Back

Question

Submit an Answer

What is the meaning and importance of analyzing wt% H2 content in Vacuum gas oil feed and product?

Our VGO hydrotreater product specification is said to have min 1.0% Delta hydrogen content w.r.t feed design value of 11.8wt%. If feed wt% H2 content is more than feed design value, will it make any difference to VGO product %wt H2 content?

Dec-2022

Answers

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

The hydrogen content in VGO (Vacuum Gas Oil) is an important characterization factor to determine the crackability of this stream as FCC feed.

Vacuum gas oils with high crackability normally presents high content of paraffin's and tends to present high hydrogen content while refractory VGO presents lower hydrogen contents indicating high concentration of aromatics compounds in the FCC feedstock. The hydrogen content can be used to estimate the yield of FCC products, once higher the hydrogen content in the FCC feedstock more hydrogen can be distributed in the FCC products and improve the final added value of the molecules.

Once the objective of residue upgrading technologies is to improve the relation H/C in the hydrocarbon molecules, there is two ways to achieve this goal. Through carbon rejection which occurs in Delayed Coking and Solvent Deasphalting Process for example or through hydrogen addition like is carried out in residue hydrotreaters and hydrocrackers. The specification of a minimum hydrogen content in the VGO is applied to ensure adequate performance to FCC units once low hydrogen content feeds indicates low crackability feedstocks which can lead to higher yields of low added value products (Decanted Oil) and high coke deposition rates over the FCC catalyst which can lead to extremely high temperatures in the hot sections of FCC units (Higher Delta Coke). Due this fact, it's important to consider the side effects of cracked feeds (Coker Gas Oil, for example) in FCC performance once these streams tends to present lower hydrogen content and, therefore lower crackability.

The raise in the hydrogen content in the VGO fed to the hydrotreater will raise the hydrogen content in the VGO product which will present a higher crackability and better performance as FCC feed. But is always important to consider what is the objective of the process, in some cases can be attractive to maximize the bottom yield in FCC units (Carbon black production for example).

Dec-2022