Dustin McLarty

Hybrid Fuel Cell Gas Turbine System Design and Optimization

Ultrahigh efficiency, ultralow emission fuel cell gas turbine (FC/GT) hybrid technology represents a significant breakthrough in electric power generation. FC/GT hybrid designs are potentially fuel flexible, dynamically responsive, scalable, low-emission generators. The current work develops a library of dynamic component models and system design tools that are used to conceptualize and evaluate hybrid cycle configurations. The physical models developed for the design analysis are capable of off-design simulation, perturbation analysis, dispatch evaluation, and control development. A parametric variation of seven fundamental design parameters provides insights into design and development requirements of FC/GT hybrids. As the primary generator in most configurations, the FC design choices dominate the system performance, but the optimal design space may be substantially different from a stand-alone FC system. FC operating voltage, fuel utilization, and balance of plant component sizing has large impacts on cost, performance, and functionality. Analysis shows that hybridization of existing fuel cell and gas turbine technology can approach 75% fuel-to-electricity conversion efficiency. [DOI: 10.1115/1.4024569]

Sisters in sustainability: municipal partnerships for social, environmental, and economic growth

Abstract While debates about sustainable development tend to focus on national- and international-scale problems, sustainability programs and research generally focus on the regional, county, municipal, or even household level. Less research has focused on evaluating the benefits of pairing two cities (i.e., sister city partnerships) with different needs and capabilities to jointly enhance the potential for sustainable practices between the cities. Given shrinking state and federal budgets and the nascent national climate policy, how might US cities use existing resources to achieve greater levels of sustainability? This paper presents a new data-driven mathematical tool—the partnership assessment for intra-regional sustainability—that city planners can use to explore the prospects for improving sustainability practices by leveraging existing resources and establishing synergistic partnerships with neighboring cities. The efficacy of the tool is assessed through the presentation of a Southern California case study and the results of a psychological survey of Southern California residents. Results indicate that cities of different size and scale would benefit from synergistic sustainability programs that pool the resources and needs of both cities. The paper concludes with a discussion of potential societal implications, methodological issues, and barriers to implementation.

System Dynamics and Control

The National Fuel Cell Research Center (NFCRC) of the University of California, Irvine (UCI), has developed and applied a dynamic simulation and control system development approach for solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) systems for almost two decades. The approach is thoroughly vetted and peer-reviewed. Simplifications (for reasonable computational effort) are required to solve the dynamic conservation equations (mass, energy, momentum) for complete systems over time because transient responses range from milliseconds to hours and the systems are comprised of multiple highly coupled and integrated components with complex feedback and recirculation. Typical bulk model methodologies (e.g., representing each component as a single node with a single set of uniform conditions) avoid much of the computational rigor, but miss key system interactions and underlying SOFC and SOEC component constraints. Many bulk models attempt to address the non-uniform distribution of reactions, temperatures, and gas composition with linearization that approximates steady operation. These approximations, typically made at nominal operating conditions, are a poor proxy for the non-uniform distributions at part load and are particularly inadequate to represent the nonlinear transient responses that must be addressed with integrated control schemes. Since SOFC and SOEC performance is inherently spatially dependent, that is, the major performance characteristics (e.g., temperature and current density) cannot be well predicted without knowledge of the spatial variations in temperature, species concentrations, etc., some degree of spatial resolution is required. An approach is presented for determining the limited spatial resolution of the geometry in such a way as to capture only the directions in which major parameters that govern performance change significantly. When applicable, symmetry within the stack and within individual repeating units of the stack is used to reduce computational effort. Typically, the most significant spatial variations of the physics, chemistry, and electrochemistry governing performance are one-dimensional (1D), for example, representing a single gas flow channel or flow path. On the other hand, cross-flow or serpentine flow patterns, or significant heat loss near the cell edges necessitates a two-dimensional (2D) model. The key simplifications to geometric resolution and timescales that are recommended are presented in a detailed description of the dynamic modeling approach. Governing equations for the physics, chemistry, and electrochemistry for SOFC and SOEC systems are presented in a manner that allows ease of application in standard math toolboxes. A complete SOFC system model and modeling framework are presented, which includes a spatially resolved cell stack, spatially resolved variable flow direction heat exchangers, and spatially resolved reformer modules. When fuel and oxidant flow manifolds or significant heat losses effect the temperature distributions in the cell stacks, then an approach for accounting for the coupling of this physics with the cell performance is presented. Presentation of the dynamic SOFC/SOEC system modeling approach is followed by presentation of two examples of model verification by data–model comparisons. The model verification efforts include application to a stand-alone integrated fuel processing SOFC system and a hybrid solid oxide fuel cell–gas turbine (SOFC–GT) system. Control system development and evaluation using the dynamic system modeling approach are demonstrated by the application of the approach to stand-alone SOFC systems of various configurations and to an experimental SOFC–GT system. The transient response and control of these systems in response to fuel composition perturbations and load-following power demands are presented as examples that demonstrate the success of the control system development approach.