Process to preheat and reduce directly reduced iron (DRI) to be fed to an electric arc furnace (EAF)

Abstract

The present invention relates to a high energy-saving process for preheating and final reduction of directly reduced iron (DRI) to be conveyed to a melting process, by using melting furnace off-gas, which is characterized by a high temperature and a high CO-content.

1 . A process for preheating and reduction of directly reduced iron (DRI) to be fed to a melting furnace, 
 including the steps of: 
 adjusting the temperature and the composition of melting furnace off-gas outside the melting furnace to a value, suitable to preheat and reduce the DRI,  
 contacting the DRI with said adjusted gas to preheat and reduce the DRI.  
   
     
     
         2 . A process according to  claim 1 , 
 characterized in that    at least the temperature of the melting furnace off-gas is measured before adjusting the temperature and the composition of the melting furnace off-gas.    
     
     
         3 . A process according to  claim 1 , 
 characterized in that    at least the composition of the melting furnace off-gas is measured before adjusting the temperature and the composition of the melting furnace off-gas.    
     
     
         4 . A process according to one or more of the preceding claims, 
 characterized in that    said melting furnace is an electric arc furnace (EAF).    
     
     
         5 . A process according to one or more of the preceding claims, 
 characterized in that    said melting furnace off-gas is adjusted to a temperature of at least 630° C. and a CO/CO 2 -ratio of at least 1.    
     
     
         6 . A process according to one or more of the preceding claims, 
 characterized in that    said melting furnace off-gas is adjusted to a temperature of 700-1100° C.    
     
     
         7 . A process according to one or more of the preceding claims, 
 characterized in that    the composition of said melting furnace off-gas is adjusted to have a CO/CO 2 -ratio of 1.5-4.    
     
     
         8 . A process according to one or more of the preceding claims, 
 characterized in that    the temperature of said melting furnace off-gas is adjusted to 700-1100° C. and its composition to have a CO/CO 2 -ratio of 1.5-4.    
     
     
         9 . A process according to one or more of the preceding claims, 
 characterized in that    the adjustment of temperature and composition of said melting furnace off-gas is performed by burning a mixture of air and/or O 2 , recycle gas and optionally CH 4 , with the melting furnace off-gas.    
     
     
         10 . A process according to  claim 9 , 
 characterized in that    said recycle gas is obtained from gas, which has been contacted with the DRI in the preheating and reduction step (preheating off-gas).    
     
     
         11 . A process according to  claim 9  or  10 , 
 characterized in that  
 said recycle gas is obtained after removing fines, cooling the gas, pressurizing and intermediate storage of the gas.  
 
     
     
         12 . A process according to one or more of the preceding claims, 
 characterized in that    said DRI is contacted with said adjusted gas by a vertically split flow.    
     
     
         13 . A process according to one or more of the preceding claims, 
 characterized in that    said DRI is preheated to a temperature of 300-700° C., preferably 500-700° C.    
     
     
         14 . A process according to one or more of the preceding claims, 
 characterized in that    said DRI is reduced to a metallization of at least 95 wt.-%.    
     
     
         15 . A process according to one or more of the preceding claims, 
 characterized in that    said DRI is reduced to a FeO-content of 1-5% wt.-%.    
     
     
         16 . A process according to one or more of the preceding claims, 
 characterized in that    said adjusted gas contains 0-30% H 2 , which is produced by the reaction of CH 4  with O 2 .    
     
     
         17 . A process according to one or more of the preceding claims, 
 characterized in that    the temperature of said melting furnace off-gas is about 1200° C.-1600° C. before adjustment thereof.    
     
     
         18 . A plant for performing the process according to  claim 1 , comprising: 
 a melting furnace,    a means for the adjustment of the melting furnace off-gas, and    a preheater for contacting the DRI with said adjusted melting furnace off-gas.    
     
     
         19 . A plant according to  claim 18 , 
 characterized in that    said means for the adjustment of the melting furnace off-gas is a combustion chamber.    
     
     
         20 . A plant according to  claim 18  or  19 , further comprising means for measuring at least the temperature of the off-gas.  
     
     
         21 . A plant according to  claim 18 ,  19  or  20 , further comprising means for measuring at least the composition of the off-gas.  
     
     
         22 . A plant according to one or more of the  claims 18  to  21 , 
 characterized in that  
 said melting furnace is an electric arc furnace.  
 
     
     
         23 . A combustion chamber, comprising a controlled burner, controlled inlets for EAF off-gas, CH 4 , air and/or O 2  and cooling recycled gas and a controlled outlet for transferring said adjusted gas to the preheater.  
     
     
         24 . A plant according to one or more of the  claims 18  to  22 , 
 characterized in that  
 said plant further comprises a device for separating fines from the preheater off-gas, a cooling device for cooling the preheater off-gas, a pressurizing device and an intermediate storage device, from which the recycled preheater off-gas is transferable to the combustion chamber and/or a fume plant.  
 
     
     
         25 . A plant according to one or more of the  claims 18  to  22  or  24 , 
 characterized in that  
 said preheater comprises at least one discharging device at the bottom and at least one gas inlet for the gas to be contacted with the DRI.  
 
     
     
         26 . A plant according to one or more of the  claims 18  to  22 ,  24  or  25 , 
 characterized in that  
 said preheater has essentially a cylindrical form.  
 
     
     
         27 . A plant according to one or more of the  claims 18  to  22  or  24  to  26 , 
 characterized in that  
 said preheater comprises at least two conical discharging devices located at the bottom of said cylindrical container and three gas inlets for the gas to be contacted with the DRI, wherein one gas inlet is located centrally at the bottom of the preheater and two gas inlets are located at the side of said conical discharging devices.  
 
     
     
         28 . Use of a process according to  claim 1  in the production of steel.