6.9 Technical questions

1. Why the naphtha stream after absorption and phase separation enters a stripping unit?

Ans: The stabilization process involves enabling naphtha to possess only those components that do not flash off in due course of storage.  Therefore, naphtha possessing any lighter hydrocarbons other than those desired should be totally eliminated.  The unstabilized naphtha obtained from the main distillation column is not given enough time to equilibriate towards stabilization cause.  Even after the phase separator and absorber units, the stabilization needs one more unit for processing and hence a stripper unit is used to remove any lighter gases that exist after phase separation.
It is further interesting to note that phase separators do not always meet the product requirements.  The phase separators only enable the separation of gas and liquid streams based on their operating temperature and pressure which may not correspond to the exact conditions required to equilibrate. Therefore, additional processing is mandatory.

2. Why steam stripping is carried out in the FCCR?

Ans:The purpose of stream stripping is to facilitate the removal of hydrocarbons adsorbed on the catalyst surface.  If this is not done, they will be burnt in the CR unit and this will be loss of product value.  In petroleum processing, always we don’t wish to loose any valuable money in the processing. That’s also the reason why the flue gas from CR is sent to the flue gas heat recovery unit for steam generation.

3. Comment on process intensification in the FCCR?

Ans:The FCCR is a complicated arrangement of the riser (where the reaction takes place), the cyclone separator (where solid fluid separation takesplace)  and the stripper (where again stripping the catalyst takes place a physical process).  Therefore, we can see that the reactor and separator are packed into a single vessel applying the finer principles of process intensification.

4. What are the main advantages of catalytic cracking over thermal cracking?