Carbon dioxide desorption behavior of potassium carbonate supported on gamma-alumina solid sorbent in wet fluidized bed under steam atmosphere

Since the carbon dioxide (CO₂) capture using solid sorbent is a reversible reaction, the solid sorbent can be regenerated by the desorption process. Therefore, the desorption process is one of the key important processes for the CO₂ capture system. Traditionally, most of the literature studies focus on the desorption of solid sorbent under an N₂ atmosphere. However, the desorption process of the solid sorbent is inappropriate in the real system because the system will need another process to separate CO₂ and nitrogen (N₂) after the desorption process. This study focused on the CO₂ desorption of potassium carbonate supported on gamma-alumina (K₂CO₃/γ-Al₂O₃) in a wet fluidized bed under a steam atmosphere by using the multiphase computational fluid dynamics (CFD) simulation. The effects of water thickness and dry restitution coefficient on CO₂ desorption rate were investigated to provide a realistic particle collision behavior and to explore their effects on CO₂ desorption phenomena. Moreover, the effect of steam velocity on the hydrodynamic behaviors of fluidization which on CO₂ desorption rate was studied. The simulated results demonstrated that all the parameters, water thickness, dry restitution coefficient, and steam velocity had significantly affected system hydrodynamics and CO₂ desorption rate in the wet fluidization desorption process. Furthermore, the effect of desorption temperature on CO₂ desorption rate was evaluated for finding the appropriate temperature for CO₂ desorption process of K₂CO₃/γ-Al₂O₃. The results showed that the appropriate desorption temperature for CO₂ desorption under steam atmosphere was the temperature over 150 °C.     

Effect of acoustic field on heat transfer in a sound assisted fluidized bed of fine powders

The fluidized beds are widely used in a variety of industries where heat transfer properties of the fluidized system become important for successful operation. Fluidized are preferred in heat recovery processes because of their unique ability of rapid heat transfer and uniform temperature. Fine powders handling and processing technologies have received widespread attention due to increased use of fine powders in the manufacture of drugs, cosmetics, plastics, catalysts, energetics and other advanced materials. A better understanding of fluidization behavior of fine powders is of great importance in applications involving heat transfer, mass transfer, mixing, transporting and modifying surface properties etc. The difficulty in putting the fine powders in suspension with the fluidizing gas is related to the cohesive structure and to the physical forces between the primary particles. The sound waves agitate bubbling and this results in improving solids mixing in the fluidized bed. The improved solids mixing results in uniform and smooth fluidization, which leads to better heat transfer rates in the fluidized bed.     

Role of Second Phase Powders on Microstructural Evolution During Sintering

The influence of second phase fine powders on solid state sintering was investigated in situ by synchrotron radiation X-ray computed tomography (SR-CT). The evolutions of microstructure during sintering of pure SiO₂ powders and SiO₂ powders mixed with Si₃N₄ powders were observed from reconstructed SR-CT images. Typical sintering parameters, which determine mechanical properties, were extracted from the experimental data, and the effects of the second phase powders were quantitatively analyzed. The experimental results showed that with second phase powders, 1) the specific surface area decreases more efficiently; 2) pore shape evolution is accelerated; 3) sintering necks grow faster and 4) densification process is notably accelerated. It was indicated that the Si₃N₄ fine powders enhanced the sintering of the original SiO₂ powders rather than hindering the process. A qualitative explanation based on the experimental results and existing powder sintering theory is provided.     

等离子体辅助球磨制备表面修饰纳米TiO2的摩擦学性能分析

以季铵盐和月桂酸钠为过程处理剂,利用等离子体辅助球磨制备表面修饰纳米TiO_2粉体,并测试其摩擦学性能.结果表明:在等离子体的热爆效应及脉冲电子轰击效应的协同作用下,辅助球磨11 h制备的表面修饰纳米TiO_2粉体粒径在20 nm左右,晶型发生由锐钛矿型向金红石型的转变.等离子体辅助球磨使得纳米TiO_2获得了良好的亲油疏水表面特性,在40CA船用润滑油中表现出稳定的分散性.由于纳米TiO_2粉体的"微轴承"作用,复合润滑油的摩擦系数降低,摩擦副的磨损失重量减少.纳米TiO_2粉体在摩擦过程中容易吸附沉积在摩擦副表面并修补磨痕,使得复合润滑油具备良好的减摩及自修复性能.     

Effect of high stirring speed on the agglomerate behaviors for cohesive SiO2 powders in gas fluidization

The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO₂ powders (mean diameter is 16 μm) were experimentally investigated in a stirring-assisted fluidized bed. The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO₂ powders, the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization. The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200 μm. Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity. The stirring applied enlarges the operational range of agglomerate particulate fluidization (APF) with a delayed onset of bubbling for cohesive particles. However, the exorbitant speed increases the collision velocity and contact area between small agglomerates, which results in the formation of unstable agglomerates and the whirlpool of powder.     

Use of silica nanopowder to accelerate CO2 sorption by Ca(OH)2

Promising technologies have recently emerged to capture CO₂ from postcombustion flue gas and to enhance the production of hydrogen from natural gas by steam-methane reforming, on the basis of sorption of CO₂ by Ca-based powders. The rate of CO₂ sorption on Ca-based powders is limited by both carbonation kinetics and transport of CO₂ to unreacted sorption sites. Ca-based powders may exhibit cohesive aggregation, thus hindering gas–solids contact efficiency. In our work, we tested the sorption rate of powder samples prepared by dry mixing of a cohesive Ca(OH)₂ powder with a silica nanopowder used as additive. The silica nanopowder serves to improve the dispersibility of Ca(OH)₂. Consequently, when a CO₂ enriched gas and the modified sorbent are brought into contact, the rate of CO₂ sorption is enhanced in the initial fast phase of interest for practical applications.     

Experimental Study of Pore-Scale Mechanisms of Carbonated Water Injection

Carbon dioxide (CO₂) injection is a well-established method for increasing recovery from oil reservoirs. However, poor sweep efficiency has been reported in many CO₂ injection projects due to the high mobility contrast between CO₂ and oil and water. Various injection strategies including gravity stable, WAG and SWAG have been suggested and, to some extent, applied in the field to alleviate this problem. An alternative injection strategy is carbonated water injection (CWI). In CWI, CO₂ is delivered to a much larger part of the reservoir compared to direct CO₂ injection due to a much improved sweep efficiency. In CWI, CO₂ is used efficiently and much less CO₂ is required compared to conventional CO₂ flooding, and hence the process is particularly attractive for reservoirs with limited access to large quantities of CO₂ (offshore reservoirs or reservoirs far away from inexpensive natural CO₂ resources). This article describes the results of a pore-scale study of the process of CWI by performing high-pressure visualisation flow experiments. The experimental results show that CWI, compared to unadulterated (conventional) water injection, improves oil recovery as both a secondary (before water flooding) and a tertiary (after water flooding) recovery method. The mechanisms of oil recovery by CWI include oil swelling, coalescence of the isolated oil ganglia and flow diversion due to flow restriction in some of the pores as a result of oil swelling and the resultant fluid redistribution. In this article the potential benefit of a subsequent depressurisation period on oil recovery after the CWI period is also investigated.     

Experimental study of the effect of friction phenomena on actual and calculated inventory in a small-scale CFB riser

Accurate information concerning riser inventory in a fluidized bed is required in some applications such as the calcium looping process, because it is related to the CO₂ capture efficiency of the system. In a circulating fluidized bed (CFB), the riser inventory is normally calculated from the riser pressure drop; however, the friction and the acceleration phenomena may have a significant influence on the total riser pressure drop. Therefore, deviation may occur in the calculation from the actual mass. For this reason the magnitude of the friction and the acceleration pressure drop in the entire riser is studied in small-scale risers. Two series of studies were performed: the first one in a scaled cold model riser of the 10 kW_th facility, and the second one in the 10 kW_th fluidized bed riser under process conditions. The velocities were chosen to comply with the fluidization regimes suitable for the calcium looping process, namely, the turbulent and the fast. In cold-model experiments in a low-velocity turbulent fluidization regime, the actual weight (static pressure drop) of the particles is observed more than the weight calculated from a recorded pressure drop. This phenomenon is also repeated in pilot plant conditions. In the cold-model setup, the friction and acceleration pressure drop became apparent in the fast fluidization regime, and increased as the gas velocity rose. Within calcium looping conditions in the pilot plant operation, the static pressure drop was observed more than the recorded pressure drop. Therefore, as a conservative approach, the influence of friction pressure drop may be neglected while calculating the solid inventory of the riser. The concept of transit inventory is introduced as a fraction of total inventory, which lies in freefall zones of the CFB system. This fraction increases as gas velocity rises.     

Experimental investigation on micro-dynamic behavior of gas explosion suppression with SiO2 fine powders

To study the effect of inert dust on gas explosion suppression mechanism, SiO₂ fine powders were sprayed to suppress premixed CH₄-Air gas explosion in a 20 L spherical experimental system. In the experiment, high speed schlieren image system was adopted to record explosion flame propagation behaviors, meanwhile, pressure transducers and ion current probes were used to clearly record the explosion flame dynamic characteristics. The experimental results show that the SiO₂ fine powders suppressed evidently the gas explosion flame, and reduced the peak value of pressure and flame speed by more than 40 %. The ion current result shows that the SiO₂ super fine powders were easy to contact with and absorb free radicals near the combustion reaction region, which greatly reduced the combustion reaction intensity, and in turn influenced the flame propagation and pressure rising.     

Laboratory Experiments on Environmental Friendly Means to Improve Coalbed Methane Production by Carbon Dioxide/Flue Gas Injection

Scaled in situ laboratory core flooding experiments with CO₂, N₂ and flue gas were carried out on coal in an experimental high P,T device. These experiments will be able to give an insight into the design of the injection system, management, control of the operations and the efficiency of an ECBM project. Although the experience gained by the oil industry represents a valuable starting point, several problems are still to be studied and solved before CO₂ improved deep coalbed methane production may be operationally feasible. These are all related to the heterogeneous nature of the pore structure of coal, and in particular to the presence of fractures. More specifically, a number of questions need to be addressed, e.g. what are the conditions under which the fluid in the micro pores of the coal is displaced by the CO₂ in the presence of competitive adsorption; what is the role of compositional heterogeneity and fracture anisotropy of coal for the injection design and the efficiency of the sequestration in relation to the swelling and shrinkage characteristics of coal; how does the mobile and the immobile water in the coal affect the exchange process. These questions can be answered by means of downscaled laboratory experiments that are capable of accurately describing the coupled process of multiphase flow, competitive adsorption and geo-mechanics. The laboratory conditions have been simulated to match pressure and temperature at depths of 800 to 1,000 m. Under those conditions the injected CO₂ remains supercritical. Upto now, the results show that dewatering will be an essential step for successful ECBM combined with a CO₂ sequestration process.     

Coreflooding Studies to Investigate the Potential of Carbonated Water Injection as an Injection Strategy for Improved Oil Recovery and CO<Subscript>2</Subscript> Storage

Carbonated water injection (CWI) is a CO₂-augmented water injection strategy that leads to increased oil recovery with added advantage of safe storage of CO₂ in oil reservoirs. In CWI, CO₂ is used efficiently (compared to conventional CO₂ injection) and hence it is particularly attractive for reservoirs with limited access to large quantities of CO₂, e.g. offshore reservoirs or reservoirs far from large sources of CO₂. We present the results of a series of CWI coreflood experiments using water-wet and mixed-wet Clashach sandstone cores and a reservoir core with light oil (n-decane), refined viscous oil and a stock-tank crude oil. The experiments were carried out to assess the performance of CWI and to quantify the level of additional oil recovery and CO₂ storage under various experimental conditions. We show that the ultimate oil recovery by CWI is higher than the conventional water flooding in both secondary and tertiary recovery methods. Oil swelling as a result of CO₂ diffusion into the oil and the subsequent oil viscosity reduction and coalescence of the isolated oil ganglia are amongst the main mechanisms of oil recovery by CWI that were observed through the visualisation experiments in high-pressure glass micromodels. There was also evidence of a change in the rock wettability that could also influence the oil recovery. The coreflood test results also reveal that the CWI performance is influenced by oil viscosity, core wettability and the brine salinity. Higher oil recovery was obtained with the mixed-wet core than the water-wet core, with light oil than with the viscous oil and low salinity carbonated brine than high-salinity carbonated brine. At the end of the flooding period, an encouraging amount of the injected CO₂ was stored in the brine and the remaining oil in the form of stable dissolved CO₂. The experimental results clearly demonstrate the potential of CWI for improving oil recovery as compared with the conventional water flooding (secondary recovery) or as a water-based EOR (enhanced oil recovery) method for watered out reservoirs.     

Liquid phase heterogeneous photocatalytic ozonation of phenol in liquid–solid fluidized bed: Simplified kinetic modeling

The isotherms of original AC (activated carbon) and photocatalysts (TiO₂-AC) calcined at 500 °C for phenol were measured. The results showed a reversible adsorption of phenol onto both kinds of particles at 25 °C, and could be fitted well to the Freundlich adsorption equation for the dilute solution. Five oxidation processes, namely O₃, O₃/UV, O₃/UV/AC, O₂/UV/TiO₂ and O₃/UV/TiO₂, for phenol degradation in fluidized bed were evaluated and compared, and the photocatalytic ozonation was found to give the highest phenol conversion because of the combined actions of homogenous ozonation in the liquid phase, heterogeneous ozonation on the surface of the catalyst support, i.e. activated carbon, and heterogeneous photocatalytic oxidation on the TiO₂ catalyst surface. With the simplified kinetic model, photolytic ozonation was confirmed to predominantly take place on the particle surface in comparison with the heterogeneous and homogeneous photolytic ozonation. Additionally, the heterogeneous photocatalytic oxidation constant was found to be enhanced by 3.73 times in photocatlaytic ozonation process with ozone as the scavenger compared to the photocatalytic oxidation process with oxygen as the scavenger.     

Preparation of spherical Y2SiO5 powders for thermal-spray coating

Yttrium silicate, for its high oxidation resistance, is an important candidate for protective coating for carbon-fiber-reinforced composites at temperatures above 1600 ℃. A novel method, consisting of coprecipitation, spray-drying, heat-treatment and plasma-densification, is developed to prepare Y2SiO5 powders for thermal-spraying. The composition, morphology and flowability of the synthesized Y2SiO5 powders are investigated by XRD, SEM and Hall Flowmeter, respectively. The results show that the synthesized Y2SiO5 powders are nearly spherical with high purity. The apparent density and flowability of the Y2SiO5 powders are 1.87 g/cm^3 and 37 s/50 g, respectively, which lead to a high deposition efficiency of up to 80700 for atmospheric plasma spraying.     

Radiocarbon dating in trondheim

Summary Naturally occurring radiocarbon is registered in a proportional counter filled with pure CO₂. THe CO₂ gas is purified in almost the same manner as has been developed by De Vries and Barendsen. Checking of the gas purity is described. A grid proportional counter with an effective volume of about 2.5 liter has been used with CO₂-pressures from 1 to 4 atmospheres. At a pressure of 4 atmospheres the net count from contemporary wood is 58 counts/min above a background of 15 eounts/min. Dating may at the present stage be extended to 35 000 years by 24 hours counting with 4 atmospheres CO₂. A method for checking the discriminating level of the counting apparatus is described.     

CO2 Injection into Saline Carbonate Aquifer Formations II: Comparison of Numerical Simulations to Experiments

Sequestration of carbon dioxide in geological formations is an alternative way of managing extra carbon. Although there are a number of mathematical modeling studies related to this subject, experimental studies are limited and most studies focus on injection into sandstone reservoirs as opposed to carbonate ones. This study describes a fully coupled geochemical compositional equation-of-state compositional simulator (STARS) for the simulation of CO₂ storage in saline aquifers. STARS models physical phenomena including (1) thermodynamics of sub- and supercritical CO₂, and PVT properties of mixtures of CO₂ with other fluids, including (saline) water; (2) fluid mechanics of single and multiphase flow when CO₂ is injected into aquifers; (3) coupled hydrochemical effects due to interactions between CO₂, reservoir fluids, and primary mineral assemblages; and (4) coupled hydromechanical effects, such as porosity and permeability change due to the aforementioned blocking of pores by carbonate particles and increased fluid pressures from CO₂ injection. Matching computerized tomography monitored laboratory experiments showed the uses of the simulation model. In the simulations dissolution and deposition of calcite as well as adsorption of CO₂ that showed the migration of CO₂ and the dissociation of CO₂ into HCO₃ and its subsequent conversion into carbonate minerals were considered. It was observed that solubility and hydrodynamic storage of CO₂ is larger compared to mineral trapping.     

Laboratory Flow Experiments for Visualizing Carbon Dioxide-Induced,Density-Driven Brine Convection

Injection of carbon dioxide (CO₂) into saline aquifers confined by low- permeability cap rock will result in a layer of CO₂ overlying the brine. Dissolution of CO₂ into the brine increases the brine density, resulting in an unstable situation in which more-dense brine overlies less-dense brine. This gravitational instability could give rise to density-driven convection of the fluid, which is a favorable process of practical interest for CO₂ storage security because it accelerates the transfer of buoyant CO₂ into the aqueous phase, where it is no longer subject to an upward buoyant drive. Laboratory flow visualization tests in transparent Hele-Shaw cells have been performed to elucidate the processes and rates of this CO₂ solute-driven convection (CSC). Upon introduction of CO₂ into the system, a layer of CO₂-laden brine forms at the CO₂-water interface. Subsequently, small convective fingers form, which coalesce, broaden, and penetrate into the test cell. Images and time-series data of finger lengths and wavelengths are presented. Observed CO₂ uptake of the convection system indicates that the CO₂ dissolution rate is approximately constant for each test and is far greater than expected for a diffusion-only scenario. Numerical simulations of our system show good agreement with the experiments for onset time of convection and advancement of convective fingers. There are differences as well, the most prominent being the absence of cell-scale convection in the numerical simulations. This cell-scale convection observed in the experiments may be an artifact of a small temperature gradient induced by the cell illumination.     

Adsorption and strain: The CO2-induced swelling of coal

Enhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO₂-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains.     

Gas Sorption and the Consequent Volumetric and Permeability Change of Coal II: Numerical Modeling

The permeability of coalbed methane reservoirs may evolve during the recovery of methane and injection of gas, due to the change of effective stress and gas adsorption and desorption. Experimental and numerical studies were conducted to investigate the sorption-induced permeability change of coal. This paper presents the numerical modeling part of the work. It was found that adsorption of pure gases on coal was well represented by parametric adsorption isotherm models in the literature. Based on the experimental data of this study, adsorption of pure \(\hbox {N}_2\) was modeled using the Langmuir equation, and adsorption of pure \(\hbox {CO}_2\) was well represented by the N-Layer BET equation. For the modeling of CO \(_2\) & N \(_2\) binary mixture adsorption, the ideal adsorbed solution (IAS) model and the real adsorbed solution (RAS) model were used. The IAS model estimated the total amount of mixture adsorption and the composition of the adsorbed phase based on the pure adsorption isotherms. The estimated total adsorption and adsorbed-phase composition were very different from the experimental results, indicating nonideality of the CO \(_2\) –N \(_2\) –Coal-adsorption system. The measured sorption-induced strain was linearly proportional to the total amount of adsorption despite the species of the adsorbed gas. Permeability reduction followed a linear correlation with the volumetric strain with the adsorption of pure \(\hbox {N}_2\) and the tested CO \(_2\) & N \(_2\) binary mixtures, and an exponential correlation with the adsorption of pure \(\hbox {CO}_2\) .     

Two-fluid modeling of Geldart A particles in gas-fluidized beds

We have investigated the effect of cohesion and drag models on the bed hydrodynamics of Geldart A particles based on the two-fluid （TF） model. For a high gas velocity U0 = 0.03 m/s, we found a transition from the homogeneous fluidization to bubbling fluidization with an increase of the coefficient C1, which is used to account for the contribution of cohesion to the excess compressibility. Thus cohesion can play a role in the bed expansion of Geldart A particles. Apart from cohesion, we have also investigated the influence of the drag models. When using the Wen and Yu drag correlation with an exponent n = 4.65, we find an under-prediction of the bed expansion at low gas velocities （U0 = 0.009 m/s）. When using a larger exponent （n = 9.6）, as reported in experimental studies of gas-fluidization, a much better agreement with the experimental bed expansion is obtained. These findings suggest that at low gas velocity, a scale-down of the commonly used drag model is required. On the other hand, a scale-up of the commonly used drag model is necessary at high gas velocity （U0 = 0.2 and 0.06 m/s）. We therefore conclude that scaling the drag force represent only an ad hoc way of repairing the deficiencies of the TF model, and that a far more detailed study is required into the origin of the failure of the TF model for simulating fluidized beds of fine powders.     

Manipulation of polymer foam structure based on CO2-induced changes in polymer fundamental properties

Foaming of polymers with CO2 has attracted increasing attention in polymer processing studies. Some of the fundamental properties of polymer/CO2 systems is discussed in this short review, including solubility and diffusivity of CO2 in the polymer, polymer crystallization, interfacial tension between the polymer and the gas, and rheology of the CO2/polymers melt. These properties understandably affect the foaming process, and the structures of the foam products. Meanwhile, these properties can be changed via manipulation of CO2 in polymer. The proposed idea is to manipulate the foaming process and the foam structure by CO2-induced changes in these properties. Two cases from the authors＇ laboratory are presented for elucidating how to use the changes to manipulate the foaming process.