Lightweight refractory monolith forming batch comprising selected high alumina materials.

BACKGROUND OF THE INVENTION 
This invention relates to insulating refractories and more particularly, to 
lightweight, porous, refractory insulating castables suitable for use in 
lining secondary ammonia reformers. 
Most ammonia and ammonia derivatives are currently manufactured by the 
steam reformed process. In this process natural gas or refinery gas is 
cracked or broken down over a catalyst, such as nickel, by combining with 
steam to yield hydrogen, carbon monoxide and carbon dioxide. These gases 
are then passed into a secondary reformer where air is introduced and 
combustion occurs removing free oxygen by conversion to water with some 
hydrogen. 
If silica is present in the refractory, it will be leached out and 
deposited downstream in the unit. The present compositions are 
characterized by having low density and are composed of low silica 
aluminas that previously had not been used in this manner. Use of these 
special aluminas in the castable results in lower density and better 
insulating values. 
It has been well known and understood in the art that various combustibles 
can be mixed with unfired refractory material so that, after forming and 
firing, a porous skeletal structure for use as a refractory insulation, 
will result. The combustibles have included various organic materials both 
naturally occurring and synthethic. Diatomaeous earth, gas developing 
materials and foaming agents, fly ash, asbestos, exfoliated pyrophyllite, 
mica and the like have also been suggested and utilized in forming a low 
density, lightweight refractory insulation material. 
The present refractories may be defined as those of the high alumina type 
and are classified according to their Al.sub.2 O.sub.3 contents into 
groups having, approximately, greater than 50% Al.sub.2 O.sub.3, by oxide 
analysis. Those containing 50 to 90% of Al.sub.2 O.sub.3 are made by 
blending the various high alumina refractory materials, while those of 99% 
content are made of high purity alumina. The more common high alumina 
refractory materials and their typical Al.sub.2 O.sub.3 contents are 
discussed and set forth in U.S. Pat. No. 3,067,050 issued Dec. 4, 1962 for 
"Alumina Refractories". 
The present invention is predicated upon a discovery that high alumina 
refractory monolithic bodies having densities typical of insulating 
refractories, and yet having high temperature strength and wear resistance 
similar to much denser bodies, may be prepared from batches according to 
this invention.

Accordingly, it is among the objects of this invention to provide high 
alumina monolithic refractories having many of the desirable properties of 
those previously available, including low permeability, but which have 
lower density and heat capacity. 
In accordance with the present invention, there is provided a lightweight 
refractory monolith forming, high alumina size graded batch. The batch 
comprises about 15 to 40%, by weight, of hydrated alumina and/or activated 
alumina. The remainder is high alumina refractory material analyzing at 
least about 50% Al.sub.2 O.sub.3 and calcium aluminate cement. The high 
alumina refractory material includes at least 25%, by weight of the batch, 
of hollow spherical particles of alumina. The cement constitutes at least 
about 15%, by weight, of the batch. 
In a preferred embodiment, the spherical alumina particles constitute from 
about 25 to 55%, by weight of the batch, and the cement constitutes from 
about 25 to 30%, by weight, thereof. 
The term "high alumina refractory monolithic lining" has a well-known 
(although unwritten) meaning in the refractories art. The ASTM 
classification of refractory castables is not based on chemical analysis 
(see ASTM designation C401-60). HIgh alumina refractory monolith refers to 
linings comprising from 70 to 90%, by weight, refractory aggregate 
containing more than about 70% alumina, such that the silica present is 
tied up as mullite and from 10 to 30% calcium alumina cement. Table I 
includes the chemical analysis of some suitable high alumina starting 
materials. Table I also includes the chemical analysis of a suitable 
calcium aluminate cement used in the practice of this invention. 
TABLE I 
______________________________________ 
Spherical 
Tabular Calcium Aluminate 
Alumina Alumina Cement 
______________________________________ 
SiO.sub.2 0.67% 0.10% 0.40% 
Al.sub.2 O.sub.3 
99.0 99.60 75.0 
TiO.sub.2 0.01 0.01 0.04 
Fe.sub.2 O.sub.3 
0.01 0.20 0.10 
CaO 0.10 0.04 24.10 
MgO 0.05 0.04 0.10 
Total Alk 0.10 0.05 0.30 
LOI -- -- 0.40 
______________________________________ 
The spherical particles of alumina may be produced by heating a high purity 
alumina material above its melting point. While it is still molten, the 
alumina charge is poured through a blast of high velocity air, to produce 
small, bubble-like hollow spheres. The tabular alumina is a commercially 
available material well known in the art as is the calcium alumina cement. 
The hydrated alumina used in the invention is preferably that produced by 
ALCOA and sold under the designation C-331 or C-30. The activated or 
desiccant alumina preferably is also that produced by ALCOA and identified 
as F-1 alumina. These aluminas analyzed greater than 99% Al.sub.2 O.sub.3. 
Preferred sizing for the mixes of the invention is about 10 to 25% -3+10 
mesh and 45 to 55% -65 mesh. 
Mixes according to the invention are preferably blended with water to 
provide a uniform, smooth, substantially non-flowing cream-like material. 
The mixes and their properties are shown in Table II below. 
TABLE II 
__________________________________________________________________________ 
Mix Designation: 
A B C D E F G H I J K L 
__________________________________________________________________________ 
Mix: 
Spherical Alumina 
35% 
35% 
35% 
35% 
35% 
35% 
35% 
25% 
45% 
35% 
55% 
55% 
Tabular Alumina 
40 30 20 10 -- 20 -- 10 -- 10 -- -- 
Cement 25 25 25 25 25 25 25 25 25 15 30 30 
Activated Alumina 
-- 10 20 30 40 -- 20 40 30 40 -- 15 
Hydrated Alumina 
-- -- -- -- -- 20 20 -- -- -- 15 -- 
Plus Addition: 
Water 17.0 
20.0 
23.5 
27.5 
31.0 
17.5 
24.0 
29.0 
29.0 
32.0 
25.7 
28.0 
Bulk Density, pcf (Av 5) 
97 96 91 84 80 93 84 88 78 77 79 76 
After Drying at 
250.degree. F. 
After Heating 
90 89 83 76 72 81 71 78 70 70 67 67 
Modulus of Rupture, 
500 
430 
380 
280 
240 
490 
340 
290 
200 
60 410 
380 
psi (Av 3), After 
Drying at 250.degree. F. 
Dimensional Change After 
Heating at 1500.degree. F. 
Linear Change, % 
.+-.0.1 
0.0 
.+-.0.1 
+0.1 
-0.1 
+0.1 
-0.1 
0.0 
0.0 
-0.2 
+0.3 
.+-.0.5 
Volume Change, % 
.+-.0.4 
+0.3 
+0.3 
+0.1 
.+-.0.2 
.+-.0.5 
.+-.0.3 
-0.2 
+0.5 
.+-.1.0 
.+-.1.0 
.+-.0.6 
__________________________________________________________________________ 
Mix A was a standard lightweight castable. In Mixes B through E, the 
percentage of activated or desiccant alumina substituted for tabular 
alumina was increased from 10 to 40%. Mix E had a water-free density of 
72% pcf compared to 90 pcf for Mix A. Mixes F and G were similar to C and 
E, respectively, except that hydrated alumina replaced the activated 
alumina at a 20% level. The substitution of hydrated alumina for activated 
alumina had little effect on density, but dried strengths were higher with 
the hydrated alumina. Mixes H and I contained 25 and 45% bubble alumina, 
respectively. The physical properties of these mixes were not quite as 
good as several other mixes that contained 35% spherical alumina. Mix J 
illustrates a mix containing a relatively small amount of calcium 
aluminate cement and Mixes K and L illustrate mixes containing larger 
amounts of spherical alumina. 
Considering density, cost and other properties, the optimum composition 
would be Mix G. However, other mixes are suitable and would be within the 
confines of the invention. 
In the foregoing discussion, all parts and percentages are by weight, and 
all chemical analyses are given on the basis of an oxide analysis in 
conformity with the common practice of reporting the chemical analyses of 
refractory materials. All screen sizes are according to the Tyler series. 
It is intended that the foregoing description be construed as illustrative 
and not in limitation of the invention. 
Having thus described the invention in detail and with sufficient 
particularity as to enable those skilled in the art to practice it, what 
is desired to have protected by Letters Patent is set forth in the 
following claims.