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• What potential limitations might arise when attempting to reduce the coke drum pressure to the design values in Delayed Coker Units? Additionally, what types of investments might be necessary if we aim to further decrease the pressure?

  Aug-2024

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Answers

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

  The pressure in the coking drum is defined by the pressure in the top vessel of the main fractionator where the pressure is controlled and added to the pressure drop between the fractionator and the transfer line between the coke drum and the fractionator. The main effects related to the reduction of the pressure in the coke drum is a higher volumetric flow rate of the gases inside the coke drum once it will make easier the vaporisation of the heavier fractions of the feed. This will lead to these consequences:
  - Raise the risks of foam formation inside the coke drum, leading to the higher risks of coke deposition in the transfer line and the bottom of main fractionator;
  - Reduction in the naphtha and light coker gas oil (LCGO) yields raising the yield of heavy coker gas oil (HCGO) once the residence time of the feed in the coke drum will be shorter;
  - Reduction in the coke production and quality raising the risk of shot coke production, mainly for extremely heavy feeds.

  As previously described, the decision to severely reduce the operating pressure of the coke drum should consider the side effects related to quality degradation of the streams and coke as well as their impacts over the downstream processes like the hydroprocessing units. The main systems which need to be verified in a reduction in the operating pressure of the coke drums are the capacity of the main fractionator aiming to deal with the additional volumetric flow rate of gases as well as the adjacent systems like the transfer line.

   

  Sep-2024