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Question

  • In Hydrotreaters for Stripping of H2S from Hydrocarbon stream, Naphtha Hydrotreater unit uses simple steam reboiler at the bottom of the stripper,  whereas Diesel and Vacuum Gas Oil hydrotreaters uses direct steam injection in strippers. why? Why can't we use reboiler system in Diesel and Vacuum gas Oil hydrotreaters strippers instead of direct steam injection?

    Jan-2023

Answers


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

    Normally, there is some limitations in the heat charge in a reboiler due to the thermodinamic and heat transfer restrictions that imposes limits in the maximum temperature reached in a reboiler, by this reason, this strategy is applied for lighter products like naphtha while heavier derivatives like diesel and VGO requires the use of live steam route which is more efective in to promote the stripping performance due to the higher temperature and the reduction in the partial pressure of the hycrocarbon achieved in the strategy of live steam injection. Another factor which that is considered in the design choice is regarding the tolerance of water content in the final hydrotreated product, normally the downstream processes of a naphtha hydrotreating unit do not deal with high water content in the naphtha like the catalytic reforming units for example, leaving to the choice of reboiler strategy in these cases.

    Another consideration that normally drives the choice is the generation of sour water in the strategy of live steam injection for stripping tower, as mentioned above this is normally the choice only for heavier streams due to the costs, environmental, and operational issues associated with sour water stripping units.

     

    Jan-2023



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