JP4792995B2 - Treatment method for exhaust gas from steel furnaces - Google Patents

Description

  The present invention relates generally to a method for removing harmful substances in exhaust gas generated from an electric furnace for steel making, and more particularly to a method for removing organic chlorine compounds including dioxins.

The exhaust gas of a general electric furnace for steelmaking, as in the prior art described in Patent Document 1, is a system that directly sucks the exhaust gas generated from the electric furnace and the exhaust gas leaked outside from the electric furnace to the upper part of the building It consists of an indirect suction system that sucks together for further ventilation, and these are combined before being processed by a filtration type dust collector. Therefore, the processing gas amount of the filtration dust collector is about 500,000 to 1,000,000 m ³ N / hr, which is much larger than the processing gas amount of the waste incineration plant.

  In many cases, a blower is arranged upstream of the filter type dust collector and an exhaust port is provided on the upper side of the filter type dust collector (push-type filter type dust collector). In this structure, the chimney can be omitted and the pressure resistance of the casing of the filtration dust collector can be lowered, so that the manufacturing cost can be suppressed.

Dioxin concentration of the exhaust gas of the steel-making electric furnace, the enforcement of the "Law Concerning Special Measures against Dioxins", for existing facilities 5ngTEQ / m ^3, for the new facility has been applied to the reference of 0.5ngTEQ / m ³ However, dioxin emissions from steelmaking electric furnaces have been decreasing year by year due to measures such as improving operational methods, and most of the facilities satisfy the regulatory values. However, it is the most industrial source, accounting for 10% of Japan's total emissions.

  Recently, since the degree of contribution to the environment has become an important factor in the evaluation of companies, there is an increasing demand for further reduction of dioxin emissions from the current level. Furthermore, since the "Automobile Recycling Law" has been fully implemented since January 2005, the concentration of dioxins emitted from electric steel furnaces can be increased by melting iron scrap with vinyl and rubber attached. There are concerns and various reduction measures are being considered.

  It has been confirmed that most of the dioxins in the exhaust gas adhere to floating dust by reducing the temperature of the exhaust gas from the steelmaking electric furnace to approximately 100 ° C. or less. Therefore, the exhaust gas temperature is about 60 to 80 ° C. by diluting the high temperature exhaust gas directly sucked from the steelmaking electric furnace with the near-normally sucked exhaust gas (substantially air), and the diluted exhaust gas is filtered. A method of reducing the concentration of dioxins in the exhaust gas by removing dust with a dust collector is employed.

On the other hand, the activated carbon blowing method is often used in the prior art in waste incineration facilities that require a significant reduction in dioxin emissions. In this system, powdered activated carbon is continuously supplied from the activated carbon storage tank and blown to the upstream side of the filtration dust collector, and a filter layer is formed on the surface of the filter cloth inside the filtration dust collector to adsorb dioxins. is there. An invention in which this method is applied to a steelmaking electric furnace has also been proposed (Patent Document 2).
JP-A-5-10687 JP 11-57373 A

  However, when the above-mentioned method is applied to dioxin treatment in exhaust gas from a steelmaking electric furnace, there are the following problems.

  (1) Since the dioxins in the exhaust gas are removed by adhering to the dust and removing the dust as described above, the dioxins are not disappeared but merely transferred to the dust. According to this method, the dust collected by the dust removing device contains the same amount of dioxins as the amount removed from the exhaust gas. Usually, it is taken out of the system by taking dust countermeasures such as humidification, but since it contains harmful substances, it must be handled with care. Exhaust gas dust discharged from steelmaking electric furnaces is mainly transported to refining factories to recycle heavy metals such as zinc, but the acceptance standards are expected to become stricter in the future as part of environmental measures. Depending on the concentration of harmful components, reuse may not be possible. In that case, it is necessary to consign the dust to a processing company with a specific permission, and the disposal cost and the like become a factor of cost increase.

  (2) The exhaust gas discharged from the steelmaking electric furnace has a high temperature (600 to 900 ° C.), and is 200 to 300 ° C. even after passing through a heat exchanger or the like. Therefore, in order to reduce the dioxins to 100 ° C. or less, which is a temperature that can be sufficiently removed in the filtration type dust collector, it is necessary to dilute the exhaust gas with a large amount of room temperature air. Must be installed.

  (3) Most of the dioxins in the gas (approximately 70 to 90%) are removed together with dust by the filtration dust collector even when activated carbon is not blown. When activated carbon is blown in, this removal efficiency is further increased, but dioxins that were originally removed by the filtration dust collector are also adsorbed to the activated carbon, so dioxins are additionally reduced by blowing activated carbon. Compared to the amount, it is necessary to blow in a considerably large amount. Since the amount of exhaust gas in a steelmaking electric furnace is as large as 10 to 100 times that of a waste incineration facility, an increase in the amount of activated carbon used is a problem that cannot be ignored in terms of maintenance costs.

  (4) Since the activated carbon blown into the exhaust gas is removed together with the exhaust gas dust by the dust collector, the amount of exhaust dust increases as compared with the case where the activated carbon is not sprayed. Furthermore, since the content ratio of valuable heavy metals with respect to the entire discharged dust is reduced, the reuse value is reduced.

  (5) Further, the generation of dioxins tends to increase temporarily when iron scrap to which vinyl or rubber adheres is dissolved. However, since the filtration layer on the filter cloth on which dioxins are adsorbed is a non-uniform layer having a thickness of about several millimeters, sufficient removal may not be possible for high concentrations of dioxins. Electric furnaces for steelmaking are subject to rapid changes in the process, and it is difficult to adjust the amount of activated carbon spray in a form that follows the concentration of dioxins generated. It is necessary to keep blowing a large amount of activated carbon constantly.

  (6) Further, it is necessary to separately provide a blowing activated carbon silo and a blowing device, and there is a problem of securing the installation space.

The present invention has been made to solve the above-described problems. In the method for treating exhaust gas of a steelmaking electric furnace or exhaust gas (exhaust gas) of a building in which the steelmaking electric furnace is installed, It is an object of the present invention to provide a method for treating exhaust gas such as an electric furnace for steel making that can efficiently remove dioxins.

  In order to solve the above problems, the present invention has the following features.

[1] A steel-making electric furnaces and / or treatment method of exhaust gas generated denominated shop or et al formulation steel electric furnace is installed,
A first step of removing dust in the exhaust gas at 100 to 200 ° C. with a filtration dust collector;
After the first step, a second step of adsorbing the organochlorine compound in the exhaust gas with granular activated carbon filled in an activated carbon cartridge made mainly of steel material;
After the treatment of the first step and the second step during the period until the adsorption performance of the activated carbon is lowered and the replacement time is reached , the activated carbon cartridge is charged into the electric furnace for steel making in a state of being filled with granular activated carbon. An exhaust gas treatment method for a steelmaking electric furnace or the like, comprising three steps.

  [2] The method for treating exhaust gas from an electric furnace for steel making or the like according to [1], wherein the activated carbon cartridge is detachably laid on a ceiling portion or an outlet duct portion of the filtration dust collector. .

  [3] The activated carbon cartridge includes a plurality of activated carbon layers, and the activated carbon layer includes a pair of parallel surfaces, one of which is a gas inflow surface and the other is a gas outflow surface. A method for treating exhaust gas such as an electric furnace for steel making according to [1] or [2].

  [4] The exhaust gas from the electric furnace for steel making according to any one of [1] to [3], wherein the filter cloth of the filtration type dust collector has a membrane surface on the filtration side Processing method.

  According to the invention described in [1] above, most of the organochlorine compounds containing dioxins that are harmful substances in the exhaust gas are adsorbed on the granular activated carbon, so that the exhaust gas discharged is extremely clean. In addition, by setting the treatment temperature in the filtration dust collector to a higher temperature (100 to 200 ° C.) than before, adsorption of dioxins to the dust is suppressed, and the organic matter of the dust discharged from the filtration dust collector is reduced. It becomes possible to reduce the content rate of a chlorine compound. The granular activated carbon in the activated carbon cartridge used for exhaust gas purification is put into the electric furnace as it is filled in the cartridge, so there is no risk that the used activated carbon will scatter around the secondary environment. The risk of contamination is low and the safety of replacement workers is high. Furthermore, after being put into the electric furnace, the organic chlorine compound is completely pyrolyzed and harmless, and the cartridge body becomes an iron raw material as an electric furnace raw material, and the internally charged granular activated carbon is a heat source as an alternative to carbon. Therefore, complete recycling can be achieved.

  According to the invention described in [2] above, since the activated carbon filling device adopts a cartridge type, the arrangement thereof has a high degree of freedom, and as described in [2] above, the upper side and the side of the filtration dust collector. It can be installed in a section. For this reason, compared with the case where an activated carbon packed tower is installed independently, installation space is small and efficient device arrangement becomes possible.

  In the invention described in [3] above, since the exhaust gas to be treated and activated carbon can be efficiently contacted, the adsorption ability of the activated carbon can be fully used. In addition, the pressure loss generated by the activated carbon cartridge is approximately 0.5 kPa lower than that of the conventional activated carbon adsorption and filling device, reducing the load on the exhaust gas fan and reducing the running costs such as equipment costs and electricity costs. And

  In the invention described in [4] above, it is possible to remove dust having a small particle size peculiar to an electric furnace by using a membrane-coated filter cloth. In the filter cloth normally used in the treatment of electric furnace exhaust gas, fine dust that is not detected by the usual measurement of dust concentration passes through the filter cloth and is released into the atmosphere. If an activated carbon cartridge is used in the subsequent stage of the filtration type dust collector, the fine dust enters the cartridge and adheres to the activated carbon surface, so that sufficient adsorption performance of activated carbon cannot be maintained. Moreover, when fine dust accumulates in the activated carbon cartridge, the pressure loss of the activated carbon cartridge increases and the load on the exhaust gas suction fan increases. On the other hand, since the filter cloth of the membrane coating can remove even fine dust, the exhaust gas is further washed, and it is possible to prevent the intrusion of dust into the activated carbon cartridge installed in the subsequent stage and the inhibition of the activated carbon adsorption ability. Moreover, since it is excellent in the releasability of the dust from the filter cloth surface, the pressure loss at the time of use of the filtration type dust collector body does not increase.

  An embodiment of the present invention will be described based on the gas flow shown in FIG.

Incidentally, as described above, there are a system in which exhaust gas from a steelmaking electric furnace is directly sucked from the electric furnace and an indirect suction system in which it is also sucked from the upper part of the building where the electric furnace is installed. The present invention is most suitable for the treatment of exhaust gas of a direct suction system considered to have a high dioxin concentration, but it is also possible to treat exhaust gas (exhaust gas) from a building considered to have a relatively low dioxin concentration, There are three possible patterns: (A) treatment of exhaust gas from the direct suction system only, (B) mixing treatment of exhaust gas from the direct suction system and exhaust from the building , and (C) treatment of exhaust from the building only. Hereinafter, the pattern (B) will be described in detail as an embodiment of the present invention, but the patterns (A) and (C) are the same processing method. Further, the present invention is not limited to dioxins but is suitable for the removal of all organic chlorine compounds including chlorobenzene, chlorophenol and the like, and therefore, the substance to be removed will be described as an organic chlorine compound.

As shown in FIG. 1, the exhaust gas 11 generated from the electric furnace is sucked by a dedicated fan 14 and conveyed to the exhaust gas filtration type dust collector 17. The exhaust gas temperature at the outlet of the electric furnace is about 900 ° C. at the outlet of the combustion tower, and this is reduced to 100 to 200 ° C. at the inlet of the filtration dust collector 17. As waste gas incineration facilities are obligated to cool the exhaust gas temperature to approximately 200 ° C or less, dioxins are likely to be re-synthesized if the temperature exceeds this upper limit temperature, and the concentration of dioxins may increase. is there. Further, if the temperature is lower than the lower limit temperature, the organic chlorine compound in the exhaust gas easily adheres to the dust, so that the concentration of the organic chlorine compound in the dust collected and discharged by the filtration dust collector 17 becomes high. . In order to avoid these phenomena more reliably, it is more desirable that the inlet temperature of the filter type dust collecting apparatus and 120 to 160 ° C.. FIG. 2 shows a graph created based on the results of measurement and analysis by the inventors regarding the relationship between exhaust gas temperature and dioxin concentration.

Various known technical means can be applied as the exhaust gas temperature reducing means. For example, a method using a radiator tower (trombone cooler) 13 or a method of mixing normal temperature exhaust air 12 from an electric furnace building (filtering) There is a method in which the inlet temperature of the dust collector 17 is measured by the thermometer 16 and the flow rate of the exhaust air 12 to be mixed is adjusted by the flow rate adjusting valve 15 based on the measurement result), or a combination thereof. The amount of exhaust gas depends on differences in furnace scale and cooling means, but if the cooling means is an exhaust air mixing system in a 50-ton furnace, it is approximately 700,000 m ³ N / h at the inlet of the filtration dust collector 17. It becomes.

  There are various types of filter cloths used in the filtration type dust collector 17, but the filter cloth suitable for the present invention is a filter cloth (hereinafter referred to as PTFE (polytetrafluoroethylene) or the like) subjected to membrane processing on the filtration side surface. , Referred to as “membrane filter”). This is because the dust generated from the electric furnace is very fine with a median diameter of about 2 to 4 μm, and therefore, there is a risk that the dust will be worn through a filter cloth not subjected to membrane processing. The material of the filter cloth is selected appropriately according to the conditions such as the temperature and properties of the exhaust gas and the required durability. For example, glass woven fabric, PPS (polyphenylene sulfide), polyimide fiber, Tetron (registered trademark), Tefayer (registered trademark), and the like can be used.

  The activated carbon cartridge is provided on the downstream side of the filtration dust collector 17. As shown in FIG. 3, the activated carbon adsorption device 18 having a plurality of activated carbon cartridges 2 may be provided independently, or the activated carbon cartridge 2 is disposed inside the filtering dust collector 17 (clean room). It is good also as a structure.

The activated carbon cartridge is, for example, a hexahedron having a side length of about 1 to 2 m, and the required number of cartridges is determined according to the amount of processing gas. The amount of activated carbon filled in one activated carbon cartridge is, for example, 0.5 to 1 m ³ (space velocity 10,000 to 20,000 h ⁻¹ ), but is appropriately selected depending on the exhaust gas properties, required performance, etc. it can. Further, the treatment gas temperature in the activated carbon cartridge can be set to substantially the same temperature as that of the filtration type dust collector. However, when the temperature is lowered, the adsorption performance to the activated carbon can be further improved.

  It is desirable that the activated carbon cartridge be easily detachable from the activated carbon adsorption device 18 and the filtration dust collector 17. With a structure that can be easily attached and detached, the time required to replace the activated carbon by replacing the activated carbon cartridge filled with deteriorated (breakthrough) activated carbon with a new or regenerated activated carbon cartridge. It is possible to reduce the maintenance time of the activated carbon adsorption device.

  The shape of the activated carbon storage section provided in the activated carbon cartridge is generally a rectangular parallelepiped, but the activated carbon storage section has one of a set of substantially parallel surfaces as a gas inflow side and the other as a gas outflow side. If it has, it will not be this limitation, What is necessary is just to have one set of substantially parallel surfaces, such as a triangular prism and a cylinder. The activated carbon cartridge including the activated carbon storage section can be used as a raw material for scraps of an electric furnace for steel making, and it is desirable to produce a large part of the steel material such as carbon steel and stainless steel having durability and heat resistance. As the gas inflow side and the gas outflow side, a gas net made of steel material, a punching metal (punched metal net) or the like having air permeability is used. These gas inflow side and gas outflow side are usually flat and need to be substantially parallel to each other. Note that these gas inflow side and gas outflow side are usually both rectangular and plane symmetric.

  The activated carbon filled in the activated carbon storage part preferably has a particle size of 0.5 mm to 3.4 mm (particle size of 6 mesh to 32 mesh). The particle size of the activated carbon generally used in the conventional activated carbon adsorption apparatus for exhaust gas is about 4 to 8 mm, but the activated carbon having a smaller particle size is used to adsorb the organic chlorine compound on the activated carbon. This is because most of the activated carbon particles are considered to be near the surface. Therefore, the smaller the particle size, the larger the contact area with the exhaust gas, and the higher the removal efficiency compared with the case where the activated carbon layer has the same thickness. Moreover, when activated carbon with a small particle diameter is used from the above, when the removal rate as an activated carbon adsorption apparatus is made the same as the past, the amount of activated carbon can be decreased.

  However, if activated carbon with a small particle size is used, there may be a problem that it becomes easy to fluidize. Therefore, even if the activated carbon is closely packed in the activated carbon storage part and the filtration flow rate is increased, any part of the activated carbon layer may be used. It is desirable to prevent fluidization from occurring. Examples of the method of filling in such a state that it cannot substantially be fluidized include a method of filling while applying vibration with a vibrator, or pressing from above with a stick or the like during filling. Moreover, you may make it crimped | bond using buffer materials, such as glass wool, so that a clearance gap may not arise between an activated carbon layer and the lid | cover of an activated carbon storage part.

  The type of activated carbon to be filled may be any of columnar charcoal (forming charcoal), crushed charcoal, granulated charcoal, and spherical charcoal. Here, spheroidal coal is most preferable in shape but very expensive, and crushed coal and granulated coal have a large variation in particle size, and some of them rub through the holes of the gas permeation plate on the gas inflow side and gas outflow side. Since it may be contained, it is most desirable to use columnar charcoal (coal).

  Here, an example of the activated carbon cartridge used in the present invention will be described based on the model diagram of FIG. 4A is a sectional view of the activated carbon layer, FIG. 4B is a perspective view of the activated carbon layer, FIG. 4C is a sectional view of the activated carbon cartridge, and FIG. 4D is a perspective view of the activated carbon cartridge.

  The activated carbon cartridge 2 used in the present invention includes four rectangular parallelepiped activated carbon layers 1. However, the number of the activated carbon layers 1 is appropriately determined according to the amount of processing gas of the activated carbon cartridge 2 and the like, and is not particularly limited to four layers. The exhaust gas enters the inside from one surface (inlet surface) having the opening of the activated carbon cartridge 2, passes through the activated carbon layer 1 by cross flow, and is discharged from the exit surface facing the inlet surface. When the exhaust gas passes through the activated carbon layer 1, the organic chlorine compound is removed from the exhaust gas by adsorption.

  The activated carbon layer 1 includes a storage portion 1a, and the activated carbon storage portion 1a has a pair of parallel surfaces, one as a gas inflow side surface 1b and the other as a gas outflow side surface 1c. The activated carbon AC having an openable and closable lid 1d that can replace the activated carbon and having a particle size of 0.5 mm or more and 3.4 mm or less inside is packed compactly without a gap with the lid 1d, The activated carbon AC is closely packed so as not to be fluidized substantially. At this time, the thickness D of the activated carbon layer made of activated carbon AC formed between the gas inflow side surface 1b and the gas outflow side surface 1c is preferably 100 mm or less.

  The exhaust gas that has passed through the activated carbon adsorption device 18 (activated carbon cartridge 2) is sucked by the fan 21 and discharged from the exhaust tower 22.

  On the other hand, the exhaust 12 from the building where the electric furnace is installed generally has a low organochlorine compound concentration and is almost normal temperature. Therefore, the exhaust 12 is sucked by the fan 19 and then only filtered with the filter-type dust collector 20 for building. Go and release to the atmosphere.

  The activated carbon cartridge 2 is put into an electric furnace in a state filled with granular activated carbon after being used for a predetermined period.

  The above is the description of one embodiment of the present invention, and further details will be described below.

  Dust, heavy metals, and the like are removed from the exhaust gas from the steelmaking electric furnace by a filtration dust collector. In conventional exhaust gas treatment equipment for steelmaking electric furnaces, the exhaust gas temperature is lowered to 80 ° C. or lower, and the organic chlorine compound in the gas phase is attached to the floating dust, and then the dust removal treatment is performed. Had been removed.

  On the other hand, in one embodiment of the present invention, the exhaust gas treatment temperature in the filtration type dust collector is 120 to 160 ° C., the proportion of the organic chlorine compound existing in the gas phase is increased, and the organic chlorine compound that adheres to the dust Reduce the amount of dust. This can reduce the organochlorine compound concentration in the dust collected by the filtration type dust collector. Most of the organic chlorine compounds present in the gas phase scrub through the filter cloth of the organic chlorine compound filtering dust collector, but these are almost completely removed by the activated carbon cartridge installed inside or downstream of the filtering dust collector. As a result, purified exhaust gas is released into the atmosphere.

  In the cartridge, exhaust gas and activated carbon come into contact with each other, and harmful components such as organochlorine compounds in the exhaust gas are adsorbed and removed by the activated carbon. Activated carbon gradually decreases in adsorption performance and adsorption capacity with the passage of gas, but it has been confirmed by tests conducted that the life of activated carbon in the present invention is about half a year to about one year. No replacement or maintenance of activated carbon is required during operation. When the adsorption performance of the activated carbon decreases and the replacement time comes, it is not the method of taking out the activated carbon from the inside of the cartridge, but the method of carrying out the cartridge from the activated carbon adsorption tower or filtration type dust collector. Then, a new cartridge filled with new activated carbon is mounted.

  The used activated carbon cartridge has a cartridge body mainly made of a steel material, and can be put into an electric furnace in this state and processed together with other scrap raw materials. Since the inside of the furnace is melted at a high temperature of 1000 ° C. or higher, the organic chlorine compound adsorbed on the activated carbon is instantly decomposed and rendered harmless. In addition, since the cartridge main body becomes a raw material for scrap iron and activated carbon becomes a heat source for carbon replacement, it becomes possible to completely recycle a used activated carbon cartridge as a resource.

Table 1 shows the results (examples of the present invention) of implementing the present invention using a small test apparatus having a processing gas amount of 300 m ³ N / hr and an activated carbon filling amount of 30 L (space velocity 10,000 h ⁻¹ ). On the other hand, Table 2 shows the results (conventional example) implemented by the prior art.

In the conventional example, as shown in Table 2, the dioxin concentration (toxic equivalent amount) after the treatment (filter-type dust collector outlet) was 0.4 ngTEQ / m ³ , whereas in the present invention example, As shown in Table 1, the dioxin concentration (toxic equivalent amount) after treatment (activated carbon cartridge outlet) was significantly reduced to less than 0.01 ngTEQ / m ³ .

  Thereby, the effectiveness of the present invention could be confirmed.

It is a gas flow in one embodiment of the present invention. It is a graph which shows the relationship between filtration type dust collector entrance exhaust gas temperature, and dioxin density | concentration. It is explanatory drawing of the activated carbon adsorption | suction apparatus in one Embodiment of this invention. It is a figure which shows an example of the activated carbon cartridge used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Activated carbon layer 1a Activated carbon storage part 1b Gas inflow side 1c Gas outflow side 1d Lid 2 Activated carbon cartridge 11 Exhaust gas from electric furnace 12 Exhaust from building (exhaust gas)
DESCRIPTION OF SYMBOLS 13 Radiation tower 14 Fan 15 Flow control valve 16 Thermometer 17 Exhaust gas filtration dust collector 18 Activated carbon adsorption device 19 Fan 20 Building filtration dust collector 21 Fan 22 Exhaust tower

Claims (4)

A processing method of an exhaust gas generated denominated shop or al steelmaking electric furnaces and / or formulation steel electric furnace is installed,
A first step of removing dust in the exhaust gas at 100 to 200 ° C. with a filtration dust collector;
After the first step, a second step of adsorbing the organochlorine compound in the exhaust gas with granular activated carbon filled in an activated carbon cartridge made mainly of steel material;
After the treatment of the first step and the second step during the period until the adsorption performance of the activated carbon is lowered and the replacement time is reached , the activated carbon cartridge is charged into the electric furnace for steel making in a state of being filled with granular activated carbon. An exhaust gas treatment method for a steelmaking electric furnace or the like, comprising three steps.   The method for treating exhaust gas of a steelmaking electric furnace or the like according to claim 1, wherein the activated carbon cartridge is detachably laid on a ceiling portion or an outlet duct portion of the filtration dust collector.   The activated carbon cartridge is composed of a plurality of activated carbon layers, and the activated carbon layer has a set of parallel surfaces, one of which is a gas inflow surface and the other is a gas outflow surface. A method for treating exhaust gas such as an electric furnace for steel making according to 2.   4. The exhaust gas treatment method for an electric furnace for steel making, etc. according to any one of claims 1 to 3, wherein the filter cloth of the filter type dust collector has a membrane surface on the filtration side.

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