Title of Invention

IMPROVED THERMAL RESISTANT TITANIA COATED COPPER TUYERS FOR USE IN BLAST FURNACE AND A METHOD OF ITS MANUFACTURE

Abstract The invention relates to an improved thermal resistant copper tuyeres and method of manufacture thereof, for use in blast furnace operations characterized by high melting point of the ceramic material, low thermal conductivity, phase stability at the tuyere body temperature and bonding characteristics with the copper substrate comprising a bond coat of Ni-Cr-AI alloy in the weight ratio of 19:5:1 deposited on the bare copper surface and a topcoat of ceramic Titania.
Full Text FIELD OF THE INVENTION
The invention relates to improved thermal resistant copper tuyeres for use in a
blast application under coal dust injection conditions.
PRIOR ART AND DRAWBACKS
A blast furnace (BF) is a counter current heterogenous reactive heat transfer
system involving dynamic interaction between gaseous, liquid and solid phases.
Preheated air, one of the inputs for iron making, is introduced through cast high purity
copper tuyeres. The tuyeres are important components of blast furnaces. The tuyeres
generally 18-24 in number, are double walled, high purity (around 99.5%), high thermal
conductivity, copper structures, through which preheated air (1100°C approximately),
termed as hot blast is introduced in to the blast furnace. These tuyeres are located at the
intersection of bosh and the hearth of the furnace along the entire periphery. The tuyeres
are exposed to the hottest region in the blast furnace where the raceway adiabatic flame
temperature (RAFT) may frequently exceed 2000°C. The tuyeres are, therefore, cooled
internally by circulating water.
In some of the blast furnaces, e.g. Blast Furnace number 6 of Bhilai Steel Plant
(BSP) in addition to hot blast, coal dust injection (CDI) is also carried out through the
tuyeres with a view to lower the coke rate (kg/ THM) and the cost of the hot metal
production. The volatile hydrocarbons in the coal dust, which constitute about 25-30%,
tend to burn inside the bore realizing sensible heat. Some of the heat from hot blast,
combustion of volatile matter and from inside the blast furnace is lost through the copper
tuyeres to the circulating cooling water. This heat loss results in increase in coke
consumption and consequently, the cost of hot metal production.
OBJECTS OF THE INVENTION
It is therefore a primary object of the invention to propose improved Thermal
barrier ceramic Titania (TiO2) coated blast furnace (BF) tuyeres for application under
coal dust injection (CDI) conditions.
It is another object to propose such an improved tuyere, the use of plurality of
which in the usual intersection of bosh and the hearth of the furnace will help in the
consumption of lower coke rate than possible so far.
It is further object to propose such use of plurality of the improved tuyeres, which
will result in lowering the cost of hot metal production.
Another object is to propose improved tuyeres, which will have satisfactorily
functioning topcoat of ceramic Titania not fully realized so far.
A further object is to propose such improved tuyeres, which will exhibit high
melting point of the ceramic material, low thermal conductivity, phase stability at the
tuyere body temperature, bonding characteristics with the copper substrate.
A still further object is to propose such improved tuyeres, the improved coatings
of which will use indigenously available commercial materials.
These and other objects will be more understood from the following paragraphs.
BRIEF STATEMENT OF THE INVENTION
According to this invention, there is provided an improved copper tuyere for use
in blast furnace operations having a bond coat of Ni-Cr-AI alloy in the weight ratio of
19:5:1 deposited on the bare copper surface and a topcoat of ceramic Titania.
In this tuyere, the bond coat is made up of essentially powders with
granulometric particle sizes of -100 +325 mesh and the topcoat is made of essential
powders with granulometric particle size of -230 meshes.
The bond coat is preferably of 0.4 mm thick and the overall thickness of the
coating (bond coat and top coat included) is around 1.0mm for inner bore and 2.0 mm
for outer nose.
According to another aspect of this invention, there is provided a method of
manufacturing the Mania-coated improved copper tuyeres stated above, which
comprises the following steps:
a. firstly, the copper tuyeres to be coated is centrally mounted on a horizantal
lathe machine;
b. the surface to be coated are machined down by 2-4 mm on diameter to
expose the fresh, virgin copper surface suitable for deposition of bond coat,
where the bond coat is of an alloy of composition: 19-21% chromium, 3-5%
aluminum and balance nickel;
c. then machined copper tuyere surface is then roughened by knurling, followed
by alumina grit blasting for better mechanical anchorage of the coatings and
adhesion of the bond coat with the copper substrate;
d. then the grit blasted copper tuyere surface is then cleaned and degreasing
the girt blasted surface with acetone and preheating to 120-150°C with an
argon plasma torch;
e. the bond coat of Ni-Cr-AI alloy is then deposited onto the tuyere surface by
argon plasma spray technique, in this the standard plasma-grade alloy
powder is injected into the high-temperature (6000 to 10000 Kelvin) argon
plasma stream, where it is fused and sprayed onto the preheated copper
metal surface, for the coating process the tuyere is mounted on a horizantal
turn-table and rotated at 3-4 rotations per minute, with the following argon
plasma spray parameters:

Stand-off distance of spray gun from job surface- 4-6 inches
f. building up around 0.4 mm thickness of bond coat in a plurality of, preferably
four runs;
g. following, cooling the job surface to around 50-100°C, where after;
h. the topcoat of Titania (TiO2) is finally deposited over the bond-coated copper
tuyere surface by means of the said argon plasma spray process using the
above mentioned spray parameters and conditions, where the overall
thickness of the coating (bond and top coats included) is around 1 mm for
inner bore and 2 mm for the outer nose portion of the tuyere;
i. after the application of coating, the tuyere surface is allowed to cool down at
ambient temperature, with typical surface roughness of the resultant ceramic
coating is around 6.91-8.47 microns Ra (average roughness).
DETAILED DESCRIPTION OF THE INVENTION
In preparing the improved tuyeres, attention was given to the strong adhesion of
the ceramic Titania to the copper surface of the tuyeres.
Fresh copper tuyeres were coated by argon plasma spray deposition technique
after careful surface preparation. Ni-Cr-AI alloy bond coat was followed by the ceramic
Titania (TiO2) topcoat. The coated tuyeres were installed in predetermined position in
Blast Furnace number 6 of BSP to evaluate their performance under plant working
conditions.
SALIENT FEATURES OF INNOVATION
In order to promote adhesion of ceramic Titania (TiO2) with the tuyere substrate,
a bond coat of Ni-Cr-AI alloy was initially applied to copper tuyere surface. The coating
materials for the Ni-Cr-AI alloy bond coat and TiO2 topcoat are essentially powders with
granulometric particle sizes of -100 +325 mesh and -230 mesh respectively. The surface
to be coated was machined down by 2-4 mm on diameter followed by grit blasting for
better mechanical anchorage of the coatings The surface was then de-greased with
acetone and preheated to 120-150°C with an argon plasma torch. Initially, the bond coat
of Ni-Cr-AI alloy was deposited on the tuyere surface. Following argon plasma spray
parameters were employed.

Stand off distance of spray gun from job surface - 4-6 inches.
In all spraying steps, it is more desirable to effect a plasma jet process from the
following two reasons:
1. In the plasma jet process, an inert gas such as nitrogen, argon, helium and the
like is used as an operating gas, so that the spraying materials and the surface of
the copper substrate are not oxidized during the spraying.
2. The temperature of the heat source in the plasma jet device is extremely
higher than that in a powder spraying device using an oxy-acetylene flame (the
former is usually 8,500.degree.-10,000.degree.C, while the latter is
3,000.degree.C at maximum), so that the spraying materials are completely
melted. And also, the spraying speeed is higher in the plasma jet process
(approximately sound speed), so that kinetic energy of the sprayed molten
particles becomes larger. Thereby, not only the bounding strength of the coating
to the surface of the substrate but also the bonding force between particles
forming the coating considerably increases as compared with the case of the
oxy-acetylene process. Furthermore, the porosity can be restrained to a few %.
Around 0.4 mm thickness of bond coat was built up in four runs. The job surface
was then allowed to cool to around 50-100° C. Following this; the topcoat of Titania
(TiO2) was deposited. The overall thickness of the coating (bond coat and topcoat
included) was around 1.0 mm for inner bore and 2.0 mm for outer nose. The coated
powders employed were commercially available plasma grade powders. The tuyeres
were mounted onto a horizontal turntable and rotated at 3-4 r.p.m. during the coating
process. Following the application of the coating, the surface was allowed to cool to the
ambient temperature and inspected for cracks and other defects.
The plasma coating results in dense, adherent and mechanically stable Titania
coating, this acts a thermal barrier to the heat flux thus leading to considerable reduction
in the heat loss through the tuyeres. It was observed that there was substantial reduction
in heat loss (up to 30%) from coated tuyeres as compared to uncoated ones under
actual plant working conditions.
Thermal barrier coatings applied to the working surface (inner bore, outer
cylindrical surface up to 6 inches and flat nose) of the tuyeres lead to considerable
reduction in the heat loss. The main properties, taken into account for selection of
thermal barrier coatings were high melting point of the ceramic material, low thermal
conductivity, phase stability at the tuyere body temperature, bonding characteristics with
the copper substrate and commercially availability of the bond powers/materials.
WE CLAIM:
1. Improved thermal resistant copper tuyeres for use in blast furnace operations
characterized by high melting point of the ceramic material, low thermal
conductivity, phase stability at the tuyere body temperature and bonding
characteristics with the copper substrate comprising a bond coat substrate
selected from the group consisting of Ni-Cr-Al alloy in the weight ratio of 19.5.1
deposited on the bare copper surface and a topcoat of ceramic Titania.
2. Improved copper tuyeres as claimed in claim 1, wherein, the bond coat is made
up of essential powders with granutometric particle sizes of -100 +325 mesh.
3. Improved copper tuyeres as claimed in claim 1 and 2, wherein, the topcoat is
made up of essential powders with granulometric particle sizes of -230 mesh.
4. Improved copper tuyeres as claimed in claim 1 to 3, wherein, the bond coat is
preferably of 0.4 mm thick and the overall thickness of the coating (bond coat
and topcoat included) is around 1.0 mm for inner bore and 2.0 mm for outer
nose.
5. A method of manufacturing improved tuyeres as claimed in claim 1 to 4, which
comprises the following steps:
a. firstly, the copper tuyeres to be coated is centrally mounted on a
horizantal lathe machine;
b. the surface to be coated are machined down by 2-4 mm on diameter
to expose the fresh, virgin copper surface suitable for deposition of
bond coat, where the bond coat is of an alloy of composition: 19-21%
chromium, 3-5% aluminum and balance nickel,
c. then machined copper tuyere surface is then roughened by knurling,
followed by alumina grit blasting for better mechanical anchorage of
the coatings and adhesion of the bond coat with the copper substrate;
d. then the grit blasted copper tuyere surface is then cleaned and
degreasing the girt blasted surface with acetone and preheating to
120-150°C with an argon plasma torch;
e. the bond coat of Ni-Cr-AI alloy is then deposited onto the tuyere
surface by argon plasma spray technique, in this the standard
plasma-grade alloy powder is injected into the high-temperature (6000
to 10000 Kelvin) argon plasma stream, where it is fused and sprayed
onto the preheated copper metal surface, for the coating process the
tuyere is mounted on a horizantal turn-table and rotated at 3-4
rotations per minute, with the following argon plasma spray
parameters:

Stand-off distance of spray gun from job surface- 4-6 inches;
f. building up around 0.4 mm thickness of bond coat in a plurality of,
preferably four runs;
g. following, cooling the job surface to around 50-100°C, where after;
h. the topcoat of Titania (TiO2) is finally deposited over the bond-coated
copper tuyere surface by means of the said argon plasma spray
process using the above mentioned spray parameters and conditions,
where the overall thickness of the coating (bond and top coats
included) is around 1 mm for inner bore and 2 mm for the outer nose
portion of the tuyere;
i. after the application of coating, the tuyere surface is allowed to cool
down at ambient temperature, with typical surface roughness of the
resultant ceramic coating is around 6.91-8.47 microns Ra (average
roughness).
6. A method as claimed in claim 5, wherein, the tuyeres were mounted onto a
horizontal turntable and rotated at 3-4 r.p.m. during the coating process and
following the application of the coating, the surface was allowed to cool to the
ambient temperature.
7. Improved copper tuyeres for use in blast furnace operations substantially as
herein described.
8. A method of manufacturing improved tuyeres substantially as herein described .

The invention relates to an improved thermal resistant copper tuyeres and
method of manufacture thereof, for use in blast furnace operations
characterized by high melting point of the ceramic material, low thermal
conductivity, phase stability at the tuyere body temperature and bonding
characteristics with the copper substrate comprising a bond coat of Ni-Cr-AI
alloy in the weight ratio of 19:5:1 deposited on the bare copper surface and a
topcoat of ceramic Titania.

Documents:

637-CAL-2002-(08-02-2012)-FORM 27.pdf

637-cal-2002-abstract.pdf

637-cal-2002-claims.pdf

637-cal-2002-correspondence.pdf

637-cal-2002-description (complete).pdf

637-cal-2002-examination report.pdf

637-cal-2002-form 1.pdf

637-cal-2002-form 13.pdf

637-cal-2002-form 18.pdf

637-cal-2002-form 2.pdf

637-cal-2002-form 26.pdf

637-CAL-2002-FORM 27.pdf

637-cal-2002-form 3.pdf

637-cal-2002-gpa.pdf

637-cal-2002-granted-abstract.pdf

637-cal-2002-granted-claims.pdf

637-cal-2002-granted-correspondence.pdf

637-cal-2002-granted-description (complete).pdf

637-cal-2002-granted-examination report.pdf

637-cal-2002-granted-form 1.pdf

637-cal-2002-granted-form 13.pdf

637-cal-2002-granted-form 18.pdf

637-cal-2002-granted-form 2.pdf

637-cal-2002-granted-form 26.pdf

637-cal-2002-granted-form 3.pdf

637-cal-2002-granted-gpa.pdf

637-cal-2002-granted-reply first examination report.pdf

637-cal-2002-granted-specification.pdf

637-cal-2002-specification.pdf


Patent Number 235856
Indian Patent Application Number 637/CAL/2002
PG Journal Number 36/2009
Publication Date 04-Sep-2009
Grant Date 02-Sep-2009
Date of Filing 18-Nov-2002
Name of Patentee STEEL AUTHORITY OF INDIA LIMITED
Applicant Address RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI
Inventors:
# Inventor's Name Inventor's Address
1 POPLI ANIL MOHAN RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
2 SRIKANTI SRIKANTH RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
3 BHATTACHARYYA AMITABH RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
4 MISHRA KUNJ BIHARI RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
5 SINGH VIJAY KUMAR RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
6 SINGH VIJAY KUMAR RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
7 POPLI ANIL MOHAN RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
8 SRIKANTI SRIKANTH RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
9 BHATTACHARYYA AMITABH RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
10 MISHRA KUNJ BIHARI RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, STEEL AUTHORITY OF INDIA LTD., DORANDA, RANCHI-834002
PCT International Classification Number F27D 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA