuel and the material being calcined, as well as oxygen remaining from the combustion of the fuel. Naturally, these combustion fumes also contain CO2, which is fed to the oxidizing mixture. As a result, the CO2 concentration in the gaseous waste discharged from the top of the furnace is significantly higher than in conventional processes. According to the present invention, a high CO2 concentration in the gaseous waste means that the dry gas contains at least 35% by volume, advantageously at least 45% by volume, preferably at least 60% by volume, particularly at least 80% by volume, and particularly advantageously at least 90% by volume. By using or recovering this CO2 under favorable conditions, the contribution of the furnace to the greenhouse effect can be dramatically reduced.

[0017] Use of this method does not necessarily require any particular design of the furnace itself. The only modifications to the furnace are external to the furnace and consist of modifying the waste circuit leaving the furnace and providing at least one source of concentrated oxygen.

[0018] According to the present invention, enriched dioxygen (hereinafter referred to as oxygen) refers to a gas with an oxygen level of more than 50% by volume. This is preferably 90% or more by volume, particularly 93% by volume, and advantageously 98-100% by volume. The enriched 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. The combustion of the fuel advantageously occurs in the presence of an excess of oxygen, preferably approximately 5-50% by volume, particularly 10-30% by volume, and advantageously 15-25% by volume, relative to the stoichiometric combustion requirement.

[0019] According to the present invention, fuel refers to any solid, liquid or gaseous fuel (for example, natural gas, hydrogen, biogas, heavy oil, oils, coal or coke powder, solid biomass such as sawdust, solid recovered fuels such as plastics, paper, cardboard, etc.). In the case of solid fuel, its introduction into the firing shaft is advantageously carried out in granular or powder form by using a further part of the collected part of the gaseous waste discharged from the furnace as carrier gas. CO2 from any other source may also be provided as carrier gas.

[0020] According to one embodiment of the present invention, cooling of the calcined material involves supplying cooling air at the bottom of each shaft, which flows countercurrently through the descending calcined material and is heated by contact with the material. The heated cooling air mixes with the gas flow containing combustion fumes in the shafts in the calcination mode before moving through the gas transfer channel, and then mixes with the gas flow in at least one of the shafts in the preheating mode after moving through the gas transfer channel. The CO2-rich gaseous waste discharged from the furnace contains combustion fumes and cooling air. In this case, only the combustion air in conventional processes is replaced by the CO2-rich gaseous waste and oxygen-based oxidizing mixture discharged from the furnace. This method allows the CO2 content of the gaseous waste discharged from conventional PFRK furnaces to be increased from 20-27% by volume of dry gas to at least 35%, advantageously at least 45%, and even up to 65% by volume of dry gas in the furnace according to the present invention. As an example, a PFRK furnace using this method could advantageously replace the coke ovens currently used in soda ash plants, providing fumes containing 40% CO by volume. Also, the PFRK is a "sustainable" energy-efficient furnace, which solves all the environmental problems associated with coke ovens, including, among other things, the significant emissions of pollutants (CO, NH, HS, etc.).

[0021] According to one particular embodiment of the invention, cooling air is supplied to the furnace with a total volume equal to or less than the thermodynamic minimum required to cool the calcined material to a reference temperature of 100°C. It is considered advantageous for the total volume of cooling air supplied to the furnace to be approximately equal to 40-60%, preferably 50%, of said 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] Cooling the calcined material may also advantageously involve supplying cooling air at the bottom of the only shaft in the firing mode, counterflowing through the descending calcined material and heated by contact with the material, the heated cooling air mixing with the gas stream containing combustion fumes before moving through the gas transfer channel, and the CO₂-rich gaseous waste product discharged from the furnace containing both combustion fumes and cooling air. Again, the cooling air may be supplied to the furnace at a total volume less than the thermodynamic minimum required to cool the calcined material to the reference temperature of 100°C. Therefore, the total volume of cooling air supplied to the furnace may advantageously be equal to approximately 40-60%, preferably 50%, of said thermodynamic minimum.

[0023] According to a particularly advantageous embodiment of the invention, the cooling of the calcined material comprises supplying cooling air at the bottom of each shaft or at the bottom of only one shaft in the firing mode, which flows countercurrently through the descending calcined material and is heated by contact with the calcined material, and the method further comprises removing the heated cooling air from the furnace, so that the gaseous waste product discharged from the furnace has a dry gas content of at least 90% by volume, preferably at least 95% by volume, of CO. In this case, the gaseous waste product discharged from the furnace is formed almost exclusively by combustion fumes, making it possible to use or recover such gases in specialized industries.

[0024] According to one particular embodiment of the invention, the method further comprises a heat exchange between the heated cooling air removed from the furnace and said collected portion of the gaseous waste material exiting the furnace before or after mixing with the enriched oxygen, thereby allowing the heat recovery of the oxidizing mixture to be introduced into the shaft in the firing mode.

[0025] Further details and features of the method according to the invention are set out in the accompanying claims.

[0026] The invention also relates to a regenerative co-current vertical shaft furnace of the PFRK type.

[0027] Such a furnace is At least two shafts interconnected by a gas transfer channel, each in an on or off position; at least one fuel supply; at least one oxygen-containing oxidant supply opening for fuel combustion; an inlet for loading carbonate mineral rock at the top of said shaft; an outlet for unloading the calcined material produced at the bottom of said shaft; At least two shafts, a gaseous waste discharge duct at the top of the shaft connected to the chimney; a cooling air source for cooling the calcined material produced; a system for reversing the operation of shafts, each shaft operating alternately in a firing mode and a preheating mode during a production mode, with one shaft being in firing mode for a predetermined period of time while at least one other shaft is in preheating mode (or vice versa), the system being configured to control said on and off positions; Equipped with.

[0028] According to the invention, the furnace comprises: a recirculation circuit disposed between the gaseous waste discharge duct of the shaft and the oxidant supply opening of the shaft, the reversal system controlling the collection of at least a portion of the gaseous waste from the shaft in a preheat mode; a high-concentration oxygen source that supplies high-concentration oxygen through a recirculation circuit to form an oxidizing mixture, the high-concentration oxygen source ensuring fuel combustion by supplying the oxidant supply opening of the shaft in firing mode in an on position through the reversing system; Further provided are:

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

[0030] As described above, the furnace according to the present invention requires only slight structural changes to the exterior of the furnace, and therefore the calcination method according to the present invention may be carried out using a simple configuration of an existing furnace.

[0031] According to one embodiment of the present invention, the shafts have a circular cross section, the gas transfer channels are connecting flue gases that allow gas transfer by connecting peripheral channels arranged around each shaft, and the shafts are provided with a collection ring below the connecting flue gases that allows the heated cooling air to be removed from the furnace by connecting it to a discharge element. Advantageously, the circular shafts further comprise a central collection element at the bottom that allows the heated cooling air to be removed from the furnace by connecting it to a discharge element below the connecting flue gases.

[0032] According to another embodiment of the furnace of the present invention, the shafts have a rectangular cross section, a first surface of the shaft faces the first surface of the adjacent shaft, and each shaft has a second surface opposite to the mutually facing surface, the gas transfer channels are connecting flue gas channels that directly connect one shaft to the other via the respective first surfaces, and the first surface and the second surface of the shafts are each provided below the connecting flue gas channels with collection tunnels that allow the heated cooling air to be removed from the furnace by connection with exhaust elements.

[0033] According to one embodiment of the present invention, the furnace comprises a unit for separating air into oxygen and nitrogen as a source of oxygen for the recirculation circuit. An oxygen tank may also be provided. Advantageously, a heat exchanger is incorporated into the recirculation circuit, supplied with heated cooling air removed from the furnace, to heat said oxidizing mixture before feeding it into the shaft in the firing mode.

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

[0035] Other features of the invention will become apparent from the following description, which is given in no way as a limitation, and which refers to the accompanying drawings, in which: [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 is a schematic diagram of a conventional PFRK reactor. [Figure 2] 2a and 2b show digital modeling of the oxygen mass % concentration in the gas stream in a conventional PFRK furnace with a circular cross section and a conventional PFRK furnace with a rectangular cross section. [Figure 3] 1A-1D are schematic diagrams illustrating several embodiments of a circular cross-section furnace according to the present invention; [Figure 4] 1A-1D are schematic diagrams illustrating several embodiments of a circular cross-section furnace according to the present invention; [Figure 5] 1 is a fragmentary view of one embodiment of a rectangular cross-section furnace according to the present invention; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0037] In the figures, 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 preheat mode. Standard parts such as loading or unloading equipment are not shown or are shown very diagrammatically to avoid cluttering the drawings.

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

[0039] When the shaft is in calcination mode (here, shaft 1), a fuel supply in the form of a nozzle 4 injects fuel 9 into the shaft, which in the illustrated example is natural gas. Carbonate rock is loaded at the top of the shaft through an inlet 5 in an open position and gradually descends down the shaft. Combustion air is introduced at the top of the shaft through a supply opening 6, which allows the fuel to be combusted at the outlet of the nozzle 4 and the carbonate rock to be decarbonated into calcined material 10. A gas stream 11 formed by the combustion and decarbonation descends against the calcined material and moves to the connecting flue 3 via a peripheral channel 13. At the bottom of the shaft, cooling air is introduced through a supply duct 7 in a countercurrent flow against the calcined material to cool it. The heated cooling air 12 mixes with the gas stream containing combustion fumes 11 and moves to the connecting flue 3. The calcined material is unloaded via an outlet 8 to an unloading facility 24.

[0040] When the shaft is in preheating mode (here, shaft 2), the fuel supply is closed, and therefore the nozzle 4 is off. The same applies to the carbonate rock inlet 5 and the opening 6 for the combustion air supply. However, the cooling air supply duct 7 and the calcination material outlet 8 are kept open. After heat exchange with the descending calcination material 10, the heated cooling air mixes with a gas stream 11 that enters the shaft from the connecting flue 3 through a peripheral channel 13. This gas stream 11 proceeds until it reaches the top of the shaft, where it leaves the furnace through an exhaust duct 14 and is transported to the chimney 15. When shaft 1 is in firing mode, this exhaust duct 14 is closed.

[0041] The furnace also includes a schematic reversal system 16, which synchronizes and directly or remotely controls the operation of the shafts during their reversal times and 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 in preheat mode and one in combustion mode.

[0043] Figure 1 shows a furnace designed to produce 430 tonnes of lime per day. All gas streams described below are in terms of the Nm of lime produced. 3 It is expressed in units of / t.

[0044] 1120 Nm due to reaction with gas injected into shaft 1 as fuel 3 The use of 100 Nm3 / t of combustion air provides an excess of 19% by weight of air relative to the stoichiometric requirement, and 3 / t of CO2 is formed. Since the inlet gas is air, the mass concentration of oxygen is 23%. The temperature then reaches well above 900°C, and decarbonation of the limestone occurs, resulting in a CO2 production of 380 Nm 3 / t of CO2 is released. 290 Nm³ is pumped through the bottom of both shafts to cool the produced lime to approximately 100°C. 3 / t of cooling air was introduced, totaling 580Nm3 / t. In the chimney, it is 480Nm 3 / t of CO2 including 2250Nm 3 / t of gaseous waste is obtained, which has a CO2 content of 23% on a dry basis. As it is difficult to use or capture such a low CO2 content, the gaseous waste is all released into the atmosphere.

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

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

[0047] Area b: Combustion fume jet released by the nozzle, with almost no oxygen remaining, but possibly unreacted O2 remaining between the jets.

[0048] Area c: Fumes gradually mix with the cooling air and penetrate deep into the cooling area C. They push the gaseous mixture into the peripheral channel 13 and thus into the connecting flue 3.

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

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

[0051] Figure 2b shows such digital modeling for a PFRK reactor with a rectangular shaft cross section, where the gas flow distribution is no longer symmetrical as it would be for a circular shaft.

[0052] 3 is a diagram of a furnace according to the invention. In this case, the furnace structure remains unchanged. A separation element 17 is provided in the external exhaust duct 14, which allows a portion of the gaseous waste discharged from the furnace to be collected and introduced into a recirculation circuit 18. In this circuit, the collected portion of the gaseous waste is advantageously treated in a treatment unit 19, which may, for example, be filtered and / or dried. An air separation unit 20 separates the air supplied by duct 21 into N2, which is discharged via duct 22, and O2, which is supplied to the recirculation circuit 18 via a supply duct 23. This circuit 18 then supplies an oxidizing mixture formed by the recycled portion of the gaseous waste and O2-enriched at the supply openings 6 at the top of each shaft.

[0053] The operation of the furnace of Figure 3 is similar to that of the PFRK furnace. The separation element 17, although continuously in operation, is the same as the treatment unit 19 and the air separation unit 20. As mentioned above, the reversal system 16 closes the discharge duct 14 at the top of the shaft in the firing mode, but at the top of the shaft, the opening of the feed opening 6 allows the introduction of the oxidizing mixture, whereas in the preheating mode, the shaft is closed at the top.

[0054] The amount of carbonate rock used and the flow rates of fuel and cooling air are the same as in the conventional furnace described above. 3 / t of gaseous waste is rich in CO2 and is collected via the recirculation duct 18. This recirculation waste is 160 Nm 3 / t of O2, maintaining the same mass concentration of O2 in the oxidizing mixture thus formed at 23%, while obtaining the same 19% excess oxygen by weight relative to the stoichiometric requirement during combustion. This replaces the nitrogen N2 of the combustion air with CO2 equivalent in mass, which is heavier than nitrogen (1.25 g / Nm3). 3 The specific gravity of the furnace is 1.977, which reduces the total amount of fumes in the furnace and results in a 13% reduction in pressure loss compared to conventional furnaces. 3 / t of gaseous waste is emitted, which contains 43% CO2 by volume on a dry basis. As explained above, this content allows for industrial use, for example in a soda ash plant.

[0055] In a variant of such a furnace according to the invention, the cooling air flow may be reduced to further reduce the air input of the process. For example, this input may be reduced by 50% to 290 Nm 3 / t of cooling air. This reduced volume can be introduced via the supply duct 7 of only one shaft in the calcination mode, or by utilizing the supply ducts 7 of both shafts. This measure reduces the dilution of the fumes by 50%. This results in a weaker cooling of the calcined material discharged via the outlet 8. It is therefore necessary to provide unloading equipment that can withstand temperatures above 100°C, such as a heat-resistant steel unloading table and steel drag chains. As the lime comes out hot, there is little heat recovery by the cooling air, which is due to the 120 Nm 3 This is compensated for by a small increase in fuel input so that 1730 Nm3 / t of CO2 is formed. 3 / t of gaseous waste collected at 865Nm 3 / t and the collected waste was reduced to 200Nm 3 / t of O2, it is necessary to maintain the same mass concentration of O2 in the oxidizing mixture thus formed at 23% and obtain the same 19% excess of oxygen by weight relative to the stoichiometric requirement during combustion. Thus, in the stack, the CO2 content is as high as 63% by volume of dry gas, 865 Nm 3 Only / t of gaseous waste is obtained.

[0056] In practice, the stack can prescribe custom CO2 concentrations between 40% and 65% by volume by adjusting the cooling air volume between 100% and 50% of the thermodynamic minimum volume required to cool the calcined material to a reference temperature of 100°C. Higher concentrations of CO2 may be possible by limiting the cooling air input below 50%, within the limits of lime temperature compatibility with the hot unloading and transfer system installed for this purpose.

[0057] Figure 4 shows a diagram of an advantageous furnace according to the invention. As mentioned above, this embodiment includes the features of the embodiment according to Figure 3, but in addition includes a slight modification of the outer structure of the furnace.

[0058] In this case, a removal system is provided so that the heated cooling air is extracted by contact with the calcined material. Each of the shafts 1 and 2 is provided below the connecting flue 3 and the peripheral channel 13 with a collection ring 25, which allows the heated cooling air to be removed from the furnace by connection with the discharge element 26. In this way, extraction of a small portion of the combustion fumes may allow for the extraction of part or all of the combustion air as needed. In practice, as shown in FIG. 2a, the descending gases penetrate deep into the cooling area C, so that the cooling air is forced against the outer wall of the furnace, on which the collection ring is located. Optionally, the shaft may further comprise a central collection element 27 at the bottom, below the connecting flue 3, which allows the central removal of the heated cooling air by connection with the discharge element 26.

[0059] In the case of rectangular furnaces, the use of side collection areas also allows for the extraction of cooling air without collection rings. As can be seen in Figure 5, each shaft has four faces. Face 28 of one shaft faces face 29 of the adjacent shaft, and each shaft has second faces 30 and 31 opposite the facing faces. The gas transfer channels are connecting flue 3, which directly connect one shaft to the other via the respective faces 28 and 29. Below the connecting flue, faces 28-31 are each provided with collection tunnels 32-35, which can remove heated cooling air from the furnace by connecting to the exhaust element 26.

[0060] Due to the asymmetrical gas flow distribution in the rectangular shaft furnace (see FIG. 2b), the cooling air is pushed to only one side by the hot fumes. Also, in the furnace shown with shaft 1 in firing mode and shaft 2 in preheating mode, the reversal system 16 opens only collection tunnels 32 and 34. In the following cycle, only collection tunnels 33 and 35 are open.

[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, the exhaust flow rate is 105 Nm 3 The introduction of fuel is carried out so that 1330 Nm / t of CO2 is formed. At the top of shaft 2, 3 / t of gaseous waste is emitted. Of this CO2-rich gaseous waste, 730 Nm 3 / t is collected via the recirculation circuit 18. This recirculation waste is 220 Nm 3 / t of O2, maintaining the same mass concentration of O2 in the oxidizing mixture thus formed at 23% while obtaining the same excess of oxygen of 19% by weight relative to the stoichiometric requirement during combustion. Thus, in the stack, the CO2 content is 96% in dry gas at 600 Nm3 3 Only / t of gaseous waste is obtained.

[0062] In the furnace shown in FIG. 4, a portion of the recycled gaseous waste may be heat exchanged using heat exchanger 36 before or after mixing with the oxygen-enriched air to recover some of the energy of the hot air removed by exhaust element 26.

[0063] Furthermore, in the connecting furnace tube 3 and the peripheral channel 13, a small portion of the collected portion of gaseous waste discharged from the furnace may be injected by using an injection duct 37. Optionally, heat exchange between the heated cooling air removed from the furnace and the injected small portion may be carried out beforehand by using a heat exchanger (for example, heat exchanger 36). If heat exchanger 36 is not present, a heat exchanger (not shown) may be provided in the injection duct 37.

[0064] According to yet another variant, the temperature of the furnace tubes may be moderated by injection of water at selected locations in the connecting furnace tubes and / or the peripheral ring, this additional water having no effect on diluting the concentration of CO2 in the dry gas.

[0065] Such an arrangement for recovering heat from the heated cooling air removed from the furnace can of course also be provided in rectangular shaft furnaces by the use of heat exchangers as well as such CO2 or water injection devices in the connecting flue.

[0066] It will be apparent that in furnace designs similar to that shown in FIG. 4, cooling air may be injected only at the bottom of one of the two shafts.

[0067] Table 1 below contains the flows in a conventional furnace and various furnace variations according to the present invention, and Table 2 contains the amounts of various gaseous elements at the furnace inlet.

[0068] In each example column, 1 indicates a conventional PFRK furnace, 2 and 3 indicate furnaces according to FIG. 3 with variable cooling air flow, and 4 and 5 indicate furnaces according to FIG. 4 with and without a heat exchanger.

[0069] [Table 1]

[0070] [Table 2]

[0071] It is understood that the invention is in no way limited to the embodiments described above, but that it can be modified without departing from the scope of the appended claims.

[0072] For example, it would be advantageous to be able to replace the air-cooled fuel injection nozzles with thermally insulated nozzles.

Claims

1. 1. A method for calcining mineral rock in a regenerative co-flow vertical shaft furnace, wherein at least two shafts are interconnected via a gas transfer channel, the method comprising, in a production mode: loading carbonate mineral rock at the top of the furnace; preheating the rock; Calcination of said rock with decarbonation to obtain a calcined material; cooling the calcined material with cooling air; unloading the calcined material at the bottom of the shaft; Including, each shaft alternately operates in a firing mode and a preheating mode, such that one shaft is in firing mode for a predetermined period of time while at least one other shaft is in preheating mode (or vice versa); In baking mode, loading carbonate mineral rock at the top of said shaft in a firing mode as described above; In the presence of the preheated carbonate mineral rock descending in the shaft, fuel is burned in the presence of oxygen, thereby calcining the rock and obtaining calcined material by decarbonation, with the release of combustion fumes in the form of a gas stream descending in the shaft in a calcination mode; the gas flow containing the combustion fumes is transferred from the shaft in a firing mode to the at least one shaft in a preheating mode by using the gas transfer channel; In preheat mode, preheating said loaded carbonate mineral rock by heat exchange with said gas stream containing said combustion fumes flowing countercurrently from said gas transfer channel to said loaded carbonate mineral rock and ascending in said at least one shaft in a preheating mode, as described above; Based on the gas flow containing the combustion fumes, gaseous waste is discharged from the furnace at the top of the at least one shaft in a preheating mode, collecting a portion of the gaseous waste discharged from the furnace; mixing the collected portion of the gaseous waste discharged from the furnace with concentrated oxygen having an oxygen concentration greater than 50% by volume to form an oxidizing mixture; introducing the oxidizing mixture at the top of the shaft in firing mode to ensure combustion of the fuel in the presence of oxygen; further comprising Further, the cooling of the calcined material includes supplying cooling air at the bottom of each of the shafts or at the bottom of only one of the shafts in a firing mode, which cooling air flows countercurrently through the descending calcined material and is heated by contact with the calcined material, and the method further includes removing the heated cooling air from the furnace below a connecting flue that connects one of the shafts to the other and allows gas transfer; CO in the dry gas of the gaseous waste discharged from the furnace ２ The method is characterized in that the concentration is at least 90% by volume.

2. 10. The method of claim 1, further comprising exchanging heat between the heated cooling air removed from the furnace and the collected portion of gaseous waste discharged from the furnace before or after mixing with enriched oxygen.

3. 3. The method of claim 1 or 2, further comprising injecting a small portion of the collected portion of gaseous effluent discharged from the furnace into the gas transfer channel, and optionally, prior to said injection, exchanging heat between the heated cooling air removed from the furnace and the injected small portion.

4. 4. The method of claim 1, further comprising injecting water into the gas transfer channel.

5. The combustion of the fuel includes introducing a gaseous, liquid, or solid fuel into the shaft in a firing mode, and in the case of a solid fuel, the introduction includes introducing a further portion of the collected portion of gaseous waste exhausted from the furnace or another CO 2 as a carrier gas. ２ 5. The method according to claim 1, wherein the method is carried out using a source.

6. 6. The method of claim 1, wherein the combustion of the fuel occurs in the presence of excess oxygen relative to the stoichiometric requirement.

7. A regenerative co-current vertical shaft furnace carrying out the method according to any one of claims 1 to 6, At least two shafts (1, 2) interconnected by a gas transfer channel, each in an on or off position, at least one fuel supply device (4); at least one oxygen-containing oxidant supply opening (6); an entrance (5) for loading carbonate mineral rock at the top of the shaft; an outlet (8) for unloading the calcined material produced at the bottom of the shaft; At least two shafts (1, 2) each having a gaseous waste discharge duct (14) at the top of said shaft connected to a chimney (15); a cooling air source (7) for cooling the calcined material produced; a system (16) for reversing the operation of the shafts, each shaft operating alternately in a baking mode and a preheating mode during a production mode, with one shaft being in baking mode for a predetermined period of time while at least one other shaft is in preheating mode (or vice versa), the reversing system (16) configured to control the on and off positions; A furnace comprising: a recirculation circuit (18) arranged between the gaseous waste discharge duct (14) of the shaft and the oxygen-containing oxidant supply opening (6) of the shaft; a separating element (17) capable of collecting a portion of the gaseous waste discharged from the furnace through the gaseous waste discharge duct (14) and introducing it into the recirculation circuit (18); a high-concentration oxygen source (20) for supplying high-concentration oxygen through the recirculation circuit (18) to form an oxidizing mixture, the high-concentration oxygen source (20) ensuring fuel combustion when the oxygen-containing oxidant supply opening (6) of the shaft (1) in firing mode is in the on position through the reversing system (16); Furthermore, the shafts have a circular cross section, the gas transfer channels are connecting flue gas channels (3) that allow the transfer of gases by connecting peripheral channels (13) arranged around each shaft, and the shafts are provided below the connecting flue gas channels (3) with a collection ring (25) that allows the removal of heated cooling air from the furnace by connecting it to an exhaust element (26), or The shafts have a rectangular cross section, the first face (28) of one shaft (1) facing the first face (29) of the adjacent shaft (2), and each shaft has a second face (30, 31) opposite to the mutually facing faces (28, 29), the gas transfer channels are connecting flue tubes (3) directly connecting one shaft to the other via the first faces (28, 29), respectively, and the first and second faces of the shafts are provided below the connecting flue tubes with collection tunnels (32-35) that allow the removal of heated cooling air from the furnace by connection with an exhaust element (26).

8. 8. The furnace according to claim 7, characterized in that the shaft of circular cross section further comprises at its bottom, below the connecting flue (3), a central collecting element (27) which allows the removal of heated cooling air from the furnace by connection with a discharge element (26).

9. 9. A furnace according to claim 7 or 8, characterized in that it comprises, as an oxygen source for the recirculation circuit, a unit (20) for separating air into oxygen and nitrogen.

10. 10. Furnace according to any one of claims 7 to 9, characterized in that the recirculation circuit (18) incorporates a heat exchanger (36) to which the heated cooling air removed from the furnace is supplied.

11. Furnace according to any one of claims 7 to 10, characterized in that it comprises a facility (24) for unloading calcined material that can withstand temperatures above 100°C.

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