精馏过程的设计型算法(Ⅰ)——常规塔

本文建立了用于常规精馏塔(仅有一股进料、无侧线出料及中间换热器的塔)设计的严格算法。按本算法,根据进料条件及对轻、重关键组分的分离要求,通过一次计算确定所需的理论板数、回流比、适宜进料位置、塔顶和塔底产量及逐板流量、组成等详细数据。 设计参数的初值由简法提供,验算则采用三对角矩阵——牛顿-拉夫森联合法。汽液平衡和焓计算可采用Peng-Robinson(简称PR)或Starling-Han-BWR(简称SHBWR)模型。 已将本算法编为电算程序(CCAC程序)并用于十六个常规精馏塔的设计计算,取得了满意的结果。     

精馏过程的设计型算法(Ⅱ)——复杂塔

本文介绍复杂精馏塔(最多可有四股进料,两股汽相侧线出料和两个中间换热器)的设计型算法。根据指定的独立变量值(各股进料条件,对轻重关键组分的收率要求,各股侧线中某组分的收率和浓度的要求等),通过优化计算,确定为达到各项设计指标的一组适宜设计参数值。设计参数的初值由简法提供,验算则采用三对角矩阵-牛顿-拉夫森联合法。汽-液平衡和焓计算可采用PR或SHBWR模型。 曾将本设计型算法应用于五个复杂塔(其中三个为实际生产装置),取得了较满意的结果。     

汽,液两相反应精馏过程的反应扩散模型与模拟计算：（Ⅱ）模拟计算

汽、液两相反应精馏实际板的反应—扩散(非平衡级)模型应用三次设计法进行了模拟研究,并用乙酸、乙醇酯化反应体系筛板塔反应精馏实验结果与模拟结果进行比较,比较结果表明本模型是可靠的。     

填料塔设计软件的开发

利用面向对象的程序设计语言和软件开发的原理,结合填料塔的工艺设计过程,开发了填料塔的设计软件。程序采用了适用的载点算法,集成了填料塔压力降、塔径、塔高的计算和主要塔内件的设计功能,主界面采用选项卡标签控件,与填料塔的设计步骤相对应。验证表明本设计程序计算结果准确、合理。     

精馏塔汽液负荷的计算

精馏是石油化学工业生产中广泛采用的、最重要的单元操作过程之一。精馏塔设计的成功与否,不仅关系到操作的稳定性,还直接影响到产品的质量。所以,精馏过程的研究受到普遍重视,国内外每年发表的论文数量相当可观。然而,这些论文主要集中于汽液相平衡、P-V-T关联式以及塔的工艺结构参数等方面,关于汽液负荷计算方面的论文却少见。众所周知,在精馏塔的工艺结构参数(诸如塔径、塔板间距、开孔率、溢流装置等)的设计和流体力学的计算中,汽液负荷则是基础数据。所以,准确地计算汽     

复杂炼油塔模拟的改进联立方程内外层算法

在内外层算法的基础上,采用联立方程思想将主塔、侧线汽提塔视为一个整体进行建模,并针对复杂炼油塔的特点对算法提出了改进。首先,由于传统内外层法简化的K值模型对组成的变化不敏感,在处理带有石油的体系时,容易出现迭代次数较多,甚至部分塔板温度更新异常的问题,因此采用了汽相分数加和式推导了简化的K值模型加权因子。其次,借鉴流量加和法思想,规定侧线汽提塔的塔底产品流量作为设计变量,增强了算法收敛的稳定性。为验证改进后算法的有效性,采用不同的算法对实际的常压塔进行了模拟,结果显示改进后的算法适合应用于复杂炼油塔的模拟计算。     

炼油减压精馏塔汽提工艺传质过程模拟与分析

为了揭示减压塔汽提工艺的传质过程特性,进而改进汽提操作,采用改进的减压精馏过程模拟方法和传质计算方法,分析了炼油常减压装置的汽提工艺的传质特点。在深化对于汽提工艺的理解基础上论证了采用填料汽提塔(段)的必要性以及设计、分析的基本方法。计算分析结果表明侧线汽提塔内填料分离性能保持恒定,汽提塔的分离效率与减压塔对应分离段接近,所以在设计和操作中应给予汽提塔(段)充分重视。减压塔底汽提段的工艺和水力学特点与侧线汽提塔相同。塔底汽提蒸汽质量流率应小于减压塔进料质量流率1%,否则将导致减压塔整体分离效率降低。     

智能CS算法在分布器设计计算中的应用

为了能够更快捷、更高效地设计计算填料塔分布器的结构参数,对分布器的计算模型及变量进行了分析,建立了填料塔分布器计算的数学模型,引入新型智能的布谷鸟演化算法(CS算法)对计算模型进行求解计算;以一个精馏填料塔为实例,计算得到了填料塔分布器结构的参数。结果表明:使用CS算法对分布器进行设计计算是快捷高效的。     

醋酸脱轻塔汽液平衡模拟计算

介绍了醋酸脱轻塔汽液平衡计算,通过醋酸体系的二元汽液平衡数据和三元液液平衡数据,回归出醋酸体系的主要二元交互作用参数,用NRTL有序双液方程与Hayden-O′Connell联立方程对非理想缔合体系的汽(液)液平衡的模拟计算,计算出醋酸精馏体系的汽液平衡与液液平衡、焓差和密度,理论模拟出醋酸脱轻塔各塔盘的流量、温度和压力与实际醋酸生产非常接近,其精度完全可满足醋酸生产的要求,对醋酸的生产具有重要的指导和借鉴意义。     

焦炉煤气氧化法脱硫补氨方式探讨

介绍了以氨为碱源的PDS湿式氧化法脱硫工艺,强调了碱源在焦炉煤气PDS法脱硫过程中的重要性,从理论和实际两方面着重分析了补氨的加入方式(氨汽或氨水)和位置(反应槽、预冷塔及预冷后煤气管道);同时提出了氨水、氨汽同补的新补氨方式,即氨汽补氨从预冷塔后煤气管道中加入,并讨论了新补氨方式的优点、缺点和防范措施。     

Logic hybrid simulation-optimization algorithm for distillation design

In this paper, we propose a novel algorithm for the rigorous design of distillation columns that integrates a process simulator in a generalized disjunctive programming formulation. The optimal distillation column, or column sequence, is obtained by selecting, for each column section, among a set of column sections with different number of theoretical trays. The selection of thermodynamic models, properties estimation, etc. is all in the simulation environment. All the numerical issues related to the convergence of distillation columns (or column sections) are also maintained in the simulation environment. The model is formulated as a Generalized Disjunctive Programming (GDP) problem and solved using the logic based outer approximation algorithm without MINLP reformulation. Some examples involving from a single column to thermally coupled sequence or extractive distillation shows the performance of the new algorithm.     

最小有效能损耗的多组分精馏流程优化设计

提出了以有效能损耗最小为目标、同时又考虑热集成的多组分复杂精馏塔序列优化设计新策略。该复杂精馏塔模型:1股进料、2股出料,每块理论板上均可有中间冷凝器或再沸器。复杂精馏过程的设计步骤是:①根据过程有效能最小确定优化塔序列;②对每个塔优化设计出含中间换热器的复杂塔;③考虑多效且允许热集成的复杂精馏流程,以塔压为决策变量,以精馏过程有效能损耗最小为目标,建立并优化设计出一个热集成的复杂精馏流程。一个3组分精馏过程的例子表明所提策略简单有效,可用来指导多组分精馏过程的优化设计。     

A flexible solution method for generalized equilibrium stage columns

This paper presents a flexible solution method for the process design and simulation of generalized equilibrium stage absorption or distillation columns for solving a wide range of multistage, multicomponent separation problems in the petroleum or petrochemical industries. Although the model was developed to increase the control flexibility of product components in a solution, it was found that it also increases the efficiency of convergence at the expense of greater core usage. The mathematical model includes overall material balances, component material balances, energy balances, summation equations and specification equations. These nonlinear equations are solved simultaneously via the matrix partitioning technique together with the popular Newton-Raphson iterative algorithm. The method is applicable for both absorption and distillation columns with multiple feeds and sidedraws. This model will offer more flexible choices of the column specifications such as tray temperature, overhead product rate, reflux ratio, boilup ratio, tray vapor/liquid flow and product purity/recovery. The composition dependent equilibrium and enthalpy correlations such as Chao-Seader, Grayson-Streed, and Soave-Redlich-Kwong are incorporated into the mathematical model. Most problems can be easily converged with less than ten iterations.     

DYNAMIC BEHAVIOR OF REACTIVE DISTILLATION COLUMNS. EQUILIBRIUM SYSTEMS

This paper deals with the dynamic behavior of simultaneous reaction-separation systems which operate at or near the chemical equilibrium in the liquid phase. The process under study comprises a whole set of “instantaneous”, and very fast reversible reactions where the difference in volatilities favors both the progress of reaction and product separation. The main aim of our study is to gain a deeper understanding of the dynamic behavior of distillation columns by using a model that is simple and efficient, yet informative. This kind of model is outstanding for synthesis and design of control schemes which require a careful modelling and understanding of process response to different changes in the environment. We use a suitable transformation of variables (after Barbosa and Doherty, 1988b) in order to define a new set of state variables; as a result, the balance equations become identical to those for conventional distillation. Also, an efficient physicochemical algorithm that can handle both the original and new state variables is used. Thus, a composition-holdup dynamic model is simulated in the “transformed field” using a stage-by-stage approach. To further reduce computational time, the transformed problem has also been solved by means of a reduction procedure based on approximating by orthogonal polynomials the transformed composition and flow profiles in the column. The performance of the two proposed methods are compared by using the top section of a quaternary reactive column. The results obtained shown that reactive distillation dynamics has certain peculiarities derived from superimposing reaction and separation phenomena.     

Optimization of the Design and Operation of Extractive Distillation Processes

The achievement of the optimal operating point of extractive distillation systems involves determining the values of the process variables, such as the solvent flowrate, the reflux ratio of the extractive, and recovery columns. From the point of view of design, the optimum involves defining the number of stages of extractive and recovery columns, as well as the feed stage positions of these columns. The above-mentioned columns are coupled through a recycle stream, which makes obtaining the optimal operating and design points a more complex task. This study arose from a new procedure for the analysis of extractive distillation columns, in which the solvent mole fraction in the solvent feed stage is the primary variable to be analyzed. The procedure allows for determining the values of the process and design variables that provide the global minimum for the total annual cost and the specific energy consumption of the extractive distillation processes (extractive and recovery columns). Furthermore, it is possible to determine the minimum solvent flowrate and the minimum reflux ratio for separation. Obtaining anhydrous ethanol using ethylene glycol as solvent is the case study of this work.     

Short-cut methods for the optimal design of simple and complex distillation columns

New short-cut methods providing optimal design parameters for distillation columns with simple and complex configurations including two-feed and one-feed-one-side-stream columns are presented. The methods assume constant relative volatilities and constant molar flow rates within each distillation section. The design equations are based on the Underwood equations for the calculation of minimum reflux (reboil) ratio, the analytical formulations of the distillation line, the Eigenfunction and the number of theoretical stages for each mass transfer section of the column. Furthermore, the geometrical properties of a given separation are considered. Optimization algorithms based on the minimization of the total number of theoretical stages of the column with taking into account the mass balance at each feed section have been elaborated. In comparison to the boundary value method the new short-cut methods require a minimum number of specifications; they do not need any graphical support, and provide a lower total number of theoretical stages particularly for complex configurations. The new short-cut methods have been extended to the design of columns separating azeotropic mixtures by approximating the latter by appropriate pseudo-ideal mixtures. Several separation examples for azeotropic mixtures, including different types of splits as well as columns with simple and complex configurations were tested and show a very good agreement with the simulation results obtained with Radfrac (Aspenplus).     

Design of memetic algorithms for the efficient optimization of chemical process synthesis problems with structural restrictions

In Urselmann et al., 2011a, Urselmann et al., 2011b we presented a memetic algorithm (MA) for the design optimization of reactive distillation columns. The MA is a combination of a problem-specific evolutionary algorithm (EA) that optimizes the design variables and a mathematical programming (MP) method that solves the continuous sub-problems with fixed discrete decisions which are proposed by the EA to local optimality. In comparison to the usual superstructure formulation, the search space of the MA is significantly reduced without excluding feasible solutions. The algorithm computes many different local optima and can handle structural restrictions and discontinuous cost functions. In this contribution, a systematic procedure to modify the MA to solve more complex design problems is described and demonstrated using the example of a reactive distillation column with an optional side- or pre-reactor with structural restrictions on the number of streams. New concepts to handle connected and optional unit operations are proposed.     

A framework for efficient large scale equation-oriented flowsheet optimization

Despite the economic benefits of flowsheet optimization, many commercial tools suffer from long computational times, limited problem formulation flexibility and numerical instabilities. In this study, we address these challenges and present a framework for efficient large scale flowsheet optimization. This framework couples advanced process optimization formulations with state-of-the-art algorithms, and includes several notable features such as (1) an optimization-friendly formulation of cubic equation of state thermodynamic models; (2) a new model for distillation column optimization based on rigorous mass, equilibrium, summation and heat (MESH) equations with a variable number of trays that avoids integer variables; (3) improvements on the Duran–Grossmann formulation for simultaneous heat integration and flowsheet optimization; and (4) a systematic initialization procedure based on model refinements and a tailored multi-start algorithm to improve feasibility and identify high quality local solutions.Capabilities of the framework are demonstrated on a cryogenic air separation unit synthesis study, including two thermally coupled distillation columns and accompanying multistream heat exchangers. A superstructure is formulated that includes several common ASU configurations in literature. As part of the optimization problem the solver selects the best topology in addition to operating conditions (temperatures, flowrates, etc.) for coal oxycombustion applications. The optimization problem includes up to 16,000 variables and 500 degrees of freedom, and predicts specific energy requirement of 0.18 to 0.25 kWh/kg of O₂ depending on design assumptions. These results are compared to literature and plans to extend the framework to an entire coal oxycombustion power plant optimization study are discussed.     

Design and synthesis of multicomponent thermally coupled distillation flowsheets

The design and synthesis of thermally coupled distillation flowsheets for separations of five-component mixtures are studied. Four types of possible configurations are identified when simple and complex columns are both considered in a flowsheet. A universal design procedure is developed for design of any types of the identified configurations based on the abstraction of the three basic units in the flowsheets. Two examples demonstrated that this shortcut design method can be used in design of any types of the identified multicomponent thermally coupled distillation flowsheets, as well as give very good initializations for rigorous simulation of such configurations. Moreover, with a proposed computer representation of all the types of the feasible configurations, a synthesis algorithm is developed for synthesizing of multicomponent complex distillation flowsheets with both simple and complex columns. It is practical by the proposed methods for optimal design of multicomponent distillation systems in an extended search space to include the complex distillation flowsheets for industrial problems.