POWER January 2015 - 49

FUNDAMENTALS
Primer on Fuel Quality Analysis
Fuel quality is vitally important for combustion power plants, yet fuel quality
testing is still uncommon and analyses often incorrect. Improved knowledge
about the primary energy input to your power plant will help maximize
your potential for improved operation and reduced generation costs.
Una Nowling, PE
B
ack in the " good old days " of the power
industry, fuel was cheap, fuel supplies
were fairly constant, air emissions regulations
were loose, and power plant coffee was
as dark as sin and worse for you. Since those
days the power industry has seen tremendous
change in every way-save for the coffee.
In those same good old days, fuel quality
testing wasn't given serious attention. Socalled
" short proximate " analyses were conducted
monthly, but a full analysis might not
have been done since the day the local beauty
queen broke a champagne bottle on the turbine
casing. Even when analyses were done,
they were often rife with errors, ranging from
simple typographical and mathematical errors,
to blatant sloppiness. When I started
my career in the power industry more than
20 years ago, I wondered how a power plant
could pay so much for an analysis containing
so many significant errors, and thus I learned
to devote considerable time to checking for,
advising upon, and fixing such errors.
One would hope that in this era of massively
instrumented and logged modern power
plants-struggling to cut costs while meeting
performance, operations and maintenance,
reliability, and emissions targets-that our
fuel quality sampling and testing practices
would significantly improve. Unfortunately,
that does not seem to be the case, and as a
result the power engineer is frequently called
upon to review the fuel quality data assumptions
and analyses that are conducted.
How serious is this problem? In my career
I've reviewed well over 10,000 fuel quality
samples, and I would estimate that perhaps 1 in
10 has a significant error that prevents a full and
accurate analysis of the fuel without engineering
judgment to correct the error. For example, I
recently received 12 coal quality analyses from
a power plant, and three of that 12-25%-
featured some significant error or omission.
To help you avoid such problems, this article
provides tips and guidelines for ensuring
that you and your power plant staff have the
best possible knowledge about your fuels.
It All Begins with Sampling
Understanding where, how, and when the fuel
January 2015 | POWER
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49
sample is collected will provide information
on how representative that sample is of your
average fuel quality. Unfortunately, fuel sampling
is often considered just another messy
chore, where someone takes a quick scoop
of a coal pile with a bucket and pronounces
" mission accomplished. " Unfortunately, this
will often yield an inaccurate sample, especially
as it may be possible that no one really
knows what coal or coals are mixed together
in that particular region of the pile.
A better way of sampling is to take directly
from the train during the unloading
process (Figure 1). Even better is to take
small samples of coal from five or more train
cars, as they are being unloaded, and mix the
samples together to produce a composite coal
for analysis. If sampling is being conducted
during a performance test (Figure 2), the best
method is often to collect equal samples at
each of the coal feeders and combine these to
create the composite sample.
For the best sampling guidelines, refer to the
engineering standards in use in your country. For
the U.S. this would be the American Society for
Testing and Materials (ASTM) standards. Good
examples of sampling standards include ASTM
D 2234/D 2234M-07 for belt samples, D 688304
for sampling from stockpiles and delivery
vehicles, and D 4596-99 for mine samples.
Which Tests Should Be Conducted?
After a representative sample has been safely
collected, the next step is determining what
tests should be performed upon the sample.
The answer to this depends upon what your
goals are for attempting to solve fuel quality-
related problems at your power plant. Here's
a look at the typical coal analyses, in order
from least to most complete, and what impacts
they can help predict:
■ The most basic analysis, a " short proximate, "
will typically consist of the heating
value, moisture, ash, and sulfur in the fuel.
This is a barely acceptable analysis, which
will only allow one to make general estimates
about the plant performance.
■ A full proximate analysis will add volatile
matter and fixed carbon to the results,
which can be useful for determining
unburned carbon, CO production, coal
fineness requirements, excess air requirements,
and the like.
■ An ultimate analysis will provide the carbon,
hydrogen, nitrogen, sulfur, ash, moisture,
oxygen, and (sometimes) chlorine. With this
analysis one can determine combustion air
1. What's really on that train? Not having an accurate measure of your fuel quality is
like grocery shopping blindfolded. Courtesy: Una Nowling
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POWER January 2015

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