Steel plant with electric arc furnace
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SMS GRP SPA
- Filing Date
- 2024-08-06
- Publication Date
- 2026-06-17
AI Technical Summary
Current fumes treatment systems in steel plants with electric arc furnaces are unable to efficiently abate carbon dioxide (CO2) from gaseous emissions, due to low CO2 concentrations and the need to treat carbon monoxide effectively.
The implementation of a fume collection and treatment system that includes a primary suction line with a post-combustion chamber, fume cooling apparatus, and CO2 capture apparatus, along with a recirculation line to enhance CO2 concentration and a control system to manage comburent air intake.
This system efficiently increases the CO2 concentration in fumes to levels suitable for capture, allowing for effective CO2 abatement while maintaining operational reliability and simplicity.
Smart Images
Figure IB2024057608_13022025_PF_FP_ABST
Abstract
Description
"STEEL PLANT WITH ELECTRIC ARC FURNACE"DESCRIPTIONField, of application
[0001] The present invention relates to a steel plant with an electric arc furnace.Background art
[0002] Typically, the direct melting of materials which contain iron, such as scrap, is performed in electric arc furnaces (EAF) .
[0003] The primary feedstock for EAFs is ferrous scrap, which can consist of scrap coming from within the steel mill, scrap from mechanical industries (e.g., vehicle manufacturers) , and demolition or post-consumer scrap (e.g., end-of-life products such as cars, buildings) .
[0004] Direct reduced iron (DRI) is also increasingly being used as a feedstock for EAFs because of its low gangue content, lower content of undesired metals (e.g. copper) , and low CO2 footprint in the manufacturing process.
[0005] Finally, liquid pig iron could also be used in the material mix to feed an electric arc furnace.
[0006] An electric arc furnace is usually charged with scrap and / or DRI and / or liquid pig iron by:
[0007] - metal baskets: the scrap / DRI is usually loaded into baskets and then charged into the furnace after opening the roof;
[0008] - continuous charging systems from the wall : vibrating, traversing or rotating conveyors for scrap / DRI continuously discharge raw materials into the furnace ; instead, liquid pig iron is charged with dedicated chutes ; continuous wall charging can include scrap preheating or not .
[0009] - continuous charging system from the roof : vibrating, translating, rotating or pneumatic conveyors for DRI / scrap discharge the raw material onto a dedicated opening of the furnace roof ( called 5th hole or 3rd hole ) .
[0010] Secondary metallurgy is performed on the molten steel after melting in the EAR to the casting point . It is typically performed at ladle treatment stations , with the molten steel remaining in the ladle itsel f . These treatment stations generally consist of an arc heating unit , referred to as a ladle furnace ( LF) , which allows adj usting the final temperature of the liquid steel for the casting operation . The treatment includes adding scouring agents and binding elements to adj ust the chemical composition of the finished steel . In some cases , the vacuum processing units are used to achieve special gas content requirements .
[0011] A simpli fied diagram of a steel plant provided with an electric arc furnace and a ladle furnace is shown inFigure 1 .Fume collection systems
[0012] A steel plant generally comprises an emission collection system, which in particular can suck the emissions generated during the melting process and convey them to a treatment system .
[0013] Each electric arc furnace (EAF) and ladle furnace ( LF) is provided with its own suction system . In Figure 1 , the EAF suction system is shown as Pl and named primary suction, while the LF suction system is shown as S2 and is part of the secondary suction .
[0014] In the EAF, primary suction can be performed either through an appropriate hole in the furnace roof ( called the 4th hole or 2nd hole ) or through the material feed channel into furnaces with continuous charging systems . In the latter case , the fumes are sucked through the continuous charging system and preheat the scrap before it is charged into the EAF .
[0015] Furthermore , the EAF electric arc furnace is provided with a hood C located on the roof of the building containing the furnace . The function of the hood C is to ventilate the building during the melting step and to collect the fumes generated inside the building following the opening of the furnace roof during the basket loading step . This additional suction system ofthe EAF is also part of the secondary suction and is indicated by SI in figure 1.
[0016] The gases emitted in the basket loading step are diffused inside the building and are strongly diluted before being collected by the hood C. The secondary suction SI must thus treat much larger volumes of fumes than the primary suction Pl. For this reason, the suction capacity of the secondary suction system is much greater than that of the primary suction. Furthermore, due to dilution, the fumes treated by the secondary suction system SI are much cooler than those treated by the primary suction Pl .
[0017] The fumes collected from the suction systems of the EAF and the LF contain dust, nitrogen oxides and sulphur oxides, carbon monoxide, and organic pollutants, e.g., such as volatile organic compounds (VOCs) , chlorobenzenes, polychlorinated biphenyls (PCBs) , polycyclic aromatic hydrocarbons (PAHs) , dioxins (PCDDs) , and furans (PCDFs) . The presence of organics in emissions depends mainly on the quality of the scrap and the raw materials used.
[0018] As shown in the diagram in figure 1, there can also be other points of possible fume emissions in the steel plant, e.g., such as the dust collection of additive conveyor systems AD, refractory demolition and lining ofthe ladle L and the tundish P . These emissions are a consequence of mechanical activities not the combustion and / or melting process ; for such reasons , they contain mainly dust , and not gaseous emissions , such as nitrogen and sulphur oxides . The fume collection system thus comprises auxiliary suctions Al and A2 dedicated to these possible emission points .
[0019] Figure 1 diagrammatically shows a fume collection and treatment system in a steel plant provided with an EAF .
[0020] The fume collection and treatment system comprises a main duct LI into which all the suction systems Pl , P2 , S I , Al and A2 di scharge ; al l the fumes collected by the suction systems are conveyed to a fumes treatment system, which will be explained in greater detail below, through the main duct LI .
[0021] Primary suction Pl from EAF electric arc furnace : the hot fumes from the EAF furnace are collected from the furnace roof through a water-cooled elbow, and conveyed to a cooled post-combustion chamber CPC, where the postcombustion chamber of the CO generated in the melting process is completed; the primary fumes are sucked at a high temperature ( over 1000 ° C ) and are then cooled by means of water-cooled ducts CH, and then by water cooling towers or convection exchangers (natural or forced) QT toreduce the temperature so that they can be treated downstream in a bag filter BF installed in the main duct LI and part of the fumes treatment system .
[0022] Secondary suction S2 from ladle furnace LF : the fumes are collected from the LF furnace roof with a single-wall (uncooled) pipe and conveyed into the main duct LI of the fume system . The temperature of the fumes sucked from the LF is below 180 ° C
[0023] Secondary suction S I from EAF electric arc furnace : the hood C, installed on top of the building, captures the fumes during the EAF charging steps and allows ventilation during the melting steps ; it also allows the suction of the air necessary to further cool the fumes collected by the primary suction Pl before being processed in the bag filter BF .
[0024] Auxiliary suction points Al , A2 , and A3 : the fume collection system can comprise auxiliary suction points , which depend on s ite-speci fic plant configurations , which can include , for example , material or additive handling, tundish ladle demolition, tundish ladle tipping, EAF refractory material demolition, etc .
[0025] fumes treatment system
[0026] The collected fumes are treated in a bag filter BF and then dispersed into the atmosphere .
[0027] Substantially, the bag filters capture dust ,including all heavy metals present as particulate matter at the filtering temperature, as well as some organic compounds .
[0028] Generally, in order to reduce persistent organic pollutants, in particular to control the content of PCDD dioxins and PCDF furans, adsorbent materials (e.g., activated carbon, pulverized activated lignite coke or mixtures of these with lime, clay) are dosed into the main fume pipe LI upstream of the bag filter by means of a special dosing device. The adsorbent material is retained by the filter bags BF and, after absorbing dioxins and furans, is disposed of with the dust collected by the filter.
[0029] Currently, the fumes treatment systems of a steel plant are configured to abate the following pollutants:
[0030] - Dust, in the bag filter with mechanical filtration;
[0031] - Dioxins by injecting activated carbon or lignite or clay before the filter to adsorb dioxins; the injected adsorbent is collected in the filter along with the dust; the dust is a special waste (containing heavy metals, dioxins, organics etc.) and must be properly treated / disposed of.However, the current fumes treatment systems in a steel plant do not allow the abatement of carbon dioxide CO2 inthe gaseous emissions .
[0032] In the current configuration of arc steel mills shown in figure 1 , most of the CO2 is produced by the EAF during the melting process and captured by the primary fume capture line Pl .
[0033] The CO2 content present in the aforesaid line Pl is variable during the process steps and varies between 3 and 12 % by volume during melting .
[0034] As already highlighted earlier, the primary gases are then cooled and diluted with the other suctions , such as secondary hood C and ladle furnace LF, and the CO2 content after mixing is in the range of 1-3% by volume at the stack .
[0035] The CO2 capture , i f any, is performed on the dustfree gases .
[0036] In the current plant configuration, however, the CO2 concentration upstream of the filter is so low that it does not allow CO2 capture with economically viable systems .
[0037] The operational situation is further complicated by the need to treat carbon monoxide .
[0038] In more detail , as already pointed out , the gases produced by the EAF electric furnace contain high levels of carbon monoxide and organic components which need to be treated . Such gases are mixed with comburent air inpost-combustion chambers CPC where combustion reactions of carbon monoxide and organic components take place .
[0039] The combustion reaction of carbon monoxide is an exothermic reaction which introduces signi ficant amounts of heat into the system . Once post-combustion in the chamber is completed, the fumes are cooled so that they can be then processed in the plant . Cooling can be done with di f ferent technologies such as : cooled pipes , steam boilers , air heat exchangers ( forced or natural convection) , quenching tower with water inj ection, and most commonly a combination of these technologies .
[0040] The supply of comburent air must be appropriately modulated to ensure :
[0041] - a mix of fuel and comburent air ;
[0042] - presence of oxygen to complete the reactions ; and
[0043] - temperature in the combustion chamber between 900 and 1300 ° C .
[0044] Compliance with the temperature range is critical for proper CO treatment and is controlled with comburent air .
[0045] An excess of comburent air cools below 850 ° C and blocks the combustion process ; conversely, a reduced amount of post-comburent air raises fume temperatures with problems of pollutant emissions , such as NOx, and does not ensure proper post-combustion . Furthermore , asillustrated by the oxygen, carbon monoxide and carbon dioxide equilibrium diagram shown in figure 2 , at temperatures above 1300 / 1500 ° C , the three chemical species 02 , CO and CO2 coexi st in equilibrium and therefore the combustion of carbon monoxide stops at the equilibrium point . Such a condition is maintained in the chamber, and subsequent cooling of the fume at the chamber outlet stops the process .
[0046] The presence of unburned CO is extremely hazardous to safety because it is a potentially explosive , odourless , colourless gas , which is lethal to humans i f inhaled in concentration and timing .
[0047] Furthermore , the high temperatures increase the formation of other pollutants , such as NOX .
[0048] Operatively, the need to increase the CO2 content in the fume to make CO2 capture more ef ficient would drive the reduction o f the amount of comburent air to the stoichiometric minimum; however, such a reduction cannot be achieved because the temperatures obtained in the chamber would exceed the maximum safe operating temperature . Therefore , this is an unfeasible strategy .
[0049] Thus , in the reference technical field, the need to capture CO2 ef ficiently from the gaseous emissions of a steel plant with an electric arc furnace is still completely unsatis fied .Overview of the invention
[0050] Therefore , it is the main obj ect of the present invention to eliminate the drawbacks of the aforementioned prior art either entirely or in part by providing a steel plant with electric arc furnace which is provided with a fume collection and treatment system capable of ef ficiently abating the CO2 .
[0051] It is a further obj ect of the present invention to provide a steel plant with electric arc furnace which is provided with a fume collection and treatment system capable of ef ficiently abating CO2 while being operatively reliable and simple to operate .
[0052] It is a further obj ect of the present invention to provide a method of collecting and treating the fumes generated by a steel plant with electric arc furnace to ef ficiently abate CO2 from the emi ssions generated by the plant itsel f .Brief description of the drawings
[0053] The technical features of the invention according to the aforesaid obj ects can be clearly found in the contents of the claims hereinbelow and the advantages thereof will become more apparent from the following detailed description, given with reference to the accompanying drawings which show one or more non-limiting and exemplary embodiments , in which :
[0054] - Figure 1 shows a simpli fied diagram of a steel plant with electric arc furnace provided with a traditional fume collection and treatment system;
[0055] - Figure 2 shows the oxygen, carbon monoxide and carbon dioxide equilibrium diagram expressed as the degree of combustion as a function of temperature ;
[0056] - Figure 3 shows a simpli fied diagram of a steel plant with electric arc furnace provided with a fume collection and treatment system according to a first preferred embodiment of the invention ;
[0057] - Figure 4 shows a simpli fied post-combustion air control diagram o f the type with mechanical adj ustment of the air intake opening;
[0058] - Figures 5 and 6 show two particular embodiments o f the mechanical adj ustment system of the air suction opening, with movable tube of the telescopic sleeve type and of the sliding type , respectively;
[0059] - Figure 7 shows a simpli fied post-combustion air control diagram of the type with air suction adj ustment by fan;
[0060] - Figure 8 shows a simpli fied diagram of a steel plant with electric arc furnace provided with a fume collection and treatment system according to a second preferred embodiment of the invention ; and
[0061] - Figure 9 shows a simpli fied diagram of a steelplant with electric arc furnace provided with a fume collection and treatment system according to a third preferred embodiment of the invention .Detailed description
[0062] The steel plant with electric arc furnace according to the invention is indicated as a whole by reference numeral 1 in Figures 3 , 8 and 9 .
[0063] According to a general embodiment of the invention, the steel plant 1 comprises at least one electric arc furnace 10 and a fume collection and treatment system 100 adapted to collect and treat gaseous emissions produced by said steel plant 1 .
[0064] In this description and the appended claims , the expressions " gaseous emissions , " " emissions , " or " fumes" are synonymous and, unless expressly stated otherwise , refer generically to gas and dust mixtures generated during the operation of the steel plant 1 . The composition of such gaseous emissions varies according to the zone of the steel plant 1 . In some zones , such emissions can contain primarily only dust , such as in the dust collecting apparatus of the additive transport systems , the ladle and tundish refractory material demolition and lining areas , or in the slag handling zone . In the case of the electric arc furnace , such emissions contain, in addition to dust , combustionproducts such as nitrogen oxides and sulphur oxides , CO2 , carbon monoxide and organic pollutants , e . g . , such as volatile organic compounds (VOC ) , chlorinated benzenes , polychlorinated biphenyls ( PCB ) , polycyclic aromatic hydrocarbons ( PAH) , dioxins ( PCDD) and furans ( PCDF) . The presence of organics in emissions depends mainly on the quality of the feedstock used . On the other hand, in the case of the ladle furnace , such emissions mainly contain only NOx, SOx and dust .
[0065] As shown in figures 3 , 8 and 9 , the fume collection and treatment system 100 comprises :
[0066] - a primary suction line 110 fluidically connected to the electric arc furnace 10 to suck the fumes generated in said electric arc furnace 10 ;
[0067] - at least a first secondary suction line 120 adapted to ventilate the environment surrounding the electric arc furnace 10 by means of at least one fume hood 120a .
[0068] Advantageously, the steel plant 1 can comprise at least one ladle furnace 20 . In this case , the fume collection and treatment system 100 comprises a second primary suction line 121 which is fluidically connected to the ladle furnace 20 to suck in fumes generated in said ladle furnace 20 and leads into the first secondary suction line 110 .
[0069] Advantageously, the steel plant 1 can comprise one or more auxiliary stations 31 , 32 , 33 which are adapted to operatively support the steel production activity and are likely to generate emissions containing mainly dust . In particular, such auxiliary stations can be used for dedusting the additive transport systems 33 or cons ist of demolition and refractory zones of the ladle 31 and the tundish 32 . In this case , the fume collection and treatment system 100 comprises for each auxiliary station 31 , 32 , 33 an auxiliary suction line 231 , 232 , 233 , which is fluidically connected to the respective auxiliary station to suck the emissions generated by said station and flows , either directly or indirectly, or into the first secondary suction line 120 .
[0070] As shown in figures 3 , 8 and 9 along the aforesaid primary suction line 110 there are arranged in sequence starting from the electric arc furnace 10 at least :
[0071] - a post-combustion chamber 111 ,
[0072] - a fume cooling apparatus 112 , and
[0073] - a CO2 capture apparatus 113 .
[0074] Thus , operatively, the hot fumes from EAF furnace 10 are collected from the furnace roof (preferably through a water-cooled elbow) and conveyed to the post-combustion chamber 111 , in which the post-combustion of the CO generated in the melting process is completed; the fumesgenerated by furnace 10 are sucked at a high temperature ( over 1000 ° C ) and after post-combustion are then cooled in the fume cooling apparatus 112 to reduce their temperature so that they can then be treated downstream .
[0075] In the post-combustion chamber 111 , the gases produced by the EAF electric furnace 10 ( containing high contents of carbon monoxide and organic components ) are mixed with comburent air . The carbon monoxide and organic component reactions take place in the chamber combustion 111 .
[0076] The combustion reaction of carbon monoxide is an exothermic reaction which introduces signi ficant amounts of heat into the system . Once post-combustion in the chamber is completed, the fumes are cooled so that they can be then processed in the plant .
[0077] More in detail , the supply of comburent air must be appropriately modulated to ensure :
[0078] - a mix of fuel and comburent air ;
[0079] - presence of oxygen to complete the reactions ; and
[0080] - temperature in the combustion chamber between 900 and 1300 ° C .
[0081] Compliance with the temperature range is critical for proper CO treatment and is controlled with comburent air .
[0082] An excess of comburent air would cool below 850 ° Cand block the combustion process ; conversely, a reduced amount of post-comburent air would raise the fume temperatures with problems of pollutant emissions , such as NOx, not ensuring proper post-combustion . Furthermore , as illustrated by the oxygen, carbon monoxide and carbon dioxide equilibrium diagram shown in figure 2 , at temperatures above 1300 / 1500 ° C , the three chemical species 02 , CO and 002 coexi st in equilibrium and therefore the combustion of carbon monoxide stops at the equilibrium point . Such a condition is maintained in the chamber, and subsequent cooling of the fume at the chamber outlet stops the process .
[0083] Advantageously, the fume cooling apparatus 112 can consist of , for example , cooled piping, air dissipative exchangers ( forced or natural convection) , or evaporative exchangers ( such as a quenching tower with water inj ection) or a combination of such devices .
[0084] For example , in the embodiments shown in figures 3 , 8 and 9 , the fume cooling apparatus 112 comprises cooled pipes 112a and a quenching tower 112b placed in series with each other .
[0085] Advantageously, as shown in figure 9 , the fume cooling heat can be exploited for steam production through a boiler 112c . The steam produced can be reused directly in the plant 1 , as shown in figure 9 , and bestored in appropriate tanks or accumulators . In particular, such a steam can be used as a heat source in the C02 capture process ( i f it requires it as in solid absorption systems ) and as an energy source to feed an electrical energy generation system 112d .
[0086] According to a first essential aspect of the present invention, as shown in figure 3 , the first secondary suction line 120 :
[0087] - flows into the primary suction l ine 110 downstream of the CO2 capture apparatus 113 ; or
[0088] - discharges to the atmosphere separately from said primary suction line 110 .
[0089] In this manner, the gases generated by the EAF furnace 10 during the melting phase (which make up most of the CO2 produced by plant 1 ) are not diluted with the gaseous emissions collected by the first secondary suction line 120 and the other secondary suction lines 231 , 232 , 233 avoiding lowering the CO2 content to values between 1-3% by volume as is the case in conventional plants .
[0090] By virtue of such a contrivance , the fumes passing through the primary suction line 110 upstream of the CO2 capture apparatus 113 have CO2 concentration values (varying during process steps and during melting) that , at a minimum, are in the range of 3 to 12 % by volume .
[0091] According to a second es sential aspect of the invention, the primary suction line 110 comprises a recirculation line 130 to recirculate at least part of the gaseous emissions to the post-combustion chamber 111 .
[0092] As shown in figures 3 , 8 and 9 , said recirculation line 130 fluidically connects the section of the primary suction line 110 between the cooling apparatus 112 and the CO2 capture apparatus 113 with the section of the primary suction line 110 upstream of the post-combustion chamber 111 .
[0093] The steel plant 1 comprises a control system 132 , 133 of the recirculation flow rate of the gaseous emissions to the post-combustion chamber 111 configured to adj ust the recirculation flow rate at a suf ficient value to reduce the entry of comburent air to the postcombustion chamber to the stoichiometric minimum, maintaining the temperature in the post-combustion chamber within a predetermined temperature range .
[0094] By virtue of the fact that the gases generated by the EAF furnace 10 are not diluted the concentration of CO2 in the gases flowing through the primary suction line 110 is not less than 3 to 12 % by volume .
[0095] The combustion gas recirculation allows further enriching the combustion gases with CO2 once cooled in the cooling apparatus 112 to a temperature preferablybetween 300 to 120 ° C . The gases , once cooled, are partially recirculated to the inlet of the postcombustion chamber 111 . The recirculation allows maintaining a good fume mixture at all times and controlling the combustion temperature by optimi zing the process and achieving final CO2 concentrations between 15 and 50% by volume , preferably between 20 and 30 % .
[0096] Unlike conventional plants , increasing CO2 concentration allows CO2 capture with economically viable systems .
[0097] Operatively, combustion gas recirculation allows reducing the comburent air inlet to the stoichiometric minimum while controlling the temperature in the chamber by dosing the amount of cold gas introduced into the post-combustion chamber 111 .
[0098] In other words , by virtue of the invention, it i s possible to increase the CO2 content of fume ( to make CO2 capture more ef ficient ) by reducing the amount of comburent air to the stoichiometric minimum; the temperature rise resulting from the reduction of comburent air is counteracted by the supply of cooled recirculation gas . This allows enriching the fume withCO2 and at the same time pushing the combustion reaction to completion .
[0099] Advantageously, said recirculation line 130comprises at least one fan 131 , preferably of the booster type , which serves to guarantee the necessary head and control the flow of recirculating gas .
[0100] In greater detai l , according to the preferred embodiment of the invention, the aforesaid control system controls the fan 131 and comprises :
[0101] - at least one gas analysis system 132 ; and
[0102] - at least one temperature sensor 133 .
[0103] The gas analysi s system 132 is designed to analyse the content of gases exiting the fumes cooling apparatus 112 and in particular to detect the concentration of CO2 and CO .
[0104] The aforesaid at least one temperature sensor 133 can detect the temperature exiting the fumes cooling apparatus 112 or exiting the post-combustion chamber 111 .
[0105] Advantageously, the steel plant 1 comprises a comburent air inlet control device 134 in the postcombustion chamber 111 . Said control system 132 , 133 is connected to said comburent air inlet control device 134 .
[0106] Advantageously, the fumes cooling apparatus 112 is adapted to generate an adj ustable cooling capacity so that the fumes output from such an apparatus 112 have a temperature in a temperature range predetermined as a function of post-combustion control needs by means of the recirculation of the fumes in the post-combustion chamber111 .
[0107] Preferably, the fumes cooling apparatus 112 ( in particular when it includes forced circulation heat exchangers and / or quenching towers ) is controlled in feedback by said control system 132 , 133 .
[0108] Preferably, when the fume exiting the cooling apparatus 112 has a temperature between 450 and 100 ° C, it is cool enough to be fed back into the post-combustion chamber 111 .
[0109] Entirely preferably, the combustion is controlled in the post-combustion chamber 111 by adj usting the comburent air flow rate and / or fume recirculation rate , while keeping the cooling capacity of the apparatus 112 fixed .
[0110] Preferably, the comburent air inlet control device 134 in the post-combustion chamber 111 is also controlled in feedback by said control system 132 , 133 as a function of the CO2 concentration and / or CO concentration exiting the cooling apparatus 112 or the post-combustion chamber 111 .
[0111] Preferably, the control system 132 , 133 - based on measured temperature and gas concentration values - modulates the flow of recirculated fumes and comburent air to maximi ze CO2 concentration .
[0112] The gases thus concentrated are conveyed bymeans of fans 170 to the C02 capture apparatus 113.
[0113] Advantageously, the comburent air inlet control device 134 in the post-combustion chamber 111, which allows adjusting the air flow into the chamber, can be of two types:
[0114] - with mechanical adjustment;
[0115] - with fan adjustment.
[0116] In more detail, as shown in figure 4, the comburent air inlet control device 134 with mechanical adjustment provides for maintaining a gap 12 between the fume inlet 11 of the furnace 10 and the fume suction Illa of the post-combustion chamber 111 at all times, so that comburent air is drawn in through such a gap 12. The device 134 includes a movable duct 135, which can be of two types:
[0117] - sleeve (see figure 5) : the movable duct 135 moves in a telescopic motion with respect to the fixed duct (the fume suction Illa of the post-combustion chamber 111) ;
[0118] - sliding (see figure 6) : i.e., the movable duct 135 slides into the end plane of the fixed duct (the fume suction Illa of the post-combustion chamber 111) .
[0119] In both solutions, a moving system consisting of a cylinder 136 and a frame with wheels 137 allows moving the movable duct 135 with respect to the fixedduct 136 and thus varying the gap between the furnace and the suction system .
[0120] In more detail , as shown in f igure 7 , the comburent air inlet control device 134 with fan adj ustment provides for keeping the position of the suction pipe I l la fixed during the process and introducing comburent air by means of a fan 138 . The system includes a fan 138 , which sucks in ambient air, and through a ducting system 139 introduces it into the post-combustion chamber . The air quantity is controlled by means of an adj ustment damper placed on the line , or by modulating the fan rotation speed
[0121] Advantageously, the CO2 capture apparatus 113 can be of any type suited for the purpose . A few examples are given below, providing a brief , non-exhaustive description of each, since they are in themselves familiar to a person skilled in the f ield .
[0122] In particular, said CO2 capture apparatus can be an absorption apparatus with chemical solvents .
[0123] Absorption with chemical solvents is the most commonly used technology for gas separation . It takes advantage of the formation of van der Waals chemical bonds to capture CO2 . In an absorption process , a component gas dissolves in a liquid solvent , forming a solution . Because of the di f ferent degree of solubilityof gas components in a particular solvent , the solvent can be used for selective separation . In low CO2 partial pressure , chemical solvents have a higher adsorption capacity . This makes them more attractive for use in low partial pressure gas conditions . The solvent , after capturing the CO2 , must be regenerated . In the solvent regeneration process , chemical solvents are usually regenerated by raising the temperature to release the captured CO2 . There are several processes : the most common are glycol-based Selexol™ and methanol-based Rectisol® systems .
[0124] Alternatively, said CO2 capture apparatus can be a solid absorption apparatus .
[0125] Solid absorption is based on the principle that di f ferent molecules have di f ferent af finities for the surface of a solid; such a principle allows the separation of a speci fic component from a gaseous mixture .
[0126] Based on the interaction between gas molecules and the surface o f the solid adsorbent , adsorption can be characteri zed as : chemical adsorption or physical adsorption .
[0127] Chemical adsorption occurs through chemical bonding resulting in a strong interaction between the gas molecule and adsorbent , and it is an appropriate choicefor gas streams at low concentrations . The adsorbent is regenerated through heating to release CO2 .
[0128] Physical adsorption - by means of van der Waals forces - has a weaker interaction between the gas molecule and adsorbent and is typically applied to gas streams with high CO2 concentration . The adsorbent is regenerated through a pressure reduction which releases CO2 . A typical adsorption technology is the Svante ( formerly Inventys ) VeloxoTherm™ System . This technology uses an adsorbent architecture , arranged in a circular manner to expose di f ferent sectors simultaneously at each step of the process .
[0129] Alternatively, said CO2 capture apparatus can be a membrane separation apparatus .
[0130] Membrane separation utilises a physical barrier or medium which can separate the chemical constituents of a gas mixture based on the permeability of the constituents through the membrane itsel f at di f ferent rates . In other words , particular components of a mixture pass through the barrier faster than other components . Membrane separation uses partial pressure as the driving force and is usually most favourable when the feed gas flow is at high pressure . Research ' s Polaris™ process (MTR) is a typical example .
[0131] Alternatively, said CO2 capture apparatus canbe a solid ring absorption apparatus .
[0132] Solid ring adsorption technologies involve the use of metal oxides (MeOx ) or other compounds as regenerable adsorbents . There are two reactors ( typically fluidi zed beds ) in the process . The technology requires high-temperature gas flows .
[0133] Preferably, the primary suction line 110 comprises a by-pass line 140 which fluidically connects the section of the primary suction line 110 upstream of the CO2 capture apparatus 113 with the section of the primary suction line 110 downstream of the CO2 capture apparatus .
[0134] More in detai l , said by-pass line 140 fluidically connects the section of the primary suction line 110 between the cooling apparatus 112 and the CO2 capture apparatus 113 with the section of the primary suction line 110 downstream of the CO2 capture apparatus 113 .
[0135] Advantageously, the primary suction line 110 is provided with one or more by-pass valves 141 , 142 , which are adapted to adj ust the passage of fume through the bypass duct 140 .
[0136] Operatively, the actuation of such by-pass valves 141 , 142 is controlled by a control system according to the CO2 concentration in the fumes upstreamfrom the C02 capture apparatus 113 measured by at least one gas analysis system 143 .
[0137] Operatively, the bypass line 140 is used to exclude the CO2 capture apparatus from the fume flow when CO2 contents are very low ( e . g . , in the steps in which the furnace is not melting) .
[0138] Advantageously, the steel plant 1 can comprise along said primary suction line 110 at least one filtration apparatus 150 .
[0139] Preferably, as shown in figure 8 and 9 , the filtering apparatus 150 is arranged in the section of said primary suction line 110 between said fumes cooling apparatus 112 and said CO2 capture apparatus 113 .
[0140] In particular, the filtration apparatus 150 can be an electro- filter or a bag filter .
[0141] Advantageously, the steel plant 1 can comprise a fumes treatment system along said primary suction line 110 , which fumes treatment system can be arranged :
[0142] - in the section of said primary suction line 110 between said fumes cooling apparatus 112 and said CO2 capture apparatus 113 ; or
[0143] - in the section of said primary suction line 110 downstream of said CO2 capture apparatus 113 .
[0144] Advantageously, said fumes treatment system can comprise :
[0145] - an NOx abatement apparatus ; and / or
[0146] - an SOx abatement apparatus .
[0147] Preferably, before being fed into the CO2 capture apparatus 113 , the fumes are treated to ensure their characteristics are compatible with the capture process .
[0148] The present invention also relates to a method for collecting and treating the fumes generated by a steel plant 1 comprising :
[0149] - at least one electric arc furnace 10 and
[0150] - a fume collection and treatment system 100 adapted to collect and treat gaseous emissions produced by said steel plant 1 .
[0151] Said fume collection and treatment system 100 comprises :
[0152] a primary suction line 110 fluidically connected to the electric arc furnace 10 to suck the fumes generated in said electric arc furnace 10 ;
[0153] - at least a first secondary suction line 120 adapted to ventilate the environment surrounding the electric arc furnace 10 by means of at least one fume hood 121 .
[0154] Along said primary suction line 110 there are arranged in sequence starting from the electric arcfurnace 10 at least :
[0155] - a post-combustion chamber 111 ,
[0156] - a fume cooling apparatus 112 , and
[0157] - a CO2 capture apparatus 113 .
[0158] In particular, the method according to the invention is a method of collecting and treating fume generated by a steel plant 1 according to the invention and speci fically as described above .
[0159] According to the invention, the method comprises the following operative steps :
[0160] - sending only the gaseous emiss ions generated by the electric arc furnace 10 during the melting phase to the CO2 capture apparatus 113 ;
[0161] increasing the CO2 content of the gaseous emissions by recirculating at least one part of the gaseous emissions in output from the fumes cooling apparatus 112 to the post-combustion chamber 111 by adj usting the recirculation flow rate at a suf ficient value to reduce the entry of comburent air to the postcombustion chamber to the stoichiometric minimum, maintaining the temperature in the post-combustion chamber within a predetermined temperature range .
[0162] Preferably, said predetermined temperature range is between 900 and 1300 ° C .
[0163] Advantageously, the CO2 content of the gaseousemissions in output from the fumes cooling apparatus 112 with active recirculation is between 15% and 50% by volume , preferably between 20% and 30 % .
[0164] The advantages resulting from the method according to the invention are the same as those highlighted for the steel plant and for brevity of exposition will not be repeated again .
[0165] The invention provides several advantages , some of which have already been described .
[0166] The steel plant 1 according to the invention is provided with a fume collection and treatment system capable of ef ficiently abating CO2 .
[0167] The steel plant 1 with an electric arc furnace according to the invention is provided with a fume collection and treatment system capable of ef ficiently abating CO2 and is both operatively reliable and simple to manage .
[0168] The method of col lecting and treating the fumes generated by a steel plant with an electric arc furnace according to the invention allows ef ficiently abating CO2 from the emissions generated by the plant itsel f .
[0169] Therefore , the invention thus devised achieves the preset obj ects .
[0170] Obviously, in practice, it may also take di f ferent shapes and configurations from that disclosedabove, without departing from the present scope of protection .
[0171] Furthermore, all details may be replaced by technically equivalent elements, and any size, shape, and material may be used according to needs.
Claims
CLAIMS1.
1. A steel plant (1) comprising at least one electric arc furnace (10) and a fumes collection and treatment system (100) suitable to collect and treat the gaseous emissions produced by said steel plant (1) , wherein said fumes collection and treatment system (100) comprises :- a primary suction line (110) fluidically connected to the electric arc furnace (10) to suck the fumes generated in said electric arc furnace (10) ;- at least a first secondary suction line (120) suitable to ventilate the environment surrounding the electric arc furnace (10) by means of at least one fume hood (120a) ; and characterised in that along said primary suction line (110) are arranged in sequence starting from the electric arc furnace (10) at least:- a post-combustion chamber (111) ,- a fumes cooling apparatus (112) , and- a CO2 capture apparatus (113) , wherein the first secondary suction line (120) flows into the primary suction line (110) downstream of the CO2 capture apparatus or discharges into the atmosphere separately from said primary suction line (110)and in that the primary suction line (110) comprises a recirculation line (130) for recirculating at least a part of the gaseous emissions to the post-combustion chamber (111) , said recirculation line (130) fluidically connecting the section of the primary suction line (110) comprised between the cooling apparatus (112) and the CO2 capture apparatus (113) with the section of the primary suction line (110) upstream of the post-combustion chamber (111) , said plant (1) comprising a control system (132, 133) of the recirculation flow rate of the gaseous emissions to the post-combustion chamber (111) configured so as to regulate the recirculation rate at a value which is sufficient to reduce the entry of comburent air to the post-combustion chamber to the stoichiometric minimum, maintaining the temperature in the post-combustion chamber within a predefined temperature range.
2. Steel plant (1) according to claim 1, wherein said recirculation line (130) comprises at least one fan (131) and wherein said control system controls said fan (131) and comprises:- at least one gas analysis system (132) ;- at least one temperature sensor (133) , suitable to detect the content of the gases and the temperature in output from the fumes cooling apparatus(112) , respectively.
3. Steel plant (1) according to claim 1 or 2, comprising a comburent air inlet control device (134) in the post-combustion chamber (111) and wherein said control system (132, 133) is connected to said comburent air inlet control device (134) .
4. Steel plant (1) according to any one of the preceding claims, wherein said fumes cooling apparatus (112) is suitable to generate an adjustable cooling capacity so that the fumes in output from such an apparatus (112) have a temperature comprised in a temperature range predetermined as a function of postcombustion control needs by means of the recirculation of the fumes in the post-combustion chamber.
5. Steel plant (1) according to claim 4 when dependent on claim 2, wherein said fumes cooling apparatus (112) is controlled in feedback by said control system (132, 133) .
6. Steel plant (1) according to any one of the preceding claims, wherein said C02 capture apparatus is an absorption apparatus with chemical solvents.
7. Steel plant (1) according to any one of claims 1 to 5, wherein said C02 capture apparatus is a solid absorption apparatus.
8. Steel plant (1) according to any one of claims 1 to 5, wherein said C02 capture apparatus is a membrane separation apparatus.
9. Steel plant (1) according to any one of the preceding claims, wherein said CO2 capture apparatus is a solid ring absorption apparatus.
10. Steel plant (1) according to any one of the preceding claims, wherein the primary suction line (110) comprises a by-pass line (140) which fluidically connects the section of the primary suction line (110) upstream of the CO2 capture apparatus (113) with the section of the primary suction line (110) downstream of the CO2 capture apparatus .
11. Steel plant (1) according to claim 10, wherein said by-pass line (140) fluidically connects the section of the primary suction line (110) comprised between the cooling apparatus (112) and the CO2 capture apparatus (113) with the section of the primary suction line (110) downstream of the CO2 capture apparatus (113) .
12. Steel plant (1) according to claim 10 or 11, wherein the primary suction line (110) is provided with one or more by-pass valves (141, 142) , which are suitable to regulate the passage of the fumes through the by-pass duct (140) and whose operation is controlled by a control system as a function of the concentration of CO2 in the fumes upstream from the CO2 capture apparatus (113) , measured by at least one gas analysis system (143) .
13. Steel plant (1) according to any one of the preceding claims, comprising along said primary suction line (110) at least one filtration apparatus (150) , preferably arranged in the section of said primary suction line (110) between said fumes cooling apparatus (112) and said CO2 capture apparatus (113) .
14. Steel plant (1) according to any one of the preceding claims, comprising along said primary suction line (110) a fumes treatment system, which is arranged: in the section of said primary suction line (110) comprised between said fumes cooling apparatus (112) and said CO2 capture apparatus (113) ; or in the section of said primary suction line (110) downstream of said CO2 capture apparatus (113) .
15. Steel plant (1) according to claim 14, wherein said fumes treatment system comprises:- an NOx abatement apparatus; and / or- an SOx abatement apparatus;16. Steel plant (1) according to any one of the preceding claims, comprising at least one ladle furnace (20) , wherein said fumes collection and treatment system (100) comprises a second secondary suction line (121) which is fluidically connected to the ladle furnace (20) to suck the fumes generated in said ladle furnace (20) and flows into the first secondary suction line (110) .
17. Steel plant (1) according to any one of the preceding claims, comprising one or more auxiliary stations (31, 32, 33) which are suitable to operationally support the steel production activity and are likely to generate emissions containing mainly dust, wherein said fumes collection and treatment system (100) comprises for each auxiliary station (31, 32, 33) an auxiliary suction line (231, 232, 233) which is fluidically connected to the respective auxiliary station to suck the emissions generated by said station and flows, directly or indirectly, into the first secondary suction line (120) .
18. A method for collecting and treating fumes generated by a steel plant (1) comprising at least one electric arc furnace (10) and a fumes collection and treatment system (100) suitable to collect and treat gaseous emissions produced by said steel plant (1) , wherein said fumes collection and treatment system (100) comprises:- a primary suction line (110) fluidically connected to the electric arc furnace (10) to suck the fumes generated in said electric arc furnace (10) ;- at least a first secondary suction line (120) suitable to ventilate the environment surrounding the electric arc furnace (10) by means of at least one fume hood (121) ; andwherein along said primary suction line (110) are arranged in sequence starting from the electric arc furnace (10) at least:- a post-combustion chamber (111) ,- a fumes cooling apparatus (112) , and- a CO2 capture apparatus (113) , said method being characterised in that it: sends only the gaseous emissions generated by the electric arc furnace (10) during the melting phase to the CO2 capture apparatus (113) ;- increases the CO2 content of the gaseous emissions by recirculating at least one part of the gaseous emissions in output from the fumes cooling apparatus (112) to the post-combustion chamber (111) by adjusting the recirculation flow rate at a sufficient value to reduce the entry of comburent air to the post-combustion chamber to the stoichiometric minimum, maintaining the temperature in the post-combustion chamber within a predefined temperature range.
19. Method according to claim 18, wherein any one of the preceding claims, wherein said predefined temperature range is comprised between 900 and 1300 °C.
20. Method according to claim 18 or 19, wherein the CO2 content of the gaseous emissions in output from the fumescooling apparatus (112) with active recirculation is comprised between 15% and 50% by volume.5