化工企业供应链网的协同评价模型

目前对于供应链网的协同性评价研究主要局限在单一核心供应链模型难以全面评价具有网络结构的企业与供应链的协同性,且在化工企业供应链网的协同性评价方向少有报道。为了解决这个问题,提出了面向多节点无核心的供应链网结构模型。并根据化工企业的特性,从工业代谢平衡、企业竞争力、契约执行力和信息交互能力等方面建立了适用于化工企业供应链网协同评价模型体系,同时定义了工业代谢平衡度、企业竞争力评价指数、契约执行度等指标,给出了各指标的计算公式。通过对供应链网的结构体系的分析,给出了合作型、竞争型和混合型供应链网基本构型的评价模型。最后以煤化工行业为例,对煤化工行业供应链网结构分析,并应用评价模型计算,通过结果分析证实了面向供应链网协同评价模型的可行性和准确性。     

Computer aided flowsheet drawing—I: Equipment layout

A computer aided methodology is presented for determining the positions of equipment symbols in a flowsheet given only the equipment connection information. A two pass logic is used. In the first pass the location of process sections is determined by reducing the process section level flowsheet and generating a mesh structure using a modification of Rubin's algorithm. The approximate dimensions of each section are determined using a depth first search, and, the locations of the process section centroids are selected heuristically. In the second pass, the equipment symbols are positioned within the sections taking into account external equipment connections to other process sections as well as the flow patterns within the section. An experimental program has been developed and some test examples are presented.     

Balancing design and control of an olefin metathesis reactive distillation column through reactive section distribution

In this contribution, balance of design and control is investigated through reactive section distribution in an olefin metathesis reactive distillation column. Four designs with different strategies for reactive section distribution are studied and these include one with all stages as reactive ones (design-I), one with the distribution of reactive section according to the principle of internal mass integration (design-II), and ones with the extension of the reactive section of the design-II by five stages to either the stripping section (design-III) or the rectifying and stripping sections simultaneously (design-IV). The design-II appears to be more thermodynamically efficient than the design-I but with considerable degradation in process controllability. The design-III and design-IV retain most of the economical advantages of the design-II with only slight deterioration in controllability as compared with the design-I. This outcome demonstrates the fact that the strategy for reactive section distribution could be an effective decision variable for the balance of design and control in the development of reactive distillation columns.     

Multilevel strategies for the retrofit of large‐scale industrial water system: A brewery case study

This article presents an approach to designing a large‐scale water system, which integrates water‐using operations and wastewater treatment units in different production sections within the same network. This approach uses a mixed‐integer nonlinear programming (MINLP) model for water reuse and regeneration reuse in batch and semicontinuous processes. The application of this mathematical formulation to large‐scale industrial problems with changing daily production schedule leads to huge and complex mathematical models. Two alternative multilevel strategies are proposed to solve such problems by means of temporal decomposition. The approach is illustrated with a brewery case study that integrates water consumers in two production sections. The results obtained show that, despite the high piping cost, integration of both sections yields better result than the separate water network design in each section. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Performance evaluation of a full-scale advanced phase isolation ditch process by using real-time control strategies

This paper proposes real-time control strategies that can be applied in a full-scale advanced phase isolation ditch (APID) process. Real-time operation mode control (OMC) and aeration section control (ASC) strategies were developed to cope more stably with fluctuations in the influent loading and to increase the nitrification and denitrification reactions within the entire volume. The real-time OMC and ASC strategies were evaluated using mathematical models. When the NH₄-N in the reactor was maintained at a high level, appropriate control actions, such as continuing the aeration state, stopping the influent inflow and increasing the aeration section, were applied in the APID process. In contrast, when the NO _X -N in the reactor was maintained at a high level, the non-aeration state, influent inflow, and decreased aeration section were continued. It was concluded that stable operation in the APID process could be achieved by applying real-time OMC and ASC strategies developed in this study.     

NOVEL ENERGY-SAVING METHOD OF RECTIFICATION

The conventional rectification method to separate and purify chemical mixtures has the disadvantage of being an energy-intensive unit operation. The innovative method proposed in this article employs vapor and liquid recycles to the trays that in turn reduce the reflux rate and vapor boil-up rate, resulting in energy reduction without compromising the separations.

These findings were supported with examples of ethanol-water and butane- pentane system separations. With ethanol-water system, the experiments were conducted without overhead liquid recycle and using 16 and 5 vapor recycles. The energy saved was found to be 25-35% for 16 recycles and 20-30% for 5 recycles. Butane-pentane system was chosen as an example of industrial use of the proposed method. A liquid overhead reflux ratio of 0.5 (L/D) was used with vapor recycles, compared to a reflux ratio of 1.25 for the conventional separation without vapor recycles. This resulted in 30-35% saving in energy while giving the same productivity of the column. Butane-pentane separation was also simulated using a commercial process simulator (ASPEN^©PLUS).     

NOVEL ENERGY-SAVING METHOD OF RECTIFICATION

The conventional rectification method to separate and purify chemical mixtures has the disadvantage of being an energy-intensive unit operation. The innovative method proposed in this article employs vapor and liquid recycles to the trays that in turn reduce the reflux rate and vapor boil-up rate, resulting in energy reduction without compromising the separations.

These findings were supported with examples of ethanol-water and butane- pentane system separations. With ethanol-water system, the experiments were conducted without overhead liquid recycle and using 16 and 5 vapor recycles. The energy saved was found to be 25–35% for 16 recycles and 20–30% for 5 recycles. Butane-pentane system was chosen as an example of industrial use of the proposed method. A liquid overhead reflux ratio of 0.5 (L/D) was used with vapor recycles, compared to a reflux ratio of 1.25 for the conventional separation without vapor recycles. This resulted in 30–35% saving in energy while giving the same productivity of the column. Butane-pentane separation was also simulated using a commercial process simulator (ASPEN^©PLUS).     

一种混杂系统数据校正新方法

对于既包含连续生产过程又包含离散事件的混杂系统,尤其是对于带有生产方案切换的实际生产过程,通过在物料平衡模型中引入随机调度方程,从而构造出包含随机调度方程参数变量θ的新型协调模型,然后利用一种不确定模型的协调算法对此模型进行求解,最后,通过仿真研究证实了该方法的有效性和鲁棒性.     

A parallel function evaluation approach for solution to large-scale equation-oriented models

The equation-oriented (EO) approach is widely used for process simulation and optimization. Nevertheless, large-scale EO models consist of a huge number of nonlinear equations and make the solution procedure a challenging and time-consuming task. For most gradient-based numerical algorithms, function evaluations are the dominant step during the solution procedure. Here, a parallel computation method is developed for function evaluations within EO optimization strategies. After dividing the equations into several groups, function evaluations are calculated by using multiple threads on a parallel hardware platform simultaneously. Theoretical analysis for the speedup ratio is conducted. The implementation of the proposed method on a multi-core processor platform as well as a graphics processing unit (GPU) platform is then presented with several case studies. Numerical results are compared and discussed to show that the multi-core processor implementation has good computational performance, whereas the GPU implementation only achieves computational acceleration under relatively specific conditions.     

Two‐Phase Sequential Simulation of a Fluidized Bed Reformer

A two‐phase flow model is adapted in order to predict the performance of a fluidized bed reformer using the sequential modular simulator. Since there are physical and chemical phenomena interacting in the reformer, two sub‐models appear to be necessary to describe the overall model. These are the hydrodynamic and reaction sub‐models. The hydrodynamic sub‐model is based on the dynamic two‐phase model and the reaction sub‐model is derived from the literature. In the overall model, the bed is divided into several sections. At each section, the flow of the gas is considered as plug flow through the bubble phase and to be perfectly mixed through the emulsion phase. Two sets of experimental data from the literature at different hydrodynamic regimes were used in order to validate the proposed model. A close agreement was observed between the model predictions and the experimental data. The model proposed in this work may be used as a framework for the development of sophisticated models for non‐ideal reactors inside process simulators.     

A Novel Strategy for Simulating the Main Fractionator of Delayed Cokers by Separating the De-superheating Process

Delayed coking is an important process in refinery to convert heavy residue oils from crude distillation units (CDUs) and fluid catalytic cracking units (FCCUs) into dry gas, liquefied petroleum gas (LPG), gasoline, diesel, gas oils and cokes. The main fractionator, separating superheating reaction vapors from the coke drums into lighter oil products, involves a de-superheating section and a rectifying section, and couldn't be simulated as a whole column directly because of non-equilibrium in the de-superheating section. It is very important to correctly simulate the main fractionator for operational parameter and energy-use optimization of delayed cokers. This paper discusses the principle of de-superheating processes, and then proposes a new simulation strategy. Some key issues such as composition prediction of the reaction vapors, selection of thermodynamic methods, estimation of tray efficiency, etc. are discussed. The proposed simulation approach is applied to two industrial delayed cokers with typical technological processes in a Chinese refinery by using PRO/II. The simulation results obtained are well consistent with the actual operation data, which indicates that the presented approach is suitable to simulate the main fractionators of delayed cokers or other distillation columns consisting of de-superheating sections and rectifying sections.     

Conjugated Graetz problems—II: Fluid-fluid problems

Conjugated Graetz problems [1], involving two co- or counter-currently flowing phases are discussed following the general formalism of [1]. Although the difficulty, which arises from the changing sign of the velocity profile over the total cross-section of the two-fluid conduit of the counter-current problems, may be readily handled by the general formalism, the inclusion of axial heat conduction in the analysis presents special difficulties in obtaining analytical and/or computationally efficient solutions. The present analysis shows that analytical and computationally efficient solutions may be obtained only for these problems where the temperature profile at the entrance of the heating section is known for at least one of the fluids. The solution of a class of problems with long heating sections is obtained untilizing the general formalism together with the Gram-Schmidt orthonormalization process in the spirit of [5]. Problems with low Peclet numbers for both fluids and with an adiabatic section preceding the heating section or problems with very short heating sections are also briefly discussed.     

小型尿素装置工艺结垢问题与化学清洗

论述水溶液全循环法尿素中碳丙脱碳和尿素分解系统产生结垢的原因，并分别介绍了用ＬＡＮ２６７Ｃ和ＬＡＮ２５７Ｃ清洗技术清除结垢的方法及清除效果。     

催化蒸馏合成乙二醇乙醚的过程模拟

修正了非平衡级速率模型,使之能适用于催化蒸馏过程的模拟.此催化蒸馏塔的精馏段和提馏段为一般的填料塔结构,而反应段为CR＆L公司提出的特定结构的催化剂填充层.采用专门测定此特殊结构的催化剂填充层的气膜和液膜传质系数关联式来计算反应段中的传质速率,用Onda的关联式计算精馏段和提馏段填充层中的传质速率.结合在NKC-01分子筛催化剂上环氧乙烷与乙醇反应的动力学方程式,采用Newton-Raphson技术完成了催化蒸馏合成乙二醇乙醚过程的模拟,结果是令人满意的.     

滚筒造粒过程建模与控制策略的发展与展望

介绍滚筒造粒过程控制的建模方法和控制策略两个方面的发展现状，造粒过程数学建模的发展趋势是集合平衡模型，因此建模部分主要是集合平衡模型的建立、降阶及求解等；控制部分根据控制方法分为优化控制、预测控制、容错控制及智能控制等。最后通过现状分析，给出可能的发展方向。     

Homotopy continuation enhanced branch and bound algorithms for strongly nonconvex mixed-integer nonlinear optimization

Large-scale strongly nonlinear and nonconvex mixed-integer nonlinear programming (MINLP) models frequently appear in optimization-based process synthesis, integration, intensification, and process control. However, they are usually difficult to solve by existing algorithms within acceptable time. In this study, we propose two robust homotopy continuation enhanced branch and bound (HCBB) algorithms (denoted as HCBB-FP and HCBB-RB) where the homotopy continuation method is employed to gradually approach the optimum of the NLP subproblem at a node from the solution at its parent node. A variable step length is adapted to effectively balance feasibility and computational efficiency. The computational results from solving four existing process synthesis problems demonstrate that the proposed HCBB algorithms can find the same optimal solution from different initial points, while the existing MINLP algorithms fail or find much worse solutions. In addition, HCBB-RB is superior to HCBB-FP due to much lower computational effort required for the same locally optimal solution.     

Hydrogen production from steam methane reforming coupled with in situ CO2 capture: Conceptual parametric study

The work deals with fundamental analysis of the sorption-enhanced steam methane reforming (SE-SMR) process in which the simultaneous removal of carbon dioxide by hydrotalcite-based chemisorbent is coupled. A two-section reactor model is developed to describe the SE-SMR reactor, decoupling the complexity in process analysis. The model defines two subsequent sections in the reactor: an equilibrium conversion section (upstream) and an adsorption reforming section (downstream). The material balance relationship in the equilibrium conversion section is directly determined by thermodynamic equilibrium calculation, providing an equilibrated atmosphere to the next section. The adsorption reforming section is described using an isothermal multi-component dynamic model into which the SMR reactions and the high-temperature CO₂ adsorption are embedded. The multiple requirements (including H₂ purity, H₂ productivity, CH₄ conversion enhancement, and carbon oxides concentrations) are taken into account simultaneously so as to analyze and define feasible operation window for producing high-purity hydrogen with ppm-level CO impurity. The performances of the reactors with different dimensions (laboratory-scale and pilot-scale) are explored, highlighting the importance of operation parameter control to the process feasibility.     

Integrated run-to-run and on-line model-based control of particle size distribution for a semi-batch precipitation reactor

The dynamics of particle size distribution (PSD) in a precipitation process are represented by a population balance (PB) and related differential–algebraic equations. The control of PSD is studied by using a closed-form solution of the PB. Batch-to-batch control and on-line single batch control strategies are investigated for controlling a semi-batch reactor. A systematic integration of the two strategies is shown to have a complementary effect on the control performance.     

Graphical processing unit (GPU) acceleration for numerical solution of population balance models using high resolution finite volume algorithm

Population balance modeling is a widely used approach to describe crystallization processes. It can be extended to multivariate cases where more internal coordinates i.e., particle properties such as multiple characteristic sizes, composition, purity, etc. can be used. The current study presents highly efficient fully discretized parallel implementation of the high resolution finite volume technique implemented on graphical processing units (GPUs) for the solution of single- and multi-dimensional population balance models (PBMs). The proposed GPU-PBM is implemented using CUDA C++ code for GPU calculations and provides a generic Matlab interface for easy application for scientific computing. The case studies demonstrate that the code running on the GPU is between 2–40 times faster than the compiled C++ code and 50–250 times faster than the standard MatLab implementation. This significant improvement in computational time enables the application of model-based control approaches in real time even in case of multidimensional population balance models.     

Simulation of Aerosol Coagulation and Deposition Under Multiple Flow Regimes with Arbitrary Computational Precision

In computational aerosol coagulation models, a widely used technique is the sectional treatment of the particle size distribution. This approach is used in many first- and second-generation computer codes, where the section boundaries are selected to obey a geometric constraint. While this technique improves computational efficiency, it introduces a number of limitations, including poor representation of the initial size distribution and loss of resolution in the coagulated or final distribution. A robust and versatile computer model, SEROSA, has been developed, which permits an arbitrary number of sections with arbitrary size boundaries to simulate the temporal evolution of coagulation and deposition under multiple flow-regimes and coagulation types. The code permits a large number of parameter combinations and what-if scenarios under user control. Results are benchmarked against an analytical model as well as three coagulation models using coincident section boundaries and coagulation mechanisms. The comparison shows excellent agreement in cases where other computer models are known to perform well. The test cases also included scenarios where previously published computational coagulation models lack capabilities or exhibit numerical difficulties. Computational time varies depending on the number of sections, ageing, and coagulation types from a few seconds to minutes. The software is distributed by the Radiation Safety Information Computational Center of Oak Ridge National Laboratory as Code Package PSR 573.

Copyright 2013 American Association for Aerosol Research