Fundamental thermodynamics of fuel cell,engine,and combined heat and power system efficiencies

Abstract

At the 2001 Grove Symposium on Fuel Cells attended by representatives of the world-wide fuel cell industry, fuel cells and fuel cells integrated with gas turbines were discussed. Combined heat and power (CHP) aspects were also discussed. Without exception, efficiency figures were irrationally based on the measured, Carnot-limited, lower calorific value (CV) of the fuel in energy units J. The rational basis, on the other hand, is the fuel chemical exergy (work units, Ws) calculated via an equilibrium diagram. In Joules experiment 1 Ws ≫ 1 J, where the irreversible ≫ must not become an = sign. A misnomer like potential energy (exergy) fits on the left of the diagram, CV on the right. Moreover credence was also given, at the symposium, to the popular misconception that a CHP system has an efficiency of the order of 80 per cent.

An essential precursor to reading the paper is to grasp the theory of chemical equilibrium and equilibrium constants [3] as an aid to exploring the equilibrium diagram mentioned above.

Keywords

irreversibility calorific value (CV)chemical exergy fuel cell engine equilibrium constant

Get full access to this article

View all access options for this article.

References

Barclay

F. J.

Combined Power and ProcessâAn Exergy Approach, 2nd edn, 1998 (Professional Engineering Publications Ltd., London and Bury St. Edmunds).

Kotas

T. J.

The Exergy Method of Thermal Plant Analysis, 1995 (Krieger Publishing Company, Malabar, Florida).

Atkins

P. W.

Physical Chemistry, 5th edn, 1995 (Oxford University Press).

Chase

M. W.

JANAF thermochemical tables. J. Phys. Chem, 1985, 14, Suppl. 1.

Carrette

Friedrich

K. A.

Stimming

Fuel cells: Principles, types, fuels, and applications. Chem. Phys. Chem., 2000, 1, 162–193.

Grove Fuel Cell Symposium, London, 11–13 September, 2001. J. Power Sources, Special Edition, Spring 2002.

Koryta

Ions, Electrodes, and Membranes, 2nd edn, 1991 (John Wiley and Sons Ltd., Chichester).

Koryta

Principles of Electro-Chemistry, 1993 (John Wiley and Sons Ltd., Chichester).

Adams

A. M.

Bacon

F. T.

Watson

R. G. H.

The High Pressure Hydrogen Oxygen Cell. In Chemical TechonologyâVol. 1, 1963 (Academic Press Inc., New York).

10.

Bacon

F. T.

Fuel cells, past, present and future. Electrochimica Acta, 1969, 14, 569–585.

11.

Minh

N. Q.

Takahashi

Science and Technology of Ceramic Fuel Cells, 1995 (Elsevier, Amsterdam).

12.

Dyer

P. N.

Richards

R. E.

Russek

R. L.

Taylor

D. M.

Ion transport membrane technology for oxygen separation and syngas production. Solid State Ionics, 2000, 134, 21–33.

13.

Moran

M. J.

Shapiro

H. N.

Fundamentals of Engineering Thermodynamics, 2nd edn, 1993 (John Wiley and Sons, New York).

14.

Barclay

F. J.

Fuel cells in the UK. IMechE Symposium, London, 10 January 2001, Document S715, Paper 5.

15.

Barclay

F. J.

Fuel Cells, Evolution, Development, and Application (Professional Engineering Publications, London and Bury St Edmunds). In preparation:.

16.

Gardiner

Thermodynamic Processes in Solid Oxide and Other Fuel Cells. S455 Paper 3, Fuel Cells for Power and Propulsion. IMechE HQ, 24 September 1996.