Reactor Modeling Tools - STANJAN

Tools for Reactor Modeling:
THE ELEMENT POTENTIAL METHOD FOR CHEMICAL EQUILIBRIUM ANALYSIS: STANJAN

CONTENTS
1 SCOPE
2 SUMMARY
3 INTRODUCTION
4 EXAMPLES
4.1 CARBON-RICH C-0 SYSTEM
4.2 EXAMPLE WITH TWO COMPLEX PHASES
4.3 GAS TURBINE ENGINE EXAMPLE
4.4 OTHER APPLICATIONS
APPENDIX
FIGURES
5.1 EXAMPLE RUN LOG FOR CARBON-RICH C-O SYSTEM
5.2 OUTPUT FOR EXAMPLE WITH TWO COMPLEX PHASES
5.3 FIRST STEP IN THE TURBINE EXAMPLE: CALCULATION OF THE ENTHALPY OF THE REACTANTS
5.4 SECOND STEP IN THE TURBINE EXAMPLE: CALCULATION OF THE ADIABATIC FLAME TEMPERATURE
5.5 THIRD STEP IN THE TURBINE EXAMPLE: CALCULATION OF THE NOZZLE EXIT STATE

AVAILABILITY AND IMPLEMENTATION OF STANJAN

REFERENCES

1. A,
CPT
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CONSULTANCY

Process Engineering Guide:

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Tools for Reactor Modeling:
“THE ELEMENT POTENTIAL METHOD FOR CHEMICAL
EQUILIBRIUM ANALYSIS: STANJAN”

Process Disclaimer

2. INTRODUCTION

EXAMPLES

4.1 CARBON-RICH C-0 SYSTEM
4.2 EXAMPLE WITH TWO COMPLEX PHASES

4.3 GAS TURBINE ENGINE EXAMPLE

4.4 OTHER APPLICATIONS

APPEND

4. a

The program is an interactive program designed for use on either a desktop or a
mainframe computer. ts name is derived from Stanford University, where it w
developed, and the JANNAF thermochemical data tables, from which the ba:
data are taken. It relates mol fractions of each species to element potentials for
each independent atom in the system.

The program assumes that the gas phase is a mixture of ideal gases and that the
condensed phases are ideal solutions. lts origin lies in combustion systems.

ction 4 gives a more detailed description and examples

‘SUMMARY

The element potential method for chemical equilibrium analysis is a powe
technique that is virtually unknown in the thermodynamics community. It pr

a superior means for solution of complicated problems, especially those involving
several phases. The concept of element potentials is so useful that it should be
included, i not preferred, in any advanced instruction on chemical equilibrium,

5. hat all mols are non-negative. When there are important rare
tem, this can be a very dificult task.

In search of a better way to solve combustion-equilbrium problems, the author
reinvented what he later discovered to be a "lost" method, the so-called method
of element potentials. Early development of the method was done by Powell [1]
The RAND method for equilibrium calculation described by Clasen [2] is
essentially an early implementation of the method. White [3] pointed out some
computational advantages of the method. Bigelow [4] extended the nonlinear
programming theory of the method. The author's contribution is the development
of the dual problem and a powerful numerical implementation.

For pre-STANJAN history of the method, see Van Zeggeren and Storey [5]. The
purpose of this paper is to make the method of element potentials known to the
combustion community and to outline an interactive computer program based on
the method that is available for solving chemical equilibrium probler

The method of element potentials uses theory to relate the mol fractions of eac
sto quantities called element potentials. There is one element potential for
each independent atom in the system, and these element potential,
total number of mols in each phase, are the only variable
the s In large problems this h smaller

6. program. À
prepare data for other species from the JANNAF table data. Both are vi
User-friendly interactive programs.

With STANJAN, the user selects the
tem, sets the atomic populations and state parameters, and t
solves for the equilibrium state using the method of element potentials

This is extremely rapid, and, with an ¡7 processor on a PC, solutions for typical
combustion problems are returned almost immediately. The results include the
imposition of each phase (mols and mol fractions), and the thermodynamic

properties of the system, including (if desired) the speed of sound.

Thermodynamic cycle analysis Is easily executed with STANJAN
user may specify the state parameters in a variety of ways, including:

(0 temperature and pressure,

(i) pressure and entropy

(ii) enthalpy and pressure same as

7. In summary, STANJAN is a powerful and eas;
chemical equilibrium in single- or multiple-p!
program disks are freeware and may be fre
Use. The FORTRAN source programs are
users w to recompile for other machines or uses

4 EXAMPLES

41 CARBON-RICH C-0 SYSTEM

The first example in carbon-rich mixture CO of CO», O> and O, with the
possibilty of a solid carbon phase,

The user begins by calling STANJAN. After an opening opportunity to see a brief
iption of the element potential method, the dialog begins. The users
jonses are underined in the log in Fig. 5.1. The margin numbers refer to the
notes that follow. This example is similar to the first two examples in Section 3,
and the reader may find it useful to make the comparison.

8. a

is calculated. Equilibrium states will be used to calculate c unless the froz
composition option is selected, in which case it becomes the sound speed with
frozen chemistry

'STANJAN includes an optional instructive monitor, which can be used to
learn about the method. It is included here to display the features of the
initializer and dual problem solution described in previous sections,

This is what the user would have seen had he chosen to check the atomic
composition.

These are the properties as computed from the JANNAF table data.

The initializer first finds that CO will be the dominant species. The
balancing requires the presence of CO», in the amount estimated. The
initializer then redistributes the atoms to the phases to provide the target
mol fraction of the balancing species CO.

9. a

This example shows how STANJAN can be used to calculate the adiabatic lame
temperature in a gas turbine engine combustor, and then the composition after
isentropic expansion in the turbine nozzle.

The fist step is to get the enthalpy of th
inlet state. Here we took T

H4 + 202 + 7.52 N2

The results are shown in Fig. 5.3.

The next step is to get the adiabatic flame temperature by finding the state of the

products at the same enthalpy and pressure as the last run. The reactants and a
of products are allowed species. The results are sh

The final step is to get the temperature following k

finding the equilibrium state for the same species at the case entropy
ssure (here 1 alm.). The results are given in Fig. 5.5.

44 OTHER APPLICATIONS

10. FH
3

Beganraggasgagge:

11. N
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it

14. ‘SECOND STEP IN THE TURBINE EXAMPLE: CALCULATION OF THE
ADIABATIC FLAME TEMPERATURE

15. AVAILABILITY AND IMPLEMENTATION OF STANJAN

Special Note:

JAN: A

16. appropriate derived proper energy, Helmholz energy, internal energy,
enthalpy—or maximize entropy for the user-supplied gas mixture.

At this time all species must be gaseous; the calculator will not consider multiple
phases. Thus, while solid and liquid species are present in the database they
cannot be included in the equilibrium calculation,

‘navier.engy.colostate.edu/~dandy/code/code-4/

‘Depending on the constraint chosen, the calculation invokes STANJAN to
10 appropriate derived property—Gibbs energy, Helmholz energy.

17. Bigelow, JR, "Computing Equilibrium Compositions of Ideal Chemical

Systems; TR7 Research House, March, 1970. See also
TA70-1, TR-70-2, TA-70-3 (1970)

Jan Zeggeren, F, and Storey, S H, The Computation of Chemical
Equilibria, Cambridge Univ. press (1970).

feinott, A F, Mather Studies in Management
New York, pp. 5-8 (

IcAffeo, K 5, Laudise, R A, and Hozack, R S, "Equilibria Concentrations.
in the Oxidation of SICI4 and GeCH for Optical Fibers,” J Lightwave
Technology, VLT-1, No. 4 (1983), pp. 555:

McAfee, KB, Walker, JR, Laudise, R A, and Hozack, R S, "Dependence
of Equilibria in the Modified Chemical Vapor Deposition Process on SICH
and GeCl4 and O2" J. Am. Ceramic Soc. Vol. 67, No. 6 (1984), pp. 420:
444,

18. [10

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