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.

In the blast furnace, nut coke is utilized in a mixture with the ferrous burden to improve the gas permeability. Although applied in a broad range (10-40 mm, 2-23 wt-%), limited information is available on changed burden behaviour in its presence. In the present study, the detailed characterization was performed on the iron ore pellets quenched during sintering, softening and before complete melting. The quantified information of the phase distribution across the pellets is compared for the samples mixed with and without nut coke. The principal role played by the nut coke is on bringing higher reduction and lower sintering among the pellets. For the pellet mixed with nut coke, at the core, ∼25 vol.-% of the material is observed in a network arrangement. The core structure consists of a wüstite matrix (10-20 vol.-%) reinforced with the iron nuclei (5-15 vol.-%). On the contrary, in the absence of nut coke, the pellet core is observed being hollow.

The melting and dripping behaviour of an iron ore pellet bed mixed with nut coke are investigated through a series of quenching, melting and dripping experiments. In the melting bed of iron ore pellets, nut coke acts as a frame to maintain the passage for the gas flow. The iron carburisation level of the pellet shell is found to control the melting temperature of the pellet bed. Simultaneous and layer-wise melting is observed for the pellet bed with and without mixed nut coke, respectively. In the case of pellet bed mixed with nut coke, the liquid dripping starts at a lower temperature (1 500°C) compared to the case when nut coke is absent (1 518°C). Subsequently, a steady rate of liquid dripping is observed for the pellet bed mixed with nut coke. However, in the case of the pellet bed without nut coke, most of the liquid drips (~50 wt%) at high temperature (1 550°C). The difference in carbon content of the quenched pellets and the dripped metal reveals that a substantial iron carburisation occurs when liquid iron flows over the regular coke particles. The nut coke is noticed to consumed preferentially in place of the regular coke. Additionally, the total coke consumption decreases with an increase in nut coke addition in the pellet bed. These results give support for more extensive use of nut coke as a replacement of the regular coke in the ironmaking blast furnace.

Physicochemical behaviour of the pellets, sinters and its mixture (60% pellets: 40% sinter) is investigated by a series of smelting and quenching experiments. For all ferrous raw-material beds, three distinct stages of bed shrinkage occur due to indirect reduction, softening and melting. However, the characteristic nature (displacement, temperature and permeability) differ with the ferrous raw-material type. In mixed ferrous bed, the first and third stages are found to be controlled by the pellets (individual particle shrinkage) and sinter (slow melting rate), respectively. Second stage behaviour is initially observed to be close to the pellet and later to that of sinter. In mixed bed (upto 1505°C), the interaction between the pellet and sinter is limited to the interface only. The sinter slag is observed to control the melting and dripping properties of the mixed bed.These results gives an understanding of individual and mixed burden behaviour under blast furnace conditions.

This article presents a process model of a phosphorus-producing, submerged arc furnace. The model successfully incorporates accurate, multifield thermodynamic, kinetic, and industrial data with computational flow dynamic calculations and thus further unifies the sciences of kinetics and equilibrium thermodynamics. The model is structurally three-dimensional and uses boundary conditions, initial values, and material specifications provided by industrial measurements, laboratory experiments, and a combination of empirical and thermodynamic data. It accounts for fully developed gas flows of gaseous product generated from within the packed bed; the energy associated with chemical reactions, heating, and melting, as well as thermal conductivity and the particle-particle radiation within the burden. The model proves the existence of a narrow, gas-solid reduction zone where the bulk of phosphorus is produced. It shows that fast reaction rates in this narrow reaction zone in combination with long residence times diminish the influence changing reaction rates have on the process. It indicates that most heat exchanged between the new pellets entering the furnace and the gaseous product produced in the reduction zone takes place in the top 0.5 m of the furnace bed. The gaseous product and flow information shows low and recirculating gaseous flow velocity areas that cause dust accumulation.