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
Coal Particles Combustion Model and Micro Feeding Technology in Drop Tube Furnace
For investigation of wide use of drop tube furnace (DTF), the design and characterization of DTF and shaftless screw microfeeder are presented. With a developed group combustion model, a introduced non-dimensional number is to characterize the combustion zone of coal particles in DTF. Calculated relation is proposed to be operation criteria of DTF and design principle of feeder. It is found that the test results of coal feeder show good performance for micro feeding.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.