Page 15 - Steel Tech India eMagazine Volume April 2022
P. 15

VOL. 16 • NO. 3 • April 2022

                 While some plants majorly adopted ladle treatment for   medium pressure to augment slag/ metal reaction
                 reducing P by building a highly basic slag with higher   Sample analysis and continuation of process as needed
                 FeO contents, some desulphurisationhappened as well
                 due to the final reducing slag build up after deoxidation   De slagging and Al /c/Alloy addition based on sample
                 of the bath when the FeO content of the slag is reduced   analysis
                 to a large extent favouring desulphurisation.      lime/synthetic slag addition

                                         0
                 tap from IF at nearly 1600  c  Slag skimming/drain out   Sample  analysis/trimming  addition/temperature
                 before tapping
                                                                    adjustment
                 Target tap chemistry C 0.10 max   Mn< 0.05   Si /Al Nil  transfer to caster
                 ladle addition-  lime/ Mill Scale/Fluorspar - On  line   the total treatment time from IF tapping to transfer to
                 Purging                                            caster varies from 60 to 75 minutes but does not impact
                 Arcing and further lime/ mill scale addition- Purging at   sequence casting continuity.

                 Table 2 : Typical Chemistry obtained before and after LRF treatment

                    Heat   IF Tap  IF Tap  IF tap  IF Tap   S +P   LF    LF     LF      LF      LF      LF      P
                  Number    C %    Mn %    P %     S%      %     Final   Final   Final   Final   Final   Final   Drop
                                                                 C%     Si%    Mn%      P%     S%     P+S%
                     1      0.10    0.03   0.108  0.037  0.145   0.19    0.10   0.50   0.030   0.035  0.065    72%

                     2      0.08    0.02   0.106  0.039  0.145   0.16    0.12   0.51   0.035   0.036  0.071    67%
                     3      0.12    0.02   0.098  0.031  0.129   0.18    0.18   0.53   0.036   0.032  0.068    63%
                     4      0.09    0.01   0.113  0.036  0.149   0.17    0.17   0.52   0.034   0.032  0.066    70%
                     5      0.14    0.02   0.110  0.040  0.150   0.17    0.17   0.55   0.034   0.037  0.071    69%

                 In plants where the facilities for ladle furnace arrangements not yet installed, for an estimate, the cost of
                 installation a 20T capacity ladle refining furnace with all accessories would be nearly Rs 7-8 crores.
                 Table 3 : Specific Consumption of various ingredients (an idea)

                  Heats       Lime  Spar  Argon  Mill Scale/De   Carburiser/  Ferro   Al Kg/T  Power  Electrode  Refractory  Typical
                              Kg/T  Kg/T NM3/T  Phosphoriser   Deoxidiser  Alloy     Kwh/T  Kg/T   etc Rs/T  Total Cost
                                               Kg/T        Kg/T       Kg/T
                  Various heats  22  2    0.28      11         1.2     12.5    1.0    100    0.8      700       -
                  Average
                  typical  Unit  7   7    100       3          23       90     250    5.5    150      700       -
                  cost Rs
                  typical  total  154  14  28       33         27      1125    250    550    120      700     2745
                  cost Rs

                 this Process enables replacing Fe-Alloy addition completely in Induction Furnace and shifting the same to lRF
                 which, since added after deoxidation with coke and aluminium, might reduce consumption of ferro alloys as well.

                 If Fe alloy cost which is common even when direct heat is made through Induction furnace is subtracted, the total
                 cost for lF treatment comes around Rs 1620/ton and can be taken in the range of Rs1500 to Rs1800 per ton
                 depending on the process and it’s efficient adoption.
                 Table 4: Typical slag chemistry at various stages

                  Slag Origin  %CaO      %Si02     %Al203     %MgO     %FeO      %P2O5     %MnO     Remarks
                  IF           < 5       40-50     12-15      <5       30-35     Nil       <5       Tap Slag

                  LRF          40-50     12-15     12-14      <5       25-30     1-1.5     <2       After De P
                  LRF          45-60     8-10      20-25      <5       <2        < 0.1     5-10     Final-After De
                                                                                                    P/De Oxidation

                 Steel tech                                                                                        13
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