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From a fluid dynamics perspective, the slurry-bed residue hydrogenation reactor is essentially a multiphase flow in a vertically upward pipe flow. Due to the differences in density between gas, liquid, and solids during this vertical upward movement, the gas flows at a faster speed than the liquid, while the solids drift behind the liquid at a slower speed; this results in turbulence at different heights, that is, a phenomenon of vertical mixing. Conversely, to achieve a highly mixed and stable bed, a certain range of difference in the apparent velocities of gas and liquid must be maintained; lower relative flow velocities lead to the formation of vortices, while an increase in relative flow velocity results in a transition to bubble flow or circular flow. Excessively high flow velocities can even cause misty flow, that is, foaming, which is reflected in monitoring parameters such as temperature differences and density differences. In the design of slurry-bed residue hydrogenation reactors, the ratio of the apparent gas to liquid velocity ranges from 6 to 20; considering the efficiency of the reactor at a certain liquid holdup, a value of 10 is typically adopted in the design. During the upward movement of the liquid in the reactor, due to the central chimney effect, the gas flow velocity is highest at the center, resulting in different sliding speeds of the liquid from the center toward the wall. In various cross-sections, there are flow patterns characterized by an increase in mixing density; this gives rise to the actual flow velocity of the liquid within the reactor (which is greater than the apparent velocity), and this is beneficial for the conversion reactions of residue oil. For hydrogen, as hydrogen is consumed during the reaction, the actual hydrogen retention rate gradually decreases. Meanwhile, due to the lightening of the reaction products and an increase in the proportion of large bubbles, the gas retention rate inside the reactor gradually increases. Therefore, the initial zone and reaction zone of the slurry bed reactor (the height corresponding to 1.5 times the diameter of the distributor) are crucial, which requires a suitable distributor to ensure the appropriate initial size and velocity of bubbles, an optimal initial gas retention rate, liquid circulation speed, as well as efficient mass and heat transfer.