Apparatus and method for optimizing the use of oxygen in the direct reduction of iron

Abstract

An apparatus and method for adjusting the parameters of a reducing gas stream prior to introduction into a direct reduction furnace, such parameters including temperature of the gas stream, and amount of hydrocarbon, carbon monoxide, and hydrogen contained in the reducing gas. The apparatus is placed in-line with the reducing gas recycle loop of a direct reduction furnace, which has an enrichment section which introduces hydrocarbon components to the main stream, and an oxygen/fuel injection system, located downstream from the enrichment section, which injects a shrouded stream of oxygen and hydrocarbon gas into the reducing gas stream. Temperature, carbon monoxide content, and hydrogen content of the reducing gas are adjusted by controlling the flow of oxygen and the ratio of hydrocarbon to oxygen injected in the oxygen/fuel injection system. Hydrocarbon content of the reducing gas is adjusted primarily by controlling the flow rate of the enrichment section.

What is claimed is:  
     
         1 . A method of controlling the properties of a stream of bustle gas for use in the direct reduction of iron, comprising: 
 supplying a hydrocarbon-containing enrichment gas at a controlled flow rate;    supplying a hydrocarbon-containing fuel gas at a controlled flow rate;    supplying an oxygen containing gas at a controlled flow rate;    injecting the enrichment gas into the bustle gas stream; and    simultaneously mixing the fuel gas with the oxygen containing gas to form a fuel/oxygen gas mixture, and injecting the fuel/oxygen gas mixture into the bustle gas stream and causing the injected fuel/oxygen gas mixture to be substantially combusted prior to becoming dispersed within the bustle gas stream.    
     
     
         2 . A bustle gas control method according to  claim 1 , further comprising: 
 receiving reformed bustle gas from a bustle gas reforming unit prior to injecting enrichment gas into the bustle gas stream.    
     
     
         3 . A bustle gas control method according to  claim 2 , further comprising: 
 introducing the stream of bustle gas into a direct reduction furnace after injecting the enrichment gas and the fuel/oxygen gas mixture into the bustle gas.    
     
     
         4 . A bustle gas control method according to  claim 1 , wherein the enrichment gas is injected into the bustle gas stream by projecting the enrichment gas stream substantially perpendicular to the flow of the bustle gas stream.  
     
     
         5 . A bustle gas control method according to  claim 1 , further comprising: 
 analyzing the hydrocarbon content of the bustle gas stream at a point downstream from the point of injection of the fuel/oxygen gas mixture; and,    adjusting said controlled flow rate of enrichment gas such that the resulting analyzed hydrocarbon content is within a predetermined range.    
     
     
         6 . A bustle gas control method according to  claim 5 , wherein said hydrocarbon is methane.  
     
     
         7 . A bustle gas control method according to  claim 6 , wherein said methane content is from about 1% to about 10%.  
     
     
         8 . A bustle gas control method according to  claim 1 , further comprising: 
 measuring the temperature of the bustle gas stream at a point downstream from the point of injecting the fuel/oxygen gas mixture; and    adjusting the controlled oxygen flow rate so that the resulting bustle gas temperature is within a predetermined range.    
     
     
         9 . A bustle gas control method according to  claim 8 , wherein the resulting bustle gas temperature range is from about 950° C. to about 1250° C.  
     
     
         10 . A bustle gas control method according to  claim 8 , further comprising: 
 adjusting the controlled fuel gas flow rate in relationship to the adjusted oxygen flow rate such that said resulting fuel/oxygen gas mixture contains an excess of fuel.    
     
     
         11 . A bustle gas control method according to  claim 1 , further comprising lowering the temperature of the bustle gas stream prior to the injection of enrichment gas.  
     
     
         12 . A bustle gas control method according to  claim 1 , further comprising preheating the enrichmnent gas.  
     
     
         13 . A bustle gas control method according to  claim 1 , further comprising preheating the fuel gas.  
     
     
         14 . An apparatus for installation between the spent bustle gas output and the reformed bustle gas input of a direct reduction furnace for improving the efficiency of the direct reduction furnace, such apparatus comprising: 
 a shaft means for containing a stream of said bustle gas;    means for injecting a hydrocarbon-containing enrichment gas into said shaft; and,    means for injecting an oxygen-hydrocarbon gas mixture into said shaft downstream of said enrichment gas injecting means.    
     
     
         15 . An apparatus according to  claim 14 , wherein said enrichment gas injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft.  
     
     
         16 . An apparatus according to  claim 15 , wherein the internal surface of the portion of the shaft through which the nozzles protrude is generally cylindrical; and the protruding nozzles are flush with the internal surface of the shaft.  
     
     
         17 . An apparatus according to  claim 14 , wherein the gas mixture injection means comprises an oxygen injection component and a fuel injection component.  
     
     
         18 . An apparatus according to  claim 17 , wherein said oxygen injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft; and, 
 wherein said fuel gas injection means comprises a header, positioned exterior to the shaft, in communication with several separate nozzles which protrude into the interior of the shaft.    
     
     
         19 . An apparatus according to  claim 18 , wherein said oxygen injection component is disposed within said fuel injection component.  
     
     
         20 . An apparatus according to  claim 19 , wherein said oxygen injection component is coaxially disposed within said fuel injection component.  
     
     
         21 . An apparatus according to  claim 18 , wherein the nozzles of the gas mixture injection means are angled with respect to the internal surface of the shaft such that a mixture of oxygen and fuel injected into the shaft is injected at an angle of between 15° and 75° with respect to the direction of flow of the bustle gas.  
     
     
         22 . An apparatus according to  claim 21 , wherein a portion of the inner surface of the shaft forms a protrusion between the enrichment gas injection means and the mixture gas injection means of the shaft; 
 whereby bustle gas flowing through the shaft is directed towards the center of the shaft by said protrusions.    
     
     
         23 . An apparatus according to  claim 17 , further comprising 
 a temperature measurement means in communication with said bustle gas stream downstream of said gas mixture injection means; and,    an oxygen flow control valve operatively connected to said temperature measurement means, said oxygen valve situated in-line with said oxygen injection component.    
     
     
         24 . An apparatus according to  claim 15 , further comprising: 
 a hydrocarbon measurement means in communication with said bustle gas stream downstream of said enrichment gas injection means;    an enrichment gas supply line in communication with said enrichment gas injection means; and    an enrichment flow control valve operatively connected to said hydrocarbon measurement means, said enrichment valve situated in-line with said enrichment gas supply line.