Abstract: The resist stripping waste liquid regenerating apparatus of the invention regenerates a resist stripping waste liquid to obtain a resist stripping regenerated liquid. The apparatus is provided with a membrane separating apparatus which employs a membrane with a molecular weight cutoff of 100-1500 to separate a resist stripping waste liquid into a concentrated liquid and a permeating liquid, an adjusting tank which stores the permeating liquid and adjusts the concentration of an alkanolamine and organic solvent, means for supplying the alkanolamine to the adjusting tank, and means for supplying the organic solvent to the adjusting tank. This construction adequately reduces the resist concentration of the permeating liquid since the resist in the resist stripping waste liquid cannot permeate the membrane. It is thereby possible to lessen the need for dilution of the resist concentration and thus satisfactorily reduce the amount of alkanolamine and organic solvent supplied to the adjusting tank.

Abstract: In a straight barrel type vacuum refining apparatus, use is made of a combination of: a decarburization method wherein the flow rate of oxygen fed into a vacuum tank and the flow rate of an inert gas fed into the vacuum tank are regulated and, at the same time, the flow rate of oxygen gas blown is reduced at a rate of 0.5 to 12.5 Nm3/h/t/min in a low carbon concentration region having a carbon concentration of not more than the critical carbon concentration; and a vacuum refining apparatus provided with dust accumulation preventing means.

Abstract: A method for vacuum decarburization refining of a molten steel includes providing a vacuum tank having a one-legged, straight barrel snorkel as a lower portion of the vacuum tank. The a degree of vacuum in the vacuum tank is regulated at a high carbon concentration region to a value in a range of −35 to −20 in terms of G defined by the following equation (1): G=5.96×10−3×T×ln(P/Pco)  (1), wherein Pco=760{10(−13800/T+8.75)}×(% C)/(% Cr)  (2), and wherein P<760, T represents molten steel temperature, K, and P represents the degree of vacuum in the vacuum tank, Torr.