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 cm 2 g 21 , which contributes to achieving a better bed permeability, a faster sintering speed and higher productivity.

In this study, the optimisation model of fuel distribution base on numerical simulation was proposed to reduce the fuel consumption of sintering process. The simulation model of sintering process was carried out according to the heat and mass transfer, and the physical and chemical reactions of sintering. Then the heat income and expenditure of solid mixture in different materials unit was analysed via the simulation model. And the fuel proportion was adjusted on the basis of the difference between total heat quantity and heat quantity that the materials unit required to reach setting temperature. This model was validated by sintering pot test, the simulation results of bed temperature at different depth were very close to the detection results. The sintering pot test shows that the sinter yield and quality indices had little change after the optimisation of fuel distribution, while the solid fuel consumption was decreased by 3.83 kg t −1 .

The catalytic reduction behaviours between NO x and CO in sinter zone were studied as using flue gas recirculation (FGR). Minerals in sinter can act as catalysts during NO x 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 N 2 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 NO x emission during FGR sintering.

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.

The process state of iron ore sintering is characterised via the bed permeability, the temperature rising point, the burn rising point and the burn through point. The intelligent control strategy of sintering process based on fan frequency conversion is put forward. The stability of process state is firstly evaluated based on the knowledge of domain experts. If process state is fluctuating, an expert controller is activated to realise a normal production. If process state becomes steady, then a fuzzy controller is activated to obtain the optimisation of process state and reduce the power consumption of main exhaust fan. The closed-loop control of sintering production showed that the system can realise the optimisation of sintering process state, and reduce the energy consumption of sintering production while ensure the stability of sinter quality indices, it theoretically saves power consumption of 1×10 4 kWh every day.