Chemical Engineering May 2013 - 41

Feature Report
Feature Report
Correcting Improper
Performance of
Direct Fired Heaters
A practical, step-by-step approach for finding the
root cause and troubleshooting burner problems
Babak Maghbooli and Afshin Bakhtiari
Tarahan Naftoon Arya Engineering Co.
Hamidreza Najafi
Farayand Sabz Engineering Co.
O
ccasionally, direct fired heaters
that have operated satisfactorily
for long periods of time
subsequent to startup develop
operating problems that do not allow
for operation at design conditions, as
specified in the manufacturers' API
data sheets for the heater.
Performance that may be guaranteed,
or otherwise specified by the
supplier would include the type and
characteristics of the feedstock processed,
the heater duty, inlet and outlet
temperatures and pressures, heat
flux, tube-metal temperature and
any other process conditions that are
measurable by instrumentation provided
with the heater or calculable
through the use of the heater instrumentation
data.
In many cases, operators cannot
identify the cause of an operating
problem by simply comparing the
specified data and faulty data obtainable
from the heater instrumentation.
For example, although the measured
tube-metal temperatures demonstrate
no significant increases, an unexpected
pressure drop may occur in
heater passes because of internal
fouling, mainly caused by coke formation.
In many cases, operators are
unable to achieve the design heater
duty and overall thermal efficiency,
while the cause of faulty performance
is unknown to them. Most of these
cases may be due to faulty burner
performance. Such performance could
be caused by heating surface burnerflame
impingement, improper excess
air-fuel ratios, damaged burner tiles
or tiles of improper diameter, improper
burner spacing and other causes.
For example, continuous flame impingement
with heater tubes in places
where no tube-skin thermocouple is installed
can be the cause of unexpected
coke buildup, as shown in Figure 1. In
cases such as this, the main question is:
Why has the operator ignored the problem
for such a long period of time so
that it has eventually led to disastrous
coke buildup and heater shutdown?
For the most part, human factors,
such as inadequate training, improper
scheduling of visual inspections and
the lack of troubleshooting skills are
to be blamed. While many firms do believe
that the first two reasons are the
most important, one should not forget
the significance of effective troubleshooting
procedures, too.
In many cases, recognizing the
problem and observing indications
of it are not enough, because without
proper knowledge and understanding
of the troubleshooting sequence, any
attempts to solve the problem will
fail. For example, in one of our experienced
case histories, despite many
trial-and-error efforts, operators were
unable to tune improper flame shapes
(Figure 2) because of two reasons.
First, they couldn't diagnose the root
cause of the problem according to its
symptoms (that is, a lack of knowledge
39 CHEMICAL ENGINEERING WWW.CHE.COM MAY 2013
FIGURE 1. Faulty burner performance
and continuous fl ame impingement have
caused excessive tube-metal temperatures
and coke buildup in heater tubes
FIGURE 2. Faulty burner performance
and improper fl ame-shape problems
could not be solved by operators for a
long period of operation time due to lack
of troubleshooting knowledge
for performing root-cause analysis);
and second, they didn't know how to
treat the problem following a logical,
stepwise procedure (in other words, a
lack of knowledge for taking corrective
action).
Such situations are not unfamiliar
for fired heater operators and field engineers,
because these problems happen
frequently in many petroleum refineries
or petrochemical plants.
A proper root-cause analysis of
burner performance problems and
a proper troubleshooting algorithm
can be a great help to operators for
overcoming problems. In this article
we have proposed a simple rootcause
analysis and also a computerized
troubleshooting algorithm that
sequentially directs the heater operator
from one burner problem to
another, indicating how each of the
CHEMICAL ENGINEERING WWW.CHE.COM MAY 2013 39
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Chemical Engineering May 2013

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