Method and KILN for calcining carbonate mineral stones in a parallel flow regenerative KILN (PFRK) with rectangular shaft

Abstract

Method and kiln for calcining carbonate mineral stones in a rectangular shaft parallel flow regenerative kiln (PFRK) in oxycombustion conditions, with improved extraction of cooling air.

Description

[0001]METHOD AND KILN FOR CALCINING CARBONATE MINERAL STONES IN A PARALLEL FLOW REGENERATIVE KILN (PFRK) WITH RECTANGULAR SHAFT The present invention relates to a method for calcining carbonate mineral stones in a parallel flow regenerative kiln (PFRK). Such a kiln comprises at least two shafts interconnected by means of a crossover channel. In each shaft the stones are introduced in a top portion and follow a downward gravity displacement during which the stones are successively preheated, calcined and thereafter cooled in order to be collected in a low portion of each shaft. By the terms “stones, carbonate mineral stones, limestone stones”, it is meant according to the present invention pieces of raw carbonated material having a median particle size d50comprised between 20 mm to 12 cm, preferably higher than 25 mm, preferably lower than 10 cm, more preferably lower than 8 cm, and typically between 3 and 5 cm. Carbonate mineral according to the present patent application is typically a calcium-magnesium carbonate, also known as limestone, when containing low amount of magnesium, and dolostone, when the magnesium content is close to the one of calcium on a molar basis. The calcined mineral according to the present patent application is typically a calcium-magnesium oxide, also known as quicklime, when containing a low amount of magnesium and dolime when the magnesium content is close to the one of calcium on a molar basis. A Parallel Flow Regenerative Kiln of rectangular section usually has 2 shafts, which do not work in a continuous way. In standard operation, in every period, usually of 12 to 20 minutes, fuel is injected inside a calcining zone of one shaft by means of lances and is burned in presence of combustion air. Thereafter the descending calcined product is cooled in a cooling zone by heat exchange with a cooling gas introduced at the bottom of the shaft. The flue gas comprises or consists of the combustion fumes, the gas of decarbonation and the heated cooling gas. This flue gas is drawn into another shaft through the crossover channel and goes thereafter through the stones present in this shaft and thereafter outward the kiln. So, in this “preheating” shaft, the stones are preheated by the exiting flue gas. Consequently, during this period the shaft wherein the combustion takes place works according to a calcining mode (calcining shaft) and the shaft wherein the flue gas is drawn through the stones works according to a preheating mode (preheating shaft). Thereafter, there is a period, usually between 30 seconds and 2 minutes, called inversion period, which is provided, notably for reverting the air and fuel circuits. And the shaft having worked in a calcining mode works now in a preheating mode and the shaft having worked in a preheating mode works now in a calcining mode. The classical method for calcining carbonate mineral stones in a parallel flow regenerative kiln having at least two shafts interconnected by a crossover channel, comprises, in standard operation, - loading carbonate mineral stones at the top of each shaft, - preheating these loaded stones in a preheating zone, - calcining these preheated stones in a calcination zone with production of a decarbonated calcined material, - cooling the calcined material with cooling gas in a cooling zone, with formation of a heated cooling air, by heat exchange, - discharging the calcined material from the bottom of the shafts, - exhausting an exhaust effluent from the kiln, - each shaft alternately working in a calcining mode and in a preheating mode, one shaft working in a calcination mode during a predetermined time period during which at least another shaft works in a preheating mode, and inversely, - the calcining mode comprising : said calcining step by means of an increase of temperature inside said carbonate mineral stones having been preheated, with production of said decarbonated calcined material and release of a gas stream which flows in co-current with the calcined material, and through said crossover channel, a passage of said gas stream toward the at least one shaft working in a preheating mode, - said preheating mode comprising : said preheating step of the loaded carbonate mineral stones by heat exchange with said gas stream coming from the crossover channel, which is ascending and flows in counter-current through the loaded carbonate mineral stones, and said exhausting step of said gas stream as exhaust effluent at the top of said at least one shaft in preheating mode, said cooling step comprising a supply of cooling air at the bottom of each of said shafts or only of the shaft working in the calcining mode. In the calcining zone of a classical kiln, it is required in calcining mode to inject and burn a fuel into the mass of the stones to be calcined under the preheated stones in order to benefit from the heat of the flue gas that was transferred to the stone in the preheating zone. In preheating mode, the stones introduced into the kiln are at ambient temperature and the flue gas drawn outside the kiln has a temperature typically comprised between 80 and 250°C, preferably between 100 and 200°C and generally at about 150°C, limiting the energy losses. According to the invention, standard operation means that the kiln produces the calcined material in a continuous manner. This operation does not concern the phases of starting, stopping or maintenance of the kiln. According to the invention, carbonate mineral stones particularly mean calcareous stones (limestones), dolomitic stones (dolostones or unburnt dolomites) and / or magnesite stones which are calcined into quicklime, (quick) dolime and / or magnesia, respectively. The calcination reaction of limestone into quicklime is : CaCO3 (solid) + heat CaO (solid)+ CO2 (gas) This is a reversible endothermic reaction and the lime recombines with the CO2 at the first opportunity below 900°C, with an equilibrium and more or less fast kinetics depending on the temperature and the ambient concentration of CO2. Below 850 to 900°C lime and CO2 can easily recombine. But from a temperature of the order of 900°C the starting stones give off a significative volume of CO2during their decarbonation. In order to obtain such a decarbonation, the temperature must consequently be significatively increased in the calcining zone. Today this increase is mainly obtained by combustion of a fuel, frequently fossil, in presence of an oxidizer such as air. In turn this fuel combustion contributes also to an important release of CO2. Globally the current calcination methods actively participate in increasing the greenhouse effect. This common calcination method also has the disadvantage that the fuel is burnt with air and the calcined product is cooled by air. This results in an exhaust effluent being released at the top of the kiln having a high level of diatomic nitrogen and a comparatively low level of CO2 (volume concentration of about 20% to 27% on dry gas) which is expensive to capture because of the large presence of dinitrogen from the air used. To capture this CO2, it may be considered to use an “end-of- pipe” method of CO2concentration and abatement, notably cryogenic or by chemical solvent called "amines", which is the most widespread technique applied to the kiln fumes at the end of the line, after the dust collection filter However, for carrying out end-of-pipe methods as aforementioned, constrains are existing, notably in terms of concentration of CO2, but also in terms of compliancy of the fumes, which may require intermediate devices, the price and the use of hazardous solvents. Alternatively, one may consider to increase the CO2 concentration in the exhaust effluent. In this respect, to be able to capture the CO2 emitted in a PFRK kiln, operating PFRK in oxy-combustion seems to be a promising solution, since the exhaust effluent will have a higher CO2 concentration. An example of operation of PFRK in oxy-combustion has been proposed in JP2002060254. However, the concentration of CO2 in the exhaust effluent is still below 50 % vol on a dry basis. For the same purpose, it has also been proposed to replace all the air from the method, combustion air carrying the solid fuel and cooling air, with recycled combustion fumes and introducing pure oxygen into the shaft in calcining mode (see CN105000811). For any person skilled in the art, it is clear that this process is unfeasible, since the lime will recarbonate during cooling. As seen above, the CO2cannot be recirculated to cool the lime, since the lime will immediately recombine with this CO2 to form again a carbonate, notably CaCO3. On the other hand, using pure oxygen at the top of the kiln poses serious problems in terms of material compatibility (notably due to excessive temperature) and this input will not be a sufficient mass flow to effectively recover the heat accumulated in the regeneration area. The disadvantages and feasibility problems of this method have also been discussed in the patent application US2020 / 0048146. It should also be noted that the cooling air in the PFRK, in contrast to the rotary kiln, for example, does not play a significant role on the combustion and the calcination process in the shaft in calcining mode. Standard mode means that the kiln is in normal service during which it continuously produces calcined material. This mode therefore does not apply to the start-up and shut-down phases of the kiln or to maintenance in the event of a malfunction. Variation of the common calcination process have been proposed in order to improve capture of CO2, such as for example in WO2022 / 002869, WO2022 / 238387 or WO2022 / 229120. In PFRK kiln working in oxy-combustion, the exhaust effluent should be as concentrated in CO2 as possible. Accordingly, there has been some proposals to produce concentrated exhaust gas. One proposal that was discussed above is to replace the cooling air by exhaust effluent such as disclosed in CN10500081 and in JP2002060254. Other proposals are to isolate the cooling air from the exhaust effluent (see W02022 / 238385, WO2022 / 238384 or WO2022 / 229120). In WO2022 / 002869, it was proposed to extract the cooling air in a ring collector, through a collector tunnel or through a central device, located below a connecting channel (crossover channel) to avoid as much as possible mixing between the exhaust gaseous effluent concentrated in CO2 and the cooling air. As it can be understood, the isolation of cooling air or its replacement to avoid CO2 dilution is a key challenge, in particular for the oxyfuel operation of a kiln. However, the replacement of cooling air by another cooling gas is not without impact on the process. Indeed, it can have an impact on the quality of the produced calcined stones or on the CO2 concentration or even requiring additional devices. There is therefore a need to provide a method to be carried out in PFRK without changing the cyclical operation thereof and with few or no changes to the structure thereof while making it possible to concentrate and improve the capture of the CO2present in the exhaust effluents emitted by the kiln at a level that enhances its value industrially. To solve these problems, the present invention provides a method for calcining carbonate mineral stones in a parallel flow regenerative kiln having at least two shafts interconnected by a crossover channel, comprising, in standard operation, - loading carbonate mineral stones at the top of each shaft, - preheating these loaded stones in a preheating zone, - calcining these preheated stones in a calcination zone with production of a decarbonate calcined material, - cooling the calcined material with cooling gas in a cooling zone, with formation of heated cooling gas by heat exchange, - discharging the calcined material from the bottom of the shafts, - exhausting an exhaust effluent from the kiln, - each shaft alternately working in a calcining mode and in a preheating mode, one shaft working in a calcining mode during a predetermined time period during which at least another shaft works in a preheating mode, and inversely after activation of the inversion means, - the calcining mode comprising : • in the presence of said preheated carbonate mineral stones descending into said shaft, oxy-combusting fuel in the presence of oxygen so as to obtain said calcination of said stones in said combustion zone, and the decarbonation thereof into calcined material with the release of combustion fumes descending co- currently in the shaft in calcination mode, and • through said crossover channel, a passage of said combustion fumes toward the at least one shaft working in a preheating mode, - said preheating mode comprising : • said preheating step of the loaded carbonate mineral stones by heat exchange with said combustion fumes coming from the crossover channel, which is ascending and flows in counter-current through the loaded carbonate mineral stones, and • said exhausting step of said combustion fumes as exhaust effluent at the top of said at least one shaft in preheating mode, said method further comprises - recirculating a fraction of the exhaust effluent exhausted from the top of said at least one shaft in preheating mode, - injecting the exhaust effluent, exhausted from the top of said at least one shaft in preheating mode, at least partially to the shaft in calcining mode, either under the form of a comburant mixture or with an injection of a combustion stream containing a comburant, for said step of oxy-combusting the fuel, said comburant being preferably O2-rich gas, - extracting said heated cooling gas outside of said kiln, characterized in that during said extracting step of the heated cooling gas outside of the kiln, - the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in calcining mode, by exit means located in a first part of the first shaft or by exit means located in a first part of the second shaft, said first part of the first shaft facing said first part of said second shaft, both first part being located below the cross- over channel and - the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in calcining mode, by exit means located in a second part of said first shaft or by exit means located in a second part of said second shaft, the second part of the first shaft being at the opposite of the first part of the first shaft and the second part of the second shaft being at the opposite of the first part of the second shaft, and - the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in preheating mode, by exit means located in said second part of said first shaft or by exit means located in said second part of said second shaft, and - the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in preheating mode, by exit means located in said first part of said first shaft or by exit means located in said first part of said second shaft. As it can be seen, in the method according to the present invention, the exhaust effluent is extracted from the preheating shaft and is at least partially introduced in the calcining shaft with a comburant. This can be done either by a separated injection of a comburant and the exhaust effluent or by injection of a comburant mixture containing the exhaust effluent and a comburant. The comburant is preferably a O2-rich gas, such as dioxygen. Accordingly, the method according to the present invention carries out fuel combustion in a comburant and a recirculated gas which results in exhaust effluent containing the combustion fumes and CO2from decarbonation of the carbonate stones and results in the calcination of the carbonate stones. This produces mainly CO2and steam with some impurities, present as traces in the fuel and in the material to be calcined, and some oxygen not used up by the fuel combustion. Naturally, these combustion fumes also contain the CO2supplied from the preheating shaft. This evidently results in a significant increase in the CO2 content of the exhaust effluent discharged from the top of the kiln, compared to the conventional method. According to the invention, an exhaust effluent concentrated in CO2 means that it has a CO2 content of at least 60%, more preferably of at least 70%, more particularly of at least 75%, especially at least 80% and particularly advantageously at least 90% by volume on dry gas. This CO2can then be used or sequestered under favorable conditions, drastically decreasing the contribution of the kiln to the greenhouse effect. According to the present invention, the kiln possesses external wall, wherein the first shaft has an external wall comprising 4 sides and the second shaft has an external wall comprising 4 sides. According to the present invention, the first part of the first shaft and second shaft comprises an interior side, being the side which faces respectively the second shaft and the first shaft, and a proximal zone of the two adjacent sides, in proximity of said interior side. According to the present invention, the second part of the first shaft and second shaft comprises an exterior side, being the side opposed to the interior side and a distal zone of the two adjacent sides, in proximity of said exterior side. The use of this oxy-combustion method does not necessarily require any particular design of the kiln itself. The only changes to be made to the kiln may be simply external to the kiln and consist of changing the effluent circuits leaving the kiln and providing at least one source of concentrated dioxygen. To keep the concentration in CO2high enough, the cooling gas entering the kiln, preferably from the bottom of the shaft or of the shafts, flows upwardly through the cooling zone in counter-current with the calcined stones descending in the shafts. The cooling gas is then heated by heat exchange with the calcined stones and is extracted outside of said kiln before it can mix with the effluent gas stream. According to the present invention, the extraction of the heated cooling gas is performed as follows : - the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis (relative to the cooling air introduced in the same shaft) from the shaft in calcining mode by exit means located in a first part 36 of a first shaft 1 or by exit means located in a first part 37 of the second shaft 2, and - the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis (relative to the cooling air introduced in the same shaft) from the shaft in calcining mode by exit means located in a second part 35 of said first shaft 1 or by exit means located in a second part 38 of said second shaft 2, and - the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis (relative to the cooling air introduced in the same shaft) from the shaft in preheating mode by exit means located in said second part 35 of said first shaft 1 or by exit means located in said second part 38 of said second shaft 2, and - the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis (relative to the cooling air introduced in the same shaft) from the shaft in preheating mode by exit means located in said first part 36 of said first shaft 1 or by exit means located in said first part 37 of said second shaft 2. Indeed, it has been identified according to the present invention that the heated cooling gas should be extracted at different location depending to the role of the shaft and the period in the cycle of calcining / preheating to maximize the recovery of CO2 and keep as low as possible cooling gas leakage. In the shaft in calcining mode the combustion fumes and the CO2 exhausted from the decarbonation of the carbonate stone form the exhaust effluent. This effluent pushes the cooling air towards the first part 36 of the first shaft 1 when the first shaft is in calcining mode or towards the first part 37 of the second shaft 2 when the second shaft 2 is in calcining mode. In the preheating shaft, the exhaust effluent arrives from the calcining shaft and is mainly spread towards the inside walls of the cooling zone. Due to its momentum, the exhaust effluent pushes the heated cooling gas to the second part 35 of the first shaft 1 when the first shaft is in preheating mode or towards the second part 38 of the second shaft 2 when the second shaft 2 is in preheating mode. The process according to the present invention foresees an extraction step of the heated cooling gas in the calcining shaft in majority (from 50 to 100%) by volume on dry gas basis, relative to the cooling air introduced in the same shaft, by exit means located in a first part 36 of a first shaft 1 or by exit means located in a first part 37 of the second shaft 2, while a minority portion of the heated cooling gas, from 0 to 50% by volume on dry gas basis relative to the cooling air introduced in the same shaft, may be at the same time extracted from the shaft in calcining mode by exit means located in a second part 35 of said first shaft 1 or by exit means located in a second part 38 of said second shaft 2. Thereby, the fact that in the calcining shaft the cooling gas is extracted in majority in the first part of the shaft, below the crossover channel and that in the preheating shaft is extracted in majority through exit means located in the second part of the shaft allows to minimize the CO2 dilution of the exhaust effluent by minimizing leakage of cooling gas in the exhaust effluent, but also reduce the leakage of CO2 in the cooling gas where it end ultimately lost. Within the meaning of the present invention, the momentum of a fluid flow is defined as the mass flow of this fluid (in kg / s) multiplied by its average velocity (in m / s). It is expressed in Newtons (kg*m / s²). The momentum ratio between a mixing gas and the combustion fumes flow is defined as the ratio of the momentum of the mixing gas and the momentum of the combustion fumes. The momentum of the mixing gas is calculated at the mixing gas outlet. The momentum of the combustion fumes is calculated at the cross-section perpendicular to its flow direction and intersecting the center of the mixing gas entry means. Advantageously, the heated cooling gas is extracted from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis, relative to the cooling air introduced in the same shaft, from the shaft in calcining mode through said exit means located in a first part 36 of a first shaft 1 or by exit means located in a first part 37 of the second shaft 2 and from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% by volume on dry gas basis, relative to the cooling air introduced in the same shaft, from the shaft in calcining mode through said exit means located in a second part 35 of said first shaft 1 or by exit means located in a second part 38 of said second shaft 2 and the heated cooling gas is extracted from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% by volume on dry gas basis, relative to the cooling air introduced in the same shaft, from the shaft in preheating mode through said exit means located in said first part 36 of said first shaft 1 or by exit means located in said first part 37 of said second shaft 2 and from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis, relative to the cooling air introduced in the same shaft, from the shaft in preheating mode through said exit means located in said second part 35 of said first shaft 1 or by exit means located in said second part 38 of said second shaft 2. Preferably, the loading of carbonate mineral stones occurs during the inversion period at the top of the shaft that will work in a preheating mode after said inversion period. Alternatively, or in addition, the loading of carbonate mineral stones occurs during the cycle at the top of the shaft that works in a preheating mode or at the top of the shaft that works in a calcination mode. Preferably, the loading of carbonate mineral stones occurs during the cycle at the top of the shaft that works in a preheating mode, but can optionally also be done during reversal. In a preferred embodiment of the present invention, the process further comprises a CO reduction step in the crossover channel by injecting a mixing gas through a series of mixing gas entry means at high velocity in such a way that a ratio of momentum J between the mixing gas and the combustion fumes is higher than 1. The momentum ratio between a mixing gas and the combustion fumes flow is defined as the ratio of the momentum of the mixing gas and the momentum of the combustion fumes. The momentum of the mixing gas is measured at the mixing gas outlet. The momentum of the combustion fumes is measured at the cross-section perpendicular to its flow direction and intersecting the center of the mixing gas entry means. In order to complete the combustion of the CO, an intense mixing of the combustion fumes with comburant gas must be ensured. This is obtained by jet mixing, i.e. the injection of a mixing gas through entry means at high velocity in the crossover channel. The mixing gas can be steam, O2-rich stream or CO2-rich stream such as the exhaust effluent. Advantageously, said ratio of momentum J is higher or equal to 2, more preferably higher or equal to 4, more preferably higher or equal to 5, more preferably higher or equal to 6, in particular higher than or equal to 7, more particularly higher than or equal to 8, even higher than or equal to 9 or higher than or equal to 10 or higher than or equal to 11 or higher than or equal to 12 or higher than or equal to 13 or higher than or equal to 14 or higher than or equal to 15 or higher than or equal to 16 or higher than or equal to 17 or higher than or equal to 18 or higher than or equal to 19 or higher than or equal to 20 or higher than or equal to 21 or higher than or equal to 22 or higher than or equal to 23 or higher than or equal to 24 or higher than or equal to 25 or higher than or equal to 26 or higher than or equal to 27 or higher than or equal to 28 or higher than or equal to 29 or higher than or equal to 30 to ensure a good mixing between the mixing gas and the exhaust effluent. It must be noted that the mixing gas does not require to be continuous or constant. It can be advantageous to enhance mixing to supply the mixing gas in the form of jets incorporating periodic oscillations. Such periodic oscillations can notably take the form of intermittent pulsed jets, but also include sinusoidal oscillations in flow, pressure or velocity, or other shapes of oscillation waves. In the case of jets with periodic oscillations, including pulsed jets, the momentum shall be calculated using the average properties of the jet over the duration of several oscillations or pulsations. More particularly according to the present invention, said mixing gas is pressurized before passing through the series of mixing gas entry means to reach a differential pressure between said mixing gas before the mixing gas entry means and the gas inside the connecting channel comprised between 100 mbar and 10 000 mbar, preferably between 200 and 1000 mbar to achieve high velocity, wherein preferably the gas inside the connecting channel has an average velocity (calculated on a cross-section, preferably according to a median plan between two shafts, the average velocity being the volume flow (in m3 / s) divided by the cross-section of the passage perpendicular to the general direction of the gas flow in m2) of at least 5 m / s, preferably comprised between 5 m / s and 30 m / s, preferably between 10 m / s and 25 m / s, more preferably between 12 m / s and 20 m / s wherein preferably said mixing gas has an average velocity of at least 50 m / s, preferably comprised between 50 m / s and 400 m / s, preferably between 100 m / s and 350 m / s, more preferably between 150 m / s and 300 m / s, wherein the average velocity of said mixing gas is higher than the average velocity of said gas inside the connecting channel, for example higher by 20 m / s, 30 m / s, 40 m / s, 50 m / s, 60 m / s, preferably the ratio between the average velocity of said mixing gas and the average velocity of said gas inside the connecting channel is higher than 2, 3, 5, 10, or even 20, 25, or 30 in such a way that a ratio of momentum J between the each gas stream and the combustion fumes is higher than 1, forming combustion fumes depleted in CO exiting the connecting channel. More particularly, said mixing gas is pressurized before passing through the series of mixing gas entry means by a pressurization device in order to achieve said differential pressure between said mixing gas and the gas inside the connecting channel. Preferably, the pressure of said mixing gas will be set to fixed value high enough to ensure that we have enough momentum independently of the conditions of the kiln, for example said mixing gas is pressurized before passing through the series of mixing gas entry means to a fixed value in order to reach a differential pressure between said mixing gas before the mixing gas entry means and the gas inside the connecting channel preferably comprised between 200 and 1000 mbar to achieve high velocity. Preferably or alternatively, the pressure of said mixing gas is measured by a first pressure sensor within or before at least one mixing gas entry means of the series of mixing gas entry. Preferably, the pressure of the gas inside the connecting channel is either measured by a second pressure sensor preferably located on an upper part of a cross-section of the connecting channel, for example located in the roof of the connecting channel to facilitate the access to the sensor and / or preventing dust accumulation on sensor, or is accepted to be between 100 and 400 mbar due to the inherent operation of the kiln. This accepted value is significantly different from the pressure at the entry of the series of mixing gas to not be measured but taken as a reference for determining the pressure of the mixing gas which should then be preferably higher than 400 mbar. Preferably, the first pressure sensor and the second pressure sensor are connected to the pressurization device wherein the pressurization device receives either (i) a signal from the first pressure sensor and a signal from the second pressure sensor and wherein the pressurization device adapts the pressurization of the mixing gas based on the signals received from the first and second pressure sensors in order to reach a differential pressure between said mixing gas and the gas inside the connecting channel comprised between 100 mbar and 10000 mbar, preferably between 200 and 1000 mbar, or (ii) a signal from the first pressure sensor and the accepted value of the pressure of the gas inside the connecting channel being between 100 and 400 mbar due to the inherent operation of the kiln and wherein the pressurization device adapt the pressurization of the mixing gas based on the signal received from the first pressure sensor and this accepted value in order to reach a differential pressure between said mixing gas and the gas inside the connecting channel comprised between 100 mbar and 10 000 mbar, preferably between 200 and 1000 mbar. This accepted value is significantly different from the pressure at the entry of the series of mixing gas to not be measured but taken as a reference for determining the pressure of the mixing gas which should then be preferably higher than 400 mbar to achieve high velocity, in a manner that the average velocity of said mixing gas is higher than the average velocity of said gas inside the connecting channel, for example higher by 20 m / s, 30 m / s, 40 m / s, 50 m / s, 60 m / s, in such a way that a ratio of momentum J between the each gas stream and the combustion fumes is higher than 1, forming combustion fumes depleted in CO exiting the connecting channel. Advantageously, the exhaust effluent is partially or fully collected in at least one buffer after said exhausting step. Preferably, said oxy-combusting step of fuel in the presence of oxygen is carried out in the combustion zone fed by the exhaust effluent and by the combustion stream containing a comburant, simultaneously or separately, or by a mixture of said exhaust effluent and said combustion stream containing a comburant. In one advantageous embodiment, said cooling step comprises a supply of cooling gas at the bottom of each of said shafts or only of the shaft working in the calcining mode, or only in the shaft working in the preheating mode. Preferably, said cooling step comprises a supply of cooling gas at the bottom of each of said shafts with the same rate of supply or a different rate of supply between the calcining shaft and the preheating shaft. In yet an advantageous embodiment, in the process according to the present invention, said oxy-combusting step of fuel in the presence of oxygen is carried out in the combustion zone fed by the exhaust effluent and by the combustion stream containing a comburant, simultaneously or separately, or by a mixture of said exhaust effluent and said combustion stream containing a comburant. In another advantageous embodiment, said cooling step comprises a supply of cooling gas at the bottom of the shaft having worked in the preheating mode and before the activation of the inversion means, in order to have each shaft encountering sequentially said preheating mode, a cooling step and then a calcining mode. In a particular embodiment, said exhaust effluent, exhausted from the top of said at least one shaft in preheating mode injected, at least partially to the shaft in calcining mode is injected directly or indirectly: - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode and to the preheating shaft, for example in the preheating zone, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode and in the crossover channel, for example in the cross-over channel, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode, in the crossover channel, for example in the cross-over channel and to the preheating shaft, for example in the preheating zone or at the outlet of the fuel lances. Within the meaning of the present invention, the wording “injected indirectly” means that the injection can be done from a temporary device, such as for example from a buffer or a storage reservoir, located between the origin of the exhaust effluent and the injection point(s). In yet a preferred embodiment the present invention further comprises at least one heat exchange between the heated cooling gas, which has been extracted outside the kiln, and said recirculated fraction of effluent, for example before injection at least partially to the shaft in calcining mode and / or in preheating mode and / or in the crossover channel. In yet a preferred embodiment the present invention further comprises at least one heat exchange between the heated cooling gas, which has been extracted outside the kiln, and said recirculated fraction of exhaust effluent for example before injection - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode and to the preheating shaft, for example in the preheating zone, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode and in the crossover channel, or - in the shaft in calcining mode in an upper portion of the shaft in calcining mode or in the combustion zone of the shaft in calcining mode, in the crossover channel and to the preheating shaft, for example in the preheating zone or at the outlet of the fuel lances. In a particular embodiment of the present invention, said fuel combustion comprises introducing a gaseous, liquid or solid fuel into the shaft in calcining mode and in that, in the case of a solid fuel, said introduction is carried out using a portion of said collected portion of exhaust effluent discharged from the kiln, or using another source of CO2as a carrier gas. In another particular embodiment, a portion of the exhaust effluent discharged from the kiln is introduced in an outer envelope, enclosing lances for fuel injection for cooling said lances. Alternatively, or in addition, a portion of the exhaust effluent discharged from the kiln is introduced into the preheating shaft and / or the crossover channel 3. The outer envelope is typically a sleeve inside which the lance is concentrically installed having a proximal end and a distal end. The outer envelope can have one proximal inlet and one proximal outlet both installed in proximity of the proximal end, for respectively feeding and exiting the exhaust effluent inside the outer envelope. In a variant, the out envelope is a through-sleeve, where the proximal end is an open end for admitting the exhaust effluent and the distal end is an open end for abutting in the combustion zone and exiting the exhaust effluent around the lance or the injected fuel. The exhaust effluent can further sleeve the fuel in a portion close to the end of the outer envelope. Alternatively, or in addition, a portion of the exhaust effluent discharged from the kiln can be introduced in a shaft in preheating mode directly through the lances for fuel injection for cooling said lances. According to the present invention, in a preferred embodiment, oxygen is introduced in the kiln at one or more locations to provide a total amount of oxygen introduced in the kiln available for combustion higher than the amount required for a stoichiometric combustion for the oxy-combustion of fuel in presence of oxygen in excess, and is preferably is introduced at an excess from 2 to 30%, preferably from 3 to 20 %, in particular from 4 to 17%, advantageously from 5 to 15 % in volume with respect to the stoichiometric need of the combustion reaction. In other words, the amount of oxygen introduced in the kiln available for combustion is equal to the amount of oxygen needed for a stoichiometric combustion for the oxy-combustion of fuel in presence of oxygen multiplied by an excess factor from 1.02 to 1.30, preferably 1.03 to 1.2, in particular from 1.04 to 1.17, advantageously from 1.05 to 1.15. According to the present invention, by the term “the total amount of oxygen available for combustion”, it is preferably meant that the oxygen present in the extracted cooling air is not considered and should be excluded of the total amount of oxygen available for combustion. More particularly, in the method according to the present invention, the oxy-combusting step of fuel in the presence of oxygen is carried out in the combustion zone fed by the exhaust effluent and by the combustion stream containing a comburant, simultaneously or separately, or by a mixture of said exhaust effluent and said combustion stream containing a comburant. Preferably, the gas temperature in the combustion zone is comprised between 900°C and 1500 °C, more preferably between 01000°C and 1400°C or between 1100°C and 1300°C. Preferably, the temperature of the heated cooling gas, preferably of the heated air, extracted at a level below the crossover channel is comprised between 500°C and 1000°C, more preferably between 600°C and 950°C. It is important to keep the overall oxygen excess for combustion low to keep the final CO2 in the exhaust effluent sufficiently high (i.e. to not dilute with additional oxygen). In oxyfuel operation, the comburant supplied to the combustion shaft is preferably also high purity oxygen mixed with recycled exhaust effluent. The overall quantity of oxygen supplied to the kiln will be calculated by the control system according to the stoichiometric requirement for combustion, multiplied by an excess factor supplied by the operator (typically between 1.02 and 1.30, preferably between 1.03 and 1.2, in particular from 1.04 to 1.17, advantageously from 1.05 to 1.15). This global quantity will then, if relevant, be split between oxygen sent to the shaft in calcining mode, at the level of or in the combustion zone (first O2-rich stream) and oxygen sent to the crossover channel (second O2-rich stream). In a further advantageous embodiment of the present invention, the process according to the present invention comprises a step of collecting a portion of the exhaust effluent in a storage unit, preferably after purification for producing a substantially pure CO2 gas, before or after the step of collecting the exhaust effluent in said buffer, preferably after. In a particular embodiment of the present invention, said mixing gas is exhaust effluent or substantially pure CO2 gas, optionally fed from the storage unit and / or the buffer, O2-rich gas or steam. In a further preferred embodiment, according to the present invention, the O2-rich gas or the O2-rich stream is produced in one air separation unit, said separation unit producing from an air entry, a stream enriched in oxygen and optionally a stream enriched in nitrogen. Preferably, by the terms O2-rich gas or stream, it is meant according to the present invention, a gas containing more than 70 vol% on dry basis of di-oxygen with respect to the volume of combustion stream containing a comburant, more preferably a gas containing more than 80 vol%, even more than 90 vol%, more particularly more than 93 vol% on dry basis di-oxygen, with respect to the volume of combustion stream containing a comburant, such as for example oxygen generated by pressure swing adsorption method which has generally a O2 concentration of 93 vol% on dry basis di-oxygen. In a particularly preferred embodiment, during the step of recirculating said fraction of the exhaust effluent and before the step of injecting the exhaust effluent to the kiln, the exhaust effluent is cooled in a device such as a heat exchanger or a scrubber in which at least a part of the water vapor is condensed and discarded forming a cooled and dried exhaust effluent. Within the meaning of the present invention, by the wording “dried exhaust effluent”, it is meant a gaseous effluent substantially depleted in water vapor. Obviously, in the dried exhaust effluent, a few percents of water vapor can remain. Preferably, according to the present invention, a portion of the cooled and dried exhaust effluent is further introduced to the kiln, such as for example at the top of the shaft in calcining mode at a temperature below 350°C, preferably below 200°C, preferably below 100°C, more preferably between 30 and 80°C. In a preferred embodiment, the exhaust effluent discharged from the shaft in preheating mode has a temperature of 60°C to 250° C, preferably around 150° C. Other embodiments of the process according to the present invention are mentioned in the appended claims. The present invention also relates to a parallel-flow regenerative kiln for implementing the method according to anyone of the preceding claims, comprising - at least two shafts, interconnected by a crossover channel, - each of said shafts comprising, in the on or off position, - at least one fuel supply device, - at least one supply opening for oxygen-containing oxidant, - an inlet, for loading carbonate mineral stones, at the top of the shafts, - an outlet for unloading the calcined material produced, at the bottom of the shafts, an exhaust effluent discharge duct at the top of the shafts, which is connected to a chimney, and - a supply of cooling gas to cool the calcined material produced, the kiln comprising a system for reversing the operation of the shafts, arranged so that each shaft, in standard mode, operates alternately in calcining mode and in preheating mode, a shaft being in calcining mode for a predetermined time period while at least one other shaft is in preheating mode, and vice-versa, this reversing system therefore controlling said on and off positions, wherein it further comprises - a recirculation circuit which is arranged between the above-mentioned exhaust effluent discharge duct of the shafts and said oxidant supply openings of the shafts, - a separating member, capable of collecting a portion of exhaust effluent discharged from the kiln via the duct and introducing it into the recirculation circuit, and - a source of concentrated dioxygen, connected with the recirculation circuit in order to supply it with concentrated dioxygen and thereby form an oxidizing mixture, said oxidant supply opening of the shaft in calcining mode being supplied in the on position via said reversing system to ensure fuel combustion, - said crossover channel being provided to transfer combustion fumes from the shaft in calcining mode to at least one shaft in preheating mode, wherein the shafts have a rectangular cross-section wherein a first part of a first shaft faces a first part of a second neighboring shaft, a second part of said first shaft is opposite to said first part of said first shaft 1 and a second part of said second neighboring shaft is opposite to said first part of said second neighboring shaft, wherein said crossover channel for transfer for gas connects directly the first and second shafts, and wherein, each side of said first parts and said second parts comprises exit means, wherein exit means comprises a series of orifices comprising X columns of N orifices and Y rows of T orifices, wherein X, N, Y and T are integer comprised between 0 and 20 in which X, N, Y and T cannot be all equal to 0 for each first parts and each second parts, wherein the exit means of each side is connected to at least one extracting element being controlled by a control means so as to allow heated cooling gas to be removed from the kiln. Preferably, the exit means comprises a series of orifices comprising X columns of N orifices and Y rows of T orifices wherein the columns and rows are staggered to provide staggered exit means. Preferably, the number of orifices N is different from one column to another column. Preferably, the number of orifices T is different from one row to another row. Preferably, the proximal zone of the two adjacent sides, in proximity of said interior side of the first shaft and the second shaft is in the shape of a polyhedron whose vertical section plane is triangular wherein - the base of the polyhedron is the base of the shaft, - the interior side is one face of the polyhedron or, - any vertical line intersecting the upper edge of the polyhedron does not pass through the base of the polyhedron. Preferably, the proximal zone has a height which is comprised between 20% and 40% of the total height of the first shaft or of the second shaft. Preferably, the distal zone of the two adjacent sides, in proximity of said exterior side is in a band shape having a height and a width wherein - the exterior side is one face of the band shape, - the height of the band shape is approximatively the height of the shafts, and - the width of the band shape in the upper part of the band shape is comprised between 5% and 20% in width starting from the exterior side as compared to the width of the base of the shafts, wherein the upper part of the band shape represents at least 60% in height towards the height of the band shape, - the width of the band shape in the bottom part of the band shape becomes larger when the height of the band shape decreases, wherein the width of the band shape is equal to the width of the base of the shafts at the bottom of the shafts. According to the present invention, by the term “width” it is preferably meant the horizontal dimension that is perpendicular to the plane of symmetry between the two shafts. According to the present invention, by the term “depth” it is preferably meant the horizontal dimension that is parallel to the plane of symmetry between the two shafts. According to the present invention, by the term “height” it is preferably meant the vertical dimension that is perpendicular to width and to the depth. Preferably, the exit means of the first shaft and second shaft are located : (i) inside the first part: either inside the proximal zone and / or inside said interior side, and (ii) inside the second part: either inside the distal zone and / or inside the exterior side. Preferably, the exit means of the first shaft and second shaft located inside the first part are located inside an upper part of the first part, such as an upper part of the polyhedron shape wherein said upper part starts at 25% in height, preferably 40% above the base of the polyhedron (the height being defined as the vertical distance between the plane of the base of the polyhedron and the upper edge of the polyhedron). Preferably, the exit means of the first part of a first shaft and the exit means of the second part 38 of said second neighboring shaft is connected, preferably through a collector tunnel, to a first extracting element being controlled by a first control means, and wherein the exit means of the first part of the second shaft and the exit means of the second part of the first shaft is connected, preferably through a collector tunnel, to a second extracting element being controlled by a second control means so as to allow heated cooling gas to be removed from the kiln, said first control means and said second control means being synchronized with said reversing system. Preferably, X is comprised between 1 and 50, more preferably between 1 and 20, even more preferably between 1 and 10. Preferably, Y is comprised between 1 and 50, more preferably between 1 and 20, even more preferably between 1 and 10. Preferably, N is comprised between 1 and 100, more preferably between 1 and 50, even more preferably between 1 and 20, or even between 1 and 10. Preferably, T is comprised between 1 and 100, more preferably between 1 and 50, even more preferably between 1 and 20, or even between 1 and 10. In a preferred embodiment, in the kiln according to the present invention, the first and the second extracting element both include at least one control element, able to extract, based on a signal respectively from the first or second control means, from 0 to 100% of the heated cooling gas. Preferably, each column of N orifices and / or each row of T orifices are connected to a collector tunnel communicating with the first extracting element and / or with the second extracting element so as to allow extraction of heated cooling air from the kiln. Preferably, each column of N orifices and each row of T orifices of the exit means are shifted between each other. Preferably, the exit means of each side of said first parts and said second parts are located in the bottom part of each side and / or in the middle part of each side and / or in the upper part of each side, preferably the exit means of said second parts are located at the top of said second parts. Preferably, the collector tunnel comprises a series of openings means being able to provide (i) a fluid communication between the exit means and the first extracting element, or alternatively (ii) a fluid communication between the exit means and the second extracting element. Preferably, the exit means of the first shaft and / or the second shaft is a single opening covering respectively most of the depth and / or the width of the shafts . Preferably, the collector tunnel is fluidly connected to the first part 36 of the first shaft and to the second part of the second shaft, and the collector tunnel is fluidly connected to the first part of the first shaft and to the second part of the first shaft, wherein each collector tunnels comprise preferably an upper horizontal plane wherein the exit means, in the form of a single opening or a plurality of openings, are located. In a further preferred embodiment, said crossover channel comprises a series of mixing gas entry means, provided to feed a mixing gas from outside of the kiln into the lumen of the crossover channel, said series of mixing gas entry means being operatively connected to a pressurization device so as to be able to inject a mixing gas at high velocity in said crossover channel throughout said series of mixing gas entry means in such a way that a ratio of momentum J between the mixing gas and the combustion fumes is higher than 1. Advantageously, said ratio of momentum J is higher or equal to 2, more preferably higher or equal to 4, more preferably higher or equal to 5, more preferably higher or equal to 6, in particular higher than or equal to 7, more particularly higher than or equal to 8, even higher than or equal to 9 or higher than or equal to 10 or higher than or equal to 11 or higher than or equal to 12 or higher than or equal to 13 or higher than or equal to 14 or higher than or equal to 15 or higher than or equal to 16 or higher than or equal to 17 or higher than or equal to 18 or higher than or equal to 19 or higher than or equal to 20 or higher than or equal to 21 or higher than or equal to 22 or higher than or equal to 23 or higher than or equal to 24 or higher than or equal to 25 or higher than or equal to 26 or higher than or equal to 27 or higher than or equal to 28 or higher than or equal to 29 or higher than or equal to 30 to ensure a good mixing between the mixing gas and the exhaust effluent. In yet a further preferred embodiment, said crossover channel comprises a series of obstacles arranged to increase the mixing between said mixing gas and said combustion fumes. Advantageously, according to the present invention, the parallel-flow regenerative kiln comprises, downstream or upstream the pressurization means, heating means to heat said mixing gas before injection in the crossover channel, said heating means being preferably chosen amongst a heat exchanger, a combustion chamber, electrical heater. In a particular embodiment according to the present invention, the kiln comprises, as a dioxygen source for the recirculation circuit, a unit for separating air into dioxygen and dinitrogen. In a further particular embodiment of the present invention, a heat exchanger supplied with heated cooling gas removed from the kiln, is mounted on the recirculation circuit. In yet a further particular embodiment, the kiln according to the present invention comprises equipment for unloading calcined material that is resistant to temperatures greater than 200°C, preferably greater than 300°C, such as equipment in refractory steel. Preferably, in the parallel-flow regenerative kiln according to the present invention, said recirculation circuit is connected to at least one buffer unit. More preferably, said recirculation circuit is connected to storage unit provided to store a CO2-rich exhaust effluent, optionally before or after a buffer unit. In yet a preferred embodiment according to the present invention, said central collector element has a tubular central collecting element with at its lower end, at least one extraction outlet and, at its upper end located at a level lower than the crossover channel, a harvesting opening oriented axially upwards, each shaft further comprising a protective element which, fixed in the shaft in a position independent of the tubular central collecting element, covers the upper end of the latter by surrounding it up to a level lower than the harvesting opening. Preferably, the protective element is arranged above and at a distance from the harvesting opening, flaring downwards conically to a cylindrical lower part which extends coaxially and at a distance from the upper end of the tubular central collecting element, leaving between the upper end of the collecting element and the protective element, a free passage for collecting heated cooling air through the opening of the central tubular collecting element, said protective element being supported centrally in the shaft by several support spacers, such as 4, 6, 8 or 10 spacers. Other embodiments of the parallel-flow regenerative kiln according to the present invention are mentioned in the appended claims Other characteristics and advantages of the present invention will be derived from the non-limitative following description, and by referring to the drawings and the examples. In the drawings, figure 1 schematically shows a PFRK kiln of rectangular cross-section. Figure 2 schematically shows one embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 3 schematically shows a further embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 4 schematically shows a further embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 5 schematically shows a further embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 6 schematically shows a further embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 7 schematically shows a further embodiment of the kiln with a rectangular cross-section according to the invention carrying out one embodiment of the process according to the present invention. Figure 8 represents a numerical modelling of the oxygen concentration in weight% of the several flows in the PFRK according to the present invention. Figure 9 illustrates different embodiments of the exit means of the kiln with a rectangular cross-section according to the invention. In the drawings, the same reference numbers have been allocated to the same or analog element. Conventionally, the shaft shown on the left is in calcining mode and the shaft shown on the right is in preheating mode. Standard parts, such as loading or unloading equipment, are not shown or they are shown very schematically, in order to not overload the drawings. As can be seen in figure 1, the parallel-flow regenerative kiln shown is a vertical double-shaft kiln 1, 2, where the fuel is injected alternately in one shaft 1 then in another 2 for approximately 12 minutes with a stop period between cycles of 1 to 2 minutes to reverse the circuits. This is the “reversing” period. Both shafts have a rectangular cross-section which are interconnected by a crossover channel comprising a crossover channel 3. The shafts are divided vertically into three areas, the preheating area A where the carbonate stones are preheated before calcination, the combustion area B where the calcination of the carbonate stones occurs and the cooling area C where the cooling of the calcined material occurs. When a shaft is in calcination mode, here the shaft 1, a fuel supply device in the form of lances 4 injects a fuel 9 into the shaft, which, in the example shown, is natural gas. The carbonate stones, loaded at the top of the shaft via an inlet 5, progressively descends in the shaft. Combustion air is introduced at the top of the shaft via a supply opening 6, which allows for fuel combustion at the outlet of the lances 4 and a decarbonation of the carbonate stones to calcined material 10. The exhaust gas 11 formed by the combustion and decarbonation descends co-currently to the calcined material and, moves into the crossover channel 3. Cooling gas is introduced via a supply duct 7 at the bottom of the shaft, counter-currently to the calcined material, to cool it. The heated cooling gas 12 introduced in the calcination shaft mixes with the combustion fumes 11 in order to move into the crossover channel 3. The calcined material is unloaded via the outlet 8 into a piece of unloading equipment 24. When a shaft is in preheating mode, here the shaft 2, the fuel supply device is closed and the lances 4 do not receive any fuel, but still can be supplied with cooling gas. The inlet 5 of the shaft in preheating mode is supplied by the carbonate stones. The opening 6 for supplying combustion air is closed. However, the supply duct 7 for the cooling gas and the outlet 8 for the calcined material remain in the open position. After heat exchange with the descending calcined material 10, the heated cooling gas mixes with the combustion fumes 11 which, from the crossover channel 3, enters the shaft. The combustion fumes 11 progresses until reaching the top of the shaft where it is discharged from the kiln via a discharge duct 14 and transferred to a chimney 15, possibly after treatment in equipment’s such as filters. In the shaft in calcination mode 1, this discharge duct 14 is closed. The kiln also comprises a reversing system 16, shown schematically. It controls, in a synchronized manner, the operation of the shafts during the reversing time of the shafts, either directly or remotely. It controls the on and off switching of all elements of the kiln in such a way that, in production mode, each shaft operates alternately in calcination mode and in preheating mode. Figure 2 is a view of one embodiment of the kiln according to the present invention where the combustion of fuel is performed in oxy- combustion conditions, i.e. in presence of CO2and oxygen. As can be seen, this embodiment comprises a separating member 17, capable of collecting a portion of exhaust effluent discharged from the kiln and introducing it into the recirculation circuit 18, and which has been provided on the exterior, on the discharge duct 14. In this circuit, the collected portion of exhaust effluent is advantageously treated in a treatment unit 19, where it may, for example, be filtered and / or dried for example in a condensation unit. An air separation unit 20 separates air supplied by the duct 21 into a N2- enriched stream discharged via the duct 22 and a O2 – rich stream supplied to the recirculation circuit 18 via the supply duct 23. This circuit 18 then brings the oxidizing mixture formed from the recirculated portion of exhaust effluent and concentrated O2 to the top of each of the shafts at the supply opening 6. While this embodiment is illustrated with a feed of a mixture between the exhaust effluent and the oxygen, another embodiment, included within the scope of the present patent application can have a double feed, one for the exhaust effluent and one for the oxygen, even if less preferable because the composition of the gaseous atmosphere in the calcination zone can lack uniformity in the latter embodiment. Further, the mixture or the separated input of exhaust effluent and oxygen is illustrated at the top of the shaft, it is also conceivable within the scope of the present invention to have a feed directly in the calcination zone. The separating member 17 is continuously in service during combustion, the same as the treatment unit 19 and the air separation unit 20 unless oxygen storage is foreseen. As has already been seen, the reversing system 16 closes the discharge duct 14 at the top of the shaft in calcination mode. However, at the top of this shaft, it opens the supply opening 6 to allow the oxidizing mixture to be introduced, while it is closed at the top of the shaft in preheating mode. In addition, according to the present invention, the heated cooling gas is extracted outside the kiln after contact with the calcined material. A removal system is present in each shaft. Figure 3 illustrates an embodiment of the kiln with a rectangular cross-section according to the invention with a focus on the first parts 36, 37 and second parts 35, 38 of the shafts, together with a schematic representation of the proximal zone of the first shaft 36’ and the distal zone 38’ of the second shaft. The proximal zone of the second shaft and the distal zone of the first shaft are not represented. Figure 4 further illustrates an embodiment of the kiln with a rectangular cross-section according to the invention with a focus on the connection of the collector tunnel 25 to the first extracting element 26 and the connection of the collector tunnel 25’ with the second extracting element 28, for example for further processing. In more details, the shafts are provided, below the crossover channel, with a collector tunnel 25, 25’. The collector tunnel 25 connects the exit means 39 of the first part 36 of the first shaft 1 and the exit means 39 of the second part 38 of the neighboring shaft 2 with a first extracting element 26 so as to allow heated cooling gas to be removed from the kiln, said first extracting element 26 being controlled by a first control means (not shown), and the collector tunnel 25’ connects the exit means 39 of the second part 35 of the first shaft 1 and the exit means 39 of the first part 37 of the second shaft 2 with the second extracting element 28 so as to allow heated cooling gas to be removed from the kiln, said second extracting element 28 being controlled by a second control means (not shown), said first control means and said second control means being synchronized with said reversing system. In the embodiments of Fig.2 and Fig. 4, the collector tunnels 25 and 25’ connecting exit means 39 are all located in the bottom of the shaft, below the crossover channel. As illustrated, the collector tunnel(s) 25 connected to exit means 39 are located inside the first part of the first shaft 1 and inside the second part of the second shaft 2. The collector tunnel(s) 25’ connected to exit means 39 are located inside the second part of the first shaft and inside the first part of the second shaft. Alternatively to the embodiment of Fig. 4, Figure 5 illustrates an embodiment of the kiln with a rectangular cross-section according to the invention with a focus on the connection of the collector tunnel(s) 25 to the first extracting element 26 and the connection of the collector tunnel(s) 25’ with the second extracting element 28 wherein (i) the collector tunnels 25’ each connected to exit means 39 are located inside an upper part of the second part of the first shaft and inside an upper part of the first part of the second shaft , and (ii) the collector tunnels 25 each connected to exit means 39 are located inside an upper part of the second part of the second shaft and inside an upper part of the first part of the first shaft. In addition, Figure 6 illustrates an embodiment of the kiln with a rectangular cross-section according to the invention combining the embodiment of Fig.4 and the embodiment of Fig.5 wherein (i) the collector tunnels 25’ each connected to exit means 39 are located inside an upper part and a bottom part of the second part of the first shaft and inside an upper part of the first part of the second shaft, and (ii) the collector tunnels 25 each connected to exit means 39 are located inside an upper part and a bottom part of the second part of the second shaft and inside an upper part of the first part of the first shaft. In the illustrated embodiment, the first extracting element 26 and the second extracting element 28 both include at least one control element, able to extract, based on a signal respectively from the first or second control means, from 0 to 100% of the heated cooling gas. Preferably, the first and / or second control means comprises at least an active and an inactive configuration, wherein the active configuration controls the first extracting element 26 and / or the second extracting element 28 in order to extract an amount of extracted heated cooling gas comprised between 0 and 100 vol%, and wherein the inactive configuration prevents the first extracting element 26 and / or the second extracting element 28 to extract an amount of extracted heated cooling gas in the shaft in calcining mode and / or the shaft in preheating mode, wherein preferably, the passage from the inactive to the active configuration is set when the signal sent by a temperature probe linked to the first or second control means passes above a first temperature threshold, wherein preferably the passage from the active to the inactive configuration is set when the signal sent by the temperature probe to the first extracting element 26 and / or the second extracting element 28 decreases below a second temperature threshold. Preferably, the first and / or second control means comprises a series of active configurations wherein each active configuration of the series of active configurations controls the first extracting element 26 and / or the second extracting element 28 in order to extract a particular amount of extracted heated cooling gas, wherein the passage from one active configuration to another active configuration of the series of active configuration is set when the signal sent by the temperature probe to the first extracting element 26 and / or the second extracting element 28 passes above or below a temperature threshold. Alternatively, the active configuration of the first and / or second control means controls the first extracting element 26 and / or the second extracting element 28 in order to increase, preferably progressively increase, the extraction of the heated cooling gas during one cycle of the kiln, preferably the extraction of the heated cooling gas passes, during one cycle of the kiln, from 0% to 100vol% of said heated cooling gas, wherein preferably the temperature of the exhaust effluent is maintained above a threshold value but as close as possible to said threshold value of at least 60°C, preferably above 70°C, more preferably above 80°C, for example the temperature of the exhaust effluent is maintained between 60°C and 100°C. Indeed, it allows optimizing energy consumption while increasing the concentration of CO2 in the exhaust effluent. The control element of the first extracting element 26 connected to the collector tunnel 25 of the shaft in calcining mode allows for example to extract from 50 to 100%, preferably from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis of heated cooling gas from the shaft in calcining mode, relative to the cooling gas introduced in the same shaft, through said collector tunnel 25, based on a signal from the first control means. The control element of the second extracting element 28 connected to the collector tunnel 25’ of the shaft in calcining mode allows for example to extract from 50 to 100%, preferably from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis of heated cooling gas from the shaft in calcining mode, relative to the cooling gas introduced in the same shaft, through said collector tunnel 25’, based on a signal from the second control means. The control element of the first extracting element 26 connected to the collector tunnel 25 of the shaft in preheating mode allows to extract from 50 to 100%, preferably from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis of heated cooling gas from the shaft in preheating mode, relative to the cooling gas introduced in the same shaft, through said collector tunnel 25, based on a signal from the first control means. The control element of the second extracting element 28 connected to the collector tunnel 25’ of the shaft in preheating mode allows for example to extract from 0 to 50%, preferably from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% by volume on dry gas basis of heated cooling gas from the shaft in preheating mode, relative to the cooling gas introduced in the same shaft, through said collector tunnel 25’, based on a signal from the first control means. Moreover, in order to recover a portion of the energy from the hot air removed by the extraction element 26, (but also possibly 28) a heat exchange may be provided with the portion of recirculated exhaust effluent using a heat exchanger 42, before or after the mixing thereof with concentrated dioxygen. In the crossover channel 3, an injection of a fraction of said collected portion of exhaust effluent discharged from the kiln using an injection duct 37 may also be provided, preferably at a high velocity to create turbulences and reduce the CO concentration in the exhaust effluent, during the passage of said combustion fumes towards the at least one shaft working in a preheating mode. The ratio of momentum J between the collected portion of exhaust effluent and the combustion fumes is preferably higher than 1. Optionally beforehand, a heat exchange between the heated cooling gas removed from the kiln, and this above-mentioned fraction to be injected may occur using a heat exchanger, for example the heat exchanger 42. In the absence thereof, another heater not shown may be provided on the injection duct 37. Preferably, in the crossover channel 3, the injection of a fraction of said collected portion of exhaust effluent discharged from the kiln using the injection duct 37 also comprises an addition of oxygen by a fluid connection of the injection duct 37 with the supply duct 23. Alternatively, extracting element can have a closed position and an open position, whereinthe first extracting element connected to the collector tunnel 25 of the shaft in calcining mode is in open position to extract nearly 100% by volume of heated cooling gas on dry gas basis and the second extracting element connected to the collector tunnel 25’ of the shaft in calcining mode is in closed position to not extract cooling gas or only extract a very few % of the heated cooling gas due to some unavoidable leakage. The first extracting element connected to the collector tunnel 25 of the shaft in preheating mode is in open position to extract nearly 100% of heated cooling gas by volume on dry gas basis and the second extracting element connected to the collector tunnel 25’ of the shaft in preheating mode is in closed position to not extract cooling gas or almost extract a very few % of the heated cooling gas due to some unavoidable leakage. Alternatively, Figure 7A illustrates an embodiment of the kiln with a rectangular cross-section according to the invention wherein each collector tunnel 25, 25’ of the first shaft 1 and the second shaft 2 comprises an upper horizontal plane 25’’, wherein each collector tunnel 25, 25’ is connected to the exit means 39 and wherein the exit means 39 is a single opening located in the upper horizontal plane 25’’, wherein the single opening covering respectively most of the depth and / or the width of the shaft 1 and / or of the shaft 2. Figure 7b illustrates an enlargement of one collector tunnel 25 having the upper horizontal plane 25’’ and wherein the collector tunnel 25 is connected to the exit means 39 wherein the exit means 39 consists of a single opening. Figure 8 represents a numerical modeling of the Parallel-flow regenerative kiln with a rectangular section showing the path of the gases as a function of their oxygen content. It only shows the combustion zone B, from the end of the lances, and the cooling zone C, and therefore the top of the shafts is not represented. Zones a: in the shaft in calcining mode, combustion oxygen mixed with exhaust fumes, content of oxygen can be about 20-25% or even a bit more when working in oxygen excess in the combustion zone. Zones b: jets of combustion fumes emitted by the lances, in which there is almost no more oxygen and between which we can still find a little O2 which has not reacted. Zone c’: interface between the fumes and the cooling gas / air in the shaft in calcining mode. Zone d: in the shaft in preheating mode, cooling gas / air. Zone e: mixture between the gas stream coming from the collector channel and the cooling gas / air. Zone f: the fumes penetrate deep into cooling zone C, below the level of the crossover channel in the shaft in calcining mode, mixing little with the cooling gas, such as cooling air. They push the gas mixture laterally to the crossover channel 3. Zone g: in the shaft in calcining mode, cooling gas / air. Figure 9 illustrates different embodiments of the exit means 39 wherein Fig.9A illustrates a series of exit means comprising X columns of N aligned orifices. Fig.9B illustrates a series of exit means where the columns and rows are staggered providing an arrangement of staggered exit means. The exit means can be in the form of a single slit shape (Fig.9C) or in the form of a plurality of slit shape (Fig.9D). It should be understood that the present invention is not limited to the described embodiments and that variations can be applied without going outside of the scope of the appended claims.

Claims

CLAIMS 1. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln having at least a first and a second shafts (1,2) interconnected by a crossover channel (3), comprising, in standard operation, - loading carbonate mineral stones at the top of each shaft (1, 2), - preheating these loaded stones in a preheating zone, - calcining these preheated stones in a calcination zone with production of a decarbonated calcined material (10), - cooling the calcined material (10) with cooling gas in a cooling zone, with formation of heated cooling gas by heat exchange, - discharging the calcined material (10) from the bottom of the shafts (1, 2), - exhausting an exhaust effluent from the kiln, - each shaft alternately working in a calcining mode and in a preheating mode, one shaft working in a calcining mode during a predetermined time period during which at least another shaft works in a preheating mode, and inversely after activation of the inversion means, - the calcining mode comprising : • in the presence of said preheated carbonate mineral stones descending into said shaft, oxy-combusting fuel in the presence of oxygen so as to obtain said calcination of said stones in said combustion zone, and the decarbonation thereof into calcined material with the release of combustion fumes (11) descending co- currently in the shaft in calcination mode, and• through said crossover channel (3), a passage of said combustion fumes (11) toward the at least one shaft working in a preheating mode, - said preheating mode comprising : • said preheating step of the loaded carbonate mineral stones by heat exchange with said combustion fumes coming from the crossover channel (3), which is ascending and flows in counter-current through the loaded carbonate mineral stones, and • said exhausting step of said combustion fumes (11) as exhaust effluent at the top of said at least one shaft in preheating mode, said method further comprises - recirculating a fraction of the exhaust effluent exhausted from the top of said at least one shaft in preheating mode, - injecting the exhaust effluent, exhausted from the top of said at least one shaft in preheating mode, at least partially to the shaft in calcining mode, either under the form of a comburant mixture or with an injection of a combustion stream containing a comburant, for said step of oxy-combusting the fuel, said comburant being preferably O2-rich gas - extracting said heated cooling gas outside of said kiln, characterized in that during said extracting step of the heated cooling gas outside of the kiln, the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in calcining mode, by exit means (39) located in a first part (36) of the first shaft (1) or by exit means located in a first part (37) of the second shaft (2), said first part (36) of the first shaft (1) facing said first part (37) ofsaid second shaft (2), both first part (36,37) being located below the cross- over channel (3) and the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in calcining mode, by exit means (39) located in a second part (35) of said first shaft (1) or by exit means (39) located in a second part (38) of said second shaft (2), the second part (35) of the first shaft (1) being at the opposite of the first part (36) of the first shaft (1) and the second part (38) of the second shaft (2) being at the opposite of the first part (37) of the second shaft (2), and the heated cooling gas is extracted from 50 to 100% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in preheating mode, by exit means (39) located in said second part (35) of said first shaft (1) or by exit means located in said second part (38) of said second shaft (2), and the heated cooling gas is extracted from 0 to 50% by volume on dry gas basis relative to the cooling gas introduced in the same shaft, from the shaft in preheating mode, by exit means (39) located in said first part (36) of said first shaft (1) or by exit means (39) located in said first part (37) of said second shaft (2).

2. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to claim 1, wherein the heated cooling gas is extracted from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis from the shaft in calcining mode through said exit means (39) located in a first part (36) of a first shaft (1) or by exit means (39) located in a first part (37) of the second shaft (2) and from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% by volume on dry gas basis from the shaft in calcining mode through said exit means (39) located in a second part (35) of said first shaft (1) or by exit means (39) located in a second part (38) of said second shaft(2) and the heated cooling gas is extracted from 0 to 30%, preferably from 0 to 25%, more preferably from 0 to 20% by volume on dry gas basis from the shaft in preheating mode through said exit means (39) located in said first part (36) of said first shaft (1) or by exit means (39) located in said first part (37) of said second shaft (2) and from 70 to 100%, preferably from 75 to 100%, more preferably from 80 to 100% by volume on dry gas basis from the shaft in preheating mode through said exit means (39) located in said second part (35) of said first shaft (1) or by exit means (39) located in said second part (38) of said second shaft (2), all the percentages given being relative to the cooling gas flow introduced in the same shaft.

3. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the claims 1 or 2, further comprising a CO reduction step in the crossover channel (3) by injecting a mixing gas through a series of mixing gas entry means at high velocity in such a way that a ratio of momentum J between the mixing gas and the combustion fumes (11) is higher than 1.

4. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the claims 1 to 3, wherein the exhaust effluent is partially or fully collected in at least one buffer after said exhausting step.

5. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein said oxy-combusting step of fuel in the presence of oxygen is carried out in the combustion zone fed by the exhaust effluent and by the combustion stream containing a comburant, simultaneously or separately, or by a mixture of said exhaust effluent and said combustion stream containing a comburant.

6. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein said cooling step comprises a supply of cooling gas at the bottom of eachof said shafts or only of the shaft working in the calcining mode, or only in the shaft working in the preheating mode.

7. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the claims 1 to 5, wherein said cooling step comprises a supply of cooling gas at the bottom of the shaft having worked in the preheating mode and before the activation of the inversion means, in order to have each shaft encountering sequentially said preheating mode, a cooling step and then a calcining mode.

8. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein said cooling gas is air, nitrogen (such as nitrogen from the air separation unit when present) or steam or a combination thereof and preferably air.

9. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein said fuel combustion comprises introducing a gaseous, liquid or solid fuel into the shaft in calcining mode and in that, in the case of a solid fuel, said introduction is carried out using a portion of said collected portion of exhaust effluent discharged from the kiln, or using another source of CO2as a carrier gas.

10. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein a portion of the exhaust effluent discharged from the kiln is introduced in an outer envelope, enclosing lances for fuel injection for cooling said lances.

11. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, further comprising a step of collecting a portion of the exhaust effluent in a storage unit, preferably after purification for producing a substantially pure CO2gas, before or after the step of collecting the exhaust effluent in said buffer, preferably after.

12. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein said mixing gas is exhaust effluent or substantially pure CO2gas, optionally fed from the storage unit and / or the buffer, O2-rich stream or steam, or a combination thereof.

13. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the previous claims, wherein the O2- rich gas or the O2- rich stream is produced in one air separation unit, said separation unit producing from an air entry, a stream enriched in oxygen and optionally a stream enriched in nitrogen.

14. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to any of the preceding claims, wherein during the step of recirculating said fraction of the exhaust effluent and before the step of injecting the exhaust effluent to the kiln the exhaust effluent is cooled in a device such as into a heat exchanger (42) or a scrubber in which at least a part of the water vapor is condensed and discarded forming a cooled and dried exhaust effluent.

15. Method for calcining carbonate mineral stones in a parallel flow regenerative kiln according to claim 14, wherein a portion of the cooled and dried exhaust effluent is further introduced at the top of the shaft in calcining mode at a temperature below 350°C, preferably below 200°C, preferably below 100°C, more preferably between 30 and 80°C.

16. Parallel-flow regenerative kiln for implementing the method according to anyone of the preceding claims, comprising - at least two shafts (1, 2), interconnected by a crossover channel (3), - each of said shafts (1, 2) comprising, in the on or off position, - at least one fuel supply device (4),- at least one supply opening for oxygen-containing oxidant (6), - an inlet (5), for loading carbonate mineral stones, at the top of the shafts (1, 2), - an outlet (8) for unloading the calcined material produced, at the bottom of the shafts, an exhaust effluent discharge duct (14) at the top of the shafts (1, 2), which is connected to a chimney (15), and - a supply of cooling gas (7) to cool the calcined material produced, the kiln comprising a system (16) for reversing the operation of the shafts (1, 2), arranged so that each shaft (1, 2), in standard mode, operates alternately in calcining mode and in preheating mode, a shaft being in calcining mode for a predetermined time period while at least one other shaft is in preheating mode, and vice-versa, this reversing system (16) therefore controlling said on and off positions, wherein it further comprises - a recirculation circuit (18) which is arranged between the above-mentioned exhaust effluent discharge duct (14) of the shafts (1, 2) and said oxidant supply openings (6) of the shafts (1, 2), - a separating member (17), capable of collecting a portion of exhaust effluent discharged from the kiln via the duct (14) and introducing it into the recirculation circuit (18), and - a source of concentrated dioxygen (20), connected with the recirculation circuit (18) in order to supply it with concentrated dioxygen and thereby form an oxidizing mixture, said oxidant supply opening of the shaft in calcining mode being supplied in the on position via said reversing system (16) to ensure fuel combustion,- said crossover channel (3) being provided to transfer combustion fumes (11) from the shaft in calcining mode to at least one shaft in preheating mode, wherein the shafts (1, 2) have a rectangular cross-section wherein a first part (36) of a first shaft (1) faces a first part (37) of a second neighboring shaft (2), a second part (35) of said first shaft (1) is opposite to said first part (36) of said first shaft (1) and a second part (38) of said second neighboring shaft (2) is opposite to said first part (37) of said second neighboring shaft (2), wherein said crossover channel (3) for transfer for gas connects directly the first and second shafts, and wherein, each side of said first parts (36,37) and said second parts (35, 38) comprises exit means (39), wherein exit means comprises a series of orifices comprising X columns of N orifices and Y rows of T orifices, wherein X, N, Y and T are integer comprised between 1 and 20, wherein the exit means (39) of each side is connected to at least one extracting element (26, 28) being controlled by a control means so as to allow heated cooling gas to be removed from the kiln, wherein the exit means of the first part (36) of a first shaft (1) and the exit means (39) of the second part (38) of said second neighboring shaft (2) is connected to a first extracting element (26) being controlled by a first control means, and wherein the exit means (39) of the first part (37) of the second shaft (2) and the exit means (39) of the second part (35) of the first shaft (1) is connected to a second extracting element (28) being controlled by a second control means so as to allow heated cooling gas to be removed from the kiln, said first control means and said second control means being synchronized with said reversing system (16).

17. Parallel-flow regenerative kiln according to claim 16, wherein each columns of N orifices and / or each rows of T orifices are connected to a collector tunnel (25) communicating with the firstextracting element (26) and / or with the second extracting element (28) so as to allow extraction of heated cooling air from the kiln.

18. Parallel-flow regenerative kiln according to claim 16 or claim 17, wherein each column of N orifices and each rows of T orifices of the exit means (39) are shifted between each other.

19. Parallel-flow regenerative kiln according to any of the claims 16 to 18, wherein the exit means (39) of each side of said first parts (36,37) and said second parts (35, 38) are located in the bottom part of each side and / or in the middle part of each side and / or in the upper part of each side, preferably the exit means (39) of said second parts (35, 38) are located at the top of said second parts (35, 38).

20. Parallel-flow regenerative kiln according to any of the claims 16 to 19, wherein said collector tunnel (25) comprises a series of openings means being able to provide (i) a fluid communication between the exit means (39) and the first extracting element (26), or (ii) a fluid communication between the exit means (39) and the second extracting element (28).

21. Parallel-flow regenerative kiln according to any of the claims 16 to 20, wherein the first (26) and the second (28) extracting element both include at least one control element, able to extract, based on a signal respectively from the first or second control means, from 0 to 100% of the heated cooling gas.

22. Parallel-flow regenerative kiln according to any of the claims 16 to 21, wherein said crossover channel (3) further comprises a series of mixing gas entry means, provided to feed a mixing gas from outside of the kiln into the lumen of the crossover channel (3), said series of mixing gas entry means being operatively connected to a pressurization device so as to be able to inject a mixing gas at high velocity in said crossover channel (3) throughout said series of mixing gas entry means in such a way that a ratio of momentum J between the gas stream and the combustion fumes (11) is higher than 1.

23. Parallel-flow regenerative kiln according to any of the claims 16 to 22, wherein said crossover channel (3) further comprises a series of obstacles arranged to increase the mixing between said mixing gas and said combustion fumes (11).

24. Parallel-flow regenerative kiln according to any of the claims 16 to 23, further comprising, downstream or upstream the pressurization means, heating means to heat said mixing gas before injection in the crossover channel (3), said heating means (42) being preferably chosen amongst a heat exchanger, a combustion chamber, or an electrical heater.

25. Parallel-flow regenerative kiln according to any one of claims 16 to 24, wherein the kiln comprises, as a dioxygen source for the recirculation circuit (18), a unit for separating air (20) into a dioxygen-rich stream and optionally a dinitrogen-rich stream.

26. Parallel-flow regenerative kiln according to any one of claims 16 to 25, wherein a heat exchanger (42) supplied with heated cooling gas removed from the kiln, is mounted on the recirculation circuit (18).

27. Parallel-flow regenerative kiln according to any one of claims 16 to 26, wherein it comprises equipment (24) for unloading calcined material that is resistant to temperatures greater than 200°C, preferably greater than 300°C, such as equipment in refractory steel.

28. Parallel-flow regenerative kiln according to any of the claims 16 to 27, wherein said recirculation circuit (18) is connected to at least one buffer unit.

29. Parallel-flow regenerative kiln according to any of the claims 16 to 28, wherein said recirculation circuit (18) is connected to storage unit provided to store a CO2-rich exhaust effluent, optionally before or after a buffer unit.

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