Flexibility and operability analysis of a HEN-integrated natural gas expander plant

In the heat-exchanger network (HEN) literature, synthesis, design, and flexibility analyses of HENs are done independently from processes to which HENs are integrated. Such analyses are made mostly based on nominal operating conditions at which the HEN's source- and target-stream properties are evaluated. However, terminal-stream properties of HENs depend upon temperatures, pressures, and compositions of the process connected to the HEN. In this work, flexibility and operability issues of a HEN are investigated with rigorous simulations using the process flowsheet simulator HYSYS for a HEN-integrated natural gas turbo-expander plant (TEP) operating under ethane-recovery mode. The contribution of this work is threefold. First, the HEN-plant interactions are exemplified via the process flowsheet simulator. Second, flexibility and operability issues are tackled using the optimization capability of the flowsheet simulator. Third, for highly energy-integrated complex plants like the TEP, the difficulties or impossibilities of automated HEN synthesis and flexibility analysis with process flowsheet simulators are demonstrated.     

Similarities and differences between the concepts of operability and flexibility: The steady‐state case

This article presents a comparative review on the operability and flexibility concepts and their application to process design and control. First, the operability and flexibility methodologies are summarized. Then the application of the operability framework to steady‐state and dynamic systems is illustrated through the examination of several example categories such as linear and nonlinear, square and non‐square systems. The flexibility approach based on the active set strategy is used to study the same examples from the flexibility point of view. The discussed results show that the operability and flexibility approaches examine a process from different perspectives and provide valuable complementary information. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Analysis of process operability at the preliminary design stage

A hierarchical procedure is presented for assessing the steady-state operability of a process. The method can be applied as new processes are being designed, or it can be used as a decomposition procedure for studying the operability of existing processes. The results indicate that operability alternatives are often encountered, i.e. different problem formulations are obtained depending on the assumptions that are made. In addition, the analyses indicate that the equipment design should be based on the mean value of the disturbances, the “worst-case” conditions or the expected profit, depending on the particular equipment in the flowsheet.     

Consequence Identification for Maloperation in Batch Process

Batch processes are important in chemical industry, in which operators usually play a major role and hazards may arise by their inadvertent acts. In this paper, based on hazard and operability study and concept of qualitative simulation, an automatic method for adverse consequence identification for potential maloperation is proposed. The qualitative model for production process is expressed by a novel directed graph. Possible operation deviations from normal operating procedure are identified systematically by using a group of guidewords. The proposed algorithm is used for qualitative simulation of batch processes to identify the effects of maloperations. The method is illustrated with a simple batch process and a batch reaction process. The results show that batch processes can be simulated qualitatively and hazards can be identified for operating procedures including maloperations. After analysis for possible plant maloperations, some measures can be taken to avoid maloperations or reduce losses resulted from maloperations.     

Automatic HAZOP analysis method for unsteady operation in chemical based on qualitative simulation and inference

Comparing with continuous production process, unsteady operation process, such as startup and shutdown, tends to abnormal situations due to a large number of operations of operators and dynamic state changes involved. To guarantee a safe operation, process hazard analysis (PHA) is very important to proactively identify the potential safety problems. In the chemical process industry, hazard and operability (HAZOP) analysis is the mostwidely used method. In this paper, based on proposed qualitative simulation and inferencemethod, an automatic HAZOP analysis method for unsteady operation processes is proposed. Mass transfer and relationships among process variables are expressed by Petri net-directed graphmodel based fuzzy logic. Operating procedure is expressed according to a formal expression. Possible operation deviations from normal operating procedure are identified by using a group of guidewords. Hazards are identified automatically by qualitative simulation and inference when wrong operation process is performed. The method is validated by a rectification column system.     

WSA制酸回收工艺在醇氨联产项目中的应用

概述了WSA制酸回收工艺流程及其特点,同时与超级克劳斯(Super Claus)工艺进行了工艺对比。实际运行情况表明,WSA制酸回收工艺具有流程短、硫回收率高、综合能耗和运行成本低、操作弹性大等特点。     

Stochastic optimization of flexibility in retrofit design of linear systems

In this paper the problem of obtaining the degree of flexibility that maximizes the total profit in an existing process flowsheet is addressed. Assuming a linear model for the process and given probability distribution functions for the uncertain parameters, the curve relating the expected revenue to the flexibility index is generated. An efficient stochastic optimization method is developed for this purpose that is coupled with a parametric analysis. This then allows determination the level of flexibility in a retrofit where the proper trade-off is established between investment cost and expected revenue. Two examples are presented to illustrate the proposed procedure.     

Computer aided operability analysis via interactive graphics

A comprehensive computer-aided design methodology utilizing the highly interactive capabilities between a graphics computer and the user is described. The program, CHESOPS, enables a flexible simulation of any arbitrary chemical process by synthesizing the process design about several steady state values and extending the analysis to the effects of design changes on process operability. In this way the process may be visualized within a dynamic environment from which interactive control system design and dynamic simulation takes place. The highly flexible nature of the program enables efficient and comprehensive investigation of alternative designs, control structures, and optimal operating conditions.     

Flexibility and resiliency of process systems

Because chemical plants are never operating at the nominal design conditions or at a steady state it is important to include aspects of flexibility, operability and control into the design procedures. The available techniques for this purpose are reviewed and future research needs are identified.     

Process synthesis,design and analysis using a process-group contribution method

This paper describes the development and application of a process-group contribution method to model, simulate and synthesize chemical processes. Process flowsheets are generated in the same way as atoms or groups of atoms are combined to form molecules in computer aided molecular design (CAMD) techniques. The fundamental pillars of this framework are the definition and use of functional process-groups (building blocks) representing a wide range of process operations, flowsheet connectivity rules to join the process-groups to generate all the feasible flowsheet alternatives and flowsheet property models like energy consumption, atom efficiency, environmental impact to evaluate the performance of the generated alternatives. In this way, a list of feasible flowsheets are quickly generated, screened and selected for further analysis. Since the flowsheet is synthesized and the operations in the flowsheet designed through predictive models to match a set of design targets, optimal solution of a given synthesis problem is guaranteed.     

ARS技术剖析

本文对国外最新的烯烃分离工艺—ARS技术进行了剖析。提出了ARS技术关键设备分馏器的模拟方法;指出了ARS技术的核心和节能原理。提出了分馏器初级试算流程。该流程的模拟计算结果表明,脱甲烷塔塔顶冷量消耗仅为常规流程的三分之一左右,并且无需—101℃乙烯冷剂。此外分馏器可以在较低压力下操作,从而大大减少了裂解气压缩机的功率消耗。     

基于ASPEN PLUS用户模型技术的催化重整全流程模拟

采用用户模型技术,将自主开发的17集总反应动力学模型与ASPEN PLUS稳态流程模拟软件集成在一起,从而在ASPEN PLUS平台实现了包含重整反应装置在内的催化重整全流程模拟.这一技术既可以利用ASPEN PLUS强大的数据库、模型库和模拟优化功能,大大拓展模拟范围,又可以保持自定义反应模型的特点.整个流程全部仿照反应动力学模型,将300多种化合物定义成18种集总组分（含氢气）,并采用专用于石油系统的物性计算方法.建立的ASPEN PLUS二次开发软件在某连续重整装置上获得了成功应用,模拟结果与实际操作值吻合得相当好,完全满足工业应用的要求.此软件可用于催化重整装置的生产调优、扩能改造和新装置的工艺设计.     

化工过程综合问题MINLP算法中整型变量的连续化

化工过程系统综合问题需要同时考虑设备结构参数和工艺操作参数,一般用整型变量表示设备的取舍,用连续变量表示操作参数,这就构成一个流程的超结构,在数学形式表现为一个混合整型非线性规划（MINLP）问题。混合整型非线性规划问题的求解成为化工过程综合优化的关键。今根据超结构中整型变量的特征,提出整型变量连续化处理的思路,将MINLP问题简化为NLP问题,然后采用罚函数法求解。最后将该算法运用于加氢脱烷基化（HDA）过程综合的实例研究,结果表明该算法克服了传统方法在处理整型变量时出现的麻烦,为有效快速地进行化工过程综合优化问题提供了一种新的途径。     

Operability and control in process intensification and modular design: Challenges and opportunities

In this article, the importance of considering operability and control criteria in the analysis and design of intensified and modular processes is discussed. We first analyze the impact on operability of key factors including: (i) degrees of freedom, (ii) process constraints, (iii) numbering up vs. scaling up, and (iv) dynamic/periodic operation. Comparative examples are presented to showcase the pros and cons in intensified/modular systems vs. their conventional counterparts from operability and control aspects. Then we look into metrics and tools to address these challenges such as: (i) flexibility analysis, (ii) operability-based design, and (iii) advanced model-based control. Considering different conceptual design stages as synthesis intensification, steady-state design, and dynamic operational optimization, we highlight the need to incorporate different levels of operability considerations. Future research opportunities and perspectives are also identified, particularly emphasizing the importance of a holistic strategy for integrated design, operability, and control of intensified and modular process systems.     

Process Simulation of Combustion Drying with Simprosys Software

This article presents a software tool, Simprosys, and its newly added burner unit operation model for process modeling and simulation of drying. Combustion generation using the burner unit operation is described briefly. Humid gas properties of combustion are compared and found to be different from those of air. The effects of pressure on both air and combustion humid gas properties are investigated. It is found that both combustion and air could be significantly different in their moisture carrying capability when the operating pressure is different from standard atmospheric pressure, especially for some vacuum drying cases where the operating pressure is well below atmospheric pressure. A model combustion drying flowsheet is simulated with Simprosys 3.0 and simulation results are presented and discussed.     

Dynamische Prozeßsimulation in der industriellen Praxis

Dynamic process simulation in industrial practice. Dynamic process simulation is gaining in importance in process development and plant design. In addition to simulation tools for steady state calculations and optimization, recent years have seen increased development of software tools suitable for dynamic simulation. In particular, dynamic process models have been developed for various unit operations at universities and in industry. Application of the models includes synthesis and analysis of the control structure, start-up and shut down, safety assessments, optimization, and training. In addition, dynamic flowsheet programs analogous to the steady state programs were developed. Wider use of these program systems requires increased flexibility, solving procedures, user interfaces, model library, interfaces to external programs, etc. The present article is intended not only to describe the state of the art and describe some typical applications, but in particular to examine the demands placed on dynamic process simulation and the simulators and to delineate the current limitations of dynamic process simulation from an industrial viewpoint.     

通过调整进出料热状况消除隔离壁精馏塔的黑洞

隔离壁精馏塔在同时控制4个质量指标（塔顶、侧线、塔底产品浓度以及侧线采出杂质比）时会产生设计与操作黑洞,黑洞的产生对隔离壁精馏塔的应用范围带来很大的限制。本文提出了一种通过调整进料和侧线采出的热状况对隔离壁精馏塔的黑洞进行填补的策略。这两个操作变量通过对全塔热平衡的影响,改善预分离塔与主塔之间的耦合关系,进而改善两者分离能力并最终消除黑洞,同时改善了隔离壁精馏塔的动态特性。针对进出料热状况的调整,本文结合牛顿法给出了简单的调整规则,调整会形成3种不同的方案,为不同能量供应条件下填补隔离壁精馏塔的黑洞提供了可能。通过使用Aspen Plus模拟理想三元物系分离,对黑洞填补方法进行稳态分析和动态响应验证,证明采用调整进出料热状况的方法可以有效的填补隔离壁精馏塔的设计与操作黑洞并使其动态特性得到改善。本文所提出的方法完善了填补黑洞的方法体系,增加了隔离壁精馏塔的灵活性与适应性。     

FLEXIBILITY STUDY ON A DUAL MODE NATURAL GAS PLANT IN OPERATION

This work addresses a flexibility study on a natural gas processing plant through the integration of a process simulator to a "worst case" flexibility strategy. The plant has a gas subcooled turboexpansion design, which is suitable for working in dual operation mode; i.e., in either ethane production or ethane rejection mode. The selected uncertain parameters (feed flowrate, condensable hydrocarbons content, carbon dioxide content, and ambient temperature) have great impact on process operating conditions. The use of the worse case algorithm with the KS overestimation function for inequality constraints has also been explored to improve computational time, and numerical results are compared for both solution strategies. Results show, in terms of both robustness and speed of computation, that this approach can be a useful tool to complement operational analysis of large processing units, commonly performed by simulation and "what if" studies.     

Problem-oriented modules for process simulation. resolution strategies for simulation and optimization

A new resolution strategy is presented to overcome short-comings of the sequential modular process flowsheeting. Following a logic flow of information, different from the material flow of streams in the flowsheet, changes the mathematical structure of the system of equations that models the units. New programs have been generated, very different from traditional modules. Deciding an appropriate resolution strategy usually leads to a dramatic reduction in required CPU times and to an increased flexibility to handle different problems. The simulation convergence and process optimization can be approached from a different perspective.     

Flexibility study on a dual mode natural gas plant in operation

This work addresses a flexibility study on a natural gas processing plant through the integration of a process simulator to a "worst case" flexibility strategy. The plant has a gas subcooled turboexpansion design, which is suitable for working in dual operation mode; i.e., in either ethane production or ethane rejection mode. The selected uncertain parameters (feed flowrate, condensable hydrocarbons content, carbon dioxide content, and ambient temperature) have great impact on process operating conditions. The use of the worse case algorithm with the KS overestimation function for inequality constraints has also been explored to improve computational time, and numerical results are compared for both solution strategies. Results show, in terms of both robustness and speed of computation, that this approach can be a useful tool to complement operational analysis of large processing units, commonly performed by simulation and "what if" studies.