POWER September 2021 - 34

COAL
Types of Coal and Fuel Blending
Tips for Coal Power Plants
There are a handful of reasons why coal-fired power plant managers may want
to blend fuel, but often the driving factor is economics. While the cost of the
delivered coal is an important aspect, there could be adverse side effects that
negate the savings, if the blending process is not done right.
Aaron Larson
T
he U.S. Geological Survey, the science
agency for the U.S. Department
of the Interior, categorizes
coal into four major types or ranks.
The ranks are lignite, subbituminous,
bituminous, and anthracite. Rank refers
to the step in the coalification process
that buried plant matter is in as
it changes into an ever denser, drier,
more carbon-rich, and harder material.
Lignite, also known as brown coal,
is the lowest grade with the least concentration
of carbon. It generally has
the lowest heating value and highest
moisture content of all the major ranks.
Next in order comes subbituminous
and bituminous coal. These are black
in color and gradually go from dull to
a more shiny and smooth appearance
as the rank increases. Anthracite, the
highest rank of coal, is hard, brittle, and
has a lustrous black appearance. It is
often referred to as hard coal, and contains
a high percentage of fixed carbon
and a low percentage of volatile matter.
The U.S. Energy Information Administration
(EIA) says bituminous coal,
which has a heating value two to three
times that of lignite, is the most common
rank found in the U.S. It accounted
for about 48% of U.S. coal production
tonnage in 2019. Subbituminous coal-
most of it from the Powder River Basin
in Wyoming-was a close second,
accounting for 44% of U.S. coal production
in 2019, with lignite (8%) and
anthracite (<1%) rounding out the list.
Why Blending Could Make Sense
(and Why It May Not)
Economics is what usually leads managers
to investigate coal blending
schemes. The EIA reported that the average
annual sale prices of coal in 2019
from mines by main rank in dollars per
short ton (2,000 pounds) were:
■ Anthracite - $102.22
34
1. A bridge-type bucket wheel reclaimer, equipped with a rake or an active scraper in case of
poor flow properties, provides a good degree of homogenization. Using this type of equipment
for coal blending is usually only practical at a mine. Source: Creative Commons / Bernard S.
Jansen
■ Bituminous - $58.93
■ Subbituminous - $14.01
■ Lignite - $19.86
The cost of the physical coal is one
part of the equation, but there are also
other factors that must be considered.
The cost of transportation to a power
plant is often significant. It's not unusual
for rail costs from the Powder
River Basin to a coal-fired plant outside
of Wyoming to exceed the price
of the coal. Of course, therein lies one
of the greatest potential opportunities.
If a plant can cut transportation costs
significantly by switching to a closer
mine, for example, it could make a
higher-ranking coal more economical
and worth blending. In the end, the
delivered cost per Btu is often most
relevant.
Perhaps the single most important
thing to contemplate is how the boiler
will perform when a new coal is introduced.
If a non-spec coal is being considered,
there can be problems, even if
a blended version of the fuel looks fine
on paper. If the blended coal regularly
causes upsets to plant operation, the
result could be derates, boiler fouling,
www.powermag.com
excessive emissions, or a variety of
other trouble.
Decision-makers must not overlook
the cost of blending either. Blending
could require double handling of the
coal, which is significant. Blending
costs should be studied in depth because
they could add $1 to $2 per ton,
which quickly erodes potential savings.
Rod Hatt, owner of Coal Combustion
Inc., gave an informative training session
on the practicalities of coal blending
during a Coal Users' Group webinar
in 2020. Some of the details that follow
were gleaned from his presentation.
To learn more about the Coal Users'
Group, visit: coalusersgroup.org. For
more information on Coal Combustion
Inc., visit: www.coalcombustion.com.
Methods of Blending
Blending coal can be done in several
ways including at the mine, in shipping
vessels, at the plant in the coal yard,
or even in the boiler. It's important for
managers to have a good understanding
of how a plant's potential coal
supplies are produced in order to ensure
possible blending techniques will
be implementable. Furthermore, the
POWER | September 2021

http://www.coalusersgroup.org http://www.coalcombustion.com http://www.powermag.com

POWER September 2021

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