Method for preliminary treatment of molten iron

Patent metadata

Field	Value
Publication number	US-9920390-B2
Application number	US-201314371359-A
Country	US
Kind code	B2
Filing date	Jan 17, 2013
Priority date	Jan 19, 2012
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

There is proposed a method for preliminary treatment of molten iron wherein heat source for dissolving scrap is ensured sufficiently to improve iron yield while decreasing phosphorus concentration efficiently by suppressing the amount of flux solvent used in the process of desiliconization, dephosphorization and decarburization. In the method for preliminary treatment of molten iron by conducting desiliconization and dephosphorization of molten iron with a converter type container, molten iron is first charged into the converter type container to conduct desiliconization and then intermediate slag removal is conducted, and subsequently a lime-based flux solvent is added to the container while blowing oxygen to conduct dephosphorization of the molten iron, and thereafter newly untreated molten iron is charged into the container to conduct desiliconization, and subsequently the above treatments are repeatedly conducted with the same container.

First claim

The invention claimed is:

1. A method for preliminary treatment of molten iron by conducting desiliconization and dephosphorization of molten iron with a converter container, the method comprising:
charging untreated molten iron tapped from a blast furnace into the converter container to conduct a first desiliconization;
then retaining the molten iron and a part of a slag after the first desiliconization in the converter container to conduct intermediate slag removal;
subsequently adding a lime-based flux solvent to the molten iron and slag retained in the converter container after the first desiliconization while blowing oxygen to conduct a first dephosphorization of the molten iron, not less than 30 mass % of a slag having a slag basicity of not less than 1.2 after the first dephosphorization is retained in the converter container,
then charging more untreated molten iron into the converter container containing the slag after the first dephosphorization to conduct a second desiliconization, and adjusting a basicity of the slag during the second desiliconization such that the basicity is in the range of 0.8 to 1.5, silicon concentration of molten iron at the end of the second desiliconization is not more than 0.2 mass %, a basicity of the slag after the second desiliconization is in the range of 0.5 to 1.5 and a temperature of the molten iron is in the range of 1240° C. to 1400° C.;
thereafter conducting a second intermediate slag removal of discharging not less than 40 mass % of the slag after the second desiliconization from the converter container; and
subsequently conducting a second dephosphorization in the converter container, wherein
the basicity of the slag during the second desiliconization is obtained by dividing a numerical value obtained by adding an amount of CaO contained in the slag after the first dephosphorization with a CaO amount generated, with a numerical value obtained by adding a SiO 2 amount in a residual dephosphorized slag with a SiO 2 amount generated,
the CaO amount generated is calculated by multiplying (i) a CaO content in an auxiliary material, (ii) a retention time of the auxiliary material in a furnace, and (iii) a dissolution rate of the auxiliary material in the furnace, and
the SiO 2 amount generated is calculated by multiplying (i) an oxygen feeding rate in blowing, (ii) the molecular weight of SiO 2 divided by the atomic weight of Si and further divided by a theoretical Si amount burnt by oxygen of 1 Nm 3 , (iii) an oxygen efficiency for desiliconization in blowing, and (iv) a total amount of molten iron and scrap.

2. The method for preliminary treatment of molten iron according to claim 1 , wherein the basicity of the slag after the first dephosphorization is not more than 3.0.

3. The method for preliminary treatment of molten iron according to claim 1 , wherein the slag after the first dephosphorization is retained in the converter container at not less than 60 mass % of an amount generated in the dephosphorization.

4. The method for preliminary treatment of molten iron according to claim 1 , wherein the slag after the second desiliconization has a slag basicity in the range of 0.8 to 1.5 and T. Fe in the range of 5 mass % to 25 mass %.

5. The method for preliminary treatment of molten iron according to claim 1 , wherein cold iron source is charged during the second desiliconization.

6. The method for preliminary treatment of molten iron according to claim 1 , wherein the second desiliconization is conducted by charging cold iron source into the converter container in addition to the molten iron tapped from the blast furnace and blowing oxygen to render a temperature of the molten iron at the end of the desiliconization to be in the range of 1260° C. to 1350° C.

7. The method for preliminary treatment of molten iron according to claim 1 , wherein an amount of cold iron source satisfying the following equation is charged in the second desiliconization per a total amount of molten iron charged in the converter container and the cold iron source:
Y =(3+34.5[%Si]+0.21 T i )·(1000- X s )/1000

where Y is 230˜270, [%Si] is a silicon concentration by mass % in the molten iron charged, T i is a temperature ° C. of the molten iron charged ,and X s is a basic unit kg/t of cold iron source.

8. The method for preliminary treatment of molten iron according to claim 1 , wherein silicon concentration of molten iron at the end of the second desiliconization is not more than 0.1 mass %.

9. The method for preliminary treatment of molten iron according to claim 1 , wherein the second desiliconization is conducted by charging or adding 100˜250 kg/t of cold iron source per total weight of molten iron and cold iron source and 2˜10 kg/t of iron silicide, metallic silicon, silicon carbide or silicon nitride as an oxidizable silicon into the converter container.

10. The method for preliminary treatment of molten iron according to claim 1 , wherein the second dephosphorization is conducted by retaining 4˜20kg/t of a slag after the second desiliconization per total weight of cold iron source and molten iron in the converter container after the intermediate slag removal, adding a lime-based flux solvent and blowing oxygen so as to render a basicity of the slag after the second dephosphorization to be in the range of 1.2 to 3.0 and a temperature of the molten iron after the end of the second dephosphorization to be in the range of 1280° C. to 1360° C.

11. The method for preliminary treatment of molten iron according to claim 1 , wherein the dephosphorizations are conducted by jetting a refining agent containing at least one ingredient of powdery lime, calcium carbonate and iron oxide toward molten iron through a top blowing lance.

Assignees

• Jfe Steel Corp

Inventors

• Iwaki Yozo
• Ikeno Shizuhiko
• Ejima Kochiro
• Ishii Takeshi
• Nishikori Masanori
• Fukushima Hironori
• Kikuchi Naoki
• Suzuki Norihiko
• Tanaka Kotaro
• Yamamoto Kazuhito
• Kawabata Ryo
• Sasaki Naotaka
• Ogasawara Yasushi
• Ogasawara Futoshi
• Uchida Yuichi
• Senoo Masaomi
• Tano Manabu

Classifications

• Y02P10/216

  Cross-Sectional Technologies · mapped topic

• C21C1/02 Primary

  Dephosphorising or desulfurising · CPC title

• C21C5/36

  Processes yielding slags of special composition · CPC title

• C21C7/076

  Use of slags or fluxes as treating agents (C21C7/06, C21C7/064, C21C7/068 take precedence) · CPC title

• C21C1/04 Primary

  Removing impurities other than carbon, phosphorus or sulfur · CPC title