System and process for producing cement together with the separation of carbon dioxide
Patent Information
- Application Number
- AU2025256578
- Authority / Receiving Office
- AU · AU
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-04-16
- Filing Date
- 2025-04-10
- Publication Date
- 2026-08-27
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The invention relates to a process for producing cement clinker from raw meal, comprising the following steps: preheating the raw meal to give hot meal, separating out the hot meal in a cyclone separator and introducing the hot meal via a hot meal conduit into an entrained flow reactor, calcining the hot meal to form deacidified raw meal in the entrained flow reactor as a calciner, separating out the deacidified raw meal in a cyclone separator downstream of the entrained flow reactor as a calciner in gas flow direction, sintering the separated deacidified raw meal in a rotary kiln to give cement clinker, and to a plant corresponding thereto. In the known production of cement clinker from a mixture of a silicate-containing and carbonate-containing rock meal, the raw meal, carbon dioxide (CO2) is formed directly from two mutually independent sources. Firstly, carbon dioxide (CO2) is formed in the combustion of fossil fuels and also in the combustion of alternative secondary fuels for the strongly endothermic process. Secondly, carbon dioxide (CO2) is formed in the calcination of the carbonate-containing rock meal, in which carbon dioxide (CO2) is formally driven out of the carbonate in order thus to obtain calcined lime (CaO) as an intermediate. Carbon dioxide (CO2) from both sources is usually discharged into the free atmosphere as offgas. Carbon dioxide (CO2) in the Earth's atmosphere has been identified as a cause of climate change as currently being observed on Earth. Therefore, efforts are currently being made to prevent or at least reduce the introduction of carbon dioxide (CO2) into the atmosphere. The separation of carbon dioxide (CO2) from offgases is a highly endothermic process and requires thermal energy. It is therefore obvious to utilize the waste heat from the cement process for the operation of the CO2 separation. However, the waste heat available in the process for production of cement clinker is insufficient for separating out all the CO2. Cement production by the current process produces more carbon dioxide (CO2) than can be separated out by waste heat available in the process. One means of mustering the missing thermal energy is to replace this heat by means of heat pumps. However, heat pumps require electrical power for their operation, the conversion of which from heat is very inefficient. Another means of providing the thermal energy necessary for the separation and storing of carbon dioxide (CO2) is a separate hot gas generator, but this incurs additional plant costs and, when it is operated with fossil fuels, further CO2 is emitted, and the ash of the fuel occurs as waste. This waste itself presents a disposal problem. It would therefore be necessary to construct this hot gas generator in such a way that as little problematic ash as possible occurs as waste. The construction and operation of such a plant is again very costly in economic terms. It is therefore an object of the invention to modify a known process for producing cement clinker in such a way that sufficient waste heat is available in the production process. In a conventional process for producing cement clinker, efforts are made to optimize the overall process in such a way that a minimum amount or only a small amount of waste heat is obtained, since heat loss is associated with low economic viability. According to this present object of the invention, exactly the opposite is desired, namely that the process throws out as much waste heat as possible that can be utilized for the operation of a process for separating off carbon dioxide (CO2). If the process known per se for producing cement clinker is modified so as to give rise to a maximum amount of waste heat, it is possible to make use of further process properties that make an ash aftertreatment superfluous. The process to be proposed fundamentally alters the requirements on the process design. While the aim has to date been to avoid the occurrence of waste heat as far as possible, the aim now is to generate as much waste heat as is required in the separation of CO2 from the offgas in a very substantially targeted manner. Nevertheless, the production of cement clinker remains the primary aim. The first finding is that it is impossible to operate a known plant for production of cement clinker by means of an excess of fuel and hence an excess of waste heat, because this would result in overheating of the plant. The object of the invention is achieved by modifying the known production process of preheating the raw meal, calcining the preheated raw meal, sintering the raw meal and subsequently cooling the sintered cement clinker such that, rather than utilizing waste heat that arises in the course of cooling and waste heat that exists in the sintering furnace for the endothermic calcination, and rather than utilizing the waste heat that arises in turn in the calcination for preheating again, this waste heat is first utilized for preheating and only then is the heat that is still surplus used for calcination, in which case the thermal energy still lacking is added to the calcination by burning preferably waste-based secondary fuels. According to the concept of the invention, the sequence of waste heat utilization in the course of preheating, calcination and sintering is modified. Only this makes it possible to work with a high fuel surplus, such that a maximum amount of waste heat arises. Specifically, the object of the invention is achieved by preheating a portion of the raw meal in an entrained flow reactor as the first entrained flow reactor and charging this first entrained flow reactor with the hot offgases from the rotary kiln. Further advantageous configurations of the process are specified in the claims dependent on claim 1. The reaction in the process of the invention can take place in a plant as claimed in claim 10. Further advantageous configurations of the plant are specified in the claims dependent on claim 10. In order to be able to implement the concept of the invention as optimally as possible, it is advantageous to replace the established cyclone heat exchanger with an entrained flow reactor, where this entrained flow reactor acts as a preheater. Two requirements then arise for the from gas and waste heat flow direction calcination in the downstream reactor. The temperature required for the ignition of the fuel that takes place therein must have been transferred to the meal stream serving as heat carrier in this second step in the first entrained flow reactor, and so the fuel is to be ignited in an atmosphere of raw meal, air and oxygen that is now too cold. A very long residence time in the entrained flow reactor, which acts as a calciner, is required in order to heat the tertiary air, from which heat can optionally be removed for preheating, and the fuel and the raw material, and to enable burning to completion. These requirements can be achieved by the person skilled in the art by appropriately optimized design of the process. In addition to the process reversed from gas flow direction and waste heat flow direction that involves first utilizing the waste heat from the rotary kiln for preheating a portion of the meal (20-50%) and using the remaining heat for the CO2 separation, there are further means according to the concept of the invention of generating even more waste heat in the process, specifically cooling the cement clinker in a clinker cooler connected downstream of the rotary kiln in material flow direction, and the introducing of heated cooling air as tertiary air from a cooler head housing of the clinker cooler into a second entrained flow reactor that acts as a calciner via a tertiary air conduit. The thermal energy in the tertiary air is then used to ignite the fuel in the calcination. In order to increase the available amount of waste heat even further, it is possible to remove waste heat from the tertiary air via a heat exchanger, with connection of the heat exchanger into the tertiary air conduit. The tertiary air entrains heat of high calorific value, which is readily utilizable as operating energy in a further process for separating off carbon dioxide (CO2). This significantly cools down the tertiary air. In order to compensate for this heat loss, it is then possible to use far more fuel in the entrained flow reactor that acts as a calciner. In order to be able to utilize even more waste heat from the process for producing cement clinker, it is possible to remove waste heat from heated cooling air as waste air via a heat exchanger which is connected into a gas conduit for discharging waste air from the cooler. This waste heat is heat of low calorific value and is suitable for drying fuels or for heating catalysts that are used in the chemical conversion of carbon dioxide (CO2). The removal of the waste heat from the cooler does not require any additional compensation of the thermal energy in the existing process for producing cement clinker. The thermal energy still present in the offgas from the rotary kiln after preheating of the raw meal can be tapped off directly by removing waste heat from heated offgas separated off by means of a cyclone separator from the first entrained flow reactor, which acts as a preheater, via a heat exchanger connected into a gas conduit for discharging the offgas from this first entrained flow reactor. In order to be able to utilize even more waste heat from the process for producing cement clinker, it is possible to remove waste heat from heated offgas separated off by means of a cyclone separator from the entrained flow reactor acting as a calciner via a heat exchanger connected into a gas conduit for discharging the offgas from the second entrained flow reactor. The process can generate even more waste heat by use of a further entrained flow reactor which also acts as a calciner. This third entrained flow reactor is connected downstream in gas flow direction of the second entrained flow reactor which likewise acts as a calciner. It is then possible to remove waste heat from heated offgas separated off by means of a cyclone separator from the entrained flow reactor acting as a calciner via a heat exchanger connected into a gas conduit for discharging the offgas from the second entrained flow reactor. The invention is elucidated in detail with reference to the figures that follow. The figures show: Fig. 1 a plant for implementing the process of the invention in a first configuration, Fig. 2 a plant for implementing the process of the invention in a second configuration, Fig. 3 a flow diagram of the process of the invention in a first configuration, Fig. 4 a flow diagram of the process of the invention in a second configuration. Figure 1 shows a plant 100 for implementing the process of the invention in a first configuration. This plant 100 is designed primarily for production of cement clinker 110 from raw meal 120, but, unlike known plants, is intended to generate as much waste heat as possible. Like other known plants, this plant 100 has at least one rotary kiln 130 for sintering deacidified raw meal 121 to give cement clinker 110. The rotary kiln is fired by means of a burner which is itself supplied with primary fuel 200 and primary air 202. Downstream of the rotary kiln 130 in material flow direction is at least one clinker cooler 140 for cooling the cement clinker 110, where the clinker cooler 140 shown here has a tertiary air conduit 150 for taking up cooling air 147 heated in the cooler head housing 149 of the clinker cooler 140 as tertiary air 151. Atmospheric cooling air 147 is blown into the clinker cooler 140 and flows from below through the cement clinker 110 and cools the hot cement clinker 110, which is at a temperature of about 1400°C on exit from the rotary kiln 130. In the vicinity of the rotary kiln head, i.e. the part of the rotary kiln 130 that projects into the cooler 140, the cooling air 147 heated up assumes a temperature of close to 1250°C. This hot cooling air 151 formed in the cooler head housing 149 is partly conducted further into the plant 100 through a tertiary air conduit 150 for recuperating the heat present in the hot cooling air. It is possible here to extract heat, which is otherwise utilized for recuperation, from the tertiary air 150 as waste heat Q via a heat exchanger 155. A further portion of the hot cooling air formed there is conducted as secondary air 203 into the rotary kiln 130. Cooling air 147 which flows into the cooler 140 further away from the rotary kiln head meets already cooled cement clinker 110, where it assumes only the lower temperature of the cement clinker 110 there. At the end of the clinker cooler 140, the heated cooling air is only at a temperature between 200°C and 300°C. Downstream of the rotary kiln 130 in gas flow direction, which in the plant 100 is for the most part the opposite of material flow direction, a first entrained flow reactor 160 is connected downstream as a heat exchanger, in which raw meal 120 is preheated to hot meal 122 by the hot offgases in the rotary kiln 130. This entrained flow reactor 160 is followed in gas flow direction by a first cyclone separator 161 for separating out the hot meal 122. The cyclone separator 161 separates the hot meal 122 from the now cooled offgases from the rotary kiln 130. A first hot meal conduit 163 conducts the hot meal 122 into a second entrained flow reactor 170, which acts as a calciner, which is itself connected to the tertiary air conduit 150 and is fed with tertiary air 151 therefrom. A meal conduit 179 conducts deacidified raw meal 121 originating from the second entrained flow reactor 170 acting as a calciner into the rotary kiln 130, with separation of this deacidified raw meal 121 from the process gas in the entrained flow reactor 170 by a cyclone separator 177. In this plant 100, there are several points at which heat can be removed from an offgas or a process gas. The heat removed, which is lacking in the process for producing cement clinker, can then be compensated for by using more fuel in the rest of the plant. A first point at which plenty of waste heat Q can be removed is the gas conduit 168. This discharges an offgas from the aforementioned cyclone separator 161 and carries waste heat which is still valuable in itself and which is removed via a heat exchanger 165 connected into this gas conduit 168. In the diagram, the heat Q is shown with a dot above it, which means that what is meant here is a heat flow. In order to draw off the offgas from the cyclone separator 161, there may be a compressor 166 downstream of the heat exchanger 165 that assists the flow of gas from the rotary kiln 130 to the heat exchanger 165 by drawing off cooled offgas 169 that includes carbon dioxide (CO2). The second entrained flow reactor 170, which acts as a calciner, is designed for a residence time of 4 s to 8 s and thus has a longer residence time than is typical of known calciners. This longer residence time is intended to ensure that the secondary fuel 201 which is fed into the entrained flow reactor 170 via a fuel feed 171 reliably ignites and burns to completion. Since the supply air to the entrained flow reactor 170 consists of cooled tertiary air 150, the tendency of the secondary fuel 201 to ignite is somewhat reduced. In order nevertheless to bring about ignition, the secondary fuel is fed together with the hot meal 122 into the entrained flow reactor acting as a calciner, with the hot meal supplying the necessary ignition energy. Not only is hot meal 122 from the first entrained flow reactor 160, which acts as a heat exchanger, introduced into the entrained flow reactor 170 acting as a calciner, but also cold raw meal which is fed into the entrained flow reactor via a raw meal feed 172. The feeding-in of cold raw meal makes it possible to control the temperature in the entrained flow reactor 170. The hot meal 122 calcined in the entrained flow reactor 170 to deacidified raw meal 121 is separated by a cyclone separator 177 and, as mentioned above, is directed via a meal conduit 179 to the rotary kiln. Offgas 189 which is formed in the entrained flow reactor 170 and is separated off via the cyclone separator 177 leaves the plant 100 via the gas conduit 188. Prior to this, however, waste heat Q is removed from this offgas 189 via a heat exchanger 185 in the gas conduit 188 before it leaves the plant 100 as cooled offgas 189. Offgas from the second entrained flow reactor 170, which acts as a calciner, passes through a burnout chamber 175 in order to reliably burn the fuel to completion. Thereafter, the meal / gas suspension formed in the entrained flow reactor 170 takes the path via the descending branch 176 into the cyclone separator 177. Figure 2 shows a plant 200 for implementing the process of the invention in a first configuration. This plant differs from the plant 100 in figure 1 by an additional, third entrained flow reactor 180. The second entrained flow reactor 170 which acts as a calciner is followed downstream in gas flow direction by this third entrained flow reactor 180, which has a fuel feed 181 for secondary fuel 201 and a raw meal feed 182 for raw meal 120. This third entrained flow reactor 180 also has an effect as a calciner, in that a meal conduit 183 conducts deacidified raw meal 121 which originates from the third entrained flow reactor 180 and has been separated off by means of a cyclone separator 187 into the rotary kiln 130. The offgas from the second entrained flow reactor 170, which acts as a calciner, is directed with an oxygen content of 10-15% into this third entrained flow reactor 180, which also acts as a calciner. Further secondary fuel 201 is fed in there together with a portion of the raw meal 120. The raw meal 120 also serves for temperature control in this entrained flow reactor 180. After the secondary fuel 201 has been ignited, the remaining raw meal 120 is added, heated and calcined. This third entrained flow reactor 180, which also acts as a calciner, is also designed for a residence time of 4 to 8 seconds and has, at its deflection, a combustion chamber 185 in order to assist full combustion of the secondary fuel 201. For the remaining plant components of the plant 200, reference is made to the description relating to figure 1. Figure 3 shows a flow diagram of the process of the invention in a first configuration. The process for producing cement clinker 110 from raw meal 120 comprises the following steps beginning with the provision of raw meal, a mixture of silicate-containing rock and carbonate-containing rock: a preheating 10 of the raw meal 120 to give hot meal (122), followed by separating out 20 of the hot meal 122 in a cyclone separator 161 and introduction of the hot meal 122 via a hot meal conduit 163 into an entrained flow reactor 170. This is followed by calcining 30 of the hot meal 122 to deacidified raw meal 121 in the entrained flow reactor 170, which acts as a calciner. The deacidification is followed by separating out 40 of the deacidified raw meal 121 in a cyclone separator 177 following downstream of the entrained flow reactor 170 acting as a calciner in gas flow direction. From that point, the deacidified raw meal 121 separated out is sintered 50 into a rotary kiln 130 to form cement clinker 110. According to the concept of the invention, the following procedure is proposed: preheating 10 of the raw meal 120 to give hot meal 122 in an entrained flow reactor 160 as the first entrained flow reactor and charging 55 of this first entrained flow reactor 160 with the offgases from the rotary kiln 130. At that point, the procedure differs from known processes for producing cement clinker 110 in that the offgas from the rotary kiln 130 is utilized not for calcination but for preheating 10 and the preheating takes place in an entrained flow reactor 160 in order to be able to withstand the high offgas temperatures of the rotary kiln 130. The sintering may be followed by a process step known per se, namely cooling 60 of the cement clinker 110 in a clinker cooler 140, which is connected downstream of the rotary kiln 130 in material flow direction, and subsequently introduction 65 of heated cooling air as tertiary air 151 from a cooler head housing 149 of the clinker cooler 140 into the second entrained flow reactor 170 via a tertiary air conduit 150. Four particular points are suitable for removal of waste heat from the process. A first tapping point for waste heat Q is in the gas pathway downstream of the separator 161 of the first entrained flow reactor 160, which is utilized for preheating of the raw meal 120, in process step 20 "separating". A second tapping point for waste heat Q is in the gas pathway downstream of the separator 177 of the second entrained flow reactor 170, which is utilized for calcining of raw meal / hot meal, in process step 40 "separating". A third tapping point for waste heat Q is in the gas pathway after the cooling in clinker cooler 140, in process step 60 "cooling". A fourth tapping point for waste heat Q is in the gas pathway of the tertiary air 150, specifically in the tertiary air conduit, in process step 65 "introducing". The waste heat Q that can be removed at the aforementioned tapping points can be used for the operation of a further process for separating off carbon dioxide (CO2) which inevitably arises in the production of cement clinker 110. Figure 4, finally, is a flow diagram of the process of the invention in a second configuration. The process according to this flow diagram differs from the process according to the flow diagram in figure 3 by a further process step of calcining 70. This is provided downstream of the first calcination step 30 and separation step 40. This second calcination step increases the capacity of the second entrained flow reactor, which acts as a calciner. This is because the second entrained flow reactor 170, which acts as a calciner, is operated at a reduced temperature of the tertiary air fed to it. LIST OF REFERENCE SYMBOLS 10 preheating 146 waste air 20 separating 147 cooling air 25 removing 148 gas conduit 30 calcining 149 cooler head housing 40 separating 150 tertiary air conduit 45 removing 151 tertiary air 50 sintering 155 heat exchanger 60 cooling 160 first entrained flow reactor 65 introducing 161 cyclone separator 66 removing 162 raw meal feed 67 removing 163 hot meal conduit 70 calcining 165 heat exchanger 75 removing 166 compressor 100 plant 168 gas conduit 110 cement clinker 169 offgas 120 raw meal 170 second entrained flow reactor 121 deacidified raw meal 171 fuel feed 122 hot meal 172 raw meal feed 130 rotary kiln 175 burnout chamber 131 inlet chamber 176 descending branch 140 clinker cooler 177 cyclone separator 145 heat exchanger 179 meal conduit 180 third entrained flow reactor 186 compressor 181 fuel feed 200 primary fuel 182 raw meal feed 201 secondary fuel 183 meal conduit 202 primary air 185 heat exchanger 203 secondary air 186 descending branch Q waste heat 187 cyclone separator B fuel 188 gas conduit 189 offgas
Claims
1. A process for producing cement clinker (110) from raw meal (120), having the following steps:- preheating (10) the raw meal (120) to give hot meal (122),- separating out (20) the hot meal (122) in a cyclone separator (161)and introducing the hot meal (122) via a hot meal conduit (163) into an entrained flow reactor (170),- calcining (30) the hot meal (122) to give deacidified raw meal (121) in the entrained flow reactor (170) as a calciner,- separating out (40) the deacidified raw meal (121) in a cyclone separator (177) downstream of the entrained flow reactor (170) as a calciner in gas flow direction,- sintering (50) the separated deacidified raw meal (121) in a rotary kiln (130) to give cement clinker (110),characterized by- preheating (10) the raw meal (120) to give hot meal (122) in an entrained flow reactor (160) as the first entrained flow reactor,- charging (55) said first entrained flow reactor (160) with the offgases from the rotary kiln (130).
2. The process as claimed in claim 1,characterized by- cooling (60) the cement clinker (110) in a clinker cooler (140) connected downstream of the rotary kiln (130) in material flow direction,- introducing (65) heated cooling air as tertiary air (151) from a cooler head housing (149) of the clinker cooler (140) into the second entrained flow reactor (170) via a tertiary air conduit (150).
3. The process as claimed in claim 2,characterized by- removing (66) waste heat (Q) from the tertiary air (151) via a heat exchanger (155) connected into the tertiary air conduit (150).
4. The process as claimed in claim 2 or 3,characterized by- removing (67) waste heat (Q) from heated cooling air (147) as waste air (146) via a heat exchanger (145) connected into a gas conduit (148) for discharging waste air (146) from the cooler (140).
5. The process as claimed in any of claims 2 to 4,characterized by- removing (25) waste heat (Q) from heated offgas (169) separated by means of a cyclone separator (161) from the first entrained flow reactor (160) via a heat exchanger (165) connected into a gas conduit(168) for discharging the offgas (169) from the first entrained flow reactor (160).
6. The process as claimed in any of claims 2 to 5,characterized by- removing (45) waste heat (Q) from heated offgas (189) separated by means of a cyclone separator (177) from the entrained flow reactor (170) acting as a calciner via a heat exchanger (185) connected into a gas conduit (188) for discharging the offgas (189) from the second entrained flow reactor (170).
7. The process as claimed in any of claims 1 to 5,characterized by- switching a third entrained flow reactor (180) as a further calciner downstream of the entrained flow reactor (170) acting as a calciner in gas flow direction,- calcining (70) further raw meal (120) in the third entrained flow reactor (180) to give deacidified raw meal (121),- separating (80) the raw meal (121) deacidified in the third entrained flow reactor (180) in a cyclone separator (187),- introducing deacidified raw meal (121) separated from the cyclone separator (187) into the rotary kiln (130).
8. The process as claimed in claim 7,characterized by- removing (85) waste heat (Q) from heated offgas (189) separated via a cyclone separator (187) from the third entrained flow reactor (180) via a heat exchanger (185) connected into a gas conduit (188) for discharging the offgas (189) from the third entrained flow reactor (180).
9. The process as claimed in any of claims 3 to 6 and 8,characterized byusing the waste heat (Q) removed for operation of a further process for separating and / or storing carbon dioxide (CO2) from the offgases formed in the process as claimed in any of claims 1 to 8.
10. A plant (100) for producing cement clinker (110) from raw meal (120), bythe process as claimed in claims 1 to 9, having- at least one rotary kiln (130) for sintering deacidified raw meal (121) to cement clinker (110),- at least one clinker cooler (140) for cooling the cement clinker (110), where the clinker cooler (140) is connected downstream of the rotary kiln (130) in material flow direction,- at least one tertiary air conduit (150) for taking in cooling air (147) heated in the cooler head housing (149) of the clinker cooler (140) as tertiary air (151),characterized in thatdownstream of the rotary kiln (130) in gas flow direction is a first entrained flow reactor (160) as a heat exchanger, in which raw meal (120) is preheated to give hot meal (122), followed in turn downstream bya first cyclone separator (161) in gas flow direction for separating out the hot meal (122),wherein a first hot meal conduit (163) conducts the hot meal (122) into a second entrained flow reactor (170) as a calciner, which is itself connected to the tertiary air conduit (150) and is fed with tertiary air (151) therefrom, andwherein a meal conduit (179) conducts deacidified raw meal (121) originating from the second entrained flow reactor (170) acting as a calciner into the rotary kiln (130).
11. The plant as claimed in claim 10,characterized in thatthe second entrained flow reactor (170) acting as a calciner has a fuel feed (171) for secondary fuel (201).
12. The plant as claimed in claim 10 or 11,characterized in thatthe second entrained flow reactor (170) acting as a calciner has a raw meal feed (172).
13. The plant as claimed in any of claims 10 to 12,characterized in thatthe second entrained flow reactor (170) acting as a calciner is followed downstream in gas flow direction by a third entrained flow reactor (180) which has a fuel feed (181) for secondary fuel (201) and a raw meal feed (182) for raw meal (120), wherein a meal conduit (183) conducts deacidified raw meal (121) originating from the third entrained flow reactor (180) into the rotary kiln (130).
14. The plant as claimed in any of claims 10 to 13,characterized in thatone heat exchanger (145, 165) in each case is connected downstream in a gas conduit (148, 168) in gas flow direction in the gas pathway of the clinker cooler (140) and / or of the first entrained flow reactor (160), by means of which heat (Q) is separated out for the operation of a further plant for separating carbon dioxide (CO2).
15. The plant as claimed in any of claims 10 to 14,characterized in thata heat exchanger (155) is connected into the tertiary air conduit (150), by means of which heat (Q) is separated out for the operation of a further plant for separating out carbon dioxide (CO2).
16. The plant as claimed in claim 13,characterized in thata heat exchanger (185) is connected in a gas conduit (188) in gas flow direction in the gas pathway of the third entrained flow reactor (180), by means of which heat (Q) is separated out for the operation of a further plant for separating out carbon dioxide (CO2).