Introduction

Traditionally, fossil fuels have supplied most of the world's energy requirements. Currentpredictions are that the United States-as well as many other countries-will continue to rely heavily on these fuels well into the twenty-first century.

One of the largest users of fossil fuels is the electric utility industry. The combustion of fossil fuels produces high-pressure [typically 2400 to 3500/lb/in ² (gage)] and high-temperature (most commonly 1000 F) steam, which is used to drive a turbine at 3600 r/min. The turbine drives an electrical generator. There is more than 600,000 MW of electrical generating capacity installed in the United States. Well over half of this capacity is powered by fossil fuels.

5.1.2 Thermodynamic Cycles

Rankine Cycle. The cornerstone of the modern steam power plant is a modification of the Carnot cycle proposed by W.J.M.Rankine, a distinguished Scottish engineering professor of thermodynamics and applied mechanics. The temperature-entropy and enthalpy-entropy diagrams of Fig. 5-1 illustrate the state changes for the Rankine cycle. With the exception that compression terminates (state a) at boiling pressure rather than the boiling temperature (state a ?) the cycle resembles a Carnot cycle. The triangle bounded by a-a ? and the line connecting to the temperature-entropy curve in Fig. 5-1a signify the loss of cycle work because of the irreversible heating of the liquid from state a to saturated liquid. The lower...