DECARBONATION PROCESS OF CARBONATED MATERIALS IN A MULTI-SHAFT VERTICAL KILN

Abstract

The present disclosure relates to a decarbonation process of carbonated materials, in particular limestone and dolomitic limestone, with CO.sub.2 recovery in a multi-shaft vertical kiln (MSVK) comprising a first and a second shaft with preheating, heating and cooling zones and a cross-over channel between each shaft. The method includes alternately heating carbonated materials by a combustion of at least one fuel with at least one comburent, up to a temperature range in which carbon dioxide of the carbonated materials is released, the combustion of the fuel and the decarbonation generating an exhaust gas. Decarbonated materials are cooled in the cooling zones with one or more cooling streams. The process further includes extracting the exhaust gas from the multi-shaft vertical kiln and feeding a buffer with the extracted exhaust gas.

Claims

1. A decarbonation process of carbonated materials (10) with CO.sub.2 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) and a cross-over (412) channel between each shaft (100, 200), the process comprising: alternately heating carbonated materials (10) by a combustion of at least one fuel (20) with at least one comburent (30, 31, 32), the comburent comprising less than 70% N.sub.2 (dry volume) of N.sub.2, the 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, generating an exhaust gas (40) from the combustion of the fuel (20) and the decarbonation, cooling the decarbonated materials (50) in the cooling zones (130, 230) with one or more cooling streams (90), the streams (90) comprising at least 10% N.sub.2 (dry volume), and/or the streams (90) comprising at least 30% water (dry volume), and extracting the exhaust gas (40) from the multi-shaft vertical kiln (MSVK) and feeding a buffer (910) with said extracted exhaust gas (40), the buffer (910) being connectable to a CO.sub.2 purification unit (CPU) which can be fed at any time and/or or continuously with the exhaust gas (40), wherein the buffer (910) has a constant or variable storage volume.

2. The process of claim 1, further comprising pressurizing the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before being fed to the buffer (910) using one or more compressors (1400), to a level comprised in the range 0.5 to 40 bars above the atmospheric pressure in case the buffer (910) has a constant volume.

3. The process of claim 1, further comprising pressurizing the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before being fed to the buffer (910) using one or more compressors (1400), to a level comprised in the range of 0.1 to 500 mbars above the atmospheric pressure, via the displacement of at least one wall section of the buffer (910) in case the buffer (910) has a variable volume.

4. The process of claim 1, further comprising cooling the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before entering the buffer (910), upstream and/or downstream from the one or more compressors (1400), in at least one heat exchanger, preferably cooled by air and/or water.

5. The process of claim 1, further comprising transferring the exhaust gas (40) from the buffer (910) to the CO.sub.2 purification unit (CPU) at least during a combustion cycle, a reversal and/or a non-combustion phase in all shafts (100, 200).

6. The process of claim 1, further comprising extracting a portion of the exhaust gas (40) from the buffer (910) and recycling said exhaust gas (40) to one of the first (100), second (200) or third shaft, said shaft (100, 200) being in combustion.

7. The process of claim 1, further comprising controlling a flow of at least one of the portion of the exhaust gas (40) extracted from the buffer (910) and/or the exhaust gas (40) transferred to the CO.sub.2 purification unit (CPU).

8. The process of claim 1, further comprising pressurizing the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before being fed to the buffer (910) using one or more compressors (1400), to a level above the atmospheric pressure in case the buffer (910) has a constant volume; controlling a flow of at least one of the portion of the exhaust gas (40) extracted from the buffer (910) and/or the exhaust gas (40) transferred to the CO.sub.2 purification unit (CPU); and recovering energy from the flow of at least one of the portion of exhaust gas (40) extracted from the buffer (910) and/or the exhaust gas (40) transferred to the CO.sub.2 purification unit (CPU), expanding during the flow control.

9. The process of claim 1, further comprising pressurizing the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before being fed to the buffer (910) using one or more compressors (1400), to a level above the atmospheric pressure, via the displacement of at least one wall section of the buffer (910) in case the buffer (910) has a variable volume; controlling a flow of at least one of the portion of the exhaust gas (40) extracted from the buffer (910) and/or the exhaust gas (40) transferred to the CO.sub.2 purification unit (CPU); and compressing the flow of at least one of the portion of exhaust gas (40) extracted from the buffer (910) and/or the exhaust gas (40) transferred to the CO.sub.2 purification unit (CPU) during the flow control.

10. The process of claim 1, wherein a mixing between the exhaust gas (40) and the one or more cooling streams (90) is minimized by feeding the cooling zone (130, 230) of at least one of the first, the second and/or the third shaft with at least one of the cooling streams (90), and extracting the at least one of the heated cooling streams (90) at an upper portion (131, 231) of said cooling zone (130, 230).

11. The process of claim 1, wherein a mixing between the exhaust gas (40) and the one or more cooling streams (90) is minimized by operating said kiln (MSVK) in a mode in which between two subsequent alternating heating cycles between the first (100) and the second (200) or the third (300) shaft, the decarbonated materials (50) in at least the first (100), the second (200) and/or the third shaft are cooled with the one or more cooling streams (90) while a supply of the fuel (20) in each shaft (100, 200, 300) is stopped.

12. The process of claim 1, further comprising feeding the cooling zone (130, 230), of at least one of the first, the second and/or the third shaft with the one or more cooling streams (90) and extracting the one or more heated cooling streams (90) at least at an upper portion (131, 231) of said cooling zone (130, 230) and/or from the (412) or at least one of the cross-over channels (412), reinjecting at least some of the one or more heated cooling streams at a lower portion (112, 212) of the preheating zone (110, 210) of at least one of the first (100) and/or the second (200) shaft while a supply of the fuel (20) in each shaft (100, 200) is stopped.

13. The process of claim 12, wherein the feeding of the one or more cooling streams (90) in the first (100), the second (200) or third (300) shaft is stopped, during the two subsequent alternating heating cycles.

14. The process of claim 13, wherein the mass flow of the one or more cooling streams (90) supplied, is set up so that it represents at least 90% of the maximal mass flow of the one or more cooling streams (90), said maximal mass flow corresponding to the maximal pressure that any of the shafts (100, 200) is capable to sustain, the pressure is comprised in the range 300 to 600 mbars over the atmospheric pressure.

15. The process of claim 1, further comprising draining water condensate formed in the buffer (910).

16. The process of claim 1, further comprising filtering the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK) before being fed to the buffer (910) using a dust filter (1600).

17. The process of claim 1, said cooling streams (90) consisting in air, water steam or a mixture thereof.

18. The process of claim 1, further comprising performing switching from a given combustion cycle in the first shaft (100) to a subsequent combustion cycle in the second shaft (200) in less than 1 minute.

19. The process of claim 1, comprising feeding the carbonated materials (10) into and/or discharging the decarbonated materials (50) from at least one of the first, second and/or third shaft (100, 200), via a feeding and/or discharging system (1100, 1200), respectively, each system (1100, 1200) comprising a lock chamber delimited by an upstream valve assembly and a downstream valve assembly, said feeding or discharging system (1100, 1200) being configured to collect the carbonated (10) or decarbonated materials (50), respectively, while the upstream valve assembly is open and the downstream valve assembly is closed, to store in a substantially gas tight manner the carbonated (10) or decarbonated materials (50), respectively, while both the upstream and downstream valve assemblies are closed, and to release the carbonated (10) or decarbonated materials (50), respectively, while the upstream valve assembly is closed and the downstream valve assembly is open.

20. The process of claim 1, comprising feeding a storage tank (920) with the exhaust gas (40) extracted from the multi-shaft vertical kiln (MSVK), said storage tank (920) being connected to a CO.sub.2 purification unit (CPU) which can be fed at any time with the exhaust gas (40).

21. The process of claim 1, comprising boiling liquid CO.sub.2 stored in the storage tank (920) to form recycled exhaust gas (40) and transferring said gas (40) to the multi-shaft vertical kiln (MSVK).

22. The process of claim 1, comprising transferring the CO.sub.2 from the storage tank (920) to the buffer (910).

23-25. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Aspects of the present disclosure will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features.

[0050] FIGS. 1 to 9 show embodiments according to the present disclosure.

LIST OF REFERENCE SYMBOLS

[0051] MSVK multi-shaft vertical kiln [0052] CPU CO.sub.2 purification unit [0053] 10 carbonated materials [0054] 14 exhaust gas from combustion chamber 600 [0055] 20 Fuel [0056] 30,31,32 Comburent [0057] 40 exhaust gas (from fuel+decarbonation) [0058] 50 decarbonated materials [0059] 90 cooling streams: at least air and/or CO.sub.2 and/or water steam [0060] 100,200 1st, 2nd shafts [0061] 110,210 preheating zones [0062] 111,211 upper end of preheating zones [0063] 120,220 heating zones [0064] 130,230 cooling zones [0065] 131,231 upper end of cooling zone [0066] 132,232 lower end of cooling zone [0067] 412 cross over channel [0068] 700, 700 Heat exchanger (e.g. condensation unit) [0069] 910 Buffer [0070] 920 Tank [0071] 1100 Feeding system for the carbonated material feeding [0072] 1200 Discharge system for the decarbonated material discharge [0073] 1300 Discharge table [0074] 1400 Compressor [0075] 1500, 1500 Flow control device (e.g. throttle valve, pump-turbine, turbine, compressor) [0076] 1600 Dust filter [0077] 1700 Exhaust gas passage collecting system

DETAILED DESCRIPTION

[0078] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present disclosure 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.

[0079] FIG. 1 shows a multi-shaft vertical kiln MSVK according to a first embodiment of the present disclosure. 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, preferably 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 decarbonation generate the exhaust gas 40.

[0080] 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 CO.sub.2. Preferably, the comburent is an oxygen-enriched air or substantially pure oxygen. One or more comburents are foreseen, in particular: [0081] a comburent 30, or [0082] a first 31 and a second comburent 32.

[0083] FIG. 1 schematically shows a multi-shaft vertical shaft MSVK with three separate supply passages per shaft: [0084] a first passage 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 FIG. 1 shows one first supply passage, 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. [0085] a second passage (e.g. fuel lance) is traditionally supplying fuel 20 (e.g. natural gas, oil) and optionally the second comburent 32 (e.g. air). Even if FIG. 1 shows only 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. 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 some of the lances can be used to recycle the exhaust gas 40 in the shaft in combustion. [0086] a third passage is shown in FIG. 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.
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 passages. The one or more first passages can feed the corresponding shaft 100, 200 with: [0087] 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 [0088] the recycled exhaust gas 40 according to the second preferred alternative.

[0089] 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.

[0090] 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).

[0091] The first, second and third passages can be found in other embodiments of the present disclosure.

[0092] In FIG. 1, the decarbonated materials 50 formed after the release of the CO.sub.2 from the carbonated materials 10 are cooled in the cooling zones 130, 230 by an air stream 90.

[0093] 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 CO.sub.2 concentration in the exhaust gas 40 compatible with CO.sub.2 flue gas storage.

[0094] In order to minimize the flow intermittency, a buffer 910 is provided downstream from the multi-shaft vertical kiln MSVK. The exhaust gas 40 can be accumulated in the buffer 910 during the combustion phases, in order to have enough quantity of gases to continuously feed the post-combustion system, in particular the CO.sub.2 purification unit CPU during reversal or non-combustion phases. The buffer 910 in FIG. 1 presents a constant volume, knowing that the dimensions in the drawing are not limiting and present for illustrating purposes.

[0095] The multi-shaft vertical kiln MSVK according to FIG. 2 differs from that in FIG. 1 in that the heated cooling gas 90 are 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 kiln MVSK with a high content of CO.sub.2 of at least 45% (dry volume), even 60% or more.

[0096] FIG. 3 shows a multi-shaft vertical kiln MSVK according to a third embodiment of the present disclosure. The third embodiment differs from the second embodiment in that a dust filter 1600, a flow control device 1500 and two heat exchanger 700, 700 are illustrated/

[0097] In FIG. 3, the compressor 1400 fluidly arranged between the multi-shat 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, whose volume is constant and in some application restricted because of space available. The buffer 910 ensures that the CO.sub.2 purification unit CPU can be fed at any time with the exhaust gas 40. The CO.sub.2 purification unit CPU is configured to remove at least one of the following elements: acid gases, O2, Ar, CO, H2O, NOx, sulfur compounds, heavy metals, in particular Hg, Cd, and/or organic compounds, in particular CH4, benzene, hydrocarbons. Preferably, the CO2 purification unit CPU is adapted to adjust the composition of the exhaust gas 40 to the specification required by a carbon capture and utilization or carbon capture and storage application, preferably with a CO.sub.2 content above 80% (dry volume) and more preferably above 95% (dry volume).

[0098] 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.

[0099] 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.

[0100] Advantageously, flaps (not shown) can be provided upstream from an inlet of the buffer 910 and downstream for one or more outlets of the buffer 910 so as to restrain depressurization in particular when the compressor 1400 is not pumping.

[0101] The buffer 910 can be provided with a drain system to remove water condensates, as the exhaust gas 40 is cooled.

[0102] The exhaust gas 40 stored in the buffer 910 can be recirculated to the multi-shaft vertical kiln MSVK in the fourth embodiment as shown in FIG. 4, as a complement to the recirculation of exhaust gas extracted directly from the shaft in regeneration as illustrated in the previous embodiment. Alternatively, the exhaust gas 40 stored in the buffer 910 can be recirculated to the multi-shaft vertical kiln MSVK without recirculation of exhaust gas extracted directly from the shaft in regeneration as illustrated in the previous embodiment. This alternative is not illustrated.

[0103] FIG. 4 shows two flow control devices 1500, 1500. A flow control device 1500 is positioned between the buffer 910 and the CO.sub.2 purification unit CPU and another 1500 positioned between the buffer 910 and the multi-shaft vertical kiln ensuring the exhaust gas recirculation to the shaft in combustion. The two flow control devices 1500, 1500 shown in FIG. 5 comprise one element selected in the list comprising a throttle valve, a pump-turbine, a turbine, a compressor or any combination thereof. Such a compressor, pump-turbine or turbine can be a fan with/without a fixed distributor/diffusor alone or coupled to a variable distributor and/or diffusor. In a preferred embodiment, the pump-turbine(s) and/or turbine(s) selected are mechanically connected to at least one electric motor-generator(s) and/or electric generator(s) allowing electrical power recovering using pressure difference between the buffer 910 and the multi-shaft vertical kiln, thereby producing regenerative current.

[0104] The fifth embodiment according to FIG. 5 shows that the exhaust gas 40 stored in the buffer 910 can also be recirculated to some of the lances of the shaft that is in combustion as a complement of supplying the recirculated exhaust gas via the upper portion 111, 211 of the preheating zone 110, 210 as shown in any of FIG. 1 to 4.

[0105] An typical amount of exhaust gas 40 stored in the buffer 910 necessary for a continuous supply of the CO.sub.2 purification unit CPU can be reduced if the multi-shaft vertical kiln MSVK is operated in such a manner that the occurrences and/or the duration phases, in which no or a limited amount of exhaust gas 40 is extracted, are reduced. This can be performed using one or more of the following measures: [0106] ensuring short reversals and/or short non-combustion phases, [0107] providing double flaps to load stone and discharge the lime during combustion or cooling cycle (without kiln depressurization), as shown in FIG. 6; [0108] preventing kiln depressurizing during reversal; [0109] boosting of cooling air flow when cooling is performed without combustion, as shown in FIG. 8; [0110] increasing allowable pressure in buffer 910; and/or [0111] shortening kiln cycle duration.

[0112] FIG. 6 shows a sixth embodiment according to the present disclosure, which differs from the embodiment in FIG. 2 in that the MSVK comprises feeding and discharging systems 1100, 1200, respectively, for the feeding of carbonated materials 10 and the discharge of the decarbonated material 50, in order to minimize the idle time between cycles (reversal time) and to reduce or even eliminate the need for exhaust gas buffering before the CO2 purification unit (CPU). The feeding and discharge systems 1100, 1200, with for instance an upstream gas-tight flap valve and a downstream gas-tight flap valve can be integrated to anyone of the previously mentioned embodiment. A lock chamber of the feeding 1100 or discharging system 1200 is delimited by the upstream gas-tight flap valve and a downstream gas-tight flap valve. The lock chamber presents a working volume adapted to store the material batches to be fed into or discharged from the corresponding shaft 100, 200. By gas tight, is meant a valve assembly that substantially limits the gas exchanges to as to ensure an efficient usage of the MSVK and to minimize combustion gas leakage into the atmosphere. The MSVK in FIG. 6 can ensure short reversals, for instance less than 1 minute, in particular in less than 30 seconds.

[0113] A multi-shaft vertical kiln MSVK according to the seventh embodiment according to FIG. 7 differs from the fourth embodiment in that a tank 920 is positioned downstream for the CO.sub.2 purification unit CPU. The tank 920 is be provided to store a CO.sub.2 gas purified by the CO.sub.2 purification unit CPU. In case of too low pressure in the buffer 910 (not enough pressure to insure the exhaust gas recirculation), CO.sub.2 gases could be supplied by the storage tank 920 to the multi-shaft vertical kiln MSVK as shown in FIG. 7. Furthermore, the buffer 910 can be directly supplied with CO.sub.2 stored in the storage tank 920. With this measure, any pressure loss in the buffer 910 can be rapidly compensated.

[0114] FIG. 8 shows a eight embodiment of a multi-shaft vertical kiln MSVK. Contrary to any of the previous embodiments, this embodiment differs from a traditional parallel-flow regenerative kiln PFRK in that the control of the kiln leads to a CO.sub.2-enriched exhaust gas besides structural modifications. For instance, the control of the opening or closing of the valves (e.g. louvers) as well as the activation of the blowers are set up so that the contacts of combustion flows and cooling flows are minimized. This embodiment is characterized in that between two subsequent, alternating heating cycles between the first 100 and the second 200 shafts, the decarbonated materials 50 in at least the first 100 and/or the second 200 shaft are cooled with a cooling stream 90, in particular air, while a supply of the fuel 20 and optionally the at least one comburent 30, 31 in each shaft 100, 200 is stopped. This operation mode is also named intermittent flush. Generally, this embodiment requires few modifications to an existing parallel-flow regenerative PFRK to operate. The modifications may comprise for instance the provision of an oxygen-enriched comburent and new software. Starting from a MSVK, this embodiment is therefore practical to implement. Nevertheless, this embodiment may require further hardware modifications as show in FIG. 8 such as the provision of collecting rings arranged at the lower portion of the preheating zones 112, 212 and passages connecting said rings to the cross over channel 412. This way of operating the MSVK in which the cooling steams 90 and the exhaust gas stream are separated in the time allows to generate exhaust gas with a high CO.sub.2 content, as the previous embodiments relying on physical separation between cooling steams 90 and the exhaust gas stream do.

[0115] In this embodiment, the control of the MVSK can comprise the following sequential cycles:

[0116] Cycle 1 comprises feeding the first shaft 100 with fuel 20, at least one comburent 30, 31, 32 (e.g. air, air enriched with oxygen or substantially pure oxygen) and the recycled exhaust gas 40 from the second shaft 200, while transferring the generated exhaust gas 40 to the second shaft 200 via the cross-over channel 412: H1R2 (heating shaft 1, regeneration shaft 2).

[0117] Cycle 2 comprises feeding the second 200 shaft with a cooling stream 90 at the lower portion 232 of its cooling zone while extracting the heated cooling stream 90 (e.g. air) in the cross over channel 412 and reinjecting the heated cooling stream 90 in the lower portion 212 of the preheating zone of the second shaft 200, by means of a collecting ring: C1-2 (cooling shaft 2).

[0118] Cycle 3 comprises feeding the second shaft 200 with the fuel 20, the at least one comburent 30, 31, 32 (e.g. air, air enriched with O.sub.2 (i.e. oxygen-enriched air) or substantially pure oxygen) and the recycled exhaust gas 40 from the first shaft 100, while transferring the generated exhaust gas 40 to the first shaft 200 via the cross-over channel 412: R1H2 (heating shaft 1, regeneration shaft 2)

[0119] Cycle 4 comprises feeding at least the first 100 shaft with the cooling stream 90 at the lower portion 132 of its cooling zone while extracting the heated cooling stream 90 in the cross over channel 412 and reinjecting the heated cooling stream 90 in the lower portion 212 of the preheating zone of the first shaft 100, by means of a collecting ring: C1-2 (cooling shaft 1).

[0120] Even if FIG. 8 shows that only one shaft is flushed per cooling cycle, in an alternative, both shaft can be flushed simultaneously (C1-2) to reduce the cooling phase duration.

[0121] The above mentioned sequence can be described as H1R2, C2, R1H2, C1, . . . , H1R2, C2, R1H2, C1. The eight embodiment is not limited to this sequence and can follow various patterns that can be adjusted depending on the circumstances such as H1R2, C1-2, R1H2, C2, C1-2, C2, R1H1, C1, R1H2, . . . .

[0122] The embodiment in FIG. 8 shows that the intermittency is not limited to the reversal phase as the cooling phase is not concomitant with the combustion phase. As, there is no exhaust gas 40 generated by combustion during the cooling phases, the buffer 910 ensures a continuous supply of exhaust gas 40 even if no combustion takes place in the multi-shaft vertical kiln MSVK.

[0123] FIG. 9 shows an ninth embodiment that differs from the third embodiment in that the multi-shaft vertical kiln MSVK comprises a variable volume reservoir such as a bellow arranged inside a receptacle. The pressure exerted on the bellow is controlled, in particular in a range of 0.1 to 500 mbars, preferably 0.1 to 100 mbars above atmospheric pressure so that the variable volume of the bellow expands or contracts depending on the amount of exhaust gas 40 stored therein. A variable volume reservoir suitable for the present disclosure is not limited to a bellow and can comprise for instance a bladder reservoir or equivalent. The cooling of the exhaust gas 40 allows to have thermal conditions compatible with elastomeric elastic membrane used for certain type of variable volume reservoir (e.g. bladder or below reservoir).

[0124] The control of the pressure within the gas storing variable chamber can be passively controlled to the extent that the variable volume is a function of the elastic properties of a gas containing element comprised in the list: a membrane, bladder, bellow, one or more resilient means acting on at least one slidable wall of the chambre, or any combination thereof. Equally, the pressure exerted on the gas containing element also influences said element. But, in a passive control, the pressure, such as atmospheric pressure would not be controlled.

[0125] Alternatively, the control of the pressure within the gas storing variable chamber can be actively controlled to the extent that at least one actuator influences the displacement of at least a portion of the gas containing element. Equally the pressure exerted on the gas containing element can be controlled as illustrated in FIG. 9.

[0126] Complementary or alternatively to any of the previous embodiment, at least one air separation unit ASU is provided in the proximity of the MSVK and optionally one or more additional kilns. The one or more ASU generate an Oxygen-enriched composition that can be fed in the MSVK and optionally in at least one another kiln as comburent 30, 31, 32. An ASU also produces a Nitrogen-enriched composition that can be released in the atmosphere.

[0127] Typically, an ASU produces both an Oxygen-enriched composition comprising at least 70% (dry volume) O.sub.2, preferably at least 90% (dry volume), in particular at least 95% and a Nitrogen-enriched composition comprising at least 80% (dry volume) N.sub.2 preferably at least 90% (dry volume), particular at least 95% (dry volume) and less than 19% (dry volume) O.sub.2, preferably less than 15% (dry volume), in particular less than 10% (dry volume).

[0128] Preferably, the comburent 30, 31, 32 fed in the MSVK comprises at least 40% (dry volume), preferably at least 70% (dry volume), in particular at least 90% (dry volume), in particular at least 95% (dry volume) of the Oxygen-enriched composition.

[0129] The Nitrogen-enriched composition can be advantageously used to cool the MSVK during the heating cycles. Indeed, on one hand, the supply of comburent 30, 31, 32 fed in the pre-heating 110, 210 and combustions 120, 220 zones is adjusted so that a near stoichiometric combustion is achieved in the MSVK in the combustion zones 120, 220 of the MSVK, on the other, the cooling stream 90 comprising at least 80% (dry volume), preferably at least 90% (dry volume), in particular at least 95% (dry volume) of said Nitrogen-enriched composition is expected to dilute the exhaust gas 40. The amount of residual Oxygen present in the nitrogen-enriched composition is however sufficiently low to the extent that it dilutes the exhaust gas 40 without changing significantly the overall stoichiometric balance. A reduction in the amount of Oxygen introduced via the cooling stream 90 will improve the purification efficiency of the CPU.

[0130] Advantageously, the at least one fuel 20 used in a kiln MSVK according to the present disclosure, 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, coal, peat, dung, coke, 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 kiln MVSK can use, for instance, two sources of fuel with different compositions.

[0131] Advantageously, the decarbonated materials 50 produced in a kiln MSVK according to the present disclosure, in particular in any of the previous embodiments have a residual CO.sub.2<5%, preferably <2%, resulting from the rapid cooling of the decarbonated materials 50.

[0132] Preferably, measures are undertaken to recover heat from the one or more cooling streams 90, and/or the recirculated exhaust gas 40.

[0133] 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.

[0134] The comburent comprises less than 70% N.sub.2 (dry volume), in particular less than 50% of N.sub.2 (dry volume), in particular oxygen-enriched air. In particular, the comburent used in the present disclosure, is a mixture of air with a substantially pure oxygen, the comburent comprising at least 50% O2 (dry volume), preferably more that 80% O.sub.2 (dry volume).

[0135] The meaning of substantially pure oxygen in the present disclosure is an oxygen gas comprising at least 90% (dry volume) dioxygen (i.e. O.sub.2), preferably at least 95% (dry volume) dioxygen (i.e. O.sub.2).

[0136] The meaning of multi vertical-shaft 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 is not encircled by the other or another shaft 100, 200 of said group. In other words, the cross-over channel(s) 412 are arranged outside the shafts 100, 200. This definition excludes an annular-shaft kiln being interpreted as a multi vertical-shaft kiln. A parallel-flow regenerative kiln is a specific form of a multi vertical-shaft kiln in the present definition. The multi vertical-shaft kiln of the first to the fourteenth embodiment falls in the definition of a parallel-flow regenerative kiln (in German: Gleich Gegenstrom Regernativ Ofen). According to the present disclosure, the term vertical in multi vertical-shaft 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).

[0137] 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.

[0138] 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.