Temperature inferential control of a reactive distillation column with double reactive sections

Temperature inferential control (TIC) is studied for a reactive distillation column with double reactive sections (RDC-DRSs) processing a hypothetical two-stage consecutive reversible reaction (A + B■C + D, C + B■E + D with αD > αB > αC > αA > αE). Because of the complicated dynamic behaviors, the controlled stages by sensitivity analysis lead to great steady-state deviations (SSDs) in top and bottom product purities. Since TIC involves considerably reduced settling times in comparison with direct composition control, small SSDs in product qualities correspond generally to small transient deviations (TDs) in product qualities. An objective function that measures SSDs in product qualities is formulated to represent the performance of a TIC system and an iterative procedure is devised to search for the best control configuration. The application of the procedure to the RDC-DRS gives considerably suppressed TDs and SSDs in top and bottom product qualities as compared with the one by sensitivity analysis. The method is simpler in principle and less computationally intensive than the current practice. These striking outcomes show the effectiveness of the proposed principle for the development of TIC systems for complicated reactive distillation columns.

Reactive dividing-wall column for the co-production of ethyl acetate and n-butyl acetate

Reactive dividing-wall column(RDWC) technology plays a critical role in the energy saving and high efficiency of chemical process.In this article, the process of co-producing ethyl acetate(EA) and n-butyl acetate(BA) with RDWC was studied.BA was not only the product, but also acted as entrainer to remove the water generated by the two esterification reactions.Experiments and simulations of the co-production process were carried out.It was found that the experimental results were in good agreement with the simulation results.Two kinds of RDWC structures(RDWC-FC and RDWC-RS) were proposed, and the co-production process operating parameters of the two types of RDWC were optimized by Aspen Plus respectively.The optimal operating parameters of the RDWC-FC were determined as follows: 0.6 of the reflux ratio of aqueous phase(RR), 0.66 of the vapor split(R_V) and 0.51 of the liquid split(R_L).And the optimal operating parameters of the RDWC-RS were shown as follows: RR was 0.295 and R_V was 0.61.Furthermore, the energy saving analysis of the co-production process was based on the annual output of 10000 tons of EA, compared with the traditional reaction distillation(RD) to prepare EA and BA, the reboiler duty of the RDWC-FC column could save 20.4%, TAC saving 23.6%; RDWC-RS reboiler energy consumption could save 17.0%, TAC 22.2%.

Experimental and simulation of the reactive dividing wall column based on ethyl acetate synthesis

Reactive dividing wall column(RDWC) is a highly integrated unit which combines reaction distillation(RD) with dividing wall column separation technology into one shell, and it realized the chemical reaction and the separation of multiple product fractions simultaneously. In this paper, the reaction of esterification with acetic acid and ethanol to produce ethyl acetate was used as the research system, experiments and simulations of the RDWC were carried out. This system in the traditional process mostly used the homogeneous catalyst(e.g. sulfuric acid). However, in view of the corrosion of the equipment caused by the acidity of the catalyst, we used the heterogeneous catalysts – iron exchange resins – Amberlyst15 and proposed a novel catalyst loading method. Firstly,the reliability of the model of the simulation was verified by the experimental study on the change of liquid split ratio and reflux ratio. After that, the four-column model was established in Aspen Plus to analyze the effects of the amount of azeotropic agent, reflux ratio and acetic acid concentration. Finally, for a fair comparison, the economic analysis was conducted between traditional RD column and RDWC. The results showed that RDWC can save34.7% of total operating costs and 18.5% of TAC.

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 desired purities.It is proved that this RDWC process is an energy efficiency alternative with good controllability.

Control of reactive dividing wall column for selective hydrogenation and separation of C3 stream

In our previous work, the reactive dividing wall column(RDWC) was proposed and proved to be effective for selective hydrogenation and separation of C3 stream. In the present paper, the dynamics and control of the proposed RDWC are investigated. Four control structures including composition and temperature controls are proposed. The feed forward controllers are employed in the four control strategies to shorten the dynamic response time, reduce the maximum deviations and offer an immediate adjustment. The control structures are compared by applying them into the RDWC system with 20% disturbances in both the feed flow rate and the feed compositions, and the results are discussed.

Methodology for Design of Reactive Distillation Column and Kinetics for Isoamylene Etherification Catalysed by Amberlyst 35

Isoamylene from the Fischer-Tropsch syncrude can be transformed to valuable fuel oxygenate additives through an equilibrium limited etherification reaction with methanol. A reactive distillation process is established to increase isoamylene conversion. Facing the challenge of improving product purity at the same time, an equilibrium stage model based design methodology is proposed and illustrated step-by-step for converting the Fischer-Tropsch C_5 olefins to tert-amyl methyl ether(TAME) process by using Aspen Plus. Under the guide of the proposed methodology, the design leads to a TAME product purity of higher than 95% and an isoamylene conversion of higher than 90%. The etherification kinetics over Amberlyst 35 is also studied within a temperature range of 60 ℃ to 75 ℃ to shed more light on the feasibility of process development. The methodology provides an effective reactive distillation column design to achieve the target reactant conversion and product purity simultaneously.

Reinforced temperature control of a reactive double dividing-wall distillation column

The mass and thermal coupling makes the control of the reactive double dividing-wall distillation column(R-DDWDC) an especially challenging issue with a highly interactive nature. With reference to the separation of an ideal endothermic quaternary reversible reaction with the most unfavorable ranking of relative volatilities(A + B ■ C + D with α_(A)>α_(C)>α_(D)>α_(B)), the operation rationality of the R-DDWDC is studied in this contribution. The four-point single temperature control system leads to great steady-state discrepancies in the compositions of products C and D and the reason stems essentially from the failure in keeping strictly the stoichiometric ratio between reactants A and B. A temperature plus temperature cascade control scheme is then employed to reinforce the stoichiometric ratio control and helps to secure a substantial abatement in the steady-state discrepancies. A temperature difference plus temperature cascade control scheme is finally synthesized and leads even to better performance than the most effective double temperature difference control scheme. These outcomes reveal not only the operation feasibility of the R-DDWDC but also the general significance of the proposed temperature difference plus temperature cascade control scheme to the inferential control of any other complicated distillation columns.

Interpreting the dynamic effect of internal heat integration on reactive distillation columns

In this work,the impact of internal heat integration upon process dynamics and controllability by superposing reactive section onto stripping section,relocating feed locations,and redistributing catalyst within the reactive section is explored based on a hypothetical ideal reactive distillation system containing an exothermic reaction:A + BC + D.Steady state operation analysis and closed-loop controllability evaluation are carried out by comparing the process designs with and without the consideration of internal heat integration.For superposing reactive section onto stripping section,favorable effect is aroused due to its low sensitivities to the changes in operating condition.For ascending the lower feed stage,somewhat detrimental effect occurs because of the accompanied adverse internal heat integration and strong sensitivity to the changes in operating condition.For descending the upper feed stage,serious detrimental effect happens because of the introduced adverse internal heat integration and strong sensitivity to the changes in operating condition.For redistributing catalyst in the reactive section,fairly small negative influence is aroused by the sensitivity to the changes in operating condition.When reinforcing internal heat integration with a combinatorial use of these three strategies,the decent of the upper feed stage should be avoided in process development.Although the conclusions are derived based on the hypothetical ideal reactive distillation column studied,they are considered to be of general significance to the design and operation of other reactive distillation columns.

Unique influences of reboiler inventory control on the operation of totally reboiled reactive distillation columns

In this work,the dynamics and operation of the totally reboiled reactive distillation columns are visualized in terms of transfer function based process models.This kind of processes is found to be characterized by underdamped step responses due to the special topological configuration and the intricate interplay between the reaction operation and the separation operation involved.The under-dampness can be substantially alleviated through the tight inventory control of bottom reboiler and this presents beneficial effects to process dynamics and operation.Two totally reboiled reactive distillation columns,separating,respectively,a hypothetical synthesis reaction from reactants A and B to product C,and a real decomposition reaction from 1,4-butanediol to tetrahydrofuran and water,are employed to demonstrate these uncommon behaviors.The results obtained give full support to the above qualitative interpretation.Despite the strong influences of reaction kinetics and thermodynamic properties of the reacting mixtures,the totally reboiled reactive distillation columns are generally considered to present such unique behaviors and require tight inventory control of bottom reboiler to facilitate their control system development.

The mechanism and criterion of tectonic zone around karstic collapse column reactivation-induced water-conducting

In order to study the mechanism of tectonic zone around karstic collapse col-umn reacts to leak water and prevent water invasion in mine. According to the character of the surrounding cracks- penetrated water KCC, The fracture mechanics theory can be used to study the propagation and perforation process of cracks and hitches around the KCC. The criterion of crack start rupture and the length of secondary crack and criterion of crack propagation have been attained. The influencing factors of KCC reacts to water con-duction were analyzed.

A dynamic control structure of liquid-only transfer stream distillation column

The intention of this fundamental work is to explore the manipulation of a mixture of benzene,toluene and o-xylene separated from liquid-only transfer divided-wall column(LTS-DWC).First,two control structures are clearly proposed,including seven component control loops(CS1)and seven temperature control loops(CS2).However,two control structures can handle ±10% feed disturbances rather than larger feed disturbances.Subsequently,an equivalent four-column model by introducing withdraw ratio is developed to discuss the effect of two liquid-only side-stream on the overall reboiler duty.It is indicated that the second liquid-only side-stream withdraw ratio strongly affects the overall energy consumption.Hence,six-component control loops within the fixed second liquid-only side-stream withdraw ratio(CS3)is proposed and the purity of products returns to set value even as facing ±20% feed disturbances.Finally,based on the above results,it is established a temperature control structure(CS4)for controlling fixed second liquid-only side-stream withdraw ratio,which can cope with ±15% disturbances.Inspired by these findings,an insight into the dynamic control of LTS-DWC promotes the industrial implementation of DWC through new liquid-only side-stream configurations.

RPC外包方钢管混凝土柱轴压受力性能研究

为了研究活性粉末混凝土(Reactive powder concrete,RPC)外包方钢管混凝土柱的轴压受力性能,以RPC厚度和长细比为参数,对6根构件开展轴压试验研究,探讨该类组合柱的破坏模式、受力机理、套箍效应和承载力。试验结果表明:外层RPC可为内部方钢管混凝土柱提供较强的约束力,在受力后期套箍效应凸显。随着RPC厚度的增加,组合柱的承载力逐渐提高;随着组合柱长细比的增大,虽然其弹性刚度和承载力逐渐降低,但延性改善。采用ABAQUS软件建立RPC外包方钢管混凝土柱的有限元模型,分析RPC强度、RPC厚度、钢管强度等级、含钢率、内部混凝土强度和长细比等参数对组合柱承载力的影响规律,可得方钢管混凝土柱发挥系数的变化幅值为0.78~1.01。在试验研究、有限元参数分析和理论探讨的基础上,借鉴钢管混凝土结构技术规范,提出了RPC外包方钢管混凝土轴压短柱和长柱的承载力简化计算方法,公式计算值与已有数据样本吻合良好。

负载下活性粉末混凝土钢筋网加固足尺混凝土柱轴压性能试验研究

为提高负载下钢筋混凝土(RC)柱的轴心抗压性能,使用活性粉末混凝土钢筋网(RPCSM)对负载下的RC足尺柱进行加固,设计制作了7根RC方柱试件,其中1根未加固对比柱、1根端部箍筋加密加固柱、2根RPCSM加固柱、3根端部箍筋加密RPCSM加固柱。考虑加固层厚度、钢筋网配筋率和端部箍筋加密对轴心受压RC柱性能的影响,进行了试验研究并分析了各试件的破坏模式、荷载-变形关系和应变变化规律。结果表明:加固柱的承载力提高了2.81~3.82倍;原混凝土柱与RPCSM加固层界面粘结可靠,共同工作良好;随着钢筋网配筋率的提高以及加固层厚度的增加,端部箍筋加密后整体性的提高,承载力和轴向变形能力提高,但延性有所下降。结合规范和破坏机理,给出了承载力计算公式,以促进该加固技术的推广。

HeOH与BuAc酯交换反应共强化系统的评价

鉴于己醇(HeOH)与乙酸正丁酯(BuAc)酯交换反应的不利动力学和热力学特性,采用基于过程强化的反应蒸馏装置是一条有利的途径。常规反应蒸馏塔(CRDC)虽然考虑了反应-分离操作之间的相互耦合,但却完全忽略了分离操作之间的相互耦合,必然导致过大的不可逆性同时可进一步降低系统的稳态性能。单隔离壁反应蒸馏塔(R-SDWDC)的确在一定程度上考虑了分离操作之间的相互耦合,但其外部限定耦合方式致使仍然无法有效降低分离操作的不可逆性。本文基于本课题组最近提出的共强化原理给出了两种双隔离壁反应蒸馏塔(R-DDWDC)的拓扑结构,并将其与CRDC和R-SDWDC进行了深入系统的比较与分析。结果表明,R-DDWDC明显优于CRDC和R-SDWDC,是实施HeOH与BuAc酯交换反应的最佳拓扑结构。得出这一结论的根本原因在于R-DDWDC既能充分考虑分离操作之间的相互耦合,又能有效协调R-DDWDC与反应-分离操作耦合子系统的相互作用。虽然上述结论是通过具有最有利相对挥发度排序的HeOH与BuAc酯交换反应所得到的,但对于任何具有不利动力学与热力学特性的该类反应物系均具有普遍性的指导意义。

反应精馏隔壁塔提纯乳酸工艺研究

以反应精馏隔壁塔替换传统的反应精馏塔,形成了新型双向反应精馏隔壁塔提纯乳酸工艺,并通过灵敏度分析和遗传算法对工艺流程进行了优化,优化后的反应精馏隔壁塔工艺与传统反应精馏工艺相比年度总费用减少10.15%,CO_(2)排放速率降低31.75%,乳酸收率提升4.68%。

反应精馏隔壁塔制二甲醚过程模拟与分析

针对生产二甲醚工艺过程提出了3种反应精馏隔壁塔的设计,利用Aspen Plus模拟软件对常规反应精馏序列和反应精馏隔壁塔进行了流程模拟,并根据隔板的上下侧右侧是否封闭设计3种反应精馏隔壁塔。结果表明:隔板下侧封底以及两侧的结构在经济和环境指标均优于常规反应精馏塔,而隔板上部右侧封顶的结构的经济环境指标均低于常规反应精馏塔。采用隔板下侧封底的结构相比于常规反应精馏塔,年总费用降低了53.54%,CO_(2)排放量降低了61.81%,热力学效率提高了124.86%。

金选厂节能降耗措施及应用

针对金选厂磨机衬板磨损快、浮选柱作业故障率高、碎磨电能损耗较高、精矿浓密沉降效果差及采矿疏干水未利用等问题,采取了针对性措施,不仅技术指标提高,而且经济效益增加349.93万元/a,有利减少碳排放。

丹江库区典型土壤磷的淋溶模拟研究

通过室内土柱模拟试验对湖北省丹江库区典型土壤磷的淋溶特征进行了研究。结果表明,淋溶液中的钼酸盐反应磷(MRP)的累计淋溶量和浓度都随着施肥量的增加而增加。在连续淋溶3-4次后,淋溶液中钼酸盐反应磷(MRP)的浓度达到峰值,然后随着淋溶的持续进行,其浓度逐渐下降,最后变化趋势趋于平稳。磷的淋溶受土壤粘粒含量的影响较大,尤其当土壤的粘粒很高时,它的影响程度表现更明显。湖北省丹江库区的3种主要土壤:黄棕壤、紫色土和石灰土,相同条件下,淋溶液中钼酸盐反应磷的淋溶量和浓度大小顺序依次为:石灰土>紫色土>黄棕壤,因此,石灰土中磷发生淋溶损失的程度比较大,而黄棕壤则比较小。

反应精馏隔壁塔的模拟研究

以乙酸甲酯酯转换体系为例提出了一种反应精馏隔壁塔的设计和优化方法,应用该方法可将常规双塔反应精馏序列转化为反应精馏隔壁塔并保证各操作参数的最优值。首先通过在反应精馏塔与甲醇塔之间交换汽液相物流来实现反应精馏隔壁塔的简捷设计;然后利用Aspen Plus模拟软件,对常规反应精馏序列和反应精馏隔壁塔进行了模拟分析;最终以2个产品的纯度以及2个再沸器总负荷为目标函数进行了系统优化。结果表明:与常规反应精馏序列相比,反应精馏隔壁塔不但可以节能15.19%,提高热力学效率0.35%,而且能大幅度地减少CO2排放量。研究表明:反应隔壁精馏塔不但在乙酸甲酯酯转换体系上存在很大优势,而且在节能减排和减少设备投资上具有较大的潜质。