JPH08114389A - Furnace for melting waste - Google Patents

Abstract

PURPOSE: To provide the erosion resistance and the wear resistance in the case of melting waste and to endure for a long time use by forming the part of melted material in contact with its liquid surface and the part of the material in contact when the material flows out of zirconia refractory containing a specific amount or more of ZrO2 . CONSTITUTION: A furnace 1 for melting waste is formed at the part in contact with at least the liquid surface 16 of molten material 14 and the part in contact when the material 14 of a discharge port 15 flows out of zirconia refractory 13 containing 85wt.% of more of ZrO2 . Generally, the waste becomes belted state at 1300-1400 deg.C. The refractory containing much Al2 O3 is melted to molten material near at 1360 deg.C in reaction with melting CaO during melting at the Al2 O3 in the refraction. On the contrary, ZrO2 in the refractory containing much ZrO2 is not reacted with the melted material even at 1900 deg.C, and not melted. The crystal of the ZrO2 has high hardness, and particularly electroforming refractory has further excellent wear resistance as compared with baked refractory due to the denseness of the structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste melting furnace, and more particularly to a waste melting furnace at least partially using zirconia refractory.

[0002]

2. Description of the Related Art In recent years, the amount of waste such as municipal waste, industrial waste, and sewage sludge has been increasing.

As one of the methods for disposing of these wastes, the volume of the wastes is reduced by incineration or drying. At that time, the incinerated ash and incinerated fly ash produced by the incineration process and the sewage sludge cake produced by the drying process are landfilled.

However, recently, a shortage of landfill sites and pollution problems have been expected. Therefore, it is considered that wastes such as incineration ash, incineration fly ash, and sewage sludge cake are melted at high temperature and then solidified to reduce the volume and detoxify, and further reuse.

Some furnaces for melting waste are already in operation. For example, burner, electric resistance, arc,
There are various melting furnaces using heating methods such as plasma and coke mixing.

Since a plasma furnace heated by plasma uses a water-cooled electrode called a compact plasma torch, there is an advantage that the installation area of the furnace can be reduced. In the heating method using a plasma torch, an extremely high temperature of 20,000 to 30,000 ° C. can be obtained at a high temperature portion and 3000 ° C. or more at a relatively low outer peripheral portion, so that the melt can be homogenized. A for the lining of the furnace
Refractory materials such as 1 ₂ O ₃ —SiC type, MgO—Cr ₂ O ₃ type, and SiC type are used.

The chemical composition of incinerated ash, incinerated fly ash and sewage sludge cake is generally 15 to 45% by weight of SiO ₂ , Al ₂
O ₃ 10 to 20 wt%, Na ₂ O1~15 wt%, Ca
O is 5 to 45% by weight. In addition to this, volatile components such as S and Cl are contained. Especially for incinerated ash and incinerated fly ash, F
Metals such as e, Cd, Pb, Zn, Cu, As, Cr and Hg are included.

The incineration fly ash is an ash produced when the exhaust gas is treated with an alkali or alkaline earth component agent for the purpose of removing sulfur oxides, chlorine gas and the like in the exhaust gas generated when the waste is incinerated. Therefore, the incinerated fly ash contains a large amount of alkali and alkaline earth components, especially CaO. Also, of course, the sewage sludge cake contains not only alkaline earth components,
It contains a large amount of P ₂ O ₅ .

[0009]

When melting a waste containing these components, abrasion due to foreign matter, peculiar erosive strength of ash, and further, metal contained in ash is accumulated on the bottom of the furnace. Therefore, the refractory used for the lining of the furnace is highly eroded and worn. In particular, the temperature of the portion coming into contact with the outlet or the liquid surface of the melt becomes high. Further, such a portion is a place that is easily subject to physical erosion due to the flow of the melt. Therefore, the refractory is severely damaged.

In a plasma furnace, the melting temperature is usually 1500 ° C.
It may be around, and sometimes reaches 1900 ° C. Due to such high temperature, Al ₂ O ₃ —SiC system, MgO—Cr ₂ O ₃ system, Si and Si, which are considered to have relatively high corrosion resistance.
Even C-based fired refractories are significantly corroded.

It is an object of the present invention to provide a waste melting furnace which has sufficient erosion resistance and wear resistance when melting waste and can withstand long-term use.

[0012]

As a result of various studies to achieve this object, the present invention makes contact with at least a portion of the melt that contacts the liquid surface and the melt at the outlet when the melt flows out. The gist is a furnace for melting waste, which is characterized in that a part thereof is made of a zirconia refractory material containing 85% by weight or more of ZrO ₂ .

[0013]

In general, the above-mentioned waste is in a molten state at 1300 to 1400 ° C because of its chemical composition. The reactivity of the molten waste with each refractory is as follows.

[0014] Al ₂ O _3-rich refractories have Al ₂ O ₃ in the refractory from dissolving into the melt in the vicinity of the reaction to 1360 ° C. and CaO in the molten. Then, the melt penetrates into the refractory structure that has melted and hollowed out, and erosion is promoted.

On the other hand, ZrO ₂ which is a refractory containing a large amount of ZrO ₂ does not react with the melt even at 1900 ° C. and does not dissolve. Further, the crystal of ZrO ₂ has a large hardness, and especially the electroformed refractory has a more excellent wear resistance than the fired refractory because of the dense structure.

The ZrO ₂ content is preferably 85% by weight or more, and particularly preferably 90% or more. If the ZrO ₂ content is less than 85% by weight, the advantage cannot be utilized.

[0017]

EXAMPLES The present inventors have found that S in ash and fly ash.
Focusing on the fact that iO ₂ , CaO and alkali oxide components are contained, the inventors have invented that a zirconia refractory can be used as a refractory used for a waste melting furnace.

The composition of the waste is 10-40% by weight of alkali oxide and alkaline earth oxide components, which is very different from the ordinary glass composition and is very special. Therefore, it was examined whether or not the commonly used refractory material for glass melting can be used in a waste melting furnace.

First, a refractory material containing a large amount of Al ₂ O ₃ ,
For example, Al ₂ O ₃ system, Al ₂ O ₃ —SiO ₂ system, Al ₂
O ₃ -ZrO ₂ -SiO _{2 system, Al 2 O 3 -Cr 2 O} 3
A study was conducted on refractory materials.

Regardless of the manufacturing method, these refractories cannot be used because they have a significantly large amount of erosion that resists the melt of waste. That is, when used in a melting furnace for these refractory materials, the refractory material is easily eroded or melted by the melt material.

Then, a refractory containing almost no Al ₂ O ₃ was examined next.

As a refractory containing no Al ₂ O ₃ , S
iO ₂ system, ZrO ₂ —SiO ₂ system, SnO ₂ system, ZrO
_{There are 2} series, Cr ₂ O ₃ series, MgO—Cr ₂ O ₃ series, and MgO series refractories.

Since SiO ₂ refractory is inferior in corrosion resistance, it cannot be used. In the case of a ZrO ₂ —SiO ₂ -based refractory, SiO ₂ in the refractory dissolves in the melt, the structure of the refractory collapses, and the erosion resistance becomes extremely low.

The SnO ₂ type refractory is difficult to use because of its low electric resistance and weakness against thermal poling.

The refractory material containing Cr ₂ O ₃ has a low erosion resistance to the melt, and has environmental problems due to the toxicity of chromium itself.

The refractory containing MgO is the MgO in the refractory.
Is eluted into the melt or dissolved,
The structure of the refractory is collapsed and the erosion resistance is extremely poor.

The above results are found from many tests conducted by the present inventors.

[0028]

[Table 1] Table 1 shows the chemical compositions of Al ₂ O ₃ -based refractories used in the tests as Comparative Examples 1 to 5, and the chemical compositions of Cr ₂ O ₃ -based refractory materials as Comparative Examples 6 and 7, and MgO-Cr ₂ O. The chemical composition of the ₃ type refractory is shown as Comparative Example 8, and Al ₂ O ₃ —Si
The chemical compositions of C-based refractories are shown as Comparative Examples 9 and 10.

[0029]

[Table 2] Table 2 shows the amount of corrosion of the melts of Comparative Examples 1 to 10.
Comparative Examples 2, 6, 8, 9, 10 are examples of fired refractories.
Other comparative examples are examples of electroformed refractories.

The test method for the amount of erosion was as follows. A test piece with a diameter of 20 mm and a length of 80 mm was taken out from each refractory, and the waste was put into an internal volume of 1600.
These test pieces were placed in a crucible of cc such that the test pieces were immersed in the melt, and kept in a furnace at 1550 ° C. for 48 hours. After heating, the test piece was cut in half and the depth of the recess appearing in the cross section was measured with a caliper. The erosion amount was expressed in mm and evaluated.

The chemical composition of the melt used in this test is shown in Table 7.

[0032]

[Table 7] Next, the present inventors have recently studied by focusing on a zirconia electroformed refractory that is proposed and used as a refractory having excellent erosion resistance and load softening characteristics for melting a special glass. . As a result, they have found that zirconia electroformed refractories can be sufficiently used as refractories for waste melting furnaces.

[0033]

[Table 3] Table 3 shows electroformed refractories containing 85% by weight or more of ZrO _2.
The chemical composition of the examples (Examples 1 to 4) is shown.

[0034]

[Table 4] Table 4 shows the chemical compositions of four examples (Examples 5 to 8) of fired refractories containing 85% by weight or more of ZrO ₂ containing stabilized zirconia grains.

[0035]

[Table 5] Table 5 shows ZrO ₂ blended with high zirconia electroformed refractory particles.
Two examples of fired refractories of 85% by weight or more (Examples 9 and 10)
The chemical composition of

[0036]

[Table 6] Table 6 shows the erosion resistance (unit: mm) of the refractories of Examples 1 to 10 to the melt.

The test method for the amount of erosion is the above-mentioned Comparative Examples 1 to 1.
It is the same as when 0.

As is clear from the results of Table 6, Example 1
Refractories of ~ 4 are hardly eroded by the waste melt. On the other hand, MgO, Y of Examples 5-8
Fired refractories stabilized with ₂ O ₃ , CaO, etc. also show strong erosion resistance to the melt. However, since the stabilizer dissolves into the melt, the composition is slightly inferior to that of the electroformed refractory. The refractories of Examples 9 and 10 show strong erosion resistance comparable to that of Examples 5 to 8.

The above Examples 1 to 10 and Comparative Examples 1 to 10
From the experimental results, it was found that various effects can be obtained by using the zirconia refractory containing 85 wt% or more of ZrO ₂ in the liquid surface contact portion and the outlet of the waste melting furnace.
This refractory is especially effective when used in a plasma furnace.

Illustrative Example FIG. 1 is a vertical sectional view of a model of a plasma furnace for melting waste. The furnace 1 is lined with a refractory material consisting of a heat insulating material 3 and a high corrosion resistant material 4 in two layers on the entire inside of the shell 2. A plasma torch 1 is attached to the ceiling of the furnace 1 lined with refractory material in this way.
1 is provided vertically. Correspondingly, the electrode 12 on the bottom of the furnace
Is provided vertically. The waste (not shown) put in the furnace 1 through the charging port 17 at the upper left of the figure is melted in the furnace and accumulated in the lower part of the furnace 1. The melt 14 is appropriately discharged from an outlet 15 formed in the side portion of the furnace 1. At that time, a predetermined portion 13 of the outlet 15 that contacts the melt 14 (hatched portion in the drawing) and a portion 19 that contacts the liquid surface 16 of the melt 14.
A zirconia refractory material containing 85% by weight or more of ZrO ₂ is lined in the shaded area in the figure. A gas outlet 18 is provided on the ceiling of the furnace 1 as needed.

As shown in FIG. 2, the zirconia refractory materials of Examples 9 and 10 used in the furnace of the present invention were the coarse particles 5 of high zirconia electroformed refractory material and the high zirconia electroformed refractory material. It consists of medium particles 6, small particles 7 of high zirconia electroformed refractory, and matrix portion 8 made of clay and tabular alumina fine particles, and the matrix portion 8 has minute pores (not shown).
It is included.

As shown in FIG. 3, in each of the coarse particles 5, the medium particles 6 and the small particles 7, each particle is composed of a zirconia particle a and a glass matrix b.

Since the liquid surface 16 and the outlet 15 are likely to be in an oxidizing atmosphere, the Al ₂ O ₃ --SiC refractory material is oxidized and cannot be used, and MgO--which has a relatively high corrosion resistance in an oxidizing atmosphere. Even Cr ₂ O ₃ -based refractories were inadequate as indicated by the results of the erosion test.

Since zirconia refractory containing 85% by weight or more of ZrO ₂ is extremely stable physically and chemically in an oxidizing atmosphere and a reducing atmosphere, it may be used at a portion other than the liquid surface and the outlet.

[0045]

INDUSTRIAL APPLICABILITY The waste melting furnace of the present invention, in particular, the plasma furnace operated at a high temperature has sufficient chemical resistance to withstand severe erosion and wear due to waste melting. Further, the melting loss of the inner lining of the furnace is reduced over a long period of time, and it has durability, and the life of the furnace is dramatically extended, which is extremely advantageous in practical use.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a plasma furnace as an optimum example of a waste melting furnace according to the present invention.

FIG. 2 is a sectional view schematically showing a part of a zirconia refractory used for lining a waste melting furnace according to the present invention.

3 is an enlarged cross-sectional view showing in detail one of the coarse particles in the zirconia refractory material of FIG.

[Explanation of symbols]

1 furnace 2 shell 3 heat insulating material 4 high corrosion resistance material 5 coarse particles of high zirconia electroformed refractory material 6 medium particles of high zirconia electroformed refractory material 7 small particles of high zirconia electroformed refractory material 8 matrix composed of clay and tabular alumina fine particles ( A) Zirconia particles b Glass matrix 11 Plasma torch 12 Electrode 13 Portion of outlet lined with zirconia refractory material 14 Melt 15 Outlet port 16 Liquid level 17 Charge port 18 Gas outlet 19 Furnace lined with zirconia refractory material Part of

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Claims (3)

[Claims] 1. At least a portion that comes into contact with the liquid surface of the melt and a portion that comes into contact with the melt at the outlet when the melt flows out are Z
A furnace for melting waste, which is composed of a zirconia refractory material containing 85% by weight or more of rO ₂ . 2. The furnace for melting waste according to claim 1, wherein the furnace is a plasma furnace. 3. The furnace for melting waste according to claim 1, wherein the zirconia refractory material is an electroformed refractory material.