Pelletising and exhaust-gas cleaning plant and method for converting green iron-ore pellets into indurated pellets using said plant
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-27
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026051991_13082026_PF_FP_ABST
Abstract
Description
[0001] 202400325
[0002] 1
[0003] Description
[0004] Pelletizing and exhaust gas cleaning plant and process for converting raw iron ore pellets into hardened pellets with this plant
[0005] The invention relates to a pelletizing and exhaust gas cleaning system comprising a pelletizing unit for converting raw iron ore pellets into hardened pellets. The invention further relates to a method for converting raw iron ore pellets into hardened pellets using this pelletizing and exhaust gas cleaning system.
[0006] Pelletizing plants are used to convert iron ore into pellets that can be used in blast furnaces and direct reduction plants. Pellets are typically spherical or cylindrical particles of comparable shape and size, supplied in bulk. The conversion process involves mixing fine iron ore with binders and initially forming raw pellets. These raw pellets are unhardened and moist, sometimes referred to as green pellets. They have their final shape but are not yet mechanically stable and contain residual moisture. For transport and use in blast furnaces or direct reduction plants, these raw pellets are hardened by heating in pelletizing plants to increase their strength.
[0007] Pelletizing plants can include, for example, a traveling grate kiln or a rotary kiln. In a traveling grate kiln, the raw pellets are placed on a moving grate bed to pass through various zones, such as a drying zone, a preheating zone, a burner zone, a post-burner zone, and a cooling zone, with the various zones sometimes being present in duplicate or multiple times. Moisture is removed in the drying zone. The binder is activated in the preheating zone.
[0008] 2
[0009] In the combustion zone, the pellets are solidified through a thermochemical reaction. In a rotary kiln, the raw pellets move through an inclined tube that rotates continuously around its own axis. Pelletizing plants with rotary kilns also pass through various zones, such as a drying zone, a preheating zone, a combustion zone, a post-burning zone, and a cooling zone, with the different zones sometimes being present in duplicate or multiple times.
[0010] In pelleting plants with a traveling grate furnace, the raw pellets are usually not applied directly to the grate bed.
[0011] Instead, a so-called hearth layer of already hardened pellets is first applied to the grate bed to protect the grate bed and improve process stability and the quality of the produced pellets. The raw pellet layer is then applied to the hearth layer.
[0012] In the pelletizing plant, process gas flows around the raw pellets to achieve the desired effect in each zone, such as drying, heating, and / or cooling. For this purpose, the process gas has the required temperature. For energy efficiency reasons, the process gas is at least partially recirculated. For example, the hot process gas from a burner zone and / or afterburner zone and / or cooling zone is used in one, two, or more drying zones and / or a preheating zone. To cool the process gas to the desired temperature of the drying zone and / or preheating zone, air is injected into the process gas as it is transferred from the burner zone to the one, two, or more drying zones and / or the preheating zone, also known as "bleed-in air." This air injection requires energy and causes corresponding CO2 emissions.
[0013] The exhaust gas from pelleting plants is usually subjected to exhaust gas cleaning to minimize environmental impact. 202400325
[0014] 3
[0015] For example, dust, nitrogen oxides and sulfur oxides are removed.
[0016] DeNOx systems are known for reducing nitrogen oxides and thus removing the NtB from exhaust gases. One well-known method for nitrogen oxide reduction is selective catalytic reduction, also known as SCR. In SCR, ammonia or urea, for example, is used as a reducing agent. The reaction takes place in a reduction reactor in the presence of a catalyst. SCR requires exhaust gas temperatures of at least 200 °C, and in particular at least 250 °C. Since the exhaust gas stream to be cleaned from pelletizing plants often does not reach the required temperature, SCR systems must provide heating devices for this exhaust gas stream upstream of the reduction reactor. One known method is to provide an internal heat exchanger that extracts heat from the exhaust gas stream after it has passed through the reduction reactor and transfers this heat back to the exhaust gas stream before it passes through the reactor.Since this often still does not achieve the required temperature, it is known to additionally provide a supplementary heating device to further heat the exhaust gas stream. These heating devices are operated, for example, with natural gas and result in additional CO2 emissions.
[0017] From CN 112 316 587 A a device for the treatment of sintered gases is known, which combines sintered gas recirculation technology with desulfurization, dust removal and denitrification technology.
[0018] A circulation system for sintered gases is known from CN 111 569 623 A.
[0019] The invention is based on the objective of providing a new pelleting and exhaust gas cleaning plant comprising a pelleting unit for converting raw iron ore pellets into hardened pellets and a method for converting raw iron ore pellets into hardened pellets with this plant, in particular-202400325
[0020] 4
[0021] re a pelletizing and exhaust gas cleaning plant and a process in which the CO2 emissions generated in the pelletizing unit during the conversion of raw iron ore pellets into hardened pellets and / or during the denitrification of the exhaust gases are reduced or eliminated.
[0022] This problem is solved with respect to the pelleting and exhaust gas cleaning system by the features of the pelleting and exhaust gas cleaning system according to claim 1, and with respect to the method by the features of the method according to claim 13. Embodiments and further developments are specified in the respective dependent claims.
[0023] The pelletizing and exhaust gas cleaning system according to the invention comprises a pelletizing unit for converting raw iron ore pellets into hardened pellets, an SCR denitrification unit for exhaust gas cleaning, and an exhaust gas line arranged between the pelletizing unit and the SCR denitrification unit, through which an exhaust gas stream from the pelletizing unit is fed to the SCR denitrification unit for the reduction of nitrogen oxides.
[0024] The invention provides that a heat transfer unit is arranged between the pelletizing unit and the SCR denitrification unit, which extracts heat from a process gas stream of the pelletizing unit and transfers this heat to the exhaust gas stream to be cleaned in the SCR denitrification unit.
[0025] The pelleting unit can, for example, be a pelleting unit with a traveling grate furnace or with a rotary tube furnace.
[0026] Process gas flow refers to a gas flow that surrounds the raw pellets in the pelletizing unit. This process gas flow can also circulate, meaning it can be routed out of certain zones of the pelletizing unit and into the pelleting unit.
[0027] 5
[0028] The pellets are returned to the zones of the pelleting unit.
[0029] In contrast, exhaust gas flow refers to a gas flow that, after exhaust gas cleaning, is released from the pelleting unit into the environment.
[0030] The advantages of the invention lie particularly in the fact that waste heat from the pelletizing unit—that is, heat that is not required for further processing in the pelletizing unit and that might otherwise have to be removed, for example, by cooling or adding cooler air—is converted into usable heat in the SCR denitrification unit, thereby at least reducing the additional heat required for the operation of the SCR denitrification unit from other sources. Both aspects reduce the resulting CO2 emissions or even eliminate them entirely. The invention thus enables CO2-neutral heating of the exhaust gas stream to a temperature required for the operation of the SCR denitrification unit.
[0031] Specifically, the invention, through the heat transfer unit, enables two things: firstly, to reduce or completely eliminate the energy input required to heat the exhaust gas stream to the temperature necessary for operating the SCR denitrification unit; and secondly, to eliminate or at least reduce the cooling of the process gas during its transfer between zones by air injection, also known as "bleed-in air," as described above. Eliminating or reducing air injection saves the energy required for this process and thus reduces the corresponding CO2 emissions. Furthermore, eliminating or reducing air injection reduces the volume of exhaust gas, which lowers the overall energy requirement for exhaust gas purification and therefore also contributes to CO2 emission reductions.
[0032] 6
[0033] Due to the additional heat transfer unit, the investment costs for the system may be somewhat higher than for a system without this heat transfer unit provided according to the invention. However, the several energy-saving contributions of the system according to the invention, as explained above, not only lead to a reduction in CO2 emissions but also to lower operating costs of the system.
[0034] Further training stipulates that the heat transfer unit is, or includes, a gas-to-gas heat exchanger. A primary side of the gas-to-gas heat exchanger is thus traversed by the process gas flow, which transfers heat to the exhaust gas flowing through a secondary side of the gas-to-gas heat exchanger. The gas-to-gas heat exchanger can, for example, be a plate heat exchanger.
[0035] One embodiment of the invention provides that the heat transfer unit is or comprises a waste heat recovery system, also known as a WHR system (Waste Heat Recovery System), for example based on water and / or steam and / or thermal oil and / or melting salt.
[0036] It may be provided that the temperature of the process gas stream before heat extraction by the heat transfer unit is higher than the temperature of the exhaust gas stream in the SCR denitrification unit before heat transfer by the heat transfer unit. It may also be provided that the temperature of the process gas stream after heat extraction by the heat transfer unit is lower than the temperature of the process gas stream before heat extraction by the heat transfer unit. Furthermore, it may be provided that the temperature of the exhaust gas stream after heat transfer by the heat transfer unit is higher than the temperature of the exhaust gas stream before heat transfer by the heat transfer unit.
[0037] 7
[0038] One embodiment provides that the temperature of the process gas stream before heat extraction by the heat transfer unit is at least 360 °C, in particular at least 400 °C, and / or after heat extraction by the heat transfer unit is a maximum of 360 °C, in particular a maximum of 320 °C. Alternatively or additionally, it can be provided that the temperature of the exhaust gas stream in the SCR denitrification unit before heat transfer by the heat transfer unit is a maximum of 240 °C, in particular a maximum of 200 °C, and / or after heat transfer by the heat transfer unit is a maximum of 200 °C, in particular a minimum of 250 °C.
[0039] According to one embodiment of the invention, the process gas flow from which heat is extracted is the process gas flow between a burner zone and / or afterburner zone and / or cooling zone of the pelletizing unit located upstream of the heat transfer unit in the flow direction and an upward flow drying zone and / or downward flow drying zone and / or preheating zone of the pelletizing unit located downstream of the heat transfer unit in the flow direction.
[0040] Further training stipulates that the exhaust gas line, through which the exhaust gas flow is supplied to the SCR denitrification unit, is connected to an upward flow drying zone and / or a downward flow drying zone and / or a preheating zone of the pelleting unit, and that the exhaust gas flow routed out of the pelleting unit via the exhaust gas line thus originates at least partially from the upward flow drying zone and / or the downward flow drying zone and / or the preheating zone of the pelleting unit.
[0041] One embodiment provides that the SCR denitrification unit comprises a catalytic reduction reactor through which the exhaust gas stream flows, with the heat transfer to the Ab-202400325 taking place via the heat transfer unit.
[0042] 8
[0043] gas flow in the direction of the exhaust gas flow before passing through the reduction reactor.
[0044] Additionally, the SCR denitrification unit may include an internal heat exchanger, wherein the internal heat exchanger extracts heat from the exhaust gas stream after it has passed through the reduction reactor and supplies this heat to the exhaust gas stream before it passes through the reduction reactor. In particular, the internal heat exchanger is an internal gas-to-gas heat exchanger, through whose heat-releasing primary side the exhaust gas stream passes after it has passed through the reduction reactor, and through whose heat-absorbing secondary side the exhaust gas stream passes before it passes through the reduction reactor.
[0045] It may be provided that the temperature of the exhaust gas stream after passing through the reduction reactor and before heat removal by the internal heat exchanger is higher than the temperature of the exhaust gas stream in the SCR denitrification unit before heat transfer by the internal heat exchanger. It may also be provided that the temperature of the exhaust gas stream after passing through the reduction reactor and after heat removal by the internal heat exchanger is lower than the temperature of the exhaust gas stream after passing through the reduction reactor and before heat removal by the internal heat exchanger. For example, the temperature of the exhaust gas stream after passing through the reduction reactor and after heat removal by the internal heat exchanger is approximately 170 °C.Furthermore, it may be provided that the temperature of the exhaust gas stream after the transfer of heat through the internal heat exchanger and before the transfer of heat through the heat transfer unit is greater than the temperature of the exhaust gas stream in the SCR denitrification unit before the transfer of heat through the internal heat exchanger. 202400325.
[0046] 9
[0047] One design provides that the heat is supplied from the heat transfer unit in the direction of the exhaust gas flow after the heat has been supplied from the internal heat exchanger.
[0048] According to a further development, an auxiliary heating device for reheating the exhaust gas stream is arranged downstream of the heat transfer unit and before the gas flows through the reduction reactor. This auxiliary heating device can be electric or powered by hydrogen and / or natural gas (NG) and / or other gases such as coke oven gas (COG), mixed gas, converter gas (BOF gas), blast furnace gas (BF gas), or biogas. This auxiliary heating device is required if the temperature of the exhaust gas stream after heat transfer has not yet reached the minimum temperature required for the reduction reactor, which is at least 200 °C, and in particular at least 250 °C.However, the CO2 emissions of this auxiliary heating device are lower than without this heat transfer, due to the heat transfer through the heat transfer device, as the auxiliary heating device has to generate less additional heat.
[0049] One embodiment of the invention provides that a dust removal and / or desulfurization system is arranged upstream of the SCR denitrification unit in the direction of exhaust gas flow. Additionally, the dust removal and / or desulfurization system can also be designed to reduce heavy metals such as mercury or lead and / or to degrade dioxins and furans.
[0050] A CO catalyst can also be provided to convert carbon monoxide present in the exhaust gas stream into carbon dioxide, for example, also in the direction of exhaust gas flow before it passes through the SCR denitrification unit. The [202400325]
[0051] 10
[0052] The heat generated by the oxidation of carbon monoxide can also contribute to heating the exhaust gas stream to the temperature required for the operation of the SCR denitrification unit.
[0053] Furthermore, it may be possible to integrate an SCR reduction reactor directly into a process gas discharge after the burner zone and / or afterburner zone in the pelletizing unit in order to reduce the nitrogen oxide concentration already in the process gas, which is hot at this point.
[0054] It is also possible to supplement the SCR denitrification unit with an SNCR denitrification unit. SNCR refers to the selective non-catalytic reduction of nitrogen oxides. The SNCR denitrification unit can be arranged upstream or downstream of the SCR denitrification unit, particularly downstream of the dust removal and / or desulfurization system described above. The SNCR denitrification unit can also be integrated directly into the process gas discharge downstream of the burner zone and / or afterburner zone, in addition to the aforementioned SCR reduction reactor.
[0055] The inventive method for converting raw iron ore pellets into hardened pellets uses a pelletizing and exhaust gas cleaning system according to the invention, as described above. The method provides that an exhaust gas stream from the pelletizing unit is fed to the SCR denitrification unit for the reduction of nitrogen oxides in the exhaust gas stream, and that heat is extracted from a process gas stream of the pelletizing unit and transferred to the exhaust gas stream to be cleaned in the SCR denitrification unit.
[0056] The advantages of this method correspond to the advantages of the pelleting and exhaust gas cleaning system according to the invention described above. 202400325
[0057] 11
[0058] It may also be provided that the temperature of the process gas stream before heat extraction by the heat transfer unit is higher than the temperature of the exhaust gas stream in the SCR denitrification unit before heat transfer by the heat transfer unit. It may also be provided that the temperature of the process gas stream after heat extraction by the heat transfer unit is lower than the temperature of the process gas stream before heat extraction by the heat transfer unit. Furthermore, it may be provided that the temperature of the exhaust gas stream after heat transfer by the heat transfer unit is higher than the temperature of the exhaust gas stream before heat transfer by the heat transfer unit.
[0059] It may be provided that the temperature of the process gas stream before heat extraction by the heat transfer unit is at least 360 °C, in particular at least 400 °C, and / or that the temperature of the process gas stream after heat extraction by the heat transfer unit is a maximum of 360 °C, in particular a maximum of 320 °C. Alternatively or additionally, it may be provided that the temperature of the exhaust gas stream in the SCR denitrification unit before heat transfer by the heat transfer unit is a maximum of 240 °C, in particular a maximum of 200 °C, and / or that the temperature of the exhaust gas stream in the SCR denitrification unit after heat transfer by the heat transfer unit is at least 200 °C, in particular a minimum of 250 °C.
[0060] A further development of the process provides that the process gas flow from which heat is extracted is the process gas flow between a burner zone and / or afterburner zone and / or cooling zone of the pelletizing unit located upstream of the heat transfer unit and an upward flow drying zone and / or downward flow drying zone and / or preheating zone of the pelletizing unit located downstream of the heat transfer unit. Alternatively or additionally, it can be provided that Ab-202400325
[0061] 12
[0062] gas line, with which the exhaust gas flow is supplied to the SCR denitrification unit, is connected to an upward flow drying zone and / or a downward flow drying zone and / or a preheating zone of the pelleting unit and the exhaust gas flow carried out of the pelleting unit via the exhaust line thus comes from the upward flow drying zone and / or the downward flow drying zone and / or the preheating zone of the pelleting unit.
[0063] Furthermore, the SCR denitrification unit may include a catalytic reduction reactor through which the exhaust gas stream flows, with the heat transfer unit transferring heat to the exhaust gas stream in the direction of flow before the exhaust gas stream passes through the reduction reactor. Alternatively or additionally, the SCR denitrification unit may include an internal heat exchanger, wherein the internal heat exchanger extracts heat from the exhaust gas stream after it has passed through the reduction reactor and supplies heat to the exhaust gas stream before it passes through the reduction reactor.
[0064] It may be provided that the heat is supplied from the heat transfer unit in the direction of the exhaust gas flow after the heat has been supplied from the internal heat exchanger.
[0065] One embodiment of the process provides that, downstream of the exhaust gas stream, after the heat transfer unit has supplied heat and before the exhaust gas flows through the reduction reactor, an additional heating device is arranged to reheat the exhaust gas stream. This device reheats the exhaust gas stream to the minimum temperature required for the reduction reactor, or even above, as needed. The additional heating device can be an electric heating device or one powered by hydrogen and / or natural gas (NG) and / or other gases such as coke oven gas (COG), mixed gas, or converter gas (BOE-202400325).
[0066] 13
[0067] Heating equipment powered by gas, blast furnace gas (BF gas) or biogas.
[0068] A further development of the process provides for the installation of a dust collection and / or desulfurization system upstream of the SCR denitrification unit, thus removing dust and / or desulfur from the exhaust gas stream. Additionally, the dust collection and / or desulfurization system can also be designed to reduce heavy metals such as mercury or lead and / or to degrade dioxins and furans.
[0069] The invention is further explained below with regard to its features and advantages by means of a description of an exemplary embodiment and with reference to the accompanying schematic drawings. These show
[0070] FIG 1 shows an embodiment of a prior art pelletizing unit, and
[0071] FIG 2 shows an embodiment of a pelletizing and exhaust gas cleaning system according to the invention.
[0072] Corresponding or comparable parts, components and gas flows are provided with the same reference numerals in both figures.
[0073] FIG 1 shows a schematic representation of a known embodiment of a pelletizing unit 11 from the prior art. This representation serves to explain the embodiment of a pelletizing and exhaust gas cleaning system 10 according to the invention, which is explained with reference to the schematic representation in FIG 2.
[0074] The pelletizing unit 11 shown in FIG. 1 serves to convert raw iron ore pellets 13 into hardened pellets 16. The pelletizing unit 11 thus forms part of a process chain-202400325
[0075] 14
[0076] The unit converts iron ore into pellets that can be used in blast furnaces and direct reduction plants. Pellets are typically spherical or cylindrical particles of comparable shape and size, supplied in bulk. For conversion, fine iron ore is mixed with binders and initially formed into raw iron ore pellets 13. These raw iron ore pellets 13 are unhardened, moist pellets, also known as green pellets. They have their final shape but are not yet mechanically stable and contain residual moisture. For transport and use in blast furnaces or direct reduction plants, these raw iron ore pellets 13 are hardened by heating in the pelletizing unit 11 shown in FIG. 1 to increase their strength.The result is the aforementioned hardened pellets 16, which can be stored and transported as bulk material and can be used in blast furnaces and direct reduction plants.
[0077] The pelletizing unit 11 shown in FIG. 1 comprises a traveling grate furnace 31. Alternatively, the pelletizing unit can also be a different type of pelletizing unit, for example, a pelletizing unit comprising a rotary kiln. In this traveling grate furnace 31, the iron ore pellets 13 are applied to a movable grate bed 32 to pass through different zones 1 to 7 on this grate bed 32: an upward-flow drying zone 1, a downward-flow drying zone 2, a preheating zone 3, a burner zone 4, an afterburner zone 5, a first cooling zone 6, and a second cooling zone 7.
[0078] The enlarged section shown in FIG. 1 illustrates that the iron ore crude pellets 13 are not applied directly to the grate bed 32. Instead, a so-called hearth layer 14 made of already hardened pellets is first applied to the grate bed 32 to protect the grate bed 32 and to improve process stability and the quality of the pellets produced. A crude pellet layer 15 made of iron ore crude pellets 13 is then applied to the hearth layer 14.
[0079] 15
[0080] In the first cooling zone 6 and the second cooling zone 7, ambient air is introduced from below through the grate bed 32 as process gas to cool the hardened pellets 16. In the second cooling zone 7, the portion of the heated process gas generated there is then directed to the upward-flow drying zone 1 and blown from below through the grate bed 32 to dry and heat the raw iron ore pellets 13. The cooled process gas typically has a temperature of about 80 °C and is then subjected to exhaust gas purification and released into the environment via a stack 33.
[0081] In the first cooling zone 6, the portion of the heated process gas that accumulates there is then fed in parallel to the afterburner zone 5 and the burner zone 4.
[0082] In the afterburner zone 5, the heated process gas flows through the grate bed 32 containing the pellets without additional heating from above.
[0083] In burner zone 4, the heated process gas is first further heated by a heating system 34, for example a burner, typically to at least 400 °C, and then flows from above through the grate bed 32 with the pellets to harden them.
[0084] The hot process gas from burner zone 4, except for a small portion which is discharged below the grate bed 32 along with the process gas from the downward flow drying zone 2 and the preheating zone 3, is conveyed together with the warm process gas from the afterburner zone 5 after passing through the grate bed 32 as process gas stream 20 and fed in parallel from above to the downward flow drying zone 2 and the preheating zone 3. Since the temperature of the process gas after passing through burner zone 4 or afterburner zone 5 is too high for feeding into the 202400325
[0085] 16
[0086] In the downflow drying zone 2 and the preheating zone 3, the process gas stream 20 is cooled to the desired temperature by means of air injection 35 into the process gas as it passes from the burner zone 4 or the afterburner zone 5. This air injection 35 is also referred to as "bleed-in air". This air injection 20 requires energy and causes corresponding CO2 emissions.
[0087] In the downward flow drying zone 2 and in the preheating zone 3, the process gas stream 20 j, which has already been cooled by the air injection 35, flows from above through the grate bed 32 containing the pellets in order to dry and heat them.
[0088] Below the grate bed 32, the process gas from the downward flow drying zone 2 and the preheating zone 3, together with a small portion of the discharged process gas from the burner zone 4, is fed as exhaust gas stream 18 to the exhaust gas cleaning system and discharged to the environment via the chimney 33. The exhaust gas stream typically has a temperature of approximately 160 to 180 °C.
[0089] The pelletizing and exhaust gas cleaning system 10 shown in FIG. 2 according to the invention comprises a modification of the pelletizing unit 11 shown in FIG. 1 for converting raw iron ore pellets 13 into hardened pellets 16. Furthermore, the pelletizing and exhaust gas cleaning system 10 comprises an SCR denitrification unit 12 for exhaust gas cleaning and an exhaust gas line 17 arranged between the pelletizing unit 11 and the SCR denitrification unit 12.
[0090] In contrast to the pelletizing unit 11 shown in FIG. 1, the exhaust gas flow 18 derived from the downward flow drying zone 2 and the preheating zone 3, together with a small portion of the discharged process gas from the burner zone 4, is not fed to the chimney 33, as illustrated by dashed lines in FIG. 2, but rather via the aforementioned exhaust gas line 17 to the SCR denitrification unit 12, specifically to the 202400325
[0091] 17
[0092] Reduction of nitrogen oxides contained in the exhaust gas stream 18. As shown in FIG. 2, an induced draft fan 38, also called an ID fan, can be arranged in or adjacent to the exhaust gas pipe 17 to generate the necessary exhaust gas stream 18.
[0093] As an alternative to the representation in FIG 2, it can be provided that the process gas derived from the upward flow drying zone 1 is also fed to the exhaust gas stream 18 and thus also fed to the SCR denitrification unit 12 via the exhaust gas line 17 and not to the chimney 33.
[0094] As shown in FIG. 1, a dust removal and / or desulfurization system 30 can be arranged in the exhaust gas line 17, in the direction of flow of the exhaust gas stream 18, upstream of the SCR denitrification unit 12. Additionally, the dust removal and / or desulfurization system 30 can also be designed to reduce heavy metals such as mercury or lead and / or to degrade dioxins and furans.
[0095] The SCR denitrification unit 12 is a DeNOx system that includes a catalytic reduction reactor 22 for selective catalytic reduction, also known as SCR. The exhaust gas stream 18 flows through this reduction reactor 22. The reducing agent required for the SCR is injected into the exhaust gas stream 18 upstream of the reduction reactor 22. Figure 2 shows an ammonia injection system 28 as an example.
[0096] SCR requires exhaust gas temperatures of at least 200 °C, in particular at least 250 °C. The exhaust gas stream 18 from the pelletizing unit 11 typically has a temperature of about 160 to 180 °C and therefore does not reach the required temperature. Therefore, several devices for heating the exhaust gas stream 18 are provided, which are explained below.
[0097] One such device is an internal heat exchanger 23 in the SCR denitrification unit 12. The internal heat exchanger 23 extracts heat, designated by reference numeral 24 in FIG. 2, from the exhaust gas stream 18 after it has passed through the reduction reactor 22, and transfers this heat 24 to the exhaust gas stream 18 before it passes through the reduction reactor 22. The internal heat exchanger 23 can, for example, be an internal gas-to-gas heat exchanger.
[0098] As a further means of heating the exhaust gas stream 18, an auxiliary heating device 25 is provided for reheating the exhaust gas stream 18. This is arranged in the direction of flow of the exhaust gas stream 18 between the heat supply 24 via the internal heat exchanger 23 and the reduction reactor 22. This auxiliary heating device 18 is operated, for example, with natural gas, but it can also be operated, for example, with hydrogen and / or other gases such as coke oven gas (COG), mixed gas, converter gas (BOF gas), blast furnace gas (BF gas), or biogas. It can also be an electrically operated auxiliary heating device. The supply of combustion gas 26, for example, natural gas or hydrogen or other gases, and combustion air 27 for the operation of the auxiliary heating device 25 is shown by way of example in FIG. 2.
[0099] In the pelletizing and exhaust gas cleaning plant 10 shown in FIG. 2, a heat transfer unit 19 is arranged between the pelletizing unit 11 and the SCR denitrification unit 12. The heat transfer unit 19 can be a gas-to-gas heat exchanger, as shown in FIG. 2. However, it is also possible that the heat transfer unit 19 is a waste heat recovery system based on water and / or steam and / or thermal oil and / or molten salts, i.e., a waste heat recovery system, also called a WHR system.
[0100] 19
[0101] The heat transfer unit 19 can be associated with a dust removal system 36 for cleaning, as shown in FIG 2, which includes, for example, a soot blower.
[0102] The heat transfer unit 19 extracts heat, designated by reference numeral 21 in FIG. 2, from the process gas stream 20 of the pelletizing unit 11 and transfers it to the exhaust gas stream 18 to be cleaned in the SCR denitrification unit 12. In the example shown in FIG. 2, the heat 21 is supplied from the heat transfer unit 19 in the flow direction of the exhaust gas stream 18 after the supply of heat 24 from the internal heat exchanger 23.
[0103] In FIG. 2, the process gas flow 20, from which the heat 21 is extracted, is the process gas flow 20 between burner zone 4 and afterburner zone 5 of the pelletizing unit 11 on the one hand, and the downward flow drying zone 2 and the preheating zone 3 of the pelletizing unit 11 on the other. Burner zone 4 and afterburner zone 5 are located upstream of the heat transfer unit 19 in the flow direction of the process gas flow 20. Downstream flow drying zone 2 and preheating zone 3 are located downstream of the heat transfer unit 19 in the flow direction of the process gas flow 20.
[0104] The difference to the pelletizing unit 11 in FIG. 1 is therefore that the direct transfer of the process gas flow 20 between burner zone 4 and afterburner zone 5 on the one hand, and the downward flow drying zone 2 and the preheating zone 3 on the other, is interrupted and replaced by the routing of the process gas flow 20 through the primary side of the heat transfer unit 19. This interruption of the direct transfer is indicated by dashed lines in FIG. 2. The secondary side of the heat transfer unit 19 is traversed by the exhaust gas flow 18 in the SCR denitrification unit 12.
[0105] 20
[0106] As the process gas stream 20 flows through the heat transfer unit 19, it is cooled. This has the advantage that the air injection 35 (see FIG. 1), which is otherwise provided for cooling, can be omitted. Therefore, to illustrate this difference, the air injection 35 is shown only as a dashed line in FIG. 2.
[0107] The provision of the heat transfer unit 19 has the advantage that waste heat from the pelletizing unit 11—that is, heat that is not required for further process operation in the pelletizing unit 11 and that would even have to be removed by the air injection 35—is converted into usable heat in the SCR denitrification unit 12. This reduces the additional heat required for the operation of the SCR denitrification unit 12 from other sources, in particular the auxiliary heating device 25. Both aspects reduce the overall CO2 emissions generated during the operation of the pelletizing and exhaust gas cleaning system 10 compared to a corresponding system without the heat transfer unit 19.
[0108] In the pelletizing and exhaust gas cleaning plant 10 in FIG. 2, the temperature TI of the process gas stream 20 before heat extraction 21 is higher than the temperature T4 of the exhaust gas stream 18 in the SCR denitrification unit 12 before heat transfer 21. Furthermore, the temperature T2 of the process gas stream 20 after heat extraction 21 is lower than the temperature TI of the process gas stream 20 before heat extraction 21. Also, the temperature T5 of the exhaust gas stream 18 after heat transfer 21 is higher than the temperature T4 of the exhaust gas stream 18 before heat transfer 21.
[0109] Specifically, it can be provided that the temperature TI of the process gas stream 20 before the removal of heat 21 by the heat transfer unit 19 is at least 400 °C and the temperature T2 of the process gas stream 20 after the removal of heat 21 by the heat transfer unit 19 is a maximum of 360 °C. Furthermore, it can be provided that the temperature T4202400325
[0110] 21
[0111] The temperature T5 of the exhaust gas stream 18 in the SCR denitrification unit 12 before the transfer of heat 21 by the heat transfer unit 19 is a maximum of 240 °C and the temperature T5 of the exhaust gas stream 18 in the SCR denitrification unit 12 after the transfer of heat 21 by the heat transfer unit 19 is at least 200 °C, in particular at least 250 °C.
[0112] Furthermore, it can be specifically provided that the temperature T3 of the exhaust gas stream 18 in the SCR denitrification unit 12 before the transfer of heat 24 through the internal heat exchanger 23 is lower than the temperature T4 of the exhaust gas stream 18 in the SCR denitrification unit 12 after the transfer of heat 24 through the internal heat exchanger 23 and before the transfer of heat 21 through the heat transfer unit 19. It can also be provided that the temperature T6 of the exhaust gas stream 18 in the SCR denitrification unit 12 before the extraction of heat 24 by the internal heat exchanger 23 is higher than the temperature T7 of the exhaust gas stream 18 in the SCR denitrification unit 12 after the extraction of heat 24 by the internal heat exchanger 23.
[0113] After passing through the SCR denitrification unit 12, the cleaned exhaust gas stream 18 is discharged via an exhaust gas duct 37 to the environment. If the SCR denitrification unit 12 is not to be used, or not to be used, for the entire exhaust gas stream 18, a bypass 29 can be provided, which is shown as a dashed line in FIG. 2 between the exhaust gas duct 17 and the discharge duct 37.
[0114] 22
[0115] Reference symbol list
[0116] 1 Upward flow drying zone
[0117] 2 Downward flow drying zone
[0118] 3 Preheating zone
[0119] 4 burner zones
[0120] 5 Afterburner zone
[0121] 6 first cooling zone
[0122] 7 second cooling zone
[0123] 10 Pelletizing and exhaust gas cleaning system
[0124] 11 Pelletizing unit
[0125] 12 SCR denitrification units
[0126] 13 iron ore crude pellets
[0127] 14th layer of the hearth
[0128] 15 raw pellet layer
[0129] 16 hardened pellets
[0130] 17 Exhaust pipe
[0131] 18 Exhaust gas flow
[0132] 19 Heat transfer unit
[0133] 20 Process gas flow
[0134] 21 Heat, transferred through the heat transfer unit 19 22 Reduction reactor
[0135] 23 internal heat exchangers
[0136] 24 Heat, transferred through the internal heat exchanger 23 25 Auxiliary heating device
[0137] 26 Combustion gas, for example hydrogen, natural gas and other gases
[0138] 27 Combustion air
[0139] 28 Ammonia injection system
[0140] 29 Bypass of the SCR denitrification unit 12
[0141] 30 Dust removal and / or desulfurization plant
[0142] 31 Traveling grate oven
[0143] 32 slatted bed
[0144] 33 Fireplace
[0145] 34 Heating system
[0146] 35 Air injection
[0147] 36 Dust removal system 202400325
[0148] 23
[0149] 37 Exhaust duct for diverting the exhaust gas flow 18
[0150] 38 Induced draft fan
[0151] TI Temperature of the process gas stream 20 before heat removal 21
[0152] T2 Temperature of the process gas stream 20 after heat removal 21
[0153] T3 Temperature of the exhaust gas flow 18 in the SCR denitrification unit 12 before heat transfer 24
[0154] T4 Temperature of the exhaust gas flow 18 in the SCR denitrification unit 12 before heat transfer 21 and after heat transfer 24
[0155] T5 Temperature of the exhaust gas flow 18 in the SCR denitrification unit 12 after heat transfer 21
[0156] T6 Temperature of the exhaust gas flow 18 in the SCR denitrification unit 12 before heat extraction 24
[0157] T7 Temperature of the exhaust gas flow 18 in the SCR denitrification unit 12 after heat removal 24
Claims
202400325 24 Patent claims 1. Pelletizing and exhaust gas cleaning plant ( 10 ) comprising a pelletizing unit ( 11 ) for converting iron ore raw pellets ( 13 ) into hardened pellets ( 16 ) , an SCR denitrification unit (12) for exhaust gas purification, and an exhaust gas line (17) arranged between the pelletizing unit (11) and the SCR denitrification unit (12), through which an exhaust gas stream (18) from the pelletizing unit (11) is fed to the SCR denitrification unit (12) for the reduction of nitrogen oxides, characterized by a heat transfer unit (19) arranged between the pelletizing unit (11) and the SCR denitrification unit (12), which extracts heat (21) from a process gas stream (20) of the pelletizing unit (11) and transfers it to the exhaust gas stream (18) to be cleaned in the SCR denitrification unit (12).
2. Pelletizing and exhaust gas cleaning plant ( 10 ) according to claim 1 , wherein the heat transfer unit ( 19 ) is a gas-to-gas heat exchanger or comprises the sen st .
3. Pelletizing and exhaust gas cleaning plant ( 10 ) according to claim 1 or 2 , wherein the heat transfer unit ( 19 ) is or comprises a waste heat recovery system .
4. Pelletizing and exhaust gas cleaning plant ( 10 ) according to one of claims 1 to 3 , wherein the temperature (TI) of the process gas stream (20) before heat removal (21) by the heat transfer unit (19) is greater than the temperature (T4) of the exhaust gas stream (18) in the SCR denitrification unit (12) before heat transfer (21) by the heat transfer unit (19), wherein the temperature (T2) of the process gas stream (20) after heat removal (21) by the heat transfer unit (19) is less than the temperature (TI) of the process gas stream. 25 ( 20 ) before the removal of heat ( 21 ) by the heat transfer unit ( 19 ) is , and where the temperature (T5) of the exhaust gas stream (18) after the transfer of heat (21) by the heat transfer unit (19) is greater than the temperature (T4) of the exhaust gas stream (18) before the transfer of heat (21) by the heat transfer unit (19).
5. Pelletizing and exhaust gas cleaning plant ( 10 ) according to one of claims 1 to 4 , where wherein the temperature (T5) of the exhaust gas stream (18) in the SCR denitrification unit (12) after the transfer of heat (21) through the heat transfer unit (19) is at least 200 °C.
6. Pelletizing and exhaust gas cleaning system (10) according to one of claims 1 to 5, wherein the process gas flow (20) from which the heat (21) is extracted is the process gas flow (20) between a burner zone (4) and / or afterburner zone (5) and / or cooling zone (6, 7) of the pelletizing unit (11) located upstream of the heat transfer unit (19) in the flow direction and an upward flow drying zone (1) and / or downward flow drying zone (2) and / or preheating zone (3) of the pelletizing unit (11) located downstream of the heat transfer unit (19) in the flow direction.
7. Pelletizing and exhaust gas cleaning system (10) according to one of claims 1 to 6, wherein the exhaust gas line (17) through which the exhaust gas stream (18) is supplied to the SCR denitrification unit (12) is connected to an upward flow drying zone (1) and / or a downward flow drying zone (2) and / or a preheating zone (3) of the pelletizing unit (11) and the exhaust gas stream (18) discharged from the pelletizing unit (11) via the exhaust gas line (17) is thus at least partially removed from the upward flow drying zone (1) and / or the Ab-202400325 26 wärt s flow-drying zone ( 2 ) and / or the preheating zone ( 3 ) of the pelletizing unit ( 11 ) comes .
8. Pelletizing and exhaust gas cleaning plant (10) according to one of claims 1 to 7, wherein the SCR denitrification unit (12) comprises a catalytic reduction reactor (22) through which the exhaust gas stream (18) flows, wherein the transfer of heat (21) to the exhaust gas stream (18) by means of the heat transfer unit (19) takes place in the direction of flow of the exhaust gas stream (18) before the reduction reactor (22) flows through it.
9. Pelletizing and exhaust gas cleaning system (10) according to claim 8, wherein the SCR denitrification unit (12) comprises an internal heat exchanger (23), wherein the internal heat exchanger (23) extracts heat (24) from the exhaust gas stream (18) after it has passed through the reduction reactor (22) and supplies it to the exhaust gas stream (18) before it passes through the reduction reactor (22).
10. Pelletizing and exhaust gas cleaning system ( 10 ) according to claim 9, wherein the supply of heat ( 21 ) from the heat transfer unit ( 19 ) in the flow direction of the exhaust gas stream ( 18 ) takes place after the supply of heat ( 24 ) from the internal heat exchanger ( 23 ).
11. Pelletizing and exhaust gas cleaning system ( 10 ) according to one of claims 8 to 10 , wherein in the direction of flow of the exhaust gas stream ( 18 ) after the supply of heat ( 21 ) from the heat transfer unit ( 19 ) and before the flow through the reduction reactor ( 22 ) an additional heating device ( 25 ) for reheating the exhaust gas stream ( 18 ) is arranged .
12. Pelletizing and exhaust gas cleaning system (10) according to one of claims 1 to 11, wherein a dust removal and / or desulfurization system (30) is arranged in the direction of flow of the exhaust gas stream (18) upstream of the SCR denitrification unit (12). 202400325 27 13. Method for converting iron ore crude pellets (13) into hardened pellets (16) using a pelletizing and exhaust gas cleaning system (10) according to any one of claims 1 to 12, wherein a) an exhaust gas stream (18) from the pelletizing unit (11) is fed to the SCR denitrification unit (12) for the reduction of nitrogen oxides, and b) heat (21) is extracted from the process gas stream (20) of the pelletizing unit (11) and transferred to the exhaust gas stream (18) to be cleaned in the SCR denitrification unit (12).
14. Method according to claim 13, wherein a) the process gas flow (20) from which the heat (21) is extracted, the process gas flow (20) between a burner zone (4) and / or afterburner zone (5) and / or cooling zone of the pelletizing unit (11) located upstream of the heat transfer unit (19) and an upward flow drying zone (1) and / or downward flow drying zone (2) and / or preheating zone (3) of the pelletizing unit (11) located downstream of the heat transfer unit (19) is, and / or b) the exhaust gas line (17) through which the exhaust gas stream (18) is supplied to the SCR denitrification unit (12) is connected to an upward flow drying zone (1) and / or a downward flow drying zone (2) and / or a preheating zone (3) of the pelletizing unit (11) and the exhaust gas stream (18) carried out of the pelletizing unit (11) via the exhaust gas line (17) thus comes from the upward flow drying zone (1) and / or the downward flow drying zone (2) and / or the preheating zone (3) of the pelletizing unit (11).
15. Method according to claim 13 or 14, wherein a) the SCR denitrification unit (12) comprises a catalytic reduction reactor (22) through which the exhaust gas stream (18) flows, wherein the transfer of heat (21) to the exhaust gas stream (18) by means of the heat transfer unit (19) takes place 28 in the direction of flow of the exhaust gas stream ( 18 ) before flowing through the reduction reactor ( 22 ), and / or b) the SCR denitrification unit ( 12 ) comprises an internal heat exchanger ( 23 ) wherein the internal heat exchanger ( 23 ) extracts heat ( 24 ) from the exhaust gas stream ( 18 ) after passing through the reduction reactor ( 22 ) and supplies heat ( 24 ) to the exhaust gas stream ( 18 ) before passing through the reduction reactor ( 22 ).