Steel plant equipped with electric arc furnace

Abstract

The present invention relates to a steel plant (1) comprising at least one electric arc furnace (10) and a fume recovery treatment system (100). The fume recovery treatment system (100) comprises a first primary suction line (110) fluidly connected to the electric arc furnace (10) for sucking fumes generated in the electric arc furnace (10), a secondary suction line (120) suitable for ventilating the environment around the electric arc furnace (10) by means of at least one suction hood (121), and at least one filtering device (130) suitable for filtering effluents collected by the fume recovery treatment system (100) before discharging them into the atmosphere. The electric arc furnace (10) is charged with raw materials by a continuous charging system (11). Along the first primary suction line (110), starting from the electric arc furnace (10), a fume cooler (111), a dust collector (112), and a Denox selective catalytic reduction device (113) are arranged in sequence. The secondary suction line (120) joins the first primary suction line (110) downstream of the Denox selective catalytic reduction device (113) and upstream of the at least one filtration device (130).

Description

Technical Field

[0001] The present invention relates to an ironmaking plant equipped with an electric arc furnace.

Background Art

[0002] Normally, the direct melting of materials containing iron such as scrap is carried out in an electric arc furnace (EAF).

[0003] The main raw material for an electric arc furnace is iron scrap (iron filings). This iron scrap can be composed of, for example, scrap from within a steelworks, scrap from the machinery industry (e.g., automobile manufacturers), waste, and scrap after disassembly or use (e.g., used products such as automobiles and buildings).

[0004] Direct reduced iron (DRI) is also increasingly being used as a raw material for electric arc furnaces because it has a low content of gangue, a low content of unwanted metals (e.g., copper), and a low CO2 emission in the manufacturing process.

[0005] Finally, liquid hot metal can also be used in the material mixture supplied to the electric arc furnace.

[0006] Scrap, DRI, and / or liquid hot metal are usually charged into an electric arc furnace in the following manner.

[0007] [Metal basket] Scrap and / or DRI are usually loaded into a basket and then charged into the furnace after the furnace lid is opened.

[0008] [Continuous wall charging system] A vibrating conveyor, traversing conveyor, or rotating conveyor for scrap and / or DRI continuously discharges the raw materials into the furnace. Alternatively, liquid hot metal is charged through a dedicated chute. Continuous wall charging may or may not include preheating of the scrap.

[0009] [Continuous charging system from furnace lid] The raw materials are discharged into a dedicated opening in the furnace lid (also called the fifth or third hole) by a vibrating conveyor, traverse conveyor, rotary conveyor, or pneumatic conveyor for scrap and / or DRI.

[0010] Secondary metallurgy is performed on molten steel after it has been melted to the casting point in an electric arc furnace (EAF). Secondary metallurgy is typically carried out in a ladle processing station, where the molten steel remains in the ladle itself. These processing stations usually consist of an arc heating unit called a ladle furnace (LF), which allows for adjustment of the final temperature of the molten steel for casting. This process involves the addition of slag treatment agents and binding elements to adjust the chemical composition of the finished steel. In some cases, a vacuum processing unit is used to meet specific gas content requirements.

[0011] Figure 1 shows a schematic diagram of a steelmaking plant equipped with an electric arc furnace and a ladle furnace.

[0012] [Fume Recovery System] Steelmaking plants generally have exhaust recovery systems that can draw in exhaust gases, particularly those generated during the melting process, and transport them to a processing system.

[0013] Electric arc furnaces (EAFs) and ladle furnaces (LFs) are each equipped with their own unique suction systems. In Figure 1, the EAF suction system is indicated by reference numeral P1, and the LF suction system is indicated by reference numeral P2. The suction of these suction systems P1 and P2 is called primary suction.

[0014] In an electric arc furnace (EAF), primary suction may be performed through a suitable hole in the furnace lid (also called a fourth hole or second hole) or through a material supply channel to the furnace equipped with a continuous charging system. In the latter case, fumes are drawn in through the continuous charging system to preheat the scrap before it is charged into the electric arc furnace (EAF).

[0015] Furthermore, the electric arc furnace (EAF) is equipped with a hood C. Hood C is located on the roof of the building housing the furnace. The function of hood C is to ventilate the building during the melting process and to collect fumes generated inside the building after the furnace lid is opened during the basket loading process. This additional suction system of the electric arc furnace (EAF) is called a secondary suction system and is indicated by reference numeral S1 in Figure 1.

[0016] The gas generated during the basket loading process diffuses within the building, is strongly diluted, and collected in hood C. Therefore, the secondary suction system S1 needs to process a much larger volume of fumes than the primary suction system P1. For this reason, the suction capacity of the secondary suction system is much greater than that of the primary suction system. Furthermore, due to dilution, the fumes processed by the secondary suction system S1 are at a much lower temperature than those processed by the primary suction system.

[0017] Fumes recovered from the suction systems of electric arc furnaces (EAF) and ladle furnaces (LF) contain soot, nitrogen oxides, sulfur oxides, carbon monoxide, and organic pollutants such as volatile organic compounds (VOCs), chlorobenzene, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dioxins (PCDDs), and furans (PCDFs). The presence of organic matter in the emissions is primarily determined by the quality of the scrap used.

[0018] As shown in Figure 1, there may be other areas within the steel plant where fume emissions may occur (e.g., the dust collection zone of the additive conveyor system AD, the refractory dismantling and lining zone of the ladle L and tundish P, and the slag MS processing zone). These fume emissions are the result of mechanical activity and not of combustion and / or melting processes. For these reasons, these fumes mainly consist of soot and do not contain gaseous emissions such as nitrogen oxides or sulfur oxides. Therefore, the fume recovery system is equipped with auxiliary suction units A1, A2, and A3 specifically for these emission areas.

[0019] Figure 1 schematically shows a fume recovery and treatment system in a steelmaking plant equipped with an electric arc furnace (EAF).

[0020] The fume recovery and treatment system is equipped with a main duct L1 from which all suction systems P1, P2, S1, A1, A2, and A3 are discharged. All fumes recovered by the suction systems are guided through the main duct L1 to the fume treatment system, which is described in more detail below.

[0021] [Suction from the primary suction system P1 of an electric arc furnace (EAF)] High-temperature fumes from the electric arc furnace (EAF) are collected from the furnace lid through a water-cooled elbow and transported to a cooling chamber (water-cooled duct) CH, where post-combustion of carbon monoxide produced during the melting process is completed. The primary fumes are drawn in at high temperatures (over 1000°C), cooled by the cooling chamber CH, and then their temperature is reduced by a water-cooled tower QT or a convection exchanger (natural or forced). This allows the fumes to be processed downstream in the main duct L1 and bag filters BF installed in part of the fume treatment system.

[0022] [Suction from the ladle furnace (LF) using the primary suction system P2] Fumes are collected from the ladle furnace (LF) lid using single-walled (uncooled) pipes and transported to the main duct L1 of the fume system. The temperature of the fumes drawn from the ladle furnace (LF) is below 180 degrees Celsius.

[0023] [Suction from the secondary suction system S1 of an electric arc furnace (EAF)] Hood C, installed at the top of the building, captures fumes during the charging step of the electric arc furnace (EAF) and allows ventilation during the melting step. Hood C also allows for the suction of air necessary to further cool the fumes collected by the primary suction system P1 before they are processed by the bag filter BF.

[0024] [Auxiliary suction parts A1, A2, A3] The fume recovery system may include auxiliary suction parts according to the plant configuration specific to the location. The plant configuration specific to the location may include, for example, handling of materials or additives, disassembly of tundish ladles, tipping of tundish ladles, disassembly of refractories in electric arc furnaces, etc.

[0025] [Fume treatment system]

[0026] The collected fumes are dispersed into the atmosphere after being treated by the bag filter BF.

[0027] Substantially, the bag filter collects dust containing all heavy metals and some organic compounds present as particulate matter at the filtration temperature.

[0028] Generally, an adsorbent (e.g., activated carbon, pulverized activated lignite coke, or a mixture of these with lime and clay) is introduced into the fume main duct L1 upstream of the bag filter using a suitable dosing device ADS, thereby reducing persistent organic pollutants so that the content of dioxins (PCDD) and furans (PCDF) is particularly controlled. The adsorbent is retained in the bag filter BF, adsorbed dioxins and furans, and then disposed of together with the dust collected by the bag filter.

[0029] Currently, the fume treatment system of the ironmaking plant is configured to reduce the following pollutants.

[0030] [Dust in the bag filter with mechanical filtration function]

[0031] Dioxins are adsorbed by injecting activated carbon, lignite, and clay before the bag filter. The injected adsorbent is collected by the bag filter together with the dust. The dust is a special waste (containing heavy metals, dioxins, organic substances, etc.) and needs to be properly treated / disposed of.

[0032] However, current fume treatment systems in steel plants cannot reduce nitrogen oxides (NOx) in gaseous exhaust.

[0033] Nitrogen oxides (NOx) can be contained upstream by combustion control technology. However, while technologies to reduce nitrogen oxides (NOx) from after-combustion exhaust are widely applied in plants such as fossil fuel boilers and incinerators, they have not yet been successfully implemented in steelmaking plants equipped with electric arc furnaces.

[0034] Nitrogen oxides (NOx) are generated through several mechanisms.

[0035] In electric arc furnaces (EAFs), nitrogen oxides (NOx) are primarily formed by thermal dissociation and the continuous reaction of nitrogen and oxygen molecules in the combustion air, known as "thermal NOx." Other NOx generation mechanisms, namely "fuel NOx" (due to the generation and reaction of nitrogen compounds in oxygen-containing fuels) and "prompt NOx" (due to the formation of hydrogen cyanide (HCN) and its subsequent oxidation to nitrogen oxides (NOx)), contribute less to NOx emissions from electric arc furnaces (EAFs).

[0036] Afterburn NOx reduction and control systems include the following:

[0037] [Selective Catalytic Reduction (SCR)]

[0038] [Non-selective catalytic reduction (NSCR)]

[0039] [Selective SNCR (Small-Circuit Reducing)]

[0040] More specifically, an SCR unit chemically reduces nitrogen oxides (NOx) to nitrogen molecules and water vapor using nitrogen-based reagents such as ammonia (NH3) and urea. The reagents are injected into the fume flow upstream of the catalyst bed (i.e., the reactor) via an injector system. The exhaust gas mixes with the reactants and enters the reactor module containing the catalyst. The high-temperature combustion gases and reactants diffuse through the catalyst, where the reactants selectively react with nitrogen oxides (NOx). This reaction occurs when the fume temperature is within a specific range. Generally, for the catalytic reduction process to be efficient, the operating temperature of the gas flow in the catalyst bed must be between 220°C (430°F) and 420°C (800°F). The reaction between ammonia (NH3) and nitrogen oxides (NOx) is facilitated by the presence of excess oxygen (more than 1%).

[0041] Below the optimal temperature range, catalytic activity decreases significantly, and unreacted ammonia (known as "ammonia slip") may be released directly into the atmosphere. SCR systems can also be subjected to catalyst deactivation over time due to physical deactivation and / or chemical poisoning.

[0042] Therefore, for an SCR system to effectively reduce NOx emissions, a relatively stable gas flow rate, NOx concentration, and temperature must be supplied to the exhaust gas flow.

[0043] On the other hand, it is known that the Denox system cannot be applied to fume treatment systems for electric arc furnaces (EAFs) because operating conditions such as gas flow rate, temperature, and NOx concentration fluctuate significantly during the dissolution cycle.

[0044] In particular, SCR systems cannot be installed after particulate matter removal due to their low fume temperature (above 90°C (195°F) and below 150°C (300°F)), which significantly exceeds their effective operating range.

[0045] Currently, there are no known applications of SCR technology for controlling NOx emissions from steel plants equipped with electric arc circuits. In fact, NOx reduction (denox) systems are considered technically impossible to implement due to the unresolved technical problems outlined above.

[0046] Therefore, in this field, the need to reduce NOx emissions from gaseous emissions of steel plants equipped with electric arc furnaces remains unmet. [Overview of the Initiative]

[0047] Therefore, the main objective of the present invention is to completely or partially eliminate the aforementioned drawbacks of the prior art by providing an electric arc furnace steel plant equipped with a fume recovery treatment system capable of efficiently reducing NOx using an SCR-type Denox device.

[0048] A further object of the present invention is to provide an electric arc furnace steel plant equipped with a fume recovery system that can efficiently remove NOx using an SCR-type Denox device and is highly reliable and easy to operate.

[0049] A further object of the present invention is to provide a method for recovering and treating fumes generated by electric arc furnace steelmaking plants, and to efficiently reduce NOx emissions from exhaust generated by the steelmaking plant itself. [Brief explanation of the drawing]

[0050] The technical features of the present invention in accordance with the above objectives are clearly evident in the claims. The advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings showing one or more embodiments, which are given only as non-limiting examples.

[0051] [Figure 1] A simplified diagram of a steelmaking plant equipped with an electric arc furnace and a conventional fume recovery system is shown. [Figure 2]A simplified diagram of an electric arc furnace steelmaking plant equipped with a fume recovery treatment system according to a preferred embodiment of the present invention is shown. [Modes for carrying out the invention]

[0052] In Figure 2, the electric arc furnace steelmaking plant according to the present invention is shown overall by reference numeral 1.

[0053] According to a general embodiment of the present invention, the steelmaking plant 1 comprises at least one electric arc furnace 10 and a fume recovery and treatment system 100 suitable for recovering and treating gaseous emissions generated by the steelmaking plant 1.

[0054] In this description and the attached claims, the terms “gaseous emissions,” “emissions (exhaust),” and “fumes” are synonymous and, unless otherwise explicitly stated, refer collectively to the mixture of gases and soot generated during the operation of the steel plant 1. The composition of the gaseous emissions varies depending on the zone of the steel plant 1. For example, in some zones, such as the dust collector of the additive transport system, the refractory dismantling and lining areas of the ladles and tundishes, or the slag processing area, the emissions may consist mainly of soot. In the case of an electric arc furnace, the emissions, in addition to soot, include combustion products such as nitrogen oxides and sulfur oxides, carbon monoxide, and organic pollutants (e.g., volatile organic compounds (VOCs), chlorinated benzenes, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dioxins (PCDDs), furans (PCDFs), etc.). The presence of organic matter in the emissions is mainly determined by the quality of the raw materials used. On the other hand, in the case of a ladle furnace, the emissions mainly consist only of nitrogen oxides (NOx) and soot.

[0055] According to the general embodiment described above, the fume recovery and treatment system 100 comprises the following elements:

[0056] The fume recovery and processing system 100 includes a first primary suction line 110. The first primary suction line 110 is fluidly connected to the electric arc furnace 10 to draw in fumes generated within the electric arc furnace 10.

[0057] The fume recovery and treatment system 100 includes a secondary suction line 120. The secondary suction line 120 is suitable for ventilating the environment around the electric arc furnace 10 by at least one suction hood 121.

[0058] Preferably, the electric arc furnace 10 is installed inside a building (not shown in Figure 2). The suction hood 121 is installed near the roof of the building and is used to ventilate the surrounding environment of the electric arc furnace 10, which is separated by the building.

[0059] Furthermore, as shown in Figure 2, the fume recovery and treatment system 100 includes at least one filter device 130. The filter device 130 is suitable for filtering the waste recovered by the fume recovery and treatment system 100 before it is released into the atmosphere. As shown in Figure 2, the treated fumes may be discharged into the atmosphere through the exhaust pipe 131.

[0060] The aforementioned at least one filtration device 130 may be of any type suitable for the purpose. Preferably, the filtration device 130 is a bag filter.

[0061] According to the present invention, the electric arc furnace 10 is charged with raw materials by a continuous charging system 11.

[0062] This configuration eliminates the need to open the furnace lid, thereby avoiding the direct release of fumes from the electric arc furnace 10 into the surrounding environment during the charging step of the electric arc furnace 10. Therefore, the air drawn in from the secondary suction line 120 through the suction hood 121 is substantially free from direct fumes from the electric arc furnace 10. In fact, the fumes remain substantially confined within the electric arc furnace 10 and / or the continuous charging system 11, with only small emissions due to unavoidable leakage. In particular, the air drawn in from the secondary suction line 120 contains no NOx or has negligible NOx concentrations. Therefore, operationally, substantially all NOx generated by the electric arc furnace 10 is drawn in through the primary suction line 110.

[0063] In particular, the continuous charging system 11 for the electric arc furnace 10 is of a type that can be connected to the furnace wall or furnace lid of the electric arc furnace 10.

[0064] In particular, the first primary suction line 110 may be fluidly connected to the electric arc furnace 10 through a hole made in the furnace lid of the electric arc furnace 10, or through a material supply channel of the continuous charging system 11.

[0065] According to the present invention, along the primary suction line 110, starting from the electric arc furnace 10, the following elements are arranged in order.

[0066] [Fume cooling device 111]

[0067] [Dust collector 112]

[0068] [Denox Selective Catalytic Reduction (SCR) Apparatus 113]

[0069] Furthermore, according to the present invention, the secondary suction line 120 merges with the first primary suction line 110 downstream of the Denox selective catalytic reduction device 113 and upstream of the at least one filtration device 130.

[0070] According to the present invention, fumes recovered from the primary suction line 110 are supplied to the Denox selective catalytic reduction unit 113 before being mixed with fumes recovered from the secondary suction line 120 and sent to the filtration unit 130. Therefore, the fumes drawn from the electric arc furnace 10 are not diluted or cooled by the fumes drawn from the secondary suction line 120. Thus, the Denox selective catalytic reduction unit 113 can operate under stable and controllable conditions. In particular, the Denox selective catalytic reduction unit 113 can process uncooled fumes and undiluted NOx. Therefore, NOx generated in the steel plant 1 can be efficiently reduced using the Denox selective catalytic reduction unit 113.

[0071] Furthermore, given that the first primary suction line 110 upstream of the Denox selective catalytic reduction unit 113 is equipped with a fume cooler 111 and a dust collector 112, the fumes recovered from the first primary suction line 110 can be treated preventively as follows:

[0072] The fumes recovered from the first primary suction line 110 are cooled to a predetermined temperature range according to the operating requirements of the Denox selective catalytic reduction unit 113.

[0073] To prevent excessively high concentrations of dust from damaging the catalyst bed of the Denox selective catalytic reduction unit 113, dust is removed from the fumes recovered from the first primary suction line 110.

[0074] The dust collector 112 may be any dust filter that is suitable for the purpose and capable of processing fumes generated by the electric arc furnace 10.

[0075] Preferably, the dust collector 112 is an electrostatic filter, also known as an electrostatic precipitator. An electrostatic precipitator is a device that does not have a mechanical filtration function and removes particles such as soot and fumes from a gas stream by utilizing the force of static charge induced by dust.

[0076] Preferably, as shown in Figure 2, the Denox selective catalytic reduction apparatus 113 comprises the following elements.

[0077] [Catalyst bed (i.e., reactor) 113a] The catalyst bed (i.e., reactor) 113a is fluidly connected to the primary suction line 110 so that fumes can pass through.

[0078] [Method 113b for administering nitrogen-based reagents] The nitrogen-based reagent administration means 113b (e.g., nitrogen-based reagents such as ammonia and / or urea) is suitable for injecting a metered amount (determined amount) of reagent into the portion of the primary suction line 110 upstream of the catalyst bed 113a.

[0079] In particular, the administration means 113b is suitable for injecting reagents upstream or downstream of the dust collector 112. Preferably, as shown in Figure 2, the administration means 113b is suitable for injecting reagents into the portion of the primary suction line 110 between the dust collector 112 and the catalyst bed 113a.

[0080] Advantageously, the administration means 113b is controlled by a control system to adjust the dose of the nitrogen-based reagent as a function of the following:

[0081] [Fume flow rate at the inlet to the catalyst bed 113a, as measured by at least one flow meter 113c]

[0082] [NOx concentrations upstream and / or downstream of the catalyst bed 113a, as detected by one or more gas analyzers 113d, 113e]

[0083] The operation of the Denox selective catalytic reduction apparatus 113 itself is well known to those skilled in the art and will therefore not be described in detail.

[0084] The Denox selective catalytic reduction system 113 chemically reduces nitrogen oxides (NOx) to nitrogen molecules and water vapor using nitrogen-based reagents such as ammonia (NH3) and urea. The nitrogen-based reagents are injected into the fume flow either before or after the dust collector 112 upstream of the catalyst bed. The flow of the nitrogen-based reagents is automatically controlled by an automated / control system using a gas analyzer and flow meter installed in the fume flow path, which can measure the amount of contaminants and reagent "slip".

[0085] Advantageously, while catalysts injected with nitrogen-based reagents reduce NOx, they can also chemically reduce dioxins, furans, and carbon monoxide (CO). This capability makes it possible to avoid inserting injection devices for adsorbent materials (e.g., activated carbon, pulverized activated lignite coke, or mixtures of these with lime and clay) into the fume recovery system, which are traditionally provided in known fume recovery systems to reduce dioxins, furans, and carbon monoxide from fumes. Eliminating the injection devices for adsorbent materials reduces the operating costs of the injected material and the amount of soot generated and recovered within the filtration unit 130.

[0086] For operational reasons, it was chosen to reduce NOx emissions using a Denox selective catalytic reduction system (Denox selective catalytic reduction device 113) rather than a Denox non-selective catalytic reduction (NSCR) system.

[0087] In non-selective catalytic reduction (NSCR) systems, carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons are converted to carbon dioxide (CO2) and nitrogen (N2) through a catalyst. This technique does not require the injection of additional reagents because unburned hydrocarbons are used as reducing agents. However, the oxygen content of the gas must be very low. NOx removal is carried out in two consecutive steps. In the first step, excess oxygen is removed because oxygen reacts better with carbon monoxide (CO) and hydrocarbons than with nitrogen oxides (NOx). In the second step, hydrocarbons react with and reduce the NOx in the mixture. Therefore, the oxygen concentration in the fume must be very low, especially less than 0.5%. Consequently, non-selective catalytic reduction (NSCR) systems can only be used with fuel-rich, oxygen-poor mixtures. However, this limitation does not apply to Denox selective catalytic reduction (SCR) systems, which can also process oxygen-rich mixtures characteristic of fumes extracted from electric arc furnaces.

[0088] Preferably, as shown in Figure 2, the first primary suction line 110 includes at least one fan 110e. The operation of the fan 110e is controlled by a control system to adjust the suction capacity as a function of the pressure in the electric arc furnace 10, as measured by at least one pressure sensor 110f.

[0089] Steelmaking in an electric arc furnace (EAF) is a discontinuous process consisting of alternating melting and tapping / / or charging steps. During the tapping step, the fumes generated by the electric arc furnace are at low temperatures, and NOx emissions are essentially negligible. When fumes captured during the tapping step are transported to the Denox selective catalytic reduction (SCR) unit 113, the catalyst bed is cooled below its operating temperature, potentially damaging the system.

[0090] Therefore, it is preferable that the first primary suction line 110 includes a bypass line 110a that fluidly connects the upstream portion of the first primary suction line 110 to the downstream portion of the first primary suction line 110 of the Denox selective catalytic reduction apparatus 113.

[0091] In particular, as shown in Figure 2, the bypass line 110a fluidly connects the portion of the first primary suction line 110, which is located between the fume cooler 111 and the dust collector 112, to the portion of the first primary suction line 110, which is located between the Denox selective catalytic reduction unit 113 and the filtration unit 130.

[0092] Advantageously, the first primary suction line 110 is provided with one or more bypass valves 110b, 110c. The bypass valves 110b, 110c are suitable for regulating the passage of fumes through the bypass line 110a. The operation of the bypass valves 110b, 110c is controlled by a control system as a function of the temperature of the fumes exiting the fume cooler 111, which is measured by at least one temperature sensor 110d.

[0093] In operation, when the temperature sensor 110d detects that the temperature of the fume coming out of the cooling device 111 is below a predetermined value, one or more bypass valves 110b, 110c are activated to allow the fume to pass through the bypass line 110a, thereby preventing it from passing through the catalyst bed 113a at the same time.

[0094] The melting process in an electric arc furnace (EAF) generates a large amount of carbon monoxide (CO). For this reason, the post-fume combustion chamber 114 is preferably located upstream of the fume cooler 111 in the first primary suction line 110 described above. In the post-fume combustion chamber 114, carbon monoxide (CO) can be burned to significantly reduce the carbon monoxide (CO) concentration in the fume.

[0095] Advantageously, the fume cooler 111 is suitable for generating a cooling capacity that can be adjusted so that the fumes exiting the fume cooler 111 have a temperature within a predetermined temperature range as a function of the operating requirements of the Denox selective catalytic reduction unit 113. Generally, the operating requirements of the Denox selective catalytic reduction unit 113 may require a fume temperature range that falls between 220°C and 350°C.

[0096] Preferably, the fume cooler 111 is feedback-controlled by a control system as a function of the temperature of the fume coming out of the fume cooler 111, as measured by at least one temperature sensor 110d.

[0097] In a preferred embodiment, the fume cooling system 111 described above may include a shell-and-tube heat exchanger and a plurality of fans 111a. The operation of the fans 111a is controlled by a control system to adjust the flow rate of cooling air over the shell-and-tube heat exchanger as a function of the cooling capacity required by the fume cooling system 111.

[0098] Alternatively, the fume cooling system 111 may include a water cooling tower. However, a shell-and-tube heat exchanger system is preferable to a cooling tower in order to avoid water contamination of the fume.

[0099] As shown in Figure 2, the steelmaking plant 1 may include at least one ladle furnace (LF) 20. In this case, the fume recovery and processing system 100 includes a second primary suction line 140 as follows.

[0100] The second primary suction line 140 is fluidly connected to the ladle furnace 20 to suck up fumes generated within the ladle furnace 20.

[0101] The second primary suction line 140 joins the primary suction line 110 upstream of the fume cooling device 111, or within the fume cooling device 111.

[0102] As mentioned above, the emissions from the ladle furnace contain NOx. The fumes drawn in from the second primary suction line 140 may be mixed with the fumes recovered from the first primary suction line 110 and processed together in the Denox selective catalytic reduction unit 113.

[0103] However, the fumes generated by the ladle furnace 20 and drawn in by the second primary suction line 140 are too cold to be efficiently processed by the Denox selective catalytic reduction unit 113. For this reason, the fumes drawn in by the second primary suction line 140 are combined with the fumes generated in the electric arc furnace 10 and heated.

[0104] Because the fumes produced by the electric arc furnace 10 are at a high temperature (and further heated by the final after-combustion), the mixture of the two fume flows (the flow from EAF10 and the flow from LF20) is still too hot for the Denox selective catalytic reduction unit 113. For this reason, the fumes drawn in from the second primary suction line 140 merge with the fumes drawn in from the first primary suction line 110 upstream of the fume cooler 111, thereby effectively controlling the temperature of the fumes.

[0105] Preferably, the second primary suction line 140 includes at least one fan 141. The operation of the fan 141 is controlled by a control system as a function of the pressure in the ladle furnace 20, which is measured by at least one pressure sensor 142.

[0106] As shown in Figure 2, the steelmaking plant 1 may have one or more auxiliary stations 51, 52, 53, 54. The auxiliary stations 51, 52, 53, 54 are suitable for operationally supporting steel production activities and are likely to generate emissions mainly containing soot. For example, the auxiliary stations 51, 52, 53, 54 may be a ladle refractory dismantling and lining zone 51, a tundish refractory dismantling and lining zone 52, an additive transport system dust collection zone 53, or a slag treatment zone 54. In this case, the aforementioned fume recovery treatment system 100 includes auxiliary suction lines 151, 152, 153, 154 for each auxiliary station 51, 52, 53, 54. Auxiliary suction lines 151, 152, 153, and 154 are fluidically connected to the corresponding auxiliary stations 51, 52, 53, and 54 to suction the waste generated by those stations, and directly or indirectly join the secondary suction line 120 or the first primary suction line 110 in the section between the Denox selective catalytic reduction unit 113 and the filtration unit 130.

[0107] The connection zone between the electric arc furnace continuous charging system 11 and the electric arc furnace 10 is a connection between two moving parts and cannot be mechanically closed, thus becoming a source of incorrect air intrusion into the electric arc furnace, resulting in increased nitrogen oxide production from the electric arc furnace.

[0108] Advantageously, as schematically shown in Figure 2, the steelmaking plant 1 may include a containment casing 12 configured to enclose a connection zone between the continuous charging system 11 and the electric arc furnace 10. In such a case, the aforementioned fume collection and treatment system 100 includes a seal suction line 160 that is fluidly connected to the containment casing 12 to draw in air penetrating into the interior of the containment casing 12. The seal suction line 160 either joins a secondary suction line 120 in a section comprising the Denox selective catalytic reduction unit 113 and the filtration unit 130, or joins directly to the primary suction line 110.

[0109] Preferably, the seal suction line 160 includes at least one fan 161. The operation of the fan 161 is controlled as a function of the pressure inside the housing casing 12, which is measured by at least one pressure sensor 162.

[0110] The sealing system in the connection zone between the electric arc furnace and the charging system can be defined as "active" because its suction capacity is adjusted based on the pressure measured in the charging zone of the electric arc furnace, and the correct degree of suction is ensured relative to the operating pressure inside the electric arc furnace.

[0111] The object of the present invention is to provide a method for recovering and treating fumes generated in a steelmaking plant.

[0112] The method according to the present invention is applicable to a steelmaking plant equipped with an electric arc furnace, and in particular to a steelmaking plant that is the object of the present invention as described above. For this reason, the method according to the present invention will be described below using the same reference numerals that were used to describe steelmaking plant 1.

[0113] Generally, a steelmaking plant 1 comprises at least one electric arc furnace 10 and a fume recovery and treatment system 100 suitable for recovering and treating gaseous emissions generated by the steelmaking plant 1.

[0114] The aforementioned fume recovery and processing system 100 includes the following:

[0115] [First primary suction line 110] The first primary suction line 110 is fluidly connected to the electric arc furnace 10 and sucks up fumes generated inside the electric arc furnace 10.

[0116] [Secondary suction line 120] The secondary suction line 120 is suitable for ventilating the environment around the electric arc furnace 10 by at least one suction hood 121.

[0117] [At least one filtration device 130] At least one filtration device 130 is suitable for filtering the waste recovered by the fume recovery treatment system 100 before releasing it into the atmosphere.

[0118] The method according to the present invention has the following features.

[0119] The method according to the present invention prevents the direct release of fumes from the electric arc furnace 10 into the environment during the charging step of the electric arc furnace 10 by the continuous charging system 11, thereby ensuring that the air drawn in by the secondary suction line 120 is not substantially contaminated by fumes coming directly from the electric arc furnace 10.

[0120] The method according to the present invention treats the fumes collected by the first primary suction line 110 in a Denox selective catalytic reduction unit 113 before sending them to the filtration unit 130 together with the fumes collected by the secondary suction line 120, thereby preventing the fumes drawn from the electric arc furnace 10 from being diluted and cooled by the fumes drawn by the secondary suction line 120 before being treated in the Denox selective catalytic reduction unit 113.

[0121] Furthermore, according to the present invention, before the fume recovered by the first primary suction line 110 is processed in the Denox selective catalytic reduction unit 113, the fume is freed from soot in the dust collector 112 and cooled in the fume cooler 111, thereby bringing the temperature of the fume within a predetermined temperature range as a function of the operating requirements of the Denox selective catalytic reduction unit 113.

[0122] Preferably, during the molten steel tapping step from the electric arc furnace 10, the fumes recovered by the first primary suction line 110 are sent to the filtration device 130, bypassing the Denox selective catalytic reduction device 113, thereby preventing low-temperature fumes having a temperature below a predetermined temperature range as a function of the operating requirements of the Denox selective catalytic reduction device 113 from being sent to the Denox selective catalytic reduction device 113.

[0123] Preferably, the steelmaking plant 1 includes at least one ladle furnace 20. The fume recovery processing system 100 includes a second primary suction line 140 that is fluidly connected to the ladle furnace 20 in order to suck up the fumes generated in the ladle furnace 20. The fumes recovered by the second primary suction line 140 are mixed with the fumes recovered by the first primary suction line 110 before being cooled in a fume cooling device 111.

[0124] Preferably, the aforementioned steelmaking plant 1 may include one or more auxiliary stations 51, 52, 53, 54 which are likely to generate emissions mainly containing soot, with the aim of operationally supporting steel production activities. The fume recovery treatment system 100 includes auxiliary suction lines 151, 152, 153, 154 for each auxiliary station 51, 52, 53, 54. The auxiliary suction lines 151, 152, 153, 154 are fluidly connected to the corresponding auxiliary stations 51, 52, 53, 54 to suction the emissions generated by those stations. The emissions recovered from each auxiliary suction line 151, 152, 153, 154 are sent directly to the filtration device 130.

[0125] The present invention offers many advantages, some of which are described above.

[0126] The steelmaking plant 1 equipped with an electric arc furnace according to the present invention is equipped with a fume recovery treatment system that can efficiently remove NOx using an SCR type Denox device.

[0127] The steelmaking plant 1 equipped with an electric arc furnace according to the present invention is equipped with a fume recovery treatment system that can efficiently remove NOx using an SCR type Denox device, and at the same time has high operational reliability and is easy to operate.

[0128] The present invention, which involves recovering and processing fumes generated from a steelmaking plant using an electric arc furnace, can efficiently reduce NOx emissions from the plant itself.

[0129] Therefore, the invention devised in this manner can achieve the set objective.

[0130] In implementation, it is clear that different shapes and configurations from those disclosed above may be taken, as long as they do not deviate from the scope of protection of the present invention.

[0131] Furthermore, all details are technically replaceable with equivalent elements, and any size, shape, and material can be used as needed.

Claims

1. A steelmaking plant (1) comprising at least one electric arc furnace (10) and a fume recovery and treatment system (100), The fume recovery and treatment system (100) is configured to recover and treat gaseous emissions generated by the steelmaking plant (1), The fume recovery and treatment system (100) comprises a first primary suction line (110) fluidly connected to the electric arc furnace (10) to draw in fumes generated in the electric arc furnace (10), a secondary suction line (120) configured to ventilate the environment around the electric arc furnace (10) by at least one suction hood (121), and at least one filtration device (130) configured to filter the exhaust collected by the fume recovery and treatment system (100) before releasing it into the atmosphere. The electric arc furnace (10) is charged with raw materials by a continuous charging system (11), Along the first primary suction line (110), starting with the electric arc furnace (10), a fume cooler (111), a dust collector (112), and a Denox selective catalytic reduction device (113) are arranged in order. The secondary suction line (120) merges with the first primary suction line (110) downstream of the Denox selective catalytic reduction device (113) and upstream of the at least one filtration device (130). The first primary suction line (110) includes a bypass line (110a) that fluidly connects the portion of the first primary suction line (110) upstream of the Denox selective catalytic reduction device (113) to the portion of the first primary suction line (110) downstream of the Denox selective catalytic reduction device (113). Steel plant.

2. The bypass line (110a) fluidly connects the portion of the first primary suction line (110) between the fume cooling device (111) and the dust collector (112) to the portion of the first primary suction line (110) between the Denox selective catalytic reduction device (113) and the filtration device (130). The steelmaking plant according to claim 1.

3. The first primary suction line (110) is provided with one or more bypass valves (110b, 110c) configured to regulate the passage of fumes in the bypass line (110a), The operation of the bypass valves (110b, 110c) is controlled by a control system according to the temperature of the fume coming out of the fume cooling device (111), as measured by at least one temperature sensor (110d). The steelmaking plant according to claim 1.

4. The aforementioned Denox selective catalytic reduction apparatus (113) A catalyst bed (113a) is fluidly connected to the first primary suction line (110) so that fumes can pass through, The reagent administration means (113b) is configured to inject a nitrogen-based reagent into the portion of the first primary suction line (110) upstream of the catalyst bed (113a), The steelmaking plant according to claim 1.

5. The reagent dispensing means (113b) is controlled by a control system to adjust the dosage of the nitrogen-based reagent in accordance with the flow rate of fumes entering the catalyst bed (113a), measured by at least one flow meter (113c), and the NOx concentrations upstream and / or downstream of the catalyst bed (113a), measured by at least one gas analyzer (113d, 113e). The steelmaking plant according to claim 4.

6. The fume cooling device (111) is configured to generate an adjustable cooling capacity such that the fumes emitted from the fume cooling device (111) have a temperature within a predetermined temperature range in accordance with the operating requirements of the Denox selective catalytic reduction device (113). The steelmaking plant according to claim 1.

7. The fume cooling device (111) is feedback-controlled by a control system according to the temperature of the fume emitted from the fume cooling device (111), which is measured by at least one temperature sensor (110d). The steelmaking plant according to claim 6.

8. The fume cooling device (111) comprises a shell-and-tube type heat exchanger and a plurality of fans (111a), The operation of the fan (111a) is controlled by a control system to adjust the flow rate of cooling air over the shell-and-tube heat exchanger according to the cooling capacity required by the fume cooling device (111). The steelmaking plant according to claim 6 or claim 7.

9. It further comprises at least one ladle furnace (20), The fume recovery and processing system (100) includes a second primary suction line (140), The second primary suction line (140) is fluidly connected to the ladle furnace (20) to suck up fumes generated in the ladle furnace (20), and is located upstream of the fume cooling device (111), or joins the first primary suction line (110) at the fume cooling device (111). The steelmaking plant according to claim 1.

10. The second primary suction line (140) comprises at least one fan (141), the operation of which is controlled by a control system in accordance with the pressure in the ladle furnace (20) measured by at least one pressure sensor (142). The steelmaking plant according to claim 9.

11. It is configured to operationally support steel production activities and further comprises one or more auxiliary stations (51, 52, 53, 54) that are prone to generating emissions mainly containing soot, The fume recovery and processing system (100) is equipped with auxiliary suction lines (151, 152, 153, 154) for each of the auxiliary stations (51, 52, 53, 54), The auxiliary suction lines (151, 152, 153, 154) are fluidly connected to the corresponding auxiliary stations (51, 52, 53, 54) to suction the waste generated by the auxiliary stations, and directly or indirectly merge with the secondary suction line (120) or the first primary suction line (110) in the portion between the Denox selective catalytic reduction unit (113) and the filtration unit (130). The steelmaking plant according to claim 1.

12. In the first primary suction line (110), the post-fume combustion chamber (114) is located upstream of the fume cooling device (111). The steelmaking plant according to claim 1.

13. The first primary suction line (110) is fluidly connected to the electric arc furnace (10) through a hole made in the furnace lid of the electric arc furnace (10) or through a material supply channel of the continuous charging system (11). The steelmaking plant according to claim 1.

14. The continuous charging system (11) of the electric arc furnace (10) is of a type that can be connected to the furnace wall or furnace lid of the electric arc furnace (10). The steelmaking plant according to claim 1.

15. The storage casing (12) is further configured to be able to close the connection zone between the continuous charging system (11) and the electric arc furnace (10), The fume recovery and processing system (100) includes a seal suction line (160) that is fluidly connected to the storage casing (12) to suck air that enters the inside of the storage casing (12), The seal suction line (160) either merges with the secondary suction line (120) or directly merges with the first primary suction line (110) in the portion between the Denox selective catalytic reduction device (113) and the filtration device (130). The steelmaking plant according to claim 1.

16. The seal suction line (160) comprises at least one fan (161) whose operation is controlled in accordance with the pressure inside the storage casing (12) as measured by at least one pressure sensor (162). The steelmaking plant according to claim 15.

17. The dust collector (112) is an electrical filter. The steelmaking plant according to claim 1.

18. The at least one filtration device (130) is a bag filter. The steelmaking plant according to claim 1.

19. A method for recovering and processing fumes generated by a steelmaking plant (1) according to Claim 1, The aforementioned method, The continuous charging system (11) prevents the direct release of fumes from the electric arc furnace (10) into the environment during the charging phase, so that the air drawn in by the secondary suction line (120) is not substantially contaminated by fumes coming directly from the electric arc furnace (10). The procedure includes the step of processing the fume collected by the first primary suction line (110) in the Denox selective catalytic reduction device (113) before sending it together with the fume collected by the secondary suction line (120) to the filtration device (130), so as not to dilute and cool the fume drawn from the electric arc furnace (10) in the Denox selective catalytic reduction device (113) with the fume drawn by the secondary suction line (120), Before the fume recovered by the first primary suction line (110) is processed in the Denox selective catalytic reduction unit (113), the fume is freed from soot in the dust collector (112) and cooled in the fume cooling unit (111), thereby bringing the temperature of the fume within a predetermined temperature range according to the operating requirements of the Denox selective catalytic reduction unit (113). During the molten steel tapping stage from the electric arc furnace (10), the fumes recovered by the first primary suction line (110) are sent to the filtration device (130) via the bypass line (110a), bypassing the Denox selective catalytic reduction device (113), thereby preventing low-temperature fumes having a temperature below a predetermined temperature range according to the operating requirements of the Denox selective catalytic reduction device (113) from being sent to the Denox selective catalytic reduction device (113). method.

20. The aforementioned steelmaking plant (1) is equipped with at least one ladle furnace (20), The fume recovery processing system (100) includes a second primary suction line (140) that is fluidly connected to the ladle furnace (20) to suck up fumes generated in the ladle furnace (20), The fumes collected by the second primary suction line (140) are mixed with the fumes collected by the first primary suction line (110) before being cooled in the fume cooling device (111). The method according to claim 19.

21. The aforementioned steelmaking plant (1) is configured to operationally support steel production activities and includes one or more auxiliary stations (51, 52, 53, 54) that are prone to generating emissions mainly containing soot and dust. The fume recovery and processing system (100) is equipped with auxiliary suction lines (151, 152, 153, 154) for each of the auxiliary stations (51, 52, 53, 54), The auxiliary suction lines (151, 152, 153, 154) are fluidly connected to the corresponding auxiliary stations (51, 52, 53, 54) to suction the waste generated by the auxiliary stations (51, 52, 53, 54), The waste collected by each of the aforementioned auxiliary suction lines (151, 152, 153, 154) is sent directly to the filtration device (130). The method according to claim 19.

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