What are the basic procedures for starting up and shutting down the pre-hydrogenation system (using reformer hydrogen)?

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The startup steps for the pre-hydrogenation system are roughly as follows: (1) Catalyst drying. Similar to catalyst reforming, catalyst drying is one of the important steps in starting up the pre-hydrogenation system. This is typically carried out at a pressure of 0.5 MPa, with the oxygen content in nitrogen being ≥0.5% and the (hydrocarbons + H2) content being ≥0.5%; the temperature is then raised to the required drying temperature [such as 350°C] to remove any moisture and condensed water present on the catalyst. After drying is complete, the temperature is reduced to 200°C; pre-vulcanization and oil feeding are carried out depending on the operation status of the reformer (vulcanization is not necessary if desired). (2) Starting up with reformed hydrogen – After hydrogen is produced via reforming, reformed hydrogen is used to raise the pressure in the pre-hydrogenation system to the required level [e.g., 2.0 MPa]. Ignition and heating are carried out until the temperature at the reactor inlet reaches the value required for pre-sulfidization or feed introduction; at that point, pre-sulfidization or feed introduction can also be undertaken. Conditions for feed introduction (the feedstock is usually refined oil): Temperature: 250–300°C; Pressure: Reach the desired level (e.g., 2.0 MPa); Feed rate: 50% of the design value. If pre-vulcanization is to be done, it should be carried out before oil is introduced. Before feeding the pre-hydrogenation feedstock, it is also necessary to consider a heating and circulation cycle using refined oil in the dehydration tower, so as to ensure smooth synchronization with the startup of the pre-hydrogenation system. When the pre-hydrogenation product oil enters the evaporation and dehydration tower, and all conditions are normal as well as the quality of the oil at the bottom of the tower meeting the requirements for reforming, it is also possible to supply feedstock to the reforming system earlier, thereby saving stored refined oil. If external hydrogen is available, pre-hydrogenation can also be carried out prior to the start of reforming to produce refined oil for use in that process. The basic procedures for shutting down the pre-hydrogenation system are as follows: For the pressurized type of pre-hydrogenation, shutdown of this unit takes place before the shutdown of the reformer. Specifically: ① The temperature of the reformer is reduced to 460°C, after which refined oil is used; ② The temperature of the pre-hydrogenation unit is reduced to 300°C, at which point feeding of oil is stopped and the reformer hydrogen is used for cooling; ③ The oil produced during this shutdown and cooling period is transferred to the gasoline tank. For cyclic pre-hydrogenation, once the reforming temperature drops to 460°C, it is disconnected from the reforming system, and both systems cool down and shut down separately.