Encyclopedia of Environmental Science and Engineering, Volume I and II

314 ENERGY SOURCES—ALTERNATIVES

worthy of generous support by governments. In any case, the

studies will be continued, and progress is considerable.

Refuse

Solid waste products including paper, rags, cardboard, and

plastics may be considered as an energy resource. Combustible

wastes may be used as a fuel for electric power production and

process heat and have a heating value of about 5000 Btu/lb. If

fully utilized, these wastes could furnish about 10% of the fuel

needs of central station power plants. Environmental problems

are encountered in burning this material just as in the incinera-

tion of waste, and emissions depend upon the chemical char-

acteristics of the refuse.

An alternate use of refuse, studied by the Bureau of

Mines,^42 involves its conversion by pyrolysis into fuels such

as combustible gases and light oils as well as other useful

by-products. A ton of urban refuse containing mainly plas-

tics can be converted, by pyrolysis at 900°C, into 328 lb of

solid residue, 1.5 gal of tar, 0.5 gal of light oil (mostly ben-

zine), 97.4 gal of aqueous liquor, 31.5 lb of ammonium sul-

fate, and 18,058 ft^3 of gas consisting of hydrogen, methane,

CO, and ethylene. Other processes may be used to produce

predominantly liquid fuels rather than a gaseous product.

Agricultural wastes, from animals and vegetation, are

more abundant than urban wastes and constitute a large,

though difficult to exploit, energy resource.

ENERGY CONVERSION

Most of the air pollutant and waste heat discharges attribut-

able to energy-related activities are released in the energy

conversion step. Here, energy resources are consumed to

provide other energy forms either for direct utilization or for

transmission to centers of energy demand.

The range of technological alternatives available in

energy conversion is illustrated in Figure 6. The columns and

rows represent input and output energy forms, respectively,

with specific devices or power plants capable of making

the transformation indicated in the appropriate block. The

most widely used systems involve chemical (fossil fuel)

and nuclear energy inputs and the following conversions or

series of conversions:

1) For space heat (non-electric);

chemical → thermal.

2) For the generation of electricity;

Chemical or nuclear → thermal → kinetic →

electrical.

3) For the propulsion of a vehicle (non-electric);

chemical → thermal → kinetic.

In the conversion from thermal to kinetic energy a power

cycle is used and its efficiency is limited by the second law

of thermodynamics to a value less than that of the theoretical

Carnot cycle. The Carnot cycle efficiency is equal to the dif-

ference between the temperatures at which heat is supplied

to and rejected from the cycle working fluid, divided by the

absolute temperature at which the heat is added. This theo-

retical limit on conversion efficiency increases for a given

heat rejection temperature as the temperature at which heat

is supplied to the cycle working fluid is raised.

A 1968 inventory of prime movers that are involved in

the kinetic energy portion of various conversion systems is

given in Table 17. Although automotive engines make up

over 90% of the total installed horsepower, this figure is

deceptive because of differences in the annual usage of the

various power plants. A better indication of their relative use

can be obtained from fuel consumption data.

The state-of-the-art in energy conversion systems and

associated operations has been reviewed in a study per-

formed for the OST^43 and by the FPC in both its 1964 and

most recent 1970 National Power Survey.^29 It is convenient

in reviewing alternative power devices that might be used to

reduce harmful environmental effects, to maintain the dis-

tinction between centralized and decentralized power plants,

where the latter may be either stationary or mobile.

TABLE 15

Data for solar power plants

Name SSPS Eurelios Sunshine CESA 1 Themis Solar One

Location Almeria Adrano Nio Almeria Targasonne Barstow

Country Spain Italy Japan Spain France USA

Completion year 1981 1981 1981 1983 1982 1982

El. output (MW) 0.5 0.7 0.8 1.0 2.5 10

Heat transfer fluid sodium steam steam steam molten salt steam

TABLE 16

Principal data of Solar One in Barstow, California, USA

Reflecting heliostat area 71,447 m^2

Heat transfer medium in receiver steam

Storage capacity equivalent to 28 M Whe

Net electrical output 10 M We

C005_006_r03.indd 314C005_006_r03.indd 314 11/18/2005 12:05:48 PM11/18/2005 12:05:48 PM