Chemical Engineering May 2015 - 79

8,500
8,000
7,500
7,000
6,500
6,000
5,500
5,000
4,500
4,000
3,500
3,000
- Pass A
- Pass B
- Pass C
- Pass D
Acknowledgment
The authors wish to thank the help
and contribution of Alan Cross. He
is always a mentor to us who gives
us the courage and motivation for
preparing and submitting our experiences
in engineering papers.
References
1. American Petroleum Institute, " Inspection of Fired Boilers
and Heaters, " Recommended Practice No. 573, API,
Washington, D.C., Feb. 2003.
Early warnings of internal fouling in
pass A (rapid decrease in feed flowrate,
accompanied by 80 psig pressure
increase in pass inlet)
4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92
Time, days
FIGURE 7. This graph shows the operating history of the process fluid flowrate in four passes of a vacuum
distillation unit charge heater. Ignoring early signs of internal fouling caused by rapid coke buildup,
led to disastrous tube rupture, like the one depicted in Figure 1
future internal-fouling problems, as
for the case history shown in Figure
1. Surveying the operating history
of the heater proved that long-time
local flame impingement was the
main cause of this event, and tuning
the draft and excess-air amounts
could have solved the problem in
the first place.
As a final note, we should add
that our experiences have proven
that in similar case histories, increasing
the awareness and knowledge
of operating teams about the
initial signs of internal fouling phenomena
is as important as knowing
the troubleshooting sequences.
For example, in a similar case that
happened in a vacuum charge
heater, operators were too much
dependent on infra-red pyrometer
measurements of tube-skin temperatures.
That misreading of the
skin temperature made them ignorant
to the actual problem that was
taking place. As depicted in Figure
7, the process fluid flowrate had
decreased during coke buildup and
simultaneously, the heater pass
inlet pressure increased 80 psig.
These two events are very obvious
early warnings of internal fouling in
the specified heater pass (Pass A
of Figure 7).
The operators had simply related
the decreased flowrate to
the control equipment malfunction
and ignored it. If the operators
were aware of other warning signs
of possible internal fouling, this
problem may not have endured for
such a long operating period that
would lead to tube rupture. This is
another reason for the necessity
of an operator-involved reliability
program in refineries in addition to
good troubleshooting knowledge
and training.
Computerized algorithm
A computer program (computer wizard)
can easily be developed based
on logic described in Figures 3-6,
and 8-15. By using this program in
industrial environments, like petroleum
refineries and petrochemical
plants, operators will be able to understand
and correct the root causes
of a possible deterioration mechanism
in more efficient ways. As a
result fewer maintenance operations
or mandatory tube replacements will
be needed.
It should not be forgotten that the
main cost saving and also safety
benefits of this program will result
from the following:
* Fewer forced direct-fired-heater
outage events due to tube failure
* Elimination of disastrous events,
such as a heater explosion caused
by unpredicted tube ruptures
* Extending the operating lifetime of
heater tubes
* The possibility of increasing
throughput and decreased downtime
for decoking operations ■
Edited by Gerald Ondrey
ChemiCal engineering www.Chemengonline.Com may 2015
2. Maghbooli B., Najafi H., Bakhtiari A., Correcting Improper
Performance of Direct Fired Heaters: A practical, stepby-step
approach for finding the root cause and troubleshooting
burner problems, Chem. Eng., May 2013, pp.
39-46.
3. American Petroleum Institute, " Damage Mechanisms Affecting
Fixed Equipment in the Refining Industry, " Recommended
Practice No. 571, API, Washington, D.C., April
2011.
4. Patel S., Typical Fired Heater Problems and Root Causes,
Hydrocarbon Process., March 2007, pp.68-69.
The complete set of troubleshooting algorithms is
available online at www.chemengonline.com
Authors
Babak Maghbooli is a
member of the research and development
team of Farayand
Sabz Engineering Co. (No.117,
Somaye Street, Tehran, Iran;
Email:maghbooli@xthermo.
com). With more than six years
of experience in the field of tuning
process fired heaters and
troubleshooting their problems,
he has provided consultancy services to more than
five petroleum refineries in the field of troubleshooting,
maintenance and analyzing mechanical and thermal
behavior of fired heaters and boilers. He also has
practical and professional experience in the field of
process simulation and developing root cause analysis
procedures for chemical process problems. He is
an advanced VBA programmer and has developed
many process simulation solutions in MS-Excel for
various consulting projects. He holds a B.Sc.Ch.E.
degree from Arak University and he is an associate
member of IAChE and CSChE.
Hamidreza Najafi is head of
the research and development
team of Farayand Sabz Engineering
Co. (same address as above;
Email:hrnajafi@xthermo.com). He
is a professional object-oriented
programmer and his main interest
is developing simulator packages
for industrial processes. With
more than 12 years of experience,
he has practical and professional experience in the
fields of thermal radiation, especially for design and
simulation of thermal cracking furnaces and process
fired heaters, and also development of chemical kinetics
and thermodynamics framework for simulator software.
He has provided numerous solutions for process
problems in these fields for various oil and petrochemical
companies. He has a B.Sc.Ch.E. degree from Sharif
University of Technology and a M.Sc.Ch.E. degree from
Shiraz University. He is an associate member of IAChE
and CSChE.
77
Heater pass flowrate, bbl/d

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Chemical Engineering May 2015

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