Pressure control in direct smelting process

Abstract

A process for direct smelting metalliferous feed material in a direct smelting vessel and producing process outputs of molten metal, molten slag, and an off-gas from the vessel is disclosed. The process includes controlling pressure in the direct smelting vessel by controlling off-gas pressure in an off-gas stream supplied to a fluidised bed pretreatment apparatus while the process is operating in the “hold” and “idle” process states.

1 - 22 . (canceled) 
     
     
         23 . A process for direct smelting metalliferous feed material in a direct smelting vessel that forms part of a direct smelting plant and producing process outputs of molten metal, molten slag, and an off-gas from the vessel in a “hot metal production” state of the process, which process includes:
 (a) selectively operating the process in a number of process states as required given process conditions, the process states including the “hot metal production” state wherein metalliferous feed material is smelted in the vessel to produce molten metal, and “hold” and “idle” states wherein a bath of molten material is maintained in the direct smelting vessel in a molten state without additional molten metal being produced;   (b) while the process is operating in the “hot metal production” state, splitting the off-gas released from the direct smelting vessel into at least two off-gas streams and supplying one off-gas stream to a fluidised bed pretreatment apparatus for pretreating metalliferous feed material that is subsequently supplied to the direct smelting vessel, and supplying another off-gas stream to the plant for use as a fuel gas;   (c) while the process is operating in the “hold” and “idle” process states, supplying an off-gas stream released from the direct smelting vessel to the fluidised bed pretreatment apparatus for at least fluidising metalliferous feed material that is subsequently supplied to the direct smelting vessel; and   (d) while the process is operating in the “hold” and “idle” process states, controlling pressure in the direct smelting vessel by controlling off-gas pressure in the off-gas stream supplied to the fluidised bed pretreatment apparatus.   
     
     
         24 . The process defined in  claim 23  includes controlling the pressure in the direct smelting vessel whilst operating in the “hot metal production” state by controlling the flow of off-gas in the other off-gas stream supplied to the plant for use as a fuel gas. 
     
     
         25 . The process defined in  claim 23  includes supplying at least one stream of off-gas as a fuel gas to at least one of (i) a waste heat recovery unit for generating steam for use in the process and (ii) stoves for producing a hot blast of air for use in the process. 
     
     
         26 . The process defined in  claim 23  wherein the “hold” state comprises supplying a hot blast of air or oxygen-enriched air, solid carbonaceous material and fluxes to the direct smelting vessel without supply of metalliferous material. 
     
     
         27 . The process defined in  claim 23  wherein the “idle” state comprises supplying a hot blast of air or oxygen-enriched air to the direct smelting vessel without supply of metalliferous material and solid carbonaceous material. 
     
     
         28 . The process defined in  claim 23  includes cooling and removing particulate material and soluble gaseous species and metal vapours from the off-gas stream supplied to the fluidised bed pretreatment apparatus in a water scrubber downstream of the pretreatment apparatus. 
     
     
         29 . The process defined in  claim 28  wherein step (d) includes controlling pressure in the direct smelting vessel while the process is operating in the “hold” and “idle” process states by controlling the flow of off-gas flowing through the scrubber by opening or closing an off-gas control valve in the scrubber. 
     
     
         30 . The process defined in  claim 23  wherein step (c) includes supplying at least substantially all of the off-gas stream released from the direct smelting vessel as the off-gas stream to the fluidised bed pretreatment apparatus and thereby minimising any splitting of off-gas while the process is operating in the “hold” and “idle” process states. 
     
     
         31 . The process defined in  claim 25  includes supplying another fuel gas, such as natural gas, to the stoves for generating the hot blast of air or oxygen-enriched air for the process while the process is operating in the “hold” and “idle” process states. 
     
     
         32 . The process defined in  claim 25  includes cooling and removing particulate material and soluble gaseous species and metal vapours from the other off-gas stream in a water scrubber upstream of the stoves and the waste heat recovery apparatus when the process is operating in the “hot metal production” state. 
     
     
         33 . The process defined in  claim 31  includes at least substantially closing an off-gas control valve in the stream scrubber at the commencement of the “hold” and “idle” process states. 
     
     
         34 . The process defined in  claim 25  includes supplying off-gas from the pretreatment apparatus to the waste heat recovery apparatus for use as the fuel gas for generating steam for the process. 
     
     
         35 . The process defined in  claim 23  includes recycling a portion of the off-gas stream supplied to the fluidised bed pretreatment apparatus within the pretreatment apparatus during the “hold” and “idle” process states. 
     
     
         36 . The process defined in  claim 23  includes supplying the hot blast of air or oxygen-enriched air to the direct smelting vessel at a first volumetric flow rate while the process is operating in the “hot metal production” state and at a second lower volumetric flow rate while the process is operating in the “hold” and the “idle” process states. 
     
     
         37 . The process defined in  claim 23  includes controlling the pressure in the direct smelting vessel to a first pressure set point while the process is operating in the “hot metal production” state and to a lower pressure set point while the process is operating in the “hold” and “idle” process states. 
     
     
         38 . The process defined in  claim 23  includes monitoring the molten metal temperature in the direct smelting vessel during the “idle” process state and supplying a fuel gas to the vessel and combusting the fuel gas in the vessel as required to maintain the molten metal temperature in the vessel. 
     
     
         39 . The process defined in  claim 23  includes reducing the level of molten slag in the direct smelting vessel while the process is operating in the “idle” state and the process is combusting the fuel gas in the vessel. 
     
     
         40 . A process for direct smelting metalliferous feed material in a direct smelting vessel and producing process outputs of molten metal, molten slag, and an off-gas from the vessel that includes controlling pressure in the direct smelting vessel by controlling off-gas pressure in an off-gas stream supplied to a fluidised bed pretreatment apparatus while the process is operating in the “hold” and “idle” process states as described herein. 
     
     
         41 . A process for operating a direct smelting plant with a direct smelting vessel that operates under pressure and a fluidised bed pre-treatment unit for pre-treating metalliferous material subsequently fed to the direct smelting vessel, the plant producing outputs of molten metal, molten slag, and off-gas wherein the process includes:
 (a) selectively operating the plant in a number of process states as required given process conditions, the process states including a “hot metal production” state wherein metalliferous feed material is smelted in the vessel to produce molten metal, and “hold” and “idle” states wherein a bath of molten material is maintained in the direct smelting vessel in a molten state without additional molten metal being produced;   (b) while the plant is operating in the “hot metal production” state, splitting the off-gas released from the direct smelting vessel into at least two off-gas streams and supplying one off-gas stream in a fluidised bed pretreatment apparatus for pretreating metalliferous feed material that is subsequently supplied to the direct smelting vessel, and supplying another off-gas stream to the plant for use as a fuel gas;   (c) while the plant is operating in the “hold” and “idle” process states, supplying an off-gas stream released from the direct smelting vessel to the fluidised bed pretreatment apparatus for at least fluidising metalliferous feed material that is subsequently supplied to the direct smelting vessel; and   (d) while the process is operating in the “hold” and “idle” process states, controlling pressure in the direct smelting vessel by controlling off-gas pressure in the off-gas stream supplied to the fluidised bed pretreatment apparatus.   
     
     
         42 . A direct smelting plant for direct smelting a metalliferous feed material and producing molten metal that includes:
 (a) a fluidised bed pretreatment apparatus for pretreating metalliferous feed material;   (b) a direct smelting vessel for producing molten metal by way of a process for direct smelting preheated metalliferous feed material in the vessel, the process including a number of process states including “start-up”, “hot metal production”, “hold”, “idle”, and “off-wind”, as described herein;   (c) an off-gas duct for taking away off-gas generated in the direct smelting vessel and supplying off-gas in an off-gas stream to the pretreatment apparatus; and   (d) a process controller for controlling pressure in the direct smelting vessel by controlling off-gas pressure in the off-gas stream supplied to the pretreatment apparatus while the process is operating in the “hold” and “idle” process states, as described herein.   
     
     
         43 . A direct smelting plant for direct smelting a metalliferous feed material and producing molten metal that includes:
 (a) a fluidised bed pretreatment apparatus for pretreating metalliferous feed material;   (b) a direct smelting vessel for producing molten metal by way of a process for direct smelting preheated metalliferous feed material in the vessel, the process including a number of process states including “start-up”, “hot metal production”, “hold”, “idle”, and “off-wind”, as described herein;   (c) stoves for generating a hot blast of air or oxygen-enriched air for the process;   (d) a waste heat recovery unit for generating steam for the plant;   (e) an off-gas duct for taking away off-gas generated in the direct smelting vessel and splitting the off-gas into two off-gas streams, one of which is supplied by way of a first duct section to the pretreatment apparatus and the other of which is supplied to a second duct section; and   (f) a process controller for controlling pressure in the direct smelting vessel by controlling off-gas pressure in the off-gas stream supplied to the pretreatment apparatus while the process is operating in the “hold” and “idle” process states.   
     
     
         44 . The plant defined in  claim 43  wherein the process controller is also capable of controlling pressure in the direct smelting vessel by controlling off-gas pressure in the off-gas stream supplied to the second duct section while the process is operating in the “hot metal production” state.