What are the precautions for shutting down a hydrorefining unit?

Be careful to avoid hydrogen sulfide poisoning; please read the following report: On May 11, 2007, an incident of hydrogen sulfide poisoning occurred at the diesel hydroprocessing unit in the hydrorefining complex of Urumqi Petrochemical Company’s refinery during a shutdown period, resulting in 5 people being poisoned, 2 of whom fell from a height after being poisoned. On May 11, the hydrogenation refining unit of the refinery at Urumqi Petrochemical Company carried out maintenance work on the diesel hydrogenation plant. At 14:50, the new hydrogen compressor of the reaction system was stopped, and the boundary valve that supplies new hydrogen to the device’s new hydrogen tank was closed; preparations were made to install a blind flange behind this valve (the valve is located in a pipe rack, 4.3 meters above the ground). At 15:30, the new hydrogen tank was depressurized. At 18:30, the pressure in the new hydrogen tank increased, so the tank was depressurized again. At 18:50, the supervisor in charge of the maintenance work led four workers to the site; the supervisor and a staff member from the workshop monitored the situation on the ground. At 19:15, after loosening all eight bolts, the workers removed the upper two bolts; suddenly a stream of air was emitted, and a worker on the downwind side collapsed on the tunnel deck. The other workers immediately rushed to provide assistance. A worker fainted during the process of removing the safety belt to carry out rescue, and then fell through a gap in the pipe tunnel. The two supervisors immediately went to the workshop to call for help. A process technician and two operators from the workshop rushed to the scene to provide assistance. The process technician was poisoned while trying to rescue others and fell from the scaffolding, while the two operators also became poisoned one after another. Other rescuers who arrived wore air respirators, climbed into the pipe gallery, and rescued the poisoned individuals to the ground before transporting them to Urumqi Petrochemical Workers’ Hospital for treatment. Upon investigation and analysis, the main cause of the accident was that after the flange of the boundary valve on the new hydrogen tank was opened to allow communication with the atmosphere, the drain valve at the bottom of the new hydrogen tank, which was connected to the low-pressure gas venting and liquid separation tank, was not properly closed or suffered from internal leakage. As a result, low-pressure gas containing high levels of hydrogen sulfide entered the new hydrogen tank and escaped through the open flange, causing poisoning among the workers and those carrying out rescue efforts. The accident revealed a lack of safety awareness among some of the plant’s grassroots units; after an abnormal increase in pressure in the new hydrogen tank, they proceeded with operations without conducting inspections and verifications in accordance with the established production control procedures ； Construction workers carry out their work blindly without sufficient identification of the hazards associated with it ； The rescuers carried out emergency rescue efforts without taking any preventive measures, resulting in additional injuries to people and an escalation of the consequences of the accident. At the same time, it also reveals weaknesses in safety management, gaps in the controlled management of production, as well as insufficient attention and inadequate measures to prevent hydrogen sulfide poisoning accidents.

There is a difference between normal shutdowns and shutdowns in the event of a failure or emergency. I’m not sure which one you specifically mean? But personally, I believe that in any case, shutting down the hydrogenation section is of utmost importance. It’s because of the high temperature and pressure, plus that nasty substance H2. Our facility once experienced an H2 leak; thinking about it now still gives me chills. Therefore, analysis and testing of hydrocarbons, gas, and air/oxygen must be carried out. For safety reasons, the stabilizer tower, hydrogen, and recycled hydrogen should be separated from air; meanwhile, if HC is not completely removed, the possibility of sulfur and polymer formation must be eliminated (it is important to protect the catalyst).

What are the precautions for shutting down a hydrorefining unit? ⒈Be careful to connect high voltage to low voltage ； ⒉Preventing hydrogen sulfide poisoning ； ⒊Implementation of maintenance tasks, materials, and teams ； ⒋Implementation of safety measures. Wait.

It seems to me that information regarding precautions for shutting down the equipment as well as some related accident cases should be shared on forums, so as to keep a constant warning signal active.

1. Nitrogen purging and steam cleaning must leave no dead corners. 2. The rate of temperature and pressure reduction must be strictly controlled in accordance with the requirements. 3. The reaction system, low-pressure areas, and other locations containing hydrogen sulfide must pass analysis before manholes can be opened. 4. Construction and maintenance should comply with specifications.

It is mainly considered from two aspects: one is equipment safety, and the other is catalyst activity. Regarding equipment safety, factors such as the rate of temperature and pressure reduction And the level of high-boiling-point liquids are taken into account. As for catalysts, their resistance to damage and their activity are important considerations; when it comes to temperature reduction, factors such as the thoroughness of oil removal and the H2S content in the recycled hydrogen are considered, along with the CO concentration and other factors.

Personally, I believe that the shutdown plan should be followed strictly. In reality, there is often a tendency to seek quick results and to rush things, which leads to mistakes. It is essential to emphasize the seriousness of this plan, ensure unified command and action, and prevent situations where different leaders have different ideas or plans.

1. To prevent overheating of the reactor bed, the principle of cooling first and then reducing the flow rate should be followed. 2. To prevent catalyst damage, after feeding to the reactor is stopped, the system should be kept circulating with the highest possible amount of recycled hydrogen until the oil in the feed lines and the reactor has been completely purged. 3. After stopping the feed, flush hydrogen should be introduced immediately into the fresh feed line; the introduction of hydrogen must be done slowly to prevent high-pressure flanges from leaking due to thermal shock ； When a flange leaks due to cooling, steam should be used promptly to purge the oil and gas in order to prevent ignition. 4. Regarding the temper brittleness of chromium-molybdenum steel, pressure limits must be observed during shutdown, and the cooling rate should be less than 25°C/h ； When opening stainless steel equipment, be aware of the risk of stress corrosion cracking due to persulfuric acid ； Before opening the reactor, it must be cooled to below 40°C, and simultaneously purged thoroughly with nitrogen to reduce the risk of spontaneous combustion from hydrocarbon-oxygen compounds and iron sulfide. 5. The distillation system should avoid vacuum formation due to overcooling in the columns; if steam purging is not carried out in a column temporarily, nitrogen should be introduced into the top reflux drum to maintain positive pressure. 6. The contaminated oil must be thoroughly stripped before being discharged into the contaminated oil system, to prevent hydrogen sulfide from causing harm to operators.

1. The reactor bed temperature must not exceed the limit. 2. Protect the catalyst by using hydrogen for circulation. 3. The cooling rate should not be too fast. 4. Implement nitrogen protection measures

Simply put, there are two points: protecting the catalyst and the equipment. Follow the shutdown plan strictly; under no circumstances take shortcuts to save time. The emergency shutdown is primarily to prevent high pressure from affecting low pressure and to protect the catalyst.

Reduce temperature first then volume; increase volume first then temperature; reduce pressure first then temperature. Prevent overheating and overpressure