Blowing control method for maintaining mushroom head of bottom-blowing nozzle converter

A blowing control method for maintaining a mushroom head of a bottom-blowing converter, comprising the following steps:

• (1) blowing nitrogen as a cooling protection gas by a narrow annuli channel of a bottom-blowing nozzle, and measuring a flow rate and a gas pressure of nitrogen in the narrow annuli channel-blowing by a nozzle, and calculating a state coefficient of the mushroom head;
• (2) starting a smelting process in the bottom-blowing converter, with oxygen as a carrier gas blow blown with a lime powder by an inner pipe channel of the bottom-blowing nozzle;
• then after blowing the lime powder with the oxygen, blowing a carbon dioxide-oxygen mixed gas by the inner pipe channel of the bottom-blowing nozzle to maintain the mushroom head of the bottom-blowing converter;
• according to the calculated state coefficient of the mushroom head and a molten steel overheating degree ΔT adjusting a blowing intensity of carbon dioxide in the carbon dioxide-oxygen mixed gas;
• the molten steel overheating degree ΔT being calculated according to Formula 1:
• ΔT=T−Tu (Formula 1)
• wherein, T is a temperature of the molten steel measured or calculated during the smelting process;
• Tu is calculated according to formula 2:
• Tu=1536.6-88×ω[C]−8×ω[Si]−5×ω[Mn]−30×ω[P] (Formula 2)
• wherein, ω[C] is a mass fraction of carbon in the molten steel, ω [Si] is a mass fraction of silicon in the molten steel, ω[Mn] is a mass fraction of manganese in the molten steel, and ω [P] is a mass fraction of phosphorus in the molten steel wherein, in step (1), the flow rate is Q, the gas pressure is P, a ratio of Q and P is defined as actual flow pressure ratio ε.sub.A, a ratio of the actual flow pressure ratio ε.sub.A to a reference flow pressure ratio ε.sub.R is defined as the state coefficient of the mushroom head n, wherein the reference flow pressure ratio
• ε.sub.R=α×ε.sub.u,
• ε.sub.u is a flow pressure ratio of the end of the narrow annuli channel blowing by the nozzle freely;
• a ranges 0.6 to 0.7.