JP2002310573A - Exhaust gas treatment apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a reduction in an energy/utility unit requirement due to shortening of a refining time, a decrease in an oxidation loss of a valuable element such as iron, chromium or the like, an improvement in a refractory life and an increase in a production efficiency or the like by lowering a pressure loss in an exhaust gas treating unit and maintaining a vacuum degree in a refining furnace at a high level in a process for vacuum-refining a molten metal. SOLUTION: A method for treating the exhaust gas comprises the steps of cooling the exhaust gas generated from a vacuum degassing unit of the molten metal by two or more stages of coolers, branching a bypass duct 7 from a duct 2 between the first and second stage coolers, and connecting the duct 7 to the rear side of the final stage cooler or the duct after a dust collector. In this case, the first stage cooler is preferably of a water tube type, and the second stage cooler is preferably of a smoke tube type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION An apparatus and a method for treating exhaust gas generated from a smelting furnace in a process of refining a molten carbon containing carbon produced by a smelting furnace such as a blast furnace, an electric furnace or a converter in a vacuum. About.

[0002]

2. Description of the Related Art In a vacuum refining furnace, the exhaust gas usually generated in the refining furnace is cooled by a one-stage cooling device and then sent to a dust collecting / evacuating device. When the heat capacity of the exhaust gas is large, for example, the size of the one-stage cooling device 8 is increased (that is, the cooling capacity is increased) as shown in FIG. 2 to reduce the temperature of the exhaust gas after the cooling device. Pressure loss is also large,
There are examples in which bypass ducts are installed in ducts before and after a cooling device (Japanese Patent Application Laid-Open Nos. 6-17115 and 20/17).
00-227284). That is, as shown in FIG. 3, when the required vacuum degree is low and the exhaust gas treatment flow rate is large in the first half of the refining process, the damper 9 of the bypass duct 7 is closed or the opening degree is reduced, and the exhaust gas is mainly supplied to the cooling device 8. Shed.
When the required vacuum degree is high and the exhaust gas flow rate is low in the latter half of the refining process, the opening degree of the damper 9 of the bypass duct 7 is increased, so that a large amount of exhaust gas flows through the bypass duct and the pressure loss of the cooling device 8 is reduced.

[0003]

When the load on the exhaust gas treatment system becomes higher, such as an increase in the concentration of dust in the exhaust gas, an increase in the temperature and an increase in the flow rate, the exhaust gas is directly bypassed before the cooling device as in the past. The following problems were found in the method of causing the problem. That is, dust accumulates in the bypass duct and closes the flow path. A large amount of dust flows into the dust collector 5 and the vacuum exhaust device 6 installed after the merging of the bypass duct, thereby increasing the dust load. Bypass ducts exposed to high-temperature exhaust gas require refractory coating or water cooling as a measure against the heat load of the temperature load, and dampers that control the flow rate also require heat measures such as water cooling. Problems such as an increase and an increase in maintenance cost occur. In order to avoid such a problem, the exhaust gas flowing into the bypass duct has to be increased after the temperature and the flow rate have sufficiently decreased and the dust concentration has reached a low level. However, this cannot be a fundamental measure for reducing the pressure loss at a high flow rate of the exhaust gas.

According to the present invention, in the process of vacuum refining a molten metal, the pressure loss in an exhaust gas treatment device is reduced and the degree of vacuum in a refining furnace is maintained at a high level. It is an object of the present invention to reduce units, reduce oxidation loss of valuable elements such as iron and chromium, improve refractory life, increase production efficiency, and the like.

[0005]

The gist of the present invention to achieve the above object is as follows. (1) Exhaust gas generated from the vacuum degassing device for molten metal
It is characterized by cooling by a cooling device of more than one stage, branching the bypass duct 7 from the duct between the first and second stage cooling devices, and connecting to the duct behind the last stage cooling device or after the dust collector. Waste gas treatment equipment. (2) The exhaust gas treatment apparatus according to (1), wherein the first-stage cooling device is a water tube type having a low pressure loss, and the second-stage cooling device is a smoke tube type having a high cooling capacity. (3) The exhaust gas treatment device according to (1) or (2), wherein a dust collection device is installed after the bypass duct joins, and the exhaust gas is removed and then connected to a vacuum exhaust device. (4) Any one of (1) to (3), wherein the first-stage cooling device is a water tube type cooling device, and a duct attached to the water tube is removed by a dust blower.
An exhaust gas treatment apparatus according to any one of the preceding claims. (5) When performing exhaust gas treatment using the exhaust gas treatment apparatus according to any one of (1) to (4), a movable damper is installed in a bypass duct, and the temperature and the degree of vacuum after the first-stage gas cooler are set. Alternatively, an exhaust gas treatment method characterized by controlling an opening degree of a damper based on both a temperature and a degree of vacuum.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention treats high-temperature, high-concentration dust and high-flow exhaust gas in a low vacuum in the early to middle stages of refining, and uses low-temperature, low-concentration dust and low flow in the middle to late stages of refining. An apparatus and method for treating exhaust gas in a high vacuum.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. Exhaust gas 11 from the vacuum refining furnace 1
Through the exhaust gas cooling device 3 of the first stage to cool and remove coarse dust. Further, it enters the second-stage exhaust gas cooling device 4 and is cooled and dust-removed. The exhaust gas 11 sufficiently cooled is removed by the dry dust collector 5 and the exhaust gas 6
Is sucked out and released out of the system. Here, the bypass duct 7 is branched from the exhaust duct 2 between the first-stage and second-stage exhaust gas cooling devices and joins the exhaust duct 2 in front of the dust collector. An on-off valve or a flow control valve 9 is provided in the bypass duct 7, and a control device is provided based on data obtained from a vacuum gauge 13 in the refining furnace 1 and a detection device of a thermometer 14 provided in an exhaust duct in front of the dust collector. The calculation is performed at 15 to adjust the on-off valve or the flow control valve (movable damper) 9.

[0008] The above-mentioned bypass path may be joined before the dust collector, or may be connected to a duct after the dust collector. Further, the opening / closing valve or the flow control valve 9 may be provided in the bypass path and after the second-stage cooling device or after the dust collector as shown in the drawing, and the two may be linked to control the flow rate.

In the early to middle stages of vacuum refining, that is, when the molten steel having an initial C of 0.4 to 0.6% by weight in a molten metal is subjected to blowing acid decarburization treatment under vacuum, the exhaust gas flow rate and dust generation amount are large and the exhaust gas is large. The temperature is also high. Therefore, the degree of vacuum in the refining furnace is about 200 to 350 Torr, but the pressure loss of the exhaust gas cooling device and the dust collecting device is about 5 to 15 Torr, respectively. However, in the middle stage to the end stage, that is, molten metal C = 0.01 to
When performing vacuum treatment on molten steel of 0.05% by weight, the exhaust gas flow rate, dust generation amount and exhaust gas temperature decrease, and the degree of vacuum becomes a value dependent on the flow rate of the stirring inert gas blown into the refining furnace. In the case of an AOD furnace, it becomes 30 to 50 Torr. Further, when the stirring gas is small as in the vacuum treatment in the ladle refining, the degree of vacuum is further increased and the C in the molten metal becomes 0.01%.
%, The exhaust gas flow rate, dust generation amount and exhaust gas temperature are further reduced, and the degree of vacuum is several tons.
High vacuum of rr or less. As described above, since a high vacuum process is performed from the middle stage to the end stage, the pressure loss of the flue gas type exhaust gas cooling device and the dry dust collector is a serious problem in the refining process.
Therefore, in the past, a bypass duct was installed from the middle stage to the end stage to avoid pressure loss of a flue gas type exhaust gas cooling device and a dry dust collector.

However, in the vacuum evacuation process in which dust is generated and the exhaust gas flow rate is large, the above-described problem has occurred and the bypass duct cannot be used effectively. Therefore, this problem can be solved by the apparatus configuration and the processing method according to the present invention. In the present invention, since the large-flow high-temperature exhaust gas is processed by the first-stage cooling device, the exhaust gas temperature is reduced, and the heat load in the bypass duct is greatly reduced.
Further, since the cooling device of the first stage also has an effect of removing dust, dust clogging in the bypass duct and dust adhesion to the on-off valve or the flow control valve are reduced. In particular, since the dust to be removed is mainly coarse-grained dust, the effect of preventing clogging and adhesion of dust is further increased.

The flow rate and timing of the exhaust gas flowing into the bypass duct are determined as parameters using the exhaust gas temperature in consideration of the degree of vacuum in the refining furnace required for operation and the heat-resistant temperature of the dry dust collector required for equipment protection. Therefore, in the middle stage to the end stage of the vacuum refining, the detection values of the in-furnace vacuum gauge 13 and the exhaust gas thermometer 14 are taken into the control device 15, and the required degree of vacuum and the allowable upper limit temperature which are set in advance are calculated. The flow control valve 9 is controlled. When opening the flow control valve of the bypass duct, the flow control valve after the second-stage cooling device may be fully closed, or may be fully closed or at an intermediate opening degree. The degree of opening of these exhaust gas flow control valves is determined from the relative balance between the required furnace vacuum degree and the actual furnace vacuum degree, the allowable upper limit temperature before dust collector, and the actual temperature.

The cooling capacity and pressure loss differ depending on the type of the exhaust gas cooling device. Although there are some differences depending on the detailed structure, generally, a flue-tube type cooling device has a large cooling capacity but a large pressure loss for the same volume. On the other hand, the water pipe type cooling device has a small cooling capacity but a small pressure loss. Conventionally, as shown in FIG.
A single-stage large-tube flue-tube cooling device 8 from 0 to 1000 ° C. to 120 to 140 ° C. which is a general allowable temperature of the dry dust collector 5
Required cooling. However, in this case, an extremely large pressure loss occurs, which is a problem in operation. In the present invention, a cooling device is provided in two stages for the above-mentioned purpose, and the first stage is a water tube type cooling device having a small pressure loss. Thus, the pressure loss reduction effect of the first and subsequent bypass ducts and the pressure loss of the first stage cooling device itself can be reduced.

Further, in the first-stage cooling device 3, a dust blower 10 for spraying an injection medium such as steam, air, or nitrogen onto the water pipe to blow off a duct attached to the water pipe is provided. As a result, the surface of the water pipe can be always kept in a dust-free state, and it is possible to maintain the cooling capacity and prevent an increase in pressure loss. The dust blower 10 can be arranged as needed, such as the front, rear, and intermediate positions of the water pipe, or a combination thereof.

[0014]

EXAMPLES Table 1 is a table showing operating conditions when vacuum refining is performed by AOD, and shows examples of the present invention together with comparative examples of the conventional method. In the process configuration of the present invention, a two-stage exhaust gas cooling device was used, the first stage was a water tube type, and the second stage was a smoke tube type.
Install a bag filter type dry dust collector in front of the vacuum exhaust system that combines a vacuum air pump and ejector,
Prevention of contamination of cooling water of the vacuum pump by dust.
A bypass duct was connected from the exhaust duct between the first stage and the second stage to the front of the dust collector, and a damper capable of controlling the opening was installed in the middle of the duct. Dust blowers were installed before and after the first-stage exhaust gas cooling device, and dust in the water pipe was removed between vacuum treatments. On the other hand, the process configuration as a comparative example of the conventional method is the same as that of the present invention in the dust collector and the vacuum exhaust device, but the cooling device is a single-stage large-sized smoke tube type.
An example in which bypass ducts are arranged before and after that (an example shown in FIG. 3) is shown.

[0015]

[Table 1]

As shown in Table 1, in the first to middle stages of refining, both are under almost the same operating conditions. However, in the present invention, since the exhaust gas temperature is reduced by the first-stage cooling device, the damper of the bypass duct is opened to allow about 30% of the exhaust gas to be bypassed. However, in the comparative example, when the bypass was used, high-temperature exhaust gas flowed, so that the temperature in front of the dust collector rapidly increased, and the gas could not be flown into the bypass at all. Although the effect of the degree of vacuum on the metallurgical refining effect during this period did not differ greatly as described above, in the comparative example, dust attached to the flue of the cooling device increased, whereas the influence on the cooling device of the present invention increased. At the same time, the dust was dispersed in the first and second stages, and at the same time, the dust in the smoke pipe of the second-stage cooling device was relatively small because the exhaust gas partially flowed to the bypass duct. .

In the latter stage of the refining, the flow rate and temperature of the exhaust gas are greatly reduced, so that both can use a bypass duct. However, in the present invention, the exhaust gas temperature was further reduced by the first-stage cooling device, so that the flow rate of the exhaust gas flowing through the bypass duct could be greatly increased up to about 70%. The exhaust gas temperature is still high, so a large amount of exhaust gas could not flow through the bypass duct due to exhaust gas temperature restrictions in front of the dust collector, and about 30%
Was the limit. In addition, if such operation is continued, the cooling device itself, in the present invention, the first-stage cooling device is dust-removed by a heat dust blower every time, and the second-stage cooling device also has a high exhaust gas bypass ratio, The pressure loss of the cooling device main body is suppressed to be small. Further, since the bypass ratio is high, the pressure loss of the entire system including the duct is also reduced. On the other hand, in the comparative example, the pressure loss of the cooling device main body and the entire system was increased, and eventually the difference in the degree of vacuum in the refining furnace as shown in Table 1 was obtained. The difference between the two degrees of vacuum increases as the number of times the exhaust gas cooling device is used increases. This is because there is a large difference in the amount of dust adhering to the inside of the smoke pipe or the surface of the water pipe of the cooling device, and the difference further increases as the number of heats increases.

[0018]

As described above, a high degree of vacuum can be maintained by providing two stages of exhaust gas cooling devices and installing bypass ducts before and after the second stage. Due to the difference in the degree of vacuum, the present invention increases the decarburization efficiency, shortens the refining time, reduces energy consumption and utility unit, reduces oxidation loss of valuable elements such as iron and chromium, and improves refractory life. In addition, significant advantages have been brought about, such as an increase in production efficiency.

[Brief description of the drawings]

FIG. 1 is a flow sheet of an exhaust gas treatment facility showing an embodiment of the present invention.

FIG. 2 is a flow sheet showing the conventional apparatus 1.

FIG. 3 is a flow sheet showing a conventional apparatus 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vacuum refining furnace 2 Exhaust duct 3 Water tube gas cooling device 4 Smoke tube gas cooling device 5 Dry dust collector 6 Vacuum exhaust device 7 Bypass exhaust duct 8 Large smoke tube gas cooling device 9 Opening / closing valve or flow control valve 10 Dust blower 11 Exhaust gas 12 Cooling water 13 Vacuum gauge 14 Thermometer 15 Controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K056 AA01 AA02 BA04 CA02 DB05 DB13 DC15 DC17 FA08

Claims (5)

[Claims] An exhaust gas generated from a vacuum degassing device for molten metal is cooled by a cooling device of two or more stages, and a bypass duct is branched from a duct between the first and second cooling devices.
An exhaust gas treatment device connected to a duct behind a cooling device in the last stage or after a dust collector. 2. The exhaust gas treatment apparatus according to claim 1, wherein the first-stage cooling device is a water tube type having a low pressure loss, and the second-stage cooling device is a smoke tube type having a high cooling capacity. 3. The exhaust gas treatment apparatus according to claim 1, wherein a dust collection device is installed after the bypass duct joins, and the exhaust gas is removed and then connected to a vacuum exhaust device. 4. The exhaust gas purifying apparatus according to claim 1, wherein the first-stage cooling device is a water tube type cooling device, and a duct attached to the water tube is removed by a dust blower. Processing equipment. 5. When performing exhaust gas treatment using the exhaust gas treatment apparatus according to any one of claims 1 to 4, a movable damper is installed in a bypass duct, and a temperature and a degree of vacuum after a first-stage gas cooler are provided. Alternatively, an exhaust gas treatment method characterized by controlling an opening degree of a damper based on both a temperature and a degree of vacuum.