Note: Descriptions are shown in the official language in which they were submitted.
s~
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
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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~
mix would be used where good abras:ion resistance is neces-
5 sary. Mix U is based on a vitreous silica grain. This mixwould be used where a combination of good abrasion resist~
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.
5~
.12.
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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~
.14.
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~
.15.
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.16.
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.
