Effects of Stefan Flow on Metallurgical Coke Gasification with CO₂

Abstract

Stefan flow that is caused by non-equimolar diffusion in the boundary layer is often neglected in studies of the coke gasification reaction (Ccoke + CO2 = 2CO). An inaccurate and incomplete understanding of the metallurgical coke gasification reaction mechanism has had a major influence on the coke-making industry. Meanwhile, it is adverse to the reasonable use of the resources of coking coal as well as energy savings. Therefore, this paper has treated the external diffusion coefficient, mass transfer coefficient, concentration of carbon dioxide (CO2) on the outside and inside of coke, and kinetic parameters as objects to study the effect of Stefan flow. Isothermal experiments of metallurgical coke gasification with CO2 were carried out for 1100–1300 °C and at atmospheric pressure. After modification, the coefficients of external diffusion and mass transfer decreased and the deviation of corrections were 45 and 35%, respectively. Under the different temperatures, the concentration of CO2 on the outer surface of coke together with its distribution inside coke all decreased. Meanwhile, the region of the coke gasification reaction was reduced as well as close to the outer surface area of coke because of Stefan flow. Kinetic parameters were affected by Stefan flow, and they increased to a certain degree.

Particle Size Distribution Models for Metallurgical Coke Grinding Products

“…Metallurgical coke is a crucial raw material in the iron and steelmaking industry and is considered a critical raw material in the EU due to its high consumption volume and the strong EU import dependence [1][2][3]. Heat supplier, reducing agent, adequate permeability, and burden mechanical support are the features that render it a fundamental material for blast furnaces that perform metallurgical processes such as cast iron, ferroalloy, lead, and zinc production, and in kilns for lime and magnesium production [4,5]. According to particle size, metallurgical coke is used at different process stages.…”

Transport Properties of CO2 in Different Reactivity Coke Solution Loss Reaction Based on Stefan Flow Theory

“…The kinetic model of the coke solution loss reaction with the effect of Stefan flow has been established in the previous study. 40 For the external and internal diffusion processes of the coke solution loss reaction, the original calculation method was presented, and the corresponding modified calculation method with the effect of Stefan flow was established. By comparing and analyzing the external diffusion coefficient, mass transfer coefficient, carbon dioxide concentration on the outer surface of coke, and the concentration distribution of carbon dioxide inside coke with and without Stefan flow, the influence of Stefan flow on coke solution loss reaction was illustrated.…”

“…AVE( D CO 2 ,CO,SF ) and AVE( h D,SF ) are increased with coke reactivity at each temperature. According to the previous study, 40 considering Stefan flow, the calculation of D CO 2 ,CO,SF involves the molar fraction of carbon dioxide on the outer surface of coke. The lower the reactivity of coke is, the higher the molar fraction of carbon dioxide on the outer surface of coke is, which leads to the smaller values of D CO 2 ,CO,SF .…”

“…This effect is embodied in the concentration distribution of carbon dioxide in coke. Therefore, according to the previous work, 40 the concentration distribution of carbon dioxide inside the three kinds of coke is calculated, and the original and modified carbon dioxide concentration distribution in the coke is shown in Figure 10 .…”

“…However, this has not been reported in many previous studies on coke gasification. − This results in an inaccurate and incomplete understanding of the mass transfer mechanism of the coke solution loss reaction. Huang et al successfully applied the Stefan flow theory into the coke solution loss reaction process and established a kinetic model to discuss the influence of Stefan flow on the coke solution loss reaction. However, the focus of his work was to establish a kinetic model for only one kind of coke, but the application of other kinds of coke is not mentioned.…”