Abstract
In the residual ebullated-bed hydrocracking process, the transportation mediums of catalyst addition/withdrawal drum are heavy distillate oil and catalysts. The bidirectional metal seal floating ball valve used in the outlet pipeline of this drum occurs internal leakage after a period of operation. Aiming at this phenomenon, the computational fluid dynamics and discrete phase model (CFD-DPM) is employed to calculate the erosion-wear of the valve in liquid-solid two-phase flow, and study the erosion-wear characteristics of the ball valve during the closing process. In order to better explain the influence of different openings of the ball valve for the erosion-wear characteristics, the relationship between the erosion-wear rate and the resistance coefficient is established. The results show that the erosion-wear of the valve is more serious when it has a greater resistance coefficient under the condition of constant inlet velocity. When the valve is closed from 60% to 20% relative opening, the erosion-wear rate increases slowly with the change of opening. When the valve is closed from 20% to 10% relative opening, the erosion-wear rate increases sharply with the change of opening. In order to reduce the erosion-wear rate of the valve, different structural optimization schemes are proposed to reduce the resistance coefficient of the valve at a small opening. These schemes include changing the flow channel in the valve ball from a circular cross section to a polygonal cross section and changing the seat structure to change the flow direction of the fluid entering the ball. The results show that the scheme of changing the flow direction of the fluid entering the valve ball by changing the valve seat structure works best, and the erosion-wear rate is reduced by 79.7%.
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