Performance modelling of an open volumetric receiver CSP plant incorporating rock bed thermal storage

Pitot de la Beaujardiere, Jean-François Philippe (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Open volumetric receiver (OVR) concentrating solar power (CSP) plant technology utilises air as a heat transfer fluid, which enables higher peak power cycle temperatures in comparison to conventional heat transfer fluids. This creates the potential for improvements in solar-electric conversion efficiency and reduced electricity generation costs. Despite the promise of the technology, it still faces appreciable technical challenges that have inhibited its commercial adoption. R&D activities have enabled progress in overcoming these challenges. However, a deeper understanding of plant behaviour is required to improve the competitiveness of the technology. In this regard, computational performance modelling at a system and plant level has served as a powerful tool for the exploration of new concepts and the evaluation of improved plant arrangements. Yet little attention has been paid to performance optimisation, and there is still a fairly limited understanding of plant performance characteristics. The objective of this work is to develop a comprehensive plant modelling capability to enable further investigation of key aspects of OVR CSP plant operational behaviour. Of particular interest is the investigation of component inter-dependencies and the sensitivity of plant performance to variations in design parameters at a system and plant level. Firstly, a comprehensive review of performance modelling studies associated with OVR CSP plant technology is presented, detailing recent developments in the simulation of open volumetric receivers, packed bed thermal energy storage systems and OVR CSP plants. The review establishes the state-of-the-art in modelling methodologies, evaluates the extent to which system and plant performance have been investigated, and identifies aspects of plant design and behaviour that require further attention. A design-point model of a 100 MWe OVR CSP plant is then developed and applied to parametrically study the sensitivity of plant performance to heat recovery steam generator (HRSG) configuration and design parameters. The study provides novel insight into the thermodynamic interaction that exists between OVR and HRSG, and identifies the HRSG characteristics that permit the best utilisation of solar energy. The effectiveness of the local thermal equilibrium (LTE) assumption in the long-term performance modelling of rock bed thermal energy storage systems is then evaluated. A one-dimensional LTE performance model is formulated and validated, and applied to simulate the annual performance of a CSP rock bed. Predictions are compared to those associated with an analogous two-phase model to establish, for the first time, the applicability of the LTE assumption for the conditions typically associated with air-rock CSP packed beds. Finally, a detailed OVR CSP plant model with off-design fidelity is developed and applied to parametrically study the long-term performance of a 100 MWe plant, incorporating rock bed thermal energy storage and operating in a peaking role. In this manner, the annual performance of a plant of this configuration is predicted for the first time. Furthermore, the relationships between plant solar-electric efficiency, energy yield, heliostat field size and thermal energy storage capacity are detailed.

AFRIKAANSE OPSOMMING: Oop volumetriese ontvanger (OVO) konsentrasie sonkrag (KSK-) aanlegtegnologie gebruik lug as ʼn warmteoordragsvloeistof, wat hoër kragopwekkingskringloop-temperature moontlik maak in vergelyking met konvensionele warmteoordrags-vloeistowwe. Dit skep die potensiaal vir verbeteringe in son-elektriese omsettingsdoeltreffendheid en verlaagde elektrisiteitsopwekkingskoste. Ondanks die belofte wat die tegnologie inhou, kom dit steeds voor aanmerklike tegniese uitdagings te staan wat die kommersiële implementering daarvan belemmer. Aktiwiteite in navorsing en ontwikkeling het vordering ten opsigte van oorkoming van hierdie uitdagings moontlik gemaak. ʼn Meer diepgaande begrip van aanleggedrag is egter nodig om die mededingendheid van die tegnologie te verbeter. In hierdie opsig het rekenaarverrigtingmodellering op stelsel- en aanlegvlak as ʼn sterk instrument gedien vir die verkenning van nuwe konsepte en die evaluering van verbeterde aanlegopstellings. Tog word min aandag gegee aan die optimalisering van verrigting, en is daar steeds redelik beperkte begrip van aanlegverrigtingeienskappe. Die doelstelling van hierdie studie was om ʼn omvattende aanlegmodelleringvermoë te ontwikkel om verdere ondersoek van sleutelaspekte van OVO KSK-aanlegbedryfsgedrag moontlik te maak. Die ondersoek van komponente se onderlinge afhanklikheid en die sensitiwiteit van aanlegverrigting vir verskille in ontwerpparameters op stelsel- en aanlegvlak was van besondere belang. Eerstens word ʼn omvattende oorsig van verrigtingmodelleringstudies verbonde aan OVO KSK-aanlegtegnologie aangebied, waarin onlangse ontwikkelinge in die simulasie van OVO’s, gepakte bed termiese energiebergingstelsels en OVO KSK-aanlegte in besonderhede bespreek word. In die oorsig is die ultramoderne modelleringsmetodologieë bepaal, die mate waarin stelsel- en aanlegverrigting ondersoek is, geëvalueer, en aspekte van aanlegontwerp en -gedrag wat verdere aandag verg, geïdentifiseer. ʼn Ontwerppuntmodel van ʼn 100 MWe OVO KSK-aanleg is ontwikkel en toegepas om die sensitiwiteit van aanlegverrigting vir die konfigurasie en ontwerpparameters van warmteherwinningstoomgenerators (WHSG’s) parametries te bestudeer. Die studie bied nuwe insigte in die termodinamiese interaksie tussen OVO’s en WHSG’s en identifiseer die WHSG-eienskappe wat die beste benutting van sonenergie moontlik maak. Die doeltreffendheid van die aanname van plaaslike termiese ewewig (PTE) in die langtermynverrigtingsmodellering van rotsbed- termiese energiebergingstelsels is daarna geëvalueer. ʼn Eendimensionele PTE-verrigtingsmodel is geformuleer en bekragtig, en toegepas om die jaarlikse verrigting van ʼn KSK-rotsbed te simuleer. Voorspellings is vergelyk met dié wat met ʼn analoë tweefase-model geassosieer word om vir die eerste keer die toepaslikheid van die PTE-aanname vir die toestande wat tipies met die lug-rots-KSK-stapellae geassosieer word, te bevestig. Laastens is ʼn gedetailleerde OVO KSK-aanlegmodel met buiteontwerp-getrouheid ontwikkel en toegepas om die langtermynverrigting van ʼn 100 MWe-aanleg parametries te bestudeer, insluitende rotslaag- termiese energieberging en met verrigting in ʼn piekrol. Sodoende is die jaarlikse verrigting van ʼn aanleg met hierdie konfigurasie vir die eerste keer voorspel. Voorts word die verhoudings tussen aanleg-sonelektriese doeltreffendheid, energieopbrengs en veelvuldige en termiese sonenergie-bergingskapasiteit uitvoerig uiteengesit.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106188
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