SO2 and O2. But the highly alkaline condition in the kiln can
absorb 90% of the sulphur oxides. Sox emission can be
controlled by using low slphur fuel and raw material.
Table 2: Process SO2 Emission
The sulfur oxides react with water vapor and other chemicals
high in the atmosphere in the presence of sunlight to form
sulfuric acids. The acids formed usually dissolve in the
suspended water droplets, which can be washed from the air
on to the soil by rain or snow. This is known as acid rain. It is
responsible for so much damage to life and health. Respiratory
illnesses such as bronchitis are seen to increase with sulfur
oxide levels [21]. Increased level of SOx in the atmosphere
can also degrade agricultural productivity and death of some
plants.
Nitrogen Oxide (NOx):
Nitrogen oxides are produced in the combustion flame of a
rotary kiln, which enter the atmosphere with the exit gases,
and undergo many reactions in the atmosphere. Majorly NOx
are formed by thermal oxidation, which happens in
temperature range between 1,200-1,600 °C. Due to high
temperature significant amounts of thermal NO are generated
in the Kiln. Combustion of nitrogen-bearing fuels such as
certain coals also produces N2, or NO. [16].
N2 + O → NO + N
N + O2 → NO + O
As temperature increases, NO formation also increases. About
90% of the nitrogen oxides are produced in the form of nitric
oxide (NO) and the remaining 10% are in the form of nitrogen
dioxide (NO2) [21].
Produced NO converts to NO2 at the exit of the stack at
atmospheric conditions and appears in brown-yellow color.
NO + 1/2O2→ NO2 [16].
NOx causes a wide variety of health and environmental
impacts because of various compounds and derivatives in the
family of nitrogen oxides, including nitrogen dioxide, nitric
acid, nitrous oxide, nitrates, and nitric oxide.
Similar to sulphur dioxide, NOx react with water and other
of compounds to form various acidic compounds. When these
acidic compounds that are deposited to the earth’s surface,
they can impair the water quality of different water bodies and
acidify lakes and streams. Acidification (low pH) and the
chemical changes result in making it difficult for some fish
and other aquatic species to survive, grow, and reproduce.
Acid rain can also harm forest ecosystems by directly
damaging plant tissues [22].
Nitrous oxide is a greenhouse gas and it accumulates in the
atmosphere with other greenhouse gasses causing a gradual
rise in the earth's temperature. This will lead to global
warming and climate change.
NOx and volatile organic compounds react in the atmosphere
in the presence of sunlight to form ground-level ozone, which
causes smog in cities and rural areas. This ground level ozone
when breathed, it causes respiratory disease and other health
problems [22]. Nitrogen dioxide affects body functions such as
difficulty in breathing, chronic lung diseases, such as chronic
inflammation and irreversible structural changes in the lungs,
which with repeated exposure, can lead to premature aging of
the lungs and other respiratory illness. Studies indicate
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