REFINING METHOD

PROBLEM TO BE SOLVED: To be able to satisfactorily perform dust collection while efficiently performing refining treatment.SOLUTION: At first, a relation between an oxygen supplying rate at a refining treatment time and a dust amount inflowing to a building 2 is obtained; at second, an oxygen supplying rate X1 in which dust generating in refining treatment does not inflow to the building 2 is obtained; at third, when refining treatment is performed by an oxygen supplying rate X2 larger than the oxygen supplying rate X1, a relation of a refining processing time of the refining treatment and a dust concentration in the building 2 is obtained; at fourth, a decreasing time in which a dust concentration decreases to a dust concentration corresponding to a first management division defined by operation environmental control is obtained based on relation between a refining processing time when refining treatment is performed by the oxygen supplying rate X2, then refining treatment is performed by an oxygen supplying rate of at most the oxygen supplying rate X1, and a dust concentration in the building 2. In addition, at fifth, when refining treatment is performed, refining treatment is performed by the oxygen supplying rate X2 larger than the oxygen supplying rate X1, and an oxygen supplying rate is lowered to the maximum of the oxygen supplying rate X1 before at least the decreasing time from a refining finishing time.