Erosion resistant, ceramic fiber lining

Simply stated, the present invention contemplates the use of a ceramic fiber insulation material which is impregnated with an agent capable of stiffening the blanket and reducing erosion of the insulation material under conditions of use.

FIELD OF THE INVENTION 
The invention relates to improvements in the internal insulation of 
vessels. 
BACKGROUND OF THE INVENTION 
In processes in which gas suspended solids such as catalyst or coke are 
contacted or reacted in metal vessels at relatively high temperature 
conditions, it is conventional to line the interior of the vessel with a 
suitable refractory material to insulate the metal wall of the vessel from 
the process temperatures as well as to protect the metal wall from the 
corrosive and erosive effects of the material being processed within the 
vessel. 
There are several conventional methods for installing insulating linings in 
such "cold wall" reactor vessels. One method is to secure a pre-cast or 
molded refractory brick lining to the vessel internal wall by metal 
anchors, adhesives or the like. Another method is to cast or gun a 
castable refractory lining in place inside the vessel. 
None of these methods has proved entirely satisfactory for a number of 
reasons. Thermal stresses often result in cracking of the lining and its 
separation from the wall during thermal cycling of the reactor with the 
concomitant loss of heat from the vessel and access of the hot gases and 
erosive solids to the vessel wall. As a consequence, the lining requires 
repair which is costly in terms of material labor, and also in terms of 
loss of production from downtime of the reaction vessel. 
Consequently, numerous attempts have been made to improve on the method of 
installing refractory linings in vessels requiring them. For example, in 
U.S. Pat. No. 2,398,546 there is disclosed a vessel lining system which 
consists of a refractory lining which is spaced from the vessel wall. A 
particulate refractory material is included within the space between the 
wall and the lining, serving to insulate and minimize contact of the wall 
by erosive solids. 
In U.S. Pat. No. 2,982,623, a monolithic thermal insulating lining for a 
vessel is disclosed which includes a metal grid spaced from the vessel 
wall by studs. The metal grid has two castable layers applied to it. The 
first layer is a low density, high insulating castable refractory. A 
second layer contains an abrasion resistant castable. It is included to 
protect the refractory layer from erosion. 
U.S. Pat. No. 4,490,333 discloses a dual insulating layer in a reactor 
vessel using a ceramic anchor to fasten the second refractory layer to a 
previously-applied first insulating layer. Dual layer systems as 
represented by the foregoing references, of course, frequently fail 
because of the thermal stresses between the two layers. Moreover, they 
tend to be expensive to install and repair. Special anchoring systems are 
sometimes necessary for satisfactory installation of these. 
In U.S. Pat. No. 4,490,334 there is described the use of curved ribs and 
mesh to hold a ceramic fiber blanket in place in a domed portion of a 
cylindrical reactor. Use of a ceramic fiber blanket in this application is 
practical only because the fiber blanket is not exposed to erosive 
fluidized solids which would otherwise quickly destroy the blanket. 
Since there has been a trend toward conducting petrochemical processes at 
ever more severe conditions than heretofore, further improvements in 
lining systems used in cold wall reactor vessels is even more important. 
Changing economic conditions and the necessity to increase productivity 
are additional factors driving the constant search for improved lining 
systems for reactor vessels. 
Accordingly, it is an object of the present invention to provide an 
improved erosion-resistant ceramic insulating lining system for cold wall 
vessels which is heat resistant. 
It is another object of the present invention to provide an improved 
erosion-resistant ceramic insulating lining for cold wall vessels that can 
be installed at lower cost than other lining systems. 
These and other objects of the present invention will be apparent from a 
reading of the description which follows. 
SUMMARY OF THE INVENTION 
Simply stated, the present invention contemplates the use of a flexible 
ceramic fiber insulating blanket which is impregnated with a material 
capable of stiffening the blanket and reducing erosion of the insulating 
blanket under conditions of use.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings and, in particular, to FIG. 1, there is shown 
a process vessel 10 which includes an outer metal shell 12 having gas 
inlet and outlet openings 14 and 16, respectively, and a solids inlet and 
outlet 17 and 19, respectively. Perforated plates or grids 15 (not shown) 
may be horizontally disposed within vessel 10 to support one or more beds 
of fluidized particulate solid material such as fluidized catalysts. The 
vessel 10 also may contain cyclones (not shown) for separation of solids 
from product gas streams. 
Fastened to the inner wall of the metal shell 12, for example, by welding, 
are a plurality of metal anchor members 22 on which to tie back the 
insulating layer 18 of the present invention. 
The insulating layer 18 of the present invention consists of a high density 
ceramic fiber insulating blanket which is impregnated with a material 
capable of stiffening the fiber insulating blanket and protecting it 
against erosion. In general, the insulating blanket will have a density in 
the range of about 6 to 25 pounds per cubic foot, and preferably in the 
range of 12 to 25 pounds per cubic foot. In general, the fibers are in the 
range of about 2 to 3 .mu.m in diameter and from 2 to 10 inches long, and 
are compressed or formed into a predetermined shape. 
Among the ceramic fiber materials useful in the practice of the present 
invention are alumina-silicate fibers. Typically useful materials have 
alumina to silica weight ratios of from about 90 alumina to 10 silica to 
about 20 alumina to 80 silica. 
An example of an alumina-silicate ceramic fiber insulation material formed 
as a modular panel is the alumina-silicate product sold under the 
Trademark Pyro-Bloc by Thermal Ceramics, Augusta, Ga. 
It is a particularly important feature of the present invention that the 
ceramic fiber insulating blanket be impregnated with material which is 
capable of stiffening the ceramic fiber insulating blanket and protecting 
it against erosion under conditions of use. Particularly preferred agents 
for impregnating the insulating blanket include sodium silicate, potassium 
silicate, silica and mixtures thereof. In order to impregnate the 
insulating blanket with the agent, the agent is best used as aqueous 
dispersions or colloidal sols and injected into the blanket at a plurality 
of points to assure substantially uniform distribution of the agent within 
the blanket. The agents may be injected into the blanket before or after 
the insulation system is installed on the vessel wall. The amount of agent 
used will be that sufficient to render the insulating blanket rigid. In 
general, sufficient agent is used to provide from about 0.1 to about 10 
pounds of agent per cubic foot of ceramic fiber material and preferably 
from about 2 pounds to about 6 pounds per cubic foot of fiber. Since the 
agent is best applied as a liquid dispersion containing about 40 percent 
solids, the amount of dispersion used preferably is such that from about 5 
to about 15 pounds of dispersion is absorbed per cubic foot of ceramic 
fiber. After injecting the liquid agent into the insulating blanket 
material, the blanket material can be dried by any convenient means. 
Indeed, it is most convenient and practical to allow the material to dry 
out during the initial start-up of a vessel in which it is installed. 
Optionally and preferably, the rigidizing agent is modified with a wetting 
and dispersing agent such as potassium and sodium sulfates, phosphates and 
mixtures thereof. In general, from about 0.01 weight percent to about 5.0 
weight percent, and preferably from about 0.5 to 1.0 weight percent, of a 
wetting and dispersing agent is added to the rigidizing agent prior to its 
application to the ceramic fibers. 
Impregnating the ceramic fiber blanket with rigidizing agent, as described 
above, results in an insulating material which has a cross-section 
substantially similar to a castable refractory material. Importantly, the 
rigidizing agent is dispersed within the fiber structure, thereby acting 
as a bonding agent between the fibers and not merely a hard facing which 
may be prone to thermal-mechanical failure. 
As should be appreciated, shaped panels or sections of ceramic fiber 
blanket material can be impregnated with the rigidizing agent, thereby 
providing ceramic insulation modules. Typically, such ceramic fiber 
insulation modules will range in size from about 1 to about 4 square feet, 
and have thickness in the range of about 2 inches to about 8 inches. 
The insulating capability of a ceramic fiber insulating module having a 
fiber density of 12 pounds per cubic foot and impregnated with 12 pounds 
of aqueous colloidal silica rigidizing agent per cubic foot of ceramic 
fiber was compared with the thermal insulating property of a typical 
castable refractory lining using the hot wire technique, JISR2618-1979 of 
the Japan Standards Association. The ceramic fiber with agent was found to 
be about 65 percent lower in thermal conductivity than a typical castable 
refractory material. The reduced heat losses associated with reduced 
thermal conductivity are shown graphically in FIG. 2. Basically, they 
demonstrate that the insulating material of the present invention shows a 
fifty to sixty percent reduction in heat loss when compared with an 
equivalent thickness of a typical castable refractory lining material. 
Laboratory tests have also demonstrated that the ceramic fiber impregnated 
with the same concentration of colloidal silica rigidizing agent as stated 
above had an erosion resistance comparable to a conventional vessel lining 
castable. This was determined by ASTM C704 erosion tests in which the 
quantity of SiC grit was reduced to 125 grams. In identical tests, the 
ceramic fiber material, without rigidizing agent, was completely 
destroyed. 
Laboratory tests have additionally shown that fiber shrinkage can be 
effectively controlled with fiber compression and injection techniques. 
These techniques eliminated shrinkage gaps and cracking which formed in 
earlier test panels. 
In a field test, sections of ceramic fiber insulating blanket impregnated 
with agent, as described above, were installed in a fluid catalytic 
cracking vessel where they were exposed to erosive solids and hot gases. 
The test sections were inspected after approximately 8 months of operation 
when the unit was shut down. No significant cracking or erosion was found 
at that time. Shell temperatures during subsequent operation indicate that 
the test sections continue to perform well after approximately 6 
additional months of operation. 
The modular design of the insulating material of the present invention is 
easily installed, and, of course, does not require curing and dry-out as 
castable lining systems require. Moreover, special equipment is not 
required to install the ceramic fiber lining system of the present 
invention. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles 
herein, it will be understood that the invention may be embodied or 
practiced otherwise without departing from such principles. In particular, 
while applicants have chosen to illustrate the invention in the 
environment of a process vessel, those skilled in the art will readily 
appreciate that the invention may be practiced in other environments, such 
as circulation and overhead lines, where it is necessary to provide an 
insulating layer adjacent to a metal surface in order to protect the metal 
surfaces from high temperature and erosion or corrosive materials that 
would otherwise contact the metal surface.