A STUDY ON THE DEPHOSPHORIZATION EQUILIBRIUM IN LDCONVERTER
Motozo Maeda, Kikuo Tajima, Eturo Homma
The authors applied the dephosphorization equilibrium formula reported by Chipman to mostly the final slag and metal samples of the 3 ton experimental LD converter.
The results obtained were as follows.
(1) The observed values of Kp, dephosphorization constant calculated from oxygen in metal, were in fairly good accordance with Chipman's equilibrium values, while the values of Kp, dephosphorization constant calculated from (FeO) in slag showed a definite descrepancy from Chipman's equilibrium values.
Furthermore the descrepancy increased almost proportionally with the increase of (FeO)% or T.Fe% in slag.
Experessing this descrepancy as ΔlogKp'(=logKp'(ehip)-logKp'(obs)) the ahthors obtained the following relations statistically.
(2) During the final stage of the blow, the oxygen in bath did not increase proportionally with (FeO) in slag and at the end of the blow the oxygen in bath was generally lower than the value predicted from the distribution equilibrium of oxygen between metal and slag.
Therefore less effect of "after-blow" to dephosphorization could be expected compared to the bottom blown converter.
(3) In the final slag of the converter there existed somewhat a definite relation between NCaO' and NFeO according to the operation condition such as the amount of lime charged, [Si]% of pig iron, pig ratio, etc.
NCaO' tended to decrease with the increase of NFeO because of the dilution effect of (FeO).
For the slag they studied, the following relation was obtained.
(4) The relation between phosphorus-distribution ratio, logNCa4P2O9/[%P]2 and NFeO was calculated as follows.
from Eq. (2), (5) and (4)
from Eq. (3) and (6)
With the increase of NFeO the value of logNCa4P2O9/[%P]2(obs) increased to a maximum value at about NFeO=0.3 but with the further increase of NFeO it began to decrease.
This relation is very interesting when they consider the practical phenomenon that during "after-blow" dephosphorization is not so much improved in spite of the rapid increase of (FeO) content in slag.