Title of Invention | IMPROVED THERMAL RESISTANT TITANIA COATED COPPER TUYERS FOR USE IN BLAST FURNACE AND A METHOD OF ITS MANUFACTURE |
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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. |
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637-CAL-2002-(08-02-2012)-FORM 27.pdf
637-cal-2002-correspondence.pdf
637-cal-2002-description (complete).pdf
637-cal-2002-examination report.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-reply first examination report.pdf
637-cal-2002-granted-specification.pdf
637-cal-2002-specification.pdf
Patent Number | 235856 | |||||||||||||||||||||||||||||||||
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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:
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PCT International Classification Number | F27D 3/00 | |||||||||||||||||||||||||||||||||
PCT International Application Number | N/A | |||||||||||||||||||||||||||||||||
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