Gas-Solid Flow in a Fluidized-Particle Tubular Solar Receiver: Off-Sun Experimental Flow Regimes Characterization

Ronny Gueguen,Gilles Flamant,Samuel Mer,Adrien Toutant,Guillaume Sahuquet,Françoise Bataille

doi:10.3390/en14217392

Abstract

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were conducted with Geldart Group A particles at ambient temperature with a 0.045 m internal diameter and 3 m long tube. Various temporal pressure signal processing methods, applied in the case of classical risers, are applied. Over a short acquisition time, a cross-reference of the results is necessary to identify and characterize the fluidization regimes. Bubbling, slugging, turbulent and fast fluidization regimes are encountered and the two operation modes, without and with particle circulation, are compared.

Highlights

Concentrated solar power (CSP) plants convert solar radiation into electricity using a thermodynamic cycle
A heliostat field focuses the solar irradiation onto a solar receiver located at the top of the tower, in which a heat transfer fluid (HTF) absorbs the heat from the concentrated solar power
This paper aims to compare several analysis methods of temporal pressure signals to identify and characterize the different fluidization regimes in an upward, dense, gas-solid flow inside a tube with a large aspect ratio, at ambient

Summary

Introduction

Concentrated solar power (CSP) plants convert solar radiation into electricity using a thermodynamic cycle. A heliostat field focuses the solar irradiation onto a solar receiver located at the top of the tower, in which a heat transfer fluid (HTF) absorbs the heat from the concentrated solar power. The HTF circulates through a heat exchanger to transfer the heat either to a storage tank or to another fluid like air or steam. This working fluid powers a turbine that produces electricity. The stored part is used to supply electricity on demand. The commonly used HTF is the solar salt (KNO3 –NaNO3 eutectic), which is efficient because it can be used as HTF and storage medium but is limited in minimum and maximum operating temperatures because of solidification (≈220 ◦ C) and chemical decomposition (565 ◦ C) respectively [1,2]

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