Gas Reactor Research Articles

Multi-objective optimization of a clean combined system based gasifier-solid oxide fuel cell

Biomass can be used as fuel of fuel cells by conducting thermochemical process such as biomass gasification. In this study, the required fuel of a solid oxide fuel cell was supplied through pine gasification in a gasifier reactor. The purpose of this study was provided an appropriate configuration to a co-generation system produced heat and power and the state with maximum heat and power production and minimum carbon dioxide emission was obtained. The outputs were power, heat, and CO2 emission investigated with respect to steam to biomass ratio of gasification and current density and fuel utilization factor of solid oxide fuel cell. The results indicated that fuel utilization factor contributed the most on power and hot water with shares of 73.64% and 47.27%, respectively. However, current density had the highest influence on carbon dioxide emission with a share of 83.41%. Parametric analysis illustrated that increasing fuel utilization factor remarkably enhanced the power production and mitigated hot water production. A considerable reduction was observed in carbon dioxide emission by increasing current density. Single-objective and multi-objective optimizations revealed that steam to biomass ratio of 2, 4600 A/m2 of current density, 0.77 of utilization factor are the optimum states. Power production of 196.8 kW, hot water production of 1203 g/s, and carbon dioxide emission of 1261 kg/MW.h were the outputs of the optimum state.

Techno-economic assessment of application of particle-based concentrated solar thermal systems in Australian industry

Australia has significant areas with high quality solar resources, but the requirement for large scale solar thermal plants to be financially competitive in the electricity market appears to have hindered uptake. Industrial use of heat provides an alternative route to market where the technology is not impacted by poor efficiencies in converting heat to electricity and an appropriate scale can be applied to the demands of a specific site. A re-examination of prior industrial energy use studies in Australia was used in combination with solar data and published data on industrial sites to identify three specific industrial sites for case studies. These sites were selected to cover applications in three industries with varying scale and temperature requirements. The primary solar technology selected utilizes a particle receiver on a tower with associated storage and heat exchanger for hot water/steam production or heating a gas reactor. The wide range of temperatures possible with this technology appears to be desirable for development of a general-purpose industrial heat system. Comparison with parabolic trough systems that are commercially available was conducted for cases where the required temperatures were appropriate. In all assessments, the optimized solar plant designs approach cost competitiveness with the estimated cost of natural gas purchase for the relevant locations and industrial scales. In smaller and lower temperature applications, parabolic trough systems are likely to be appropriate conventional choices, but the particle system exhibited a high degree of flexibility across multiple sites and applications, which is encouraging to future commercial application.

On the nonlinear dynamics of biomass throated tubular gasification reactors

The problem of modeling the complex nonlinear dynamics of continuous biomass throated gasification tubular reactors is addressed. The problem is solved with first principles modeling and efficient discretization-based bifurcation analysis, yielding a systematic and tractable means to characterize: (i) steady-state (SS) multiplicity, (ii) robust stability, (iii) bifurcation behavior, and (iv) transient behavior. The approach is illustrated and tested with a commercial Imbert pilot scale reactor case example, studied before with experiments and simulation, and with multiplicity-bifurcation assessment as open problem. It was found that: (i) the nominal operation is tristable (with three stable steady-states -SSs- and two unstable ones), (ii) the reactor can bebi or tristable (with three or five SSs, respectively), depending on the within-range air feed flow-biomass moisture content value pair, (iii) there are not limit cycles (LCs), and (iv) the transient behavior agrees with the multiplicity structure found in this study and reported experimental data. The developments and results are put in perspective with previous related studies.

Fluidization Dynamics of a New Two-Staged Fuel Reactor for Chemical Looping Gasification

A new staged fuel reactor (FR), which integrates a bubbling bed and a spouted fluidized bed, is proposed in the present work with regard to lowering the pressure drop of the staged FR during chemical looping applications. In order to gain insights into the gas–solid fluid dynamics of the new design, a cold experimental setup was established. The fluidization dynamics of the staged FR was investigated based on the pressure pulsation signal analysis using time domain analysis, power spectral density analysis, wavelet analysis, and the Hurst exponent analysis by the R/S method. There are four flow types of funnel-like flow, spout-fluidization, spouting motion, and unsteady spouting motion to be classified, and the transition boundaries of the corresponding flow types were determined. The design provides a way to lower the overall pressure drop of FR and then reduces the fan energy consumption to hold the oxygen carrier particle circulation.

Optimization of process parameters of Zy4/TRISO composite using processing maps and breakage rate

Coated fuel particles have been developed into isotropic tristructure (TRISO) for the high-temperature gas reactors. The Zy4/TRISO composite belongs to a Zy4 matrix with distributed coated surrogated nuclear fuel particles (ZrO2 kernel). In this study, the thermal deformation behavior of a Zy4/TRISO composite was investigated at temperatures of 750–950 °C and strain rates of 0.01–1.0 s−1. Thermal compression experiments were carried out with a small deformation rate of 10% height reduction. The constitutive models and processing maps of the Zy4/TRISO composite were established, and combined with scanning electron microscopy characterization. The microstructure evolution of TRISO particles during hot compression behavior was analyzed, the breakage rates of TRISO particles under different deformation conditions were evaluated, and the optimized high-temperature deformation conditions were determined. The optimization parameters were the temperature of 900°C-950 °C with strain rates of 0.01–0.1 s−1, and TRISO particles maintained their integrity. This shows that TRISO particles under a small deformation rate will not be damaged during hot compression deformation. These stable deformation conditions are hopeful to provide valuable guidance for follow-up hot deformation processes of the Zy4/TRISO composite.

Numerical prediction on minimum fluidization velocity of a supercritical water fluidized bed reactor: Effect of particle shape

Supercritical water fluidized bed reactor (SCWFBR) is a novel gasification reactor for hydrogen production. Compared with traditional hydrogen production technique, the SCW-based gasification has outstanding advantages such as high hydrogen production efficiency, no emission of gaseous pollutants, low water consumption and strong material adaptability. In this paper, based on Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations, numerical investigation is conducted on the effect of particle aspect ratio (α) on the minimum fluidization velocity (Umf) of a SCWFBR containing cylindrical biomass particles. The coupled CFD-DEM model is firstly validated against previously published experimental data. Then, the Umf for six types of particle shapes are calculated under different working conditions of temperature ranging from 633 to 693 K, pressure ranging from 25 to 27 MPa and α ranging from 1 to 6. Numerical results show that Umf increases with the temperature, but decreases with the pressure. Moreover, Umf is increasing with α. The underlying mechanisms are revealed by investigating the micro-structure of different shaped particles. It is shown that the increase of Umf with α is caused by the weakened fluid-solid interaction force and enhanced inter-particle locking. And the weakened fluid-solid interaction force is mainly due to the increase of the voidage. Finally, a predictive correlation of Umf for the SCWFBR is proposed considering α which demonstrates strong predictive capability for cylindrical particles.

Study of increasing thermodynamic efficiency and hydrogen amount in the process of solid fuels and biomass gasification

The effect of fuel composition such as hard coal and biomass in fluidized bed on the thermodynamic efficiency of three gasifier types, low heating value (LHV) and syngas composition was studied by simulation in CFD program. The paper presents various small gasification systems with fluidized bed of water-coal mixture and water-biomass mixture both with oxygen (air) and without oxygen. The work presents the extended mathematical model of gasification process taking into account also 13 kinetic chemical reactions enabled to apply them in CFD program. The chemical model is based on surface reactions given in the model of Equivalent Reactor Network (ERN) in Ansys Energetico. Simulation of gasification of different reactor designs enabled to obtain the mass concentration of chemical compounds in the syngas which influenced on thermodynamic efficiency and LHV. Additionally, heating of the gasifier walls by electrical system without air gives higher mass ratio of hydrogen (15%) and carbon monoxide (75%) in the syngas than in the oxidized gasification system. The simulation tests showed high thermodynamic efficiency, taking into account the exergy above 80%, both for the oxygen gasification of hard coal-slurry and biomass as well as for the externally heated gasifier without the supply of oxygen. The highest thermodynamic efficiency 90.5% was obtained during gasification of energy willow in the oxidation reactor due to the large difference in LHV of syngas and fuel. Obtaining the maximum possible mass ratio of H2 in syngas and a high thermal efficiency for the OXGR system from the gasification of subbituminous coal dust occurs at a ratio C/O2 = 0.314 and at almost stoichiometric ratio of C/H2O = 0.63. In the case of gasification of biomass in the form of finely ground energy willow in the OXGR system, these ratios were respectively: O2/C = 1.82 and C/H2O = 0.47. While maintaining the almost stoichiometric ratio C/H2O = 0.75, resulting from the water-gas shift reaction, low heating value of the syngas for the analysed gasification systems was over 25 MJ/kg. The paper shows comparison of mass fractions of CO, H2, H2O, H2S, CO2, O2, CH4, tar and other chemical compounds in the syngas. Application of the gasification reactor with external heated walls and without oxygen inflow produces the syngas without tar and volatile species in comparison to the systems with additional oxygen supply. In oxidized reactors the syngas contains a large amount of CO2 about 25–30% of total mass.

Design and Development of a Catalytic Fixed-Bed Reactor for Gasification of Banana Biomass in Hydrogen Production

Hydrogen produced from biomass is an alternative energy source to fossil fuels. In this study, hydrogen production by gasification of the banana plant is proposed. A fixed-bed catalytic reactor was designed considering fluidization conditions and a height/diameter ratio of 3/1. Experimentation was carried out under the following conditions: 368 °C, atmospheric pressure, 11.75 g of residual mass of the banana (pseudo-stem), an average particle diameter of 1.84 mm, and superheated water vapor as a gasifying agent. Gasification reactions were performed using a catalyzed and uncatalyzed medium to compare the effectiveness of each case. The catalyst was Ni/Al2O3, synthesized by coprecipitation. The gas mixture produced from the reaction was continuously condensed to form a two-phase liquid–gas system. The synthesis gas was passed through a silica gel filter and analyzed online by gas chromatography. To conclude, the results of this study show production of 178 mg of synthesis gas for every 1 g of biomass and the selectivity of hydrogen to be 51.8 mol% when a Ni 2.5% w/w catalyst was used. The amount of CO2 was halved, and CO was reduced from 3.87% to 0% in molar percentage. Lastly, a simulation of the distribution of temperatures inside the furnace was developed; the modeled behavior is in agreement with experimental observations.

Optimizing the operational strategy of a solar-driven reactor for thermochemical hydrogen production

In this paper the operational strategy of a pilot plant for regenerative hydrogen production based on two-step thermochemical redox cycles is investigated with focus on optimal operational parameters for highest solar-to-fuel efficiency. The current plant consists of a solar driven large-scale 250 kW thermochemical inert gas reactor using ceria as reactive material for water splitting and an efficient fluid heat recovery system. Here we analyse the most important process conditions, which are operating temperatures, mass flow rates and duration times for both steps in the cycle. A highly accurate and detailed simulation model combined with well-suited optimization routines reveals new insights in most efficient operational strategies. Within the optimization material and technical limits of the used components are considered, thereby yielding reliable practical results. Optimal operational parameters are found by using a temperature swing strategy with corresponding solar-to-fuel plant efficiency determined by up to 1.1%.

Application of Machine Learning to Predict the Performance of an EMIPG Reactor Using Data from Numerical Simulations

Microwave-driven plasma gasification technology has the potential to produce clean energy from municipal and industrial solid wastes. It can generate temperatures above 2000 K (as high as 30,000 K) in a reactor, leading to complete combustion and reduction of toxic byproducts. Characterizing complex processes inside such a system is however challenging. In previous studies, simulations using computational fluid dynamics (CFD) produced reproducible results, but the simulations are tedious and involve assumptions. In this study, we propose machine-learning models that can be used in tandem with CFD, to accelerate high-fidelity fluid simulation, improve turbulence modeling, and enhance reduced-order models. A two-dimensional microwave-driven plasma gasification reactor was developed in ANSYS (Ansys, Canonsburg, PA, USA) Fluent (a CFD tool), to create 644 (geometry and temperature) datasets for training six machine-learning (ML) models. When fed with just geometry datasets, these ML models were able to predict the proportion of the reactor area with temperature above 2000 K. This temperature level is considered a benchmark to prevent formation of undesirable byproducts. The ML model that achieved highest prediction accuracy was the feed forward neural network; the mean absolute error was 0.011. This novel machine-learning model can enable future optimization of experimental microwave plasma gasification systems for application in waste-to-energy.

Modeling the devolatilization and fragmentation of biomass pellets with the bonded particle method for fluidized bed applications

By extending the bonded particle method, the major structural changes during the devolatilization of a wood pellet in a fluidized bed and the resulting mechanical behavior have been successfully reproduced. A comparison with experiments from the literature showed that the implemented particle-based pyrolysis model enables predicting the entire pellet’s kinetics with a high agreement. The developed shrinkage model for the particles and bonds further allowed to emulate the reported formation of a large-scale pore network inside the pellet. The simulation of a radial compression test with the predicted structure showed good agreement with experimental data and could confirm the importance of the pores for the mechanical behavior. The results demonstrated that the large pores cause the fragmentation of agglomerates already at low mechanical loads which could promote attrition. In general, the results have shown that the developed extension of the bonded particle method allows studying and predicting the behavior of a single pellet during conversion inside a fluidized bed gasification reactor in more detail.

Holistic energy flow analysis of a solar driven thermo-chemical reactor set-up for sustainable hydrogen production

In this contribution, a holistic energy flow analysis of a solar driven pilot plant for green hydrogen production using two-step thermochemical cerium-based redox cycles is carried out. The plant consists of a heliostat field, a large-scale inert gas reactor, an efficient fluid heat recovery system and an electrical vaporizer for steam generation. The system behaviour is physically described, and energy flows are quantified using a complex simulation model considering material and geometric properties of the complete system design. The system energy flow and corresponding impact on plant efficiency is thoroughly analysed with emphasis on plant design, operational strategy, and influence of the crucial control parameters. Influences of a heat recovery system and the size of various types of heat losses are investigated, potential efficiency improvements are revealed and useful possibilities for plant design and material modifications are discussed. The transient system behaviour is investigated by varying temperatures and mass flow rates in a broad practicable range to gain more insight in efficient reactor design and plant control. Two temperature swing strategies are investigated in more detail, which are by far more efficient than any near-isothermal or isothermal strategy for this application.

Entrained Flow Plasma Gasification of Sewage Sludge–Proof-of-Concept and Fate of Inorganics

Sewage sludge is a residue of wastewater processing that is biologically active and consists of water, organic matter, including dead and living pathogens, polycyclic aromatic hydrocarbons, and heavy metals, as well as organic and inorganic pollutants. Landfilling is on the decline, giving way to more environmentally friendly utilisation routes. This paper presents the results of a two-stage gasification–vitrification system, using a prototype-entrained flow plasma-assisted gasification reactor along with ex situ plasma vitrification. The results show that the use of plasma has a considerable influence on the quality of gas, with a higher heating value of dry gas exceeding 7.5 MJ/mN3, excluding nitrogen dilution. However, dilution from plasma gases becomes the main problem, giving a lower heating value of dry gas with the highest value being 5.36 MJ/mN3 when dilution by nitrogen from plasma torches is taken into account. An analysis of the residues showed a very low leaching inclination of ex-situ vitrified residues. This suggests that such a system could be used to avoid the problem of landfilling significant amounts of ash from sewage sludge incineration by turning inorganic residues into a by-product that has potential use as a construction aggregate.

Positron Annihilation Spectroscopy Complex for Structural Defect Analysis in Metal-Hydrogen Systems.

The current work is devoted to developing a system for the complex research of metal–hydrogen systems, including in an in situ mode. The system consists of a controlled gas reactor with a unique reaction chamber, a radioisotope positron source, and a positron annihilation spectroscopy complex. The use of the system enables in situ investigation of the defect structure of solids in hydrogen sorption–desorption processes at temperatures up to 900 °C and pressures up to 50 bar. Experimental investigations of magnesium and magnesium hydride during thermal annealing were carried out to approve the possibilities of the developed complex. It was shown that one cycle of magnesium hydrogenation–dehydrogenation resulted in the accumulation of irreversible hydrogen-induced defects. The defect structure investigation of the magnesium–hydrogen system by positron annihilation techniques was supplemented with a comprehensive study by scanning electron microscopy, X-ray diffraction analysis, and hydrogen sorption–desorption studies.

Influence of the Contamination of Fuel with Fly Ash Originating from Biomass Gasification on the Performance of the Anode-Supported SOFC

The integration of solid oxide fuel cells (SOFCs) with biomass gasification reactors raises the possibility of solid particle contamination of the gaseous fuel entering the cell. Technical specifications from SOFC manufacturers, among other sources, claim that SOFCs do not tolerate the presence of solid particles in fuel. However, there is very limited literature on the experimental investigation of feeding SOFCs with particulate matter aerosols. In this study, a standard 5 × 5 cm anode-supported SOFC was fueled by two types of aerosols, namely, (1) inert powder of grain sizes and concentration equivalent to gasifier fly ash and (2) a real downdraft gasifier fly ash, both suspended in a gaseous fuel mixture. For reference, cells were also investigated with a dust-free fuel gas of the same composition. A straightforward negative influence of the inert powder aerosol could not be confirmed in experiments with a duration of 6 days. That said, the introduction of carbonaceous fly ash aerosol caused slow but irreversible damage to the SOFC. The degradation mechanisms were studied, and the presence of carbon-containing particles was found to clog the pores of the SOFC anode. The maximum measured power density of the SOFC equaled 855 mW/cm2 (850 °C, reference fuel). Feeding inert aerosol fuel caused no rapid changes in power density. A moderate drop in performance was observed throughout the experiment. The contamination of fuel with fly ash resulted in an initial performance gain and a ca. 25% performance drop longer term (43 h of contamination). Post-mortem analysis revealed contamination on the walls of the gas channels, with some visible alumina or fly ash spots in the anode area.

Efficient high-fidelity TRISO statistical failure analysis using Bison: Applications to AGR-2 irradiation testing

The ability of tri-structural isotropic (TRISO) fuel to contain fission products is largely dictated by the quality of the manufacturing process, since most of the fission product release is expected to occur due to coating layer failure in a small number of particles containing defects. The Bison fuel performance code has capabilities to predict failure in individual particles, accounting for the presence of defects, and to apply statistical analysis methods to compute the probability of failure in a set of fuel particles. Bison has recently undergone significant development both to improve its physical representations of fuel particle behavior and to improve the efficiency of its statistical failure calculations. Physical model improvements include new capabilities to account for the pressure generated by fission gases on inner pyrolytic carbon (IPyC) crack surfaces and to use local material coordinate orientation to accurately incorporate the anisotropy in the material properties in aspherical particles. To improve statistical modeling efficency, a direct integration approach which involves directly integrating the failure probability function associated with statistically varying parameters has been developed. The direct integration approach is much more efficient than the Monte Carlo (MC) schemes commenly employed, and allows Bison to directly run high-dimensional fuel performance models, which improves the accuracy of failure probability calculations. A set of benchmark problems is considered here to compare the MC and direct integration approaches, and a statistical failure analysis of compacts in the Advanced Gas Reactor (AGR)-2 experiments is performed using the direct integration approach.

Chemical Model for Thermal Treatment of Sewage Sludge

Sewage sludge is here studied as a valuable source for processing or energy conversation thanks to its high nutrition and energy content. However, various origins of the wastewater, different water cleaning technologies, and seasonal and regional dependencies lead to the high variability of the sewage sludge properties. In thermal treatment units, that is, incineration, gasification and pyrolysis, sewage sludge serves as feedstock or fuel, hence a proper characterization and a mathematical description of the sewage sludge are required to estimate product streams and to formulate numerical simulations and optimization methods. The presented work introduces a surrogate concept that allows replication of sewage sludge’s ultimate composition, moisture, and ash content. The surrogate approach aims to model the decomposition of any sewage sludge sample, opposite to the established determination of kinetic rates for individual samples. Based on chemical solid surrogate species and corresponding reaction mechanisms, the thermal decomposition path is described. Sewage sludge is represented by a combination of lignocellulosic species, proteins, sugars, lipids, and representative inorganic species. The devolatilization and heterogeneous reactions are formulated such that they can be used together with a detailed gas-phase model, including tar oxidation and emission models for nitrogen and sulfur oxides, recently proposed by the authors. The developed chemical model is applied using a zero-dimensional gasification reactor in order to model weight loss within the thermogravimetric analysis, pyrolysis, gasification and combustion conditions. Weight loss, the composition of product gases, and emission release (nitrogen and sulfur oxides) are captured well by the model. The flexible surrogate approach allows us to represent various sewage sludge samples.

Test and performance optimization of nozzle inclination angle and swirl combustor in a low-tar biomass gasifier: a biomass power generation system perspective

A nozzle inclination angle and swirl combustor inside the low-tar biomass (LTB) gasifier reactor were tested and optimized to evaluate these effects on tar reduction to design tar-free producer gas. The tar reduction process is mainly based on the concept of a swirling flow created by the nozzle inclination angle, with the inclination angle of 55° to the radial line, allowing good mixing between pyrolysis gases and gasifying agents. A separate swirl combustor has created large internal annular and reverses flow zones with the help of swirl flow, resulting in homogenized temperature inside the combustor and providing longer residence time; both have a positive effect on the combustion of mixed gasifying air-pyrolysis gases by the thermal cracking in the partial oxidation zone. Recircling ratio (RR) and combustion degree of volatiles are the two optimization parameters for evaluating the performance of NIA and swirl combustor. The result observed that outstanding tar reduction occurred in this novel system. About 86.5 and 12.8% of tar compounds are broken down in the partial oxidation zone and pyrolysis zone using the novel swirl combustor and NIA, respectively; gas outlet has observed producer gas having tar concentration of less than 1%. The optimization results reveal that a lower recycling ratio (recycle gas/gasifying air) and a higher combustion degree of volatiles perform better in biomass gasification. Finally, this system generated producer gas with the tar concentration at an extremely low level of 7.4 mg/Nm3 for a biomass moisture content of 9% and appeared the lower heating value of 4.6–5.1 MJ/Nm3. This lower tar concentration might be directly coupled with an internal combustion engine or a gas turbine for power generation.

Atomistic and cluster dynamics modeling of fission gas (Xe) diffusivity in TRISO fuel kernels

TRISO fuel particles are candidates for use in next generation reactors including gas reactors, fluoride salt-cooled high temperature reactors, and micro-reactors. The UCO fuel kernel consists of a uranium dioxide (UO2) and uranium carbide mixture. The addition of UC2 helps suppress the formation of carbon monoxide gas, which led to failures during initial TRISO development. The addition of uranium carbide alters the chemistry of the UO2 kernel, which is known to influence performance parameters such as fission gas diffusivity, although the impact has not been quantified and no models exist that take the change in chemistry into account. Therefore, better understanding and more accurate models of the impact of chemistry on fuel performance are of high priority. In this paper, a first-principles density functional theory (DFT) and empirical potential based multi-scale study has been carried out to model the diffusivity of fission gas xenon (Xe) in UCO TRISO fuel kernels. The focus is on the UO2 component in the UCO fuel kernels, as that represents the largest volume fraction of the fuel kernels. The study relies on DFT and empirical potential calculations to determine Xe and point defect properties, which are then used in thermodynamic and kinetic models to predict diffusion for intrinsic conditions. In addition, the information is utilized in cluster dynamics simulations using the Centipede code to estimate the impact of irradiation on defect transport. The presence of UC2 or UC2−x in the UCO fuel kernels is shown to have a substantial impact on the UO2 non-stoichiometry by inducing oxygen vacancies and driving UO2 sub-stoichiometric, which causes much slower Xe diffusion in UCO compared to light water reactor UO2 fuel. The application of this model in fuel performance simulations using the Bison code is also demonstrated.

Europium diffusion in IG-110 nuclear graphite

Europium diffusion in graphite has been recognized to be of interest in high-temperature gas reactor safety analysis, particularly as an indicator of strontium diffusion. However, no measurements of europium diffusion coefficients have been reported in the literature. In this work, the effective diffusion coefficient of europium was measured using a time-release method. Natural europium was loaded into pre-milled unirradiated IG-110 graphite spheres using a pressurized acid digestion vessel. The time-release experiments were performed in the temperature range 1823 K – 1973 K using a SiC diffusion cell connected to an inductively-coupled plasma mass spectrometer (ICP-MS) via a He gas line. The results of this work are:DEu,IG−110=(1.5×10−3m2/s)exp(−2.87×105J/molRT)This effective diffusion coefficient can be used to aid in predictive modelling of europium transport in HTGRs.