Effect of Nut Coke Addition on Physicochemical Behaviour of Pellet Bed in Ironmaking Blast Furnace

Abstract

One of the primary causes that limit the blast furnace productivity is the resistance exerted to the gas flow in the cohesive zone by the ferrous burden. Use of nut coke (10-40 mm) together with ferrous burden proves beneficial for decreasing this resistance. In present study, effect of nut coke addition on the olivine fluxed iron ore pellet bed is investigated under simulated blast furnace conditions. Nut coke mixing degree (replacement ratio of regular coke) was varied from 0 to 40 wt% to investigate the physicochemical characteristics of the pellet bed. Three distinct stages of bed contraction are observed and the principal phenomena governing these stages are indirect reduction, softening and melting. It is observed that nut coke mixing enhances the reduction kinetics, lowers softening, limits sintering and promotes iron carburisation to affects all three stages. In the second stage, the temperature and displacement range is reduced by 60°C and 24%, respectively upon 40 wt% nut coke mixing. Addition of nut coke exponentially increases the gas permeability (represented by pressure drop and S-value). A higher degree of carburisation achieved on the pellet shell (iron) is suggested to be the principal reason for decrease in the pellet melting temperature. The pellets softening temperature increases by approximately 4°C, melting and dripping temperature drops by 11°C and 12°C, respectively, for every 10 wt% nut coke addition. Consequently, the nut coke addition shortens the softening, melting and dripping temperature ranges, which shows improved properties of the cohesive zone.

Melting Behaviour of Iron Ore Pellet Bed under Nut Coke Mixed Charge Conditions

“…It was found that the nut coke addition in the pellet bed improves the bed permeability substantially. 16) Furthermore, the cohesive zone temperature range was observed to reduce by 16°C for every 10 wt% nut coke addition. 16) In the study, it was suggested that along with enhanced reduction kinetics, the higher iron carburisation would be the main cause for such behaviour.…”

“…16) Furthermore, the cohesive zone temperature range was observed to reduce by 16°C for every 10 wt% nut coke addition. 16) In the study, it was suggested that along with enhanced reduction kinetics, the higher iron carburisation would be the main cause for such behaviour. However, the complete characterisation was not presented and discussions were not made about melting pattern in the presence or absence of nut coke in the pellet bed.…”

“…Therefore, in our previous study, 16) a thorough investigation was performed to understand the physicochemical behaviour of the pellet bed when nut coke (0-40 wt%) was added as a replacement of the regular coke. It was found that the nut coke addition in the pellet bed improves the bed permeability substantially.…”

“…The quenching temperature for the sample bed was determined based on a series of high-temperature experiments. 16) In order to understand the prime reason of the pellet bed melting, samples were quenched from a temperature close to the bed melting temperature. In addition, to understand the liquid flow behaviour in the presence of nut coke, the sample bed was quenched around the dripping temperature.…”

“…The effect of nut coke addition on the pellet bed contraction and pressure drop was discussed comprehensively in our previous article. 16) In the present study, the fundamentals of pellet bed melting and dripping are investigated.…”