JPS60248812A - Method and apparatus for melting scrap - Google Patents

Abstract

PURPOSE:To improve the basic unit of electric power by utilizing inexpensive pulverized coal as a source for heat energy besides electric power in common use and by properly combining them. CONSTITUTION:A pulverized coal burner is inserted in a hole for an electrode pierced in the cover of an arc furnace, and air is fed to the burner to heat scraps. After heating the scraps to 500-600 deg.C, oxygen is fed in place of air to heat the scraps to 1,200-1,400 deg.C, and the burner is removed from the hole. An electrode is then inserted in the hole to carry out arc heating.

Description

[Detailed description of the invention]

Purpose of invention

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to a method for melting scrap, and also includes an apparatus for carrying out the method. [Prior Art] In the production of special steel, which is mainly carried out in an arc furnace,
Using electricity to melt the scrap material, which is the preparatory step, is disadvantageous from a cost standpoint, and it is desirable to replace at least a portion of the operating power with a heat source. As one specific measure, preheating of the charging material was previously carried out using a heavy oil burner, but since oxygen is used to obtain a high temperature, oxidation of Fe is unavoidable and the yield is reduced. Conventional burners have disadvantages in that the flame shape is inappropriate (it does not spread enough and takes too long), and only local heating occurs, which causes sagging of the charged material and makes work difficult. In addition, the cost advantage has diminished due to soaring oil prices. The present inventors selected coal-based fuel as a fuel that is generally cheaper than petroleum-based fuel and can be expected to be supplied stably, and researched the use of pulverized coal burners. As a result, the scrap melting method disclosed earlier (Japanese Patent Application No. 58-88287) first heats the scrap with a pulverized coal burner, and while the scrap is at a low temperature, air is supplied to burn the pulverized coal. A certain degree of high temperature (e.g. 500℃)
When this temperature is reached, the flame temperature is increased by supplying oxygen to cause combustion, and then the stage of melting and capping is carried out by arc heating. This is based on the consideration of keeping thermal efficiency high at all times. The present inventors have also invented and already proposed a burner having a structure that meets this purpose (Japanese Patent Application No. 194423/1982). In the above melting method, as the melting process progresses, it is necessary to replace the burner and the furnace cover equipped with the electrodes. This process takes several minutes to several hours in actual equipment, and a considerable amount of heat is dissipated during that time, and the heat carried away by the furnace lid cannot be ignored, so I would like to avoid doing it if possible.

Problem 1 to be Solved by the Invention The purpose of the present invention is to eliminate the need to replace the furnace cover equipped with burners and electrodes, and reduce heat loss in scrap melting, which reduces energy costs by adopting a pulverized coal burner. The objective is to provide an operating method that minimizes the Another object of the invention is to provide a device for implementing the above method. Structure of the Invention [Means for Solving Problems 1] The scrap melting method of the present invention heats the scrap put into the furnace by inserting a pulverized coal burner into an electrode hole provided in the furnace lid of an arc furnace. When the temperature of the melt reaches a high temperature, the burner is removed, an electrode is inserted in its place, and arc heating is performed to achieve melting. The apparatus for carrying out the above scrap melting method is -
The furnace lid of the arc furnace has a height sufficient to provide the combustion space necessary for flame formation of the pulverized coal burner, and the pulverized coal burner can be inserted into the electrode and electrode hole, and the burner and electrode are installed alternately in the electrode hole. It is characterized by having the means to do so. [Function] As shown in Figure 1, the above-mentioned arc furnace, in which the furnace lid has a height sufficient to provide the combustion space necessary for the flame formation of the pulverized coal burner, has a lid that is slightly deeper than the conventional arc furnace. In addition, although the shape is raised, there is no need to substantially increase the length of the electrode used. The improved pulverized coal burner proposed by the present inventors (Japanese Patent Application No. 58-194423) is extremely suitable for this application. As shown in Figure 1A, when the temperature of the charged scrap increases due to heating by the pulverized coal burner, the burner is stopped, the scrap is removed from the electrode hole, and the electrode is inserted as shown in Figure 1B to create an arc. Apply heat to melt the scrap.
During this time, there is no need to replace the large and heavy furnace lid, just the burners and electrodes, so the downtime for heating is very short. Furthermore, if the lid is not opened, there is no loss of heat due to heat radiation inside the furnace, and there is no heat loss due to replacement of the furnace lid. [Embodiment] It is appropriate to switch from pulverized coal burner heating to arc heating when the average temperature of the scrap in the furnace, that is, the average temperature of the entire molten metal and unmelted material, reaches 1200 to 1400°C. be. In a temperature range higher than this, heating by a burner is less efficient. In actual operation,
This temperature is normally reached when approximately 60-80% of the charge in the furnace has been melted by volume. Heating with a burner can also be carried out with a switch from air to oxygen, as proposed by Sagi. In other words, when the scrap is low, air is supplied to the pulverized coal burner to burn it, and once the temperature reaches 500°C to 600°C, oxygen is supplied to burn it, raising the temperature of the flame and increasing thermal efficiency. That's why. Since the exhaust gas from scrap heating has a high temperature, it is desirable to lead it to a preheater and use it to preheat the cold scrap to be charged into the furnace. Including the adoption of these techniques, one of the preferred embodiments of the present invention is to use burners and electrodes interchangeably for two furnaces of the same type. In this method, scrap is charged into one of the two furnaces and heated with a pulverized coal burner, and when the temperature of the scrap rises, an electrode is inserted in place of the burner to switch to arc heating. The scrap is transferred to the other furnace and heated. Once the scrap in one furnace has melted, it is tapped and new scrap is charged and heated with a pulverized coal burner. During this time, an electrode is placed in the other furnace. Insert the metal, switch to arc heating, and repeat the process of melting the scrap. To explain with reference to the drawings, initially, as shown in FIG. 3, scrap is charged into one furnace A and heated with a pulverized coal burner. Next, as shown in (2), an electrode is placed in the furnace △ and the scrap is arc heated to raise the temperature. Meanwhile, the pulverized coal barb is transferred to the other furnace B and the charged scrap is heated. After the scrap in furnace A is melted by arc heating, tap the metal as shown in (■). Furnace B continues heating with its burner. Next, scrap is charged again into the empty furnace A, an electrode is inserted into the furnace B, and arc heating begins. While the scrap in furnace A is heated again by the pulverized coal burner, the arc heating of the scrap in furnace B continues. Once the contents of Furnace B have been melted, tap the metal as shown in Vl and reload the scrap into Furnace B as shown in Vl. The electrodes are moved to furnace A and arc heating is started, and furnace B is heated using a pulverized coal burner. In this way, we reach the stage ■,
After that, repeat ■ → VI [. Whether one furnace or two furnaces are used, the high-temperature exhaust gas from the furnace is preferably used to preheat the scrap to be charged and the scrap to be loaded in parallel. In an experimental reactor with a capacity of 2 tons, the ratio of initial loading: double loading - 6:4,
Total 2. /1. t-ton scrap is charged, and the pulverized coal burner (air supply) is preheated and arc heated (Fig. 1).
It was melted by the relay to Figure 2). As disclosed earlier,
The specifications compared with the melting method in which a set of pulverized coal burner and electrodes each attached to a dedicated furnace cover are replaced are shown below. Conventional method Inventive pulverized coal burner thermal efficiency (%) 36 46 Power unit (KW/ch, t) 634' 592 Cycle time (min) 147 131 Effects of the invention By using low-source pulverized coal as a thermal energy source, combining the two appropriately, and minimizing the heat loss associated with switching, the C1 power consumption rate is improved and the thermal efficiency of the pulverized coal burner is maintained at a high level. At the same time, cycle time can be shortened.

[Brief explanation of drawings]

1 and 2 are longitudinal cross-sectional views of an apparatus for explaining the scrap melting method of the present invention.
The figure shows the stage of heating with a pulverized coal burner.
FIG. 2 shows the stages of arc heating. FIG. 3 is a conceptual sectional view for explaining a preferred embodiment of the scrap melting method of the present invention, where ■ indicates star 1 to hour, ■, ■, IV, ■, ■, and ■ ,
The steps are shown in order during regular operation. Patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga No. 3 1 ■ A 8 A B A B ◇ ■ ■

Claims (7)

[Claims] (1) A pulverized coal burner is inserted into the electrode hole in the furnace lid of an arc furnace to heat the scrap inside the furnace, and when the temperature of the scrap rises, the burner is removed and an electrode is inserted in its place to start the arc. A scrap melting method characterized by heating and covering. (2) Average temperature of scrap is 1200-1400℃
2. The melting method according to claim 1, wherein the above-mentioned burner heating is switched to arc heating when the melting method is reached. (3) The melting method according to claim 1, wherein air is supplied to a pulverized coal burner for combustion until the average temperature of the scrap reaches 500 to 600°C, and thereafter oxygen is supplied for combustion. (4) Two furnaces are used, and scrap is charged into one furnace and heated by the pulverized coal burner, and when the temperature of the scrap rises, an electrode is inserted in place of the burner to switch to arc heating. During that time, the burner is transferred to the other furnace to heat the scrap, and once the scrap in one furnace is melted, it is tapped and new scrap is charged and heated by the pulverized coal burner.
2. The melting method according to claim 1, in which the process of repeatedly inserting an electrode into the other furnace and switching to arc heating to melt the scrap. (5) The melting method according to claim 1, wherein exhaust gas from a furnace is used to preheat cold scrap to be charged. (6) The furnace lid of the arc furnace has a height sufficient to provide the combustion space necessary for the formation of the flame of the pulverized powder burner, and the pulverized coal burner can be inserted into the electrode and the electrode hole, and the burner and electrode are inserted into the electrode hole. A scrap melting device characterized by having means for alternately attaching the scrap melting device to the scrap melting device. (7) two furnaces - a set of pulverized coal burners and electrodes;
The melting apparatus according to claim 6, further comprising means for attaching the burner and the electrode to each furnace in an exchangeable manner.