Downward Particles Flow Characteristics In The Outlet Area Of A Combined Restraint Riser

There are many researches and applications of combined restraint riser in the form of“riser- gas-solid distributor- fluidized bed” in the field of petroleum refining. The main features of this reactor is outlet structure of “gas-solid distributor- fluidized bed”.Downward particles and clusters is not only a visual reflection of outlet restraint, but also an important factor of affecting gas- solid overall flow characteristics in the outlet area of a riser. In this paper the research area is near outlet of the riser upper part and the research object is downward particles. The flow parameters of downward particles is measured and compared with the conventional riser. It is through the comprehensive analysis of downward particles flow characteristics in the outlet area of a combined restraint riser in order to provide reference of deeply revealing the influence mechanism of “gas-solid distributor- fluidized bed” outlet.Experimental results showed that it can be divided into three regions along the axial direction in the outlet area of a combined restraint riser: ① Ⅰarea-- the synergistic effect area of outlet restraint and reducing structure; ② Ⅱarea-- the synergistic effect area of outlet restraint and gas lift; ③ Ⅲ area-- the effect area of gas lift. The dynamic properties of downward particles cluster and downward particles is related. The radial distribution of downward particles local solids hold-up, velocity, back-mixing ratio and downward particles cluster local solids hold-up, velocity, frequency, existence time, size are lower in the center region and higher in the wall region. In the radial these parameters increase with decrease of superficial gas velocity and distributor opening rate, increase with increase of solids flux and upper fluidized bed pressure drop. These parameters are first increased and then decreased, and then increased along the axial direction in the riser outlet area.Downward particles cluster frequency is opposite. There is a corresponding relationship between the downward particles cluster characteristic and flow parameters. Downward particles cluster size increases with decrease of frequency, increases with increase of downward particles cluster velocity and solids hold-up. Downward particles cluster frequency increases with decrease of downward particles cluster velocity and solids hold-up.Downward particles cluster increases with increase of downward particles cluster velocity.Comprehensive research on the effects of superficial gas velocity, solids flux, upper fluidized bed pressure drop and distributor opening rate, a relationship about different axial and radial positions downward particles cluster size in the synergistic effect area of outlet restraint and gas lift is correlated, of which the average relative error is within 7.5%.