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。     

多组分复杂精馏流程的简捷设计法

基于对含多个侧线汽提和／或侧线精馏塔的复杂精馏流程的分析,构造了分离五组分的复杂精馏流程。提出了基于流程水平的多组分侧线汽提和／或侧线精馏塔的复杂精馏流程的设计方法。该法不仅可用于多组分复杂精馏流程的优化设计,并且能为复杂精馏流程的严格模拟提供良好的初值,从而为探讨复杂精馏流程的合成提供有效的途径。     

复杂精馏塔的用能分析法

针对多组分分离复杂精塔的用能分析,结合精馏原理和夹点分析方法,采用塔的总曹线描述塔内能流沿的分布,并发展了复杂精馏塔的用能分析法。实例应用表明本文所提出的方法是指导分离系统用能优化和热集成的有效工具。     

基于有效能分析的复杂精馏塔优化设计

提出了以有效能消耗最小为目标的复杂精馏塔优化设计新方法。给出了精馏塔优化设计模型及最佳进料位置、适宜理论板数NT、塔内换热器简约的确定方法,并以两组分正庚烷和乙苯的混合物为例进行设计与讨论。优化后的精馏塔含有中间换热器,与传统的简单塔有本质的区别,平衡线和操作线均处于相对平均的位置,更节能。     

热集成复杂精馏系统综合的研究

将夹点分析法应用于热集成复杂精馏系统综合的换热网络设计中,避免了以换热网络结构作为独立变量,建立了一个以预分馏塔组分回收率、回流比及操作压力为连续变量,以分离序列和热耦合方式为离散变量的混合整数非线性规划(MINLP)模型。该模型用改进的模拟退火算法求解,可同时得到优化的流程结构和操作参数。对多个五组分混合物分离问题进行了求解,并对不同优化方案的优化结果及其经济性作了比较和分析,结果表明采用热集成复杂精馏塔流程可以显著地降低系统的总费用,还表明该方法是求解热集成复杂精馏系统综合问题的有效方法。     

热泵精馏隔壁塔分离宽沸程物系的模拟

将中间换热和热泵精馏两种精馏节能技术应用到隔壁塔中,提出了带中间换热器的热泵精馏隔壁塔流程,以解决隔壁塔在分离宽沸程物系时出现的塔顶与塔底温差过高而不宜应用热泵精馏的问题。利用精馏塔总复合曲线图,可确定中间产品塔板采出流股的相态,从而得到不同类型的热泵精馏隔壁塔流程。宽沸程物系分离实例的模拟计算结果表明,该类流程在主塔气液相流量较大的情况下具有较高的节能效率。     

基于流程模拟器和列队竞争算法的蒸馏优化设计

文章提出了基于流程模拟器与列队竞争算法的蒸馏过程优化设计方法。以总费用最少为目标函数,建立了蒸馏过程优化设计的混合整数非线性规划模型,其中考虑了蒸馏序列和热集成情况。流程模拟器对蒸馏过程的模拟与列队竞争算法的优化搜索交替进行,迭代计算直到收敛到最优解。将文中提出的方法应用于从C4混合物中分离1-丁烯的蒸馏过程优化设计,得到了最优的蒸馏序列和热集成流程结构,以及各塔的最优设计与操作参数。     

乙酸甲酯-甲醇-水的热集成萃取精馏工艺

首先在50 kPa下用水萃取精馏分离乙酸甲酯、甲醇和水的混合物,得到了高质量分数的乙酸甲酯,之后利用普通精馏分离甲醇和水。使用热集成技术改造该工艺流程,将甲醇单塔精馏改造为并流双效精馏,两塔压力分别为101.325、500.000k Pa。同时采用高温水对萃取精馏塔两股进料预热,以降低萃取精馏塔塔釜的能耗。在操作参数单因素灵敏度分析的基础上,以系统塔釜总能耗及乙酸甲酯质量分数为目标函数,采用响应面方法优化操作参数。结果表明,热集成工艺较之前工艺节能23.43%。     

大温差热敏性体系节能精馏工艺研究

基于乙醛-水-巴豆醛-3-羟基丁醛大温差热敏体系的特点,采用合适的操作压力,控制精馏塔塔内温度,提出了多种节能精馏工艺。使用Aspen Plus流程模拟软件中的Radfrac模块模拟精馏塔,对该体系的常规精馏、带中间冷凝器的精馏以及带中间冷凝器的热集成精馏工艺进行模拟。以年总费用(TAC)和能耗为目标函数,对各种工艺参数进行优化。研究结果表明,与常规精馏工艺相比,带中间冷凝器的精馏工艺TAC节约了10. 35%,能耗相当;带中间冷凝器的热集成精馏工艺TAC节约了28. 78%,能耗节省24. 20%。带中间冷凝器的热集成精馏工艺是分离该体系的一条高效节能的路线。     

热泵精馏隔壁塔分离宽沸程物系的模拟

将中间换热和热泵精馏两种精馏节能技术应用到隔壁塔中,提出了带中间换热器的热泵精馏隔壁塔流程,以解决隔壁塔在分离宽沸程物系时出现的塔顶与塔底温差过高而不宜应用热泵精馏的问题。利用精馏塔总复合曲线图,可确定中间产品塔板采出流股的相态,从而得到不同类型的热泵精馏隔壁塔流程。宽沸程物系分离实例的模拟计算结果表明,该类流程在主塔气液相流量较大的情况下具有较高的节能效率。     

Thermodynamic optimisation of distillation columns

In this paper a methodology for thermodynamic analysis and distillation column ‘targeting’ is presented, with emphasis on the use of side condensers and side reboilers. Research in the past has been towards the establishment of a heat distribution curve, showing the way in which heat can be added or extracted across the different column sections. One major disadvantage of these profiles is that they refer to reversible columns, and cannot be used effectively to target for modifications in a real column.The main feature of the proposed methodology is the introduction of a minimum driving force, defined in terms of exergy loss distribution of the existing column, to set realisable targets for side reboiling/condensing in real columns, resulting in considerable energy savings. In addition to providing realisable targets, the new approach also provides the design engineer with information about the best location to place a side exchanger, and the required additional column modifications. The methodology can be applied using conventional column models in commercial process simulation programs, but can be significantly simplified by using reboiled and refluxed absorber models in a bespoke program. Simulation results for modified designs set by the new approach, for binary and multicomponent separations, verify the feasibility of the targets. This contrasts with previous approaches, which result in temperature shifts and heat load penalties after placing side reboilers/condensers, thus requiring additional simulation time and experienced judgement.     

Global minimization of total exergy loss of multicomponent distillation configurations

The operating cost of a multicomponent distillation system comprises two major aspects: the overall heat duty requirement and the temperature levels at which the heat duties are generated and rejected. The second aspect, often measured by the thermodynamic efficiency of the distillation system, can be quantified by its total exergy loss. In this article, we introduce a global optimization framework for determining the minimum total exergy loss required to distill any ideal or near-ideal multicomponent mixture using a sequence of columns. Desired configurations identified by this new framework tend to use milder-temperature reboilers and condensers and are thus attractive for applications such as heat pump assisted distillation. Through a case study of shale gas separations, we demonstrate the effectiveness of this framework and present various useful physical insights for designing energy efficient distillation systems.     

Retrofit of Distillation Columns Using Thermodynamic Analysis

Abstract

Thermodynamic analysis provides the column grand composite curves and exergy loss profiles, which are becoming readily available for a converged distillation column simulation. For example, the Aspen Plus simulator performs the thermodynamic analysis through its Column–Targeting tool for rigorous column calculations. This study uses the column grand composite curves and the exergy loss profiles obtained from Aspen Plus to assess the performance of the existing distillation columns, and reduce the costs of operation by appropriate retrofits in a methanol plant. Effectiveness of the retrofits is also assessed by means of thermodynamics and economics. The methanol plant utilizes two distillation columns to purify the methanol in its separation Section. The first column operates with 51 stages, has a side heat stream to the last stage, a partial condenser at the top and a side condenser at stage 2, and no reboiler. The second column operates with 95 stages, has a side heat stream to stage 95, a total condenser, and high reflux ratio. Despite the heat integration of the columns with the other Sections and a side condenser in column 1, the assessment of converged base case simulations have indicated the need for more profitable operations, and the required retrofits are suggested. For the first column, the retrofits consisting of a feed preheating and a second side condenser at stage 4 have reduced the total exergy loss by 21.5%. For the second column, the retrofits of two side reboilers at stages 87 and 92 have reduced the total exergy loss by 41.3%. After the retrofits, the thermodynamic efficiency has increased to 55.4% from 50.6% for the first column, while it has increased to 6.7% from 4.0% for the second. The suggested retrofits have reduced the exergy losses and hence the cost of energy considerably, and proved to be more profitable despite the fixed capital costs of retrofits for the distillation columns of the methanol plant.     

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.     

精馏过程多工况优化设计的能量流结构理论

以“三环节”能量流结构理论为基础建立了精馏过程多工况优化设计的火用经济数学模型,提出了精馏过程的多工况优化设计策略方法：将其分解为单个塔的多工况优化设计和塔间热集成的优化两个层次,有效输出火用价c_U和待回收火用价c_O为协调变量来解决多工况优化设计问题.并给出了应用实例.     

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。     

模拟退火方法用于带有中间换热器精馏塔的优化综合

This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermediate reboilers, the placement locations, the.operating pressure of column, and the heat duties of intermediate heat exchangers are treated as optimization variables. A novel coding procedure making use of an integer number series is proposed to represent and manipulate the structure of system and a stage-to-stage method is used for column design and cost calculation. With the representation procedure, the synthesis problem is formulated as a mixed integer nonlinear programming （MINLP） problem, which can then be solved with an improved simulated annealing algorithm. Two examples are illustrated to show the effectiveness of the suggested approach.     

Internally heat-integrated distillation system for quaternary separation

A new internally heat-integrated distillation column for quaternary separation modified from a conventional three-column system is proposed, and its performance is examined here. Two sets of heat integration between the rectifying section and the stripping section of two adjacent columns are placed in the conventional three-column system. The proposed system has been applied two example processes, the hexane and BTX processes, for the performance evaluation of energy saving and reduction of entropy production. In the hexane process, the duty reductions in reboilers and condensers are 28.5% and 30.5%, respectively, and the entropy production is reduced by 12.2% compared with the conventional system. In the BTX process, the duty reductions are 27.8% and 31.6%, respectively, and the entropy production is decreased 9.8%. The compressor utilized in the existing internally heat-integrated distillation column is not used in the proposed system leaving no difficulty of its operation and maintenance. Also, the structural similarity of the new system to the conventional system gives the column operation as easy as the conventional system.