| Chemical looping hydrogen generation ?CLHG? is a novel technology for hydrogen generation. It can produce hydrogen of high purity without complicated system and catalyst. Fe2O3 is considered to be the best oxygen carrier for CLHG process. In this paper, iron ore was used to be the oxygen carrier for experimental investigation on CLHG process. Iron ore has a wide distribution in nature. Its main component is Fe2O3 and also has a small part of other components, so its reaction characteristics are different from single Fe2O3. At present, there are few studies of iron ore for CLHG process, so it has great value of research.Experiments on chemical looping hydrogen generation were conducted in a fluidized bed reactor with Australian hematite as oxygen carrier. The effect of reaction temperature and concentration of reduction gas on reduction reaction kinetics and hydrogen generation process was examined, and cycle characteristics were also researched. The results indicated that the reduction process of iron ore was speeded up by the increase of reaction temperature and concentration of reduction gas, the reaction activation energy was on a decreasing trend, and the volume of generated H2 also increased. In the cycle process, the weight loss of iron ore and the volume of generated H2 showed a decreasing trend. XRD analysis results showed that few FeO and Fe were generated by iron ore in the reduction process of subsequent cycle. Surface sintering of iron ore was observed during the cycle process from SEM analysis results.In order to improve the reaction characteristics of iron ore as oxygen carrier, KNO3 was used to be the modified compound for iron ore. The effect of reaction temperature and KNO3 ratio on reduction reaction kinetics and hydrogen generation process of the modified oxygen carrier was examined, and cycle characteristics were compared with the characteristics of unmodified iron ore. The results indicated that the reduction process of the modified oxygen carrier was speeded up by the increase of reaction temperature and KNO3 ratio, the reaction activation energy was on a decreasing trend, and the volume of generated H2 also increased. KNO3 was reacted with iron ore in the preheating process, and the generated substances had good catalytic effect. In the cycle process, the weight loss of the modified oxygen carrier and the volume of generated H2 remained stable, and had a great increase compared to the unmodified iron ore. FeO and Fe were generated greatly by the modified oxygen carrier in the reduction process of subsequent cycle, and no obvious surface morphological change was observed. The content of K was decreased during the cycle process, especially in the first cycle, but the content remained stable in the subsequent cycle.During the reduction process, a small amount of deposition of carbon will be generated by the catalytic effect of iron ore as oxygen carrier, then CO and CO? will be generated in the hydrogen generation process and the purity of H2 will be decreased. In order to solve the problem, carbon deposition characteristics of unmodified and modified iron ore with KNO3 were investigated. A transitory intermediate oxidation process was added between the traditional reduction process and hydrogen generation process of CLHG. The results indicated that in the middle and later periods of reduction process of both unmodified and modified iron ore, a small amount of deposition of carbon generated, but the purity of generated H2 increased from 98.19% to 98.59%. After adding intermediate oxidation process, the volume of generated H2 of modified iron ore was decreased about 9.4% compared to the traditional process, but the purity of H2 could get up to 99.9%. In the cycle process, the volume of generated H2 still remained stable with the intermediate oxidation process added. The volume was decreased about 16.7% compared to the traditional process, but the purity of H2 could also get up to 99.9%. The chemical components and surface morphological of oxygen carrier had no significant change after undergoing intermediate oxidation process. |
PDF Full Text Request