FIELD OF THE INVENTION:
The present invention relates to improved refractory panels having high
temperature resistance and good erosion and/or corrosion resistance for
use as protective liners in circulating fluidized combustion boilers (CFBC)
and other related applications.
The present invention also relates to a method of manufacturing of pre-
shaped and pre-fired refractory panels, which have substantially high
thermal shock resistance and erosion resistance.
BACKGROUND OF THE INVENTION:
Refractory liners have long been used for the protection of water walls,
boiler walls in waste incinerators and other heat exchanger applications.
The primary function of the refractory lining has been to shield the steel
alloy boiler walls, which typically include water wall tubes, from the
temperature, erosion, and corrosion by acid vapor attack associated with
boiler operation. Conventionally high alumina or alumino silicate based
refractory castables or concrete have been used, which are casted/
rammed in the site and cured. Final strength usually expected to achieve
during high temperature attained during operations. Circulating fluidized
Bed Combustor (CFBC) boilers are operating at lower temperature.
Hence, the refractory lining should have excellent abrasion resistance at
comparatively lower temperature for some critical areas of CFBC boiler.
The abrasive particulate is impinging on the refractory lining at a
considerable speed. As such their impact break down the matrix of the
material that is holding the primary and coarser aggregate. Due to the
failure of the matrix the coarser aggregate comes out from the shape,
leaving more matrix directly exposed to abrasion. Hence, it is
clearly understood that more than aggregate, the matrix needs to be
more abrasion resistant at lower temperature (900-1000ºC). Generally
the traditional castable material for application in this area is based on a

hard aggregate with good abrasion resistance. This approach needs to be
changed and attention is necessary to develop strong matrix with high
abrasion resistance. Besides this abrasion resistant properties, other
criterion includes good thermal shock resistance, high modulus of
rapture (MOR) at 900-1000ºC, low permanent linear change (PLC) during
heating, higher thermal conductivity at 1000°C and desired
density/strength and porosity.
Conventional alumino silicate based refractory castables or concrete has
not shown good performance in this sever conditions hence requires
frequent repair. Different approaches to solve the problem were
attempted. One is to use SiC based material either in the form of
castables, plastic ramming mass or tiles. The refractory tile option
is found to be preferred because it decreases the time of installation and
repair. Refractory tiles for boiler tube protection have traditionally been
fabricated from a material such as silicon carbide (SiC). Such tiles
generally have been fabricated as a variant of one of three configurations,
namely bolted tiles; hanging tiles, such as disclosed in various patents.
Each method has advantages and disadvantages.
WO2014123291A1 discloses a refractory material for a circulating
fluidized bed combustion boiler comprises silicon carbide (SiC) having
excellent high heat conductivity, high strength, high hardness, and wear
resistance.
GB1085527A describes a method of relining a furnace is both quicker
and cheaper using 2-3 layers of refractory gunning/insulating monolithic
materials.
JP429818382 assigned to MHI environment engineering co. ltd. discloses
a refractory panel/tile formed of a material (SiC) of thermal conductivity
of 20 kcal/mh°C or higher. SiC is more than 85 wt %, 5 wt % or more of
C and the main component.

EP1001213B1 describes a method of fixing of Corrosion and/or abrasion
protection shells for a tube panel.
JP101699404 discloses a method of building incinerator wall using
unbaked SiC molded body. The inner layer part and is made of a
homogeneous phase SiC. SiC non-calcined of stacked molded,
amorphous SiC molded body adjacent to the gap is filled with the same
material of the refractory monolithic SiC. Therefore, the furnace wall is
formed, and a single-phase structure of SiC.
JP10122534A explains construction of furnace wall structure of
circulating fluidized bed combustion furnace. Refractory furnace material
wear resistance on the top surface of the block body is provided to be
detachably fixed to the cooled wall.
US6,267,066 assigned to Saint-Gobain discloses Refractory tile system
for boiler tube/heat exchanger. Refractory tiles are fastened to the tube
wall utilizing a floating attachment mechanism to provide a relatively
high degree of freedom of movement relative to the tube wall.
Refractory tiles for boiler tube protection generally have been fabricated
as a variant of one of three configurations, namely bolted tiles; hanging
tiles, such as disclosed in U.S. Pat. No. 4,768,447; and modified hanging
tiles also known as slotted or T-slotted tiles such as disclosed in U.S.
Pat. No. 5,243,801 and in WO97/09577.
U.S. Pat. No. 1,719,642, discloses tile for use in such an array of closely
spaced tubing Metal-backed, ceramic-faced tiles are hung from bolts
anchored between the tubes.
U.S. Pat. No. 3,797,415 describes boiler tube protection for powdered
coal-fired boilers' A substantially monolithic protective wall with tongue
and groove connections between the protective parts completely encircles
the tubing.

U.S. Pat. No. 3,828,735 discloses a substantially monolithic wall of tile to
protect a closely-spaced boiler tube array. The tiles are hung from T-
shaped anchors between the tubes.
U.S. Pat. No. 4,809,645 discloses a closely-spaced boiler tube array
covered with a substantially monolithic wall of individual refractory tiles
held against the tubing by means of fins projecting from the tubing.
U.S. Pat. No. 3,1914,100 describes protective ceramic tile for spaced
apart water tubes in a steel mill reheat furnace. A pair of hollowed
ceramic tiles interlock along their longitudinal edges to completely
encircle the tubing.
U.S. Pat. No. 4,071,1311 discloses refractory sheathing for horizontal
water pipes in a steel mill reheat furnace; the sheathing consists of two
layers which completely surround the tubing, a fibrous layer overlaid
with refractory tile.
U.S. Pat. No. 4,682,568 describes ceramic tile for protecting individual
spaced superheater tubes.
US 5,558,045 assigned to Carborundum, the Refractory tile is hung on
the tube with a threaded stud anchored on the tube and a nut threaded
on the stud, urging the tile against the tube.
US 5,214,006 provide a cement-free silicon carbide based refractory
adapted for use in non-ferrous applications useful as a refractory
covering for boiler tubes.
US 4,934,322 system for protecting a heat-recovery boiler screen, and a
method of manufacturing the system.
US 4,773,356 discloses lining of Refractory tiles inside of the furnace in
which the design of the tiles vary straight, curved shiplapped or rebated.
The tiles may be generally rectangular hexagonal in the barrel Refractory
material is SiC.

All these disclosures however are general and give little or no teaching as
to their suitability for Circulating fluidized Bed Combustor (CFBC) boilers
especially in combustor area of the boiler. Most of the disclosures use
silicon carbide (SiC) based materials for making refractory tiles or panels
which have very good wear resistance and thermal conductivity but they
are very expensive because of costly raw materials and manufacturing
method used. Moreover they are prone to oxidize if the furnace
temperature is beyond 1200°C.
Hence, there is always a need to produce an alternative refractory panels
which will be cost effective yet provide desired resistance at higher
temperature.
Alumina based materials are cost effective materials which are commonly
used for wear resistance applications at room temperature but suffer
from thermal shock when used at high temperature.
Hence alumina based material need to be modified to increase its
thermal shock resistance keeping its high wear resistance property
intact. Hence, the present invention meets the above mentioned long-felt
need by providing an improved composition for refractory panels from
alumina which has higher thermal shock resistance.
Further, the Conventional method of fabrication used for this purpose is
powder pressing. But to make pre-shaped product matching the
contours of water tubes, the refractory tiles are to be manufactured by
other methods.
Hence the present invention also fulfils this need by providing an
improved method of preparing the pre-shaped and pre-fired refractory
panels.
SUMMARY OF THE INVENTION:
A method for preparation of high wear resistance refractory panels in
CFBC boiler comprises the steps of: - selecting inert refractory powders

for providing refractoriness and thermal shock resistance; - forming of a
bonding phase with reactive ceramic powder for better sintering behavior
with selective particle size; shaping or fabrication of panels with
inorganic bonding; at last subjected to firing at high temperature for high
strength.
OBJECTS OF THE INVENTION:
The principal object of the present invention is to provide an improved
refractory panel which has high temperature resistance, good
erosion/corrosion resistance and substantially higher thermal shock
resistance.
Another object of the invention is to provide a pre-shaped, pre-fired
refractory panels to replace refractory concrete hence resulting in
reduction of installation time and repairing/replacement time.
Yet another object of the invention is to provide an improved refractory
panel which has excellent abrasion resistance during high temperature
in water or steam carrying boiler tubes of circulating the dried bed
combustor (CFBC) boiler.
A further object of the present invention is to propose refractory panels
enabling easy fixing and replacement of protective layers for circulating
fluidized combustion boilers (CFBC) and other related applications.
Another object of the present invention is to propose manufacturing
method of fabrication of pre-shaped refractory panels matching to the
contours of water wall in the boilers.
DETAILED DESCRIPTION OF THE INVENTION:
Accordingly, the present invention provides an improved refractory
panels for use as protective liners in circulating fluidized combustion
boilers (CFBC) and other related applications, which provides high

temperature resistance, good erosion/corrosion resistance and higher
thermal shock resistance.
The refractory panels comprises alumina for providing high wear
resistance along with substantially optimum amount of refractory
powders. The refractory powders helps to increase the thermal shock
resistance.
The refractory panel is prepared from the batch containing three parts;
i) First part
ii) Second part
iii) Third part
The first part of containing inert refractory powders to provide
refractoriness and thermal shock resistance to the product; the second
containing reactive ceramic powder to form bonding phase after firing
resulting in high strength both at room tempt and high temperature. The
third part consists of organic or inorganic bonding material to give good
strength during shaping or fabrication of panels.
The first part is selected from inert refractory powders prepared by high
temperature such as sintered mullite, fused mullite, sintered alumina,
tabular alumina, fused alumina, zircon, SiC or combination of these
refractory grains more preferably fused refractory powders.
Second part is selected from lower particle size for better sintering
behaviour in the chosen firing temperature preferably of particle size
below 5 microns more preferably below 2 microns. Preferred materials
are reactive alumina, micro silica, fused silica, clay etc.
Third part is selected from high alumina cement bonding, phosphate
bonding for pre-cast products, organic binders for pressing, organic
binder and water for extrusion.

The manufacturing process involves shaping of the panels to suit the
contours of the water tubes and firing or sintering to get low porosity to
induce good mechanical properties. Shaping of the panels is generally
done by casting or pressing or extrusion depending the shapes to be
fabricated. The panels are manufactured with shapes and size to match
the contours which will includes slots or grooves or steps to fix the
panels to water wall using appropriate metallic anchors or studs or bolts
or hinges which are designed keeping in view of the deflection of water
wall and expansion of refractory panels.
EXAMPLE 1:
Different size fraction of tabular alumina ranging from 6-1 mm and for
fillers 0.5 mm to -20 micron fraction were used as inert refractory in first
part which is totaling 8.3 kg. Microsilica and reactive alumina was also
used as second part which is totaling 1.2 kg. For binding agent calcium
aluminates cements were used with their respective flow additives as
third part which is 0.5 kg. They are mixed in a planetary mixer for 2 to 5
min then required amount of water, which is 0.4 to 0.5 litrs was added to
get good flowing consistency. Then this mix was poured to casting mould
under vibration. After minimum 8 hr of setting, the mould was released
and panel produced are dried in oven for 24 hr. Then they are fired at
1400 to 1550 C.
EXAMPLE 2:
In this case, brown fused alumina was used as inert refractory in first
part.
The properties of the refractory panels provided by the casting method as
per above Examples are given below:
Table 1:


Although embodiments for the present subject matter have been
described in language specific to features, it is to be understood that the
present subject matter is not necessarily limited to the specific features
described. Rather, the specific features and methods are disclosed as
embodiments for the present subject matter. Numerous modifications
and adaptations of the method of the present invention will be apparent
to those skilled in the art, and thus it is intended by the appended claims
to cover all such modifications and adaptations which fall within the
scope of the present subject matter.

WE CLAIM:
1. A method for preparation of high wear resistance refractory panels in
CFBC boiler comprises the steps of:
- selecting inert refractory powders for providing refractoriness and
thermal shock resistance;
- forming of a bonding phase with reactive ceramic powder for
better sintering behavior with selective particle size;
- shaping or fabrication of panels with inorganic bonding; and
- subjected to firing at high temperature for high strength.

2. The method for preparation of high wear resistance refractory panels
as claimed in claim 1, wherein said inert refractory powders are prepared
form sintering or fusion with sintered ingredients at high temperature.
3. The method for preparation of high wear resistance refractory panels
as claimed in claim 2, wherein said ingredients are selected from sintered
mullite, used mullite, sintered alumina, tabular alumina, fused alumina,
zircon, SiC or combination of these refractory grains more preferably
fused refractory powders.
4. The method for preparation of high wear resistance refractory panels
as claimed in claim 1, wherein the particle size is below 5 microns.
5. The method for preparation of high wear resistance refractory panels
as claimed in claim 1, wherein the particle size below 2 micron.
6. The method for preparation of high wear resistance as claimed in
claim 1, wherein said reactive materials are selected from reactive
alumina, micro silica, fused silica and clay.
7. The method for preparation of high wear resistance refractory panels
as claimed in claim 1, wherein said bonding are selected from high

alumina cement bonding, phosphate bonding for pre-cast products,
organic binders for pressing, organic binder and water for extrusion.
8. The method for preparation of high wear resistance refractory panels
as claimed in claim 1, wherein shaping of panels can be achieved by
pressing or extrusion, characterized in that the panels are manufactured
to match the contours to fix the panels to the water wall.
9. The method for shaping of refractory panels as claimed in claim 8,
wherein said contour further comprises slots, groves and steps.
10. The method for shaping of refractory panels as claimed in claim 8,
wherein the fixing of panels with water wall takes place by using metallic
anchors, studs, bolts and/or hinges to facilitate the defection of water
wall and expansion of refractory panels.