Hydrodynamics of a novel multi-stage external loop airlift reactor

In the present investigation a novel multi-stage external loop airlift reactor with hydro-dynamically induced continuous bubble generation, breakup and regeneration has been proposed. The system has been designed to operate with relatively large sized bubbles, so that interfacial circulation can be induced in the liquid-bubble interfaces and faster transfer of components can take place by turbulent diffusion through the interface of the bubbles and also due to the physical rupture and reformation of the bubbles. The system was also designed to operate in three stages operating in series so that in each stage completely deaerated liquid could be brought in contact with freshly generated bubbles. Detailed studies on the gas holdup and liquid circulation velocity have been carried out with respect to various values of superficial gas as well as liquid velocities. The gas holdup of the proposed multi-stage system is 45% higher than the single stage system, which results in better mass transfer characteristics. Empirical correlations describing the performance of the proposed reactor have been presented in this paper.     

气升式环流反应器的特性及应用

综述了气升式环流反应器的特性及其主要影响因素研究,简要介绍了这种反应器的应用情况,并提出了今后研究工作的方向。     

气升式反应器的优化

从强化传质与节能方面概述了近年来国内外在气升式反应器结构参数优化、操作参数的优化及溶液性质等方面的研究工作 ,提出了今后的研究方向     

石油焦脱硫技术研究进展

综述了高硫焦的现状,分析了高硫焦对铝用预焙阳极的危害,总结归纳了目前国内外的各项脱硫技术.     

Solid effects on hydrodynamics and heat transfer in an external loop airlift reactor

The effect of a solid presence on global hydrodynamic parameters and heat transfer in an external loop airlift reactor has been experimentally investigated. Results obtained in both two- and three-phase flow are presented in this study. Two different external loop airlift reactor sizes have been used and local hydrodynamic characteristics including local gas hold-up and bubble velocity have been obtained in two-phase flow. Optical and ultrasound probes have been used to obtain this information, respectively. It was found that an increase of solid hold-up leads to a decrease of liquid velocity and heat transfer coefficient. Measured in a two- and three-phase reactor using a horizontal-heating probe, a correlation of the average gas hold-up and heat transfer coefficient is proposed. Correlation parameters are identified in homogeneous and heterogeneous flow regimes, which have been derived from the gas slip velocity concept. The experimental liquid velocity and gas hold-up in the riser have been represented in a satisfactory way by a hydrodynamic model, either in the absence or in the presence of solid particles.     

Preparation of natural gas adsorbents from high-sulfur petroleum coke

HSPC (high-sulfur petroleum coke) has been used as precursor in the preparation of natural gas adsorbents with chemical activation. The effects of activating parameters, such as activating temperature and duration, on the pore-structure of adsorbents and methane uptake were investigated systematically in this study. The results show that the adsorbents derived from HSPC have comparable pore-structural characteristics and methane uptake to that derived from LSPC (low-sulfur petroleum coke). As evidenced by methane adsorption measurements, the highest deliverable capacity of methane, 129.7 v/v at 3.5 MPa and 25 °C, is obtained on HSR4 prepared at activating agent/coke mass ratio of 4:1. Furthermore, sulfur distribution analyses show that the sulfur in HSPC was almost removed by chemical activation and that sulfur content of as-synthesized adsorbent was as low as 0.18 wt% for HSR4. This study shows that HSPC could be used potentially as a good precursor to prepare high quality adsorbents with lower cost.     

旋流气升式环流反应器的局部气、固含率研究

新开发的有机玻璃制成的旋流气升式环流反应器高为2m、内径75mm,内部的导流筒(材料为PVC)高1.5m、内径30mm、壁厚1mm且装有10组扇形翅片。以空气-水为两相物系、空气-水-K树脂为三相物系,常温常压下,利用直接取样法和压差法测量了上升区局部的气含率、固含率,研究了不同底部间隙、不同固体装填体积分数下表观气速和轴向高度对上升区气含率、固含率的影响规律。结果表明:在均匀鼓泡流时上升区气含率随着表观气速的增大而增大,随着固体装载量的增加而下降;在非均匀鼓泡流时,三相物系的气含率高于两相物系的气含率。随着上升区轴向高度的增大,上升区局部气含率变化不大;底部间隙越大,气含率越小。在轴向高度较低时上升区固含率随着轴向高度的增大而减小,轴向高度较高时上升区固含率基本保持不变。     

石油焦质量下滑对预焙阳极的危害及控制

深入分析当前石油焦质量下滑的三大因素:杂质含量高、粉焦和丸状焦比例增加等,以及对炭阳极质量造成的危害,并有针对性的提出一些预防措施,旨在引起石化和炭素行业提高对石油焦质量的重视程度。     

Global modelling of a gas-liquid-solid airlift reactor

This paper presents a global model of three phase flow (gas-liquid-solid) in an internal airlift reactor. The airlift is composed of four zones: a riser (on the aerated side on the internal wall), a downcomer (on the opposite side) and two turning zones above and below the internal wall. Tap water is the liquid continuous phase and the dispersed phases are air bubbles and polyethylene particles. The global modelling of the airlift involves mass and momentum equations for the three phases. The model enables phase velocities and phase volume fractions to be estimated, which can be compared to experimental data. Closure relations for the gas and solid drift velocities are based on the model proposed by Zuber and Findlay. The drift flux coefficients are derived from CFD numerical simulations of the airlift. Gas bubble and solid particle averaged slip velocities are deduced from momentum balances, including drag coefficient correlations. The link between Zuber and Findlay model and the two-fluid model is established. In the experiment as well as in the model, the gas flow rate is fixed. However, the liquid and solid flow rates are unknown. Two closure relations are needed to predict these flow rates: the first closure relation expresses that the volume of solid injected into the airlift remains constant; the second closure relation expresses a global balance between the difference of column height in the riser and the downcomer and the total pressure drop in the airlift. The main parameters of a three phase airlift reactor, like gas and solid volume fractions, are well predicted by the global model. With increasing solid filling rate (40%), the model starts to depart from the experimental values as soon as coalescence of bubbles appears.     

CFD simulation and experimental measurement of gas holdup and liquid interstitial velocity in internal loop airlift reactor

This paper documents experiments and CFD simulations of the hydrodynamics of our two-phase (water, air) laboratory internal loop airlift reactor (40 l). The experiments and simulations were aimed at obtaining global flow characteristics (gas holdup and liquid interstitial velocity in the riser and in the downcomer) in our particular airlift configurations. The experiments and simulations were done for three different riser tubes with variable length and diameter. Gas (air) superficial velocities in riser were in range from 1 to 7.5 cm/s. Up to three circulation regimes were experimentally observed (no bubbles in downcomer, bubbles in downcomer but not circulating, and finally the circulating regime). The primary goal was to test our CFD simulation setup using only standard closures for interphase forces and turbulence, and assuming constant bubble size is able to capture global characteristics of the flow for our experimental airlift configurations for the three circulation regimes, and if the simulation setup could be later used for obtaining the global characteristic for modified geometries of our original airlift design or for different fluids. The CFD simulations were done in commercial code Fluent 6.3 using algebraic slip mixture multiphase model. The secondary goal was to test the sensitivity of the simulation results to different closures for the drag coefficient and the resulting bubble slip velocity and also for the turbulence. In addition to the simulations done in Fluent, simulation results using different code (CFX 12.1) and different model (full Euler–Euler) are also presented in this paper. The experimental measurements of liquid interstitial velocity in the riser and in the downcomer were done by evaluating the response to the injection of a sulphuric acid solution measured with pH probes. The gas holdup in the riser and downcomer was measured with the U-tube manometer. The results showed that the simulation setup works quite well when there are no bubbles present in the downcomer, and that the sensitivity to the drag closure is rather low in this case. The agreement was getting worse with the increase of gas holdup in the downcomer. The use of different multiphase model in the different code (CFX) gave almost the same results as the Fluent simulations.     

石油焦配煤炼焦试验研究

通过对石油焦的特性研究及配煤炼焦试验,考察其对配煤黏结性能及焦炭质量的影响,研究结果表明,添加石油焦会引起煤的黏结指数下降,加入石油焦配煤炼焦会降低焦炭灰分,提高焦炭硫分,降低焦炭冷强度,提高焦炭热强度。     

Hydrodynamics of an annulus airlift reactor

The hydrodynamics of an annulus airlift reactor (AALR) was studied and compared with that of a slurry bubble column reactor (SBCR) with silica sands of 75-125 μm in size as solids, city tapping water as liquid phase, and air as gas phase in the present investigation. The effects of superficial gas velocity and solids concentration on gas holdup and solids distributions were investigated. The results showed that the local average gas holdup decreased along the column height, and the average gas holdup decreased with the increasing solids concentration, but this tendency became less at higher solids concentrations. It was found that the effect of superficial gas velocity on axial solids distribution was negligible over the gas velocity range investigated, as long as the solids in the column could be suspended. Increasing solids concentration led to flatter axial solids holdup profiles. The axial distributions of solids concentration and gas holdup in the AALR were much more uniform than those in the SBCR, and slurry circulation in the AALR damped the effects of increasing solids concentration on the hydrodynamics. These advantages of an AALR over a SBCR are especially important for some catalytic reaction processes in three-phase systems such as Fischer-Tropsch synthesis and methanol synthesis.     

化学预氧化对高硫石油焦煅烧脱硫的影响

对高硫石油焦采用化学预氧化再经高温煅烧(1 300℃)进行脱硫处理,并采用XRD和SEM对脱硫前后石油焦样品的结构和表面微观形貌进行分析表征。实验结果表明:常压室温下多种化学氧化剂脱硫效果比较,A酸-过氧化氢混合溶液对石油焦脱硫效果最好,其脱硫率达到20.72%;经A酸-过氧化氢混合溶液化学预氧化再高温煅烧(1 300℃)脱硫处理的石油焦的脱硫率相对直接煅烧或者只进行氧化脱硫处理的样品有显著提高,脱硫率可达55%;A酸-过氧化氢混合溶液化学预氧化处理不会破坏煅烧后石油焦存在的石墨雏晶结构,并且促使石油焦表面形成细微裂纹,这有利于煅烧时焦内部硫的逸出以及生产过程中煅烧石油焦原料与煤沥青的结合。     

Hydrodynamics and mass transfer characteristics in an internal loop airlift reactor with sieve plates

Effects of the sieve plate on hydrodynamics and mass transfer in an annulus sparged airlift reactor (0.08 m³, 1.3 m tall, and 0.284 m in diameter) were investigated. It is found that the sieve plate can significantly enhance gas holdup and volumetric mass transfer coefficient. The sieve pore plays an important role in breaking up bubbles. With a given free area ratio, the sieve plate with a larger sieve pore diameter is more efficient in increasing the volumetric mass transfer coefficient. Four different free area ratios between 37% and 73% are tested, and then an optimal free area ratio is determined. The effect of the sieve plate is found to be related to sparger types. The sieve plate leads to a larger increase of volumetric mass transfer coefficient with the O-ring distributor as compared to the 4-orifice nozzle. Empirical correlations and a hydrodynamic model are proposed to predict gas holdup, volumetric mass transfer coefficient and liquid velocity in airlift reactors with sieve plates.     

Macro-mixing in a draft-tube airlift bioreactor

Airlift reactors are pneumatically agitated reactors that have been widely used in industries, particularly in bioprocesses. Extensive studies about the flow dynamics in airlift column reactors exist; however, most of these studies have focused on global hydrodynamic parameters using conventional techniques. The local flow characteristics, such as the macro-mixing and the turbulence intensity, are crucial for reliable design and scale-up, and they remain unclear. This work focuses on studying the macro-mixing in a draft-tube airlift bioreactor utilizing an advanced flow dynamic measurement technique, computer automated radioactive particle tracking (CARPT). True residence time distribution analyses for the overall column as well as individual regions, i.e., the riser, the downcomer, the top, and the bottom regions, are conducted for the first time based on CARPT measured particle trajectories. The effects of the superficial gas velocity and the top/bottom clearances on the macro-mixing are also discussed. The results suggest that although the flow structures in the overall draft-tube column reactor, as well as in the riser and in the downcomer, are close to plug flows, bypassing and stagnancy exist in the top and the bottom regions.     

带辐照改性聚丙烯填料的气升式内环流反应器处理废水的研究

应用高能射线辐照技术,在聚丙烯填料表面接枝丙烯酸单体进行改性。将此改性填料应用于气升式内环流反应器中,并对模拟生活废水进行间歇法和连续法处理。实验结果表明,该反应器运行稳定,适应浓度范围广,COD去除率较高,出水COD浓度波动小。     

石油焦系活性炭2-甲基噻吩吸附性能研究

以石油焦为原料经高温炭化和水蒸气活化处理制备出石油焦基活性炭,经硝酸氧化处理后,采用静态吸附法测试了2-甲基噻吩在石油焦基活性炭上的吸附性能。研究结果显示,制备的活性炭比表面积高于800 m2·g-1,孔容大于0.45 cm3·g-1,经硝酸处理后比表面积和总孔容有所下降。样品经硝酸处理后,对2-甲基噻吩的饱和吸附量显著增加,硝酸处理40 min得到的活性炭对2-甲基噻吩的饱和吸附量最大。2-甲基噻吩在石油焦基活性炭上的吸附动力学均遵循拟二级动力学模型,饱和吸附量随吸附温度的增加而减小,热力学上表现为放热,熵减且是自发进行的过程。     

Study of a Chilean petroleum coke fluidized bed combustion fly ash and its potential application in copper, lead and hexavalent chromium removal

This work deals with the characterization of a circulated fluidized bed combustion (CFCB) Chilean petroleum coke fly ash (FA) from a petroleum coke power plant, and its potential use in neutralization and heavy metals removal from acid wastewaters. FA presents a high Ca and content, being anhydrite the major crystalline mineral phase, with minor proportions of calcite, portlandite and lime. Regarding to environmental characterization of this fly ash, leaching tests allowed concluding that FA is a non-hazardous residue. Heavy metals removal tests indicate that FA is able to remove Cu²⁺ and Pb²⁺ mainly due to a precipitation process, while Cr(VI) is being removed probably due to a reduction process to Cr(III), at high liquid to solid ratios. Cu²⁺, Pb²⁺ and Cr(VI) kinetic experimental data present acceptable fit to a pseudo-second order kinetic model. According to these results, FA may be used to remove heavy metals and neutralize acid wastewaters, suggesting a possible replacement of pure and costly alkaline materials.     

Reaction rates for the oxidation of highly sulphurised petroleum cokes: the influence of thermogravimetric conditions and some coke properties

The reaction with air of a large number (22) of high-sulphur petroleum cokes was studied by temperature-ramped thermogravimetric analysis. The kinetic parameters for each coke were established, based on BET surface areas. The oxidation rates (kg_C m⁻² s⁻¹ atm⁻¹) were found to vary with sample mass. This was a result of limitations on oxygen transfer, despite the small masses and low heating rates used. Limitations were present both externally (from the crucible mouth to the bed surface) and internally (from the sample surface to the bed interior). A method to take these effects into account was adopted, based on an analysis of the relevant diffusion rates. Application of this method reconciled the rate data for four different sample masses, except at high temperatures. The formation of a partially fused ash crust is believed to be the reason for this latter effect.The activation energies of the cokes varied between 195 and 280 kJ mol⁻¹, and the absolute rates varied by a factor of 10. They were between 1000 and 10,000 times higher than the average reactivity of carbon as reported in the literature. The elevated apparent rates are believed to have two causes, one in the combustion process and the other in the interpretation of the results. The first cause is the strong catalytic effect of the inorganic components, although the ash contents ranged only from 0.3 to 1.5%. The most active metal is vanadium, which is present in significant concentrations. The effectiveness of V₂O₅ as a gasifying catalyst is believed to be due to its low melting point. Increasing sulphur content in the cokes produces no perceptible change in the combustion rates. The second cause for poor combustion correlation is the inadequacy of BET surface area for expressing combustion rates.     

Local characteristics of hydrodynamics in draft tube airlift bioreactor

Airlift column reactors have been widely used in bioprocesses. The design, scale-up, and performance evaluation of such reactors all require extensive and accurate information about the gas–liquid flow dynamics, particularly as computational fluid dynamics (CFD) has become more popular in the last decade. However, due to the limitation of most conventional techniques for gas–liquid flow dynamics measurement, only global hydrodynamic parameters (e.g., cross-sectionally averaged liquid circulation velocity, overall gas holdup, and overall mass transfer rate) have been extensively studied. The local flow characteristics (e.g., the macro-mixing and the turbulence intensity) remain unclear. In this study, we use the computer automated radioactive particle tracking (CARPT) technique to investigate the details of the multiphase flow dynamics in a draft tube airlift bioreactor, such as the liquid velocity field, turbulent kinetic energy field, distributions of shear stresses, etc. The flow structures in the whole reactor, as well as the structure in individual regions, i.e., the top, the bottom, the riser, and the downcorner are also characterized. We found significantly large turbulent kinetic energy in the top and the bottom regions, with spots of very high shear stress, which were also found in the vicinity of the sparger. The results also suggest that the top and bottom clearances have significant effects on the flow structures, which may have substantial effects on the bioreactor performance.