All considerations about the need for a rigorous kinetics modelling program, described for the Visbreaking unit, are in general valid also for the Coking unit heaters as well. However, the higher criticality of Coking versus Visbreaking reaction result in some specific differences:
- Faster coke build up means shorter run time and requires more than one heater (typically two) to be installed in the unit. This allows to run at reduced capacity during the decoking operation.
- Much lower residence time / higher mass velocity are required to have the smallest possible difference between bulk and film temperature, thus allowing for the required conversion rate at minimal coke build up on the inner tube surface.
Simulation software and field feedback data show that the preferable configuration is the horizontal tube lay out with two heaters running in parallel