Use of thermal energy originating from a process for producing cement clinker, for operating a stage for removing carbon dioxide (co 2) from off-gases of the process

Abstract

The invention relates to the use of thermal energy that originates from a process for producing cement clinker in which off-gas is produced that is enriched with carbon dioxide (CO2).

Description

[0001] Using thermal energy resulting from a process for producing cement clinker to operate a stage for capturing carbon dioxide (CO2) from exhaust gases of the process The invention relates to the use of thermal energy resulting from a process for producing cement clinker, which produces exhaust gas enriched with carbon dioxide (CO2). In recent decades, the harmful influence of anthropogenic carbon dioxide (CO2) emissions on the global climate has become apparent. The industrial sector, including cement clinker production plants, remains one of the main sources of anthropogenic CO2 emissions. With the increasing demand for cement, there is an urgent need for solutions to reduce the environmental impact of this important sector in terms of carbon dioxide (CO2) emissions.A key step in cement clinker production is the calcination of limestone, which leads to significant carbon dioxide (CO2) emissions in addition to the release of carbon dioxide (CO2) from the combustion of fossil fuels. Carbon dioxide (CO2) is formally thermally expelled from limestone (calcium carbonate, CaCO3) to obtain quicklime (CaO) for further sintering of the quicklime with silicate rock. To remove the carbon dioxide (CO2) generated during cement clinker production from the exhaust gases, it is necessary to operate separators, which require a great deal of energy to operate. This applies regardless of whether the separation is chemical or physical.Amine scrubbing, as an example of an energy-intensive carbon dioxide (CO2) separator, is a well-known and effective method for cleaning exhaust gases, particularly in industrial processes that emit climate-damaging exhaust gas components such as carbon dioxide (CO2) and sulfur dioxide (SO2). It is a chemical absorption method in which an aqueous solution of amines is used to remove these pollutants from the exhaust gases by absorption. The principle of amine scrubbing, as an example of an energy-intensive carbon dioxide (CO2) separator, is based on the ability of amine compounds to react with and absorb the acidic components of the exhaust gases, in this case carbon dioxide (CO2). In a typical amine scrubbing plant, the exhaust gas is passed through a scrubber or absorber, where it comes into contact with the aqueous amine solution.The amines react with the acidic components of the exhaust gas, in this case with carbon dioxide (CO2), to form chemical compounds in the form of ammonium carbonates, which remain dissolved in the solution. Alkanamines such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and / or diglycolamine (DGA) in aqueous solution are typically used as amines. The amine solution, which contains the captured pollutants, is then fed into a regenerator or desorber. There, the amine solution is heated to release the bound gases. This separates the dissolved ammonium carbonate back into carbon dioxide (CO2) and amine. Carbon dioxide (CO2) escapes into the gas space, while the amine remains in aqueous solution. Amine scrubbing works through the selective transport of carbon dioxide (CO2), thus allowing carbon dioxide (CO2) to be separated in its pure form from the exhaust gases.The captured carbon dioxide (CO2) can either be further processed or safely disposed of. The amine solution, purified of the captured carbon dioxide (CO2), is then returned to the scrubber or absorber to continue the purification process. The amine solution thus has the task of selectively transporting the carbon dioxide (CO2), and it remains in circulation within the scrubbing process. Amine scrubbing, as an example of an energy-intensive carbon dioxide (CO2) capture system, has several advantages as an exhaust gas purification technology. It is capable of achieving high removal efficiencies for both carbon dioxide (CO2) and sulfur dioxide (SO2), which contributes to reducing greenhouse gas emissions and air pollution. Furthermore, it is capable of removing other pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) to a certain extent.The process is also relatively flexible and can be adapted to different exhaust gas compositions and volumes. However, there are also some challenges with amine scrubbing, an example of an energy-intensive carbon dioxide (CO2) separator. The use of amines as solvents is associated with an energy-intensive regeneration process. Although the absorption process in amine scrubbing is exothermic and occurs spontaneously, the subsequent separation of the exhaust gas, in this case carbon dioxide (CO2), and the amines used for scrubbing is an endothermic process that requires energy input. To release the absorbed carbon dioxide (CO2) from the absorbent, the so-called "desorption," either the pressure above the absorbent must be reduced and / or the temperature of the absorbent must be increased. The required temperature level depends on the nature of the absorbent. A typical value from the literature is 120 °C.The required energy consumption also depends on the selected absorbent and is between 2.2 and 3.4 MJ / kg. CO2 . The average value of 2.8 MJ / kg CO2was determined in a test facility at the Norcem cement plant in Brevik. All separation processes that remove carbon dioxide (CO2) from exhaust gases are energy-intensive at the scale typically found in a cement clinker production plant. It would be desirable to combine a cement clinker production plant with a carbon dioxide (CO2) separation device. However, amine scrubbing, as an example of an energy-intensive carbon dioxide (CO2) separation process, consumes a very significant amount of energy, so that amine scrubbing, as well as all other carbon dioxide (CO2) separation processes, makes cement clinker production unattractive both energetically and economically.As a reference for estimating the energy requirement for carbon dioxide (CO2) capture, a reference plant for the production of cement clinker with a production capacity of 3000 tons of clinker per day, a 5-stage heat exchanger, an inline calciner and a grate cooler with an efficiency of 74% (@ 0.8 Nm) is used below. 3 / kg Kli Recuperation air). The basic structure of a generic plant for the production of cement clinker is assumed to be known here. Such a plant has a so-called tertiary air line, with which air is transported from the beginning of the grate cooler, where the cement clinker to be cooled is still very hot and thus heats up the cooling air considerably, to the calciner in order to recover heat from the production process. Coal is used as fuel in the reference plant (H u = 25,121 kJ / kg Br ) and the total heat requirement is 3,134 kJ / kg Kli. A heat balance of this system shows that the largest sources of heat loss are the exhaust gases from the preheater and the exhaust gases from the cooler. Both exhaust gases account for 1,262 kJ / kg Kli for this system accounts for around 70% of the heat losses. With CO2 emissions of 0.86 kg CO2 / kg KliThis amount of heat covers 39% of the energy required to operate the amine scrubber in direct operation without a raw mill and 28% in combined operation with a raw mill. The remaining heat for operating the amine scrubber must be provided by an additional hot gas generator or an electric heater. The object of the invention is to combine a process for producing cement clinker with a device for separating carbon dioxide (CO2) and to make it energetically and economically attractive. The object of the invention is achieved by a process having the features of claim 1. Further advantageous embodiments are specified in the subclaims to claim 1. The solution to the object of the invention can in principle be implemented with four different embodiments of a generic plant for producing cement clinker.In a first embodiment of the process according to the invention, the cement plant remains unchanged with the exception of the tertiary air line. A heat exchanger is installed on the tertiary air line, and the heat in the tertiary air is used for the amine scrubber. The cooled tertiary air is then fed back into the calciner as cooled combustion air. Compared to the reference case, it has been shown that in a plant modified in this way, heat consumption is reduced by 21% to 3782 kJ / kg. Kliincreased. The increase in heat consumption now stems from the necessary increased fuel supply to the calciner in order to maintain the calcination temperature. With the energy extracted from the tertiary air line, 52% of the CO2 emissions can be absorbed in combined operation with the raw mill and 62% in direct operation. The amount of heat available for the desorption of carbon dioxide (CO2) is the cause of the absorption rate of carbon dioxide (CO2), since the scrubbing liquid cannot be completely desorbed with the available heat, and thus carbon dioxide (CO2) bound as an ammonium compound is fed back into the scrubber (absorber). In a second embodiment of the invention, it is provided that the system according to the first embodiment of the invention is further modified in favor of a higher heat extraction.For this purpose, the number of heat exchanger cyclones in the cyclone heat exchanger is reduced from five to three. This intervention results in the exhaust gas leaving the plant at a higher temperature. Although the higher exhaust gas temperature reduces the efficiency of the cement plant in terms of energy consumption per kg of cement clinker, more energy is available for regenerating the absorbent. The proposed reduction in the number of heat exchanger cyclones as preheater stages increases the exhaust gas outlet temperature to approximately 480 °C. With this concept, the plant's heat requirement increases by 36% to 4255 kJ / kg compared to the reference case. Kli. A downstream scrubber, which utilizes this recovered exhaust gas energy, can absorb 68% of the CO2 emissions in combined operation with a raw mill and 77% of the CO2 emissions in direct operation. In a third embodiment of the invention, the plant for the production of cement clinker is operated without a preheater and calciner, but instead uses a fluidized bed reactor. The raw material is heated and calcined in the fluidized bed of the reactor, while the dust and exhaust gas are separated from each other in a single connected cyclone. Downstream of the cyclone, both the material and the exhaust gas have a temperature of up to 850 °C. In this embodiment of the process, it was calculated that the total heat requirement of the plant could be reduced by 60% to 5000 kJ / kg compared to the reference case. Kliincreases. With a scrubber that utilizes the waste heat from this plant, 89% of the CO2 emissions can be absorbed in combined operation with raw mills and 98% of the CO2 emissions in direct operation. In a fourth embodiment of the invention, the third embodiment is further modified, and in addition to the operation of the fluidized-bed reactor, a heat exchanger is operated in the tertiary air line. In this embodiment of the invention, the total heat requirement of the cement clinker production plant increases by 72% to 5388 kJ / kg compared to the reference case. KliWith a scrubber that utilizes the waste heat from this plant, 100% of the CO2 emissions can be absorbed in combined operation with a raw mill, and theoretically 108% of the CO2 emissions in direct operation. This means that the scrubbing liquid must be cooled again in the desorber. The process presented here can be varied. Various substances can be used as absorbent. Suitable absorbents are alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), and alkylalkanolamines such as methyldiethanolamine (MDEA) and / or diglycolamine (DGA) in aqueous solution. Furthermore, it is possible to use ammonia or ammonia water, i.e. ammonia instead of amine, in an organic solvent. It is also possible to use liquid ammonia at low temperatures, i.e. below 33°C.With appropriate sizing, carbonic anhydrase can also be used as a biological catalyst to accelerate absorption by the absorbent. The invention is explained in more detail with reference to the following figures. They show: Fig. 1 a generic plant for producing cement clinker from the PRIOR ART as a reference plant, Fig. 2 a first, individual measure for removing heat from the process for producing cement clinker, Fig. 3 a second, individual measure for removing heat from the process for producing cement clinker, Fig. 4 a third, individual measure for removing heat from the process for producing cement clinker. Figure 1 shows a generic plant 100 for producing cement clinker from the PRIOR ART as a reference plant.In this illustration, the material flows, namely the flow of raw meal to the finished cement clinker and the flow of gas from the cooling gas and primary air to the exhaust gas, are not shown. Reference is made to the relevant literature for this. Generic plants of this type have a cyclone heat exchanger 110 with five heat exchanger cyclones 111, 112, 113, 114, and 115, through which the raw meal flowing through these five heat exchanger cyclones 111, 112, 113, 114, and 115 is heated to just below the calcination temperature. Furthermore, a generic plant 100 for the production of cement clinker contains a calciner 120, in which the preheated raw meal is calcined, i.e., formally converted into quicklime (CaO) by thermally expelling carbon dioxide (CO2).The calciner is followed by a rotary kiln 130, in which the sintering process takes place at an even higher temperature. This is followed in the direction of material flow by a clinker cooler 140, in which the sintered cement clinker is cooled. The very hot cooling air generated during cooling of the cement clinker is fed back into the calciner 120 via a tertiary air outlet 150 to return thermal energy to the process. The energy conditions in a generic plant 100 for the production of cement clinker are comparable despite the different designs worldwide. For example, the performance of a heat exchanger cyclone is known, so that generally five heat exchanger cyclones 111, 112, 113, 114, and 115 are used, unless other plant types with special process steps require a different number of heat exchanger cyclones.The sketched vertical mill 160 for grinding raw meal as an example of a raw mill is often included in the energetic analysis of how much energy must be used per kg of cement clinker produced in order to assess the overall effectiveness of the plant. Figure 2 shows a first, individual measure for removing heat from the cement clinker production process. In order to provide heat for a scrubber 200, consisting of absorber 201 and desorber 202, heat is extracted from the tertiary air with the help of a heat exchanger 210 installed in the tertiary air line 150. This heat is then used to heat the desorber 202 in the scrubber 200. Exhaust gas originating from the cyclone heat exchanger 110 is passed through the scrubber 200, where the exhaust gas is separated into carbon dioxide (CO2) and the remaining exhaust gas.In comparison to a reference plant as shown in Figure 1, tests have shown that in such a modified plant for the production of cement clinker the total heat consumption is reduced by 21% to 3782 kJ / kg. Kliincreased. The increase in heat consumption now stems from the necessary increased fuel supply to the calciner, which is now fed with colder tertiary air to maintain the calcination temperature. With the energy extracted from the tertiary air line, 52% of the CO2 emissions can be absorbed in combined operation with the raw mill and 62% in direct operation. Figure 3 shows a second, individual measure for removing heat from the cement clinker production process. In this modified plant, only three heat exchanger cyclones 111, 112, and 113 are used in cyclone heat exchanger 110 to preheat the raw meal. Since the reduced number of heat exchanger cyclones means the exhaust gas experiences less cooling by the raw meal, the outlet temperature of the exhaust gas increases and is approximately 480 °C. The exhaust gas is cooled with a heat exchanger 211.The heat recovered is used in the desorber 202, while the cooled exhaust gas is fed into the absorber 201. It is possible to take this single measure and use the waste heat recovered from the exhaust gas temperature in the desorber 202. If this measure is used together with the measure in Figure 1 to extract heat from the cement clinker production process, the plant's heat demand increases by 36% to 4255 kJ / kg compared to the reference case. Kli. Via a downstream scrubber 200, which utilizes this recovered exhaust gas energy, 68% of the CO2 emissions in combined operation with a raw mill and 77% of the CO2 emissions in direct operation can be absorbed. Figure 4 shows a third, individual measure for removing heat from the cement clinker production process. In this modified plant, the cyclone heat exchanger 110 and also the calciner 120 are replaced by a fluidized bed reactor 121. Instead of first preheating and then calcining the raw meal, the cold raw meal is fed into the fluidized bed reactor 121 and heated and calcined in a concerted step. After the cyclone of the fluidized bed reactor 121, both the material and the exhaust gas have a temperature of up to 850 °C. In this version of the process, it was calculated that the total heat demand of the plant was reduced by 60% to 5000 kJ / kg compared to the reference case. Kliincreases. With scrubber 200 utilizing this waste heat, 89% of CO2 emissions can be absorbed in combined operation with raw mill 160 and 98% of CO2 emissions in direct operation. It is possible to implement this single measure and utilize the resulting waste heat from the exhaust gas temperature in desorber 202. If this measure is used together with the measure in Figure 2, the total heat demand of the cement clinker production plant increases by 72% to 5388 kJ / kg compared to the reference case. Kli With a 200 scrubber, which utilizes the waste heat from this plant, 100% of CO2 emissions can be absorbed in conjunction with a raw mill, and 108% of CO2 emissions in direct operation. This means that the scrubbing liquid must be cooled again in the desorber.

[0002] LIST OF REFERENCE SYMBOLS E100 Plant 150 Tertiary air line 110 Cyclone heat exchanger 160 Vertical mill 111 Heat exchanger cyclone 112 Heat exchanger cyclone 200 Scrubber 113 Heat exchanger cyclone 201 Absorber 114 Heat exchanger cyclone 202 Desorber 115 Heat exchanger cyclone 210 Heat exchanger 120 Calciner 211 Heat exchanger 121 Fluidized bed reactor 212 Heat exchanger 130 Rotary kiln 140 Clinker cooler

Claims

P A T E N T A N S P R Ü C H E 1. Using thermal energy originating from a process for producing cement clinker, in which a carbon dioxide (CO2)-enriched exhaust gas is produced, to operate a stage for separating carbon dioxide (CO2) from the exhaust gases of this process.

2. Using thermal energy according to claim 1, characterized in that the process for producing cement clinker comprises the following steps: - preheating the raw meal in a heat exchanger, - calcining the raw meal in a calcination stage, and - sintering the calcined raw meal in a sintering stage, finally - Cooling the sintered cement clinker in a cooling stage, wherein thermal energy from the cooling stage is recuperated for use in the process.

3. Use of thermal energy according to claim 2, characterized by - Extracting the thermal energy with a heat exchanger that is arranged a) in a tertiary air line that carries thermal energy from the cooling stage to the calcination stage, and / or b) at the outlet of the heat exchanger for the carbon dioxide-enriched exhaust gas.

4. Use of thermal energy according to claim 2 or 3, characterized in that the process comprises the following steps: - Compressing the exhaust gases, - Introducing the compressed exhaust gases into an absorber (201) as a reactor of a scrubber (200), - Injecting a scrubbing liquid into the absorber (201), - Transporting the scrubbing liquid from the absorber (201) to a desorber (202), as a further reactor of the scrubber, - heating the scrubbing liquid in the desorber (202), - discharging the carbon dioxide (CO2) released during heating of the scrubbing liquid, - returning the scrubbing liquid from the desorber (202) to the absorber (201), characterized by heating the desorber (202) with waste heat from the cement clinker production plant.

5. Use of thermal energy according to claim 4, characterized by heating the desorber (202) with heat extracted from the cement clinker production plant via a heat exchanger (210) and a tertiary air line (150). 6.Use of thermal energy according to claim 5, characterized by additional heating of the desorber (202) with heat which is taken from an exhaust gas line of the plant for the production of cement clinker via a heat exchanger (211), wherein the plant for the production of cement clinker achieves a sufficiently high exhaust gas temperature for the complete regeneration of the absorbent by omitting heat exchanger cyclones (114, 115), wherein the number of heat exchanger cyclones (114, 115). between one and four heat exchanger cyclones (111, 112, 113, 114) and the exhaust gas temperature is preferably 360 °C to 850 °C by selecting the number of heat exchanger cyclones (111, 112, 113, 114).

7. Use of thermal energy according to one of claims 4 or 5, characterized by heating the desorber (202) with heat which is taken from an exhaust gas line of the cement clinker production plant via a heat exchanger (212), wherein the cement clinker production plant exhibits an exhaust gas temperature higher than 800°C by omitting a calciner (120) and a heat exchanger (110) and using a fluidized bed reactor (121).Use of thermal energy according to one of claims 4 to 7, characterized by the use of alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), alkylalkanolamines, such as methyldiethanolamine (MDEA) and / or diglycolamine (DGA) in aqueous solution as absorbent in the absorber (201), or the use of ammonia or ammonia water in an organic solvent or ammonia at low temperature, i.e. below 33°C, as absorbent in the absorber (201), and / or the use of carbonic anhydrase as catalyst to accelerate absorption by the absorbent in the absorber (201).

9. Plant for producing cement for carrying out the method according to one of claims 4 to 8, characterized in that a tertiary air line (150) for conducting hot exhaust air from a clinker cooler (140) into a calciner (120) has a heat exchanger (210) which conducts waste heat for heating the desorber (202).

10. A cement production plant for carrying out the method according to one of claims 4 to 8, characterized in that a cyclone heat exchanger (110) of the cement clinker production plant has three heat exchanger cyclones (111, 112, 113), whereby the exhaust gas temperature increases compared to the use of five heat exchanger cyclones (111, 112, 113, 114, 115), wherein a heat exchanger (211) conducts waste heat from the exhaust gas to heat the desorber (202).Plant for producing cement for carrying out the method according to one of claims 4 to 8, characterized in that a tertiary air line (150) for conducting hot exhaust air from a clinker cooler (140) into a calciner (120) has a heat exchanger (210) which conducts waste heat for heating the desorber (202), and. a cyclone heat exchanger (110) of the cement clinker production plant has three heat exchanger cyclones (111, 112, 113), whereby the exhaust gas temperature increases compared to the use of five heat exchanger cyclones (111, 112, 113, 114, 115), wherein a heat exchanger (211) supplies waste heat from the exhaust gas to heat the desorber (202).

12. A cement production plant for carrying out the method according to one of claims 4 to 8, characterized in that the plant has a fluidized-bed reactor (121) instead of a cyclone heat exchanger (110) and a calciner (120), whereby the exhaust gas temperature increases, wherein a heat exchanger (212) supplies waste heat from the exhaust gas to heat the desorber (202). 13.Plant for producing cement for carrying out the method according to one of claims 4 to 8, characterized in that a tertiary air line (150) for conducting hot exhaust air from a clinker cooler (140) into a calciner (120) has a heat exchanger (210) which conducts waste heat for heating the desorber (202) and the plant has a fluidized bed reactor (121) instead of a cyclone heat exchanger (110) and a calciner (120), whereby the exhaust gas temperature increases, wherein a heat exchanger (212) conducts waste heat from the exhaust gas for heating the desorber (202).

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