High temperature flooded expansion for solar thermal power generation

Nelson James, Purdue University

Abstract

Even though solar power usage has seen rapid growth over the past decade, fossil fuel generation sources are still generally a less expensive means of producing power. The Liquid-Flooded Ericsson Cycle (LFEC) was investigated as a high efficiency power cycle for reducing the cost of concentrated solar power (CSP) plants and helping to address this cost disparity. High temperature flooded expansion was identified as one of the main challenges in regards to utilizing the LFEC as a power cycle. Thermodynamic models were developed to help assess the performance of the LFEC and a load stand was constructed to test a prototype high temperature flooded scroll expander. The thermodynamic model allowed for the investigation of the impacts of working fluid selection on the performance of the LFEC. The selection of the flooding agent was found to be of particular importance for high temperature operation. The maximum operating temperature, specific heat capacity, and vapor pressure of individual liquids governed the potential performance of the LFEC. This model was used to help develop design criteria for a prototype high temperature scroll expander. Nitrogen and the thermal oil Duratherm LT were chosen as the working fluids for the experimental load stand. The data collected showed poor performance of the prototype scroll expander. This was partially attributed to excessive leakage in the device. A mismatch between the internal volume ratio and the imposed system conditions was believed to have exaggerated the leakage problem. Regardless of the poor performance these test have demonstrated the operation of a scroll machine at higher temperatures and flooding ratios than previously investigated in the literature. They provide a platform upon which to build to further knowledge of high temperature flooded expansion. A comparative study was performed to assess the potential performance of the LFEC against other power cycles proposed for use in CSP facilities. This consisted of comparisons between variations of Rankine, Brayton, and combined cycles. From this analysis it was found that for sufficiently high component efficiencies the LFEC can provide higher conversion efficiencies than the other cycles under consideration. The work done in this study has identified the LFEC as a promising power cycle for solar thermal power generation. The need for high efficiency components necessitates continued design and experimental investigation of machines capable of tolerating liquid flooding. Special attention needs to be given to the design of high temperature expansion devices and the challenges they bring. Through further development of system components the LFEC can become a viable alternative for CSP power blocks.

Degree

M.S.M.E.

Advisors

Groll, Purdue University.

Subject Area

Alternative Energy|Mechanical engineering

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