POWER May 2020 - 18

FOCUS ON O&M
3. The Renergia Zentralschweiz AG plant supplies process steam to Perlen Papier AG, and district
heating networks Rontal and Emmen with hot water. It also provides electricity for several
thousand homes in the area in Switzerland. Courtesy: Integrated Global Services (IGS)
WtE Boiler Fireside Corrosion
The Hitachi Zosen Inova (HZI) furnace installed
at Renergia is an inclined moving
grate four-pass WtE boiler with an external
economizer. The boiler's thermal capacity
is 47 MW, with steam flow of 58
metric tons per hour and steam pressure
of 41 bar at 410C.
Alloy 625 weld overlay was shop-applied
on the fireside waterwall panels to
protect the WtE boiler tubes from fireside
corrosion. After months of operation, an
inspection revealed accelerated degradation
of the Alloy 625 just above the grate.
Several solutions were considered to
manage the boiler tube metal wastage,
and improve reliability and lifetime of the
waterwalls, including replacement, fieldapplied
weld overlay, and high-velocity
thermal spray (HVTS).
Evaluation of Alternatives
The replacement of affected waterwall
sections with new tubes would have
been time-consuming and expensive,
considering the estimated frequency of
replacement of five years or less. Likefor-like
weld overlay repair (Figure 4) is
an intensive and lengthy process, requiring
preliminary grinding of the degraded
surface layer prior to the application of
new weld overlay. Moreover, both of
those solutions-installing new tubes or
a weld overlay-wouldn't exactly solve
the problem, as the same corrosive media
attacking existing weld overlay would
still be present.
The third option was thermal spray.
The technology had mixed results in
boiler applications and the plant invited
four thermal spray vendors to perform
test applications on different sections
within the boiler. Each vendor was given
a side wall inside the two lines. Out of
the four claddings applied, only two delivered
satisfactory results. Integrated
Global Services (IGS) HVTS solution
was found to be superior, both in terms
of performance and capacity. Multiple
IGS HVTS guns can be operated inside
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POWER May 2020

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