JP2018159508A - Scrap preheating device of melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the scrap preheating device of a melting furnace provided with a single preheating chamber, capable of effectively preventing excessive oxidation of scrap.SOLUTION: A single preheating chamber 14 for preheating scrap pieces Sc is installed in a shaft 13 installed at the upper part of a furnace body 11, exhaust gas of an arc furnace 1 is circulated to the preheating chamber 14 in the shaft 13 to preheat the scrap pieces Sc, and a bypass passage 2 is installed for connecting an exhaust gas inlet side to an exhaust gas outlet side of the preheating chamber 14, and a flow controlling damper 21 is installed in the bypass passage 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a scrap preheating device for a melting furnace, and more particularly to a scrap preheating device capable of appropriately managing the amount of exhaust gas flowing through a preheating chamber.

  A melting furnace having a structure in which a single preheating chamber for preheating scrap is provided in a shaft provided above the furnace body is shown, for example, in Patent Document 1, in which a melting chamber is formed below the preheating chamber from the side of the furnace body. The scrap supplied to the preheating chamber is supplied to the molten metal while preheating with the exhaust gas from the melting furnace.

JP2004-84044

  However, in the conventional scrap preheating apparatus, exhaust gas flowing from the melting furnace into the preheating chamber is not managed at all. For this reason, especially at the end of the temperature increase and reduction period when the exhaust gas temperature rises to around 1600 ° C, the scrap is excessively heated and oxidized by the exhaust gas, reducing the yield and reducing the productivity due to the longer reduction time. There is a problem of inviting.

  Accordingly, the present invention solves such problems, and an object of the present invention is to provide a scrap preheating apparatus for a melting furnace that can effectively prevent excessive oxidation of scrap in a melting furnace provided with a single preheating chamber. And

  In order to achieve the above object, according to the first aspect of the present invention, a single preheating chamber (14) for preheating scrap (Sc) is provided in a shaft (13) provided above the furnace body (11) for melting. Bypassing the exhaust gas from the furnace (1) to the preheating chamber (14) in the shaft (13) to preheat the scrap (Sc) and connecting the exhaust gas inflow side to the exhaust gas outflow side of the preheating chamber (14) ( 2), and the flow rate adjusting means (21, 4) is provided in the bypass passage (2).

  In the first invention, when the temperature of the exhaust gas in the melting furnace rises or the amount of exhaust gas increases, the amount of heat input to the scrap in the preheating chamber becomes excessively large and the oxidation proceeds. Therefore, in the present invention, a part of the exhaust gas is diverted to the bypass passage without being supplied to the scrap by the flow rate adjusting means of the bypass passage. This prevents excessive preheating of the scrap and avoids its oxidation progress.

  In the second invention, at least one of the valve body (21) and the fan (4) is provided as the flow rate adjusting means.

  In the third invention, the pressure loss of the bypass passage (2) is set so that the upper limit of the amount of exhaust gas flowing through the bypass passage (2) is 25 to 35% of the amount of exhaust gas discharged from the melting furnace (1). ing.

    In addition, the following operation methods may be sufficient as this invention. That is, a single preheating chamber (14) for preheating the scrap (Sc) is provided in the shaft (13) provided above the furnace body (11), and the exhaust gas from the melting furnace (1) is discharged into the shaft (13). In the preheating chamber (14) of the melting furnace, the scrap (Sc) is preheated, and a bypass passage (2) connecting the exhaust gas inflow side and the exhaust gas outflow side of the preheating chamber (14) is provided. The upper limit of the amount of exhaust gas flowing through the bypass passage (2) is set to 25 to 35% of the amount of exhaust gas discharged from the melting furnace (1).

  The reference numerals in the parentheses refer to the correspondence with specific means described in the embodiments described later.

  As described above, according to the scrap preheating apparatus for a melting furnace of the present invention, excessive oxidation of scrap can be effectively prevented in a melting furnace provided with a single preheating chamber.

It is a schematic sectional drawing of the arc furnace which provided the scrap preheating apparatus in 1st Embodiment of this invention. It is a schematic sectional drawing of the arc furnace provided with the scrap preheating apparatus in 2nd Embodiment of this invention.

  The embodiment described below is merely an example, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

(First embodiment)
FIG. 1 shows a shaft type arc furnace as an example of a melting furnace. In FIG. 1, an electrode 12 is inserted into the furnace body 11 of the arc furnace 1 from above the center, and the scrap Sc in the furnace is melted by arc discharge. A cylindrical shaft 13 is erected at an eccentric position above the furnace body 11, and a single preheating chamber 14 is formed therein. A fork type gate 15 that can be opened downward is provided at the lower end opening of the preheating chamber 14. The fork type gate 15 is a gate having a structure in which a plurality of parallel bars are arranged in a fork shape, and exhaust gas can flow through a gap between the parallel bars.

  A door body 16 that can be opened and closed is provided at the upper end opening of the preheating chamber 14. When charging the scrap Sc into the preheating chamber 14, the door Sc 16 is opened and the scrap Sc transported by a bucket (not shown) is dropped and supplied into the preheating chamber 14. During operation, the high-temperature exhaust gas generated in the furnace of the arc furnace 1 passes through the gate 15 and rises in the preheating chamber 14 to preheat the scrap Sc. The preheated scrap Sc is supplied by dropping into the lower furnace body 11 with the gate 15 opened at an appropriate timing during operation.

  Here, in this embodiment, the bypass path 2 is provided, and the lower end of the bypass path 2 is open on the side wall below the lower end opening of the shaft 13 on the exhaust gas inflow side. The bypass 21 is provided with a damper 21 as a valve body that constitutes a flow rate adjusting means in the middle. The damper 21 may be manually opened or closed, or may be automatically opened or closed based on a calculation formula described later. Anyway.

  However, according to the experience of the inventors, even when the damper 21 is fully opened, only about 30% of the amount of exhaust gas discharged from the arc furnace 1 becomes the upper limit exhaust gas amount flowing to the bypass passage 2. It is good to set the pressure loss of 2. The upper end of the bypass passage 2 is open to the upper end side wall of the preheating chamber 14 on the exhaust gas outflow side. This opening position is set to a position higher than the height of the scrap Sr when the preheating chamber 14 is filled with the scrap Sr. A flue 3 is connected to an upper end side wall of the preheating chamber 14, and the flue 3 reaches a dust collector through a blower from a cooling tower (not shown).

  Here, Table 1 shows the results of experiments in more detail on how much of the amount of exhaust gas discharged from the arc furnace 1 is optimal to flow to the bypass passage 2. According to Table 1, in order to suppress the surface oxidation of the preheated scrap Sc (the degree of inhibition of scrap oxidation), 25% or more of the amount of exhaust gas discharged from the arc furnace 1 should flow to the bypass 2. . On the other hand, when the preheating time during which the scrap Sc can be sufficiently preheated is compared, when the preheating time when 5 to 35% of the amount of exhaust gas discharged from the arc furnace 1 flows to the bypass passage 2 is T (min), 35 When it is set to ˜40%, the preheating time is as long as T to 1.5 T (min), and when it is set to 43% or more, a preheating time of 1.5 T (min) or more is required. Therefore, in order to shorten the preheating time as much as possible while suppressing the surface oxidation of the scrap Sr, it is optimal to flow 25 to 35% of the amount of exhaust gas discharged from the arc furnace 1 to the bypass passage 2.

  In such a structure, the high-temperature exhaust gas from the arc furnace 1 passes through the gate 15 as described above and rises in the preheating chamber 14 to preheat the scrap Sc, and then the upper end of the preheating chamber 14. The air is exhausted through the flue 3. When the exhaust gas temperature rises or the amount of exhaust gas increases, the amount of heat input to the scrap Sc becomes excessively large and the oxidation proceeds.

  In this case, in this embodiment, an appropriate amount of the damper 21 is opened, and a part of the exhaust gas is directly flowed into the upper end portion of the preheating chamber 14 via the bypass path 2 without being supplied to the scrap Sc. Drain to road 3. This prevents excessive preheating of the scrap Sc and avoids the progress of oxidation.

Here, the heat rate Qva discharged from the arc furnace 1 is represented by the following equation (1), where Q (m 3 / min) is the amount of exhaust gas in the arc furnace 1 and t (° C.) is the exhaust gas temperature.
Qva = (Q · t · gas specific heat) · K1 (Kwh / min) (1)
Here, K1 is an appropriate coefficient (the same applies hereinafter).

The amount of heat Q Qve taken away from the flue 3 is the exhaust amount (flue) determined by the rotational speed of a blower (not shown) installed in the flue 3 when the exhaust gas temperature in the flue 3 is t1 (3 air flow rate) is Q1, and the following equation (2) is obtained.
Qve = (Q1, t1, gas specific heat), K1 (Kwh / min) (2)

Furthermore, since the exhaust gas temperature of the bypass path 2 is t (° C.), the carry heat rate Qvb of the bypass path 2 is expressed as It will be as shown in (3).
Qvb = (Q2 · t · gas specific heat) · K1 (Kwh / min) (3)

Therefore, if other heat loss is not taken into consideration, the heat input speed Qvp to the preheating chamber 14 is obtained by the following equation (4).
Qvp = Qva- (Qve + Qvb) (4)

  Thereby, if the heat capacity of the scrap Sc in the preheating chamber 14 is calculated in advance, the preheating temperature change of the scrap Sc can be estimated from the heat input speed Qvp calculated by the equation (4). Therefore, the exhaust amount Q2 in the equation (3) is adjusted by controlling the opening degree of the damper 21 so that the estimated preheating temperature is maintained within an appropriate range. For example, this adjustment is performed such that when the exhaust gas amount Q increases, the exhaust amount Q2 is increased accordingly, and when the temperature t increases, the exhaust amount Q2 is increased accordingly. In addition, the temperature t, t1 and the exhaust gas amount Q in the formulas (1) to (3) are measured by an appropriate measuring means.

  When direct measurement of the exhaust gas quantity Q is difficult, the electric power input to the arc furnace, [C] blowing speed, [O2] blowing speed, auxiliary combustion energy blowing speed, first-in [C] quantity, metal The calorific value Qva may be directly calculated from the oxidation amount, assumed slag generation heat, waste tire amount, waste plastic amount, and assumed attached oil amount.

  When other heat losses are considered in equation (4), the heat losses include fork gate cooling water removal heat rate Q21, preheating chamber water cooling panel cooling water removal heat rate Q22 (Kwh / min), preheating chamber iron surface Heat dissipation rate Q23 (Kwh / min) from the air, and heat dissipation rate Q24 (Kwh / min) due to the flue gas, etc. In this case, in addition to Qve and Qvb, Q21 to Q24 are subtracted from Qva in equation (4) Qvp is calculated.

(Second Embodiment)
As shown in FIG. 2, a booster fan 4 that is automatically controlled in rotation is provided in the bypass path 2 in series with the damper 21. In this way, the booster fan 4 can accurately control the air flow rate Q2 of the bypass passage 2 even if the shape of the scrap in the preheating chamber fluctuates and its pressure loss changes greatly. Progress can be effectively prevented.

DESCRIPTION OF SYMBOLS 1 ... Arc furnace (melting furnace), 11 ... Furnace body, 13 ... Shaft, 14 ... Preheating chamber, 2 ... Bypass path, 21 ... Damper (flow control means), 4 ... Booster fan, Sc ... Scrap.

Claims (3)

A single preheating chamber is provided in the shaft above the furnace body to preheat the scrap, and the exhaust gas from the melting furnace is circulated through the preheating chamber in the shaft to preheat the scrap, and the exhaust gas inflow side of the preheating chamber A scrap preheating device for a melting furnace in which a bypass path is provided to connect the exhaust gas to the exhaust gas outflow side, and a flow rate adjusting means is provided in the bypass path. The scrap preheating apparatus for a melting furnace according to claim 1, wherein at least one of a valve body and a fan is provided as the flow rate adjusting means. The scrap preheating device according to claim 1 or 2, wherein the pressure loss of the bypass passage is set so that the upper limit of the amount of exhaust gas flowing through the bypass passage is 25 to 35% of the amount of exhaust gas discharged from the melting furnace.

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