Lab-scale Solar Reactor Research Articles

Dynamic simulation and control of solar biomass gasification for hydrogen-rich syngas production during allothermal and hybrid solar/autothermal operation

Solar biomass steam gasification using concentrated sunlight offers an efficient means of storing intermittent solar energy into renewable solar fuels while upgrading the carbonaceous feedstock. Such solar-driven (allothermal) processes have demonstrated the ability and the effectiveness for the production of high quality hydrogen-rich syngas, but they suffer from inherent barriers related to the variability of solar energy caused by cloud passages and shut off at night. The concept of hybrid solar/autothermal gasification appears promising to meet the requirement for stable and continuous operation under fluctuating or intermittent solar irradiation. To date, dynamic modelling to simulate coupled solar/combustion heating and steam gasification using real solar irradiation data has never been proposed and could be used to predict the annual performance of large-scale solar gasification plants. In this study, a dynamic mathematical model of a scaled-up solar gasification reactor was developed. The model was composed of a system of differential equations that were derived from unsteady mass and energy conservation equations. After an experimental validation step with the results from a lab-scale solar reactor, the dynamic model was applied at large scale to determine the reactor temperature and syngas production evolution during continuous day and night operation in both solar-only (allothermal) and hybrid solar/autothermal modes. Different reactants feeding management strategies were proposed and compared with the aim of achieving enhanced syngas productivity and optimized use of solar energy during solar-aided steam gasification. It was shown that the hybrid mode with partial oxy-combustion of the feedstock and dynamic feeding control results in the most stable process operation upon fluctuating solar power input, while ensuring continuous production of H2 and CO at night and during cloudy periods.

Solar chemical looping gasification of biomass with the ZnO/Zn redox system for syngas and zinc production in a continuously-fed solar reactor

The high-temperature solar-driven chemical looping gasification of lignocellulosic biomass with ZnO/Zn redox pair was investigated as a novel process producing both syngas and metallic zinc. A lab-scale solar reactor (1.5 kW) was operated for continuous combined biomass gasification and ZnO carbo-thermal reduction using solar energy as the source of high-temperature process heat. Experiments were performed at temperatures ranging from 1050 °C to 1300 °C with biomass/ZnO molar ratios from 0.5 to 1, using beech wood as a biomass feedstock. The objective of this study was to unveil the advantages and reliability of the combined process involving biomass pyro-gasification with solid ZnO as an oxidizing agent under continuous process operation for co-production of syngas and metallic Zn. The influence of temperature and reactant molar ratio on syngas production was highlighted and compared to the case of a pyrolysis process without any oxidant. Moreover, the chemical conversion of ZnO to Zn obtained by this endothermic step was also addressed, confirming pure Zn production with low recombination in the collected solid products. The evolved H2 increased significantly, CO production also tended to increase slightly, while CO2 and CH4 decreased when increasing the temperature. The syngas yield of the combined gasification/carbo-thermal reduction (up to ∼8 molsyngas/molbiomass for a biomass/ZnO molar ratio of 0.75 at 1250 °C) was much higher in comparison with pyrolysis. The calorific value of the feedstock was solar up-graded through syngas and Zn production in the case of the biomass gasification using ZnO, whereas pyrolysis was not energetically efficient because of the energy content still remaining in the produced char. The optimal biomass/ZnO molar ratio was evidenced at 0.75 yielding maximum syngas production. The energy upgrade factor of the feedstock by the solar power input and the solar-to-fuel energy conversion efficiency were 1.17 and 19.8% respectively for a molar ratio of 0.75 at 1250 °C.

Comprehensive CFD modelling of solar fast pyrolysis of beech wood pellets

The present work focuses on the study of the solar pyrolysis of beech wood pellets. The biomass degradation process was modelled in the CFD (Computational Fluid Dynamics) platform ANSYS FLUENT 14.0. The results of simulations were compared to experimental tests conducted in a lab-scale solar reactor in order to validate the CFD model. The biomass pyrolysis was carried out at temperatures ranging from 600 to 2000°C, at two heating rates: 10 and 50°C/s.This new 2D single particle model represents a significant improvement of previous simpler version, not only because it allows monitoring the evolution of gas speciation but also because its formulation enables to deal with different types of biomass feedstock. The model structure comprises a multi-step complex kinetic framework that involves competitive reactions –including secondary tar reaction- along with rigorous heat and mass (species) transport inside the particle.On this basis, char, tar and gas predicted yields are compared with experimental data. In addition, the gas composition (CH4, CO, CO2, H2 and CxHy) is also compared. CFD results are in good agreement with the experimental values, validating this approach as a useful tool to predict the products yields and their composition when pyrolyzing biomass particles. Furthermore, the model can be used when modelling any process where pyrolysis occurs and it can even be easily coupled to any reactor scale model.

Product distribution from solar pyrolysis of agricultural and forestry biomass residues

Solar pyrolysis of pine sawdust, peach pit, grape stalk and grape marc was conducted in a lab-scale solar reactor for producing fuel gas from these agricultural and forestry by-products. For each type of biomass, whose lignocellulose components vary, the investigated parameters were the final temperature (in the range 800°C–2000 °C) and the heating rates (in the range 10–150 °C/s) under a constant sweep gas flow rate of 6 NL/min. The parameter influence on the pyrolysis product distribution and syngas composition was studied. The experimental results indicate that the gas yield generally increases with the temperature and heating rate for the various types of biomass residues, whereas the liquid yield progresses oppositely. Gas yield as high as 63.5wt% was obtained from pine sawdust pyrolyzed at a final temperature of 2000 °C and heating rate of 50 °C/s. This gas can be further utilized for power generation, heat or transportable fuel production.

Solar Pyrolysis of Wood in a Lab-scale Solar Reactor: Influence of Temperature and Sweep Gas Flow Rate on Products Distribution

Abstract Experiments of solar pyrolysis of beech wood have been conducted to study the effect of temperature and sweep gas flow rate on the pyrolysis product yields.Investigated variables were pyrolysis temperature, from 600 to 2000 °C, and argon flow rates,between 3Nl/minand 12Nl/min. The heating rate was constant, 50 °C/s. A 50.9 wt.% maximum gas yield(mainly CO and little CH 4 ) was obtained at pyrolysis temperature of 2000 °Candargon flow rate of6Nl/min. The gas yield increased with temperature but the trend is not linear. The most important increase of gas yield (from 15.3 wt.% to 37.1 wt.%) anddecrease of liquid yield (from 70.7 wt.% to 51.6 wt.%) were found between 600 and 1000 °C,which meansthat most of tar decomposed in this temperature range. The gas yield decreased when the argon flow rate increased. The two temperature zones of solar reactor were determined by CFD simulation at different sweep gas flow rates.The higher the sweep gas flow rate, the lower the average temperature and the smaller the hot zone in the vicinity of the sample in the solar reactor. This trend is not favorableto the gas formation from tar cracking.

The effect of temperature and heating rate on char properties obtained from solar pyrolysis of beech wood

Char samples were produced from pyrolysis in a lab-scale solar reactor. The pyrolysis of beech wood was carried out at temperatures ranging from 600 to 2000°C, with heating rates from 5 to 450°C/s. CHNS, scanning electron microscopy analysis, X-ray diffractometry, Brunauer–Emmett–Teller adsorption were employed to investigate the effect of temperature and heating rate on char composition and structure. The results indicated that char structure was more and more ordered with temperature increase and heating rate decrease (higher than 50°C/s). The surface area and pore volume firstly increased with temperature and reached maximum at 1200°C then reduced significantly at 2000°C. Besides, they firstly increased with heating rate and then decreased slightly at heating rate of 450°C/s when final temperature was no lower than 1200°C. Char reactivity measured by TGA analysis was found to correlate with the evolution of char surface area and pore volume with temperature and heating rate.

Hydrogen production from CO2-free thermal decomposition of methane: Design and on-sun testing of a tube-type solar thermochemical reactor

This study addresses the development of a solar thermochemical reactor for CO2-free production of hydrogen from solar-aided methane decomposition. The developed lab-scale solar reactor basically pertaining to the indirect heating concept is chiefly based on a tube-type configuration in tandem with a cavity receiver. The reactor design and performance prediction were first appraised via 3-dimensional CFD thermal simulation as a function of internal geometry. The model including coupled heat/mass transfer and chemical reaction aimed to simulate the reactor in order to determine the temperature distribution and the conditions for maximum reactor efficiency. The designed 1kW solar reactor was then constructed and installed for reaction testing at the focus of a 2m-diameter parabolic solar concentrator. Solar CH4 decomposition experiments were performed between 1300 and 1400°C to demonstrate the feasibility of hydrogen production and the reliability of the solar process using the developed reactor concept, and the results were used to validate simulations. Regarding the estimated kinetic parameters, the best fitting was obtained for an activation energy of 320kJ/mol and a pre-exponential factor of 1011s−1. The chemical conversion was improved when increasing the temperature or decreasing the inlet gas flow rate or the CH4 mole fraction. A maximum CH4 conversion (resp. H2 yield) of 90% (resp. 85%) was achieved at 1400°C and the thermochemical reactor efficiency reached 5% for the highest CH4 content in the feed.

A Novel Lab-scale Solar Reactor for Kinetic Analysis of Non-volatile Metal Oxides Thermal Reductions

Thermal reduction of metal oxides is of primary interest within the R&D field of solar driven thermochemistry, because it is frequently involved in processes such as thermochemical cycles for hydrogen production or in thermochemical energy storage systems for solar thermal power plants. A lab-scale solar reactor has been designed to test and analyze solar-driven reduction of non-volatile metal oxides arranged in a packed bed. The test bed allows monitoring of oxygen evolution to determine the reaction rate. Experimental tests with Mn2O3, Mn3O4 and CeO2 have been carried out and the performance of each reaction has been analyzed. Total conversion is obtained for Mn2O3 reduction. However, only some zones of the Mn3O4 and CeO2 samples achieve reaction temperature. Different types of sample-holders have been used to hold the particles packed-bed, in order to enhance the conversion. The high influence of the irradiance distribution on the sample surface is demonstrated by a testMn3O4 reduction.

Thermal performance of lab-scale solar reactor designed for kinetics analysis at high radiation fluxes

The availability of lab-scale reactor designs with suitable control and monitoring of reaction parameters becomes essential when high flux/temperature conditions reproducing solar-driven thermochemical processes are needed. Since the chemical kinetics strongly depends on irradiance, temperature and fluid flow distribution around the reactant, a detailed thermal analysis supports the understanding of reactor response and kinetics assessment for specific solar reactor designs. This study describes a numerical model for analyzing the thermal performance of a laboratory-scale solar thermochemical reactor, which has been designed and built for analysis of reduction of metal oxides. Model validation is accomplished by comparing the simulation results with experimental measurements and previous published numerical results. Parametric simulations are performed to examine the influence of gas flow rate and sample position on the reactor's thermal performance. Thermo-fluid flow inside the reactor, the total energy absorption, radiation losses, absorption efficiency, and maximum temperature attained by the sample are predicted for different operating conditions.

Design of a Lab-Scale Rotary Cavity-Type Solar Reactor for Continuous Thermal Dissociation of Volatile Oxides Under Reduced Pressure

A high-temperature lab-scale solar reactor prototype was designed, constructed and operated, allowing continuous ZnO thermal dissociation under controlled atmosphere at reduced pressure. It is based on a cavity-type rotating receiver absorbing solar radiation and composed of standard refractory materials. The reactant oxide powder is injected continuously inside the cavity and the produced particles (Zn) are recovered in a downstream ceramic filter. Dilution/quenching of the product gases with a neutral gas yields Zn nanoparticles by condensation. The solar thermal dissociation of ZnO was experimentally achieved, the reaction yields were quantified, and a first concept of solar reactor was qualified. The maximum yield of particles recovery in the filter was 21% and the dissociation yield was up to 87% (Zn weight content in the final powder) for a 5 NL/min neutral gas flow-rate (typical dilution ratio of 300).