PRECAST REFRACTORY BLOCK FOR COKE OVEN

Abstract

A precast refractory block for a coke oven having high hot strength and stable under-load expansion/shrinkage behavior at high temperatures. Specifically, a silica-based precast refractory block contains a P.sub.2O.sub.5 component in an amount of 0.3 to 2.0 mass %.

Claims

1. A silica-based precast refractory block for a coke oven, the precast refractory block containing a P.sub.2O.sub.5 component in an amount of 0.3 to 2 mass %.

2. The precast refractory block as recited in claim 1, which contains a SiO.sub.2 component in an amount of 65 to 99 mass %.

3. The precast refractory block as recited in claim 1, which contains a SiO.sub.2 component in an amount of 80 to 99 mass %.

4. The precast refractory block as recited in claim 1, wherein, in a raw material mixture thereof, fused silica is mixed in an amount of 65 mass % or more.

5. The precast refractory block as recited in claim 1, wherein, in a raw material mixture thereof, silica stone is mixed in an amount of 17 mass % or less, and fumed silica is mixed in an amount of 0.5 to 15 mass %.

6. The precast refractory block as recited in claim 1, wherein, in a raw material mixture thereof, a hardening accelerator is mixed in an amount of 0.05 to 1.9 mass %.

7. The precast refractory block as recited in claim 1, wherein the precast refractory block is free of cement as a binder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a graph presenting under-load expansion/shrinkage behaviors in Inventive Example 1 and Comparative Example 5.

DESCRIPTION OF EMBODIMENTS

[0013] A precast refractory block for a coke oven (coke oven precast refractory block) of the present invention is a silica-based precast refractory block, i.e., a precast refractory block comprising a primary component consisting of a SiO.sub.2 component. Although a specific content of the SiO.sub.2 component falls within a range of common technical knowledge of a person of ordinary skill in the art, it is preferably set in the range of 65 to 99 mass %, more preferably in the range of 80 to 99 mass %.

[0014] As a SiO.sub.2 component source, it is possible to use any of various silica-based raw materials, such as fused silica, silica stone (calcined silica, non-calcined silica, etc.), and fumed silica. However, in the present invention, the amount of fused silica in a raw material composition is preferably 65 mass % or more, more preferably 72 mass % or more. Further, the amount of silica stone is preferably 17 mass % or less, and the amount of fumed silica is preferably in the range of 0.5 to 15 mass %. Particularly, from a viewpoint that shrinkage due to dehydration during drying can be canceled out, the amount of fused silica is preferably 65 mass % or more, and the amount of silica stone is preferably 17 mass % or less. In this case, the amount of silica stone may be 0 mass %. Further, from a viewpoint of maintaining high hot strength, the amount of fumed silica is preferably in the range of 0.5 to 15 mass %. As regards a particle size of the silica-based raw material, in view of filling performance and work efficiency, an aggregate having a top size of 5 mm and submicron particles are preferably used in combination. In addition, in order to further stabilize thermal expansion rate/shrinkage rate under a load (hereinafter referred to as under-load expansion/shrinkage rate), the amount of coarse particles having a particle size of 1 mm or more is preferably 25 mass % or more. Here, an alumina-based raw material can also be used in combination, as a primary aggregate other than silica-based raw material. As the alumina-based raw material, it is possible to use fused alumina, sintered alumina, or the like. However, when the content of the SiO.sub.2 component becomes less than 65 mass %, the hot strength deteriorates. Thus, it is undesirable to add the alumina-based raw material in a large amount.

[0015] In the coke oven precast refractory block of the present invention, while the P.sub.2O.sub.5 component functions as a binder component as described above, the content thereof is set in the range of 0.3 to 2.0 mass %. If the content of the P.sub.2O.sub.5 component is less than 0.3 mass %, a bonding function thereof as a binder component is not brought out. On the other hand, if the P.sub.2O.sub.5 component exceeds 2.0 mass %, a low melting point substance (SiO.sub.2P.sub.2O.sub.5 based substance) is excessively formed, so that deformation due to under-load shrinkage at high temperatures becomes large.

[0016] As a P.sub.2O.sub.5 component source, it is possible to use phosphate. In this case, from a viewpoint of suppressing formation of the low melting point substance, Na.sub.2O component and K.sub.2O component contained as impurities in phosphate are preferably contained in a total amount of 0.5 mass % or less, with respect to 100 mass % of the precast refractory block.

[0017] In the raw material composition for the coke oven precast refractory block of the present invention, from a viewpoint of increasing strength during curing, the amount of hardening accelerator is preferably 0.05 mass % or more. Further, from a viewpoint of maintaining high hot strength, it is preferably 1.9 mass % or less. Examples of the hardening accelerator include a fine powder of magnesia, and slaked lime.

[0018] Preferably, the coke oven precast refractory block of the present invention is free of cement. If it contains cement, under-load shrinkage occurs due to hydration reaction of the cement. On the other hand, when it is free of cement, it is possible to suppress such under-load shrinkage.

[0019] The coke oven precast refractory block of the present invention can be obtained by a conventional precast refractory block production method comprising: mixing together the aforementioned silica-based raw material (SiO.sub.2 component source) as a primary raw material, sodium phosphate (P.sub.2O.sub.5 component source) as a binder, and optionally an organic fiber, a dispersant, a hardening accelerator, a hardening retarder, a sintering aid, etc. as other additives; adding an appropriate amount (e.g., 5 mass % to 7 mass %) of casting water; and subjecting the obtained mixture to kneading, shaping, curing, demolding and drying.

EXAMPLES

[0020] In accordance with a raw material composition of Table 1, raw materials were mixed together, and after casting water in an amount of 6.5 mass % was added to the raw material mixture, they were subjected to kneading, shaping, curing, demolding and drying. By using the obtained test samples of precast refractory block for a coke oven, under-load expansion/shrinkage behavior and hot strength were measured to perform a comprehensive evaluation. The obtained test samples were also subjected to analysis for chemical composition. Here, fused silica, calcined silica, non-calcined silica, and fused alumina each having a particle size of 1 to 5 mm and a particle size of less than 1 mm mixed at a ratio of 6:4, were used. In addition, fumed silica having an average particle diameter of 0.5 m was used. For each of the chemical components of raw materials, fused silica containing a SiO.sub.2 component in an amount of 99.7 mass %, calcined silica containing a SiO.sub.2 component in an amount of 99.5 mass %, non-calcined silica containing a SiO.sub.2 component in an amount of 99.7 mass %, fumed silica containing a SiO.sub.2 component in an amount of 96 mass % and a Na.sub.2O component in an amount of 0.2 mass %, fused alumina containing Al.sub.2O.sub.3 in an amount of 100 mass %, sodium phosphate containing a P.sub.2O.sub.5 component in an amount of 65 mass % and a Na.sub.2O component in an amount of 23 mass %, silicate soda containing a SiO.sub.2 component in an amount of 65 mass % and a Na.sub.2O component in an amount of 22 mass %, colloidal silica containing a SiO.sub.2 component in an amount of 40 mass %, Portland cement containing a SiO.sub.2 component in an amount of 24 mass %, fine powders of magnesia containing a MgO component in an amount of 100 mass %, and slaked lime containing CaO in an amount of 100 mass %, were used.

[0021] An under-load expansion/shrinkage behavior was measured under a load of 0.2 MPa according to JIS-R2207-2 in a temperature range from room temperature to 1300 C. When the under-load expansion/shrinkage rate was in the range of 0.1% or more to less than 0.5%, the sample was evaluated as Excellent (); when it was in the range of 0.3% or more to less than 0.1%, or in the range of +0.5% or more to less +0.7%, the sample was evaluated as Good (); when it was in the range of 0.5% or more to less than 0.3% or in the range of +0.7% or more to less than +0.8%, the sample was evaluated as Acceptable (); when it was less than 0.5% or equal or more than +0.8%, the sample was evaluated as NG (x); and when the evaluation was Acceptable () or better, the sample was evaluated as Pass. Here, the sign (minus) denotes the under-load shrinkage behavior, and the sign + (plus) denotes the under-load expansion behavior.

[0022] A hot bending strength was measured according to JIS-R2213 at 1000 C. In order to set the test samples to the measurement temperature, they were held in a furnace for 1 hour, and then the hot bending strength was measured. When the hot bending strength was 10 MPa or more, the sample was evaluated as Excellent (); when it was 5 MPa or more and less than 10 MPa, the sample was evaluated as Good (); when it was 3 MPa or more and less than 5 MPa, the sample was evaluated as Acceptable (); when it was less than 3 MPa, the sample was evaluated as NG (x); and when the evaluation was Acceptable () or better, the sample was evaluated as Pass.

[0023] And the comprehensive evaluation was determined as:

[0024] Excellent () when the sample has two Excellent () in the above two evaluations;

[0025] Good () when the sample has one Excellent () and one Good ();

[0026] Acceptable () when the sample has one Excellent () or one Good () and one Acceptable ();

[0027] NG (x) when the sample has at least one NG (x); and

[0028] when the comprehensive evaluation was Acceptable () or better, the sample was evaluated as Pass.

[0029] Table 1 presents results of these evaluations together.

Table 1

[0030] In TABLE 1, all of Inventive Examples 1 to 15 are a precast refractory block for a coke oven, which fall within the scope of the present invention. The comprehensive evaluations thereof were Acceptable () or better, and both the under-load expansion/shrinkage behavior and the hot bending strength were acceptable level or better.

[0031] Comparative Example 1 is an example in which the content of the P.sub.2O.sub.5 component is low. In Comparative Example 1, the bond function was not sufficiently obtained and the hot bending strength did not reach the acceptance level. On the other hand, Comparative Example 2 is an example in which the content of the P.sub.2O.sub.5 component is high. In Comparative Example 2, the under-load expansion/shrinkage behavior did not reach the acceptance level because of excessive generation of a low melting point substance (SiO.sub.2P.sub.2O.sub.5).

[0032] Comparative Example 3 is an example in which P.sub.2O.sub.5 component is applied as a binder component in a precast refractory block for a coke oven whose primary component is Al.sub.2O.sub.3 component. In Comparative Example 3, the under-load expansion/shrinkage behavior did not reach the acceptance level.

[0033] Comparative Example 4 is corresponding to the above Patent Document 1, and an example in which colloidal silica and silicate soda are applied as a binder. In Comparative Example 4, the hot bending strength did not reach the acceptance level.

[0034] Comparative Example 5 is an example in which only Portland cement is used as a binder. In Comparative Example 5, the under-load expansion/shrinkage behavior did not reach the acceptance level.

[0035] FIG. 1 is a graph presenting the under-load expansion/shrinkage behavior from room temperature to 1300 C. for Inventive Example 1 and Comparative Example 5. In Inventive Example 1 which falls within the scope of the present invention and in which phosphate (P.sub.2O.sub.5 component source) as a binder was mixed, the under-load expansion/shrinkage behavior was stable, whereas in Comparative Example 5 in which a large amount (5 mass %) of Portland cement as a binder was mixed, the shrinkage under load occurred markedly from the vicinity of 1,000 C.

TABLE-US-00001 TABLE 1 Inventive Inventive Inventive Inventive Example 1 Example 2 Example 3 Example 4 Raw Material Primary Silica-based Raw Material Fused Silica 91.2 91.5 89.3 89.9 Composition Aggregate Calcined Silica (mass %) Non-calcined Silica Fumed Silica 8.0 8.0 8.0 8.0 Alumina-based Raw Material Fused Alumina Binder Sodium Phosphate 0.7 0.4 2.6 2.0 Sodium Silicate (Solid) Colloidal Silica (Solid) Portland Cement Curing Fine Powders of Magnesia 0.1 0.1 0.1 Accelerator Slaked Lime 0.1 Chemical SiO2 98.6 98.9 96.7 97.3 Composition P2O5 0.5 0.3 1.7 1.3 (mass %) Na2O 0.2 0.1 0.6 0.5 Al2O3 Evaluation Under-Load Expansion/Shrinkage Behavior Items Hot Bending Strength Comprehensive Evaluation Inventive Inventive Inventive Inventive Example 5 Example 6 Example 7 Example 8 Raw Material Primary Silica-based Raw Material Fused Silica 90.4 88.9 90.3 89.8 Composition Aggregate Calcined Silica (mass %) Non-calcined Silica Fumed Silica 8.0 8.0 8.0 8.0 Alumina-based Raw Material Fused Alumina Binder Sodium Phosphate 1.5 3.0 0.7 0.7 Sodium Silicate (Solid) Colloidal Silica (Solid) Portland Cement Curing Fine Powders of Magnesia 0.1 0.1 1.0 1.0 Accelerator Slaked Lime 0.5 Chemical SiO2 97.8 96.3 97.7 97.2 Composition P2O5 1.0 2.0 0.5 0.5 (mass %) Na2O 0.4 0.7 0.2 0.2 Al2O3 Evaluation Under-Load Expansion/Shrinkage Behavior Items Hot Bending Strength Comprehensive Evaluation Inventive Inventive Inventive Inventive Example 9 Example 10 Example 11 Example 12 Raw Material Primary Silica-based Raw Material Fused Silica 65.0 91.0 98.4 91.0 Composition Aggregate Calcined Silica 6.0 (mass %) Non-calcined 11.0 Silica Fumed Silica 15.0 8.0 0.5 8.0 Alumina-based Raw Material Fused Alumina Binder Sodium Phosphate 2.0 1.0 1.0 1.0 Sodium Silicate (Solid) Colloidal Silica (Solid) Portland Cement Curing Fine Powders of Magnesia 1.0 0.05 0.1 Accelerator Slaked Lime Chemical SiO2 96.1 98.4 98.6 98.4 Composition P2O5 1.3 0.6 0.7 0.7 (mass %) Na2O 0.5 0.2 0.2 0.2 Al2O3 Evaluation Under-Load Expansion/Shrinkage Behavior Items Hot Bending Strength Comprehensive Evaluation Inventive Inventive Inventive Comparative Example 13 Example 14 Example 15 Example 1 Raw Material Primary Silica-based Raw Material Fused Silica 70.9 57.9 98.3 91.7 Composition Aggregate Calcined Silica (mass %) Non-calcined Silica Fumed Silica 8.0 8.0 8.0 Alumina-based Raw Material Fused Alumina 20.0 33.0 Binder Sodium Phosphate 1.0 1.0 0.7 0.2 Sodium Silicate (Solid) Colloidal Silica (Solid) Portland Cement Curing Fine Powders of Magnesia 0.1 0.1 1.0 0.1 Accelerator Slaked Lime Chemical SiO2 78.4 65.4 98.0 99.1 Composition P2O5 0.7 0.7 0.5 0.1 (mass %) Na2O 0.2 0.2 0.2 0.1 Al2O3 20.0 33.0 Evaluation Under-Load Expansion/Shrinkage Behavior Items Hot Bending Strength X Comprehensive Evaluation X Comparative Comparative Comparative Comparative Example 2 Example 3 Example 4 Example 5 Raw Material Primary Silica-based Raw Material Fused Silica 86.9 30.9 74.5 91.0 Composition Aggregate Calcined Silica (mass %) Non-calcined Silica Fumed Silica 8.0 8.0 8.0 4.0 Alumina-based Raw Material Fused Alumina 60.0 Binder Sodium Phosphate 5.0 1.0 Sodium Silicate (Solid) 0.7 Colloidal Silica (Solid) 16.7 Portland Cement 5.0 Curing Fine Powders of Magnesia 0.1 0.1 0.1 Accelerator Slaked Lime Chemical SiO2 94.3 38.5 89.1 95.8 Composition P2O5 3.3 0.7 (mass %) Na2O 1.2 0.2 0.2 Al2O3 60.0 Evaluation Under-Load Expansion/Shrinkage Behavior X X X Items Hot Bending Strength X Comprehensive Evaluation X X X X