POWER June 2015 - 57

OPERATIONS AND MAINTENANCE
equivalent to a 0.66% change in power and
heat rate.
In this example, a reasonable estimate of
the CT heat rate at standard conditions is
~9,500 Btu/kWh, so the fouled HRSG increased
the CT heat rate by ~63 Btu/kWh at
a nominal average load of 40 MW. If a plant
is operating at 70% capacity factor, using
an average price of $4/million Btu fuel, the
increased heat rate added ~$62,000 to the
plant's fuel bill, assuming the HRSG remains
clean for the entire year. A better prediction
assumes that the HRSG will gradually return
to its pre-clean condition during the following
12 months, so the annual heat rate savings
is linearly interpolated as $30,000.
The power loss equates to ~0.24 MW,
which represents ~$75,000 in lost power sales
during the year, if power is sold at $50/MWh.
In summary, the annualized value of this
clean HRSG is estimated as ~$105,000 per
year in avoided lost energy sales and increased
CT fuel consumption. In this example,
the cost of the HRSG cleaning would be
recouped in a month or two.
Case Study 2: Avoiding Expensive
Upgrades. A combined cycle cogeneration
plant located in the United Kingdom (UK)
produces steam and electricity for two paperboard
mills. The plant uses a GE LM6000
and a Siemens steam turbine. Sticky combustion
products were condensing out on
the HRSG economizer tubes as a tar-like
substance due to the flue gas temperatures
dipping below the dew point. In addition,
ceramic fiber insulation blocks used in the
HRSG combustion zone were deteriorating,
with fiber strands coming loose into the
gas flow and sticking on the economizer fin
tubes. The combined effect was a loss of heat
transfer in the economizer and a rise in the
HRSG gas-side pressure drop that severely
decreased steam production.
The plant owner's initially considered
option was to replace the entire economizer
module with one that is equipped with an
economizer recirculation system. An economizer
recirculation system takes a portion
of the hotter economizer outlet water and
returns it to the inlet to ensure the economizer
tube metal temperature remains above
the dew point temperature, thereby avoiding
condensation of sticky combustion products.
However, procuring an expensive new economizer
module was going to require at least
40 days, which would put the plant owners
at commercial risk for failing to supply the
contracted amount of steam.
As an alternative approach, the plant owner
investigated cryogenic cleaning of the economizer,
even though at the time there was no
large boiler experience with the technology
in the UK-only cleaning of small equipJune
2015 | POWER
Designed, manufactured and tested in Switzerland
Featuring:
̈ Maintenance optimized sampling and analyzer system designed
for automatic HRSG operations
̈ Sample conditioning: according to VGB-S006-2012
SWAN's customer is METKA Athens, Greece. System manufactured
first quarter 2014. Commissioning first quarter 2015.
Please visit us:
ACHEMA 2015
Frankfurt am Main
Germany
15. - 19. June 2015
Hall 11.0 Stand C44
SWAN SYSTEME AG · www.swansystems.ch
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57
ment, such as motors or generator windings.
The plant owner sent representatives to the
U.S. to observe the cleaning process in action,
and the decision was made to bring the
process to the UK for the first time. The CO2
pellet blasting equipment was shipped to the
UK for a planned HRSG outage. Figures
5 and 6 show the state of economizer tube
fowling before and after cleaning. Figure 7
shows the debris removed from the HRSG
after the cleaning was completed.
The cleaning process was very successful,
and at the close of the outage, the plant resumed
supply of the contracted amounts of
steam to the customer. By selecting CO2
pellet
cleaning, the plant owner avoided an unnecessary
replacement economizer expense
and sidestepped an extended outage for the
economizer replacement. ■
-Chris Norton (cjnorton@eai-inc.com)
is president of Environmental Alternatives
Inc. Rich Taikowski Jr. (rtaikowski@
purenergyllc.com) is plant manager of
PurEnergy Operating Services LLC.
SYSTEMS ENGINEERING
Water/Steam Sampling and Analysis Systems for
a 143 MW Combined Cycle Project, Zarqa, Jordan
http://www.swansystems.ch http://www.powermag.com
POWER June 2015

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