Transient Performance of Integrated SOFC System Including Spatial Temperature Control

Spatial temperature feedback control has been developed for a simulated integrated non-pressurized simple cycle solid oxide fuel cell (SOFC) system. The fuel cell spatial temperature feedback controller is based on (1) feed-forward set-points that minimize temperature variation in the fuel cell electrode-electrolyte solid temperature profile for the system operating power range, and (2) decentralized proportional-integral based feedback to maintain the fuel cell spatial temperature profile during transients and disturbances. Simulation results indicate the fuel cell spatial temperature variation can be maintained within 15 degrees of nominal to significant load perturbations. Temperature gradients through the fuel cell are needed to remove the heat generated within the cell and cannot be avoided. The goal of the developed spatial temperature control is to minimize temperature variations from a nominal temperature profile in time. Minimal temperature variations in the SOFC electrode-electrolyte solid assembly will result in decreased thermal stresses and thereby decreased degradation and probability-of-failure. Simulation results demonstrating the ability to maintain the SOFC spatial temperature during large load perturbations indicates SOFC could be designed and controlled for rapid load following capability. Such performance can greatly improve SOFC system operating flexibility and thereby open new markets for SOFC systems including load following or spinning reserve services for the utility grid. © 2010 by ASME

Modeling Dust Formation in Lime Kilns

Dusting is one of the major problems in the operation of lime kilns because dust particles interfere with kiln operation and reduce its efficiency. A numerical model is developed to predict the rate of dust formation in rotary lime kilns. The model consists of four major components: 1) a 3D model for the kiln gas, solving fluid flow, heat transfer, and combustion in the gas region; 2) a 1D model for the kiln bed, solving for variation of the solids composition, including moisture content, along the kiln; 3) a 3D model to predict the motion of the solids in the bed, and to estimate the reaction rates; 4) a mathematical model to predict the rate of particle pickup from the bed. Additionally, motion of dust particles was modeled, for the first time, using Stochastic Separated Flow model (a Lagrangian approach). The developed model of particle tracking enables the user to predict distribution of dust particles in the gas section of the kiln. Different components of the model were validated using experimental data published in the literature. The developed model was used to simulate operation of a full-scale lime kiln at typical operating conditions, i.e. at different fuel and air flow-rates. Dusting signatures were also estimated for each setting to determine the effect each operating condition has on dusting. The results presented in this thesis indicate that dust formation is mainly affected by the kiln gas velocity. Effect of other operating conditions was found to be negligible within the ranges studied. The results presented here suggest that dust formation can be controlled by minimizing the input gas flow rate.Ph

Predicting fatigue failure of power conductors

Natural frequency and fatigue failure lifetime of finger projections were investigated for the purpose of design of a reliable and inexpensive vibration indicator to be mounted on power transmission lines. The effect of notches on the natural frequency of the fingers was investigated. A computer script based on the Finite Element Method was developed to find the natural frequency of the notched rods. Aluminum alloy 6061-T6 material was chosen as the material of the fingers. Several fingers with different lengths and notch radii were designed and machined. An experimental setup was designed to measure the lifetime and natural frequency of the designed fingers. The optimum length and notch radius for a given frequency of 20Hz were obtained. It was found that inclusion of notch adds a random factor and large scattering to the fatigue lifetime due to the creation of random surface defects. It was also found that grinding the surface of the rod decreases the scatter of the lifetime results. The most appropriate finger that has a natural frequency of 20 Hz has a length of 670mm with no notch.M.A.Sc

Modeling Dust Formation in Lime Kilns

Dusting is one of the major problems in the operation of lime kilns because dust particles interfere with kiln operation and reduce its efficiency. A numerical model is developed to predict the rate of dust formation in rotary lime kilns. The model consists of four major components: 1) a 3D model for the kiln gas, solving fluid flow, heat transfer, and combustion in the gas region; 2) a 1D model for the kiln bed, solving for variation of the solids composition, including moisture content, along the kiln; 3) a 3D model to predict the motion of the solids in the bed, and to estimate the reaction rates; 4) a mathematical model to predict the rate of particle pickup from the bed. Additionally, motion of dust particles was modeled, for the first time, using Stochastic Separated Flow model (a Lagrangian approach). The developed model of particle tracking enables the user to predict distribution of dust particles in the gas section of the kiln. Different components of the model were validated using experimental data published in the literature. The developed model was used to simulate operation of a full-scale lime kiln at typical operating conditions, i.e. at different fuel and air flow-rates. Dusting signatures were also estimated for each setting to determine the effect each operating condition has on dusting. The results presented in this thesis indicate that dust formation is mainly affected by the kiln gas velocity. Effect of other operating conditions was found to be negligible within the ranges studied. The results presented here suggest that dust formation can be controlled by minimizing the input gas flow rate.Ph

Enhanced performance of counter flow SOFC with partial internal reformation

We study a counter-flow solid oxide fuel cell system and consider the challenges faced in minimizing thermal variations from the nominal operating conditions for a reasonable range of power tracking. Blower dynamics, reformer transport delays, spatial distribution of the heat generated and the resulting thermal response are among the issues considered. A novel approach, relying on partial internal reformation of the feedstock is proposed as a remedy to maintain a strong level of power tracking with minimal thermal stress to the fuel cell