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• How do you manage the pressure in the Fractionator within a Delayed Coker Unit? From what I understand, both the Fractionator and Coke Drum pressures are regulated by the inlet pressure of the Wet Gas Compressor. However, during drum switch operations, significant fluctuations in the Fractionator top pressure make it challenging to maintain stable control. Are there any control strategies or philosophies that could be applied to effectively manage the pressure in the Fractionator and Coke Drum in the Delayed Coker Unit in addition to inlet pressure control of WGC?

  Aug-2024

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Answers

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

  The control of a fractionator of a delayed coking unit is really a challenge for the process control experts. The batch characteristics of the delayed coking units lead to sudden variations to the mass and energy flow rates to the fractionator during the coke drum switch, where the hydrocarbon vapour flow to the column is practically cutted off. Normally, these disturbances are minimised through the anticipatory manipulation of circulating refluxes, side flow rates, and other heat sources capable to restore the energy and mass balance in the fractionator and minimise the disturbances, this control strategy demands a lot of agility and training from the operating personal and failures can lead to the production of off-spec streams which will cause financial losses and operating issues in the downstream units like hydrotreating units.

  Due to these characteristics the conventional feedback process control strategy is not adequate to manage the operational challenges of delayed coking fractionators. In the literature it's possible to find publications describing advanced process control strategies for delayed coking fractionators using multivariable predictive control and inferential quality estimators in order to minimise the disturbances caused by the process variations in delayed coking units. An excellent reference about this topic is the article published in the Q3 2016 issue of PTQ Magazine by Mr. Dinesh Jaguste titled Handling delayed coker disturbances with APC, which you can READ HERE

  Sep-2024