(184e) Gaining Insights into the Fouling Rates of Delayed Coker Heaters

For most refiners operating Delayed Coking Units, one of the
main issues negatively impacting the unit operating margin is lost production
due to heater fouling. In the extreme case of a process upset, a Coker Heater
can foul in a matter of days. A typical design basis for a new unit is a ten to
twelve month run length before a shut down for decoking is required. More
commonly, run lengths of four to eight months between decoking shut downs can
be expected.

Developing a detailed understanding of the current heater
operation and fouling rates is a critical first step when initiating a project
to optimize the operation of the Delayed Coking unit. From this analysis, the
impact that a change in the unit operation will have on future heater coking
rates can be made and the results factored into the overall project economic
benefit.

The main factors influencing Delayed Coker Heater fouling
rates are:

·        
Operating severity relative to the heater design basis

·        
Feedstock properties

·        
Radiant box firing characteristics

In most cases, the results of an accurate process simulation
of the fired heater is sufficient to evaluate base coking rates and determine
the root cause of accelerated heater fouling .  In some cases, due to inherent
limitations of available general purpose heater rating programs, computational
fluid dynamic modeling may also be required to develop a full understanding of
the heater operation.

This paper will review typical heater design standards and how
the identified factors influence heater fouling rates before discussing the
role of simulation modeling in evaluating a delayed coker heater operation.