JP2601129B2 - Alumina-chromia castable refractory and precast block using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina-chromia castable refractory having corrosion resistance and thermal shock resistance, and to a precast block formed using the castable refractory.

[0002]

2. Description of the Related Art Refractories containing chromia and alumina as main components are resistant to erosion by high silica slag, so that they are used in coal gasifiers, glass melting furnaces, sludge melting furnaces and the like. It has been widely used as a material. However, with the severer use conditions, conventional alumina-chromia refractories cannot be used.

The prior art of alumina-chromia castable refractories is disclosed in, for example, JP-A-62-207772 and JP-A-59-50081. Japanese Patent Application Laid-Open No. Sho 62-207772 discloses that the addition of a relatively small amount of chromium oxide, such as 1 to 7% by weight, improves the corrosion resistance to low basicity slag. Is not specifically described,
It is considered that a normal commercial product (average particle size of about 0.5 μm) is used. JP-A-59-50081 is disclosed in
0.5 to 15% by weight of chromium oxide is used as a member of a member that exerts a strength developing effect by van der Waals force. It is shown as one. Therefore, chromium oxide is not used as a material for imparting corrosion resistance.

In a Cr ₂ O ₃ —Al ₂ O ₃ —ZrO ₂ castable refractory disclosed in JP-A-3-174369, coarse aggregate particles having a particle diameter of 1 to 10 mm and a particle diameter of 1 mm C for any of the following fine aggregate particles:
r ₂ O ₃ is used, and its Cr ₂ O ₃ content is 50 to 90% by weight in both coarse and fine particles, and a large amount of C of 50 to 90% by weight with respect to the entire castable refractory.
r ₂ O ₃ content. Therefore C used here
Since the entire amount of r ₂ O ₃ is not incorporated into a matrix portion of 1 mm or less, which is important for corrosion resistance, the effect of improving the corrosion resistance of chromia is not effectively utilized. Therefore, in the invention of JP-A-3-174369, Z
Corrosion resistance is improved by using rO ₂ in combination.

[0005] As a prior art of castable refractories containing Cr ₂ O ₃ , there is Japanese Patent Publication No. 60-9983, in which chromite is used as a Cr ₂ O ₃ source.
Since chromite contains MgO, it reacts with slag and
O.MgO.2SiO ₂ (diopside, melting point = 1
390 ° C) and CaO ・ MgO ・ SiO ₂ (montic
(melting point = 1610 ° C.), which is disadvantageous in that the erosion is large.

[0006]

Chromia has the effect of improving the corrosion resistance. However, if it is added in a large amount, the corrosion resistance is improved, but the workability is reduced and the thermal shock resistance is also reduced. In particular, when a large amount of ultrafine chromium oxide having an average particle diameter of about 0.5 μm, such as a commercially available product, is used in a large amount, the cohesive force is too large, the pot life is short, and the workability is poor. According to an experiment by the present inventors, when such ultrafine chromium oxide is used, the limit of addition of chromium oxide is about 7% by weight. It has been found difficult to use.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an improved alumina-chromia castable refractory which does not reduce the thermal shock resistance and the workability while improving the corrosion resistance by adding chromia. It was done.

[0008]

The inventor of the present invention has stated that in order to effectively utilize the effect of improving the corrosion resistance of chromia, it is necessary to use a chromia coarse angle having a specific particle size. Alumina-chromia castable refractories that can effectively improve corrosion resistance even if the amount of chromia added is kept relatively low, and do not reduce thermal shock resistance or workability. And completed the present invention.

That is, the alumina-chromia castable refractory according to the present invention comprises a chromia coarse having a particle size-adjusted alumina raw material or a mixture of an alumina raw material and a zircon raw material of 30 to 85% by weight and a particle diameter of 1 mm to 1 μm. 7 to 50% by weight, 3 to 20% by weight of refractory fine powder having a particle diameter of 45 μ or less, 0.5 to 10% by weight of alumina cement having a particle diameter of 100 to 1 μm, and an appropriate amount of a dispersant. It is characterized in that the SiO ₂ content is 6% by weight or less.

[0010] By adding a small amount of water to the castable refractory, kneading, molding and drying, an alumina-chromia precast block can be obtained.

The coarse chromia used in the present invention has a particle diameter of 1 mm to 1 μm. This is because such a particle diameter can effectively utilize the function of improving corrosion resistance. Use of coarser particles weakens the effect of improving corrosion resistance. On the other hand, in the case of a commercially available ultrafine powder such as chromium oxide (average particle size of about 0.5 μm), the effect of improving corrosion resistance is slightly better than the coarse angle of 1 mm to 1 μm, but when used in large quantities, the cohesive force is too large The pot life is shortened, and the workability deteriorates. Therefore, in the present invention, a commercially available ultrafine chromium oxide may be used in combination with the chromia coarse angle as needed within a range of about 7% by weight or less that does not deteriorate the workability.

In the present invention, the amount of the chromia coarse angle to be added is 7 to 50% by weight. If the addition amount is less than 7% by weight, the effect of improving corrosion resistance is not sufficient,
On the other hand, even if the chromia coarse angle is added in excess of 50% by weight, the improvement in corrosion resistance is limited and not only wasteful,
It tends to reduce workability and thermal shock resistance.

The coarse chromia angle used in the present invention can be prepared, for example, by the following method. An organic binder and water are added to 90 to 99% by weight of a commercially available chromium oxide, 0 to 4% by weight of alumina, and 0.5 to 5% by weight of a mineralizer, and the mixture is uniformly mixed.
Molding is performed by applying a pressure of 0 kgf / cm ² . 12 after drying
After baking at 00 to 1800 ° C. for 5 to 20 hours, it is pulverized and sieved. As a mineralizer, TiO ₂ , SiO ₂ , Mg
Conventionally known materials such as O and Fe ₂ O ₃ can be used. Table 1 shows an example of the chromia coarse angle characteristics used in the present invention.

[0014]

Although the physical properties of the chromia coarse angle vary depending on the chemical composition, molding pressure, firing temperature and firing atmosphere, those having an apparent porosity of 5.0 to 15.0% can be preferably used.

The higher the chromia coarse angle Cr ₂ O ₃ content,
Since the effect of improving the corrosion resistance of castable refractories using the same increases, the Cr ₂ O ₃ content in the chromia coarse angle is 90%.
It is preferable to make the above. When a chromia coarse angle having a lower Cr ₂ O ₃ content is used, the effect of improving corrosion resistance tends to be weakened.

The coarse chromia angle has a particle size distribution because it is obtained by pulverizing the material once sintered. Depending on the pulverization method, particles of 1 mm or more may be mixed, but 90% or more may be 1 mm or less. In addition, it is acceptable that 90% or more is 100 μm or less by sufficiently pulverizing. This is because once chromia is sintered under the above conditions, it grows and loses its activity, so that the workability of the castable refractory is not impaired.

As the alumina raw material used in the present invention, fused alumina or sintered alumina having an Al ₂ O ₃ component of 95% by weight or more can be preferably used. Although calcined bauxite, mullite, kyanite, etc. can be used as a part of the alumina-based raw material, SiO in castable refractories can be used.
_{2 When the} content increases, the corrosion resistance decreases. Therefore, the amount of use must be limited to a range where the total SiO ₂ content in the castable refractory falls within 6% by weight or less.

As the zircon material, zircon sand and zircon flower can be preferably used in the present invention. The spalling resistance of the alumina-chromia castable refractory can be improved by adding such a zircon material.

These alumina-based raw materials and zircon-based raw materials can be used alone or as a mixture of both.
It is added in the range of 0 to 85% by weight. If the amount is less than 30% by weight, the thermal shock resistance of the castable refractory obtained will be poor, while if it is more than 85% by weight, the corrosion resistance will decrease.

As the refractory fine powder, alumina, chromium oxide, refractory clay, kaolin, silica flour, white carbon, evaporated silica, hydrated amorphous silicic acid and the like can be preferably used. The particle size of these refractory fine powders is 45 μm or less, preferably 10 μm or less. When the particle size is larger than this, the water reducing effect due to the combined use with the dispersant is lost. The addition amount of the refractory fine powder is 3 to 20% by weight. 3
When the amount is less than the weight%, the fluidity becomes insufficient. Meanwhile, 2
If it is added in excess of 0% by weight, excessive sintering causes a large shrinkage, which causes cracks. When a refractory fine powder containing silica is used, its amount must be limited so that the total content of SiO ₂ in the castable refractory falls within 6% by weight or less. These refractory fine powders impart fluidity to the castable refractory at the time of construction, and are strongly bound by van der Waals bonds by Ca ⁺⁺ ions eluted from alumina cement used as a binder component in the present invention. Improves body strength and compactness.

In the present invention, the alumina cement which acts as a binder and exerts strength is mainly composed of Ca
Since O causes deterioration of corrosion resistance, the amount of addition should be reduced as much as possible. However, a certain amount of strength is required to prevent the furnace material from being worn by the contents of the furnace such as slag and glass, and the minimum required amount of alumina cement is determined from such a viewpoint. Suitable addition amounts range from 0.5 to 10% by weight. 0.5
If the amount is less than 10% by weight, the required strength will not be obtained.

The dispersants used in the present invention include sodium hexametaphosphate, sodium pyrophosphate, polycarboxylates, humates, sodium tripolyphosphate,
Conventionally used materials such as sodium ultrapolyphosphate and sodium polyacrylate can also be used. The dispersant may be added in an appropriate amount that is conventionally used, generally in the range of 0.01 to 0.5% by weight. When the amount of the dispersant added is small, the dispersibility of the refractory fine powder becomes poor. On the other hand, if the addition amount is too large,
Conversely, the viscosity increases and the flow does not flow unless the amount of added water is increased, and the construction body tends to be porous and low in strength.

The castable refractory of the present invention can be worked with good fluidity by adding a small amount of water by the action of the dispersant and the refractory fine powder, and a dense work can be obtained. As a result, chromia is less likely to be peroxidized and disappear during operation, so that corrosion resistance can be maintained for a long time.

If the castable refractory of the present invention is used under conditions of rapid temperature rise without sufficient drying time after the application, metal aluminum may be further added to the metal if necessary. It can be added in the range of weight%. This can also prevent explosions.

[0026]

The present invention will be described in detail below with reference to examples, comparative examples and conventional examples. In Examples, Comparative Examples, and Conventional Examples, the raw materials shown in Table 2 were used in proportions of 15 to 20 shown in Table 3.
The mixture was kneaded at an ambient temperature of ℃, and the pot life and other various physical properties were measured. The kneading was performed with a Dalton mixer, and the mixture was poured into a parallel test frame of 65 × 114 × 230 mm while being immediately vibrated, cured at 15 to 20 ° C. for 24 hours, and then removed from the frame. Dried specimens dried at 110 ° C. for 24 hours;
The apparent porosity and compressive strength of the fired specimens fired at 0 ° C. for 3 hours were measured. The measured values of physical properties and evaluation data are also shown in Table 3. The measuring methods and evaluation criteria for various physical properties are as follows.

Thermal shock resistance : A 65 × 114 mm side of a 65 × 114 × 230 mm parallel-shaped specimen was kept in an electric furnace maintained at 1400 ° C. for 15 minutes, then taken out of the furnace and forced-air cooled for 15 minutes. The work cycle was performed up to 40 times. Evaluation was made based on the number of work cycles up to spalling. The thermal shock resistance is better when the number of repetitions of the work cycle up to spalling is larger. In addition, the specimen is 1400 in advance.
What was fired at 8 ° C. × 8 hours was used.

Erosion test : Rotating drum method. Sample shape: 50 × 50 × 230 mm. Slag _{... CaO 7%, SiO 2 50} %, Al 2
O ₃ 20%, MgO 2%. Time: Hold at 1600 ° C for 18 hours. The erosion ratio is shown with the erosion amount of Conventional Example 1 (no chromium raw material added) as 100. The smaller the numerical value of the erosion ratio, the smaller the erosion.

Apparent porosity : 65 × 114 × 230 mm parallel-shaped specimens were treated at each temperature and measured according to JIS R2205.

Compressive strength : Measured in accordance with JIS R2206 on a specimen molded to a size of 65 × 114 × 230 mm.

[0031] The pot life: at the time of construction, after the hydrolysis kneading,
It is shown by the time until it becomes unworkable due to curing.

[0032]

[0033]

[0034]

[0035]

As shown in Table 3, chromia added in the form of fine powder is effective for improving corrosion resistance. The particle diameter of the chromia coarse angle is 3 to 1 mm (Comparative Example 2) than 5 to 3 mm (Comparative Example 1) and 1 mm to 1 μm than 3 to 1 mm (Example 1).
Use of a particle size of is effective in improving corrosion resistance. 1mm-1
It can be seen that 1 μm to 0.1 μm of chromium oxide (conventional example 3) is slightly more effective in improving corrosion resistance than chromia coarse angle of μ (example 1), but there is almost no difference. However, 1
It is shown that the one using chromium oxide of μ-0.1 μ as it is (conventional example 3) has poor thermal shock resistance. Further, when 1 μm to 0.1 μm of chromium oxide is added in the same amount (13% by weight) as the chromia coarse angle of 1 mm to 1 μm (conventional example 3), the pot life is shortened and it becomes unusable. The one using chromite ore containing MgO as the chromic raw material (conventional example 2) is inferior in corrosion resistance.

It has been shown that the addition of zircon as an aggregate improves thermal shock resistance (Example 2). However, when a large amount of zircon is added, the total SiO ₂ content becomes 6
It can be seen that the case where the amount exceeds the weight% (Comparative Example 3) is deteriorated in corrosion resistance. 1 μm to 0.1 μm of chromium oxide is within a range of about 7% by weight or less such that workability is not deteriorated.
It can be used together with a chromia coarse angle of 1 mm to 1 μ (Example 3).

The limit of chromia coarse angle addition is 50% by weight. Even if the amount is further increased, no improvement in corrosion resistance is observed (Example 4, Example 5, Comparative Example 4). Although calcined bauxite having a low alumina content can be used (Example 7,
8) The fact that the total SiO ₂ content should be limited to 6% by weight or less is the same as in the case of adding zircon. S
When calcined bauxite with a high iO ₂ content is used,
When the total SiO ₂ content exceeds 6% by weight (Comparative Example 5), the corrosion resistance decreases.

As the refractory fine powder, any of alumina fine powder, refractory clay, silica flour and the like can be used, but from the viewpoint of imparting fluidity, silica flour addition is most effective, and dense powder with low apparent porosity is used. A construction body is obtained.

Use Example The castable refractories having the compositions of Examples 1 and 2 were used in a sludge melting furnace (processed material: sewage sludge dewatered cake having a water content of 80%, throughput: 160 tons / day, furnace temperature: 1500)
C), a service life of 6 months or more was obtained. When the same furnace was lined with the castable refractory according to Comparative Example 3 or Conventional Example 4, the service life was one to two months. The refractory according to Example 1 exhibited its performance in a portion directly in contact with the slag. The refractory according to Example 2 exhibited characteristics in a portion where temperature change was remarkable.

[0041]

As can be seen from the above description,
The castable refractory of the present invention has an effect of improving the corrosion resistance to low basicity slag even when the chromia content is relatively low by using the coarse angle of chromia having a particle diameter of 1 mm to 1 μ, and furthermore, the heat resistance is high. There is no reduction in impact and workability. Furthermore, since the pot life is long, there is no need to worry about hardening even if a large amount is kneaded at a time, so the work efficiency is good. . Therefore, it can be suitably used as a lining material for, for example, a coal gasifier, a glass melting furnace, a sludge melting furnace, and the like.

Further, the castable refractory of the present invention can be constructed with good fluidity by adding a small amount of water, and can be used as a precast block. In this case, a molded article having higher strength and higher density than the cast product can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinori Onda 15-2, Shiratoridai, Midori-ku, Yokohama-shi, Kanagawa Onda-ryo (72) Inventor Masakatsu Yamazaki 292, Higashikatagami, Bizen-shi, Okayama Prefecture (72) Inventor Nobuharu Moriya Waki, Okayama Prefecture 434-9 Suga, Nissei-cho, Gunma (72) Inventor Tetsuo Hasegawa 2519 Nissei, Nissei-cho, Wake-gun, Okayama Prefecture

Claims (2)

(57) [Claims] An alumina-based raw material whose particle size has been adjusted or a mixture of an alumina-based raw material and a zircon-based raw material.
Chromia coarse angle 7 to 50% by weight, particle diameter 1 mm to 1 μm
%, 3 to 20% by weight of refractory fine powder having a particle diameter of 45 μ or less, alumina cement 0.5 having a particle diameter of 100 to 1 μm.
An alumina-chromia castable refractory comprising 10 to 10% by weight and an appropriate amount of a dispersant, and having a total SiO ₂ content of 6% by weight or less. 2. An alumina-based raw material or a mixture of an alumina-based raw material and a zircon-based raw material whose particle size has been adjusted.
Chromia coarse angle 7 to 50% by weight, particle diameter 1 mm to 1 μm
%, 3 to 20% by weight of refractory fine powder having a particle diameter of 45 μ or less, alumina cement 0.5 having a particle diameter of 100 to 1 μm.
Alumina-chromia castable refractories having a total SiO ₂ content of not more than 6% by weight, comprising a small amount of water, kneaded, molded and dried. Precast block using castable alumina / chromia refractories.