Adaptive generalised predictive control of high purity internal thermally coupled distillation column

Internal thermally coupled distillation column (ITCDIC) is a frontier in the energy‐saving distillation researches. One of the bottlenecks to prevent the column from being commercialised is the difficulty in control design due to the high sensitivity to disturbances, strong asymmetric nonlinearity and inverse response especially under high purity. An adaptive multivariable generalised predictive control (AM‐GPC) strategy of ITCDIC process is proposed to solve the difficulties in high purity. The simulation results of AM‐GPC are compared with single input and single output GPC (S‐GPC), multivariable GPC (M‐GPC), modified IMC (M‐IMC) and traditional PID control in detail. The performances confirm the accuracy and validity of AM‐GPC for the high‐purity ITCDIC process. © 2011 Canadian Society for Chemical Engineering     

Generalized generic model control of high‐purity internal thermally coupled distillation column based on nonlinear wave theory

A new model‐based control strategy for the internal thermally coupled distillation column (ITCDIC) is presented. Based on the nonlinear wave theory that describes the nonlinear dynamics in the separation processes, a simplified nonlinear wave model is established that concerns both the wave propagation and the profile shape. An advanced controller (WGGMC) is formulated by combining the nonlinear wave model with a generalized generic model control (GGMC). Compared with a conventional generic model controller based on a data‐driven model (TGMC), and another wave‐model based generic model controller (WGMC) developed in our previous work, WGGMC exhibits the best performances in both servo control and regulatory control. Furthermore, WGGMC can handle a very‐high‐purity system of ITCDIC with top product composition of 0.99999, while the other two controllers fail to work. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4133–4141, 2013     

基于一般模型控制的高纯内部热耦合精馏策略

内部热耦合精馏塔（ITCDIC）是精馏节能控制的一个前沿。本文提出了一种基于一般模型控制（GMC）的内部热耦合精馏塔的先控策略,以解决导致传统线性控制策略难以得到较好控制效果的高纯下内部热耦合精馏塔的非线性。以苯-甲苯物系作为研究实例,对所提出的高纯ITCDIC控制策略进行了详细研究。设定值改变和过程扰动下的控制品质表明了所提出的高纯ITCDIC的GMC控制策略的切实有效性。     

基于内部热耦合精馏塔非线性wave模型的高纯控制

首先建立内部热耦合精馏塔（ITCDIC）的非线性波动降阶模型,并将非线性波动理论（wave）应用到ITCDIC控制问题中,实现一般模型控制（GMC）方案.与传统控制方案相比,基于波动理论的一般模型控制（waveGMC）不再采用ITCDIC的近似线性模型,更好地解决了高纯控制过程中的非线性问题,通过对波形的速度和位置控制能够在短时间内使系统达到稳定.苯-甲苯物系的实例研究表明,ITCDIC波动模型在高纯控制过程中能够精确反映ITCDIC的动态特征,waveGMC控制方案较传统控制方案更加稳定可靠.     

内部热耦合精馏塔基于非理想物系的最优评价

Internal thermally coupled distillation column(ITCDIC) is a frontier in energy saving distillation research. In this paper, the optimal assessment on the energy saving and the operating cost for ITCDIC of nonideal mixture is explored. An evaluating method is proposed, and the pertinent optimization model is then derived. The ethanol-water system is studied as an illustrative example. The optimization results show that the maximum energy saving in ITCDIC process is about 35% and the maximum operating cost saving in ITCDIC process is about 30%,as compared with a conventional distillation column(CDIC) under the minimum reflux ratio operating; the optimal operating pressure of the rectifying section is found to be around 0.25 MPa; the effects of the feed composition,operating pressure and the heat transfer rate on operation are also found and analyzed. It is revealed that ITCDIC process possesses high energy saving potential and promising economical prospect.     

Modeling,Control, and Optimization of Ideal Internal Thermally Coupled Distillation Columns

Internal Thermally Coupled Distillation Columns (ITCDIC) are the frontier of energy saving distillation research. In this paper, the ideal ITCDIC is considered. A novel mathematical model and a related simulation algorithm are proposed. The dynamic responses of open‐loop, PID controllers and the responses of closed‐loops are carried out. The results show that the ITCDIC is a self‐balance process and could be operated smoothly with two PID controllers; the steady‐state optimization met the need of ITCDIC optimization. Furthermore, a steady‐state optimization model of the operation parameters is presented, which can be used to directly obtain the optimal operation parameters simultaneously guaranteeing not only the product quality and the maximum energy savings but also the dynamic operability and controllability. The benzene‐toluene system is studied as an illustrative example.     

Nonlinear wave modeling and dynamic analysis of internal thermally coupled distillation columns

Internal thermally coupled distillation column (ITCDIC) is a frontier in the energy saving distillation research. It is well known for the complex dynamics, which challenge the establishment of an excellent reduced model for further control strategy design greatly. In this article, a physical approach of the ITCDIC process based on nonlinear wave theory is explored, where it is first discovered that traditional wave theory in conventional distillation columns (CDIC) could not be directly applied in ITCDIC, due to: First, the internal thermal coupling results in mole flow rates varying evidently over each stage, which not only makes the wave modeling of the wave phenomenon in ITCDIC more difficult but also makes wave dynamics greatly different between ITCDIC and CDIC; Second, an interesting wave phenomenon of ITCDIC is discovered that waves located in the rectifying section and stripping section travel under opposite tendencies when the steady state is disturbed by the step change of thermal condition q, one sharpens and the other is likely to spread synchronously, it means the movement of wave profiles in ITCDIC could not be simply described by shock wave velocity, which is usually used in wave modeling of CDIC; more seriously, shapes of the self‐sharpening wave profiles in ITCDIC change obviously during the traveling processes, which further reveals that shape influence on wave velocity has to be considered in the wave modeling of ITCDIC. A rigorous wave velocity and a natural wave velocity are derived, respectively, based on which, the detailed analyses of traveling wave characteristics are carried out. A novel wave velocity, based on the profile trial function which has been well developed by Marquardt, is further derived to consider the obvious change of profile shape. And a completed nonlinear wave model of ITCDIC is thereby established by combining the proposed wave velocity with thermal coupling relations and material balance relations. The benzene‐toluene system is illustrated as an example, where component concentration prediction and distinct dynamic characteristics are carried out in detail based on the proposed nonlinear wave models. The research results reveal the accuracy and validity of the proposed nonlinear wave model of ITCDIC. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

基于内模控制的内部热耦合精馏策略

精馏过程约占工业总能耗的1/3,其节能控制潜力很大。内部热耦合精馏(ITCDIC)是迄今为止所提出的节能效果最好(比常规精馏节能40%以上)却没有商业化的节能技术。主要原因在于该过程具有较强的非线性、复杂的动态特性以及耦合性,给控制方案的设计带来了极大的困难。通过建立更为精确的二阶内部模型,提出了一种有效的ITCDIC内模控制方案。实例研究结果表明,与传统控制方案PID相比,控制品质更加稳定可靠;同时,与目前国际上公开报道的最好结果相比,该控制方案有更广泛的操作域,鲁棒性更强。     

Thermodynamic analysis, simulationand optimization on energy savings of ideal internal thermally coupleddistillation columns

Internal thermally coupled distillation columns (ITCDIC) are the frontier of distillation energy saving research. In this paper, a novel energy saving model of ideal ITCDIC and a simulation algorithm are presented,upon which a series of comparative studies on energy savings with conventional distillation columns are carried out. Furthermore, we present an optimization model of ideal ITCDIC, which can be used to achieve the maximum energy saving and find the optimal design parameters directly. The binary system of benzene-toluene is adopted for the illustrative example of simulation and optimization. The results show that the maximum energy saving of ITCDIC is 52.25% (compared with energy consumption of conventional distillation under the minimum reflux ratio operation); the optimal design parameters are obtained, where the rectifying section pressure and the feed thermal condition are Pr=0.3006 MPa and q=0.5107 respectively.     

内部热耦合精馏塔的初步设计(I) 模型化和操作分析

引　言将热量从精馏段传到提馏段来实现节能是精馏过程节能的一种有效方法 ,即二次回流和蒸发[1](ＳＲＶ) .内部热耦合精馏塔 (ＩＴＣＤＩＣ)的热耦合机理仍是ＳＲＶ方法 ,但去掉了再沸器和冷凝器 ,具有较大的节能潜力 .它的研究只有近 1 0年的历史[2 ,3],目前 ,还没有见到详细的操作分析和设计优化的文献报道 ,只有一些较为相关的文献[4 ,5 ].本文对理想热耦合精馏塔进行了建模和操作分析 .1　模型化图 1是ＩＴＣＤＩＣ的示意图 .精馏段和提馏段被分为两个塔 .热耦合通过两段之间的热交换器来实现 .为了提供传热必须的推动力 ,精馏段将在较…     

内部热耦合空分塔的节能优化分析

内部热耦合精馏是迄今为止所提出的节能效果最好,而唯一没有商业化的节能技术。将内部热耦合技术用于空分塔,可以带来良好的节能效果。根据低温空气分离过程以及三组分精馏的特点,提出了一种新的内部热耦合空分精馏塔优化模型。在优化模型基础上,对热耦合塔进行了深入的节能优化与分析,并且与常规空分仿真结果进行了比较分析,压缩机能耗下降20.75%,产值增加17.46%,单位产值能耗下降32.53%。内部热耦合空分塔的提取率以及能耗均优于常规热耦合空分塔,节能效果显著。     

二异丁烯反应精馏生产过程控制策略设计

二异丁烯是一种重要的化工中间体,近年来研究者提出了以催化裂化C₄为原料、采用反应精馏技术同时生产高纯二异丁烯和汽油添加剂的新工艺。由于反应精馏过程中非线性程度高,稳定控制困难,使得采用反应精馏技术生产二异丁烯过程的控制策略研究较少。采用Aspen dynamic软件进行动态模拟,针对反应精馏生产二异丁烯过程开发了温度控制方案、组分温度联合控制方案和组分温度串级控制方案。对3个控制系统进行（±10）%的进料流量扰动和（±5）%组成扰动测试并进行对比。结果表明：组分温度串级控制方案在添加扰动的情况下依然保证了二异丁烯质量分数99%,三异丁烯质量分数小于10%以及异丁烯转化率大于99%的要求,并且最终稳定时间约5 h,具有更好的抗干扰性能。研究结果能够为二异丁烯产品的生产工艺工业化应用提供设计依据。     

甲醇-苯共沸体系变压精馏分离工艺的动态控制

基于甲醇和苯共沸体系的压敏性,利用Aspen Plus和Aspen Dynamics软件对变压精馏分离该体系的稳态工艺进行了模拟和优化,研究了该工艺的动态特性,提出了控制产品纯度的3种控制结构：基础控制结构、比例控制结构和双比例与温度?组分联合控制结构,通过对控制结构添加±20%的组分和流量干扰测试控制结构的稳定性. 结果表明,基础控制结构基本能实现稳健控制,但不能解决组分干扰引起的产品纯度偏差过大等问题;比例控制结构可实现相对稳健的控制,但改进效果不显著;双比例与温度?组分联合控制结构在受到20%进料和组分干扰后,产品纯度能较快恢复至设定值的99.90%,实现稳健控制.     

Active disturbance rejection generalized predictive control for a high purity distillation column process with time delay

High purity distillation processes have been widely used in the chemical industry. These processes have unique characteristics including higher order, nonlinearity, strong coupling, and time delay. In order to overcome these control issues, an active disturbance rejection generalized predictive control strategy is designed for the distillation column with time delay. The strategy combines the structures of both active disturbance rejection control and generalized predictive control. A delayed designed extended state observer can estimate the model uncertainty and external disturbance, and a non‐incremental generalized predictive control is proposed to deal with the integrators with time delay. Therefore, it rejects disturbances well and has the capability of overcoming time delay. The computation load is also less than the generalized predictive control. In the simulation experiments, the proposed strategy is compared with robust control and model predictive control. The results illustrate that the proposed control strategy has improved robustness performance in dealing with model uncertainties, various disturbances, and time delay.     

Modeling,Characteristic Analysis and Optimization of an Improved Heat‐Integrated Air Separation Column

Cryogenic air separation as the most important part of an integrated gasification combined cycle is a widely used operation unit for producing large quantities of high‐purity oxygen and nitrogen. However, cryogenic distillation requires a large amount of energy due to the work needed to compress the air feed. An improved heat‐integrated air separation column (HIASC) is proposed. The requirements of high‐purity separation in the industrial cryogenic air separation process are achieved. An optimization model of the heat transfer coefficient (UA), a key parameter in column structure design and operation, is presented. The optimized UA value is obtained within the accepted value range reported in the international open literature, which ensures the practicability of the improved HIASC.     

内部热耦合精馏塔的初步设计(II) 控制分析和参数优化

Based on the previous design model, degrees of freedom analysis and transient analysis are carried out. A PID control model is proposed. The results show that ITCDIC is a self-regulating process, and could be operated smoothly with two PID controllers; the steady state design could be disassociate with the dynamic design. An optimization model of ITCDIC design parameters is derived, which can directly achieve the optimal design parameters providing the maximum energy savings and the product quality simultaneously. Benzene-toluene system is studied as an illustrative example.     

内部热耦合精馏塔的初步设计(II) 控制分析和参数优化

引　言研究表明[1,2 ],控制和设计优化往往是节能方法实际应用中的主要困难 .关于二次回流和蒸发(ＳＲＶ)、Ｐｅｔｌｙｕｋ、热交换网络 (ＨＥＮ)等方法的控制设计已经有了大量的研究[3,4].这些研究方法可以借鉴到内部热耦合精馏塔 (ＩＴＣＤＩＣ)的控制研究上[5 ].本文对理想ＩＴＣＤＩＣ进行了自由度分析、暂态分析和ＰＩＤ控制研究 ,并进行了设计参数的优化和分析 .目前 ,尚未见到设计优化的文献报道 .1　自由度分析对于理想二元混合物 ,ＩＴＣＤＩＣ动态系统由6.5ｎ 1 0个独立方程 (ｅ)、 6.5ｎ 2 7个变量υ构成 ,系统的自由度为 ｆ =…     

Synthesis of High‐Purity Methylal via Extractive Catalytic Distillation

An integrated continuous process, which combines catalytic distillation and extractive distillation in one column, is investigated for the synthesis of high‐purity methylal from methanol and formalin in the presence of a cation‐exchange resin catalyst. A feed with methanol:formaldehyde 2:1 molar ratio is chosen to evaluate the effects of operating parameters, such as extractant feeding position, ratio of extractant to feed, reflux ratio, and reboiler temperature, on the continuous synthesis of methylal. Under the optimum operating conditions and with water as extractant, the extractive catalytic distillation process operated continuously, producing a methylal purity of 98.7 % (H₂O: < 1.30 %) with 98.0 % formaldehyde conversion.     

Model based control of a high purity distillation column

In this paper, the problem of dual product composition control of an industrial high purity distillation column, a deisohexanizer (DIH), is addressed using a Generic Model Control framework. A dynamic simulation of the DIH was performed for preliminary studies of the performance of different controller strategies/algorithms. The performance of Generic Model Control incorporating different process models was studied. Process models are presented ranging from simple first order approximations to mechanistic short cut distillation models where a tradeoff between model complexity and model adaptivity is investigated. The different controllers were implemented and compared using a dynamic simulation of an industrial deisohexanizer (DIH) to select the best condidate controller. A controller using a nonlinear process model emerged as the best controller and was implemented on the actual process, resulting in improved performance over the original controller. Simulation results and industrial plant data are presented.     

Dehydration of Methanol to Dimethyl Ether by Catalytic Distillation

The kinetics of liquid catalytic dehydration of methanol over an ion exchange resin (Amberlyst 35) has been determined for the temperature range 343 to 403 K using a batch reactor. The experimental data are described well by an Eley‐Rideal type kinetic expression, for which the surface reaction is the rate‐determining step. A catalytic distillation process for methanol dehydration to dimethyl ether (DME) has been modeled using the experimentally determined kinetic data. The results were incorporated into the rate‐controlled reaction mode for RadFrac, a part of the commercial simulation program Aspen Plus. It was shown that synthesis of high purity DME can be achieved using a single catalytic distillation column. Thus there is significant potential for reduction of overall capital cost for a plant for methanol dehydration to DME when compared to conventional production facilities that involve separate reaction and distillation processes.