Environmental Engineering Reference
In-Depth Information
photovoltaic power, account for only a small portion of current energy production. Like other
mineral deposits, fossil fuels are not distributed uniformly around the globe, but are found on
continents and their margins that were once locations of great biomass production. They need to be
discovered and removed, and often processed, before they can be available for energy production.
Current and expected deposits would appear to last for a few centuries at current consumption rates.
Within the time horizon of most national planning, there is no impending shortage of fossil fuel
despite the continual depletion of what is a finite resource. In contrast, renewable energy sources are
not depletable, being supplied ultimately by the flux of solar insolation that impinges on the earth.
Like food, energy needs to be stored and transported from the time and place where it becomes
available to that where it is to be used. Fossil and nuclear fuels, which store their energy in chemical
or nuclear form indefinitely, are overwhelmingly the preferred form for storing and transporting
energy. Electrical energy is easily transmitted from source to user, but there is no electrical storage
capability in this system. Hydropower systems store energy for periods of days to years in their
reservoirs. For most renewable energy sources, there is no inherent storage capability so they
must be integrated into the electrical network. Many forms of mechanical and electrical energy
storage are being developed to provide for special applications where storage in chemical form is
not suitable. Efficient transformation of energy from mechanical to electrical form is an essential
factor of modern energy systems.
Although fossil fuels may be readily burned to provide heat for space heating, cooking, or in-
dustrial and commercial use, producing mechanical or electrical power from burning fuels required
the invention of power producing machines, beginning with the steam engine and subsequently
expanding to the gasoline engine, diesel engine, gas turbine, and fuel cell. The science of thermo-
dynamics prescribes the physicochemical rules that govern how much of a fuel's energy can be
transformed to mechanical power. While perfect machines can convert much of the fuel's energy
to work, practical and economic ones only return between a quarter and a half of the fuel energy.
Nevertheless, the technology is rich and capable of being improved through further research and de-
velopment, but large increases in fuel efficiency are not likely to be reached without a considerable
cost penalty.
Initially, steam engines were used to pump water from mines, to power knitting mills, and
to propel trains and ships. Starting in the late nineteenth century, electrical power produced by
steam engines became the preferred method for distributing machine power to distant end-users.
By the time electricity distribution had become universal (supplying mechanical power, light, and
communication signals), the generation of electrical power in steam power plants had become the
largest segment of energy use. Currently, 55% of world fossil fuel is consumed in electric power
plants.
The modern fossil-fueled steam power plant is quite complex (see Figure 1.1). Its principal
components—the boiler, the turbine, and the condenser—are designed to achieve maximum thermal
efficiency. But the combustion of the fuel produces gaseous and solid pollutants, among which are
the following: oxides of carbon, sulfur, and nitrogen; soot; toxic metal vapors; and ash. Removing
these pollutants from the flue gases requires complex machinery, such as scrubbers and electrostatic
precipitators, that increases the operating and capital cost of the power plant and consumes a small
percentage of its electrical output. The removed material must be disposed safely in a landfill. But
because of the size and technical sophistication of these plants, they provide a more certain avenue
of improvement in control than would many thousands of small power plants of equal total power.
Nuclear power plants utilize a steam cycle to produce mechanical power, but steam for the
turbine is generated by heat transfer from a hot fluid that passes through the nuclear reactor, or by
