Environmental Engineering Reference
In-Depth Information
Unfortunately, the replacement of fossil fuels by new sources of energy is not so straight
forward because of low return on the energy investment (EROI) of most sources, the
intermittency of others, such as solar and wind, the technical difficulty to store energy in large
volumes, and the lack of capacity to produce enough energy to satisfy society.
On the other hand, we need to become more efficient in the way energy is used. Typically,
the use of fuel to produce electricity has an efficiency of around 30 percent; the rest is lost as
heat released back to the environment. This efficiency is eventually boosted upward of 40 to
57 percent by using combined cycles. An even more efficient way to increase the overall effi-
ciency is using the concept of production of combined heat and power (CHP), which can boost
the efficiency of fuel utilization to 75 percent or more.
In the food industry, there are multiple opportunities to improve energy utilization in
processes and to recover energy that is normally wasted. In the section “Improving Energy
Efficiency of Food-Processing Plants” of this chapter there are several suggestions about
energy improvements for steam production and use as well as for direct-fired heating systems.
Heat coming out as a result of processes can be recovered with different technologies such
as heat pumps, machines working according to the “Rankine Cycle,” and absorption refrigera-
tion systems, and low-pressure steam can be updated by steam vapor recompression.
Mechanical systems powered by electrical motors can benefit from using motors with
higher efficiency, choosing the right motor for the equipment, and using variable speed motors.
The electrical consumption of fans and pumps can be reduced by matching the motor with
the  fan or pump and using high-efficiency fans and pumps. Compressors are inherently
inefficient, so compressed air should only be used for what cannot be replaced by other
hydraulic or electric mechanism. Also, it is important to fix air leaks, which are normally a
small but constant waste of energy.
Energy efficiency of refrigeration systems can be improved by using efficient compressors
and auxiliary motors, and other actions such as the installation of floating-head pressure
control, liquid-pressure amplifiers, refrigerant subcooling, evaporative condensers, automatic
purge systems, and reducing the cooling load by avoiding heat gains at refrigerated areas.
The environmental impact of energy use can be lessened by buying green power or generat-
ing it on site. Green power is electricity that has been produced using renewable resources,
such as wind, solar, geothermal, low-impact hydro, biomass, and geothermal sources. On-site
generation is possible if renewable sources are available in the vicinity, which includes biogas,
landfill gas, biomass, solar, and wind sources.
REFERENCES
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American Wind Energy Association (AWEA). 2009. Small wind turbine global market study. Washington,
D.C.: AWEA.
Barber-Nichols. n.d. Waste heat recovery systems & geothermal power generation equipment. Available at: <http://
www.barber-nichols.com/products/waste_heat_power_generation_equipment/> [Accessed January 29, 2011].
Beaty, H. W. and Kirtley, J. L. 1998. Electric motor handbook . New York: McGraw-Hill.
Belgiorno, V., De Feo, G., Della Rocca, C. and Napoli, R. M. A. 2003. Energy from gasification of solid
wastes. Waste Management 23: 1-15.
Bessette, R. 2003. Energy efficiency and industrial boiler efficiency: An industry perspective. DOE document
DOE/GO-102003-1805. Washington, D.C.: Department of Energy.
Boundy, B., et al. 2010. Biomass energy data book , 3rd ed. Energy Efficiency and Renewable Energy, Oak
Ridge National Laboratory. Washington, D.C.: Department of Energy.
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