Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Summary

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Abstract

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

Introduction

Solid oxide fuel cell (SOFC) innovations have been reported in recent years as the technology continues to develop. Among the many advantages, SOFCs have become known for high fuel efficiency, low emissions and moderate fuel flexibility compared to other combustion based power generation techniques¹. Furthermore, SOFCs are scalable allowing for high fuel efficiency even at small scales. Unfortunately, limitations in current hydrogen infrastructure have created a need for fuel reforming systems that are often inefficient. A recent development is the micro-tubular flame-assisted fuel cell (mT-FFC) reported in the author's previous work². The mT....

Protocol

1. Combustion Calculations

1. Select fuel for analysis. Here, choose methane as the reference fuel, but the principles are transferable to other hydrocarbon fuels.
2. With 1 mole of methane as the fuel, balance equation (1) for stoichiometric combustion to get equation (2).
   
   

Results

The combustion characterization chamber should be checked prior to testing at the desired equivalence ratios for back-flow of air into the chamber or other air leakage during testing. Combustion processes in open chambers are known to be nearly isobaric. As a result, pressure within the combustion chamber may not be enough to ensure that no air from the external environment is back-flowing into the combustion chamber from the chamber exhaust port or other leakage points. There are several.......

Discussion

The protocol discussed here is an important bridge between previous combustion characterization research and fuel cell testing. The use of combustion for fuel reforming and fuel cell testing has been applied for several years in DFFC setups^10-15. However, the characterization of the combustion process in DFFCs is primarily concerned with in-situ characterization of the flame composition¹⁶ and uses a MS⁸. As the DFFC is open to the ambient, the exhaust composition consists mostly .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Gas chromotograph	SRI Instruments, Inc.	SRI 8610C
K type thermocouples	Omega	KQXL-116G-6	Custom length
K type thermocouple extension wire	Omega	EXTT-K-20-SLE-100
Mass flow controller	Omega	FMA5427	0-40 L/min (N2) Used for methane
Mass flow controller	Omega	FMA5443	0-200 L/min (N2) Used for air
Mass flow controller	Omega	FMA5402A	0-10 ml/min (N2) Used for CO
Mass flow controller	Brooks Instrument	SLA5850	200 SCCM (Propane) Used for CO2
Mass flow controller	Brooks Instrument	SLA5850	5 L/min (Air) Used for N2
Mass flow controller	Brooks Instrument	SLA5850	500 SCCM (N2) Used for H2
Regulator	Harris Products Group	HP721-125-350-F	Methane tank
Regulator	Harris Products Group	HP702-050-590-E	Air tank
Regulator	Airgas	Y11-SR145B	CO tank
Regulator	Harris Products Group	HP702-050-320-E	CO2 tank
Regulator	Airgas	Y12-215B	N2 tank
Regulator	Harris Products Group	HP702-015-350-D	H2 tank
Methane, Compressed, Ultra high purity	Airgas	UN1971	Extremely Flammable
Air, Compressed, Ultra pure	Airgas	UN1002	Not classified as hazardous to health.
CO, Compressed, Ultra high purity	Airgas	UN1016	Toxic by inhalation, Extremely flammable
CO2, Compressed, Research grade	Airgas	UN1013	Asphyxiant in high concentrations
N2, Compressed, Ultra high purity	Airgas	UN1066	Not classified as hazardous to health.
H2, Compressed, Ultra high purity	Airgas	UN1049	Extremely flammable, burns with invisible flame
Source meter	Tektronix, Inc.	Keithley 2420	Connects to computer via USB
Horizontal split tube furnace	MTI Corportation	OTF-1200X
Data acquisition	National Instruments	NI cDAQ-9172	Connects to computer via USB
Thermocouple input	National Instruments	NI 9211	Connects to cDAQ-9172
Computer control for Mass Flow Controllers	National Instruments	NI 9263	Connects to cDAQ-9172 Computer control for Mass Flow Controllers
Testing software	National Instruments	LabVIEW 8.6
Ceramabond	Aremco	552-VFG	1 Pint