双通道气流式MTP反应喷嘴雾滴粒径分布的研究

雾化喷嘴的性能直接取决于索泰尔平均粒径SMD、雾滴粒径分布PSD和雾滴覆盖直径DCD。利用冷模实验,以双通道气流式MTP反应雾化喷嘴为研究对象,考察了喷嘴结构与雾化性能之间的关系,研究了具有不同旋流结构的喷嘴在不同气液比q_(mG)/q_(mL)下SMD,PSD及DCD之间的变化规律。结果表明,旋流槽尺寸与结构、液相通道内径dL对SMD,PSD和DCD具有显著地影响。当喷嘴结构参数为:旋流通道数n=2,旋流通道尺寸b×h=0.5mm×1.0 mm,液相通道内径dL=1.0 mm时,随着q_(mG)/q_(mL)由8.70增加至20.32,喷嘴对应SMD由20.02μm降至17.88μm,雾滴粒径分布介于9.91μm和48.8μm之间,特征中径D_(0.5)达到21.45μm。当n=3,b×h=1.5 mm×2.0 mm和2.0 mm×2.0 mm,dL=2.5 mm时,SMD随着q_(mG)/q_(mL)的增加分别由62.48μm降至58.89μm,由63.02μm降至59.39μm,雾滴粒径分布变宽,介于34.3μm和111.6μm之间,D_(0.5)达到64.02μm。当n=4,b×h和dL保持不变时,PSD和D_(0.5)基本不变,SMD随气液比q_(mG)/q_(mL)的增加由64.07μm变至60.65μm。而且,DCD由φ640mm增至φ800 mm。     

2D and 3D simulations of an internal airlift loop reactor on the basis of a two-fluid model

Two- and three-dimensional (2D and 3D) simulations of an airlift reactor under steady state conditions at low gas flow rates are presented. The simulations are based on a two-fluid model with a k–ε model for the turbulence and as little as possible ad hoc closure terms. The results are compared with an one-dimensional mechanical energy balance and are found to be in good agreement. The 2D results show sensitivity to the gas inlet geometry: whether or not the gas is partially sparged into the liquid directly next to a wall affects the liquid velocity distribution and thereby the gas disengagement at the top of the airlift. The three-dimensional calculations make a more realistic geometry possible. The friction in the system is found to be about a factor of two larger in the 3D case at the same gas inlet conditions. For a given gas flow rate, the mean gas fraction in the riser is the same for the 2D and 3D simulations, the liquid circulation rate is about 30% higher in the 2D case than in the 3D one. A comparison is made with experimental data obtained in an airlift of the same dimensions. The simulated overall gas fraction is in agreement with the experimental findings. The simulated superficial velocity in the riser is compared to LDA data. For the lowest superficial velocities the LDA data coincide with the results from the 2D simulations, for higher gas flow rates the LDA results switch over towards the 3D results.     

Chemical absorption of mercaptan in an aerosol operated loop reactor

A mechanistic mathematical model for the chemical absorption of mercaptan in sodium hypochlorite solution has been derived. In order to describe the process adequately, a semi-verified complex scheme of the involved kinetic reactions based on stopped-flow measurements with UV-detection has been implemented. The overall system of differential equations has been solved numerically. For some asymptotic cases, approximation formulae are given. The process has been carried out in an aerosol operated jet loop reactor which is characterized by high interfacial areas at low liquid flow rates. Fitting the model solution to the experimentally obtained conversion data enabled determination of the unknown hydrodynamic parameters. By means of a sensitivity analysis, the influences of the different parameters are discussed.     

喷嘴结构对射流鼓泡反应器混合和传质性能的影响

喷嘴结构对射流鼓泡反应器的混合和传质性能具有重要的影响。以空气-水作为模拟介质,使用双探头电导探针、电解质示踪法和动态溶氧法,对比研究了缩径式圆形喷嘴和旋扭三角形喷嘴对射流鼓泡反应器中气泡尺寸分布、平均气含率、液相混合时间和气液传质系数的影响规律。实验发现,随着气速或液体射流Reynolds数的增大,两种喷嘴对应的平均气含率、液相混合时间和气液传质系数具有相同的变化规律;与缩径式圆形喷嘴相比,采用旋扭三角形喷嘴的射流鼓泡反应器中气泡尺寸更小,平均气含率更高,宏观混合时间更短;当气体输入功占总输入功比例超过20%时,喷嘴结构对气液传质系数的影响较小,当气体输入功占总输入功比例小于20%时,旋扭三角形喷嘴的气液传质性能优于缩径式圆形喷嘴。研究结果可为工业射流鼓泡反应器喷嘴结构的优化提供理论指导。     

CFD simulation of hydrodynamics and mass transfer in an internal airlift loop reactor using a steady two-fluid model

Steady state simulation of the hydrodynamics and mass transfer in bubbly flow in an axisymmetric internal airlift loop reactor (IALR) with the special treatment of interphase decoupling and outlet boundary conditions is performed, which is based on a Favre averaging two-fluid model for multiphase flow. Different models of mass transfer coefficient are compared and validated with the literature data. A model for describing the mass transfer for a wide range of superficial gas velocity is chosen and the predicted mass transfer coefficient agrees well with the experimental data in the literature. The numerical procedure can be used as a tool for the design and scale-up of IALRs.     

Ammonia removal by air stripping in a semi-batch jet loop reactor

Ammonia is very toxic chemical and it can be removed by air stripping at high pH. JLRs have found applications in wastewater treatment processes due to their high mass transfer rates. In JLRs, intrinsic high turbulence result in a very large air-liquid surface area for greater mass transfer. Therefore, in this study, ammonia removal by air stripping from synthetically prepared ammonia solution at the high pH in a semi-batch JLR due to its high mass transfer capabilities have been investigated. Investigated parameters in a JLR were initial ammonia concentration (10–500 mg/L), temperature (20–50 °C), air flow rate (5–50 L/min) and liquid circulation rate (35–50 L/min). While it was demonstrated that temperature and air flow rate have a significant effect on the ammonia removal, it was determined that initial ammonia concentration and liquid circulation rate have no significant effect on the ammonia removal. The overall volumetric mass transfer coefficients (K_La) have been calculated from obtained model and it was determined that increasing temperature and air flow rate have a very significant effect on K_La. It was concluded that JLR provides higher mass transfer capabilities than other type of reactors even if less air is given.     

混合胺溶剂吸收CO_2的内冷流程模拟

为降低醇胺溶液吸收法捕集分离CO_2的能耗问题,采用在吸收塔增加内部冷却即内冷的方法,使用乙醇胺和甲基二乙醇胺混合溶剂水溶液,采用化工模拟软件AMSIM进行了CO_2吸收的过程模拟。分析了内冷位置、一级和二级内冷的冷却量、贫液流量和混合溶液浓度对捕集能耗的影响。结果表明采用混合胺溶剂和内冷流程的CO_2捕集能耗比乙醇胺传统流程的能耗降低了17%,说明将捕集溶剂和捕集流程结合起来进行研究,可以明显降低CO_2捕集能耗。     

CO2 absorption performance in a rotating disk reactor using DBU-glycerol as solvent

Gas–liquid mass transfer of rotating disk reactor was studied in CO_2 absorption using 1,8-diazabicyclo-[5.4.0]-undec-7-ene(DBU)-glycerol solution as solvent. Effects of the rotating disk structure and various operation parameters on the CO_2 absorption rate and CO_2 removal efficiency were investigated. The rotating disk with optimal holes is conducive to mass transfer of CO_2 and the formation of thin liquid film at the opening increases the gas–liquid contact area. With the increase of rotating speed, the liquid flow pattern on the rotating disk surface changes from thin film flow to separated streams and creates extra liquid lines attached to the rim of the disk,which leads to a very complicated change on the CO_2 absorption rate and CO_2 removal efficiency. The overall gas-phase mass transfer coefficient increases 138% as the rotating speed increasing from 250 to 1400 r·min~(-1).Increasing temperature from 298 to 338 K can enhance the CO_2 absorption rate due to lowering the viscosity of the solvent. The rate-determined step for the absorption is focused on the gas side. The rotating disk reactor can effectively enhance the absorption of CO_2 with viscous DBU-glycerol solvents.     

Influence of geometry on gas holdups in a reversed flow jet loop reactor

The effects of ratio of draft tube to reactor diameter (D_d/D), liquid nozzle diameter (d_N), aeration tube diameter (d_G) and immersion height of the two-fluid nozzle into the draft tube (H_N) on overall and annulus gas holdups for the air-water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasing d_N and H_N. The influence of d_G on gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas holdups.     

Gas holdup in a two‐phase reversed flow jet loop reactor

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two‐fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas–liquid mixture in draft tube only (E_gd) and gas holdup with circulation loop (E_g). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two‐fluid nozzle.     

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.     

Equilibrium model for CO2 absorption in an aqueous solution of 2-amino-2-methyl-1-propanol

A semi-empirical gas-liquid equilibrium model for the absorption of CO₂ in aqueous 3M AMP (2-amino-2-methyl-1-propanol) is presented. It applies to high CO₂ loadings (y > 0.5) in the temperature range between 20 and 50 °C, and is based on experimental solubility and pH determinations. For a given amine concentration, it yields the equilibrium partial pressure of CO₂ as a function of only two variables: the CO₂ loading and temperature. The model correlates the expressions for the chemical equilibria involved as follows: p = m y × 10^x, where p is the equilibrium partial pressure, x = logK - pH, m is the amine molarity, y the CO₂ loading, and K is a parameter involving Henry's law constant, H, and the first dissociation constant, K₁, of carbonic acid. pH is found to depend on both temperature and CO₂ loading while logK depends only on the CO₂ loadIng. Correlations for pH and logK are presented. The model fits own data for 3M AMP very well as well as the equilibrium data found in recent literature.     

基于NaOH溶液CO2膜吸收系统的膜结构及传质性能

碳捕集与利用技术是实现减碳目标的有效方案。膜系统气体吸收技术能够实现CO₂以\mathrm{H}\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{-}、\mathrm{C}{\mathrm{O}}_{\mathrm{3}}^{\mathrm{2}-}形式存储在无机碱性吸收剂中,并还原成甲醇、乙醇等清洁燃料。本文采用膜单侧浸泡实验法和传质实验,分别考察了疏水性微孔滤膜聚四氟乙烯（PTFE）膜、聚偏氟乙烯（PVDF）膜、聚丙烯（PP）膜在NaOH碱性溶液中的结构和CO₂传质特性的变化。结果表明,PTFE膜和PP膜在NaOH碱性溶液中溶胀率上升,孔径减小,孔隙率下降,疏水性下降,传质系数下降;PVDF膜在NaOH溶液中会发生反应,结构被破坏,传质系数接近无膜吸收,但无法起到相界面的作用,不能直接用于以NaOH为吸收剂的膜吸收系统。     

Effect of liquid viscosity on gas holdups in a reversed flow jet loop reactor

The effect of draft tube diameter and liquid viscosity on overall and annulus gas holdups were studied in a reversed flow jet loop reactor. The draft tube diameter to reader diameter ratio (D_d / D) and liquid viscosity were varied in the ranges 0.34-0.67 and 1.5-43 mPa. s, respectively. The maximum gas holdup was obtained when the D_d / D value ranged btween 0.47 and 0.61. The gas holdup decreased with increasing viscosity. Empirical correlations are presented to predict the gas holdups.     

Formation and stabilization of an EHD jet from a nozzle with an inserted non-conductive fibre

The formation and stabilisation of an EHD jet from a nozzle with an inserted non-conductive fibre were investigated. The fibre introduced two main effects. First the fibre eliminated backflow in liquid meniscus and allowed the electric field only to accelerate the liquid, while using common capillary nozzle required electric field to overcome the kinetic velocity by convection. Second the accelerating of shear electric stress acted on the liquid surface while the liquid was flowing along the fibre, which did not exist in common nozzle. The above two factors all helped to reduce the potential needed to obtain cone-jet mode, and the second effect highly stabilized the spraying. Among high flow rate range, the influence induced by fibre became significant. Also results show for the same flow rate applied potential affected the thickness of liquid layer on fibre surface slightly. In addition, using the present nozzle intermittent spraying could be obtained and controlled by application of pulsed electric potential.     

Influence of recycling on mass transfer and reaction in a G-L jet loop reactor with variable interfacial area

The effect of recycling on mass transfer, characterized by the volumetric mass transfer coefficient k_La, was investigated by absorbing CO₂ into water in a laboratory jet loop reactor. Based on a mathematical model, which includes the correlation function k_La = k_La(r_L), a first order chemical reaction and the variation of interfacial area, a = a(ε_G), caused by strong absorption effects, the interaction ‘recycling – mass transfer – reaction’ was simulated and its influence on the reactor performance is discussed.     

磁场对氨水吸收烟气中CO2的促进作用

开发了一种新型磁场辅助氨法烟气脱碳技术。含碳烟气通入混有磁性颗粒的氨水溶液,在外加磁场的作用下发生脱碳反应。对该技术的运行特性开展了实验研究。结果表明,外加8 mT恒稳磁场,2 g·L^-1纳米级Fe₃O₄颗粒,氨水的CO₂脱除效率比不添加磁场和颗粒时最多可提高8.8%。外加磁场可以有效提高低浓度氨水的CO₂脱除效率。在模拟烟气流量增加时,外加磁场能有效减缓CO₂脱除效率下降的趋势。同时,外加磁场使得CO₂脱除效率曲线向低温方向移动5℃,有助于提高低温条件下的CO₂脱除效率。磁场可提高气液接触效率、降低相间传质阻力、增强氨水反应活性,从而提高氨水吸收CO₂性能。     

Unsteady-state absorption of CO2 into w/o emulsion with aqueous alkaline liquid droplets

Unsteady-state absorption of CO₂ into w/o emulsion was studied by experimental measurements and prediction from mathematical modeling. Absorption experiments were performed by using a stirred vessel with a flat gas-liquid interface under 0.101 MPa and 25 °C. Continuous phase was benzene that has larger solubility than water. Dispersed phase was an aqueous solution of NaOH and AMP. The effects of reactant concentration, size of emulsified droplets, volume fraction of continuous phase and stirring speed on the absorption rate of CO₂ were investigated. In the mathematical model, the mechanism of CO₂ absorption into the continuous phase through a gas-liquid interface was described on the basis of the penetration model, while the subsequent absorption/reaction in the dispersed aqueous droplets was modeled by the film model.     

Gas dynamics and thrust in the exhaust system of a jet engine with an annular nozzle

Results of a comprehensive numerical and experimental study of the dynamics of the flow of equilibrium combustion products of stoichiometric acetylene-air mixtures in the exhaust system of a jet engine with an annular nozzle are presented. Results of the numerical solution of unsteady Navier-Stokes equations for a chemically nonequilibrium model of a multispecies gas medium are reported. Experiments are performed in a hotshot aerodynamic setup. Thrust characteristics of the exhaust system of the jet engine are determined, and specific features of the structure of a steady flow formed there are found.