TECHNOLOGY STUDIES
STATUS OF
NOx CONTROL TECHNOLOGIES
Effect of NOx
reduction technologies in 419 coal based power plants has been studied. It is observed that the extent of reduction
achieved with the same technology in similar units has varied considerably. Not only in many of the installations has
the reduction fallen short of expectations but also in several of them the
result has even been negative. A
significant number of coal-fired units without any control had NOx
levels equal to or lower than the median values of similar units with controls
imposed. The impact of the operating technologies can therefore, be only
considered as unit specific. These
anomalies might have arisen due to incompatibility of the system design to the
fuel characteristics - both physics and chemistry. Coal reburn as the base technology for NOx reduction is seen to
hold promise.
TECHNOLOGIES FULL
REPORT SERVICE
Kotur S.
Narasimhan
Consultant, 10928,
Greenaire Pl
Richmond VA 23233
ABSTRACT
World
over, consumption of energy resources is disproportionate to the known
reserves. Even though coal accounts for
more than 90 percent of the known fossil energy sources, its share in meeting
the energy needs is significantly low.
Any deliberate attempt to increase the use of coal will be met with
economic constraints controlled by environmental considerations. On the other
hand, it is well recognized that hydrogen, with its zero emission potential, is
the ultimate energy source. Absence of
free hydrogen source and want of economical way to derive it from water is
holding its domination on the energy scene.
Technological developments are however, being pursued towards this end
of hydrogen based energy scenario. Such
efforts can be complemented and hastened by operating all conventional steam
cycle power plants to their full capacity and make use of surplus power to
generate hydrogen for use as transportation fuel.
By such
a practice, it is observed that additional 620 million megawatt hour energy
generation is annually possible by operating 335 plants situated in 42 states to
85 percent capacity. This is equivalent
to 340 million barrels of oil on the basis of 75 percent conversion efficiency
for hydrogen generation. In 15 states
the oil replacement capacity can exceed 10 million barrels. Oil replacement potential will proportionately
increase by increasing capacity utilization (some plants are run at 98%) and
improving conversion efficiency (90% is possible with solid polymer
electrolytes). Additional 38 percent
oil replacement value is possible.
While toxic emissions from automobile exhaust can be eliminated totally,
the net generation of carbon dioxide will apparently increase. Such an increase is however be comparable to
other means of using coal for hydrogen generation. More importantly, its generation will be restricted to a few
locations as against thinly dissipating the same all over the country by way of
automobile exhaust. This would enable
application of any carbon sequestration process very practical.
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STATUS OF NOx CONTROL TECHNOLOGIES
Kotur S.
Narasimhan
Consultant, 10928,
Greenaire Pl
Richmond VA 23233
ABSTRACT
A
study is made on the emissions of oxides of nitrogen (NOx) from power plants in
the country in order to:
q
Assess the impact of coal based units on the
environment
and
q
Gauge the utility of NOx reduction technologies
that are currently in vogue.
86
percent of 5.5 million tons of NOx emitted during the year 1999 came from
exclusively coal-based units. Such
emissions ranged from 0.12 lbs/mmBtu to 1.8 lbs/mmBtu in sharp contrast to oil
and gas fired units that had a shorter range.
419 coal-based units equipped with NOx control measures emitted 2.14
million tons (0.4 lbs/mmBtu on average) compared to 2.64 million tons (0.58
lbs/mmBtu on average) from 634 units that had no control.
Most of the coal-based units having controls acquired them
during the years 1995-1999. A
comparison of NOx emissions from them before and after the retrofit has brought
out some interesting observations. The
extent of reduction achieved with the same technology in similar units has
varied considerably. Not only in many
of the installations has the reduction fallen short of expectations but also in
several of them the result is even negative.
A significant number of coal-fired units without any control had NOx
levels equal to or lower than the median values of similar units with controls
imposed. The impact of the operating technologies can therefore, be only
considered as unit specific. These
anomalies might have arisen due to incompatibility of the system design to the
fuel characteristics - both physics and chemistry.
Eventually
it may be necessary to reduce NOx to below 0.1 lbs/mmBtu. For this purpose a combination of
technologies may be required involving Selective Catalytic Reduction (SCR),
Coal Reburn (CR) and some others unique to each case. A better understanding of the relation between system design and
fuel characteristics could minimize the number of technologies needed.
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