Optimised partial decarbonisation in clinker production

Abstract

The present invention relates to a device for thermally treating a mineral material, wherein the device comprises a preheater (10) and a calciner (20), wherein the preheater (10) is arranged upstream of the calciner (20) in the direction of material flow, wherein the device comprises an oxygen gas source (70), wherein the oxygen gas source (70) is connected to the calciner (20), characterised in that a heat exchanger (60) is arranged between the oxygen gas source (70) and the calciner (20), wherein the oxygen gas source (70) and the heat exchanger (60) are connected for conveying an oxygen-containing gas, wherein the heat exchanger (60) and the calciner (20) are connected for conveying an oxygen-containing gas, and wherein the calciner (20) and the heat exchanger (60) are connected to one another for conveying a material stream.

Description

[0001] Optimized partial decarbonation in clinker production

[0002] The invention relates to a device for the thermal treatment of a mineral material, in particular for the production of clinker, which separates a portion of the carbon dioxide produced.

[0003] In the current situation, reducing carbon dioxide emissions is a political, social, and economic imperative. Rapid implementation is crucial, particularly finding solutions that allow existing plants to be retrofitted to capture at least a significant portion of the carbon dioxide, thus focusing on a rapid, though not complete, reduction of carbon dioxide emissions. The cement industry offers significant potential in this regard, as the production of clinker from limestone releases substantial amounts of CO2 from the mineral material. This means that only about one-fifth of the CO2 emissions originate from the fuel itself, while simultaneously generating very high quantities of CO2.

[0004] One of the most interesting options for decarbonizing the cement industry is oxyfuel technology, which uses the purest possible oxygen for combustion. Ideally, the combustion of organic material produces carbon dioxide and water. Water is very easy to separate, while nitrogen separation is considerably more complex. Therefore, reducing the nitrogen input significantly simplifies carbon dioxide removal. To integrate this technology as a retrofit into existing plants, the current concept involves constructing a new calciner based on the oxyfuel principle, separated from the gas stream exiting the kiln.Since the calciner is where the majority of the fuel is burned and where the highest proportion of the material's deacidification occurs—i.e., the release of mineral-bound carbon dioxide—it is possible to capture roughly 80% of the resulting CO2. The kiln's exhaust gases bypass the new oxyfuel calciner and pass through the existing preheater. Due to their high nitrogen content, these exhaust gases are then released into the atmosphere. This allows for maximum climate protection with minimal modifications. Oxyfuel clinker production without recirculation of the preheater exhaust gases is known from WO 2019 / 211 196 A1.

[0005] One drawback of such a retrofit solution is that the oxygen would be supplied to the calcinator at a low temperature. To ensure sufficient lifting capacity, the use of hot lifting gas at least 750 °C is advantageous to prevent the flow cross-sections from becoming too small and to simultaneously enable the ignition of fuel in the downstream calciner. Therefore, burners or separate combustion chambers are currently used to preheat the oxygen and subsequently ignite the fuel supplied to the calciner. For technical reasons, however, only high-quality fuels such as pulverized coal or natural gas are suitable for this purpose, whereas alternative fuels, such as biomass, can often be used in the calciner itself. It would therefore be desirable to be able to forgo these primary resources for preheating the oxygen.

[0006] WO 2022 / 179847 A1 discloses a height-optimized device for the heat treatment of mineral substances.

[0007] From WO 2024 / 033831 A1 a process and a plant for the production of cement-like materials are known.

[0008] From DE 10 2022 209877 A1, the exclusive use of substitute fuels for the thermal treatment of mineral substances, in particular clays, is known.

[0009] From WO 2024 / 170265 A1, an optimized heat management system in a plant for the thermal treatment of mineral substances is known.

[0010] A calcination process for carbonates is known from WO 2024 / 102480 A1. The object of the invention is to adapt the oxygen supply to the calcinator in such a way that valuable primary fuels can be dispensed with.

[0011] This problem is solved by the device with the features specified in claim 1 and by the method with the features specified in claim 7. Advantageous embodiments are described in the dependent claims, the following description, and the drawing.

[0012] The device according to the invention is used for the thermal treatment of a mineral material, in particular a device for the production of clinker. The device comprises a preheater, a calciner, and a furnace. The preheater is arranged upstream of the calciner in the direction of material flow, and the calciner is arranged upstream of the furnace in the direction of material flow. This corresponds to the classic arrangement in a cement plant. However, the furnace is not connected to the calciner for the transfer of the gas flow as is usual. Rather, in this embodiment, the gas flow from the furnace is not directed into the calciner so that the furnace can continue to be operated with air and no conversion of the furnace is necessary. Therefore, the furnace is connected to the preheater for the direct transfer of the gas flow (i.e., not via the calciner as usual). The device includes an oxygen gas source.The oxygen gas source can, for example, and preferably, be an air separation unit, such as a cryogenic air separation process (Linde process). It can also be a liquid oxygen tank. The oxygen gas source preferably provides an oxygen-containing gas with at least 50% by volume, more preferably at least 75% by volume, more preferably at least 90% by volume, and most preferably at least 95% by volume oxygen. The oxygen gas source is connected to the calciner for transferring the oxygen-containing gas.

[0013] According to the invention, a heat exchanger is arranged between the oxygen gas source and the calcinator. The oxygen gas source and the heat exchanger are connected to transfer an oxygen-containing gas. The heat exchanger and the calcinator are also connected to transfer an oxygen-containing gas. The calcinator and the heat exchanger are connected to transfer a material stream of the material being calcined in the calcinator. Furthermore, the heat exchanger and the furnace are connected to transfer a material stream. This material has a very high temperature according to the calcination conditions. If the device includes a furnace, this material is transferred directly from the calcinator to the furnace, where it is heated further and to a higher temperature, thus completing the calcination process.In this embodiment, the heat exchanger and the furnace are connected to transfer the material stream cooled in the heat exchanger. This means that the material entering the furnace is colder. This can be compensated for in two ways. Firstly, the material can be calcined in the calciner at a slightly higher temperature. Since the treatment in the furnace takes place at even higher temperatures, this is theoretically possible, but not preferred for various reasons. Alternatively, a higher firing rate in the furnace can compensate for the heat loss. Since heat is extracted from the main process in either case, this embodiment appears disadvantageous. However, this embodiment makes it possible to bring the oxygen-containing gas to the required inlet temperature for the calciner without the need for high-quality fuels, thus conserving valuable resources.

[0014] In a further embodiment of the invention, the heat exchanger is selected from the list comprising reactors capable of parallel or countercurrent flow, in particular a cyclone, a fluidized bed reactor, a stationary or non-stationary fluidized bed reactor.

[0015] In a further embodiment of the invention, the heat exchanger comprises at least a first heat exchanger stage and a second heat exchanger stage. Such a cascaded design makes it possible to preheat the oxygen-containing gas to a higher temperature. Furthermore, the pure oxygen gas flow is comparatively small, so the capacity for calcined, i.e., hot, material may be limited, and thus the maximum amount of heat that can be supplied is also limited. Due to the cascaded design, the oxygen-containing gas can be brought into contact with a larger amount of calcined, i.e., hot, material and thus be heated more effectively if the capacity is insufficient. In a further embodiment of the invention, the oxygen gas source and the first heat exchanger stage are connected for transferring the oxygen-containing gas. The first heat exchanger stage and the second heat exchanger stage are connected for transferring an oxygen-containing gas.Furthermore, the second heat exchanger stage and the calcinator are connected for transferring an oxygen-containing gas. The oxygen-containing gas thus cascades through the stages of the heat exchanger. The calcinator and the first heat exchanger stage are connected to transfer the material flow. The calcinator and the second heat exchanger stage are also connected to transfer the material flow. Calcined material at the maximum temperature is fed into both heat exchanger stages. This differs from the usual cascaded process, where the solid material is also fed in a counterflow to the gas flow. This ensures that the material passing through the heat exchanger is not cooled down as much and is therefore delivered to the furnace or material cooler at a warmer temperature.Furthermore, this maximizes the respective temperature difference, which in turn accelerates the heating of the oxygen-containing gas and ultimately leads to a higher final temperature. The first heat exchanger stage and the furnace or material cooler are connected to transfer the material flow, and the second heat exchanger stage and the furnace or material cooler are also connected to transfer the material flow. The final thermal treatment of the mineral material then takes place in the furnace, while the material cooler cools it to a temperature suitable for storage or transport.

[0016] In a further embodiment of the invention, an electric heating device for heating the oxygen-containing gas is arranged between the heat exchanger and the calcinator. Since the preheater can already achieve an elevated temperature, but this must always be lower than that in the calcinator, the difference can be made, if necessary, by an electric heating device, as this can be operated without the insertion of a new CO2 source. However, since electricity is usually more expensive than the fuels, only superheating after the heating in the preheater is advantageous here in order to keep costs as low as possible. In a further embodiment of the invention, the calcinator is connected to the heat exchanger for the transfer of carbon dioxide-containing gas. This can be done directly or via the additional preheater and optionally further components, for example, a dust filter.By recirculating carbon dioxide, the volume flow rate in the calcinator can be increased, thus easily enhancing its carrying capacity for solids. Preferably, the hot gas directly after the calcinator is used. However, the carbon dioxide-containing gas can also originate from a further preheater located downstream of the calcinator in the gas flow direction. In this case, the carbon dioxide-containing gas can be fed to the oxygen-containing gas before, within, or after the preheater. To optimally utilize the temperature gradients, feeding the gas after the preheater is preferred. Conversely, feeding it before the preheater allows for a higher solids loading, and thus the feeding of more calcined material and consequently more heat.

[0017] In another embodiment of the invention, the calcinator is connected downstream of a carbon dioxide separator. Preferably, the furnace is not connected downstream of a carbon dioxide separator. This takes advantage of the fact that the largest proportion of carbon dioxide is generated in the calcinator, which can be converted to oxyfuel operation, for example, particularly efficiently and easily. This allows a high proportion, for example around 80%, of the carbon dioxide to be separated. If biomass is used in the calcinator, a higher separation rate can be achieved through carbon balancing, since carbon dioxide released from biomass is considered climate-neutral. However, this carbon dioxide is separated in the carbon dioxide separator and can thus compensate for the total amount of carbon dioxide released in the furnace.To make this possible, the invention is particularly helpful, as it eliminates the need for primary raw materials such as coal and natural gas, which would prevent eligibility here.

[0018] In another aspect, the invention relates to a method for the thermal treatment of a mineral material, particularly in the cement industry, and especially for the production of clinker from limestone. The mineral material is successively preheated in a preheater, calcined in a calciner, and fired in a kiln. This corresponds to the conventional process. However, the gas heated in the kiln is not fed to the calciner as usual. Normally, the gas is fed countercurrently to the material, i.e., from the kiln to the calciner, thereby optimally utilizing the heat from the gases in the kiln. This economically important point is precisely what is omitted in conventional systems. The gas heated in the kiln is fed directly to the preheater, bypassing the calciner. An oxygen-containing gas is supplied to the calciner, but this gas does not originate from the kiln.Preferably, the oxygen-containing gas is an oxygen-enriched gas used to operate the calcinator in the oxyfuel process. However, only the calcinator, and not the furnace itself, is operated in this way, which significantly simplifies retrofitting. The oxygen-containing gas is preheated in a heat exchanger before entering the calcinator. This is advantageous because, firstly, the gas does not exit the furnace at high temperatures, and secondly, it ensures a reliable ignition temperature in the calcinator, particularly when using alternative fuels such as biomass. At least a portion of the material calcined in the calcinator is fed into the heat exchanger. There, the calcined material releases some of its heat, warming the oxygen-containing gas without requiring any additional fuel.This is disadvantageous for the actual process because the calcined material is fed from the heat exchanger to the furnace or material cooler and thus reaches the furnace at a lower temperature. However, the saving of valuable primary fuels for preheating the oxygen-containing gas has proven to be more advantageous than the aforementioned disadvantages. Additionally, the lower partial pressure of carbon dioxide in the calcined material, when introduced into the oxygen-containing gas stream in the heat exchanger, further reduces its carbon dioxide content. This increases the area operated in the oxyfuel process and therefore the total amount of carbon dioxide separated. The calcined material is fed from the heat exchanger to the furnace. As already mentioned above, this is initially disadvantageous due to the reduced temperature of the material.

[0019] In a further embodiment of the invention, the heat exchanger has at least one first heat exchanger stage and one second heat exchanger stage. However, it can also have three or more stages. The oxygen-containing gas is first fed into the first heat exchanger stage and then from the first heat exchanger stage into the second heat exchanger stage. If the heat exchanger has further stages, the oxygen-containing gas is also passed through these in a cascaded manner. From the second heat exchanger stage (possibly via further stages), the oxygen-containing gas is fed into the calciner. Calcined material is fed from the calciner in parallel into the first heat exchanger stage and into the second heat exchanger stage, i.e., not in a cascaded counterflow to the oxygen-containing gas. This ensures that each stage receives the mineral material at the highest temperature.Furthermore, the carrying capacity of the oxygen-containing gas is lower than that of the calcined material due to the smaller gas volume compared to the calciner, which generates large quantities of carbon dioxide. Therefore, by distributing the solids stream across the different stages, sufficient carrying capacity can be more easily ensured, allowing a larger proportion or even the entire solids stream to be used for preheating. The calcined material from the first and second heat exchanger stages is recombined and fed back into the furnace. This ensures that the maximum amount of heat from the calcined material is available in each stage, making it easier to achieve a higher final temperature.

[0020] In an alternative embodiment, the mineral material is cascaded and passed in counterflow through the stages of the heat exchanger.

[0021] In a further embodiment of the invention, the oxygen-containing gas between the heat exchanger and the calciner is electrically heated. Since the heat exchanger can only ever reach a lower temperature level than the material used for heating, in this case the calcined material, additional electric heating can be advantageous. The benefit of electric heating is that it is easier to integrate into a carbon dioxide reduction concept.

[0022] In a further embodiment of the invention, the carbon dioxide coming from the calciner is separated in a carbon dioxide separation device. Preferably, the carbon dioxide coming from the furnace is not separated. This facilitates quick and easy integration into existing systems, particularly without having to modify the rotary kiln.

[0023] In a further embodiment of the invention, the calcinator is operated according to the oxyfuel process. This means that the supplied oxygen-containing gas has at least 50 vol%, preferably at least 75 vol%, more preferably at least 90 vol%, and particularly preferably at least 95 vol% oxygen. Two different operating modes of the oxyfuel process are distinguished. In the first operating mode, carbon dioxide-containing gas is recirculated after the calcinator to its gas inlet. In simplified terms, the recirculated carbon dioxide essentially replaces the nitrogen from the air in the conventional process, so that the calcinator can be operated practically like a conventional one with regard to load-bearing capacity and combustion properties. In the second operating mode, no gas is recirculated.This reduces the amount of gas in the calcinator; the process must be adapted to the reduced amount of gas. However, the process is more efficient due to the lack of gas recirculation, because the calcinator and preheater can be built considerably smaller, the thermal efficiency of the process is significantly improved, the amount of air drawn in through recirculation and larger cross-sections is reduced, leading to a lower proportion of inert gases, such as nitrogen and argon, in the exhaust gas and improving the energy efficiency of the downstream CO2 purification.

[0024] In a further embodiment of the invention, the oxygen-containing gas supplied to the calcinator is heated to at least 500 °C, preferably to at least 700 °C, particularly preferably to at least 1000 °C, before it is supplied to the calcinator.

[0025] In a further embodiment of the invention, a substitute fuel is supplied to the calcinator for combustion. Biomass is particularly preferably chosen as the substitute fuel, so that, in combination with carbon dioxide separation, a negative carbon dioxide emission can be achieved for the calcinator, thus at least partially compensating for the emissions from the furnace. In a further embodiment of the invention, the heat exchanger is designed as a gravity separator. The heat exchanger is operated with a loading of at least 3 kg of solids per kg of gas, preferably at least 5 kg of solids per kg of gas, and particularly preferably at least 10 kg of solids per kg of gas.

[0026] In a further embodiment of the invention, the heat exchanger is designed as a multi-stage direct heat exchanger. The heat exchanger is operated with a loading of at most 3 kg of solids per kg of gas, preferably at most 2 kg of solids per kg of gas.

[0027] The device according to the invention is explained in more detail below with reference to an embodiment shown in the drawing.

[0028] Fig. 1 schematic exemplary device

[0029] Fig. 2 schematic further exemplary device

[0030] Fig. 3 schematic further device not according to the invention without oven

[0031] Figure 1 shows a schematic representation of an exemplary device. For example, the area shown on the right in the illustration can be an existing older plant, while the area shown on the left shows the retrofit with a calcinator 20 operated according to the oxyfuel process with a carbon dioxide separation device 50, i.e., in particular a retrofit solution for an existing plant for a significant reduction of carbon dioxide emissions.

[0032] The raw material, in particular limestone, is fed into the preheater 10 and heated there by a gas stream from the kiln 30. The preheated material is transferred to the calciner 20 and calcined there. The calcined material is then transferred to the kiln 30, fired there, and subsequently cooled in the material cooler 40. The air from the material cooler 40 is preheated and supplied to the kiln 30. The material cooler 40, kiln 30, and preheater 10 are operated with normal ambient air, and the exhaust gases are released back into the environment. Optionally, a further calciner 22 can be provided, which may, for example, be existing equipment. This can be partially operated or simply used as a gas line.

[0033] The calcinator 20 is preferably operated according to the oxyfuel process in a gas stream separate from the furnace 30 and preheater 10. For this purpose, a gas with at least 95 vol% oxygen is provided by means of an oxygen gas source 70, for example by means of a membrane process. The oxygen-containing gas is transferred to the heat exchanger 60, which is configured here as a three-stage unit. The oxygen-containing gas is passed successively through the third heat exchanger stage 63, the second heat exchanger stage 62, and the first heat exchanger stage 61, and is thus preheated before entering the calcinator 20. The calcined material coming from the calcinator 20 serves to preheat the oxygen-containing gas in the heat exchanger 60. This material is fed in parallel, and thus at its highest temperature, to the first heat exchanger stage 61, the second heat exchanger stage 62, and the third heat exchanger stage 63, and is then fed to the furnace 30.The gas coming from the calcinator 20 is fed via a further preheater 12 to the carbon dioxide separator 50 for heat recovery. Since only small amounts of nitrogen or argon are introduced into the gas stream from the oxygen gas source 70, the gas at the inlet of the carbon dioxide separator 50 consists mainly of water vapor and carbon dioxide, which significantly simplifies the carbon dioxide separation.

[0034] Figure 2 shows another exemplary device, which differs from the exemplary device shown in Figure 1 in that the heat exchanger 60 is designed entirely in counterflow. The material flow is thus guided from the calcinator 20 through the first heat exchanger stage 61, the second heat exchanger stage 62, and the third heat exchanger stage 63 into the furnace 30.

[0035] Fig. 3 shows an alternative, non-inventive solution that operates without a furnace 30. Therefore, in the example shown, the material cooler 40 is three-stage, consisting of a first material cooler stage 41, a second material cooler stage 42, and a third material cooler stage 43. The device also includes a preheater 80. This allows the material cooler 40 and the preheater 80 to be operated, for example, with a gas stream of air without introducing unwanted gases into the calciner 20.

[0036] Reference sign

[0037] 10 preheaters

[0038] 12 additional preheaters

[0039] 20 Calcinator

[0040] 22 more Calcinators

[0041] 30 oven

[0042] 40 material coolers

[0043] 41 first material cooling stage

[0044] 42 second material cooling stage

[0045] 43 third material cooling stage

[0046] 50 Carbon dioxide separator

[0047] 60 heat exchangers

[0048] 61 first heat exchanger stage

[0049] 62 second heat exchanger stage

[0050] 63 third heat exchanger stage

[0051] 70 Oxygen gas source

[0052] 80 pre-heaters

Claims

Patent claims 1. Device for the thermal treatment of a mineral material, wherein the device comprises a preheater (10), a calcinator (20) and a furnace (30), wherein the preheater (10) is arranged upstream of the calcinator (20) in the material flow direction, wherein the calcinator (20) is arranged upstream of the furnace (30) in the material flow direction, wherein the furnace (30) is connected to the preheater (10) for the direct transfer of the gas flow, wherein the device comprises an oxygen gas source (70), wherein the oxygen gas source (70) is connected to the calcinator (20), characterized in that a heat exchanger (60) is arranged between the oxygen gas source (70) and the calcinator (20), wherein the oxygen gas source (70) and the heat exchanger (60) are connected for the transfer of an oxygen-containing gas, wherein the heat exchanger (60) and the calcinator (20) are connected for the transfer of an oxygen-containing gas.wherein the calcinator (20) and the heat exchanger (60) are connected to each other for transferring a material flow, wherein the heat exchanger (60) and the furnace (30) are connected to each other for transferring a material flow.

2. Device according to claim 1, characterized in that the heat exchanger (60) is selected from the list comprising a co-current or counter-current reactor, in particular a cyclone, a fluidized bed reactor, a stationary or non-stationary fluidized bed reactor.

3. Device according to one of the preceding claims, characterized in that the heat exchanger (60) has at least a first heat exchanger stage (61 ) and a second heat exchanger stage (62).

4. Device according to one of the preceding claims, characterized in that an electric heating device for heating the oxygen-containing gas is arranged between the heat exchanger (60) and the calcinator (20).

5. Device according to one of the preceding claims, characterized in that the calcinator (20) is connected to the heat exchanger (60) for transferring carbon dioxide-containing gas.

6. Device according to one of the preceding claims, characterized in that the calcinator (20) is connected downstream of a carbon dioxide separation device (50).

7. A method for the thermal treatment of a mineral material, wherein the mineral material is successively preheated in a preheater (10), calcined in a calcinator (20) and fired in a furnace (30), wherein an oxygen-containing gas is supplied to the calcinator (20), wherein the oxygen-containing gas is preheated in a heat exchanger before the calcinator (20), wherein at least a portion of the material calcined in the calcinator (20) is supplied to the heat exchanger (60), wherein the calcined material is supplied from the heat exchanger (60) to the furnace (30), wherein the gas heated in the furnace (30) is supplied directly to the preheater (10), and wherein the calcined material is supplied from the heat exchanger (60) to the furnace (30).

8. Method according to claim 7, characterized in that the heat exchanger (60) has at least a first heat exchanger stage (61) and a second heat exchanger stage (62), wherein the oxygen-containing gas is first fed into the first heat exchanger stage (61) and from the first heat exchanger stage (61) is fed into the second heat exchanger stage (62) and from the second heat exchanger stage (62) into the calcinator (20), wherein calcined material from the calcinator (20) is fed in parallel into the first heat exchanger stage (61) and into the second heat exchanger stage (62), wherein the calcined material from the first heat exchanger stage (61) and from the second heat exchanger stage (62) is fed into the furnace (30).

9. Method according to one of claims 7 to 8, characterized in that the oxygen-containing gas is electrically heated between the heat exchanger and the calcinator (20).

10. Method according to one of claims 7 to 9, characterized in that the carbon dioxide coming from the calcinator (20) is separated in a carbon dioxide separation device (50).

11. Method according to one of claims 7 to 10, characterized in that the calcinator (20) is operated according to the oxyfuel method.

12. Method according to one of claims 7 to 11, characterized in that the oxygen-containing gas supplied to the calcinator (20) is heated to at least 500 °C, preferably to at least 700 °C, particularly preferably to at least 1000 °C, before it is supplied to the calcinator (20).

13. Method according to one of claims 7 to 12, characterized in that a substitute fuel is supplied to the calcinator (20) for combustion.

14. Method according to one of claims 7 to 13, characterized in that the heat exchanger (60) is designed as a gravity separator, wherein the heat exchanger (60) is operated with a loading of at least 3 kg of solids per kg of gas, preferably at least 5 kg of solids per kg of gas, particularly preferably at least 10 kg of solids per kg of gas.

15. Method according to one of claims 7 to 13, characterized in that the heat exchanger (60) is designed as a multi-stage direct heat exchanger (60), wherein the heat exchanger (60) is operated with a loading of at most 3 kg of solids per kg of gas, preferably at most 2 kg of solids per kg of gas.

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