Improving efficiency of carbon dioxide recovery in high temperature processes

Abstract

According to the present invention, there is provided a cylindrical device for thermal processing of solid materials, with a gas inlet for supplying gas that is led into the device, having its end within the device at a section of the device that leaves a smaller distance to a solid product discharge end than to a feed end. Further, there is provided a thermal process suitable for carrying out in said device.

Description

IMPROVING EFFICIENCY OF CARBON DIOXIDE RECOVERY IN HIGHTEMPERATURE PROCESSESFIELD

[0001] The present invention relates to a device and a process for the thermal processing of a carbonate-containing raw-material to produce a solid product and a product gas stream containing carbon dioxide (CO2) to be recovered.BACKGROUND

[0002] Conventional calcinations and other similar heat treatments typically rely on the heat produced by the burning of fossil fuels. Such processes result in significant carbon emissions. For example, cement and lime production processes have been considered to be among the world largest CO2 emitters.

[0003] There are numerous development projects taking place worldwide aimed at carbon capture and the utilization of the carbon dioxide formed in high-temperature processes, or at developing replacements to fossil fuels. US 4,354,829 provides a further improvement of such a high-temperature process, and uses oxygen-enriched air to increase the rate of a calcination.

[0004] There is, however, still a need for further development in providing more environmental solutions for high-temperature processes and particularly for efficiently recovering their off gases.SUMMARY OF THE INVENTION

[0005] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0006] According to a first aspect of the present invention, there is provided a device that is suitable for the thermal processing of solid materials, particularly being natural rawmaterials.

[0007] According to a second aspect of the present invention, there is provided a process that may be carried out in said device, the process providing thermal processing of carbonate-containing raw materials.

[0008] According to a further aspect of the invention, there is provided a device and a process that provide an efficient recovery of the carbon dioxide formed in such high- temperature treatments.

[0009] The present invention thus relates to a device for thermal processing of solid materials, the device being in the form of a thermal processing unit, said unit being configured to be rotated around an axis of rotation, the unit having two ends, with one end positioned by the feed end of the device, and the other end positioned by the discharge end of the device, the feed end positioned at a higher level than the discharge end, a feed inlet for solid materials to be processed being positioned by the feed end of the device, and a solid product outlet being positioned by the discharge end, while a gas inlet for supplying gas into the thermal processing unit, is provided with its end opening into the device at a section of the device that leaves a smaller distance to the discharge end of the device than to the feed end.

[0010] Further, the invention relates to a thermal process for reacting a carbonate- containing raw-material in a reaction unit, in a heat-treatment step, to produce a solid product and a product gas stream containing CO2, the process including the step of feeding oxygen to the reaction unit in an oxygen-containing reactant gas stream containing <50vol-% nitrogen.

[0011] Several advantages are achieved using the present process. Among others, the invention achieves a high content of carbon dioxide in the product gas stream, while maintaining an efficient calcination of the solid material. This is achieved by utilizing an oxygen feed to avoid the low-pressure conditions typically forming at the discharge end of high-temperature reaction units. These low-pressure conditions can cause a leakage of gases from surrounding air into the reaction unit. Thus, the oxygen feed will, among others, reduce the carbon dioxide content at the solid product discharge end of the device used for carrying out the process, thus avoiding unnecessary re-carbonation of the solid product without compromising the high carbon dioxide content in the gaseous product. In fact, by eliminatingthis leakage of gases into the reaction unit, the carbon dioxide content in the gaseous product can be increased to almost 100%.

[0012] Another alternative for increasing the CO2 contents in the product gas stream would be to utilize overpressure in the reaction unit. However, the overpressure further increases the contents of undesired gaseous by-products, such as carbon monoxide and carbonyl sulphide, which is a disadvantage. This can be avoided using the oxygen feed described herein.

[0013] Further, the optional electric calcination offers a cost-effective solution of capturing CO2 by decreasing the consumption of energy from burning fossil fuels, while eliminating emissions of e.g. carbon and carbon dioxide from thermal energy production. Further, the electrical heating improves the control of the gas environment in the heat treatment, such as in a calcination, since the amount of flue gas components originating from fuel can be minimized.

[0014] Particularly for cement production, the new process enhances the process sustainability by decreasing the need for external fuel supply and decreasing the emissions.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIGURE 1 illustrates a device encompassed by the present invention, showing a thermal processing unit, forming a rotatable section of the device, with a feed end and a discharge end that may be stationary, the feed end fitted with an inlet for a carbonate material, and the discharge end fitted with an outlet for a solid product, the discharge end further fitted with a gas inlet and the feed end further fitted with an outlet for a gaseous product, while the dotted line represents the axis of rotation.

[0016] FIGURE 2 illustrates a device incorporating some preferred embodiments of the below description, showing for example the optional circulation gas line with one end connected to the gas outlet and another end connected to the gas inlet.

[0017] FIGURE 3 is a graph showing the contents of carbon dioxide (CO2), water (or steam, i.e. H2O), remaining oxygen (O2), and other gases (including nitrogen (N2)) of a gaseous product obtained from a thermal treatment carried out according to the presentinvention, the reference samples processed using the same conditions as the sample of the invention, but without the oxygen feed, and one reference sample processed at overpressure.

[0018] FIGURE 4 is a graph showing the contents of carbon monoxide (CO), sulphur dioxide (SO2), nitric oxide (NO), methane (CH4) and carbonyl sulphide (COS) of the same gaseous product as described above for Figure 3.EMBODIMENTS

[0019] DEFINITIONSIn the present context, the term “heat treatment” encompasses high- temperature process steps, particularly steps that generate carbon dioxide as a by-product. Examples of high-temperature process steps include calcination, sintering and clinkering.In connection with the device, the term “height” or “higher / lower level” refers to a vertical position, or a distance from sea level. Likewise, the terms “feed end” and “discharge end” refer to the ends of the device, where the solid feed inlet and solid product outlet, respectively, are positioned.The term “oxygen-containing reactant gas stream” is, in turn, intended to describe a gas stream, typically in the form of a gas mixture, including molecular components that are at least partially formed of oxygen atoms, such as oxygen gas (O2), carbon dioxide (CO2) or steam (H2O), the latter defined as water in the gas phase. This oxygen-containing reactant gas stream is also defined by its low nitrogen content, as it contains only a limited amount of nitrogen gas (N2). In a preferred alternative, the gas stream can also be defined as having a certain content of oxygen gas (O2). The oxygen percentages of such a gas stream thus refers to the contents of oxygen gas (O2).

[0020] The present invention thus relates to a cylindrical device for thermal processing of solid materials. As shown in Fig. 1, the device is in the form of a thermal processing unit 1 , said thermal processing unit 1 being configured to be rotated around an axis of rotation,the thermal processing unit 1 having two ends, with one end positioned by the feed end of the device, and the other end positioned by the discharge end of the device, these ends of the device preferably being stationary, the feed end positioned at a higher level than the discharge end, a feed inlet 2 for solid materials to be processed being positioned by the feed end of the thermal processing unit 1, and a solid product outlet 3 being positioned by the discharge end, the thermal processing unit 1 further being characterized in that a gas inlet 4 for supplying gas into the thermal processing unit 1 is provided with its end opening into the device, at a section of the device that leaves a smaller distance to its discharge end than to its feed end.

[0021] The oxygen feed is intended particularly to provide a supply of sealing gas, preventing the leakage of atmospheric gases into the device from the outside atmosphere. Thus, the gas inlet 4 is preferably positioned in close vicinity of the seams between the rotatable and the stationary sections of the device, where the risk of leakage is most remarkable. More preferably, the gas inlet 4 for the oxygen feed is positioned inside the device at the third of the device that is closest to the discharge end, whereby the gas inlet 4 can open up into the rotatable unit 1 (see Fig. 1) or into the stationary sections at the discharge end of the device (see Fig. 2). Another equally preferred alternative is to position the gas inlet 4 at the seams between the rotatable and the stationary sections of the device, whereby the oxygen feed is allowed to spray into the device through the seams. A gas outlet 5 for the gaseous product is also typically provided, preferably positioned at the feed end of the device.

[0022] The thermal processing unit 1 is thus preferably rotatable, whereby it typically is supported by a stationary feed end and a stationary discharge end. The feed end may include e.g. a feed chamber, while the discharge end may include e.g. a discharge chamber.

[0023] The feed inlet 2 is typically provided in the form of a feed screw or a funnel, opening into the feed end of the device.

[0024] Although not shown in the Figures, the device is typically fitted also with heating equipment for heating the material in the thermal processing unit 1.

[0025] The device may be for example in the form of a rotary kiln, and may be positioned in various manners, but typically its axis of rotation is orientated horizontally or substantially horizontally, preferably with the two ends of the cylinder at slightly differentlevels. The term ’’axis orientated horizontally” means an axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. Similarly, the term ’’axis orientated substantially horizontally” means an axis that is tilted a few degrees, for example less than 10 degrees, from the axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. In other words, when the device or the thermal processing unit 1 is positioned substantially horizontally, a feed end is fixed at a higher level than a discharge end. Thus, the material carried through the kiln will gradually move from the feed end to the discharge end when the device or the unit 1 is rotated. Additionally, the material is distributed over an inner surface of the cylindrical thermal processing unit 1 by the rotation. When the thermal processing unit 1 is positioned substantially horizontally, the feed inlet 2 is preferably positioned at the front end of the unit 1 that is fixed at a higher level than the back end at which the solid product outlet 3 is positioned.

[0026] The rotational speed of the hollow cylindrical thermal processing unit 1 may be, for example, in the range between 0.1 and 10 revolutions per minute (rpm). The rotational speed may be adjustable.

[0027] Based on the above embodiments, the heat treatment step carried out in said device will take place during a time interval that is determined by the time it takes for the material to move from the feed end of the hollow cylindrical thermal processing unit 1 to the discharge end.

[0028] The heating of the device can be applied using electrical heating equipment or a fuel-powered burner, or a combination of these, the heating equipment preferably positioned to provide a heating effect over substantially the entire area of the thermal processing unit 1. A further option is to position the heating equipment by the discharge end of the substantially horizontal unit 1. However, a larger heated area is preferred. Heating of the cavity within the hollow cylindrical unit 1 thus typically takes place by increasing a wall temperature of the rotatable hollow cylindrical thermal processing unit 1 of the device. The heating equipment may be capable of adjusting the temperature within the cavity, for example in a range between 150 °C and 1600 °C.

[0029] The gas inlet 4 of the device is preferably positioned at the third of the device that is closest to the discharge end, preferably at the quarter of the device closest to the discharge end, and most suitably at the fifth of the device closest to the discharge end.

[0030] In an embodiment, as shown in Fig. 2, the device, or the thermal processing unit 1 further includes a circulation gas line 6 with one end connected to the gas outlet 5 and another end connected to the gas inlet 4, the circulation gas line 6 or the gas inlet 4 being fitted with a separate supply inlet suitable for feeding fresh gas to the device.

[0031] Further, the invention relates to a thermal process for reacting a carbonate- containing raw-material in a thermal processing unit 1, in a heat-treatment step, to produce a solid product and a product gas stream containing CO2, the process being characterized by feeding oxygen to the thermal processing unit 1 in an oxygen-containing reactant gas stream containing <50vol-% nitrogen, and typically >20 vol-% oxygen gas.

[0032] Said process can be carried out using the above described device.

[0033] The oxygen feed is intended particularly to function as a sealing gas, preventing the leakage of atmospheric gases into the device from the outside atmosphere. Such leakage would cause among others an increase in the nitrogen contents in the device used for the process, which would have an undesirable effect on the contents of the product gas streams.

[0034] The raw material is typically a carbonate-containing material, preferably a material containing carbonates in the form of calcium carbonate (CaCCh), calcium magnesium carbonate (CaMgfCCFh), magnesium carbonate (MgCCh), lithium carbonate (Li2CO3), potassium carbonate (K2CO3), or sodium carbonate (ISfeCCh), or a mixture of two or more of these, most suitably being a mineral raw material, such as limestone or dolomite.

[0035] In an embodiment of the process described herein, the oxygen containing reactant gas stream is fed to the heat treatment step as a gas stream consisting of carbon dioxide or steam, or a mixture thereof, the steam e.g. being in the form of superheated steam.

[0036] In another embodiment, the oxygen-containing reactant gas stream is fed to the heat treatment step as a gas stream containing >20 vol-% oxygen (O2), suitable upper limits of the oxygen contents being 65 vol-%, or even 50 vol-%, since the oxygen is not required as a fuel. Preferably, the oxygen-containing reactant gas stream is fed to the heat treatment step as a gas stream containing from > 20 vol-% to 65 vol-%, or 22 - 65 vol-%,more preferably 25 - 55 vol-%, and most suitably 25 - 50 vol-%, or even 30 - 50 vol-%, typically as a mixture being based on carbon dioxide and / or steam, e.g. in the form of superheated steam.

[0037] In either embodiment, the nitrogen (N2) content of the reactant gas stream is <50vol-%, as stated above, but is preferably even lower, such as <20 vol-%, or even <10 vol-%. Thus, according to a particularly preferred alternative, the reactant gas stream that is fed to the process contains 0% nitrogen gas. The oxygen is preferably fed to the process into a section of the device described above that is rich in solid product. In that manner, recarbonation can be efficiently avoided.

[0038] The heat treatment step used in the process may be selected from a wide range of high-temperature processes, and is preferably selected from a calcination, a sintering and a clinkering step, most suitably being a calcination step, e.g. for use as a section of a cement manufacturing process. Other application areas include lime and pulp processes, or other similar combustion processes.

[0039] The heating of the heat treatment step is preferably at least partly achieved via electrical heating, and optionally by combining the electrical heating with heating achieved by combustion, i.e. by burning fuel. It may, however, also be carried out entirely by electrical heating.

[0040] Thus, this electrical heating is particularly suitable for use in the calcination step when applied to the above-mentioned cement manufacturing process.

[0041] The temperature in the heat treatment step is typically >750 °C, preferably 750 - 1500 °C, more preferably 900 - 1100 °C, and most suitably 950-1050 °C, typically determined by measuring the temperature of the air surrounding the material being heated. However, the electrical heating is particularly suitable for use at lower temperature ranges of 750 - 1000 °C, and most suitably when the heat treatment is carried out as the above- mentioned calcination.

[0042] Generally, this heat treatment is carried out at a pressure that is close to atmospheric pressure, typically at a slight overpressure level of 0.1 to 0.5 bar, but electric calcination can also be operated at a slight vacuum, which facilitates the calcinationreaction. In practice, the calcination reaction occurs within the range of -0.5 to 2 bar pressure, preferably 0.1 - 0.5 bar, while the pressures for other heat treatments have larger variation within the range of -1 - 10 bar. The duration of the heat treatment step may range from 2 seconds to 10 days, partly based on the temperature and on the rate of energy transfer, which are significantly influenced by the type of equipment and process. Further, the selected raw material has an influence. Typically, the residence time in a rotary kiln could be 1 - 30 h, or 6 - 24 h.

[0043] The scope of this description also includes the alternative, wherein a preheating step is carried out, e.g. to pre-dry the raw material before the above-described heat treatment, which pre-heating step can be carried out at a lower temperature than the heat treatment step, such as a temperature of 150 - 800 °C, preferably 200 - 750 °C, and more preferably 500 - 750 °C. In the device described above, such a pre-heating step can be carried out in a separate storage unit (not shown in the Figures) provided with heating and preferably with mixing, including an outlet for solid material, from which the pre-heated material can be carried via a line to the solid material inlet 2 of the device.

[0044] In the present process, the heat treatment step is carried out with added oxygen. No further additives are required. In an embodiment, the added oxygen is in the form of oxygen gas (O2), thus resulting in a higher quality for the CO2 in the resulting product gas stream, and a more efficient burning, particularly in a high-temperature heattreatment, such as a clinkering step, also allowing an adjustment of the temperature used in such a step, thus providing further variety in the choice of fuel as the requirements for the energy content are reduced. The oxygen can for example be oxygen produced by electrolysis from water using Reaction (1),Thus, the oxygen can optionally be produced at the same site of the present process, and is preferably used as a mixture of oxygen gas and steam.

[0045] In another embodiment, the heat treatment step is carried out in the presence of steam, preferably in the form of superheated steam. This steam (H2O) will, among others, in addition to forming a supply of oxygen, also have the effect of reducing the temperature required for the heat treatment, which will further increase the durability of theprocess equipment and the wear resistance of the materials of the equipment, as well as improve the structural strength of the equipment structures. Further, it may improve both the energy efficiency of the process and the quality of the products. Further, the steam and other added components are also beneficial, at least indirectly, in optimizing the specific contents of the product gas stream containing CO2, particularly increasing the CO2 content of the recovered dry gas. A particular advantage of the steam is that it, among others, is easy to condense, and thus separate from the other components of the product gas.

[0046] The heat treatment step of the present invention produces both a solid product, e.g. containing calcium oxide (CaO) in case of a calcination, as well as the product gas stream containing CO2 that may be recovered after the present process. This gas product is rich in CO2, typically containing >50 vol-% CO2, preferably 85 - 95 vol-%. Further, it may contain oxygen (O2), hydrogen (H2), nitrogen (N2), and / or steam (H2O), and traces of other gases.

[0047] In an embodiment, the product gas stream containing carbon dioxide (CO2), obtained from the heat treatment step, can be separated from the other components of the product gas stream to provide a purified gas stream, or it can be purified or concentrated in connection with the recovery, to increase the CO2 content of this gas stream, and / or to remove undesired components, such as excess oxygen, nitrogen or sulphur dioxide. This purification can take place e.g. by washing, cooling or drying the gas stream, or by a combination of two or more such techniques, and preferably results in a CO2 concentration of >85 vol-%.

[0048] In another embodiment, the CCh-containing product gas stream obtained from the heat treatment step is recovered or is utilized as dilution gas in the heat treatment step, preferably being utilized as dilution gas, more preferably by being mixed with the oxygen being fed to the device in the reactant gas stream.

[0049] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0050] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0051] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0052] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0053] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0054] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. Thefeatures recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a pluralityEXAMPLE - Gas products formed by calcination with oxygen feed

[0055] A calcination of a calcium carbonate (CaCCh) material was carried out at a temperature of 1000 °C, using electrically assisted heating and a continuous feed of an oxygen-containing reactant gas stream (here provided as a mixture of O2 and CO2 having an oxygen content of 40 vol-%). Two reference samples were also processed, at the same temperature of 1000°C, one at normal pressure, and one at overpressure, but both reference samples were processed without the oxygen feed.

[0056] A solid product of calcium oxide (CaO) was obtained from all samples, as well as a gaseous product containing mainly carbon dioxide (CO2). The contents of CO2 and other gases in the gaseous product is shown in Figs. 3 and 4, and these contents varied due to the different conditions, particularly due to the presence or absence of oxygen feed.

[0057] Particularly, Fig. 3 shows the contents of carbon dioxide (CO2), water (or steam, i.e. H2O), remaining oxygen (O2), and other gases (including nitrogen (N2)) of the gaseous product, and Fig. 4 shows its contents of carbon monoxide (CO), sulphur dioxide (SO2), nitric oxide (NO), methane (CH4) and carbonyl sulphide (COS).

[0058] As the results show, high CO2 contents (or low N2 contents) of the product gas were achieved by either using an oxygen feed (the invention) or by using overpressure in the reaction unit. As the middle column of Fig. 3 shows, the leakage of N2 into the reaction unit results in more than double the amount of N2 to be removed from the product gas, as compared to the reference utilizing overpressure. The overpressure is the conventional measure used to prevent the leakage of atmospheric gas (~78% N2 content) into the reaction unit. However, the overpressure further increased the contents of CO and COS, which is another disadvantage.INDUSTRIAL APPLICABILITY

[0059] The present invention provides a high-temperature process for treating a carbonate-containing raw material, and resulting in a high content of carbon dioxide, with a low content of harmful by-products, in a product gas stream, while maintaining an efficient thermal reaction in the solid material.

[0060] Due to the suitable reaction scheme, the process steps of the invention are most suitably used as a section of a cement manufacturing process.REFERENCE SIGNS LISTAs shown in Figs. 1 and 2, the device described herein may at least according to some embodiments include:1 Thermal processing unit2 Feed inlet3 Solid product outlet4 Gas inlet5 Gas outlet6 Circulation gas lineCITATION LISTPatent LiteratureUS 4,354,829

Claims

CLAIMS:

1. A cylindrical device for thermal processing of solid materials, the device being in the form of a thermal processing unit (1), said thermal processing unit (1) being configured to be rotated around an axis of rotation, the thermal processing unit (1) having two ends, with one end positioned in the feed end of the device, and the other end positioned in the discharge end of the device, the feed end positioned at a higher level than the discharge end, a feed inlet (2), for solid materials to be processed, being positioned by the feed end of the device, and a solid product outlet (3) being positioned at the discharge end, characterized in that a gas inlet (4) for supplying gas into the thermal processing unit (1) is provided with its end opening into the device at a section of the device that leaves a smaller distance to the discharge end than to the feed end, and in that the device is fitted with electrical heating equipment.

2. The device of claim 1, which is orientated substantially horizontally.

3. The device of claim 1 or 2, the electrical heating equipment being positioned to provide a heating effect over substantially the entire area of the device.

4. The device of any preceding claim, wherein the gas inlet (4) is positioned at the third of the device that is closest to the discharge end, preferably at the quarter of the device closest to the discharge end, and most suitably at the fifth of the device closest to the discharge end, and a gas outlet (5) is positioned at the feed end of the device.

5. The device of any preceding claim, which includes a circulation gas line (6) with one end connected to a gas outlet (5) of the device and another end connected to a gas inlet (4) of the device, the circulation gas line (6) or the gas inlet (4) being fitted with a separate supply inlet, suitable for feeding fresh gas to the device.

6. The device of any preceding claim, being a rotary kiln.

7. A thermal process for reacting a carbonate-containing raw-material in a thermal processing unit (1), by carrying out a heat-treatment step, to produce a solid product and a product gas stream containing CO2, the process being characterized by feeding oxygen to the thermal processing unit (1) in an oxygen-containing reactant gas stream containing >20vol-% oxygen gas and <50vol-% nitrogen, carrying out the heat treatment step by electrical heating, and recovering the carbon dioxide.

8. The process of claim 7, wherein the carbonate-containing raw material contains the carbonates in the form of calcium carbonate (CaCCh), calcium magnesium carbonate (CaMgt'CChh), magnesium carbonate (MgCCh), lithium carbonate (I^CCh), potassium carbonate (K2CO3), or sodium carbonate (Na2COs), or a mixture of two or more of these, and is preferably a mineral raw material, such as limestone or dolomite.

9. The process of claim 7 or 8, wherein the oxygen-containing reactant gas stream is fed to the process into a section of the thermal processing unit (1) that is rich in solid product.

10. The process of any of claims 7 to 9, wherein the oxygen-containing reactant gas stream is fed to the heat treatment step as a gas stream consisting of carbon dioxide or steam, or a mixture thereof, the steam e.g. being in the form of superheated steam.

11. The process of any of claims 7 to 9, wherein the oxygen-containing reactant gas stream is fed to the heat treatment step as a gas stream containing from >20 vol-% to 65 vol-% oxygen gas, preferably 22 - 65 vol-%, more preferably 25 - 55 vol-%, and most suitably 30 - 50 vol-%, typically in the form of a gas mixture being based on carbon dioxide and / or steam, e.g. in the form of superheated steam.

12. The process of any of claims 7 to 11, wherein the oxygen is fed to the heat treatment step as a reactant gas stream containing <20 vol-% nitrogen gas, preferably <10 vol-% nitrogen gas.

13. The process of any of claims 7 to 12, wherein the heat treatment step is carried out to produce a calcined material.

14. The process of any of claims 7 to 13, wherein the temperature during the heat treatment step is >750 °C, preferably 750 - 1500 °C, more preferably 900 - 1100 °C.

15. The process of any of claims 74to 14, wherein the heat treatment step is carried out in the device of any of claims 1 to 6.

16. The process of any of claims 7 to 15, wherein the CCh-containing product gas stream is recovered or is utilized as dilution gas in the heat treatment step, preferably being utilized as dilution gas, more preferably by being mixed with the oxygen being fed to the reaction unit in the reactant gas stream.

17. The process of any of claims 7 to 15, wherein the CO2 is separated from the remaining components of the CCh-containing product gas stream to provide a purified CO2 gas stream.

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