On dehydrogenation of the hydrogenation reactor wall
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During the shutdown process, and to maintain a constant pressure during the dehydrogenation at a constant temperature on the reactor walls, should nitrogen or hydrogen be used?
It’s not needed now, as the materials have been upgraded.
Many plants within Sinopec’s system have clearly decided to stop carrying out isothermal dehydrogenation.
Hydrogen is used in the isothermal oil-cooled process; there is no isothermal dehydrogenation step. The material used for reactors is usually austenitic stainless steel, which offers good quality. For medium or high-pressure hydrogenation, nitrogen cannot be used due to its inability to be compressed at sufficient pressures, and the exhaust temperature of the compressor also remains high, which hinders the proper operation of the system. Additionally, using nitrogen requires large quantities of it, resulting in waste. After the isothermal oil-cooled process using hydrogen is completed, the reaction system is brought to a slight positive pressure, and then nitrogen is used to displace any remaining gases to ensure purity.
It cannot be said that the reactor material is austenitic stainless steel. The base material is usually chromium-molybdenum steel or vanadium-added chromium-molybdenum steel, to which austenitic stainless steels such as 347, 321, 316, and 309 are surfaced welded.
Do all surfacing layers made of austenitic stainless steel not require a dehydrogenation process? Are there any other requirements?
Isothermal hydrogenolysis is something that beginners in hydrogenation often come into contact with； But when the device stops operating, this process simply does not take place ； The cooling and pressure reduction rates required during the shutdown process, as well as operations such as hot hydrogen flushing to remove oil from the system, include the reactor dehydrogenation process ；