Hydrocarbon Processing - December 2022 - 60

Heat Transfer
CONVECTION SECTION
EFFICIENCY
How does fouling occur? Fouling occurs
when deposits accumulate on the
tube or fin surfaces. The burner operates
with one part per million (ppm) airborne
particulates. This means that a single
burner can pass 2.5 tpy of debris through
a heater, some of which will deposit.
Airborne debris is drawn in from the
surrounding environment.
One of the most significant effects
of fouling is an increase in emissions. If
fouling is left to worsen and the emissions
become excessive, refineries may
be liable to pay government fines (FIG. 1).
Fouling requires fired heaters to burn
more fuel to operate at the desired capacity-higher
fuel consumption results in
a higher stack temperature and reduced
heat transfer. High operating temperatures
cause heat stress on tubes, creating
uneven expansion and irregular heat
distribution, potentially leading to tube
failure. These side effects can cost plants
millions of dollars in lost revenue.
Two commonly used offline cleaning
methods are used to tackle the issue of
fouling: chemicals and dry-ice blasting.
Chemical cleaning. Chemicals can be
used when an asset is online; however, if
the nature of the fouling is unknown, it is
difficult to predict how it will react with
certain chemicals. Therefore, chemicals
can compound the issue of fouling, creating
hotspots in areas that the chemical
has not managed to penetrate or reach.
During a shutdown, the refractory
lining of the convection section can become
saturated with water-borne chemicals,
which may change the refractory's
high-temperature properties, leading to
premature failure.
Dry-ice blasting. Dry-ice blasting can
be undertaken during the unit's operation
and is offered by the author's company. It
provides a limited benefit since accessibility
reduces the ability to reach > 40%
of the tube surface area. However, this is
often sufficient to provide a significant
improvement until a planned shutdown.
The author's company offers a comprehensive
solution that uses robotic
cleaning systems to clean more than 90%
of convection section tube fouling during
planned turnarounds (FIG. 2).
Takeaway. Fired heaters are a critical
piece of equipment for refineries and facilities
worldwide. With rising fuel costs
and stringent emissions legislation, it is
becoming increasingly important to ensure
that mission-critical assets, particularly
fired heaters, perform efficiently and
at full capacity.
Maintaining these assets regularly
and thoroughly will maintain output,
increase asset life, reduce the likelihood
of unplanned outages, reduce stack temperatures
and emissions, and deliver a
significant return on investment.
LITERATURE CITED
1
XRG Technologies, Matthew, M., et.al., " Carbon
dioxide emissions from fired heaters, " June 2021,
online: https://cdn.digitalrefining.com/data/articles/file/1002643-carbon-dioxide-emissions-fromfired-heaters.pdf
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Hydrocarbon Processing
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Hydrocarbon Processing - December 2022

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