JP2004217517A - Chromium-free monolithic refractory for waste material melting furnace and waste material melting furnace lined with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-free monolithic refractory which exhibits a service life comparable to that of the alumina-chromia monolithic refractory as the lining of a waste material melting furnace. <P>SOLUTION: The chromium-free monolithic refractory for the waste material melting furnace has a composition containing a refractory raw material mainly containing alumina, a binder and a dispersant, and includes >96 mass% Al<SB>2</SB>O<SB>3</SB>by chemical analysis and ≤10% apparent porosity in a formed body obtained by curing and drying after pouring. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a chromium-free amorphous refractory used for lining a waste melting furnace such as a gasification melting furnace and an ash melting furnace, and a waste melting furnace lined with the chromium-free amorphous refractory.

  In recent years, gasification melting furnaces that directly melt waste and ash melting furnaces that melt incineration ash of waste have emerged as waste treatment furnaces excellent in reducing the volume of waste and suppressing dioxin generation.

The main cause of wear of refractories lined in these waste melting furnaces is the attack of slag generated by melting the waste. This slag contains an alkali such as sodium (Na ₂ O + K ₂ O: 2 to 10% by mass) derived from waste components and an acid such as chlorine, and has a CaO / SiO ₂ mass ratio of 0.3 to 1.5. Low basicity. The operation of the waste melting furnace is performed at an extremely high temperature of 1300 ° C. or more, and the slag component is extremely severely damaged by alkali, acid and low basicity.
Refractories used in waste melting furnaces are broadly classified into fixed refractories and irregular refractories. The construction of fixed refractories involves brickwork, requires heavy labor and requires advanced skills. Therefore, in recent years, lining made of irregular-shaped refractories has been widely used.

   A material conventionally used as an amorphous refractory for a waste melting furnace is a chromia-containing product represented by alumina-chromia (for example, see Patent Document 1). This material exhibits excellent corrosion resistance in combination with the fire resistance and volume stability of alumina and the slag resistance of chromia. However, there is a problem that chromium oxide as a refractory component changes into hexavalent chromium which is harmful to the human body, and slag discharged from the furnace and refractory after use cause environmental pollution.

Therefore, a chromium-free material containing no chromia raw material has been proposed as an amorphous refractory for a waste melting furnace or an incinerator. For example, they are alumina-zirconia (for example, see Patent Document 2), alumina-magnesia (for example, see Patent Document 3), and alumina-silicon carbide (for example, see Patent Document 4).
JP-A-10-324562 (pages 1-3) JP-A-2000-281455 (pages 1-6) JP 2001-153321 A (pages 1-7) JP-A-2000-203952 (pages 1-8)

   However, none of the conventional chromium-free materials has sufficient durability. Since the slag of the waste melting furnace has a low basicity, the zirconia component and the magnesia component of alumina-zirconia or alumina-magnesia are eluted into the slag, resulting in poor corrosion resistance. Alumina-silicon carbide is inferior in corrosion resistance due to oxidative decomposition of silicon carbide components because the operation of the waste melting furnace is in an oxidizing atmosphere.

   An object of the present invention is to provide a chromium-free amorphous refractory having a service life comparable to that of an alumina-chromia amorphous refractory as a lining of a waste melting furnace.

The chrome-free amorphous refractory for a waste melting furnace of the present invention is an amorphous refractory having a composition including a refractory raw material of an alumina main material, a binder and a dispersant.After pouring, curing and drying. In the measurement of the molded body, the chemical analysis value is characterized by an Al ₂ O ₃ content of more than 96% by mass and an apparent porosity of 10% or less.

The conventional chromium-free material combines alumina with a considerable amount of zirconia, magnesia, and silicon carbide. On the other hand, in the present invention, the material of the alumina main material having an Al ₂ O ₃ purity of more than 96% by mass in the measured value of the molded body cured and dried after the casting is used. Further, the apparent porosity is limited to 10% or less in the measured values of the molded article. As a result, the present invention significantly improves the durability as a lining for a waste melting furnace, for the following reasons.

    The slag of the waste melting furnace has low viscosity in addition to the low basicity and the extremely high operating temperature of the waste melting furnace. In the present invention, by limiting the apparent porosity of the molded article of the alumina-based amorphous refractory to 10% or less, more preferably 5.0 to 8.5%, the alkali and acid peculiar to the waste melting furnace can be reduced. Slag infiltration caused by low-viscosity slag containing a large amount is prevented, and erosion due to alkali, acid, and low basicity of the slag component is largely suppressed.

    Factors for improving the durability of refractories include spalling resistance in addition to corrosion resistance. The operating temperature of the waste melting furnace is an extremely high temperature of 1300 ° C. or higher, and since the furnace generally has a water-cooled structure, spalling easily occurs due to a temperature difference between the inside and outside of the furnace.

In the present invention, the volume stability of alumina itself is maximized by setting the Al ₂ O ₃ purity of the molded body to more than 96% by mass. Moreover, the thermal conductivity is improved by the low porosity of the molded body having an apparent porosity of 10% or less, and the temperature difference in the thickness direction of the lining is reduced. In addition, because of the irregular refractory structure, the refractory structure is excellent in thermal shock buffering unlike the pressure molded refractory or the sintered refractory.

   The refractory structure usually has a tendency to decrease the thermal shock buffering effect when densified, resulting in inferior spalling resistance.However, the chromium-free amorphous refractory of the present invention has a combined effect of its material and use. Despite its dense nature, it exhibits excellent spalling resistance. The improvement of the spalling resistance suppresses crack generation, suppresses the penetration of low-viscosity slag peculiar to a waste melting furnace, and greatly contributes to the improvement of corrosion resistance.

Conventional materials such as alumina-chromia, alumina-zirconia, and alumina-magnesia have a larger coefficient of thermal expansion than the alumina of the present invention having high Al ₂ O ₃ purity. When these alumina-chromia and alumina-zirconia materials have a low porosity having an apparent porosity of 10% or less, over-sintering occurs due to the reaction between alumina and other components, and the alumina-magnesia material is in use. An Al ₂ O ₃ —MgO-based spinel is generated at a high temperature to cause volume expansion. All of these materials have reduced spalling resistance, and the effect of the present invention cannot be obtained.

   Due to the above effects, the chromium-free amorphous refractory of the present invention has excellent corrosion resistance and spalling resistance under the use conditions of a waste melting furnace, and has a durability equivalent to that of alumina-chromia.

  A dispersant is added to the composition of the amorphous refractory to impart fluidity during construction. Conventionally, various dispersants have been known. In the present invention, a carboxyl group-containing polyether dispersant is used as the dispersant, and one or more Ca compounds selected from slaked lime, lime, calcium carbonate, calcium chloride or calcium lactate are combined with the refractory raw material. By adding 0.01 to 1% by mass based on the total amount of the agent, a molded product having a low porosity having an apparent porosity of 10% or less, more preferably 5.0 to 8.5% can be easily obtained. be able to.

  An organic dispersant such as sodium polyacrylate, which is generally used as a dispersant, adsorbs on the surface of the refractory fine powder and forms an adsorbing layer for repelling the particles to exhibit a dispersing effect.

    On the other hand, the carboxyl group-containing polyether dispersant has a long ethylene oxide chain and has a dispersing action due to a large steric repulsion effect of the long ethylene oxide chain. However, the steric repulsion of the ethylene oxide chain cannot be sufficiently utilized simply by using the carboxyl group-containing polyether dispersant.

When a carboxyl group-containing polyether dispersant is used as a dispersant, one or more Ca compounds selected from slaked lime, lime, calcium carbonate, calcium chloride or calcium lactate are further added. The Ca compound elutes Ca ₂ ⁺ ions in the solution and accelerates the adsorption rate to the alumina particles, thereby promoting the steric repulsion of the ethylene oxide chain of the carboxyl group-containing polyether dispersant, and when applying the amorphous refractories. Is significantly improved. As a result, it is possible to easily obtain a molded product having a low porosity of 10% or less in apparent porosity necessary for the effect of the corrosion resistance and spalling resistance of the present invention, and more preferably 5.0 to 8.5%.

    Waste treatment furnaces operate at high temperatures, unlike incinerators, and their refractory wear mechanisms are unique to waste treatment furnaces due to low basicity slag, alkali, and acids derived from waste components.

    The amorphous refractory of the present invention exhibits excellent durability as an amorphous refractory for this waste treatment furnace. In addition, since the chromium-free material is used, there is no problem of environmental pollution unlike the conventional chromia-containing material.

    In the present invention, the alumina used for the amorphous refractory may be an electrofused product or a sintered product. These are appropriately adjusted to coarse, medium, and fine particles for use. For the fine powder portion, calcined alumina that is easily available as ultrafine powder may be used.

Examples of the binder include alumina cement, phosphate, and silicate, and alumina cement is preferable from the viewpoint of the strength of the construction body. Further, since the alumina cement contains an Al ₂ O ₃ component, its use is preferable in order not to lower the Al ₂ O ₃ and the purity of the molded body necessary for obtaining the effects of the present invention. The amount of the binder to be used is suitably 1 to 10% by mass relative to the total amount of the refractory raw material and the binder.

    As the dispersant, for example, sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, sodium acid hexametaphosphate, sodium borate, sodium citrate, sodium tartrate, sodium polyacrylate, sodium sulfonate, and the like are known. In order to obtain the molded product having a low porosity of the present invention, it is preferable to use a carboxyl group-containing polyether-based dispersant as described above.

    The carboxyl group-containing polyether-based dispersant may be in powder or liquid form. The liquid is, for example, a substance dispersed or dissolved in water or the like. The amount of addition is not particularly different from a general dispersant, and is preferably 0.01 to 0.8% by mass, more preferably 0.05 to 0. 0% by mass, based on the total amount of the refractory raw material and the binder. 6% by mass. In the case of use in a liquid state, the above ratio is a solid content converted value. If the addition amount is small, the effect of imparting fluidity becomes insufficient, and if it is too large, the workability is inferior due to curing delay.

    This carboxyl group-containing polyether-based dispersant can be obtained from a commercial product, for example, as TAILOCK (registered trademark) or Mighty (registered trademark) manufactured by Kao Corporation.

By using the carboxyl group-containing polyether-based dispersant in combination with a Ca compound, a molded product having a low porosity limited in the present invention can be obtained. Specific examples of the Ca compound are one or more selected from slaked lime, lime, calcium carbonate, calcium chloride or calcium lactate. If the ratio is less than 0.01% by mass based on the outer weight of the refractory raw material, there is no effect. Since the Ca compound is inferior in corrosion resistance to slag having a small CaO / SiO ₂ ratio, if it exceeds 1% by mass, it causes a decrease in corrosion resistance.

    The Ca compound is preferably added in the form of a powder, but when the Ca compound is added in an aqueous solution or the like, the amount of the Ca compound to be added is converted into a solid.

In addition to the above alumina raw materials, binders, dispersants and Ca compounds, fire-resistant raw materials other than alumina, a curing regulator, aluminum lactate, organic fibers, a drying accelerator, etc. are added to the extent that the effects of the present invention are not impaired. You may. In the present invention, even when these are added, it is necessary that the shaped body of the amorphous refractory is not less than 96% by mass of Al ₂ O ₃ by a chemical analysis value by adjusting the amount of addition.

    Examples of the refractory raw material other than the above-mentioned alumina include silica such as silica stone, titanium oxide, metal powder such as metal silicon, nickel and aluminum, aluminum phosphate, refractory coarse particles, volatile silica, and glass.

    In the construction, about 3 to 5% by mass of water is added to the above-mentioned irregular-shaped refractory composition, the mixture is kneaded, and the mixture is poured using a mold. At the time of pouring, vibration is applied to achieve filling. After construction, cure and dry. In this work, besides directly pouring into the furnace, a precast product obtained by pouring into the formwork at another place may be lined with the furnace.

The amorphous refractory of the present invention has an Al ₂ O ₃ content of 96% by mass, more preferably 96.5 to 99.5% by mass, as measured by a chemical analysis in the measurement of a cured and dried compact after casting. And When the Al ₂ O ₃ content is small, both the corrosion resistance and the spalling resistance decrease. When the content of Al ₂ O ₃ is large, the amount of the binder is small and a dense structure cannot be secured, and also in this case, the corrosion resistance and the spalling resistance are reduced.

    Also, when the apparent porosity of the molded product exceeds 10%, the corrosion resistance and spalling resistance are similarly poor. A more preferable range of the apparent porosity is 5.0 to 8.5%. If the apparent porosity is too small, the spalling resistance is poor. The adjustment of the apparent porosity is performed by adjusting the particle size of the refractory aggregate, the amount of water for construction, and the like, in addition to the selection of the type of the dispersant.

    In the present invention, a carboxyl group-containing polyether-based dispersant is used as a dispersant, and one or more Ca compounds selected from slaked lime, lime, calcium carbonate, calcium chloride or calcium lactate are added to form an amorphous form. The fluidity at the time of refractory construction is improved, and accordingly, the construction moisture can be reduced, and the construction body has low porosity.

    The apparent porosity can be measured according to JIS R2205. Although this standard is for measurement of refractory bricks, since the object of measurement in the present invention is a measurement of a molded article, the specific method is not different from the JIS regulations.

    The waste melting furnace is generally provided with a cooling device. The cooling device is, for example, an arrangement of a water-cooled pipe, a water-cooled jacket, an air-cooled jacket, a sprinkler, and the like. The amorphous refractory according to the invention is particularly suitable as a lining of a waste melting furnace provided with this cooling device.

Hereinafter, Examples of the present invention and Comparative Examples thereof will be described. At the same time, the test results of each example are shown. Table 1 shows the chemical components of the refractory raw materials used in each example, Table 2 shows the examples of the present invention, and Table 3 shows the comparative examples.

  Here, as the carboxyl group-containing polyether dispersant, TAILOCK (registered trademark) P-100 manufactured by Kao Corporation was used. The sodium polyacrylate dispersant was manufactured by Toagosei Co., Ltd.

  In each case, the compounded composition of the irregular refractories shown in the table was kneaded with a mixer and then poured into a metal mold. At the time of pouring, vibration was applied to the formwork to promote filling of the construction body. Then, it was cured for 24 hours, and after demolding, further dried at 110 ° C. for 24 hours.

The Al ₂ O ₃ content of the molded body was measured by a fluorescent X-ray analysis method (JIS R2216) for the molded body obtained by constructing a normal brick having a size of 230 mm × 114 mm × 65 mm under the above conditions.

   The apparent porosity of the molded article was measured by a vacuum method according to JIS R2205, by cutting a molded article obtained by applying a regular brick size under the above conditions to a quarter size.

  The spalling resistance was determined by using a sample of the molded article having the above-mentioned average brick size. After heating one side in the length direction in an electric furnace at 1400 ° C. for 15 minutes, the air-cooling was performed, and this heating-cooling was repeated 10 times. …: Almost no cracks. …: Occurrence of fine cracks. Δ: The crack is large. ×: Cracks are extremely large or peeled.

The corrosion resistance was measured by a rotary erosion test using a molded body obtained by constructing a regular brick under the above conditions as a sample. As an erosion agent, the chemical component values are SiO ₂ : 42.8, CaO: 31.7, Al ₂ O ₃ : 12.4, Fe ₂ O ₃ : 4.8, Na ₂ O: 3.7, by weight ratio, A gasification melting furnace slag of CaO / SiO ₂ : 0.74) was used. After erosion at 1650 ° C. × 20 hours, the erosion dimensions were measured.

  As an actual machine test, a waste gas treatment amount per day was 100 t, and the inside was lined with a gasification melting furnace having a water cooling device on a side wall. The wear rate (mm / month) was measured after 12 months of use. The operating temperature of this gasification melting furnace was about 1400 ° C.

  As shown by the test results, all of the examples of the present invention are excellent in corrosion resistance and spalling resistance, and their durability is almost equal to that of the chromium oxide-containing product of Comparative Example 6 in an actual machine test.

On the other hand, Comparative Examples 1 to 3 contain a considerable amount of magnesia, zirconia or silicon carbide, and the Al ₂ O ₃ content of the molded product is smaller than the limited range of the present invention. In Comparative Examples 4 and 5, the apparent porosity of the molded product is larger than the limited range of the present invention. In Comparative Example 6, although the apparent porosity of the molded product was within the range of the present invention, the content of Al ₂ O ₃ was small. All of Comparative Examples 1 to 5 are inferior in corrosion resistance and spalling resistance.

  Comparative Example 7 contains a large amount of chromium oxide and is excellent in corrosion resistance. However, there is a concern about formation of hexavalent chromium, and the effects of the present invention cannot be obtained due to environmental problems.

  Further, in a case where a carboxyl group-containing polyether-based dispersant is used as a dispersant, and in combination with a Ca compound, a molded article having a low porosity required for the present invention can be obtained. Although not shown in the table, within the scope of the present invention, it is possible to similarly obtain a molded product having a low porosity by using lime which is a CaO compound other than slaked lime, calcium carbonate, calcium chloride or calcium lactate. Was.

FIG. 1 shows the amorphous refractories of alumina (Al ₂ O ₃ content 98.3% by mass), alumina-zirconia (ZrO ₂ content 40% by mass), and alumina-magnesia (MgO content 10% by mass). In the article, the relationship between the apparent porosity of the molded article and the corrosion resistance was tested, and the results are shown in a graph. The test was performed in the same manner as in the corrosion resistance test in the above-mentioned Example. The smaller the index, the better the corrosion resistance.

From the results of the graph, it can be confirmed that the reason that the corrosion resistance is remarkably improved by setting the apparent porosity in the range limited by the present invention is alumina having a high Al ₂ O ₃ content.

4 is a graph showing the relationship between apparent porosity and corrosion resistance of a molded article of an amorphous refractory.

Claims (5)

An amorphous refractory having a composition including a refractory raw material of an alumina main material, a binder and a dispersing agent. After the pouring, curing and drying of the molded product, the chemical analysis value shows the Al ₂ O ₃ content. A chromium-free amorphous refractory for a waste melting furnace having a porosity of more than 96% by mass and an apparent porosity of 10% or less.   The dispersant is a carboxyl group-containing polyether dispersant, and one or more Ca compounds selected from slaked lime, lime, calcium carbonate, calcium chloride or calcium lactate are cross-linked to the total amount of the refractory raw material and the binder. The chromium-free amorphous refractory for a waste melting furnace according to claim 1, which is added in an amount of 0.01 to 1% by mass.   The chromium-free amorphous refractory for a waste melting furnace according to claim 1 or 2, having an apparent porosity of 5.0 to 8.5%.   A waste melting furnace lined with the chromium-free amorphous refractory according to any one of claims 1 to 3.   5. The waste melting furnace according to claim 4, wherein the waste melting furnace includes a water cooling device.

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