Advanced Gas Turbine Cycles

A Brief Review of Power Generation Thermodynamics

J.H. Horlock

• Publisher: Pergamon
• Year: 2013
• Print ISBN: 9780080442730
• eBook ISBN: 9780080545561
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Primarily this book describes the thermodynamics of gas turbine cycles. The search for high gas turbine efficiency has produced many variations on the simple "open circuit" plant, involving the use of heat exchangers, reheating and intercooling, water and steam injection, cogeneration and combined cycle plants. These are described fully in the text. A review of recent proposals for a number of novel gas turbine cycles is also included. In the past few years work has been directed towards developing gas turbines which produce less carbon dioxide, or plants from which the CO2 can be disposed of; the implications of a carbon tax on electricity pricing are considered. In presenting this wide survey of gas turbine cycles for power generation the author calls on both his academic experience (at Cambridge and Liverpool Universities, the Gas Turbine Laboratory at MIT and Penn State University) and his industrial work (primarily with Rolls Royce, plc.) The book will be essential reading for final year and masters students in mechanical engineering, and for practising engineers.

Chapter 1

A BRIEF REVIEW OF POWER GENERATION THERMODYNAMICS

1.1 Introduction

A conventional power plant receiving fuel energy (F), producing work (W) and rejecting heat (Q_A) to a sink at low temperature is shown in Fig. 1.1 as a block diagram. The objective is to achieve the least fuel input for a given work output as this will be economically beneficial in the operation of the power plant, thereby minimising the fuel costs. However, the capital cost of achieving high efficiency has to be assessed and balanced against the resulting saving in fuel costs.

Fig. 1.1 Basic power plant.

The discussion here is restricted to plants in which the flow is steady, since virtually all the plants (and their components) with which the book is concerned have a steady flow.

It is important first to distinguish between a closed cyclic power plant (or heat engine) and an open circuit power plant. In the former, fluid passes continuously round a closed circuit, through a thermodynamic cycle in which heat (Q_B) is received from a source at a high temperature, heat (Q_A) is rejected to a sink at low temperature and work output (W) is delivered, usually to drive an electric generator.

Fig. 1.2 shows a gas turbine power plant operating on a closed circuit. The dotted chain control surface (Y) surrounds a cyclic gas turbine power plant (or cyclic heat engine) through which air or gas circulates, and the combustion chamber is located within the second open control surface (Z). Heat Q_B is transferred from Z to Y, and heat Q_A is rejected from Y. The two control volumes form a complete power plant.

Fig. 1.2 Closed circuit gas turbine plant (after Haywood [3]).

Usually, a gas turbine plant operates on ‘open circuit’, with internal combustion (Fig. 1.3). Air and fuel pass across the single control surface into the compressor and combustion chamber, respectively, and the combustion products leave the control surface after expansion through the turbine. The open circuit plant cannot be said to operate on a thermodynamic cycle; however, its performance is often assessed by treating it as equivalent to a closed cyclic power plant, but care must be taken in such an approach.

Fig. 1.3 Open circuit gas turbine plant (after Haywood [3]).

The Joule–Brayton (JB) constant pressure closed cycle is the basis of the cyclic gas turbine power plant, with steady flow of air (or gas) through a compressor, heater, turbine, cooler within a closed circuit (Fig. 1.4). The turbine drives the compressor and a generator delivering the electrical power, heat is supplied at a constant pressure and is also rejected at constant pressure. The temperature–entropy diagram for this cycle is also shown in the figure. The many variations of this basic cycle form the subject of this volume.

Fig. 1.4 Joule–Brayton cycle (after Ref. [1]).

An important field of study for power plants is that of the ‘combined plant’ [1]. A broad definition of the combined power plant (Fig. 1.5) is one in which a higher (upper or topping) thermodynamic cycle produces power, but part or all of its heat rejection is used in supplying heat to a ‘lower’ or bottoming cycle. The ‘upper’ plant is frequently an open circuit gas turbine while the ‘lower’ plant is a closed circuit steam turbine; together they form a combined cycle gas turbine (CCGT) plant.

Fig. 1.5 Combined p...

Table of contents

• Cover
• Title page
• Table of Contents
• Copyright
• Dedication
• PREFACE
• NOTATION
• Chapter 1: A BRIEF REVIEW OF POWER GENERATION THERMODYNAMICS
• Chapter 2: REVERSIBILITY AND AVAILABILITY
• Chapter 3: BASIC GAS TURBINE CYCLES
• Chapter 4: CYCLE EFFICIENCY WITH TURBINE COOLING (COOLING FLOW RATES SPECIFIED)
• Chapter 5: FULL CALCULATIONS OF PLANT EFFICIENCY
• Chapter 6: ‘WET’ GAS TURBINE PLANTS
• Chapter 7: THE COMBINED CYCLE GAS TURBINE (CCGT)
• Chapter 8: NOVEL GAS TURBINE CYCLES
• Chapter 9: THE GAS TURBINE AS A COGENERATION (COMBINED HEAT AND POWER) PLANT
• DERIVATION OF REQUIRED COOLING FLOWS
• ECONOMICS OF GAS TURBINE PLANTS
• SUBJECT INDEX