Shrinking Core Reaction Model Research Articles

Ammonia leaching mechanism and kinetics of LiCoO2 material from spent lithium-ion batteries

In this paper, the ammonia leaching process and high-energy ball milling method were adapted to recover spent LiCoO2 material. The ammonia reduction leaching mechanism of LiCoO2 material in the ammonia-sodium sulfite-ammonium chloride system was elucidated. Compared with untreated LiCoO2 material, the leaching equilibrium time of LiCoO2 after ball-milled for 5 h was reduced from 48 h to 4 h, and the leaching efficiency of lithium and cobalt was improved from 69.86% and 70.80% to 89.86% and 98.22%, respectively. Importantly, the apparent activation energy and leaching kinetic equation of the reaction was calculated by the shrinking core reaction model, indicating that the reaction was controlled by the chemical reaction.

Property of drying, pyrolysis, gasification, and combustion tested by a micro fluidized bed reaction analyzer for adapting to the biomass two-stage gasification process

In the present research, a concept of fluidized bed two-stage gasification has been proposed to gasify the wet industrial biomass, which decouples the direct gasification of biomass into the main sub-processes of drying, pyrolysis, gasification, and combustion. To better understand the reaction behavior and kinetics of these main sub-processes, a micro fluidized bed reaction analyzer was adopted. Moreover, a kind of water-adsorbing char was chosen to simulate the drying behavior of wet biomass. In the examined temperature range of 1123–1223 K, the processes of pyrolysis and combustion were conducted in the second scale, while that of gasification and drying was in the minute level, dominating the whole gasification process. For the reaction rate, at above 1173 K, they followed the order of pyrolysis > combustion > gasification > drying. The volume reaction model and shrinking core reaction model can be used to describe the process of pyrolysis/gasification and drying/combustion, respectively. For pyrolysis, combustion, drying, and gasification, the calculated activation energies were about 29.51, 62.39, 83.75, 210.23 kJ/mol, respectively. Finally, a schematic diagram of the FBTS gasification process was proposed for treating the wet Chinese distilled grains according to the reaction behavior and kinetics.

Development of an integrated heap leach solution flow and mineral leaching model

A 1-dimensional solution flow and mineral leaching model was developed to simulate data from leach columns and to demonstrate a dual porosity approach whereby an ore bed is divided into mobile (advective) flow and stagnant (diffusional control) regimes. Hydrodynamic properties were modelled with Richard's and van Genuchten's equations, and hydrodynamic column tests were performed to measure the parameters needed to solve these equations. The solute balance was performed using the standard advection-dispersion equation used in soil dispersion models. However, the term describing the desorption of solute (copper) from the solid into the liquid phase was replaced with a shrinking core reaction model rate term.The model shows that the proportion of the ore bed governed by diffusion increases as the diameter and height of the bed increase. The hydrodynamic properties therefore appear to have a significant effect on the copper extraction profiles and, if so, this could provide an explanation as to why large scale heaps leach slower than columns. The mass transfer coefficients for solute transfer between the mobile and stagnant regimes were of a similar order of magnitude as reported in tracer studies in literature.

CFD–PBE numerical simulation of CO2 capture using MgO-based sorbent

In this work a novel regenerative sorption enhanced water gas shift (SEWGS) process for high temperature and high pressure CO2 removal from Syngas in a circulating fluidized bed has been proposed. The process is based on an MgO-based solid sorbent. The major advantages of this sorbent include reducing the amount of WGS catalyst required to fully shift the Syngas to CO2 and H2 and eliminating Syngas cooling/reheating that is necessary for current CO2 separation systems. Another goal of this study was to improve the existing mono-disperse continuum models, i.e., Eulerian-Granular models that describe multiphase systems such as fluidized bed reactors, by considering the effect of poly-dispersity through a novel mathematical approach. As a result, a two-way coupled Computational Fluid Dynamics–Population Balance Model (CFD–PBM) along with an efficient numerical solution for the population balance equation has been proposed. The coupled CFD–PBM model along with the two-zone variable diffusivity shrinking core reaction model was utilized in baseline design of a bench scale high temperature, high pressure regenerative carbon capture process in the riser section of a circulation fluidized bed.

Characteristics of rice husk char gasification with steam

Abstract Biomass char gasification with steam refers to the reaction of the steam and biomass char under high temperature when the biomass char converts to combustible gas. Rice husk was selected as the raw material for char preparation. A gasification reactor was designed and built for the study of characteristics of rice husk char gasification with steam. Results show that the temperature is the primary factor that influences the steam gasification reaction of rice husk char. The conversion rate increases significantly from 27.7% to 90.73% with the temperature from 700 to 950 °C. H 2 accounts for 46.9% of the product gas at 950 °C. The conversion rate of rice husk char increases with temperature. The conversion rate of rice husk char increases as the steam flow rate. H 2 and CO gradually increase while CO 2 and CH 4 decrease as the steam flow rate. The conversion rate can be increased by decreasing particle size at low temperature, but the influence of the particle size becomes smaller above 900 °C. The reactivity of rice husk char prepared at low temperature is relatively high. Both surface reaction controlled shrinking core reaction model and homogeneous reaction model can describe the steam gasification reaction of rice husk char when the temperature is less than 850 °C. However, when the temperature is more than 850 °C, the diffusion through gas controls the overall reaction.

Study on Kinetics of Straw Stalk Gasification in CO<sub>2</sub> with Random Pore Model

The gasification of straw stalk in CO2 environment was studied by isothermal thermogravimetric analysis. The characteristics of rice straw and maize stalk gasification at different temperatures were examined under CO2 atmosphere. The relationship between reaction time and carbon conversion of two biomass chars was analyzed by the random pore model (RPM), and compared with the simulation of the shrinking core reaction model (SCRM). The results show that the random pore model is better to predict the experimental data at different temperatures. This means that the characteristics of pore structure for the influence of biomass chars gasification is well reflected by parameter ψ used in RPM. It indicates that the RPM can be applied to the comprehensive simulation of biomass chars gasification in CO2 environment.

Regenerable MgO-based sorbent for high temperature CO2 removal from syngas: 3. CO2 capture and sorbent enhanced water gas shift reaction

Regenerable MgO-based sorbent, which was prepared and evaluated in the thermogravimetric analyzer (TGA) in part 1, was also evaluated in high-pressure packed-bed unit in CO2/N2/H2O mixture and simulated pre-combustion syngas environment. In CO2/N2/H2O environment, the CO2 absorption capacity of the sorbent increases with increasing temperatures from 6.7% at 350°C to 9.5% 450°C. The sorbent is capable of achieving over 95% CO2 capture and 40% conversion in the water gas shift (WGS) reaction, which should be attributed to positive effect of WGS reaction in producing CO2 during the process. The sorbent reactivity and absorption capacity toward CO2, as well as its WGS catalytic activity decreases with increasing temperature. The maximum pre-breakthrough WGS conversion occurs at 350°C, which diminishes as the sorbent is carbonated. The variable diffusivity shrinking core reaction model coupled with the two-fluid computational fluid dynamics (CFD) model was shown to accurately predict the break-through gas compositions at different operating conditions.

Influence of pressure on the kinetics of synthetic llmenite reduction in hydrogen

In-situ thermogravimetric measurements were used in the hydrogen reduction of poly-granular synthetic ilmenite discs at temperatures in the range 823 to 1173 K and at pressures in the range 1.2 to 13 atm. A symmetrical beam microbalance was used, coupled with twin reactors and twin furnaces, to minimize buoyancy and drag effects. Stable operation was achieved at high gas flow rates where gas film transport effects were negligible. Polishing the ilmenite discs prior to reduction eliminated the formation of dense surface metallic iron films that can impede gas diffusion into the discs. Macroscopically, the reduction reaction proceeded topochemically and a shrinking core reaction model was found to be appropriate to predict conversion-time relationships. It was necessary to allow for water vapor adsorption onto the reacting interface in order to model the effect of pressure on the reduction kinetics. The observed reduction rate increased sharply with pressure up to approximately 3 atm and then approached a plateau with further pressure increase. The porosity in the reduced ilmenite samples was very fine, with pore diameters of typically 0.05 to 0.3 µm. Intragrain gas pressure buildup in the fine pores due to the influence of Knudsen diffusion was incorporated into the modeling of the kinetic data.

Modeling on Combustion Characteristics of Biocoalbriquettes

A biocoalbriquette, a new artificial solid fuel, is manufactured by a mixture of coal and biomass under a high-compression pressure. The combustion characteristics of biocoalbriquettes were investigated in this study experimentally and numerically. The combustion process of biocoalbriquettes appears in two stages: the volatile combustion stage followed by the char combustion stage. It was found that the volatile combustion happens over the whole pellet of biocoalbriquette, whereas the char combustion proceeds in a shrinking-core mode. A volume model and a shrinking-core reaction model were introduced and modified here to simulate the two stages of combustion process. The simulation results are found to be consistent with the experimental results.

Experimental Study on Self-Desulfurization Characteristics of Biobriquette in Combustion

A new kind of biobriquette, with scallop shell as desulfurizer, was developed in this study, and its self-desulfurization behavior was studied by combustion experiments. For comparison and further understanding on the self-desulfurization characteristics, the biobriquettes with Tsukumi limestone and calcium hydroxide as desulfurizers were also investigated experimentally. The influence of the furnace temperature, types of coal and desulfurizer, and structure of added desulfurizer on the behavior of desulfurization was elucidated by measuring the time concentration history of SO2 emission in combustion flue gas and calculating the desulfurization efficiency. The desulfurization efficiency was not sensitive to the temperature in the range 973−1173 K. However, the efficiency was strongly affected by coal type, and it changed from about 25 to 67% for the eight tested types of coals under the same experiment conditions. The desulfurization efficiency has been found to also be a function of the calcination temperature of desulfurizer. On the basis of experimental results, a shrinking-core reaction model was used to simulate the desulfurization process during the char combustion of biobriquette by a finite volume numerical method. The calculated results generally agreed with the experimental results. Finally, an improvement on the biobriquette structure, namely dual layered biobriquette, was proposed and tested in order to improve the desulfurization efficiency.

Chlorination kinetics of zirconia in an RF chlorine plasma tail flame

AbstractThe chlorination kinetics of zirconia were studied in a single stationary particle reactor system. A plasma of pure chlorine generated by an induction torch provided both the high enthalpy field and the reacting gas. The influence on the rate of conversion of such parameters as temperature, chlorine concentration (in the presence of argon) and particle diameter and porosity were investigated. Based on experimental and theoretical studies, rate equations were developed under different rate controlling mechanisms.The chlorination of zirconia in the particle temperature range of 1 540° to 2 480°K obeyed a shrinking core reaction model. The reaction was chemically controlled below 1 950°K, and above this temperature both chemical and mass transfer resistances were important. The experimental results confirmed the theoretical analysis.