Modeling the Direct Solar Conversion of COModeling the Direct Solar Conversion of CO22 to CO to CO

Ralph Price, David Morse, Steven Hardy, Thomas FletcherRalph Price, David Morse, Steven Hardy, Thomas FletcherBrigham Young University, Provo, UTBrigham Young University, Provo, UTScott HillScott Hill Reed JensenReed Jensen

Combustion Resources, Provo, UTCombustion Resources, Provo, UT Renewable Energy Corporation, Los Alamos, NMRenewable Energy Corporation, Los Alamos, NM

Objectives Used Fluent and PCGC-3 to predict the following:

Flow profiles

Temperature profiles

Reaction kinetics

Reaction mechanisms

Thermodynamic equilibrium

Photolysis reaction

Prototype Apparatus

Converter in sun 6 m2 solar mirrors

Silver solar converter 8 cm zirconia rod

Prototype Description Mirrors focus sunlight into

converter.

Zirconia rod in converter is heated by sunlight to

approximately 2350°C.

CO2 stream is passed over hot rod causing CO2 to dissociate into CO and O2.

Product stream (4-6 mole percent CO) is cooled quickly.

CO is separated and used in water-gas shift reaction.

Fluent Profiles

Predicted temperature Predicted CO mole profile with reactions fraction profile

Predicted radially- Predicted velocity averaged temperature profile versus axial distance

Introduction At high temperatures CO2 is known to dissociate into CO and O.

A prototype unit using only solar energy has achieved a 4-6 mole percent CO

conversion from CO2.

The prototype device was modeled using two different modeling

programs (PCGC-3 and Fluent).

PCGC-3 Profiles

Predicted temperature Predicted CO mole profile with reactions fraction profile

Predicted radially- Predicted CO mole averaged temperature fraction from versus axial distance photolysis

Conclusions Fluent model accurately

predicted experimental CO conversion.

PCGC-3 model was accurate in modeling formation of CO, but not cooling.

Residence time and temperatures in the throat

were too low to permit significant photolysis.

The formation of CO occurs only in the throat area and not upstream of the rod.

Solar conversion of CO2 to CO has the potential to provide a useable fuel from a CO2 stream.

ACERC    

AcknowledgementsThis work was sponsored by

Renewable Energy Corporation Los Alamos,

NM

Elementary Reactions

The following reversible elementary reactions are known to occur in the converter.

CO2 + M CO + O + M

CO2 + O CO + O2

O2 + M O + O + M

CO2 + hν CO + O (photolysis)

Reaction Kinetics and Equilibrium

Parameters were found for the equation:

k=A*Tb*exp(-Ea/RT)

Reaction rate parameters

Equilibrium species fractions

1.0

0.8

0.6

0.4

0.2

0.0

Mol

e F

ract

ion

300028002600240022002000180016001400

Temperature (K)

CO2 O2 O CO