Reduction Kinetics of Ilmenite Ore for Pressurized Chemical Looping Combustion of Simulated Natural Gas

摘要

Reduction kinetics of ilmenite ore as an oxygen carrier for the chemical looping combustion of a simulated natural gas mixture under elevated pressure was studied using a pressurized thermogravimetric analyzer (PTGA). The fuel gas is a mixture of hydrocarbon, carbon dioxide, and nitrogen to simulate an actual combustion environment. The oxidation phase of the experiments was carried out in air. Effects of temperature (1023-1223 K), total pressure (0.6-1.6 MPa), fuel partial pressure (0.126-0.34 MPa), and CO, partial pressure (pFuel/pCO(2) = 0.5-1) were studied. The results showed that the presence of small amounts of ethane and propane clearly led to a higher ilmenite reactivity at temperatures below 1123 K, but this effect became less significant as temperature increased and completely disappeared above 1123 K. The results also showed that increasing CO2 partial pressure had little effect on ilmenite conversion rate, though it did have some slightly negative influence on ilmenite oxygen carrying capacity that was especially noticeable at lower total pressure. A higher fuel partial pressure appeared to have a slightly negative impact on ilmenite oxygen carrying capacity, especially at higher temperature. A kinetic model based on a phase boundary controlled mechanism with contracting sphere was developed by incorporating the total pressure, fuel and CO2 partial pressures, and temperature, and it was able to satisfactorily reproduce most of the test results with a conversion ratio of up to 70%. This model predicted that the ilmenite conversion rate had a strong positive correlation with the temperature and fuel partial pressure, and a relatively weaker negative correlation with the total pressure and CO2 partial pressures. Overall conversion rate will increase when total pressure increases, which justify the pressurized chemical looping combustion technology.