Direct smelting plant with waste heat recovery unit

Abstract

A direct smelting plant for producing molten metal from metalliferous feed material in a direct smelting process is disclosed. The plant includes a process controller for adjusting the volumetric flow rate of fuel gas supplied to a burner unit of at least one of the unit operations of the plant so as to at least meet selected requirements of the plant to operate the direct smelting process.

1 - 35 . (canceled) 
     
     
         36 . A direct smelting plant for producing molten metal from metalliferous feed material in a direct smelting process that includes:
 (a) a direct smelting vessel for producing molten metal, molten slag, and an off-gas by way of a process for direct smelting metalliferous feed material in the vessel;   (b) a first fuel gas supply apparatus for supplying off-gas from the direct smelting vessel for use as a fuel gas in burner units of two or more unit operations of the plant and/or external to the plant;   (c) a second fuel gas supply apparatus for supplying another fuel gas, such as natural gas, from another source to the burner unit of at least one of the unit operations, and   (d) a process controller for adjusting the volumetric flow rate of fuel gas supplied to a burner unit of at least one of the unit operations so as to at least meet selected requirements of the plant to operate the direct smelting process.   
     
     
         37 . The plant defined in  claim 36  wherein the unit operations include one or both of (i) a waste heat recovery unit for producing steam for use in the plant and/or for generating electricity for use in the plant or externally of the plant and (ii) a plurality of stoves for producing a hot blast of air or oxygen-enriched air for use in the direct smelting process. 
     
     
         38 . The plant defined in  claim 37  wherein the second fuel gas supply apparatus is adapted to supply fuel gas, such as natural gas, to one or both of the waste heat recovery unit and the stoves. 
     
     
         39 . The plant defined in  claim 37  or  claim 38  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas supplied to the burner unit of the waste heat recovery unit. 
     
     
         40 . The plant defined in  claim 39  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas, such as natural gas, supplied to the burner unit of the waste heat recovery unit via the second fuel gas supply apparatus. 
     
     
         41 . The plant defined in  claim 37  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas supplied to the burner unit of the stoves. 
     
     
         42 . The plant defined in  claim 41  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas, such as natural gas, supplied to the burner unit of the stoves via the second fuel gas supply apparatus. 
     
     
         43 . The plant defined in  claim 37  wherein the process controller is responsive to the flow rate and/or the calorific value of off-gas and to the steam requirements of the plant and/or to the hot air or oxygen-enriched air requirements of the process and determines the volumetric flow rate of fuel gas, such as natural gas, required for the burner units of the waste heat recovery unit and/or the stoves via the second fuel gas supply apparatus having regard to the flow rate and/or calorific value of off-gas and the requirements of the plant and/or the process at any point in time. 
     
     
         44 . The plant defined in  claim 43  wherein the process controller is responsive to the flame temperature of the burner unit of the waste heat recovery unit. 
     
     
         45 . The plant defined in  claim 44  wherein the process controller is responsive to the flame temperature of the burner unit of the waste heat recovery unit so as to maintain the flame temperature above a minimum temperature. 
     
     
         46 . The plant defined in  claim 43  wherein the process controller is responsive to the steam requirements of the plant by reference to required values of steam flow rate or steam pressure during different operating states of the process, as defined herein. 
     
     
         47 . The plant defined in  claim 43  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas supplied to the burner unit of the stoves via the second fuel gas supply apparatus so that the combined fuel gas supplied to the stove burner unit is a predetermined flow rate and/or calorific value. 
     
     
         48 . The plant defined in  claim 43  wherein the process controller is adapted to adjust the flow rate of fuel gas supplied to the burner unit of the stoves via the second fuel gas supply apparatus so that the stove burner unit operates at a constant calorific value at least at the commencement of a heating phase of the stoves. 
     
     
         49 . The plant defined in  claim 43  includes an apparatus for monitoring the calorific value of off-gas at different locations of the plant. 
     
     
         50 . The plant defined in  claim 49  wherein the off-gas calorific value monitoring apparatus is a mass spectrometer. 
     
     
         51 . The plant defined in  claim 49  or  claim 50  wherein the process controller is responsive to monitored values of calorific values. 
     
     
         52 . The plant defined in  claim 36  includes a unit operation in the form of a pretreatment unit for pretreating metalliferous feed material. 
     
     
         53 . The plant defined in  claim 52  includes an apparatus for supplying off-gas from the direct smelting vessel for use as a fluidising gas in the pretreatment unit. 
     
     
         54 . The plant defined in  claim 53  includes an apparatus for splitting off-gas discharged from the direct smelting vessel into (i) a first stream for the stoves and the waste heat recovery unit and (ii) a second stream for the pretreatment unit. 
     
     
         55 . The plant defined in  claim 54  includes an apparatus for forming a combined off-gas stream from (i) off-gas in the first stream and (ii) off-gas in the second stream that is discharged from the pretreatment unit. 
     
     
         56 . The plant defined in  claim 55  wherein the off-gas calorific value monitoring apparatus is adapted to monitor the calorific value of off-gas in the combined off-gas stream. 
     
     
         57 . The plant defined in  claim 56  wherein the process controller is responsive to the monitored calorific value of off-gas in the combined off-gas stream. 
     
     
         58 . The plant defined in  claim 57  wherein the process controller is adapted to adjust the volumetric flow rate of fuel gas supplied to the waste heat recovery unit via the second fuel gas supply apparatus in response to the monitored values of calorific value of the combined off-gas stream. 
     
     
         59 . The plant defined in  claim 56  wherein the off-gas calorific monitoring means is adapted to monitor the calorific value of off-gas in the first and the second streams. 
     
     
         60 . A molten bath-based direct smelting process for producing molten metal from a metalliferous feed material in a direct smelting plant that includes:
 (a) direct smelting metalliferous feed material in a direct smelting vessel containing a molten bath of metal and slag and producing molten metal, molten slag, and an off-gas, the process having different process states;   (b) supplying off-gas produced in the vessel during a smelting campaign as a fuel gas to burner units of two or more unit operations of the plant and/or external to the plant, and   (c) supplying another fuel gas, such as natural gas, from another source to the burner unit of at least one of the unit operations,   (d) adjusting the volumetric flow rate of fuel gas supplied to the burner units of the unit operations so as to at least meet requirements of the plant during the course of the process.   
     
     
         61 . The process defined in  claim 60  wherein the unit operations include one or both of (i) a heat recovery furnace of a waste heat recovery unit for producing steam for use in the plant and/or for generating electricity for use in the plant or externally of the plant and (ii) a plurality of stoves for producing a hot blast of air or oxygen-enriched air for use in direct smelting metalliferous feed material in the vessel. 
     
     
         62 . The process defined in  claim 61  includes adjusting the volumetric flow rate of the other fuel gas supplied to the burner units of the waste heat recovery unit and/or the stoves to maintain a predetermined flow rate and/or calorific value to the burner units. 
     
     
         63 . The process defined in  claim 62  includes monitoring the calorific value of off-gas at different locations of the plant. 
     
     
         64 . A direct smelting plant for producing molten metal from metalliferous feed material in a direct smelting process that includes:
 (a) a direct smelting vessel for producing molten metal, molten slag, and an off-gas by way of a process for direct smelting metalliferous feed material in the vessel;   (b) at least two off-gas processing units for receiving and combusting the off-gas;   (c) a first fuel gas supply apparatus for supplying off-gas from the direct smelting vessel for use in burner units of the off-gas processing units;   (d) a second fuel gas supply apparatus for supplying another fuel gas, such as natural gas, from another source to burner units of said at least two off-gas processing units;   (e) process controller for controlling:   i) volumetric flow of off-gas to one of the off-gas processing units to meet the requirenments of the unit with a balance of off-gas being supplied to a remaining off-gas processing unit or units;   ii) volumetric flow of the other fuel gas to the off-gas processing units.   
     
     
         65 . The plant defined in  claim 64  wherein the off-gas processing units comprise stoves for supplying hot blast to the direct smelting vessel and a waste heat recovery unit for generation of steam. 
     
     
         66 . The plant defined in  claim 65  wherein the process controller is adapted to control supply of off-gas and the other fuel gas to the stoves such that the combined supply of off-gas and the other fuel gas to the stoves has a substantially constant calorific value. 
     
     
         67 . The plant defined in  claim 65  or  claim 66  wherein the process controller is adapted to control supply of the other fuel gas to the waste heat recovery unit in response to variations in the volumetric flow of the off-gas to effect combustion of the off-gas in the waste heat recovery unit. 
     
     
         68 . The plant defined in  claim 65  comprises one or more than one off-gas supply valve for controlling the volumetric flow rate of off-gas to the stoves and for diverting supply of off-gas to the waste heat recovery unit, and off-gas calorific value sensing apparatus for sensing calorific value of off-gas, and wherein the process controller is adapted to monitor off-gas calorific value and to operate the off-gas supply valve or valves to divert off-gas to the waste heat recovery unit in response to the calorific value of the off-gas falling below a pre-determined threshold value. 
     
     
         69 . The plant defined in  claim 68  wherein the pre-determined threshold value is a value at which the off-gas no longer makes a positive contribution to the calorific value of the combined fuel gas steam of the off-gas and the other fuel gas. 
     
     
         70 . The plant defined in  claim 68  wherein the pre-determined threshold value is 1.8 MJ/Nm3 (mega-joules per normal cubic meter).