Hydrodynamics Of Gas-solid Flow Research Articles

Hydrodynamics of polydisperse gas-solid flows: Kinetic theory and multifluid simulation

Polydisperse gas-solid flows, which is notoriously difficult to model due to the complex gas-particle and particle-particle interactions, are widely encountered in industry. In this article, a refined kinetic theory for polydisperse flow is developed, which features single-parameter Chapman-Enskog expansion (the Knudsen number) and exact calculation of the integrations related to pair distribution function of particle velocity without any mathematical approximations. The Navier-Stokes order constitutive relations for multifluid modeling of polydisperse gas-solid flow are then obtained analytically, including the solid stress tensor, the solid-solid drag force, the granular heat flux and the energy dissipation rate. Finally, the model is preliminarily validated by comparing to the discrete element simulation data of one-dimensional granular shear flow and by showing that the hydrodynamic characteristics of gas-solid flows in a bubbling fluidized bed containing bidisperse particles can be successfully predicted.

Optimizing Design and Operational Parameters for Enhanced Mixing and Hydrodynamics in Bubbling Fluidized Bed Gasifiers: An Experimental and CFD-Based Approach

An experimental investigation of hydrodynamics of gas-solid flow is carried out by engaging different designs of air distributor plates. An analysis of three different plates, i.e., perforated, 45° slotted and novel hybrid plate, revealed the difference in pressure drop and minimum fluidization velocities (Umf) for varying input operational variables. Umf is found to be lowest for perforated and highest for 45° slotted plate, whereas pressure drop is found to be highest for 45° slotted plate and lowest for novel hybrid distributor plate. The bubbles rise velocity ratio (Umf,b/Umf,f) is noticed minimum for 45° slotted plate due to relatively larger bubbles originating from the bigger slot openings and maximum for perforated distributor plate owing to smaller bubbles with dominant axial rise. Furthermore, the bed height rise ratio (h/L) is observed as a minimum for perforated distributor and maximum for 45° slotted plate due to larger bubbles through 45° slots rupturing the bed surface, causing more bed expansion. Furthermore, CFD analysis is also carried out to observe the insight flow dynamics using the distributor plates. The simulations use a two-fluid model (TFM) and K-Epsilon turbulence models. CFD model shows promising results in agreement with the experimental results. CFD results revealed that the lower portion enhanced lateral dispersion/mixing of solid particles due to 45° angular openings of an air inlet. In contrast, the perforated plate exhibited a straight upward motion of small air bubbles, causing no radial/lateral mixing. CFD results for the hybrid plate show the mixed axial as well as lateral mixing of solids by revealing velocity distribution; therefore, the novel hybrid plate is found to be an optimum distributor plate due to its lowest pressure drop, adequate Umf, intermediary bed height rise ratio and moderate bubble rise velocity ratio across the bed.

Emissions Reduction by Combustion Modeling in the Riser of Fluidized Bed Combustor for Thar Coal Pakistan

Pakistan has experienced a protracted electricity shortage for the past few years. However, despite Pakistan’s abundant coal deposits, modern coal combustion technology is still required to reduce emissions. Pakistan is struggling to utilize its energy resources and currently experiencing an electrical shortage of more than 8000 MW. The research study models the combustion performance in a fluidized bed riser using ANSYS FLUENT software to understand the combustion behavior of low-rank Thar coal. A simple circulating fluidized bed (CFB) combustion riser was modeled for computational fluid dynamics (CFD) to study the hydrodynamics of gas-solid flow in a circulating fluidized bed riser to reduce emissions and operating costs. Three different types of risers/combustors geometries were used center flow, counter flow, and parallel flow. The CFD model for the solids segment with a k-e turbulence model and the viscosity of static particles in the gas segment both showed excellent mixing performance. According to the FLUENT data, the riser/combustor maximum temperature is around 1400 K or 1130 o C at the primary burning sector in the bed center. According to velocity contours, the greatest velocity in the center-oriented riser/combustor peaks at 3.3 m/s. The CO and CO2 both mass fraction counters show maximum concentration in the center geometry, whereas lower CO concentration is found in parallel geometry. The lowest level of NOx is established in the parallel geometry at around 15 ppm, whereas the counter contours establish the maximum level of NOx at about 31 ppm. Circulating Fluidized Bed Combustor is found to be the most advantageous and effective technology for producing power from Thar lignite coal and reducing emissions.

Heterogeneity analysis of gas–solid flow hydrodynamics in a pilot-scale fluidized bed reactor

Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid Eulerian–Eulerian two-fluid model (TFM) simulations of gas–solid flow hydrodynamics in fluidized bed reactors. Although numerous mesoscale drag models have been reported in the literature, a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking. In this study, in order to investigate the effect of several typical drag models on the hydrodynamic behaviors, the nonuniformity analysis and the sensitivity to material properties, extensive coarse-grid TFM simulations of a bubbling pilot-scale fluidized bed reactor are carried out. The results demonstrate that the mesoscale drag models outperform the empirical drag model in terms of nonuniformity due to the consideration of the influence of the mesoscale structures on the drag force in the bubbling region. Furthermore, the results reveal that our previously developed three-marker gradient-based drag model considering the solid concentration gradient exhibits satisfactory performance in predicting the bubbling flow hydrodynamics. Besides, the material-property-dependent drag model considering the explicit effect of material properties on drag corrections is most sensitive to the particle diameter. This work provides guideline for possible future improvements of mesoscale models to simulate gas–solid flow more accurately and universally.

MP-PIC investigation of glycerol steam reforming in bubbling fluidized bed for high-quality hydrogen production

A reactive multiphase particle-in-cell approach is adopted to numerically investigate the physical and thermochemical characteristics of glycerol steam reforming process in a three-dimensional bubbling fluidized bed. Via the model verification, the simulated results are in acceptable agreement with the experimental measurements. The gas-solid flow hydrodynamics and the particle thermochemical properties are explored. In addition, the effects of different operating parameters (reaction temperature, particle diameter, steam/glycerol ratio, operating pressure) on the performance of the glycerol steam reforming system are discussed. The results reveal the significantly non-uniform spatial distribution of particle temperature and heat transfer coefficient (HTC) due to the intense endothermic reactions and nonlinear hydrodynamics. Comparatively large HTC of solid particles appears in the lower part of the bed. Enlarging the reaction temperature and operating pressure give rise to a larger particle HTC. The back-mixing and internal circulation behavior of particles highly influence the spatial distribution of particle velocity inside the bed. The slip velocity of particle accumulated around the gas feeding port is obviously large. The slip velocity and HTC of particle are almost positively correlated. Decreasing the steam/glycerol ratio enhances the particle thermochemical properties. Moreover, elevating the reaction temperature significantly promotes the yields of H2 and CO while the formation of CH4 is suppressed.

CFD simulation of hydrodynamics and heat transfer characteristics in gas–solid circulating fluidized bed riser under fast pyrolysis flow condition

• Proper heat is needed for Circulating fluidized bed riser for fast pyrolysis. • A 3D EE-TFM model was developed and validated with experiment. • Hydrodynamics and heat transfer characteristics were examined for CFB riser. • Demonstrate the gas–solid heat transfer affected under different hydrodynamics. Pyrolysis process through circulating fluidized bed (CFB) is a promising technology to produce synthetic fuel and other products from biomass feedstocks. Computational fluid dynamics (CFD) computing means provide valuable insights to better understand gas–solid flow hydrodynamics, troubleshoot performance issues and optimize reactor operations. In this study, gas–solid flow hydrodynamics and heat transfer characteristics of a CFB riser for fast pyrolysis are investigated using a three-dimensional (3D) Eulerian-Eulerian CFD model. The main observations are discussed to provide insights on the factors affecting CFB riser performance. The model parameters, specularity and particle–particle restitution coefficients, were considered and tuned to accurately predict of gas–solid flow hydrodynamics and heat distribution with respect to different gas velocities and solid circulation rates. The results have shown that the CFD model predicted well the flow hydrodynamics and both specularity and particle–particle restitution coefficients are critical parameters as they affect particle behavior and temperature distribution fields. The lower specularity coefficient (Φ − 0.00001) was fairly able to predict the axial solid holdup profile into CFB riser. However, the lower value for particle–particle restitution coefficient ( e s s - 0.8) significantly overpredict the bottom dense region. The results shows that the increase of operating velocity promotes the mixing behaviors and heat transfer performance. In this work the suitable gas and solid circulation flow rates are U g = 4.5 m/s and G s = 81.23 kg/m 2 s.

CFD simulation for characterization and scale-up of pulsed biomass transport

Stable feeding of biomass powders into reactors represents a technical operational challenge for renewable energy generation. The injection of sawdust powders has been recently published with a horizontal pressurized gas injector under several experimental conditions. Valid numerical models based on computational fluid dynamics (CFD) are useful for hydrodynamics characterization of different equipment scales. In this study, the applicability of the CFD multiphase particle-in-cell approach (MP-PIC) for the considered injector is investigated. The model is tested under different operating conditions, showing relative deviations lower than 14% and 2% respectively for solids flux and flow concentration experimental data. The effect of model inputs (mesh refinement, drag model, particle-to-wall interaction) on the system’s hydrodynamics is discussed. The gas–solid flow hydrodynamics is obtained from the simulations providing additional insight on pulsed biomass transport. Ultimately, the model is used to investigate different injector diameters and to propose a feeder operation map as a function of dimensionless parameters.

CFD simulation of mesoscale structures in mono and bidispersed fluidized bed pyrolysis reactors

Pyrolysis of biomass and organic matter in fluidized bed reactors have become popular in recent years due to the efficient conversion of biomass to bio-fuels. Among others, the presence of mesoscale structures produced by the transient nature of gas solid flow governs the performance of fluidized bed reactors. In the present study, monodispersed system with the particle size of 155 µm and bidispersed system with particle sizes of 128 and 1500 µm are simulated by the multi-fluid model with the kinetic theory of granular flow closure laws. The objective is to investigate the effect of size distribution and solid volume fraction on the hydrodynamics of gas-solid flows. The ANSYS Fluent® software is used for the simulations and the slip velocity, heterogeneity index as well as mixing index are investigated. A two dimensional fully periodic domain is used to investigate the slip velocity at five different solid concentrations in dilute range. The slip velocity, which represents the interaction between solid particles and gas, calculated by simulation is higher than that calculated through Richardson-Zaki’s correlation. The mixing index is found to be minimum for a solid volume concentration of 5%. The heterogeneity index is significantly less than 1 for both cases with bidisperesed system having lower value as compared to monodispersed system. The image analysis of solid fraction contours exhibits that mesoscale structures are dense and non-uniform for solid fractions of 0.05 and are small and uniform of solid fractions of 0.025 and 0.075.

Hybrid CFD-neural networks technique to predict circulating fluidized bed reactor riser hydrodynamics

Circulating fluidized bed (CFB)-based co-pyrolysis is a promising technology for producing synthetic fuel and chemical co-products from biomass and waste feedstocks. Computational fluid dynamics (CFD) tools provide valuable insights for understanding gas-solid flow hydrodynamics, troubleshooting performance issues, and optimizing reactor operations. CFD simulations are computationally expensive and time-consuming; therefore, in this study, we developed an artificial neural network (ANN)-based machine learning model from a wide CFD simulation campaign. The CFB riser axial solid holdup profile was predicted using a two-fluid model and validated using the experimental data. Finally, a dataset connecting the input features of the model parameter-based simulations with their axial solid holdup was constructed for training the ANN. The performance of the developed model was later compared with the experimental data. The developed ANN model exhibited low mean square error values of order of 10−3 for both validation datasets to predict axial solid holdup. The ANN model performed well with an interpolated solid circulation rate of 45 kg/m2s and 62 kg/m2s and an extrapolated solid circulation rate of 30 kg/m2s and 80 kg/m2s.

Experiment and multiphase CFD simulation of gas-solid flow in a CFB reactor at various operating conditions: Assessing the performance of 2D and 3D simulations

Accurate prediction of gas-solid flow hydrodynamics is key for the design, optimization, and scale-up of a circulating fluidized bed (CFB) reactor. Computational fluid dynamics (CFD) simulation with two-dimensional (2D) domain has been routinely used, considering the computational costs involved in three-dimensional (3D) simulations. This work evaluated the prediction capability of 2D and 3D gas-solid flow simulation in the lab-scale CFB riser section. The difference between 2D and 3D CFD simulation predictions was assessed and discussed in detail, considering several flow variables (superficial gas velocity, solid circulation rate, and secondary air injection). The transient Eulerian-Eulerian multiphase model was used. CFD simulation results were validated through an in-house experiment. The comparison between the experimental data and both computational domains shows that the 3D simulation can accurately predict the axial solid holdup profile. The CFD simulation comparison considering several flow conditions clearly indicated the limitation of the 2D simulation to accurately predict key hydrodynamic features, such as high solid holdup near the riser exit and riser bottom dense region. The accuracy of 2D and 3D simulations was further assessed using root-mean-square error calculation. Results indicated that the 3D simulation predicts flow behavior with higher accuracy than the 2D simulation.

Numerical study on influence of exit geometry in gas–solid flow hydrodynamics of HDCFB riser by CPFD

The understanding of gas–solid flow is of great importance for various high-density circulating fluidized bed (HDCFB) practices. In this work, the effects of exit geometry on the gas–solid flow behavior in an HDCFB riser were numerically studied by using the computational particle fluid dynamics (CPFD) method. The simulated results were compared against experimental data on bed pressure and solid volume fraction distributions along the riser and a satisfactory agreement was found between them, which indicated the capability of the CPFD for the HDCFB riser simulation. Thereafter, simulations were conducted for the HDCFB risers with six different exit geometries and comparisons of hydrodynamics characteristics between each other were made. It was found that exit geometry significantly affected the axial solid volume fraction distribution through the whole riser. The abrupt exits gave rise to higher SRT than the smooth ones due to the solids back-mixing and packing effects. The angle between the exit duct and the horizontal plane also has a great influence on the gas–solid hydrodynamics and the abrupt exit with 15° was found to be appropriate for HDCFB riser due to its promotion on solid dispersion and reduction in solids back-mixing and packing.

An Assessment of Drag Models in Eulerian–Eulerian CFD Simulation of Gas–Solid Flow Hydrodynamics in Circulating Fluidized Bed Riser

Accurate prediction of the hydrodynamic profile is important for circulating fluidized bed (CFB) reactor design and scale-up. Multiphase computational fluid dynamics (CFD) simulation with interphase momentum exchange is key to accurately predict the gas-solid profile along the height of the riser. The present work deals with the assessment of six different drag model capability to accurately predict the riser section axial solid holdup distribution in bench scale circulating fluidized bed. The difference between six drag model predictions were validated against the experiment data. Two-dimensional geometry, transient solver and Eulerian–Eulerian multiphase models were used. Six drag model simulation predictions were discussed with respect to axial and radial profile. The comparison between CFD simulation and experimental data shows that the Syamlal-O’Brien, Gidaspow, Wen-Yu and Huilin-Gidaspow drag models were successfully able to predict the riser upper section solid holdup distribution with better accuracy, however unable to predict the solid holdup transition region. On the other hand, the Gibilaro model and Helland drag model were successfully able to predict the bottom dense region, but the upper section solid holdup distribution was overpredicted. The CFD simulation comparison of different drag model has clearly shown the limitation of the drag model to accurately predict overall axial heterogeneity with accuracy.

Study on scale-up characteristics of oxy-fuel combustion in circulating fluidized bed boiler by 3D CFD simulation

The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MWth to 330 MWe). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO2 in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.

Deviation of continuum formulation for solid-solid momentum transfer rate in terms of spatial averaging in mixtures with large particle size ratios

In a fluidized bed system, mean trajectories of fuel particles within the bed of fluidized inert particles are governed by the associated drag forces and characterize hydrodynamic, chemical and thermal processes taken place in the system. A large particle size ratio between the bed material and the fuel particles affects the hydrodynamics of gas-solid multiphase flows via influencing the drag forces between solid phases. The present work focuses on the analysis of forces between the two solid phases with large size ratios using the Lagrangian simulations of discrete element method (DEM). The results are spatially averaged over variable control volume size for comparison to the continuum interphase momentum transfer model. Using our DEM simulation results, a correction factor of drag force is presented versus the size of averaging control volume usable in continuum models. In addition, the role of inhomogeneity of particles distribution within the averaging box is discussed.

A critical comparison of two-fluid model, discrete particle method and direct numerical simulation for modeling dense gas-solid flow of rough spheres

Interphase drag coefficient is a critical input in two-fluid model (TFM) and discrete particle method (DPM). In this study, extensive TFM and DPM simulations were carried out to study of the hydrodynamics of gas-solid flows of monodisperse, rough particles in a dense fluidized bed using fourteen drag coefficient correlations available in literature, the simulation results were then compared to the direct numerical simulation (DNS) and experimental data of Tang et al. (2016). It was shown that (i) all TFM and DPM simulations result in a lower bed expansion rate than those of DNS and experiment, which indicates that the true interphase drag force is underestimated by all fourteen drag coefficient correlations; (ii) all DPM simulations can correctly capture, at least in a qualitative sense, the main hydrodynamic features obtained from DNS, but some TFM simulations with the exactly same drag coefficients show anomalous phenomena. This is not an indicator of the failure of the used drag coefficients but might be a sign of the deficiency of the used particle phase stress model in this specific situation; (iii) the time-averaged differential pressure drops of DPM and TFM simulations agree well with DNS results, but the characteristic frequency of pressure fluctuation found in DNS is overestimated by a factor of 2–3 by all DPM and TFM simulations; and (iv) the magnitude of local and global granular temperatures of TFM, DPM and DNS are all in a fair agreement, but the degree of the anisotropy of both local and global granular temperature found in DNS is systematically underestimated by DPM and TFM, especially, the local granular temperature in TFM simulations is inherently isotropic due to the fundamental assumption of the used kinetic theory. This study highlights the need of a better interphase drag coefficient and a better particle phase stress model for modeling dense gas-solid flow.

Comparison of Euler-Euler and Euler-Lagrange Approaches for Simulating Gas-Solid Flows in a Multiple-Spouted Bed

Abstract In this work, a comparative study of Euler-Euler and Euler-Lagrange approaches for modeling gas-solid flows in the multiple-spouted bed has been carried out to investigate the hydrodynamics of gas-solid flows. The influence of inlet gas velocity on the hydrodynamics of gas-solid flows in the multiple-spouted bed is investigated as well. Hydrodynamic characteristics of gas-solid flows such as flow behaviors, solid volume fraction, particle velocity and particle trajectory are analyzed and discussed in detail, providing some basic mechanism analysis of the gas-solids in the multiple-spouted bed. It is found that the central spout gas jet is a little confined by the auxiliary gas jets, and the hole-to-hole synergy is quite obvious when the auxiliary spout gas velocity is higher than the central spout gas velocity. When central/auxiliary gas velocity is 10/20 m/s, the maximum vertical particle velocities predicted by Euler-Euler and Euler-Lagrange approaches are 452 mm/s and 721 mm/s at the height of 10 mm respectively. A typical cycle period of a single particle is about 1.25 s, and the residence time in the spout regions is about 0.14 s in one cycle period in auxiliary dominant pattern. The curves of bed expansion height versus time calculated by Euler-Lagrange approach rise and fall periodically, while the curves calculated by Euler-Euler approach keep steady with little change. It is much easier for particles to be blew in the multiple-spouted bed using the Euler-Lagrange approach. The simulation results obtained from two models can provide some guidance for modifying the multiple-spouted bed to optimize physical operations such as drying and coating in the multiple-spouted bed.

Process simulation of a dual fluidized bed chemical looping air separation with Mn-based oxygen carrier

Chemical looping air separation (CLAS), a simple and efficient oxygen production technology, can be efficiently integrated with the moderate or intense low-oxygen dilution (MILD) combustion and oxy-fuel combustion technologies. Mn-based oxygen carrier is considered to be a hopeful candidate for the CLAS, but its redox kinetics has rarely been reported. In this work, the most suitable kinetic mechanisms for reduction and oxidation reactions are determined by thermogravimetric analyses. By coupling the obtained redox reaction kinetics and gas-solid flow hydrodynamics, a one-dimensional model of the interconnected fast fluidized bed and bubbling fluidized bed is built using sequential modular approach for simulating the chemical and physical phenomena in the CLAS process. The effects of main operation parameters on the CLAS performance are investigated by sensitivity analyses. The mole fraction of generated oxygen is found increasing with the increments of reduction temperature and air flow rate. Moreover, the system specific power consumption (SPC) is decreased when the temperatures of the two fluidized beds are similar. SPC can be as low as 0.076 kWh/m3 at the oxidation and reduction temperatures of 770 °C, the air flow rate of 50 Nm3/h, and the CO2 flow rate of 23 Nm3/h, which is 18% of the energy requirement of conventional cryogenic air separation system.

Comparisons of TFM and DEM-CFD simulation analyses on the influence mechanism of electrostatics on single bubble in gas-solid fluidized bed

Electrostatics occurs in the gas-solid fluidization processes, which influences the hydrodynamics of gas-solid flow. Numerical simulation has been applied to study the electrostatic phenomena in gas-solid flow in recent years, including Eulerian-Eulerian and Eulerian-Lagrangian approaches. However, few detailed research has investigated the influence mechanism of electrostatics on the hydrodynamics of gas-solid flow, while no study has focused on comparisons of Eulerian-Eulerian and Eulerian-Lagrangian approaches. In this work, both Two-Fluid Model (TFM) and Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) are implemented to analyze the reason of single bubble deformation in charged system. The analyses are carried out from the magnitude and direction of the electrostatic force acting on the particles. For a more comprehensive study of the influence mechanism, mono-charged system and bipolar-charged system are simulated respectively. This paper compares the Eulerian-Eulerian and Eulerian-Lagrangian approaches and elaborates on their calculation principles respectively. The advantages and disadvantages of these two approaches are also analyzed in this work. During the compilation of Two-Fluid Model, a scalar equation describing the electric potential gradient is derived by Maxwell's equations and the Bruggeman's equation. The direction of the electrostatic force is obtained by solving the electric potential gradient. And the magnitude of electrostatic force is described by Lorentz force equation. In the simulation applying DEM-CFD, the magnitude and direction of the electrostatic force acting on the single particles are obtained by solving Coulomb's law directly. Both approaches have their pros and cons. The basic mathematical representations of these two approaches are the same, while the simulation results differ significantly, which is due to the respective characteristics.

Hydrodynamics similarities in cold flow model of chemical looping combustors: An experimental study

The hydrodynamics of gas-solid flow in chemical looping combustors (CLC) is often studied in cold flow models (CFMs). The opportunity of working at the ambient conditions has been found to be beneficial for scaling purposes. In this study, a 200-kWth demonstration pilot plant CFM–CLC system (the first of its kind in Australia) that is a scaled-up unit of a lab scale 10-kWth unit is designed, fabricated and commissioned. The hydrodynamics similarities of the two units in terms of pressure drop profile and solids circulation rate are investigated. The results showed that the scaling factor for the operating velocity calculated based on the dimensionless relation of the fluidisation gas velocity ratio and the square root of the fluidised bed height ratio (of the air reactor) is 2.36, which was in good agreement with the measured value of 2.55. The same solids circulation rate (SCR) between the units was achieved using the scaling factor of 2.55 whilst maintaining the ratio of normalised total solids inventory of the system equal 1. It was also demonstrated that as the ratio of normalised total inventory increased from 1 to 1.4, the gas velocity to achieve similar SCR needs to be reduced proportionally (in the unit which inventory was increased). Therefore, a simple method of calculating the required gas velocity for achieving the same SCR for systems with non-equivalent normalised total solids inventory is proposed. The prediction results using this method were compared against the experimental data, with an average deviation of less than 10%. The validity of the proposed prediction method (for other cases of non-equivalent normalised total solids inventory) however requires further investigation.

On a carbon-negative energy production scheme via a quadruple fluidized bed gasifier

To restrain the CO2 concentration in atmosphere, deployment of the carbon-negative energy generation devices is indispensable on account of the vast net carbon discharge every year. In this work, a novel and promising quadruple fluidized bed (QFB) reactor for the biomass/coal co-gasification is proposed to generate the high-quality syngas whilst separate CO2 for further sequestration or utilization. To reveal the fundamental rules governing the reactor, a one dimensional model coupling the gas-solid flow hydrodynamics and the chemical reaction kinetics is built to simulate the physicochemical processes in the QFB, and the effects of several pivotal operation parameters on the reactor performance are comprehensively analyzed. It is found that the QFB runs stably under the given condition. The H2 mole fraction in the dry syngas is higher than 70%, the CO2 mole fraction in the dry flue gas is around 97%, and the net carbon discharge can be negative when the biomass blending ratio is over 0.5. The methodology and findings in this work are of reference value for the lab, pilot or industrial scale QFB designation and operation, and can be extended to develop similar novel reactors for the carbon-negative energy generation.