POWER February 2021 - 34

OPERATIONS & MAINTENANCE
can furthermore reduce the need-or
even eliminate the need-for boilers to
go offline for manual cleaning between
annual outages.
Figure 5 shows the results of de4.
This chart shows the before and after effects of manual cleaning and mobile shockwave
cleaning through two operating cycles between outages. Courtesy: ECOVE Environment
Services Corp.
thoroughly. However, soon after annual
outages, the trends show that waterwall
tubes and superheater tubes begin
to build up with fly ash again, which
gradually reduces the amount of space
the flue gas can pass through, and
therefore the flue flow resistance increases-as
indicated by the rising differential
pressure values.
On average, the EfW plant requires
its boilers to go offline to clean fouling
manually at least twice between two
annual outages, but manual cleaning
only has a short-term effect and cannot
help reduce the differential pressures
as well as annual outages can, which
is evident from the line chart between
October and the following May. At a
certain threshold, the slope of the differential
pressure curve sharply rises,
which means there is an abrupt hike in
differential pressure.
From May to December, the mobile
shockwave method was introduced in
addition to manual cleaning, so that
the effects of both methods could be
better compared. Mobile shockwaves
were deployed online three times, and
offline manual cleaning one time. The
result shows that within a few days
after the deployment of mobile shockwaves,
the differential pressure first
gradually decreased before gradually
increasing. The slopes of the curves after
each deployment of mobile shockwaves
is much smaller than that of
manual cleaning, suggesting far better
performance of the former method
than the latter.
Normally in boiler operations, the
differential pressure control threshold
(that is, the limit requiring fouling
to be cleaned) is set at some point
lower than the differential pressure
34
value where the superheater passes
are completely stuck with fouling.
Whenever the boiler pressure nearly
reaches the differential pressure control
threshold, boiler operators would
shut down the boiler to clean fouling
manually to avoid superheater passes
being completely stuck with fouling,
because when the latter happens,
the flue gas cannot circulate and the
induced draft
fan will not be able to
function. The line chart shows that
by deploying the mobile shockwave
method,
the
differential
pressures
were successfully controlled to stay
below the differential control threshold,
which is better than the performance
of offline cleaning.
It can therefore be inferred that
when the mobile shockwave method
is deployed routinely, it can effectively
help control a boiler's differential presploying
the mobile shockwave method.
Compared to Figure 1, which was before
the mobile shockwave method
was deployed, the superheater bundles
are much cleaner. The stalactite-shaped
fouling is gone in Figure 5. Furthermore,
by probing into the operating
boiler with an infrared camera, it was
observed that high-temperature, lighter-grey
areas identified before mobile
shockwave cleaning was implemented
were replaced by lower-temperature,
darker-grey tubes, confirming the positive
results.
To sum up, the mobile shockwave
method can be deployed without the
need for boilers to go offline, and indeed
effectively reduces fouling and clinkers
on superheater bundles, as seen from
the differential pressure charts, visual
images, and infrared images.
Takeaways
It is important for boiler designers to
properly account for the interval between
superheater bundles as well as
the number of bundle layers, because
these parameters greatly affect the
smooth flow of flue gas and differential
pressures. An ill-designed superheater
can cause differential pressures to rise
too quickly and therefore reduces the
uptime rate of the boiler, which also increases
the cost of cleaning and boiler
shutdowns.
After adjustments and testing for
more than two years, ECOVE can now
precisely control the fouling buildup
period and deploy the mobile shockwave
method effectively to inhibit
fouling and clinkers on boiler tubes.
The uptime per boiler at the EfW plant
was boosted by more than 200 hours
annually, helping to significantly increase
waste-handling
2,500 tons.
capacity
5. This image shows reduced fouling on superheater
tubes as a result of deploying the
mobile shockwave system compared to the
fouling shown in Figure 1, which was prior to
the change in cleaning methods. Courtesy:
ECOVE Environment Services Corp.
sures and ensure that such pressures
stay below control thresholds. The
amount of fouling between superheater
bundles will therefore stay within the
normal operation range of boilers, and
www.powermag.com
by
Compared to the stationary shockwave
method, the mobile method is
advantageous in that it does not require
the installment of stationary devices.
It can be used with mobility to
clean the desired parts, offering timely
fouling and clinker removal. ■
-Chien-Pang Yang, Chieh-Ming Yang,
Ching-Yun Yi, and Teng-Hui Huang
are engineers in Taiwan with
ECOVE Environment Services Corp.,
a CTCI company.
POWER | February 2021
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POWER February 2021

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