This document discusses refractories and the operation of RH and RH-OB vacuum degassing processes. It provides details on the purpose, activities, and products of various refining units. It also summarizes the theoretical aspects and operational controls of RH processing, including factors that influence the removal of carbon, hydrogen, and nitrogen from steel. Finally, it discusses refractory materials used in RH degassers and strategies for improving RH lining performance and extending degasser lifetime.

1. Refractories and Operation
of RH and RH-OB Process
Department Of Ceramic
Engineering
Seminar and Technical Writing September 2021
Presented By:-Sampad Mishra
Roll-919CR5010
Faculty Advisor- Prof. Debasish Sarkar

2. Unit Purpose Activity Time Product
ARU  To decrease Temp.
 Homogenization of Comp.
 Removal of Impurities
Ar-Purging 5-10
Min.
Plain C-steel
LF Removal of Inclusions
Alloying
Homogenization of Temp.
Homogenization of Comp.
Desulphurization
Buffer Station
Ar-Purging
Arcing
Alloying
30-40
min
Plain C-steel
Micro-alloy
steel
Alloy steel
Low S steel
AOD Removal of Inclusions
Alloying
Temp. adjustment (Inc.)
De-Carborisation
Ar-Purging
O2-lancing
60-70
min
Stainless Steel
Secondary refining

3. Unit Purpose Activity Time Product
VAD Removal of Inclusions
Alloying
De-gassings
Temp. adjustment
Desulphurization
Buffer Station
Ar-Purging
De-gasing
Arcing
Alloying
60-70 min Alloy steel
Special quality
steel (rail steel
/CRNO)
VOD  Removal of Inclusions
 Alloying
 Increase in temperature
 De-Carborisation
Ar-Purging
De-gasing
O2 blowing
60-90 Min. ELC grade steel
CRNO
SS
RH Removal of Inclusions
Alloying
Desulphurization
H2 removal
Ar-Purging
De-gasing
15-20 Min. Rail steel
RH-OB Removal of Inclusions
De alloying
De-Sulphurization/CO
H2 removal
Ar-Purging
De-gasing
O2 blowing
15-20 Min Extra low
carbon steel
 EDD steel
IF steel
Secondary refining

4. Vacuum De-gasing of Steel
 Primarily for H removal
 During the past 30 years significant
development in Vacuum Degassing
 Production of ultra low C ( < 30ppm)
 Extra low H ( <1ppm)
 Extra low N ( <30ppm)
 Presently most of the high quality steels
produced through Vacuum Degassing

5. Types of Vacuum Degassers
 Non-Recirculating
 VD, VAD, VOD & Stream Degassers
Generally used for full range of
metallurgical operations
 Recirculating
 RH, RH-OB/RH-TOB, DH etc.
In general operated in large integrated
shops for C, H & N control

6. Use of Ar gas in Vacuum Refining
 Non-Recirculating
 Stirring gas : Mixing, homogenisation,
removal of S, H, N & inclusion
 Recirculating
 Lifting gas : Reduces the density of
liquid steel to be lifted through
snorkel into Vacuum Vessel of RH
degasser

7. Theoretical Aspects
of Vacuum de-gasing
 Carbon Removal
C removal depends on bath O (VD, VAD),
injected O2 (RH-OB. VOD)&(FeO) C removal
is controlled by liquid phase mass transfer
 In RH-OB & VOD decarburisation depends on
O2 rate
 In recirculation system rate of C removal
depends on circulation rate & rate of removal
 Rate increases with circulation rate,
decarburisation rate & size of the unit
C removal is controlled by vacuum level, Ar flow
rate, initial level of C, Bath O, oxygen injected

8. Theoretical Aspects
of Vacuum Refining
 Carbon Removal
Reaction for C & O removal is given by,
[C]+[O]=CO; [C]+1/2O2= CO; [C]+(FeO)=CO+Fe
 C removal depends on bath O(VD, VAD), injected
O2(RH-OB. VOD) & (FeO)
Amount of C removed is governed by Kinetic
considerations, ln{[C]fin/[C]in} = - KC t
» C removal is controlled by liquid phase mass
transfer
 In RH-OB & VOD decarburisation depends on oxygen
flow rate
 In recirculation system rate of C removal depends on
circulation rate & rate of removal
C removal is controlled by vacuum level, Ar flow rate,
initial level of C, Bath O, oxygen injected

9.  Hydrogen Removal
2[H] = H2
[H] = k √p H2
 H content varies with √p H2
 To get very low H, vacuum level must be very low
 Amount of H removed is governed by kinetic
consideration,
Overall Rate constant for H removal is given by,
ln{[H]fin/[H]in} = - KH t
» Governed by liquid phase mass transfer
 Improved by stirring
H removal is controlled by vacuum level, Ar flow rate,
initial level of H
Theoretical Aspects
of Vacuum de-gasing

10.  Nitrogen Removal
2[N] = N2
[N] = k √p N2
 N content varies with √p N2
 To get very low N vacuum level must be very low
Amount of N removed is governed by kinetic consideration
ln{[N]fin/[N]in} = - KN t
» Governed by liquid phase mass transfer
 Also controlled by chemical rate of [O] & [S] transfer
Rate = [%N] 2 KN/{[%O]KO + [%S]KS}
» Rate is low at lower N content
» Rate is high at lower O & S content
 Compared to H , nitrogen removal rate is low due to low N
diffusivity
N removal is controlled by vacuum level, Ar flow rate, initial level
of N, Bath O & S level
Theoretical Aspects
of Vacuum de-gasing

11. RH i.e. Ruhrstahl
Heraeus named on The
steel works in Ruhrstahl
Germany, where the
first RH-D installed &
Heraeus was the main
supplier of vacuum
pump for the first
RH- Degasser.
RH-Degasser

12. Schemetic RH

13.  RH snorkels are immersed in to the liquid
steel up to a certain standard level. This
initiates vacuum creation in the vessel.
 Molten steel is sucked upward through
inlet snorkels while some level of vacuum
force is maintained.
 Argon purging begins from inlet snorkel
allows metal flow upward that snorkel
and at the same time some metal flow
downwards from the outlet snorkel. This
continuous purging provides circulation of
metal from ladle to both the snorkel and
back to the ladle.
 Due to this circulation, the metal comes
in contact with vacuum and gases are
removed from the steel bath.
RH Process

14. RH OPERATION
• Two snorkels/legs
• Ar injection in up leg to pump
metal in RH unit( ~ 150Nm3/Hr)
• Metal comes back into ladle
through down leg
• Circulation rate(100-200T/min)
depends on snorkel dia(500-750mm) &
Ar flow rate(2000-3000Nlpm)
• No. of circulation varies 20-40
depending on process requirements
Snorkels
Lower vessel
Ladle

15. Types of RH-Degasser
• RH-O : O2 is blown on circulating molten
steel in vacuum chamber from its top
with water cooling O2 lance for refining
low carbon stainless steel
• RH-OB : O2 blowing decarburizing and
Al-adding temperature rising of circulating
flowing molten steel are achieved by Ar
cooling O2 blowing nozzle installed in
tuyere bricks lined in side wall of lower vessel

16. Types of RH-Degasser
• RH-TOB : O2 blowing, vacuum decarburizing,
and CO secondary combustion temperature
rising of circulating flowing molten steel are
achieved by the top O2 blowing lance for
producing ultra low carbon
• RH-IJ : Ar and desulphurization powder
are injected from the molten steel below
the RH up-leg through the injection lance
inserting

17. Types of RH-Degasser
• RH-PB : Desulphurization powder or other
powders are blown into flowing molten steel
from O2 blowing hole in side wall of lower vessel
• RH-KPB :Desulphurization powder and refining
powder are blown into flowing molten steel from
the top of vacuum chamber
• RH-MFB : Multifunction burner developed by
Nippon Steel. Natural gas is blown during vacuum
blowing refining. Combustion of gas raise steel
temp. and cause less skull in vacuum chamber

18. Basic Functions of RH
 Fine composition adjustment
 Decarburisation for low and extra low
carbon steel
 Degassing for low & extra low H & N
steel
 Improving cleanliness

19. Operating Conditions
of RH refining abroad
•Refining temperature:1560-1650oC
•Vacuum degree max. : 66 Pa (0.5 Tor)
•Longest vacuum treating/heat: 40 min.
•RH degasser capacity: 265 ton
•Steel circulating quantity: 200t/min.
•Slag layer thickness in ladle: 50-100 mm
•Basicity of slag: >2.0

20. Operational Control of RH
 Treatment Time
- Metallurgical functions
- Degassing rate
- Decarburisation rate
- Circulation rate
- Ar flow rate
- Input parameters

21. Operational Control of RH
 Initial temperature
 Slag conditions
* Actual Treatment Time : 10-45 minutes
* Ultra low C (30ppm) : 30 minutes
* Light treatment for low H (6ppm to
1ppm) : 10 minutes
Handling Time: 10-12 minutes

22. Operational Control of RH
 Temp.Control
RH-OB
- Chemical heating
(8 OC/min)
- Scrap cooling
RH Process
- Temp. Drop
- LF treatment
after/before RH
- High vessel temp
before treatment
Rise in
temp by
chemical
heating
Temperature
loss

23. Operational Control of RH
Snorkel
- Slag attack
- Long treatment time
Improvement in
snorkel life
- -Low treatment time
(4-7 heats/min decrease)
- Gunning
(80 hts to 100 hts)
Influence of treatment time
on snorkel life

24. Improvement in RH design and
operating parameters
Over all reaction rate
K=ak/(Q+ak)
Q=Circulation rate, t/min
ak=mass trans.parameter
- Increased snorkel dia
- Increased Ar flow rate
- Additional Ar injection

25. RH refractories
•Upper Vessel
Free space for steel erosion & slag corrosion
Refractories used:
-Ordinary magnesite-chrome
-Magnesia spinel bricks is also used
-MgO-C not used as its self consumption
reaction in vacuum[MgO+C Mg(g)+CO(g)]
-Al2O3-MgO.Al2O3 castable lining

26. RH refractories
Lower Vessel,Bottom& Throat
Erosion for high speed circular flow of
molten steel
Refractories used:
- Direct bonded mag-chrome bricks with
high Cr2O3 in the matrix
-Fused grain rebonded mag-chrome bricks
with high Cr2O3 in the matrix
- New generation mag- chrome bricks with
lower porosity and permeability

27. RH refractories
Lower Vessel
Future trend of Refractories :
-Chrome free bricks( MgO-Al2O3-ZrO2)
-MgO-Y2O3 bricks(new phase Ca4Y6O(SiO4)6
with high melting point found near hot face
as a result of CaO&SiO2 in slag&Y2O3 in brick
- Low carbon containing MgO-C bricks
(Fused MgO,Fine graphite2-3%with high
specific surface area5m2.g-1 , Si powder)

28. RH refractories
•Snorkel(Inner lining)
Errosin by high circulation,Corrosion by >2
basicity slag,Thermal&structural
Refractories used:
-Magnesite-chrome bricks with less FeO &
more Al2O3
-Chrome free magnesia spinel bricks
- Low carbon containing MgO-C/MgO-CaO-C
bricks if refining is not ultra low C steel

29. RH refractories
•Snorkel(Outer lining)
Directly contact with basic slag thus requires
corrosion resistance
Refractories used:
-Calcium aluminate cement bonded
corrundum or high Al2O3 spinel castable
-Magnesia spinel castable
- Repair by Al2O3-MgO/MgO-Cr2O3 based
injection material

30. RH refractories performances
in Europe
RH Vessel components Treatments
(Heats)
Snorkel 150 (90)
Lower vessel 450 (200)
Upper Vessel >3500 (600)
Specific consumption(kg/t)
Bricks 0.4
Gunning mass 0.4-1.5
Castable,Mortar,Ramming mass 0.15

31. Upper vessel
Middle vessel
Lower vessel
Bottom
Leg
Snorkel
RH Degasser at RSP

32. Properties Upper
vessel
Lower vessel,
Bottom & Leg
MgO(%), min. 55 60
Cr2O3 (%), min. 18 20
Fe2O3 (%), max. 20 10
SiO2 (%), max - 1.5
B.D(g/cm3 ), min. 3.25 3.0
A.P(%),max. 17 16
RUL, 0C min. - 1680
C.C.S(kg/cm2 ),min. 550 550
RH refractories at RSP

33. Description Unit RH-OB
Avg. Life of
Snorkel
Heats 120
Life of Leg/
Bottom/ Lower
Vessel
Heats 120
Life of Middle
Vessel
Heats 6*120
Life of Upper
Vessel
Years 2
Heats/day/RH Nos 25-26
Process Time Min. ~ 20
Refr. Materials - Direct Bonded
Mag. Chrome
Performance of RH at RSP

34. Damaged areas in RH Degasser
• Lower vessel,Bottom of vacuum chamber,
Throat and Inner of Snorkel are similar
• In RH-OB, places around O2 blowing hole
in lower vessel due to local high temp. and
penetration of Fe-oxides rich slag
• Wear of snorkel & throat is severest
(durability of snorkel restricts life of RH)

35. Ways of improving RH lining
•To select one kind of steel refining in
a campaign
• Zonal lining matching to wear profile
•Operating temperature Not > 1650oC
•Inner temp. of vessel not< 900oC during
non-operating
• Vacuum treatment time not > 40min/heat
•Regular snorkel maintenance( Service life
is 20-30% oflower vessel life)

36. Conclusions
 Under modernization of all steel plants RH
and RH-OB will be an essential vacuum
degassing units for production of ultra low
C(< 30ppm),extra low H(<1ppm),extra low
N(<30ppm)& special quality steels
 Selection and application of suitable bricks
particularly in lower vessel and snorkel
inner along with proper repair in snorkel
outer are the deciding factors for increasing
RH degasser life