John VanOsdol

Fuel Cell Gas Turbine Hybrid Simulation Facility Design

Fuel cell hybrid power systems have potential for the highest electrical power generation efficiency. Fuel cell gas turbine hybrid systems are currently under development as the first step in commercializing this technology. The dynamic interdependencies resulting from the integration of these two power generation technologies is not well understood. Unexpected complications can arise in the operation of an integrated system, especially during startup and transient events. Fuel cell gas turbine systems designed to operate under steady state conditions have limitations in studying the dynamics of a transient event without risk to the more fragile components of the system. A 250kW experimental fuel cell gas turbine system test facility has been designed at the National Energy Technology Laboratory (NETL), U.S. Department of Energy to examine the effects of transient events on the dynamics of these systems. The test facility will be used to evaluate control strategies for improving system response to transient events and load following. A fuel cell simulator, consisting of a natural gas burner controlled by a real time fuel cell model, will be integrated into the system in place of a real solid oxide fuel cell. The use of a fuel cell simulator in the initial phases allows for the exploration of transient events without risk of destroying an actual fuel cell. Fuel cell models and hybrid system models developed at NETL have played an important role in guiding the design of facility equipment and experimental research planning. Results of certain case studies using these models are discussed. Test scenarios were analyzed for potential thermal and mechanical impact on fuel cell, heat exchanger and gas turbine components. Temperature and pressure drop calculations were performed to determine the maximum impact on system components and design. Required turbine modifications were designed and tested for functionality. The resulting facility design will allow for examination of startup, shut down, loss of load to the fuel cell during steady state operations, loss of load to the turbine during steady state operations and load following.Copyright

Evaluation of methods for thermal management in a coal-based SOFC turbine hybrid through numerical simulation

Managing the temperatures and heat transfer in the fuel cell of a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid fired on coal syngas presents certain challenges over a natural gas based system, in that the latter can take advantage of internal reforming to offset heat generated in the fuel cell. Three coal based SOFC/GT configuration designs for thermal management in the main power block are evaluated using steady state numerical simulations developed in ASPEN Plus. A comparison is made on the basis of efficiency, operability issues and component integration. To focus on the effects of different power block configurations, the analysis assumes a consistent syngas composition in each case, and does not explicitly include gasification or syngas cleanup. A fuel cell module rated at 240MW was used as a common basis for three different methods. Advantages and difficulties for each configuration are identified in the simulations.

Examination of Ambient Pressure Effects on Hybrid Solid Oxide Fuel Cell Turbine System Operation Using Hardware Simulation

The effect of ambient inlet air pressure variations on the compressor performance in a direct fired solid oxide fuel cell gas turbine hybrid power system has been studied using the Hybrid Performance (Hyper) project hardware simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The Hyper facility at NETL makes use of a high speed numerical model which controls a burner and a series of pressure vessels and piping to collectively simulate a direct-fired, high-temperature fuel cell. The hardware simulating the fuel cell is integrated into the system with a modified single shaft turbine driven compressor and a pair of recuperates to provide cathode air preheat from the turbine exhaust. Orifice plates were employed at the compressor inlet of the facility to parametrically vary the inlet pressure. The compressor inlet temperature for all tests conducted was held within a 2 Kelvin range. Variation in inlet pressure was shown to have a significant effect on many hybrid system performance parameters. Some system parameters were shown to have a linear dependency on the inlet pressure, leading to the implementation of correction factors. Similar dependence of compressor discharge pressure and temperature on compressor inlet pressure was predicted by dynamic models based on isentropic compression principles. Transient operation was also impacted by changes in compressor inlet pressure. Startup profiles are shown against the compressor stall line for indication of changes in surge margin.Copyright

Forced convection in a circular pipe with a partially filled porous medium

A study of forced convection in a circular pipe with a partially filled porous medium was numerically investigated. The Brinkman-Forchheimer extension of the Darcy model was used to analyze the and temperature distribution in the porous medium. Our study includes two types of porous layer configurations : (1) a layer attached at the tube wall extending inward towards the centerline and (2) a layer at the centerline extending outward. The effect of several parameters, such as Darcy number, effective viscosity, effective thermal conductivity, and inertia parameter, as well as the effect of geometric parameters, were investigated.

Scaling a Solid Oxide Fuel Cell Gas Turbine Hybrid System to Meet a Range of Power Demand

In recent years there has been significant interest in using the heat generated from the normal operation of a solid oxide fuel cell (SOFC) to supplant the normal combustion process of a gas turbine system. By doing this a gas turbine fuel cell hybrid power generation system is formed. Because the heat produced by a SOFC is utilized by the turbine to produce work, the hybrid system can have an overall system efficiency that greatly exceeds those of either the stand alone SOFC system, or the stand alone gas turbine system. One of the most critical problems that must be addressed in gas turbine fuel cell hybrid technology is temperature control. A hybrid system that is designed to operate efficiently for a given base load may not be easily extended to accommodate peek load. In this paper a simple hybrid system configuration using a standard SOFC and a single compressor-turbine pair is presented. This simple system is used to establish the effect that key configuration parameters have on system temperatures. The configuration model is then scaled over a range of fuel input and power output to show the limitations of the system. The system is modeled using the ASPEN PLUS ® simulation software with special modules to calculate fuel cell performance.

Experimental Analysis of Flow Unbalance in Two Parallel Counter-Flow Recuperators

The aim of this study was to provide a characterization of non-symmetrical operation in two counter-flow primary surface exhaust gas recuperators installed in parallel flow loops. The hybrid system emulator test rig and facility designed and operated by the Department of Energy, National Energy Technology Laboratory located at the West Virginia (USA) campus was used for the study. Various tests from the past years often resulted in non-symmetrical operation, indicated by significantly variant temperature measurements at the outlets of the recuperators.Some specific tests have been carried out in order to identify the possible cause of this flow unbalance. The isolated effects of bleed air, cold air and hot air valve on the heat exchangers flow unbalance have been studied. Also, the impact of load bank changes on flow distribution has been considered in this study. Each test has been carried out in close loop fuel valve speed control. The influence of each independent variable in the study on parallel recuperator flow distribution has been quantitatively characterized using temperatures and a heat balance. Both the bleed and the cold air compressor bypass valves showed an appreciable impact on the heat exchangers flow unbalance, while hot air valve and load bank changes had minimal effect.Copyright

Examination of the Effect of System Pressure Ratio and Heat Recuperation on the Efficiency of a Coal-Based Gas Turbine Fuel Cell Hybrid Power Generation System With CO2 Capture

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2 . One configuration uses a standard Brayton cycle, and the other adds heat recuperation ahead of the fuel cell. Results show that peak efficiencies near 55% are possible, regardless of cycle configuration, including the cost in terms of energy production of CO2 capture and compression. The power that is required to capture and compress the CO2 is shown to be approximately 15% of the total plant power.

Examination of the Effect of System Pressure Ratio and Heat Recuperation on the Efficiency of a Coal Based Gas Turbine Fuel Cell Hybrid Power Generation System With CO2 Capture

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2 . One configuration uses a standard Brayton cycle, and the other adds heat recuperation ahead of the fuel cell. Results show that peak efficiencies near 55% are possible, regardless of cycle configuration, including the cost in terms of energy production of CO2 capture and compression. The power that is required to capture and compress the CO2 is shown to be approximately 15% of the total plant power.

Using Staged Compression to Increase the System Efficiency of a Coal Based Gas Turbine Fuel Cell Hybrid Power Generation System With Carbon Capture

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2 . One system uses a single compressor to compress and partially preheat the cathode air flow. The second system replaces the single compressor with a two stage compression process with an intercooler to extract heat between the stages, and to reduce the work that is required to compress the air flow in the cathode stream. Calculations are presented for both systems with and without heat recuperation. For the single compressor system with heat recuperation the hybrid system assumes the form of a recuperated Brayton cycle; when the recuperator is not present the hybrid system assumes the form of a standard Brayton cycle. The calculation results show that an increase of 2.2% in system efficiency was obtained by staging the compression for these cycles.