Introduction to Processes for the conversion of heavy feed Flashcards
Which cuts are send to conversion units ?
- Atmospheric residues (if no vacuum column)
- VGOs
- Vacuum residue
- Deasphalted oil (DAO)
Where does DAO come from ?
DAO is vacuum residue after deasphalting unit
What is the goal of the deasphalting unit ?
The goal is to concentrate the impurities of the vacuum residue in the asphlalt
What is a comon deasphalting solvent ?
Light HC (butane or pentane) to extract mostly saturated components and aromatics but not resins and asphlatene
What does SARA stand for ?
Saturated Aromatics Resins Asphaltenes
What is SARA ?
SARA is an analytical method to recognize famlily of molecules and separate the families using specific solvents
How do we measure the capacity of a cut to generate coke in conversion operations ?
We use Condrason carbon in %wt
Why is DAO interesting compared to vacuum residue ?
Low asphaltene and metal content
What are the tools for the different cracking techniques ?
- Thermal cracking -> T + residence time
- Catalytic cracking -> T + catalyst
- Catalytic hydrocracking -> T + catalyst + H2
What is the difference between Visbreaking and Coker ?
In visbreaking we want a moderate thermal cracking to limit coking whereas in a coker we want intensive cracking which leads to coke formation
What family of product is found in thermal and catalytic cracking but not HCK ?
Olefins
Are cracking reactions endoT or exoT?
EndoT
What is the advantage of thermal cracking over catalytic cracking and hydrocracking ?
No catalyst so we don’t care about metal content
What is the selectivity and quality of thermal cracking processes ?
Low selectivity and quality (rich in olefins and diolefins)
What is the maximum conversion in a visbreaker ?
Max 40 %
What is the state of the catalyst in a catalytic cracking unit ?
The catalyst is used as a fine powder ciruclating in a fluidized state
What are the advantages of using a catalyst ?
- More selectivity
- Better quality products (only olefins)
What is the proble of using a catalyst ?
To avoid poisoning the catalyst, we need feed with low metal content (< 20 ppm wt)
What is the usual gasoline yield of a FCC ?
40 to 50 %
What are the advantages of HCK ?
- High selectivity
- No coke because no cracking of aromatics
What are the problems with HCK ?
- High H2 consumption
- Catalyst requiring high purity feed
