Calcination KILN plant with a carbon capture unit

Abstract

Calcination kiln plant with a carbon capture unit (6) (CC) comprising a calcination kiln (1) having a flue gas (FG) exit, a carbon capture pathway (7) with said carbon capture unit (6) and a FG compressor (12) for feeding said FG to said CC, said CC being connected to said FG compressor, and having a treated FG exit through which a treated FG (13) exit, and a CO2 exit through with a CO2-rich stream (14) is collected and one or more mass transfer loops (16,17), feeding a gaseous stream to said FG compressor (12) of the carbon capture pathway (7).

Description

[0001]CALCINATION KILN PLANT WITH A CARBON CAPTURE UNIT The present invention relates to a calcination kiln plant with a carbon capture unit. Industrial calcination kilns, especially cement kilns and lime kilns, typically require the combustion of fuel to reach the high temperatures required for calcination. The calcination process itself can entail the release of carbon dioxide from the raw material. Together with the burning of fossil or biogenic fuels, calcination processes thus tend to have a high carbon intensity. The following introduction will be given taking limestone calcination as an example, without being limited thereto. The production of lime is one of the most carbon intensive processes, with average direct emissions of 1.1 tCO2 / t lime. With an estimated worldwide production of 430 Mt in 2022, and associated “scope 1” emissions of ~470 MtCO2 annually, it follows that it is crucial to decarbonize this industry. The calcination process taking place in the lime kilns is endothermic. Traditionally the heat for the calcination is produced by the combustion of fuel, with air as the oxidant. In order to increase the CO2concentration in the flue gases emitted by these kilns and thus enhance the efficiency of downstream carbon capture or utilization processes, these kilns can also be operated with oxygen-enriched air, or high-purity oxygen coming from an air separation unit. Alternatively, the heat can be produced with electric energy, eschewing the need for fuel, and thus both reducing the CO2 emissions to those stemming from the limestone calcination only (so-called process emissions), and resulting in a flue gas with a high CO2 content. Various types of lime kilns are currently in use in the industry, with a wide variation in thermal efficiencies. Rotary kilns with preheating (PRK) typically operate in a range of thermal efficiency of 41 to 62%, Annular Shaft Kilns (ASK) operate at efficiencies above 65%, while Parallel Flow Regenerative Kilns (PFRK) typically operate above efficiencies of 75%. Other types of regenerative vertical shaft kilns, or Chisaki-type rotating bed kilns (as described in US4207061A) also operate at high thermal efficiencies, typically in excess of 75%. Frequently, in the lime industry, the players have a wide variety of kilns, especially of rotary kilns, ASKs, PFRKs, and other regenerative vertical shaft or Chisaki- type kilns. Carbon capture technologies are already referenced for the decarbonization of industrial flue gases. For example, in the cement industry, it is known to have a device downstream of the kiln connected to the flue gas exit which can act to capture CO2from the flue gas (see for example CN206823510). Another example relates to the power industry, also using carbon capture technologies (see for example CN116036826) connected to the flue gas of a power plant. The carbon capture technologies that are considered for decarbonization notably of the lime industry are sensitive to variations in the flue gas flow rate or CO2 concentration. The cryogenic capture technologies in particular, which require compressors with a high duty on the flue gas, are particularly impacted by any disruptions in flow. A loss in CO2 concentration also impacts cryogenic, adsorption, permeation and physical absorption technologies heavily, since the efficiency of these processes varies with the CO2partial pressure. Chemical absorption technologies can also be affected adversely by sudden changes in flue gas flow rate and composition, notably in the event of peaks in impurities such as SOx or NOx, which can lead to the formation of degradation products with the solvent. As many industrial calcination kilns, carbonate mineral stone kilns, such as lime kilns can, however, experience frequent disturbances for a variety of reasons, from the batch nature of the stone extraction or stone loading logistics, to the numerous steps that are required for treatment of the carbonate mineral stones (primary crushing, screening, etc.), and which can result in sizeable disruptions of the flue gas flow rate or CO2 content. Even in stationary operations of the kiln, the irregularities of the combustion and calcination processes lead to variations in flue gas flow rate and composition. Flow or CO2concentration variations will affect the downstream carbon capture or utilization unit adversely. Positive peaks can be dealt with by venting the excess flow or CO2, at the expense of a reduced carbon capture rate, but negative peaks can cause severe disturbances in the downstream processes or equipment. The more energy efficient Parallel Flow Regenerative Kiln (PFRK), which consists of two kilns in parallel with a cross-over channel for recuperation of energy, operates on a cycle of typically ~12 to 20 min. The process requires regular inversion steps in the typical range of 0.5 to 2 minutes per cycle, however, during which the flue gas flow rate can drop to ~30% of the nominal flow rate, and during which the CO2 concentration decreases rapidly. The inlet guide vanes on a centrifugal blower or compressor typically operate in a range of 85 to 100% of the nominal flow rate, so that they cannot regulate such high variations in flow rate rapidly. Similarly, the bypass or recycle loops around blowers or compressors cannot react instantaneously. Furthermore, this solution would not work for the entire carbon capture unit. A recycle around the first compressor would necessitate that the flow rate to the rest of the carbon capture unit be curtailed (e.g. by means of a valve), with a consequent adverse impact on any downstream compressors, and possibly other equipment. Pulling extra air from an upstream stack into the carbon capture unit is similarly undesirable. In the case of a chemical absorption technology, the increase in O2 content will lead to faster degradation of the solvent. For physical separation technologies (cryogenics, adsorption, permeation, etc.), the dilution in CO2 content may disrupt the carbon capture process. A solution is thus required for all these variations, whether they stem from the natural variations of the combustion and calcination processes, the regular inversion between the shafts of a multi-shaft kiln (e.g. PFRK), or unplanned disturbances. For flow variations we are mainly concerned by negative peaks as any positive peak (excess in flow or CO2%) can simply be vented upstream of the CC (carbon capture) unit. In order to smoothen the flue gas flow rate and CO2concentration variations, it can consequently be desirable to install a buffer, or gas holder such as described for example in WO2022 / 238383. A sizing of a gas holder on a state-of-the-art PFRK can thus be designed for two criteria: - Mitigating the fluctuations linked to the transient steps (post-combustion, reversal, and return to stationary conditions) in the PFRK (1 or 2 inversions, covering a 1x 12min or complete 2x12 min cycle). - Providing sufficient capacity to compensate for a short shutdown of the kiln (10 or 15 min). In Table 1, we consider the case of a PFRK in an oxycombustion setup, with a production capacity of 300tpd of lime, and calculate the volume required for both conditions: Table 1: Volume of gas holder for various design criteria Criteria 2 - Criteria 1 - compensation of compensation of unexpected transient steps shutdowns No of cycles to cover 1 2 Time of shutdown (s) 600 (s) 900 (s) Volume of gas 378(Nm³) 756(Nm³) 2890(Nm³) 4334(Nm³) holder* Volume of gas 412 m³ 824 m³ 3148 m³ 4722 m³ holder** * At normal conditions: 0C and 1.013 bara ** actual volume with flue gas at 1.1 bara, 50C It is immediately apparent that designing for a shutdown entails a very high capacity for the buffer, and consequently additional costs. The main issue, however, lies in the plot plan requirements for such a gas holder, which would be impractical on many sites where the availability of plot space is severely constrained. It is thus desirable to develop a solution to avoid having to design the gas holder for the shutdown scenario, while ensuring that the variations in flow rate and CO2concentration to the carbon capture units are relatively limited in the event of a shutdown. To this end, it is provided according to the present invention, a calcination kiln plant with a carbon capture unit comprising: - a calcination kiln having a flue gas exit, - a carbon capture pathway having a said carbon capture unit and a flue gas compressor in fluid communication with said flue gas exit of the kiln for feeding said flue gas compressor and with said carbon capture unit, said carbon capture unit having a flue gas entry connected to a flue gas exit of said flue gas compressor, a treated flue gas exit through which a treated flue gas depleted in CO2 exit said carbon capture body, and a CO2 exit through with a CO2-rich stream is collected, - a stack pathway, in fluid communication with said flue gas exit and positioned in parallel of said carbon capture pathway, - one or more mass transfer loops, provided for feeding a gaseous stream to said flue gas compressor of the carbon capture pathway. As it can be seen, the calcination kiln plant with a carbon capture unit according to the present invention comprises a calcination kiln having a flue gas exit, from which a flue gas, comprising combustion fumes exits the kiln. A carbon capture pathway is provided in fluid communication with the flue gas exit from the kiln to remove CO2 from the flue gas and separate the flue gas into a CO2rich gas and a treated flue gas depleted in CO2. The CO2-rich stream can be reused immediately in downstream applications or shipped through a CO2pipeline or stored into a relevant storage device. The stack pathway provided downstream of the flue gas exit of the kiln and forming a pathway in parallel to the carbon capture pathway allows to compensate for the excess flow or CO2flow during positive peaks in flow or CO2concentration variation by providing venting capabilities to the plant. According to the present invention, as it has been said, the calcination kiln plant with a carbon capture unit further comprises one or more mass transfer loops, provided for feeding a gaseous stream to said flue gas compressor of the carbon capture pathway to compensate negative peaks in flow or CO2 concentration variation in the flue gas and therefore provide a plant resilient to upstream disturbances. Indeed, the one or more mass transfer loops provide a fast reacting loop to the inlet of the compressor of the carbon capture unit which is independent of the upstream kiln process and can palliate the expected and unexpected disturbance or shutdown of the calcination kiln. Further, while not excluding the presence of a sizeable gas holder in the calcination kiln plant according to the present invention, the one or more mass transfer loops can replace the sizeable gas holder or reduce drastically the needed size for the latter. The flue gas compressor, within the meaning of the present invention (also called FG compressor) can be a blower, for example a centrifugal blower or a compressor as such. It is an equipment delivering a pressure differential between the inlet and the outlet of the FG compressor of at least 110 mbar, taking the atmospheric pressure as the inlet condition, by opposition to fans typically delivering a pressure differential between the inlet and the outlet of less than 110 mbar. Advantageously, said mass transfer loop is a bulk flow rate adjustment loop or a CO2concentration adjustment loop to respectively compensate for the bulk of flow rate variations or to compensate for CO2concentration variations. The calcination kiln plant with a carbon capture unit according to the present invention has one or more mass transfer loops and can accordingly have one or more bulk-flow rate adjustment loop and / or one or more CO2 concentration adjustment loop. Preferably, according to the present invention, said bulk flow rate adjustment loop feeds to said flue gas compressor as gaseous stream an additional-air stream, an additional flue gas stream from another kiln or plant, a treated flue gas depleted in CO2, or a CO2-rich stream, wherein one or both of the latter two streams originate from a source chosen in the group comprising the carbon capture unit, more particularly from the treated flue gas exit or from an intermediate step of the carbon capture unit through which an internal compressed gas exits, a CO2utilization unit, a pressurized gas storage unit, such as a pressurized gas buffer. Indeed, in some advantageous embodiments, said bulk flow rate adjustment loop feeds to said flue gas compressor as gaseous stream, a treated flue gas depleted in CO2, or a CO2- rich stream originating from a source chosen in the group comprising the carbon capture unit, more particularly from the treated flue gas exit or from an intermediate step (hereinafter designated as side exit) of the carbon capture unit through which an internal compressed gas exits, a CO2 utilization unit, a pressurized gas storage unit, such as a pressurized gas buffer. Alternatively the bulk flow rate adjustment loop may draw additional air from the atmosphere, or additional flue gas from another process, particularly for carbon capture technologies that are less sensitive to O2concentration or CO2concentration respectively. In the event of an upstream disturbance (e.g. kiln shutdown), the bulk flow rate adjustment loop for example feeding to the compressor of the carbon capture unit the treated flue gas depleted in CO2, recycles back to the inlet of the carbon capture unit said treated flue gas depleted in CO2, to ensure a minimal stable flow rate (typically 80% of the nominal flow rate for centrifugal blowers or compressors). Advantageously, according to the present invention, said CO2 concentration adjustment loop feeds to said flue gas compressor a gaseous CO2-rich stream from said carbon capture unit or from a side exit of the carbon capture unit through which an CO2-rich stream exits, CO2from a downstream source, such as a CO2pipeline, CO2storage device, CO2from a secondary carbon capture unit, CO2pressurized buffer. In the event of an upstream disturbance (e.g. kiln shutdown), via the CO2concentration adjustment loop, part or all of a CO2-rich stream, for example the CO2-rich stream from said carbon capture unit or from a side exit of the carbon capture unit is recycled back to the inlet of the carbon capture unit through the compressor to ensure that the CO2 concentration remains stable. For carbon capture technologies or utilization technologies (CC / U technologies) that are sensitive to flow rate variations only, a bulk flow rate adjustment loop may be used without a CO2 concentration adjustment loop. Conversely, for CC / U technologies primarily sensitive to CO2concentration, a CO2concentration adjustment loop may be used without a bulk flow rate adjustment loop. The setup is not specific to any carbon capture technology. In a preferred embodiment, the calcination kiln plant with a carbon capture unit according to the present invention comprises a gas cooler, preferably a direct contact cooler in fluid communication with said flue gas exit of the kiln, with the carbon capture pathway and the stack pathway. In also a preferred embodiment, the calcination kiln plant with a carbon capture unit according to the present invention comprises a flue gas treatment unit in fluid communication with said flue gas exit of the kiln, with the carbon capture pathway and the stack pathway. In another preferred embodiment according to the present invention, said flue gas treatment unit is located downstream said gas cooler, said gas cooler having an inlet connected to a gas exit of the flue gas treatment unit provided to output a flue gas depleted in pollutants, such as NOx, SOx, carbon or VOC, dust and their combination for establishing the fluid communication with the flue gas exit of the kiln. Preferably, according to the present invention, said calcination kiln is a carbonated mineral stones kiln, such as a lime kiln, such as a parallel flow regenerative kiln, a annular shaft kiln, a rotary shaft kiln, a regenerative vertical shift kiln, a Chisaki-type kiln, and preferably a plurality of PFRKs, or annular shaft kilns, of rotary shaft kilns or regenerative vertical shaft or Chisaki-type kilns. More preferably the calcination kiln is chosen in the group consisting of a parallel flow regenerative kiln, an annular shaft kiln, a regenerative vertical shaft kiln, a Chisaki-type kiln, a plurality of PFRKs, annular shaft kilns, regenerative vertical shaft or Chisaki-type kilns. The plurality of PFRKs, annular shaft kilns or regenerative vertical shaft kilns contains typically 2, 3, 4, 5, 6, 7, 8 or even 10 kilns, respectively PFRKs, annular shaft kilns, regenerative vertical shaft kilns, or Chisaki-type kilns. By the terms “stones, carbonate mineral rocks, limestone stones”, it is meant according to the present invention pieces of raw carbonated material having a median particle size comprised between 20 mm to 20 cm, preferably higher than 25 mm, preferably lower than 18 cm, more preferably lower than 16 cm, and typically between 3 and 15 cm. In a particular embodiment of the present invention, the carbon capture unit is a cryogenic carbon capture unit and wherein said one or more mass transfer loops comprises at least a CO2 concentration adjustment loop or comprises at least a bulk flow rate adjustment loop and a CO2 concentration adjustment loop. In a particular embodiment of the present invention, the carbon capture unit is a physical absorption carbon capture unit and wherein said one or more mass transfer loops comprises at least a CO2concentration adjustment loop or at least a bulk flow rate adjustment loop and a CO2concentration adjustment loop. In another particular embodiment of the present invention, the carbon capture unit is a chemical absorption carbon capture unit and wherein said one or more mass transfer loops comprises at least a bulk flow rate adjustment loop. In yet a particular embodiment of the present invention, the calcination kiln plant with a carbon capture unit comprises additional calcination kilns. In a preferred embodiment of the present invention, the calcination kiln plant with a carbon capture unit comprises an ejector fed by a motive fluid and provided to entrain the gaseous stream to said flue gas compressor of the carbon capture pathway. More preferably, the motive fluid is a CO2-rich stream from (the outlet of) said carbon capture unit or from a side exit of the carbon capture unit, optionally after being compressed by a compressor connected to said CO2-rich stream exit of the carbon capture unit or said side exit. In this case, a compressed stream (e.g. the CO2-rich stream taken downstream of a CO2 compressor or pump from the carbon capture unit), is used as the motive fluid in an ejector to entrain a low pressure stream (e.g. the treated flue gas depleted in CO2 downstream of the CC / U unit), thus avoiding the use of an extra blower, and improving the overall reliability of the setup. In an embodiment of the present invention, the calcination kiln plant with a carbon capture unit further comprises a gas holder, in fluid communication with said flue gas exit of the kiln, with the carbon capture pathway and the stack pathway, provided for storing or buffering flue gas from the calcination kiln. More particularly, said gas holder is a pressurized gas holder, fed by a pressurized flue gas from a blower or a compressor, in fluid communication with said flue gas exit of said calcination kiln. The gas holder can be also a membrane gas holder, fed by a pressurized flue gas, such as from a blower, a compressor or a fan. The pressurized gas holder is then installed as close as possible to the inlet of the flue gas blower or compressor of the carbon capture pathway, to compensate for sudden flow rate variations in the time required for the mass transfer loop to provide sufficient flow. In a particular embodiment, said compressor feeding said gas holder has an inlet connected to a gas exit of the cooler for feeding in the gas holder a pressurized, cooled flue gas depleted in pollutants, such as NOx, SOx, carbon or VOC, dust and their combination for establishing the fluid communication with the flue gas exit of the kiln. In an embodiment of the present invention, the calcination kiln plant with a carbon capture unit further comprises a secondary gas holder, in fluid communication with the exit of the compressor of the carbon capture pathway and with the inlet of compressor of the carbon capture pathway. This secondary pressurized gas holder is then designed to compensate for planned variations in flow rate or CO2 concentration (e.g. inversion steps on multi shaft kilns). Preferably, in another embodiment, an energy recuperation device, such as an expansion turbine, is placed on one or more mass transfer streams to recover some of the electrical energy expended in the flue gas or CO2compression. Other embodiments of the calcination kiln plant with a carbon capture unit according to the present invention are mentioned in the appended claims. The present invention also relates to a calcination method in a calcination kiln plant with a carbon capture unit according to the present invention, comprising: - a calcination step of minerals producing flue gas, where said flue gas exits said plant either through a stack pathway or after being treated for carbon capture by passing through a carbon capture pathway comprising said carbon capture unit and a flue gas compressor in fluid communication with said flue gas exit of the kiln, said flue gas produced during said calcination step being a gaseous stream feeding said flue gas compressor - a carbon capture step producing a treated flue gas depleted in CO2and a CO2-rich stream. Said method is characterized in that the gaseous stream entering said flue gas compressor has a flow rate stabilized by said bulk flow rate adjustment loop in the range between 50 to 100% of the nominal flow rate. In a preferred embodiment of the calcination method according to the present invention, said gaseous stream has a CO2 concentration stabilized by said CO2 concentration adjustment loop in the range between 70 to 130 % of the nominal CO2 concentration. Other characteristics and advantages of the present invention will be derived from the non-limitative following description, and by making reference to the drawings and the examples. In the drawings, figure 1 represents one embodiment of the calcination kiln plant with a carbon capture unit according to the present invention having a bulk flow rate adjustment loop and a CO2concentration adjustment loop. Figure 2 represents a variation of figure 1, where a by- pass of the gas holder is foreseen. Figure 3 represents another variation of figure 1 showing a CO2 compressor and the ejector. Figure 4 represents a further variation of figure 1, showing the CO2 compressor and pressurizing means, and showing optionally a by-pass of the gas holder. Figure 5 represents the surge protection of the FG compressor through combination of compressor recycle loop, and recycle of streams from the carbon capture unit. Figure 6 represents a variation of the calcination kiln plant of figure 1 further comprising a turbine. Figure 7 represent a variation of figure 3 comprising a heater for the CO2-rich stream in the CO2concentration adjustment loop. Figure 8 represents the flow rate and the CO2concentration variation in time for PFRK operate in oxycombustion, cycle time of 12 min) Figure 9 represent a variation of figure 5 where a secondary gas holder is present in a recycle / by-pass loop of the FG compressor. Figure 10 represents a further recycle circuit to stabilize CO2 concentration at carbon capture unit inlet. Figure 11 is a variation of the embodiment of figure 10, where secondary pressurized buffers are included. Figure 12 illustrates an embodiment of the present invention with 3 kilns and 3 ejectors. Figure 13 & 14 illustrate the motive pressure and the ejector inlet flowrate. Figure 15 illustrates an embodiment of the present invention with 2 annular shaft kilns. Figure 16 illustrates an embodiment of the present invention with a medium response time external recycle loop, a fast response time loop with a small pressurized gas holder and one optional CO2 recycle loop. In the drawings, the same reference numbers have been allocated to the same or analog element. For the sake of simplicity, in what follows we will describe the invention using the example of a parallel-flow regenerative kiln (PFRK) for calcination of limestone, followed by a carbon capture unit. The illustrated PFRK can be operated in normal combustion of fuel, i.e. using combustion air in excess of the stoichiometric conditions, below the stoichiometric conditions or at the stoichiometric conditions, in oxycombustion, i.e. using O2-rich stream in total or partial replacement of nitrogen in the combustion gas or even operated with electric heating of the limestone. When the PFRK is operated with combustion air or with O2-rich combustion gas, the flue gas contains CO2 from the combustion of fuel and CO2 from decarbonation of limestone. When the kiln is electrically operated, the flue gas contains mainly CO2 from decarbonation of limestone. During calcination of limestone as carbonate mineral stones, quicklime stones / pebbles are produced with CO2 at a temperature typically around 1000°C. Before being discharged from the kiln, the quicklime stones or pebbles have to be cooled by a cooling gas, typically cooling air. The parallel-flow regenerative kiln 1 is a vertical double-shaft kiln 2a, 2b where the fuel is injected alternately in one shaft then in another for approximately 12 minutes with a stop period between cycles of about 1 minute to reverse the circuits. This is the “reversing” period. Both shafts are interconnected by a crossover channel 3. The shafts are divided vertically into three zones, the preheating zone A where the carbonate mineral rocks is preheated before calcination, the combustion zone B where the calcination of the carbonate mineral rocks occurs and the cooling zone C where the cooling of the calcined material occurs. When a shaft is in calcination mode, a fuel supply device in the form of lances injects a fuel into the shaft, such as natural gas. The carbonate mineral rocks, loaded at the top of the shaft via a charging inlet, progressively descend in the shaft. Combustion air is introduced at the top of the shaft via a supply opening, which allows for fuel combustion at the outlet of the lances and a decarbonation of the carbonate stones to calcined material. The combustion fumes formed by the combustion and decarbonation descends co-currently to the calcined material and, moves into the crossover channel 3. Cooling gas is introduced via a supply duct at the bottom of the shaft, counter-currently to the calcined material, to cool it. The heated cooling gas introduced in the calcination shaft mixes with the combustion fumes in order to move into the crossover channel 3 and forms the flue gas. The calcined material is unloaded at the bottom of the shaft. When a shaft is in preheating mode, the fuel supply device is closed and the lances do not receive any fuel, but still can be supplied with cooling gas. The inlet of the shaft in preheating mode is supplied by the carbonate stones. The opening for supplying combustion air is closed. However, the supply duct for the cooling gas and the outlet for the calcined material remain in the open position. After heat exchange with the descending calcined material, the heated cooling gas mixes with the combustion fumes which, from the crossover channel 3, enters the shaft. The exhaust gas containing the combustion fumes progresses until reaching the top of the shaft where it is discharged from the kiln via a discharge duct. The discharged flue gas contains at least the combustion fumes, dust and pollutants at a temperature typically comprised between 100 and 180°C and is transferred to a stack 4 via a stack pathway 5 or a carbon capture unit 6 via a carbon capture pathway 7. When the kiln is operated in oxycombustion, a portion of the flue gas is recycled to the combustion zone of the shaft in burning mode and mixed with O2-rich stream before entering the combustion zone or in the combustion zone while another portion is transferred to the stack 4 via the stack pathway 5 or the carbon capture unit 6 via the carbon capture pathway 7. When the kiln is electrically operated, CO2from decarbonation is also recycled to the calcination zone and heated before being introduced in the shaft at a temperature higher that the decarbonation temperature of the limestone. In this case, neither fuel nor combustion gas (air or O2-rich stream is introduced). In the three calcination operation modes of the PFRK, it can be desirable to extract out of the kiln part or all the heated cooling air to avoid CO2 dilution in the flue gas by the heated cooling air. Typically, the heated cooling air is extracted at a level below the cross-over channel. The flue gas leaves the PFRK through a flue gas exit and is routed to a flue gas treatment unit 8 comprising for example a scrubber, various additional flue gas treatment units (e.g. DeNOx, removal of VOC, SOx), and a cooler as required for the downstream units. The treated flue gas depleted in NOx, SOx, VOC, dust, … 9 is then sent to a compressor, to a blower or to a fan 10 feeding a gas holder 11, which is designed to compensate the transient steps linked to the inversion in the PFRK. In normal operation, the flue gas is then fed in the carbon capture pathway 7 to a flue gas compressor 12 feeding the carbon capture unit 6, which will hereinafter be referred to as ‘FG compressor’ 12. It is well understood, however, that this designation can comprise a compressor, blower, or any other motive device to drive the flue gas flow towards the carbon capture unit, and overcome the pressure drop of the downstream equipment. In the carbon capture unit 6, the CO2is separated from the flue gas, resulting in a treated flue gas depleted in CO213, and a CO2-rich stream 14. In other words, the FG compressor is an equipment delivering a pressure differential between the inlet and the outlet of the FG compressor of at least 110 mbar, taking the atmospheric pressure as the inlet condition. In figure 1, the treated flue gas depleted in CO213 may be, at least partially, recycled back to the inlet 15 of the FG compressor 12 forming the bulk flow rate adjustment loop. The CO2-rich stream 14 is optionally recycled back to the inlet 15 of the FG compressor 12 forming the CO2 concentration adjustment loop 17, particularly in cases where the downstream equipment in the carbon capture technology is sensitive to the CO2 concentration. The recycle of treated flue gas depleted in CO213 and / or CO2- rich stream 14, at the required pressure for the FG compressor inlet 15, can be effected by a pressure changing device (not illustrated). Figure 2 represents the embodiment of figure 1, where a by-pass 30 of the gas holder 11 is foreseen, for example, when the gas holder is full, the by-pass 30 conducting the flue gas to the stack 4. As it can be seen in figure 3, with some carbon capture technologies (e.g. cryogenic) the CO2-rich stream 14 can be obtained in liquid or gaseous phase, at a pressure in a range of 10 to 20 bara. With post-combustion amine units, the pressure of the CO2 is typically in the range of 1.5 to 5.0 bara, preferably in the range of 1.5 to 2.0 bara. For other chemical absorption technologies (e.g. hot potassium carbonate, chilled ammonia) the CO2-rich stream 14 may be available from the stripper at up to 20 bara. For all CO2capture technologies, further CO2compression is thus typically required for transport of CO2in gaseous or dense phase. Accordingly, a CO2compressor 18 is provided at the CO2- rich stream exit of the carbon capture unit 6. With carbon capture technologies involving CO2separation at high pressure, such a compressor 18 may not be required. For carbon capture units producing liquid CO2for downstream applications, the liquid CO2may be recycled directly within the process for the CO2concentration adjustment loop 17, or a vaporizer may be required instead of a compressor to obtain a CO2 adjustment stream in the CO2 concentration adjustment loop 17. In the following example we consider a gaseous CO2 stream in the CO2 concentration adjustment loop 17 with a CO2 compressor 18. In order to avoid an additional blower for the CO2 concentration adjustment loop 17, part or all of the pressurized CO2-rich stream can thus be taken from an intermediate stage or downstream of the CO2 compressor 18, and used as the motive fluid in an ejector 19, to entrain the treated flue gas depleted in CO2back to the inlet 15 of the FG compressor 12 in the bulk flow rate adjustment loop 16. The gaseous stream of the illustrated scheme is treated flue gas depleted in CO2.Of course, in a variant, it can be air. In figure 4, the same by-pass 30, as for the embodiment of figure 2 is foreseen, conducting the gas to the stack when the gas holder 11 is full. Further, in this embodiment, an additional pressurizing means 31, such as a blower, a compressor or a fan is foreseen for the CO2 concentration adjustment loop 17, part or all of the pressurized CO2-rich stream can thus be taken from an intermediate stage or downstream of the CO2 compressor 18, by said pressurizing means 31 to entrain the treated flue gas depleted in CO2back to the inlet 15 of the FG compressor 12 in the bulk flow rate adjustment loop 16. As it can be seen in figure 5, a guide vanes is provided at the inlet 15 of the FG compressor 12 and a recycle loop 21 connecting the outlet of the compressor to the inlet 15 of the FG compressor 12 is further provided. A control valve 20 is further provided on the recycle loop 21. The control valve 20 regulates a pressure or flow rate to prevent the occurrence of a surge. In the event of an unexpected shutdown, and a sudden drop in flow rate, the guide vanes of the inlet 15 and recycle loop 21 of the FG compressor 12 may not react sufficiently rapidly to avoid undesirable phenomena such as surge, in which an insufficient flow rate leads to a local reversal of the flow across the blades of the FG compressor 12, which can in turn damage the machine. The control valve 20 on the recycle loop 21 will often regulate a pressure or flow rate to prevent the occurrence of a surge, but it cannot react instantaneously to large sudden drops in flow rate. The additional flow rate provided by the CO2concentration adjustment loop 17 or bulk flow rate adjustment loop 16 from the carbon capture unit, comprising part or all of the treated flue gas depleted in CO213 and / or air and / or part or all of the CO2-rich stream 14, can thus contribute to avoiding flow or pressure conditions which could lead to damage to the machine. As it can be seen in figure 6, which is a variation of figure 1, the calcination kiln plant further comprises an energy recuperation device 22, such as an expansion turbine 22 to recover energy from pressurized streams. Indeed, for carbon capture technologies, such as cryogenic technologies involving a stripping column (e.g. US5974829) or cryogenic desublimation technologies (e.g. US20110226010A1), in which one or more streams within the carbon capture unit 6 are already compressed at a pressure above atmospheric, part or all of these streams can be recycled directly to the inlet of the FG compressor as CO2concentration adjustment loop 17 or bulk flow rate adjustment loop 16. The FG compressor 12 is typically designed for a low inlet pressure. An energy recuperation device, such as an expansion turbine, can be added to recover energy from these pressurized streams. As it can be seen, Figure 7 is a variation of figure 2, where the CO2-rich stream 14 is used as motive fluid in the ejector 19 to entrain the treated flue gas depleted in CO2 with a heater 29 upstream of the expansion of the CO2-rich stream 14 to the required ejector’s inlet conditions. As described in some of the previous embodiments, the CO2-rich stream 14 would be recycled back to the inlet 15 of the FG compressor 12, for the CO2 concentration adjustment loop 17 or bulk flow rate adjustment loop 16 respectively either to stabilize the CO2 concentration, or as a motive fluid in the ejector 19 with a view to stabilizing the flow rate. When using the pressurized CO2product to entrain the treated flue gas depleted in CO213 in an ejector 19 as shown in Figure 7, or when recycling it directly back to the inlet 15 of the FG compressor 12, the CO2-rich stream 14 will need to be expanded to the appropriate inlet pressure for the ejector 19 or the FG compressor 12 for the CO2concentration adjustment loop 17. The expansion of a CO2-rich stream beneath the inversion temperature of the mixture of CO2 and any remaining impurities (e.g. N2, O2, NOx, etc.) will cool the stream by the Joule- Thomson effect. To avoid any risks associated with the expansion of the recycled CO2 -rich stream 14 for the CO2 concentration adjustment loop 17, the heater 29 can be installed upstream of the expansion, and / or the CO2-rich stream 14 can be taken upstream of a CO2compressor intercooler or aftercooler (not shown). Moreover, when using an ejector 19, the latter will be more efficient with a hotter motive fluid. Conversely, the expansion of the motive fluid can be done with an energy recuperation device to recover, as much as possible, the energy used for CO2compression. Figure 8 represents the flow rate and the CO2concentration variation in time of a PFRK operated in oxycombustion without cooling air extraction and having a cycle time of 12 min. As it can be seen, during the inversion phase, the flow rate drops to 30% of the nominal flow rate, and the CO2 concentration in the flue gas decreases from 40% to 11%. Of course, in case of cooling air extraction, concentrations of CO2 from 60% up to 95% can be experienced. The recycle loop 21 of the FG compressor 12 (as shown in Figure 5) may not be able to react quickly enough to compensate for such an abrupt decrease in flow rate. Alternatively, the control valve 20 would have to be opened ahead of the kiln inversion phase, in order to maintain the flow rate to the carbon capture unit 6. However, such a solution would entail oversizing the compressor 12 substantially, with a consequent penalty on the energy consumption and turndown flexibility of the machine. For carbon capture technologies in which the pressure downstream of the FG compressor 12 is substantially above atmospheric pressure (e.g. cryogenic, desublimation), it may be preferable to provide a secondary gas holder 23 on an additional recycle / bypass loop 24 of the FG compressor 12 (see Fig.9), or on the recycle / bypass loop 21 that is usually used for surge protection of the FG compressor 12. The additional recycle / by- pass loop 24 of the FG compressor 12 also comprises upstream of the secondary gas holder 23 a first valve 25 and downstream of the secondary gas holder 23 a second valve 26. In the above example, the average flow rate over the entire cycle is 93.4% of the nominal flow rate, and various design criteria can be considered for the for the sizing of the secondary gas holder 23: - If the secondary gas holder 23 is designed such that the flow rate at the inlet 15 to the FG compressor 12 must reach ~80% of the nominal flow rate (the threshold at which the Guide Vanes of the inlet 15 can regulate) during the inversion, a continuous stream of 4.5% of the nominal flow rate could be taken downstream of the FG compressor 12 to fill this secondary pressurized gas holder. - If we consider that the FG compressor recycle loop 21 will protect the machine against surge conditions, and the secondary gas holder 23 is designed instead for the turndown of the downstream carbon capture unit 6, e.g. 50% of the nominal flow rate for distributors on stripping or rectifying columns, a smaller continuous stream of 1.4% of the nominal flow rate would be required to fill the secondary gas holder 23. The first valve 25 in Fig.9 would thus ensure that 4.5% or 1.4% of the flow is continuously directed to the secondary pressurized gas holder 23 respectively. The second valve 26 would be programmed to compensate the decrease in flow rate linked to the inversion in a feed-forward or model predictive control. Accordingly, the secondary pressurized gas holder 23 on the recycle loop 24 will be much smaller than a gas holder (11) designed on the flue gas, in a ratio of the pressure downstream of the FG compressor 12 to the pressure of the flue gas. With an FG compressor 12 designed for an outlet pressure of 5 bara, for instance, the gas holder 23 on the recycle loop 24 would be ~5 x smaller than a gas holder (11) placed on the flue gas 9 from the kiln (not shown), at the expense of some additional energy consumption of the FG compressor 12. This setup would be particularly attractive for cases where plot space availability is restricted. In further variations of figure 9, an orifice plate could be used rather than the first control valve 25, for cases with upstream flue gas sources which experience regular variations in flow rate over a specific cycle (see above example with PFRK – Fig. 8). For cases where the source of flue gas is usually stable, this additional circuit 24 and secondary gas holder 23 would be used to compensate sudden unexpected flow variations, until the external recycle loop (for example Fig.3) can take over. In such cases the secondary gas holder 23 could be filled once between every shutdown of the upstream process, and a simple on-off valve could with an orifice could be used for filling the secondary gas holder. The stream used to fill the secondary gas holder 23 could come from the carbon capture unit 6, particularly with technologies in which there is further downstream compression. For carbon capture technologies that are sensitive to the CO2 concentration, a secondary recycle circuit can be established, to stabilize the CO2 concentration at the inlet to the CC unit. In figure 10, an illustration is provided in which part of the CO2-rich stream 14 is further, beside the CO2 concentration adjustment loop 17, recycled back in a recycle loop 27 to the inlet of the carbon capture unit 6. In this particular example, a control valve 28 determines how much CO2needs to be recycled, based on the measurement of an Analyzer Transmitter (AT). Many variations are of course possible. The CO2-rich stream could be recycled upstream of the FG compressor 12, or directly upstream of the first equipment in the carbon capture unit 6 that is sensitive to the concentration of CO2(not shown). Similarly, the portion of the CO2-rich stream to be recycled could be part of an internal stream within the carbon capture unit 6, or taken upstream or at an intermediate stage of the CO2compressor 18. In the event that the upstream process (kiln, flue gas treatment, etc.) experiences a severe disruption, and the ejector circuit (bulk flow rate adjustment loop 16) is opened to stabilize the flow rate to the FG compressor 12, this secondary CO2 recycle loop 27 would be closed. Figure 11 illustrates a variation of figure 10, where one or multiple storage tanks such a pressurized secondary buffer 23 could be placed upstream or downstream of the CO2 compressor 12, with a view to providing an extra buffer capacity on the CO2 rich gas, and improving the control of the CO2concentration at the inlet to the carbon capture unit through the CO2concentration adjustment loop 17. Conversely, in the event of a loss of CO2purity at the outlet of the carbon capture unit 6, the CO2rich gas 14 could be recycled back to the inlet of the carbon capture unit 6 to reach the required purity. If the carbon capture unit produces liquid CO2, a heat exchanger can be installed to vaporize the CO2 prior to recycling it back to the inlet of the carbon capture unit 6. Alternatively the liquid CO2 product could be recycled at some intermediate step in the carbon capture unit 6 (not shown). Figure 12 illustrates an embodiment of the present invention with 3 kilns and 3 ejectors. Ejectors are usually designed for one specific operating point, and do not allow for precise control of flow rate. In cases where multiple kilns or upstream processes are connected to the same carbon capture unit 6, it may be desirable to have multiple ejectors 19, designed such that any combination of shutdown of kilns can be compensated for. The ejectors 19 may all have the same design, or different operating points reflecting the capacity of the individual kilns or upstream processes. Figure 15 illustrates an embodiment according to the present invention with two annular shaft kilns 1,1’. The annular shaft kilns 1 or 1’ can be for example the one according to EP 4133212, incorporated herein by reference. Preferably, the annular shaft kilns 1 or 1’ are two annular shaft kilns according to figure 2 or figure 3 of EP 4133212. When the annular shaft kilns are operated in oxycombustion, in each kiln, a portion of the flue gas is recycled to the burner of the inferior section of the kiln and mixed with O2-rich stream before entering the burner while another portion is transferred to the stack 4 via the stack pathway 5 or the carbon capture unit 6 via the carbon capture pathway 7. When the annular shaft kilns 1, 1’ are electrically operated (see for example WO 2024 / 141397 incorporated herein by reference), CO2from decarbonation is also recycled to the burner of the inferior section and heated before being introduced in the shaft at a temperature higher that the decarbonation temperature of the limestone. In this case, neither fuel nor combustion gas (air or O2-rich stream is introduced). In the three calcination operation modes of the ASK (normal operation, such as disclosed in figure 1 of EP 4133212; oxyfuel operation, such as disclosed in figure 3 of EP 4133212 or 4133212, by electric energy such as disclosed in WO 2024 / 141397), it can be desirable to extract out of the kiln part or all the heated cooling air to avoid CO2dilution in the flue gas by the heated cooling air. Typically, the kiln comprises also at least one gas outlet duct (not shown), as second gas outlet means, which is equipped with an aspiration fan for extracting from the inner cylinder the gaseous stream containing the heated cooling air and removing it outside the kiln toward a second stack. The flue gas leaves the ASK kilns 1,1’ through a flue gas exit and is routed to a collecting pipe 32, which in turn is connected to a flue gas treatment unit 8 comprising for example a dust collector, a scrubber, various additional flue gas treatment units (e.g. for DeNOx, removal of VOC, SOx), and a cooler as required for the downstream units. The treated flue gas depleted in NOx, SOx, VOC, dust, … 9 is then sent to a compressor, to a blower or to a fan 10. Optionally a gas holder 11 can be installed, to provide a buffer for the treated flue gas. In normal operation, the flue gas is then fed in the carbon capture pathway 7 to a flue gas compressor 12 feeding the carbon capture unit 6, which will hereinafter be referred to as ‘FG compressor’ 12. It is well understood, however, that this designation can comprise a compressor, blower, or any other motive device to drive the flue gas flow towards the carbon capture unit, and overcome the pressure drop of the downstream equipment. In other words, the FG compressor is an equipment delivering a pressure differential between the inlet and the outlet of the FG compressor of at least 110 mbar, taking the atmospheric pressure as the inlet condition. In the carbon capture unit 6, the CO2 is separated from the flue gas, resulting in a treated flue gas depleted in CO213, and a CO2-rich stream 14. The treated flue gas depleted in CO213 may be, at least partially, recycled back to the inlet 15 of the FG compressor 12 forming the bulk flow rate adjustment loop 16. The CO2-rich stream 14 is optionally recycled back to the inlet 15 of the FG compressor 12 forming the CO2concentration adjustment loop 17, particularly in cases where the downstream equipment in the carbon capture technology is sensitive to the CO2concentration. The recycle of treated flue gas depleted in CO213 and / or CO2- rich stream 14, at the required pressure for the FG compressor inlet 15, can be effected by a pressure changing device (not illustrated). Further, on the illustrated embodiment, a by-pass 30 of the gas holder 11 is foreseen, for example, when the gas holder is full, the by-pass 30 conducting the flue gas to the stack 4. As it can be seen on figure 15, the carbon capture unit is connected to 2 ASKs on a common duct. In the event one of them shuts down, the loss in volume flow rate (~50%) would exceed what can typically be compensated with Inlet Guide Vanes (IGVs) on a centrifugal blower or compressor. A centrifugal compressor in particular would be at risk of surge, which could lead to severe damage to the impeller and shutdown of the downstream carbon capture unit. In the event of a shutdown of a kiln, the bulk flow rate adjustment loop would thus be activated to recycle sufficient volume flow rate to stabilize the flue gas blower or compressor. Figure 16 shows an additional embodiment according to the present invention. The carbon capture unit is connected to a calcination kiln which is a carbonated mineral stones kiln, such as a lime kiln. The lime calcination kiln can be a parallel flow regenerative kiln, an annular shaft kiln, a rotary shaft kiln, a regenerative vertical shaft kiln, or a Chisaki-type kiln, and preferably a plurality of PFRKs, annular shaft kilns, of rotary shaft kilns, regenerative vertical shaft kilns, or Chisaki-type kilns. More preferably the calcination kiln is chosen in the group consisting of a parallel flow regenerative kiln, an annular shaft kiln, a regenerative vertical shaft kiln, a Chisaki-type kiln, a plurality of PFRKs, annular shaft kilns, regenerative vertical shaft kilns, or Chisaki-type kilns. The plurality of PFRKs, annular shaft kilns, regenerative vertical shaft kilns, or Chisaki-type kilns contains typically 2, 3, 4, 5, 6, 7, 8 or even 10 kilns, respectively PFRKs, annular shaft kilns, regenerative vertical shaft kilns, or Chisaki-type kilns. In figure 16, as explained previously for figure 9, for carbon capture technologies in which the pressure downstream of the FG compressor 12 is substantially above atmospheric pressure (e.g. cryogenic, desublimation), it may be preferable to provide an additional recycle / bypass loop 24 of the FG compressor 12 with a gas holder 23, or on the recycle / bypass loop 21 that is usually used for surge protection of the FG compressor 12. The additional recycle / by-pass loop 24 of the FG compressor 12 also comprises upstream of the secondary gas holder 23 a first valve 25 and downstream of the secondary gas holder 23 a second valve 26. As for the embodiment shown on figure 9, in the embodiment according to figure 16, the FG compressor recycle loop 21 would eventually protect the machine against surge conditions, but it cannot react instantly to a large disruption in flue gas flow rate. The recycle loop 24 with the secondary gas holder 23 can be designed to provide a sufficient flow rate to avoid compressor surge, in the event of a sudden disruption in the upstream flow 7, and in the time it takes for the FG compressor recycle loop 21 to recycle sufficient flow. The recycle loop 24 can also allow for operation for turndown operation of the downstream carbon capture unit 6 for a limited amount of time, whereas the FG compressor recycle loop 21 reduces the flow rate to the carbon capture unit 6. For cases where the source of flue gas is usually stable, this additional circuit 24 and secondary gas holder 23 would be used to compensate sudden unexpected flow variations, until the external recycle loop 16 can take over. In such cases the secondary gas holder 23 could be filled once between every shutdown of the upstream process, and a simple on-off valve with an orifice could be used for filling the secondary gas holder. The stream used to fill the secondary gas holder 23 could come from the carbon capture unit 6, particularly with technologies in which there is further downstream compression. For carbon capture technologies that are sensitive to the CO2 concentration, a secondary recycle circuit can be established, to stabilize the CO2 concentration at the inlet to the CC unit. Further, in the illustrated embodiment on figure 16, part of the CO2-rich stream 14 is further, beside the CO2concentration adjustment loop 17, recycled back in a recycle loop 27 to the inlet of the carbon capture unit 6. In this particular example, a control valve 28 determines how much CO2needs to be recycled, based on the measurement of an Analyzer Transmitter (AT) 33. Accordingly, the recycle loop 24 is a fast response time loop with a small pressurized gasholder. The fast response recycle loop 24 compensates for predicted variations (e.g. PFRK inversion) or compensates for unpredicted shutdowns in the time required for the external recycle loop to take over. The external recycle loop 16 is a medium response time « external » recycle loop, with CO2 as motive fluid to entrain treated flue gas in ejector. The medium response time « external » recycle loop compensates for unpredicted shutdowns, the carbon capture unit can run continuously even if the upstream process is not delivering flue gas. The carbon capture unit can run in normal mode (e.g. no loss of cold for cryogenic units). In cases with multiple upstream flue gas sources (e.g. kilns), multiple ejectors may be installed, where each ejector is designed for the flue gas capacity of one kiln This setup avoids installation of an additional recycle blower or compressor, the CO2compressor provides the energy for the recycle. The recycle loop 27 to the inlet of the carbon capture unit 6 is an optional CO2 recycle loop downstream of the FG compressor: The recycle loop 27 to the inlet of the carbon capture unit 6 stabilizes CO2 concentration at the carbon capture unit inlet (especially for technologies sensitive to CO2 concentration) In connection with a pressurized storage tank, and in the event of a loss CO2 purity, the CO2-rich stream can also be recycled to the carbon capture unit until the required CO2specification is reached. Examples.- In the following examples we consider a flue gas flow rate of 100,000 kg / h, at 50°C and 1.11 bara, with a CO2concentration of 20 mol%, which is routed to the inlet of the FG compressor and carbon capture unit. The carbon capture unit removes 95% of the CO2, resulting in the treated flue gas depleted in CO2 flow rate of 70,000 kg / h, at 13°C and 1.03 bara, and a CO2-rich stream. The CO2 rich gas is routed to a CO2 compressor, or to a combination of CO2 compressor and CO2supercritical pump, to yield a CO2product at 99.0% CO2, 20°C and 100 bara. The CO2-rich stream used as the motive fluid can be taken from an intermediate stage of the CO2compressor or pump, or downstream of said compressor or pump. It may be preferable to take the CO2-rich stream downstream of the CO2compression, rather than from an intermediate stage, in order to avoid instances of surge on any of the CO2compression stages. The motive fluid can then be expanded to the pressure required by the ejector by means of a pressure reducing device, such as a valve or turbine. Example 1.-variation of ejector outlet pressure In the following case, the full flow rate of the treated flue gas depleted in CO2 is entrained in the ejector by the full CO2 -rich stream flow rate, and both streams are recycled back to the inlet of the FG compressor. Fig.13 illustrates how the pressure of the motive CO2-rich stream affects the pressure of the outlet stream. In the above example, with an FG compressor designed for an inlet flue gas pressure of 110 mbarg, and taking into account any additional pressure losses linked to pipes or instrumentation, we would thus need a motive fluid pressure in excess of ~14 bara. The CO2-rich stream would then be expanded from 100 bara to 14 bara, before being routed to the inlet to the ejector. Alternatively the ejector and recycle piping could be designed for a high motive fluid pressure, and the streams could be recycled at the FG compressor inlet at 210 mbarg or higher. Example 2.- variation of ejector outlet pressure In this example, the outlet pressure of the ejector is fixed at the required 110 mbarg, and the full CO2-rich gas flow rate is used as motive fluid. Fig.14 then shows how the suction flow rate of the treated flue gas depleted in CO2, and thus the ejector outlet flow rate, varies with the motive fluid pressure. Centrifugal blowers and compressors can typically operate in a range of 80 to 100%. In this case, if we consider that we need to recycle 90,000 kg / h back to the carbon capture unit inlet (i.e. 90% of the design mass flow rate), a pressure of ~9 bara would be required for the motive fluid. The entrainment ratio, defined as the mass flow ratio of entrained to motive fluid, is in the range of 2.0 to 2.6 in the above examples, with a flue gas containing 20 mol% CO2. A moderate variation in the CO2-rich motive fluid flow rate would thus affect the CO2concentration at the ejector outlet significantly. For technologies that are sensitive to CO2 concentration it is therefore preferable to vary the pressure rather than the flow rate of the CO2-rich motive fluid. Conversely, for technologies that are not particularly sensitive to the CO2 concentration, such as chemical absorption units, the flow rate of the CO2-rich motive fluid could be varied, thereby allowing for continued export of some CO2 product. It should be understood that the present invention is not limited to the described embodiments and that variations can be applied without going outside of the scope of the appended claims. For example, for cases involving a cryogenic cycle on which a CO2-rich stream is used for the refrigeration (Joule Thomson) cycle, and for which the refrigeration duty is thus sensitive to the CO2content at the inlet to the carbon capture unit, a CO2 adjustment stream from a downstream process may provide additional cold to the process. If the CO2 concentration adjustment loop is taken from a downstream system in liquid phase (e.g. Liquid CO2 pipeline, CO2 storage tank, CO2 liquefier), the cold from the CO2-rich liquid stream can be used as a cold assist to compensate for losses of cold in the system. The CO2-rich stream could thus be used as a reflux stream in a stripping or distillation column, or fed to the liquid sump of such a column. If the CO2concentration adjustment loop from a downstream process is in supercritical or compressed gaseous phase, the stream can be expanded through a valve or turbine to generate additional cold for a cryogenic process.

Claims

CLAIMS 1. Calcination kiln plant with a carbon capture unit (6) comprising: - a calcination kiln (1) having a flue gas exit, - a carbon capture pathway (7) having a said carbon capture unit (6) and a flue gas compressor (12) in fluid communication with said flue gas exit of the kiln (1) for feeding said flue gas compressor (12), said carbon capture unit (6) having a flue gas entry connected to a flue gas exit of said flue gas compressor (12), a treated flue gas exit through which a treated flue gas depleted in CO2exits said carbon capture unit (6), and a CO2exit through which a CO2-rich stream (14) is collected, - a stack pathway (5), in fluid communication with said flue gas exit and positioned in parallel of said carbon capture pathway (7), - one or more mass transfer loops (16,17), provided for feeding a gaseous stream to said flue gas compressor (12) of the carbon capture pathway (7).

2. Calcination kiln plant with a carbon capture unit (6) according to claim 1, wherein said mass transfer loop is a bulk flow rate adjustment loop (16) or a CO2 concentration adjustment loop (17).

3. Calcination kiln plant with a carbon capture unit (6) according to claim 2, wherein said bulk flow rate adjustment loop (16) feeds to said flue gas compressor (12) as gaseous stream an additional-air stream, an additional flue gas stream from another kiln or plant, a treated flue gas depleted in CO2, or a CO2- rich stream, wherein one or both of the latter two streams originatefrom a source chosen in the group comprising the carbon capture unit (6), more particularly from the treated flue gas exit or from an intermediate step of the carbon capture unit (6) through which an internal compressed gas exits, a CO2utilization unit, a pressurized gas storage unit, such as a pressurized gas buffer.

4. Calcination kiln plant with a carbon capture unit (6) according to claim 2, wherein said CO2 concentration adjustment loop (17) feeds to said flue gas compressor (12) as gaseous stream CO2-rich stream (14) from said carbon capture unit(6) or from an intermediate stage of the carbon capture unit (6) through which a CO2-rich stream exits, CO2 from a downstream source, such as a CO2 pipeline, CO2 storage device, CO2 from a secondary carbon capture unit, CO2 pressurized buffer.

5. Calcination kiln plant with a carbon capture unit (6) according to any of the previous claims, comprising a gas cooler, preferably a direct contact cooler in fluid communication with said flue gas exit of the kiln (1), with the carbon capture pathway (7) and the stack pathway (5).

6. Calcination kiln plant with a carbon capture unit (6) according to any of the previous claims, comprising a flue gas treatment unit (8) in fluid communication with said flue gas exit of the kiln (1), with the carbon capture pathway (7) and the stack pathway (5).

7. Calcination kiln plant with a carbon capture unit (6) according to claim 5 and claim 6, wherein said flue gas treatment unit (8) is located downstream said gas cooler, said gas cooler having an inlet connected to a gas exit of the flue gas treatment unit (8) provided to output a flue gas depleted in pollutants (9), such as NOx, SOx, carbon or VOC, dust and their combination for establishing the fluid communication with the flue gas exit of the kiln (1).

8. Calcination kiln plant with a carbon capture unit (6) according to any of the previous claims wherein said kiln (1) is a carbonated mineral stones kiln, such as a parallel flow regenerative kiln, a annular shaft kiln, a rotary shaft kiln.

9. Calcination kiln plant with a carbon capture unit (6) according to any of the previous claims, wherein the carbon capture unit (6) is a cryogenic carbon capture unit and wherein said one or more mass transfer loops comprises at least a CO2 concentration adjustment loop (17) or at least a bulk flow rate adjustment loop (16) and a CO2 concentration adjustment loop (17).

10. Calcination kiln plant with a carbon capture unit (6) according to any of the claims 1 to 8, wherein the carbon capture unit (6) is a physical absorption carbon capture unit and wherein said one or more mass transfer loops comprises at least a CO2concentration adjustment loop (17) or at least a bulk flow rate adjustment loop (16) and a CO2concentration adjustment loop (17).

11. Calcination kiln plant with a carbon capture unit (6) according to any of the claims 1 to 8, wherein the carbon capture unit (6) is a chemical absorption carbon capture unit and wherein said one or more mass transfer loops comprises at least a bulk flow rate adjustment loop (16).

12. Calcination kiln plant with a carbon capture unit according to any of the previous claims comprising additional calcination kilns (1).

13. Calcination kiln plant with a carbon capture unit according to any of the previous claims, further comprising an ejector (19) fed by a motive fluid and provided to entrain the gaseous stream to said flue gas compressor(12) of the carbon capture pathway (7).

14. Calcination kiln plant with a carbon capture unit (6) according to claim 13, wherein the motive fluid is a CO2-rich stream (14) from said carbon capture unit (6) or from a side exit of the carbon capture unit (6), optionally after being compressed by a compressor (18) connected to said CO2-rich stream exit of the carbon capture unit (6) or said side exit.

15. Calcination kiln plant with a carbon capture unit (6) according to any of the previous claims, further comprising a gas holder (11), in fluid communication with said flue gas exit of the kiln (1), with the carbon capture pathway (7) and the stack pathway (5), provided for storing or buffering flue gas from the calcination kiln (1).

16. Calcination kiln plant with a carbon capture unit (6) according to claim 15, wherein said gas holder (11) is a pressurized gas holder, fed by a pressurized flue gas from a blower, a fan or a compressor (10), in fluid communication with said flue gas exit of said calcination kiln (1).

17. Calcination kiln plant with a carbon capture unit according to claim 16 and claim 7, wherein said compressor (10) feeding said gas holder (11) has an inlet connected to a gas exit of the cooler for feeding in the gas holder (11) a pressurized, cooled flue gas depleted in pollutants (9), such as NOx, SOx, carbon or VOC, dust and their combination for establishing the fluid communication with the flue gas exit of the kiln (1).

18. Calcination method in a calcination kiln plant with a carbon capture unit (6) according to any of the claims 1 to 17, comprising: - a calcination step of minerals producing flue gas, where said flue gas exits said plant either through a stack pathway (5) or after being treated for carbon capture by passing through a carbon capturepathway (7) comprising said carbon capture unit (6) and a flue gas compressor (12) in fluid communication with said flue gas exit of the kiln (1), said flue gas produced during said calcination step being a gaseous stream feeding said flue gas compressor (12) - a carbon capture step producing a treated flue gas depleted in CO2 (13) and a CO2-rich stream (14), Said method being characterized in that the gaseous stream entering said flue gas compressor (12) has a flow rate stabilized by said bulk flow rate adjustment loop (16) in the range between 50 to 100% of the nominal flow rate.

19. Calcination method in a calcination kiln plant with a carbon capture unit (6) according to claim 18, wherein said gaseous stream has a CO2concentration stabilized by said CO2concentration adjustment loop (17) in the range between 70 to 130 % of the nominal CO2 concentration.

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