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• What could be the reasons for excessive foaming in DCU reactors, apart from processing a large number of batches produced from crude oil containing a large amount of paraffins? How can this be prevented? We dose an antifoaming agent, but it has limited effectiveness

  Jan-2025

Answers

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

  The foam formation in the reactors of delayed coking units is a common trouble faced by refiners. The use of antifoaming agents is a good strategy but have limited effectiveness as quoted in the question and simply raising the dosage of the antifoaming agent can lead to severe issues to the downstream processing units like hydrotreaters once the antifoaming agents are based on silicon which can plug the catalytic beds. Further the antifoaming agent it's possible to control the foam formation through operating variables as described below: 1 - Feedstock's characteristics: The paraffinic feed tends to present a higher foam level in the reactor than aromatic feeds once the paraffinic compounds cracking faster than aromatics compounds, creating a flow of gas through the liquids in the reactor. Another parameter of the feedstock which can cause foam production is the presence of high sodium and solids concentration in the feed. In this case it's possible to minimize this issue through blending the paraffinic feed with heavier (aromatic) streams like decanted oil from FCC units; 2 - Avoid sudden depressurization of the reactors: This disturbance can cause excessive velocity in the reactor, favouring foam formation; 3 - Inadequate heating of the feed: Some refiners can try to reduce the temperature to minimize the coking issues in the fired heaters and reduce excessively the feedstock temperature leading to an increase of the foam in the reactors. It's necessary to make a balance between the coking of the fired heaters and foaming formation in the reactors; 4 - Excessive velocity in the reactors: The high velocity in the delayed coking reactors can be caused by an excessive flow rate of the feed as well as reduced pressure of the reactors; As described above, acting on the temperature and pressure of the reactors it's possible to minimize the foaming formation. Higher temperature and pressure tend to reduce the foaming production in delayed coking reactors, but it's necessary to consider another aspects once the increasing of pressure and temperature affects directly the quality of the produced coke as well as over the side streams like coker gas oil which will be processed in downstream units and can lead to quality issues to final derivatives like diesel.

   

  Jan-2025