Abstract
In recent years, turbine ships have seldom been built because of the remarkable improvement of thermal efficiency of Diesel engine ships. But, there still exists some room for the formers which utilize coal. However, even in the case of coal firing ships, high thermal efficiency is the crucial point from the economical point.
The turbine ships adopt non-repeat regenerative cycle with usually three heaters. In this cycle, the choice of optimum extraction points is one of the most important problems to maximize its thermal efficiency. Only few studies based on approximative methods have been published on optimization of regenerative cycle with surface-type heaters which are used in actual plants rather than contact-type ones, but their analyses were not thoroughly executed and their modellings not realistic.
In this paper, an exact numerical and two approximative methods are employed to analyse two idealized and one practical schemes of regenerative cycle with surface-type heaters assuming the same assumptions and simplifications as earlier works. First, correct formulae of thermal effi-ciency are led in terms of non-dimensional parameters representing the turbine inlet condition and extraction points. Then, the influences of the number of heaters on the optimum efficiency and extraction points are clarified. Next, the degree of approximation is examined on two approxi-mative methods and the constant enthalpy rise method is proven good. Finally, a practical method to apply the results obtained to the cycle calculation using the steam table is given.
