• What is the purpose of Hot H2 Stripping in Diesel and Vacuum gas oil hydrotreater units at 360degC, during shutdown steps for catalyst replacement work?

    Significance of maintaining H2S and not maintaining H2S in the HP loop during Hot H2 stripping? What are the consequences?.



  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    The use of hot hydrogen stripping in hydrotreating units is related to the cleaning the reactor internals previous the maintenance services (hydrocarbon removal) as well as the coking removal over the catalysts which also help the spent catalyst draining step. Another purpose of the hot hydrogen stripping is to reduce the H2S content in the reaction section, previously the access of the maintenance workforce, leading to safer work conditions.

    The hot hydrogen stripping can also be used to minimize the pressure drop of the catalyst bed through the removal of "soft" coke which lay down over the catalyst, over the time this coke can be converted into "hard" coke which is more difficult to be removed, normally requiring a catalyst regeneration step.

    Despite the benefits, the hot hydrogen stripping needs to be carried out carefully once the process can lead to the reduction of the metals in active phases of the catalyst if a very low H2S concentration is applied in the reaction system. By this reason, the catalyst licensors recommend a minimum concentration of H2S in the recycle gas (normally above 1.000 ppm) during the hot hydrogen stripping process to minimize the risk of catalyst deactivation by metal reduction.