Experimental Study on the Circulating Characteristics of the Return Particles in CFB and the Validity of the Particles to Desulphurization
The cold-model experimental system that particles flow from the top of CFB reactor is set up to study the circulating characteristics of the particles in the reactor. In order to get further information about the particles distribution and interaction with air flow, the two-phase gas-particle flow and particle concentration in the tower are studied with the use of phase-Doppler particle dynamic analyzer (PDA) system. The effects of the operating parameters including the mass flow rate and the superficial gas velocity on the process of the particles return to the main flow were investigated. The definition of valid internal circulation is put forward in this paper to describe the contribution of the particle to the SO 2 removal reaction. The results showed that the concentration distribution tends to be right high and left low in the radial direction. In axial, more particles concentrated in the upper of the reactor, especially in the case of high superficial gas velocity. With the decrease of the superficial gas velocity, the maximum fallback length of particle and the average particle concentration increase quickly. While the valid particle concentration increases slowly. The quantity of valid particles increases a little. Sending the particle from the top of the reactor has little contribution to the SO 2 removal reaction.
Material Balance Calculation and Experimental Research of Dry FGD Process
During the desulphurization process, the equilibrium concentration of particulates and the time of reaching it can be calculated by the material balance law. Comparison was then made between the stoichiometric concentration and the experimental results. Based on a dry flue gas desulphurization system, the effects of paniculate circulation on the efficiency, resistance profile and operational stability of the system were analyzed and studied. The results show that particulate circulation enhances the desulphurization efficiency by 10%-15%. It takes about 30 min to reach the equilibrium concentration. The experimental results, indicate that the concentration of particulates should be controlled between 600 g/m3 and 1 000 g/m3.
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.