Operation, Modeling and Analysis of the Reverse Water Gas Shift Process Jonathan Whitlow Florida Institute of Technology NASA/ASEE Summer Faculty Program August 1, 2001

Overview of Presentation Description of RWGS Process Gas Chromatograph Composition Analysis Presentation and Analysis of Operating Data Problems Encountered with RWGS Operation Description and Evaluation of Matlab Models Conclusions and Recommendations

RWGS Photo

CO 2 Condenser Catalytic Reactor Membrane Separator O 2 in Q F 1 W 23 4 R Electrolysis Recycle Compressor 2 2 O 2 H H CO H H H Q out H O 2 2 RWGS Process Flow Diagram

RWGS Flow Schematic

Composition Analysis Analysis is Key to Mass Balance Models Insufficient Calibration for use of Mass Spectrophotometer Gas Chromatograph utilized for Analysis – TCD for CO and CO 2 – HID for H 2

Carbon Dioxide GC Calibration

Carbon Monoxide GC Calibration

Hydrogen GC Calibration

Summary of RWGS Operating Data

July 3 Reactor Temperatures (Electrolysis On)

July 19 Reactor Temperatures

July 3 CO Vent {R9} Flow (Electrolysis On)

July 18 CO Vent {R9} Flow PC1 Set Point = 53 psia

July 19 CO Vent {R9} Flow Feed Flow=1.3 slpm CO 2 & H 2

July 27 CO Vent {R9} Flow Feed Flow=1.1 slpm CO 2 & H 2

July 3 Membrane  P (Electrolysis On)

July 18 Membrane  P PC1 Set Point = 53 psia

July 19 Membrane  P Feed Flow=1.3 slpm CO 2 & H 2

July 27 Membrane  P Feed Flow=1.1 slpm CO 2 & H 2

July 3 Recycle {R12} Flow & Membrane Feed (R8) (Electrolysis On)

July 18 Recycle {R12} PC1 Set Point = 53 psia

July 19 Recycle {R12} & Membrane Feed (R8) Flow Feed Flow=1.3 slpm CO 2 & H 2

July 27 Membrane Feed (R8) Flow Feed Flow=1.1 slpm CO 2 & H 2

RWGS July 18 Mass Balance Summary

RWGS July 18 Operation Summary

RWGS July 19 Mass Balance Summary

RWGS July 19 Operation Summary

RWGS July 27 Mass Balance Summary

RWGS July 27 Operation Summary

RWGS Operation Summary

Problems Encountered in RWGS Operation Water Level Control is a Major Process Disturbance Non Uniform Temperature Across Reactor Catalyst Bed Temperature T2 had to be controlled by adjusting T3 Set Point Solenoid Valves (SV13 & SV14) tied to RWGS Interlocks Stuck Shut (Replaced with Coupling) Calibration on Flow Sensors is Inaccurate Some of the Redundant Sensors don’t work (P7 & R11) Electrolysis use is Limited by High Water Conductivity

RWGS Model Development (Mass Balance Algorithm)

Equilibrium favors left side of reaction unless very high temperatures are achieved CO 2 + H 2 CO + H 2 Centigrade K = [CO][H 2 O] = [CO 2 ][H 2 ] RWGS Reactor

Reactor analysis assumes that equilibrium conversion is achieved. Conversion is found by solving a quadratic equation. RWGS Reactor

Condenser Condenser is used to remove water from the reactor exit stream Ideal cases are assumed in modeling the condenser  Raoult’s Law for water in vapor phase Partial Pressure = Vapor Pressure  Henry’s Law for dissolved gases in liquid phase Solubility is a function of temperature in pure H 2 O

Model Representation for N Stage Counter-Current Membrane Feed Permeate V N-1 y j,N-1 V k+1 y j,k+1 V N y j,N L N+1 x j,N+1 L k+2 x j,k+2 L k+1 x j,k+1 V k y j,k L k x j,k L 2 x j,2 L 1 x j,1 V k-1 y j,k-1 V 1 y j,1 V 0 y j,0 m j,N m j,k-1 m j,k m j,1 Residue Sweep Stage NStage k+1Stage kStage 1 L N x j,N

Summary of Membrane Modeling

Conclusions High Conversion of H 2 can be Achieved with Proper Operating Conditions Modifications are needed to Improve Operation and Analysis of RWGS with Electrolysis Further Experimental Testing is Needed to Better Characterize RWGS Process Membrane Model is Valid, Further Work is Needed to Refine and Validate the rest of RWGS Models

Recommended Modifications Make Modifications to Sampling System Evaluate Other Methods for H 2 Analysis –Calibrate Mass Spec –GC using TCD with Argon Carrier Install Low Pressure Drop Bleed Valves for Water Level Control Recalibrate Flow Sensors Around Membrane (R8 & R12) Control Reactor Temperature with T2 Add Integral Action to Pressure & Temperature Controller

Further Experimental Tests Examine Additional Steady States at Different System Pressures/Membrane  P Constant Temperature & Feed Ratio) Examine Additional Steady States at Different Feed Rates Constant Temperature & Feed Ratio) Examine Effects of Varying Reactor Temperature Examine Effects of Varying Fresh Feed Ratios