Process to preheat and carburate 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 carburation 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 carburation 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 carburate the DRI,    contacting the DRI with said adjusted gas to preheat and carburate 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 ≦800° 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    the temperature of said melting furnace off-gas is adjusted to 450-800° 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 1-3.    
     
     
         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 450-800° C. and its composition to have a CO/CO 2 -ratio of 1-3.    
     
     
         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 carburation 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.    
     
     
         14 . A process according to one or more of the preceding claims, 
 characterized in that    said DRI is carburated to a C-content of 0-3 wt.-%.    
     
     
         15 . 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 .    
     
     
         16 . 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.    
     
     
         17 . 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.    
     
     
         18 . A plant according to  claim 17 , 
 characterized in that    said means for the adjustment of the melting furnace off-gas is a combustion chamber.    
     
     
         19 . A plant according to  claim 17  or  18 , further comprising means for measuring at least the temperature of the melting furnace off-gas.  
     
     
         20 . A plant according to  claim 17 ,  18  or  19 , further comprising means for measuring at least the composition of the melting furnace off-gas.  
     
     
         21 . A plant according to one or more of the  claims 17  to  20 , characterized in that said melting furnace is an electric arc furnace (EAF).  
     
     
         22 . A combustion chamber, comprising a controlled burner, controlled inlets for the 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.  
     
     
         23 . A plant according to one or more of the  claims 17  to  21 , 
 characterized 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.  
 
     
     
         24 . A plant according to one or more of the  claims 17  to  21  or  23 , 
 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.  
 
     
     
         25 . A plant according to one or more of the  claims 17  to  21 ,  23  or  24 , 
 characterized in that  
 said preheater has essentially a cylindrical form.  
 
     
     
         26 . A plant according to one or more of the  claims 17  to  21 ,  23 ,  24  or  25 , 
 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.  
 
     
     
         27 . Use of the process according to  claim 1  in the production of steel.