Agglomeration of Iron Ore Fines Avoided

Description And Advantages

Lurgi Germany has designed a new 500,000 tpa plant to produce direct reducing iron that avoids agglomeration. The plant, built for Cliffs & Associates, USA is the first to use Lurgi's Circored process which employs hydrogen from natural gas to reduce iron ore fines. 

The problem involves the discharge of the fines into the briquetter at the end of the process. The particles, swirling in a stream of hydrogen at 4 bars have to be heated above 670°C for hot briquetting, to avoid reoxidation when exposed to the atmosphere. Lurgi's original system was a three stage lock hopper with specially designed ball valves, but the fines tended to agglomerate and clog the system. The new system has a refractory lined 1 m diameter Y or U tube that has no moving part. Fines drop down the first leg of the tube and are blown up the second leg to a feed hopper by injecting nitrogen. A constant reservoir of solids in the tube serves as a seal, both, to prevent the release of hydrogen as well as counter the 4 bars pressure differential.     

Source : Chemical Engineering 2001