Oxidation of Low Calorific Value Gases-Applying Optimization Techniques to Combustor Design

The design of an optimal air-staged combustor for the oxidation of a low calorific value gas mixture is presented. The focus is on the residual fuel emitted from the anode of a molten carbonate fuel cell. Both experimental and numerical results are presented. The simplified numerical model considers a series of plug-flow-reactor sections, with the possible addition of a perfectly-stirred reactor. The parameter used for optimization, Z, is the sum of fuel-component molar flow rates leaving a particular combustor section. An optimized air injection profile is one that minimizes Z for a given combustor length and inlet condition. Since a mathematical proof describing the significance of global interactions remains lacking; the numerical model employs both a ''Local'' optimization procedure and a ''Global'' optimization procedure. The sensitivity of Z to variations in the air injection profile and inlet temperature is also examined. The results show that oxidation of the anode exhaust gas is possible with low pollutant emissions

Effect of Natural Gas Fuel Addition on the Oxidation of Fuel Cell Anode Gas

The anode exhaust gas from a fuel cell commonly has a fuel energy density between 15 and 25% that of the fuel supply, due to the incomplete oxidation of the input fuel. This exhaust gas is subsequently oxidized (catalytically or non-catalytically), and the resultant thermal energy is often used elsewhere in the fuel cell process. Alternatively, additional fuel can be added to this stream to enhance the oxidation of the stream, for improved thermal control of the power plant, or to adjust the temperature of the exhaust gas as may be required in other specialty co-generation applications. Regardless of the application, the cost of a fuel cell system can be reduced if the exhaust gas oxidation can be accomplished through direct gas phase oxidation, rather than the usual catalytic oxidation approach. Before gas phase oxidation can be relied upon however, combustor design requirements need to be understood. The work reported here examines the issue of fuel addition, primarily as related to molten-carbonate fuel cell technology. It is shown experimentally that without proper combustor design, the addition of natural gas can readily quench the anode gas oxidation. The Chemkin software routines were used to resolve the mechanisms controlling the chemical quenching. It is found that addition of natural gas to the anode exhaust increases the amount of CH3 radicals, which reduces the concentration of H and O radicals and results in decreased rates of overall fuel oxidation

Aerovalve Pulse Combustion: Technical Note

The authors present a mathematical model and an experimental investigation of aerodynamically valved pulse combustion. The model uses a control-volume approach to solve conservation laws in several regions of a pulse combustor. Mixing between the fresh charge and combustion products is modeled as a two-step process, with the mixing occurring slowly for a specified eddy time during each cycle, and then changing to a higher rate. Results of model simulations demonstrate that eddy time plays a significant role in determining the frequency and amplitude of combustion oscillation. The authors show that short eddy times produce steady, rather than pulsating, combustion. And they show that changes to the mixing process alter the temperature-species history of combustion gases in a manner that could prevent or promote the formation of nitrogen oxides, depending on specific mixing rates. The relatively simple control-volume approach used in this model allows rapid investigation of a wide range of geometric and operating parameters, and also defines characteristic length and time scales relevant to aerovalve pulse combustion. Experimental measurements compare favorably to model predictions. The authors place particular emphasis on time-averaged pressure differences through the combustor, which act as an indicator of pressure gain performance. They investigate both operating conditions and combustor geometry, and they show that a complex interaction between the inlet and exit flows of a combustor makes it difficult to produce general correlations among the various parameters. They use a scaling rule to produce a combustor geometry capable of producing pressure gain

POWER 2008-60111 USING STAGED COMPRESION TO INCREASE THE SYSTEM EFFICIENCY OF A COAL BASED GAS TURBINE FUEL CELL HYBRID POWER GENERATION SYSTEM WITH CARBON CAPTURE

ABSTRACT This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO 2 . 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

Development of Dynamic Modeling Tools for Solid Oxide and Molten Carbonate Hybrid

ABSTRACT This paper describes some generic solid oxide and molten carbonate hybrid fuel cell gas turbine systems and dynamic modeling tools that are being developed to simulate the performance of these and other hybrid fuel cell systems. The generic hybrid systems are presented to introduce issues and technical development challenges that hybrid fuel cell gas turbine systems must address and to provide a platform for the development of the dynamic modeling tools. The present goals are to develop dynamic models for the basic components of solid oxide and molten carbonate fuel cell gas turbine hybrids, ensure their reliability, and obtain a basic understanding of their performance prior to integration into a complete hybrid system model. Preliminary results for molten carbonate and solid oxide fuel cell types are presented. These results provide understanding of some of the operational characteristics of fuel cells, and indicate the complexity of the dynamic response of fuel cell hybrid components. For the fuel cell models, generic planar designs are analyzed showing voltage and current behavior following step changes in load resistance and steady state performance curves. The results provide confidence in each of the model's reliability, enabling them to be integrated for hybrid system simulation. Results from the integrated simulations will provide guidance on future hybrid technology development needs. NOMENCLATURE INTRODUCTION Fuel cells have the potential to play a significant role in meeting near-and medium-term requirements for efficient and environmentally responsible power generation. Hybrid fuel cell and gas turbine technology is potentially superior to other power generation technologies due to its high efficiency (70 to 80 percent LHV) and low emissions (less than 3 parts per million NOx and CO). However, to advance the technology to the commercial level requires a better understanding of how gas turbines and fuel cells should be integrated and how they will behave when fused into a single hybrid system. The combination of a fuel cell and a gas turbine is a natural evolution in the quest for improved generation efficiency with low emissions. Integrated hybrid cycles exhibit synergies not present in typical combined cycles with fuel-to-electricity efficiencies higher than either the fuel cell or gas turbine alone and costs for a given efficiency lower than either alone. This paper begins with a description of some basic operational characteristics of two generic hybrid systems. The paper continues with a presentation of the fuel cell submodels necessary for eventual integration into a complete hybrid model. Two commercial transient analysis software packages, ProTRAX, which is widely employed for power generation applications, and SABER, which is widely used for electronics and automotive applications, are used for model development and integration. These analysis packages contain many process elements required for typical power generation applications; however, at this time the user is required to supply specialized submodels for the fuel cells and other non-standard hybrid components

Mass transport from a flat plate and cylinder in a strong, high temperature, oscillating flow field.

The mass transfer enhancement from two liquid surfaces placed inside a strong, high temperature, oscillating flow field was investigated. The device used for creating this flow field was a "Helmholtz type" pulse combustor. These devices operate in resonance with velocity oscillation amplitudes typically ranging between 20 and 100 m/s, frequencies between 50 and 200 Hz, and tailpipe gas-phase temperatures between 700-1500 K. To quantify the mass transport enhancement under various operating conditions, and to model a realistic drying application, attention is focused on the evaporation rates from two different surfaces: a cylindrical surface placed transverse to the tailpipe flow and a flat plate surface placed against the tailpipe wall. The mass transfer enhancements from both surfaces were investigated by examining their time-average evaporation rates and surrounding flow field properties. The flow field properties were determined using Laser Doppler Velocimetry and Laser Schlieren. Both the velocity data and schlieren video indicate that the momentum transport (and therefore heat or mass transport) is non-quasi-steady. Over the range and combination of operating conditions studied, the results show mass transfer enhancements approaching 100% for both the cylinder and flat plate. The mass transfer rates are strongly affected by the pressure amplitude, weakly affected by the mean flow Reynolds number, and insignificantly affected by the frequency. The enhancements are attributed to increased turbulence and significant non-quasi-steady flow behavior over the transport surfaces.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104779/1/9610126.pdfDescription of 9610126.pdf : Restricted to UM users only

Overview of the NETL Onsite Fuel Cell R&D Program

Onsite fuel cell R&D at the National Energy Technology Laboratory (NETL) has been ongoing since the late 1990's. The objective of the onsite program is to support development efforts of the fuel cell technology-related product lines and conduct fundamental research of advanced fuel cell technology. Of special focus is NETL's new 10-yr, multimillion dollar development program call the Solid State Energy Conversion Alliance (SECA). This program is aimed at developing low-cost mass manufactured solid oxide fuel cell technology for a wide variety of applications. In addition to SECA, there are a variety of other products/programs at NETL that can be supported by the onsite R&D group. Vision 21 is one such program and is the U. S. Department of Energy's initiative to deploy high efficiency, ultra-clean co-production coal conversion power plants in the twenty-first century. These plants will consist of power and coproduction modules, which are integrated to meet specific power and chemical markets. In response to these program initiatives, NETL's onsite R&D group is developing significant capability and focusing current activity on the following areas: (1) High-Temperature Fuel Cell Test & Characterization; (2) Integrated Fuel Processing; (3) Fuel Cell Component and Systems Modeling; and (4) Sensors, Controls, and Instrumentation. This report discusses plans and ongoing activities in each of these areas