Page 59 - Handbook of Energy Engineering Calculations

Since the amount of fuel burned in a steam plant is a function of the steam
cycle efficiency, this section provides a number of pertinent cycle and
equipment efficiency calculations. With a higher cycle efficiency, less fuel is
burned, and the plant’s operating cost is lower. When a smaller amount of
coal fuel is burned, less atmospheric and landfill pollution will be caused by

the fossil-fueled generating plant. Oil and gas fuels contribute to GHG (at a
lesser amount than coal) but not to landfill pollution.
Power magazine recently studied coal-fired steam plant thermal efficiency

and found that ultra super critical (USC) plants in the United States are
projecting a net thermal efficiency of 39 percent, based on the higher heating
value (HHV) of the coal. Power also reports that seawater- and ocean-water-
cooled coal-fired plants have up to 1.5 percent higher thermal efficiency than
cooling-tower-cooled steam plants.

European coal-fired steam plants often report higher thermal efficiencies
than those in the United States. Thus, one European plant reports 43.2
percent, based on the lower heating value (LHV) of the coal burned.

Likewise, steam plants in other parts of the world report thermal efficiencies
in the 40 percent plus range. Such efficiencies are usually based on the LHV
of the coal fuel.
Because central-station power plants, and many industrial power plants,
are built to function for 50 or more years, fuel-selection choices are

extremely important. Thus, a fuel chosen today—coal, oil, gas, or any of the
waste-product types—may become much costlier in future years if carbon
dioxide or other GHG caps are lowered for the chosen fuel. So, engineers are

becoming much more cautious about fuels they choose for all new power
plants. With recent development of large shale-gas sources, this fuel is
getting more attention than ever before for steam power plants.
Another area where steam plants are finding greater examination by
regulatory bodies is in cooling water use. With the once-through cooling

systems used for steam condensers, the major impact is the temperature rise
of the water. There is little evaporation in once-through cooling systems
because the temperature rise of the cooling water is modest. In recirculating

cooling systems, such as with cooling towers, there are evaporative water
losses. Also, water must be blown down or discharged from the system to
reduce chemical buildup. The blow-down water is lost.
To reduce carbon dioxide emissions to the atmosphere, water is used to