1. Techniques of Hearth Protection in Blast Furnace R&D and SS Department
Venkatesan J

2. Why hearth protection is necessary ?
To increase the campaign life of furnace
Relining of the hearth is not easy
To avoid heat loss at hearth and to hold hot metal
To avoid hearth break out
10 BFs in China have accidents due to breakout of hearth and bottom
Reference : AISTech 2015 Proceedings © 2015 by AIST

3. BF Hearth and Bottom Carbon based grades Carbon Blocks
- Calcinated anthracite baked with tar
Micropore Grades
- Carbon blocks with Al2O3 impregnated with tar in vacuum
- Baking twice to reduce size and number of pores
Super Micropore Grades
- Metallic Si and Al2O3 mixed with Carbon
Graphite Blocks
To smooth out temperature gradients
To conduct heat to the side walls
Semi - Graphite Blocks
Very low porosity and high thermal conductivity

4. BF Hearth and Bottom Ceramic Material – High Alumina brick/ Clay brick
Carbon Brick
Damages
Flushing wear abrasion
Chemical erosion
Advantages
High temperature resistant
Anti –erosion
Resistance to wear

5. Hearth Deterioration
Penetration corrosion of carbon brick by hot metal
Corrosion damage of carbon brick by hot metal
Mechanical flushing & erosion of high temperature slag and iron
Working Conditions of Blast Furnace hearth
Chemical corrosion by alkali metal and alkali oxide
Oxidative damage of oxidising substances such as H2O
Damage due to differential temperature thermal stress

6. following the path of least resistance
Hearth Deterioration
Floating deadman
hot metal flows through bottom of the hearth – through coke free zone
increases the hearth pad temperature
decreases the side wall temperature
Sitting deadman
larger temperature variation inside the deadman
following the path of least resistance
Floating deadman
Sitting deadman

7. Tap hole outlet temperature following the path of least resistance
Hearth Deterioration
Erosion profile
Tap hole outlet temperature
following the path of least resistance

8. TiO2 provides protection to BF hearth lining against premature erosion
Hearth Protection
Possible ways to decrease wear rate of BF hearth
Lowering the BF Productivity
Reducing coal injection rates
Grouting of the ramming mass between staves and carbon blocks
Increasing the cooling rates of the wall
Addition of the TiO2 containing materials
TiO2 provides protection to BF hearth lining against premature erosion

9. Methods of Charging TiO2 into BF
Added with burden materials and charge into furnace from top
Ilmenite - Titanium Magnetite Ore {(Fe,Ti)3O4}
TiO2 mixed with Sinter
Synthetic TiO2 containing materials
Characteristics
Reactions initiate and proceed with increasing temperature
Delayed time of action
Impairment of slag quality in cohesive zone
Occasional deposition in the BF shaft
High input rates

10. Methods of Charging TiO2 into BF Fine particled TiO2 Source
Injected into furnace through tuyeres
Ilmenite - Titanim Magnetite Ore {(Fe,Ti)3O4}
Synthetic TiO2 containing materials
Fine particled TiO2 Source
Characteristics
Injection occurs in the immediate vicinity of the damaged worn out area
TiO2 direct has interaction with gas, metal and slag phases
No delayed time of action
No accumulation of TiO2 containing materials in shaft
Lower input rates
Higher efficiency of conversion to Ti(C,N) compounds
Improved slag quality with less TiO2 in slag

11. Protection Layers Titanium Rich Layer Iron Rich Layer Slag Rich Layer
Graphite Rich Layer

12. Protection Layers Titanium Rich Layer Mechanism
Formation of solid solution of Titanium Carbide and Titanium Nitride
Most effective method
Change of blast furnace operating conditions
Variation of the hot metal temperature
N2 partial pressure
Mechanism
TiO C -- > [Ti] + 2CO
Then Ti in hot metal diffuses to low temperature regions
H = Kcal/mol
Once Ti in HM reaches the saturation point ---> TiC and TiN
Deposit in the abnormal hearth erosion areas
Regions where the hot metal circulation has a low fluid speed

13. Protection Layers Titanium Rich Layer
TiO2 concentration in slag greater than 1.2 %, TiO2 will be reduced and precipitate as titanium carbonitride.
TiO2 increases the viscosity of liquid slag
TiO2 in slag should be less than 3% and
Ti in Hot metal should be less than 0.3 %
 Factors which affect Ti/TiO2 equilibrium
Hearth temperature
Slag basicity
Si levels in the hot metal

14. Protection Layers <1150oC Iron Rich Layer
Lining erosion over time promotes the heat loss through the furnace lining
It reduces the hot face temperature
If it below freezing point – Iron layer forms due to solidification of hot metal at hot face
Embrittlement of carbon blocks occurs due to alkali & thermal stress
Iron-rich layer can effectively prohibit
<1150oC
direct contact of hot metal with carbon blocks and also prevent the infiltration of alkalis

15. Protection Layers Slag Rich Layer Density of molten slag – 2.4 g/cm3
Density of hot metal – 7.0 g/cm3

16. Protection Layers Graphite Rich Layer
Graphite precipitates in the hearth sidewall and hearth bottom areas at low temperatures
Furnace temperature fluctuation leads to
solidification of hot metal
promotes the graphite precipitation
 Factors influencing precipitation of graphite
Transformation ability of carbon in hot metal to graphite
Cooling rate of hot metal

17. Technical route for control of protection layer formation

18. Technical route for control of protection layer formation
Increase the refractory conductivity
Control of flow of cooling water
Reduce the circulation intensity of hot metal
Block the tuyeres above the abnormal erosion regions
Charging high quality coke to increase permeability of deadman

19. Technical route for control of protection layer formation
Increase C in hot metal
Increase blast pressure
Lowering the level of oxygen enrichment through low RAFT
by reducing S content in HM

20. Technical route for control of protection layer formation
Si content in hot metal
Compare to C, Si has stronger tendency to combine with Fe
It promotes precipitation of graphite
Increase of Si in hot metal leads the rise in solubility of Ti

21. Technical route for control of protection layer formation
S content in hot metal
It forms ternary eutectic product ( C-0.17%, S- 31.7%)
It inhibits the atom diffusion process
Precipitation of graphite is adversely affected
It increase hot metal viscosity
Low S content is desirable

22. Technical route for control of protection layer formation
Ti content in hot metal
[Ti] – determines the effectiveness of hearth protection
Protection layer starts when the TiC exceeds the critical value
This layer decreases the hot face temperature and HM viscosity

23. Thank You