Chansaem Park

Simultaneous synthesis of a heat exchanger network with multiple utilities using utility substages

Abstract Heat exchanger network synthesis (HENS) has progressed by using mathematical programming-based simultaneous methodology. Although various considerations such as non-isothermal mixing and bypass streams are applied to consider real world alternatives in modeling phase, many challenges are faced because of its properties within non-convex mixed-integer nonlinear programming (MINLP). We propose a modified superstructure, which contains a utility substage for use in considering multiple utilities in a simultaneous MINLP model. To improve model size and convergence, fixed utility locations according to temperature and series connections between utilities are suggested. The numbers of constraints, discrete, and continuous variables show that overall model size decreases compared with previous research. Thus, it is possible to expand the feasible search area for reaching the nearest global solution. The models effectiveness and applications are exemplified by several literature problems, where it is used to deduce a network superior to that of any other reported methodology.

Simultaneous Optimization Models for Heat Exchanger Network Synthesis with Multiple Utilities: A New Strategy by Using Utility Sub-stage

Abstract In simultaneous method area of heat exchanger network synthesis (HENS), a mixed integer nonlinear programming (MINLP) model with stagewise superstructure is developed to minimize the total annualized cost (TAC). However, most of the preceding researches do not allow to consider the multiple utilities. Unlike previous superstructure, the utility sub-stage is located between the stages and multiple utilities are arranged in series. The heuristic, the optimal utility position should not be located in splitting stream, increase the searching area by expanding the number of stage and reduce the model size which is related to convergence of model. To verify the model, two examples are proposed and they show the effectiveness by deducing a network superior to any reported methodology.

A Comparative Study of Various Fuel for Newly Optimized Onboard Fuel Processor System under the Simple Heat Exchanger Network

− PEM fuel cell vehicles have been getting much attraction due to a sort of highly clean and effective transportation. The onboard fuel processor, however, is inevitably required to supply the hydrogen by conversion from some fuels since there are not enough available hydrogen stations nearby. A lot of studies have been focused on analyses of ATR reactor under the assumption of thermo-neutral condition and those of the optimized process for the minimization of energy consumption using thermal efficiency as an objective function, which doesn’t guarantee the maximum hydrogen production. In this study, the analysis of optimization for 100 kW PEMFC onboard fuel processor was conducted targeting various fuels such as gasoline, LPG, diesel using newly defined hydrogen efficiency and keeping simply synthesized heat exchanger network regardless of external utilities leading to compactness and integration. Optimal result of gasoline case shows 9.43% reduction compared to previous study, which shows the newly defined objective function leads to better performance than thermal efficiency in terms of hydrogen production. The sensitivity analysis was also done for hydrogen efficiency, heat recovery of each heat exchanger, and the cost of each fuel. Finally, LPG was estimated as the most economical fuel in Korean market.

Optimal Unloading Procedure for a Mixed Operation of Above-ground and In-ground LNG Storage Tank using Dynamic Simulation

Publisher Summary Natural gas is used as a heating fuel and its usage has increased due to its cleanliness. At the source, natural gas is usually transformed into liquefied natural gas (LNG) to decrease its volume. It is then transported to the demand region by carrier ship. LNG is then transferred from the carrier ship to an onshore storage tank. The process of unloading liquefied natural gas (LNG) from a carrier ship to a storage tank consists of three steps: recirculation, depressurization and unloading. Because LNG is typically maintained at a cryogenic temperature near –160 °C, a recirculation process is needed to keep the unloading pipeline cool and prevent vaporization of the LNG. The unloading line is then depressurized to a pressure valve that lies between the ship and the storage tank. Finally, the LNG in the carrier ship is transferred to the storage tank. There are two different types of LNG storage tanks: above-ground and in-ground tanks. When a single type of tank is used for storage, there are no critical problems encountered between the recirculation and unloading steps. However, for the mixed operation of above-ground and in-ground LNG storage tanks, the depressurization of an unloading pipeline can generate vapor on top of the unloading pipeline of the above-ground tank due to the pressure head. The vapor produced from the above-ground tank can congest depressurization, which can in turn cause excessive BOG(Boil-Off Gas) inflow.

BOG Handling Method for Energy Saving in LNG Receiving Terminal

Abstract Generation of Boil-off gas (BOG) in liquefied natural gas (LNG) receiving terminal affects considerably operating energy costs and safety issue. For that reason, the BOG handling method is determinant for design of LNG receiving terminal. This study proposes the concept of new design for BOG handling and calculates the design variables using sensitivity analysis for minimum send-out case. This design provides 21.9% energy saving and 0.197y payback period.