POWER December 2016 - 20

2. The firing sequence. The series of events in a shock pulse cycle includes dosing containers
being filled with O2 and CH4. Once the glow plug triggers combustion, a pressure wave
is released into the boiler, resulting in a short-term vibration that cleans contamination from
tubes. Source: Explosion Power GmbH
Oxygen
(O2)
Nitrogen
(N2)
Natural gas/
methane(CH4) O2
N2
CH4
O2
N2
CH4
4. Retrofit reduces abrasion and
erosion. Two SPGs were added on the
Werdohl-Elverlingsen Block E4 boiler in the
Reheater 1 area, shown near the top of this
diagram, allowing three sootblowers to be retired
with excellent results. Courtesy: Explosion
Power GmbH
O2
N2
CH4
O2
N2
CH4
O2
N2
CH4
3. Ready for action. This image shows a horizontally mounted TwinL SPG. Courtesy:
Explosion Power GmbH
using a shower cleaning system, the plant
could keep the temperature around 700C
for two to three weeks. However, in order
to avoid a further increase in temperature
at that point, a manual online boiler
cleaning was required, which in practice
reduced the temperature to a similar value
as after a maintenance stop. Thereafter,
the periods until shower cleaning and
manual online boiler cleaning were again
necessary became shorter and shorter.
One TwinL SPG was installed in 2016
two chambers and double U-firing (Figure
4). The dimensions of the steam generator
are approximately 11 m x 13 m x 80 m.
The plant has been cleaning Reheater
1 using two SPGs since September 2011,
and three sootblowers have thereby been
shut down. In addition to the steam savings,
inspections have shown that the service
life of Reheater 1 has been extended
considerably, as damage caused by abrasion
and erosion have been reduced.
Another installation was completed at
the Josefstrasse waste-to-energy (WTE)
power plant in Zürich, Switzerland. The
four-pass horizontal boiler has a radiation
20
pass width of 7.2 m and processes up to
13.25 tons of waste per hour, including
up to 15% sewage sludge. The steam capacity
is 52 tons/hr at 40 bar and 400C.
A membrane evaporation wall subdivides
the third radiation pass into a left and a
right half. By design, flue gas temperature
should not be allowed to exceed 700C at
the inlet to the horizontal pass to prevent
excessive corrosion of superheater tubes.
In 2015, the flue gas temperature at the
inlet of the horizontal pass increased during
operation almost linearly 7C per day,
reaching the critical value of 700C less
than one month after boiler startup. By
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near the lower part of the second radiation
pass (Figure 5) to enhance cleaning.
The improvement was immediately noticeable.
The SPG was commissioned one week
after boiler startup. During weeks two and
three, the interval between shock pulses
was four hours. During weeks four and
five, the interval decreased to two hours,
and from week six onward, pulses were required
every hour. Although the flue gas
temperature at the inlet to the horizontal
pass increased in the first month to 600C,
it was then maintained between 600C and
650C for the rest of the four-month operating
period through use of the SPG.
Not only did the reduced flue gas temperature
decrease the corrosion rate in
the superheater bundles, but the operator
also noticed positive effects in the manual
online cleaning regimen necessary in the
horizontal pass. It could be reduced from
three interventions to one intervention
every six months of operation. Additionally,
sand blasting during the maintenance
stop could be carried out faster and with
POWER | December 2016

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POWER December 2016

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