Control and optimization of the divided wall column

The divided wall column (DWC) is, in terms of capital costs and energy savings, a promising alternative for separating ternary mixtures. Since its design was proposed, almost 50 years ago, many authors have addressed design considerations. Operation and control of the DWC have received much less attention. However, some works have been published recently. Preliminary results reported indicate that feedback diagonal control structures may be used to control the DWC. In this work, the study of feedback diagonal control strategies has been further extended to consider the DWC control design in detail. Different control structures have been systematically analyzed and compared under performance and robustness considerations. In order to study the effect of the energy optimization on the controllability of the DWC, a column at optimal nominal operating conditions is compared to a column under non-optimal operation. Finally, a complete control strategy is proposed. Linear analysis tools are used for the multiple input multiple output (MIMO) feedback control analysis, and simulations using a non-linear model are performed to study the non-linear behavior of the control systems.     

隔板精馏塔分离氯化亚砜的模拟及工艺优化

利用AspenPlus软件对常规的两塔间接序列精馏工艺分离氯化亚砜进行了模拟计算,并提出了一种新型分离工艺—隔板精馏塔工艺。通过对隔板精馏塔的模拟计算,研究了预分离段进料位置、侧线采出位置、回流进料比和分配比对产品纯度和再沸器能耗的影响,结果说明最佳的工艺条件为:预分离段第6块板进料,主塔第55块板采出,回流进料比为4.45,液相分配比为1.60,汽相分配比为1.98。将隔板塔在最佳操作条件下的能耗与常规两塔工艺操作能耗和设备投资进行比较,隔板精馏塔节约冷凝器负荷和再沸器负荷分别为34.62%和34.64%;然后运用专业的设备投资计算软件CAPCOST计算2种工艺设备投资,结果表明,隔板精馏塔新工艺可以降低17.27%的设备投资。综上可知隔板精馏分离氯化亚砜是一种节能、高效的新型分离工艺。     

基于热耦合的分隔塔装置的研究进展

从热耦合的角度介绍了几种新型的精馏装置—分隔塔 ,着重于介绍分隔塔在三组分、四组分混合物的分离上的应用 ,并给出了用于三组分分离的分隔塔的数学模型。     

Controllability and energy efficiency of a high-purity divided wall column

The divided wall column system is a promising energy-saving alternative for separating multi-component mixtures. However, high energy efficiency and stable operations can only be achieved with careful design of steady state operation and control scheme. In this study, the effects of liquid split and vapor split ratios on the energy efficiency and controllability of a divided wall column system for separating ethanol, n-propanol, and n-butanol were investigated. A region with high energy efficiency was identified. However, relative gain analysis found that the performance of multi-loops composition control would be very poor. Dynamic tests showed that multi-loop temperature control cannot return the product compositions to the desired values in case of feed composition disturbances. Outside this region, composition control can compensate for external disturbances such as feed flow rate and feed composition changes but not changes in operating region caused by internal variations such as liquid and vapor splits. Offsets in the product purities were found if temperature controls were used and there are disturbances in feed composition or changes in operating region caused by upsets in liquid and vapor splits. There is a trade-off between energy efficiency and controllability. A composition + temperature cascade scheme was proposed to stabilize the operation with high energy efficiency. The proposed scheme was able to maintain high product purity and reject external disturbances in feed flow and composition changes as well as internal disturbances such as changes in liquid and vapor splits.     

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。     

Response surface methodology in optimization of a divided wall column

dividing wall column (DWC) is a thermally coupled distillation system with a high energy efficiency that requires lower space and investment compared to the conventional column system. The design of a DWC involves a number of structural and process parameters that need to be optimized simultaneously to improve energetic and economic potential and reduce space requirement. We used response surface methodology (RSM) to optimize DWC nonlinearly and to figure out the effect of parameters and their interactions on energy consumption, product quality, and dimensions of a DWC. Results demonstrate that process variables have significant effects on the energy efficiency of a DWC as compared to the effect of structural variables. The optimum DWC parameters can be found by RSM with minimal simulation runs and the prediction results of RSM agree well with the rigorous simulation results.     

隔板塔气体调配装置数值模拟及实验研究

针对隔板塔中隔板两侧气体分配比难以调节的问题,提出了一种新型隔板塔气体调配装置。利用计算流体力学软件STAR-CCM+对该装置的性能进行了模拟分析,并经实验研究对模拟结果进行验证;对不同塔径下升气槽个数进行了模拟研究。结果表明:该气体调配装置能够有效地调节气体在隔板两侧的分配,并且气体通过该装置后分布较均匀,成功实现了气相在隔板塔内的分配控制,实验结果和模型模拟值符合良好。     

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。     

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。     

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.     

Application of a divided wall column for gas separation in floating liquefied natural gas plant

A divided wall column (DWC) has widely been utilized as an energy-efficient distillation column. When it is applied to the offshore floating liquefied natural gas (FLNG) plant, its compactness can provide a favorable distillation system for the unconventional plant on top of its high energy efficiency. We investigated the design characteristic, cost evaluation and operation difficulty of the DWC at its utilization in the FLNG plant. The results from the HYSYS simulation of the DWC were compared with those of the conventional distillation system, and the following was found from the study. The DWC replacing the depropanizer and debutanizer of the conventional distillation system requires 12.5% less investment cost. While the saving of 25% in steam cost is expected from the DWC, the total utility cost including the refrigerant cost is reduced by 20.2% due to the lower cost reduction of refrigeration in the DWC.     

Reactive dividing wall column for hydrolysis of methyl acetate:Design and control☆

Reactive distillation and dividing wall column distillation are two kinds of effective separation technologies, and their integrated configuration, reactive dividing wall column (RDWC), presents attractive advantages. In this study, the rigorous simulation of RDWC for methyl acetate hydrolysis is performed, and sensitivity analysis is conducted to obtain the minimum reboiler duty. Then a comparison is made between the conventional process and RDWC process, and it shows that 20.1%energy savings can be achieved by RDWC process. In addition, the dynamic characteristic of RDWC is studied and an effective control strategy is proposed. The simple PI control scheme with three temperature loops can obtain reasonable control performance and maintain products at de-sired purities. It is proved that this RDWC process is an energy efficiency alternative with good controllability. ? 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

Sampled-data feedback control of a binary distillation column

The design of sampled-data controllers for a binary distillation column was studied for several types of controllers and for various control tray locations, sampling rates and disturbances. Minimal prototype control was superior to continuous PI control under some conditions but, as expected, was only satisfactory for a specified disturbance. dual “A” control scheme that compensates for both setpoint and load disturbances was developed. Two separate algorithms are implemented simultaneously, one receiving its input signal from the setpoint and the other from the measured variable. Dual control is superior to continuous control, particularly when both disturbances are encountered at the same time, and is superior to the “switching” method proposed by Mosler et al.     

反应精馏隔壁塔生产乙酸正丁酯的优化与控制

对反应精馏隔壁塔生产乙酸正丁酯过程进行了模拟、优化与控制的系统研究。利用Aspen Plus软件模拟乙酸甲酯与正丁醇的酯交换反应过程,以年总费用（TAC）为目标函数进行过程优化,通过稳态敏感性分析及相对增益矩阵（RGA）判据得到不同的操纵变量与控制变量匹配关系,以此为基础,在Aspen Dynamics平台建立了若干控制结构并进行分析对比。结果表明,利用两股反应物呈比例进料可较为有效地抵抗进料扰动,最后提出的无再沸器热负荷与混合物进料量比值（Q_r/F）控制的改进控制结构CS3,在降低反应精馏隔壁塔控制过程超调量方面有较大的优越性。     

分壁精馏塔分离芳烃的稳态及动态研究

采用分壁精馏塔（DWC）严格稳态模型,对比苯、甲苯、二甲苯以及均三甲苯四组分混合物的常规分离和分壁精馏塔分离方法,稳态分析结果表明：直接序列分壁精馏塔流程较常规三塔分离序列可减小再沸器负荷18.9%,年度总成本TAC可降低13.0%,DWC有效避免了常规塔器分离过程中中间组分的返混现象。在Aspen Dynamic环境下对最优序列进行组分控制,结果表明组分控制可很好地应对进料流量和组分组成波动。     

基于常数对角优势补偿阵的多变量控制系统逆Nyquist阵列设计

化工过程中的多变量系统变量之间往往存在耦合作用,在控制系统设计时一般将传递函数阵对角优势化,对角优势化后按多个单变量系统进行设计。由于传递函数逆阵的对角优势化更容易实现,本文采用伪对角化方法设计常数对角优势补偿阵实现传递函数逆阵的对角优势化,在一个或多个频率点上通过使开环传递函数逆阵每行的非对角项元素模平方之和最小,实现对角优势。然后,利用逆Nyquist阵列设计法对补偿后的系统设计控制器,基于逆Nyquist稳定判据,通过绘制优势度曲线和Gershgorin带判断系统的优势程度,根据Gershgorin带选定反馈矩阵的参数范围,按照单变量控制系统的方法设计动态补偿器,使系统满足动态控制品质的要求。最后通过3个示例说明本文的设计方法简便,且具有良好的控制性能。     

用于分离三氯氢硅合成过程中主副产品的隔壁塔模拟

以三氯氢硅合成过程中得到的主副产品混合物二氯二氢硅-三氯氢硅-四氯化硅为分离物系,提出采用隔壁塔代替常规精馏序列分离的新工艺.利用Aspen Plus软件对隔壁塔进行模拟,考察回流比、隔板位置、进料位置、侧线采出位置、液相分配比以及气相分配比对塔顶、侧线以及塔釜产品摩尔分数的影响,得到隔壁塔的最佳工艺参数,并通过模拟比较隔壁塔与常规精馏序列分离此混合物的能耗情况.模拟结果表明:当回流比为6、隔板位置为主塔的第8块板和第24块板、进料位置为预分馏塔的第10块板、侧线采出位置为主塔的第15块板、液相分配比为0.21、气相分配比为0.5时,隔壁塔的分离效果最佳,主产品三氯氢硅的摩尔分数为99.999%;相比于常规精馏序列,隔壁塔再沸器节能29.09%以上,冷凝器节能29.48%以上.     

Decentralized temperature control of a pilot dividing wall column

The technology of dividing wall columns offers to save high amounts of operating and investment cost compared to conventional distillation columns and their configurations. The practical application is still limited due to a lack of experience and high interactions among the process variables.The present work deals with the development and test of a control system for a pilot dividing wall column. Within this, decentralized temperature control systems are designed by a systematic approach. Furthermore, these systems are evaluated concerning the process stability, the providing of defined product purities and the respective requirement of energy in case of disturbances. The focus is on simulative and experimental investigations in order to assure the practicability of the developments. The presented results show the effectiveness of the applied methods.     

清水混凝土应用于墙柱的质量控制技术

结合具体工程,对清水混凝土进行了实践,通过精细设计、严格控制、加强施工组织,建立良好的管理系统。从组织设计、安排施工到项目管理与监理督检,每一个环节加强质量要求,取得了预期效果。     

Optimization and control of vertical double wall dividing-wall column for separating a quaternary system

In this paper, the new separation structure (VDWDWC) for separation of a quaternary system is proposed for the first time, which has lower energy consumption and higher separation efficiency than the traditional three-column and Kaibel column. Sensitivity analysis and response surface optimization (RSM) are applied to the structural design and parameter optimization of VDWDWC. In addition, the dynamic control of VDWDWC is also investigated. Specifically, the performances of temperature-composition cascade control (TC-CC) with and without feed-forward ratio control are compared and analyzed. The results suggested that the TC-CC structure can achieve outstanding controllability for VDWDWC, when the feed flow rate and feed composition is disturbed. In particular, TC-CC with feed-forward ratio control has better dynamic response: the maximum deviation was reduced by 53.7%, and the settling times are significantly shortened, while the steady state deviation of product purity was slightly reduced.