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S. Nagraj et al.
gases also act as a reductant for the ZnO reduction reaction [4]. Since these technologies require fossil fuel as both an energy source and a reductant, a significant amount
is used, thereby emitting a considerable amount of greenhouse gases. Therefore, a
new fuming technology has been developed in which fossil fuel burners are replaced
with electrically powered non-transferred arc plasma torches as an energy source,
and combustion gases are replaced with petroleum-coke pellets as a reductant [5].
Assuming that the electrical energy for the plasma torches is derived from renewable
sources, the overall carbon footprint of the process is reduced significantly.
Several mathematical and empirical models of the conventional fuming process
have been developed in the past to predict the Zn fuming rate, and to understand the
rate-limiting factors of the process. Bell et al., Kellogg et al., and Grant et al. reported
that the process happens at thermodynamic equilibrium, and fitted their model by
adjusting the activity coefficient of ZnO [4, 6, 7]. On the contrary, the evidence from
experimental studies, pilot and industrial tests showed that the fuming rate is limited
by kinetic factors. Suzuki et al. investigated the effects of gas and slag composition,
gas blast intensity, bath temperature, viscosity and surface tension of the slag on the
fuming rate, and found that when the gas blast intensity is increased, the fuming rate
also increased. Suzuki et al. also reported that the surface tension and the viscosity of
the slag have a significant influence on the fuming rate [8]. Richards et al. conducted
measurements of over 11 industrial fuming cycles and found that when coal particles
were injected through the tuyeres, 55 wt% of the coal particles were combusted in
the tuyere gas column, 33 wt% entrained in the slag, and 12 wt% bypassed the slag
bath [9]. Using the industrial data, Richards et al. developed a mathematical model
of the fuming process and found that by increasing the amount of entrained coal in
the slag, the fuming rate can be enhanced [10, 11]. A study by Floyd et al. on solid
reductants for slag fuming supported this idea [12]. Huda et al. developed a CFD
model based on the study of Richards et al. to understand the fluid dynamics in the
fuming reactor. It was found that there is a significant amount of splashing in the
reactor, and the bypassed coal is undergoing a Boudouard reaction above the slag
bath to form CO. This newly formed CO is also contributing to the Zn fuming on
the slag bath surface [13].
A thermodynamic model of a continuous submerged plasma fuming process constructed by Verscheure et al. showed that the plasma enhances the fuming rate by a
factor of 4.6 compared to the conventional fuming process [14, 15]. However, Verscheure’s model was a steady state model and did not include kinetics which plays
an essential role in the rate of fuming. Therefore, to investigate the thermodynamics and kinetics of the submerged plasma zinc fuming process, a dynamic model
is developed based on the industrial scale plasma-driven fuming furnace at Metallo
Belgium.
S. Nagraj et al.
gases also act as a reductant for the ZnO reduction reaction [4]. Since these technologies require fossil fuel as both an energy source and a reductant, a significant amount
is used, thereby emitting a considerable amount of greenhouse gases. Therefore, a
new fuming technology has been developed in which fossil fuel burners are replaced
with electrically powered non-transferred arc plasma torches as an energy source,
and combustion gases are replaced with petroleum-coke pellets as a reductant [5].
Assuming that the electrical energy for the plasma torches is derived from renewable
sources, the overall carbon footprint of the process is reduced significantly.
Several mathematical and empirical models of the conventional fuming process
have been developed in the past to predict the Zn fuming rate, and to understand the
rate-limiting factors of the process. Bell et al., Kellogg et al., and Grant et al. reported
that the process happens at thermodynamic equilibrium, and fitted their model by
adjusting the activity coefficient of ZnO [4, 6, 7]. On the contrary, the evidence from
experimental studies, pilot and industrial tests showed that the fuming rate is limited
by kinetic factors. Suzuki et al. investigated the effects of gas and slag composition,
gas blast intensity, bath temperature, viscosity and surface tension of the slag on the
fuming rate, and found that when the gas blast intensity is increased, the fuming rate
also increased. Suzuki et al. also reported that the surface tension and the viscosity of
the slag have a significant influence on the fuming rate [8]. Richards et al. conducted
measurements of over 11 industrial fuming cycles and found that when coal particles
were injected through the tuyeres, 55 wt% of the coal particles were combusted in
the tuyere gas column, 33 wt% entrained in the slag, and 12 wt% bypassed the slag
bath [9]. Using the industrial data, Richards et al. developed a mathematical model
of the fuming process and found that by increasing the amount of entrained coal in
the slag, the fuming rate can be enhanced [10, 11]. A study by Floyd et al. on solid
reductants for slag fuming supported this idea [12]. Huda et al. developed a CFD
model based on the study of Richards et al. to understand the fluid dynamics in the
fuming reactor. It was found that there is a significant amount of splashing in the
reactor, and the bypassed coal is undergoing a Boudouard reaction above the slag
bath to form CO. This newly formed CO is also contributing to the Zn fuming on
the slag bath surface [13].
A thermodynamic model of a continuous submerged plasma fuming process constructed by Verscheure et al. showed that the plasma enhances the fuming rate by a
factor of 4.6 compared to the conventional fuming process [14, 15]. However, Verscheure’s model was a steady state model and did not include kinetics which plays
an essential role in the rate of fuming. Therefore, to investigate the thermodynamics and kinetics of the submerged plasma zinc fuming process, a dynamic model
is developed based on the industrial scale plasma-driven fuming furnace at Metallo
Belgium.