Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
LOW MELTING TUNDISH COVERING COMPOSITION(TCC) FROM FLYASH AND PRODUCTION METHOD THEREOF.



2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.



3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION

The present invention relates to development of new Tundish Covering Composition(TCC) from fly ash, calcined lime fines. This invention relates to the in house development of TCC by using Flyash generated as waste from coal based power plants, Calcined lime fines which are generated at JSW lime calcinations plant is used as binder in the process of making acidic TCC. The product is produced by mixing the above said waste fines in pilot scale pelletizing machine of R&D centre of JSW steel Ltd. Comparison of physical and chemical properties of commercial and in house developed TCC were done and found that both are matching.

BACKGROUND OF THE INVETION

The drive to produce clean steel has resulted in employing the addition of tundish covering compounds (TCCs) to tundishes, thus making it an integral part of continuous casting process. The process demands not only minimization of heat loss from the liquid steel, but also prevention of steel reoxidation by the atmosphere and removal of inclusions from liquid steel during its residence time in the tundish. Tundish being the last refining vessel in today’s steelmaking process, the function of a tundish covering compound thus becomes critical in ensuring cleanliness of the final product [J Strandh, K Najima, R Eriksson and P Jonnson, “”, ISIJ, Vol-45[11], 2005, pp. 1597-1606]. The main objective of using a TCC is to provide an insulating layer to the molten steel and fulfill the above basic requirements.

Due to its low cost and excellent insulating property owing to its low density (0.2-0.3 g/cc), rice husk ash becomes the natural choice as TCC material [A Kumar, K Mohanta, D Kumar and O Parkash, “Properties and Industrial Applications of Rice husk: A review”, IJETAE, Vol-2; 2012]. These are basically organic wastes rich in amorphous silica (SiO2) phase and hence acidic in nature.

Fly ash, the residue of coal combustion, mostly consists of both amorphous and crystalline SiO2, alumina (Al2O3) and calcium (CaO). Due to presence of glassy phases, it can be considered as a prefused material with mullite (3Al2O3.2SiO2) and quartz as the crystalline phases. Though literatures report about fly ash as an alternative covering compound however, no reported literature is available on plant trial conducted using flyash as TSS. Hence, efforts have been made to explore the feasibility of using fly-ash tundish covering compound as a replacement of rice husk based commercial grades. The present study also investigates a comparative evaluation of the fly-ash based TCC and commercial TCC in terms of its properties and performance.

TUNDISH COVERING COMPOUNDS (TCC):
TCC is used in the tundish area of steelmaking to reduce the heat loss in the tundish while transferring the liquid steel from tundish to caster. It forms a thin slag layer and acts as insulator. It also prevents the entrapment of atmosphere oxygen to the metal.
It is used in the tundish area of steel making. The main purpose of TCC are insulator to avoid heat loss and for inclusion absorbing material.
Functions of a good TCC:
• Minimizes heat loss due to radiation.
• Prevents direct contact of liquid steel to atmosphere.
• Provides insulation for longer time duration at temperatures even more than 1600o C
• Maintains consistent temperature of liquid steel in the tundish
• Helps in inclusion absorption
TCC are the insulating materials used in the tundish area of the steel. TCC are made from burnt rice husk ash which consists of silica from 85-90%. The present TCC are granules in shape size of 3-5 mm, purchased from outside market. Cost of TCC is around 12000-13000/ton.

Applicant JSW steel Limited is a 13MTPA capacity steel producer .Around 10000 tons of liquid steel is producing daily for each unit. Consumption of acidic TCC is around 2100tons per annum. TCC used at present are in the form of granules to avoid the dust generation while charging on the liquid steel. In SMS -1,90% of total TCC used is acidic in nature and remaining 10% is basic in nature.

Table 1: Liquid steel production and TCC consumption details at JSW Steel Melting Shops (SMS)
Unit Tons of steel
produced per day Total TCC consumption per day
SMS 1 11000 6.0
SMS 2 17000 9.0

So, taking all this into consideration, the properties and composition of present TCC can be matched by making a new compound using waste like fly ash and calcined lime. The cost of new developed product is also less as compared to the commercial product, which drove us in the direction for making this useful product.

Fly ash is a byproduct of coal combustion. The material is composed primarily of complex aluminosilicate glass, mullite, hematite, magnetite spinel and quartz. The proportion of quartz (crystalline silica) in the fly ash varies depending on the quartz content of the coal. Class C fly ash may have 1-7% free CaO and calcium sulfate as well as calcium aluminosilicate glass.Depending upon the coal source, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) and calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata. Chemical analysis of flyash used in the present invention is given below.
Table 2: Chemical analysis of fly ash generated from JSW Energy
Unit Carbon,
% SiO2,
% Al2O3,
% Fe2O3,
% CaO,
% MgO,
% TiO2,
% Na2O,
% K2O,
% P2O5,
% Sulphur, % LOI
SB1-U1
(HC) 6.50 47.26 28.13 6.17 4.33 2.13 1.16 1.08 0.63 1.00 0.48 7.63
SB1-U2
(HC) 7.02 46.46 28.61 5.81 3.63 2.03 1.23 0.92 0.64 0.80 0.36 9.51
SB2-U1
(LC) 3.8 50.80 29.22 3.96 4.32 1.85 1.41 0.61 0.84 1.55 0.29 5.15
SB2-U2
(LC) 4.2 51.87 28.65 3.7 3.78 1.90 1.27 0.51 0.96 1.49 0.20 5.67
(High carbon:HC; Low Carbon LC)

Table 3: Ash fusion characteristics of flyash
Sample ID Flow temp. Flow range
SB1-U1(High carbon) 1489 1447-1489
SB2-U2(Low carbon) 1510 1479-1510
Commercial TCC Not flowing >1600

Fly ash as major TCC ingredient:
Flyashis used as the main ingredient to develop the TCC for the present study. The reason for selection of flyash for TCC is that it is rich of silica and alumina, which acts as a good insulating agent. The flyash generated from SB-2 thermal power plantis having good quality with respect to chemistry and fusion characteristics. Flyash from SB2,is having low carbon and high silica compared to high carbon flyash. Flyash is a prefused slag with major phases of aluminium silicate (refer XRD analysis) with lower melting point compared to traditional rice husk based compounds.The flyash from SB2 (LC) is not deformed even at high temperature i.e.up to 1600 whereas the sample from SB 1 (HC) unit is deformed. Since fly ash from SB2 (LC)is not deformed even after 1600o C and contains low carbon of below 5.0% so it is tried as TCC material. Commercial grade TCC used in the plant has been considered for comparison. The denotations used for commercial grade and developed materials are TCC_C and TCC_D respectively.

Calcined Lime fines
It is basically the anhydrate lime named as Calcium oxide. It is usually made by the thermal decomposition of materials such as limestone, which contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C , a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2); leaving quicklime. The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until it is completely converted back to calcium carbonate. Calcined lime is being used as binder in various agglomeration processes like briquetting, pelletizing. It is also used in cement making. It is having very high melting point >2000 o C which is suitable to used as binder for making TCC.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide a low melting Tundish covering composition from fly ash and calcined lime binder.

A further object of the present invention is directed to provide a low melting Tundish covering composition to reduce the heat loss in the tundish while transferring the liquid steel from tundish to caster, by forming a thin slag layer that acts as insulator.

A still further object of the present invention is directed to provide a low melting Tundish covering composition having fusion property of tundish slag found to be higher having a glassy like appearance with lower melting point compared to traditional rice husk based compounds.

A still further object of the present invention is directed to provide a low melting Tundish covering composition having parameters such as spreadability, dust emission, temperature drop, steel quality after casting, nitrogen pick-up, Aluminum drop in steel, deskulling, refractory erosion comparable with conventional rice husk based Tundish covering composition.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a low melting Tundish covering composition comprising :

of a tundish covering obtained of 85 to 98% preferably 95% by wt. flyash of particle size of below 200 microns and 2 to 8% binder preferably 5 % by wt. and having melting temperature range of 1300 to 1500deg C preferably 1400 deg C.

A further aspect of the present invention is directed to said low melting Turdish covering composition wherein the binder is selected from calicined lime fines, calcined dolomite fines, hydrated lime fines, bentonite, preferably calcined lime fines of particle size of below 150 microns.

A still further aspect of the present invention is directed to said low melting Turdish covering composition which is in the form of micro pellets of size 2-5 mm.

A still further aspect of the present invention is directed to said low melting Turdish covering composition having
SiO2,% CaO,% MgO,% Fe2O3,% Al2O3,% P2O5,% TiO2,% Alkalies (Na2O+K2O),% Carbon,% LOI,%
45 to 60 preferably 55.0 6.0 to 15.0 preferably 10.06 1.0 to 3.0 preferably 1.48 4.0 to 8.0 preferably 4.52 15.0 to 30.0 preferably 24.1 0.5 to 2.0 preferably 1.68 1.0 to 2.0 preferably 1.61 0.5 to 1.0 preferably 0.65 5 to 15 preferably 7.6 8 to 20 preferably 8.5

Another aspect of the present invention is directed to said low melting Turdish covering composition having physical properties of size 2-5mm, moisture of below 5% after 48 hrs of natural curing, drop number more than 5 and Dry compression strength (DCS) of more than 0.5kg. Rice husk bases TCC is having melting temperature of more than 1600 o C , drop number is 2 and Dry compression strength (DCS) is 0.2 kg.

Yet another aspect of the present invention is directed to said low melting Turdish covering composition having phase constitution of mullite of 34%, Quarzite of 22%, Hatrurite 36% and Aluminium Magnesium of 8%.

A still further aspect of the present invention is directed to said low melting Turdish covering composition which acts as a aluminum silicate source in tundish of steel making process and forms a fluid slag in the tundish that acts as insulator for reducing temperature loss.

A still further aspect of the present invention is directed to a process for the manufacture of low melting Tundish covering comprising:

i) Providing fly ash in amounts of 85 to 98 % and binder in amounts of .. 2 to 8 % ;
ii) Dry mixing of the above combination of fly ash and binder;
iii) Adding water 10-15% by wt to said dry mix and subjecting to micro pellet making by ball formation in a micro pellet disc pelletizer; and
iv) Finally curing for removal of moisture and pellets having said low melting in the temperature range of 1300 to 1500 Deg C.

A further aspect of the present invention is directed to said process wherein in said step of curing micropellets are naturally cured in atmosphere for 3-4 days for removal of moisture and attaining desired strength.

Another aspect of the present invention is directed to said process wherein the micropellets are obtained in the size range of 3-5mm.

Yet another aspect of the present invention is directed to said process wherein pelletizer disc angle is set at 400-450 with a rotating speed of 8-10 rpm.

Theabove andother aspect and advantages of the present invention are described hereunder with reference to following accompanying non limiting illustrative drawings and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1:Process flow sheetfor preparation of TCC of the present invention/ micro pellet making
Fig. 2: Method of making TCC by using pellet disc
Fig. 3: schematic view of Tundish during operation with invented TCC use.
Fig 4: shows (a) actual Pelletizing machine and (b) Green pellets during preparation in pelletizing machine.
Fig 5:show Granules of TCC (a) Commercial(TCC_C), (b) TCC_D Developed according to present invention.
Fig 6:show Spreadability of covering compounds after addition: (a) TCC_C, (b) TCC_D.
Fig 7: show condition of permanent refractory lining after deskulling of (a) TCC_C, (b) TCC_D added tundishes.
Fig 8: show Tundish slag samples; (a)TCC_C, (b) TCC_D.
Fig 9:show comparision of average chemistry for TCC_C and TCC_D added steel grades.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLE OF A PREFERRED EMBODIMENT

Currently, rice husk based TCC of SiO2 around ~85-90% is using in tundish area of steel making in everywhere. In the present invention newly developed TCC (TCC _D) made by using fly ash as base material is replaced with commercial TCC (TCC_C) and found that TCC_D is at par with commercial TCC_C. It is also found that there is no process abnormalities were found during the experimentation.
New TCC is prepared by using 90-95% flyash, 5-15% of calcined lime fines as binder. Both the ingredients are mixed thoroughly initially and pelletized in a micro pellet machine by adding 15-20% water for ball formation. Pellets of size 3-5mm are prepared and naturally cured for 3-4 days for removal of moisture and attaining the strength. Calcined lime acts as a binder and attributes the strength during natural atmosphere curing. After 3-4 days of curing pellets were tested for readiness of usage by testing moisture, drop number, cold compression strength. After testing micropellets will be packed in the quantity of 5-10 kg bags.After packing trial was conducted by adding around 1.0 ton of new TCC in the form of granules (3-5mm size) in 2 nos of tundishes. Parameters such as spreadability, dust emission, temperature drop, steel quality after casting, nitrogen pick-up, Aluminum drop in steel, deskulling, refractory erosionwere comparable with conventional rice husk TCC. It is found that there was no impact on the operation as well as quality.

Figure 1 represents the complete flowsheet of TCC development process. This includes raw material addition system,water and binder addition, pellet disc for mirco pellet making process, curing process of pellets, testing of properties.

Figure 2 represents the method of making TCC by using pellet disc. This includes the rotating pellet disc with shaft connected to motor, lever for adjusting the angle of the disc, input rawmaterial charging process on to the pellet, Addition of water, binder during pellet making, output product collection.

Figure 3 represents the application of invented TCC in tundish of steel making. This includes the slag layer formed on the top portion of the tundish, liquid steel flow from ladle to tundish and tundish to caster, shroudpipe, mono block refractory, and refractory layer of the tundish.

Experimental results:

Lab scale Experimental Procedure

Sample preparation of TCC through micro pellet plant:

fly-ash based micro pellets (TCC_D) were prepared in a micro pellet disc pelletizer using lime binder and 10-15% moisture content (IS 11373). The disc angle was fixed at 450 with a rotating speed of 8-10 rpm. Fig. 1 shows the pellet disc used for preparation of TCC, Fig 2 shows the pellet disc during preparing of green TCC_D. Granules prepared using the disc are subjected to atmospheric drying for 72 hrs to remove the moisture and attain the handling strength. After drying micro pellets were screened to 3-5mm particle size, tested for suitability and bagged for usage in tundish.

Chemical analyses of the samples were determined by X-Ray Fluorescence (XRF, Thermo Scientific, Model No– ARL 9900). Moisture content was measured by calculating the percent weight difference after oven drying at 1100C.

Dry Compressive Strength (DCS) of the pellets was measured by placing the dried pellets in a compressive testing machine and applying load at a constant speed until the pellet breaks (IS: 8604 - 1977). The maximum load applied where the pellet breaks is recorded in kilograms.

Drop number is determined by dropping the dried pellets from a height of 0.5m on an MS plate of 3 mm thick (IS : 11373 - 1985). The no of drops at which the pellet breaks is referred as the drop number of that pellet. This property indicates the handling strength of the pellet.

Softening and melting range was determined using Ash fusion equipment (HESSE Instruments, Model No- EM201-17K) in oxidizing atmosphere.

Micro structural and elemental analyses of the samples were carried out in an Electron Probe Micro-Analysis (EPMA, JEOL, Model No-JXA8230) equipment using Energy Dispersive Spectroscopy (EDS) mode.

Accompanying Fig 4(a) showsactual Pelletizing machine for experimental trials and Figure Fig 4(b)Green pellets during preparation in pelletizing machine. The process parameters for pellet making is shown in following Table 4.

Table 4: Process parameters of pellet making
Specifications of micro pellet disc
Pellet disc rotating speed, RPM 8-10
Diameter of disc, meter 1.0
Motor capacity 500W
Motor speed, RPM 200
Disc angle, deg 40-45
Batch size, kg 5-10
Binder used calcium oxide
Binder % 5-8%
Moisture added 10-15%
Curing time 24-72 hrs of
atmosphere

Accompanying Fig. 5 shows (a) the granules of as received existing commercial TCC_C and (b)completely dried TCC_D covering compounds developed according to present invention.

Chemical analysis of both the TCC:
Chemical analyses of both the compounds are shown in Table 5. Higher lime content in TCC_D can be attributed to the lime content in fly-ash and added lime binder. The physical properties of both the materials are shown in Table 6. As can be seen from the data, the density was found to be slightly higher for TCC_D owing to higher Fe2O3 content in it compared to TCC_C. Drop number and DCS were found to be comparable for both the materials. Since fly-ash is a prefused material, the melting temperature range of TCC_D was found to be lower compared to SiO2 rich rice husk based TCC_C.

Table 5: Chemical Analysis of commercial and developed TCCs (wt%)
SiO2,% CaO,% MgO,% Fe2O3,% Al2O3,% P2O5,% TiO2,% Alkalies (Na2O+K2O),% Carbon,% LOI,%
TCC_C 89.0 2.4 2.7 0.9 1.13 1.1 0.01 2.65 7.4 8.1
TCC_D 55.0 10.06 1.48 4.52 24.1 1.68 1.61 0.65 7.6 8.5

The range of components in the TCC composition is as follows:
SiO2,% CaO,% MgO,% Fe2O3,% Al2O3,% P2O5,% TiO2,% Alkalies (Na2O+K2O),% Carbon,% LOI,%
45 to 60 preferably 55.0 6.0 to 15.0 preferably 10.06 1.0 to 3.0 preferably 1.48 4.0 to 8.0 preferably 4.52 15.0 to 30.0 preferably 24.1 0.5 to 2.0 preferably 1.68 1.0. to 2.0 preferably 1.61 0.5 to 1.0 preferably 0.65 5 to 15 preferably 7.6 8. to 20 preferably 8.5

Table 6: Physical properties of commercial and developed TCCs
Moisture (%) Density (g/cc) Drop No DCS (kg/pellet) Melting Range (0C)
TCC_C 1.8 0.5 7-10 0.4-0.5 > 1600
TCC_D 1.5 0.8 8-10 0.4-0.55 1300-1500

XRD analysis
R&D TCC -D:

Rice husk based Commercial acidic TCC-C:

Plant trial data
Plant trial was conducted with the developed TCC_D in tundishes of Al-killed steel with an average sequence length of 8 heats and the performance was compared with the commercial one. Its performance was evaluated in terms of spreadability, refractory corrosion, heat loss and impact on steel quality. The quantity added was approximately 67 kg/heat for developed material compared to approximately 54 kg/heat for commercial one.

Spreadability & Refractory wear
Fig. 6 shows the TCC layer after addition to the tundish for commercial material and developed material. As can be seen from the figures, the spreadability was found to be comparable. Fluidity of TCC_D slag was found to be slightly higher compared to commercial one. The permanent refractory lining of the tundish was found to be in good condition after deskuling of the disposable layer with no significant slag line corrosion for both the materials (Fig. 7 a & b).

Fusion property of TCC_D added tundish slag was found to be higher having a glassy like appearance compared to TCC_C one owing to its lower melting temperature (Fig. 8).

Steel and slag chemistries
Comparative average steel chemistries for TCC_C and TCC_D added tundishes are shown in Fig. 9. As can be seen, the chemistries are comparable for both the grades without significant variation.

Chemical analysis of the tundish slags collected after dumping for both the covering compounds is listed in Table 7. Higher CaO content in TCC_C added slag is indicative of ladle carry over slag into the tundish. The MgO content was found to be slightly higher for TCC_D added slag.

Table 7: Chemical analysis of dumped tundish slags (wt%)
SiO2 CaO MgO Fe2O3 Al2O3 MnO TiO2
Slag_C 42.37 29.42 5.03 4.08 14.73 1.02 0.97
Slag_D 31.20 29.11 6.13 4.24 24.33 2.35 1.01

, Claims:We Claim:
1. Low melting Tundish covering composition comprising :

of a tundish covering obtained of 80 to 98% preferably 95% by wt. flyash and 2 to 8% preferably 5% by wt binder and having melting temperature range of 1300 to1500 degC, preferably 1400 degC.

2. The low melting Turdish covering composition as claimed in claim 1 wherein the binder is selected from calcined lime fines, calcined dolomite fines, hydrated lime fines, bentonite, preferably calcined lime fines.

3. The low melting Turdish covering composition as claimed in anyone of claims 1 or 2 which is in the form of micro pellets of size 2-5 mm.

4. The low melting Turdish covering composition as claimed in anyone of claims 1 to 3 having

SiO2,% CaO,% MgO,% Fe2O3,% Al2O3,% P2O5,% TiO2,% Alkalies (Na2O+K2O),% Carbon,% LOI,%
45 to 60 preferably 55.0 6.0 to 15.0 preferably 10.06 1.0 to 3.0 preferably 1.48 4.0 to 8.0 preferably 4.52 15.0 to 30.0 preferably 24.1 0.5 to 2.0 preferably 1.68 1.0. to 2.0 preferably 1.61 0.5 to 1.0 preferably 0.65 5 to 15 preferably 7.6 8. to 20 preferably 8.5

5. The low melting Turdish covering composition as claimed in anyone of claims 1 to 4 having physical properties of size 2-5mm, moisture of below 5% after 48 hrs of natural curing, drop number more than 5 and Dry compression strength (DCS) of more than 0.5kg/pellet, melting temperature of 1400oC.

6. The low melting Turdish covering composition as claimed in anyone of claims 1 to 5 having phase constitution of mullite of 34%, Quarzite of 22%, Hatrurite 36% and Aluminium Magnesium of 8%.

7. The low melting Turdish covering composition as claimed in anyone of claims 1 to 5 which acts as a aluminum silicate source in tundish of steel making process and forms a fluid slag in the tundish that acts as insulator for reducing temperature loss.

8. A process for the manufacture of low melting Tundish covering as claimed in anyone of claims 1 to 7 comprising:

i) Providing fly ash in amounts of 85 to 95% and binder in amounts of 2 to 8% ;
ii) Dry mixing of the above combination of fly ash and binder with calcined lime fines, calcined dolomite fines, hydrated lime fines, bentonite.. preferably calcined lime fines;
iii) Adding water 15-20% by wt to said dry mix and subjecting to micro pellet making by ball formation in a micro pellet disc pelletizer; and
iv) Finally curing for removal of moisture and pellets having said low melting in the temperature range of 1300 to 1500 oC.

9. The process as claimed in claim 8 wherein in said step of curing micropellets are naturally cured in atmosphere for 3-4 days for removal of moisture and attaining desired strength.

10. The process as claimed in anyone of claim 8 or 9 wherein the micropellets are obtained in the size range of 2-5 mm.

11. The process as claimed in anyone of claims 8 to 10 wherein pelletizer disc angle is set at 400-450 with a rotating speed of 8-10 rpm.

Dated this the 22nd February, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199