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Research Papers

# Optimal Design of a Molten Salt Thermal Storage Tank for Parabolic Trough Solar Power Plants

[+] Author and Article Information
R. Gabbrielli

Dipartimento di Energetica, Università di Pisa, via Diotisalvi 2, Pisa 56126, Italyr.gabbrielli@ing.unipi.it

C. Zamparelli

ENEL GEM, Area Tecnica Ricerca, Via A. Pisano 120, 56100 Pisa, Italycarlo.zamparelli@enel.it

J. Sol. Energy Eng 131(4), 041001 (Sep 17, 2009) (10 pages) doi:10.1115/1.3197585 History: Received February 22, 2007; Revised November 27, 2007; Published September 17, 2009

## Abstract

This paper presents an optimal design procedure for internally insulated, carbon steel, molten salt thermal storage tanks for parabolic trough solar power plants. The exact size of the vessel and insulation layers and the shape of the roof are optimized by minimizing the total investment cost of the storage system under three technical constraints: remaining within the maximum allowable values of both temperature and stress in the steel structure, and avoiding excessive cooling and consequent solidification of the molten salt during long periods of no solar input. The thermal, mechanical and economic aspects have been integrated into an iterative step-by-step optimization procedure, which is shown to be effective through application to the case study of a $600MWh$ thermal storage system. The optimal design turns out to be an internally insulated, carbon steel storage tank characterized by a maximum allowable height of $11m$ and a diameter of $22.4m$. The total investment cost is about 20% lower than that of a corresponding AISI 321H stainless steel storage tank without internal protection or insulation.

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## Figures

Figure 1

Optimization procedure for design of the storage system

Figure 2

Flexible protective liner made of AISI 321H stainless steel

Figure 3

Insulating firebrick layer, which protects the tank shell

Figure 4

Scheme of the storage-tank foundation construction

Figure 5

Scheme of the storage-tank roof construction

Figure 6

Scheme of the thermal losses to the environment

Figure 7

Total heat loss from the storage tank as a function of tank height for a particular insulation configuration

Figure 8

Shell temperature as a function of the lateral insulating material

Figure 9

Roof temperature as a function of the top liner insulating material

Figure 10

Unsteady thermal behavior of the storage tanks

Figure 11

Maximum principal stresses with ellipsoid shape, rise=5.5m, thickness=12.5mm, and overpressure=120kPag

Figure 12

Maximum allowable overpressure of the storage tank with ellipsoidal roof

Figure 13

Critical vacuum condition vs average shell thickness

Figure 14

Overall investment cost of the storage system as a function of H

Figure 15

Total investment cost of the storage system as a function of the lateral insulating material for some values of H and number of lateral insulating firebricks

Figure 16

Total investment cost of the storage system as a function of the liner insulating material for some values of the roof insulating material

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