Transient behaviour and optimal start-up procedure of closed Brayton cycle with high thermal inertia

Abstract

• Precise dynamic simulation of a closed Brayton cycle with high thermal inertia is achieved based on test data and optimization algorithm. • Thermal inertia of the regenerator is critical to fast and stable full-load operation. • Initial pressure ratio takes great effect on the start-up time and start-up power consumption. • The rotor speed should be accelerated when the compressor inlet pressure arrives at 60%-65% design value. The closed Brayton cycle is promising as a power generation system owing to its output flexibility and compactness. In this study, a small closed Brayton cycle device was developed and its transient characteristics were studied experimentally and numerically. The start-up procedure for a closed Brayton cycle with considerable thermal inertia and heat dissipation was investigated. First, a modelling method based on both test data and an optimisation algorithm was developed to improve the accuracy of the dynamic simulation of the closed Brayton cycle. The optimal values of model parameters describing the thermal inertia and heat dissipation of the components were obtained by matching a group of dynamic test data using a genetic algorithm. The precision of the model was validated against additional experimental data. Then, the Pareto front of the start-up procedure, which was characterised by the time parameters concerning acceleration and injection, pressure coefficient, androtor speed, was acquired using a double-objective genetic algorithm with the goal of obtaining the smallest values for the start-up time and start-up power. Further studies showed that adjusting the sequence of acceleration and injection could help overcoming the thermal inertia of the regenerator, which was critical for fast and stable full-load operation. Firstly, selecting the appropriate initial pressure coefficient, then accelerating and then injecting was a favourable start-up procedure.