Thermal Cracking Processes Flashcards
What is the range of temperature where cracking of heavy HC starts ?
400-420°C
What is the minimum temperature to operate a thermal cracking unit ?
440-450°C
What are the two controling parameters for thermal cracking ?
Temperature and residence time
What are the operating conditions in a visbreaker ?
450°C and 20 minutes residence time -> low severity thermal cracking
What are the two versions of the visbreaking unit ?
- Coil cracker
- Soaker cracker
Where does the reaction occur in the two versions of the visbreaking unit ?
- Coil cracker -> in the heater tubes
- Soaker creacker -> mainly in the soaker drum
How is the soaker drum designed in a visbreaking unit ?
It is designed to have a residence time of 20 minutes
What are the products of a visbreaker ?
- Gas, Gasoline and Gasoil in small quantities
- Vacuum Gasoil -> fuel pool or feedstock for FCC or VGO HDT/HDC
- Visbroken vacuum residue (65-80%) -> base for fuel pool
What is the quality of the products at the outlet of the visbreaker ?
Low quality : rich in sulfur and unsaturated HC (olefins and diolefins)
What are the advantages of using a visbreaker (vs nothing) ?
- Decrease heavy fuel production (we don’t know what to do with it)
- Increase gas oil production (higher value product)
What is the feed temeprature in a delayed coker ?
500°C
What is the difference between Visbreaker and delayed coker ?
Visbreaking we stop before we make coke while delayed coker we stop when all the feed has been converted
How is the decoking done in a delayed coker ?
Through hydraulic decoking
What are the products of the delayed coker ?
- Gas, gasolines and gasoil that need to be hydrotreated
- Distillate used as feedstock for FCC or HCK
- Coke
What are the three grades of coke that can be produced ?
- Electrode grade
- Metallurgical grade
- Fuel grade
