Performance characteristics of a spiky central receiver air pre-heater (SCRAP)

Lubkoll, Matti (2017-03)

Thesis (D.Phil)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: A combined cycle concentrating solar power (CSP) plant provides significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to provide such a receiver and overcome barriers experienced by developments to date. The SCRAP receiver is a novel metallic receiver technology aimed at preheating an air stream to about 800◦C, either prior to a combustion chamber or alternatively a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures. The SCRAP receiver is distinguished in shape and functioning from receiver concepts presented to date for the application in Brayton or combined cycles. The receiver is predicted to perform at solar-thermal efficiencies exceeding 80%. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4% – 5%, whereas the relatively large surface results in vulnerability to convective heat losses. The pressure drop was found to be dependent on the geometries selected but relatively low, compared to existing alternative receiver designs, with system pressure drops below 40mbar achievable. A ray-tracing analysis showed that the flux impinging on the absorber assemblies is in its spatial distribution dependent on the solar field, more specific, the heliostat size and design. A thermodynamic model was developed to investigate the performance characteristics of the SCRAP receiver. The developed thermodynamic computer model was verified against an experimental test setup designed and built at the heat transfer laboratory at Stellenbosch University. Tests with steam heating at nominally 100◦C show good agreement between the experimental results and the modeled predictions, at various air flow rates. Further work on the SCRAP receiver technology is recommended. On the modelingsideworkisproposedondevelopingsolutionsforjetimpingementheat transfer on the spike tip to improve heat transfer while reducing pressure drop. Furtherworkonhelicallyswirledfinsissuggestedtocontributetoincreasedheat transfer characteristics. The receiver showed vulnerability towards convective heat losses; further work to better predict and mitigate these is required. Experiments under solar flux or simulated solar flux should further improve understanding of the technology. Cost effective manufacturing processes need to be developed to satisfy economic suitability of the receiver technology.

AFRIKAANS OPSOMMING: ’n Saamgestelde siklus gekonsentreerde sonkrag (GS) aanleg bied aansienlike potensiaal vir ’n toename in doeltreffendheid en ’n vermindering in elektrisiteitskoste in vergelyking met huidige enkel-siklus aanlegte. ’n Saamgestelde siklus GS aanleg vereis ’n ontvangertegnologie wat in staat is om warmte doeltreffend oor te dra vanaf sonstraling na ’n saamgedrukte lugstroom binne ’n gasturbine. Die nuwe Puntige Sentrale Ontvanger Lug-Voorverwarmer (PSOLV) tegnologie word voorgestel as so ’n ontvanger om hindernisse te oorkom wat tot dusver deur ontwikkelaars ervaar is. Die PSOLV ontvanger is ’n nuwe, metaal-ontvanger tegnologie wat daarop gemik is om ’n lugstroom tot sowat 800◦C voor ’n verbrandingskamer te verhit, of alternatiewelik in ’n kaskade met ’n sekondêre nie-metaal ontvangerstelsel, wat in staat is om verhoogde temperature te bereik. Die PSOLV ontvanger word onderskei in vorm en funksionering van ontvanger konsepte tot op datum voorgestel vir toepassing in Brayton- of saamgestelde kringlope. Die voorspelling is dat die ontvanger son-termiese doeltreffendhede van 80% sal oorskry. Die geometriese ontwerp van die ontvanger bereik ’n relatief lae voorspelde stralingswarmteverlies van sowat 4% – 5%. Die relatief groot oppervlakte toon daarteenoor ’n kwesbaarheid vir konveksie warmteverliese. Daar is bevind dat die PSOLV drukval afhanklik is van die geselekteerde geometrieë, maar relatief laag is in vergelyking met bestaande alternatiewe ontvangers, met stelsel drukvalle onder 40mbar bereikbaar. ’n Straalspoor analise het getoon dat die ruimtelike verdeling van die vloed wat inval op die ontvangersamestelling afhang van die sonversamelveld, en meer spesifiek van die heliostaat grootte en ontwerp. ’n Termodinamiese model is ontwikkel om die gedragskenmerke van die PSOLV ontvanger te ondersoek. Die ontwikkelde rekenaar model is geverifieer teen ’n eksperimentele toetsopstelling, ontwerp en gebou in die warmteoordrag laboratorium by Stellenbosch Universiteit. Toetse met stoomverwarming by nominaal 100◦C toon goeie ooreenkoms tussen eksperimentele resultate en model voorspellings, by verskeie lugvloeitempo’s. Verdere werk op die PSOLV ontvanger tegnologie word aanbeveel. Op die modelleringskant word werk voorgestel op die ontwikkeling van oplossings vir straalbotsing-warmteoordrag binne die die stekelpunt om warmteoordrag te verbeter, terwyl drukval verminder word. Verdere werk op heliese vinne word anbeveel om by te dra tot verhoogde warmte-oordrag eienskappe. Die ontvanger het kwesbaarheid teenoor konvektiewe warmteverliese getoon; verdere werk word vereis om dit beter te voorspel en te beperk. Eksperimente onder direkte of gesimuleerde sonvloede behoort begrip van die tegnologie verder te verbeter. Koste-effektiewe produksieprosesse behoort ontwikkel te word om ekonomiese toepaslikheid van die ontvanger tegnologie te bevredig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101295
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