Wärmehaushalt einer Karbonat-Brennstoffzelle zur Wasserstoffherstellung für eine Polymerelektrolyt-Brennstoffzelle

Molten carbonate fuel cells (MCFC) are being used in decentralised power plants, as they can reform hydrocarbon bound fuels internally, e.g. netural gas with a energy density of 10 kWh/m3 at standard conditions, and the efficiency of this mode of operation is around 50%. However in comparison to other fuel cell systems the power density is only 5 kW/m3. The power density of a polymerelectrolyte fuel cell (PEFC) ismuch higher (50 kW/m3). These systems can be run with an efficiency of 50%, too. Therefore they need hydrogen as a fuel, with an energy density of 2,9 kWh/m3 at standard conditions. Efficiency decreases to 35 to 40% using Methane as fuel, because of the reforming losses. The power density than is 6 kW/m3 and therefore as high as for a MCFC-system. Acombination of MCFC and PEFC, the so called CoCell, offers the following advantages:• A highly energetic, hydrocarbon based fuel can be used, e.g. Methane.• A high electrical efciency is achieved.• The power density of this system is higher than for a fuel cell with reformer.In the CoCell the MCFC is working as electricity producing reformer for the PEFC. The offheat of the MCFC is used for reforming, whereby hydrogen is available, being utilised further in the powerdense PEFC. The reforming capacity of the MCFC is limited by the internal heat balance. If the endothermic reforming consumes more heat than supplied by the material streams and the fuel cell waste heat, the stack cools down. The performance of such a combined fuel cell system has been evaluated in this thesis using the thermodynamic simulation software Aspen. Calculations reducing the utilisation in the MCFC by various heating techniques showed, that additional heat is supplied most efficiently by increasing the current density of the MCFC. Thereby the stack is heated electrically and the power density of the system is increased by the improved power density of the MCFC. The reduction of the utilisation is achieved by increasing fuel supply. Thereby the stack is cooled sufficiently at low utilisation and low air supply. In this configuration the current density can be increased up to 350 mA/cm2. This is 2,5 times the value of 140 mA/cm2 of typical, conventional operation. This limitation was explored experimentally. Based on the presented model calculations the power density of the CoCell increases to 14 kW/m3 at a current density in the MCFC of 280 mA/cm2. It is thereby almost three-times as high as for other fuel cell reformer systems (see above). The electrical efficiency accounts for 38% and is as good as a PEFC-Reformer system.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Adamek, Lars

Contributors dc:contributor

• Stolten, Detlef

• info:eu-repo/classification/ddc/600
• Technik
• Brennstoffzelle
• Leistungsdichte
• Elektrische Stromdichte
• CoCell
• autotherm
• Schiff

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121439%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59676