Thermal reduction of iron–manganese oxide particles in a high-temperature packed-bed solar thermochemical reactor

https://doi.org/10.1016/j.cej.2020.128255Get rights and content

Highlights

  • An indirectly-irradiated packed-bed solar thermochemical reactor is developed.

  • The reactor is experimentally tested under simulated high-flux solar irradiation.

  • A CFD model coupling reaction kinetics, heat transfer and fluid flow is developed.

  • The maximum solar-to-chemical energy conversion efficiency reaches 9.3%.

Abstract

The reduction of iron–manganese oxide particles in a high-temperature packed-bed solar thermochemical reactor is investigated using an advanced transient three-dimensional heat and mass transfer model. The model couples the reaction kinetics and fluid flow to conductive, convective, and radiative heat transfer. A reactor prototype that features a reaction tube confining the packed particles and a surrounding diffuse reflective cavity is tested under simulated high-flux solar irradiation to validate the model. The numerically predicted temperature profiles and oxygen generation rates are in good agreement with the experimental data. The validated model is applied to evaluate the thermochemical performance of the reactor. The calculated temperature profiles indicate that uniform temperature distribution in the reactive packed particles is achieved from the onset of the reaction. An energy rate balance analysis shows the instantaneous peak solar-to-chemical energy efficiency reaches 9.3%.

Introduction

Thermal energy storage (TES) allows for continuous operation of concentrated solar power (CSP) plants [1], [2]. Compared to the conventional sensible and latent heat TES systems, thermochemical energy storage (TCES) is a promising alternative as it provides stable energy storage at higher density and temperature [3]. TCES is compatible with a wide variety of media, such as metal oxides, metal hydrides, carbonates, hydroxides, ammonia, and organic materials [4], [5]. TCES based on metal oxide redox cycles offers numerous advantages, including high operating temperature in a flexible range, high energy storage density, convenient operation using air as both the reactant and heat transfer medium, and simple product separation due to gas–solid reactions [6], [7], [8], [9]. In a two-step metal-oxide redox cycle, the solar energy is stored in a high-temperature endothermic reduction step and later released in an exothermic oxidation step in the form of heat,MxOy+ΔHMxOy-δ+δ2O2.

The redox cycles of various metal oxides have been extensively studied [10], [11], [12], [13], [14]. Of particular interest is the Fe/Mn binary metal oxide system, bearing promising TCES characteristics—fast oxidation kinetics, high cycle robustness, narrow thermal hysteresis, and high energy storage density [15], [16], [17], [18], [19]. The binary oxide system with a Fe/Mn molar ratio of 2:1 (Fe67) has been developed and characterized as an attractive medium for TCES [20], [21], [22].

A laboratory-scale solar thermochemical reactor was proposed by Wang et al. for the thermal reduction of fluidized manganese oxide particles [23]. An optimized compound parabolic concentrator (CPC) is incorporated into the reactor to concentrate the incident radiation, reduce the spillage loss, and increase the uniformity of the flux distribution [24], [25]. The thermal performance of the reactor operated in the fluidized-bed mode was evaluated numerically using the Kunii–Levenspiel model [23], [26]. Despite its capability to predict the effective properties of the reactor, the model lacks the inherent physics for in-depth simulation of high-temperature solid–gas reactive flows.

High-temperature solid–gas reactive flows are frequently encountered in diverse solar thermochemical processes, such as cracking [27], [28], gasification [29], [30], [31], [32], [33], thermal reduction of metal oxides [34], [35], [36], [37], and calcium carbonate calcination [38], [39], [40], [41], [42]. Numerous models have been developed for high-temperature solid–gas reactive flows for various flow configurations: dilute particle suspensions, fluidized beds, and fixed and moving bed of porous media and packed particles [43], [44]. Typical studies on dilute suspensions focus on numerical models that couple reaction kinetics with radiative heat transfer [32], [33], [34], [35], [36], [42]. In these studies, the radiative heat transfer of the non-gray non-isothermal absorbing–emitting–scattering particle suspension under direct solar irradiation is predominantly modeled with the Monte Carlo ray-tracing (MCRT) method. Studies on fluidized beds deal with, in addition to the heat transfer and kinetics, the momentum transport introduced by the complex motion of particles. Example studies include coal gasification under direct [29], [30] and indirect irradiation [31], CO2 capture [45] and energy storage [46] based on the calcium carbonation–calcination cycle. The momentum transfer in the fluidized bed can be modeled with an Eulerian approach [47], [48] or a Lagrangian approach [49], [50], [51], [52], [53]. Fixed and moving beds of porous media and packed particles generally have higher solid-phase volume fractions, resulting in non-negligible thermal diffusion within the solid phase. Previous studies encompass modeling heat transfer in redox cycles of zinc [54], [55], [56], [57] and ceria [58], [59], [60], [61], [62], carbonaceous waste gasification [63], and CO2 capture based on the carbonation–calcination cycle [64].

In this paper, we propose a comprehensive transient three-dimensional (3D) multiphase computational fluid dynamics (CFD) model to study the reduction of indirectly irradiated packed Fe67 particles in the high-temperature solar thermochemical reactor proposed in [23]. The model couples reaction kinetics and fluid flow with the conductive, convective, and radiative heat transfer in packed Fe67 particles to obtain a detailed description of the transport phenomena in the bed. A reactor prototype that features a reaction tube confining the packed particles and a surrounding diffuse reflective cavity is tested under simulated high-flux solar irradiation provided by a multi-source high-flux solar simulator (HFSS) [65], [66]. Model validation is achieved by comparing the numerically predicted temperature profiles and oxygen generation rates with the experimental data. The validated model is then applied to evaluate the thermochemical performance of the reactor.

Section snippets

Experimental setup

The experimental setup is shown in Fig. 1. The reactor is heated by the high-flux simulated solar irradiation provided by an HFSS, which consists of 18 identical radiation modules arranged in two concentric rings [65]. The HFSS can provide 10.6 kW of radiative power with a peak flux of 9.5 MW m−2 on a 60-mm diameter flat target at its focal plane. The radiation modules of the HFSS are aligned with photogrammetry and calibrated with a flux gauge, a charge-coupled device (CCD) camera, and a

Numerical model

The numerical model is divided into three sub-models due to the complexity of the problem. We first present the hydrodynamic and heat transfer model with conduction and convection. The model assumes local nonequilibrium—each phase is described with its own energy and momentum conservation equations. The equations are coupled by closure laws for interfacial energy and momentum transfer. Secondly, a reaction kinetics model is developed for the simulation of the heterogeneous reaction. The

Physical properties

The properties of materials used in the numerical simulation are listed in Table 9. The boundary value is used when properties are required beyond the application range.

It was observed that the quality of the CPC reflective surface gradually deteriorates due to dust deposition and vapor condensation throughout the experiment. To quantify this effect, we propose an indirect experimental–numerical method to calculate the effective absorptance of the CPC from the temperature rise of the cooling

Mesh size, time step, and ray number

The structured hexahedral mesh is built for the computing domains of the reactive, participating packed particles and the confining reaction tube for accurate and stable simulation of the multiphysical process. The non-structured tetrahedral mesh is used in the rest of the domains, including the cavity and insulations. A minimum thickness of 0.21 mm is selected for the first layer of mesh on the particle–tube interface, and the irradiated tube and cavity surfaces as the highest energy flux are

Results and discussion

The validated model is applied to analyze the thermal performance of the high-temperature solar thermochemical reactor.

Conclusions

A transient 3D computational fluid dynamic model has been developed to study the reduction of iron–manganese oxide particles in a high-temperature packed-bed solar thermochemical reactor. The model coupled the reduction kinetics and the hydrodynamics with the conductive, convective, and radiative heat transfer to give a comprehensive description of the transport phenomena in the reactor. The solar thermochemical reactor featuring a reaction tube confining the packed particles and a surrounding

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank Dr Roman Bader, Dr Joe Coventry, Dr Peter Kreider, Dr Keith Lovegrove, Dr John Pye, and Dr Jose Zapata for discussing the solar reactor design. We thank Dr Mahesh Venkataraman for his help with measurements of the gas phase composition, Mr Mustafa Habib for the calibration of the ANU high-flux solar simulator, Mr Morteza Hangi and Ms Sha Li for discussing the volume-averaging theorem, and Mr Colin Carvolth, Mr Jason Chen and Mr Kevin Carvolth for the technical support. We thank Prof.

Funding

This work was supported by the Australian Renewable Energy Agency [grant number 2014/RND005].

References (87)

  • I.A. Al-Shankiti et al.

    Particle design and oxidation kinetics of iron-manganese oxide redox materials for thermochemical energy storage

    Sol. Energy

    (2019)
  • M. Hamidi et al.

    Effective thermal conductivity of a bed packed with granular iron–manganese oxide for thermochemical energy storage

    Chem. Eng. Sci.

    (2019)
  • M. Hamidi et al.

    Reduction kinetics for large spherical 2:1 iron–manganese oxide redox materials for thermochemical energy storage

    Chem. Eng. Sci.

    (2019)
  • L. Li et al.

    Design of a compound parabolic concentrator for a multi-source high-flux solar simulator

    Sol. Energy

    (2019)
  • L. Li et al.

    Temperature-based optical design, optimization and economics of solar polar-field central receiver systems with an optional compound parabolic concentrator

    Sol. Energy

    (2020)
  • G. Maag et al.

    Solar thermal cracking of methane in a particle-flow reactor for the co-production of hydrogen and carbon

    Int. J. Hydrogen Energy

    (2009)
  • S. Abanades et al.

    Experimental study and modeling of a high-temperature solar chemical reactor for hydrogen production from methane cracking

    Int. J. Hydrogen Energy

    (2007)
  • J. Martinek et al.

    Computational modeling and on-sun model validation for a multiple tube solar reactor with specularly reflective cavity walls. Part 1: Heat transfer model

    Chem. Eng. Sci.

    (2012)
  • J. Martinek et al.

    Computational modeling of a multiple tube solar reactor with specularly reflective cavity walls. Part 2: Steam gasification of carbon

    Chem. Eng. Sci.

    (2012)
  • P. von Zedtwitz et al.

    Numerical and experimental study of gas–particle radiative heat exchange in a fluidized-bed reactor for steam-gasification of coal

    Chem. Eng. Sci.

    (2007)
  • W. Lipiński et al.

    Unsteady radiative heat transfer within a suspension of ZnO particles undergoing thermal dissociation

    Chem. Eng. Sci.

    (2006)
  • P.G. Loutzenhiser et al.

    CO₂ splitting in an aerosol flow reactor via the two-step Zn/ZnO solar thermochemical cycle

    Chem. Eng. Sci.

    (2010)
  • A. Steinfeld et al.

    Theoretical and experimental investigation of the carbothermic reduction of Fe2O3 using solar energy

    Energy

    (1991)
  • A. Meier et al.

    Solar chemical reactor technology for industrial production of lime

    Sol. Energy

    (2006)
  • L. Yue et al.

    A numerical model of transient thermal transport phenomena in a high-temperature solid–gas reacting system for CO₂ capture applications

    Int. J. Heat Mass Transf.

    (2015)
  • V. Nikulshina et al.

    Kinetic analysis of the carbonation reactions for the capture of CO2 from air via the Ca(OH)2–CaCO3–CaO solar thermochemical cycle

    Chem. Eng. J.

    (2007)
  • V.M. Wheeler et al.

    Modelling of solar thermochemical reaction systems

    Sol. Energy

    (2017)
  • V. Nikulshina et al.

    CO₂ capture from atmospheric air via consecutive CaO-carbonation and CaCO3-calcination cycles in a fluidized-bed solar reactor

    Chem. Eng. J.

    (2009)
  • Y.A. Criado et al.

    Experimental investigation and model validation of a CaO–Ca(OH)2 fluidized bed reactor for thermochemical energy storage applications

    Chem. Eng. J.

    (2017)
  • J. Marti et al.

    A numerical investigation of gas-particle suspensions as heat transfer media for high-temperature concentrated solar power

    Int. J. Heat Mass Transfer

    (2015)
  • S. Noorman et al.

    A theoretical investigation of CLC in packed beds. Part 2: Reactor model

    Chem. Eng. J.

    (2011)
  • S. Bellan et al.

    A CFD-DEM study of hydrodynamics with heat transfer in a gas-solid fluidized bed reactor for solar thermal applications

    Int. J. Heat Mass Transfer

    (2018)
  • S. Bellan et al.

    CFD-DEM investigation of particles circulation pattern of two-tower fluidized bed reactor for beam-down solar concentrating system

    Powder Technol.

    (2017)
  • S. Bellan et al.

    Numerical and experimental study on granular flow and heat transfer characteristics of directly-irradiated fluidized bed reactor for solar gasification

    Int. J. Hydrogen Energy

    (2018)
  • H. Zhou et al.

    DEM-LES of coal combustion in a bubbling fluidized bed. Part I: gas-particle turbulent flow structure

    Chem. Eng. Sci.

    (2004)
  • S. Bellan et al.

    Thermal performance of a 30 kW fluidized bed reactor for solar gasification: A CFD-DEM study

    Chem. Eng. J.

    (2019)
  • L. Dombrovsky et al.

    An ablation model for the thermal decomposition of porous zinc oxide layer heated by concentrated solar radiation

    Int. J. Heat Mass Transfer

    (2009)
  • L.O. Schunk et al.

    Heat transfer model of a solar receiver-reactor for the thermal dissociation of ZnO—Experimental validation at 10 kW and scale-up to 1 MW

    Chem. Eng. J.

    (2009)
  • R. Müller et al.

    Transient heat transfer in a directly-irradiated solar chemical reactor for the thermal dissociation of ZnO

    Appl. Therm. Eng.

    (2008)
  • P. Furler et al.

    Heat transfer and fluid flow analysis of a 4 kW solar thermochemical reactor for ceria redox cycling

    Chem. Eng. Sci.

    (2015)
  • D.J. Keene et al.

    The effects of morphology on the thermal reduction of nonstoichiometric ceria

    Chem. Eng. Sci.

    (2014)
  • C.K. Ho et al.

    Review of high-temperature central receiver designs for concentrating solar power

    Renew. Sustain. Energy Rev.

    (2014)
  • V.V.R. Natarajan et al.

    Kinetic theory analysis of heat transfer in granular flows

    Int. J. Heat Mass Transfer

    (1998)
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    Current affiliation: SkyCell AG, 8005 Zurich, Switzerland.

    2

    Current affiliation: School of Science, Engineering and Information Technology, Federation University, VIC 3350, Australia.

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