Method for Producing Cold Direct Reduced Iron

Abstract

A method for producing direct reduced iron (DRI), comprising the steps of: controlling a flow rate of a non-heated hydrogen gas into a cooling section (5) such that Tdriout<Tdrioutmax, wherein Tdrimax is a set maximum allowable temperature of the DRI exiting the cooling section (5), measuring temperature of cooling gas Tcooltop leaving the cooling section and increasing the flow rate of the cooling gas, FRcoolgas, introduced into the cooling section (5) until Tcooltop=Tcooltopmin, adjusting a flow rate of a separately heated reduction gas introduced into a reduction section (4) and measuring the degree of metallization of the produced DRI and measuring the top gas temperature Ttopgas, and determining a minimum top gas temperature, Ttopgasmin, below which the degree of metallization is below a minimum allowable value, and measuring the top gas temperature Ttopgas and controlling at least one of the flow rate of the heated reducing gas and the temperature Tredgas to which the heated reducing gas is heated such that Ttopgasmin≤Ttopgas≤Topgasmax, wherein Topgasmax is a set maximum allowable temperature of the top gas.

1 . A method for producing direct reduced iron (DRI), the method comprising the steps of:
 a) introducing iron ore to an iron ore inlet ( 2 ) of a direct reduction shaft ( 1 );   b) heating a reducing gas consisting essentially of hydrogen to a reduction gas temperature Tredgas and introducing the heated reducing gas into a reducing section ( 4 ) of the direct reduction shaft to form a first component part of a reducing gas that reduces the iron ore to hot DRI at a reduction temperature Tred, wherein Tredgas>Tred;   c) introducing a cooling gas consisting essentially of hydrogen and having a temperature Tcoolgas into a cooling section ( 5 ) of the direct reduction shaft ( 1 ), said cooling section ( 5 ) being located downstream the reducing section ( 4 ) as seen in a flow direction of the DRI, wherein the cooling gas is introduced at an end of the cooling section ( 5 ) opposite to the end of the cooling section ( 5 ) which is adjacent to reducing section ( 4 ), and thereby cooling the hot DRI, which has a temperature Tdritop when entering the cooling section ( 5 ), to cold DRI and heating the cooling gas to a temperature Tcooltop, wherein the cold DRI exiting the cooling section ( 5 ) has a temperature Tdriout;   d) permitting the hot cooling gas to enter the reducing section ( 4 ) of the direct reduction shaft ( 1 ) to mix with the heated reducing gas and form a second component part of the reducing gas; and   e) removing a spent reducing gas as top gas from an upper part of the reducing section ( 4 ) of the direct reduction shaft ( 1 ), said top gas having a temperature Ttopgas; said method being characterized in that it further comprises the steps of:   f) measuring Tdriout and controlling the flow rate of the cooling gas, FRcoolgas, into the cooling section ( 5 ) such that Tdriout<Tdrioutmax, wherein Tdrioutmax is a set maximum allowable temperature of the DRI exiting the cooling section ( 5 ),   g) measuring the temperature of the heated cooling gas Tcooltop and increasing the flow rate of the cooling gas, FRcoolgas, introduced into the cooling section ( 5 ) until Tcooltop=Tcooltopmin, wherein Tcooltopmin is a predetermined lowest allowable temperature of the heated cooling gas and Tcooltopmin≤Tdritop,   h) adjusting a flow rate of the heated reduction gas, FRredgas, forming the first component part and determining the degree of metallization of the produced DRI and measuring the top gas temperature Ttopgas while doing so, and determining a minimum top gas temperature, Ttopgasmin, below which the degree of metallization is below a minimum allowable value,   i) measuring the top gas temperature Ttopgas and controlling at least one of the flow rate of the heated reducing gas and the temperature Tredgas to which the heated reducing gas is heated before being introduced into the reducing section such that Ttopgasmin≤Ttopgas≤Topgasmax, wherein Topgasmax is a set maximum allowable temperature of the top gas.   
     
     
         2 . A method according to  claim 1 , wherein Ttopgasmax=Topgasmin+50° C. 
     
     
         3 . A method according to  claim 1 , wherein Ttopgasmax=Topgasmin+25° C. 
     
     
         4 . A method according to  claim 1 , wherein Ttopgasmax=Topgasmin. 
     
     
         5 . A method according to  claim 1 , wherein Tcooltopmin=Tdritop−50° C. 
     
     
         6 . A method according to  claim 1 , wherein Tcooltopmin=Tdritop−25° C. 
     
     
         7 . A method according to  claim 1 , wherein Tcooltopmin=Tdritop−10° C. 
     
     
         8 . A method according to  claim 1 , wherein Tcooltopmin=Tdritop. 
     
     
         9 . A method according to  claim 1 , wherein Tdritop=Tred. 
     
     
         10 . A method according to  claim 1 , wherein the minimum allowable value of the degree of metallization is 90 wt %, preferably 94 wt %, even more preferably 96 wt %, or even more preferably 98 wt %. 
     
     
         11 . A method according to  claim 1 , wherein 850° C.<Tredgas<1 200° C. 
     
     
         12 . A method according to  claim 1 , wherein 900° C.<Tred<1 000° C.