A COMBINED MILP AND LOGIC-BASED APPROACH TO THE SYNTHESIS OF OPERATING PROCEDURES FOR BATCH PLANTS

Synthesizing a set of operating procedures for the safe and efficient transient operation of chemical plants is a difficult problem owing to the enormous number of possible combinations of actions in a typical plant. In most current industrial plant design practice, there are no formal methods for systematically transforming process specifications into operating procedures for the plant operators and into sequence control instructions for the control computers. There is much scope for a formalized computer-based procedure synthesis methodology to assist the design engineer/plant operator with both the formulation and assessment of procedures off-line and, eventually, with the on-line problem of procedure synthesis in response to unexpected situations

A recently developed approach for operating procedure synthesis for multipurpose batch plants is considered. The modelling formalism used includes the separate definition of process operations, as State Task Networks, and of physical plant, at the level of detail of a piping and instrumentation diagram. In this paper, a subgoaling procedure is developed using the State Task Network representation which decomposes the procedure synthesis goals into simpler subgoals by means of an efficient Mixed Integer Linear Programming (MILP) technique. Detailed control sequences are then generated for each subgoal using a set of rules and algorithms specific for each type of subgoal. The procedure sequences thus generated are validated by simulation on a plant model with checking of physical and operational constraints at each new plant state. We have found that this hierarchical approach to the procedure synthesis problem greatly reduces the problem complexity

The usefulness of the general approach and of the subgoaling procedure in particular are demonstrated through a multiproduct batch plant example.     

从不规范设计书到系统逻辑控制器顺序功能流程图的设计

Today＇s automation industry is driven by the need for an increased productivity, higher flexibility, and higher individuality, and characterized by tailor-made and more complex control solutions. In the processing industry, logic controller design is often a manual, experience-based, and thus an error-prone procedure. Typically, the specifications are given by a set of informal requirements and a technical flowchart and both are used to be directly translated into the control code. This paper proposes a method in which the control program is constructed as a sequential function chart （SFC） by transforming the requirements via clearly defined intermediate formats. For the purpose of analysis, the resulting SFC can be translated algorithmically into timed automata. A rigorous verification can be used to determine whether all specifications are satisfied if a formal model of the plant is available which is then composed with the automata model of the logic controller （LC）.     

Efficient Engineering by Modularization into Package Units

The development of efficient engineering methods is an objective of many current research activities. One of the main areas of focus in this context is modularization and standardization in order to reduce project execution time. The intellectual key issue of this approach is the definition of modules that can be reused in a multitude of plant designs, thereby gaining efficiency in comparison to individually created designs. The paper describes an approach to configure any plant design for vendor offers based on customer requests concerning varying capacities, product specifications, plant locations and individual modifications. The novel idea is to assemble a set of tools that allows for a direct connection of 3D plant layouts and the corresponding cost calculations. Ultimately, it is aiming to be able to calculate the equipment size by using a process simulation tool in accordance with defined capacities and the local boundaries of the construction site. As a first proof of principle for the concept HPLC technical plants in a scale of 150 to 1000 mm ID are presented and discussed.     

Sicherheitsanalysen zur systematischen Überprüfung von Verfahren und Anlagen — Methoden,Nutzen und Grenzen

Safety analyses for the systematic checking of chemical plant and processes–methods, benefits and limitations . Safety analyses, i. e. systematic procedures for the safety checking of chemical plant and processes, are useful for the completion and optimization of safety concepts. A literature survey of this topic reveals that hitherto procedures proposed can be divided into identifying and evaluating methods and can also be reduced to four basic working principles with a total of eight different methods. These eight main methods are presented using examples and are evaluated with regard to their appropriate use and the limitations which have to be kept in mind.     

A comprehensive formal approach to the evaluation of bids for desalination plants using verbal judgment

Evaluation of competitive bids for large engineering projects such as desalination plant construction requires careful consideration of several factors other than pure economic merits; namely, technical characteristics of bids, the socio-political situation, safety merits, environmental aspects, public acceptance and other non-financial aspects. A method is developed here based on verbal judgment and fuzzy set theory to allow for comprehensive and systematic formal evaluation of bids. The method is applied to a case study and can be directly used by the technical team to make the final conclusion. The method is implemented in the form of a computer code (MAFDA) which is suitable for interactive computer facilities.     

化工中试装置性能化设计思路探讨

中试装置在设计中存在着"标准真空"问题,国内外均无针对中试装置的专业标准规范,造成中试装置在设计时出现无规范可依的状况。本文首先对化工中试装置设计现状及其特点进行了了解,并在此基础上对中试装置的设计采用了一种新的设计思路,即性能化设计的思路,建立起了中试装置性能化平面布局设计框架,并对框架的步骤进行了简要说明。     

Flexible and economical operation of chlor-alkali process with subsequent polyvinyl chloride production

Demand response (DR) can compensate for imbalances in variable renewable energy supplies. This possibility is particularly interesting for electrochemical processes, due to their high energy intensity. To determine the technical feasibility and economic viability of DR, we chose the chlor-alkali process with subsequent polyvinyl chloride production, including intermediate storage for ethylene dichloride. We estimate the maximum possible cost savings of implementing load flexibility measures. A process model is set up to determine the system characteristic. Subsequent optimizations result in the facility's best possible dispatch depending on additional and minimum power load, storage volume, and cost of a load change. Real plant data are used to specify model parameters and validate the system characteristic and the plant dispatch. An economic evaluation reveals the economic advantages of efficiency and flexibility. The approach can be used to analyze the DR potential of other chlorine value chains or facilities with high electricity demand in general.     

MODEL REFERENCE ADAPTIVE CONTROL BASED ON LIAPUNOV'S DIRECT METHOD Part II: Hybrid Computer Simulation and Experimental Application

A Model Reference Adaptive Control (MRAC) system is evaluated via hybrid computer simulation and experimental application to a computer-controlled, pilot plant evaporator. In both the simulation and experimental studies, the MRAC system performed well and was insensitive to unmeasured process disturbances, to the choice of the initial control policy and to changes in plant operating conditions. In addition to providing an algorithm for adapting control systems to accommodate changing process parameters, MRAC also provides a systematic approach for tuning or developing multivariable control systems for time-invariant processes.     

MODEL REFERENCE ADAPTIVE CONTROL BASED ON LIAPUNOV'S DIRECT METHOD Part II: Hybrid Computer Simulation and Experimental Application

A Model Reference Adaptive Control (MRAC) system is evaluated via hybrid computer simulation and experimental application to a computer-controlled, pilot plant evaporator. In both the simulation and experimental studies, the MRAC system performed well and was insensitive to unmeasured process disturbances, to the choice of the initial control policy and to changes in plant operating conditions. In addition to providing an algorithm for adapting control systems to accommodate changing process parameters, MRAC also provides a systematic approach for tuning or developing multivariable control systems for time-invariant processes.     

基于决策树算法的石化装置过程安全管理评估技术研发及应用

针对当前石油化工企业装置安全生产管理现状,为提升石化装置过程安全管理水平,借鉴国内外过程安全管理体系和相关标准要求及典型管理经验,采用基于关联度的决策树算法构建了石化装置过程安全管理评估指标体系,并运用多层次综合模糊评价方法建立了评估模型,设计开发了装置过程安全管理评估系统,并结合实例进行了验证分析. 结果表明,该技术可量化分析装置过程安全管理存在的薄弱环节,有助于过程安全管理改进和水平提升,对保障装置安全稳定运行、提升装置安全管控水平具有现实意义.     

Optimization of the Design and Operation of Seawater RO Desalination Plants

Abstract

In this work a straightforward procedure for the optimum design and operation of the seawater reverse osmosis (SWRO) plants is being proposed. The analysis is based on analytical equations for the permeate flow rate and quality and the salt flow rate. The mathematical model and the developed software can predict the brine and permeate characteristics for any SWRO plant regardless of the number of the membrane modules in the pressure vessels. The results of the developed software were verified by experimental data from a 280 m³/d RO plant, with 8″ membrane module made by FilmTec, and they were compared with the predictions made by ROSA 6.0 software. An excellent agreement was observed between the prediction of the suggested model and the experimental data. The model can be applied in any type of membrane modules as long as the geometry and the membrane characteristics are known.

Different operating conditions were tested and an effort was made for the optimum design and operation of the plant so that the minimum specific energy consumption can be achieved. It is believed that the analytical model presented in this work is a very useful tool not only because of its accuracy for the SWRO plant design and operation but also because of its simplicity.     

Risk management approach for monitoring UF membrane integrity and experimental validation using Ms2-phages

Microfiltration (MF) and ultrafiltration (UF) systems, as an alternative to conventional water treatment for drinking water, have been developed very fast due to their ability for the removal of microbial pathogens, especially Cryptosporidium and Giardia. One of the most important tasks for the application of UF systems is to monitor membrane integrity during operation, detect and repair the defects because small defects could result in significant reduction of pathogen removal efficiency and consequently reduce UF membrane performance. The objective of this project is to develop a decision-aid tool for operators that gives them the integrity level of their plant without having to disconnect all the modules and indicates if the measured level puts in danger the plant effectiveness and so if he has to immediately repair or if he can differ the repairing.     

小氮肥工艺指标与考核管理

从研究工艺指标的意义入手，介绍了工厂建立工艺指标网络体系及相应的工艺指标考核制度，推动生产管理迈新水平的情况。     

基于模型校核的生化网络自动辨识方法

This study focuses on automatic searching and verifying methods for the teachability, transition logics and hierarchical structure in all possible paths of biological processes using model checking. The automatic search and verification for alternative paths within complex and large networks in biological process can provide a considerable amount of solutions, which is difficult to handle manually. Model checking is an automatic method for verifying if a circuit or a condition, expressed as a concurrent transition system, satisfies a set of properties expressed in a temporal logic, such as computational tree logic （CTL）. This article represents that model checking is feasible in biochemical network verification and it shows certain advantages over simulation for querying and searching of special behavioral properties in biochemical processes.     

Improving uncertainty evaluation of process models by using pedigree analysis. A case study on CO2 capture with monoethanolamine

This article aims to improve uncertainty evaluation of process models by combining a quantitative uncertainty evaluation method (data validation) with a qualitative uncertainty evaluation method (pedigree analysis). The approach is tested on a case study of monoethanolamine based postcombustion CO₂ capture from a coal power plant. Data validation was used to quantitatively assess the uncertainty of the inputs and outputs of the MEA model. Pedigree analysis was used to qualitatively assess the uncertainty in the current knowledge base on MEA carbon capture systems, the uncertainty in the MEA process model, and the uncertainty of the MEA model results. The pedigree review was done by 13 international experts in the field of postcombustion carbon capture with chemical solvents.The data validation showed that our MEA model is accurate in predicting specific reboiler duty, and CO₂ stream purity (4% and 1% difference respectively between model and pilot plant results), but in first instance it was less accurate in predicting liquid over gas ratio, and cooling water requirement (54% and 23% difference respectively between model and pilot plant results). The pedigree analysis complemented these results by showing that there was fairly high uncertainty in the thermodynamic, and chemistry submodels, as reflected in the low pedigree scores on most indicators. Therefore, the model was improved to better resemble pilot plant results.The results indicate that using a pedigree approach improved uncertainty evaluation in three ways. First, by highlighting sources of uncertainty that quantitative uncertainty analysis does not take into account, such as uncertainty in the knowledge base regarding a specific phenomenon. Second, by providing a systematic approach to uncertainty evaluation, thereby increasing the awareness of modeller and model user. And finally, by presenting the outcomes in easy to understand numerical scores and colours, improving the communication of model uncertainty. In combination with quantitative validation efforts, the pedigree approach can provide a strong method to gain deep insight into the strengths and weaknesses of a process model, and to communicate this to policy and decision-makers.     

玻壳检验可重构控制系统的实现

结合对玻壳检验项目的改造,把可重构制造系统引入到玻壳检验中,着重分析了检验系统的重构功能.采用PLC集中控制,并从控制软件上介绍了部分模块的功能,在PLC中模块以子程序的形式进行调用,同时给出了控制软件流程图.文中提到的技术对其他家电行业具有借鉴意义.     

An Improved Hybrid Genetic Algorithm for Chemical Plant Layout Optimization with Novel Non-overlapping and Toxic Gas Dispersion Constraints

New approaches for facility distribution in chemical plants are proposed including an improved non-overlapping constraint based on projection relationships of facilities and a novel toxic gas dispersion constraint. In consideration of the large number of variables in the plant layout model, our new method can significantly reduce the number of variables with their own projection relationships. Also, as toxic gas dispersion is a usual incident in a chemical plant, a simple approach to describe the gas leakage is proposed, which can clearly represent the constraints of potential emission source and sitting facilities. For solving the plant layout model, an improved genetic algorithm （GA） based on infeasible solution fix technique is proposed, which improves the globe search ability of GA. The case study and experiment show that a better layout plan can be obtained with our method, and the safety factors such as gas dispersion and minimum distances can be well handled in the solution.     

A Hybrid Method for Stochastic Performance Modeling and Optimization of Chemical Engineering Processes

As chemical engineers seek to improve plant safety, reliability, and financial performance, a wide range of uncertaintyladen decisions need to be made. It is widely agreed that probabilistic approaches provide a rational framework to quantify such uncertainties and can result in improved decision making and performance when compared with deterministic approaches. This article proposes a novel method for design and performance analysis of chemical engineering processes under uncertainty. The framework combines process simulation tools, response surface techniques, and numerical integration schemes applied in structural reliability problems to determine the probability of a process achieving a performance function of interest. The approach can be used to model processes in the presence or absence of performance function(s), with or without parameter interactions, at both design and operational phases. With this, process behavior can be quantified in terms of stochastic performance measures such as reliability indices and the associated most probable process design/operating conditions, providing a simple way to analyze a wide range of decisions. To validate the applicability of the proposed framework, three case study systems are considered: a plug flow reactor, a heat exchanger, and finally a pump system. In each case, performance criteria based on the original physical model and the surrogate model are set up. Reliability analysis is then carried out based on these two models and the results are assessed. The results show that the proposed framework can be successfully applied in chemical engineering analysis with additional benefits over the traditional deterministic methods.     

PTA装置氧化单元结晶器的模拟研究

利用PRO/II模拟软件,对精对苯二甲酸(PTA)装置对二甲苯(PX)氧化单元结晶器进行了模拟研究,建立了对苯二甲酸(TA)晶体的结晶动力学模型以及第一结晶器、第二结晶器和第三结晶器的模拟模块,并进行了其应用分析。结果表明:模拟结果与设计数据的偏差在可接受的范围内,可以应用于PTA装置的工程设计;利用结晶器模拟模块,可得到结晶器的TA晶体生成量和TA粒径随结晶器温度和体积的变化规律;对于采用的BP-AMOCO工艺的PTA装置,在最优温度和压力条件下以单个结晶器代替串接的3台结晶器进行生产不一定具有优势。