High temperature corrosion is often a problem in biomass combustion and
waste incineration boilers. Critical components are heat transfer surfaces,
such as water walls and superheaters. Instead of using more corrosion
resistant high alloy steels for critical components more economical low alloy
steels can be protected by coatings. These coatings can be applied by
thermal spray techniques. This work investigates the possibility of
integrating thin copper jacketed optical sensing fibres in this kind of
coatings during the spray process. This kind of sensing fibres would provide
new methods for managing boiler life and controlling the combustion process.
The coating embedded fibres can be used for example to locate hot spots and
places where corrosion and erosion are destroying the coating. In this work
the cheapest possible method (direct spraying) for embedding the fibre was
chosen even if it was known that this is close to the limits of what the
fibre can sustain in order to retain its optical and mechanical integrity.
The results of the direct spraying method are presented and some more
advanced methods will be discussed. Methods for monitoring the state of the
sprayed coating can extend from simple on-off methods to advanced distributed
sensing methods. On-off methods mean monitoring the light transmission of
the embedded fibre; when the corrosion or erosion reaches the fibre and
destroys it the light transmission will cease. Using optical time domain
reflectometry (OTDR) also onset of fibre destruction can be observed as well
as the locations of these critical points. More advanced techniques are the
use of in-fibre Bragg gratings for temperature and strain monitoring and the
use of distributed temperature sensing (DTS) for hot spot detection. Both
OTDR and DTS techniques will be presented in this work. The work presented
was mainly done in the CEC funded Craft project PROCOMO (Protective coatings
with combined monitoring system to control process conditions in boilers).
The DTS demo shown in this work was carried out within the STYX project,
which was a part of the Finnish nuclear safety research.
|Conference||BALTICA VII - International Conference on Life Management and Main-tenance for Power Plants|
|Period||12/06/07 → 14/06/07|