| Iron ore sintering is a critical process in steel plants, which can provide qualified iron-bearing material for blast furncace. Iron ore sintering can influence energy consumption of blast furnace and the productivity and quality of pig iron. With the steel production continually increasing in China, this means that sintering plant should provide more sinter and have higher yield. In order to improve the pig iron quality from blast furnace and increase the market competitiveness of steel plants, it is necessary to improve the quality of sitner. With the increasely serious environment problem in China, measurements should be taken to make sure lowest pollution emission in sintering plants which is one of the main pollution sources in steel plants. All this needs that the sinter meachnism should be investigated further to get high sinter productivity, good sinter quality and low emission during iron ore sintering.Sinter productivity is closely related to high-temperature zone resistance during iron ore sintering which controls the sinter bed resistane. But because of high temperature and phase change in high-temperature zone, it is very hard to measure high-temperature zone resistance, the knowledge of high-temperature zone resistance is still not very clear. Although some researchers investigated the NOx emission during iron ore sintering, work about NOx formation and migration is also still insufficient. Base on the mentioned reaearch satus in iron ore sintering, the factors influencing high-temperature zone flow resistance and NOx emission characteristics were investigated during iron ore sintering.Firstly, the influence of temperature and high-temperature zone structure on high-temperature zone flow resistance to airflow was investigated in iron ore sintering. According to Ergun equation, the equantion to calculate the pressure drop when high-temperature zone structure keeps constant was established and the airflow rate can be obtained if high-temperature zone structure has no change by the equation. At same time the sinter pot tests which iron ore was replaced by quartz sand, the rationality and reliability of the equation were validate. The theoretical arithmetic and sinter pot tests show that increasing sinter bed temperature will increase high-temperature zone resistance if high-temperature zone structure has no change. Compared the airflow rates from theoretical arithmetic to those from sitner pot tests, we can find that high-tempertaure zone structure changes during iron ore sintering, gas channels in the middle and bottom layers increase to improve bed permeability.Secondly, a sandwich structure was used to investigate the factors controlling the bed strucutre in high-temperature zone and the influence of sinter parameters on high-temperature zone flow resistance in different layers. Results show that gas momentum is very important for gas channels, increasing gas momentum can get through the close gas channels and dilate gas channels. The change of high-tempertaure zone structure can be quantified. When suction is 8 kPa and coke rate is 4.85 wt.% in the bottom layer, gas channels decrease by 15%.Thirdly, at the basis of previous research and combining SVM regression, a new model which can show the influence of high-temperature zone on sinter bed flow resistance was proposed. The model can be embedded into siniter model to predict sinter airflow rate. The model was validated by sinter pot results and it can predict sinter airflow rate well. The predicted error is in ±20%. The model can illustrate the entitative factors controlling the sinter bed flow resistance after high-temperature zone was established.Fourthly, in order to study the the influence of high temperature flow resistance on iron ore sintering further, sinter pot tests with uniform bed structure was carried out to study the influence of flame front speed on high-temperature zone flow reistance during pisolite ore sintering. Results show that high-temperature zone flwo resistance can affect flame front speed; in turn flame front speed can also have great influence on high-temperature zone flwo resistance.Fifthly, on the basis of mentioned work, a new approach to investigate the relationship between sinter composition and flame fron properties was proposed to investigate the flame front properties in iron ore sintering further. This can make us understand the distribution of high-temperature structure better. Combining the thermocouple, it can make us study the coke combustion from a new view.Finally, the influence of coke combustion on NOx formation and migration in iron ore sintering was investigated by sinter pot tests and simulation. The thermal NOx, fuel NOx, the reactions between C and NOx, CO and NOx were investigated, and results show that NOx emission mainly comes from fuel NOx, the reactions between C and NOx, CO and NOx both can lower NO* emission in iron ore sintering. If N content in the raw materials keeps constant, increasing sinter bed temperature can low NOx and improve sitner quality. |
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