JPH11325750A - Apparatus for cooling exhaust gas from arc furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive prevention of generation of polychlorinated-dibenzo-dioxins by operation of an arc furnace, elimination of inflow of exhaust gas into a bag filter with a temperature more than a heat-resistance temperature thereof and inflow of the exhaust gas containing high water content and capability of constantly stable operation regardless of sudden variation of an exhaust gas temperature. SOLUTION: A cooling tower 4 is provided on an exhaust route 3 of exhaust gas emitted from an arc furnace 1 and provided with a plurality of spray nozzles 9a-9f. A specified cooling state of each operation state of the arc furnace 1 at a period of raw material charging, melting, refining or the like is determined preliminarily in a controller 7, and ejection of cooling water from each of the spray nozzles 9a-9f is allowed to be controlled by instructions from the controller 7 according to ongoing of an operation state of the arc furnace 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an arc furnace provided in a steel mill, a waste melting facility, and the like.
The present invention relates to an exhaust gas cooling device for preventing generation of dioxin.

[0002]

2. Description of the Related Art As is well known, arc furnaces are widely used for melting metal scrap or incinerated ash. By the way, in the exhaust gas discharged from the arc furnace,
Because it contains harmful substances and extremely toxic dioxin (generic term for isomers such as polychlorinated dibenzoparadioxin and polychlorinated dibenzofuran), a bag filter is conventionally installed in the exhaust gas discharge route to prevent diffusion into the atmosphere. Dioxin is collected along with dust.

FIG. 7 shows a change in temperature of exhaust gas in an exhaust gas discharge path of such a conventional arc furnace.
a is an arc furnace, b is an exhaust gas discharge path thereof, and c is a bag filter. Exhaust gas of 1200 ° C. or more is discharged from the arc furnace a during the melting period, and the temperature of the exhaust gas gradually decreases while passing through a scrap preheating device (not shown) or the like. The temperature becomes 250 ° C. or less, which is discharged to the atmosphere through the bag filter c.

However, when the temperature of the exhaust gas gradually decreases in the exhaust gas discharge path b, if the exhaust gas is exposed to a temperature range of 600 ° C. to 300 ° C. where dioxin is easily generated for a long time, dioxin is generated and the dioxin concentration becomes high. Thus, there is a problem that the dioxin concentration is high even after passing through the bag filter c.

[0005] Therefore, conventionally, by providing a cooling tower capable of rapidly cooling the exhaust gas by the heat of vaporization by water spray, the time during which the exhaust gas is in the above temperature range is as short as possible to suppress the generation of dioxin. Had been done.

[0006]

However, in general, in an arc furnace, the temperature of the discharged exhaust gas fluctuates greatly within a short period of time due to a change in operating conditions such as a material charging period, a melting period, and a refining period. Conventional cooling towers cannot cope with such temperature changes, and the exhaust gas containing a large amount of water flows into the bag filter due to excessive spraying, impairing its function, or it is insufficiently cooled and rapidly cooled to below the dioxin generation temperature range There was something I couldn't do. That is, in the conventional exhaust gas cooling device, the control of jetting the cooling water from the nozzle cannot follow a rapid change in the exhaust gas temperature, and there is a possibility that an excessive amount of water or insufficient cooling may occur. For this reason, there was a problem that dioxin was not sufficiently collected by the bag filter.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an exhaust gas cooling device capable of effectively preventing generation and diffusion of dioxin due to operation of an arc furnace. For this purpose, the exhaust gas cooling apparatus of the present invention is provided with a cooling tower in a discharge path of the exhaust gas discharged from the arc furnace, a plurality of spray nozzles provided in the cooling tower, and a controller in a material charging stage, a melting stage, a refining stage. The required cooling mode for each operation state of the arc furnace is set in advance, and the ejection of cooling water from the spray nozzle is controlled by a command from the control device according to the transition of the operation state of the arc furnace. It is characterized by the following. Further, the present invention is characterized in that in the above exhaust gas cooling device, the control device controls the number of spray nozzles for jetting cooling water. Further, the present invention is characterized in that in the above exhaust gas cooling device, the control device detects an operation state of the arc furnace from a change in electric power supplied to the arc furnace. Further, the present invention is characterized in that in the exhaust gas cooling device, the control device supplementarily controls the ejection of the cooling water from the spray nozzle by the exhaust gas temperature detected by the sensor provided at the exhaust gas outlet of the cooling tower. .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an exhaust gas treatment apparatus and a temperature transition of the exhaust gas. In FIG. 1, reference numeral 1 denotes an arc furnace in which electrodes are suspended in a furnace body; Reference numeral 4 denotes a cooling tower, and 5 denotes a bag filter. The arc furnace 1 is provided with a burner 12 for auxiliary heating, a lance for blowing oxygen,
A carbon charging device (not shown) and the like are provided.

As shown in FIG. 2, the cooling tower 4 is branched from a water supply source into a plurality of water supply pipes 6a to 6f.
Electromagnetic shut-off valves 8a to 8f are provided for a to 6f, and spray nozzles 9a to 9f are provided on the secondary sides of the respective shut-off valves.

The control device 7 is provided with a programmable setting device 13, which has a required cooling mode for each operating state of the arc furnace such as a material charging period, a melting period, a refining period, and a tapping period. It is set in advance.

FIG. 3 is a diagram showing the operating conditions of the arc furnace 1 and the temperature transition of the exhaust gas discharged at that time. In this arc furnace, material charging and melting are repeated twice, and then refining, tapping, and repair are performed, and a series of steps is completed in about 60 minutes in total. Then, as shown in the figure, the burner 12 is burned for auxiliary heating during the melting period, oxygen is blown into the furnace from the melting period to the refining period, and carbon is injected during the refining period. Further, the input power supplied through the electrodes fluctuates as illustrated. As can be seen from FIG. 3, the temperature of the exhaust gas discharged from the arc furnace generally fluctuates with the transition of the above-mentioned operation state. Generally, in the initial stage of melting, the arc, which is the largest heat source, is surrounded by the scrap, and the temperature of the exhaust gas is low because much of the heat from the arc is given to the scrap. When the melting proceeds and the arc is exposed on the scrap or the molten steel, the ratio of the heat generated by the arc to the scrap decreases and the ratio to the exhaust gas increases, so that the temperature of the exhaust gas increases.
Furthermore, the temperature of the exhaust gas rises due to the heat of combustion of the burner, the heat of oxidation due to the blowing of oxygen, and the heat of oxidation of the carbon due to the blowing of carbon. Therefore, the exhaust gas discharged from the arc furnace 1 has a temperature of 1200 ° C. or more during the refining period. Therefore,
It is possible to predict a sudden change in exhaust gas temperature depending on the operating conditions, and controlling the amount of cooling water from the spray nozzle according to changes in the operating conditions is very useful for improving the controllability of the spray, which tends to delay response. It is valid.

Thus, the setting device 13 of the control device 7 includes:
Cooling conditions such as the amount of cooling water necessary to constantly cool the exhaust gas having such a violently changing temperature to a predetermined temperature of 200 to 300 ° C. by passing through the cooling tower 4 are set in advance. FIG. 4 shows the amount of cooling water and the exhaust gas temperature at the outlet of the cooling tower 4 according to such settings.

Each of the shut-off valves 8a to 8f is opened / closed by a command from the control device 7, and the number of spray nozzles for jetting cooling water is controlled so that the cooling capacity of the cooling tower is always appropriate. Is controlled.

As shown in the timing chart of FIG. 5, the shutoff valves 8a to 8f are opened and closed a plurality of times within the time required for the exhaust gas to pass through the cooling tower (in this case, about 2 seconds). At T, the opening and closing are repeated at a high speed, and the ratio of the time T1 during which the shut-off valve is in the open state, that is, the open time ratio (T1 / T) varies as illustrated in (a) to (c) in the figure. By doing so, the jet of cooling water from each spray nozzle may be controlled. That is, a command signal for operating the open time ratio is output from the control device 7 to each of the shut-off valves 8a to 8f, and the open time ratio is increased as shown in FIG. By jetting the cooling water to increase the cooling capacity, or by decreasing the open time ratio as shown in (c), the amount of the cooling water jetted from each spray nozzle is reduced to lower the cooling capacity, and the exhaust gas outlet 10 The exhaust gas temperature in the above may be always kept in the range of 200 ° C to 300 ° C.

The exhaust gas thus discharged from the combustion tower 2 is cooled to 300 ° C. or less in a short time as shown in FIG. 4 by passing through the cooling tower 4, so that the generation of dioxin can be suppressed. it can. In addition, the response to a rapid change in the temperature of the exhaust gas due to the change in the operation state also becomes faster, and the temperature of the exhaust gas at the cooling tower outlet 10 is reduced by 200%.
It can be easily stabilized to a predetermined value of from 300C to 300C.

The bag filter 5 is formed by suspending a plurality of bag-shaped filters 14 formed by sewing filter cloths in a vertical house 13.
Exhaust gas cooled to a predetermined value of ° C. passes through the eyes of the filter, dust is collected on its inner surface, and purified exhaust gas is discharged from the upper part of the house 13 to the atmosphere.

In the cooling tower 4 shown in FIG. 6, two water supply pipes 15a and 15b are provided in a branched form from a water supply source, and each of the water supply pipes is fully opened or fully closed by an open / close command signal from a control device 7, respectively. Shut-off valves 8a and 8b and the control device 7
The flow control valves 16a and 16b whose opening is controlled by the opening command signal from the controller are provided, and the secondary side of each of the flow control valves is further branched into a plurality of branch pipes 6a to 6f, and spray nozzles 9a to 9 9f, and the same reference numerals as those in FIG. 2 denote the same components. In this case as well, the opening and closing of the shut-off valves 8a and 8b are controlled by the opening and closing command signal from the control device 7, so that a large temperature change can be quickly dealt with. In this case, the opening degree is controlled by the flow control valves 16a and 16b in an auxiliary manner, so that the exhaust gas temperature at the exhaust gas outlet 10 is always 200 ° C.
It can be maintained at a predetermined temperature of ~ 300 ° C.

It is to be noted that the required cooling mode for each operating state of the arc furnace 1 is set in advance in the control device 7, and that the control device 7 detects the current operating state of the arc furnace 1 from a change in the input power. Thus, it is also possible to set so that an appropriate command signal at that time is always output to the cooling tower. That is, since the amount of heat generated by the arc furnace can be known in advance by detecting a change in the input power, the controller 7 may set an appropriate amount of cooling water based on the value. Also, at this time, it may be set by the integrated electric energy input from the first melting period, or may be set by the integrated electric energy input within a certain fixed time.

A temperature measuring sensor (not shown) such as a thermocouple is provided at the exhaust gas outlet 10 of the cooling tower 4 and an exhaust gas temperature signal detected by the sensor is fed back to the control device 7 so that each of the spray nozzles The control accuracy can be complemented by controlling the jet of cooling water.

Although not shown in this embodiment,
It is, of course, possible to additionally provide the exhaust gas treatment apparatus with a device that adsorbs dioxin by adding an adsorbent such as activated carbon to the exhaust gas and collects the dioxin with a bag filter.

[0021]

As described above, the exhaust gas cooling device of the present invention has the following features.
The required cooling mode for each operating state of the arc furnace, such as a material charging period, a melting period, and a refining period, is set in advance in the control device, and the spray of cooling water from the spray nozzle follows the transition of the operating state of the arc furnace. Since it is controlled by the command from the control device, if the operation state changes, the cooling mode of the exhaust gas can be changed at the same time without delay, the cooling water amount is always appropriate, and the exhaust gas exceeding the heat resistant temperature is passed to the bag filter. There is a beneficial effect that the inflow or exhaust gas containing a large amount of water is prevented from flowing in, so that stable operation can be always performed and generation and diffusion of dioxin can be suppressed.

[Brief description of the drawings]

FIG. 1 is an exhaust gas discharge path diagram of an arc furnace showing an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a cooling tower shown in FIG. 1 and a cooling water piping system diagram thereof.

FIG. 3 is a diagram showing operating conditions of an arc furnace and changes in the temperature of exhaust gas.

FIG. 4 is a transition diagram of the operating state of the arc furnace according to the embodiment of the present invention.

FIG. 5 is a timing chart for opening and closing a shutoff valve according to the embodiment of the present invention.

FIG. 6 is a longitudinal sectional view showing another embodiment of the cooling tower of FIG. 2 and its cooling water piping system diagram.

FIG. 7 is an exhaust gas discharge path diagram of a conventional arc furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc furnace 2 Combustion tower 3 Discharge path 4 Cooling tower 5 Bag filter 6a-6f Water supply pipe 7 Control device 8a-8f Shutoff valve 9a-9f Spray nozzle 10 Exhaust gas outlet 13 Setting device

Claims (4)

[Claims] 1. A cooling tower is provided in a discharge path of exhaust gas discharged from an arc furnace, a plurality of spray nozzles are provided in the cooling tower, and a controller is provided with the arc furnace during a material charging period, a melting period, a refining period, and the like. The required cooling mode for each operating state is set in advance, and the ejection of cooling water from the spray nozzle is controlled by a command from the control device according to the transition of the operating state of the arc furnace. An exhaust gas cooling device for an arc furnace. 2. The exhaust gas cooling device for an arc furnace according to claim 1, wherein the control device controls the number of spray nozzles for jetting cooling water. 3. The exhaust gas cooling device for an arc furnace according to claim 1, wherein the control device detects an operation state of the arc furnace from a change in electric power supplied to the arc furnace. 4. The cooling device according to claim 1, wherein the controller controls the ejection of the cooling water from the spray nozzle based on the exhaust gas temperature detected by a sensor provided at an exhaust gas outlet of the cooling tower. An exhaust gas cooling device for an arc furnace according to claim 1.