Page 162 - Advanced Gas Turbine Cycles

Chapter 8

NOVEL GAS TURBINE CYCLES

8.1. Introduction

In the previous chapters, we have been concerned mainly with the thermodynamics of
‘standard’ gas turbine cycles, in a variety of forms. In this chapter, we consider some
novel types of gas turbine cycles recently proposed, most of which have not yet been
built.
So far, we have focussed on the achievement of maximum thermal efficiency and
maximum specific work in power producing plants (or maximum energy utilisation and
fuel savings in cogeneration plants). Practical gas turbines built up to the present time have
been mainly based on those cycles already described, with designers seeking higher
efficiency through
(a) advancing the basic thermodynamic parameters (such as turbomachinery polytropic
efficiency, turbine inlet temperature, and compressor pressure ratio);
(b) use of better materials able to withstand higher temperatures; and
(c) introducing additional features, such as recuperation, intercooling, reheating, water
injection, etc.
But for power station applications, the thermal efficiency is not the only measure of
the performance of a plant. While a new type of plant may involve some reduction in
running costs due to improved thermal efficiency, it may also involve additional capital
costs. The cost of electricity produced is the crucial criterion within the overall
economics, and this depends not only on the thermal efficiency and capital costs, but also
on the price of fuel, operational and maintenance costs, and the taxes imposed. Yet
another factor, which has recently become important, is the production by gas turbine
plants of greenhouse gases (mainly carbon dioxide) which contribute to global warming.
Many countries are now considering the imposition of a special tax on the amount of
C02 produced by a power plant, and this may adversely affect the economics. So
consideration of a new plant in future will involve not only the factors listed above but
also the amount of C02 produced per unit of electricity together with the extra taxes that
may have to be paid.
A brief and simplified description of how electricity price may be determined is given
in Appendix B, giving some comparisons between different basic plants. We also describe
there how the economics of a new plant may be affected by the imposition of an extra
carbon tax associated with the amount of carbon dioxide produced.
Thus there are now three objectives for the plant designer:

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