Co-pyrolysis of biomass tar and iron ore fines for the production of direct reduced iron

Abstract

Biomass tar can be used as reducing agent for reduction of iron oxide, and simultaneously iron is a good catalyst for tar cracking. Thus, an iron ore reduction system integrated tar cracking and iron ore reduction was proposed. The influences of raw material characteristics, the equivalence ratio of tar to iron ore fines as well as reduction conditions on the reduction behaviors of iron ore fines were discussed. Also, the co-pyrolysis of mixture of tar and iron ore fines was investigated. The results show that the iron ore reduction using tar is reliable with a high tar cracking efficiency and a high reduction degree. Due to the formation of porous structures, preheated iron ore fines showed an excellent reduction behavior than those without preheating. At the initial stage, iron oxide did not exert any obvious effect on tar destruction, while as reaction temperature raised above 600 °C, a noticeable decline of tar content was observed, which was attributed to the enhanced reduction consumption and catalytic decomposition by the reduced iron. Increasing the ratio of tar to iron ore was favorable for the reduction of iron oxide, while, when the ratio exceeding 0.6, the effect became less notable. The introduction of proper amount of steam can improve tar cracking and further improve iron oxide reduction. At optimum conditions (iron ore fines was first preheated at 400 °C and then mixed with tar according to tar/iron ore fines 0.6, reacted at 900 °C for 30 min under the steam atmosphere with the mass ratio of steam/tar 0.87), the reduced iron product with metallization rate 94.1% was achieved.