En Sup Yoon

A web-based, interactive virtual laboratory system for unit operations and process systems engineering education: issues, design and implementation

The development of real educational content and customized virtual education systems satisfying the needs of a specific engineering education domain is getting more and more research attention in this era of ubiquitous Web and virtual technologies. By analyzing the characteristics of computer-based educational methods and adopting the rapidly changing Internet and object component technologies, we have developed a Web-based, interactive virtual laboratory system for unit operations and process systems engineering education, and validated its effectiveness by surveying student users of the implemented prototype system. In this paper, we also discuss many technical issues in building Web-based interactive virtual education systems and share the experience obtained. The proposed system is expected to overcome many obstacles in performing the unit operations laboratory in the current setting. More teachware and experiment suites are being added for more extensive, quantitative evaluation of educational efficiency of the proposed methodology and the system.

On the solution of population balance equations (PBE) with accurate front tracking methods in practical crystallization processes

Abstract The PBE (population balance equation) containing birth, growth, agglomeration and breakage kinetics is described by a conservation law with a moving source term. For the solution of the PBE, we compare two accurate front tracking methods such as a modified method of characteristics (MOC) and a finite difference method with the weighted essentially non-oscillatory (WENO) scheme. Both methods are applied to a potassium sulfate crystallization problem (K 2 SO 4 –H 2 O system) with a discontinuous initial condition. Parameters of agglomeration and breakage kinetics are estimated on the basis of the experimental data of the K 2 SO 4 –H 2 O system. Owing to moving axis along a crystal growth rate (i.e. elimination of the growth term), the modified MOC is able to provide a highly accurate solution even at discontinuous points without numerical diffusion error. However, in the case of stiff nucleation which can commonly appear in practical crystallization processes, it is necessary to adaptively determine time levels to add a mesh of the nuclei size. For solving PBEs involving agglomeration and breakage terms, the MOC can take more long computational time than the spatial discretization methods like the WENO scheme. It is pointed out that the MOC is not available to solve more than two coupled PBEs in general. WENO schemes for spatial discretization are firstly addressed in this study for the dynamic simulation of batch crystallization processes. The WENO schemes show improvements of accuracy and stability over conventional discretization methods (e.g., backward, central or common upwinding schemes). However the WENO schemes on fixed meshes show, to some extent, the numerical diffusion error near discontinuities or steep moving fronts like other finite difference methods. Hence, they require spatially-adaptive mesh techniques in order to track more accurately the moving fronts. Even though the WENO schemes are less accurate than the MOC, they are of practical use for solving complex PBEs owing to a short computational time and little limitation to use.

Web-based interactive virtual laboratory system for unit operations and process systems engineering education

Abstract The development of the real educational contents and customized virtual education satisfying the needs of specific engineering education domain is getting more and more research attention in this area of Web and virtual technologies. By analyzing the characteristics of computer-based educational methods and using the rapidly changing Internet and object technologies, we developed a Web-based, interactive virtual laboratory system of unit operations and process systems engineering education. The proposed system is expected to overcome many obstacles in performing the unit operations laboratory at the current setting. More teachwares and experiments suites are being added for the extensive, quantitative evaluation on educational efficiency of the proposed system, and the result will be reported at the conference.

STRATEGIES FOR MODELING AND CONTROL OF NONLINEAR CHEMICAL PROCESSES USING NEURAL NETWORKS

A nonlinear predictive control framework is presented, in which nonlinear processes are modeled using neural networks. Several important issues concerning the modeling of nonlinear processes using neural networks are treated, with the emphasis placed on the convergence of neural networks to desired steady states. For nonlinear process predictive control where the neural network model is employed, an important case is examined. A typical nonlinear process, pH control problem, is taken as a case study to demonstrate the proposed approach, some significant results are given.

Cooperative problem solving in diagnostic agents for chemical processes

Abstract In this paper we introduce an agent-based framework for the diagnosis of chemical processes, based on spatially distributed diagnosis architecture. Although the suggested multi-agent diagnostic system uses only the information about process topology and control structure, making the most of local information produces global diagnostic solution. A function-behavior model is also suggested to make possible the collaborative problem solving in chemical process fault diagnosis. To demonstrate the benefits of the suggested collaborative problem solving approach, we solve the diagnostic problem of a stirred-tank reactor system with recycle.

Simulation of fixed bed reactor for dimethyl ether synthesis

Dimethyl Ether (DME) is considered as one of the most promising candidates for a substitute for LPG and diesel fuel. We analyzed one-step DME synthesis from syngas in a shell and tube type fixed bed reactor with consideration of the heat and mass transfer between catalyst pellet and reactants gas and effectiveness factor of catalysts together with reactor cooling through reactor wall. Simulation results showed strong effects of pore diffusion. We compared two different arrangements of catalysts, mixture of catalyst pellets (methanol synthesis catalyst and methanol dehydration catalyst) and hybrid catalyst. Hybrid catalyst gave better performance than a mixture of pellets in terms of CO conversion and DME productivity, but more difficulties with reactor temperature control. Use of inert pellets and inter-cooling was also simulated as a means of controlling maximum reactor temperature.

Simulation of commercial dimethyl ether production plant

The process of Dimethyl ether(DME) production consists of the four parts which are syngas synthesis from natural gas, absorbing CO2 from syngas, DME synthesis reactor and DME separation/purification. KOGAS has developed a process in which syngas is produced from natural gas and converted to DME using a single reactor[1]. For the construction of commercial scale DME plant, the modeling of one-step DME synthesis reactor is required prior to beginning the construction. Since then, the simulation of DME production process should represent actual operation data of pilot or demo scale plant. The simulations of reactor had been conducted using a one-dimensional steady-state model of a shell-and-tube type fixed-bed reactor[2]. Using the result of a reactor analysis, we have conducted simulations of all processes using steady-state models in Aspen Plus®. The simulation of process in this paper reflects the result of a reactor simulation and the real operation data of demo scale DME plant. And the simulation results are satisfied with the requirements for the basic design and engineering of commercial DME plant construction.

A Review of Sustainable Energy – Recent Development and Future Prospects of Dimethyl Ether (DME)

Abstract DME can be synthesized from natural gas, coal, biomass, and/or coal seam, and is a sulfur-free, near-zero aromatics synthetic fuel which is considered as an excellent substitute for conventional diesel and liquefied petroleum gas. Currently, various production technologies are developed and many commercial projects are actively being progressed. This paper presents recent development and future prospect of Dimethyl Ether (DME) as an alternative energy and simple review for biomass energy.

Robust fault diagnosis based on clustered symptom trees

Abstract This study suggests a new methodology for fault diagnosis, based on the signed digraph (SDG), in developing the fault-diagnostic system of a boiler plant. The suggested methodology uses a new model, the clustered symptom tree (CST). The CST utilizes the advantage of the SDG to represent the causal relationship between process variables and/or the propagation paths of faults in a simple and graphical way, and is therefore easy to understand. It also covers the problems, such as symptom variation, that conventional SDG-based methods cannot handle. The advantages of the presented method were confirmed through case studies.

SAFETY ANALYSIS USING AN EXPERT SYSTEM IN CHEMICAL PROCESSES

A knowledge-based expert system for hazard and operability study (HAZOP) is developed. HAZOP study is regarded as one of the most systematic and logical qualitative hazard identification methodologies. But, it requires a multidisciplinary team and is very time-consuming and repetitious task in nature. By developing an computer-aided automation system, these drawbacks of HAZOP study can be overcome. Considerable manpower and time can be reduced and even past experiences of engineers and existing checklists can be stored for future use in the form of knowledge base. The developed knowledge-based HAZOP expert system has a frame-based knowledge structure for equipment failures and process properties, and rule networks for consequence reasoning which uses both forward and backward chaining. The system is open-ended and modular in structure to make it easy to implement wide process knowledge for future expansion. LPG storage and fractionation process has taken as example to test the applicability of the developed system as an automated HAZOP study system. The result shows that savings more than 50% of the required manpower and time for HAZOP studies can be achieved, and the system is very efficient and reliable, too.