Page 17 - Advanced Gas Turbine Cycles

xiv Prefwe

output of 4MW. Here the objective of the engineering designer was to develop as much
power as possible in the turbine, discharging the final gas at low temperature and velocity;
as opposed to the objective in the Whittle patent of 1930, in which any excess energy in the
gases at exhaust from the gas generator-the turbine driving the compressor-would be
used to produce a high-speed jet capable of propelling an aircraft.
It was the wartime work on the turbojet which provided a new stimulus to the further
development of the gas turbine for electric power generation, when many of the aircraft
engineers involved in the turbojet work moved over to heavy gas turbine design. But
surprisingly it was to be the late twentieth century before the gas turbine became a major
force in electrical generation through the big CCGTs (combined cycle gas turbines, using
bottoming steam cycles).
This book describes the thermodynamics of gas turbine cycles (although it does touch
briefly on the economics of electrical power generation). The strictures of classical
thermodynamics require that “cycle” is used only for a heat engine operating in closed
form, but the word has come to cover “open circuit” gas turbine plants, receiving “heat”
supplied through burning fuel, and eventually discharging the products to the atmosphere
(including crucially the carbon dioxide produced in combustion). The search for high gas
turbine efficiency has produced many suggestions for variations on the simple “open
circuit” plant suggested by Barber, but more recently work has been directed towards gas
turbines which produce less COz, or at least plants from which the carbon dioxide can be
disposed of, subsequent to sequestration.
There are many books on gas turbine theory and performance, notably by Hodge [6],
Cohen, Rogers and Saravanamuttoo [7], Kerrebrock [8], and more recently by Walsh and
Fletcher [9]; I myself have added two books on combined heat and power and on
combined power plants respectively [10,11]. They all range more widely than the basic
thermodynamics of gas turbine cycles, and the recent flurry of activity in this field has
encouraged me to devote this volume to cycles alone. But the remaining breadth of gas
turbine cycles proposed for power generation has led me to exclude from this volume the
coupling of the gas turbine with propulsion. I was also influenced in this decision by the
existence of several good books on aircraft propulsion, notably by Zucrow [12], Hill and
Peterson [13]; and more recently my friend Dr Nicholas Cumpsty, Chief Technologist of
Rolls Royce, plc, has written an excellent book on “Jet Propulsion” [ 141.
I first became interested in the subject of cycles when I went on sabbatical leave to
MIT, from Cambridge England to Cambridge Mass. There I was asked by the Director of
the Gas Turbine Laboratory, Professor E.S.Taylor, to take over his class on gas turbine
cycles for the year. The established text for this course consisted of a beautiful set of
notes on cycles by Professor (Sir) William Hawthorne, who had been a member of
Whittle’s team. Hawthorne’s notes remain the best starting point for the subject and I
have called upon them here, particularly in the early part of Chapter 3.
Hawthorne taught me the power of temperature-entropy diagram in the study of cycles,
particularly in his discussion of “air standard” cycles-assuming the working fluid to be a
perfect gas, with constant specific heats. It is interesting that Whittle wrote in his later
book [15] that he himself “never found the (T,s diagram) to be useful”, although he had a
profound understanding of the basic thermodynamics of gas turbine cycles. For he also
wrote