CA1247151A - Abrasion resistant refractory composition - Google Patents

Abstract

Abstract of the Disclosure A refractory composition characterized by relative-ly high abrasion resistance, good flowability and long work-ing time, comprising of 0.5 to 5 weight percent volatilized silica, 3.0 to 15 weight percent -65 mesh alumina, 10 - 40 weight percent cement, and the balance a refractory aggre-gate.

Description

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A13E~ASION RESISTANT REF'RACIORY (~MEOSIlqON

Backaround of the Invention This invention relates to a refractory ccmposition characterized by high abrasion resistance, and in particular, to such a ccmposition which may be used as a refractory castable.
Refractory castables are hydraulic ætting compositions. They comprise granular refractory aggreaates and chemical binders. rrhe refractory castables are shipped in dry form, and when mixed with water to the desired consistencyr may be poured like concrete, tamped or rann~d into place, troweled or applied with an air gun. Refractory castables take a strong hydraulic set at room temperatures and maintain good strength until the desired ceramic bond is developed as the temperature is increased.
Castahles are specially suited for furnace linings of irregular contours, for patching brick work and for casting special shapes which may be uraently reauired. Numerous castable compositions are known, with each of the known co~positions, having different properties, mr~king each one useful for different applications.
One such application involves the use of refractory castables in lining trans~er lines employed in fluid catalytic cracking units used in petr~chemical processes. In such unites, highly abrasive catalysts travel at high speeds, thereby creating extreme erosion potential throughout the catalytic cracking unit. In such units, early abrasion resistant lininys were formed from phosphate bo~ded refractories, which required extensive anchoring and hand ,i ~,f~
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ramming to install. To reduce the expense of installing phosphate bonded refractories, the refining industry began using castables with field additions of stainless steel fibers which required less anchoring on the metal shell, and 5which could be poured relatively quickly. Although the foregoing improved on the time and cost of installation, increased abrasion resistance was desired.
Abrasion resistant linings in petrochemical ves-sels are typically chemically bonded or cement bonded re~`
10 fractory compositions. Abrasion resistance is generally obtained by utili7ing a strong, dense refractory grain such as calcined fireclay, and a strong bond consisting of alu-minum orthophosphate, or calcium aluminate cement. In the case of cement, the abrasion resistant bond is achieved by 15 using large amounts of cement, or a combination of fumed silica, cement in amounts less than ten percent, and a sur-face active agent which allows flow at low water contents.
Improved density, which is achieved by casting at low water contents, results in a highly abrasion resistant bond at low 20 cement levels.
Trying to effect further economies in installa-tion, operators of the fluid catalytic cracking units start-ed casting larger sections of transfer lines, eliminating the assembly of many smaller sections. The refractory cas-25 tables used on the transfer lines were made with relativelyfast setting cements, and did not stay flowable a sufficient time for use in such applications. Refractory manufacturers reformulated their abrasion resistant castables to incorpo-rate casting grade cements to lengthen working time. These 30 products provided the flowability and working time needed, but strengths and abrasion resistance were often lower than similar mixes containing regular calcium aluminate cement.

Summary of the Invention Accordingly, it is an object of this invention to provide a refractory composition characterized by good flow-ability and relatively long working times, with improved .3.
densities, strength and abrasion resistance. The foregoing objective is achieved in a refractory composition compris-ing of 0.5 - 5~, by weight, volatilized silica; 3.0 - 15.0~, by weight, -65 mesh alumina; 10 - 40%, by weight, calcium 5 aluminate cement; and the balance a refractory aggregate selected from the class consisting of silica, alumina, or fireclay.

Description of the Preferred Embodiment The utilization of refractory castable composi-tions in highly abrasive environments, requires the casta-bles to have excellent abrasion resistant properties. In addition, when used to line relatively large memhers, such as lining of transfer lines used in fluid catalytic cracking 15 units, the castable should have good flowability and rela-tively long working times, so that the castable can be in-stalled.
A first series of mixes was prepared (see Table I
below). In describing the various mixes, all percentages 20 will be on a weight percent basis unless otherwise indicat-ed. This mix series shows the effects of increasing the fine alumina content from 0 - 15% in a fireclay castable.
As may be observed, density, strength and abrasion resist-ance improve as the alumina content increases. Abrasion 25 resistance improvement from 8.4cc loss in the mix having 0~
alumina to 7.0cc loss in the mix having 15% alumina, is sig-nificant for a type of refractory which has relatively good abrasion resistance before the alumina addition. Fine, syn-thetic aluminas are commonly used in the refractory industry to improve the refractoriness of the bonding portion of the refractory, and as a source of fine material to insure that the refractory has a proper grain size distribution.

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A second series of mixes were made to determine the effect of adding O - 5% volatilized silica to the same abrasion resistant fireclay castable. Volatilized silica additions of 0.5% and 2% resulted in improved densities, 5 strength and abrasion resistance. At volatilized silica levels of 3% and 5%, the mix became sticky and did not flow as well as previously. Densities and strength suffered, but the improved abrasion resistance is maintained. Volatilized silica is a sub-micron, amorphous bi-product of ferrosilicon lO production and is a well known refractory raw material. It is used primarily as a source of ultrafine particles, as a source of reactive silica and as an additive to improve flow properties. As Table II illustrates, only small amounts can be used in cement containing mixes or flow properties would 15 be adversely affected.

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A third series of mixes were made to determine the effects of adding volatilized silica to a fireclay castable containing fine alumina. As the alumina is replaced by up to 2% silica, density, strength and abrasion resistance im-5 prove. At a silica level of 3%, the mix becomes sticky andflow is impaired. The abrasion resistance, however, conti-nues to improve. Mix P has outstanding abrasion resistance, but mix N is preferred because of its superior flowability, a necessary property when the composition is employed as a 10 refractory castable for use in relatively large applica-~tions. The synergistic effect of using volatilized silica and fine alumina together should be noted. The abrasion resistances of mixes N and P are superior to any of the mixes set forth in Tables I and II, where each material was 15 used separately.

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A fourth series of mixes were made, with each of the mixes being compounded according to the teachings of the present invention. Each of the mixes contained 2% volati-lized silica and 8% fine alumina of three different types.
5 All four mixes had high cold crushing strengths and out standing abrasion resistance. The A-17 and A-lS reactive aluminas are almost entirely composed of fine, sintered corundum (alpha-alumina) crystals. Their high surface area and small crystal size makes them thermally reactive, that lO is, they will further sinter or react with other compounds~
at relatively low temperatures. T-61 tabular alumina is also essentially 100~ corundum crystals, but this material has been fired to a high temperature, resulting in coarse, tablet-shaped, non-reactive crystals. A-2 calcined alumina 15 is about 90~ corundum crystals and 10% beta-alumina (Na2O.llAl2O3) crystals. The thermal reactivity of the A-2 calcined alumina is between tabular alumina and reactive alumina. Table VIII lists the various properties of these aluminas.

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Three further mixes were made according to the invention with 1~ volatilized silica and 9% fine alumina.
Mix T was based on a calcined fireclay grain. I'his type o~
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ance and low thermal conductivity are desired. Mix V is based on coarse, tabular alumina, and represents the ulti-mate strength and abrasion resistance. Since tabular alu-10 mina is over ten times more expensive than calcined fire-clay, the increased cost may not be justified by the modest property improvements. The three mixes are intended to illustrate the types o~ base grains which may be used from 100~ silica to a fire clay of roughly 50% silica and 45%
15 alumina to 100% alumina. There are a variety of high alu-mina grains having alumina contents between fireclay and tabular alumina, such as calcined bauxitic kaolin, calcined bauxite, kyanite and andalusite, which would also work sa-tisfactorily in this invention. In addition, non alumino-silicates such as silicon carbide, silicon nitrides or anyacid aggregate would be satisfactory.

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The next series of mixes was intended to show the effects of variations of the cement content. As may be ob-served, as cement increase from 10 to 40%, cold crushing strength and abrasion resistance generally improved.

TABLE VI
Cement Content Evaluations 10 Mix Designation: W X Y
Mix: L
Calcined Super Duty Flint Clay) -3 mesh 70% 50% 50 15 Calcined Super Duty Flint Clay, BMF 10 10 --A-17 Reactive Alumina 8 8 8 Volatilized Silica 2 2 2 CA-25C Casting Grade Cement lO 30 40 Casting Water Required, ~: 8.0 8.0 9.0 Bulk Density, pcf After Drying at 250F: 138 151 151 After Heating 5 Hrs. at 1500F: 136 141 141 Cold Crushing Strength After Heating 5 Hrs at 1500~F, psi: 5,600 12,44012,420 Abrasion Resistance (ASTM C-704) Volume Loss of Samples Heated 5 Hrs at 1500F, cu cm: 14.9 5.7 5.5 ~ k7~
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The last series of mixes establishes the upper and lower lower limits of volatilized silica and fine alumina contents as well as illustrates the preferred mix which was chosen for its good combination of ~low properties and 5 physical properties.
TABLE VII
Fine Alumina and Volatilized Silica Ranges With Preferred Mix Mix Designation: Z X AA
10 MiX:
Calcined Super Duty Flint Clay, -3 mesh 50% 50% 50%
Calcined Super Duty Flint Clay, BMF 4~510 12 15 A-17 Reactive Alumina, -325 mesh 15 ~ 3 Volatilized Silica 0.5 2 5 CA-25C Casting Grade Cement 30 30 30 20 Casting Water Required, %: 8.4 8.0 7.6 Casting Characteristics: The mix containing 0.5% volatilized silica had acceptable flow properties during casting, but not as good as the mix containing 2%
volatilized silica. The mix containing 5~
volatilized silica had poor flow,was difficult to handle because of its stickiness and dried out quickly during casting.
Bulk Density, pcf After Drying at 250F: 154 151 149 After Heating 5 Hrs at 1500F: 145 141 141 Cold Crushing Strength After Heating 5 Hrs at 1500~F, psi 15,05012,44011,540 40 Abrasion Resistance (~STM
C-704) Volume Loss of Samples Heated 5 Hrs at 1500F, cu cm: 6.55.7 4.9 5~
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The composition of the present invention provides a refractory castable which may be used in applications requiring high abrasion resistance, good flowability and long working times. Such properties are required in lining 5 transfer lines of fluid catalytic cracking units.
In the present specification, all percents have been provided on a weight percent basis, and all mesh sizes have been determined in accordance with Taylor Standard Series.
While only calcined clay has been used in forming~
the refractory aggregate for each of the mixes, other re-fractory aggregates such as silica, and alumina as well as other acid aggregates, can also be used.
While a preferred embodiment of the present 15 invention has been described and illustrated, the invention should not be limited thereto but may be otherwise embodied within the scope of the following claims.

Claims (8)

.17.

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as fol-lows:

1. A refractory composition comprising of 0.5 to 5 weight percent volatilized silica; 3.0 to 15 weight percent -65 mesh alumina; 10 to 40 weight percent calcium aluminate cement; and the balance a refractory aggregate.

2. The composition of claim 1 including the addition of tempering water for using the composition as a refractory castable characterized by relatively high abrasion resistance.

3. The composition of claim 1 wherein the refractory aggregate is selected from the class consisting of silica, alumina and fireclay.

4. The composition in accordance with claim 3 wherein the refractory aggregate includes 4.5 to 12 weight percent -65 mesh calcined clay.

5. The composition in accordance with claim 4 wherein the -65 mesh alumina comprises substantially 8 weight percent.

6. The composition in accordance with claim 5 wherein the volatilized silica comprises substantially 2 weight percent.

7. The composition in accordance with claim 1 wherein the -65 mesh alumina comprises substantially 8 weight percent.

8. The composition in accordance with claim 1 wherein the volatilized silica comprises substantially 2 weight percent.