(90a) Olefins Cracking Furnace Recovery: Key Factors To Consider When Repairing After An Unplanned Shutdown

Olefins Cracking Furnace Recovery:

Key Factors to Consider When
Repairing After An Unplanned Shutdown

Robert
(Bob) Pritchett

Fired
Equipment Engineer

Global
 Engineering Services

LyondellBasell

Abstract:  When Ethylene Cracking (Pyrolysis) Furnaces
are shutdown, ?Decoking? is typically performed prior to removing heat from the
furnace.  The Decoking step removes
reacted hydrocarbons, in the form of coke, which have adhered to the internal
wall of the furnace tubes.  The coke and
the metal of the tube have significantly different coefficients of thermal
expansion, so when the tubes go through a large temperature change, such as making
a transition  from normal operation
(1900F) to shutdown (ambient), the tube contracts significantly more than the
coke inside. If the coke is not removed prior to this action, it can cause the tubes
to break.  A broken tube will then
back-feed the furnace effluent from the downstream manifold and equipment into
the damaged furnace.  The effluent acts
as uncontrolled fuel to the fire within the furnace, which leads to additional
secondary damage.  The response is to
isolate the remaining potential fuel sources to the furnace and extinguish the
fire.  Once things have cooled, repair of
the furnace can begin.

This paper will start at this point
using some specific examples about personal safety, mechanical integrity, and
environmental hazards that need to be evaluated to
begin the repair effort and some of the tactics, tools, and tasks used to
overcome these issues.