What are the most important issues to pay attention to during the maintenance of high-pressure hydrocracking units? ?

When removing the agent, pay attention to: 1. The unloaded catalyst is directly placed in iron drums and covered with dry ice; after the lids are tightly sealed, it is transported to a safe location for storage. Consider whether the dry ice is ready. 2. During unloading, care must be taken to prevent the spontaneous combustion of ferrous sulfide; the reactor should be protected with nitrogen, and a temporary nitrogen line should be connected at the reactor outlet or the cold hydrogen valve. If an increase in bed temperature is detected, measures such as increasing the nitrogen flow rate or adding dry ice should be taken immediately. 3. It is best to have a professional company carry out the degreasing process, as it is usually done under anaerobic conditions. It can save one a lot of trouble. 4. After the descaling is completed, the reactor must be neutralized and cleaned; when cleaning, use demineralized water to prevent corrosion caused by chloride ions. During maintenance, care must be taken to prevent spontaneous combustion of ferrous sulfide in the equipment. Before opening the access panels on the equipment, it is essential to confirm that the conditions for doing so are met, and that areas where ferrous sulfide tends to accumulate have been passivated ； Consider the process carefully; when removing the cores from some heat exchangers, have fire-fighting water ready to be used as soon as the cover is opened. Be careful of hydrogen sulfide poisoning; therefore, ensure that the pipeline equipment has been thoroughly purged. When using equipment to open manholes, it is important to ensure proper ventilation and to monitor oxygen levels. It is advisable to have warning signs at the manholes to prevent people from entering accidentally and suffering from asphyxiation. During the handover, it is essential to provide clear instructions; one must be aware of which pipelines are movable. Additionally, during maintenance work, many safety hazards such as falling objects from heights must be taken into account; therefore, proper safety training is essential, and it is advisable to have safety warning signs in place at the work site. With so many people around, it’s necessary to take precautions against theft (after all, there are still people who need stainless steel bolts and things like that:lol :lol)

What was said on the 2nd floor is very good – it prevents spontaneous combustion due to ferrous sulfide and protects against hydrogen sulfide poisoning. Prevent suffocation accidents during nitrogen displacement.

1. Catalyst deactivation – Deactivation should be carried out by specialized companies in this field; there are several such companies in China that perform this task excellently, as they have qualified personnel and the necessary equipment. Prepare dry ice for use during degassing to cool down. The removed waste materials need to be stored in a dedicated area. 2 Inspection of the reaction system and internal components of the reactor ⑴ Check the purging and drain of condensate at the lowest points in the reaction system; no water or oil should remain in the equipment and pipelines within the system ； ⑵ Before workers enter the reactor, it is essential to thoroughly purge and replace the gas inside the reactor. Sampling and analyzing the gas within the reactor must be carried out to ensure that its oxygen content is above 20% before workers are allowed to enter. Safety comes first, and no negligence is permitted. ⑶ After the cleaning company cleans the reactor, it assigns a specialist to conduct a thorough inspection of it to ensure that there is no moisture, dust, or waste catalyst inside. Filling can only be carried out after passing the inspection: a. Great attention should be paid to the inspection of the outlet collector inside the reactor; b. Check whether the distribution tray is clean and level. c. Check whether the cold hydrogen tank is installed in accordance with the requirements. Check whether the cold hydrogen tank is clean and level; its levelness should be within the normal range. Ensure that the quench hydrogen nozzle is not blocked. d. The catalyst gel and lumps on the inner walls of all pipelines as well as on the internal components must be removed completely. e. Effective measures should be taken to protect the sealing surfaces of the top of the reactor and other removed flanges; apply grease to these surfaces and cover them with temporary lids. 3 Inspection of the catalyst loading site ⑴ The catalyst loading area (the floor and the top platform of the reactor) should be cleaned thoroughly; there should be no debris, and sufficient rags should be available or rain shelters should be set up. ⑵ The lifting hopper and the filling hopper should be clean, free of rust and other debris. ⑶ Lifting equipment such as cranes and electric hoists used for loading catalysts, as well as tools like sieves, scales, tape measures, ladders, hoppers, canvas hoses, wooden rakes, and levels, are all ready. ⑷ Dust removal and ventilation equipment is ready. ⑸ The equipment for on-site communication and the lighting fixtures for work illumination are ready. 4 Inspection of catalysts ⑴ Follow the order in which the catalysts were loaded, and transport the catalysts of corresponding grades from the storage warehouse to the site in batches. During transportation, it is essential to handle them gently, unload them carefully, and arrange them in an orderly manner ； ⑵ There should be a dedicated person to keep track of the quantity (number of barrels) and types of catalysts transported ； ⑶ Check the storage, transportation, and handling of the catalyst (to determine if it has absorbed moisture or become contaminated) ； Check the condition of the catalyst for any damage and keep a record of it ； If in the catalyst

1. The impact of deposits inside the equipment. After operating for a period of time, a large amount of iron sulfide impurities accumulate in the system; during production fluctuations, some of this iron sulfide can be carried away by the jet fuel, affecting the corrosion compliance rate. Therefore, during maintenance, the impurities in the heat exchangers and distillation towers should be thoroughly cleaned. 2. Preparatory work before tower maintenance: ① After shutting off the steam, release the pressure inside the tower and remove all oil remaining in it ； ②Install blind flanges on equipment and pipelines connected to the tower ； ③Open the vent blind at the top of the tower to allow steam to escape ； ④Steam dehydration ； ⑤Steam is introduced slowly into the tower without causing overpressure; steam is visible at the tower top ； ⑥Steaming tower ； ⑦After the cooking tower operation is complete, drain all the condensed water from within the tower; after cooling, open the manholes in the tower from top to bottom ； ⑧Before maintenance, proper safety measures against fire, explosion, and poisoning must be taken ； ⑨To analyze and test gases inside the tower, safety requirements must be met. 3. Heating furnace maintenance: During shutdown for maintenance, cleaning the scale accumulated on the surface of the furnace tubes can also enhance the convective heat transfer process, thereby reducing the flue gas temperature. 4. Heat exchanger maintenance: The characteristic of hydrosulfuric acid stress corrosion cracking is the brittle cracking that occurs in a certain metal (steel) under the combined effect of tensile stress and specific corrosive agents. Austenitic stainless steels are relatively sensitive to sulfide stress corrosion cracking. Stress corrosion cracking caused by polythiosulfuric acids (H2Sx06, x=3–6) also falls under the category of sulfide stress corrosion cracking, and it is generally intergranular cracking. During the shutdown of a refining unit, when the system’s temperature and pressure drop, water vapor is condensed; or when the equipment is opened for maintenance, its interior and pipelines come into contact with moist air. When iron/chromium sulfides react chemically with water and oxygen, sulfurous acid and polythionic acid are formed, thereby causing corrosion. In petrochemical plant equipment, sulfide stress corrosion cracking of austenitic stainless steel or pipelines is commonly observed. Polyoxysulfate stress corrosion cracking has also occurred in hydrogenation units. For this reason, multiple breakage damages occurred to the connection bolts of the floating head covers on several condensers in some hydrogen desulfurization units in Japan.

Maintenance is the phase with the highest safety risks for the installation; first and foremost, attention must be paid to safety issues such as suffocation, hydrogen sulfide poisoning, and spontaneous combustion of ferrous sulfide. Secondly, there is the problem of corrosion of stainless steel equipment by polysulfuric acid, especially in the overhead coolers of the distillation system. Additionally, during maintenance, the welding quality of high-voltage areas must be carefully monitored; otherwise, it could lead to serious safety hazards.