Page 37 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

10 1 Air Emissions

Air emissions are the byproducts of energy production and consumption; for
example, the combustion of methane in pure oxygen can be written in a simplified
form as

CH 4 þ O 2 ! CO 2 þ H 2 O þ Heat ð1:2Þ

The main objective offuel combustion is heat, which is used for other engineering
applications. Unfortunately, CO 2 is released as an air emission from the combustion
process, which is complicated and generates many pollutants. In reality, air instead
of pure oxygen (as shown in Eq. (1.2)) is used for fuel combustion. Moreover, fuels
are not purely carbon and hydrogen, and their compositions have to be analyzed
before the potential pollutants can be predicted. A power plant can be used as a more
realistic example. When burning coal to generate thermal energy to heat the water for
steam, primary air emissions including CO 2 ,SO 2 ,NO x , heavy metals, and partic-
ulates are produced and emitted from the stack into the atmosphere.
The emissions of air pollutants and GHGs from the stack depend on many
factors, including but are not limited to the properties of the fuel, the combustion
process, and downstream flue gas treatment devices. There is much more SO 2 in
flue gas when high sulfur coal is used as the fuel instead of gasoline. Nonetheless,
commercial natural gas is much cleaner than other fossil fuels because of it is free of
ash and sulfur. Fossil energy consumption is the main source of air emissions. In
the United States, more than 80 % of the CO 2 emissions are related to direct energy
consumption [26, 27].

1.4.2 Growing Population and Energy Consumption

From a global point of view, the growing population and the desire of human
beings in pursuit of high-speed transportation and comfortable lives are at the roots
of the air emissions. There has been a worldwide growth in population in both
developed and developing countries. However, the world population growth is
mainly attributed to that in developing countries. The twentieth century saw the
biggest increase in human population in history, due to medical advances and
massive increases in agricultural productivity. The United Nations [24] estimated
that the world’s population was growing at the rate of 1.14 % or about 75 million
people per year in 2012. By 2050, the world population is projected to be in the
range of 7.4–10.6 billion.
Global emissions of CO 2 , for example, also increased with the population [1],
rising from 21.2 to 26.9 billion metric tons. There were nearly no increases in North
American emissions, and a significant decrease occurred in Europe, whereas CO 2
emissions from Asia have doubled.
The growing global population demands more energy consumption to maintain
the same level of lifestyle; and, for developing countries, the increasing population