Optimisation of pump operation to increase the cycle efficiency of an ORC during part load

Master thesis (2021)

Authors

A. van der Vries Mechanical Engineering

Contributors

Rene Pecnik Energy Technology - Mechanical, Maritime and Materials Engineering (mentor)
S.H.H.J. Smit Energy Technology - Mechanical, Maritime and Materials Engineering (mentor)
S.A. Klein Energy Technology - Mechanical, Maritime and Materials Engineering (graduation committee member)
Faculty
Mechanical Engineering, Mechanical Engineering
Copyright: © 2021 André van der Vries
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Published Date

27-09-2021

Language

English

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Faculty

Mechanical Engineering

Abstract

The global warming and increase in energy use demands the industry to come up with ideas to lower the CO2 production and save valuable energy. Organic Rankine cycles have a great potential as low grade heat can be converted into electrical energy. In the last ten years, research in this particular field has increased together with the amount of installed systems. Triogen is a company which does a lot of research on how to increase the power output of their Organic Rankine Cycle systems. Their product involves a radial inflow cantilever turbine connected to a single shaft to the generator and the main pump which makes the system quite unique. Because of the fluctuating heat input the system scarcely runs on its design condition so research has to be done to ensure the turbine efficiency is as high as possible to extract as much power out of the heat source as possible. This study investigates whether the pump strategy can be modified in order to increase the system power output for part load situation. By means of elaborate turbine computational fluid dynamics simulations, an optimal rotational speed op n = 475 hz is found for all turbine inlet pressures. A simple cycle model is made in Excel in order to compute the increased power output, given the optimal rotational speed. The most cost effective and straight forward way to implement the fixed rotational speed in the system, a throttle valve is chosen. The amount of extra power gained using the optimal rotational speed is approximately 7 kW, which is an increase of 8 %. For evaporator heat inputs higher than 900 kWth, the operation with throttle valve is no longer beneficial and the operation on design condition is favoured.