Superheater pipes corroded by chlorine |
There are 3 groups of biomass used as powerplant fuel around
the world based on its quality such as calorific value, ash content and ash
chemistry. First, woody biomass includes
all woody trees such as eucalyptus, calliandra, gliricidia and so on. The
second group is agro-industry wastes such as ricehusk, baggase, coconut shell,
palm shell and so on. While in the third group is grasses.
Although in general the biomass has a low concentration of
chlorine (except straw) compared with coal, heavy corrosion occurs in a
powerplant that use biomass fuel and cause leaks in the pipes of heat exchanger
with less than 10,000 hours of
operation. Corrosion of heat transfer apparatus is strongly associated with ash
deposits in the pipes. The mechanism of the complex reactions of chlorine
corrosion in boiler pipes like this chart:
The mechanism of corrosion chemical reaction of chlorine |
Superheater steam pipes are generally not designed to
accommodate the chlorine in biomass fuels. Corrosion mechanisms above are quite
well understood by designers and users of biomass boilers in Europe,
indications are superheater pipes installed in the low temperature gas zone. Another
technology that is able to accommodate biomass fuels with high chlorine levels
such as agro-industry wastes and grasses are Circulating Fluidised BedCombustion (CFBC). Temperature pulverized coal (PC) boilers which operate at
temperatures up to 1500 C 1400 causing severe corrosion in the superheater
pipes, while the CFBC operating at lower temperatures ranging from 850C to
900C.
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