A Fundamental Investigation On Flue Gas Circulation Sintering

Chinese steel industry has developed rapidly in recent years, and the environmental problem caused by ironmaking and steelmaking have also aroused the greatest concern, especially the atmospheric pollution caused by SO2, CO2, etc. Iron ore sintering process is the main source of SO2 generated in the steel industry. The larger equipment investment, higher operation cost, lower desulfurization efficiency, complex by-products and greater technique risks are common drawbacks of the existing sintering flue gas (SFG) desulfurization processes. SFG desulfurization technology is developed slowly hereby.Flue gas circulation sinter process sucked sinter flue gas in sinter layer by circulation system. The novel technology not only can reduce the amount of sinter flue gas, but also make SO2 gas enriched in sinter exhaust gas, which cut the cost of follow-up gas desulfurization process.In this paper, a systematic study on flue gas circulation sinter process, especially its principle and technical parameter, has been done with simulating flue gases.It was shown that reducing O2 content in recycle gas would obviously cause the main output and quality indexes worse, O2 content in recyle gas should be controlled more than 18%; and a-little CO gas existing in recycle gas is favorable for sintering and the latent heat of CO could be used to promote sinters quality; recycle gas with less SO2 has little effect on sinter main output and quality indexes, but when SO2 content in recyle gas is more than 1000ppm, S would be concentrated in sinter. On the whole, when flue gas circulation sinter process is adopted, the most of SO2 enriched in the final exhaust gases, and High-quality sinters would be produced under the suitable processing conditions.The results of the mineralizaiton properties with different O2 content in recycle gas show that:the amount of calcium ferrite decrease after a increase when temperature rising; the maximum generation temperature of calcium ferrite are as follows, hematite and limonite is 1275℃, specularite and magnetite is 1250℃; the maximum generation amount of calcium ferrite, hematite is 73.14%, limonite is 97.13%, specularite is 67.47%and magnetite is 62.88%; effects of O2 content on the amount of calcium ferrite are similar, the more the O2 content in recycle gas is, the larger the amount of calcium ferrite is, on the whole, the high-low sequence of effects of O2 content on the mineralizaiton properties is as follows:magnetite>hematite> specularite> limonite.The behaviour of SO2 in flue gas circulation sintering was studied. In combustion zone, rising the highest temperature of sinter process woulds bring to lower residual sulphur content in sinters; when the SO2 content in recycle gas is increasing and basicity of briquette is rising, SO2 would be enriched in sinters. In over-wetting zone, CaO and H2O is the major factor for absorbing SO2; desorption of SO2 is primarily decomposition of sulphurous acid and sulphite, which occured in drying-preheat zone and combustion zone respectively.