POWER January 2015 - 51

FUNDAMENTALS
to understand how " typical " the fuel is compared
to its peers.
For example, a Powder River Basin (PRB)
coal with a moisture content of 10% and
higher heating value of 12,500 Btu/lb should
immediately raise a red flag. As you collect
analyses of fuels in your career, you should
build a knowledge base using a spreadsheet
or database that can allow for a quick external
consistency comparison.
Common Problem Areas
Several issues are common problems when reviewing
fuel analyses. Ask, and carefully consider
the answers to, the following questions.
Is the heating value consistent with
the ultimate analysis? Performing a quick
heating value estimate via an equation such
as the Dulong formula can greatly increase
your confidence in the accuracy and internal
consistency of both the heating value and the
ultimate analysis. The Dulong formula is a
simple formula that, in my experience, yields
surprising accuracy for most U.S. coals:
Higher Heating Value, Btu/lb = 14,600 x C
+ 62,000 x (H - O/8) + 4,050 x S,
where C, H, O, and S refer to the as-received
mass fractions of carbon, hydrogen,
oxygen, and sulfur, respectively.
Typically, if the Dulong-calculated heating
value differs from the given heating value by
more than +/-300 Btu/lb, I take a harder look
at the heating value and the ultimate analysis
to ensure they are accurate.
What is the moisture basis? It is very
common to see an as-received or " wet " analysis
reported as " dry, " or vice-versa. You can
confirm the moisture base by simple math: If a
proximate analysis is " wet, " then the moisture,
ash, volatile matter, and fixed carbon must sum
to 100%. If they sum to 100% plus the moisture,
then the analysis is on a dry basis.
Converting to a different moisture basis is
a simple arithmetic function. To convert a dry
analysis value to as-received:
Valuewet
= Valuedry
x ((100 - moisture, %)
/ 100)
To convert an as-received analysis value
to dry:
Valuedry
= Valuewet
x (100 / (100 - moisture,
%))
Does it use air-dried basis? Air-dried base
results are sometimes impossible to convert to a
" wet " or " dry " basis, because one requires the
" as-received " moisture content in addition to the
air-dried moisture for completeness. Often one
of these is omitted from the analysis.
January 2015 | POWER
Is the heating value on a higher (gross)
or lower (net) heating value basis? Errors
abound here when purchasing world-market
coals. Note that the lower heating value by
definition will always be less than or equal to
the higher heating value.
Has the ultimate analysis divided the
moisture into hydrogen and oxygen? Although
this is becoming less common, one
still finds this error in some analyses. For the
sake of simpler calculations, it is preferable
to keep the moisture separate from the hydrogen
and oxygen analyses.
Is the equilibrium or inherent or airdried
moisture greater than the total
moisture? In some cases this occurs due to
performing analyses on two different samples.
However, given the importance of moisture
on your engineering calculations, it's a
problem you should work to resolve.
Is the ash content suspiciously low?
Sometimes the person taking the samples
will excessively " hand screen " rock, pyrites,
clay, and other inorganic materials from the
sample. This can be especially problematic
with biomass fuels, where the power plant
should expect the possibility of significant
inorganic material sometimes coming along
for a ride with the fuel. The solution is to adhere
to official sampling guidelines.
Are the oxidizing ash fusion temperatures
higher than the reducing ones? This
should be the case for nearly all coals and biomass
fuels. However, petroleum coke and some
biomass fuels can see these trends reversed.
Is chlorine in ppm, or %? If chlorine is only
listed in the trace element or another analysis, it
can sometimes be omitted from consideration.
This is a critical mistake when analyzing highchloride
fuels. Note that if chlorine is included
with the trace element analysis, it is typically on
a whole-coal dry basis.
Is the ash mineral analysis on an SO3free
basis? Some laboratories list the ash
mineral constituents exclusive of SO3
. If this
is not taken into account, it can lead to significant
errors when attempting to estimate
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POWER January 2015

Table of Contents for the Digital Edition of POWER January 2015

Contents
POWER January 2015 - Cover1
POWER January 2015 - Cover2
POWER January 2015 - Contents
POWER January 2015 - 2
POWER January 2015 - 3
POWER January 2015 - 4
POWER January 2015 - 5
POWER January 2015 - 6
POWER January 2015 - 7
POWER January 2015 - 8
POWER January 2015 - 9
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POWER January 2015 - Cover3
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