Page 372 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

12.1 Background Information 351

Levels of GHGs have increased dramatically since the industrial revolution. For
example, about 75 % man-made carbon dioxide emissions were from burning fossil
fuels during the past 20 years. About 3.2 billion metric tons is added to the
atmosphere annually. The U.S. produces about 25 % of global CO 2 emissions
where 85 % of the US energy is produced through fossil fuel combustion [32].
Global carbon dioxide emissions continue increasing annually between 2001 and
2025, and the emerging economies (China and India, for example) contribute to
much of the enhanced GHG effect. These developing countries’ GHG emissions are
expected to grow at 2.7 % annually by 2025 [22].
Combustion is the major source for the increase of CO 2 in the atmosphere. It can
be concluded that reduction of CO 2 emissions from fossil fuel combustion will have
the largest impact on GHG emissions. In this chapter, we focus primarily on
approaches to CO 2 emission control. Readers are referred to the literature for the
approaches to the GHG emission control.

12.2 CO Generation in Combustion
2

According to IPCC [30–32] data, CO 2 emissions from large fossil fueled power
plants account for half of the total carbon emissions. Other sources include
industrial processes such as cement production, integrated steel mills, and oil-gas
refinery. The mechanisms of CO 2 generation in combustion processes have been
introduced in Parts I and II, and it is briefly summarized as follows for readers who
are interested in this chapter only.
Stoichiometric combustion process of a hydrocarbon fuel C a H b perfectly mixed
with oxygen can be described as

b b

C a H b þ a þ O 2 ! aCO 2 þ H 2 O ð12:2Þ
4 2
Thus the stoichiometry of a general hydrocarbon C a H b mixed with dry air
perfectly can be described by the following formulas:

1 b b 3:76 b
C a H b þ a þ ð O 2 þ 3:76N 2 Þ ! aCO 2 þ H 2 O þ a þ N 2 ð12:3Þ
/ 4 2 / 4
where / is the equivalence ratio.
The fuel-lean reaction formula for the combustion of C a H b perfectly mixed with
excess air is

1 b
C a H b þ a þ ð O 2 þ 3:76N 2 Þ
/ 4
ð12:4Þ
b 3:76 b 1 b

! aCO 2 þ H 2 O þ a þ N 2 þ 1 a þ O 2
2 / 4 / 4