JP4723893B2 - Method for preventing oxidation of working surface of silicon carbide castable refractories in waste melting furnace - Google Patents

Description

The present invention generally waste relates waste furnace operation plane method for preventing oxidation of waste carbonization silicon castable refractory of the melting furnace for melting processes in a shaft furnace, such as industrial waste.

  As one of the waste processing methods, there is a waste melting processing method in which waste is dried, pyrolyzed, burned and melted in a shaft furnace type waste melting furnace to form slag and metal.

  FIG. 2 is a sectional view of a general waste melting furnace. In order to melt the waste, oxygen-enriched air is blown into the furnace from the blower tuyere 30 at the lower part of the furnace, and the waste 50 is charged into the furnace together with coke and limestone from the upper part of the furnace. Then, drying and dry distillation gasification (thermal decomposition) proceed while the waste 50 descends in the furnace, and the remaining ash is melted by the combustion heat of the furnace bottom coke 60 forming a coke bed near the blower tuyere 30. Then, it falls as molten slag and molten metal to the hearth surface. The molten material in the hearth is discharged from a hot water outlet 40 that leads from the hearth surface to the outside of the furnace. The in-furnace process of such a waste melting furnace is disclosed in Patent Document 1.

  However, in a waste melting furnace where such an in-furnace process occurs, particularly in the lower part of the furnace, the refractories (the furnace wall refractory 10 and the hearth refractory 20 shown in FIG. 2) are placed in a very harsh environment. For example, refractory repairs and replacements were required every year.

  In other words, high-alumina refractories have been used in the lower part of the furnace to withstand high temperatures, but in the upper part of the blower tuyere, the furnace on the blower tuyere is slag generated by the active combustion of coke at the upper part of the blower tuyere. Wall refractories are eroded. Similarly, the hearth is eroded by high-temperature slag.

In order to prevent erosion by slag, it is considered to use a silicon carbide refractory having low reactivity with slag, but in the furnace wall directly above the blower tuyere, CO generated by combustion of oxygen and coke from the blower tuyere _{With two} gases, the silicon carbide refractory is easily oxidized and worn.

  Also, in the hearth, the hearth surface is always covered with slag, so there is no oxidation by the gas in the furnace, but silicon carbide refractories have high heat transfer, so the temperature rises to the back, and refractory joints and cracks From the above, a metal such as iron or copper penetrates to the heat insulating layer on the back surface in a molten state, and enters the pores of the porous heat insulating material, so that the heat insulating property is remarkably deteriorated. In this case, the iron skin at the bottom of the furnace rises in temperature, and the heat dissipation of the furnace bottom increases, the hearth is cooled, the melt is solidified on the hearth surface, and it is difficult to discharge the melt.

  On the other hand, in order to improve the slag resistance, there is an example of using a chrome refractory, but the durability is not sufficient, and in use, harmful hexavalent chromium may be generated from this refractory, There is a drawback that it requires careful handling.

In addition, for the purpose of extending the life of these refractories, a method of cooling with a jacket or a cooling pipe has been proposed (see Patent Document 2). However, high alumina refractories and chrome refractories have thermal conductivity. It is difficult to obtain a practical refractory life without being sufficiently cooled down to the operation surface in the furnace.
Japanese Patent Publication No.55-21923 JP 2004-156875 A

The problem to be solved by the present invention is to provide a refractory structure capable of improving the durability of the refractory in the lower part of the furnace, particularly in a waste melting furnace, and more specifically, slag. carbonization silicon castable refractory waste melting furnace reactivity with high thermal conductivity lower silicon carbide refractory, and can solve the above problems of the high-temperature oxidation or the like which is a weak point of the silicon carbide refractory of the An object of the present invention is to provide a method for preventing oxidation of a working surface of a product in a furnace.

In order to prolong the durability of the refractory in the lower part of the waste melting furnace, the furnace wall refractory structure of the present invention includes at least 30% by mass or more of silicon carbide as the furnace wall refractory in the furnace wall at the portion in contact with the molten slag. A silicon carbide castable refractory is used, and a cooling water pipe is embedded inside. In this way, by burying the cooling water pipe inside the silicon carbide castable refractory material having high slag resistance and high thermal conductivity and cooling it, the furnace gas (which is a major weak point of the silicon carbide refractory material ( The problem of wear due to high-temperature oxidation due to O ₂ and CO ₂ ) can be eliminated. Further, since the molten slag is solidified on the surface of the cooled silicon carbide castable refractory, the molten slag becomes a surface-coated state and is protected from the furnace gas. Here, since the oxidation of the silicon carbide refractory with O ₂ and CO ₂ gas starts at 1000 ° C. or higher, the silicon carbide castable refractory on the furnace wall is cooled so that the operation surface in the furnace becomes less than 1000 ° C. It is preferable.

  According to the furnace wall refractory structure of the present invention, by cooling the silicon carbide castable refractory used as the furnace wall refractory, high temperature oxidation by the furnace gas of the silicon carbide castable refractory is prevented. The slag resistance effect by the silicon castable refractory can be sufficiently exhibited.

Therefore , according to the present invention, it is possible to remarkably improve the durability of the refractory in the lower part of the waste melting furnace particularly in the waste melting furnace, and the useful life is to be at least 5 years from the conventional about 1 year. Can do.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a sectional view of a lower part of a waste melting furnace to which the refractory structure of the present invention is applied. The structure of the waste melting furnace shown in the figure is the same as that of the conventional one shown in FIG. 2, and in order to melt the waste, oxygen-enriched air is supplied from the blower tuyere 6 at the lower part of the furnace. Blowing into the furnace, waste is charged into the furnace together with coke and limestone from the top of the furnace. Then, drying and dry distillation gasification (pyrolysis) proceed as the waste descends in the furnace, and the remaining ash is melted by the combustion heat of the bottom coke forming a coke bed not shown near the blower tuyere 6. Then, it falls as molten slag and molten metal to the hearth surface. The molten material in the hearth is discharged from a hot water outlet 7 that leads from the hearth surface to the outside of the furnace.

  In the furnace wall refractory structure of the present invention, the silicon carbide castable refractory 1 is used as the furnace wall refractory in the furnace wall at the portion in contact with the molten slag, and the cooling water pipe 2 is provided inside the silicon carbide castable refractory 1. Buried. Here, the furnace wall in contact with the molten slag is generally the furnace wall of the combustion melting zone that melts the ash remaining after dry distillation gasification (pyrolysis) of the waste. It is a furnace wall below the part 8.

  The silicon carbide castable refractory 1 needs to have high thermal conductivity in order to sufficiently exhibit the cooling effect by the cooling water pipe 2, and for this purpose, it is a material containing at least 30% by mass of silicon carbide. In this example, a silicon carbide castable refractory containing 70% by mass of silicon carbide, alumina + silica = 29% by mass as the other components, and 1% by mass of the remaining calcium oxide was used.

In the portion (combustion melting zone) where the silicon carbide castable refractory 1 is used, coke combustion is actively performed in the vicinity of the blower tuyere 6 and immediately above it, and reaches 1700 ° C to 1800 ° C. When exposed to this high temperature atmosphere, the silicon carbide refractory is usually easily oxidized, and SiC becomes SiO ₂ , causing structural changes and wear. On the other hand, in the present invention, the silicon carbide castable refractory 1 is cooled by the cooling water pipe 2, and the silicon carbide castable refractory 1 has high thermal conductivity, so that the oxidation starts to the operation surface in the furnace. The temperature is kept at about 400 ° C. to 500 ° C., which is lower than the temperature (1000 ° C.), and high temperature oxidation by the furnace gas is prevented.

  This furnace wall refractory structure makes it possible to use silicon carbide castable refractories that could not be used on the furnace wall in contact with the molten slag, making use of the slag resistance of silicon carbide castable refractories Refractory life is greatly improved. In this part, erosion progresses mainly due to melting loss due to contact with molten slag and spalling due to rapid temperature change, but silicon carbide castable refractories have good durability in any respect. The conventional high-alumina castable refractory can have a service life of 5 years or more, which was normally about 1 year.

On the other hand, in the hearth refractory structure in the present embodiment , the silicon carbide refractory 3 having high slag resistance is disposed as the first layer in contact with the melt, and the high alumina refractory as the second layer on the back surface thereof. A refractory layer consisting of 4 is disposed. Further, a heat insulating refractory 5 is provided on the back surface to prevent a temperature drop of the hearth portion.

  Since the hearth surface is always covered with slag, there is no risk of oxidation due to the gas in the furnace. Therefore, the silicon carbide refractory 3 of the first layer sufficiently exhibits slag resistance. A material containing silicon carbide is used. In this example, a silicon carbide castable refractory containing 70% by mass of silicon carbide, alumina + silica = 29% by mass as the other components, and 1% by mass of the remaining calcium oxide was used.

  However, since the silicon carbide refractory 3 of the first layer has high thermal conductivity as described above, the entire first layer is maintained at a high temperature, and the molten metal (Fe, Cu) Easy to penetrate through cracks. When this molten metal reaches the adiabatic refractory 5, the heat insulation is lost, the hearth is cooled, the melt (slag, metal) is solidified on the hearth surface, and the discharge of the melt from the tap 7 is not possible. It becomes possible.

Therefore, in order to prevent the molten metal from reaching the adiabatic refractory 5, in this embodiment , as described above, the high-alumina refractory 4 as a second layer on the back surface of the first layer of silicon carbide refractory 3. And the back surface temperature of the second layer is set to 1000 ° C. or lower which is not higher than the solidification temperature of the molten metal, thereby preventing the molten metal from penetrating into the heat insulating refractory 5. In this case, the alumina content of the high-alumina refractory 4 is 50% by mass or more in terms of fire resistance. In this example, a high-alumina castable refractory containing 93% by mass of alumina, 6% by mass of silica and 1% by mass of calcium oxide as other components was used. Further, as the heat insulating refractory 5, a heat insulating castable refractory was used. Further, in this embodiment, the castable refractory is used for the hearth, but it is also possible to use a pre-castable refractory or a fixed refractory that has been molded into a predetermined shape in advance.

It is sectional drawing of the melting furnace for wastes to which the refractory structure of this invention is applied. It is sectional drawing of a general waste melting furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon carbide castable refractory 2 Cooling water pipe 3 Silicon carbide refractory 4 High alumina refractory 5 Thermal insulation refractory 6 Blower tuyeres 7 Hot spring outlet 8 Morning glory 10 Furnace wall refractories 20 Hearth refractories 30 Blower wings Mouth 40 Hot spring outlet 50 Waste 60 Furnace bottom coke

Claims (1)

In- furnace operation surface of silicon carbide castable refractory for waste melting furnace containing at least 30% by mass of silicon carbide used as a furnace wall refractory in the furnace wall at the portion in contact with the molten slag of the waste melting furnace In the high temperature oxidation prevention method by the furnace gas of
A cooling water pipe is embedded in the silicon carbide castable refractory so that the in-furnace operating surface of the silicon carbide castable refractory exposed to a high temperature atmosphere of 1700 ° C. to 1800 ° C. is maintained at 400 ° C. to 500 ° C. The method for preventing oxidation of the silicon carbide castable refractory with the gas in the furnace on the working surface of the furnace, characterized in that the cooling is performed .

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