间壁式精馏塔在芳烃分离工艺中的研究与应用

芳烃混合物由炼油厂的石脑油催化重整装置产生,芳烃分离物是重要的化工原料。传统工艺中,采用两塔序列从混合芳烃中依次分离出苯,甲苯,二甲苯和重组分等产品。本文以国内某石化企业实际芳烃分离工艺为研究对象,采用间壁式精馏塔工艺代替传统的两塔序列工艺,使用gPROMS模拟软件对新工艺过程进行建模和模拟计算。通过对间壁塔的回流比、气相分配比、液相分配比、塔顶产品量等参数的优化,在满足产品纯度要求下,得到了最优工艺操作条件。对两种工艺的分离效果的比较分析,表明间壁式精馏塔工艺比传统两塔序列工艺节能19.57%。     

基于改进分析的间壁塔节能效果评价

精馏过程是化工生产中应用最多,最重要的分离过程,同时也是耗能最大的单元操作。间壁精馏塔不仅大幅度提高了热力学效率,降低能耗,而且又减少了设备投资。与常规2塔分离序列相比,能够节省约30%左右的能量,因此在工业上得到了迅速应用。为了进一步研究间壁塔系统的节能潜力,本文基于可避免和不可避免损的概念,应用改进的?分析法对苯-甲苯-二甲苯间壁塔进行分析。以最小回流比下对应的损计算分离塔的不可避免损,通过最小传热温差计算换热器的损,从而分别计算出该体系中各单元设备的可避免损的大小,并指出在当今技术经济条件下,体系中各设备的节能潜力,指明改进方向。     

间壁塔内壁间有无换热对分离效果影响初探

间壁塔的应用显著提升了精馏操作的节能效果,减少了设备投资费用,受到了研究者的广泛关注。现有的研究和设计中尚未考虑间壁两侧传热对精馏过程的影响,但实际过程应当存在一定程度的热传递,对精馏操作的分离效果及其能量投入产生影响。为了研究间壁塔隔板的热传递对分离效果影响的趋势与程度,选择在能量投入一定的情况下分析分离效果的变化。本文以丙烷、正丁烷、正戊烷三组分精馏为例,研究当能量输入一定时,间壁塔各塔板浓度与温度参数变化情况,对间壁传热对分离效果影响的趋势与程度做一初探。计算结果表明,对该体系塔釜加热量不变时,首先,间壁塔的间壁传热使得各个组分的产品纯度下降,对分离效果不利;其次,不同间壁传热系数与不同塔板间匹配方式的间壁换热对分离效果不利影响的程度不同。本文对该体系与假设下的传热影响趋势与程度的分析,可以为间壁塔相关工程设计提供一定的参考。     

三类典型间壁式精馏塔分离给定BTX物系的效果探究

间壁式精馏塔(DWC)利用间壁形成特殊的塔内部结构,从而实现精馏过程的节能以及过程设备的综合。在实际生产中待分离三组分原料组成、间壁安装位置将影响间壁式精馏塔的节能效果。本文以苯-甲苯-二甲苯(BTX)三组分精馏为研究对象,使用gPROMS过程模拟软件,建立基于MESH方程的三类典型间壁式精馏塔模型,研究当进料组成和产品纯度一定时,三类典型间壁安装位置的间壁式精馏塔的能量投入情况,探究间壁式精馏塔选用的一般原则。计算结果表明,对本研究体系,在进料轻组分摩尔比小于0.5时或中间组分大于0.4时亦或重组分大于0.2小于0.6时,应选用完全热耦合间壁式精馏塔;只有在轻组分较多时,选用间壁式侧线提馏塔;在重组分较多时,选用间壁式侧线精馏塔。本文对三类典型间壁式精馏塔分离不同组成原料的节能情况进行分析,可以为间壁塔的设计选用提供一定的参考。     

一种新型节能回收N,N-二甲基甲酰胺的过程研究

提出了从废水中回收N,N-二甲基甲酰胺(DMF)的萃取-精馏法节能新工艺,利用Aspen Plus软件对该回收过程进行了模拟计算,详细分析了各个因素对分离效果的影响,并进行能耗比较。结果表明,采用萃取-精馏分离工艺,以氯仿为萃取剂能够很好地实现DMF与水的分离,较佳的操作条件为:萃取塔理论塔板数22,溶剂比2.84,精馏塔理论塔板数18,进料位置7,回流比0.08,精馏塔塔釜DMF含量可达99.98%。与单塔精馏法、双塔精馏法、传统三塔精馏法和节能型三塔精馏法相比,节约能耗分别为78.6%、56.4%、28.8%年和30.1%,节能效果显著,为回收废水中DMF提供理论和设计依据。     

双效精馏在MTP装置废水处理中的应用

甲醇制丙烯(MTP)装置在生产丙烯的同时,产出大量含低浓度甲醇的废水,采用传统单塔分离甲醇和水能耗较大。本文在单塔分离的基础上,采用双效精馏技术,在有效分离甲醇和水的同时大幅度降低了分离能耗。本文首先对逆流、平流和顺流双效精馏技术的分离和节能效果进行了对比和优选,并对优选分离方案的工艺参数进行了考察及优化。结果表明,在MTP装置废水处理中,平流双效精馏技术为较优的节能方案。与单塔分离相比,在实现分离目标的同时可节约能耗20.04%左右,达到了节能降耗的目的。     

甲苯二胺分离过程的综合

传统的甲苯二胺分离工艺存在一些缺点，如甲苯二胺产品的纯度不高、过程的能耗大等。在通用化工模拟软件中对多塔连续精馏流程进行模拟分析，并结合生产实际提出过程的约束条件，以能耗最小为目标对分离过程进行优化，得到各塔的最优操作条件。在此基础上，对过程中的换热网络进行综合，得到热集成流程。该热集成流程在最优条件下操作时，产品的纯度满足生产要求，而且能耗比原流程减少约30％。     

合成气制乙二醇粗产品提纯工艺的模拟研究

本文利用流程模拟软件Aspen Plus对合成气制乙二醇粗产品的提纯工艺进行研究,通过选用合适的热力学方法、分离模块和恰当的分离顺序等对合成气制乙二醇生产过程中产品的提纯工艺进行了模拟研究。运用Aspen中灵敏度分析工具分别对乙二醇分离过程中的脱甲醇塔、中杂塔、脱乙醇塔、脱丁二醇塔系和精制塔等进行模拟和优化,对与乙二醇形成共沸的组分1,2-丁二醇,文中对比了共沸精馏和萃取法两种分离方法,最终选择了分离效率高、能耗小的萃取方法。通过对各个塔的理论塔板数、进料位置以及回流比等参数的模拟确定了其最优操作条件。并基于这些最优操作条件和连续萃取的分离方法,对整个提纯工艺进行了模拟,得到了纯度较高的乙二醇产品和甲醇、1,2-丁二醇等副产品。论文的结果将为乙二醇的工业生产提供参考。     

带有热量集成的乙醇-水萃取精馏过程模拟

使用Aspen Plus,首先对乙醇-水萃取精馏过程的7种萃取剂的分离效能进行了模拟比较,结果显示:丙三醇DMSO乙二醇DMF糠醛苯甲醛NMP;接着,以丙三醇为萃取剂,设计了最优的萃取精馏工艺流程,并确定了萃取精馏过程中萃取精馏塔(理论板数:16,回流比:2,原料进料位置:12,萃取剂的进料量:230 kmol/hr和进料位置:4)和溶剂回收塔(理论板数:7,进料位置:3和回流比:3)的最佳工艺条件;最后,本文还利用热量集成的方法对系统的废热进行了回收利用,不但节约能耗3262.72 kW,还顺产1 MPa低压蒸汽127 kmol/hr。本研究为乙醇.水萃取精馏分离工艺的工业化提供了理论依据和设计参数。     

甲醇制烯烃分离工艺的热集成

本文利用Aspen Plus软件对甲醇制烯烃分离工艺中的前脱丙烷-中冷丙烷吸收工艺进行了模拟分析。在模拟分析基础上,通过降低乙烯精馏塔和脱丁烷塔的操作压力,实现了塔间的热集成;同时,对丙烯精馏塔进行了热泵精馏模拟。经过热集成优化后,系统综合能耗降低了38.8%,表明在前脱丙烷-中冷丙烷吸收分离流程中应用热集成技术优化工艺具有显著的节能效果。     

用分隔壁精馏塔分离松节油中蒎烯的模拟

提出采用分隔壁精馏塔代替常规精馏塔序列分离松节油以得到α-蒎烯和β-蒎烯的新工艺。为了选择适合松节油体系的分隔壁塔结构,采用Aspen软件分别模拟计算了DWC、DWC-SS和DWC-SR三种塔型,结果表明,与常规工艺相比DWC塔可节能26%,DWC-SS塔可节能16.6%,DWC-SR塔可节能12.5%。在此基础上考察了DWC塔进料位置、回流比、隔板位置、气液相分配比和中间产品出料位置对分离效果和热负荷的影响,得出气液相分配比是影响分隔壁塔操作稳定性的主要因素。     

分隔精馏塔分离烷烃混合物的模拟

提出采用分隔精馏塔替代常规精馏塔分离烷烃混合物的新工艺。通过Aspen模拟和灵敏度分析,着重探讨分隔精馏塔中进料位置、回流比、连接流的位置、回流气液分配比等工艺参数对分离效果和热负荷的影响,并确定分隔精馏塔的最佳操作条件是。结果表明,分隔精馏塔单塔就能达到常规的烷烃分离要求,但是对精馏塔的控制要求更高。能耗分析表明分隔精壁塔工艺比传统的分离过程节能45%。     

Operation of divided wall column with vapor sidedraw using profile position control

Divided wall column is a promising energy-alternative for separation process which is capable of achieving typically 30% energy and capital cost savings compared with a conventional distillation system. Despite such advantages, divided wall column (DWC) is not widely used from the fear to run into controllability problems due to the DWC complexity. A profile position control scheme was proposed to overcome the control problems. Relative gain array analysis and singular value decomposition were used to determine optimal control configuration. Dynamic simulation showed that the profile position–product composition cascade control can keep the product purities at the desired values in the face of feed and internal disturbances.     

Decentralized control and identified-model predictive control of divided wall columns

As a thermal separation method, distillation is one of the most important separation technologies in the chemical industry. Given its importance, it is no surprise that increasing efforts have been made in reducing its energy inefficiencies. A great deal of research is focused in the design and optimization of the divided-wall column (DWC). Its applications are still reduced due to distrust of its controllability and robustness. Previous references have studied the decentralized control of DWC but still few papers deal about model predictive control (MPC) applied to DWC.In this work we present a decentralized control of both a divided-wall column along with its equivalent MPC schema, both approaches are compared. Instead of building a rigorous model or performing the step test to an existing plant, the MPC model is obtained by identification of a rigorous simulation. An ARX model is demonstrated to represent adequately the DWC column behavior. This approach might be very convenient if plant testing is not available.     

Comparison of pressure-swing distillation and extractive distillation with varied-diameter column in economics and dynamic control

Pressure-swing distillation and extractive distillation are two common methods for azeotrope separation. The economics and controllability are two crucial factors for evaluating the feasibility of a separation process. A varied-diameter column (VDC) was used in the process design to evaluate its economics and controllability. Five azeotropic systems were investigated in order to compare the economics of pressure-swing distillation and extractive distillation with a VDC. Results indicate that pressure-swing distillation with a VDC saves more money than extractive distillation. The dynamic control were evaluated in the acetone-methanol system for both processes with a VDC. The improved control structure for pressure-swing distillation with a VDC can handle ±20% disturbances effectively, while the improved control structure for extractive distillation with a VDC can only handle ±10% disturbances. A comparison of the two methods from the viewpoint of economics and controllability demonstrates that pressure-swing distillation is more suitable when using a VDC.     

A wave propagation approach for reduced dynamic modeling of distillation columns: Optimization and control

Reduced models enable real-time optimization of large-scale processes. We propose a reduced model of distillation columns based on multicomponent nonlinear wave propagation (Kienle 2000). We use a nonlinear wave equation in dynamic mass and energy balances. We thus combine the ideas of compartment modeling and wave propagation. In contrast to existing reduced column models based on nonlinear wave propagation, our model deploys a hydraulic correlation. This enables the column holdup to change as load varies. The model parameters can be estimated solely based on steady-state data. The new transient wave propagation model can be used as a controller model for flexible process operation including load changes. To demonstrate this, we implement full-order and reduced dynamic models of an air separation process and multi-component distillation column in Modelica. We use the open-source framework DyOS for the dynamic optimizations and an Extended Kalman Filter for state estimation. We apply the reduced model in-silico in open-loop forward simulations as well as in several open- and closed-loop optimization and control case studies, and analyze the resulting computational speed-up compared to using full-order stage-by-stage column models. The first case study deals with tracking control of a single air separation distillation column, whereas the second one addresses economic model predictive control of an entire air separation process. The reduced model is able to adequately capture the transient column behavior. Compared to the full-order model, the reduced model achieves highly accurate profiles for the manipulated variables, while the optimizations with the reduced model are significantly faster, achieving more than 95% CPU time reduction in the closed-loop simulation and more than 96% in the open-loop optimizations. This enables the real-time capability of the reduced model in process optimization and control.     

Actuator fault monitoring and fault tolerant control in distillation columns

This paper presents, from a practical viewpoint, an investigation of real-time actuator fault detection, propagation and accommodation in distillation columns. Addressing faults in industrial processes, coupled with the growing demand for higher performance, improved safety and reliability necessitates implementation of less complex alternative control strategies in the events of malfunctions in actuators, sensors and or other system components. This work demonstrates frugality in the design and implementation of fault tolerant control system by integrating fault detection and diagnosis techniques with simple active restructurable feedback controllers and with backup feedback signals and switchable reference points to accommodate actuator fault in distillation columns based on a priori assessed control structures. A multivariate statistical process monitoring based fault detection and diagnosis technique through dynamic principal components analysis is integrated with one-point control or alternative control structure for prompt and effective fault detection, isolation and accommodation. The work also investigates effects of disturbances on fault propagation and detection. Specifically, the reflux and vapor boil-up control strategy used for a binary distillation column during normal operation is switched to one point control of the more valued product by utilizing the remaining healthy actuator. The proposed approach was implemented on two distillation processes: a simulated methanol-water separation column and the benchmark Shell standard heavy oil fractionation process to assess its effectiveness.     

认知OFDM系统中基于能耗受限的频谱感知方法

针对传统频谱感知方法没有考虑能耗受限对认知系统的影响,以认知正交频分复用(OFDM)系统为背景,提出一种基于能耗受限的联合优化频谱感知方法。该方法基于传统能量检测方法,以最大化吞吐量性能为目标,将频谱感知问题建模为一个优化问题,联合多个频带选取最优感知时间和判决门限参数,使其在能耗受限的情况下,总吞吐量达到最大。仿真结果表明,与传统使用能耗均分的检测方法相比,该方法具有更大的吞吐量,能够更好地节约能耗。     

有序搜索法加调优法研究有机硅单体的分离序列

针对有机硅单体混合物(甲基氯硅烷混合物)中组分较多、分离塔系复杂的特点,提出了利用有序搜索法加调优法研究其最优分离序列的方法。利用AspenPlus模拟软件中的DSTWU模块和WILSON热力学计算模型,对提出的合成序列中涉及到的各分离子问题进行初步模拟计算。将模拟结果代入相关的费用计算模型,并利用探试成本函数概念,估算不同切割位置分离序列的年总成本。以年总成本最低为目标函数,利用有序搜索法递减确定不同组分混合物的最佳切割点。结果表明,序列Ⅰ为最佳切割点分离序列。然后,以序列Ⅰ作为初始序列,提出相关的3组相邻分离序列,采用渐进调优法对其进行调优。利用AspenPlus模拟软件中的RADFRAC严格精馏计算模块对以上4组分离序列进行精确模拟计算,分别对其各塔的进料位置和回流比进行优化,将优化结果代入相关的费用计算模型,计算并比较以上4组序列的年总成本。研究结果表明,序列Ⅳ的年总成本最低,较初始序列Ⅰ的年总成本降低了2.31%,因此选择序列Ⅳ作为分离有机硅单体混合物的最优方案是合适的。