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.
Circulating characteristics of return particles in circulating fluidized bed
In order to investigate the process of circulating particles returning to the main flow and to make the further discovery about the circulating characteristics of the particles in circulating fluidized bed(CFB).The cold model experimental system of the particle flowing from the top of the CFB was set up.The gas-particle two-phase flow and the mass concentration of particles in the tower were measured by using the 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 returning to the main flow were investigated.The results indicate that the process of the particles returning to main flow can be divided to three parts: the return field,the mixing and accelerating field and the main flow field.The return particles make the flow field become non-homogeneous.The main factors which influence the back flow length are the mass flow rate and the superficial gas velocity.
Similar profiles of solid flux in circulating fluidized-bed risers
Results of detailed experimental measurements of solids mass flux profiles in circulating fluidized-bed risers of internal diameter 0.152 and 0.305 m are described. The ranges of superficial gas velocity and mean solids mass flux used were 3–5 m s−1 and 2–111 kg m−2 s−1, respectively, and the solids used had a surface-volume mean diameter of 74.9 μm and a particle density of 2456 kg m−3. The existence of the “similar profiles” regime first suggested by Monceaux and co-workers is confirmed. In this regime of gas—particle upflow radial profiles of reduced solids flux (local solids flux divided by cross-sectional mean solids flux) are insensitive to changes in imposed solids flux at a given superficial gas velocity. This regime is found to lie within the refluxing transport regime, characterized by a dilute, rapidly rising suspension in the core surrounded by a slowly falling denser suspension in the region adjacent to the walls. The onset of the similar-profiles regime is studied in detail and it is found that the mean solids flux, at which this regime begins, increases with superficial gas velocity. The authors' experimental findings are linked with those of other workers to produce a semi-empirical model for this regime capable of predicting profiles of solids flux and solids velocity. Comparison of predicted solids flux profiles with experimental data is very encouraging and indicates that, although the flow patterns in such vertical gas—particle systems are complex, their fluid-dynamic analysis may be relatively straightforward.