THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
September 2007
Volume 22, Number 4
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A TYPICAL FGD set up for the removal of sulphur from the emissions of coal-fired electric
generators.
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SPRAY PIPING of N08367
at Northern Indiana Public Service Co’s Bailly Generating Station Units 7 & 8. These have been in service
for more than 12 years.
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Air pollution conference shows a new generation of engineers a fresh direction
By Richard E. Avery
Nickel Magazine, September 2007 -- More than 100 people traveled to
Louisville, Kentucky, U.S.A., in June 2007 to attend NACE International’s AIRPOL conference and hear what’s
new in air pollution control for fossil-fuel burning power plants. The timing was appropriate because
government regulations, especially in the U.S., have led to a marked increase in the construction of flue gas
desulphurization (FGD) systems since the last AIRPOL meeting in 2004.
In the first two days of the conference there were 24 presentations on materials of construction for the
corrosive conditions of FGD systems, as well as system design considerations. There are typically 12
component sections in a wet FGD system, starting with the flue gas inlet duct into the absorber and exiting
through the chimney stacks. Corrosive conditions can vary considerably as the flue gas progresses through the
system, which in turn allows various materials to be used. These range from high nickel alloys in the most
corrosive areas to nickel-containing stainless steels in the less corrosive areas.
An informative status report on FGD system materials was authored by William Mathay and Richard Avery,
consultants to the Nickel Institute, and David Gandy, technical leader of the Electric Power Research
Institute. The report was based on an EPRI report on material performance at 42 installations. The oldest two
units were started 40 years ago and the six most recent were started in the current decade. Two-thirds of the
units surveyed were started in the period 1975-1990, and most of those have been rebuilt or had a major
retrofit.
The most corrosive areas in the FGD systems are at the inlet and outlet ducts and associated areas in the
absorber. The flue gases are normally carried directly into the absorber by the inlet duct after leaving the
electrostatic precipitators. Gas temperatures are above the dew point and range from 120 to 200°C, making
unlined carbon steel a suitable material. However, in the duct work immediately ahead of the absorber,
blow-back of the gas and the scrubbing medium can lead to serious corrosion. Where corrosion is a concern,
nickel alloys such as N10276
and N06022
(either solid or as linings on carbon steel) are preferred. The EPRI survey found that more than half the
units used one of these nickel alloys at that location.
A field trip was offered to the Ghent Station of Kentucky Utilities on the last day of the conference. The
station is involved in a major expansion of its FGD facilities, including absorbers and chimney stacks. The
absorbers are of a newer design, which uses a Stebbins tile inner lining backed by concrete on the outside
for structural support. The tile structure extends up past the demister (a device that removes entrained
liquid droplets from a gas stream) to a N10276
dome section. N10276
is also used in the lower section where a metallic material is needed.
Kentucky Utilities, a division of German-based E.ON, hosted the trip.
Richard E. Avery is a Londonderry, NH-based consultant to the Nickel Institute.
Photos: ATI Allegheny Ludlum and Rolled Alloys and Thyssenkrupp VDM.
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