Nitrogen issues in residue hydrogenation accidents
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1. Residue hydrogenation is equipped with emergency pressure relief facilities; when should accident nitrogen be used, and does the refinery need to have a dedicated pipeline network for accident nitrogen? 2. What is the purpose of having low-pressure and high-pressure nitrogen gas networks in refineries, such as 0.8MPA and 2.5MPA? 3. How should the residue hydrogenation unit respond in the event of a complete power outage across the plant? How can anti-freezing measures be implemented during winter in the northern regions? With few sealing points in the reaction system, how can the oil be removed and the unit restarted? How can the heavy oil inside the reactor be replaced? Terrifying:funk: Trouble! 4. The residue hydrogenation unit is starting up; what are some effective ways to raise the temperature in the thermal fractionator above the temper embrittlement temperature in order to minimize the startup time? Looking forward to guidance from experts.
1 The accident nitrogen is primarily used to be injected into the system when the bed temperature rises too high, in order to terminate the reaction and cool the catalyst bed in the reactor, thereby preventing the catalyst from being damaged due to excessive temperatures. At this time, strict requirements are placed on the purity of nitrogen, which must be above 99. 99%, and the system pressure must be lower than the pressure of the emergency nitrogen when it is introduced! 2 As we all know, the nitrogen pipeline network is a safety system in various refineries, used for isolation, pressurization, purging, cleaning, and more. There are also sealed tanks for various devices, etc. The division into different pressure levels is intended to facilitate operation and save energy; it’s not practical to use 2 when only a small amount of nitrogen is needed. 5Mpa of nitrogen – actually, 0.85 is sufficient! Achieve energy savings! A power outage on a large scale requires an emergency plan for the unit or workshop; in such cases, operations are usually halted immediately! Antifreeze formation is indeed a problem in the north, so proper management is necessary, along with higher requirements for insulation. Regarding the issue of removing oil during startup and shutdown, the common practice is to increase the speed of the recycle hydrogen compressor in order to circulate the oil, with a high liquid level serving as an indicator that there is no increase in oil volume 4 When it comes to starting work, there’s no need to rush. We need to proceed steadily. Follow the instructions of the unit technician step by step. There are specific requirements regarding the initial temperature rise of the catalyst, as this can affect its activity. During this period, various tests must also be carried out carefully, including system airtightness checks, static and dynamic pressure drops, cold hydrogen tests, and emergency pressure relief tests. If the temperature is increased or the amount of material processed is raised too quickly, it could lead to leaks at other flanges, fires, or even explosions – so what should be done in such cases? Specific requirements also need to be determined based on the actual situation; there’s no rush! I’m not sure if this will be helpful to you! :handshake :handshake Last edited by byrant on 2007-12-13 09:38 ]
Regarding the several issues you mentioned, I will address them separately: 1. Compared to the amount of circulating hydrogen, the amount of nitrogen used in accidents is much smaller; therefore, the cooling effect it has on the reactor is very limited. Its main purpose is to remove the oils from the catalysts inside the reactor, replace the hydrogen present there, reduce exothermic reactions, and prevent further increases in the temperature of the catalyst bed. After the bed temperature exceeds the limit, pressure is first released; then it is determined based on the bed temperature whether there is still an upward trend, and if so, accident nitrogen is used. A large amount of nitrogen is required for emergency use, so dedicated storage tanks are necessary. For ease of management, these tanks are located within the facility; refineries generally do not install dedicated pipelines for emergency nitrogen. 2. The pressures of nitrogen aren’t limited to those you mentioned; each factory has its own classification system. Conventionally, it is divided into low-pressure nitrogen and medium-pressure nitrogen: low pressure: 0.4~1.0 MPa, medium pressure: 1.5~3.0 MPa. Nitrogen pressure grading is primarily aimed at rational energy utilization; where low-pressure nitrogen can be used, such as for purging compressors or for nitrogen isolation, there is no need to use medium-pressure nitrogen. In some applications, higher-pressure nitrogen is required due to process specifications, while in other cases, using low-pressure nitrogen poses a risk of backflow. The temperature inside the reactor will not drop too low in the short term, and there is no issue using recycled hydrogen to carry oil. 3. Regarding winter anti-freezing measures, it is crucial to ensure proper heating of the equipment first. 4. Use a feed line with high-temperature regulation.
During the study*, thank you all for sharing