316 ENERGY SOURCES—ALTERNATIVES
of control systems for SO 2 and NO x emissions from steam
plants fired with coal or high sulfur oil will increase the cost
of power generation. Baron^41 estimates that flue gas scrub-
bing would add about 7% to the cost of power generation in
a 1000 MW output plant using oil with a 1% sulfur content.
The provision of dry cooling towers that reject waste heat
to the atmosphere with no waste usage would increase the
cost in the same plant by another 30%. The EPA has recently
proposed^46 emission standards for coal-fired steam genera-
tors that would limit particulate releases to 0.2 lb per 10^6
Btu, SO 2 releases to 1.2 lb per 10^6 Btu, and NO x to 0.7 lb per
10 6 Btu heat input.
The necessity to substitute oil by other energy agents as
well as the little acceptance of nuclear power plants by the
population of industrialized countries may lead for a certain
time to a renaissance of conventional coal and lignite fired
power plants but with a more sophisticated equipment for
protection of environment. This protection will not include
dry cooling towers, but washing equipment of flue gas to
wash out partly SO 2 and NO x as well as precipitators for dust.
This environment protecting equipment increased the cost of
the last built 750 MW coal fired power plant in Germany up
to 27%. With full desulfurization and wet cooling tower the
provision of environment protection will cost about 35%. It
seems that there are two tendencies:1) Big power plants of coal and lignite fired units
with full SO 2 protection, and wet cooling tower
(350 and 750 MW).
2) In the second place nuclear power plants with two
and more units of 1000 and 1300 MW consider-
ing the difficulty to find new locations accepted
by the population.Improvements in the efficiency of energy conversion
reduce the fuel consumption and attendant environmentaleffects directly for a given electrical output. Steam-cycle
power plants operating with fossil fuels attain a thermal effi-
ciency of about 40% with a maximum steam temperature in
the power cycle of 1000° to 1050°F, which is well below
the combustion temperature of these fuels. Current nuclear
power plants operate with a maximum steam temperature of
about 550°F and have a lower thermal efficiency. The cycle
efficiency increases as the steam temperature is raised but
the more severe temperature and pressure conditions would
lead, in both fossil and nuclear systems to materials prob-
lems and higher plant capital costs that would more than
offset the economic gains of increased efficiency. Topping
cycles, which are added to the steam cycle and use other
thermodynamic working fluids such as mercury or potas-
sium in higher temperature ranges, therefore providing
higher efficiency, have been studied for fossil-fueled sys-
tems and actually operated in the case of mercury but the
gains appear to be marginal. Thermionic topping devices^47
that convert thermal energy directly to electrical energy
have also been proposed and promise to increase the over-all
efficiency of conventional plants to about 50% performance
must be improved before they can be used to advantage. A
combined cycle, involving a gas turbine topping unit that
would operate at high temperature on gas produced from
coal and would reject its heat to a conventional steam cycle,
is another promising system and could have an overall effi-
ciency in the 42 to 43% range.
Some promising alternatives for centralized power pro-
duction that can utilize fossil resources are fuel cells and
magnetohydrodynamic (MHD) generators. The number of
nuclear reactor plants being installed by utilities is expand-
ing and further developments in breeder reactors and fusion
systems are also anticipated. Solar power plants are of great
interest in the longer term as a clean energy source.Fuel Cells
This direct conversion device is not limited in efficiency
by thermodynamic considerations and can convert chemi-
cal energy directly into electrical energy without the inter-
mediate conversion to thermal and kinetic energy. Over-all
efficiencies as high as 75% have been attained in special
purpose applications. With hydrogen and oxygen fuel fed
to electrodes submerged in a suitable electrolyte, this device
produces 0.7 to 0.85 volts (dc)/cell and many cells must be
connected in series to produce useful voltages for transmis-
sion. Development work is in progress on cells that could
operate on gasified coal or other gaseous fuels with air as
the oxidizer and a conceptual design has been completed for
such a plant.^48
Air pollution and waste heat discharges would be reduced
in a fuel cell power plant because of the improved efficiency
of fuel utilization. If coal were used as the source of a gas-
eous fuel, the impurities in the coal and particulates would
have to be controlled in the gasification plant, but such con-
trol would be easier to provide in this operation than in a
conventional power plant. In the course of the development
of fuel cells, it is more likely that they will be applied first to
smaller decentralized power systems.TABLE 17
Total horsepower of all prime movers, 1968 (10^6 horsepower)Item Horsepower
Automotivea 16,854
Nonautomotive
Factories 52
Mines 43
Railroads 58
Merchant ships and vessels 20
Farmsb 292
Electric central stations 372
Aircraft 137
Total 17,828
a Includes cars, buses, trucks, and motorcycles.
b Includes about 1.3 × 10^6 hp in work animals and 22,000 hp in windmills.
Source: Statistical Abstracts of the US, 1970.C005_006_r03.indd 316C005_006_r03.indd 316 11/18/2005 12:05:49 PM11/18/2005 12:05:49 PM