Discussion of the Effects of Recirculating Exhaust Air on Performance and Efficiency of a Typical Microturbine

This paper reports on a specific phenomenon, noticed during steam injection experiments on a microturbine. During the considered experiments, measurements indicated an unsteady inlet air temperature of the compressor, resulting in unstable operation of the microturbine. Non-continuous exhaust air recirculation was a possible explanation for the observed behaviour of the microturbine.
The aim of this paper is to investigate and demonstrate the effects of exhaust recirculation on a microgasturbine. Depending on wind direction, exhaust air re-entered the engine, resulting in changing inlet conditions which affects the operating regime of the microturbine.
For this paper, two series of experiments were performed. The first experiment was a visualization test of the flue gasses on the existing microturbine installation, which allowed to confirm the hypothesis of exhaust recirculation. A second series of experiments was performed in the wind tunnel. These series of experiments allowed investigation of the effect of the wind direction and position of the stack on flue gasses flow. Next to the experiments, steady-state simulations in ASPEN® of partial exhaust recirculation were performed in order to study the effect of exhaust recirculation on thermodynamic performance of the microturbine. Dynamic Simulink® simulations of the non-continuous recirculation revealed the effects of frequency and amplitude on average performance and stability.
Experiments visualizing the exhaust flow confirmed the hypothesis of exhaust recirculation. Results from simulation supported the important impact of this phenomenon. Wind tunnel tests demonstrated the influence of the wind direction on recirculation and revealed the necessity to heighten the stack, thus preventing exhaust recirculation.