JP2005321121A - Electric melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve melting efficiency by uniforming current distribution in molten slag. <P>SOLUTION: In an incinerated ash melting furnace, a direct current is carried between a rod furnace top electrode 4 arranged at the center of the upper part in the furnace and a disc furnace bottom electrode 5 arranged on the furnace bottom and incinerated ashes charged into the furnace are melted to produce the molten slag 7. A conductive powder charging mechanism 16 is provided for charging a conductive powder and grain material 15 into the furnace. The conductive powder and grain material 15 is added to a forming slag layer 13 on the surface of the molten slag 7. The conductive powder and grain material 15 is forcibly added to the surface of the molten slag 7 contacting the incinerated ashes 3 to form a current passage 19, whereby the direct current is carried from the surface of the molten slag almost perpendicularly to a molten metal layer 8 to improve the melting efficiency and promote the reducing reaction of metal oxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a direct current electric resistance type incineration ash melting furnace that melts incineration ash and incineration fly ash generated from incineration disposal of municipal waste, industrial waste, sewage sludge or contaminated soil, and more specifically to improve melting efficiency Relating to the means.

  A technology has been developed in which the above incineration ash is reduced and melted in an electric melting furnace instead of landfill disposal, and the molten slag is crystallized and reused for building materials, etc., and the metal is separated as valuable resources. Is described in Patent Document 1, for example. As the melting furnace, an electric resistance type having high thermal efficiency is suitable. In particular, a direct current resistance type melting furnace provides a stable and quiet melting, and the specific gravity separation between the molten slag and the metal easily proceeds.

  FIG. 5 is a longitudinal sectional view showing a conventional configuration of a DC resistance melting furnace. In FIG. 5, the incinerated ash 3 charged from the raw material charging device 2 into the upright furnace body 1 is a rod-shaped top electrode 4 disposed at the upper center of the furnace and a disk-like shape disposed at the bottom of the furnace. The melted slag 7 is generated by being melted by the Joule heat of the direct current supplied from the direct current power source 6. The incineration ash 3 is mixed with a reducing agent (carbon powder or the like), and the metal oxide in the reduced incineration ash is separated from the molten slag 7 as the molten metal 8 and settles in the lower layer of the melting furnace.

The molten slag 7 is taken out from the upper outlet 9 and cast into a mold (not shown). The molten metal 8 is taken out from the outlet 10 at the bottom of the furnace. The upper surface of the furnace body 1 is closed by a furnace lid 11, and the gas in the furnace is discharged from an exhaust port 12 of the furnace lid 11 to an exhaust gas treatment device (not shown). Here, bubbles are generated in the molten slag 7 as the gas components are evaporated, and a foamed layer (forming slag layer) 13 is generated in the surface layer portion. The molten slag 7 is blocked from the furnace atmosphere by the incinerated ash 3, and the metal oxide is reduced and melted in the forming slag layer 13 by the added reducing agent.
JP-A-9-196573

  In FIG. 5, the furnace wall refractory 1a of the furnace body 1 (where 1b is an iron skin) and the furnace electrode 4 are made of a carbon material, and the furnace bottom electrode 5 made of iron is a conductive amorphous refractory 14 on the furnace bottom. It is buried inside. In FIG. 6, the resistivity (Ωcm) of the furnace electrode 4, the furnace bottom electrode 5, the molten slag 7, the molten metal 8 and the conductive amorphous refractory 14 and the resistivity of the conductive amorphous refractory 14 are set to 1. The magnification of each resistivity is shown. From the relationship of FIG. 6, the distribution of the current flowing in the furnace is as shown by the arrow in FIG. 6, but the current in the molten slag is the distance between the furnace electrode 4 and the furnace bottom electrode 5 having a small electrical resistance. Are concentrated at the shortest furnace center and flow in an umbrella shape from the tip of the furnace electrode 4 toward the molten metal layer as shown in the figure. Therefore, the current in the molten slag is partially uneven, and as a result, the melting efficiency of the incinerated ash 3 is poor.

  On the other hand, in FIG. 5, the furnace bottom electrode 5 is not in direct contact with the molten slag 7 or the molten metal 8, and is mechanically cut off by the conductive amorphous refractory 14. In that case, in order to increase the electrical conductivity between the furnace bottom electrode 5 and the conductive amorphous refractory 14, it is important to bring them into close electrical contact as much as possible and to increase the contact area. Further, the diameter of the furnace electrode 4 is generally as small as about 1/10 of the furnace inner diameter, and the current flows linearly or parabolically from the tip toward the molten metal 8 and thus hardly spreads in the molten slag.

  Accordingly, an object of the present invention is to make the current distribution in the molten slag uniform and improve the conductivity of the furnace bottom electrode, thereby improving the melting efficiency.

  The present invention comprises a rod-shaped furnace top electrode disposed at the center of the upper part of the furnace and a disk-shaped furnace bottom electrode disposed at the furnace bottom, and a direct current is provided between the furnace electrode and the furnace bottom electrode. In an incineration ash melting furnace that melts the incinerated ash charged into the furnace to produce molten slag, the conductive powder charging mechanism for charging the conductive particles into the furnace The conductive powder material is charged into the surface of the molten slag by the conductive powder charging mechanism (claim 1).

  According to the first aspect of the present invention, a conductive powder is forcibly added to the surface of the molten slag in contact with the incinerated ash to create a current path, whereby the molten slag surface is substantially perpendicular to the molten metal layer. A direct current flows, melting efficiency is increased, and reduction reaction of the metal oxide is promoted.

  In the first aspect of the present invention, it is preferable that the conductive granular material is charged on the forming slag layer of the molten slag (second aspect). Since the forming slag layer is foamed, the conductive powder particles on the forming slag layer tend to spread in the lateral direction, and a wide current path is easily obtained. However, the spread of the conductive particles is limited to a range in which the insulation between the furnace electrode and the furnace wall can be maintained. Coke powder (Claim 3) or an inorganic reducing agent (Claim 4) is preferably used for the conductive powder.

  The present invention also includes a rod-shaped furnace top electrode disposed at the upper center of the furnace and a disk-shaped furnace bottom electrode disposed at the bottom of the furnace, between the furnace electrode and the furnace bottom electrode. In the incineration ash melting furnace that melts the incinerated ash charged into the furnace to generate molten slag by applying a direct current, irregularities are formed on the surface of the furnace bottom electrode (claim 5), Alternatively, a large number of holes penetrating in the axial direction are formed in the furnace bottom electrode. By forming irregularities on the surface of the furnace bottom electrode or making a large number of holes in the furnace bottom electrode, the contact area increases and the adhesion between the furnace bottom electrode and the conductive amorphous refractory becomes tight. Will be better.

  The present invention also includes a rod-shaped furnace top electrode disposed at the upper center of the furnace and a disk-shaped furnace bottom electrode disposed at the bottom of the furnace, between the furnace electrode and the furnace bottom electrode. In the incineration ash melting furnace that melts the incinerated ash charged in the furnace to generate molten slag by applying a direct current, the on-furnace electrode is formed by self-firing the self-firing electrode paste. (Claim 7). In the furnace, there is heat of molten slag and gas generated in the furnace, and the electrode itself also generates electric resistance heat. Therefore, if the self-fired electrode paste is placed in a cylindrical body made of steel plate and self-fired with the heat in the furnace to form an on-furnace electrode, a large-diameter electrode capable of covering the surface of the molten slag over a wide area is obtained. It becomes easy to obtain, and thereby the current in the molten slag can be made uniform.

  According to the present invention, the distribution of the current flowing through the molten slag is improved, and the conductivity around the furnace bottom electrode is increased. As a result, the melting efficiency of the incineration ash is improved, the power consumption is reduced, and the running cost is reduced. I can plan.

  Embodiments of the present invention will be described below with reference to FIGS. In addition, the same code | symbol shall be used for the part corresponding to a prior art example.

  FIG. 1 is a longitudinal sectional view of an incineration ash melting furnace showing Embodiment 1 of the present invention. 1 is different from the prior art of FIG. 5 in that a conductive powder charging mechanism 16 for charging the conductive powder 15 into the furnace is provided. The conductive powder charging mechanism 16 includes a hopper 17 that opens above the furnace lid 11, and a charging cylinder 18 that penetrates the furnace lid 11 from the hopper 17 and reaches the upper surface of the forming slag layer 13. A plurality of mechanisms 16, for example, four groups, are arranged in an annular shape at an equal pitch. Coke powder or an inorganic reducing agent (for example, a compressed aluminum can) is used for the conductive powder 15.

  After the conductive powder charging mechanism 16 starts up the operation of the illustrated melting furnace, the conductive powder 15 is melted to produce the incinerated ash 3 to form the molten slag 7, and the forming slag layer 13 is formed. The top surface is charged. The granular material 15 diffuses in the horizontal direction on the surface of the molten slag 7 to form a flat current passage 19 as shown in FIG. The current path 19 is one digit or more higher in conductivity than the molten slag 7. Therefore, the current flowing from the tip of the furnace electrode 4 spreads in the current passage 19 and flows in the molten slag 7 almost vertically toward the molten metal layer 8 as indicated by arrows in FIG. As a result, the current distribution in the molten slag 7 is made uniform, the melting efficiency of the incinerated ash 3 is improved, and the reduction melting of the metal oxide in the forming slag layer 13 is promoted. The charged granular material 15 exhibits a strong reducing action. In the case of coke powder, it is finally discharged together with the exhaust gas as CO. In the case of an inorganic reducing agent, an oxide is generated in the slag.

  2 and 3 show Embodiment 2 of the present invention, in which (A) is a plan view of a furnace bottom electrode and (B) is a side view. First, in FIG. 2, the surface of the furnace bottom electrode 5 is roughened by sandblasting to form minute irregularities. By forming the irregularities in this way, the surface area can be increased and the electrical conductivity can be enhanced by close contact with the conductive amorphous refractory 14, and as a result, the current distribution in the molten slag 7 can be made uniform. Can be planned. In order to form unevenness on the electrode surface, tooth shapes 5a such as a rectangular cross section shown in FIG. 2C, a corrugated cross section shown in FIG. 2D, and a sawtooth cross section shown in FIG. . On the other hand, FIG. 3 shows a structure in which a large number of holes 5 b penetrating in the axial direction are formed in the furnace bottom electrode 5. Such a large number of holes 5b can also increase the surface area of the furnace bottom electrode 5 and make the contact with the conductive amorphous refractory 14 tight.

  FIG. 4 is a longitudinal sectional view of an essential part of a melting furnace showing Embodiment 3 of the present invention. In FIG. 4, the furnace electrode 4 is formed by self-baking of a paste for self-baking electrodes. That is, the furnace electrode 4 is initially configured by filling a self-baking electrode paste 21 into a cylindrical body 20 made of a steel plate as shown. Next, when the molten slag 7 is generated by energization, the self-fired electrode paste 21 is self-fired by the heat of the molten slag 7 in the furnace, the heat of the gas generated in the furnace, and the electric resistance heat of the electrode itself, and the upper electrode 4 Is formed. The bottom part (two-dot chain line part) of the cylindrical body 20 is melted away in the initial stage of firing, and the tip of the electrode is exposed as shown. According to such electrode formation, the furnace body electrode 4 having a wide end surface capable of covering the slag surface in a wide range is obtained by configuring the cylindrical body 20 to have a large diameter, for example, about 1/3 of the furnace inner diameter. The current flowing between the molten metal layer and the molten metal layer can be made uniform.

It is a longitudinal cross-sectional view of the incineration ash melting furnace which shows Example 1 of this invention. Example 2 of this invention is shown, (A) is a top view of the furnace bottom electrode of an incineration ash melting furnace, (B)-(E) is the side view. (A) is a plan view of a bottom electrode of an incinerated ash melting furnace, and (B) is a longitudinal sectional view thereof. It is a principal part longitudinal cross-sectional view of the incineration ash melting furnace which shows Example 3 of this invention. It is a longitudinal cross-sectional view of the incineration ash melting furnace which shows a prior art example. It is a figure which shows the comparison of the resistivity of a melting furnace structural member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Incinerated ash 4 Furnace electrode 5 Furnace bottom electrode 7 Molten slag 8 Molten metal 13 Forming slag layer 15 Conductive granular material 16 Conductive powder charging mechanism 20 Cylindrical body 21 Self-baking electrode paste

Claims (7)

A rod-shaped top electrode disposed in the center of the top of the furnace and a disk-shaped bottom electrode disposed on the bottom of the furnace, and a direct current is passed between the top electrode and the bottom electrode. In the incineration ash melting furnace that melts the incineration ash charged into the furnace to produce molten slag,
A conductive powder charging mechanism for charging the conductive powder particles into the furnace is provided, and the conductive powder particles are charged into the surface of the molten slag by the conductive powder charging mechanism. Incinerated ash melting furnace.   The incinerated ash melting furnace according to claim 1, wherein the conductive powder particles are charged onto a forming slag layer of the molten slag.   The incinerated ash melting furnace according to claim 1 or 2, wherein coke powder is charged as the conductive granular material.   The incinerated ash melting furnace according to claim 1, wherein an inorganic reducing agent is charged as the conductive powder. A rod-shaped top electrode disposed in the center of the top of the furnace and a disk-shaped bottom electrode disposed on the bottom of the furnace, and a direct current is passed between the top electrode and the bottom electrode. In the incineration ash melting furnace that melts the incineration ash charged into the furnace to produce molten slag,
An incineration ash melting furnace, wherein irregularities are formed on the surface of the furnace bottom electrode. A rod-shaped top electrode disposed in the center of the top of the furnace and a disk-shaped bottom electrode disposed on the bottom of the furnace, and a direct current is passed between the top electrode and the bottom electrode. In the incineration ash melting furnace that melts the incineration ash charged into the furnace to produce molten slag,
An incineration ash melting furnace characterized in that a large number of holes penetrating in the axial direction are formed in the furnace bottom electrode. A rod-shaped top electrode disposed in the center of the top of the furnace and a disk-shaped bottom electrode disposed on the bottom of the furnace, and a direct current is passed between the top electrode and the bottom electrode. In the incineration ash melting furnace that melts the incineration ash charged into the furnace to produce molten slag,
An incinerated ash melting furnace, wherein the furnace electrode is formed by self-baking a paste for self-fired electrodes.

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