Production of high titania slag from ilmenite

Abstract

A process is provided for the production of titania rich slag from ilmenite. The ilmenite is fed together with carbonaceous reductant, and in the absence of fluxes, to the molten bath of a DC arc furnace. The molten bath of the furnace forms the anode and one or more electrodes in the roof of the furnace forms the cathode. A frozen lining is established and maintained between the refractory lining of the furnace and the molten bath and the process includes means to control the thickness of the frozen lining as well as the whole smelting process.

What we claim as new and desire to secure by Letters Patent is:  
     
         1 . A continuous process for the reduction of ilmenite in a d.c. transferred arc furnace having a refractory lining and operating with a molten bath, one or more electrodes situated in the roof of the furnace acting as cathode, the molten bath acting as anode, and a frozen lining at least partly between the refractory lining and the molten bath; the process comprising fining the ilmenite simultaneously with carbonaceous reductant, in the absence of fluxes, to the molten bath, withdrawing titania rich stag and pig iron from the furnace, and means to control the operation of the furnace, the control means including means to take temperature measurements of a wall adjacent the frozen lining, means to estimate the thickness of the frozen lining as a unction of the temperature in the wall and means to control the rate of heat production in the furnace to urge a thickness of the frozen lining towards a predetermined reference value.  
     
     
         2 . A process as claimed in    claim 1    in which the control means includes means to measure furnace gas plant variables, means to measure furnace cooling system variables, means to measure furnace in-feed variables, means to measure furnace electrical system variables, and means to measure furnace charge chemical composition variables.  
     
     
         3 . A process as claimed in    claim 2    in which the frozen lining thickness and hot face temperatures are estimated as a function of the wall temperature measurements and gas plant measurements.  
     
     
         4 . A process as claimed in    claim 1    or    claim 3    in which the means to control the rate of heat production in the furnace includes control over the rate of addition of carbonaceous reductant to the furnace, the rate of heat reduction increasing with an increase in the rate of addition of carbonaceous reductant to the furnace to thereby urge the thickness of the frozen lining to decrease; and the rate of heat production decreasing with a decrease in the rate of addition of carbonaceous reductant to the furnace to thereby urge the thickness of the frozen lining to increase.  
     
     
         5 . A process as claimed in    claim 2    or    claim 3    in which the control means includes means to estimate heat losses in the furnace as a function of the estimated frozen lining thickness and hot face temperatures, the gas plant measurements, and the cooling system measurements.  
     
     
         6 . A process as claimed in    claim 1    or    claim 2    in which the control means includes means to measure sensible heat changes of spray cooled roof panels, spray cooled off gas ducts, film cooled shell panels air cooled hearth panels, hot gasses and dust, and charge removed from the furnace.  
     
     
         7 . A process as claimed in    claim 3    and    claim 6    in which the control means includes means to estimate heat losses in the furnace as a function of the estimated frozen lining thickness and hot face temperatures, the gas plant measurements, the cooling system measurements, and the measured sensible heat changes.  
     
     
         8 . A process as claimed in    claim 2    or    3    in which the control means includes means to estimate a material balance of the furnace as a function of the estimated frozen lining thickness and hot face temperatures, the gas plant measurements, the ineed measurements, the electrical system measurements, and the furnace charge chemical composition measurements.  
     
     
         9 . A process as claimed in    claim 8    in which inventory control is performed an the furnace using the material balance.  
     
     
         10 . A process as claimed in    claim 8    and    claim 7    in which the control means includes means to estimate a future furnace charge chemical composition as a function of the estimated frozen lining thickness and hot face temperatures, the estimated heat losses, and the estimated material balance.  
     
     
         11 . A process as claimed in    claim 10    in which the control means includes means to perform chemistry control of the furnace using the estimated material balance, the estimated future furnace charge chemical composition, the in-feed measurements, the electrical system measurements, and the furnace charge chemical composition measurements.  
     
     
         12 . A process as claimed in    claim 2    and    claim 5    or    claim 7    in which the control means includes means to perform start-up control of the furnace using the in-feed measurements, the electrical system measurements, the furnace charge chemical composition measurements, and the estimated heat losses.  
     
     
         13 . A process as claimed in    claim 1    or    claim 2    in which a process of error detection and validation is conducted on the measurements, the process of error detection and validation to including analysis of the range of the measurements and the rate of change of the measurements to validate the measurements, and invalid measurements being replaced by pre-ordained measurements according to a set of logical rules.  
     
     
         14 . A process as claimed in    claim 1    or    claim 2    in which the furnace is circular, one or more of the electrodes is hollow and serves as a feed port for at least part of the ilmenite and the carbonaceous reductant, and the ilmenite and the carbonaceous reductant are fed to a central region of the furnace.  
     
     
         15 . A method for controlling a frozen lining between a furnace lining and a molten bath in a d.c. transferred arc furnace used for the continuous reduction of ilmenite, the method comprising the steps of 
   1 . establishing the frozen lining,      2 . measuring at least the temperature in a wall of the furnace adjacent the frozen lining,      3 . estimating the thickness of the frozen lining as a function of the temperature in the wall, and      4 . controlling the rate of heat production in the furnace to urge a thickness of the frozen lining towards a predetermined reference value.    
     
     
         16 . A method as claimed in    claim 15    in which step  2  of the method includes measuring furnace gas plant variables, measuring furnace cooling system variables, measuring furnace in-feed variables, measuring furnace electrical system variables, and measuring furnace charge chemical composition variables.  
     
     
         17 . A method as claimed in  15  or  16  in which a process of error detection and validation is performed on the measurements, the process of error detection and validation including the steps of 
 a) analysing the range of the measurements and the rate of change of the measurements,  
 b) validating the measurements, and  
 c) replacing invalid measurements by pre-recorded measurements according to a set of logical rules.  
 
     
     
         18 . A method as claimed in    claim 15    in which step  3  of the method includes an estimation of the thickness of the frozen lining as a function of the temperature in the wall and the furnace gas plant measurements.