JPS5810674B2 - Electric furnace equipment with preheating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio-controlled electric furnace (hereinafter referred to as electric furnace) equipment for metal melting with a preheating furnace.

Recently, electric furnaces for metal melting have been operated in a batch manner, and in order to improve energy efficiency, raw metal (hereinafter referred to as raw material scrap or scrap) is generated using the exhaust gas of the electric furnace. Often preheated.

To explain the configuration using an example of electric furnace equipment for steelmaking shown in FIG. The scrap is combusted by the heated air and the temperature rises, and the scrap is preheated in the preheater 3 (passing through the bypass 4 without being preheated depending on the work circumstances), cooled with water or air in the cooler 5, and then removed from the dust remover 6. The dust is removed by the fan, sucked in by the fan 7 (therefore, equipment upstream of the fan other than the electric furnace is kept at a negative pressure), and discharged from the staff 8.

(Upstream and downstream are defined by the flow of exhaust gas.

) On the other hand, the raw material scrap is charged into a preheating furnace, and when the prescribed preheating is completed in the preheating furnace, the preheating furnace is separated from the above system, and the raw material scrap is directly or transferred to a scrap bag and charged into an electric furnace. It recovers heat energy.

This type of electric furnace equipment is energy efficient because the electric furnace and scrap preheating furnace are operated in batches, and scrap is charged into the electric furnace multiple times for each electric furnace. is generally low, and various measures are required to improve it.

In order to charge scrap into the electric furnace, the electric current must be turned off, the earthen cover with the electrode attached must be removed, and the scrap must be loaded. Therefore, the temperature of the exhaust gas drops significantly as shown in Figure 2 (operation after initial loading, operation after additional equipment), and becomes lower than the temperature inside the preheating furnace, causing a situation where the preheating furnace is cooled in the opposite direction. .

As a countermeasure for this, for example, according to Utility Model Application Publication No. 55-26255, a thermal energy recovery route in which (a) a heat storage tower and a plurality of scrap preheating furnaces are connected in series is installed at the outlet of the electric furnace;
(b) A preheating device is disclosed that forms a bypass route for all of these and uses route (a) only when the exhaust gas temperature is high, but this device does not have the action of a heat storage tower beam generator. , acts as a thermal accumulator that averages the heat input and outputs the heat, reduces the average effective temperature difference as is clear from the second law of thermodynamics, and uses one series preheating furnace. Therefore, there is a drawback that if one preheater is stopped due to taking in or taking out scrap, all preheating devices will stop.

The present invention has been made to eliminate the above-mentioned drawbacks, and includes:
To be more specific, an electric preheating furnace with a preheating furnace that does not cause the cooling phenomenon described above, does not use a thermal accumulator, and has preheating furnaces installed in parallel, has a high heat recovery rate, and has a high operating rate. The purpose is to provide furnace equipment.

That is, the present invention uses a plurality of parallel preheaters that burns exhaust gas from an electric furnace as it is or with air supplemented, and then uses this exhaust gas to preheat raw metal to be melted in the electric furnace next time or after the next time. For each preheating furnace, the flow rate is adjusted by an automatic control valve that opens when the temperature of the exhaust gas flowing into the preheating furnace is higher than the preset temperature set for that preheating furnace, and closes when it is lower than the temperature set in advance for that preheating furnace. This is electric furnace equipment with a preheating furnace in which when the automatic valve closes, the valve leading to the bypass opens and the exhaust gas flows through the bypass.

The above-described set temperature may be a fixed value or may be a temperature that changes over time, such as the temperature at a specific location in the preheating furnace.

The above configuration clearly avoids cooling of the preheating furnace by exhaust gas.

Next, we will describe how the automatic control valve is used when one preheating furnace is used (FIG. 3), and then we will explain the case where a plurality of parallel preheating furnaces are used (FIG. 4).

Figure 3 is a process diagram illustrating the case where continuous loading is performed once and only the first loading scrap is preheated in a preheating furnace. In the example, the bypass 4 is used only when there is a malfunction in the preheating furnace or when there is a particular need to stop the preheater. Detect the temperature at the position shown in the figure and compare it with the preset set temperature. If the detected temperature is lower than the set temperature, the exhaust gas will flow to bypass 4, and if it is higher, it will flow only to preheating furnace 3. Adjust.

As mentioned above, the set value does not necessarily have to be a fixed value, and may be, for example, the furnace wall temperature at a specific position within the preheating furnace.

In addition, until the electric furnace is stopped for reloading after paddy bags, the second
As is clear from the figure, in normal operation, the temperature of the exhaust gas does not fall below the temperature of the preheating furnace, so the automatic switching valve 9 may be operated after the electric furnace 1 is restarted after being connected.

The so-called on-off control method is sufficient, the valve is a three-way butterfly valve, and the operating method is a fluid cylinder and rack-and-pinion type transmission mechanism, which is inexpensive.

The process diagram shown in Figure 3 shows the case where one preheating furnace is used, and when the electric furnace is in operation and the preheating furnace is stopped, high-temperature exhaust gas is sent to the cooler 5, so it is cooled. You cannot reduce the capacity of a vessel.

Therefore, in the present invention, a plurality of preheating furnaces are used in parallel, and an example thereof will be shown below.

FIG. 4 is a process diagram illustrating the case where both the paddy bag scrap and the continuous scrap are preheated in one continuous loading process, in which two preheating furnaces are used for one electric furnace.

The preheating furnaces 3 and 3' process approximately the same amount of scrap during the entire operating time of the electric furnace 1, but the preheating furnace 3 is used for paddy bagging in the electric furnace 1, and is used for discharging and charging scrap at the time of paddy bagging. On the other hand, A3' is used for continuous loading, and is discharged and charged during continuous loading.

The control valves 11 and 12 are fully closed when the temperature detected by the temperature detector 10 is lower than the set temperature, and are fully closed when the temperature is higher than the set temperature.
The two-way switching control valve 9 allows exhaust gas to flow through the bypass 4 when both control valves 11 and 12 are fully closed, and when exhaust gas is flowing through either or both of the preheating furnaces 3 and 3'. It's made to look like it's closed.

As with the embodiment of FIG. 3, the control valves 11, 12 may be of the on-off type, and butterfly valves operated by fluid cylinders are commonly used.

In the case of one continuous loading, other modifications can be considered, such as increasing the number of preheating furnaces and preheating over multiple times. Furthermore, if the number of consecutive loadings becomes two or more times, the number of preheating furnaces and charging for each time may be considered. Various combinations are possible depending on whether or not the scrap is preheated, but for all of these variations,
If the set temperature determined for each preheating furnace is higher than the detected temperature, an operation method can be applied in which the control valve is fully closed and exhaust gas is allowed to flow through the bypass only when no exhaust gas flows to any of the preheating furnaces. .

If the exhaust gas does not flow to all the preheating furnaces, the detected temperature is low, and if the detected temperature is low, the amount of exhaust gas produced is small. Even if the exhaust gas flows only through the cooler 5, it does not place a large load on the cooler 5 and the downstream packing equipment.

Using preheating furnaces in parallel generally reduces pressure loss, and using multiple preheating furnaces increases energy recovery.

Since the present invention is equipped with the above-mentioned configuration, the preheating furnace is not cooled by low-temperature exhaust gas as described above, resulting in high thermal energy efficiency.

Furthermore, since the bypass is used when the amount of exhaust gas generated per hour is small, the equipment cost does not increase.

[Brief explanation of the drawing]

Figure 1 is a process diagram of an example of conventional electric furnace equipment for steelmaking with a preheating furnace, Figure 2 is a relationship diagram illustrating changes in exhaust gas temperature over time, and Figure 3 is a process diagram for the case of one preheating furnace. 4 are process diagrams of an embodiment of the present invention in the case of two preheating furnaces. 1... Electric furnace, 2... Electric furnace outlet conduit, 3, 3'... Preheating furnace, 4... Bypass, 5...・Cooler, 6... Dust remover, 1
...Exhaust fan, 8...Stack, 9...
... Automatic switching valve, 10 ... Temperature detector, 1
1, 12... Control valve.

Claims (1)

[Claims] 1. A parallel method in which the exhaust gas generated when raw metal is melted in an electric furnace is burned as is or with air added, and then the exhaust gas is used to preheat the raw material metal to be melted in the electric furnace next time or in subsequent times. An automatic control valve having a plurality of preheating furnaces, and for each of the preheating furnaces, opens when the temperature of the exhaust gas that should flow into the preheating furnace is higher than a preset temperature for the furnace, and closes when the temperature is lower than a preset temperature for the furnace. Electric furnace equipment with a preheating furnace where the flow rate is adjusted by the preheating furnace, and when the automatic control valves of all preheating furnaces are closed, the valve leading to the bypass opens and the exhaust gas flows through the bypass.