TITLE:
CERAMIC LINERS FOR COAL NOZZLE TIPS AND METHOD OF PRODUCTION
FIELD OF INVENTION
The invention relates to a method of preparing Ceramic liners as lining material in
pulverized coal burner tips and other related applications.
BACKGROUND OF INVENTION
The coal nozzles used in the power plants is not lasting even for a year and requires
frequent replacement because the conventional metaliic tip undergoes sever erosion due
to fly ash, warpage because of high temperature. Problems associated are erosion of tips
& body, warpage of plates, opening & uneven distribution of coal, improper burning,
increase of eddy current due to rough surface resulting drop in velocity of coal resulting in
lowering boiler efficiency. Major causes for the above problems are high temperature,
high velocity of coal; high abrasive nature of coal, inferior coal quality: higher coal feed
rate, increase of coal impingement during flow deflection and insufficient secondary air for

cooling due to deformation/blockage. Various solutions are used or can be used such as
replacement of tips, repairing of tips, cladding of tips, coated tips and use of special alloy.
All these have many demerits such as replacement time & cost, short life enhancement,
rough surface and expensive.
Use of ceramic liners is one of appropriate method and the methods of fixing ceramic
liners are disclosed in the following patents.
US8210111B2 relates to a method and system for lining a coal burner nozzle of a
stationary coal nozzle using triangularly-shaped ceramic wall tiles.
JP2005265355A teaches of a method fixing ceramic tiles to base metal such a way the
base material on the surface of the ceramic member is locked to a different material in
order not to appear, excellent durability can be obtained
JP2010058155A is directed to a Ceramic composite liner composed of an wear-
resistant member made of silicon nitride ceramics which is fixed by insert-casting of a
metal composed of high Cr alloy in such a manner that the wear-resistant member is
exposed on the surface of the metal.

The ceramic liner material for fixing to coal nozzle tips should have very good hot
erosion properties, high temperature resistance and good thermal shock resistance.
The following materials are disclosed.
JP10094742 relates to a burner tip and its attaching structure to obtain a burner tip
excellent in wear resistance and thermal shock resistance by equally dividing a
cylindrical ceramic tip into a plurality in the circumferential direction and fitting it to a
jetting hole. The material of the ceramic tip inserted is silicon carbide (SiC) or silicon
nitride (Si3 N 4).
In JP2746917B2, the faces of the blades are covered by ceramics having
excellent wear resistance such as silicon nitride (Si3N4) or silicon carbide (SiC) or the
like to prevent the wear of rotary blades in Pulverized coal burner
JP0800S031 teaches of a method to improve the durability of a bumertip in a slurry
fired boiler using ceramic sleeves in the fuel spray hole so that slurry fuel is not brought
into contact with the base material of a burner tip. The material of the sleeves dense
SiC having excellent wear resistance as compared with conventional WC is employed

JP07062481 relates to a method of producing high strength wear resistant ceramic
made of a sintered compact obtained by bonding grains of ceramic containing at least
' one of carbides, nitrides, borides or oxides with an Nb-AI alloy by pressureless sintering
CN202915354U discloses a silicon carbide boiler burner which comprises a metal
support piece and a thermal-abrasion-resisting part. The thermal-abrasion-resisting part
is a recrystallization silicon carbide ceramic part formed by silicon carbide micro powder
and rare earth yttrium additives and the like by pulping, casting molding and sintering at
2,450-2,550 DEG C.
In JP4455908B2 The ceramic lining for pulverized coal burner and a method of fixing
ceramic liners to base metal is described
US8210111B2 is directed to a method and system for lining a coal burner nozzle of a
stationary coal nozzle using triangularly-shaped ceramic wall tiles
U.S. Pat No. 6,439,136 & WO03004935 provides a solid fuel nozzle tip that
comprises of a ceramic material from the group of ceramic materials including silicon
nitride, siliconized silicon carbide (having a silicon content of between about twenty
percent (20%) to sixty percent (60%) by weight, mullite bonded silicon carbide alumina
composite, and alumina zirconia composites.

CN102617160A discloses a pre fabricated member for coal nozzle of cement kiln using
corundum fine powder, the alpha-AI203 micro powder, the pure calcium aluminate
cement, the silicon carbide fine powder, the simple substance silicon powder, the
stainless steel fiber and the polycarboxylate water reducing agent
Indian Patent Application No. 594/KOL/2013A also describes similar castable using
alumino silicate materials selected from the group of bauxite, fused alumina (white or
brown), tabular alumina and/or sintered alumina.
The above two methods are suitable for thicker nozzles used in cement kilns but not
suitable for coal nozzle where thin lining is required.
Most of the above methods disclosed for lining of coal nozzle tips use SiC or Si3N4
materials which are very good wear resistance and thermal shock resistance but they
are very expensive because of costly manufacturing method. Alumina zirconia
composites are also expensive because of high cost of zirconia raw material. 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.

OBJECTS OF INVENTION
It is an object of the present invention to propose a ceramic liner with high wear
resistance and good thermal shock resistance.
Another object of the present invention is to propose method of manufacture ceramic
material having hot erosion resistance for use at high temperature.
A further object of the present invention is to propose the method of manufacture of
ceramic liner for use as lining material in the pulverized coal burner tips and other
related applications
BRIEF DESCRIPTION OF INVENTION
According to this invention there is provided a method of preparing ceramic liners
comprising the steps of:
- mixing the calcined alumina powder and inert refractory powders
- subjecting the mixture to the step of compaction to form tiles,
- firing the said tiles at a temperature between 1540°C and 1580oC.

DETAILED DESCRIPTION OF INVENTION
In the present invention, there is provided a method of manufacturing of ceramic liner
with high wear resistance and good thermal shock resistance and the method of
manufacture ceramic liner for use as wear resistance liner at high temperature.
Moreover, according to the present invention, there is provided a method of
manufacturing ceramic liner using a source of alumina for providing high wear
resistance along with refractory powders to increase the thermal shock resistance. In
the present invention, the ceramic product has abrasion resistance as measured by
relative abrasion resistance (RAI) is above 10, erosion at 700°C of below 0.02 gm per
kg of abrasives used when tested as per ASTM G76 and thermal shock resistance of
more than 25 cycles between 800°C to room temperature. The invented ceramic
material is hence suitable as liner material for coal burner tips in the pulverized coal
burner tips and other related applications.
The ceramic liners for coal nozzle tips required to withstand severe particle erosion at
high temperature. There is provided a method of producing ceramic liners to meet the
reouired therma! shock resistance, wear resistance and other mechanica! and thennal
properties for these apportions. The ceramic material is prepared from the batch

containing two parts: the first containing alumina powder to form corundum phase after
firing for providing high wear resistance; the second part containing inert refractory
powders to provide refractoriness and thermal shock resistance to the product. First part
is selected from the sources of alumina preferably calcined alumina. Second part is
selected from inert refractory powders prepared by high temperature treatment such as
sintering or fusion such as sintered mullite, fused mullite, sintered alumina, fused alumina,
zircon or combination of these refractory grains more preferably fused refractory powders.
The particle size of these raw materials is very important to get the required properties
after firing. First part is selected from lower particle size for better sintering behavior in the
chosen firing temperature preferably of particle size below 10 microns more preferably
below 5 microns. Second part is selected from larger particle size than that of that of First
part but preferably below 450 microns more preferably below 100 microns. Ratio of first
part to second part is also important to get desired wear resistance and thermal shock
resistance, Second part is selected preferably below 50 % of total weight more preferably
below 25 %.
Moreover, according to the present invention, there is provided a method of
manufacturing of ceramic liners for coal nozzle tips and related applications where the
production method involves the mixing of two parts of ceramic raw material in a high

intensive or similar mixer with organic binders. Organic binders are chosen depend on
the process of fabrication of shapes. Process of pressing, extrusion, casting can be
employed depending on the shapes and sizes of the product to be manufactured. For
pressing tiles, poly vinyl alcohol (PVA) is commonly used. For extrusion methyl cellulose
can be used. The dried products are fired in the kilns at 1540-1580°C, more
preferably 1550 to 1570 °C. These fired product has good abrasion resistance as
measured by relative abrasion resistance (RAI) is above 10, low erosion at 700 °C of
below 0.02 gm per kg of abrasives used when tested as per ASTM G76 and thermal
shock resistance of more than 25 cycles when quenched from 800 °C to room
temperature. These ceramic liners are fixed to metallic surfaces of coal nozzle tips or
coal burners to protect the coal nozzle tip from high temperature erosion. Such ceramic
lined coal nozzle tips are installed in different elevations of pulverized coal boilers of 500
MW power plant and used for more than two years. The temperature that the coal
nozzle tip is exposed is about 900 °C or more in this applications hence the
conventional metallic nozzle tips are typically last lesser than one year and changed or
repaired during annual shutdown. Hence the ceramic lined coal nozzle tips as per this
invention can give performance of more than 2 times than that of conventional metallic
nozzle tips.

EXAMPLES
Example 1 to 5. Raw material used for first part is calcined alumina. Raw material used
for second part is Fused mullite with particle below 40 BS mesh. Amount of fused
mullite is varied from 10 to 50 % in Examples 1 to 5. These weighed powders are mixed
first and then with PVA to get powders suitable for pressing. Tiles of different sizes
required for fixing to metal surfaces are pressed. Thickness of tiles varies from 10 to 20
mm depending on the configurations. Pressed tiles are fired at 1560 °C. Fired tiles are
tested for bulk density, water absorption, Relative abrasion resistance (RAI), Jet erosion
and thermal shock resistance. Thermal shock resistance is tested by heating the tiles to
800°C and quenching in water. Number of cycles that the ceramic tiles withstood
without any crack is recorded.


Examples 6 to 11: Ceramic tiles for liners are manufactured by the same method as
given in Example 1 to 5. But the raw material for the second part of the batch is fused
alumina with particle below 40 BS mesh. The amount of fused alumina is varied from 10
to 50 % balance being calcined alumina.

Examples 12 to 14: Ceramic tiles for liners are manufactured by the same method as
given in Example 1 to 5. But the raw material for second part of the batch is Zircon with
particle below 40 BS mesh


Examples 15: Ceramic tiles for liners are manufactured by the same method as given in
Example 6 to 11 . But the raw material for second part of the batch is fused alumina with
particle below 200 BS mesh. Fused alumina content is 25 % of total weight of batch.


WE CLAIM
1. A method of preparing ceramic liners comprising the steps of:
- mixing the calcined alumina powder and inert refractory powders
- subjecting the mixture to the step of compaction to form tiles,
- firing the said tiles at a temperature between 1540°C and 1580°C.

2. The method as claimed in claim 1, wherein the inert refractory powders are
prepared by high temperature treatment such as sintering or fusion, such as sintered
mullite, fused mullite, sintered alumina, fused alumina, zircon, etc. preferably fused
refractory powders or combination of these refractory grains
3. The method as claimed in claim 2, wherein the inert refractory powder is having
the particle size preferably below 450 microns more preferably below 100 microns
4. The method as claimed in claim 2, wherein the inert refractory powder is selected
preferably below 50 % of total weight more preferably below 25 %.
5. The method as claimed in claim 1, ceramic liners have good abrasion resistance
as measured by relative abrasion resistance (RAI) of above 10, low erosion at 700°C of
below 0.02 gm per kg of abrasives and good thermal shock resistance of more than 25
cycles between 800°C to room temperature.

6. The method as claimed in claim 1, wherein the ceramic liners are fixed to metallic
surfaces of coal nozzle tips or coal burners to protect the coal nozzle tip from high
temperature erosion and gives life of more than two times than that of bare metallic
nozzle tips when used in pulverized coal boilers.