Environmental Engineering Reference
In-Depth Information
the residential-commercial sector, by the year 2010, carbon emissions could be reduced by 10.5%
below 1990 levels with judicious and cost-effective conservation measures.
11
In the industrial sector the largest savings could come from reductions in direct use of fossil
fuels (e.g., coal for process heat or smelting), process modification, energy-efficient motors, better
heat exchangers, and so on. A “high-efficiency-low-carbon” scenario predicts that as much as
12.5% energy savings could be realized in the U.S. industrial sector by the year 2010, translating
to a 62-Mt carbon emission reduction.
12
In the transportation sector, fossil fuel energy consumption is growing by leaps and bounds
all over the world. Increasing population and living standards, coupled with the movement from
agricultural to urban-industrial societies, puts more and more people and cargo in automobiles,
trucks, trains, airplanes, and ships. The most convenient fuel for the transportation sector is a
fluid fuel (liquid or gaseous)—for example, gasoline, diesel, jet-fuel (kerosene), alcohol, methane,
propane, or synthetic fluid fuels, which usually are derived from fossil fuel. Because it is unrealistic
to expect that the
number
of transportation vehicles, or the
distances
covered, will diminish, the only
chances for reducing carbon emissions in the transportation sector lie in efficiency improvements.
Such improvements are discussed in Chapter 8. They range from smaller, lightweight automobiles to
hybrid electric-internal combustion engine or fuel-cell-powered vehicles. It is estimated that in the
United States, in the year 2010, carbon emissions from the transportation sector will be 26% higher
than in 1997 under “business-as-usual” conditions, whereas if possible efficiency improvements
were introduced, they would be only 5% higher.
13
10.4.2
Supply-Side Efficiency Improvements
By supply-side efficiency improvements we mean principally electricity supply. In the United
States, 36% of carbon emissions come from electricity generating plants, and a similar percentage
is applicable worldwide (see Section 2.4). The electricity industry has many options to reduce
carbon emissions while supplying an ever-increasing electricity demand. These options, discussed
in Chapter 5, include the following:
•
Shift from coal to natural gas. Per unit of energy, gas emits roughly half as much carbon as
coal.
•
Replacement of single-cycle gas-fired steam power plants with combined cycle gas turbine
plants (CCGT). Because single-cycle power plant thermal efficiencies are in the range
35-40%, whereas the combined cycle plants can achieve 50-55%, the carbon emission
savings are in the range of 10-20%.
•
Replacement of single-cycle coal-fired power plants with gas-fired CCGT. The carbon emis-
sion savings are in the range 60-70% (50% on account of shift from coal to gas, and 10-20%
on account of higher efficiency).
•
Replacement of single-cycle coal-fired power plants with coal-derived synthetic gas-fired
combined cycle gas turbine plants. The efficiency of such plants is 40-45% based on the
11
Brown, M. A., et al., 1998.
Annu. Rev. Energy Environ.,
23,
287-385.
12
Brown, M. A., et al., 1998.
Annu. Rev. Energy Environ.,
23,
287-385.
13
Ibid.
