Browsing by Author "Du Plessis, J. J. P."

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    A single stage dry/wet dephlegmator: development, performance evaluation and application in a hybrid ACC at CSP or NGCC Scale.
    (Stellenbosch : Stellenbosch University, 2021-12) Du Plessis, J. J. P.; Owen, Michael ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: This thesis builds on previous research on the hybrid (dry/wet) dephlegmator (HDWD) undertaken at Stellenbosch University. The aim of this study was to advance the technological readiness and corroborate the advantages of the hybrid ACC. This was accomplished by proposing and validating correlations, developing and validating a discretised single-stage HDWD model, applying it in a hybrid ACC model for detailed performance analysis and examining the techno- economic feasibility of the hybrid ACC coupled to a ~238 MW steam turbine. This thesis consists of five published and unpublished papers, each presented as a chapter (Chapters 2 to 6) with a common link to accomplish the study’s aim. In Chapter 2 the air-side pressure drop through a bare tube bundle was experimentally investigated. The investigation was conducted to develop a new empirical correlation, that is more accurate for the given context. The new correlations have an absolute average error of 3.2% (dry) and 4.5% (deluge) between the measured and predicted values. Chapter 3 investigated the steam pressure drop inside a horizontal partial condenser to identify the most suitable steam-side pressure drop correlation for the HDWD model. An experimental apparatus was designed and built to measure the steam pressure drop under varying operating conditions. The results were compared to a selection of five correlations from literature to assess the applicability of the correlations. The most fitting correlation had a mean error of ±15.6% compared to the experimental results. n Chapter 4, a discretised modelling method for an evaporative cooler/condenser was developed and validated. The novel experimental apparatus consisted of a 20 row, evaporative cooler with intermediate thermocouples to measure the process fluid temperature throughout the height of the bundle (representative of control volumes). The predicted and measured temperatures correlated well, with an average error of 0.62% for the bulk process fluid outlet and 1.87% for the intermediate process fluid. In Chapter 5, a discretised HDWD model was developed to analyse the performance of a hybrid ACC against a conventional ACC. The increased cooling capacity of the deluged HDWD units resulted in a smaller overall ACC size (4 × 6 units) for the same heat load compared to a conventional ACC (6 × 6 units). The hybrid ACC required a lower ejector pressure, it was able to operate in dry mode for 75% (0.19 kL/MWh) and was able to mitigate negative wind effects. Chapter 6 examined the techno-economic feasibility of the hybrid ACC at six locations to address the system's cost-competitiveness relative to a conventional ACC. For the six sites, the annual specific water consumption ranged from 0.31 kL/MWh to 0.69 kL/MWh. The hybrid ACC was more capital-intensive per street, but required fewer streets and it was best suited for drier to moderate humidity locations; however, the feasibility depends on the HDWD-unit costs and water prices. The hybrid ACC can also be oversized at drier locations to reduce water consumption and still have an annualised cost lower than a conventional ACC.