JPH04310561A - Magnesia spinel refractory - Google Patents

Abstract

PURPOSE:To provide a refractory having excellent durability useful for a burning zone of cement rotary kiln, having no formation of hexavalent chromium in refractory after use. CONSTITUTION:Magnesia spinel refractory comprising 5-30wt.% magnesia alumina spinel clinker and 10-50wt.% fused magnesia clinker as aggregates and 0.5-10wt.% partially stabilized zirconia with e.g. CaO in bonded part preferably contains 1-3wt.% CaO and 1-3wt.% SiO2 in the fused magnesia clinker. The refractory has no fear of pollution caused by the refractory to be abandoned after use, and waste is readily treated and labor and cast can be saved.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a basic refractory suitable for lining cement rotary kilns.

0002

BACKGROUND OF THE INVENTION Among basic refractories, magnesia chromium refractories have good durability and have been widely used as lining refractories for cement rotary kilns. However, small amounts of hexavalent chromium, which can be eluted into water, are generated in used refractories, so special consideration is required when disposing of them from the perspective of pollution prevention, and disposal is time-consuming. The problem is that it requires a lot of cost.

[0003] As a countermeasure for this, the special public
513 and U.S. Pat. No. 4,849,383 disclose chromium-free refractories, the former containing a suitable amount of iron oxide in a magnesia spinel refractory, and the latter containing a calcium zirconate (CaZrO3) clinker. A compounded magnesia refractory is shown.

[0004] However, the former refractory has some difficulty in heat resistance because it contains iron, and cannot provide sufficient durability when used as a lining at the high temperature of the firing zone of a rotary kiln. First, the latter has drawbacks such as a high specific gravity of the refractory due to its high ZrO2 content and insufficient thermal shock resistance.

[0005] In these refractories for cement rotary kilns, in order to protect the refractories from overheating caused by high-temperature flames and ensure their durability, the surface of the lined refractories is coated with a semi-molten cement clinker component. It is important to form a coating layer, and the ease with which a coating layer can be formed is considered to be a necessary characteristic for the durability of refractories.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a refractory suitable for use in a cement rotary kiln, which overcomes the above-mentioned drawbacks of the prior art refractories.

[0007]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and the magnesia spinel refractory of the present invention contains 5 to 30% by weight of magnesia alumina spinel (MgAl2O4) as an aggregate. Contains clinker and 10 to 50% by weight of electrofused magnesia clinker, and 0.5 to 50% partially stabilized zirconia in the joint.
It is characterized by containing 10% by weight.

[0008] Electrofused magnesia clinker not only has excellent heat resistance, but also has large and dense crystal grains, so it constitutes a refractory with particularly excellent corrosion resistance. It is necessary to contain 10% by weight or more of electrofused magnesia; conversely, if it is contained too much, there is a problem that the thermal shock resistance decreases.
It is considered to be 0% by weight or less.

By containing 0.5 to 10% by weight of partially stabilized zirconia in this clinker combination, the wettability to semi-molten cement components, that is, coating adhesion, is improved, and the joints in the refractory are improved. The corrosion resistance of the refractory is improved by promoting the crystal grain growth of the fine magnesia particles constituting the refractory, and the bonding strength of the joint is improved, thereby imparting thermal stability to the refractory.

[0010]To impart these effects, at least 0
．． It is necessary to contain 5% by weight of partially stabilized zirconia, and if it is contained in excess of 10% by weight, the specific gravity of the refractory increases accordingly, and the corrosion resistance against cement components in the molten state tends to decrease. The content of this partially stabilized zirconia is more preferably 1 to 3% by weight.
By doing so, a refractory with low air permeability and good coating adhesion can be obtained.

In a preferred embodiment of the magnesia spinel refractory of the present invention, the fused magnesia clinker is CaO
and SiO2 in an amount of 1 to 3% by weight, respectively.
In this case, in addition to further improving the wettability of the refractory to semi-molten cement components, the raw material for fused magnesia clinker can be inexpensive magnesia without refining, or even cheaper natural magnesite. It is also convenient to use.

[0012] In this case, both CaO and SiO2 have the effect of imparting wettability to the semi-molten cement component to the refractory, but both are usually contained in coexistence and it is not practical to remove only one. Not.

However, if the content is too large, the fire resistance of the refractory will be lowered, so the content is preferably 3% by weight or less.

In the magnesia spinel refractory of the present invention, the content of magnesia alumina spinel clinker is 5
If it is less than 30% by weight, Young's modulus increases and thermal shock resistance decreases, and if it exceeds 30% by weight, it tends to react with CaO 2 in the semi-molten cement clinker and tends to decrease erosion resistance.

The magnesia spinel refractory of the present invention is
It is particularly suitable as a refractory for lining cement rotary kilns. The partially stabilized zirconia contained in the magnesia spinel refractory of the present invention includes MgO and Y2.
Zirconia partially stabilized with O3 is also a candidate, but zirconia partially stabilized with these has little stability at high temperatures and is easily destabilized during use, so it is particularly difficult to partially stabilize it with calcium oxide (CaO). Preferred is oxidized zirconia.

[0016] The degree of partial stabilization is 75 to 95%, especially 80 to 90%, so that a refractory with excellent high temperature stability and thermal shock resistance can be obtained. The content of calcium oxide in the oxidized zirconia is approximately 3-6% by weight.

[0017]

EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples in any way. A total of eight types of refractories having the raw material compositions shown in Tables 1 and 2 were prototyped and tested, and a comparative test was conducted.

That is, high-purity magnesia clinker (with an MgO content of 99% by weight and a particle size of 5 mm or less), fused magnesia clinker (with an MgO content of 9% by weight),
7 wt% CaO and 1.2 wt% SiO2
containing 1.5% by weight and having a particle size of 1 to 5 mm) and magnesia alumina synthetic spinel clinker (particle size of 5 mm).
unstabilized zirconia powder (average particle size of approximately 30 μm).
), CaO partially stabilized zirconia (CaO content 4
．． 3% by weight, stabilization degree of about 89%, average particle size of about 40 μm
) powder and MgO partially stabilized zirconia (MgO
Content: 3% by weight, stabilization degree: approximately 40%, average particle size: approximately 40%
μm) powder etc., 20°Be (15% by weight)
After mixing 3% by weight of an aqueous magnesium sulfate solution as a binder, it was press-molded at 1000 kg/cm2, dried, and baked at 1780°C for 10 hours to give a size of 230 mm.
JIS standard standard bricks measuring 114 m x 65 mm were manufactured.

The produced ordinary bricks were cut into pieces and their properties were examined, and the results are shown in Tables 1 and 2 together with the blending conditions.

[0020] In the table, the air permeability is 50mm x 50mm x 50
Using a mm-sized test piece, the ventilation cross-sectional area A (cm2),
Air pressure difference Δ when sample thickness L (=50mm)
This is a value obtained by measuring P (cmH2O) and air flow rate Q (cc/sec) and calculating by K = (L x Q) / (A x ΔP). After heating in an electric furnace with one end heated to 1400℃,
The head of the specimen is at least 50% by cooling in the air.
We investigated the number of times until % was lost.

[0021] Also, the coating adhesion is determined by the thickness of the deteriorated layer and the rate of dimensional change.
Place the green cement clinker on the test piece of 153 m.
The temperature was raised to 0° C., maintained for 10 hours, and evaluated by the so-called button method, in which the state of the material was examined by melting the clinker. Thermal cycle volume stability was determined by placing a 40 mm x 40 mm x 110 mm test piece in an electric furnace and raising and lowering the temperature of the electric furnace.
After repeating heating and cooling between 0°C and 1300°C 300 times, the rate of change in volume of the test piece was investigated.

[0022]

[Table 1]

[0023]

[Table 2]

Next, No. 1.No. 4 and no.
．． Bricks with sills (230 mm x 114
mm x 65 to 75 mm). These were incorporated into a drum rotating test furnace as a lining, and while 300g of raw cement clinker was put into the test furnace every hour, the inside of the furnace was heated to approximately 1530℃ with a burner and held for 12 hours, during which time the total 3600g of green cement clinker was added.

[0025] As a result, No. 4 and no. Brick number 7 is No. Compared to brick No. 1, the coating adhered well from the beginning.

[0026] In the observation after the test, No. While the coating thickness for one brick was approximately 1 mm,
No. 7 brick is about 10mm, No. For 4 bricks, it was approximately 6 mm.

[0027] Furthermore, when the penetration depth of the liquid phase components mainly composed of calcium oxide and silicon oxide in cement clinker into bricks was investigated, No. Approximately 30 per brick
mm, whereas No. Approximately 15m with 7 bricks
It was found that the penetration depth was small. From the above results, No. 6, No. 7.No. Refractory No. 8 has almost all the desirable conditions as a refractory for cement rotary kiln lining, and especially No. It can be said that the refractory material No. 7 is superior.

[0028]

Effects of the Invention The magnesia spinel refractory of the present invention has the properties required as a refractory used in the firing zone including the true burning point of a cement rotary kiln, namely, good coating adhesion, corrosion resistance, and thermal shock resistance. It is a refractory that has all the characteristics such as structural strength, structural spall resistance, etc., and its performance is not inferior to that of conventional basic refractories containing chromium, and it does not contain chromium components that may cause pollution. Therefore, there is no need for a special storage place or treatment when disposing of the refractory after use, and the effect of reducing the effort and cost of disposal is achieved.

Claims (5)

[Claims] Claim 1: Containing 5 to 30% by weight of magnesia alumina spinel (MgAl2O4) clinker and 10 to 50% by weight of fused magnesia clinker as aggregate,
Partially stabilized zirconia in the joint part is 0.5 to 10
A magnesia spinel refractory characterized by containing % by weight. Claim 2: The content of partially stabilized zirconia is 1
The magnesia spinel refractory according to claim 1, wherein the magnesia spinel refractory is 3% by weight. Claim 3: Claim 1 or 2, wherein the stabilizing component of the partially stabilized zirconia is calcium oxide (CaO).
The magnesia spinel refractory described in . 4. The magnesia spinel refractory according to claim 1, wherein the fused magnesia clinker contains 1 to 3% by weight of each of CaO and SiO2. 5. A cement rotary kiln lined with the magnesia spinel refractory according to any one of claims 1 to 4.