JPH07180977A - Pre-scrap, removal method of odor and white smoke components in exhaust gas at melting - Google Patents

Abstract

PURPOSE:To perform a concurrent combustion and filtration of bad odorous white smoke constituents contained in all gases by a method wherein gases sucked from a hood enclosing a preheating furnace and the like are utilized as combustion air when bad odorous white smoke constituents contained in the gases sucked from a location of the preheating furnace and the like. CONSTITUTION:One electrical furnace D performs a scrap preheating with combustion of kerosene and the other electrical furnace E performs an arc melting operation upon completion of the preheating operation. Then, a dust collecting system is divided into a system A for performing a sucking operation from a part of one electrical furnace D and a system B for sucking from a hood enclosing both electrical furnaces. In such a configuration as above, part of gas in the system B is used as combustion air for combustion processing in the system A. In addition, residual gas at the system B is utilized by an organic substance combustion and decomposing device F without using any new combustion air so as to ignite kerosene with oxygen contained in itself. That is, the combustion air fed in from an external atmosphere used in the organic substance combustion and decomposing device Fa is eliminated and in place of it, a partial gas in the system B is used as combustion air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing harmful offensive odors and white smoke components contained in exhaust gas generated from a furnace for preheating, melting or refining scrap as a part or whole of raw material.

[0002]

2. Description of the Related Art Exhaust gas generated when preheating, melting, or refining metal raw materials, particularly scrap, may contain organic compounds, particularly visible white smoke and malodorous source components. Methods for removing these have already been proposed. (1) JP-A-56-1680
According to Japanese Patent Publication No. 83, the gas discharged from the scrap preheating device is combined with the high-temperature gas discharged from the electric furnace to oxidize and decompose the malodorous substances in the gas. (2) According to JP-A-56-16802, the gas discharged from the scrap preheating device is introduced into the combustion tower on the outlet side of the electric furnace by a blower to oxidize and decompose the malodorous substances. (3) JP-A-59-69
According to Japanese Patent No. 687, the exhaust gas discharged from the scrap preheating device is passed through a packed layer of porous plastic balls, and the bad odor and white smoke in the exhaust gas are removed by gas-liquid contact with the liquid film on the ball surface. I am trying. (4) The direct combustion method, in which exhaust gas is directly heated and burned to remove organic substances, is described in "Technique for Preventing Odor (III) / June 10, 1980"
Japan Pollution Control Technology 3-8P ”published by Doyukai. Also, (5) Badisch Stahl-Engineering Gmbh document shows the combustion decomposition method for removing organic matter in the exhaust gas of the local dust collected by the electric furnace.

[0003]

When the scrap is preheated in the electric furnace or in the scrap preheating device, oil smoke having a foul odor is generated, which is a problem in terms of working environment and pollution prevention. This oil smoke is generated by evaporation or decomposition of oil such as cutting oil adhering to scrap, and its components include aldehyde, benzene, toluene, styrene, and ketones. On the other hand, as interest in environmental issues has increased, smoke leakage from the furnace body, which has not been considered as a problem in the past, has come to the forefront. In the case of an electric furnace, while preheating or melting scrap, dust and oil smoke generated in the local dust collection duct are sucked in, but the amount of smoke leaking from the opening of the furnace to the outside is also not negligible, which deteriorates the environment. It has been pointed out that it will. From this,
In the new electric furnace, a hood (often called a clean house, a sky house, etc., which is often called a hood here) and a suction duct surrounding the entire furnace are attached and a suction duct is attached to remove the smoke leak.

However, this sucked gas also has problems of oily smoke, malodor and white smoke components, and it is not possible to solve all of these problems by simply installing a dust collector, and separate measures must be taken. That is, recently, there are many cases where a bag filter is used as a dust collector, and even if the generated dust can be removed, the malodor and white smoke components cannot be completely captured, so that an organic substance is detected on the dust collector outlet side. Oil smoke is composed of many chemical components, and if you lower the temperature of the bag filter, the proportion of oil that adheres to the dust and filter increases,
The proportion of oily smoke released to the outside is reduced. However, normal operation becomes difficult because the filter becomes clogged. Therefore, other dust collectors such as wet dust collectors (venturi scrubber, wet EP) are not used as a thorough countermeasure with bag filters alone, but the effect of removing malodorous and white smoke components can be expected very much. However, it is difficult to say enough measures. Therefore, a drastic measure to remove the offensive odor / white smoke component is a method of heating the suction gas to a high temperature of 800 ° C. or higher to decompose it, and an example thereof is described in the prior art (5). This method requires fuel, and since it is necessary to introduce air from the outside during combustion, the amount of exhaust gas increases and the downstream duct and dust collector capacity increase. .

[0005]

Means for Solving the Problems The gist of the present invention is that a method for decomposing an organic matter by burning an exhaust gas containing the organic matter with a fuel, without using new combustion air, The purpose is to reduce the amount of exhaust gas entering the dust collector by using suction gas from the hood surrounding the electric furnace or the building dust collection hood as combustion air.

That is, the present invention proposes the following two means. (1) When the scrap is preheated and further melted to produce a molten metal, the malodor and the malodor generated by the furnace during the preheating and the melting are burned to burn the malodor. In the method of decomposing and removing white smoke components from exhaust gas, a part or all of the suction gas from the hood surrounding the preheating furnace and / or the melting furnace is used as combustion air for burning and decomposing the malodorous / white smoke components, and local suction is performed. Simultaneously burning and removing the malodorous / white smoke components contained in both the total amount of exhaust gas and part or all of the suction gas from this hood.

(2) When preheating scrap and further melting it to produce molten metal, by burning locally sucked exhaust gas containing malodorous and white smoke components generated from the furnace during preheating and melting, In the method for decomposing and removing the offensive odor / white smoke component from the exhaust gas, a part or all of the suction gas from the building dust collecting hood at the upper part of the building where the preheating furnace and / or the melting furnace is installed is used to remove the offensive odor / white smoke component. The odor and white smoke components contained in both the total amount of local exhaust gas and part or all of the suction gas from this building dust collection hood are simultaneously removed by combustion as combustion air for combustion decomposition. By these means, combustion air from the outside becomes unnecessary, and the amount of gas to be treated in the dust collector is almost the same as that in the case where no combustion is performed, so that the above problems can be solved.

[0008]

The present inventors have found that the local suction exhaust gas (A), suction gas (B) from the hood surrounding the preheating furnace and / or the melting furnace,
Table 1 shows the results of an investigation of the properties of the suction gas (C) from the building dust collection hood.

[0009]

[Table 1]

FIG. 1 shows an example of a conventional device configuration.
Two electric furnaces D and E (dissolving amount 60 ton / char) in the hood
ge), D inserts cold scrap into the furnace and inserts kerosene burner to preheat, and E inserts electrodes after completion of scrap preheating to perform arc melting. The exhaust gas at this time is sucked and removed by the A system and the B system. The generated gas at the time of melting is sucked by another dust collecting system. The two electric furnaces D and E are operated by alternately repeating preheating and melting. Looking at the results in Table 1, A
For, there are also cases where kerosene combustion exhaust gas is sucked in,
Oxygen concentration is quite low. On the other hand, B can be said to be a gas close to air except for the dust content and oil content. This is because there are many openings at the bottom of the hood, and it is easy for air to enter. The building dust collection gas C is almost the same as air.

Table 1 shows the measured values when the electric furnaces D and E are performing a steady work of preheating and melting. When the cold scrap is put into the furnace or the electrode is inserted after the completion of preheating, the furnace is used. The lid needs to be replaced. At this time, dust-containing gas is generated from the furnace and stays in the hood, but this is gradually sucked. The oxygen concentration of the suction gas (B) is about 20%, which is lower than that of air itself, but there is no problem in using it as combustion air. Temporarily, in order to decompose harmful substances, fuel is added from the outside to separate the A and B gases separately from each other.
Table 2 shows the amount of fuel used and the data (1) of the produced exhaust gas when the temperature was raised to 0 ° C. Data (2) when a part of B was used as the temperature raising combustion air was also shown in Table 2 for comparison. As a result, there is a large difference between the amount of produced exhaust gas and the amount of fuel used between (1) and (2).
However, not only fuel cost but also blower, dust collector capacity, etc. can be reduced, which is advantageous in terms of equipment cost.

[0012]

[Table 2]

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, for comparison, FIG. 1 shows a conventional apparatus configuration diagram. An example in which the A and B systems are separately burned to remove organic substances is shown. Melting of stainless steel was performed in two 60 ton electric furnaces (D, E). Here, the electric furnace D is performing scrap preheating by kerosene combustion (preheating temperature of about 500 ° C.), and the electric furnace E is performing arc melting after completion of preheating. The dust collection system is divided into two systems: a local suction A of the electric furnace D during preheating of scrap and a suction B from a hood surrounding two electric furnaces. In this case, the building dust collection C system is not installed. In addition, there is a system for sucking the dust-containing gas from the melting electric furnace E, but it is omitted in this figure.

Initially, only bag filter dust collection was performed for both A and B, but measures against organic substances were required, and the following new exhaust gas combustion equipment was installed and enhanced. However, kerosene was used as the fuel for this combustor, and fresh air was introduced from the outside as combustion air. In addition, adsorbent input H before the bag filter
The a and Hb are performed for the purpose of adsorbing the oil content to protect the bug, and are not necessarily required when the oil content is small. The names of other devices in FIG. 1 will be described below. Fa, Fb: Organic substance combustion decomposition apparatus by kerosene combustion of gases A, B Ga, Gb: Gas quenching apparatus by water spray of exhaust gas after combustion Ha, Hb: Adsorbent charging device Ia, Ib: Fan Ja, Jb: Bag filter The following results were obtained by operating in the condition. A system B system Average kerosene consumption Fa = 75.8 kg / min Fb = 113.1 kg / min Combustion air amount AirA = 1035 Nm ³ / min Air B = 1549 Nm ³ / min Exhaust gas amount WA = 2620 Nm ³ / min WB = 3661 Nm ³ / Minute

Embodiment 1 FIG. 2 shows a block diagram of an apparatus according to an embodiment of the present invention. An example is shown in which a part of the gas of the B system is used as combustion air for combustion processing of the A system. The flow of the remaining gas of the B system was changed so that kerosene was burned with oxygen contained in Fb without using new combustion air. In the same electric furnace configuration as the comparative example in the case of FIG. 1 described above, the combustion decomposition device Fa
The combustion air introduced from the outside was abolished, and instead a part of the suction gas B from the hood was used as the combustion air. As a result, the amount of suction gas of the B system to be treated was reduced to 2000 to 965 Nm ³ / min, and the amount of kerosene was also able to be reduced from 113.1 kg / min of the comparative example to 29.4 kg / min. And since the B system gas is close to air,
The addition of combustion air at Fb is abolished and direct kerosene combustion is performed.

The results are shown below. A system B system Kerosene average usage amount Fa = 75.8kg / min Fb = 29.4kg / min Combustion air amount AirA = 0Nm ³ / min AirB = 0Nm ³ / min (Not necessary because B is used) (oxygen in exhaust gas) Exhaust gas amount WA = 2620 Nm ³ / min WB = 987 Nm ³ / min

Embodiment 2 FIG. 3 shows a block diagram of an apparatus according to another embodiment of the present invention. An example applied to an electric furnace that generates a combustible gas containing carbon monoxide during melting and refining is shown. This gas is combusted in the combustion furnace K with fresh air from the outside, and the exhaust gas having a high temperature is introduced into the electric furnace D during preheating to perform scrap preheating. Also electric furnace D
As in the case of FIG. 2, the dust-collected gas of the system A containing the more sucked organic matter is combusted and decomposed using the dust-collected gas from the hood as combustion air. This is different from the above-mentioned conventional example and Example 1, and shows an example in which ordinary steel is treated in an electric furnace (60 ton / charge). Since the electric furnace E during melting generates a gas containing carbon monoxide during the decarburization period, the combustible gas containing carbon monoxide is burned in the combustion furnace K, and the high temperature exhaust gas of the electric furnace E Preheating the scrap. Exhaust gas from the electric furnace D produces oily smoke containing a large amount of organic matter, as in the other examples, and therefore the output side concentration of the organic matter cannot be made sufficiently low by a simple bag filter treatment.

The results are shown below. A system B system Average kerosene consumption Fa = 75.8 kg / min Fb = 29.4 kg / min Combustion air amount AirA = 0 Nm ³ / min AirB = 0 Nm ³ / min Exhaust gas amount WA = 2620 Nm ³ / min WB = 987 Nm ³ / Minute

[Embodiment 3] FIG. 4 shows an apparatus configuration diagram of still another embodiment of the present invention. An application example in which there is no hood surrounding the electric furnace and only local dust collection A and building dust collection C are present is shown. Figure 2, except that combustion air for organic matter decomposition is sucked in from the C system
The same concept as in 3 is adopted. This is an example of processing ordinary steel with two electric furnaces (60 ton / charge),
In this case, there are only two dust collection systems, a local dust collection system A and a building dust collection system C, and no hood surrounding the electric furnace is installed. In order to decompose organic matter in the exhaust gas of the local dust collection system A by combustion, a combustion decomposition furnace Fa and an exhaust gas quenching device Ga are provided. F
In a, the temperature of the gas was raised to 800 ° C. by burning kerosene, but a part of the air volume of the building dust collecting gas C was branched and used as the combustion air at this time. The result was compared with the case where the temperature was raised to 800 ° C. using new combustion air.

In this case, the rest of the building dust collecting exhaust gas C is directly introduced into the bag filter Jc and is not decomposed by combustion. Therefore, even if the building dust collection gas decreases, it has nothing to do with the amount of fuel used. However, since the amount of gas in the bag filter Jc is reduced, there is a margin in the amount of air flow, and the amount of suction from another dust collecting hood (not shown) can be increased. The results are shown below. A system B system Kerosene average usage amount Fa = 75.8kg / min Fb = 0kg / min Combustion air amount AirA = 0Nm ³ / min AirB = 0Nm ³ / min Exhaust gas amount WA = 2620Nm ³ / min WB = 8965Nm ³ / min

[0021]

EFFECT OF THE INVENTION The most practical method for removing organic substances generated during scrap preheating and melting is the decomposition method by combustion shown in the prior art (5). However, the exhaust gas that requires countermeasures in an actual electric furnace is often divided into three systems: A: local dust collection system, B: hood exhaust system, C: building dust collection system, which has a low organic matter concentration B, Even in the C system, it is often determined that measures for removing organic matters are necessary.
In the present invention, attention is paid to the fact that the gases A, B, and C have different oxygen concentrations, and B and C are close to air. Combustion eliminates the need for new combustion air. With this method, the increase in the amount of exhaust gas after combustion is suppressed, so it is possible to reduce the size of bag filters and fans installed downstream, and the fuel consumption is also reduced compared to the case where new combustion air is introduced from the outside. Therefore, the purpose of pollution prevention can be achieved at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional device.

FIG. 2 is a device configuration diagram of an embodiment of the present invention.

FIG. 3 is a device configuration diagram of another embodiment of the present invention.

FIG. 4 is an apparatus configuration diagram of still another embodiment of the present invention.

Claims (2)

[Claims] 1. When preheating scrap and further melting it to produce molten metal, by burning locally sucked exhaust gas containing malodorous and white smoke components generated from a furnace during preheating and melting, In the method for decomposing and removing the malodorous / white smoke component from the exhaust gas, a part or all of the suction gas from the hood surrounding the preheating furnace and / or the melting furnace is used as combustion air when the malodorous / white smoke component is combusted and decomposed. Scrap preheating characterized by simultaneously burning and removing the malodorous / white smoke components contained in both the total amount of locally exhausted exhaust gas and part or all of the gas sucked from this hood, malodorous / white smoke in exhaust gas at the time of melting and melting How to remove components. 2. A part or all of the suction gas from the building dust collection hood in the upper part of the building where the preheating furnace and / or the melting furnace is installed is used as combustion air for burning and decomposing the malodorous and white smoke components, The scrap preheating and melting according to claim 1, wherein the malodorous and white smoke components contained in both the total amount of the exhaust gas and the part or all of the exhaust gas from the building dust collecting hood are burned off at the same time. How to remove offensive odors and white smoke components from exhaust gas.