Iron Ore Sintering in Milli-Pot: Comparison to Pilot Scale and Identification of Maximum Resistance to Air Flow

Abstract

In the iron ore sintering process, the resistance to air flow is a major factor in deciding the flame front speed, which influences the sinter productivity and quality. In this work, pressure drop during sintering and the resistance to air flow was investigated in milli-pot sintering for different coke rates. The sintering experiments were conducted in a milli-pot (diameter 53 mm, height 400 mm) and pressure and temperature were measured at the same locations in the bed by four taps located equidistant to each other. The yield of sinter product was measured following a modified drop test and the mineralogy of the sinter product was analysed. The results from milli-pot sintering were then compared to the reported results from standard pilot-scale sintering, and it was found that the lower half of the milli-pot bed gave a reasonable representation of the pilot-scale sintering process. The results of sinter mineralogy, yield and productivity of the lower half of milli-pot at 5.5-8.0% coke rate were found to be similar to pilot-scale sintering tests at a corresponding coke rate from 3.5 to 5.5%. The maximum resistance to air flow in the bed was found to be in the region between the leading edge of the flame front at ~100°C and the trailing edge of the flame front at ~1 200°C. This suggests that the maximum resistance to air flow includes the effect of de-humidification and combustion in addition to the high temperature "flame front" region usually defined at temperatures above 1 100°C or 1 200°C.

Quantification of Resistance and Pressure Drop at High Temperature for Various Suction Pressures During Iron Ore Sintering

“…Several zones can be classified based on temperature alone which contributes to the total pressure-drop during sintering, i.e., humidified bed (HB) zone ( < ~60°C), de-humidification and goethite dehydroxylation zone (~100°C to ~620°C), calcination zone ( > ~700°C), combustion zone ( > ~727°C), melting zone ( > ~1 200°C) and sintered bed (SB) zone ( < ~1 200°C on the cooling side). [7][8][9][10][11][12][13] Some studies have specifically focused on resistance to air flow in the flame front zone, 5,10,[14][15][16][17][18][19] however, the characteristics of this zone including the bed structure that contributes to flow resistance are complex and still not well understood. Loo 7) defined the flame front as a zone with a leading-edge where the coke particles start to combust and a trailing edge where the coke particles are fully combusted and reported that the flame front is responsible for maximum pressure drop in the bed during sintering.…”

“…Loo 7) defined the flame front as a zone with a leading-edge where the coke particles start to combust and a trailing edge where the coke particles are fully combusted and reported that the flame front is responsible for maximum pressure drop in the bed during sintering. 5,7) In a previous work of the authors, 14) it was shown that the maximum pressure-drop occurs in a zone called as "region of maximum resistance" (RMR), which starts from 100°C in the leading-edge and includes Loo's flame front (coke combustion) along with other physico-chemical processes such as de-humidification, goethite dehydroxylation, flux calcination and granulate melting.…”

“…Previous work has established that a milli-pot is a useful tool for fundamental sintering studies and can produce realistic sinter product. 14,20) In the experimental work, the region of maximum resistance was investigated at a greater spatial resolution, with varied suction pressure. The resistance of different zones was quantified by examining the dependency of bed pressured drops during sintering with the specific energy.…”

“…A typical sintering procedure was followed for conducting the sintering experiments in a milli-pot (diameter 53 mm, height 500 mm) apparatus. 5,14,16,21,22) The milli-pot was fitted with six taps to record temperature and pressure at the same location. The taps in the milli-pot were distributed along the height to obtain a better spatial resolution in the lower part of the milli-pot.…”

“…Further details of the sintering equipment are given elsewhere. 14) To analyse the structural transformation of a green bed to sintered bed, quenching was conducted with the same procedure as adopted in Hara et al 23) To quench the sintering process, it was necessary to extinguish the flame front and prevent any further coke combustion in the system. In the present study, the flame front was quenched in the bottom half of the bed by flooding the bed with nitrogen gas.…”