Session: 06-02: CSP Receivers and Reactors I

Paper Number: 170087

170087 - Continuum Modeling of Reduction Reactor-Hot Silo in a Moving-Bed Thermochemical Energy Storage System for Concentrating Solar-Thermal Power (Tces-Csp) 

Abstract: 

Reactive particle-based thermochemical energy storage (TCES) systems offer a promising solution for high-temperature energy storage, providing high energy density, efficient energy conversion, and ultra-long storage durations. Among them, metal oxide-based cycles are particularly attractive for next-generation renewable energy applications. Numerical modeling and simulation serve as essential tools to understand the complex thermophysical phenomena involved in these high-temperature thermochemical reactions.

This study presents a detailed numerical investigation of the thermochemical performance of magnesium-manganese oxide (Mg-Mn-O) particles in a counter-flow moving bed reactor coupled with a high-temperature storage silo designed for TCES applications. A two-dimensional axisymmetric CFD model was developed using the Eulerian two-fluid approach to simulate the gas-solid multiphase flow, coupled heat and mass transfer, and reduction kinetics. Both steady-state and transient simulations were performed to analyze reactor performance under varying operating conditions.

The operational principle of the reduction reactor was considered as "cold-in, hot-out", where oxidized particles enter at ambient temperature (~25°C) and exit at high temperatures (800°C to 1200°C) for direct storage in the hot silo. A simple reactor design with one single alumina tube (50.4 mm inner diameter) heated by an electric furnace (~1500°C) was considered. Parametric studies were carried out by varying the heated zone height (12–18 inches), particle mass flow rate (1.25–2.5 g/s), and target particle outlet temperature (800°C–1200°C). Governing equations for mass, momentum, energy, and oxygen species transport were solved using the finite-volume method.

Results show that the extent of reduction of the particle bed primarily depends on the particle mass flow rate and reduction zone height, ranging from 75% to 91%. The corresponding chemical energy stored varied between 0.94 kW and 1.73 kW. While increasing the particle mass flow rate enhances chemical energy storage, it reduces the extent of reduction, indicating a trade-off for optimum operation. The thermal input required to operate the reactor varied between 2.0 kW and 3.18 kW. The multi-layer insulation effectively maintained the outer shell temperature at ~51°C. Heat losses from the reduction reactor ranged from 0.91 kW to 1.17 kW, increasing with heated zone height. The thermal-to-chemical efficiency and overall reactor energy efficiency were observed to be ≥95% and ≥45%, respectively. A transient analysis revealed that the system achieved stable operation within 120 minutes.

This study offers critical insights into the design and optimization of counter-flow moving bed reactors for metal oxide-based TCES systems, supporting the development of efficient energy storage solutions for concentrating solar-thermal power.

Presenting Author: Ram Kumar Pal University of Central Florida

Presenting Author Biography: Ram Kumar Pal is a Postdoctoral Fellow at UCF.