Distributed Heat Supply for Distillation Control to Reduce Feed Composition Disturbance Effects

The introduction of heat in stages combined with a reboiler as a distillation control strategy is proposed aiming to reduce the transition time when a feed composition disturbance occurs. This is the most severe type of perturbation and results in long transition times which are economically undesirable. Experiments were carried out in a pilot distillation column with ethanol and water for testing two different control strategies: conventional, i.e., using both last stage and reboiler temperature controllers, and distributed, i.e., conventional strategy plus stage temperature controllers. The results with this operational approach indicated a significant reduction in the time required for the column to stabilize when compared with the conventional approach. The proposed strategy proved to be a viable alternative, enabling faster dynamics and smaller volumes to be processed outside the predefined quality parameters.     

苯乙烯装置塔系热集成

精馏作为过程工业中最重要和最常用的分离手段, 是耗能最大的单元操作。精馏塔一般从再沸器输入热量, 从冷凝器取走热量, 利用某些塔高温位的冷凝热加热其他塔的再沸器, 并将单塔节能技术与过程集成相结合, 实现塔系的热集成, 可充分挖掘系统内部的节能潜力, 达到减少公用工程消耗的目的。本文通过对某化工厂的苯乙烯装置精馏塔系的分析, 通过各个塔的温焓图之间的关系, 提出了精馏塔系内部热集成的措施, 包括直接热集成、调压热集成和双效精馏与间接热集成耦合等3种方案。对于后两个热集成方案, 采用Aspen Plus模拟改造后精馏塔的变化并验证了方案的可行性。结果表明, 苯乙烯装置采用该热集成措施能明显节省高品位蒸汽的消耗, 降低能量费用。     

与换热网络热集成的精馏塔压优化

调整精馏塔的操作条件是节省塔能耗的有效途径之一，然而在对已有装置进行用能优化时，需同时考虑精馏塔操作条件对塔能耗和换热网络能耗的影响。基于装置所有流股的冷热复合曲线，针对跨夹点的精馏塔，同时考虑了精馏塔的再沸、冷凝以及过程流股，分析了塔压变化对装置公用工程消耗的影响，并对某连续重整装置汽提塔进行了案例分析。结果显示，塔压降低可使冷凝器能耗增加，再沸器能耗减小，而对于塔顶塔底出装置流股，塔压降低可节省冷却公用工程但增加加热公用工程。装置总体的节能效果为塔顶冷凝器、塔底再沸器和塔顶塔底出装置流股节能效果的综合作用。对某连续重整装置汽提塔分析表明，塔压降低200.0 kPa时，其加热公用工程用量将减少577.5 kW。     

Introducing vapor recompression mechanism in heat‐integrated distillation column: Impact of internal energy driven intermediate and bottom reboiler

A novel combination of internally heat‐integrated distillation column (HIDiC) and vapor recompression column (VRC) with intermediate reboiler (IR) is proposed. Supplying heat at the highest temperature point (i.e., column bottom) of the VRC scheme is not thermodynamically favorable and, therefore, we aim to install the IR for better distribution of heat along the column length, thereby reducing the compressor work. Introducing IR in the combined HIDiC‐VRC system formulates an open‐loop variable manipulation policy to evaluate the comparative impact of internal and external heat sources on bottom liquid reboiling. With internal energy driven bottom reboiler, we further investigate the hybrid HIDiC‐VRCIR column with proposing the two modes of compressor arrangement, namely parallel and series. Finally, a multicomponent distillation system is exampled to show the promising potential of the proposed HIDiC‐VRCIR configurations in improving the energetic and economic performance over the HIDiC‐alone and HIDiC‐VRC schemes with reference to a conventional standalone column. © 2014 American Institute of Chemical Engineers AIChE J, 61: 118–131, 2015     

带有中间热集成的精馏塔序列及其性能

提出一种带有中间热集成的精馏塔序列(IHISDC)的流程,针对三组元混合物分离的简单塔直接序列,对该流程进行了分析。与传统热集成精馏序列(HISDC)相比,提出的IHISDC通过中间换热器将高压塔的精馏段与低压塔的提馏段进行局部热集成,使能量集成精馏塔之间的压力差更小,进而使能耗费用下降。同时发现,IHISDC中的高压塔再沸器热负荷和低压塔冷凝器热负荷增加,由于换热器数量的增加,IHISDC的投资费用较大。为了进一步降低IHISDC的年度总费用,需要对其设计参数进行优化。     

内部热耦合精馏塔的操作性能与模拟

对同轴式内部热耦合精馏塔的操作性能和节能效果进行了研究,考察了全回流操作条件下,压缩比对回流量、冷凝器负荷和再沸器负荷的影响。结果表明,随着压缩比的增大,回流量、冷凝器负荷和再沸器负荷均降低。通过实验数据计算得到了该塔的理论板数和两塔间的传热量,精馏段为9块理论板,提馏段为4块理论板,当压缩比为2.2:1时,两塔间传热量为9.98kW。连续操作条件下,对内部热耦合精馏塔的节能效果进行了分析,通过与常规精馏塔的比较,内部热耦合精馏塔可节约52.3%的冷量,输入的再沸器和压缩机总负荷可节约20.34%。另外,基于实验数据,对该内部热耦合精馏塔进行了动态模拟,经连续操作下的实验验证,该内部热耦合精馏塔可在2h后达到稳定操作。     

Exergy analysis of distillation processes

Distillation is a unit operation in which two main processes are involved: heat transfer for vaporizing and condensing and mass transfer for the separation of the mixture. A distillation unit can be described as an exergy converter: that is a unit which converts thermal exergy into chemical exergy. To obtain a complete graphical representation of mass, enthalpy and exergy balances in a fractional distillation, we propose the use of a diagram: the specific enthalpy (in KJ/ Kg of mixture) is plotted against the Carnot factor θ to show the heat and mass transfer effects simultaneously. The application of the methodology to the distillation of an ammonia-water mixture is presented. Conventional fractional distillation consumes a lot of exergy. We propose a new type of distillation in which the reboiler and the condenser normally located at the bottom and at the top of distillation column, are replaced by two heat exchangers integrated in the column itself. The exchanger integrated in the bottom of the column inputs heat to the column, and the other exchanger located in the upper part of the column removes heat. This arrangement minimizes the creation of entropy in the column and therefore maximizes the exegetic effectiveness. This new process, called:“diabatic” or “quasi-reversible” distillation should bring important improvement to conventional distillation, not only from the point of view of energy use (large reduction in the consumption of heat carriers fluids for heating and cooling), but also in terms of capital investment as the cost of fitting a heat exchanger in the destillation column will probably be less than the cost of reboiler or condenser and reflux head.     

Diagnosis of thermodynamic efficiency in heat integrated distillation

For the systematic diagnosis of the thermodynamic efficiency in dual column distillation with heat integration of practical modes, a computing scheme is developed in conjunction with the method of calculation of exergy and the modularized reduced-order model, which are discussed elsewhere by the present authors [1,2]. The thermodynamic efficiencies of 9 types of heat integration modes are actually calculated and compared with that of a distillation column without heat integration using 3 different kinds of hydrocarbon mixtures, i.e., tertiary, quaternary, and octanary. The results show that the separation energy demand can be reduced by 15% when single heat integration through the reboiler of the first column is made, and about 20% when dual integration through the condenser and the reboiler of the first column is made.     

考虑反应热的乙氧基化反应精馏塔能量内部集成与优化

以正丁醇和环氧乙烷为原料合成乙二醇正丁醚(EGMBE)为例,利用数学模型和模拟分析方法,研究了包含大量反应热效应的乙氧基化反应精馏(ERD)塔中反应热的利用及系统能量优化问题。研究表明,当采用常规的、将反应段直接叠加于提馏段之上的塔设计时,反应热并没有贡献于分离操作或减小再沸器的热负荷,而只是被冷凝器中的冷却介质移走。分析了反应热的可利用途径,提出一种将反应段和提馏段分割、从反应段移出反应热供提馏段加热的内部热集成乙氧基化反应精馏结构--IHIERD。模拟结果表明,IHIERD 将使再沸器的温度从462.5 K降低到420.0 K,冷凝器负荷降低11%,外部能量输入降低14%,节能效果显著。     

Argon production from air distillation: Use of a heat pump in a ternary distillation with a side rectifier

A ternary feed mixture ABC can be separated into individual components through the use of a main distillation column with a thermally linked side rectifier. To enhance such a separation, a heat pump can be implemented to transfer heat from the condenser at the top of the side rectifier to the reboiler at the bottom of the main column. In this paper, one such heat pump is described and applied to an air distillation system separating the ternary mixture containing nitrogen, oxygen and argon. The separation is performed by a conventional double column with a crude argon side column. When this system is operated at an elevated pressure to obtain higher product pressures, the separation of oxygen and argon becomes very difficult and leads to reduced argon recovery. The proposed heat pump enhances the separation by providing a supplementary crude argon condensing duty through the vaporization of a liquid oxygen stream from the bottom of the low pressure (LP) column. This scheme improves the liquid/vapour ratio (L/V) in the bottom section of the LP column and, more importantly, increases the vapour feed to the crude argon column. This increased feed rate leads to a substantial increase in argon recovery for the elevated pressure air distillation process.     

基于(火用)损失分析的反应精馏塔板上反应体积的优化设计

针对以选择性为主要目标的反应精馏塔设计中反应段塔板上反应体积或催化剂的分配问题,提出一种基于热力学(火用)损失分析和流程模拟计算相结合的优化设计策略。为了深层次分析反应精馏塔板上(火用)损失的原因并为制定调优方向提供理论依据,将塔板上的总(火用)损失区分为物理(火用)损失和化学(火用)损失两部分并分别进行计算。在此基础上,将建立的(火用)损失计算方法和流程模拟技术相结合,将反应段塔板上的反应体积的分配和对应的(火用)损失分布相关联,以再沸器热负荷最小为目标,通过建立的方法对反应体积的分配逐步调优,可实现反应精馏塔的优化设计。方法的有效性通过环氧乙烷水合制乙二醇反应精馏体系进行了验证。结果表明,与普遍采用的塔板上等反应体积分配的设计方法相比,通过本文建立的优化分配方法,可使系统的能耗降低18%以上,同时结果优于文献值。     

甲醇精馏热焓控制设计及Aspen实现

对甲醇精馏塔塔釜进行热焓控制方案设计并通过Aspen软件仿真验证。首先介绍了甲醇三塔精馏工艺背景,根据实际项目的工艺条件,精馏塔底部采用双换热器作为再沸器的特点,进行热焓控制方案的设计,然后,利用Aspen软件仿真,以出料杂质乙二醚的含量为参考标准,通过与甲醇精馏塔塔釜常规温度控制的对比验证了本控制方案中热焓控制的优势,在面对实际工况下常规的流量和组分变化扰动时,产品质量能达到工业生产的要求,具有一定的实际意义。     

Vapor flow lag in distillation columns

The vapor rate in a distillation column follows with delay the change of the heat amount introduced to the reboiler. One of the causes of the vapor flow lag is an interaction between the heat transfer process in the reboiler and the hydraulics of the column internals. This interaction may have considerable effect upon the vapor rate response producing a time lag of several minutes, yet it is not dealt with in the literature.The general theory of the vapor flow tag due to interaction is given. For sieve plates with downcomers a simplified mathematical model is developed and experimentally confirmed. The response of vapor rate to reboiler heat load changes in downcomer plate columns is approximately that of a first-order element with a time constant ranging from about 10 sec to 10 min.The effect of design, operation and system parameters is discussed and estimated for important cases.     

多晶硅生产中三氯氢硅精馏节能工艺

简述了多晶硅行业概况和差压耦合蒸馏节能技术。详述了一种高纯三氯氢硅差压耦合精馏工艺,利用高压塔塔顶蒸汽作为低压塔塔釜再沸器热源,实现了能量的集成与过程优化。运用化工模拟软件PRO/Ⅱ8.1模拟了两塔高纯三氯氢硅差压耦合精馏工艺和三塔高纯三氯氢硅差压耦合精馏工艺的设计参数。结果显示,两塔耦合三氯氢硅一次收率为92.0%,理论节能50.1%;三塔耦合三氯氢硅一次收率为92.0%,理论节能66.7%,效果更好。该技术已成功实现工业化,可使精馏单元实际能耗平均降低40%～60%,同时大幅减少了设备投资。     

基于HTRI的立式热虹吸再沸器设计优化

立式热虹吸再沸器由于其具有较大的传热系数、较小的占地面积以及安装便捷等优点,在化工行业中得到广泛的应用,本文利用HTRI软件对醋酸仲丁酯装置中醋酸精馏塔再沸器进行设计优化,计算合适的再沸器结构参数,找出合适的静压头,以及最优的进口管径。     

中间换热器及热泵对复杂塔处理能力的影响

为了研究复杂精馏塔扩容改造,文中运用流程模拟软件及Liu与Jobson提出的面积利用率曲线(FUA曲线)研究了安装中间冷凝器、中间再沸器及热泵对复杂精馏塔处理能力的影响.由模拟及计算结果可得基础工况的FUA曲线,根据该曲线形状可以确定:当复杂精馏塔处理量增加时,哪些塔板将成为其处理能力提高时的“瓶颈”;中间换热器及热泵...     

Energy saving and thermodynamic efficiency of a double-effect distillation column using internal heat integration

The existing internally heat-integrated distillation column with the problem of utilizing a compressor is modified to propose a new heat-integrated distillation column without the compressor. Two identical columns of a conventional binary distillation are implemented to the heat integration. The energy used in the reboiler is recovered by the internal heat integration between the stripping section of one of the columns at lower pressure and the rectifying section of the other higher pressure column. The heat integration is similar to double-effect distillation, but internal heat integration requires less pressure elevation. The performance of energy saving and thermal efficiency improvement of the proposed system is evaluated with the two examples of the benzene-toluene and methanol-ethanol processes. The performance comparison indicates that the proposed system requires 17.4% less of reboiler duty for the benzene-toluene process and 15.8% less of heating duty for the methanol-ethanol process. The thermal efficiencies are 16.3% and 23.8% for the benzene-toluene and methanol-ethanol processes, respectively. Elimination of the compressor makes the column operation easy and the separate reboilers and condensers for the two columns in the proposed system provide flexible control, when the controllability of the proposed system is compared with that of the existing internally heat-integrated distillation column.     

节能型甲醇精馏工艺研究

提出两种节能型甲醇精馏新工艺。在改进的三塔双效精馏工艺中,加压塔的蒸汽不仅用作常压塔的热源,还同时供给预塔的再沸器。四塔双效精馏工艺在传统三塔流程中新增一个加压塔,它的蒸汽用于预塔的再沸器,新增加压塔的塔顶得到精甲醇产品,塔底排出废水。对两种新工艺进行了稳态模拟,结果表明各换热器的两侧有合适的温差,换热器可以正常工作,对3种工艺的对比表明,改进的三塔工艺比传统三塔工艺节能16.67%,四塔工艺比传统三塔工艺节能16.17%。     

萃取精馏分离苯/环己烷共沸体系模拟与优化

以糠醛作为萃取剂分别使用常规萃取精馏、隔壁塔萃取精馏和差压热集成萃取精馏对苯和环己烷体系进行分离研究,使用流程模拟软件Aspen Plus V8.4进行模拟分析,对初步设计的三稳态流程,分别进行灵敏度分析,使用多目标遗传算法对过程进行整体优化以获得最优结构参数。结果表明,隔壁塔萃取精馏和差压热集成萃取精馏相对于常规萃取精馏所需再沸器热负荷可分别减小21.5%和15.7%。对三工艺流程进行经济性分析,发现与常规流程相比,隔壁塔萃取精馏的年总费用下降了6.0%,而差压热集成萃取精馏年总费用增加了50.8%,为萃取精馏分离苯/环己烷共沸体系工业化设计提供了理论依据和设计参考。     

具有完全热集成和水集成的合成甲醇精制工艺

提出了一种新的三塔精馏工艺用于合成甲醇的精制过程。在采用差压双效精馏实现系统内热集成的方案中,新工艺将加压塔塔顶蒸汽分为两部分,一部分作为预塔再沸器的供热源,其余部分作为常压塔再沸器的供热源,实现了供热蒸汽的完全热集成。同时将常压塔塔底出料的高纯软水和加压塔塔底部分含盐水回用为预塔萃取水,实现了系统内工艺软水的完全集成,既节约了工艺软水,又减少了系统的废水排放量。运用Aspen Plus定态模拟方法,对Lurgi工艺,文献中提到的W-C工艺和新的Z-W工艺进行对比研究,研究结果表明Z-W工艺比现有Lurgi工艺节约能量21.4 %,节约软水100 %,减少废水排出量81.4 %;比文献中W-C工艺节约能量11.7 %,节约软水100 %,减少废水排出量68.5 %。