Method for the flexible operation of a carbon dioxide capture system in a cement plant

Abstract

The present invention relates to a method for operating a device for the thermal treatment of mineral substances, wherein the device comprises a preheater 10, a calciner 20 and a furnace 30, wherein the mineral substance is partially introduced into the preheater 10, is conveyed from the preheater 10 into the calciner 20 and from the calciner 20 into the furnace 30, wherein the gas stream of the furnace 30 is guided past the calciner 20, wherein the device comprises an oxygen source 60, wherein an oxygen-rich gas is guided from the oxygen source 60 to the calciner 20, wherein the gas stream is directed from the calciner 20 into the preheater 10, wherein the device comprises a carbon dioxide processing device 70, wherein the carbon dioxide processing device 70 is arranged downstream of the calciner 20, and wherein the device comprises a furnace calciner 21 and a furnace preheater 11.wherein the gas stream from the furnace 30 is directed into the furnace calcinator 21 and from the furnace calcinator 21 into the furnace preheater 11, wherein the mineral material is introduced proportionally into the furnace preheater 11, wherein the solid stream leaving the furnace preheater 11 is divided between the calcinator 20 and the furnace calcinator 21, wherein a load-dependent proportional return of the gas stream leaving the preheater 10 to the oxygen-rich gas between the oxygen source 60 and the calcinator 20 takes place.

Description

[0001] The invention relates to a method for controlling the partial separation of carbon dioxide in a cement plant retrofitted with an oxyfuel calcinator depending on the availability of regeneratively generated electricity in order to achieve an optimum in the long term average.

[0002] The cement industry is among the largest emitters of carbon dioxide, as carbon dioxide is released directly from the limestone itself. Even when using fossil fuels, approximately two-thirds of the CO2 originates from the limestone, and only about one-third from the fuel. This opens up the possibility of easily separating a significant portion of the CO2 with a simple retrofit of the calciner, since the calciner is where the majority of the deacidification process, i.e., the release of carbon dioxide from the limestone, takes place.

[0003] The oxyfuel process is a particularly efficient method for separating carbon dioxide. Ideally, pure oxygen is used instead of air. During combustion, the oxygen is converted into carbon dioxide and water, with additional carbon dioxide from the limestone. Ideally, and in simplified terms, the resulting gas consists of carbon dioxide and water vapor. This eliminates the need for the very complex carbon dioxide separation process. However, since reality is not so idealized, and other components can be introduced through the fuel, some air can never be completely avoided, and complete separation of nitrogen from oxygen is not economically viable, the final gas purification process is significantly simplified compared to other methods. Therefore, in addition to the standard cement process, air separation and the compression and purification of the carbon dioxide are added to the process.However, these processes are usually powered by electrical energy, which plays a subordinate role in the previous clinker process.

[0004] From WO 2019 / 211 196 A1, an oxyfuel clinker production without recirculation of the preheater exhaust gases is known.

[0005] Since this process aims to avoid carbon dioxide emissions and thus achieve climate neutrality in the clinker production process, the extensive use of renewable electricity sources is particularly important for the CO2 balance. However, renewable electricity sources are subject to fluctuations, meaning that the same amount of renewably generated electricity is not available at all times.

[0006] The object of the invention is to adapt the operation of such a cement plant retrofitted with an oxyfuel calcinator in view of the fluctuating renewable electricity generation.

[0007] This problem is solved by the method with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0008] The method according to the invention serves to operate a device for the thermal treatment of mineral materials, in particular a cement plant for the production of clinker. The device comprises a preheater, a calciner, a kiln, and typically a clinker cooler. This corresponds to the usual configuration of a cement plant. The mineral material is introduced partially into the preheater. From the preheater, the preheated material is fed into the calciner and from the calciner into the kiln, where it is thermally treated. This corresponds to the usual operation of a cement plant. The gas flow from the kiln is routed past the calciner. This does not correspond to the classic operation of a conventional cement plant, in which the hot gases from the kiln are directed into the calciner to utilize the heat. The device includes an oxygen source.An oxygen source can be, for example, an air separation unit, but it can also be a liquid oxygen tank. Preferably, the oxygen content of the oxygen-rich gas leaving the oxygen source is more than 50% by volume, more preferably more than 75% by volume, more preferably more than 90% by volume, and most preferably more than 95% by volume. The oxygen-rich gas is fed from the oxygen source to the calciner. The gas stream, which is rich in carbon dioxide due to combustion and carbon dioxide release from the mineral material, is directed from the calciner to the preheater. The device includes a carbon dioxide recovery unit. The carbon dioxide recovery unit is located downstream of the calciner, i.e., not downstream of the furnace.Only the extremely carbon dioxide-rich gas stream from the calcinator, which contains approximately 75 to 80% of the total carbon dioxide from the entire process, is fed to the carbon dioxide recovery unit. This means that not all other plant components, especially the furnace, need to be modified to be gas-tight, thus enabling a simple retrofit for the rapid reduction of approximately 75 to 80% of CO2 emissions. Consequently, the carbon dioxide recovery unit can be designed for an extremely high carbon dioxide content and, in particular, a very low nitrogen content, which minimizes energy consumption during operation. A dust filter and / or a heat exchanger can be installed upstream of the carbon dioxide recovery unit. The unit includes a furnace calciner and a furnace preheater.For example, and preferably, these components are existing components from a pre-existing plant that has been expanded to include a new calciner operating on the oxyfuel process. The gas flow is directed from the furnace to the furnace calciner and from the furnace calciner to the furnace preheater. The mineral material is fed into the furnace preheater proportionally, i.e., divided between the preheater and the furnace preheater. This allows waste heat from both processes to be recovered. The solid material stream exiting the furnace preheater is divided between the calciner and the furnace calciner. It is also possible to feed the entire solid material stream exclusively into the calciner.

[0009] According to the invention, a load-dependent portion of the gas flow leaving the preheater is recirculated into the oxygen-rich gas between the oxygen source and the calcinator. This partial recirculation allows the calcinator to operate at a lower partial load without negatively affecting its operating parameters. Reducing the load on the calcinator means less fuel and material are supplied, resulting in significantly less carbon dioxide production. This is compensated for by the recirculated quantity, allowing flow conditions and residence time in the calcinator to be kept nearly constant across different load conditions, thus ensuring that product quality is not a function of the load.

[0010] The calcinator's load state is adjusted based on the availability of regeneratively generated electricity (preferably on-site) or on price (preferably grid-supplied as an equivalent to availability). If little electricity is available, the calcinator operates at a low partial load, for example, 60%. This also means that only about 60% of the oxygen is required and only about 60% of the carbon dioxide is released (efficiency losses are neglected for simplicity). This partial load is then directly transferred to the oxygen source and the carbon dioxide recovery system, thus saving approximately 60% of the electrical energy in the given example.

[0011] If one were to assume a separation of approximately 75 to 80% of the total carbon dioxide at full load, the separation would drop to approximately less than 50% in this partial load state, while the clinker production continues unchanged and the furnace calciner compensates for the partial load reduction of the calciner accordingly, thus ensuring constant production with unchanged conditions in the furnace.

[0012] Alternatively, the overall production can be throttled to reduce oxygen consumption and the CO2 flow to the carbon dioxide treatment device, while not reducing the carbon dioxide separation rate, which in turn has a greater impact on the product if the furnace is only operated at partial load, since the mineral material is not treated in a gas stream but is present as a fixed bed or moving bed.

[0013] In a further embodiment of the invention, the oxygen-rich gas is heated before entering the calcinator. Previously, in conventional systems, the gas supplied to the calcinator came from the furnace and thus entered the calcinator at a very high temperature. Since alternative fuels are often used in calciners, a high inlet temperature of the gas stream is intended to ensure reliable ignition and combustion. The supplied oxygen-containing gas now arrives cold from the oxygen source. Because this is particularly critical when using alternative fuels in the calciner, preheating is advantageous.

[0014] In a further embodiment of the invention, the oxygen-rich gas is heated to at least 900 °C, preferably at least 1050 °C, before entering the calcinator. This refers to the inlet temperature to the calcinator. If, particularly during partial load operation, the oxygen-rich gas is mixed with the recirculated gas stream leaving the preheater, this temperature applies to the mixture. In this case, the mixing can occur first (before, after, or partially mixed) and then a joint heating process, or the oxygen can be heated more intensely and then mixed with the carbon dioxide-rich recirculated gas to this temperature.

[0015] In a further embodiment of the invention, the oxygen-rich gas is heated to a maximum of 1300 °C, preferably to a maximum of 1200 °C, before entering the calcinator.

[0016] In a further embodiment of the invention, the oxygen-rich gas is heated by combustion. Since ignition must occur reliably at low temperatures, a fine-grained, liquid or gaseous fuel such as pulverized coal, oil or gas is preferably used.

[0017] In a further embodiment of the invention, the oxygen-rich gas is heated by means of a heat exchanger using the gas leaving the preheater. The heat exchanger can be designed directly or in two parts using a heat transfer medium.

[0018] Preferably, heating can first take place using a heat exchanger and then by combustion.

[0019] In a further embodiment of the invention, the device includes a material cooler arranged behind the furnace. As is known from the prior art, the material cooler serves to cool the product exiting the furnace and transfer the heat to a gas, which, according to the prior art, is then, for example, and preferably, supplied to the furnace and thereby preheated. The oxygen-rich gas is passed through the material cooler as a cooling gas stream and is thereby heated within the material cooler. Preferably, the material cooler has three zones, wherein a first zone preheats an air mixture supplied to the furnace, a second zone preheats the oxygen-rich gas supplied to the calciner, and a third zone in which the cooling gas is neither supplied to the calciner nor to the furnace, but is, for example, released directly into the environment.This third zone is usually the last one and serves for final cooling to a temperature at which the product is easy to handle.

[0020] In a further embodiment of the invention, the device has a material cooler arranged behind the furnace. A cooling gas stream flows through the material cooler. The oxygen-rich gas is heated in a heat exchanger by means of the cooling gas stream. This indirect method has the advantage that it reliably prevents the introduction of unwanted gases into the oxygen-containing gas.

[0021] In a further embodiment of the invention, when the availability of electrical energy decreases, the proportion of gas flow returning from the preheater to the oxygen-rich gas between the oxygen source and the calcinator is increased. Simultaneously, the load on the calcinator is reduced, meaning less fuel and less mineral material are introduced. The ratio of fuel to mineral material to be calcined is determined by the energy requirements of the reaction. However, reducing the partial load results in less carbon dioxide being produced by both combustion and the reaction. To maintain the flow conditions in the calcinator, carbon dioxide-containing gas is recirculated. Preferably, the recirculation rate is adjusted to keep the volumetric flow rate of CO2-containing gas exiting the calcinator constant.The effect is that only the reduced gas flow, excluding the amount of gas recirculated, is fed into the carbon dioxide processing unit. For example, if approximately one-third is recirculated, then only about two-thirds reach the carbon dioxide processing unit, resulting in a significantly reduced energy requirement. Similarly, the oxygen source only needs to supply about two-thirds of the oxygen-containing gas (neglecting the efficiency reduction) and thus operates in a more energy-efficient manner under partial load. This allows periods of reduced renewable electricity production to be bridged without impacting product quality.

[0022] In a further embodiment of the invention, when the availability of electrical energy decreases, the proportion of mineral material introduced into the preheater is reduced relative to the mineral material introduced into the furnace preheater, and / or the proportion of the solid material stream leaving the furnace preheater and being fed to the calcinator is lowered. This results in less mineral material being calcined entering the calcinator, which then operates at a reduced partial load. If the proportion of the solid material stream leaving the furnace preheater and being fed to the furnace calciner is increased, production capacity can be maintained while the product quality remains unchanged due to the constant operating mode.

[0023] In a further embodiment of the invention, when electrical energy is minimally available, 30 to 60 vol% of the gas stream leaving the preheater is recycled into the oxygen-rich gas between the oxygen source and the calcinator. When electrical energy is maximally available, less than 15 vol%, preferably less than 5 vol%, and particularly preferably 0% of the gas stream leaving the preheater is recycled into the oxygen-rich gas between the oxygen source and the calcinator.

[0024] In a further embodiment of the invention, at full load the solids stream leaving the furnace preheater is completely fed to the calcinator.

[0025] The method according to the invention is explained in more detail below with reference to an embodiment shown in the drawings. Fig. 1 first example Fig. 2 second example Fig. 3 third example

[0026] In Fig. Figure 1 shows a first exemplary device for the thermal treatment of mineral materials. The device consists, for example, of an existing system (shown outlined on the right) and a newly added calcinator 20, shown on the left, which operates according to the oxyfuel principle. The left side features an oxygen source 60. The oxygen-containing gas from the oxygen source 60 is fed into the calcinator 20 via a gas preheater 80. The gas preheater 80 can be either combustion-based or electrical. For heat recovery, the carbon dioxide-containing gas stream from the calcinator 20 is transferred to the preheater 10 and from there to the carbon dioxide recovery device 70.

[0027] The mineral material, for example limestone, comes from a storage area 50 and is divided between the preheater 10 and the furnace preheater 11. For example, at full load, 40 to 60 wt.% is fed into the preheater 10 and 60 to 40 wt.% into the furnace preheater 11. At full load, the preheated material is completely transferred from both the preheater 10 and the furnace preheater 11 into the calciner 20. After calcination, the calcined material is transferred from the calciner 20 into the furnace 30, where it is fired and subsequently cooled in the material cooler 40.

[0028] The device features a recirculation system 90, particularly for partial load operation. For example, if renewable electricity is scarce, the calcinator can be operated at 50% capacity. Accordingly, 50% of the gas flow is recirculated. This means that only half of the carbon dioxide-containing gas flow reaches the carbon dioxide processing unit 70, which therefore has a correspondingly reduced electricity demand. Similarly, the oxygen source 60, for example, an air separation unit using the membrane process, is operated at a correspondingly reduced partial load, thus saving electrical energy. For instance, only half of the mineral material from the storage area is applied to the preheater 10 and the furnace preheater 11, so that the device as a whole operates at a partial load of 50%.Alternatively, and preferably, in this case, the furnace calcinator 21 is operated in such a way that overall production remains at full capacity, so that furnace 30 also operates continuously and unchanged. In this case, only the amount of separated carbon dioxide is reduced.

[0029] Fig. Figure 2 shows a second example as a variation of the first. In the gas preheater 80, the exhaust gas flow from the preheater 10 is used to preheat the oxygen-rich gas; the gas preheater is designed as a heat exchanger. Alternatively, indirect heat transfer can also be achieved, i.e., with two heat exchangers and a heat transfer medium in between.

[0030] In Fig.Figure 3 shows a third example as a variation of the first. To preheat the oxygen-rich gas, it is passed through the material cooler 40 and thus preheated. Here, too, an indirect heat transfer is conceivable as an alternative implementation, whereby a gas, for example air, is passed through the material cooler 40 and heats the oxygen-rich gas in a heat exchanger. Reference sign 10 preheaters 11 Oven warmers 20 Calcinator 21 Oven calciner 30 oven 40 material coolers 50 storage 60 Oxygen source 70 Carbon dioxide processing device 80 Gas preheating 90 Repatriation QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2019 / 211 196 A1

[0004]

Claims

[1] A method for operating an apparatus for the thermal treatment of mineral substances, wherein the apparatus comprises a preheater (10), a calciner (20) and a furnace (30), wherein the mineral substance is partially introduced into the preheater (10), is conveyed from the preheater (10) into the calciner (20) and from the calciner (20) into the furnace (30), wherein the gas stream of the furnace (30) is guided past the calciner (20), wherein the apparatus comprises an oxygen source (60), wherein an oxygen-rich gas is guided from the oxygen source (60) to the calciner (20), wherein the gas stream is directed from the calciner (20) into the preheater (10), wherein the apparatus comprises a carbon dioxide processing device (70), wherein the carbon dioxide processing device (70) is arranged downstream of the calciner (20), and wherein the apparatus comprises a furnace calciner (21) and a furnace preheater (11) exhibitswherein the gas stream from the furnace (30) is directed into the furnace calciner (21) and from the furnace calciner (21) into the furnace preheater (11), wherein the mineral material is introduced proportionally into the furnace preheater (11), wherein the solid stream leaving the furnace preheater (11) is divided between the calciner (20) and the furnace calciner (21), wherein a load-dependent proportional return of the gas stream leaving the preheater (10) to the oxygen-rich gas between the oxygen source (60) and the calciner (20) takes place. [2] Method according to claim 1, characterized by , that the oxygen-rich gas is heated before the calcinator (20). [3] Method according to claim 2, characterized by that the oxygen-rich gas is heated to at least 900 °C, preferably to at least 1050 °C, before entering the calcinator (20). [4] Method according to claim 2, characterized bythat the oxygen-rich gas is heated to a maximum of 1300 °C, preferably to a maximum of 1200 °C, before entering the calcinator (20). [5] Method according to any one of claims 2 to 4, characterized by , that the oxygen-rich gas is heated by means of combustion. [6] Method according to any one of claims 2 to 5, characterized by , that the oxygen-rich gas is heated by means of a heat exchanger by the gas leaving the preheater (10). [7] Method according to any one of claims 2 to 6, characterized by , that the device has a material cooler (40) arranged behind the furnace (30), wherein the oxygen-rich gas is passed through the material cooler (40) as a cooling gas stream and is thereby heated in the material cooler (40). [8] Method according to any one of claims 2 to 6, characterized by, that the device has a material cooler (40) arranged behind the furnace (30), wherein the material cooler (40) is supplied with a cooling gas stream, and the oxygen-rich gas is heated in a heat exchanger by means of the cooling gas stream. [9] Method according to any of the foregoing claims, characterized by , that as the availability of electrical energy decreases, the proportionate return of the gas flow leaving the preheater (10) to the oxygen-rich gas between the oxygen source (60) and the calcinator (20) is increased. [10] Method according to claim 9, characterized by , that the proportion of the recirculation is chosen such that the volume flow rate of the CO2-containing gas exiting the calcinator (20) is kept constant. [11] Method according to any one of claims 9 to 10, characterized by, that if the availability of electrical energy decreases, the proportion of the mineral material introduced into the preheater (10) is reduced in relation to the mineral material introduced into the furnace preheater (11) and / or the proportion of the solid material stream leaving the furnace preheater (11) and being fed to the calcinator (20) is reduced. [12] Method according to any of the foregoing claims, characterized by , that at minimum availability of electrical energy 40 to 60 vol% of the gas stream leaving the preheater (10) is recycled into the oxygen-rich gas between the oxygen source (60) and the calcinator (20), wherein at maximum availability of electrical energy less than 15 vol%, preferably less than 5 vol%, of the gas stream leaving the preheater (10) is recycled into the oxygen-rich gas between the oxygen source (60) and the calcinator (20). [13] Method according to any of the preceding claims, characterized by , that at full load the solids stream leaving the furnace preheater (11) is completely fed to the calcinator (20).

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