Sulphur — waste by-product
of mining, oil-refining and energy production
By Walter H. Schneider, 2006 05 03
Sulphur mines in the world have been shut down. A sulphur glut
exists and is growing. What to do with all that waste sulphur?
The owners of oil-sands oil upgraders, of oil
 refineries
and of natural-gas-processing plants seek ways to find uses for the waste
sulphur they produce as a by-product of oil-refining and natural-gas
processing. They produce elemental sulphur of which there is as of
2006 more than 15 million tonnes in storage in sulphur blocks in various
locations throughout the province of Alberta.
Sulphur blocks pose a liability to their owners. The costs of
treating and neutralizing acidic water that runs off sulphur blocks can run as high as $3.00
annually per tonne of stored sulphur.
Waste sulphur is also produced by other industrial processes, such as in
coal-fired thermal power plants and in phosphate fertilizer production.
Those processes scrub sulphur dioxide and other unwanted impurities from flue gases by passing the gases through a calcining process (a slurry of
water and lime or limestone). Sulphur dioxide reacts with the calcium
in the slurry it is being percolated through to form gypsum (hydrated
calcium sulphate, CaSO4·2H2O).
Similarly, sulphuric acid used for phosphate fertilizer production is
passed through such a slurry and produces gypsum as well.
The slurry is being stored in settling ponds in which the
gypsum settles from its suspension in the water. The water is then returned to the scrubbing process.
That process produces mountains of gypsum with often massive proportions
(e.g. more than 30 million tons annually in Florida).
A characteristic
of
the gypsum that is a waste product of the phosphate fertilizer industry is
that it is radioactive, about 60 times more radioactive than the phosphate
fertilizer produced. That is due to the circumstance that the
phosphate rock that is a feedstock for phosphate fertilizer production
contains isotopes such as of uranium and thorium that become concentrated in the
waste gypsum (a.k.a. phosphogypsum) during the production processes.
At least in North America and mainly on account of its
radioactivity, the uses to which phosphogypsum may be put are severely
limited due to environmental regulations.
Quoted in Canadian Guidelines for the Management of Naturally
Occurring Radioactive Materials (NORM), p. 12 [PDF
file, 1MB] |
Source: Earth.Google.com |
Source: Canadian Guidelines for the Management of Naturally
Occurring Radioactive Materials (NORM), p. 14 [PDF
file, 1MB] |
The Acceptability of Occupational Risks in
Industry
LIMITATION — The maximum acceptable
occupational exposure of any individual must not involve a
radiation risk to that individual greater than the risk that
arises in working in what is generally regarded as a “safe”
industry.
The ICRP recognizes that everyone is subject to
a significant back ground radiation exposure. However, even
smaller-than-background doses from occupational practices are
unjustifiable if there is no associated benefit, or they can be
readily avoided. (Source: Canadian Guidelines for the Management
of Naturally Occurring Radioactive Materials (NORM), p. 13 [PDF
file, 1MB]) |
Comments:
The radiation dose limits identified in Table 2.1
shown above are over and above the Canadian average annual radiation
impacting on individuals from naturally occurring radioactive
materials.
mSv = milliSievert; Sievert: Effective Dose
(= Biological Effect). Different types of radiation have
different penetrating power, and different parts of the body have
different sensitivities to radiation. Dose assessment
therefore requires a knowledge of the type and amount of radiation
and the biological sensitivity of the body part ex posed.
What is the radiation dose standard?
In 2000, the permissible radiation dose to
members of the public established by Health Canada and the
Canadian Nuclear Safety Commission was lowered from 5 mSv to 1
mSv per year above background levels. For workers exposed to
NORM, Heath Canada has established exposures should not exceed
the pre-2000 public dose limit of 5 mSv/yr, however, Agrium has
always worked hard to restrict NORM exposures on plant site to
no more than the current general public dose limit.
Radiological risk assessment studies were
conducted to determine the radiation dose that a construction
worker would receive while road and dyke building with
phosphogypsum to ensure that the dose to these individuals would
be below the public dose limit. The amount of radiation dose
was determined to range from 0.185 to 0.605 mSv/yr depending on
type of work done which is well within the public dose limit.
In our phosphoric acid unit where exposures
would be highest due to close contact and continuous processing
of rock, our personnel are monitored with film badges to ensure
that dose limits are maintained, though this is not required by
the government. The results indicate improving performance each
year. (Naturally
Occurring Radioactive Material (NORM), Agrium, 2006)
The radiation dose limits mentioned by Agrium in the
preceding quote are annual doses over and above naturally occurring
radiation exposures. — ed.
Oil and gas processing are now virtually the only source of supply for
the world sulphur market. Alberta is the main producer of sulphur for
the world market, although now oil and gas processing in Asia and in the
Middle East are playing increasingly larger roles in contributing to the
escalating glut in the world sulphur market. The sources and stock piles of
sulphur in other locations are closer to harbours than those in Alberta.
That makes those other locations more competitive due to lower
transportation costs.
The glut in the world sulphur market is severe and is becoming
increasingly more severe as environmental restrictions demand more and
increasingly more stringent regulations for stripping fossil fuels of their
sulphur content.
The world's sulphur production in years past was mainly from mining
sulphur. Sulphur mines could adjust to fluctuations in demand for
their product. At times of low demand mines would restrict their
output or even shut down and pick up production when the demand for their
sulphur increased. Sulphur for industrial processes and
agricultural uses in the world is now being supplied entirely from the waste
stream of oil refining and gas processing. All sulphur mines in the
world have been shut down for good.
Natural gas plants and oil refineries cannot shut down because there is
an escalating excess of sulphur in storage in the world. The oil and
gas industries will continue to increase their production of fossil fuels
and thereby produce ever more and larger amounts of waste sulphur of which
ever larger proportions will
remain in long-term storage. The challenge is to find safe and
environmentally friendly storage processes, unless methods can be found that
can use waste sulphur and waste gypsum in environmentally safe applications,
such as in the production of construction materials or in the paving of
roads.
Some people in the sulphur-producing industries are fully aware of that challenge and
are beginning to seek opportunities for turning waste by-products of their processes from being
liabilities into profitable applications, even if that means that new market
applications must be invented, designed and constructed that never before existed. An
additional challenge is then that the new and novel design applications that
are being investigated to that end must not be allowed to become liabilities
and environmental hazards.
The state of the art of those challenges has not yet reached its infancy.
It is merely a gleam in the eyes of its creators. A far greater
challenge that needs to be overcome appears to be the reluctance of sulphur producers to
view sulphur not as waste but as a valuable commodity. The escalating
over-supply of sulphur in the world market depresses sulphur prices.
Sulphur will not be viewed as anything other than waste unless it can be
converted into a value-added product.
What they say about waste by-products of fossil fuel production and
use:
Sulphur needs to be viewed as a valuable, sustainable commodity, just
like oil and gas, and not simply as a waste by-product.
News
release (2003 04 11)
Sulphur Institute, Washington, DC
"To meet environmental standards for low nitrogen oxide
(NOx) emissions, we have redesigned the way we burn coal," says M.
Mercedes Maroto-Valer, research associate in Penn State's Energy
Institute. "We resolved the environmental problem, but we created other
problems."
Coal-fired plants now use low NOx
burners to reduce emissions. These burners do the trick, but increase
the amounts of unburned carbon left after combustion. Power plants are
left with a mixture of fly ash and unburned carbon....
"The combustion of 920 million tons
of coal generates about 80 million tons of fly ash and unburned carbon
as combustion by-products," says Maroto-Valer. "Separating this waste
and using both components is certainly more economical and
environmentally friendly than simply disposing of the waste."
Waste Makes Saleable Coal Product
Science Daily, March 24, 1999
Note: The article says nothing
about the fact that 80 million tons of
fly ash and unburned carbon produce a far greater amount of
radioactivity than the wastes do from nuclear energy production of
an equal amount of energy produced. — ed.
Phosphogypsum, a waste by-product
derived from the wet process production of phosphoric acid, represents
one of the most serious problems facing the phosphate industry today.
This by-product gypsum precipitates during the reaction of sulfuric acid
with phosphate rock and is stored at a rate of about 30 million tons per
year on several stacks in central and northern Florida. The main problem
associated with this material concerns the relatively high levels of
natural uranium-series radionuclides and other impurities which could
impact the environment and which makes its commercial use impossible.
Our general approach to this problem was to start the task of detailing
exactly where and how radionuclides are hosted within the material. In
this way, it is hoped that ultimately one may develop purification
schemes for this waste material....
....while the initial uptake mechanisms for SO4
and Po differ, once associated with the bacterial cells, polonium is
dispersed between the cell walls, cytoplasm, and protein in a manner
similar to sulfur. The uptake rate of polonium is sufficiently rapid
that the potential exists for development of a bioremediation scheme for
removal of polonium (and perhaps other contaminating ions) from process
waters and other aqueous solutions.
Microbiology and Radiochemistry of Phosphogypsum
Florida Institute of Phosphate Research
FIPR Publication #05-035-115, May 1995
The limestone in the fluidized-bed is mostly
calcium carbonate (CaCO3), which forms lime (CaO) when it is heated. The
lime reacts with the sulfur compounds formed during combustion of the
culm to produce gypsum (CaCO4) -- an inert solid that has a variety of
uses or that can be disposed of more easily than the solid by-products
of other combustion technologies.
Clean Power and Industrial Redevelopment
– The Northampton
Generating Plant
Foster Wheeler Review & Heat Engineering
Heat Engineering, Winter 1998-1999, Volume 62, No. 4
Note: The preceding quote contains factual errors:
-
The
chemical designation for gypsum is wrong (it should be CaSO4·2H2O)*;
-
The "gypsum" produced in the fluidized-bed combustion process
cannot be gypsum but is the mineral anhydrite (CaSO4)
which, when disposed of and upon exposure to environmental water,
slowly returns to its dihydrated state, and
-
The contaminants
contained in the anhydrite resulting from the combustion process
make it
anything but inert and safe. — ed.
* Heating gypsum to between 100°C and 150°C
(302°F) partially
dehydrates the mineral by driving off exactly 75% of the
water contained in its chemical structure. The temperature and
time needed depend on ambient partial pressure of H2O.
Temperatures as high as 170°C are used in industrial calcination,
but at these temperatures the anhydrite begins to be
formed. The reaction for the partial dehydration is:
CaSO4·2H2O + heat --> CaSO4·½H2O
+ 1½H2O (steam)
The partially dehydrated mineral is called calcium sulfate
hemihydrate or calcined gypsum (commonly known as
plaster of Paris) (CaSO4·½H2O).
....The anhydrous form, called anhydrous calcium sulfate
(sometimes
anhydrite), is produced by further heating to above
approximately 180°C (356°F) and has the chemical formula CaSO4.
... (http://en.wikipedia.org/wiki/Gypsum)
SULFUR COMPOUNDS (SOx)
The primary reason sulfur compounds, or SOx, are classified as a
pollutant is because they react with water vapor (in the flue gas and
atmosphere) to form sulfuric acid mist. Airborne sulfuric acid has been
found in fog, smog, acid rain, and snow. Sulfuric acid has also been
found in lakes, rivers, and soil. The acid is extremely corrosive and
harmful to the environment....
Historically, SOx pollution has been controlled by either dispersion
or reduction. Dispersion involves the utilization of a tall stack, which
enables the release of pollutants high above the ground and over any
surrounding buildings, mountains, or hills, in order to limit ground
level SOx emissions. Today, dispersion alone is not enough to meet more
stringent SOx emission requirements; reduction methods must also be
employed....
Flue gas desulfurization systems are classified as either non-regenerable
or regenerable. Non-regenerable FGD systems, the most common type,
result in a waste product that requires proper disposal. Regenerable FGD
converts the waste by-product into a marketable product, such as sulfur
or sulfuric acid. SOx emission reductions of 90-95% can be achieved
through FGD. Fuel desulfurization and FGD are primarily used for
reducing SOx emissions for large utility boilers. Generally the
technology cannot be cost justified on industrial boilers.
Emissions
Cleaver Brooks Package Boiler Systems
2002 08 17
Note: Given the escalating world sulphur glut,
converting "the waste into a marketable product" requires solutions
that have not yet been found to be practical or viable. Still,
it is wrong or only partially correct to state that "Generally the
technology cannot be cost justified on industrial boilers."
The controlling factor is not cost justification (that means it
would be a discretionary option) but environmental
regulation and therefore mandatory, not an option. — ed.
Walter H. Schneider
Bruderheim, 2006 05 03 Back to HAZCO Index Page Back to Bruderheim Main Page
Posted 2006 05 03
Updates:
2006 05 31 (added information on radiation
exposure limits related to phosphogypsum)
2006 10 16 (reformated)
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