WHY CLEAN COAL IS STILL RELEVANT
Max Fine, mwf24@pitt.edu, Mahboobin, 4:00
Abstract
"We sit on top of a 300-year supply of coal” in the
words of Saskpower CEO Robert Watson is why clean coal
remains valid in this day and age. This right here is why
we need to revisit how we use coal. We have some of the
largest coal reserves in the world, but we usually export it.
This is due to the environmental regulations that power
plants are required to adhere to. Most of the coal we mine
is very low quality coal, which when burned emits far more
greenhouse gasses that the high quality coal most domestic
users burn. This means that this coal is normally unusable
for American industry. However, scientists have found
ways to increase the quality of mined coal, and reduce the
emissions they generate. Of course, both these things are
easier said than done. When I said one could increase the
quality of the coal I wasn’t being entirely accurate. This
turns the coal into a flammable gas, from which at least
some of the CO2 can be removed. This gas is a superior
fuel when actually burned, meaning less of it can be used
to produce the same amount of power. The other option is
to make coal less environmentally destructive by removing
CO2 from the emissions from burning the coal. There are
several proven methods to remove CO2 from the emissions.
Of course then the captured CO2 must be disposed of.
There are several ongoing studies about subterranean
storage of waste CO2. Many groups are watching with
interest to see if such methods are viable for long-term
storage. The final consideration is the economic viability
of clean coal. . Facilities built in order to convert coal to
its gaseous form and use it are much more expensive than
conventional power plants. Modifying existing plants is
also a considerable expense. If it is feasible, these
measures could buy us enough to move to fully renewable
energy sources.
KEY WORDS
Clean Coal – Carbon Capture-Reduced Carbon
Footprint-Sustainable Energy
CLEAN COAL: AN INTRODUCTION
Coal has been the primary fuel used to create electricity from
the beginnings of the organized power grid. In 2008 coal
provided 49.8% of all electricity produced in the United
States [1]. To produce this amount of energy 1.2 billion
short tons of coal were burned domestically.
THE CHEMISTRY OF COAL
The definition of coal is in fact a bit broader than one might
expect, as it is not a pure substance, but rather a type of rock
that is made of several compounds. “ “In short, coal is a
chemically and physically heterogeneous, “combustible”
sedimentary rock that consists of both organic and inorganic
material.”[1] Coal is primarily made of carbon, hydrogen,
and oxygen, with varying amounts of nitrogen and sulfur
depending on the type of coal. Coal is “graded” based on
how far through its formation process it is. Coal starts out as
peat, then dries and hardens into lignite, which is the lowest
grade of coal. For each subsequent category of coal, the coal
becomes drier, harder, and usually lower in impurities
(namely sulfur). When coal is burned it mainly produces
carbon dioxide, with smaller amounts of sulfur dioxide,
carbon monoxide, and other gases.
CARBON EMMISIONS REDUCTION
TECHNOLOGY
Preprocessing Coal
The simplest way, at least from the outset, to reduce coal
CO2 emissions is to reduce the amount of coal burned. Most
modern coal plants use pulverized coal, which is a system
that normalizes the size of coal pieces to the most efficient
size for the method of combustion used at the plant. There
are three commonly used systems for burning solid coal:
fixed bed, fluidized bed, and suspension. Fixed be is simply
placing coal on a flat plane and burning. This is the least
optimal method for steam generation, and as such shall not
be discussed further. Fluidized bed is the current standard
for coal boilers. Within this system the fuel, in this case coal,
an inert material, such as sand, and limestone are suspended
above the floor of the combustion area.
This is
accomplished by the action of air distributed below this floor.
The inert material aids the spreading of the fuel, and lowers
heat waste by storing thermal energy, that is the released to
ignite additional fuel. During the combustion the limestone
decomposes due to the heat, into lime and CO2. This lime
then reacts with waste sulfur gas through the equation
CaO+SO2+1/202CaSO4.
Integrated Gasification Combined Cycle
Carbon Capture
The most mature at technology for reducing coal carbon
emissions is to capture the carbon dioxide in the waste gases
and store it in a stable medium. The most common current
method of post-combustion CO2 capture is to pass the flue
gas through a through an absorption column after being
cooled. Within this absorption column the flue gas rises
through a solvent, which strips the CO2 out of the gas. The
CO2 free gas then exits through the top of the column, while
the solvent, with the dissolved CO2, is collected at the
bottom. The solvent is then pre-heated before being fed into
a heat exchanger. Within this exchanger the solvent flows
downward as the temperature decreases, which releases the
CO2. The solvent flows out the bottom, while highly
concentrated CO2 escapes through the top. This CO2 can
then be collected for storage or other use.
Why is clean coal a good idea?
Clean coal presents an alternative to immediately shifting
our power plants to natural gas or other type of fuel. It is
more economical to refit existing power plants to use clean
coal technologies rather than build new plants that conform
to modern regulations. Furthermore, coal as a fuel has a
much lower cost to extract than many other power plant
fuels in common use. The techniques used for storing the
gases removed from coal smoke are also useful in extracting
natural gas from mining wells. Furthermore, this technology
is much more mature than many of the renewable power
generators that are its competitors. This will allow a much
faster deployment of clean coal to widespread use.
REFERENCES
[1] Miller, Bruce G. (2010) “Clean Coal Engineering
Technology.” Elsevier Science & Technology (Book)
SOURCES CONSULTED
U.S. Department of Energy. (2016) “Clean Coal Research.”
U.S. Dept. of Energy. (Webpage)
http://energy.gov/fe/science-innovation/clean-coal-research
This source is the United States Department of energy portal
to their supported clean coal research. I wish to use this
page to demonstrate the U.S. government’s stance on clean
coal. This will also relate to the economics of clean coal, as
government supported technologies are often subsidized.
C. C. Mann (2014). “Renewables aren’t Enough, Clean Coal
is the Future” Wired Magazine (Web Article)
http://www.wired.com/2014/03/clean-coal/
This magazine article from wired magazine offers a view
into why we should use clean coal, instead of immediately
switching to renewable energy sources. This source also
discusses the implications and logistics of storing emitted
carbon dioxide.
R. P. Siegel (2014). “Clean Coal: Pros and Cons” Triple
Pundit (Webpage)
http://www.triplepundit.com/special/energy-options-prosand-cons/clean-coal-pros-cons/
This web article offers a devils advocate look into clean coal.
It focuses on the downsides of clean coal, which will point
me towards further research into the cons of clean coal.
Furthermore, it is the only article I have seen that looks into
health issues surrounding coal power plants.
R. Kunzig (2014). “Clean Coal Test: Power Plants Prepare
to Capture Carbon” National Geographic. (online article).
http://news.nationalgeographic.com/news/energy/2014/03/1
40331-carbon-capture-kemper-coal-climate/
TOPIC AREA:
CHEMICAL ENINEERING
Clean coal belongs in the chemical engineering topic section
as it is about the transformation of materials. Chemical
engineering is a profession based on manipulating various
materials in order to achieve a goal. The goal of clean coal
research is to transform low quality coal into a better form of
fuel, or adjust the process used in burning said coal to be less
environmentally damaging. This sits squarely within the
mandate of chemical engineering, and as such it is a good
candidate for this conference.