MY104987A - Start-up method for a direct reduction process without an external reformer. - Google Patents

Abstract

START-UP METHOD FOR AN IRON ORE DIRECT REDUCTION PROCESS, WHERE IN THE STEADY-STATE PROCESS THE REDUCING GASES ARE PRODUCED BY STEAM REFORMATION OF NATURAL GAS CATALYZED WITHIN THE REDUCING ZONE OF THE REDUCTION VESSEL BY THE REDUCED ORE PRESENT THEREIN. DURING ESTABLISHED STEADY-STATE OPERATION, A PROCESS GAS STREAM IS CIRCULATED IN A REDUCING GAS LOOP COMPRISING THE REDUCTION VESSEL, A GAS HEATER, AND UNITS TO REMOVE H2O AND CO FROM THE GAS CIRCULATING IN SAID LOOP. NATURAL GAS AND WATER FED DIRECTLY TO THE REDUCING GAS LOOP AS MAKE-UP REACTANTS FOR THE REFORMATION. AT PLANT START-UP THERE IS A COMPLETE ABSENCE OF METALLIC IRON TO CATALYZE THE REFORMATION REATION AT ANY TEMPERATURE, AND A COMPLETE ABSENCE OF H2 OR CO SO NO EFFECTIVE REDUCTION IS POSSIBLE TO PRODUCE THE NEEDED METALLIC IRON.IN A MULTI-STAGE START-UP, THE REDUCTION VESSEL IS FIRST CHARGED WITH IRON ORE AND PRESSURIZED BY INTRODUCING NATURAL GAS TO SAID LOOP. SIMULTANEOUSLY, THE TEMPERATURE IS RAISED TO THE RANGE OF 400? TO 600?C. THE NATURAL GAS CRACKS, PRODUCING A SMALL AMOUNT OF H2 AND SOME CARBON SOOT. SECOND, THE TEMPERATURE IS FURTHER INCREASED, AND INJECTION OF WATER IS BEGUN TO PREVENT FURTHER CARBON DEPOSITION, TO PROMOTE THE PRODUCTION OF H2, AND TO AVOID H2 CONSUMPTION; UNTIL 3% TO 8% BY VOLUME OF H2 ACCUMULATES. THIRD, AT ABOUT 750?C - 820?C, WATER INJECTION IS INTERRUPTED FAVORING THE ACCUMULATION OF HYDROGEN UNTIL A CONCENTRATION OF ABOUT 65% IS ACHIEVED WHILE THE TEMPERATURE OF THE PROCESS GAS STREAM REACHES ITS STEADY-STATE VALUE OF ABOUT 950?C. FOURTH, WATER IS AGAIN INJECTED TO PROMOTE THE REFORMING OF MAKE-UP NATURAL GAS WITHIN THE REDUCTION VESSEL AND ALL PROCESS FEEDS ARE ADJUSTED TO THEIR STEADY-STATE VALUES.