The document discusses the challenges related to runaway conditions and hot spots in hydrogenation reactors within the refining and petrochemical industries. It details causes of excessive temperatures, such as loss of cooling systems and changes in feed quality, and emphasizes the importance of careful monitoring during operations to prevent dangerous situations. It also warns that localized reacting materials may go undetected, potentially leading to hazardous conditions during reactor restart.

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GBHE Technical Bulletin CTB #11
REACTOR RUNAWAY CONDITIONS
-Hot Spots in Hydrogenation Reactors-
Temperature excursions in hydrogenation reactors may have several causes, the
most common ones being:-
i) Loss of recycle quench system. This could be either the liquid or gas
stream. The condition is made worse if the make-up gas keeps flowing.
ii) Excessive temperatures. The loss of cooling medium will cause
increasing temperatures. This could then allow the reactor to reach the
point where hydrocracking occurs.
iii) A sudden change in feed quality. This could mean either an increase of
the major component or another species that can be hydrogenated.
iv) Maldistribution of flow can also cause local “hot spots” which may or may
not be detectable. This will depend on their proximity to a thermocouple.
The result of the local hot spot could be hydrocracking which could then
potentially lead to further exotherms.
A hydrogenation reactor is similar to a fire. A fire can be extinguished by
removing either the combustible material or air. Similarly a hydrogenation
reaction can be stopped by removing the feed or hydrogen. The reactor system
however will continue to react until either all the feed or hydrogen has been used,
even though both the feed and hydrogen have been stopped.
After the reactor has been shut down, it is possible to get localised reacting
material unless the reactor is well purged. This localised area cannot be
detected unless it is close to a thermocouple. This can give undetectable hot
spots. The heat can only be removed from the system once either the feed or
hydrogen flow is restored. Thus it is possible for parts of the reactor to have
excessive temperatures without being noted.

2. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com
The problem can be aggravated if hydrogen purge times are not long enough or
not monitored carefully. The local hot spot can cause a further local runaway
causing accelerated hydrogenation and hydrocracking once the feed is restored.
Many of these high temperature excursions during normal operation can be seen
by rapid increments of pressure or sudden increases in methane content of the
purge gas coupled with drop in hydrogen content. The problem remains that
after a shut down and restart following a temperature excursion there can be
local hot areas which when subjected to hydrogen at restart would exceed
equipment design conditions.
Information contained in this publication or as otherwise supplied to Users is
believed to be accurate and correct at time of going to press, and is given in
good faith, but it is for the User to satisfy itself of the suitability of the information
for its own particular purpose. GBHE accepts no liability for loss or damage or
personnel injury caused by or resulting from reliance on this information.
Freedom under Patent, ht and Designs cannot be assumed.

3. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com