Electric furnace exhaust gas circulation system and electric furnace equipment

Abstract

To provide an exhaust gas circulation device for an electric furnace and electric furnace facilities that are capable of adjusting the CO concentration and the CO2 concentration in exhaust gas discharged from the electric furnace and blowing the exhaust gas into the electric furnace.SOLUTION: An exhaust gas circulation device 1 for an electric furnace returns at least a part of exhaust gas discharged from an electric furnace 3 that melts a metal material by an electric arc to the electric furnace 3 for circulation. The exhaust gas circulation device 1 includes: an adjusted gas supply device 7 that is connected to an exhaust gas duct 5 through which the exhaust gas flows, adjusts the CO concentration and the CO2 concentration in the exhaust gas, and adjusts a flow rate thereof, and that is configured to supply adjusted gas having predetermined CO and CO2 concentrations at a predetermined flow rate; and an adjusted gas blowing device 9 that is connected to the adjusted gas supply device 7 and the electric furnace 3 and blows the adjusted gas supplied from the adjusted gas supply device 7 into the electric furnace 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric furnace exhaust gas circulation device that returns and circulates at least a portion of the exhaust gas discharged from an electric furnace that melts metal raw materials using an electric arc to the electric furnace, and to electric furnace equipment equipped with the same. [Background technology]

[0002] In electric furnaces, which melt scrap and other iron-based metal raw materials using electric arcs, it is necessary to minimize the unit power consumption, and oxygen is blown in to increase heating efficiency. However, because oxygen blowing increases iron oxide, recarburizers are added to reduce the generated iron oxide. These recarburizers react in the furnace and become carbon monoxide and carbon dioxide, which are emitted as exhaust gas outside the electric furnace.

[0003] Meanwhile, there has been a growing demand in recent years to capture carbon dioxide from exhaust gases as a measure to combat global warming, but the capture equipment and the conversion and disposal of the captured carbon dioxide into useful substances require enormous costs and a huge amount of space.

[0004] In this regard, Japanese Patent No. 6413710 (Patent Document 1) discloses a method for effectively utilizing exhaust gas containing carbonaceous gases CO / CO2 (carbon monoxide, carbon dioxide, or a mixture thereof), which enables reduction in gas costs by blowing exhaust gas generated in an electric furnace into the electric furnace. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6413710 Summary of the Invention [Problem to be solved by the invention]

[0006] The amount of exhaust gas generated in an electric furnace and the carbon content in the exhaust gas (carbon monoxide, carbon dioxide, etc.) are not constant, but vary greatly depending on the degree of solubility of the metal raw materials, the amount of recarburizer and oxygen blown in, etc. However, the technique disclosed in Patent Document 1 cannot accommodate such fluctuations.

[0007] The present invention has been made to solve the above problems, and aims to provide an electric furnace exhaust gas circulation system and electric furnace equipment that can inject an appropriate amount of CO and / or CO into an electric furnace depending on the operating conditions of the electric furnace. [Means for solving the problem]

[0008] (1) The electric furnace exhaust gas circulation device according to the present invention is a device for returning and circulating at least a portion of exhaust gas discharged from an electric furnace that melts metal raw materials using an electric arc to the electric furnace, an adjusted gas supply device connected to an exhaust gas duct through which the exhaust gas flows, configured to adjust the CO concentration and CO2 concentration in the exhaust gas and adjust the flow rate, and to supply adjusted gas having predetermined CO concentration and CO2 concentration at a predetermined flow rate; and a conditioning gas blowing device connected to the conditioning gas supply device and the electric furnace and configured to blow the conditioning gas supplied from the conditioning gas supply device into the electric furnace.

[0009] (2) In addition, in the above (1), the adjusting gas supply device is characterized by comprising a conversion device which is either an oxidation device that oxidizes CO to CO2 or a reduction device that reduces CO2 to CO.

[0010] (3) In addition, in the above-described (2), the adjusting gas supply device includes a first converter, a first damper for adjusting the flow rate of gas supplied to the adjusting gas blowing device through the first converter, a second converter connected in parallel to the first converter, and a second damper for adjusting the flow rate of gas supplied to the adjusting gas blowing device through the second converter; The present invention is characterized by the following features.

[0011] (4) In addition, in the above (3), The adjusting gas supply device a concentration measuring device for measuring the CO concentration and CO2 concentration in the exhaust gas; a control device configured to control the first damper and the second damper based on a measurement result of the concentration measuring device; The present invention is characterized by the following features.

[0012] (5) Furthermore, in the device described in any one of (1) to (4) above, the adjustment gas supply device is characterized by including a CO / CO separation device that separates CO and CO contained in the exhaust gas from the exhaust gas.

[0013] (6) In addition, in the device described in any one of (1) to (5) above, the adjusting gas blowing device is The electric furnace is characterized by including a lower blowing section connected to at least one of the bottom and the lower side of the furnace body of the electric furnace, for blowing the adjustment gas into at least one of the molten metal and the slag in the electric furnace.

[0014] (7) In addition, in the above (6), The adjusting gas blowing device is The electric furnace further includes an upper blowing section connected to at least one of the upper side surface of the furnace body and the furnace cover, for blowing the adjusting gas into the space within the electric furnace.

[0015] (8) In the above-described (7), a preheating chamber is provided directly connected to the electric furnace and connected to the exhaust gas duct, for preheating the metal raw material with the exhaust gas flowing from the electric furnace and discharged from the exhaust gas duct; a heating device for heating the metal raw material charged in the preheating chamber by a means other than the heat of the exhaust gas; It is characterized by further comprising:

[0016] (9) An electric furnace facility according to the present invention is characterized by comprising an electric furnace and the electric furnace exhaust gas circulation device according to any one of (1) to (8) above. [Effects of the Invention]

[0017] According to the electric furnace exhaust gas circulation system of the present invention, even if the amount of exhaust gas or the carbon content in the exhaust gas fluctuates, an appropriate amount of CO and / or CO can be injected into the electric furnace according to the operating conditions of the electric furnace. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is an explanatory diagram of an electric furnace exhaust gas circulation system according to a first embodiment. [Figure 2] FIG. 3 is an explanatory diagram of a first modification of the electric furnace exhaust gas circulation system according to the first embodiment. [Figure 3] FIG. 4 is an explanatory diagram of a second modified example of the electric furnace exhaust gas circulation system according to the first embodiment. [Figure 4] FIG. 10 is an explanatory diagram of a third modified example of the electric furnace exhaust gas circulation system according to the first embodiment. [Figure 5] FIG. 10 is an explanatory diagram of an electric furnace exhaust gas circulation system according to a second embodiment. [Figure 6] 1 is a graph showing the relationship between the concentration of CO and CO2 generated in an electric furnace and time. [Figure 7] FIG. 10 is an explanatory diagram of an electric furnace exhaust gas circulation system according to a third embodiment. [Figure 8] FIG. 10 is an explanatory diagram of a modified example of the electric furnace exhaust gas circulation system according to the third embodiment. [Figure 9] FIG. 10 is an explanatory diagram of an electric furnace exhaust gas circulation system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Embodiment 1] As shown in FIG. 1, the electric furnace exhaust gas circulation system 1 according to this embodiment returns and circulates at least a portion of the exhaust gas discharged from an electric furnace 3, which melts metal raw materials using an electric arc, to the electric furnace 3. The system includes an adjusted gas supply device 7 connected to an exhaust gas duct 5 through which the exhaust gas flows, and configured to adjust the CO2 concentrations and CO2 concentrations in the exhaust gas and adjust the flow rate so as to supply adjusted gas having predetermined CO2 concentrations and CO2 concentrations at a predetermined flow rate, and an adjusted gas injection device 9 connected to the adjusted gas supply device 7 and the electric furnace 3, and configured to inject the adjusted gas supplied from the adjusted gas supply device into the electric furnace 3. FIG. 1 shows a combustion chamber 11, a cooling device 13, and a dust collector 15, which are provided in an exhaust gas duct 5 of a general electric furnace. Each component will be described in detail below.

[0020] <Electric furnace> The electric furnace 3 of this embodiment is a furnace that melts scrap as a metal raw material using an arc generated from electrodes. The metal raw material is not limited to scrap as long as it is an iron-based metal raw material, and may be direct reduced iron or the like.

[0021] <Exhaust gas duct> The exhaust gas duct 5 is a duct through which the exhaust gas discharged from the electric furnace 3 flows, and leads the exhaust gas to the adjusting gas supply device 7 via the combustion chamber 11, the cooling device 13 and the dust collector 15.

[0022] <Combustion chamber> The combustion chamber 11 is located upstream of the cooling device 13 in the flow direction of the exhaust gas, and removes harmful substances by burning unburned matter such as CO and combustible substances such as oil contained in the exhaust gas to heat the exhaust gas to a high temperature.

[0023] <Cooling device> The cooling device 13 is a device that rapidly cools the exhaust gas with cooling water.

[0024] <Dust collection device> The dust collector 15 is a device that collects solid components (soot and dust) contained in the exhaust gas, and the dust collector 15 of this embodiment collects the solid components (soot and dust) by filtering the exhaust gas with a bag filter.

[0025] In this embodiment, a bag filter is used as the dust collector, but an electric dust collector may also be used, or a combination of a bag filter and an electric dust collector may also be used.

[0026] <Adjusting gas supply device> The adjusted gas supply device 7 is configured to adjust the CO concentration and CO2 concentration in the exhaust gas and adjust the flow rate, so that adjusted gas having predetermined CO concentration and CO2 concentration can be supplied at a predetermined flow rate, and is equipped with a CO / CO2 separator 17, a combustion device 19, a first inlet damper 21, a first storage tank 23, a first outlet damper 25, a CO2 reduction device 27, a second inlet damper 29, a second storage tank 31, and a second outlet damper 33.

[0027] ≪CO / CO2 separation device≫ The CO / CO2 separator 17 separates CO and CO2 contained in the exhaust gas from the exhaust gas. Examples of CO / CO2 separation devices 17 include devices that use chemical absorption (a method of chemically absorbing and separating CO2 using amines, etc.), solid absorption (a method of separating CO2 by absorbing it into a solid absorbent material), physical adsorption (a method of adsorbing CO2 into a solid absorbent material), and membrane separation (a method of separating using a membrane that selectively allows CO2 to pass through).

[0028] <Combustion device> The combustion device 19 burns unburned components such as CO in the exhaust gas and oxidizes them to CO2, and functions as an oxidation device of the present invention. The combustion device 19 may be, for example, a burner that burns CO in the exhaust gas introduced into the combustion chamber. 。

[0029] <First inlet damper> The first inlet damper 21 is for adjusting the flow rate of gas flowing into the combustion device 19.

[0030] <First storage tank> The first storage tank 23 stores the CO 2 generated by the combustion device 19 .

[0031] <First outlet damper> The first outlet damper 25 is provided downstream of the first storage tank 23 and serves to adjust the flow rate of CO2 supplied from the first storage tank 23 to the adjustment gas injection device 9. In this embodiment, the first outlet damper 25 functions as the first damper of the present invention.

[0032] <CO2 reduction device> The CO2 reduction device 27 reduces CO2 in the mixed gas of CO and CO2 to CO, and is connected in parallel to the combustion device 19 in the adjustment gas supply device 7. The method for reducing CO2 to CO can be selected from a variety of methods, including catalytic reduction, electrolysis, and chemical or biological reactions. Furthermore, in this embodiment, two CO2 reduction devices 27 are arranged in parallel, but one or three or more may be arranged.

[0033] In this embodiment, the combustion device 19 and the CO2 reduction device 27 each function as a conversion device of the present invention.

[0034] <Second inlet damper> The second inlet damper 29 is for adjusting the flow rate of the gas flowing into the CO 2 reduction device 27.

[0035] <Second storage tank> The second storage tank 31 stores the CO generated by the CO2 reduction device 27.

[0036] <Second outlet damper> The second outlet damper 33 is provided downstream of the second storage tank 31 and serves to adjust the flow rate of CO supplied from the second storage tank 31 to the adjustment gas injection device 9. In this embodiment, the second outlet damper 33 functions as the second damper of the present invention.

[0037] By adjusting the flow rates of CO2 and CO supplied through the first outlet damper 25 and the second outlet damper 33 and the ratio between them, it is possible to supply conditioned gas having predetermined CO concentrations and CO2 concentrations at predetermined flow rates.

[0038] <Adjustment gas injection device> The conditioning gas blowing device 9 is connected to the conditioning gas supply device 7 and the electric furnace 3, and is configured to blow the conditioning gas supplied from the conditioning gas supply device 7 into the furnace body of the electric furnace 3, and includes a bottom nozzle 34 disposed at the bottom of the furnace body and a side nozzle 35 provided at the lower part of the side of the furnace body. In this embodiment, the bottom nozzle 34 and the side nozzle 35 function as the lower blowing section of the present invention. It is to be noted that only one of the bottom nozzle 34 and the side nozzle 35 may be provided.

[0039] The operation of the electric furnace exhaust gas circulation system 1 configured as above will be described. When the electric furnace 3 is operated, exhaust gas is discharged through the exhaust gas duct 5, and the combustible substances CO and unburned components such as oil are burned in the combustion chamber 11. The exhaust gas is then cooled in the cooling device 13, and the solid components are collected in the dust collector 15 and supplied to the CO / CO2 separator 17.

[0040] In the CO / CO2 separator 17, CO and CO2 contained in the exhaust gas are separated, sucked in by a blower 36, and supplied to the combustion device 19 and the CO2 reduction device 27 side. Regarding gases other than separated CO / CO2, they can be released into the atmosphere from a chimney or the like after being treated so that the corresponding components are below environmental standards when released into the atmosphere.

[0041] The mixed gas of CO and CO2 is supplied to the combustion device 19 and the CO2 reduction device 27 according to the opening degrees of the first inlet damper 21 and the second inlet damper 29. The opening degrees of the first inlet damper 21 and the second inlet damper 29 may be adjusted in relation to the concentration of the adjusting gas blown into the electric furnace 3 . The concentration of the adjusted gas is determined in consideration of the scrap raw materials, additives, furnace atmosphere, target molten iron and molten steel components, etc. For example, if the adjusted gas has a CO2:CO ratio of 2:1, the first inlet damper 21 and the second inlet damper 29 are adjusted so that the amount of mixed gas supplied to the combustion device 19 is twice the amount supplied to the CO2 reduction device 27. 。

[0042] However, since the component adjustment of the adjusted gas is adjusted by adjusting the opening of the first outlet damper 25 and the second outlet damper 33, it is not necessary to adjust the opening of the first inlet damper 21 and the second inlet damper 29 precisely, and it is sufficient to set them within a rough range in relation to the predicted adjusted gas concentration.

[0043] The CO2 produced in the combustion device 19 is stored in the first storage tank 23, and the CO produced in the CO2 reduction device 27 is stored in the second storage tank 31. The openings of the first outlet damper 25 and the second outlet damper 33 are adjusted so that the concentration of the adjusted gas is determined based on the scrap raw materials, additives, the atmosphere in the furnace, the target molten iron and molten steel compositions, etc., and the adjusted gas having the predetermined CO and CO concentrations is injected into the furnace from the bottom nozzle 34 and the side nozzle 35 at a predetermined flow rate.

[0044] Injecting the adjusted gas into the molten metal in the electric furnace 3 stirs the molten steel and keeps the molten steel warm with foamy slag. Injecting CO into the molten metal in the electric furnace 3 is expected to reduce the molten metal, remove nitrogen from the steel, and heat the scrap by generating CO oxidation heat. Injecting CO2 into the molten metal in the electric furnace 3 is also expected to remove carbon from the steel. In this embodiment, an adjusted gas containing CO and CO with adjusted concentrations and flow rates is injected into the electric furnace, so that an appropriate amount of CO and / or CO can be injected into the electric furnace depending on the scrap raw material, additives, furnace atmosphere, target molten iron and molten steel components, etc.

[0045] In the above explanation, an example was shown in which the first storage tank 23, the first outlet damper 25, the second storage tank 31, and the second outlet damper 33 were used as a method for adjusting the flow rate and concentration of the adjustment gas, but other methods may also be used, such as discharging the excess gas to the outside. Furthermore, the first storage tank 23 and the second storage tank 31 may be installed upstream of the combustion device 19 and the CO 2 reduction device 27. In addition, if the amount of CO2 and CO contained in the adjusted gas is less than the required amount, CO / CO2 introduced from outside may be used.

[0046] In the example shown in Figure 1, the adjusting gas is injected into the molten steel from the bottom and side of the furnace, but it may also be injected from the top of the furnace, and the injection position may be set at an appropriate position from the viewpoint of the intended use (injection effect), prevention of interference with other equipment, etc. In addition, it may be injected from multiple nozzles at both the bottom and side. Moreover, although the example shown in FIG. 1 is one in which the adjusting gas is injected into the molten steel, it may also be injected into the slag layer formed on the molten steel to promote the formation of foamy slag by the slag.

[0047] Moreover, although the example shown in FIG. 1 is one in which the CO / CO2 separator 17 is disposed downstream of the dust collector 15, the CO / CO2 separator 17 may be disposed after the combustion chamber 11 or after the cooling device 13, and the installation position may be selected taking into consideration the heat resistance performance of the CO / CO2 separator 17 and the equipment subsequent to the CO / CO2 separator 17, as well as the types of inhibiting factors.

[0048] Furthermore, although the combustion device 19 is shown as an example of a method for oxidizing CO to CO2 in the figure, other oxidation methods may also be used.

[0049] When 100% CO2 is injected into the furnace as the adjustment gas, the CO2 reduction device 27 may be omitted as in Variation 1 shown in Figure 2, and conversely, when 100% CO2 is injected into the furnace, the combustion device 19 may be omitted as in Variation 2 shown in Figure 3. Furthermore, when 100% CO2 is injected into the furnace as the adjusting gas and CO and unburned fuel are completely burned in the combustion chamber 11, the combustion device 19 and CO2 reduction device 27 may be omitted as in Modification 3 shown in Figure 4. In this case, the combustion chamber 11 functions as a conversion device (oxidation device) of the adjusting gas supply device 7 of the present invention. The electric furnace exhaust gas circulation system 1 of this embodiment makes it possible to more appropriately perform molten steel agitation, heat retention of molten steel by foamy slag, etc. Furthermore, by injecting an appropriate amount of CO into the molten metal in the electric furnace, it is possible to appropriately achieve the reduction of the molten metal, the removal of nitrogen from the steel, and the scrap heating effect due to the generation of CO oxidation heat. Furthermore, by injecting an appropriate amount of CO into the molten metal in the electric furnace, it is possible to appropriately remove carbon from the steel.

[0050] [Embodiment 2] As shown in FIG. 5, the electric furnace exhaust gas circulation system 37 of this embodiment has the same configuration as that of the first embodiment described with reference to FIG. 1, except that it includes a concentration measuring device 38 for measuring the CO concentration and CO2 concentration in the exhaust gas, and a control device 39 configured to control the first inlet damper, the first outlet damper, the second inlet damper, and the second outlet damper based on the measurement results of the concentration measuring device 38. 5, the combustion chamber 11, the cooling device 13, and the dust collector 15 are not shown. The electric furnace exhaust gas circulation device 37 of this embodiment will be described below, focusing mainly on the differences from the first embodiment.

[0051] <Concentration measuring device> The concentration measuring device 38 is for measuring the CO concentration and CO2 concentration in the exhaust gas. A suitable example of a concentration measuring device 38 for measuring the CO and CO2 concentrations in the exhaust gas in real time is the gas component measuring device disclosed in Japanese Patent No. 6496341. This gas component measuring device introduces a portion of the exhaust gas into a cyclone device, centrifuges the solid particles of the gas-solid two-phase flow in the cyclone device, and performs gas analysis using a laser gas analyzer in the region in the center of the cyclone device where the solid particle concentration is low, thereby enabling high-precision measurement of gas components in real time. In addition, if the exhaust gas flow rate, exhaust gas temperature, and exhaust gas pressure fluctuate significantly and / or cannot be predicted from known values, the exhaust gas flow rate, exhaust gas temperature, and exhaust gas pressure may also be measured in addition to the CO / CO2 concentration and used in the calculation. It is preferable to install a collector in front of the concentration measuring device 38 to capture scattered metal and dust, as this can prevent measurement errors in the CO / CO2 concentration and prevent clogging / accumulation in ducts and pipes.

[0052] <Control device> The control device 39 controls the first inlet damper 21, the second inlet damper 29, the first outlet damper 25, and the second outlet damper 33 based on the measurement result of the concentration measuring device .

[0053] In the present embodiment configured as described above, the concentration measuring device 38 measures the CO concentration and CO2 concentration in the exhaust gas, and the control device 39 controls the first inlet damper 21, the second inlet damper 29, the first outlet damper 25, and the second outlet damper 33 based on the measurement results.

[0054] In the electric furnace 3, the CO / CO2 concentration fluctuates greatly, as shown in FIG. 6, for example, depending on the injection of oxygen and recarburizer, the melting state of the scrap in the furnace, and other factors. Therefore, in order to follow the concentration fluctuations, the CO / CO2 concentration in the exhaust gas in the furnace is measured, and the processing amount in the combustion device 19 and CO2 reduction device 27 is adjusted based on the measurement results, making it possible to arbitrarily set the amount of CO and CO2 contained in the adjusted gas injected into the furnace. According to this embodiment, even if the CO / CO2 concentration in the exhaust gas fluctuates significantly, the adjusting gas can be adjusted in accordance with the fluctuation and injected into the furnace.

[0055] [Embodiment 3] The electric furnace exhaust gas circulation system 40 of this embodiment will be described mainly with respect to the differences from the configuration of the second embodiment described with reference to Fig. 5. As shown in Fig. 7, the electric furnace exhaust gas circulation system 40 of this embodiment is provided with an upper blowing section 42 for blowing an adjusted gas into the space within the electric furnace 3. Furthermore, the CO / CO2 separator 17 is not provided, and the entire amount of gas introduced to the adjusted gas supply device 7 through the exhaust gas duct 5 is returned to the electric furnace, allowing the exhaust gas to be circulated in a closed system.

[0056] If the CO / CO2 separator 17 is not installed in the exhaust gas system from inside the furnace, the exhaust gas generated during the replacement will contain air. Therefore, an in-furnace gas exhaust duct 43 for discharging air to the outside is provided branching off from the exhaust gas duct 5, and a first exhaust damper 45 is provided in the in-furnace gas exhaust duct 43, and a second exhaust damper 47 is provided downstream near the branching point in the exhaust gas duct 5.

[0057] The operation of this embodiment configured as above will now be described. As operation progresses, nitrogen generated by denitrification of molten steel and air flowing in from seals, etc., are mixed into the circulating adjusted gas. Therefore, if the concentration of gases other than the adjusted gas rises above a certain concentration and there is a possibility that it may affect the product, the second exhaust damper 47 is closed and the first exhaust damper 45 is opened to discharge the gas mixed with gases other than the adjusted gas to the outside. When discharging to the outside, the gas components are treated to be below environmental standards before being released into the atmosphere. In addition, the gas discharged to the outside has a high CO / CO2 concentration, making it suitable for CO2 separation and capture, which has the advantage of allowing for low-cost processing.

[0058] When the amount of nitrogen in the molten steel is reduced through operation, the amount of CO injected into the furnace can also be reduced, which suppresses the operation of the CO2 reduction device 27 and reduces running costs.

[0059] According to this embodiment, by blowing in an adjustment gas from the upper blowing section 42 and preventing air from entering the furnace, it is possible to eliminate the external discharge of exhaust gas and circulate almost the entire amount, thereby eliminating the need for a CO / CO2 separator 17 and achieving further cost reductions. By using the adjusting gas to adjust the pressure inside the furnace, it is possible to suppress contact between the molten steel and the air, and to prevent nitrogen from dissolving into the molten steel.

[0060] In the above description, the inside of the electric furnace 3 is replaced with the adjusted gas, but if there is a scrap inlet, it is preferable to replace the atmosphere at the inlet with the adjusted gas as well. In the above description, the gas blown into the space inside the electric furnace 3 from the upper blowing section 42 is an adjusting gas, but the present invention is not limited to this, and CO / CO2 introduced from the outside may also be used.

[0061] In the above explanation, a mixed gas of CO and CO2 is blown into the space within the electric furnace 3 as the adjusting gas. However, in order to reduce the risk of explosion, CO2, which is an inert gas, may be blown into the space within the electric furnace 3 as the adjusting gas, as shown in FIG. 8. In this case, as shown in FIG. 8, a CO2 adjustment damper 51 may be provided in a CO2 blowing line 49 for blowing in CO2, and the opening degree may be adjusted by a control device 39 based on the measurement results of a concentration measuring device .

[0062] [Embodiment 4] Next, a fourth embodiment will be described with reference to Fig. 9. An electric furnace exhaust gas circulation device 52 of this embodiment is provided so as to be directly connected to the electric furnace 3 and has an exhaust gas duct 5 connected thereto, and is provided with a preheating chamber 53 for preheating the metal raw materials with the exhaust gas flowing in from the electric furnace 3 and discharged from the exhaust gas duct 5, and a heating device 55 for heating the metal raw materials charged in the preheating chamber 53 by a means other than the heat of the exhaust gas. This configuration is the same as that of the third embodiment described with reference to Fig. 7. Known electric furnaces 3 are those that preheat raw metal materials such as scrap by utilizing the heat of exhaust gas. However, when preheating scrap with exhaust gas, an increase in CO2 concentration affects the preheating effect. In other words, heat exchange with exhaust gas is related to the thermal conductivity of the gas (λ), the Reynolds number (Re), and the Prandtl number (Pr), and the heat transfer coefficient K during heat exchange is K ∝ λ × Re^m × Pr^n (m and n are constants). Carbon dioxide has a lower thermal conductivity and a lower constant pressure molar specific heat compared to air, its component nitrogen, and even carbon monoxide, and its heat transfer coefficient K is generally smaller than that of air. Therefore, if there is a limit to the amount of electricity supplied to the electric furnace 3 due to equipment restrictions, there is a possibility that the metal raw material cannot be heated to a predetermined temperature due to an increase in carbon dioxide.

[0063] The heating device 55 is provided so that the metal raw material can be sufficiently preheated even if the concentration of carbon dioxide in the gas circulating within the electric furnace system increases, and may be a burner heating device, induction heating device, resistance heating by passing electricity through the scrap, or indirect heating device that heats the casing containing the scrap from the outside, and may be selected based on installation space and cost. However, the heating device 55 is not limited to these. Alternatively, a thermometer may be installed on the outlet side of the preheating chamber 53, and the output of the heating device 55 may be adjusted based on the measurement results so as to reach the target temperature. If gas other than the adjusting gas remains in the preheating chamber 53 during initial filling, the gas may be replaced with the adjusting gas.

[0064] Although the present invention has been described above using the embodiments, the present invention is not limited to the configurations of these embodiments. The scope of the present invention is determined based on the description of the appended claims, and all configurations in which some of the components shown in the embodiments have been omitted or modified, or in which such improvements have been made, are included within that scope. [Explanation of symbols]

[0065] 1 Electric furnace exhaust gas circulation device (embodiment 1) 3. Electric furnace 5 Exhaust gas duct 7. Regulating gas supply device 9. Adjusting gas injection device 11 Combustion chamber 13 Cooling device 15 Dust collector 17 CO / CO2 separation equipment 19 Combustion equipment 21 First inlet damper 23 First storage tank 25 First outlet damper 27 CO2 reduction device 29 Second inlet damper 31 Second storage tank 33 Second outlet damper 34 Bottom Nozzle 35 Side nozzle 36 Blower 37 Electric furnace exhaust gas circulation device (embodiment 2) 38 Concentration measuring device 39 Control Device 40 Electric furnace exhaust gas circulation device (Embodiment 3) 42 Upper blowing section 43 Furnace gas exhaust duct 45 First exhaust damper 47 Second exhaust damper 49 CO2 injection line 51 CO2 adjustment damper 52 Electric furnace exhaust gas circulation device (Embodiment 4) 53 Preheating chamber 55 Heating device

Claims

1. An electric furnace exhaust gas circulation device that returns and circulates at least a portion of exhaust gas discharged from an electric furnace that melts metal raw materials by an electric arc to the electric furnace, A CO concentration and a CO ２ The concentration and flow rate are adjusted to achieve the desired CO concentration and CO ２ a conditioning gas supply device configured to supply a conditioning gas having a concentration at a predetermined flow rate; a conditioning gas blowing device connected to the conditioning gas supply device and the electric furnace and configured to blow the conditioning gas supplied from the conditioning gas supply device into the electric furnace; An electric furnace exhaust gas circulation device comprising:

2. The conditioning gas supply device converts CO into CO ２ and an oxidation device that oxidizes CO ２ 2. The electric furnace exhaust gas circulation system according to claim 1, further comprising a conversion device which is either one of a reduction device for reducing CO to CO.

3. the adjusting gas supply device includes a first converter, a first damper for adjusting the flow rate of gas supplied to the adjusting gas blowing device through the first converter, a second converter connected in parallel to the first converter, and a second damper for adjusting the flow rate of gas supplied to the adjusting gas blowing device through the second converter; 3. The electric furnace exhaust gas circulation system according to claim 2, further comprising:

4. The adjusting gas supply device The CO concentration and CO ２ a concentration measuring device for measuring the concentration; a control device configured to control the first damper and the second damper based on a measurement result of the concentration measuring device; 4. The electric furnace exhaust gas circulation system according to claim 3, further comprising:

5. The adjusting gas supply device adjusts the amount of CO and CO contained in the exhaust gas. ２ CO / CO is separated from the exhaust gas. ２ 5. The electric furnace exhaust gas circulation system according to claim 1, further comprising a separation device.

6. The adjusting gas blowing device is 5. The electric furnace exhaust gas circulation system according to claim 1, further comprising a lower blowing section connected to at least one of the bottom and the lower side of the furnace body of the electric furnace for blowing the adjusting gas into at least one of the molten metal and the slag in the electric furnace.

7. The adjusting gas blowing device is 7. The electric furnace exhaust gas circulation device according to claim 6, further comprising an upper blowing section connected to at least one of the upper side of the furnace body of the electric furnace and the furnace cover, for blowing the adjusting gas into the space within the electric furnace.

8. a preheating chamber that is directly connected to the electric furnace and to which the exhaust gas duct is connected, for preheating the metal raw material with the exhaust gas that flows in from the electric furnace and is discharged from the exhaust gas duct; a heating device for heating the metal raw material charged in the preheating chamber by a means other than the heat of the exhaust gas; 8. The electric furnace exhaust gas circulation system according to claim 7, further comprising:

9. An electric furnace facility comprising: an electric furnace; and the electric furnace exhaust gas circulation device according to any one of claims 1 to 4.

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