JPS6231271B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method and apparatus for preheating scrap using exhaust gas from an electric steelmaking furnace, and more specifically, to a method and apparatus for preheating scrap using exhaust gas from an electric steelmaking furnace. The present invention relates to a method and apparatus for preheating scrap that can be used to preheat scraps. This reduces the melting power consumption rate in electric steel making furnaces and makes steel by preheating the scrap charged into electric steel making furnaces using the exhaust gas containing high thermal energy that is generated during the operation of electric steel making furnaces. It is used in the field to realize time reduction. [Prior Art] Although the exhaust gas generated during the operation of an electric steelmaking furnace contains a large amount of dust, it retains a large amount of thermal energy. Therefore, by preheating the scrap charged into the electric steelmaking furnace using this exhaust gas, it is possible to save melting power and shorten the steelmaking time. However, scrap often has oil, paint, rubber, plastic, etc. attached to or mixed with it, and while the exhaust gas flows through the preheating basket containing the scrap, heat exchange with the scrap causes The temperature drops to about 300°C, which makes it difficult to maintain a temperature of 650 to 700°C that thermally decomposes the above-mentioned organic matter mixed in the scrap, and preheated exhaust gas with a foul odor due to incomplete combustion is discharged. Therefore, a scrap preheating device 20 as shown in FIG. 3 is an attempt to prevent air and environment pollution by removing the bad odor from the preheated exhaust gas. In this process, dust-containing high-temperature exhaust gas discharged from an electric steelmaking furnace 2 is burned to combust combustible substances such as CO gas contained therein in a combustion tower 3, and then the exhaust gas is introduced into a preheating basket 4a or 4b. However, the scrap charged into the electric steel making furnace 2 is preheated by the thermal energy possessed by the exhaust gas. Then, the preheated exhaust gas is returned from the circulation duct 22 to the gas supply box 24 provided in the main duct 23 upstream of the combustion tower 3 by the induction fan 21, and is mixed with the dust-containing high-temperature exhaust gas discharged from the electric steelmaking furnace 2. After mixing in the combustion tower 3, the malodorous components in the preheated exhaust gas are combusted together with combustibles, thereby deodorizing them. By the way, as mentioned above, the malodorous components are not incinerated by burning the preheated gas, but it is possible to cool the sulfur-containing waste gas with cooling water at 25°C, for example, without using an expensive cooling device. There is a method that removes it by electrostatic precipitation. For example, Japanese Patent Application Laid-Open No. 53-113762 discloses a scrubber that removes components that remain in gaseous form during the dry purification process of waste gas and condenses at low temperatures, and a scrubber that sprays water or a generated condensate into the waste gas. indirect gas coolers that operate and ensure that the water vapor content in the waste gas in the vicinity of the outlet of the indirect gas coolers is reduced to a value lower than that required for optimal separation in the subsequent wet electrostatic precipitator. A device is described in which a humidifier capable of Although this is not intended to deodorize preheated gas, it is similar to the present invention described below in that it cools the waste gas to a desired temperature and removes condensed water. Its main purpose is to cool the gas from the need to send it to a contact plant for the production of sulfuric acid, but it has the advantage of being able to cool the cold waste gas with hot cooling water. . However, there is a problem in that even if the exhaust gas is accompanied by a bad odor, it cannot be deodorized. Therefore, it is desired to elucidate the mechanism by which the odor generated by preheated scrap gas is generated, and to develop a corresponding deodorization technology. On the other hand, regarding the exhaust gas of electric steelmaking furnaces, as shown in Figure 2, the temperature inside the furnace is low during the initial melting after charging the scrap, the temperature decreases due to the mixing of outside air when the scrap is reloaded, and the temperature decreases after the reloading. Depending on the intermediate temperature during melting, the temperature drop during reloading, and the high melting temperature after reloading, the temperature of the exhaust gas may range from 400 to 1200.
It fluctuates widely over the °C range. As a result, during periods when the exhaust gas temperature is low, the temperature in the combustion tower 3 cannot be maintained at 650° C. or higher, at which thermal decomposition is possible to deodorize the preheated exhaust gas, and it may not be possible to prevent the release of bad odors. In addition, the exhaust gas in the combustion tower 3 is again introduced into the scrap preheater 4, so much of the exhaust gas circulates between the combustion tower 3 and the scrap preheater 4, which reduces the utilization rate of sensible heat of the exhaust gas. decreases significantly. In other words, since all of the preheated exhaust gas is circulated to the combustion tower to remove bad odors, the thermal energy of the electric furnace exhaust gas cannot be utilized to the maximum for preheating scrap, which is difficult to achieve on an industrial scale. It has become clear that there are fundamental flaws. [Object of the Invention] The present invention was made in view of the above-mentioned problems, and its purpose is to make it possible to utilize the sensible heat possessed by electric steelmaking furnace exhaust gas to the maximum extent possible for preheating scrap, and to reduce the amount of dust-containing high-temperature exhaust gas. A method for preheating scrap using electric steelmaking furnace exhaust gas, which can prevent pollution of the atmosphere and the environment and make exhaust gas discharged from electric steelmaking equipment pollution-free by removing dust and deodorizing the preheated exhaust gas. The purpose is to provide such equipment. It was previously thought that the bad odor contained in the preheated exhaust gas from scrap could only be removed by burning it. However, according to the research of the present inventors, the extremely unpleasant odor is caused by general odor substances caused by things other than oil, and oil mist that is the evaporation of cutting and lubricating oil contained in flour. Moreover, it was confirmed that they have a synergistic effect that mutually promotes bad odor. Based on this knowledge, in order to deodorize preheated exhaust gas, it is sufficient to remove general odorous substances and collect them with oil mist. The present invention has been completed by taking measures to enable the collection of the following information. [Structure of the Invention] To explain the features of the present invention, in the case of the invention of the method, the exhaust gas which is led out for direct dust removal after combustion is preheated by preheating the scrap and is accompanied by a bad odor. After mixing the exhaust gas and removing dust from the mixed exhaust gas, the mixed exhaust gas is brought to a predetermined temperature with cooling water adjusted according to the fluctuation of the gas temperature, and the mixed exhaust gas is primarily deodorized with a cleaning liquid and is accompanied by saturated steam. By supplying water for secondary deodorization and rapid cooling, condensing a portion of the water vapor to make it larger particles, attaching oil mist, and collecting the water vapor particles by electrostatic action, the scrap is removed. The present invention is a method for preheating scrap using electric steelmaking furnace exhaust gas that can remove the bad odor and oil mist contained in the preheated exhaust gas. Further, the invention of the device will be explained based on the drawing shown in FIG. 1. The combustion tower 3 is interposed in the main duct 6 from which dust-containing high-temperature exhaust gas is led out, and the auxiliary duct 8 introduces the exhaust gas into the scrap preheater 4. A booster fan 10 is installed in the reflux ducts 8a to 8c that lead out the preheated exhaust gas with a foul odor that has passed through the scrap to the main duct 6. At 6,
Sequentially, a dust remover 11, an induction fan 12, an exhaust gas temperature adjustment tower 13 that attempts to equalize the exhaust gas temperature, a hot water cleaning tower 14 that deodorizes the exhaust gas with a cleaning liquid and generates a large amount of water vapor depending on the temperature of the gas, and cooling. A scraping process using exhaust gas from an electric steelmaking furnace is equipped with a cold water cleaning tower 15 that deodorizes the exhaust gas with a cleaning solution and enlarges the water vapor, and a wet electrostatic precipitator 16 that collects oil mist adhering to the water vapor from the exhaust gas together with the water vapor. This means that the preheating device was installed as a preheating device. [Examples] The present invention will be described in detail below based on Examples. FIG. 1 is an overall system diagram of a preheating device 1 capable of implementing the method of preheating scrap using electric steelmaking furnace exhaust gas according to the present invention. After combustion of combustible materials, all or part of the exhaust gas is introduced into the scrap preheater 4, and the scrap charged into the electric steelmaking furnace 2 is preheated in the scrap preheater 4 by the thermal energy possessed by the exhaust gas. It is. To be more specific, a main duct 6 for discharging electric furnace exhaust gas is connected to a gas discharge port 2a provided on the furnace wall or ceiling of an electric steelmaking furnace 2 for refining scrap, and a gap adjustment ring 7 and A combustion tower 3 is interposed in sequence. A suitable amount of outside air is sucked into the gap adjustment ring 7, and this air is supplied to the combustion tower 3 together with the dust-containing high-temperature exhaust gas discharged from the electric steel making furnace 2.
The combustion tower 3 has a structure that allows mixing of the dust-containing high-temperature exhaust gas and the taken in outside air, combustion of combustible materials by spontaneous ignition based on a decrease in flow velocity, and furthermore, the removal of coarse dust. In the upper part of such a combustion tower 3, a sub duct 8 is provided to direct part or all of the exhaust gas after combustion to the scrap preheater 4, so as to bypass the main duct 6 which leads directly to the dust remover 11. There is. A scrap preheater 4 consisting of one or more preheating baskets 4a to 4c arranged in series or in parallel as shown is connected to the sub duct 8 via valves 9a to 9f provided before and after the preheating baskets 4a to 4c. There is. Note that the booster fan 10 for introducing exhaust gas into each preheating basket 4a-4c is connected to each downstream recirculation duct 8a-8.
c, and preheated exhaust gas with foul odor and oil mist flows through this duct to the main duct 6 mentioned above.
It is becoming more and more derived. Downstream from the confluence portions 6A to 6C of the main duct 6 with the reflux ducts 8a to 8c, a bag filter or the like is installed to remove dust from the mixed exhaust gas in which the exhaust gas from the combustion tower 3 and the preheated exhaust gas from the scrap preheater 4 are mixed. A dry dust remover 11, an induction fan 12 that introduces the mixed exhaust gas into the dust remover 11 and leads the exhaust gas to an exhaust gas temperature adjustment tower 13, etc., which will be described next.
is installed. The main duct 6 downstream of the induction fan 12 includes an exhaust gas temperature adjustment tower 13 that attempts to equalize the exhaust gas temperature, a hot water cleaning tower 14 that deodorizes the exhaust gas and generates a large amount of water vapor using the heat of the gas. A cold water cleaning tower 15 that deodorizes the exhaust gas again with the cooled cleaning liquid and condenses water vapor to make it larger particles, and a wet electrostatic precipitator 16 that collects oil mist adhering to the water vapor are installed, and the scrap is preheated. It is now possible to remove bad odors and oil mist contained in exhaust gas. The exhaust gas temperature adjustment tower 13 is equipped with a circulation pump 13m that circulates cooling water within the tower, and the electric steelmaking furnace 2
Even if the temperature of the exhaust gas discharged from the hot water washing tower 14 fluctuates as shown in Fig. 2 during the operating process, the cooling water is used to cool the exhaust gas to a predetermined temperature, for example, 80°C, so that the action in the hot water washing tower 14 is maintained at all times. It is intended to be maintained. This is done by detecting the gas temperature upstream of the exhaust gas temperature adjustment tower 13 using a temperature sensor (not shown), and in response to the signal, the amount of cooling water that is brought into contact with the exhaust gas in the form of mist or water spray through the water sprinkler 13s. The water temperature is now regulated. The hot water washing tower 14 is installed singly or in several groups as necessary, and an attached washing pump 14m is used to wash neutralizers such as acids or alkalis, or solvents that have a strong affinity with malodorous components, into the tower. Alternatively, the structure is such that a cleaning liquid into which ozone is blown is supplied from the water sprinkler 14s. The cleaning liquid primarily deodorizes the foul odors in the exhaust gas, but at that time, the thermal energy possessed by the exhaust gas is given to the cleaning liquid, and the temperature of the exhaust gas and the cleaning liquid are brought to an equilibrium temperature of approximately 50°C, for example. Sufficient saturated steam is involved. The cold water cleaning tower 15 into which such exhaust gas is introduced deodorizes the exhaust gas with a cleaning liquid similar to or similar to the cleaning liquid described above, condenses water vapor with oil mist as a nucleus, and further attaches oil mist. Therefore, the cold water washing tower 15 is provided with washing pumps 15m and 15n for circulating the washing liquid and a cooling tower 15p for cooling the washing liquid.
The cooled cleaning liquid is supplied to the exhaust gas from the sprinkler 15s. Wet type electric dust collector 16
This system collects the oil mist attached to the water vapor in the introduced exhaust gas from the exhaust gas along with the water vapor.
A water pump 16m is provided to supply a cleaning liquid for cleaning the electrode surface to which water vapor particles including oil mist have adhered. In addition, the oil mist in the exhaust gas temperature adjustment tower 13, hot water cleaning tower 14, and cold water cleaning tower 15 installed in the preceding stage has a function of accelerating charging by adhering water vapor to the oil mist and increasing the size of the water vapor, making it extremely compact. There is. According to the scrap preheating device 1 having such a configuration, the preheated exhaust gas can be deodorized and the oil mist in the exhaust gas can be removed in the following manner. First, scrap preheated in the scrap preheater 4 is charged into the electric steelmaking furnace 2, and the scrap is melted. In such refinement, the second
As shown in the figure, scraps are added one after another to raise the melting temperature. Meanwhile, dust-containing high-temperature exhaust gas is led out from the electric steelmaking furnace 2 to the main duct 6, and the outside air introduced through the gap adjustment ring 7 completely burns the combustible substances such as CO gas in the combustion tower 3. At the same time, coarse dust is removed. Now, if preheating of the scrap is not required, all of the exhaust gas is led out to the main duct 6.
Valves 9a to 9c in the scrap preheater 4 are closed. Exhaust gas from the combustion tower 3 is introduced into the dust remover 11 by an induction fan 12, where a predetermined amount of dust is collected, and then released into the atmosphere from a valve 17 via a dispersion tower (not shown). Electric steel making furnace 2
Since the dust-containing high-temperature exhaust gas discharged from the combustion tower 3 is completely combusted in the combustion tower 3, unlike the preheated exhaust gas after preheating the scrap, it hardly has any bad odor or oil mist. It is processed by following the following route. When the scrap is preheated by the thermal energy contained in the exhaust gas during operation of the electric steelmaking furnace 2, a booster fan 10 interposed in the recirculation duct 8a of the preheating basket containing the scrap, e.g. 4a, is driven. As a result, an amount of exhaust gas corresponding to the suction force of the booster fan 10 is led out from the combustion tower 3 to the sub duct 8, and the remaining exhaust gas is led out directly to the dust remover 1 via the main duct 6. The flue gas led out for direct dust removal in this way is mixed at a confluence point 6A with a preheated flue gas with a temperature of about 100 to 300 degrees Celsius, which is accompanied by a bad odor and whose temperature has been lowered by preheating the scrap.
The dust is removed by Since this mixed exhaust gas cannot be released from the stripping tower, the valve 17 is closed while the valve 18 is opened and the exhaust gas temperature adjustment tower 13 is closed.
will be introduced in In this system, even if the temperature of the dust-containing high-temperature exhaust gas fluctuates, as shown in Figure 2, the temperature of the dust-containing high-temperature exhaust gas is lowered to a predetermined temperature, e.g., 80°C, by using cooling water whose amount and temperature are adjusted according to fluctuations in gas temperature. . Therefore, the temperature of the mixed exhaust gas discharged from the hot water washing tower 14 is maintained constant during any process of the operating state of the electric steel making furnace 2. When the mixed exhaust gas is introduced into the hot water cleaning tower 14, it is first deodorized by a cleaning liquid such as a neutralizing agent, and the heat is given to the cleaning liquid, so that the temperature of both is balanced, and the water in the cleaning liquid evaporates to almost Saturated steam at 50℃ is generated. When the mixed exhaust gas containing water vapor is introduced into the cold water cleaning tower 15 in this way, the cooled low temperature cleaning liquid is sprayed together with the cold water appropriately replenished by the cooling tower 15p attached thereto. As a result, the mixed exhaust gas is subjected to secondary deodorization and rapidly cooled, and the water vapor becomes supersaturated, and a portion of the water vapor condenses with the oil mist as a core, and the growth of its particles is promoted. At this time, the oil mist in the exhaust gas is further encouraged to adhere to the water vapor. Up to this cold water washing tower 15, malodorous components contained in the preheated exhaust gas are completely removed by a wet method, while preparations are made for removing oil mist. To explain a little more about collecting oil mist, the oil mixed in the scrap becomes mist due to its preheating and floats in the preheated exhaust gas. This oil mist is extremely fine and cannot be removed by the above-mentioned cleaning solution, and requires a very large-capacity electrostatic precipitator. On the other hand, the electric precipitator 16 consists of a discharge electrode and a dust collection electrode, and when a high negative voltage is applied to the discharge electrode and the dust collection electrode is grounded, a strong electric field is formed around the discharge electrode and corona discharge occurs. This corona discharge generates positive and negative ions very close to the discharge electrode, the positive ions are immediately neutralized by the negative discharge electrode, and the negative ions move in the electric field to the dust collecting electrode. If dust or water vapor particles are present in the exhaust gas, they are negatively charged by the moving negative ions, and are attracted to the dust collecting electrode by electric force and collected. At this time, it is known that the larger the dielectric constant K and particle diameter of the particles, the easier they are to move to the dust collecting electrode, as can be understood from the following equation. Q=KE・Dp ² /4 ...(1) u=QE/3π・μ・Dp ...(2) However, Q: Amount of charge received by particles in the gas flow in the precipitator K; Dielectricity of particles Constant Dp; Particle diameter E; Electric field strength u; Speed at which particles move toward the electrode plate μ; Gas viscous drag coefficient By the way, the dielectric constant K of water particles is 2.93, which is larger than 1.5 for oil mist. Moreover, although the growth of oil mist is not easy, it is possible to increase the size of water particles by the cooperative action of the hot water washing tower 14 and the cold water washing tower 15 described above. Furthermore, the core of the water particles is oil mist, and other oil mist adheres to the water particles, so the oil mist is effectively collected through large water vapor particles that are easily collected by the electric precipitator 16. be done. Of course, the purified exhaust gas is released into the atmosphere from a diffusion tower (not shown), and the oil mist is treated separately. The above describes the exhaust gas that goes directly from the combustion tower 3 to the dust remover 11 at the confluence points 6A to 6C of the main duct 6.
Although we have described the case where the preheated exhaust gas is mixed after preheating the scrap, in some cases, by closing the valve 19 interposed in the main duct 6, all of the exhaust gas from the combustion tower 3 is preheated to the scrap. It may be made to flow through the vessel 4. In this case, there is an advantage that all the thermal energy possessed by the exhaust gas can be used for preheating the scrap, and furthermore, the deodorization of the preheated exhaust gas and the removal of oil mist are carried out in the same way as described above. Next, an example of implementation results according to the present invention will be introduced.
When refining in a 70-ton furnace using scrap charging of 30 tons for the initial charge, 30 tons for the additional charge, and 10 tons for the second charge, the electricity consumption per 1 ton of crude steel in the electric steelmaking furnace is approximately 415 KWH.
It is. Under these conditions, comparing (1) without a preheating device and (2) preheating all of the charged scrap with a preheating device, the power consumption reduction is 57KWH/ton as shown in the table below. achieved.

[Table] Furthermore, the contents of dust, etc. in the exhaust gas at the inlet and outlet of the dust remover 11 and the outlet of the electrostatic precipitator 16 at that time were as follows. Note that the odor concentration in the table means that the odor disappears when diluted by a numerical multiple thereof.

〔Effect of the invention〕

As can be seen from the detailed description of the embodiments above, the present invention includes a combustion tower interposed in a main duct from which dust-containing high-temperature exhaust gas is led out, and a sub-duct for introducing exhaust gas to a scrap preheater. The preheated exhaust gas with foul odor that has passed through is led out to the main duct, and in the main duct, a dust remover, induction fan, exhaust gas temperature adjustment tower, hot water washing tower, cold water washing tower, and electrostatic precipitator are arranged in order. Since the exhaust gas is made to sequentially flow through the exhaust gas, it is possible to effectively remove the bad odor and oil mist of the preheated exhaust gas from the scrap. As a result, it is possible to prevent pollution of the atmosphere and the environment, and to achieve pollution-free exhaust gas discharged from electric steel manufacturing equipment. Furthermore, since only the electric steelmaking furnace exhaust gas is introduced into the scrap preheater, the sensible heat contained in the exhaust gas can be utilized to the maximum for preheating the scrap. It is possible to realize a reduction in steel production time and a reduction in steel manufacturing time. In addition, we have created large particles of water vapor that can be easily charged in the front stage of the electrostatic precipitator that collects oil mist, increasing the speed at which the particles move to the electrode plates within the electrostatic precipitator, and increasing the speed at which exhaust gas flows through the electrostatic precipitator. can. Therefore,
An inexpensive electrostatic precipitator with a small capacity can be used, and the cost of installing pollution prevention equipment can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a scrap preheating device using electric steelmaking furnace exhaust gas to which the present invention is applied, Fig. 2 is a graph showing the temperature fluctuation of exhaust gas over time in the operating state of the electric steelmaking furnace, and Fig. 3 is a FIG. 1 is a system diagram of a prior art scrap preheating device using exhaust gas from an electric steelmaking furnace. 1... Preheating device, 2... Electric steel making furnace, 3... Combustion tower, 4... Scrap preheater, 6... Main duct, 6A to 6C... Merging point, 8... Sub duct, 8
a to 8c...reflux duct, 10...booster fan, 11...dust remover, 12...induction fan, 13
...Exhaust gas temperature adjustment tower, 14...Hot water cleaning tower, 1
5...Cold water washing tower, 16...Wet type electrostatic precipitator.

Claims (1)

[Scope of Claims] 1. After burning combustibles in dust-containing high-temperature exhaust gas generated during the operation of an electric steelmaking furnace, the scrap to be charged into the electric steelmaking furnace is preheated by the thermal energy possessed by the exhaust gas. In the scrap preheating method, the exhaust gas discharged for direct dust removal after combustion is
The preheated exhaust gas with bad odor is mixed by preheating the scrap, and after removing dust from this mixed exhaust gas, the mixed exhaust gas is brought to a predetermined temperature with cooling water adjusted according to the fluctuation of the gas temperature, and the mixed exhaust gas is heated with a cleaning liquid. The water vapor is firstly deodorized and accompanied by saturated steam, and a low-temperature cleaning liquid is supplied for secondary deodorization and rapidly cooled. A part of the water vapor is condensed to make it larger, and an oil mist is attached to the water vapor particles. A method for preheating scrap using electric steelmaking furnace exhaust gas, characterized in that the foul odor and oil mist contained in the preheated scrap exhaust gas can be removed by collecting them using electric power. 2. After burning the combustibles in the dust-containing high-temperature exhaust gas generated during the operation of the electric steelmaking furnace in the combustion tower,
In a scrap preheating device, all or part of the exhaust gas is introduced into a scrap preheater, and the scrap to be charged into the electric steelmaking furnace is preheated by the thermal energy possessed by the exhaust gas. The combustion tower is interposed in the main duct through which the scrap gas is led out, and is provided with a sub duct that introduces the exhaust gas into the scrap preheater, and a booster is installed in the reflux duct that leads the preheated exhaust gas with a foul odor that has passed through the scrap to the main duct. A fan is installed,
In the main duct downstream from the confluence with the reflux duct, there is a dust remover, an induction fan, an exhaust gas temperature adjustment tower to equalize the exhaust gas temperature, a cleaning liquid to deodorize the exhaust gas, and a large amount depending on the temperature of the gas. A hot water cleaning tower that generates water vapor, a cold water cleaning tower that deodorizes the exhaust gas with a cooled cleaning liquid and makes the water vapor larger, and a wet electrostatic precipitator that collects oil mist attached to the water vapor from the exhaust gas together with the water vapor. An apparatus for preheating scrap using electric steelmaking furnace exhaust gas, which is characterized in that it is capable of removing bad odors and oil mist contained in preheated scrap exhaust gas.