Chapter 7Chapter 7Chapter 7Chapter 7Chapter 7
Fuels and CombustionFuels and CombustionFuels and CombustionFuels and CombustionFuels and Combustion
7.1 Introduction
The components of fossil-fueled steam generators that dealt with the working fluid (water and
steam) and with the air and flue gases. We deferred discussing the fuel aspects because they require
independent treatment. There is a rather wide variety of fuels. Their preparation and feeding, often
outside the steam generators, and their methods of firing deserve special attention.
The increasing worldwide demand for energy has focused attention on fuels, their availability
and environmental effects. The fuels available to utility industry are largely nuclear and fossil, both
essentially nonrenewable. Nuclear fuels originated with the universe, and it takes nature millions of
years to manufacture fossil fuels.
Fossil fuels originate from the earth as a result of the slow decomposition and chemical conver-
sion of organic material. They come in three basic forms: solid (coal). liquid (oil), and natural gas. Coal
represents the largest fossil-fuel energy resource in the world. In the United States today (1983), it is
responsible for about 50 percent of electric-power generation. Oil and natural gas are responsible for
another 30 percent. The remaining percentage is mostly due to nuclear and hydraulic generation. Natu-
ral gas, however, is being phased out of the picture in the United States because it must be conserved for
essential industrial and domestic uses.
New combustible-fuel options include the so-called synthetic fuels, or synfuels, which are liq-
uids and gases derived largely from coal, oil shale, and tar sands. A tiny fraction of fuels used today are
industrial by-products, industrial and domestic wastes. and biomass.
This chapter will cover the combustible fuels available to the utility industry, both natural (fossil)
and synthetic, and their preparation and firing systems. Nuclear fuels and d renewable energy sources,
and the environmental aspects of power generation in general will be covered later in this text.
7.2 Coal
Coal is a general term that encompasses a large number of solid organic minerals with widely
differing compositions and properties, although all are essentially rich in amorous (without regular
structure) elemental carbon. It is found in stratified deposits at different and often great depths, although
sometimes near the surface. It is estimated that in the United States there are 270,000 million tons of
recoverable reserves (those that can be mined economically within the foreseeable future) in 36 of the
50 states. this accounts for about 30 percent of the world’s total.