Il Moon

Concentrations of volatile organic compounds in an industrial area of Korea

We measured and analyzed daily mean concentrations of volatile organic compounds (VOC) at Ulsan industrial and downtown sites from 3 to 8 June 1997. The industrial site is situated at the boundary of a petrochemical complex and the other is at downtown area in Ulsan. At each site, we collected ambient air samples in passivated stainless-steel containers by using constant flow samplers and analyzed them by a GC-FID. At Ulsan industrial site, the concentrations and their daily variations of total VOC were higher than those at the downtown site. The concentrations of oxygenated hydrocarbons were the highest among seven hydrocarbon groups at both sites. The fraction of C2–C5 light hydrocarbon concentrations to C2–C9 hydrocarbons at Ulsan industrial site was higher than that in other industrial areas. It suggests that fugitive emissions of light hydrocarbons in Ulsan industrial areas might be higher than those of other industrial areas. Under favorable wind conditions, the influence of industrial emissions of VOC on the downtown hydrocarbon levels was observed.

Analysis of purge gas temperature in cyclic TSA process

This study analyzes the effect of an operating parameter on the dynamic behavior by performing dynamic simulations of cyclic thermal swing adsorption (TSA) system, in fixed beds packed with activated carbon as an adsorbent. This TSA process purifies and regenerates the ternary mixtures consisted of benzene, toluene and p-xylene. A mathematical model, considering the dynamic variation and spatial distribution of properties within the bed, has been formulated and described by a set of partial differential algebraic equations. The models are based on non-equilibrium, non-isothermal and non-adiabatic conditions. The breakthrough curves of our simulation model are compared with those of Yuns experiments (1999). The cyclic steady-state (CSS) cycles are obtained for the various cases by cyclic simulation. The influences of the purge gas temperature on breakthrough curves, CSS convergence time, cyclic operating step time, purge gas consumed, regeneration energy requirement and adsorption ability at CSS are also discussed.

Verification of a logically controlled, solids transport system using symbolic model checking

Symbolic model checking has been used to formally verify safety and operability specifications on an industrial solids handling process. The fundamental principles behind symbolic model checking are presented along with techniques used to model process hardware, relay ladder logic control instructions, and human operating procedures for verification purposes. The computational resources required to check the example process are presented, and faults detected in this process through symbolic verification are documented.

Optimization of mixed-refrigerant system in LNG liquefaction process

Abstract LNG liquefaction is an energy intensive process. For this reason, various liquefaction processes for saving energy exist. Searching optimal process condition is very difficult because of its high nonlinearity. Pressure level, refrigerant flowrate, and refrigerant composition are key operation variables to reduce energy consumption. These variables play an important role in affecting the overall performance. Compressor is a major energy-consumption unit in LNG plant and it spends much energy depending on operating conditions. In this paper, searching optimal condition is carried out by using simultaneous optimizations. NLP model is applied for the SMR process. The optimization result shows that refrigerant composition is a major key variable and half of energy consumption can be reduced by changing operating conditions and refrigerant composition only.

Automatic generation of accident scenarios in domain specific chemical plants

Abstract This paper proposes an automatic generation method of accident scenarios in chemical process industries (CPI) and describes a computer-automated tool. One of the most powerful and widely used concepts in several risk assessment methodologies is the concept of accident scenarios. The generation of accident scenarios is on a strictly experience-based approach, and is a time and labor-consuming procedure. To reduce the effort and resources devoted to this, we developed a systematic method of generating accident scenarios and implemented software called yAGAS (Yonsei Automatic Generator of Accident Scenarios). This system automatically formulates a list of accident events and generic hazardous situations by considering the following process characteristics: process, equipment, materials, operating conditions, status, and accident progress factors. This system yields a qualitative description of accident events related to process hazards. This also provides a qualitative and quantitative ranking of hazardous situations that can be used as the top events of safety analysis.

Rigorous industrial dynamic simulation of a crude distillation unit considered valve tray rating parameters

Abstract A rigorous dynamic simulation is performed to find optimal operating conditions of a crude distillation unit with 56 trays and 65,000 barrel per day capacity. The model includes not only mass and energy balance equations but also nonlinear equations capturing the fluid behavior in the column such as downcomer load, jet flooding, hole velocity limit and downcomer backup. Discrete behavior of pump and heater on/off, valve open/close are also included. Hundreds of thousand differential algebraic equations (DAEs) are set up and solved by gPROMS simultaneously. As a result, the dynamic behavior of the unit during the starting and shutdown procedure is fully understood.

Measurement and correlation of excess molar volumes for mixtures of 1-propanol and aromatic hydrocarbons

Excess molar volumes (VmE) have been measured at 303.15 K for 1-propanol+benzene or toluene or o- or m- or p-xylene mixtures using V-shape dilatometer. The VmE values, for an equimolar composition, vary in the order: benzene>toluene∼m-xylene>o-xylene>p-xylene. The VmE data have been used to calculate partial molar volumes, excess partial molar volumes, and apparent molar volumes of 1-propanol and aromatic hydrocarbons over the entire range of composition. The excess volume data have also been interpreted in terms of graph-theoretical approach and Prigogine-Flory-Patterson theory (PFP). While PFP theory fails to predict the VmE values for systems with s-shaped VmE versus x1 graph, the VmE values calculated by graph theory compare reasonably well with the corresponding experimental values. This graph theory analysis has further yielded information about the state of aggregation of pure components as well as of the mixtures.

Safety improvement by a multimedia operator education system

Abstract The safety of chemical processing systems can be improved by training operators efficiently. More than 18% of chemical process accidents are caused by human errors during the process operation[1]. However operators are becoming apart from real processes as they are becoming more automated. As a result of operators lack of real experience, the possibility of operators misjudgement during the emergency situation is becoming high. To educate operators more efficiently, we developed an operator education system by using recent multimedia technologies including 3D motion pictures, sound effects and interactive communications. As a case study, we developed yFES(yonsei Furnace Education System) to educate the operation of a specific fired-heater in a refinery plant. yFES consists of seven chapters: introduction, structure, operation principle, operating procedure, safety, trouble-shooting and installation/inspection . The system has been used in the field and proved to be efficient and productive.

Gas management in flow field design using 3D direct methanol fuel cell model under high stoichiometric feed

This study presents a 3D CFD model for modeling gas evolution in anode channels of a DMFC under high stoichiometric feed. The improved two-phase model includes a new submodel for mass source and interphase transfer in anode channels. Case studies of typical flow field designs such as parallel and serpentine flow fields illustrate applications of the CFD model. Simulation results reveal that gas management of typical flow fields is ineffective under certain operating conditions. The CFD-based simulations are used to visualize and to analyze the gas evolution and flow patterns in anode channels. The developed CFD model is useful in flow field design for improving gas management in DMFC.

Optimization of start-up operating condition in RPSA

Abstract This study focuses on an optimization of start-up operating conditions of a rapid pressure swing adsorption (RPSA) process, which is operated in a cyclic pressure variation mode. The objective function is defined not only to reduce the operating power but also to shorten the time to reach the cyclic steady state (CSS), as well as to increase the purity of the desired product at CSS. A general mathematical model considering the dynamic variation and spatial distribution of properties within the bed has been formulated and described by a set of integrated partial differential algebraic equations (IPDAE). The number of variables for optimization is 16 825 and both the single discretization of a spatial domain and the double discretization of spatial/time domains have been used for the numerical integration. As the computation result the optimal cycle time is 14.46 s and the optimal feed pressure is 597 kPa. Under the optimal condition the purity of desired product at CSS is calculated as 96.42% and the CSS convergence time is 5857 s.