4　Hot Metal Pretreatment

4.1　Process Design

4.1.1　For hot metal desulfurization，the injection or mechanical stirring process should be adopted.After desulfurization，the sulfur content of hot metal shall not be higher than 0.015% and also that of hot metal for production of ultra-low-sulfur steel shall not be higher than 0.005%.

4.1.2　The hot metal ladle and torpedo ladle for blast furnace and the hot metal ladle for converter may be used as reaction vessels for hot metal desulfurization.However，the hot metal ladle for converter should be selected.The clearance height above the bath level of hot metal ladle shall not be less than 500mm for the injection process and shall not be less than 700mm for mechanical stirring process.

4.1.3　Hot metal dephosphorization shall be in accordance with the following provisions:

1　The injection process of hot metal ladle，the stirring process of hot metal ladle，the injection process of torpedo ladle or the preliminary dephosphorization process of converter shall be adopted for hot metal with phosphor content of＞0.12% or for production of ultra-low-phosphor steel with phosphor content of≤0.005%.

2　For the dephosphorization with injection process of hot metal ladle，a special hot metal ladle shall be provided and the clearance height above the bath level of hot metal ladle shall not be less than 1500mm.After the treatment，the phosphor content of hot metal shall not be higher than 0.030%.

3　For the dephosphorization with stirring process of hot metal ladle，a special hot metal ladle shall be provided and the clearance height above the bath level of hot metal ladle shall not be less than 700mm.After the treatment，the phosphor content of hot metal shall not be higher than 0.040%.

4　For the dephosphorization with injection process of torpedo ladle，the clearance height above the bath level of hot metal ladle shall not be less than 1000mm.After the treatment，the phosphor content of hot metal shall not be higher than 0.030%.

5　After the preliminary dephosphorization in converter，the phosphor content of hot metal shall not be higher than 0.030%.For ultra-low-phosphor steel grades，after the pretreatment，the phosphor content of hot metal shall not be higher than 0.005%.

4.1.4　When preliminary dephosphorization in converter is adopted，the ratio of scrap added to the converter shall not be higher than 10% and light scrap should be adopted.The converter adopts bottom nitrogen blowing for stirring.The bottom blowing intensity shall not be lower than 0.2Nm3/t·min.Nitrogen pressure shall not be lower than 1.6MPa.Each bottom blowing branch shall be controlled separately.The converter for dephosphorization should be provided with special oxygen lance and the oxygen supply intensity shall not be higher than 2.5Nm3/t·min.

4.1.5　When dephosphorization in hot metal ladle and torpedo ladle is adopted，hot metal shall be subject to desiliconization prior to dephosphorization and the silicon content of hot metal shall not be more than 0.20%.

4.1.6　For the converter steelmaking shop producing ultra-low-sulfur and ultra-low-phosphor steel grades，the hot metal pretreatment process（including desiliconization，dephosphorization and desulfurization）should be adopted.

4.1.7　For the pretreatment with injection process，nitrogen should be used as the carrier gas for material flow.The purity of nitrogen shall not be lower than 99.9% and its pressure shall not be lower than 1.0MPa.The flow rate of nitrogen shall be defined according to the gas-powder ratio and powder-feeding intensity for transport.

4.1.8　In the design of a hot metal pretreatment station，a complete pretreatment unit including mechanical equipment，hydraulic system，valve station，electrical equipment and instrumentation shall be equipped.In addition，the auxiliary facilities shall be provided，such as the facilities for powder storage and transport，media supply，slag treatment，fume collection and cleaning，injecting lance（or stirring device）fabrication，storage and maintenance and related safety protection.

4.1.9　The hot metal pretreatment station shall be equipped with slag removing device.