JPS6219688A - Method and device for treating previously preheated gas of scrap for electric steel-making furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for processing preheated gas from scrap for electric steelmaking furnaces, and more specifically, to a complete deodorization of malodorous exhaust gas generated by preheating scrap. The aim is to achieve a pollution-free treatment of cleaning waste liquid containing high concentrations of odorous substances and water collected by dust collectors containing oil mist, thereby completing a closed-circuit type treatment system for the scrap preheating device. This is an electric t! ! It is used in the field of reducing melting power consumption and steelmaking time in steel furnaces.

[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. By using this exhaust gas to preheat the scrap charged into the electric steelmaking furnace, it is possible to save the melting power and shorten the steelmaking time in the electric steelmaking furnace. However, scrap often has oil, paint, rubber, plastic, etc. attached to or mixed with it. On the other hand, while flowing through the preheater containing the scraps, the temperature of the waste gas exchanged with the scraps decreases to about 100 to 300°C. For this purpose, the above-mentioned organic substances mixed in the scrap are thermally decomposed 6
It becomes difficult to maintain a temperature of 50 to 700°C, and the scrap preheated gas has a bad odor.

Steel manufacturing equipment including a scrap preheating device as shown in FIG. 3 is used to remove bad odors from the preheated gas and prevent pollution of the atmosphere and environment. This is electricity 1i
! ! The high-temperature exhaust gas 2 containing a large amount of dust discharged from the steel furnace 1 is guided to the combustion tower 3, and after combusting combustible substances such as CO gas contained in the exhaust gas, the exhaust gas is passed through the preheater 5a or 5b, and the scrap 6 to be charged into the electric steel making furnace 1 is preheated by the heat energy possessed by the exhaust gas. The preheated gas 16 is returned to the gas supply box 53 provided in the exhaust gas duct 7 from the circulation duct 52 by the induction fan 51, and is returned to the electric steel making furnace 1.
It is mixed with high-temperature exhaust gas 2 discharged from. combustion tower 3
Then, the odor components in the preheated gas 16 are burned together with the combustibles, and the preheated gas is deodorized.

However, the exhaust gas from an electric steelmaking furnace fluctuates greatly during operation, as shown in FIG. In the initial molten state after scrap is charged, the temperature does not generally rise, and when the temperature rises to a certain extent, scrap is continuously loaded, so outside air mixes in and the exhaust gas temperature decreases. The exhaust gas temperature rises after the re-coupling, but decreases again during the re-coupling, and after the re-coupling, the highest exhaust gas temperature, which depends on the melting temperature, is discharged from the electric steelmaking furnace. In such a one-cycle operation, the temperature of the exhaust gas varies greatly in the range of 400 to 1200°C. When the exhaust gas temperature is low, the temperature inside the combustion tower is also low.
Temperatures above 650°C, which can be thermally decomposed to deodorize the preheated gas, are not maintained. Therefore, an extremely unpleasant odor is directly emitted into the atmosphere, and there is a problem in that it is impossible to preheat the scrap when the exhaust gas temperature is low.

In addition, regardless of the amount of odorous substances contained in the preheated gas, the entire amount of the preheated gas undergoes gas heat exchange with the exhaust gas in the combustion tower, so the thermal energy held by the exhaust gas is rapidly dissipated, resulting in combustion. The temperature of the exhaust gas inside the tower will drop significantly. Moreover, since a considerable amount of the exhaust gas in the combustion tower is again introduced into the scrap preheater, preheating of the scrap is also insufficient. Therefore, the thermal energy possessed by the electric steelmaking furnace exhaust gas cannot be utilized to the maximum extent for preheating the scrap.

Incidentally, it has been conventionally believed that the bad odor contained in the preheated gas of scrap could not be removed unless it was combusted, for example, in a combustion tower. However, the present applicant reported in Japanese Patent Application No. 152300/1983 that the extremely unpleasant odor in the preheated gas is caused by common odorous substances outside of oil removal and cutting/lubricating oil contained in dry powder. It has been mentioned that this is caused by the evaporated oil mist, and that they have a synergistic effect that mutually enhances the odor. Based on this knowledge, in order to deodorize preheated gas, while using a cleaning solution to chemically remove odorous substances, the preheated gas is accompanied by saturated steam generated from the cleaning solution, which creates oil mist that is difficult to capture on its own. We have proposed a device that collects oil mist by attaching it to vapor particles and capturing the easily charged vapor particles using the electrostatic effect.

This device has the revolutionary effect of being able to deodorize preheated gas even when the temperature of the exhaust gas discharged from an electric steelmaking furnace is low. On the other hand, the amount of cleaning fluid used to remove odorous substances and the collected water containing oil mist is not noticeable, and since it is in liquid form with no risk of dispersing into the atmosphere, the steelmaking water discharged from the electric steelmaking furnace is It can be disposed of by hanging it on slag at a slag disposal site. However, like slag, if there is no place to dispose of it, it must be disposed of separately. For example, when one ton of scrap is preheated, about 101 tons of the above-mentioned waste water is generated, but since the cleaning liquid is used repeatedly, the C
OD is extremely high at 3000-4000. If this water is further treated, equipment costs and operating costs will rise, making the scrap preheating device itself impractical.

[Purpose 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 thermal energy of electric steelmaking furnace exhaust gas to the maximum extent possible for preheating scrap, to deodorize the preheated scrap gas, and to The wastewater generated for deodorization is incinerated in a scrap preheating device, and a completely closed circuit prevents air and environmental pollution. ! An object of the present invention is to provide a method and device for processing preheated gas from scrap for electric steelmaking furnaces, which can make exhaust gas and wastewater discharged from steel equipment non-polluting.

[Structure of the invention]

To explain the features of the present invention, in the invention of the method, cleaning waste liquid containing odor substances and collected water containing oil mist are constantly heated with a constant amount of electric steel furnace exhaust gas to evaporate them. The odorous substances and oil mist produced by the steel mill are incinerated using the exhaust gas from the electric steelmaking furnace that was previously used for preheating the scrap.

Further, the invention of the device will be explained based on the drawing shown in FIG. 1. The device includes an exhaust gas cleaning tower 19 that adds saturated steam to the preheated gas 16 with a foul odor discharged from the scrap preheater 5 and removes odor substances. , a scrap preheated gas processing device equipped with a wet electrostatic precipitator 24 that collects oil mist together with steam particles, an evaporation tower 33 into which a certain amount of electric steelmaking furnace exhaust gas 34 is introduced is installed, and the evaporation tower 33 is installed. An introduction pipe 36 supplies the washing waste liquid 2LA containing odor substances discharged from the exhaust gas washing tower 19 and collected water 29A containing oil mist collected by the wet electrostatic precipitator 24 to the tower, and The present invention is equipped with a derivation duct 41 for deriving oil mist and odor substances evaporated by heat from the evaporation tower 33 to the exhaust gas duct 7 or the combustion tower 3.

〔Example〕

The present invention will be described in detail below based on examples thereof.

FIG. 1 is an overall system diagram of electric steelmaking equipment including a preheating device A capable of preheating scrap with electric steelmaking furnace exhaust gas and a preheated gas processing device B of the present invention.

In this equipment, high-temperature exhaust gas 2 containing dust generated during the operation of an electric steelmaking furnace 1 is introduced into a combustion tower 3, where combustibles in the exhaust gas are combusted, and then all or part of the exhaust gas 4 is The waste gas is led out to a scrap preheater 5, and the scrap 6 to be charged into the electric steel making furnace 1 is preheated by the thermal energy of the exhaust gas.

An electric steelmaking furnace 1 for refining scrap has a gas discharge port on its furnace wall, etc., and is connected to an exhaust gas duct 7 for discharging electric steelmaking furnace exhaust gas 2, to which a gap adjustment ring 8 and a combustion tower 3 are sequentially connected. It is connected. Gap adjustment ring 8
In this case, an appropriate amount of outside air 9 is sucked in, and it is supplied to the combustion tower 3 together with the electric steelmaking furnace exhaust gas 2. The combustion tower 3 is capable of burning combustible substances such as CO gas by mixing the exhaust gas 2 and the outside air 9 and by spontaneous ignition, and is also capable of removing coarse dust, such as a cyclone type combustion tower. The structure is as follows. At the upper part of such a combustion tower 3, there is a dust remover 1, which will be described later, which collects some or all of the exhaust gas after combustion.
A main duct 10 leading directly to 7 and a scrap preheater 5
An auxiliary duct 11 leading out to the duct is connected via a switching valve 12.

For example, a plurality of preheaters 5a to 5C arranged in parallel are connected to the sub duct 11 via switching valves 13a to 13c and 14a to 14c provided before and after each preheater. In addition, booster fans 15a to 15c are provided for introducing exhaust gas to each preheater 5a to 5C, respectively.
Preheated gas 16 containing odorous substances and oil mist and having a bad odor is led to the main duct 10 described above.

A dry dust remover 17, such as a bag filter, is installed downstream of the main duct 10 into which the preheated gas 16 is introduced, for removing dust from the exhaust gas 4 and/or the scrap preheated gas 16 from the combustion tower 3.

Immediately after that, an induction fan 18 is provided that sucks the exhaust gas in the main duct 10 into the dust remover 17 and leads it out to the preheated gas processing device B. The processing bag WB is used for the exhaust gas cleaning tower 19, wet electrostatic precipitator 24, and evaporation tower 3 described below.
Consists of 3.

The exhaust gas cleaning tower 19 lowers the temperature of the exhaust gas 20 to equalize the temperature, and at the same time removes odor substances from the exhaust gas,
Moreover, a large amount of saturated steam is generated by the heat possessed by the gas. In other words, even if the temperature of the electric steelmaking furnace exhaust gas 2 fluctuates as shown in FIG. lower the temperature.

At this time, saturated steam at the exhaust gas temperature is generated from the cleaning liquid 21, and oil mist in the exhaust gas adheres to the steam particles. At the same time, a cleaning liquid 21 containing a neutralizing agent such as acids or alkalis, a solvent that has a strong affinity with odor substances, etc.
The exhaust gas 20 flowing inside is cleaned. Note that the temperature of the exhaust gas is detected by a temperature sensor 22 or the like, and the amount of cleaning liquid adjusted in response to the temperature signal is sprayed from the water sprinkler 23.

The wet electrostatic precipitator 24 has a function of collecting fine oil mist adhering to saturated steam contained in the exhaust gas 25 together with steam particles. This consists of a discharge electrode 26 and a dust collecting electrode 27, and generates positive and negative ions in the close vicinity of the discharge electrode 26 by corona discharge. When the negative ions move toward the cylindrical inner circumferential surface of the dust collection electrode 27, the vapor particles to which the oil mist is attached are negatively charged, and the vapor particles are attracted to the dust collection electrode 27 by the electric force, and are isolated. It is designed to collect fine oil mist, which is difficult to capture, along with vapor particles.

The above-mentioned exhaust gas cleaning tower 19 and wet electrostatic precipitator 24 are provided with a pump 28 for circulating cleaning liquid 21 and a pump 30 for supplying cleaning water 29 for rinsing off the surface of the dust collection electrode 27, as well as a cleaning waste liquid to be disposed of. 21A and collected water 29
Pumps 31 and 32 are installed to send A to an evaporation tower 33.

The evaporation tower 33 evaporates the cleaning waste liquid 21A containing odorous substances and the collected water 29A containing oil mist, and leads the vapor of the odorous substances and oil mist into the electric steelmaking furnace exhaust gas upstream of the scrap preheater 5. It is.

That is, the evaporation tower 33 is connected to a gas duct 35 near its bottom that always introduces a certain amount of electric steelmaking furnace exhaust gas 34 during operation. An introduction pipe 36 for introducing the cleaning waste liquid 21A and the collected water 29A discharged from the wet electrostatic precipitator 24 is connected to the water sprinkler 37 at the top. The gas duct 35 is connected to the above-mentioned sub-duct 11 via a flow rate adjustment valve 38, and the introduction pipe 36 has a flow rate adjustment tank 39 midway therein to keep the introduced flow rate constant. The discharge amount of the pumps 31 and 32 is adjusted according to the detected liquid level height. At the top of such an evaporation tower 33, electricity is
i! ! An outlet duct 41 is connected to the exhaust gas duct 7 in order to introduce the 61 furnace exhaust gas 34, cleaning waste liquid, oil mist, and steam of odor substances evaporated by the heat of the exhaust gas into the combustion tower 3.

Note that this outlet duct 41 is provided with an induction fan 42 and a switching valve 43.

In the steelmaking equipment having such a configuration, the scrap 6 is preheated in the following manner, and the milk odor of the preheated exhaust gas 16 and the cleaning waste liquid 21A and collected water 29A generated accordingly are treated.

First, scrap 6 preheated in the scrap preheater 5 is charged into the electric steel making furnace 1, and the scrap 6 is melted. In such refining, as shown in FIG. 2, scraps are sequentially loaded and the melting temperature is raised. Meanwhile, high-temperature electricity containing a large amount of dust is flowing from the electric steelmaking furnace 1!
i! ! The steel furnace exhaust gas 2 is led out to the exhaust gas duct 7, and with the outside air 9 introduced through the gap adjustment ring 8, CO gas, which is a combustible substance, is burned in the combustion tower 3, and coarse dust 44 is is removed. If preheating of the scrap 6 is not required now, the switching valve 12 is switched so that all of the exhaust gas 4 is led out to the main duct 10. Exhaust gas from the combustion tower 3 is introduced into the dust remover 17 by the induction fan 18, where a predetermined amount of dust is collected, and then released into the atmosphere from the switching valve 45 via the diffusion tower 46. This is because the electric steelmaking furnace exhaust gas 2 is completely combusted in the combustion tower 3, so unlike the preheated exhaust gas 16 after preheating the scrap 6, it is not accompanied by a bad odor.

When the scrap 6 is to be preheated by the thermal energy contained in the exhaust gas 2 during operation of the electric steelmaking furnace 1, the opening degree of the switching valve 12 is changed and the switching valves 13a, 14a, etc. are opened. When a booster fan 15a installed downstream of a preheater 5a containing scraps such as dry powder, pig iron, rolling scraps, and iron scraps is driven, the suction force from the combustion tower 3 to the subduct 11 is equivalent to that of the booster fan 15a. The remaining exhaust gas is led out directly to the dust remover 17 via the main duct 10. The exhaust gas discharged for direct dust removal in this way is accompanied by a foul odor caused by the temperature being lowered by preheating the scrap to 100-300℃.
The preheated exhaust gases 16 are combined in the main duct 10, and the dust is removed by a dust remover 17. Since this exhaust gas has an extremely disgusting odor, it must be immediately removed from the diffuser tower.
6, the switching valve 45 is switched and the gas is introduced into the exhaust gas cleaning tower 19. Among them, exhaust gas 20
A water sprinkler 23 sprays two cleaning liquids in an amount adjusted according to temperature fluctuations. As shown in Figure 2, dust-containing high-temperature exhaust gas 2
Even if the temperature of the exhaust gas 20 fluctuates, the temperature of the exhaust gas 20 is lowered to, for example, 80° C., which is suitable for containing saturated steam, while the cleaning liquid 21 is also maintained at a temperature and concentration suitable for removing odor substances. Therefore, chemical removal of odorous substances is performed under certain conditions using a neutralizing agent or the like in the cleaning liquid 21. Moreover,
The heat given by the exhaust gas 20 and the heat received by the cleaning liquid balance their temperatures, and the moisture in the cleaning liquid 21 evaporates to generate approximately constant saturated steam. The oil mist cannot be removed by the cleaning liquid 21, but adheres to the generated vapor particles. The exhaust gas 25 from which odorous substances have been removed is introduced into the wet electrostatic precipitator 24 together with vapor particles. In an electric precipitator, the dust collecting electrode 27
A negative high voltage is applied to the discharge electrode 26 while it is grounded,
A strong electric field is formed around the discharge electrode, generating a corona discharge. The pole of the discharge electrode 26 (positive and negative ions are generated in the vicinity, the positive ions are immediately neutralized by the negative discharge electrode 26,
The negative ions negatively charge the vapor particles while moving in the electric field toward the dust collecting electrode 27, and the oil mist is collected together with the vapor particles at the dust collecting electrode 27. The purified exhaust gas is released into the atmosphere from the diffusion tower 46. Note that if all of the exhaust gas 4 passing through the switching valve 12 located downstream of the combustion tower 3 is introduced into the scrap preheater 5, most of the thermal energy possessed by the exhaust gas 2 can be used to preheat the scrap 6. Needless to say, it can be done.

Since the cleaning liquid 21 is repeatedly used in the exhaust gas cleaning tower 19, a large amount of odor substances are taken into the liquid.

Some solidify due to chemical changes, while others remain liquid. The cleaning waste liquid 21A containing such odorous substances at a high concentration has a high COO and cannot be directly disposed of in rivers or sewers. On the other hand, the collected water discharged from the wet electrostatic precipitator 24 contains a large amount of oil mist.
Similarly, it cannot be disposed of.

These waste waters are each delivered to the inlet pipe 36 by pumps 31, 32. The amount of waste water 47 supplied to the evaporation tower 33 is adjusted by a flow rate adjustment tank 39, and the waste water 47 is sprayed from a water sprinkler 37. A constant amount of electric steelmaking furnace exhaust gas 34 is always introduced from below the evaporation tower 33, and steam 48 is generated by direct contact between the rising exhaust gas and the sprayed waste water.

This includes not only water vapor generated from water such as cleaning waste, but also vapors from odorous substances and oil mist.

These vapors cause bad odors, but the amount of generated vapor varies depending on the temperature of the electric steelmaking furnace exhaust gas 34 whose supply amount is constant. In other words, when the temperature of the electric steelmaking furnace exhaust gas 2 is low, the amount of steam generated is small (and when the temperature is high, the amount of steam generated naturally increases. Therefore, in one cycle of operation, the temperature of the exhaust gas 2 fluctuates as shown in Figure 2). However, the amount of steam generated is automatically determined by the exhaust gas temperature at that time.The steam generated in this way is
Directly or indirectly from the outlet duct 41 to the combustion tower 3
will be introduced in The temperature of the electric steelmaking furnace exhaust gas in the combustion tower 3 also fluctuates as shown in Figure 2, but the amount of steam introduced into the combustion tower 3 also increases or decreases in proportion to the temperature inside the combustion tower 3, so that odor substances etc. There is no shortage of heat when incinerating steam.

Note that the amount of steam introduced into the combustion tower 3 is determined by the amount of steam introduced into the combustion tower 3.
The air volume ratio in the steam/gas heat exchange is much smaller than that in the gas/gas heat exchange described in the prior art section. Therefore, the energy of the exhaust gas in the combustion tower 3 consumed for deodorization can be extremely small.
The temperature of the exhaust gas led to the scrap preheater 5 is noticeable.
It will not decrease.

By the way, an 801-inch steelmaking furnace emits 10 million Kcal of exhaust gas heat in one cycle. On the other hand, 800 kg of waste water is discharged from the exhaust gas cleaning tower 19 and the like, and approximately 400,000 Kcal of heat is required to evaporate this waste water. However, this value is 4% of the total heat value of exhaust gas.
Therefore, it is sufficient to supply 4% of the exhaust gas in the combustion tower 3 to the evaporation tower 33 via the switching valve 38. That is, it can be said that the amount of thermal energy consumed in the evaporation tower 33 is sufficiently negligible.

〔Effect of the invention〕

As can be seen from the detailed description of the embodiments above, the present invention provides an evaporation tower into which electric steelmaking furnace exhaust gas is introduced, and an introduction pipe that supplies cleaning waste liquid containing odorous substances and collected water containing oil mist. and a discharge duct that leads the evaporated oil mist and odorous substances upstream of the scrap preheater, so that the cleaning waste liquid containing a high concentration of odorous substances and the collected water containing a large amount of oil mist are kept constant at all times. It can be heated with a certain amount of electric steelmaking furnace exhaust gas, generate an amount of odor substances and oil mist vapor according to the fluctuating temperature of the exhaust gas, and then incinerate it with the electric steelmaking furnace exhaust gas. Therefore, the scrap preheated gas is deodorized and
In addition, cleaning waste liquid and collected water generated for deodorization are treated in a fully closed circuit of the scrap preheating device, preventing air and environmental pollution and reducing exhaust gas and wastewater discharged from electric steel manufacturing equipment. Pollution-free can be achieved.

[Brief explanation of the drawing]

Fig. 1 is an overall system diagram of electric steel manufacturing equipment to which the present invention is applied, and Fig. 2 is an electric! i! ! Graph showing fluctuations in exhaust gas temperature with the passage of operating time in one cycle of a steel furnace, 3rd
The figure is a system diagram of an electric steelmaking facility including a prior art electric steelmaking furnace exhaust gas preheating device for scrap. 1-Electric steel-making furnace, 2--Electric steel-making furnace exhaust gas, 3...
Combustion tower, 5- Scrap preheater, 6- Scrap, 7
-Exhaust gas duct, 16.-Sub-heated gas, Engineering 9-Exhaust gas cleaning tower, 21A-Washing waste liquid, 24.-Wet type electrostatic precipitator,
29A--Collected water, 33-Evaporation tower, 34-Electric steel furnace exhaust gas, 36-Introduction pipe, 41--Output duct, B-Processing device.

Claims (2)

[Claims] (1) Thermal energy contained in the exhaust gas generated during the operation of an electric steelmaking furnace is used to preheat the scrap charged into the electric steelmaking furnace, and after the scrap is preheated, the cleaning liquid is added to the preheated gas with a foul odor. The preheated gas is cooled down to a predetermined temperature to be accompanied by saturated steam and odor substances are removed, while the fine oil mist floating in the exhaust gas is collected along with the steam particles by electrostatic action. In the method for processing preheated scrap gas, the cleaning waste liquid containing odorous substances and the collected water containing oil mist are always heated with a constant amount of electric steelmaking furnace exhaust gas, and the evaporated odorous substances and oil mist are preheated from the scrap. A method for preheated gas treatment of scrap for an electric steelmaking furnace, characterized in that the scrap is incinerated with exhaust gas from an electric steelmaking furnace used before. (2) Equipped with an exhaust gas cleaning tower that adds saturated steam to the preheated scrap gas with a foul odor discharged from the scrap preheater and removes odor substances, and a wet electrostatic precipitator that collects oil mist along with steam particles. In the processing equipment for preheated scrap gas, an evaporation tower is installed into which a certain amount of electric steelmaking furnace exhaust gas is introduced, and the evaporation tower collects cleaning waste liquid containing odorous substances discharged from the exhaust gas cleaning tower and is collected by a wet electrostatic precipitator. An introduction pipe that supplies collected water containing collected oil mist, and an outlet duct that leads oil mist and odor substances evaporated by the heat of electric steel furnace exhaust gas from the evaporation tower to the exhaust gas duct or the combustion tower. A preheated gas processing device for electric steelmaking furnace scrap, characterized by: