Kinetics Study of Reduction / Sulfidation of ZnO and Zinc Titanate Powders in a Drop-Tube Furnace
The reaction kinetics of fine particles of zinc oxide and zinc titanate with H2S were studied using a drop-tube furnace in order to test the potential of the sorbent injection hot-gas desulfurization process. Fine ZnO sorbent particles with diameter smaller than 50 tm were sulfided with H2S and/or reduced with H2 in a laminar flow reactor over the temperature range of 620-910 C. The reacted sorbent particles were separated from gas and size-classified using a cascade impactor and an absolute filter. Sulfidation conversion was measured by thermo-gravimetric analyses and compared for different particle sizes and reaction conditions. Other sorbents such as zinc titanate, metallic zinc, and ZnO with different porosity were also tested and compared. In the experiments of the reduction of ZnO without H2S, it was deduced from the change of size distribution of particles that a significant amount of Zn was formed and vaporized. On the other hand, the presence of H2S suppressed the change of size distribution of particles. This suggests that H2S suppresses the reduction of ZnO by rapid surface sulfidation and/or that gaseous Zn reacts with H2S immediately and forms fine particles of ZnS, most of which deposit onto the original particle surface. Formation and vaporization of elemental Zn from zinc titanate sorbents was slower than from zinc oxide with and without H2S. Surface reaction rate of ZnO and zinc titanate sulfidation was obtained and a reaction model for a single particle was formulated and compared with experimental results in the drop-tube furnace. Thesis Supervisors: Professor Maria Flytzani-Stephanopoulos Professor Adel F. Sarofim
Development of a Simultaneous Sulfur and Dust Removal Process for IGCC Power Generation System
Kawasaki Heavy Industries, LTD.(KHI) has been developing a moving bed gas cleanup process for the Integrated Coal Gasification Combined Cycle Power Plant(IGCC). Its main features are cross flow type reactor removing sulfur and particulate from gas simultaneously and the granular material which contains iron oxide as an absorbent of H2S and COS. Results of laboratory studies of sulfidation and regeneration characteristics of iron oxide sorbent, bench scale moving bed experiments, and reaction model analysis are discussed. Moreover, direct sulfur recovery from the sorbent regenerator offgas is studied and a suitable catalytic reduction process of SO2 with coal gas directly to elemental sulfur is obtained. An advanced test treating 1,000m3N/h of product gas from an entrained flow coal gasifier is being prepared.
Phase characterisation of simulated high burn-up UO2 fuel
Abstract To determine the lattice constant variation with burn-up and the oxidation behaviour at high temperatures, simulated UO2-spent fuels with burn-ups up to 200 GWd tM−1 were prepared by cold pressing and sintering and characterised by X-ray diffraction analysis and thermogravimetry. The fcc-lattice parameter of the sintered samples determined at room temperature, showed a continuous decrease with the simulated burn-up. During oxidation the conversion of the simulated fuels to the (U,FP)4O9 and (U,FP)3O8-type phases was strongly delayed when the simulated burn-up exceeded 80 GWd tM−1. Also, at high burn-ups (>100 GWd tM−1), large fractions of the (U,FP)4O9-type phase remained untransformed to (U,FP)3O8 after prolonged exposure to air at 950–1000°C. This suggests a marked widening of the (U,FP)4O9-phase field when the amount of substituted uranium atoms exceeds values of about 8%.