Sanggyu Kang

Dynamic Simulation of a Stationary Proton Exchange Membrane Fuel Cell System

A dynamic model of a stationary proton exchange membrane (PEM) fuel cell system has been developed in MATLAB-SIMULINK®. The system model accounts for the fuel processing system, PEM stack with coolant, humidifier with anode tail-gas oxidizer, and an enthalpy wheel for cathode air. Four reactors are modeled for the fuel processing system: (1) an autothermal reformation (ATR) reactor, (2) a high temperature shift (HTS) reactor, (3) a low temperature shift (LTS) reactor, and (4) a preferential oxidation reactor. Chemical kinetics for ATR that describe steam reformation of methane and partial oxidation of methane were simultaneously solved to accurately predict the reaction dynamics. The chemical equilibrium of CO with H2O was assumed at HTS and LTS reactor exits to calculate CO conversion corresponding to the temperature of each reactor. A quasi-onedimensional PEM unit cell was modeled with five control volumes for solving the dynamic species and mass conservation equations and seven control volumes to solve the dynamic energy balance. The quasi-one-dimensional cell model is able to capture the details of membrane electrode assembly behavior, such as water transport, which is critical to accurately determine polarization losses. The dynamic conservation equations, primary heat transfer equations and equations of state are solved in each bulk component, and each component is linked together to represent the complete system. The model predictions well matched the observed experimental dynamic voltage, stack coolant outlet temperature, and catalytic partial oxidation (CPO) temperature responses to perturbations. The dynamic response characteristics of the current system are representative of a typical stationary PEM fuel cell system. The dynamic model is used to develop and test a proportional-integral (PI) fuel flow controller that determines the fuel flow rate to maintain the uniform system efficiency. The dynamic model is shown to be a useful tool for investigating the effects of inlet conditions, load, and fuel flow perturbations and for the development of control strategies for enhancing system performance. Copyright

Numerical Analysis of Steam-methane Reforming Reaction for Hydrogen Generation using Catalytic Combustion

A steam reformer is a chemical reactor to produce high purity hydrogen from fossil fuel. In the steam reformer, since endothermic steam reforming is heated by exothermic combustion of fossil fuel, the heat transfer between two reaction zones dominates conversion of fossil fuel to hydrogen. Steam Reforming is complex chemical reaction, mass and heat transfer due to the exothermic methane/air combustion reaction and the endothermic steam reforming reaction. Typically, a steam reformer employs burner to supply appropriate heat for endothermic steam reforming reaction which reduces system efficiency. In this study, the heat of steam reforming reaction is provided by anode-off gas combustion of stationary fuel cell. This paper presents a optimization of heat transfer effect and average temperature of cross-section using two-dimensional models of a coaxial cylindrical reactor, and analysis three-dimensional models of a coaxial cylindrical steam reformer with chemical reaction. Numerical analysis needs to dominant chemical reaction that are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming(DSR) reaction. The major parameters of analysis are temperature, fuel conversion and heat flux in the coaxial reactor.

The Scale Up Characteristics of a Catalytic Combustor With Flow Uniformity Analysis

Catalytic combustors are used as off-gas combustors of molten carbonate fuel cells (MCFCs) because of their exhaust gas purity, geometric flexibility, and high combustion efficiency. In this study, a new design was investigated for possible application in internally reformed MCFC. The study started with performance analysis of a 5 kWe combustor, which could be precisely conducted due to availability of experimental apparatus. A 5 kWe combustor was used as a model combustor, and it was experimentally analyzed in terms of flow uniformity, catalyst screening, and reaction characteristics. The results show that the flow uniformity is able to reduce the exhaust gas concentration because temperature uniformity decreases the possibility of fuel slippages in locally lower temperature zones. As the capacity of the combustor is increased from 5 kWe to 25 kWe, the exhaust gas temperature at the same inlet condition as that of the 5 kWe combustor increases due to lower heat loss. As a result, the catalyst screening process shows different results due to higher operating temperatures, but three of four catalysts provide proper quality. On the other hand, flow uniformity improves economic competitiveness of the catalytic combustor. When the volume loading of catalytic monoliths was decreased, the performance was very similar to that of the original volume loading of catalytic monoliths.