Environmental Engineering Reference
In-Depth Information
40
35
Industrial
30
25
20
15
10
5
Residential/Commercial
Transportation
0
1973
1977
1981
1985
1989
1993
1996
Figure 2.8
Trend of U.S. energy consumption for industrial, residential-commercial, and transportation
sectors in 1973-1996. (
Source:
Same as in Figure 2.4.)
Electrochemical 3
2 Process cooling
Non-process 12
35
Boiler fuel
14
Machine
drive
Direct process 33
Figure 2.9
Proportions (%) of primary energy use in the U.S. industrial sector. (Data from U.S. Department
of Energy, Energy Information Agency, 1994.
Manufacturing Energy Consumption Survey, 1994
.)
The trend of annual consumption of energy in the three sectors over the years 1973-1996
is shown in Figure 2.8. In those years the energy consumption for industrial production barely
increased, whereas the consumption for the residential-commercial and transportation sectors in-
creased significantly. Let us consider the pattern of energy consumption within each sector.
2.6.1
Industrial Sector
Of the total energy used by the industrial sector, about 35% is used for boiler fuel. The major part
of this boiler fuel is used for direct industrial processes, including electricity generation; a smaller
part is used for space heating. Direct process heat consumes 33%, machine drive 14%, nonprocess
uses 12%, electrochemical processes 3%, and process cooling and other uses 2% of the total energy
consumed by the industrial sector (see Figure 2.9). Even though the industrial sector has become
more energy efficient over the past years, there is still room for improvement. Industry could save
energy by process modification, better heat exchangers, more efficient drive mechanisms, and load-
matched, variable-speed motors. In some cases, cogeneration can save energy. In cogeneration, heat
(steam) and electricity required by the industrial process and the other energy needs for the facility
(e.g., space heating) are supplied from the same power plant. The fuel savings are especially
