Simulation, optimisation and flexible scheduling of MSF desalination process under fouling. Optimal design and operation of MSF desalination process with brine heater and demister fouling, flexible design operation and scheduling under variable demand and seawater temperature using gPROMS.

Among many seawater desalination processes, the multistage flash (MSF) desalination process is a major source of fresh water around the world. The most costly design and operation problem in seawater desalination is due to scale formation and corrosion problems. Fouling factor is one of the many important parameters that affect the operation of MSF processes. This thesis therefore focuses on determining the optimal design and operation strategy of MSF desalinations processes under fouling which will meet variable demand of freshwater. First, a steady state model of MSF is developed based on the basic laws of mass balance, energy balance, and heat transfer equations with supporting correlations for physical properties. gPROMS software is used to develop the model which is validated against the results reported in the literature. The model is then used in further investigations. Based on actual plant data, a simple dynamic fouling factor profile is developed which allows calculation of fouling factor at different time (season of the year). The role of changing brine heater fouling factor with varying seawater temperatures (during the year) on the plant performance and the monthly operating costs for fixed water demand and fixed top brine temperature are then studied. The total monthly operation cost of the process are minimised while the operating parameters such as make up, brine recycle flow rate and steam temperature are optimised. It was found that the seasonal variation in seawater temperature and brine heater fouling factor results in significant variations in the operating parameters and operating costs. The design and operation of the MSF process are optimized in order to meet variable demands of freshwater with changing seawater temperature throughout the day and throughout the year. On the basis of actual data, the neural network (NN) technique has been used to develop a correlation for calculating dynamic freshwater demand/consumption profiles at different times of the day and season. Also, a simple polynomial based dynamic seawater temperature correlation is developed based on actual data. An intermediate storage tank between the plant and the client is considered. The MSF process model developed earlier is coupled with the dynamic model for the storage tank and is incorporated into the optimization framework within gPROMS. Four main seasons are considered in a year and for each season, with variable freshwater demand and seawater temperature, the operating parameters are optimized at discrete time intervals, while minimizing the total daily costs. The intermediate storage tank adds flexible scheduling and maintenance opportunity of individual flash stages and makes it possible to meet variable freshwater demand with varying seawater temperatures without interrupting or fully shutting down the plant at any-time during the day and for any season. Finally, the purity of freshwater coming from MSF desalination plants is very important when the water is used for industrial services such as feed of boiler to produce steam. In this work, for fixed water demand and top brine temperature, the effect of separation efficiency of demister with seasonal variation of seawater temperatures on the final purity of freshwater for both cleaned and fouled demister conditions is studied. It was found that the purity of freshwater is affected by the total number of stages. Also to maintain the purity of freshwater product, comparatively large number of flash stage is required for fouled demister

Plantwide Control and Simulation of Sulfur-Iodine Thermochemical Cycle Process for Hydrogen Production

A PWC structure has developed for an industrial scale SITC plant. Based on the performance evaluation, it has been shown that the SITC plant developed via the proposed modified SOC structure can produce satisfactory performance – smooth and reliable operation. The SITC plant is capable of achieving a thermal efficiency of 69%, which is the highest attainable value so far. It is worth noting that the proposed SITC design is viable on the grounds of economic and controllability

MSF process modelling, simulation and optimisation : impact of non-condensable gases and fouling factor on design and operation. Optimal design and operation of MSF desalination process with non-condensable gases and calcium carbonate fouling, flexible design operation and scheduling under variable demand and seawater temperature using gPROMS.

Desalination is a technique of producing fresh water from the saline water. Industrial desalination of sea water is becoming an essential part in providing sustainable source of fresh water for a large number of countries around the world. Thermal process being the oldest and most dominating for large scale production of freshwater in today¿s world. Multi-Stage Flash (MSF) distillation process has been used for many years and is now the largest sector in the desalination industry. In this work, a steady state mathematical model of Multistage Flash (MSF) desalination process is developed and validated against the results reported in the literature using gPROMS software. The model is then used for further investigation. First, a steady state calcium carbonate fouling resistance model has been developed and implemented in the full MSF mathematical model developed above using gPROMS modeling tool. This model takes into consideration the effect of stage temperature on the calcium carbonate fouling resistance in the flashing chambers in the heat recovery section, heat rejection section, and brine heaters of MSF desalination plants. The effect of seasonal variation of seawater temperature and top brine temperature on the calcium carbonate fouling resistance has been studied throughout the flashing stage. In addition, the total annual operating cost of the MSF process is selected to minimise, while optimising the operating parameters such as seawater rejected flow rate, brine recycle flow rate and steam temperature at different seawater temperature and fouling resistance. Secondly, an intermediate storage between the plant and the client is considered to provide additional flexibility in design and operation of the MSF process throughout the day. A simple polynomial based dynamic seawater temperature and different freshwater demand correlations are developed based on actual data. For different number of flash stages, operating parameters such as seawater rejected flow rate and brine recycle flow rate are optimised, while the total annual operating cost of the MSF process is selected to minimise.The results clearly show that the advantage of using the intermediate storage tank adds flexible scheduling in the MSF plant design and operation parameters to meet the variation in freshwater demand with varying seawater temperatures without interrupting or fully shutting down the plant at any time during the day by adjusting the number of stages. Furthermore, the effect of non-condensable gases (NCG) on the steady state mathematical model of MSF process is developed and implemented in the MSF model developed earlier. Then the model is used to study effect of NCG on the overall heat transfer coefficient. The simulation results showed a decrease in the overall heat transfer coefficient values as NCG concentrations increased. The model is then used to study the effect of NCG on the design and operation parameters of MSF process for fixed water demand. For a given plant configuration (fixed design) and at different seawater and steam temperatures, a 0.015 wt. % of NCG results in significantly different plant operations when compared with those obtained without the presence of NCG. Finally, for fixed water demand and in the presence of 0.015 wt. % NCGs, the performance is evaluated for different plant configurations and seawater temperature and compared with those obtained without the presence of NCG

The hybrid multi-effect desalination (MED) and the adsorption (AD) cycle for desalination

Ph.DDOCTOR OF PHILOSOPH

Mekanistisen termohydraulisen mallinnustavan soveltaminen uudentyyppisten teollisten prosessien dynaamiseen simulointiin

The PDF file of the dissertation includes the summary part and also all five publications as full texts.The process and energy industries have a remarkable position in developing sustainable future. They play an important role in mitigating climate change. Whilst aiming at energy efficient, material recycling, and emission-free processes, the industrial systems are becoming more complex. Process automation is fundamental in confirming that also complex systems can be managed and operated in an easy and safe way. Dynamic system-wide process simulation is practically the only way to verify the interoperability of the process and control solutions before building up the system. For the systems in operation, it enables virtual realistic studies without disturbances or risks for the actual process or people. The qualitative research approach in this work is case study. The modelling and dynamic simulation software Apros is used in five distinct cases, which extend the modelling from traditional nuclear and conventional power plant applications to a board machine, a carbon dioxide capturing power plant, ship energy systems, a seawater desalination plant, and a molten salt based energy storage system. The methodology relies on mechanistic thermal-hydraulic modelling and dynamic simulation. Method development was performed to model and simulate the application specific unit operations and working fluids. The functionality of the basic methodology and the extensions are demonstrated in the cases. The results of the work can be used in research and commercial simulation projects. New unit operation models and improvements for the fluid property calculation provide a variety of new potential applications. The model validation results help to estimate prediction capability in similar applications. The simulation applications guide modellers to use the methodology in both the presented and new areas. Regarding the case-specific results, the board machine simulator helped to understand complex interactions related to grade changes, to tune the related automation, and thus to shorten the grade change times. The simulation of the ship energy systems revealed design deficiencies and assisted in troubleshooting related problems during the commissioning. The study on the thermal energy storage facility uncovered systematic anomalous behaviour in the molten salt flow path. Based on the cross-case analysis, it can be stated that the methodology can be successfully applied beyond its traditional application domain and that it provides meaningful and valuable benefits. Furthermore, the methodology supports versatile use of the simulation model during the life cycle of an industrial plant: in R&D, design, testing, operator training and further development of the operating plant. The challenges that the process and energy industries meet today, require consideration of the interactions and dynamics of the process and automation systems together. The methodology used and further extended provides a valuable tool for tackling these challenges.Prosessi- ja energiateollisuudella on suuri merkitys kestävässä kehityksessä. Niillä on merkittävä rooli ilmastonmuutoksen hillinnässä. Pyrittäessä energiatehokkuuteen, materiaalien kierrätykseen ja päästöttömiin prosesseihin tulee teollisista järjestelmistä monimutkaisia. Prosessiautomaatiolla on keskeinen rooli siinä, että monimutkaisiakin järjestelmiä voidaan hallita ja käyttää helposti ja turvallisesti. Dynaaminen laitosmittakaavan prosessisimulointi on käytännössä ainoa tapa testata ja varmistaa prosessin ja automaation yhteistoiminta ennen kohdejärjestelmän rakentamista. Käytössä olevissa laitoksissa sen avulla voidaan tutkia järjestelmiä todenmukaisesti aiheuttamatta häiriötä tai riskiä prosessille tai ihmisille.  Tässä tapaustutkimuksena toteutetussa työssä käytetään Apros-ohjelmistoa mallinnus- ja simulointiympäristönä. Mallinnusta ja simulointia laajennetaan perinteisiltä ydin- ja konventionaalisten voimalaitosten sovellusalueilta kartongin valmistukseen, hiilidioksidia talteen ottavaan voimalaitokseen, laivan energiajärjestelmiin, meriveden suolanpoistoon sekä sulasuolaa käyttävään lämpövarastoon. Perusmenetelmänä hyödynnetään mekanistisia malleja ja termohydraulista dynaamista simulointia. Menetelmäkehitystä tehtiin sovelluskohtaisten laitteiden ja fluidien mallintamiseksi. Käytetyn menetelmän ja tehtyjen laajennusten toimivuus demonstroidaan simulointisovelluksissa. Työn tuloksia voidaan hyödyntää sekä tutkimuksessa että kaupallisissa simulointiprojekteissa. Uudet laitemallit ja fluidilaskennan ominaisuudet mahdollistavat uusia sovelluskohteita termisten järjestelmien parissa. Laskennan ja mallien validointitulokset auttavat arvioimaan saman tyyppisten mallien ennustuskykyä. Menetelmän hyödyntäminen sekä esitellyillä että uusilla sovellusalueilla tehostuu esimerkkimallien avulla. Tapauskohtaisista tuloksista voidaan mainita, että simulaattori auttoi ymmärtämään kartonkikoneen lajinvaihtoihin liittyviä monimutkaisia vuorovaikutuksia. Uudelleenvirittämällä lajinvaihtoautomaatio lyhennettiin lajinvaihtoihin kuluvaa aikaa. Laivan energiajärjestelmien simulointi paljasti suunnittelun puutteellisuuksia ja auttoi käyttöönoton ongelmien tutkimisessa. Sulasuolaa käyttävän, lämmönsiirron ja varastoinnin tutkimusta tukevan laitteiston toiminnasta analysoitiin systemaattinen poikkeama.  Tapausten analysoinnin perusteella voidaan todeta, että käytetty mallinnusmenetelmä soveltuu hyvin myös perinteisen sovellusalueensa ulkopuolella ja tuo merkittäviä hyötyjä. Menetelmä tukee simulointimallien monipuolista hyödyntämistä teollisuuslaitoksen elinkaaren aikana: tutkimuksessa, suunnittelussa, testauksessa, käyttäjien koulutuksessa sekä toimivan laitoksen kehittämisessä. Teollisuuden suunnittelun ja laitosten kasvavia haasteita on kyettävä ratkaisemaan eri elinkaaren vaiheissa prosessin ja automaation yhteistoiminta ja dynamiikka huomioiden. Työssä sovellettu ja laajennettu mallinnus- ja simulointimenetelmä tarjoaa tähän hyödyllisen työkalun

A SPRAY REACTOR CONCEPT FOR CATALYTIC OXIDATION OF P-XYLENE TO PRODUCE HIGH-PURITY TEREPHTHALIC ACID

Terephthalic acid (TPA), with current annual world capacity of exceeding 50 million metric tons, is a commercially important chemical used primarily in the manufacture of polyesters. A spray reactor in which the liquid phase, containing dissolved p-xylene (pX) and the catalyst (Co/Mn/Br), is dispersed as fine droplets by a nozzle into a continuous vapor phase containing the oxidant (O2) is shown to produce high-purity TPA with less than 25 ppm 4-carboxybenzaldehyde (4-CBA) in the solid TPA product. In sharp contrast, the solid TPA product obtained from a conventional stirred reactor similar to the configuration used in the conventional Mid-Century (MC) process contains nearly 1000 ppm 4-CBA even though the reactor is operated at similar pressure and temperature (15 bar and 200 °C) but with the gas phase dispersed into the liquid phase. The dramatic improvement in TPA product quality during spray reactor operation is attributed to two main factors: the alleviation of interphase gas-liquid mass transfer limitations that facilitates more complete oxidation of the pX and the intermediate oxidation products to TPA, and reduced backmixing that enhances the oxidation rates. Kinetic studies of pX oxidation to TPA performed in a well-stirred 50 mL reactor confirm that the intermediate oxidation steps are subject to mass transfer limitations even at the highest rpm used. Theoretical calculations show that the time constants for O2 diffusion in typical spray droplets (assumed to be 50 μm diameter) are one to two orders of magnitude lower than the kinetic rate constant confirming complete O2 penetration and saturation of the droplets. Gas phase concentration measurements show that in the spray reactor gas phase CO formation is roughly one-fourth of that in the MC process, indicative of solvent burning. This decrease is attributed to the shorter residence times in the spray reactor. Further, the usage of CO2 as an inert gas and the dominance of acetic acid (50 mol%) in the vapor phase under reaction conditions create a gas phase environment that falls outside of the flammability envelope. Mathematical modeling of the stirred reactor using MC process conditions accurately predicts the steady state temperatures observed in industrial reactors (195 °C). The model also clearly divulges that the cooling provided by partial evaporation of the acetic acid solvent, upon absorbing the heat of reaction at the set reactor pressure, is vital to maintain stable steady state operation. Experimental results clearly attest to the significance of reliable pressure control to prevent undesired temperature rises. Comparative economic analyses and gate-to-gate and cradle-to-gate life cycle assessments show that the spray process significantly reduces capital and operating costs by 55% and 16% respectively, and also imposes less adverse environmental impacts than the MC process. These benefits of the CEBC spray process are mainly derived from the non-requirement of the hydrogenation step required in the conventional process for purifying the crude TPA. Thus, the spray reactor concept has the potential to be a greener and more sustainable process for making polymer-grade dicarboxylic acids in one step. The results from this dissertation provide valuable guidance for the rational design and development of a continuous spray reactor

천연가스 공급망 내 초구조 최적화 및 다중모듈방식을 이용한 공정설계 및 운전

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2019. 2. 이원보.본 논문은 공정시스템 분야의 최신기술 수요에 상응하는 최적 공정설계 및 운전기술 개발을 주목적으로 한다. 최근 셰일가스 등 변화하는 천연가스 자원으로부터 지속적인 부가가치 창출과 플랜트의 내재적 안전성을 제고할 수 있는 설계 및 운전을 도모하였다는 점에서 실제 산업에의 응용가치가 매우 높다. 첫 번째로 천연가스 가솔린회수 및 액화 통합공정에 질소회수공정을 추가하여, 저품질 천연가스로부터 지속적인 액화천연가스 생산이 가능한 공정을 설계하였다. 열교환망 및 분리공정 최적화를 위해 공정요소들의 엑서지를 최소화할 수 있는 초구조를 설계함으로써 기존의 연구가 찾지 못하였던 새로운 최적 구조 및 운전조건을 결정하였다. 나아가 서로 다른 천연가스 조성에 따라 각기 적용이 가능한 대안공정을 추가 설계·최적화함으로써 변화되는 천연가스 자원에 지속적인 가치창출을 위한 해답을 제시하고 있다. 두 번째로 공정의 예비설계단계에서 내재적 안전성의 개념을 도입하여, 경제성과 안전성의 균형을 유지하기 위한 새로운 다목적최적화 알고리즘을 개발하였다. 잠재적 위험도가 높은 천연가스 액화공정을 대상으로 액화사이클에 따른 초구조를 모사하여 두 가지 목적함수의 가중치에 따른 최적해를 결정함으로써 기존 최적화의 한계를 보완하였다. 마지막으로 플랜트 안전운전을 위해 공정이상에서부터 사고의 발생 및 전파과정을 실시간으로 구현할 수 있는 시뮬레이션 모듈을 개발하였다. 동적공정시뮬레이션 및 사고시뮬레이션의 두 가지 독립된 모듈을 객체연결매입 기법을 이용하여 연동함으로써 사고상황에서 운전원의 임의조치가 모듈에 실시간 반영되도록 하였다. 해당 모듈은 임의의 사고상황에서 제어실 및 현장 운전원의 적절한 대응을 효과적으로 유도할 수 있으며 나아가 플랜트 안전시스템설계에 객관화된 지표를 제시할 수 있었다. 본 논문은 위와 같이 실제 산업의 기술적 수요를 충족시키고 이를 발전시킴으로써 공정시스템 학술분야에 기여하였다.Recently in the field of process systems engineering in natural gas processing, various researches trying to make changes in the existing framework of process design and operation have been studied with the emerging need of sustainability and safety in the chemical processes. These two considerations of sustainability and safety either result in a totally new solution for a certain decision making or require far different methods or technologies for it. Especially for a natural gas supply chain broadly from drilling of the gas/oil reservoirs to distributing the product gas to end-users like households or offices, new frameworks of process design and operation critically influence the way of producing desired products and supplying them to the users in the associated industries. Then it determines the structure, operating conditions, and operation procedures of chemical processes which are economically powerful and good in operability. Recently, as the natural gas sources becomes unconventional varying from mid-to-small size reservoirs or shale gases, this change makes the offshore natural gas plants emerge as an alternative and vital site of producing LNG (liquefied natural gas) with strict requirements of safety. It also makes additional processing units like a cryogenic nitrogen recovery be necessary for sustainable production of LNG with leaner feed natural gases. Among various processes in the overall natural gas supply chain, this thesis dealt with largely three parts including gas pre-treatment, liquefaction, and distribution to the end-users, attempting to design new processes or develop new methods of decision making in the context of the new framework considering sustainability and safety in process systems engineering. In this thesis, I will discuss the process synthesis, intensification, and optimization for sequential units, multi-objective optimization for economic feasibility and inherent safety, and multi-modular approach for interactive simulation of dynamic process and 3D-CFD (computational fluid dynamics) accident models. First of all, for designing a sustainable process of producing LNG from feed natural gases with high amounts of nitrogen, two cryogenic nitrogen recovery processes integrated with LNG production and NGL (natural gas liquid) recovery were designed and optimized based on the structural analysis of components separation: one for integrated nitrogen recovery unit and the other for standalone one. The difference of each process is the way the nitrogen is removed from the natural gas. The former recovers nitrogen in the integrated heat and mass transfer structure with natural gas liquefaction while the latter separates the nitrogen recovery unit into an independent structure apart from the liquefaction section. These sophisticated nitrogen recovery solutions follow the recent demand of highly efficient electric motors as alternative compressor drivers which require less or no fuel gas, the major sink of nitrogen in the feed gas. These two processes were compared with each other in terms of specific power (kWH/kg_LNG), which is equivalent to the overall process efficiency, with respect to the nitrogen content in the feed gas from 0mol% to 20mol%. Consequently, as the nitrogen content in the feed gas increases, the specific power of each process also increases while the standalone solution has a priority over the other until around 17mol% of nitrogen and after that point the integrated solution becomes relatively more efficient. It should be noted that all of the optimization results of each configuration were improved with the reduced specific power by up 38.6% compared to those from previous studies which have similar configurations. The way this study aimed could be reasonable guidelines for other chemical process designs as well as nitrogen recovery in natural gas processing. Secondly, for designing a safer process of natural gas processing, two different systematic approaches were newly proposed in this study: one for risk reduction method based on rigorous QRA (quantitative risk assessment) results through process design modification of an existing plant which already finished up to the detailed design stage, and the other for deciding an optimal process design through multi-objective optimization for minimizing both the TAC (total annual cost) and the risk (fatality frequency) at the preliminary design stage. This latter approach could largely lower the cost required for finalizing the design as it doesnt need to follow the general QRA procedure where the recursive loop is recycled until the risk is reduced to an acceptable level. But before this approach starts to be applied, the suitability of its method should be verified as it has to make some assumptions in assessing the safety level of the process with limited information. Also the computation load would be higher as it needs to simultaneously consider the economic feasibility and inherent safety in designing a process. Despite the differences these two approaches have each other, however, they are essentially in the same context in that they share the same purpose of deciding a process design which is safer and/or even cheaper than the existing processes. Consequently, for the former approach of which the target process is the GTU (gas treatment unit) of an existing GOSP (gas oil separation plant) for processing associated natural gas, the modified design with different operation conditions reduced the total risk integrals by 27% at the expense of only the additional $50,000 for capital cost. In addition, sensitivity analysis of total risk with respect to probability of success for safety barriers was carried out in order to show the preferences of process design modification, this study proposed, over the improvement of safety systems. Meanwhile, the latter approach of superstructure formulation and multi-objective optimization for designing an optimal heat transfer structure and operating conditions was applied to the natural gas liquefaction processes, deciding that the SMR (single-stage mixed refrigerant process) structure with the TAC of 626.6MM$/yr and fatality frequency of 1.28E-03/yr has the highest priority over all possible solutions. Finally, with the aim of safely operating a chemical plant, a new operator training module which mainly targets the interactive cooperation of control room operators and field operators was developed through using multi-modular approach with advanced simulations and data processing technologies. This interactive simulation modeling delivers the online simulation results of process operation to the operators and induces them to take proper actions in case of a random accidental situation among pre-identified scenarios in a chemical plant. Developed model integrates the real-time process dynamic simulations with the off-line database of 3D-CFD accident simulation results in a designed interface using OLE (Object Linking and Embedding) technology so that it could convey the online information of the accident to trainees which is not available in existing operator training systems. The model encompasses the whole process of data transfer till the end of the training at which trainees complete an emergency shutdown system in a programmed model. The developed module was applied to a natural gas pressure regulating station where the high pressure gas is depressurized and distributed to the end-users like households or offices. An overall scenario is simulated in the interactive simulation model, which starts from an abnormal increase of the discharge (2nd) pressure of the main valve due to its malfunction, spreads to an accidental gas release through the crack of a pressure recorder, and ends with gas dispersion and explosion. Then the magnitude of the accident outcomes with respect to the lead time of each trainees emergency response is analyzed. Consequently, the module could improve the effectiveness of operator training system through interactively linking the trainee actions with the model interface so that the associated accident situations would vary with respect to each trainees competence facing an accident.Abstract i Table of Contents vii List of Figures x List of Tables xiv CHAPTER 1. Introduction 1 1.1. Research motivation 1 1.2. Research objectives 4 1.3. Outline of the thesis 6 1.4. Associated publications 11 CHAPTER 2. Process Intensification 12 2.1. Introduction 13 2.2. Conceptual Design of the Nitrogen Recovery 17 2.3. Design Improvement and Optimization 26 2.3.1. Integrated Nitrogen Recovery Unit 26 2.3.2. Optimization of the Base Case 32 2.3.3. Design Improvement 40 2.4. Alternative Process Design and Optimization 65 2.4.1. Standalone Nitrogen Recovery Unit 65 2.4.2. Optimization of Standalone Nitrogen Recovery Unit 74 2.4.3. Comparison between End-flash and Stripping Options 78 2.5. Varying Feed Composition and Optimization 95 2.6. Concluding Remarks 105 CHAPTER 3. Safer Process Design 107 3.1. Introduction 109 3.2. Risk Reduction through Process Design Modification 112 3.2.1. Risk Assessment for the Target Process 113 3.2.2. Risk Reduction to ALARP 141 3.3. Multi-objective Optimization Including Inherent Safety 154 3.3.1. New Decision Making Schemes for Inherent Safety 159 3.3.2. Superstructure for Natural Gas Liquefaction Processes 168 3.3.3. Multi-objective Optimization 187 3.3.4. Decision Making for Final Optimal Solution 203 3.3.5. Future Works 208 3.4. Concluding Remarks 210 CHAPTER 4. Safe Operation with Multi-modular Approach 212 4.1. Introduction 213 4.2. Interactive Simulation Modeling 218 4.2.1. Model Structure 218 4.2.2. Dynamic Process and Accident Simulation Engine 221 4.2.3. Real-time 3D-CFD Data Processing Method 225 4.3. Case Study – Pressure Regulating Station 231 4.3.1. Developing a Program Prototype 231 4.3.2. Prototype Test and Training Evaluation 252 4.4. Concluding Remarks 256 CHAPTER 5. Conclusion 257 Nomenclature 261 Reference 263 Abstract in Korean (국문초록) 270Docto