Hybridization of CSP Plants: Characterization of a Molten Salt Heater for Binary and Ternary Nitrate Salt Mixtures Fueled with Gas/Biogas Heaters

Alberto Giaconia, Irena Balog and Giampaolo Caputo
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Alberto Giaconia: Casaccia Research Centre, Energy Technologies and Renewable Sources Department (TERIN), ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, 00123 Rome, Italy
Irena Balog: Casaccia Research Centre, Energy Technologies and Renewable Sources Department (TERIN), ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, 00123 Rome, Italy
Giampaolo Caputo: Casaccia Research Centre, Energy Technologies and Renewable Sources Department (TERIN), ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, 00123 Rome, Italy

Energies, 2021, vol. 14, issue 22, 1-18

Abstract: Hybridization of CSP plants with alternative energy sources (fuels) represents a means to improve flexibility of operation, power dispatchability and utilization factor of the plant. New generation CSP plants make use of molten salts as Heat Transfer Fluid (HTF) besides Thermal Energy Storage (TES) medium. Therefore, proper interfaces should be developed to effectively transfer the heat from the back-up source to the molten salt. This paper presents the results obtained in the experimental validation of an innovative gas-fueled Molten Salt Heater (MSH) prototype. The objective of this research is to validate the MSH design, where the specific properties of molten salts (compared to other HTFs, e.g., thermal oils) have to be taken into account. The developed reduced-scale MSH (90 kW thermal) consists of a heat exchanger with the molten salt flowing inside finned tubes cross-flowed with the hot flue gas generated in an upstream combustion chamber. LPG or a biogas-like mixture has been used as gas fuel. Experimental results have been obtained with two different molten salt mixtures: the “solar salt” binary mixture (NaNO 3 /KNO 3 , 60/40%w) typically used in CSP applications (up to 565 °C) and the ternary mixture known as Hitec XL ® containing sodium/potassium/calcium nitrates (NaNO 3 /KNO 3 /Ca(NO 3 ) 2 , 15/43/42%w) characterized by lower freezing temperatures. Experimental tests have been carried out changing some operative parameters like the flow rate of the molten salt (0.45–0.94 kg/s), the inlet temperatures of the molten salt (303–445 °C) and of the hot gas (596–632 °C). For both molten salt mixtures, it was demonstrated that heat transfer correlations based on the Dittus-Boelter equation allow to predict experimental results with <10% deviation between experimental and theoretical values of the heat transfer coefficient.

Keywords: concentrating solar power (CSP); heat transfer fluids; molten salt; binary and ternary nitrate mixtures; hybridization of CSP plants; molten salt heater (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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