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One-dimensional transient cold filling simulation of a molten salt central receiver pipe

Swart, Jean Jacques (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: In this study, cold filling was investigated as a more efficient means of filling a receiver panel with molten salt, eliminating or reducing the need for trace heating before filling the panel. Cold filling can be defined as the filling of a receiver that is initially at a temperature below the molten salt freezing temperature. A one-dimensional numerical model was developed to enable the investigation of the molten salt characteristic response during cold filling under various conditions. The model was verified and then validated against two cold filling studies to ensure that it produces reliable results. Some differences were observed between the results produced by the model built in the current study and the validation studies, but the characteristic trends proved to correlate well. As a result, it was determined that the validation was sufficient for the investigation of the molten salt characteristic trends, as was required by this study. A test case scenario was investigated where the molten salt temperature and solidification behaviour as well as the receiver tube temperature was analysed. It was evident from the test results that the molten salt temperature decreases with distance and increases with time. A worst-case scenario, where the receiver was subjected to strong wind and rain during the filling process, was also investigated. Although possible, it is suggested that cold filling should not be used under such harsh conditions so that damage to the receiver pipes may be prevented. Additionally, the effect that changing the size of the receiver pipe has on the cold filling characteristics was determined. Larger pipes proved to have superior cold filling characteristics up to a certain pipe size. As a result, both the filling characteristics and the molten salt response during normal heated operation need to be considered when choosing the receiver pipe size. Finally, the effect that using a different salt mixture has on the filling process was considered. It was determined that HitecTM salt has superior cold filling properties compared to Solar Salt, but Solar Salt has a higher upper operating temperature and is less expensive. A plant specific analysis is, therefore, required to determine which salt type is operationally better.

AFRIKAANSE OPSOMMING: In die huidige studie word koue vulling ondersoek as ‘n meer doeltreffende manier om ‘n ontvanger paneel met gesmelte sout te vul, eeder as om die paneel te voorverhit met elektriese verhitting. Koue vulling word gedefinieer as die vul van ‘n ontvangerpyp wat aanvanklik by ‘n temperatuur onder die gesmelte sout se vriespunt is. ‘n Eendimensionele numeriese model is ontwikkel om die gesmelte sout se reaksie tydens koue vulling onder verskeie toestande te ondersoek. Die model is geverifieer en toe teen twee koue vulling studies gevalideer om te verseker dat dit betroubare resultate lewer. Verskille tussen hierdie studie se resultate en die resultate van die validasie studies, is waargeneem. Die gesmelte sout se kenmerkende tendense het egter goed vergelyk met die validasie data. Die doel van die studie is om die gesmelte sout se kenmerkende tendense en reaksies onder ‘n verskeidenheid omstandighede te ondersoek. Daar is bepaal dat die validasie voldoende is vir die doeleindes van hierdie studie. ‘n Toets scenario is ondersoek om die gesmelte sout se temperatuur, snelheid en stollingsgedrag te bepaal. Daar is bevind dat die gesmelte sout se temperatuur daal oor afstand en styg met tyd. ‘n Ergste geval scenario is ook ondersoek waar die onvangerpyp aan sterk wind en swaar reën blootgestel is. Alhoewel koue vulling onder hierdie onstandighede moontlik is, word dit nie aanbeveel nie, omdat dit skade aan die ontvangerpype kan veroorsaak. Die effekwat ‘n verandering in die grootte van die pyp op die koue vulling eienskappe het, is ook bepaal. Die bevindinge dui daarop dat groter pype beter koue vulling eienskappe toon tot ‘n bepaalde pypgrootte. Die gevolgtrekking is dat beide die koue vulling eienskappe en die gesmelte sout se reaksie tydens die normale verhittingsproses in ag geneem moet word wanneer die ontvangerpype se grootte gekies word. Laastens is die impak, wat die gebruik van ‘n alternatiewe sout tipe op die koue vulling proses het, ook ondersoek. Die studie het bevind dat HitecTM sout beter koue vulling eienskappe toon as Solar Salt, maar dat Solar Salt ‘n hoër boonste bedryfstemperatuur het en goedkoper is. ‘n Aanleg spesifieke ontleding word dus benodig om die beste operasionele sout tipe te bepaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102907
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