METHOD OF EXCLUSION OF METAL CORROSION (METAL DUSTING) IN DIRECT REDUCTION OF MATERIAL CONTAINING IRON OXIDES (VERSIONS) Russian patent published in 1999 - IPC

FIELD: metal corrosion control. SUBSTANCE: synthesis gas is mixed with blast-furnace gas produced in direct reduction of materials containing iron oxides and used as reducing gas for reduction of materials containing iron oxides. To exclude or reduce metal corrosion (metal dusting) caused by high content of CO in reducing gas, use is made of simple methods and equipment to maintain CO/CO₂ ratio in reducing gas within the preset range of 1:3. In the first version, synthesis gas is used in the form of natural gas and CO/CO₂ ratio in reducing gas is regulated by means of regulation of operation of reformer in which steam reforming of natural gas is effected by varying the steam/natural gas ratio. The second version provides for regulation of CO/CO₂ ratio by addition of one part of volume of converted gas produced in reformer from steam and natural gas and then supplied to CO-converter to increase content of H₂, to blast-furnace gas directly, that is by bypassing CO-conversion in the amount which may be varied. The third version includes cleaning of converter gas and optionally blast-furnace gas from CO₂ before their use as reducing gas, and addition directly to reducing gas of at least a part of converted gas without cleaning from CO₂. In the fourth version, converted gas and optionally blast-furnace gas may be subjected to cleaning from CO₂ and CO/CO₂ ratio is regulated by addition directly to reducing gas of at least a part of volume of blast-furnace gas without cleaning from CO₂. In the fifth version, converted gas and optionally blast-furnace gas are subjected to cleaning from CO₂ before its use as reducing gas. In this case, content of CO₂ in cleaned gas is regulated by varying the efficiency of CO₂ separation. For the further reduction of metal corrosion (metal dusting), it is good practice to supply to reducing gas at least a part of sulfur present in material containing iron oxides in the form of H₂S formed in heating or in direct reduction corresponding together with blast-furnace gas. In so doing, it is useful to maintain the content of H₂S in reducing gas with the help of blast furnace gas equalling from 20•10^-6 to 40•10^-6, preferably 25•10^-6. EFFECT: higher efficiency. 16 cl, 1 dwg, 9 tbl