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The slurry bed also has its own \"bed\"; unlike fixed-bed and catalytic fluidized beds where a dense phase is formed by the addition and packing of CAT, the \"bed\" in a slurry bed is gradually established over time as oil-soluble CAT precursors decompose and sulfide over several days (at least 3–5 days). MoS linear catalysts, reaction semi-coke, and metals such as Ni and V are suspended in the dispersed phase (raw material gums, unconverted oil from recycled oil residues) to form a \"slurry\" or \"bed\". This bed provides the spatial environment for thermal cracking and hydrogenation reactions, as well as heat energy, and facilitates heat and mass transfer, enabling a three-phase fluidized-bed reaction involving gas, liquid, and solid. Therefore, before raising the temperature from the initial operating temperature of 370°C, it is essential to determine whether a proper \"bed\" has indeed been formed within the reactor. The key criterion for making this determination is not the Mo concentration in the mixed feed tank, but rather the Mo concentration at the bottom of the vacuum distillation column in the equilibrium phase of the reaction bed. The concentration in the mixed feed tank merely reflects the proportion of fresh reagents added relative to the fresh feed, along with the concentration of CAT in the recycled oil; the actual formation of an initial \"bed\" takes time, and maintaining a stable bed during the process requires replenishment of materials and removal of waste products.