Yun-song Huang

Detailed Adsorption Studies of Active Humic Acid Fraction of a New Binder on Iron Ore Particles

Humic acid (HA) is used as one of organic active fractions of a new binder in the process of iron ore agglomeration. The purpose of this study was to determine the detailed adsorption characteristics of HA onto iron ore particles. The results demonstrated that the adsorption of HA was strongly dependent on solution pH, concentration, contact time and temperature. The chemical adsorption controlled the adsorption process of HA onto iron ore particles as typically found in earlier reported results. The adsorption kinetics of HA onto iron ore particles at different testing conditions was well described by the first-order model, which indicated that the adsorption rate is proportional to the concentration of HA. The adsorption isotherms of HA were determined by the fittings of the experimental data to two well-known isotherm models involving models: Langmuir and Freundlich. The Freundlich model (R-square > 0.97) appeared to fit the adsorption better than the Langmuir adsorption model, which indicated that multilayer absorption dominates the reaction of HA with iron ore particles. The value of exponent n (n > 1.0) for the Freundlich model indicated that the multilayer absorption of HA was hampered because of the appearance of the adsorbed HA on iron ore particles. These findings are useful for evaluating the adsorption capacity of MHA binder.

A laboratory-based investigation into the catalytic reduction of NOx in iron ore sintering with flue gas recirculation

The catalytic reduction behaviours between NOx and CO in sinter zone were studied as using flue gas recirculation (FGR). Minerals in sinter can act as catalysts during NOx reduction. The catalytic activity of minerals has the order of calcium ferrite > kirschsteinite > fayalite. The catalytic procedure includes two steps: iron-bearing minerals are reduced to lower valence oxides by CO, and then NO is reduced to N2 by lower valence oxides. Improving the generation amount of calcium ferrite, especially acicular-type silico-ferrite of calcium and aluminium (SFCA), contributes to significantly reinforcing the catalytic performance between NO and CO. As the basicity of sinter increases to 2.2, it enables to generate maximum amount of acicular-type SFCA which has larger specific surface areas, therefore facilitates decreasing NOx emission during FGR sintering.

Reaction behavior of SO2 in the sintering process with flue gas recirculation

ABSTRACT The primary goal of this paper is to reveal the reaction behavior of SO2 in the sinter zone, combustion zone, drying–preheating zone, and over-wet zone during flue gas recirculation (FGR) technique. The results showed that SO2 retention in the sinter zone was associated with free-CaO in the form of CaSO3/CaSO4, and the SO2 adsorption reached a maximum under 900ºC. SO2 in the flue gas came almost from the combustion zone. One reaction behavior was the oxidation of sulfur in the sintering mix when the temperature was between 800 and 1000ºC; the other behavior was the decomposition of sulfite/sulfate when the temperature was over 1000ºC. However, the SO2 adsorption in the sintering bed mainly occurred in the drying–preheating zone, adsorbed by CaCO3, Ca(OH)2, and CaO. When the SO2 adsorption reaction in the drying–preheating zone reached equilibrium, the excess SO2 gas continued to migrate to the over-wet zone and was then absorbed by Ca(OH)2 and H2O. The emission rising point of SO2 moved forward in combustion zone, and the concentration of SO2 emissions significantly increased in the case of flue gas recirculation (FGR) technique. Implications: Aiming for the reuse of the sensible heat and a reduction in exhaust gas emission, the FGR technique is proposed in the iron ore sintering process. When using the FGR technique, SO2 emission in exhaust gas gets changed. In practice, the application of the FGR technique in a sinter plant should be cooperative with the flue gas desulfurization (FGD) technique. Thus, it is necessary to study the influence of the FGR technique on SO2 emissions because it will directly influence the demand and design of the FGD system.

Flue gas recirculation in iron ore sintering process

Flue gas recirculation has been introduced into iron ore sintering process to reduce pollutant emissions. Compared with the conventional process, the sintering indices reduce gradually with decreasing O2 content in the recirculating gas. With sufficient O2, the principle on the use of flue gas recirculation is proposed. The heat loss caused by the decrease in O2 content is compensated by 250°C gas and 0.5%CO. The flame and heat transfer fronts of the sintering bed coincide using mixed gases of no more than 6%CO2 and 8%H2O (g). A novel technology of 35.5% flue gas recirculation ratio is proposed with qualified sintering indices.

Effect of H2O(g) Content in Circulating Flue Gas on Iron Ore Sintering with Flue Gas Recirculation

The influence of H2O (g) content in circulating flue gas on sintering was studied by simulating the flue gas circulating sintering. The results show that the burning speed of solid fuel and the heat transfer rate during sintering process are improved when the H2O (g) content increases from 0 to 6%, which accelerates the sintering speed. However, when the H2O (g) content exceeds 6%, the over-wet zone in sinter bed is thickened, which deteriorates the permeability of sintering bed. In addition, the magnetite content in sinter increases, while the acicular calcium ferrite content decreases. Accordingly, the sinter yield and tumble index decrease with excessive H2O (g) content. To guarantee the yield and quality of sinter, the favourable H2O (g) content in circulating flue gas should be controlled to be less than 6%.

Optimising method for improving granulation effectiveness of iron ore sintering mixture

Abstract The structure of granules has been investigated and a model of granulation determined. The results show that a granule consists of an adhesive layer and a nucleus. Particles with diameter under 0.5 mm act as adhesive fines, while the remainders act as nuclei. By studying the influencing factors of granulation, two significant particle characteristics assessing granulation performance were determined. One is the relative proportion of adhesive fines and nucleus particles, and the other is the specific surface area of adhesive fines. The method of optimising granulation of sinter mixtures is proposed as follows: the proportion of adhesive fines should be 40–50% and the specific surface area should exceed 1000 cm2 g−1, which contributes to achieving a better bed permeability, a faster sintering speed and higher productivity.

Sintering behaviours of iron ore with flue gas circulation

ABSTRACT Flue gas circulation is an important method for energy conservation and pollutant emission reduction in iron ore sintering. In this paper the effects of flue gas recirculation ratio on sintering of different iron ores including haematite, magnetite and limonite were studied by illustrating the variation of sinter bed temperature, atmosphere and mineralisation characteristics of different types of iron ores induced by the circulation. It shows that the proper flue gas circulation ratios for haematite, magnetite and limonite are 37, 30 and 25%, respectively. For magnetite ore, preheating and high consumption of oxygen in combustion zone caused more silicate minerals and less acicular calcium ferrite, thereby lowering sinter tumbler strength. As for haematite ore, the rapid change of temperatures of combustion, melting and solidification zones leads to elevated combustion efficiency and increased formation of acicular calcium ferrite, which enhances the sinter strength. When using limonite ore as the main raw material, high oxygen consumption, lower maximum temperature of sintering bed, higher cooling rate and larger porosity of sinter are observed.

Mineralisation behaviour of iron ore fines in sintering bed with flue gas recirculation

Implementing flue gas recirculation brings changes to gas conditions across the sintering bed, significantly influencing the mineralisation behaviours. Compared with the conventional process, the O2 partial pressure of the sintering bed decreased while COx partial pressure increased, whereas the contents of bonding phases reduced, leading to an increase in porosity and the magnetite content in the product. Simultaneously, the reduction disintegration index of sinter products decreased owing to an increased in porosity. The phase development in roasted products showed that hematite and calcium ferrite were formed in the condensation and cooling processes while more magnetite and silicate were presented in the combustion and melting processes. Consequently, the sinter products with 30% flue gas recirculation ratio were qualified as conventional sinter.

Research on NOx Reduction by Applying Coke Breeze Pretreated with Urea Additive in Iron Ore Sintering Process

Compared with the traditional de-NOx processes by cleaning the waste gas, a new approach for reducing the formation of NOx during sintering process is proposed. Since more than 90vol% of NOx comes from the fuel combustion, the influence of sintering coke breeze pretreated by CO(NH2)2 additive on the NOx emission is researched. As adding CO(NH2)2, the reduction agents (NHi) are generated during the pyrolysis of CO(NH2)2, which reinforce the NOx reduction, And the appropriate content of CO(NH2)2 is 1.0 mass% of coke breeze.