December 2011 - SIMA

MIDREX ® Direct Reduction PlantThe cleaned, high pressure syngas (reducing gas)exiting the gasification plant contains approximately85 percent H +CO, 2.5 percent CO , and 10-1222percent CH . Table I shows the syngas quality4required for MXCOL.Syngas CharacteristicTable IMXCOL Syngas QualityMIDREX RequirementCO content 2.0-3.0%2Gas Quality* > 10Gas RequirementPressure~ 2.2 net Gcal / t DRI> 3 bargH /CO ratio 1.0-2.02Sulfur content< 5 ppmvParticulates content < 10 mg / Nm 3N + Ar content < 0.5 %2* Gas Quality is defined as ( % H+ % CO2)2+ % CO ) / ( % H O2In the MIDREX Plant, the cold syngas isdepressurized to about 3 barg in a turboexpander,which generates electricity. The low pressure syngasis mixed with recycled gas to produce the requiredreducing gas. The mixed gas is then heated to over900º C and enters the MIDREX ® Shaft Furnace,where it reacts with the iron oxide to produce DRI.The reduction reactions are shown below:Fe O2 3Fe O2 3+ 3H2—> 2Fe + 3H O2+ 3CO —> 2Fe + 3CO2The spent reducing gas (top gas) exiting the shaftfurnace is scrubbed and cooled, then passed througha CO removal system. This reduces the CO content22to 2-3 percent or less, which ensures that the mixedreducing gas (syngas from the gasification plant andrecycled top gas from the MIDREX Plant) has anacceptably high reductants (H +CO) to oxidants2(H O+CO )ratio for efficient iron oxide reduction. The2 2CO removal system will also remove the sulfur gases2contained in the recycled top gas. The recycling ofthe top gas makes MXCOL a very efficient process.The CO removed from the gasification plant gas2cleaning and conditioning plant and the CO removal2system in the MIDREX Plant are high purity. Thesestreams could be sequestered or sold for enhancedoil recovery or use in a petrochemical or otheroperation.Emissions from MXCOL are shown in Table II.Table IIMXCOL EmissionsPM10 SO NOx COmg/Nm 3 mg/Nm 3 mg/Nm 3 2kg/t DRIReheater