Initial Bed Temperature Research Articles

Inhomogeneous temperature in high temperature fluidized beds

In this work, we observe an inhomogeneous temperature distribution within a fluidized bed affects the mixing dynamics and therefore heat transfer performance. High temperature fluidized bed experiments with an initial temperature gradient are performed. As the superficial velocity increases, the bed becomes lightly fluidized. Despite fluidization, the bed temperatures do not converge, and the thermal gradients remain. Eventually the superficial velocity is sufficiently high to completely mix the bed and collapse the bed temperatures together. CFD-DEM coupled simulations are performed to investigate the mixing dynamics. Initial bed temperature differences of 100, 300, and 500 K are simulated with varying superficial velocities to create a regime map. At relatively low superficial velocities, the high temperature regions of the bed begin to bubble before the lower temperature regions due to gas density changes. To fully mix the particle temperatures in the vertical direction, the relative velocity (U/Umf) must be a minimum of 1.30.

Experimental study of the discharge process of a thermal energy storage system based on granular material operated as a fluidized or confined bed

The stable generation of green electricity by Concentrated Solar Power (CSP) plants is subjected to the proper performance of Thermal Energy Storage (TES) systems, which constitute a critical subsystem of the plant. TES systems based on granular material have already been tested for industrial scale, allowing the operation at high temperature. Depending on the particle size of the granular material and the velocity of the working fluid, the bed conforming the TES system may be operated in a bubbling fluidized or a fixed bed regime. Further, beyond minimum fluidization conditions the bed can operate as fixed if the particles are mechanically confined. The performance of the discharge process of a lab-scale TES system (20.5 cm of diameter, 1 m bed height and 55 kg of silica sand as bed material) of granular material operated as a fluidized bed and as a confined bed was experimentally analyzed for various air volumetric flow rates. For the fluidized bed configuration, the bed temperature was found to be uniform along the bed height due to the high axial mixing rate caused by gas bubbles. During the discharge process of the fluidized bed TES system, the bed temperature decreased exponentially from the initial bed temperature to the temperature of the cooling fluid, with a faster temperature reduction for higher flow rates of fluid. The confined bed operation resulted in a stable temperature of the fluid at the outlet, close to the maximum temperature of the system, for around 45 min when discharging the bed with 700 Nlpm of cold air, whereas after 45 min of the discharge process, the outlet temperature of gas for the fluidized bed was roughly half the temperature obtained from the confined bed. However, the average air pressure drop during the discharge of the TES system of granular material operated as a fluidized bed is stable at around 0.16 bar, while the pressure drop of the confined bed is significantly higher, decreasing from 0.65 to 0.30 bar as the discharge process of the bed progressed.

A one- and three-dimensional coupled model and simulation investigation for the large-scale oil-heating type Mg-based hydrogen storage tank

A large-scale oil-heating type Mg-based hydrogen storage tank is the key device for the high-efficiency and high-safety Mg-based solid hydrogen storage and transportation. However, the complicated heat and mass transfer in the Mg alloy bed and oil tube during the hydrogen desorption process impede the design of high-performance hydrogen storage tanks. In this work, a one- and three-dimensional coupled model considering the impact of oil velocity and temperature on the internal heat and mass transfer was developed to simulate the hydrogen desorption process of large-scale oil-heating type Mg-based hydrogen storage tanks. This model was then solved by the finite element method, and the simulation results agreed well with the experimental data obtained from an Mg-based hydrogen storage tank. Moreover, simulation results indicate that the oil velocity has a considerable impact on the hydrogen desorption performance of the Mg-based hydrogen storage tank, and a recommended oil velocity of 4 m s−1 was identified. In addition, high oil temperature and low hydrogen desorption pressure benefit the hydrogen desorption performance, thus should be determined by the application scenarios. Besides, the complete hydrogen desorption time was barely affected by the initial bed temperature, which is suggested as ≥ 573 K to meet the high rate requirement of hydrogen supply, otherwise as room temperature to reduce energy costs. The model and simulation results presented in this work provided a foundation for the design of high performance large-scale oil-heating type Mg-based hydrogen storage tanks that can be applied practically in the field of hydrogen energy.

Modelling of methane sorption enhanced reforming for blue hydrogen production in an adiabatic fixed bed reactor: unravelling the role of the reactor's thermal behavior

Methane sorption enhanced reforming (SER) is investigated in this work as a promising route for blue H2 production. A 1-D dynamic heterogeneous model is developed to evaluate the thermal behavior of a fixed bed reactor under adiabatic conditions. The heterogeneous model allows to decouple the feed gas temperature from the initial solid one in order to investigate the behavior of the reforming step in a temperature swing reforming/regeneration process. The effects of the feed gas temperature, the initial bed temperature, and the bed thermal capacity are studied by evaluating the global impact of each parameter through a set of key performance indices (CH4 conversion, H2 yield and purity, carbon capture ratio) calculated as integrals over the duration of the reforming step. The results highlight the minor effect of the initial bed temperature on the process performances showing the potential of minimizing the extent of a cooling step between regeneration and reforming stages. Besides, due to the endothermic nature of the methane sorption enhanced reforming process at high temperatures, thermal energy must be provided to the SER process to achieve high CH4 conversion and high carbon capture ratio. This can be made either in the form of high feed temperature or by utilizing the energy stored in the bed benefiting from the bed thermal capacity.

Effect of preheat temperature, pressure, and residence time on methanation performance

The present work studies the effect of reagent preheat temperature on methanation while maintaining the initial temperature of the catalytic bed constant. An adiabatic packed bed reactor was used with 193 g of commercial 10% Ni/Al2O3 catalyst. The tested preheat temperatures were 25 °C, 100 °C, 180 °C, and 280 °C, while the initial catalytic bed temperature was 280 °C. Two tests were performed in which the effect of preheat temperature was evaluated: the first comparing gas hourly space velocities (GHSVs) of 935 h−1 and 1559 h−1, and the second comparing gauge pressures of 0 bar, 1 bar, and 4 bar. Similar behavior was observed for the temperature inside the reactor and final CO2 conversion for preheating temperatures of 100 °C, 180 °C, and 280 °C at a gauge pressure of 0 bar. However, at this pressure, conversion was considerably reduced for the preheat temperature of 25 °C, due to a large part of the catalytic bed serving to preheat the reactants to the minimum reaction temperature. This effect can be partially attenuated by decreasing the GHSV, due to the increased residence time. Finally, increased pressure significantly improved the final CO2 conversion for all preheating temperatures (Tin), and attenuates the effect of Tin. These results show that certain operating conditions do not require as high a reactant preheat temperature for methanation, which offers energy savings in certain processes such as power-to-gas (P2G), where the hydrogen is produced from electrolysis and can leave the process at a lower temperature than that required for methanation.

Experimental hydrogen sorption study on a LaNi5-based 5 kg reactor with novel conical fins and water tubes and its numerical scale-up through a modular approach

Hydrogen sorption characteristics of 5 kg-LaNi5 reactor featuring conical fins and heat transfer tubes is experimentally studied at various water flow rates (Vs:2.5, 5, 7 LPM), inlet temperatures (Ts:30, 25, 20 °C), hydrogen pressures (Ps:10, 15, 20, 25 bar). Higher Vs, Ps, and lower Ts yield faster absorption through higher driving force (∝ln (Ps/Peq), Peq: equilibrium pressure). Ninety percent absorption takes ∼12.3 and ∼13.7 min at Vs:7 and 2.5 LPM (Ps:15 bar, Ts:30 °C). Faster atmospheric desorption needs higher Ts and/or Vs offering higher driving force (∝ (1-(1/Peq)). 90% desorption takes ∼20.1 and ∼21.8 min for initial bed temperatures of 60 and 30 °C, (Vs:5 LPM, Ts:60 °C). Absorption of this ‘Single Reactor’ and five/ten (25/50 kg) such reactors in series and parallel are studied numerically. Series configuration stores five/ten-times hydrogen than ‘Single Reactor’ within the same duration by doubling/tripling Vs (same Ps, Ts). Parallel configuration requires proportional water supply.

Parametric Effects of Fused Filament Fabrication Approach on Surface Roughness of Acrylonitrile Butadiene Styrene and Nylon-6 Polymer.

This research objective is to optimize the surface roughness of Nylon-6 (PA-6) and Acrylonitrile Butadiene Styrene (ABS) by analyzing the parametric effects of the Fused Filament Fabrication (FFF) technique of Three-Dimensional Printing (3DP) parameters. This article discusses how to optimize the surface roughness using Taguchi analysis by the S/N ratio, ANOVA, and modeling methods. The effects of ABS parameters (initial line thickness, raster width, bed temperature, build pattern, extrusion temperature, print speed, and layer thickness) and PA-6 parameters (layer thickness, print speed, extrusion temperature, and build pattern) were investigated with the average surface roughness (Ra) and root-mean-square average surface roughness (Rq) as response parameters. Validation tests revealed that Ra and Rq decreased significantly. After the optimization, the Ra-ABS and Rq-PA-6 for the fabricated optimized values were 1.75 µm and 21.37 µm, respectively. Taguchi optimization of Ra-ABS, Rq-ABS, Ra-PA-6, and Rq-PA-6 was performed to make one step forward to use them in further research and prototypes.

Simulation of Two-Phase Flow and Syngas Generation in Biomass Gasifier Based on Two-Fluid Model

The efficient use of renewable energy is receiving more and more attention in the context of “carbon neutrality” and “carbon peaking”. For a long time, biomass has been used less efficiently as a renewable energy source, but with the development of fluidized biomass gasification technology, it can play an increasing role in industrial production. A fluidized bed biomass gasifier has a strong nonstationary process due to its complex energy–mass exchange, and analysis of its complex reaction process and products has relied on experiments for a long time. This paper uses a Euler–Euler two-fluid model to establish a three-dimensional CFD model of the fluidized bed biomass gasifier, on which factors affecting syngas generation are analyzed. The simulation shows that increasing the initial bed temperature can effectively improve syngas production, while increasing the air equivalent is not beneficial for syngas production.

Transient simulation studies on a metal hydride based hydrogen storage reactor with longitudinal fins

In this study, a 50 kg LaNi5 based shell and tube type metal hydride hydrogen storage reactor is investigated. The design process for the reactor is presented and its performance analysis is carried out numerically. The metal hydride is filled in the tubes while the shell side houses the heat transfer fluid. Each of the metal hydride tubes is equipped with fins connected to a longitudinal array of concentric cylinders for support and for ensuring uniform distribution of alloy powder, which is a challenge in case of large reactors. The number of tubes MH tubes which is seven in the present case was selected on the basis of highest heat transfer capacity per unit system weight. The reactor performance was simulated under varying operating conditions. It was observed that reactor performance was quiet promising at a moderate supply pressure of 35 bar and a heat transfer fluid flow rate of as low as 30 lpm. Any increase in flow rate does not alter the reactor performance significantly. Initial bed temperature did not have any significant effect on the system performance. Thermal resistance network analysis established that heat transfer was primarily limited by conduction.

Numerical simulation of NO and SO2 emission dynamic characteristics during thermal start-up of CFB boiler

During the startup process of CFB boiler, problems such as wear, coking and excessive pollutant emission may occur, which pose a serious threat to the safe and environmental protection operation of the power plant. Based on the Computational Particle Fluid Dynamics (CPFD) method, numerical simulation was carried out for the thermal startup process of CFB boiler, so as to analyze the flow field change and pollutant emission dynamic characteristics during the thermal startup process of the boiler. The results show that the formation of NO and SO2 is mainly concentrated in the dense-phase zone of CFB boiler during the thermal startup process. After stable operation of the boiler, the production of NO, SO2, CO and O2 presents dynamic fluctuation. The bed height (H0) and the initial bed temperature (T0) have certain influences on the formation and distribution of NO and SO2. The research results provide theoretical basis for the actual thermal startup and operation of CFB boiler and have certain reference value.

High-fidelity investigation of thermochemical conversion of biomass material in a full-loop circulating fluidized bed gasifier

Olive oil production urges the energy companies to exploit the potential of the residues as biomass fuels for clean energy production. Circulating fluidized bed (CFB) gasifier gains global interest within these several years due to its promising solution for converting biomass material to renewable energy. However, the multi-physics processes and multiscale structures inside the gasifier impede the experimental measurements. As an alternative, a reactive multiphase particle-in-cell approach is developed in this work to simulate the gasification process of olive oil waste in a pilot-scale full-loop CFB gasifier. After the model validation, the heat transfer properties of solid phase and the effect of size-induced segregation on solid thermochemical properties are explored. The results show that the low-temperature biomass particles injected highly influence the spatial distribution of solid temperature and solid heat transfer coefficient (HTC). A larger particle size gives rise to a higher HTC. Moreover, the temperature and HTC of biomass are larger than that of sand. A wide and narrow residence time distribution of sand in the riser and cyclone can be observed. The scale of biomass dispersion is respectively larger and the same as that of sand in horizontal and vertical directions. Particles in the dense region have a smaller HTC, Reynolds number, and temperature. Superficial gas velocity improves the uniformity of solid distribution. Elevating the gas velocity and initial bed temperature enhances solid dispersion intensity.

CFD-DEM study of biomass gasification in a fluidized bed reactor: Effects of key operating parameters

Abstract Biomass gasification in a fluidized bed reactor is a complex process involving intricately multi-scale and multi-physics processes and may be affected by many operating parameters. In this work, it is numerically investigated at particle scale using a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach. The flow dynamics, turbulence, heat transfer via convective, conductive, and radiative paths, and heterogeneous and homogeneous reactions are considered. The effects of key operating parameters on gasification performance are studied in terms of biomass particle diameter, initial bed temperature, steam to biomass (S/B) ratio, inlet gas flow rate, and feed position. The simulation results show biomass particle diameter has an insignificant influence on the production of H2 and CH4 while it slightly affects the production of CO and CO2. Higher initial bed temperature leads to a larger decrease of gas temperature at bed exit and benefits the production of H2 and CO. Increasing S/B ratio increases H2 and CO2 production while decreases CH4 and CO production. Larger inlet gas flow rate leads to a shorter gas residence time and the decrease of S/B ratio. Biomass particles fed from the side wall give rise to higher temperature, lower H2 and CO2, and higher CO and CH4 than that fed from the center bottom. Changing feed positions on the side wall has a slight influence on gas temperature while it has an insignificant influence on product compositions.

Application of Amberlite XAD-7HP resin impregnated with Aliquat 336 for the removal of Reactive Blue - 13 dye: Batch and fixed-bed column studies

Adsorption studies were performed in both batch and column mode for the removal of Reactive Blue-13 (RB-13) dye using Amberlite XAD-7HP resin impregnated with Aliquat 336. In batch mode, the effect of adsorbent dosage (1–4 g/L), initial dye concentrations (50–100 mg/L) at various temperatures (293–333 K), pH (2–12), contact time (0–60 min), and ionic strength of salt (NaCl & Na2SO4: 1–50 mg/L) solution were studied. The Langmuir isotherm showed the best-fitted correlation for the equilibrium data at all temperatures. Adsorption kinetics followed both the pseudo-second-order (RRB2 = 0.997) and Elovich model (RRB2 = 0.998). The average values of ΔGo, ΔHo, and ΔSo were found to be -30.828 kJ/mol, −68.07 kJ/mol, and −98.19 kJ/mol, respectively, showing that the adsorption process is exothermic, feasible and spontaneous. 4 g/L of impregnated resin gave effective removal (∼99 %) of RB-13 dye (50 mg/L) within 60 min, and change in solution pH did not affect removal percent significantly. The resin could be regenerated up to 2 cycles. In fixed bed column studies, the bed height (2–4 cm), flow rate (2.5–5 mL/min), initial dye concentration (20–50 mg/L) and bed temperature (303–323 K) were changed to see their effect. All breakthrough curves were well fitted by Thomas model. A column with 0.1127 m ID, 0.0199 m height and 0.066 kg impregnated resin will be sufficient to treat 10,000 L/day of RB-13 dye solution.

Desublimation based separation of CO2 inside a cryogenic packed bed: Performance mapping with the spatiotemporal evolution of CO2 frost

Preferential desublimation of carbon dioxide from vapour phase onto cooled packing at low pressure (1–5 atm) shows great promise to separate carbon dioxide in pure from flue/natural gas. A new transport phenomena model that takes into account the interfacial heterogeneous nucleation of solid CO2 on the packing and on the bed wall and also incorporates the interstitial homogeneous nucleation, is used to simulate the performance of desublimation based separation of CO2 in a cryogenic packed bed. The spatiotemporal evolution of CO2 frost layer inside the bed is simulated for different operating conditions namely inlet flow rates, initial bed temperature profiles, flow configurations. The extent of separation of CO2 and the resulting void fraction is mapped over the space-time domain. Bed saturation and bed critical times are simulated and validated with experimental data. Non-dimensional numbers are derived for simultaneous heat and mass transfer process with phase change and their effects on the extent of separation and optimum process conditions are simulated. Apart from evaluating the extent of separation, the model additionally helps in identifying the different operative zones and operational problems namely choking. The significance of the study is in the model based inferential prediction of frost layer thickness and its application in the choice of operating and bed switching conditions of cryogenic packed bed for separation of carbon dioxide from flue gas and natural gas.

Ozone‐Assisted photocatalytic degradation of benzene using nano‐zinc oxide impregnated granular activated carbon (ZnO–GAC) in a continuous fluidized bed reactor

Benzene is one of the volatile organic compounds, exposure to which causes different complications including coughs, headache, dizziness, and even cancer. Therefore, methods are required to remove benzene from polluted air. In this study, for the first time, benzene degradation was examined using photocatalytic ozonation process in the presence of nano‐zinc oxide impregnated granular activated carbon (ZnO–GAC) in a continuous fluidized bed reactor. The experiments were performed with the aim of investigating the effect of factors including the ratio of superficial gas velocity to the minimum fluidization velocity (), initial benzene concentration, relative humidity, catalyst dosage, bed temperature, ozone dosage, and intensity of UV lamp in removing benzene from the air. The results of this study indicated that the minimum fluidization velocity (Umf) was obtained as 0.47 L/min, while benzene removal efficiency reached its maximum at = 2.5. Addition of ozone to the ZnO‐UV/GAC process enhanced the process efficiency considerably. With elevation of benzene concentration from 50 to 300 ppm, removal efficiency by UV/ZnO–GAC process declined from 84.14 to 45.12%, while with O3/ZnO–GAC/UV, it decreased from 93.8 to 68.78%. The range of the optimal humidity for benzene removal in both processes was obtained as 30–35%. With elevation of ZnO–GAC dosage from 0 to 10 mg, benzene removal efficiency increased from 42.07 to 70.24 and from 60.9 to 89.57% using UV/ZnO–GAC and O3/ZnO–GAC/UV processes, respectively. Furthermore, the efficiency of O3/ZnO–GAC was directly related to bed temperature, while UV/ZnO–GAC and UV/O3/ZnO–GAC processes were inversely related. Eventually, the removal efficiency of the processes had a direct relation with the ozone dosage and UV intensity. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13082, 2019

Modelling of debris bed reflooding in PEARL experimental facility with MC3D code

A hypothetical severe accident in a nuclear power plant has the potential for causing severe core damage, including a meltdown. To prevent or in the case of an already formed debris bed to limit the in-vessel core degradation, the basic severe accident management strategies consider the in-vessel reflooding to ensure the debris bed coolability.The purpose of our research was to understand the key processes and conditions related to the in-vessel debris bed coolability in the bottom reflooding conditions. Recently, experimental tests in the PEARL facility (IRSN, France) were performed to highlight the behaviour of the steam and water flow in a hot porous medium and to provide experimental data to validate 2-D and 3-D models for the debris bed reflooding. Our aim was to analyse chosen PEARL experiments performed at the atmospheric pressure. The objective was to analyse the importance of the uncertainties in the initial and boundary conditions on the simulation results and to assess the heat transfer modelling approaches. Simulations were performed using the MC3D code (IRSN, France).In general, the performed simulations are in good agreement with the experiments. The general features, in particular the water preferential entrainment in the bypass are recovered and the analysis of calculation gives further information on the mechanisms. In particular, the mechanism of water deviation in the bypass (2-D behaviour) is described. The hypothesis of water dragged by steam coming from the debris bed region cannot be supported. However, the simulation results are indicating a noticeable impact of the actual conditions as the water temperature and the initial support bed and bypass temperature. The simulations, varying the porosity of the test section, showed that this impact affects the flow configuration and is important for cases with the 2-D configuration. The reflooding capabilities in this configuration may depend strongly on the characteristics of the debris bed. Changes in the heat transfer modelling do not have greater effect on the simulation results.

Characterization of a dual fluidized bed gasifier with blended biomass/coal as feedstock

A one-dimensional model is built based on the commercial Aspen Plus software to kinetically simulate the biomass/coal co-gasification process in a dual fluidized bed gasifier. The synergistic effect on the co-gasification kinetics is allowed for, and is coupled with the gas–solid flow hydrodynamics. With the developed model, the effects of different key operating parameters including the biomass blending ratio (Rb), the initial bed temperature (Tg), the feedstock mass flow rate (Ffs), the bed material flux (Fbm) and the steam to carbon ratio (Rsc) on the resultant syngas composition and the supplemental fuel mass flow rate (Fsf) are investigated, and the operation parameters are optimized. It is found that increasing Rb and Tg can enhance the gasification, while increasing Ffs and Rsc restricts the gasification. Increasing Fbm has slight effect on the gasification results but can reduce Fsf. The cold gas efficiency is up to 78.9% under the proposed optimum condition.

Influence of initial bed temperature on bed performance of an adsorption refrigeration system

The study deals with the complete dynamic analysis (numerical and practical) of an existing adsorption refrigeration system. The adsorption refrigeration setup is available at Indian School of Mines (Dhanbad, India), Mechanical engineering department. The system operates with activated carbon (as an adsorbent) and methanol (as refrigerant).Numerical model is established base on energy equation of the heat transfer fluid (water) and transient heat and mass transfer equations of the adsorbent bed. The input temperature of heat source is 90?C, which is very low compared to other low-grade energy input refrigeration system. The thermo-physical properties of an adsorptive cooling system (using activated carbon?methanol pair) are considered in this model. In this analysis influence of initial bed temperature (T1) on the bed performances are analysed mathematically and experimentally. The simulation and practical results of this system show that the cycle time decreases with increase in initial bed temperature and the minimum cycle time is 10.74 hours (884 minutes for practical cycle) for initial bed temperature of 40?C. Maximum system COP and specific cooling capacity are 0.436 and 94.63 kJ/kg of adsorbent under a condenser and evaporator temperatures of 35?C and 5?C, respectively. This analysis will help to make a comparison between simulated and experimental results of a granular bed adsorption refrigeration system and also to meet positive cooling needs in off-grid electricity regions.

A two dimensional Euler–Lagrangian model of wood gasification in a charcoal bed—Part II: Parameter influence and comparison

A Euler–Lagrangian simulation was employed for a comprehensive parameter study of wood gasification in a fluidized charcoal bed. The parameters that were varied include the initial bed temperature, fuel mass flow rate, inert tar fraction, and kinetic energy losses caused by particle–particle and particle–wall collisions. The results of each parameter variation are compared with a base scenario, previously described in detail in Part I of this study (Gerber & Oevermann, 2014). The results are interpreted by comparing the reactor outlet temperature, averaged particle temperature, overall wood mass, overall charcoal mass, concentrations of several gaseous species, and axial barycenter data for particles obtained with different sets of parameters. The inert tar fraction and fuel mass flow rate are the most sensitive parameter, while the particle–particle and particle–wall contact parameters have only a small impact on the results. Increasing the reactive tar components by 19% almost doubled the amount of reactive tars at the reactor outlet, while decreasing the restitution coefficients of the particle collisions by 0.2 results in higher overall gas production but almost no change in bed height. Herein, our numerical results are discussed in detail while assessing the model restrictions.

Experimental investigation on heat extraction from a rock bed heat storage system for high temperature applications

Solar energy is available in an intermittent way, and integrating an energy storage system with solar energy collection devices may promote uninterrupted supply of energy in the absence of the availability of solar energy. It has been shown that heat can be stored using rocks packed in a bed, but limited work has been reported on heat extraction from a charged rockbed. This paper reports on the heat extraction from a charged rock bed. Discharging tests were performed under different air flow conditions and initial bed temperatures. Without the blower, the discharging rate is very slow. The discharging rate can be increased, and the cooking time controlled by adjusting the air speed through the rock-bed system.