Transient Modelling of a Positive Displacement Pump for Advanced Power Cycle Applications

Abstract

I dedicate this thesis to my beloved mother. DeclarationI hereby declare that except where specific reference is made to the work of others, all the work contained within this thesis is my original work and have not been submitted in whole or in part for consideration for any other degree or qualification. AbstractCompared to the conventional fossil-based steam Rankine cycle, supercritical carbon dioxide (sCO 2 ) power cycles possess the potential to achieve higher thermodynamic efficiencies and lower component costs. As such, they have been proposed for the next generation of renewable energy technologies in an effort to strive for a sustainable future by reducing global greenhouse gas emissions.The improvement in thermal-to-electric energy conversion efficiency in sCO 2 power cycles is primarily attributed to the reduction of power required at the compression stage. Although small-scale prototype CO 2 compressors have been developed and tested, large-scale commercial units are currently unavailable due to their inherent complexity in design. This is one of the primary drawbacks contributing to the present absence of large-scale operational sCO 2 power plants. Fortunately, large-scale CO 2 transfer pumps are commercially available today and they possess the potential for direct integration into the sCO 2 power system. This presents an opportunity to eliminate the research efforts required to develop a new large-scale CO 2 compressor technology.To assess the compatibility and performance of the CO 2 transfer pump in the sCO 2 power cycle, a detailed theoretical model of the pump system is sought. The current research focus is to establish a numerical model using the Python programming platform for predicting and analysing the transient behaviour of the single-acting positive displacement CO 2 pump, in particular, triplex and quintuplex systems were studied. Zero-dimensional (0D) lumped parameter modelling of the fluid system was initially completed to establish a baseline model. Next, compressible quasi-one-dimensional (1D) Euler equations coupled with Helmholtz energy formulation were used to describe the flow behaviour and thermophysical properties of the working fluid accounting for real gas effects. In the detailed model, valve dynamics and the multiplex system response were also investigated.The computer models developed in this thesis provided good insight into to the transient dynamics of a positive displacement CO 2 pump operating in a simple environment under x ideal inlet conditions. The response characteristics of the transient pump model showed good agreement with experimental data obtained form the literature. The primary benefit of developing an accurate numerical model of the CO 2 transfer pump without the use of commercially available computational fluid dynamics (CFD) packages is the significant savings in computational effort and cost. A dynamic model integrated into a power system not only predicts transient system behaviours, but it can also adjust system inputs accordingly to meet the desir...