A novel MINLP-based representation of the original complex model for predicting gasoline emissions

The Environmental Protection Agency (EPA) introduced Reformulated Gasoline (RFG) requirements as a measure to reduce emissions from gasoline-powered vehicles in certain geographic areas. As part of this effort, the EPA developed empirical models for predicting emissions as a function of gasoline properties and established statutory baseline emissions from a representative set of gasolines. All reformulated gasoline requires certification via this model, known as the Complex Model, and all refiners and importers calculate emissions performance reductions from the statutory baseline gasoline. The current representation of the Complex Model is extremely difficult to implement within refinery operations models or to use in combination with models for designer gasoline. RFG and boutique fuels are key driving forces in the North American refining industry.The RFG models introduce increasingly complex constraints with the major limitation that they are implicitly defined through a series of complicated disjunctions assembled by the EPA in the form of spreadsheets. This implicit and cumbersome representation of the emissions predictive models renders rigorous optimization and sensitivity analysis very difficult to address directly. In this paper, we discuss how the federal government requirements for reformulated gasoline can be restated as a set of mixed-integer nonlinear programming (MINLP) constraints with the aid of disjunctive programming techniques. We illustrate the use of this model with two simple example fuel blending problems.     

ϵ-OA for the solution of bi-objective generalized disjunctive programming problems in the synthesis of nonlinear process networks

There has been an increasing interest in multicriteria optimization (MCO) of nonlinear process network problems in recent years. Several mathematical models have been developed and solved using MCO methodologies including ϵ-constraint, weighted sum, and minimum distance. In this paper, we investigate the bi-objective nonlinear network synthesis problem and propose an effective algorithm, ϵ-OA, based on augmented ϵ-constraint and logic-based outer approximation (OA). We provide theoretical characterization of the proposed algorithm and show that the solutions generated are efficient. We illustrate the effectiveness of our novel algorithm on two benchmark problems. The ϵ-OA is compared to the straightforward use of OA with augmented ϵ-constraint algorithm (ϵ-con + OA), the augmented ϵ-constraint without OA (ϵ-MINLP), and the traditional ϵ-constraint (T-ϵ-con). Based on the results, our novel algorithm is very effective in solving the bi-objective generalized disjunctive programming problems in the synthesis of process networks.     

Optimal design of multiproduct batch plants considering duplication of units in series

A generalized disjunctive programming (GDP) model for the optimal design of multiproduct batch plants is presented. This general model manages the duplication of units in series to perform a given operation in the process, which is an alternative that has not been considered in previous general approaches. Unlike duplication in parallel, duplication in series is only applicable to some operations which present trade-offs between duplication and other cost-impacting elements in the batch process. In order to use a fixed time and size factor model some assumptions had to be made in the operations that allow the duplication in series. To show the effectiveness of this approach, a plant that produces multiple recombinant proteins is presented and solved.     

异丁烯装置醚处理塔工艺模拟与优化

利用AspenPlus工艺流程模拟软件对吉林石化公司精细化学品厂1．5万t／a异丁烯装置的醚处理塔（t-1201）进行了模拟计算,研究了回流比和塔釜液中础（MTBE）对侧线采出产品质量影响、塔顶操作压力对相关操作参数的影响,提出了工艺控制优化方案,从而达到稳定控制醚处理塔（T-1201）侧线采出产品质量,满足下步裂解反应工序生产需求,延长裂解反应催化剂的使用寿命。     

Optimization study on the azeotropic distillation process for isopropyl alcohol dehydration

Modeling and optimization work was performed using benzene as an entrainer to obtain a nearly pure anhydrous isopropyl alcohol product from dilute aqueous IPA mixture through an azeotropic distillation process. NRTL liquid activity coefficient model and PRO/II with PROVISION 6.01, a commercial process simulator, were used to simulate the overall azeotropic distillation process. We determined the total reboiler heat duties as an objective function and the concentration of IPA at concentrator top as a manipulated variable. As a result, 38.7 mole percent of IPA at concentrator top gave the optimum value that minimized the total reboiler heat duties of the three distillation columns.     

苯-环己烷萃取精馏过程模拟和优化研究

以UNIFAC方程为物性计算方法,使用化工过程模拟系统PRO/对苯-环己烷萃取精馏分离过程进行模拟和优化研究。采用双塔联用工艺,对萃取剂种类、萃取剂用量、温度、加入位置,原料液进料温度、进料位置,两塔的总理论板数分别进行了优化。结果表明:以糠醛为萃取剂,糠醛用量与原料液用量摩尔比为2.2、加入温度为298.15℃、在塔1的第7块板加入,原料液进料温度为353.85℃、在塔1的第25块板进料,塔1的总理论板数为35块,塔2总理论板数为10块时,分离过程达到最优。此时,塔1的环己烷产品纯度为0.9953,塔2的苯产品纯度为0.9890,循环糠醛纯度为0.9985。     

Experimental Reaction Equilibrium and Kinetics of the Liquid‐phase Butyl Acrylate Synthesis Applied to Reactive Distillation Simulations

Butyl acrylate, which can be produced in liquid phase from butanol and acrylic acid, is an important precursor for varnishes and adhesives. The reaction equilibrium and the kinetics of the butyl acrylate synthesis catalyzed by acid ion exchange resins were measured and the results are used to derive formulas for the equilibrium and the kinetics which is supposedly based on a Langmuir‐Hinshelwood‐Hougen‐Watson mechanism. Because of the highly nonideal reaction mixture, both the equilibrium and the kinetics are expressed in terms of activities. The equations are used in the modeling and simulation of a butyl acrylate production plant which consists of a catalytic tube reactor and a reactive distillation column. A column that is operated in the common manner, i.e. by heating only the reboiler, leads to a reactive azeotrope over a large part of the column. However, distributing the heat flow over the whole column improves the separation and the conversion significantly.     

苯乙烯装置的节能方案探讨

分析了山东某化工厂6万t/a苯乙烯装置的生产现状,介绍了Smart工艺和热泵精馏工艺及其特点,论述了对装置脱氢工段和精馏工段改造的必要性,对装置的优化方案和优化后带来的效益进行了探讨。     

低浓度醋酸-醋酸乙酯水溶液中分离醋酸乙酯

采用Aspen Plus软件模拟了醋酸-水-醋酸乙酯的精馏过程,根据实验数据优化热力学模型参数,在此基础上确定了最优的操作参数,获得了精馏操作时精馏塔各理论板的温度和气液组成分布图。然后通过精馏实验分离醋酸乙酯,塔顶醋酸乙酯的含量达到94%以上,实验结果与模拟结果吻合较好。     

Simulation and experimental study for an inverted trickle solar still

An experimental study for an inverted trickle solar still was performed. The still was basically composed of an inclined absorber plate painted black on the top. Saline water flowed at the backside of the plate and was kept attached to the plate. The water flow rate was kept low so that its temperature was raised to produce vapor. Condensation took place in another compartment where a heat exchanger was placed to provide heat recovery. The still was tested using brackish water of 6000 ppm salinity during the month of November at 47° and 32° tilt angles. The condensate obtained was 2.8 and 2 L/d at the above angles, respectively. This represents an 18% increase in this kind of output over previous work, which is due to reduction in the salinity of feed water. However, the intermediate header production, which is saline water of reduced salinity (3600 ppm), was also reduced by 13%. A computer simulation program was developed to predict the performance of the still.     

PVA生产中醋酸甲酯水解工序全流程模拟

利用ASPEN PLUS软件和醋酸甲酯痧解催化精馏工艺研究的小试数据,对PVA生产中醋酸甲酯水解工序的全流程进行了模拟计算,并给出了中试结果,模拟计算结果表明：采用催化精馏工艺可使流程中物料循环系数大大降低;满足原分离指标的条件下,分离设备的规模可养活;不改变分离设备的条件下,仍可达到原来的分离要求,而且能节约大量能量。     

An enhanced pseudo-binary-mixture (PBM) algorithm for multistage separation processes

A scale-shift approach is introduced to further refine the pseudo-binary-mixture (PBM) simultaneous correction procedure for the solution of multicomponent, multistage separation problems [Ishii, Y., & Otto, F. D. (2001). An efficient simultaneous correction procedure for multicomponent, multistage separation calculations for non-ideal systems. Computers and Chemical Engineering, 25, 1285–1298; & Ishii, Y., & Otto, F. D. (2003a). A method to extend the domain of convergence for difficult multicomponent, multistage separation problems. Computers and Chemical Engineering, 27, 855–868]. The scale-shift approach takes advantage of the fact that a solution to a stage-wise separation problem is more easily obtained the fewer the number of stages. In the approach the column specified in a given problem is initially downsized to a configuration having a small number of stages and then scaled up to the original one in a multiple-step manner. A solution is obtained at each scale-shift step and the results are used as a set of initial assumptions to solve the subsequent scaled-up problem. Combining the scale-shift approach along with the gradual non-ideal enhancing method with the PBM algorithm provides a more robust and efficient algorithm for the simulation and solution of difficult multicomponent, multistage separation problems including those involving non-ideal mixtures that are highly sensitive to the quality of initial values. A geometric consideration for the gradual non-ideal enhancing method and details of the unique procedure for the algebraic inversion of matrices employed in the algorithm are also presented.     

多元复杂精馏过程模拟和优化

采用非平衡级METSH方程组,对丙烯精馏过程进行了模拟计算和优化,提出了一种全新的、实用的塔板组成的圆整归一方法,摸索出了一套行之有效的计算程式,大大提高了模型方程组迭代计算的收敛性,求解更加稳定。本文还以精馏塔利润为目标,建立了优化目标函数,进行了优化计算,计算结果对丙烯塔生产具有一定意义。     

6万t/a苯乙烯装置精馏工艺设计与优化

介绍了苯乙烯精馏工艺及其在国内外的发展状况,并在设计过程中分别对粗分塔塔釜的不同温度工况进行了对比。采用了高釜温的精馏方案新工艺,对装置的聚合损失、化学品消耗、设备投资等进行了优化。     

三聚甲醛分离过程模拟与优化

对萃取法分离精制三聚甲醛工艺过程进行了模拟,在试验研究基础上,以经济效益为出发点,对三聚甲醛分离精制生产装置进行了优化计算,得到了最优的萃取塔操作相比和精馏塔操作回流比,优化计算结果可作为工业化装置设计依据。