非均相催化精馏过程的模拟计算

提出了多组分非均相催化精馏过程的数学模型.该微分方程组的边值是未知的,但受全塔总物料衡算方程的约束,模型的求解是一个困难的边值问题.借助于多用标打靶法和Newton-Raphson迭代,本文提出了模型的有效解法.提出的算法亦适用于在填料塔内进行的非催化反应精馏过程.计算结果与实验数据的一致性令人满意.     

Simulation of three-phase distillation towers

The approximate models of Boston & Sullivan[1] for estimating K-values and enthalpies are used to solve the MESH equations in the steady-state. The algorithm for phase-splitting uses approximate models in an inner loop and more accurate models in an outer loop. Oscillations between one and two liquid phases are aboided during interative calculations when concentrations approach the two-phase region. Simulation results compare well with those of Block & Hegner[2]. Wide- and narrow-boiling systems are simulated efficiently. For some systems, tray efficiencies determine whether or not a second liquid phase appears in the simulation results.     

Numerical aspects of the implementation of cubic equations of state in flash calculation routines

It is shown that failures in flash calculations (K₁ → 1.0) when cubic equations of state are used to estimate equilibrium K-values, result from two main deficiencies. One is the well-known problem of guessing good starting values of the phase compositions at high pressure. The other is that regular methods for solving the cubic equation in the compressibility often lead to a wrong “type” of root (i.e. vapour or liquid). An algorithm without these deficiencies is presented.     

Three‐phase fluidized distillation

Separation efficiency in distillation operations can be improved by modifying the characteristics of the dispersions formed on the trays. The present work reports on the hydrodynamic and mass transfer characteristics of liquid‐solid‐vapour dispersions formed on sieve trays without downcomers of a distillation column operating under total reflux conditions. Murphree efficiency and the operating limits of distillation using the ethanol‐n‐butanol system are analyzed for a large range of vapour velocities and liquid mixture compositions, utilising wettable PVC particles and non‐wettable silicone, PE, and Teflonr? particles. It was verified that wettable particles show a drastic reduction in the upper operating limit of vapour velocity, but this does not occur for non‐wettable particles. Tray efficiency can be increased when non‐wettable particles are used, mainly for high vapour velocity operations.     

Condensation of binary vapours of immiscible liquids

A theoretical analysis is given of the vapour phase diffusional resistance during condensation of vapours of immiscible liquids. A design procedure is developed for the condensation of vapour mixtures of eutectic and non-eutectic compositions. Experimental data are reported for condensation of the mixtures toluene—water and n-heptane-water. The design procedure predicts the experimental performance within ±30%. It is shown, both theoretically and experimentally, that when the vapour composition is non-eutectic, situations are possible where only one vapour condenses and the other behaves as a non-condensing gas. The homogeneous liquid model of Akers and Turner[1] and the shared surface model of Bernhardt et al.[2] are found to adequately quantify the condensate film coefficient.     

Numerical study of laminar condensation of downward flowing vapour on a single horizontal cylinder or a bank of tubes

The results of numerical calculations for the downward flow of pure vapour condensing on horizontal tubes are presented. An implicit finite difference method is used. The equality of shear stress at the liquid—vapour interface is used as the coupling condition between the two phases. The inertia and convection terms are retained in the analysis. The vapour phase velocity is obtained from potential flow. The method of source density distribution on the body surface is used for the determination of the vapour flow in tube banks. The effect of flooding produced by condensation on upper tubes is taken into account by assuming that the vapour velocity field is not affected by the condensate flow from one tube to another. The results presented show that the vapour boundary layer separation depends on the Froude number. The heat transfer in the intertube space is analyzed and compared with the theoretical and experimental results of other authors. Good agreement is shown.     

Study on dynamic behaviour of thermally coupled distillation processes

A dynamic mathematical model has been developed which is suitable for thermally coupled distillation processes. An algorithm known as the equation-decoupled method was used for simulation. EPISODE software and LU decomposition method were adopted to solve the ordinary differential and algebraic equations of the model, respectively. The initial conditions, viz. a solution for the steady state of the process in dynamics simulation were obtained by means of modified Naphtali-Sandholm algorithm. Research on the dynamic behaviour of thermally coupled distillation processes was carried out on two examples. It was found, via the dynamic simulation, that a disturbance in the distribution of vapour coupled stream has a large effect on the composition of vapour side withdrawal and, similarly, for liquid coupled stream, on that of liquid side withdrawal when the fraction of side withdrawal is fixed, and a smaller effect when the quantity of side withdrawal is fixed.     

Two-phase flow and mass transfer in scrubbers

Experimental investigations were carried out in spray scrubbers of different sizes with cocurrent flow of gas and liquid. Of special interest were the local processes in the mass transfer zone. The scrubber was operated with warm water/air system (cooling tower) to obtain detailed information about mass transfer. Air is being humidified with water vapour, which in turn leads to a temperature drop in the liquid. The liquid temperatures are relatively easy to measure and are shown as liquid isotherms. In the case of plug flow, the liquid isotherms should be straight horizontal lines. In reality, significant deviations from plug flow are caused by the transfer of liquid to the walls. A large part of the liquid forms a film flow at the wall. Furthermore, nearly all the mass transfer is completed in the zone of liquid atomization immediately beneath the nozzle. The number of measured transfer units was between 0.5 and 2.0 and was significantly influenced by the liquid flow rate. Based on the improved knowledge of the proceses inside the scrubber, a simplified model has been developed. Since the model simulates all the essential processes inside the mass transfer zone, liquid distribution and mass transfer efficiency can be approximately predicted.     

基于RELS的乙炔法VCM精馏过程的自适应MPC方法

为抑制非平稳扰动对具有积分特性的乙炔法VCM精馏过程的影响,提出了一种有效的自适应MPC方法。由于高沸塔塔釜中会不断沉积高沸物,表现出很强的积分特性,因此,将高沸塔塔釜液位作为积分变量进行控制;同时,针对VCM进料温度等因素对高沸塔塔釜液位产生的非平稳扰动,首先,利用RELS算法实时的估计影响高沸塔塔釜液位的扰动,然后,计算扰动在预测误差中所占的比例,最后,通过实时更新旋转因子的数值实现对积分过程的自适应MPC。工业试验结果表明:提出的自适应MPC方法能够有效克服非平稳扰动,高沸塔塔釜液位的标准差为2.6616,比采用自适应MPC方法之前减少了60.7%,验证了该方法的有效性。     

An improved algorithm for the three‐fluid‐phase VLLE flash calculation

The VLLE flash is important in water and hydrocarbons mixtures, hydrocarbon and CO₂ rich mixtures, and hydrocarbon methane rich mixtures that are encountered in reservoir performance and recovery studies. A robust VLLE flash algorithm is proposed. The equilibrium and mass balance equations are solved as a constrained minimization problem. An inverse barrier function is used to handle the inequality constrains to solve for the phase fractions. It warrants always arriving to the solution. The challenging cases analyzed showed that the initialization procedure proposed, together with successive substitution iteration in the outer loop, is a good method for a stable VLLE flash algorithm, even near critical points. Whenever the result is in the region outside the three‐phase physical domain, the solution suggests that the system has fewer phases. In one of the cases analyzed, a region with three liquid phases was encountered and the algorithm found two different solutions with positive phase fractions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3081–3093, 2015     

Modelling of hydrocracking with vapour-liquid equilibrium

Hydrocracking Fischer-Tropsch waxes is a catalytic process that occurs both in vapour phase and in liquid phase. In a previous model, worked out by the authors, only the presence of the vapour phase was considered. In this paper it is shown how to account for the vapour-liquid equilibrium (VLE). In particular, the method used to calculate the critical properties of heavy hydrocarbons and the computing procedure that allows one to introduce the VLE calculation into the reactor model are explained. The results show that by accounting for the VLE a better agreement between experimental data and model outputs can be achieved. This results from the improved ability of the model to take into account the effect of the H₂/waxes ratio both on the conversion and on the product distribution.     

Apparatetechnische Aspekte der Kultivierung von Einzellern in Turmreaktoren

Equipment effects in culturing single-cell organisms in tower reactors . The influence of the aerator, the aeration rate and the loop and the recirculation rate of liquid through the loop on the performance of tower reactors are investigated. Also the effect of different internals, upward and/or downward as well as countercurrent flow of gas and liquid and the influence of the medium are considered. The performance of equipment can be varied over a wide range by means of these construction and operational parameters. This allows adaptation of these reactors to a particular production process. Difficulties arise when the reactor volume attains very high values. In such cases, fast and uniform distribution of energy, substrate, and oxygen added to the system and the removal of the heat, gas bubbles, and CO₂ from the medium cause considerable difficulties. Further investigations will be necessary to develop quantitative relationships for scale-up purposes.     

热虹吸式重沸器循环回路的设计探讨

探讨热虹吸式重沸器循环回路设计,包括热虹吸式重沸器的分类及特点、塔釜结构型式、塔釜液位确定、塔釜至重沸器的降液管及重沸器至塔釜的升气管尺寸计算等。     

强制液体外循环气升式内环流反应器的流体力学特性

在有机玻璃制成的主体反应器(φ0.286 m×3.0 m)内,采用空气-水的气液两相体系考察了不同表观气速下带有中心下料管和环管式气体分布器的环流反应器内局部气含率和内环气泡上升速度的流体力学特性。结果表明：气含率均随表观气速的增大而增大;从外环流入内环的气泡数量比较少;在相同条件下外环的气含率远远低于内环的气含率;新型气体分布器的采用和液体外循环的引入可以增大床层气含率并使其分布趋于均匀,从而增大了内环中气液两相的接触面积和湍动强度,使传递过程得到强化。在此基础上采用商业软件ANSYS CFX10.0对该反应器进行了数值模拟研究,模拟结果与实验数据基本吻合,说明了基于实验验证的Euler-Euler法可以用于该反应器开发和放大研究。     

New two‐phase and three‐phase Rachford‐Rice algorithms based on free‐water assumption

Based on the free‐water assumption that the water‐rich liquid phase contains only pure water, we develop two simple free‐water Rachford‐Rice methods: 1) a two‐phase free‐water Rachford‐Rice method where the phase fractions can be analytically solved; and 2) a three‐phase free‐water Rachford‐Rice method where there is only one unknown in the objective function (i.e. the vapour‐phase fraction) that is used for solving the phase fractions. Combining these two Rachford‐Rice methods, a new free‐water flash algorithm is developed to perform multiphase flash calculations where single‐phase equilibria, two‐phase equilibria, and three‐phase vapour‐liquid‐aqueous equilibria can be considered. In this free‐water flash algorithm, we first test if the mixture is stable; if the mixture is found to be unstable, we directly initiate the three‐phase free‐water flash. A set of criteria is developed for one to properly switch from a three‐phase free‐water flash to either a two‐phase free‐water flash or a conventional two‐phase flash, depending on whether a water‐rich phase is present in the two‐phase equilibrium. We also develop efficient and robust methods for initializing the equilibrium ratios for the two‐phase flashes. The negative flash is allowed in the flash calculation algorithms. A number of example calculations are carried out to demonstrate the robustness of the newly developed algorithm. A good agreement can be achieved between the flash results obtained by the new flash algorithm and those obtained by the conventional full three‐phase flash algorithm.     

Performance of continuous tower loop bioreactors—II model calculations for substrate limited growth

The behavior of tower and tower loop reactors is described by the CSTR-PFR and PFR loop combination as well as by the one-dimensional dispersion model with a loop assuming negligible residence time of the cells in the loop. In tower reactors, an optimum intensity of longitudinal dispersion, Bo_opt, exists at which the substrate conversion has its maximum. Conditions are determined at which, in tower loop reactors with no cells in feed, stable steady states exist. When the intensity of longitudinal dispersion in tower loop reactors is less than optimum (Bo > Bo_opt) an optimum recirculation ratio, γ_opt′ exists at which the substrate conversion is higher than at γ = 0 (in tower reactors without a loop) and at Bo_opt. Liquid recycling not only prevents the washout of the cells at high Bo numbers but also improves substrate conversion considerably and yields maximum conversion at γ_opt.     

多碟式液体分布器在大型填料塔中的应用

碟式液体分布器由进液总管、进液支管、分液管、限流孔板、分液碟、落液管组成。具有分液均匀、流量调节范围宽、抗堵塞、重量轻、安装维修方便等优点,特别适用于大型填料塔,可极大地降低甚至可消除液体分布的放大效应。详细介绍了碟式液体分布器在乙烯急冷塔、烟气脱硫塔、SO3热回收塔中的具体应用。     

缔合体系汽-液相平衡的研究(Ⅱ)——三元缔合体系汽-液相平衡的研究

本文提出了多元缔合体系汽-液相平衡的热力学模型,并用其计算了缔合体系水-甲酸-乙酸、水-乙酸-丙酸、水-甲酸-丙酸及甲酸-乙酸-丙酸在760mmHg下的实验液相活度系数。活度系数的计算值由Wilson方程或McCann方程给出。由相应二元体系的汽-液相平衡数据对三元体系的沸点及汽相组成进行了预测。结果表明,预测值能较好地同实验数据相吻合。     

Heterogenous azeotropic distillaion-homotopy-continuation methods

An algorithm for the simulation of three-phase distillation towers and associated phase separators is presented. The algorithm utilizes the homotopy-continuation method of Allgower and Georg[1] to accurately track the homotopy path, with extensions to avoid limit points when multiple solutions are encountered and when liquid phases are introduced on the trays. The Allgower and Georg algorithm is also extended to track solution paths in parametric studies. Emphasis is placed on the calculation of liquid—liquid equilibria, with a reliable, yet efficient, homotopy-continuation algorithm introduced. An effective method for incorporating the LLE algorithm in the homotopy-continuation algorithm for heterogenous distillation is also introduced.

The combined algorithms have located two steady-state solutions for an industrial azeotropic distillation tower a very narrow range of the reflux ratios, one with a single liquid phase on the trays, the other with two liquid phases on 70% of the trays. In addition, for the dehydration of ethanol with benzene, it has detected a region in which five steady-state solutions exist for the same specifications. Three of these solutions were reported by Magnussen .[2] and observed in dynamic simulations by Prokopakis and Seider[3].