Choamun Yun

An integrated model of supply network and production planning for multiple fuel products of multi-site refineries

An integrated model of supply network and production planning is proposed for the collaboration among refineries manufacturing multiple fuel products at different locations. The simulation and optimization based on the model indicate the following. The distribution costs can be reduced by relocating distribution centers as well as by reconfiguring their linkages to various markets. Moreover, the multiple fuel products manufactured need to be segregated during storage and transportation to be able to satisfy the demands of the various markets. The production planning, therefore, should be an integral part of the supply-network planning, and vice versa. Specifically, the proposed integrated model is for the nationwide supply of multiple fuel products manufactured by the individual refineries. The efficacy and usefulness of the integrated model is illustrated with an example involving three refineries and four varieties of fuel products.

Computer-aided scale-up of a packed-bed tubular reactor

Temperature control is crucial when designing a catalytic tubular reactor for exothermic reactions because hot spots in packed-bed tubes affect conversion, selectivity and lifespan of catalysts. To resolve the hot spot problem, a computer-aided scale-up method combining process modeling software, heat exchanger design software and computational fluid dynamics (CFD) analysis is proposed. The proposed method is composed of three steps as follows: firstly, the length and the number of tubes are determined to achieve a target production rate by the simulations of a single-tube reactor model. Secondly, the detailed geometry of a scaled-up reactor comprising multiple tubes is determined using heat exchanger design software. Finally, optimal operating conditions to control the hot spots are designated by CFD analysis. As a practical application, the method is applied to scaling up the single-tube reactor producing epichlorohydrin to a demonstration-scale reactor comprising 200 tubes so its optimal design and operating conditions are determined.

Graph-theoretic approach to optimal synthesis of supply networks: Distribution of gasoline from a refinery

Abstract The synthesis of a supply network is profoundly conveluted because of its combinatorial complexity. Global or even near optimal solutions are, more often than not, unobtainable through the heuristic methods. On the other hand, the majority of the algorithmic methods, which mainly resort to mixed integer programming, in theory, can give rise to global optima; however, they are effective only for relatively minute networks. Obviously, it is highly desirable that a novel paradigm be established for optimally synthesizing supply networks; the adoption of the graph-theoretic method based on P-graphs (process graphs) is proposed herein for the synthesis of optimal supply networks. The proposed method is illustrated with examples. Each example has yielded simultaneously the optimal and near optimal structures of the supply network performing a specific task in the ranked order. The example reveals a unique feature of the method.

A method to find an optimal draw solute for cost-effective FO(forward osmosis) desalination process

Abstract A method to find a draw solute for forward osmosis desalination is developed. The economics of a forward osmosis process is largely influenced by the selection of a draw solute and energy consumed for its separation from the fresh product water. The proposed method evaluates a vast number of possible draw solutes by predicting the production rate of fresh water, investment cost and energy consumption in the separation process. The possible draw solutes are confined to electrolytes and its separation processes to thermal systems. Subsequently, a cost-minimizing draw solute is determined subject to any necessary constraints. The developed method will contribute to designing commercially viable forward-osmosis desalination processes.

Integrated Procurement and Operational Planning of a Biorefinery Considering Contracts and Futures

Abstract The profit of a biorefinery is highly affected by the supply of its raw materials and margin from the product. Taking responsive actions to the unstable supply of raw materials and the fluctuating prices are of major concern for the efficient management of biorefineries. In this study, a biorefinery complex is defined to tackle these issues by diversifying products as well as raw materials. Various raw materials are purchased based on the contracts and the spot prices of candidate raw materials while their total amount depends on product demands. The supply of required raw materials is accompanied by the futures contracts to curtail the risks involved in the procurement. In the downstream process, operational planning of fermentation and separation units is established according to the demand and margin of multiple products. The proposed model of integrated planning for a biorefinery would contribute to escalating its profitability and operational flexibility.

WebCell: An Integrated Environment For Modeling and Simulation of Cellular Networks Online

Various softwares and computational environments have been developed as listed in the systems biology community (http://sbml.org). Nevertheless, only a handful of projects adopt the platform-independent Web-based approach which is a desirable direction for simulation research and development. To this end, we developed WebCell which is an integrated simulation environment for managing information on cellular networks, and for interactively exploring their steady-state and dynamic behaviors over the Web. A user friendly Web interface allows users to efficiently create, visualize, simulate and store their reaction network models, thereby facilitating kinetic modeling and simulation of biological systems of interest. Supported analysis methods for such models include structural pathway analysis, metabolic control analysis, conservation analysis and time-course simulation. In addition, a variety of model collections publicly available have been compiled to provide comprehensive implications for cellular dynamics of the models. Thus, this comprehensive, Web-accessible and integrative system not only serves the educational demonstration site of publicly available kinetic models but also provides the customized modeling environment for quantitatively and qualitatively analyzing the cellular system

Metabolic Control Analysis of Complex Biological Systems

A systematic approach is proposed for the metabolic control analysis of various dynamic behaviors in biological systems. The complex kinetic models are reduced by identifying the conservation relations and the time scale analysis. Subsequently, the biological systems are categorized into the three groups: systems with the steady-states, sustained oscillations, or other non-steady states. The sensitivities are measured to calculate the corresponding control coefficients that are defined considering the characteristics of the dynamics of the systems. The proposed approach is illustrated with its application to the dynamic behaviors of a complex biological model.

WebCell-script: A web-based script for managing quantitative and qualitative information of cellular networks

WebCell, the integrative program for modeling and simulation of cellular networks, is based on the user-friendly Web environment. It is available at anytime, anywhere. This environment, however, has some constraints. For instance, the data format is limited. In addition, the user-interface is not really flexible. These problems can be solved with simple object access protocol (SOAP). It offers many useful functions - especially extensibility and fast response. We have been developing the WebCell-script, an add-in module for WebCell, using this technology. This also can handle many user-defined analyses independently. It is expected to contribute to developing models and analyzing pathway networks under various conditions through the advanced in silico experiments

Determination of the Metabolic Networks Fluxes Using Carbon Isotopomer Labeling and Metabolic Flux Analysis

To determine intracellular fluxes using carbon labeled experimental data, adequate techniques are needed. Metabolic flux analysis (MFA) is a useful method to simulate metabolic networks. Because the measurable extracellular flux data is always insufficient, there are more unknowns than equations. Further information or constraints are required to make fully determined system of which the degrees of freedom (DOF) is zero. It is possible to obtain mass distribution data using the carbon isotope labeling experiment for fermentation experiments. Carbon isotope labeled data can be obtained from C isotope tracer technique and GC-MS (Gas Chromatography-Mass Spectrometry) measurements. In this work, we have developed a metabolic networks simulation tool which can exactly determine intracellular fluxes using carbon isotopomer labeling data. The result can provide strict insight into complex metabolic networks