You are currently viewing: Q&A

---

---

• Q1. I would like to understand the importance of Diesel feed introduction at 180degC as feed in VGO hydrotreating units before VGO gets replaced with diesel at 260-280degC?

  Q2. What is the issue if VGO feed is introduced directly to the VGO hydrotreating reactor at 180degC?

  Q3. Where does congealing in VGO units occur and why? It is often seen cold Straight VGO coming from storage tanks maintained at 80 degC flowing freely?

  Oct-2024

---

Answers

---

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

  According to my experience and the literature review, these are some responses for the questions: Q1 - The start-up of VGO hydrotreating units are made with diesel in order to control the sulfiding reactions of the catalyst. The VGO is considered a high chemically unstable feed which presents high unsaturated compounds like aromatics as well as present high carbon residua which can lead to the severe coke deposition process over the catalyst further a severe risk of temperature runway of the catalyst bed which can produce damages to the catalyst like sinterization. Diesel is a more "controllable" feed which makes easier the catalyst sulfiding process and their temperature is controlled in the range of 180 to 200 oC ir order to allow better performance of the catalyst sulfiding process which are carried out under 180 oC to 230 oC aiming to allow the composition of the sulfiding agent to the next steps of the sulfiding process. Q2 - As previously mentioned, the high chemical instability of some compounds of the VGO and the high carbon residue can lead to a severe coke deposition process over the catalyst as well as temperature runaway in the reactors which can produce damages to the catalysts like sinterization. Q3 - This relies on the characteristics of the VGO, normally the VGOs with higher H/C ratio present more paraffinic molecules which can lead to worse performance under cold flow. I believe that this can be a significant issue for refiners processing highly paraffinic crudes where the alignments from the storage tanks to the processing unit should be heated, normally this is not a concern.

   

  Oct-2024