精馏过程的新逐板计算法 (Ⅳ)多元精馏过程的设计型计算

对于精馏过程的模拟计算,大都已有严格算法适用于操作型计算.操作型方法虽可用于设计型计算,但增长计算时间.本文则提出用于直接设计型计算的新逐板法.设计型新逐板法选择比值为迭代变量.对于理想系统和与之相近系统,比值是指塔上部各板上各重组分分流量之比和塔下部各板上各轻组分分流量之比.对于萃取精馏系统,比值是指各板上各被分离组分的浓度之比.与操作型的新逐板法”相比,强回路不再存在,迭代回路全部由弱回路构成,因此具有更快的收敛速度.由于这是逐板计算法,故各股进料和侧线出料的最优位置可以方便地确定,而不必应用最优化判据或作最优化计算.     

丙酮和乙醇分离的模拟及设计

借助Aspen Plus,对丙酮和乙醇体系精馏过程进行了模拟计算,采用简捷法、严格精馏计算法分别对初始组分为含丙酮60%和乙醇40%的混合液(F=1000kg·h~(-1),P=0.12MPa,T=30℃)进行模拟,再采用塔设计规定,设定塔顶丙酮含量99.17%,塔底乙醇含量99%,计算出实际回流比为R=2.71,塔底馏出物/进料摩尔比为0.454。再采用灵敏度分析模拟得出结果为实际理论塔板数30块、进料板位置23块时塔热负荷最低,其再沸器热负荷为336.713k W。塔内填充CY700型不锈钢丝网波纹填料,塔径为0.65m。     

精馏过程的新逐板计算法——(Ⅱ)多元萃取精馏过程的操作型计算

本文将萃取精馏模拟计算的迭代过程分解为外层萃取剂迭代和内层被分离组分迭代二个迭代过程.内层迭代无需调用热力学程序,因而只占用很少的计算时间.外层迭代回路由单一的强回路同若干弱回路组成,可以得到充分加速.通过这种分层迭代的方法使逐板计算法成功地应用于多元萃取精馏过程的操作型计算,获得了均匀快速的收敛.     

精馏过程的新逐板计算法——(I)多元精馏过程的操作型计算

本文应用迭代数学理论提出了一个适用于理想系统和与之相近的轻烃系统的多元精馏操作型计算的新逐板计算法.它将整个迭代过程重组为总量迭代和比值迭代二个平行的迭代过程,获得了快速且均匀的收敛性.本法为直接设计型计算法打下了必要基础.     

关于Aspen Plus模拟1,4-丁二醇脱水塔的研究

先利用Aspen Plus软件对脱水塔进行简洁模拟计算,初步确定最小回流比、最小理论板数、实际回流比、实际理论板数、进料位置等塔模块参数,然后利用以上参数对脱水塔进行严格模拟计算,经严格模拟计算得到的结果与实际生产有偏差,最后经过塔内设计使模拟结果与实际生产结果相符。     

Study on hybrid pervaporation/distiilation process for methyl-isobutyl-ketone synthetic liquid separation

对丙酮一步法生产甲基异丁基酮(MIBK)部分精馏流程进行了工艺分析,MIBK脱轻塔进料液中少量水的存在使MIBK脱轻塔运行不稳定,进而影响MIBK合成液的整个分离过程.针对这个问题,提出了精馏-渗透汽化集成的工艺方案,省去MIBK脱轻塔.建立了渗透汽化小试实验,研究了NaA分子筛膜的渗透汽化过程以及分离性能.用Aspen Plus软件对精馏-渗透汽化集成工艺进行了模拟,与精馏过程相比,在MIBK产品质量与收率相同情况下,操作成本降低了20％,总成本可降低15％.     

丙酮连氮非催化水解的模拟和优化

在动力学研究的基础上,建立了非催化水解反应精馏过程的平衡级模型,对现行丙酮连氮水解制肼工艺进行优化,并使用化工模拟软件对该工艺过程进行模拟,考察了全塔级数、进料位置、回流比等参数对工艺过程的影响。结果表明,全塔理论级数为25级,补充水的进料位置为第5块板,丙酮连氮和水混合进料位置在第10块板,且补充水量与混合进料中丙酮连氮的摩尔比为1,回流比为4.2时,塔釜水合肼产品的质量分数可以达到20%以上。     

变压精馏分离甲醇-丙酮的工艺模拟及优化

采用Aspen Plus软件,以塔釜能耗为目标,以甲醇、丙酮纯度为约束函数,对双效变压精馏分离甲醇-丙酮工艺过程进行模拟。分析了操作压力、理论板数、回流比、进料位置和进料温度等参数对精馏过程的影响。确定了最优工艺参数：减压塔操作压力40 kPa,理论板数37,回流比2.4,进料塔板数26,进料温度25 ℃;常压塔理论板数30,回流比4.2,进料塔板数23。减压塔所得甲醇质量分数为99.0%,常压塔所得丙酮质量分数为99.7%。对比变压精馏和萃取精馏过程,变压精馏更容易得到高纯度丙酮产品,节能约13.4%。模拟结果对工业设计和设备改造具有一定指导意义。     

分壁式精馏塔分离醇类三元物系的模拟研究

采用分壁式精馏塔分离乙醇-正丙醇-正丁醇三元物系,通过Aspen Plus软件对其进行严格计算.模拟优化之后的塔设备参数和操作条件为：主塔理论板数为35块,进料段理论板数为16块,回流比为9.15,在进料段的第9块板处进料,侧线出料位置为第18块板,隔板的上下端连接位置分别为主塔第10块板和第27块板.与常规的两塔精馏相比,再沸器热负荷减少33.79%.     

基于集合算法的高纯度精馏塔分段建模方法

多级汽液平衡过程的严格模型变量维数高,用于构建优化命题时不易收敛且计算速度较慢。采用集合算法中基于吸收因子和理论塔板数计算全塔段组分回收率的组分分配特征方程代替逐板相平衡,加入物料衡算等基本方程与若干简化关系匹配模型自由度,建立可用于联立计算的逐段降维GM模型。同时根据高纯度精馏塔吸收因子沿塔分布的强非线性特征,提出分段线性拟合求解组分回收率的线性GM模型。以空分装置的粗氩塔为例进行高纯度精馏塔的严格模型、降维GM模型和线性GM模型的对比计算。结果表明,降维GM模型的计算变量由逐板模型的2377个减少到34个,同样平台下收敛时间由6136 s缩短至1 s左右,而关键组分纯度模拟与严格机理模型一致。     

A general algorithm for multistage multicomponent separation calculations

This paper presents a new general calculational method for equilibrium stage processes. The method employs a multivariate Newton procedure to solve all equations simultaneously for corrections to temperatures, flow rates and compositions. The linearized model equations are selected so that only 2N (1 + NCP) partial derivatives need to be evaluated per iteration. Experience to date indicates that the method is reliable for both distillation and absorption problems and requires less computing time than current procedures. The rigorous solution of a reboiled absorber problem for 16 stages and 15 components required 5 iterations and 14.4 seconds on an IBM 360/67 computer even when the Chao-Seader correlation was employed for the direct calculation of composition dependent equilibrium and enthalpy data.     

Multicomponent batch distillation with distillate receiver

Based on the assumption of adiabatic equilibrium stages, a rigorous calculation procedure applicable to a multicomponent batch distillation with a distillate receiver under total reflux condition was developed. Provided that the operating conditions including the desired product purity of the most volatile component in the receiver are specified, the proposed model estimates the volume of the distillate receiver, changes in compositions in the receiver and still, concentration profiles of the column, and the batch time required to complete the separation. In order to test the validity of the proposed model, experimental data for the separation of acetone-methanol-2-propanol mixture using a 10 cm I.D. column having six theoretical stages were compared with the simulation results for the two cases when the distillate receiver is initially empty and initially full.     

A crude distillation unit model suitable for online applications

A steady state, multicomponent distillation model particularly suited for fractionation of crude oil has been developed based on equilibrium stage relations. For a mixture of C components, the present formulation uses C+3 iteration variables namely the mole fractions of the components, temperature, total liquid and total vapor flow rates on each stage. This choice of variables makes the present model numerically stable and robust rendering a separate initial guess computation unnecessary. An improved scheme of numbering the equilibrium stages when side strippers are present, was found to be advantageous with respect to computation time. Selected example problems have been included from literature as well as industry to demonstrate the efficacy and usefulness of the method. The accuracy of predictions and speed of solution of the model equations are particularly suited for online applications such as online optimization.     

Investigation of vapour—liquid equilibrium of non-ideal multicomponent systems

Fundamentals and computer-aided methods of practice for the calculation and checking of azeotropes, and for the qualitative and rigorous determination of separating spaces for closed distillation are presented, which are valid for non-ideal multicomponent systems. Separating spaces can occur in azeotropic systems only and are decisive for the separability of a system, if distillation is the separation technique. As a prerequisite, a rigorous mathematical model of the vapour-liquid equilibrium is required. The eigenvalues and eigenvectors of the Jacobian matrix of the equilibrium concentrations are the key ingredients of several methods: the eigenvalues describe the asymptotic behaviour of closed distillation profiles, which indicates the order according to which components can be separated; the eigenvalues enter a topological equation for checking the thermodynamic consistency of the azeotropes of a system; the eigenvectors initiate paths connecting azeotropes and pure substances, from the network of which separating spaces can be deduced qualitatively; and eigenvectors are essential to initiate the rigorous profiles of separating spaces.     

CALCULATION METHODS FOR DISTILLATION SYSTEMS WITH REACTION

A calculation procedure is presented for the solution of the equations describing a distillation process in which reaction is taking place. A mathematical model based on matrix notation is used to formulate the system equations. It is assumed that the distillation process can be represented by a system of interconnected stages, each of which is well mixed with the vapor and liquid phases in equilibrium. Reaction may take place in the vapor phase, liquid phase, or both. The equations describing this system are first presented. Then a calculation sequence and a correction algorithm are derived for the case in which the liquid and vapor solutions are ideal—that is, the equilibrium ratios are functions only of temperature and pressure and not of composition. The calculation sequence uses as variables of iteration the vectors of vapor flow rate, temperature, and reaction extents. A derivative correction method is used, and equations for the calculation of the Jacobian matrix are derived. The application of the method is illustrated by solution of two sample problems. The special case in which the heat of reaction is small, and constant molal overflow can be assumed, and the case in which the reaction rate is very fast and chemical equilibrium exists in each stage are considered.     

A note on an extended short-cut method for the design of multicomponent reactive distillation columns

Until now, few studies have proposed analytical short-cut methods for reliably designing multicomponent reactive distillation columns. Therefore, in this study we have improved and extended a design methodology for the design of RD columns of multicomponent systems. We have developed a graphical design method, based on distillation lines and tray-by-tray calculations defined in terms of reaction-invariant composition variables, to determine RD design parameters such as the number of theoretical stages, operating reflux ratio, the feed tray location and the top or bottom flow. In this note, we report our extended and improved method, which is analytical and useful for reliably determining the design parameters of multicomponent RD systems. We study the synthesis of TAME with inert components (with different feed thermal conditions) as case of study to show the effectiveness of the proposed strategy. Results obtained with our strategy show a significant agreement with those obtained using a rigorous model of commercial simulator AspenONE Aspen Plus^®.     

CALCULATION METHODS FOR DISTILLATION SYSTEMS WITH REACTION

A calculation procedure is presented for the solution of the equations describing a distillation process in which reaction is taking place. A mathematical model based on matrix notation is used to formulate the system equations. It is assumed that the distillation process can be represented by a system of interconnected stages, each of which is well mixed with the vapor and liquid phases in equilibrium. Reaction may take place in the vapor phase, liquid phase, or both. The equations describing this system are first presented. Then a calculation sequence and a correction algorithm are derived for the case in which the liquid and vapor solutions are ideal—that is, the equilibrium ratios are functions only of temperature and pressure and not of composition. The calculation sequence uses as variables of iteration the vectors of vapor flow rate, temperature, and reaction extents. A derivative correction method is used, and equations for the calculation of the Jacobian matrix are derived. The application of the method is illustrated by solution of two sample problems. The special case in which the heat of reaction is small, and constant molal overflow can be assumed, and the case in which the reaction rate is very fast and chemical equilibrium exists in each stage are considered.     

Optimal design of catalytic distillation columns: A case study on synthesis of TAEE

The design of catalytic distillation (CD) columns is a challenging task because of the superposition of chemical reaction and distillation in one apparatus. In this work, a method to design a cost-optimal CD column for chemical systems with large number of components and chemical reactions is presented. The method is based on the following steps: (1) estimation of the number of theoretical stages and catalyst volume by the decomposition of the CD column into a sequence of chemical reactors and non-reactive distillation columns, (2) estimation of the column diameter and operating conditions using an equilibrium stage model, and (3) design of the column applying an optimisation algorithm and using a rigorous non-equilibrium stage model to represent the CD process. The method is applied to determine the optimal column configuration and operating conditions for the synthesis of tert-amyl ethyl ether from ethanol and isoamylenes. Eight components and four chemical reactions were selected to represent the chemical system in the simulations.     

三组元全热耦合精馏过程的模拟计算

本文利用Aspen软件对三组分进料全热耦合精馏的分离流程进行设计和模拟,建立了相应的具体计算步骤。首先利用三塔模型把热耦合精馏过程简化为3个单独的简单清晰分割塔,通过简捷法设计和模拟得到塔板数和回流比等初值后进行严格法模拟,得到热耦合精馏的数据和操作条件。然后采用Aspen软件中的RadFrac模型,将三塔模型的模拟初值代入全热耦合模块进行严格模拟。结果表明,采用全热耦合精馏分离C4三组分比传统精馏的直接序列和间接序列节能约为20%。