气相分配比对隔板精馏塔性能和操作影响的模拟研究(英文)

Operability problem of dividing wall column (DWC) raised by vapor split was investigated by numerically analyzing four cases defined by different compositions of a three-component mixture. DWCs were firstly designed for each case by optimizing the vapor split to the two sides of the dividing wall, and then their feasibilities and total annual costs in operation were evaluated against different vapor split ratios. The analysis on the operability of the DWC for four cases was made based on two scenarios: (1) vapor split is shifted by the vapor resistance difference between the column sections in the two sides of the dividing wall and (2) the feed composition is changed. It was demonstrated that the positioning of the dividing wall and the decision on the vapor split may affect significantly the operability of a DWC.     

分壁精馏塔分离苯/甲苯/二甲苯的模拟工艺研究

分壁精馏塔（简称分壁塔）在节能和节约投资方面都有很大的优势和潜力,因此近几年来人们对它的深入研究也越来越多。以等比例的苯、甲苯和二甲苯为原料,通过模拟工艺流程,研究分析了分壁塔的进料位置、隔板位置、回流比、侧线采出位置以及液汽相分流比与能耗、组分纯度的关系。研究结论显示,分壁塔的最适宜液相分流比和汽相分流比分别为0.65和0.45,与常规精馏塔相比,分壁塔分离所得的苯、甲苯和二甲苯的纯度高,冷凝负荷和热负荷分别比常规精馏塔降低31.066 9%和34.167 5%。     

气相进料对隔板精馏塔优化设计的影响

隔板精馏塔（DWC）在节能和节省设备投资方面具有十分突出的优势,隔板精馏塔中隔板位置是重要的设计变量,影响分离效果及能耗,当进料中含有气相时这种影响更加显著。选用苯、甲苯和对二甲苯三元物系,研究了进料的气相分率对隔板位置的影响并确定最优隔板位置。采用严格模拟方法,以年度总费用（TAC）为评价指标,比较不同进料气相分率下隔板塔的经济性,其中气相进料较液相进料TAC最高可节省23.33%。并通过灵敏度分析展示了在进料中含有气相时确定最优隔板位置的重要性。     

气相进料对隔板精馏塔优化设计的影响

隔板精馏塔（DWC）在节能和节省设备投资方面具有十分突出的优势,隔板精馏塔中隔板位置是重要的设计变量,影响分离效果及能耗,当进料中含有气相时这种影响更加显著。选用苯、甲苯和对二甲苯三元物系,研究了进料的气相分率对隔板位置的影响并确定最优隔板位置。采用严格模拟方法,以年度总费用（TAC）为评价指标,比较不同进料气相分率下隔板塔的经济性,其中气相进料较液相进料TAC最高可节省23.33%。并通过灵敏度分析展示了在进料中含有气相时确定最优隔板位置的重要性。     

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.     

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.     

进料组成改变对隔板塔经济性影响的模拟

完全热耦合精馏相比传统精馏可以减少设备投资和操作费用,可代替传统精馏分离多组分混合物。对隔板塔（完全热耦合精馏塔）用于分离三组分混合物时的可操作性和经济性进行了研究。采用严格模拟方法,针对4种不同的进料组成设计了4种不同的隔板塔,并得出各个隔板塔气相和液相分割比对隔板塔年度总费用（TAC）的关系曲线,研究了当进料组成改变时4种隔板塔的经济性。     

萃取精馏分离苯/环己烷共沸体系的控制策略

将常规萃取精馏、差压热耦合萃取精馏以及隔壁塔萃取精馏技术应用于以糠醛为萃取剂的苯和环己烷共沸物分离过程。在稳态模型的基础上,利用Aspen Dynamics软件进行控制研究,对三工艺流程提出了若干控制策略。结果表明,对于常规萃取精馏过程,再沸器热负荷与进料量比值控制结构在降低控制过程超调量方面表现出明显优势;对于差压热耦合萃取精馏过程,带有压力-补偿控温策略的方案控制效果更佳;而对于隔壁塔,则选择了无隔板下方气液分离比控制的结构来作为较优的控制策略。     

Effects of Thermal Feed Quality on the Performance of a Divided Wall Distillation Column

The present work deals with the effect of thermal feed quality on the performance of a divided wall distillation column (DWC). The thermal condition of the feed alters the pressure profile across the two sides of the dividing wall, thereby affecting not only the mass transfer characteristics but also the hydrodynamics of a DWC. It was observed that the natural (feasible) vapor split ratio does not depend on the liquid split ratio and the reflux flow rate when the feed is saturated liquid or sub-cooled liquid (q ≥ 1). However, for q < 1, that is, for two phase (vapor-liquid), saturated vapor, or superheated vapor feed, the liquid split ratio and the reflux flow rate have profound effect on the feasible vapor split ratio, and the pressure profiles are altered significantly. For the stable operation of a DWC, the feed should be either saturated liquid or sub-cooled liquid or the feed quality may be manipulated to adjust the vapor split ratio.     

隔壁式空分精馏塔应用性能研究

为了降低空气低温分离过程的设备投资和能耗,在分析空分体系的热力学性质及流程特点的基础上,提出了一种新型的隔壁式空分精馏塔流程。应用Aspen Plus模拟软件,对空气分离的传统流程和隔壁塔流程进行了模拟对比,考察了隔壁式空分精馏塔各结构参数与操作参数对其年总成本的影响,并分析比较了空分传统流程和隔壁式空分精馏塔流程的热力学效率。结果表明,隔壁式空分精馏塔的建模合理可行,通过年总成本优化得到了该隔壁塔的最优结构参数与操作参数,分别为:液氧流量为3 kmol/h,气相分配比(体积比)为0.05,精馏段理论板数为33,侧线精馏段理论板数为30,公共提馏段理论板数为22。与传统空分流程相比,隔壁式空分精馏塔流程的有效能损失降低并且在热力学效率方面高出4.7%。     

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%.     

Design of a Dividing‐Wall Column Considering its Multiple Steady State Characteristic

A dividing‐wall column (DWC) may have more than one solution of liquid and vapor split ratio for the same feed and product streams under a fixed number of stages and reflux ratio, so the multiple steady states (MSS) of a DWC in the design stage should be considered. An improved design method of a DWC is proposed by studying its MSS characteristics. Additional steps are inserted after optimization to check if MSS exist for the obtained optimal solution of vapor and liquid split ratio, and further to select the best candidate. Finally, two cases of three‐product DWCs are described to verify this method. The results indicate that multiple solutions exist for these cases, which confirm the necessity of this method and provide an important guidance for the flowing design of a DWC.     

Modeling and energy reduction of multiple effect evaporator system with thermal vapor compression

A general and rigorous mathematical model is developed for a multiple effect evaporator system which includes various energy reduction schemes (ERSs). These ERSs are thermal vapor compression, vapor bleeding, condensate flashing and solution flashing. The model can achieve the function of pumping steam at any effect and can work as an effective screening tool for the selection of optimal feed flow sequence (OFFS). In order to solve the model, the iteration method combining with matrix methods is proposed. To study effect of different ERSs on steam consumption (SC), an example of the co-current quadruple effect evaporator system is considered. These schemes can reduce the SC up to 46.56% if the feed is heated up to 88 °C and ejection coefficient at 3rd effect is set to 0.3. The OFFS is forward sequence as long as preheating temperature is high enough when constraints of heat transfer driving force can be satisfied.     

Dividing Wall Distillation Columns: Optimization and Control Properties

The optimal design of dividing wall columns is a non‐linear and multivariable problem, and the objective function used as optimization criterion is generally non‐convex with several local optimums. Considering this fact, in this paper, we studied the design of dividing wall columns using as a design tool, a multi‐objective genetic algorithm with restrictions, written in Matlab^TM and using the process simulator Aspen Plus^TM for the evaluation of the objective function. Numerical performance of this method has been tested in the design of columns with one or two dividing walls and with several mixtures to test the effect of the relative volatilities of the feed mixtures on energy consumption, second law efficiency, total annual cost, and theoretical control properties. In general, the numerical performance shows that this method appears to be robust and suitable for the design of sequences with dividing walls.     

Application of response surface methodology for modeling and optimization of membrane distillation desalination process

In this work, response surface methodology (RSM) was applied for modeling and optimization of operating parameters for water desalination by direct contact membrane distillation (DCMD) process using polypropylene membrane (PP) with low pore size. Operating parameters including vapor pressure difference, feed flow rate, permeate flow rate and feed ionic strength were selected and the optimum parameters were determined for DCMD permeate flux. The developed model for permeate flux response was statistically validated by analysis of variance (ANOVA) which showed a high value coefficient of determination value (R² = 0.989). The obtained optimum operating parameters were found to be 0.355 × 10⁵ Pa of vapor pressure difference, feed flow rate of 73.6 L/h, and permeate flow rate of 17.1 L/h and feed ionic strength of 309 mM. Under these conditions, the permeate flux was 4.191 L/(m² h). Compared to a predicted value, the deviation was 3.9%, which confirms the validity of the model for the DCMD process desalination optimization. In terms of product water quality, the DCMD process using hydrophobic PP membrane can produce high quality of water with low electrical conductivity for all experimental runs.     

Design and control of reactive distillation–recovery distillation flowsheet with a decanter for synthesis of N-propyl propionate

Reactive distillation (RD) for the synthesis of n-propyl propionate (ProPro) is operated with an excess of the reactant n-propyl alcohol (ProOH). It is simulated as a two-column system which can be easily controlled compared with a single reactive column which is operated neat, because the recovery column acts conceptually as a composition analyzer. The optimal steady-state design of the two-column system with the minimal total annual cost (TAC) is screened first. Then, an effective control scheme is established to handle feed disturbances. Only tray temperatures are required in the dynamic control two-column process. The product purity is held close to the set value 99.5 mol% and large deviation is prevented.     

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6 °C and −42.1 °C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.     

A novel intensified reactive distillation process to produce pure ethyl acetate in one column—Part I: Parametric study

Production of pure ethyl acetate (EtAc) is a difficult and heavy energy consuming process. In this work, a novel reactive distillation (RD) process for EtAc production intensified by the hydration of ethylene oxide (EO), as an auxiliary reaction, is proposed for removing the EtAc/water azeotrope. Impacts of three important parameters, i.e., ethanol (EtOH) flow rate, EO flow rate and reflux ratio on temperature and component compositions along the RD column are investigated to achieve an optimal process design. The proposed RD process predicts the pure EtAc and ethylene glycol (EG) with low energy requirements. The results show that the proper feed rates of EtOH, EO and acetic acid are 0.45 mol/s, 0.45 mol/s and 0.42 mol/s, respectively, when the reflux ratio is 3.5.     

渗透汽化-隔壁塔精馏耦合初步分离费托合成水的过程研究

费托合成水中含有醇、酮、酸等多种高附加值含氧有机物可提取出来作为高附加值产品,但由于费托合成水处量大,共沸体系复杂,通常需要首先对其进行初步分离。设计了直接两塔精馏、渗透汽化-两塔精馏、直接隔壁塔精馏、渗透汽化-隔壁塔精馏四种可供选择的初步分离工艺。根据渗透汽化实验数据在Aspen Plus中构建渗透汽化过程模型并进行模拟,结合灵敏度分析得到精馏过程的最佳工艺参数和模拟结果,并对四种工艺的能耗和有效能损失进行对比。结果表明,渗透汽化-隔壁塔精馏工艺具有明显的节能优势,其能耗较直接两塔精馏可降低15.85%,有效能损失降低45.74%。经渗透汽化膜预浓缩后,溶液的浓度可进入隔壁塔的适宜分离浓度区间,以充分发挥隔壁塔优势。由于渗透汽化所需能量可由余热等低品位热源提供,在余热充足的煤化工领域中可显著降低有效能损失。对于该过程而言,当渗透汽化膜价格低于438元/m²时,渗透汽化-隔壁塔精馏耦合工艺将会表现出较高的经济性。     

Transesterification of palm oil with methanol in a reactive distillation column

The higher feedstock and processing costs for biodiesel production can be reduced by applying reactive distillation (RD) in transesterification process. The effects of reboiler temperature, amount of KOH catalyst, methanol to oil molar ratio and residence time on the methyl ester purity were determined by using a simple laboratory-scale RD packed column. The results indicated that from the empty column, the system reached the steady state in 8 h. Too high reboiler temperature and the amount of catalyst introduce more soap from saponification in the process. The optimal operating condition is at a reboiler temperature 90 °C, a methanol to oil molar ratio of 4.5:1.0, KOH of 1 wt.% respect to oil and 5 min of residence time in the column. This condition requires the fresh feed methanol 25% lower than in the conventional process and produces 92.27% methyl ester purity. Therefore this RD column can be applied in small or medium biodiesel enterprise.