Parametric study and optimization of closed Brayton power cycle considering the charge amount of working fluid

Abstract

With the advent of various heat sources for electric power, the interest in closed Brayton cycles (CBCs) is increasing. For an open Brayton cycle like gas turbine plants, numerous options exist to adjust cycle operation through flow control or speed modulation of turbomachines. For a CBC, however, the amount of ‘closed’ working fluid inside the cycle is constrained and the control schemes for cycle operation are limited. Thus, the performance of the CBC is analyzed considering the fact that the density of working fluid is related to the charge amount in this study. With a concept of the charge amount as a constraint, an alternative approach to reflect CBC characteristics is introduced to set the turbine inlet conditions unconstrained. As a result, the influence of the charge amount on the cycle performances is analyzed, and the optimum charge amount for the given operating conditions is obtained. Using the results of this study, the charge amount can be considered as a design and control parameter of the CBC. Furthermore, the performance of the CBC can be improved by implementing a proper inventory control strategy during off-design operation based on the calculated optimum charge amount in this study.