Degrees of freedom analysis for a distillation column

Precise determination of the number of degrees of freedom is of great significance in the design, operation, renovation, and optimization of chemical plants. Two fundamental works devoted to the determination of the number of degrees of freedom for chemical technology processes are considered, and the basic distinctions between the two approaches are discussed. It is explained why the numbers of degrees of freedom determined for the similar chemical engineering objects considered in those works are different.     

三组分精馏隔板塔的操作柔性模拟与分析

隔板精馏塔作为完全热耦合精馏塔由于具有较强的耦合性,其操作与控制相比传统精馏塔更为复杂,同时由于具有更多的自由度表现出更多的操作柔性。选用正戊烷、正己烷、正庚烷混合物的分离为例,采用严格模拟方法,通过对7 种进料条件设计的隔板塔进行模拟,考察了不同进料条件下的操作柔性,同时考察进料组成对隔板精馏塔操作柔性的影响。     

分壁式精馏塔精制丁二烯流程模拟

丁二烯是一种重要的石油化工烯烃原料,由于其生产过程能耗高,因此节能降耗成为丁二烯生产工艺的研究热点。利用Aspen Plus模拟软件对丁二烯精制工艺的两套流程进行了模拟研究,考察了分壁式精馏塔(DWC)中内部互连物流连接位置、预分离塔气液相流量和回流比对分离效果和热负荷的影响,对比了相同分离条件下DWC分离流程和传统顺序分离流程的能耗,并根据两套分离流程中塔内液相丁二烯浓度分布情况,分析DWC的节能原因。结果表明,当主塔理论板数105,预分离塔理论板数56,进入预分离塔气相流量1020kmol/h,液相流量890kmol/h,回流比7800时,DWC分离效果最好,丁二烯质量分数可达99.7%,这为DWC精制丁二烯工艺的工业化提供了理论依据。由于DWC有效减少了精馏过程中的返混效应,提高了能量利用率,使其冷凝器可节能29.36%,再沸器可节能29.19%,存在明显的节能优势。     

节能型分隔壁精馏塔分离烷烃混合物

在小型的分隔壁精馏塔装置上对烷烃混合物的分离进行了研究,考察了回流比、分配比以及实验开始时塔釜釜液中辛烷的质量分数对分离效果的影响。实验表明,最佳条件为回流比为5,分配比为1,实验开始时釜液中辛烷的质量分数为50%时,塔顶的正已烷含量达99.72%,侧线中正庚烷的含量达95.48%,塔釜辛烷的含量可达96.80%。采用Aspen plus对两塔分离流程与分隔壁精馏塔的能耗和设备投资进行了比较,结果显示,分隔壁精馏塔比两塔分离流程可节能22.3%,并可节约设备投资17.8%。     

隔板塔共沸精馏分离二氯甲烷-乙腈-水-硅醚体系

以二氯甲烷-乙腈-水-硅醚为分离体系,采用自制隔板塔小试装置,研究了共沸剂回流比和液相分配比等操作参数对隔板塔分离效果的影响。实验结果表明,当气相分配比R_v为0.5,共沸剂回流比为3时,液相分配比R_l在[0.12,0.2]范围内,隔板塔分离效果较好。在实验的基础上,采用Aspen Plus软件对隔板塔共沸精馏工艺进行模拟,考察了隔板塔共沸精馏工艺最佳操作区域及节能效果。模拟结果表明,特定分离要求下,隔板塔存在一个使再沸器热负荷最小的最佳操作区域,在此最佳操作区域内,R_l和R_v相互关联,呈一一对应关系;与三塔串联简单精馏工艺相比,完成相同的分离任务,隔板塔共沸精馏工艺再沸器节能32.74%,冷凝器热负荷减少33.70%,乙腈回收率由66.47%提高到96.01%,且大幅降低设备投资。     

Experimental study on pressure drops in a dividing wall distillation column

Previous studies in the fields of process design and process control [1] have shown the potential benefits that can be achieved through the implementation of thermally coupled distillation sequences, in particular, the dividing wall distillation column. The dividing wall distillation column meets important goals of process intensification, including energy savings, reduction in carbon dioxide emissions and miniaturization. In this paper, an experimental study on the hydrodynamic behavior of a dividing wall distillation column is presented. Several different values for gas and liquid velocities were tested in order to measure pressure drops and identify operational regions; the air/water system was used as the basis for the experimental setup. Results regarding pressure drops (fitted to the model of Stichlmair et al.) provide operational limits for the operation of the packed dividing wall distillation column. According to the results, the experimental dividing wall column can be operated at turbulent regime that is associated to proper mass transfer.     

用分隔壁精馏塔分离三组分混合物的节能研究

为了比较分隔壁精馏塔与常规精馏流程能耗,确定其应用范围,采用Aspen plus软件中的精馏严格模型,对2种常规精馏流程和3种分隔壁精馏塔进行模拟计算,比较了各种分隔壁精馏塔序的节能效果。结果表明,中间组分的摩尔分数越高,分隔壁精馏塔的节能效果越好,分隔壁精馏塔可用于分离中间组分摩尔分数较高的混合物,且适于分离指数在0.61至2.1之间的物系。分隔壁侧线精馏塔适用于分离指数≥1、轻组分摩尔分数较高的混合物。分隔壁侧线提馏塔适于重组分摩尔分数较高的混合物。     

4组分隔板塔热耦合精馏节能技术

对丙醇/丁醇/3-甲基丁醇/2-乙基丁醇组成的4组分物系的分离从完全热耦合原理出发,详细阐述了该物系精馏过程的建立模型到模拟计算,讨论了热耦合过程的自由度和隔板塔的最佳塔段数,指出了操作变量和完全热耦合在最佳热力学状态下应满足的条件,通过化工流程模拟软件Aspen Plus 11.1对该物系的分离工艺从简捷法到严格法计...     

反应精馏隔壁塔内合成乙酸甲酯的模拟

提出了一种应用反应精馏隔壁塔合成乙酸甲酯的新工艺流程,采用反应精馏隔壁塔替代常规反应精馏流程中的反应精馏塔及甲醇回收塔。利用Aspen Plus模拟软件,对反应精馏隔壁塔及常规流程进行了模拟,比较分析了两种流程塔内液相组成分布,并分析了塔顶回流比与气相分配比对反应精馏隔壁塔的影响。结果显示新流程可以节能11.9%,并能降低设备投资费用和操作费用。     

隔离壁精馏塔萃取精馏制无水叔丁醇研究

用隔离壁精馏塔萃取精馏制无水叔丁醇,在溶剂比为1.5,回流比为2∶1,叔丁醇原料进料速度为1.7 mL/min时,塔顶叔丁醇的质量分数达到99.6%;塔釜乙二醇的质量分数达到97.7%,可直接作萃取剂循环利用。用AspenPlus对该工艺和二塔萃取精馏工艺对比,结果与实验相一致,塔顶叔丁醇质量分数的相对误差为0.4%,塔釜乙二醇质量分数的相对误差1.3%。结果显示,该工艺比现有工艺省了1个塔、1个再沸器和1个冷凝器,节能27%,降低了能耗和设备投资。     

Energy saving in a crude distillation unit with a divided wall column

An energy-efficient crude distillation unit (CDU) with a divided wall column was introduced to evaluate its performance compared to the conventional CDU. The large energy demand of the CDU in the United States—equivalent to more than a half of biofuel produced—was reduced by applying a divided wall column to the unit also known as the energy-efficient distillation column. The divided wall column lowers mixing at feed tray and raises the thermodynamic efficiency of the CDU. The performance evaluation of the proposed unit indicates that the unit saves 37% of heat supply over the conventional unit and cooling by 17%. The economic analysis shows a 9% of investment saving and a 26% decrease in the utility cost from the proposed unit. The thermodynamic efficiency of the proposed CDU is improved by 8%. The modification of conventional CDU was minimal, suggesting an easy revamping of the current conventional CDUs.     

From simulation studies to experimental tests in a reactive dividing wall distillation column

The design and control of thermally coupled distillation sequences have been studied since many years, but the real implementation occurred until middle of the 1980s using a single shell divided by a wall named dividing wall distillation column. In this work, experimental results for the production of ethyl acetate in a reactive dividing wall distillation column are presented for first time. The experimental results are in agreement with those obtained using steady state simulations with AspenONE Aspen plus. These experimental results are important since it is possible to validate most of the previous results generated using simulations.     

间壁塔萃取精馏制取植物油抽提溶剂的研究

针对植物油抽提溶剂萃取精馏系统存在的萃取剂结焦问题展开研究,分析了萃取剂结焦的原因,提出了间壁塔萃取精馏制取植物油抽提溶剂的思路,并应用工艺模拟软件对比了间壁塔萃取精馏工艺和常规精馏工艺。模拟结果表明,间壁塔主塔合适的理论塔板数为30,侧线塔塔板数为10,剂油比为1.1(体积比),侧线采出位置为第27块板。与常规两塔精馏相比,再沸器热负荷降低约10%,冷凝器热负荷降低15%,且设备投资也有所减少。     

基于有效能分析的复杂精馏塔优化设计

提出了以有效能消耗最小为目标的复杂精馏塔优化设计新方法。给出了精馏塔优化设计模型及最佳进料位置、适宜理论板数NT、塔内换热器简约的确定方法,并以两组分正庚烷和乙苯的混合物为例进行设计与讨论。优化后的精馏塔含有中间换热器,与传统的简单塔有本质的区别,平衡线和操作线均处于相对平均的位置,更节能。     

Steady-state operation analysis of an ideal heat integrated distillation column

A systematic approach for the steady-state operation analysis of chemical processes is pro-posed.The method affords the possibility of taking operation resilience into consideration during thestage of process design.It may serve the designer as an efficient means for the initial screening ofalternative design schemes.An ideal heat integrated distillation column(HIDiC),without any reboileror condenser attached,is studied throughout this work.It has been found that among the various va-riables concerned with the ideal HIDiC,feed thermal condition appears to be the only factor exertingsignificant influences on the interaction between the top and the bottom control loops.Maximuminteraction is expected when the feed thermal condition approaches 0.5.Total number of stages andheat transfer rate are essential to the system ability of disturbance rejection.Therefore,more stagesand higher heat transfer rate ought to be preferred.But,too many stages and higher heat transfer ratemay increase the load of the compres     

Simulation and analysis of dehydration distillation column based on distillation mechanism integrated with neural network

In an industrial solvent dehydration distillation column (SDDC) model, the Murphree efficiency represents the separation ability of a distillation tray and the SDDC model’s performance depends on the value accuracy of the Murphree efficiency. Because there are many operation conditions having nonlinear effect on Murphree efficiency, it is difficult to determine its value. To develop a precise and robust SDDC model, a novel hybrid model combining distillation mechanism with neural network is proposed. In the SDDC hybrid model, the neural network is employed to model the nonlinear relationship between the operation conditions and Murphree efficiency, which is embedded into the SDDC mechanistic model. The results showed a good predicting and robust performance of the hybrid model under different operation conditions. Based on the hybrid model, the effect of the operation conditions on SDDC was analyzed to obtain some useful guiding rules for the SDDC operation.     

生物燃料乙醇分壁塔萃取精馏新工艺的研究

针对生物燃料乙醇生产中的"蒸馏-脱水"过程,建立基于分壁式萃取精馏塔的三塔工艺和两塔工艺,对2种工艺进行模拟计算,比较其分离效果和过程能耗。结果显示,在满足产品质量的前提下,三塔工艺比两塔工艺节约66.6%的冷凝器热负荷和77.9%的再沸器热负荷。对三塔工艺的分壁式萃取精馏塔的工艺条件进行优化,优化结果为,主塔回流比1.5,溶剂比1.0,原料进料位置为第22块板,隔板底端位置在第28块板,气相分配比为8.4。在优化工艺条件下对三塔工艺进行全流程模拟,可得到质量分数99.96%生物燃料乙醇和99.49%的水,回收萃取剂乙二醇质量分数为99.97%。     

Study of the structural characteristics of a divided wall column using the sloppy distillation arrangement

An efficient design method is proposed for determining the optimal design structure of a dividing wall column (DWC). The internal section of the DWC is divided into four separate sections and matched to the sloppy arrangement with three conventional simple columns. The light and heavy key component mole-fractions are used as the design variables in each column. The structure that gives superior energy efficiency in the shortcut sloppy case also brings superior energy efficiency in the DWC, while the optimal internal flow distribution of the DWC is different from that obtained from the sloppy configuration. Based upon an extensive simulation study, a two-step approach is proposed for the DWC design: the optimal DWC structure is first determined by applying the shortcut method to the sloppy configuration; the optimal internal flow distribution is then found from the corresponding DWC configuration. The simulation study shows that the DWC designed by the proposed method gives a near-optimal structure.     

Reactive column profile map topology: Continuous distillation column with non-reversible kinetics

In this paper we present a topologically based approach to the analysis and synthesis of reactive distillation columns. We extend the definition of Tapp et al. [Tapp, M., Holland, S., Glasser, D., & Hildebrandt, D. (2004). Column profile maps part A: Derivation and interpretation. Industrial and Engineering Chemistry Research, 43, 364–374] of a column section in non-reactive distillation column to a reactive column section (RCS) in a reactive distillation column. A RCS is defined as a section of a reactive distillation column in which there is no addition or removal of material or energy. We introduce the concept of a reactive column profile map (RCPM) in which the profiles in the RCPM correspond to the liquid composition profiles in the RCS. By looking at the singular points in the RCPM, it is demonstrated that for a single chemical reaction with no net change in the total number of moles, the bifurcation of the singular points depends on both the difference point as introduced by Hauan et al. [Hauan, S., Ciric, A. R., Westerberg, A. W., & Lien, K. M. (2000). Difference points in extractive and reactive cascades I-Basic properties and analysis. Chemical Engineering Science, 55, 3145–3159] as well as the direction of the stoichiometric vector. These two vectors combine to define what we call the reactive difference point composition. We show that there only certain feasible topologies of the RCPM and these depend only on the position of the reactive difference point composition. We look at a simple example where the vapour liquid equilibrium (VLE) is ideal and show that we can classify regions of reactive difference point compositions that result in similar topology of the RCPM. Thus, by understanding the feasible topologies of the RCPM, one is able to identify profiles in the RCPM that are desirable and hence one is able to synthesize a reactive distillation column by combining RCS that correspond to the desired profile in the RCPM.We believe that this tool will help understand how and when reaction could introduce unexpected behaviors and this can be used as a complementary tool to existing methods used for synthesis of reactive distillation columns.     

环己烯-己烷萃取精馏塔系统的改进

采用新型填料塔技术和新的工艺流程,对原环己烯分离塔系统进行改造,改造后环己烯分离塔塔顶环己烯从6.5%下降到4.0%,环己烯回收塔塔顶环己烷从3.5%～4%下降到2.5%,环己烯纯度从95%提高到97%以上。