JP4677915B2 - Refractory and melting furnace made of this refractory - Google Patents

Description

  The present invention relates to a refractory excellent in fire resistance and a melting furnace constructed using the refractory as a furnace material.

  Conventionally, a large amount of incineration residue (ash) generated by incineration of waste has been disposed of by landfill. However, in recent years, the disposal site for reclaiming the incineration residue has become very tight. For this reason, a melting process for reducing the volume of the incineration residue is performed on the incineration residue.

In order to perform the melting treatment of such an incineration residue, a high temperature of 1400 ° C. or higher is necessary, and the composition of the incineration residue is not constant. It is necessary to use a refractory that can be used over a long period of time, and as such a refractory, for example, a refractory containing chromia is known (Patent Document 1).
Japanese Patent Laid-Open No. 11-189459

  Although the refractory containing chromia is excellent in corrosion resistance to the ash melt, it has the following problems.

(1) Although chromia chromium in the refractory exists in a trivalent state in a normal state, it is oxidized to a hexavalent state at a high temperature. Hexavalent chromium is a highly toxic hazardous substance that exhibits water solubility and deliquescence.

(2) The chromia is volatilized by high temperature, and as a result, the chromia content in the refractory is lowered and the corrosion resistance is remarkably deteriorated.

  The problems (1) and (2) are both greatly affected by the atmosphere, and the problem can be solved by using an inert gas or the like as the operating atmosphere, but a special atmosphere is prepared for the melting treatment. What must be done is not preferable in view of cost, equipment, and the like.

  The present invention has been made in view of the above circumstances, has no relation to the use atmosphere, and does not cause problems of generation of harmful hexavalent chromium and chromia volatilization even in a normal air atmosphere, and the refractory. An object of the present invention is to provide a melting furnace constructed using as a furnace material.

  In order to solve the above-mentioned problems, the present inventors have intensively studied, and as a result, in addition to alumina and chromia, hexavalent chromium can be obtained even in a high-temperature state in a normal air atmosphere by adding a predetermined metal nitride or carbide. And no volatiles of chromia were found, and the present invention was completed.

  That is, the refractory according to the present invention is a refractory mainly composed of alumina and containing chromia in a proportion of 10 to 40% by weight, and nitriding a metal selected from the group consisting of silicon, zirconium, aluminum and titanium. Further, at least one kind of the product or carbide is further contained at a ratio of 3 to 10% by weight with respect to the chromia.

  When the content of chromia in the refractory is less than 10% by weight, corrosion resistance cannot be obtained, and when it exceeds 40% by weight, the thermal shock resistance is remarkably lowered.

  When the content of the nitride or carbide with respect to the chromia is less than 3% by weight, the effect of suppressing the generation of hexavalent chromium and the volatilization of chromia cannot be obtained, and if it exceeds 10% by weight, the corrosion resistance decreases. .

Any nitride or carbide of a metal selected from the group consisting of silicon, zirconium, aluminum, and titanium can provide the effect of suppressing the generation of hexavalent chromium and the volatilization of chromia. In particular, nitride or carbide of aluminum or titanium is preferable. Aluminum nitride (AlN) is oxidized to alumina (Al ₂ O ₃ ), which forms a solid solution with chromia (CrO ₃ ) at a high temperature, so that hexavalent chromium is not generated. Titanium nitride (TiN) or titanium carbide (TiC) is oxidized to TiO ₂ at a high temperature, which promotes the effect of suppressing the generation of hexavalent chromium.

The refractory may contain other components in addition to alumina as a main component, 10 to 40% by weight of chromia, and 3 to 10% by weight of a predetermined metal nitride or carbide based on the chromia. Examples of such components include other metal oxides such as cement as a binder, such as spinel (MgAl ₂ O ₄ ), zircon (ZrSiO ₄ ), and the like.

  Any form known to those skilled in the art can be used as the form of the raw material of each material constituting the refractory. For example, commercially available powdered alumina or the like may be used. Alternatively, a slip or slip + powder form may be added.

  The refractory is produced by mixing and molding the above materials, followed by firing.

  The refractory may be formed by any method known to those skilled in the art, and examples thereof include oil press, friction press, rammer press, cast molding, CIP and the like.

  The firing temperature is preferably 1400 to 1700 ° C.

  The melting furnace of the present invention is constructed using the refractory of the present invention as a furnace material. The refractory of the present invention is particularly suitable for use on the inner wall of a furnace that is in direct contact with the object to be treated and the treatment atmosphere during the melting treatment of the waste.

  The refractory material of the present invention contains, in addition to the main component alumina and 10 to 40% by weight of chromia, a metal nitride or carbide selected from the group consisting of silicon, zirconium, aluminum and titanium, based on the weight of chromia. Therefore, hexavalent chromium is not generated even in a high temperature state in a normal atmospheric atmosphere, chromia is not volatilized, and the waste is melted, particularly in the melting furnace. A refractory suitable for the furnace material can be provided.

  Hereinafter, the refractory of the present invention and a melting furnace using the refractory as a furnace material will be described in detail.

(Comparative Examples 1-3)
Chromia (particle size 200 μm) is added to commercially available alumina (particle size 200 μm to 3000 μm), and cement (Al ₂ O ₃ 73.0%, CaO 26.0%, SiO ₂ 0.3%, Fe ₂ O ₃ as binder) 0.3%) was added, 5% by weight of water was added, and this was kneaded for 30 minutes and then poured into a mold (JIS standard brick shape) to obtain a molded product.

(Examples 1 to 10)
In the same manner as in the comparative example, a predetermined amount of alumina, chromia, and 1 to 10% by weight of a predetermined metal (Si, Zr, Al, Ti) nitride or metal carbide with respect to chromia are added, and then compared. In the same manner as in the example, it was molded into the same shape to obtain a molded product.

(Comparative Example 5)
A molded product was obtained in the same manner as in Example except that metal nitride or carbide was added at a ratio of 2% by weight to chromia.

(Comparative Example 6)
A molded product was obtained in the same manner as in Example except that metal nitride or carbide was added at a ratio of 15% by weight to chromia.

  The molded articles of Examples 1 to 10 and Comparative Examples 1 to 4 were fired in the atmosphere at 1400 ° C. (the heating and cooling rate was 100 ° C./h, respectively), and the elution amount of hexavalent chromium (announcement No. 13 method) and The total chromium content (sediment survey method) was analyzed. The results are shown in Table 1. In the table, if the elution amount of hexavalent chromium was less than the regulated value of 1.5 mg / l, it was considered acceptable. Further, the volatilization amount of chromia was determined to be acceptable if the decrease amount of chromium was less than 30% by comparing the total Cr amount before and after heating.

Next, using a slag having basicity (CaO / SiO ₂ ) = 0.8, a corrosion resistance test was performed according to the JIS crucible method. The results are shown in Table 2. In addition, in the table | surface, it was set as the pass if the melting rate (maximum thickness reduction amount / time of the sample after cutting) is less than 1 mm / day.

  From the results shown in Table 1 and Table 2, it can be seen that the refractories of Examples 1 to 10 according to the provisions of the present invention have the effect of suppressing the generation of hexavalent chromium and the evaporation of chromia, and also have the effect of corrosion resistance. . On the other hand, in Comparative Example 1, corrosion resistance was not obtained. In Comparative Examples 2 to 5, it was not possible to obtain the effect of suppressing either or both of the generation of hexavalent chromium and the volatilization of chromia. In Comparative Example 6, the effect of corrosion resistance could not be obtained. From the results shown in Table 2, it was found that the corrosion resistance is remarkably lowered when the addition amount of the metal nitride or carbide exceeds 10% by weight with respect to chromia.

  In this example, a test piece was prepared by a method of manufacturing an irregular refractory, but the raw material was mixed with a binder like a brick, and this mixture was molded with a mechanical press, and then inert such as nitrogen or argon. Even if it is produced by firing in a gas atmosphere, the same effect can be obtained.

Claims (2)

A refractory mainly composed of alumina, containing 10 to 40% by weight of chromia,
A refractory further comprising at least one metal nitride or carbide selected from the group consisting of silicon, zirconium, aluminum, and titanium in a proportion of 3 to 10% by weight based on the chromia.   A melting furnace using the refractory according to claim 1 as a furnace material.