As
a consequence of the lower exhaust gas temperatures and the remaining steam
consumption requirements, the exhaust gas boiler has been designed to become
more and more efficient. This involves the use of a large heat transfer surface
and thus a boiler design with a low internal gas velocity as well as tubes with
“extended” surfaces. Furthermore, the quality of the fuels has decreased
significantly during the same period. Whereas the average fuel quality may not
have deteriorated as much as predicted, single deliveries have shown exceedings
of the normal data, as a result of a more efficient refinery process. The
residual fuel oils available on the market today contain considerably higher
quantities of asphalt, carbon and sulphur that contaminate the exhaust gas and
thereby increase the risk of
soot deposits on the exhaust gas boiler tubes.
In
recent years, and possibly as a consequence of both the deteriorated fuel and
the above highly efficient and perhaps “overstretched” design, it also seems that
the tendency to fouling, i.e. soot deposits on the exhaust gas boiler tubes, has increased
and, in some cases, has resulted in soot fires. In extreme cases, the soot fire
has developed into a high temperature iron fire in which the boiler itself
burns. The above-mentioned tendency is confirmed by DnV’s statistics, which
reveal a sudden rise in soot fireincidents since 1985.
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