Furnace and a method of controlling a furnace

Abstract

The invention provides a furnace having a frozen lining inbetween a furnace lining and a furnace charge, the furnace having means to control the operation of the furnace, including means to measure the temperature in a wall of the furnace adjacent the frozen lining, and to estimate the thickness of the frozen lining as a function 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 value. Variables including side wall thermocouple measurements, gas plant instrument measurements, cooling system measurements and electrical, in-feed and chemical composition recordings are monitored, analysed and manipulated. There is also provided means to estimate a future furnace charge composition, perform chemistry control, estimate a material balance of the furnace, and perform inventory control over the furnace.

We claim:  
     
         1 . A furnace including: 
 a furnace lining and a frozen lining which is positioned at least partly between the furnace lining and a charge within the furnace; and    control means to control the operation of the furnace, the control means including means to measure the temperature in a wall of the furnace adjacent the frozen lining, means to estimate the thickness of the frozen lining as a function 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 furnace according to  claim 1 , wherein 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, so that the rate of heat production is increased 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, or the rate of heat production is decreased 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.  
     
     
         3 . A furnace according to either one of  claim 1 , wherein the control means further comprises one or more of the following measurement means: 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.  
     
     
         4 . A furnace according to  claim 1 , which further comprises a process for conducting error detection and validation of the measurements, the process comprising analysis of the range of the measurements and the rate of change of the measurements to validate the measurements, and a process for replacing invalid measurements with pre-recorded measurements according to a set of logical rules.  
     
     
         5 . A furnace according to  claim 3 , which further comprises means to estimate the frozen lining thickness and hot face temperatures as a function of the wall temperature measurements and gas plant measurements.  
     
     
         6 . A furnace according to  claim 3 , which further comprises means to estimate heat losses in the furnace as a function of estimated frozen lining thickness and hot face temperatures, the gas plant measurements, and the cooling system measurements.  
     
     
         7 . A furnace according to  claim 1 , which further comprises 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/or charge removed from the furnace.  
     
     
         8 . A furnace according to  claim 7 , which further comprises 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 measured sensible heat changes.  
     
     
         9 . A furnace according to  claim 3 , which further comprises 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 in-feed measurements, the electrical system measurements, and the furnace charge chemical composition measurements.  
     
     
         10 . A furnace according to  claim 9 , which further comprises means to perform inventory control over the furnace using the material balance of the furnace.  
     
     
         11 . A furnace according to  claim 9 , which further comprises 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.  
     
     
         12 . A furnace according to  claim 11 , which further comprises 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.  
     
     
         13 . A furnace according to  claim 6 , which further includes means for controlling start-up of the furnace to be performed using the in-feed measurements, the electrical system measurements, the furnace charge chemical composition measurements, and the estimated heat losses.  
     
     
         14 . A method for controlling a frozen interface in a furnace between a furnace lining and a charge in the furnace, the method comprising the steps of: 
 (i) establishing the frozen lining;    (ii) measuring at least the temperature in a wall of the furnace adjacent the frozen lining;    (iii) estimating the thickness of the frozen lining as a function of the temperature in the wall; and    (iv) controlling the rate of heat production in the furnace to urge a thickness of the frozen lining towards a predetermined reference value.    
     
     
         15 . A method according to  claim 14 , wherein the step of measuring at least temperature in the wall of the furnace comprises measuring one or more of gas plant variables, furnace cooling system variables, furnace in-feed variables, furnace electrical system variables, and furnace charge chemical composition variables.  
     
     
         16 . A method according to  claim 14 , which further comprises the step of performing a process of error detection and validation on the measurements, the process of error detection and validation including the steps of: 
 (v) analysing the range of the measurements and the rate of change of the measurements;    (vi) validating the measurements; and    (vii) replacing invalid measurements by pre-recorded measurements according to a set of logical rules.    
     
     
         17 . A method according to  claim 14 , wherein the thickness of the frozen lining is estimated as a function of the temperature in the wall and the furnace gas plant measurements.