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Optimization of

desulphurization of hot

metal and Liquid steelfor RAIL

By

A.ChatterjeeS. K Gupta

C. S. Vishwanathan

S. K. Srivastava

RDCIS,SAIL Ranchi

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Introduction

o SMS-II,BSP produces 2.8Mt through

MixerDe-SConverterARULF/RHCC(Slab)

MixerDe-SConverterARU VAD/LF/RHCC(Bloom,Rail)

o Major products includes

Rails : long rails, crane rails

Plates

Light and heavy structural

o BSP is committed for superior quality of steel and henceinstallation ofDe-S unit (Oct2007 by Danieli Corus)wasdone which is based on co-injection ofMg-CaC2 reagent.

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Rail Steel

o Rail Steel requires stringent chemical composition

C: 0.65-0.7%.

Si:0.2-0.25%.

S

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Deep Injection De-S

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It helps in Reducing the constraints faced in the raw

material selection for Blast Furnace Operations

-S in Coke, fluxes, ores Ensures Lower percentage of S in Products

Helps in the Overall Cost Reduction

In Steel Making

- Allows use of cheaper scrap

- Lower Flux rate higher scrap charge

- Consistent S - high strike rate in Steel Making

Improves Casting speed

Benefits

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Roadmap

Sulphur mapping during downstream processes.

Determining efficiency of ladle desulphurization. Improvement in Slag skimming efficiency

Control of Sulphur pickup in BOF.

Steel De-S by using synthetic slag.

Optimization of Sulphur control in each unit.

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RAIL STEEL

0 032

0 02

0 024

0 015

0 017

0 021

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

HM BOF Bath ARU LF In LF out TundishStage

%

Sulphur mapping for rail heats in BOF-ARU-LF-CC route (Previous practice)

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Desulphurization process

parametersOperating

Parameters

Specification

N2 flow rate 30 50 Nm3/hr

CaC2 : Mg reagentratio

5:1

Avg. CaC2consumption

160 kg/heat

Avg. Mg

Consumption

30 kg/heat

Avg input [S] 0.035 %

Avg post deS [S] 0.01 %

Avg %S drop 70 %

Avg injection time 5 min.

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Slag skimming practice& S

Pickup in BOFSl

No

Initial

[S]

(%)

Initial

Slag

Depth

(cm)

Final [S]

(after

DeS)

(%)

Final

Slag

Depth

(cm)

Ladle Lip

Condition /

jamming

BOF Bath

[S]

(%)

1 0.04 9 0.01 4 Ok 0.014

2 0.04 - 0.01 5.5 Ok 0.013

3 0.04 12 0.011 7.5 High 0.015

4 0.039 11.5 0.019 6.5 Slightly 0.02

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Desulphurization of steel

by synthetic slago Synthetic slag : CaO Al O compound

Forms CaO Al O SiO type refining

slag.

Increases S partition Ratio.

Requires adequate De-oxidation level.

o De-S depends on Activity of oxygen

Circulation rate in bath

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Optimisation of Ladle steel

De-SNomogram 1 Nomogram 2

Bath Sulphur

(%)

Addition of

Synthetic slag(kg/heat)

Bath Sulphur

(%)

Addition of

Synthetic slag(kg/heat)

Upto 0.018 Nil Upto 0.015 Nil

0.019 0.021 300 0.016 0.020 300

0.022 0.024 400 0.021 0.025 500

0.025 & above 500 0.026 & above 600

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Trial Result continued

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0.055

HM HM Post

DeS

BOF Bath ARU LF in LF out Tundish

Stages

%S

ulphur

Sulphur mapping for rail heats without synthetic slag addition

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Trial Summary

Phase-I:

o trial heats.

o Based on nomogram- .o Average final S: . %( > . % in heats)

Phase-II:

o trial heats.

o Based on Nomogram- .

o Average final S: . %( > . % in heats)

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Results & Conclusion

Control of S < . %.

Proper slag skimming to control S pickup in

BOF within . %.

No synthetic slag additions for S in steel

< . %.

Reduction in Synthetic slag addition(fromkg/heat to kg/heat).

Average final S was found to be . %

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Thank you