The Value of Steam Purging for Delayed Coker Valves – Part 1

Coke deposits can form in cavities and crevices leading to solids formation in valves and instrumentation.  This can result in….

This 4 part series will explain how steam purging in delayed Coker valves can reduce or eliminate deposits and solids build up.

PART I: Coke Formation and Solids Deposition

Coke Formation

1. Coke formation in valve cavities can be caused by asphaltene destabilization, aggregation, and degradation in low flow areas followed by dehydrogenation.
2. It is most common at temperatures >750F (Cracking Conditions) and is particularly severe in drum feed and Heater Discharge lines.
3. The “coking” rate can be highly variable depending on temperature and feed quality.

Solids Deposition

1. Solids deposits come from foaming (“Foam-Over” implies a more catastrophic event) which can leave deposits in overhead vapor lines.
2. Solids can form in valve components during a “non-cycle” condition.
3. “Bulk Solids” (Sludge) can fall into valve cavities during valve cycling.
4. Preformed Solids (coke fines, corrosion product, etc.) most commonly form in Blowdown, Fractionator Bottoms and Heater Isolation applications.
5. Reliable, consistent Steam injection into a valve, critical components, cavity areas, introduced at a pressure above process, can prevent the Coke for forming.

This is accomplished through a continuous purging system, to be discussed further.