Swelling behavior of hot preheated pellets in reduction roasting process

Abstract

One kind of facile coal-based direct reduction process is using hot preheated pellets for reduction in grate kiln. In this work, effects of reduction parameters on swelling index of hot preheated pellets were investigated by photographic technique under isothermal conditions. Experimental results show that swelling index of pellets is firstly increased then gradually decreased with increasing reduction time, while that is found to be an obvious decrease from 175 % to 30% with the variation of temperature from 900 °C to 1100 °C. Results of XRD combined with SEM reveal that swelling behavior of pellets is decided by structure of newly formed metal iron grains. The formation and growth of fibers iron grains promote the increase in volume. Low temperature and low CO content are favored to the formation and orientated growth of metal iron grains in the one step process.

Keywords

direct reduction / hot preheated pellets / swelling index / fibers iron

References

[1] KasaiE, KitajimaT, KawaguchiT. Carbothermic reduction in the combustion bed packed with composite pellets of iron oxide and coal [J]. ISIJ international, 2000, 40(9): 842-849

[2] DancyT. The evolution of direct reduction [C]. 50th Ironmaking Conference Proceedings. Washington, USA: Iron and Steel Society, 1991611-624

[3] LiJianA study on mechanism and process of direct reduction of pellets made from concentrate and composite binder [D], 2007ChangshaCentral South University

[4] ZhuD-q, QiuG-z, JiangT, XuJ-cang. An innovative process for direct reduction of cold-bound pellets from iron concentrate with a coal-based rotary kiln [J]. Journal of Central South University of Technology, 2000, 7(2): 68-71

[5] ZhuD-q, MendesV C T-j, PanJ, LiQ-h, LiJ, QiuG-zhou. Direct reduction behaviors of composite binder magnetite pellets in coal-based grate-rotary kiln process [J]. ISIJ International, 2011, 51(2): 214-219

[6] SharmaT, GuptaR, PrakashB. Effect of gangue content on the swelling behaviour of iron ore pellets [J]. Minerals Engineering, 1990, 3(5): 509-516

[7] WangH-t, SohnH Y. Effects of firing and reduction conditions on swelling and iron whisker formation during the reduction of iron oxide compact [J]. ISIJ International, 2011, 51(6): 906-912

[8] WangH-t, SohnH Y. Effect of CaO and SiO₂ on swelling and iron whisker formation during reduction of iron oxide compact [J]. Ironmaking & Steelmaking, 2011, 38(6): 447-452

[9] YiL-y, HuangZ-c, JiangT, WangL-n, QiTao. Swelling behavior of iron ore pellet reduced by H2–CO mixtures [J]. Powder Technology, 2015, 269(1): 290-295

[10] NasrM, OmarA, HessienM, Ei-GeassyA A. Carbon monoxide reduction and accompanying swelling of iron oxide compacts [J]. ISIJ international, 1996, 36(2): 164-171

[11] FuJ-y, JiangT, ZhuD-qingSintering and palletizing [M], 1996175-178

[12] WrightJ, MorrisonA. Changes in diffusivity due to sintering in metallized iron oxide pellets [J]. Metallurgical Transactions B, 1982, 13(3): 518-520

[13] HayesP, GrievesonP. Microstructural changes on the reduction of hematite to maanetite [J]. Metallurgical Transactions B, 1981, 12(3): 579-587

[14] HayesP, GrievesonP. The effects of nucleation and growth on the reduction of Fe₂O₃ to Fe₃O₄ [J]. Metallurgical Transactions B, 1981, 12(2): 319-326

[15] ChangM, de JongheL C. Whisker growth in reduction of oxides [J]. Metallurgical Transactions B, 1984, 15(4): 685-694

[16] FuwaT, BanyaS. Swelling of iron ore pellets during reduction [J]. Trans Iron Steel Inst Japan, 1969, 9(2): 137-147

[17] MONN J, WALKER R Swelling of iron oxide compacts during reduction [J]. Ironmaking Steelmaking, 1975, 2(1): 30–35.

[18] SharmaT, GuptaR, PrakashB. Effect of firing condition and ingredients on the swelling behaviour of iron ore pellets [J]. ISIJ International, 1993, 33(4): 446-453

[19] SharmaT, GuptaR, PrakashB. Swelling of iron ore pellets by statistical design of experiment [J]. ISIJ International, 1992, 32(12): 1268-1275

[20] El-GeassyA A, NasrM, HessienM. Effect of reducing gas on the volume change during reduction of iron oxide compacts [J]. ISIJ International, 1996, 36(6): 640-649

[21] TaniguchiS, OhmiM, NakajimaT. Crushing strength of metallised iron pellets after hydrogen reduction under rising temperature conditions [J]. Transactions of the Japan Institute of Metals, 1981, 22(5): 309-314