Concentrated Thermal Radiation Research Articles

Demonstration of the Entire Production Chain to Renewable Kerosene via Solar Thermochemical Splitting of H2O and CO2

The European consortium SOLARJET has experimentally demonstrated the first ever production of jet fuel via a thermochemical H2O/CO2-splitting cycle using simulated concentrated solar radiation. The key component of the production process of sustainable “solar kerosene” is a high-temperature solar reactor containing a reticulated porous ceramic (RPC) foam structure made of pure CeO2 undergoing a 2-step redox cyclic process. During the first endothermic reduction step at 1450–1600 °C, the RPC was directly exposed to concentrated thermal radiation with power inputs ranging from 2.8 to 3.8 kW and mean solar flux concentration ratios of up to 3000 suns. In the subsequent exothermic oxidation step at 700–1200 °C, the reduced ceria was stoichiometrically reoxidized with CO2 and/or H2O to generate CO and/or H2. The RPC featured dual-scale porosity: millimeter-size pores for volumetric radiation absorption during reduction and micrometer-size pores within its struts for enhanced oxidation rates. For a cycle durati...

CO2 gasification of coal under concentrated thermal radiation: A numerical study

Solar coal gasification is a promising technology to convert coal into gaseous fuel. In this study, a steady-state one-dimensional (1D) two-phase model was developed to simulate CO2 gasification of coal in a quartz fluidized bed reactor directly exposed to concentrated thermal radiation as the heating source. Coupled with chemical kinetics, the present model encompasses energy equations for the gas phase, the solid phase, and the quartz reactor. The discretized energy equations were solved using the Levenberg–Marquardt algorithm. The initial carbon particle size was 140μm and the peak radiative heating flux was as high as 1270kWm−2. The CO2 flow velocity for fluidization was in the range of 0.10 to 4.0mmin-1 under standard conditions (25°C, 1bar). Simulated gas and coal particle temperature distributions, CO production rates, product gas compositions, and coal conversion rates were in good agreement with the experimental data reported in the literature. Furthermore, the present simulation provided insightful explanation on the optimum fluidization velocity for maximum CO production rate or maximum solar to chemical energy conversion. The present simulation also provided an energy balance analysis of the solar CO2 gasification process, which is challenging to conduct in experimental studies.

Solar Thermochemical CO2 Splitting Utilizing a Reticulated Porous Ceria Redox System

A solar cavity-receiver containing a reticulated porous ceramic (RPC) foam made of pure CeO2 has been experimentally investigated for CO2 splitting via thermochemical redox reactions. The RPC was directly exposed to concentrated thermal radiation at mean solar flux concentration ratios of up to 3015 suns. During the endothermic reduction step, solar radiative power inputs in the range 2.8–3.8 kW and nominal reactor temperatures from 1400 to 1600 °C yielded CeO2−δ with oxygen deficiency δ ranging between 0.016 and 0.042. In the subsequent exothermic oxidation step at below about 1000 °C, CeO2−δ was stoichiometrically reoxidized with CO2 to generate CO. The solar-to-fuel energy conversion efficiency, defined as the ratio of the calorific value of CO (fuel) produced to the solar radiative energy input through the reactor’s aperture and the energy penalty for using inert gas, was 1.73% average and 3.53% peak. This is roughly four times greater than the next highest reported values to date for a solar-driven d...

Syngas production by simultaneous splitting of H2O and CO2via ceria redox reactions in a high-temperature solar reactor

Solar syngas production from H2O and CO2 is experimentally investigated using a two-step thermochemical cycle based on cerium oxide redox reactions. A solar cavity-receiver containing porous ceria felt is directly exposed to concentrated thermal radiation at a mean solar concentration ratio of 2865 suns. In the first endothermic step at 1800 K, ceria is thermally reduced to an oxygen deficient state. In the second exothermic step at 1100 K, syngas is produced by re-oxidizing ceria with a gas mixture of H2O and CO2. The syngas composition is experimentally determined as a function of the molar co-feeding ratio H2O:CO2 in the range of 0.8 to 7.7, yielding syngas with H2:CO molar ratios from 0.25 to 2.34. Ten consecutive H2O/CO2-splitting cycles performed over an 8 hour solar experimental run are presented.

Thermoelectric oxide modules tested in a solar cavity-receiver

Abstract

Production of AlN by Carbothermal and Methanothermal Reduction of Al2O3 in a N2 Flow Using Concentrated Thermal Radiation

The production of AlN by thermal reduction of Al2O3 in a N2 flow, with C/CH4 as reducing agents, is investigated using concentrated thermal radiation as the energy source of high-temperature process heat. Samples were directly exposed to radiative fluxes equivalent to peak solar concentration ratios exceeding 4500 suns (1 sun = 1 kW/m2) and subjected to temperatures in the 2100−2300 K range. Experimental data were fitted to an Arrhenius-type solid−solid kinetic model with an apparent activation energy of 360 kJ·mol−1. The catalytic effect of activated carbon and metals (Fe, Ni) was examined, revealing that metallic particles served as nucleation sites for carbon filamental growth.

A two-phase reactor model for the steam-gasification of carbonaceous materials under concentrated thermal radiation

A chemical reactor for the steam-gasification of carbonaceous materials (e.g., coal or coke) is modeled by means of a two-phase formulation that couples radiative, convective, and conductive heat transfer to the chemical kinetics. A unique feature of the reactor is that the gas-particle flow is directly exposed to concentrated solar radiation, providing efficient radiative transfer to the reaction site for the high-temperature endothermic process. The governing mass, momentum, and energy conservation equations are solved by applying Monte Carlo, two-flux, and finite-volume techniques. Validation is accomplished by comparing the numerically calculated temperatures, product composition, and chemical conversions with the experimentally measured values obtained from testing a 5 kW prototype reactor in a high-flux solar furnace.

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

A heat transfer numerical model is developed for the steam-gasification of coal in a fluidized bed contained in a quartz tubular reactor that is directly exposed to concentrated thermal radiation. The Monte Carlo method is applied for solving the radiative exchange within the reactor quartz walls, the bed particles, and the gas phase. The reaction kinetics are described by Langmuir–Hinshelwood type rate laws. Steady-state mass and energy conservation equations that link heat transfer to the chemical kinetics are formulated and solved iteratively by the finite volume method and Newton algorithm. Numerically computed temperature profiles, product gas composition, and conversions are compared to experimentally measured values in a directly irradiated tubular quartz reactor, tested in a high-flux solar simulator. At above 1450 K, the gas composition consists of a nearly equimolar mixture of H 2 and CO, with less than 5% of CO 2. Heat is transferred to the particles predominantly by thermal radiation and to the gas by particle–gas convection, since radiation absorption by particles is three orders of magnitude higher than that of the gas phase.

Steam-Gasification of Coal in a Fluidized-Bed/Packed-Bed Reactor Exposed to Concentrated Thermal RadiationModeling and Experimental Validation

The steam-gasification of coal in a fluidized-bed or a packed-bed chemical reactor is considered using an external source of concentrated thermal radiation for high-temperature process heat. The energy equation that couples heat transfer with the chemical kinetics is solved by means of a numerical model that incorporates the Monte Carlo ray-tracing technique for nonisothermal, nongray, absorbing, emitting, and scattering media. The reaction kinetics are described by Langmuir−Hinshelwood type rate laws. Validation is accomplished by comparing the numerically computed temperature profiles, product gas composition, and reaction extent with the experimentally measured values using a tubular quartz reactor directly exposed to high-flux irradiation. For the packed bed, the temperature increases monotonically because the internal radiative exchange approaches a conduction-like heat transfer within the bed. For the fluidized bed, the temperature increases rapidly in the first one-quarter of the bed and then reaches a constant value because of the strong fluidization in the upper bed region derived from the 5-fold volumetric growth due to gas formation and thermal expansion. Above 1450 K, the product composition consisted mainly of an equimolar mixture of H2 and CO, a syngas quality that is notably superior than that typically obtained in autothermal gasification reactors (with internal combustion of coal for process heat), besides the additional benefit of the upgraded calorific value.

TRANSIENT RADIATION HEAT TRANSFER WITHIN A NONGRAY NONISOTHERMAL ABSORBING-EMITTING-SCATTERING SUSPENSION OF REACTING PARTICLES UNDERGOING SHRINKAGE

ABSTRACT A nonisothermal, nongray, absorbing, emitting, and anisotropically scattering suspension of reacting particles exposed to concentrated thermal radiation is considered. The steam gasification of coal is selected as the model thermochemical reaction. The unsteady energy equation that couples the radiative heat flux with the chemical kinetics is solved by means of a numerical model that incorporates Monte Carlo ray tracing, the finite-volume method, and an explicit Euler time integration scheme. Two modeling approaches are applied: (1) a quasi-continuous model that assumes a homogeneous medium and utilizes its macroscopic radiative properties (absorption and scattering efficiencies and scattering phase function), and (2) a particle-discrete model that assumes an ensemble of randomly positioned particles and traces the interaction of radiation with each particle by geometric optics. Temperature profiles and reaction extent are computed using both approaches. The quasi-continuous approach is superior in accuracy at the expense of lower spatial resolution, while the particle-discrete approach gives detailed information for every single particle in the suspension at the expense of larger stochastic errors.

Hydrogen production by steam-gasification of petroleum coke using concentrated solar power—I. Thermodynamic and kinetic analyses

The steam-gasification of petroleum coke using concentrated solar radiation as the source of high-temperature process heat is proposed as a viable transition path towards solar hydrogen production. The advantages are three-fold: (1) the calorific value of the feedstock is upgraded; (2) the gaseous products are not contaminated by the byproducts of combustion; and (3) the discharge of pollutants to the environment is avoided. The thermodynamics and kinetics of the pertinent reactions are analyzed for two types of petroleum coke: Flexicoke and Petrozuata Delayed coke. The net process is endothermic by about 50% of the feedstock's LHV, and proceeds at above 1300 K to produce, in equilibrium, an equimolar mixture of H 2 and CO. A Second-Law analysis on the processing of this syngas to H 2 (by water–gas shift followed by H 2 / CO 2 separation) for power generation in a fuel cell indicates the possibility of doubling the specific electrical output and, consequently, halving the specific CO 2 emissions, vis-à-vis conventional coke-fired power plants. Kinetic rate laws are formulated based on elementary reaction mechanisms describing reversible adsorption/desorption processes and irreversible surface chemistry. The kinetic parameters and their Arrhenius-type temperature dependence are experimentally determined using a quartz tubular reactor containing a fluidized bed of petroleum coke in steam and directly exposed to concentrated thermal radiation. Syngas containing approximately an equimolar mixture of H 2 and CO and with a relative CO 2 content of less than 5% was produced at above 1350 and 1550 K for Flexicoke and Petrozuata Delayed coke, respectively.

03/01709 Steam reforming of dodecane over supported iridium catalysts: Ando, T. et al. Journal of the Japan Petroleum Institute, 2002, 45, (6), 409–413

The steam-gasification of petroleum coke using concentrated solar radiation as the source of high-temperature process heat is proposed as a viable transition path towards solar hydrogen production. The advantages are three-fold: (1) the calorific value of the feedstock is upgraded; (2) the gaseous products are not contaminated by the byproducts of combustion; and (3) the discharge of pollutants to the environment is avoided. The thermodynamics and kinetics of the pertinent reactions are analyzed for two types of petroleum coke: Flexicoke and Petrozuata Delayed coke. The net process is endothermic by about 50% of the feedstock's LHV, and proceeds at above 1300 K to produce, in equilibrium, an equimolar mixture of H2 and CO. A Second-Law analysis on the processing of this syngas to H2 (by water–gas shift followed by H2/CO2 separation) for power generation in a fuel cell indicates the possibility of doubling the specific electrical output and, consequently, halving the specific CO2 emissions, vis-à-vis conventional coke-fired power plants. Kinetic rate laws are formulated based on elementary reaction mechanisms describing reversible adsorption/desorption processes and irreversible surface chemistry. The kinetic parameters and their Arrhenius-type temperature dependence are experimentally determined using a quartz tubular reactor containing a fluidized bed of petroleum coke in steam and directly exposed to concentrated thermal radiation. Syngas containing approximately an equimolar mixture of H2 and CO and with a relative CO2 content of less than 5% was produced at above 1350 and 1550 K for Flexicoke and Petrozuata Delayed coke, respectively.