Technical Field

[0001] The present invention relates to a decarbonation process of carbonated materials and to a multi-shaft vertical kiln for carrying said process.

Background Art

[0002] The increasing concentration of carbon dioxide in the atmosphere is recognized as one of the causes of global warming, which is one of the greatest concerns of present days. This increase is largely owed to human actions and particularly to the combustion of carbon-containing fossil fuel, for instance for transportation, household heating, power generation, etc., and in energy-intensive industries such as steel, cement and lime manufacturing.

[0003] Within the lime-production process, natural limestone (mainly composed of calcium carbonate) is heated to a temperature above 910°C in order to cause its calcination into quicklime (calcium oxide) and carbon dioxide according to the following reversible reaction :

CaCCh CaO + CO2 AH = 178 kJ/mol : Equation 1

[0004] Calcium oxide is considered as one of the most important raw materials and is used in a multitude of applications such as steel manufacturing, construction, agriculture, flue gas and water treatment as well as in glass, paper and food industry. The global annual production is estimated to be above 250 million tons.

[0005] As indicated in Equation 1 , CO2 is a co-product of the lime-production process meaning that approximately 760 to 790 kg of CO2 is unavoidably generated when producing 1 ton of lime. Moreover, the heat required for heating limestone and for conducting the reaction is usually provided by the combustion of a carbonaceous fuel, which results in additional production of CO2 (ranging between 200 and more than 700 kg per ton of lime depending on the nature of the fuel and efficiency of the kiln).

[0006] The use of vertical shaft kiln prevails in the lime industry as they are particularly suitable for the production of lumpy quicklime compared to other types of furnaces, such as rotary kiln, and because they have the advantage of lower specific energy input.

[0007] In a single-shaft vertical kiln, limestone or dolomitic limestone is fed through the top of the shaft and the produced lime is discharged at its bottom. In the pre-heating zone, the limestone is heated by hot gases flowing upward from the combustion zone. In the combustion zone, heat is produced through the direct firing of a fuel to reach a temperature above 910°C and consequently causing the decomposition of the limestone into quicklime and CO2. The lime then enters the cooling zone where it is cooled by air fed from the bottom of the shaft. The produced lime is finally discharged, ground and sieved into the desired particle size. Flue gas leaves the shaft at the top of the pre-heating zone and is fed to a filter system before it is vented to the atmosphere. Specific energy consumption for such single-shaft vertical kilns ranges between 4 and 5 GJ per ton of lime.

[0008] Parallel-flow regenerative kilns (PFRK) are a variant of vertical shafts that are considered as the best-available technology for lime production with design capacity up to 800 tons per day. They consist in several vertical shafts (usually 2 or 3) connected by a cross-over channel. Each shaft operates alternately according to a defined sequence. Initially, fuel is burnt in one of the shaft (“in combustion”) with combustion air flowing downwards (“parallel flow” with the limestone). Hot gases are then transferred to the other shafts (“in regeneration”) through the cross-over channel in order to pre-heat limestone in said other shafts. A reversal between combustion and regeneration shafts typically occurs every 15 minutes. Example of a parallel-flow regenerative kiln is illustrated in FR 2 450 241.

[0009] This operational mode enables optimal recovery of the heat contained in product and hot gases bringing the specific energy consumption down to 3.6 GJ per ton of lime. The combustion of the fuels required to bring this heat results in the production of approximately 200 kg of CO2 per ton of lime when natural gas is used.

[0010] The lime industry is making efforts for reducing its CO2 emissions by improving energy efficiency (including investment in more efficient kilns), using lower-carbon energy sources (e.g. replacing coal by natural gas or biomass) or supplying lime plants with renewable electricity. The CO2 related to energy can thus be reduced to some extent. Nevertheless, none of these actions impacts the CO2 which is inherently produced during decarbonation of limestone.

[0011] A route for further reducing emission consists in capturing CO2 from the lime kiln flue gas for permanent sequestration (typically in underground geological formation) or recycling for further usage (e.g. for the production of synthetic fuels). Those processes are known under the generic term CCLIS (Carbon Capture, Utilization and Storage).

[0012] Combustion air used in conventional lime kilns contains approximately 79 vol% nitrogen resulting in CO2 concentration in flue gas not higher than 15-25 vol%. Additional measures are thus required to obtain a CO2 stream that is sufficiently concentrated to be compatible with transportation, sequestration and/or utilization. [0013] Several technologies have been investigated for concentrating CO2 in particular for the power, steel and cement industry.

[0014] The reference technology for CO2 capture is a post-combustion technology based on absorption with aqueous amine solvents. A typical process includes an absorption unit, a regeneration unit and additional accessory equipment. In the absorption unit, CC>2-containing flue gas is contacted with amine solution to produce a CCh-free gas stream and an amine solution that is rich in CO2. The rich solution is then pumped to the regeneration unit where it is heated with steam to produce a concentrated stream of CO2 and a lean amine that can be recycled to the absorber. The CO2 stream is then cleaned and liquefied for storage and transportation.

[0015] The energy requirements for regenerating an amine solvent (e.g. monoethanolamine (MEA)) is substantial (approx. 3.5 GJ per ton of CO2 for MEA). While recovering waste heat to produce low temperature steam is often possible in other industrial processes, almost no waste heat is available from a PFRK (as a consequence of the high energy efficiency of PFRK). Fuel must thus be burnt for the purpose of generating steam, resulting in additional CO2 production.

[0016] As described above, limestone calcination in a PFRK is an intermittent process in terms of gas flow rate (e.g. absence of flow during reversal) and in term of flue gas composition (CO2 concentration varies during a cycle). In particular, there is a short interruption (called reversal) during two successive burning cycles, in order to feed fresh stone, discharge a batch of lime, and move flaps to alternate burning between the two shafts. During the reversal, the kiln is de-pressurized and the flow of exhaust gases is considerably reduced.

[0017] However, amine scrubbers optimally operate with continuous and relatively steady flue gas. In other words, adapting the process to PFR kilns could only be achieved at the expense of a negative impact on the overall efficiency and a complex control of the process.

[0018] It is estimated that amine-based CO2 capture would approximately more than double the production cost of lime or dolime. Those costs are mostly owed to fuel consumption for generating steam, electrical consumption for amine scrubbing and compression, and capital cost for equipment.

[0019] Other post-combustion technologies have been proposed for capturing CO2 from flue gas (e.g. chilled ammonia, adsorption, cryogenic distillation, membranes). All these options show with varying degrees identical drawbacks to those of amines regarding capital cost, energy penalty and adaptability to intermittent processes. Aims of the Invention

[0020] The invention aims to provide a solution to overcome at least one drawback of the teaching provided by the prior art.

[0021] More specifically, the invention aims to provide a process and a device for simultaneously allowing a decarbonation with a high production throughput of a product (e.g. quicklime, dolime) with a CCh-enriched exhaust stream, in particular a CCh-rich stream that is suitable for sequestration or use.

Summary of the Invention

[0022] For the above purpose, the invention is directed to a decarbonation process of carbonated materials, in particular limestone and dolomitic limestone in a multi-shaft vertical kiln comprising a first, a second, and optionally a third shaft with preheating zones, heating zones and cooling zones, a cross-over channel between each shaft, a first plurality of fluid-supply pipes opening in the first shaft, a second plurality of fluid-supply pipes opening in the second shaft and optionally a third plurality of fluid-supply pipes opening in the third shaft, alternately heating carbonated materials by a combustion of at least one fuel with at least one comburent, preferably said comburent comprising less than 70% N2 (dry volume), more preferably less than 50% of N2 (dry volume), in particular said comburent being oxygen-enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials is released, the combustion of the fuel and the decarbonatation generating an exhaust gas, the decarbonated materials being cooled in the cooling zones with one or more cooling streams, said process further comprising a first step of supplying with said fuel, said comburent or a combination of them, at least one of the first plurality of fluid-supply pipes, while supplying with a pipe-cooling gas at least one of the second and/or third plurality of fluid-supply pipes, when the first shaft is in a combustion state and the second and/or third shaft are(is) in a non-combustion state, in particular a regeneration state, said pipe-cooling gas comprising :

- at least 1% CO2 (dry volume), preferably at least 5% CO2 (dry volume), more preferably at least 25% CO2 (dry volume), in particular at least 50% CO2 (dry volume), and/or

- less than 79% N2 (dry volume), notably less than 78% N2 (dry volume), preferably less than 50% N2 (dry volume), more preferably less than 20% N2 (dry volume), in particular less than 10% N2 (dry volume).

[0023] For the above purpose, the invention is also directed to a decarbonation process of carbonated materials, in particular limestone and dolomitic limestone in a multishaft vertical kiln comprising a first, a second, and optionally a third shaft with preheating zones, heating zones and cooling zones, a cross-over channel between each shaft, a first plurality of fluid-supply pipes opening in the first shaft, a second plurality of fluid-supply pipes opening in the second shaft and optionally a third plurality of fluid-supply pipes opening in the third shaft, alternately heating carbonated materials by a combustion of at least one fuel with at least one comburent, preferably said comburent comprising less than 70% N2, more preferably less than 50% of N2, in particular said comburent being oxygen-enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials is released, the combustion of the fuel and the decarbonatation generating an exhaust gas, the decarbonated materials being cooled in the cooling zones with one or more cooling streams, said process further comprising a (first) step of supplying with a pipe cooling gas at least one of the second and/or third plurality of fluid-supply pipes, when the first shaft is a combustion state and the second and/or third shaft are(is) in a non-combustion state, in particular a regeneration state, said pipe cooling gas comprising:

- at least 1% CO2 (dry volume), preferably at least 5% CO2 (dry volume), more preferably at least 25% CO2 (dry volume), in particular at least 50% CO2 (dry volume), and/or

- less than 79% N2 (dry volume), preferably less than 50% N2 (dry volume), more preferably less than 20% N2 (dry volume), in particular less than 10% N2 (dry volume).

[0024] Preferred embodiments of any of the processes disclose one or more of the following features:

- a second step of subsequently supplying with the at least one fuel, the at least one comburent or a or the combination of them, the at least one of the second plurality of fluid-supply pipes, while supplying with the pipe-cooling gas the at least one of the first and/or third plurality of fluid-supply pipes when the second shaft is in a combustion state and the first and/or third shaft in a non-combustion state, in particular a regeneration state, and optionally repeating the first and second steps;

- in the first step transferring at least some of the exhaust gas generated in the multishaft vertical kiln to the at least one of the second plurality of fluid-supply pipes, wherein said exhaust gas serves as the pipe-cooling gas, preferably cooling said exhaust gas in a heat exchanger before being fed to the at least one of the second plurality of fluid-supply pipes;

- in the first step, the step of transferring comprises

- extracting at least some of the exhaust gas from: - an upper portion of the pre-heating zone of the second shaft or

- a pipe connected the upper portion of the second shaft, or

- extracting at least some of the exhaust gas flowing in an exhaust passage arranged downstream from the multi-shaft vertical kiln;

- in the second step, transferring at least some of the exhaust gas generated in the multi-shaft vertical kiln to the at least one of the first plurality of fluid-supply pipes, wherein said exhaust gas serves as the pipe-cooling gas;

- in the second step, the step of transferring comprises:

- extracting at least some of the exhaust gas from:

- an upper portion of the pre-heating zone of the first shaft or

- a pipe connected the upper portion of the first shaft, or

- extracting at least some of the exhaust gas flowing in an exhaust passage arranged downstream from the multi-shaft vertical kiln;

- at least a portion of the at the least one of the first or second plurality (optionally the third plurality) of supply pipes extends in a volume defined by the first or second shaft, respectively;

- wherein the least one of the first or second plurality (optionally the third plurality) of supply pipes comprises at least one outlet opening in the volume defined by the first or second shaft, respectively;

- feeding a buffer or a storage tank with the exhaust gas extracted from the multi-shaft vertical kiln, said buffer or storage tank being connectable to a CO2 purification unit which can be fed at any time with the exhaust gas;

- transferring at least some of the exhaust gas from the buffer or a storage tank, said exhaust gas serving as the pipe-cooling gas;

- boiling liquid CO2 stored in the storage tank to form recycled exhaust gas, the boiled CO2 serving as the pipe-cooling gas;

- feeding a buffer with at least some of the exhaust gas extracted from the multi-shaft vertical kiln, said buffer being connectable to a CO2 purification unit which can be fed at any time with the exhaust gas, preferably comprising transferring at least some of the exhaust gas from the buffer, said exhaust gas serving as the pipe-cooling gas;

- boiling liquid CO2 stored in the a storage tank to form recycled exhaust gas, preferably said tank being connected or connectable to the CO2 purification unit and/or another CO2 purification unit connected or connectable to the multi-shaft vertical kiln, the boiled CO2 serving as the pipe-cooling gas;

- in the first step supplying a combination of a water and the at least some of the exhaust gas, said combination serving as the pipe-cooling gas; - in a third step, subsequent to the first or second step, supplying with a water serving as the pipe-cooling gas the at least one of the second plurality of fluid-supply pipes, when the first shaft is in a combustion state and the second shaft is in a noncombustion state, in particular a regeneration state;

- supplying a water serving as the pipe-cooling gas;

- at least two elements in the list comprising:

- at least some of the exhaust gas alternately extracted in the upper portion of the first or second shaft,

- at least some of the exhaust gas extracted in the exhaust passage arranged downstream from the multi-shaft vertical kiln,

- at least some of the exhaust gas transferred from the buffer or a storage tank, and/or

- the water, serve as the pipe-cooling gas.

- mixing at least two elements in the list comprising:

- at least some of the exhaust gas alternately extracted in the upper portion of the first or second shaft,

- at least some of the exhaust gas extracted in the exhaust passage arranged downstream from the multi-shaft vertical kiln,

- at least some of the exhaust gas transferred from the buffer or a storage tank and

- the water, said mixture serving as the pipe-cooling gas.

- feeding the pipe-cooling gas in the at least one of the first and/or the second of plurality of fluid-supply pipes by means of a positive displacement fan or blower;

- feeding the cooling zone of at least the first and/or second (optionally the third) shaft(s) with at least one of the one or more cooling streams, and extracting the at least one of the one or more heated cooling streams at an upper portion of said cooling zone.

- recirculating at least some of the exhaust gas alternately exiting the second or the first shaft, to the first or second shaft, respectively, preferably by means of a positive displacement fan or blower;

- in the first step, supplying the at least one of the first plurality of fluid-supply pipes with at least some of exhaust gas exiting the second shaft;

- in the second step, supplying the at least one of the second plurality of fluid-supply pipes with at least some of exhaust gas exiting the first shaft; - in the first step, supplying an upper portion of the preheating zone of the first shaft with at least some of the exhaust gas exiting the second shaft;

- in the second step, supplying an upper portion of the preheating zone of the second shaft with at least some of the exhaust gas exiting the first shaft;

- in the first step, feeding the first shaft with the at least one fuel, the at least one comburent or the combination of them via an outlet of the at least one of the first plurality of fluid-supply pipes and feeding the second shaft with the pipe-cooling gas via an outlet of the at least one of the second plurality of fluid-supply pipes;

- in the second step feeding the second shaft with the at least one fuel, the at least one comburent or the combination of them via the outlet of the at least one of the second plurality of fluid-supply pipes and feeding the first shaft with the pipe-cooling gas via the outlet of the at least one of the first plurality of fluid-supply pipes.

[0025] For the above purpose, the invention is also directed to a multi-shaft vertical kiln comprising a first, a second, and optionally a third shaft with preheating zones, heating zones and cooling zones and a cross-over channel between each shaft, said kiln being arranged for being cooled with one or more cooling streams, said kiln being adapted for carrying out one of the above mentioned processes according to invention, said kiln comprising a first plurality of fluid-supply pipes opening in the first shaft, a second plurality of fluid-supply pipes opening in the second shaft and optionally a third plurality of fluidsupply pipes opening in the third shaft, wherein at least one of the first, second and third plurality of fluid-supply pipes comprises at least a portion extending in a volume defined by the first and second shaft respectively, characterized in that at least one source of a pipe-cooling gas comprising:

- at least 1% CO2 (dry volume), preferably at least 5% CO2 (dry volume), more preferably at least 25% CO2 (dry volume), in particular at least 50% CO2 (dry volume), and/or

- less than 79% N2 (dry volume), preferably less than 50% N2 (dry volume), more preferably less than 20% N2 (dry volume), in particular less than 10% N2 (dry volume), is provided, said source is in fluid communication with at least one of the first plurality of fluid-supply pipes and the second plurality of fluid-supply pipes, said source being adapted to supply said gas to the at least one of the first plurality of fluid-supply pipes and the second plurality of fluid-supply pipes.

[0026] Preferred embodiments of the multi-shaft vertical kiln disclose one or more of the following features:

- wherein the least one of the first or second plurality of supply pipes comprises at least one outlet opening in the volume defined by the first or second shaft, respectively; - the at least one source of a pipe-cooling gas comprises at least one element selected in the list: a first exhaust pipe, the first shaft, the second shaft, a buffer and storage tank, a condenser arranged in a second exhaust pipe.

[0027] For the above purpose, the invention is also directed to a decarbonation process of carbonated materials, in particular limestone and dolomitic limestone, preferably with CO2 recovery, in a multi-shaft vertical kiln comprising a first, a second, and optionally a third shaft with preheating zones, heating zones and cooling zones, a crossover channel between each shaft and a first plurality of fluid-supply pipes opening the first shaft, a second plurality of fluid-supply pipes opening in the second shaft and optionally a third plurality of fluid-supply pipes opening in the third shaft, alternately heating carbonated materials by a combustion of at least one fuel with at least one comburent, preferably said comburent comprising less than 70% N2, more preferably less than 50% of N2, in particular said comburent being oxygen-enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials is released, the combustion of the fuel and the decarbonatation generating an exhaust gas, the decarbonated materials being cooled in the cooling zones with one or more cooling streams, said process further comprising a first step of supplying with said fuel, said comburent or a combination of them, at least one of the first plurality of fluid-supply pipes while the supply of any fluid, such as the pipe-cooling gas in at least one of the second and/or third plurality of fluid-supply pipes is stopped, when the first shaft is in a combustion state and the second and/or third shaft is a non-combustion state, in particular a regeneration.

[0028] Preferred embodiments of the process disclose one or more of the following features:

- comprising a second step of subsequently supplying with the at least one fuel, the at least one comburent or a or the combination of them, the least one of the second plurality of fluid-supply pipes, while the supply of any fluid, such as the pipe-cooling gas in the at least one of the first and/or third plurality of fluid-supply pipes is stopped, when the second shaft is in a combustion state and the first and/or third shaft is a non-combustion state, in particular a regeneration, and optionally repeating the first and second steps;

- feeding the cooling zone of at least the first and/or second (optionally the third) shaft with at least one of the one or more cooling streams, and extracting the at least one of the one or more heated cooling streams at an upper portion of said cooling zone;

- recirculating at least some portion of the exhaust gas alternately exiting the second or the first shaft, to the first or second shaft, respectively, preferably by means of a positive displacement fan or blower;

- in the first step, supplying the at least one of the first plurality of fluid-supply pipes with at least some of exhaust gas exiting the second shaft;

- in the second step, supplying the at least one of the second plurality of fluid-supply pipes with at least some of exhaust gas exiting the first shaft;

- in the first step, supplying an upper portion of the preheating zone of the first shaft with at least some of the exhaust gas exiting the second shaft;

- in the second step, supplying an upper portion of the preheating zone of the second shaft with at least some of the exhaust gas exiting the first shaft.

[0029] For the above purpose, the invention is also directed to a multi-shaft vertical kiln comprising a first, a second, and optionally a third shaft with preheating zones, heating zones and cooling zones and a cross-over channel between each shaft, said kiln being arranged for being cooled with one or more cooling streams, said kiln being adapted for carrying out the process according to invention, said kiln comprising a first plurality of fluidsupply pipes opening in the first shaft, a second plurality of fluid-supply pipes opening in the second shaft and optionally a third plurality of fluid-supply pipes opening in the third shaft, wherein at least one of the first, second, and third plurality of fluid-supply pipes comprises at least a portion extending in a volume defined by the first, second and optionally third shaft respectively, characterized by :

- said at least a portion being made of a heat-resistant material selected from the group comprising ceramics or stainless steel, more preferably high alloy ferritic steel or austenitic stainless steel, in particular steel with at least 5% chromium, notably Inconel alloy; and/or

- said at least a portion comprising at least one cooling passage formed in or extending on a wall of said portion.

[0030] Preferred embodiments of the kiln disclose one or more of the following features:

- wherein the least one of the first or second plurality of supply pipes comprises at least one outlet opening in the volume defined by the first or second shaft, respectively;

- the at least one cooling passage opens in its shaft;

- the multi-shaft vertical kiln comprises a cooling circuit containing the at least one passage formed in or extending on the wall of the at least a portion of the at least one of the first and second plurality of fluid-supply pipes;

- the cooling circuit is not fluidly connected to the first and second shaft.

[0031] By “extracted .. gas or stream” is meant that the “.. gas or stream..” is transferred either by suction or expansion. Brief Description of Drawings

[0032] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features. Figures 1 to 9 show embodiments according to the invention.

List of reference symbols

Detailed description [0033] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. [0034] Figure 1 shows a multi-shaft vertical kiln (MSVK) according to a first embodiment of the present invention. The multi-shaft vertical kiln (MSVK) in Fig. 1 is based on a traditional parallel-flow regenerative kiln which is a specific case of multi-shaft vertical kiln. The multi-shaft vertical kiln, also designated kiln MSVK, comprises a first 100 and a second 200 shaft with preheating zones 110, 210, heating zones 120, 220 and cooling zones 130, 230, as well as a cross-over channel 412 arranged between the first 100 and second 200 shafts. In use, the carbonated materials 10 are introduced at an upper portion 111 , 211 of each shaft 100, 200. The carbonated materials 10 slowly move to the bottom. In the preheating zones 110, 210, the carbonated materials 10 are essentially preheated with the alternating regenerative exhaust gas 40. In the combustion zones 210, 220, the carbonated materials 10 are alternately heated by a combustion of fuel 20 with at least one comburent 30, 31 , 32 depleted in nitrogen, in particular oxygen- enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials 10 is released. Both the combustion of the fuel 20 with the at least one comburent 30, 31 , 32 and the decarbonatation generate the exhaust gas 40.

[0035] The present disclosure defines that the at least one comburent as an oxidizing agent such as either air, air enriched with oxygen (i.e. oxygen-enriched air) or substantially pure oxygen, alone or in combination with the exhaust gas 40 or substantially pure CO2. Preferably, the comburent is an oxygen-enriched air or substantially pure oxygen. One or more comburents are foreseen, in particular:

- a comburent 30, or

- a first 31 and a second comburent 32.

[0036] Figure 1 schematically shows a multi-shaft vertical kiln (MSVK) with three separate supply passages per shaft:

- a first passage 115, 215 is arranged at an upper portion of the multi-shaft vertical kiln (e.g. PFRK) traditionally supplying a (first) comburent 30, 31 (e.g. primary air supply). Even if Figure 1 shows one first supply passage (pipe), the multi-shaft vertical kiln (MSVK) may comprise more than one first supply passage per shaft 100, 200. The one or more first passage outlet openings are arranged in the corresponding shaft 100, 200. In the present disclosure, the comburent 30 or the first comburent 31 is preferably oxygen-enriched air or substantially pure oxygen.

- a second passage (e.g. fuel lance) 125, 225 is traditionally supplying fuel 20 (e.g. natural gas, oil) and optionally the second comburent 32 (e.g. air). Even if Figure 1 only shows one second supply passage, the multi-shaft vertical kiln comprises one or more second supply passage per shaft 100, 200, generally under the form of fuel/air lances (a.k.a. fluid-supply pipes). For instance, a mixture of fuel 20 and the second comburent 32 (e.g. coke with the conveying second comburent such as air) can be supplied through at least a part of the lances. Alternatively, a group of lances supplies the second comburent 32 (e.g. air) while another group of lances supplies the fuel 20 (natural gas or oil). In the present disclosure, the second comburent 32 is preferably oxygen-enriched air or substantially pure oxygen. Furthermore, at least some of the lances can be used to recycle the exhaust gas 40 in the shaft in combustion.

- a third passage 117, 217 is shown in Figure 1. Such a passage is traditionally not present on a multi-shaft vertical kiln (MSVK), in particular a parallel-flow regenerative kiln (PFRK). Said third passage is dedicated to the supply of the recycled exhaust gas 40. The present disclosure is not limited to a single third passage. Indeed, it can be foreseen that one or more third passages are in fluid connection with the corresponding shaft 100, 200.

[0037] In an alternative preferred form (shown schematically in a “window” arranged above the MSVK in Fig. 1), a downstream end of the third passage is connected to the first passage. The present disclosure is not limited to a single third passage connected to a single first passage. Indeed, it can be foreseen that one or more downstream ends of the third passage(s) are connected to one or more first passage(s). The one or more first passages can feed the corresponding shaft(s) 100, 200 with:

- a gas mixture comprising the recycled exhaust gas 40 and the first comburent 31 (e.g. oxygen-enriched air or substantially pure oxygen) according to the first preferred alternative, or

- the recycled exhaust gas 40 according to the second preferred alternative.

[0038] In the above-mentioned first preferred alternative, the fuel 20 (e.g. natural gas or oil, dihydrogen) is supplied via the one or more second passages.

[0039] In the above-mentioned second preferred alternative, the one or more second passages supply both the second comburent 32 (e.g. oxygen-enriched air or substantially pure oxygen) and the fuel 20 (e.g. natural gas, oil, coke or dihydrogen). For instance, a group of lances supply the second comburent 32 (e.g. oxygen-enriched air or substantially pure oxygen) while another group supplies the fuel 20 (e.g. natural gas, oil or dihydrogen). [0040] The first, second and third passages can be found in other embodiments of the present disclosure.

[0041] In Fig.1 , the decarbonated materials 50 formed after the release of the CO2 from the carbonated materials 10 are cooled in the cooling zones 130, 230 by an air stream 90.

[0042] The exhaust gas recirculated 40 replaces the combustion air. In order to keep the same amount of oxygen supplied, an oxygen-enriched comburent can be used. The exhaust gas recirculation allows to generate high CO2 concentration in the exhaust gas 40 compatible with CO2 flue gas storage.

[0043] Traditionally, the fuel-supply pipe(s) 225 are cooled with air during the regeneration phase, so as to preserve their integrity and prolong their operations. However, such a measure dilutes the exhaust gas 40 with air, in particular N2, lowering the CO2 concentration. It has been discovered that the fuel-supply pipes can be advantageously cooled with the recycled exhaust gas exiting the second shaft 200 as shown in Fig.1. The temperature of exhaust gas leaving the upper portion of the shaft 200 is sufficiently low to permit an efficient cooling of the fuel-supply pipe 225. The temperature of exhaust gas leaving the upper portion of the shaft 200 is relatively low, in particular in a range from 120° to 250°C because a significant portion of the sensible heat in the exhaust gas 40 is transferred to the decarbonated 10 in the pre-heating zone 210 of the second shaft 200.

[0044] Fig. 2 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 2 differs from that in Fig. 1 in that the heated cooling gas 90 is extracted at an upper portion 131 , 231 of the cooling zones 130, 230. This difference minimizes the mixing between the exhaust gas 40 and the air of the cooling stream 90. Owing to these measures, the exhaust gas 40 exits the MVSK kiln with a high content of CO2 of at least 45 % (dry volume), even 60% or more.

[0045] Fig. 3 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig.3 differs from that in Fig. 2 in that the one or more apertures (in Fig. 3, only one aperture is shown per shaft), through which the heated cooling stream 90 is extracted, are formed in a pipe assembly that is preferably centrally arranged in each shaft 100, 200. The one or more apertures are covered by a screen assembly preventing the intrusion of solid material into the cooling extraction system.

[0046] Fig. 4 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 4 differs from that in Fig. 2 in that the cooling gas stream 90 is supplied only in the shaft in combustion 100.

[0047] Fig. 5 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 5 differs from that in Fig. 2 in that a buffer 910 for collecting exhaust gas 40 is provided downstream from the multi-shaft vertical kiln (MSVK). Furthermore, a compressor 1400 fluidly arranged between the multi-shaft vertical kiln (MSVK) and the buffer 910 allow to pressurize the exhaust gas 40 and therefore to increase the mass of exhaust gas 40 that can be stored in the buffer 910.

[0048] The exhaust gas 40 extracted from the buffer 910 is preferably cooled in a first heat exchanger 700 arranged upstream from the compressor 1400 so that the power required to compress the exhaust gas 40 is reduced compared to a situation with no cooling.

[0049] The exhaust gas 40 extracted from the compressor 1400 is preferably cooled in a second heat exchanger 700’ arranged downstream from the compressor 1400 and upstream from the buffer 910 so as to improve the volumetric efficiency and therefore increase the amount of exhaust gas 40 stored in the buffer 910.

[0050] The exhaust gas 40 stored in the buffer 910 can be recirculated to the fuelsupply pipe 225 of the multi-shaft vertical kiln (MSVK) in regeneration as shown in Fig. 5, thereby cooling for the fuel-supply pipes 125, 225.

[0051] Fig. 6 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 6 differs from that in Fig. 5 in that a tank 920 is positioned downstream for the CO2 purification unit (CPU). The tank 920 is be provided to store a CO2 gas purified by the CO2 purification unit (CPU). In case of too low pressure in the buffer 910 (not enough pressure to insure the exhaust gas recirculation ), CO2 gases could be supplied by the storage tank 920 to the fuel-supply pipes 125, 225 in the shaft 100, 200 in regeneration as shown in Fig 6.

[0052] Fig. 7 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 7 differs from that in Fig. 2 in the provision of a condensation unit 700 arranged in the exhaust line. The condensation unit 700 allows to increase the concentration of CO2 by removing water steam. The water separated could be recycled and boiled for the cooling of the fuel-supply pipe(s) 125, 225 while the corresponding shaft 100, 200 is in regeneration. Alternatively or complementary, the water steam used for the cooling of the fuel-supply pipe(s) 125, 225 can originate from either from river water, rain water, industrial water, tap water, or a combination of them. As illustrated in Fig. 7, liquid water can be heated in a boiler 800 to form a steam stream before reaching the fuel supply pipes 125, 225. The supply of water steam in the shafts 100, 200 is an efficient way to cool the fuel-supply pipe(s) 125, 225 and to obtain CCh-rich exhaust gas 40 as water can be easily separated from the exhaust gas 40, for instance in a condensation unit (e.g. condenser). In another preferred embodiment, the water-steam stream can be mixed with recycled exhaust gas 40 before being fed in the fuel-supply pipes 125, 225 for their cooling. Likewise, at least some of the fuel-supply pipes 125, 225 can be supplied with a water steam while other are supplied with recycled exhaust gas 40.

[0053] Fig. 8 shows another embodiment according to the invention. The multi-shaft vertical kiln (MSVK) according to Fig. 8 differs from that in Fig. 2 in that the supply of the pipe-cooling gas is stopped in the shaft in regeneration. This measure also allows to avoid any dilution of the exhaust gas with air. The interruption can be intermittent and pursued as long as the expected temperature of the fuel-supply pipes 125, 225 is below a certain threshold.

[0054] If the interruption is maintained substantially over the entire duration of a combustion cycle, in particular between two kiln reversal phases, some structural modifications should be implemented such as the selection of heat-resistant materials for the fuel-supply pipes 125, 225, in particular ceramics or stainless steel, more preferably high alloy ferritic steel, austenitic stainless steel, in particular steel with at least 5% chromium, notably Inconel alloy. Alternatively or complementary, passages formed in or extending on a wall portion of the fuel-supply pipe 125, 225 could be provided. These passages are flown by a cooling fluid, such a liquid water. The circulation of the cooling circuit can be maintained continuously or intermittently. In case of intermittency, the circulation of the cooling circuit can be ensured for the fuel-supply pipes 125, 225 in a shaft in regeneration. These passages can form a cooling jacket and be connected to a cooling circuit typically comprising a pump and a cooling circuit cooler for cooling the cooling fluid in heat exchange with air or fuel, for instance as shown in Fig. 9. Preferably, a closed-loop cooling circuit can be selected or alternatively an open circuit with discharge openings arranged in the shaft 100, 200.

[0055] Advantageously, the at least one fuel 20 used in a MSVK kiln according to the invention, in particular in any of the previous embodiments, is either carbon-containing fuel or dihydrogen-containing fuel or a mixture of them. A typical fuel can be either wood, biomass, coal, peat, manure, coke, petcoke, charcoal, petroleum, diesel, gasoline, kerosene, LPG, coal tar, naphtha, ethanol, natural gas, hydrogen, propane, methane, coal gas, water gas, blast furnace gas, coke oven gas, CNG or any combination of them. Furthermore, the MSVK kiln can use, for instance, two sources of fuel with different compositions.

[0056] Advantageously, the decarbonated materials 50 produced in a MSVK kiln according to the invention, in particular in any of the previous embodiments, have a residual CO2 <5%, preferably <2%, resulting from the rapid cooling of the decarbonated materials 50.

[0057] Preferably, measures are undertaken to recover heat from the one or more cooling streams 90, and/or the recirculated exhaust gas 40.

[0058] Advantageously, the combustion of at least one fuel 20 with the at least one comburent 30 is under an oxygen-to-fuel equivalence ratio greater or equal to 0.9.

[0059] One or more of the at least one comburent comprise(s) less than 70% N2 (dry volume), in particular less than 50% of N2 (dry volume), in particular oxygen-enriched air. In particular, One or more of the at least one comburent used in the invention, are(is) a concentrated O2 source, for instance said comburent comprising at least 50% O2 (dry volume), preferably more that 80% O2 (dry volume).

[0060] The meaning of “substantially pure oxygen” in the present disclosure is an oxygen gas comprising at least 90 % (dry volume) dioxygen (i.e. O2), preferably at least 95% (dry volume) dioxygen(i.e. O2).

[0061] The meaning of “multi-shaft vertical kiln” in the present disclosure is a kiln comprising at least two shafts 100, 200. The shafts 100, 200 are not coaxial and are disposed side by side to the extent that any shaft of a group consisting of the first, second and optimally the third shaft 100, 200, 300 is not encircled by the other or another shaft 100, 200 of said group. In otherwords, the cross-over channel(s) 412 are arranged outside the shafts 100, 200. This definition excludes a annular-shaft kiln being interpreted as a multi-shaft vertical kiln. A parallel-flow regenerative kiln is a specific form of a multi-shaft vertical kiln in the present definition. The multi-shaft vertical kiln of the first to the fourteenth embodiment falls in the definition of a parallel-flow regenerative kiln (in German: “Gleich Gegenstrom Regernativ Oferi"). According to the invention, the term “vertical” in “multishaft vertical kiln” does not necessarily require that the longitudinal axes of the shafts 100, 200 have an exact vertical orientation. Rather, an exact vertical directional component of the alignment should be sufficient, with regard to an advantageous gravity-related transport of the material in the shafts, an angle between the actual alignment and the exact vertical alignment amounts to at most 30°, preferably at most 15°, and particularly preferably of 0° (exactly vertical alignment).

[0062] Each shaft 100, 200 of the multi-shaft vertical kiln comprises a preheating zone 110, 210, a heating zone 120, 220 and a cooling zone 130, 230. A cross-over channel 412 is disposed between each shaft 100, 200. According to the present disclosure, the junction between the heating zones 120, 220 and the cooling zones 130, 230 is substantially aligned with the lower end of the cross-over channel(s) 412.

[0063] The present disclosure presents a multi-shaft vertical kiln with two or three shafts. The present teaching applies to multi-shaft vertical kiln with four and more shafts. [0064] Embodiments of the present invention can be carried out according to one of the following clauses:

1. Decarbonation process of carbonated materials (10), in particular limestone and dolomitic limestone in a multi-shaft vertical kiln (MSVK) comprising a first (100), a second (200), and optionally a third shaft with preheating zones (110, 210), heating zones (120, 220) and cooling zones (130, 230), a cross-over channel (412) between each shaft (100, 200), a first plurality of (fluid-)supply pipes (125) opening in the first shaft (100) and a second plurality of fluid-supply pipes (225) opening in the second shaft (200), alternately heating carbonated materials (10) by a combustion of at least one fuel (20) with at least one comburent (30, 31 , 32), preferably said comburent comprising less than 70% N2 (dry volume), more preferably less than 50% of N2 (dry volume), in particular said comburent being oxygen-enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials (10) is released, the combustion of the fuel (20) and the decarbonatation generating an exhaust gas (40), the decarbonated materials (50) being cooled in the cooling zones (130, 230) with one or more cooling streams (90), said process further comprising a first step of supplying with said fuel (20), said comburent (30, 31 , 32) or a combination of them, at least one of the first plurality of fluid-supply pipes (125), while supplying with a pipe-cooling gas (93) at least one of the second plurality of fluid-supply pipes (225), when the first shaft (100) is in a combustion state and the second shaft (200) is in a non-combustion state, in particular a regeneration state, said pipe-cooling gas comprising :

- at least 1% CO2 (dry volume), preferably at least 5% CO2 (dry volume), more preferably at least 25% CO2 (dry volume), in particular at least 50% CO2 (dry volume), and/or

- less than 79% N2 (dry volume), notably less than 78% N2 (dry volume), preferably less than 50% N2 (dry volume), more preferably less than 20% N2 (dry volume), in particular less than 10% N2 (dry volume).

2. Process according to Clause 1 , further comprising a second step of subsequently supplying with the at least one fuel (20), the at least one comburent (30, 31 , 32) or a or the combination of them, the at least one of the second plurality of fluid-supply pipes (225), while supplying with the pipe-cooling gas (93) the at least one of the first plurality of fluid-supply pipes (125) when the second shaft (200) in a or the combustion state and the first shaft (100) is in a or the non-combustion state, in particular a or the regeneration state.

3. Process according to Clause 1 or 2, further comprising in the first step transferring at least some of the exhaust gas (40) generated in the multi-shaft vertical kiln (MSVK) to the at least one of the second plurality of fluid-supply pipes (225), wherein said exhaust gas (40) serves as the pipe-cooling gas (93), preferably cooling said exhaust gas (40) in a heat exchanger before being fed to the at least one of the second plurality of fluid-supply pipes (225).

4. Process according to the previous clause, wherein the step of transferring comprises:

- extracting at least some of the exhaust gas (40) from: - an upper portion of the preheating zone (210) of the second (200) shaft or

- a pipe connected the upper portion of the second (200) shaft, or

- extracting at least some of the exhaust gas (40) flowing in an exhaust passage arranged downstream from the multi-shaft vertical kiln (MSVK).

5. Process according to any of the previous clauses, further comprising feeding a buffer (910) or the storage tank (920) with at least some of the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK), said buffer or storage tank (920) being connectable to a CO2 purification unit (CPU) which can be fed at any time with the exhaust gas (40).

6. Process according to the previous clause, further comprising transferring at least some of the exhaust gas (40) from the buffer (910) or a storage tank (920), said exhaust gas (40) serving as the pipe-cooling gas (93).

7. Process according to Clause 5, comprising boiling liquid CO2 stored in the storage tank (920) to form recycled exhaust gas (40), the boiled CO2 serving as the pipecooling gas (93).

8. Process according to any of the previous clauses, further comprising supplying a water serving as the pipe-cooling gas (93).

9. Process according to any of the preceding clauses, comprising feeding the pipe-cooling gas (93) in the at least one of the first (125) and/or the second (225) of plurality of fluid-supply pipes by means of a positive displacement fan or blower.

10. Process according to any of the preceding clauses, further comprising in the first step feeding the first shaft (100) with the at least one fuel (20), the at least one comburent (30, 31 , 32) or the combination of them via an outlet of the at least one of the first plurality of fluid-supply pipes (125) and feeding the second shaft (200) with the pipecooling gas (93) via an outlet of the at least one of the second plurality of fluid-supply pipes (225).

11. Process according to any of the preceding clauses, further comprising in the second step feeding the second shaft (200) with the at least one fuel (20), the at least one comburent (30, 31 , 32) or the combination of them via the outlet of the at least one of the second plurality of fluid-supply pipes (225) and feeding the first shaft (100) with the pipecooling gas (93) via the outlet of the at least one of the first plurality of fluid-supply pipes (125).

12. Decarbonation process of carbonated materials (10), in particular limestone and dolomitic limestone, preferably with CO2 recovery, in a multi-shaft vertical kiln (MSVK) comprising a first (100), a second (200), and optionally a third shaft with preheating zones (110, 210), heating zones (120, 220) and cooling zones (130, 230), a cross-over (412) channel between each shaft (100, 200), a first plurality of (fluid-)supply pipes (125) opening the first shaft (100) and a second plurality of fluid-supply pipes opening in the second shaft (200), alternately heating carbonated materials (10) by a combustion of at least one fuel (20) with at least one comburent (30, 31 , 32), preferably said comburent comprising less than 70% N2 (dry volume), more preferably less than 50% of N2 (dry volume), in particular said comburent being oxygen-enriched air or substantially pure oxygen, up to a temperature range in which carbon dioxide of the carbonated materials (10) is released, the combustion of the fuel (20) and the decarbonatation generating an exhaust gas (40), the decarbonated materials (50) being cooled in the cooling zones (130, 230) with one or more cooling streams (90), said process further comprising a first step of supplying with said fuel (20), said comburent (30, 31 , 32) or a combination of them, at least one of the first plurality of fluid-supply pipes (125), while the supply of any fluid, such as a pipe-cooling gas (93) in at least one of the second plurality of fluid-supply pipes (225) is stopped, when the first shaft is in combustion state and the second shaft (200) is a non-combustion state, in particular a regeneration.

13. Process according to clause 12, further comprising a second step of subsequently supplying with the at least one fuel (20), the at least one comburent (30, 31 , 32) or a or the combination of them, the least one of the second plurality of fluid-supply pipes (225), while the supply of any fluid, such as the pipe-cooling gas (93) in the at least one of the first plurality of fluid-supply pipes (125) is stopped, when the second shaft (200) is in a or the combustion state and the first shaft (100) is a or the non-combustion state, in particular a or the regeneration.

14. Process according to any of the preceding clauses, further comprising feeding the cooling zone (130, 230) of at least the first (100) and/or second shaft (200) with at least one of the one or more cooling streams (90), and extracting the at least one of the one or more heated cooling streams (90) at an upper portion (131 , 231) of said cooling zone (130, 230).

15. Process according to any of the preceding clauses, comprising recirculating at least some of the exhaust gas (40) alternately exiting the second (200) or the first (100) shaft, to the first (100) or second (200) shaft, respectively, preferably by means of a positive displacement fan or blower.

16. Process according to any of the preceding clauses, further comprising in the first step supplying the at least one of the first plurality of fluid-supply pipes (125) with at least some of the exhaust gas (40) exiting the second (200) shaft.

17. Process according to any of Clauses 1 to 15, further comprising in the first step not supplying the at least one or another of the first plurality of fluid-supply pipes (125) with at least some of the exhaust gas (40) exiting the second (200) shaft.

18. Process according to any of the preceding clauses, further comprising in the first step supplying the upper portion (111) of the preheating zone (110) of the first (100) shaft with at least some of the exhaust gas (40) exiting the second (200) shaft.

19. Multi-shaft vertical kiln (MSVK) comprising a first (100), a second (200), and optionally a third shaft with preheating zones (110), heating zones (120, 220) and cooling zones (130, 230) and a cross-over (412) channel between each shaft (100), said kiln (MSVK) being arranged for being cooled with one or more cooling streams (90), said kiln (MSVK) being adapted for carrying out the process according to any of the preceding clauses, in particular any of the preceding Clauses 12 to 18, said kiln (MSVK) comprising a first plurality of fluid-supply pipes (125) opening in the first shaft (100) and a second plurality of fluid-supply pipes (225) opening in the second shaft (200), wherein at least one of the first and second plurality of fluid-supply pipes (125, 225) comprises at least a portion extending in a volume defined in the first (100) and second (200) shaft respectively, preferably characterized by:

- said at least a portion being made of a heat-resistant material selected from the group comprising ceramics or stainless steel, more preferably high alloy ferritic steel or austenitic stainless steel, in particular steel with at least 5% chromium, notably Inconel alloy, and/or

- said at least a portion comprising at least one cooling passage formed in or extending on a wall portion of said portion.

20. Multi-shaft vertical kiln (MSVK) according to the previous clause, wherein the multi-shaft vertical kiln (MSVK) comprises a cooling circuit containing the at least one cooling passage formed in or extending on the wall of the at least a portion of the at least one of the first and second plurality of fluid-supply pipes (125, 225).