Effects of Electrolyte Flow Rate, Flow Channel Thickness, and Current Density on the Regenerative Hydrogen-Vanadium

Flow Battery

By:Christopher GravesMaster’s Candidate

580: Technical Review Presentation

Motivation

• The shift to renewable sources of power requires a power storage method to store the power that was generated during off peak hours.

• Redox flow batteries have emerged as a possible candidate for full scale implementation.

• The all vanadium flow battery appears to be the device closest to grid scale implementation

Redox Flow Batteries

7 7

All Vanadium Flow Battery

• Vanadium has multiple oxidations states.– 5 oxidation states

• Since vanadium is the only redox elements in the system, cross contamination is not as large an issue as in multiple electrolyte batteries.

All Vanadium Flow Battery

• A major capital cost of the All Vanadium Flow Battery is the cost of the vanadium.

All Vanadium Flow Battery

Regenerative Hydrogen Vanadium Flow Battery

8

Regenerative Hydrogen Vanadium Flow Battery Chemistry

8

Regenerative Hydrogen Vanadium Flow Battery

• The Hydrogen Vanadium benefits:– Decreased dependency on vanadium

• The Hydrogen Vanadium Battery retains all of the benefits of the all Vanadium battery

Purpose

• Analyze 3 variables for effects on capital cost of the Regenerative Hydrogen Vanadium Flow Battery– Electrolyte (vanadium) flow rate– Flow Channel thickness– Current density

Method

• Three variables were selected to be varied in a simulation.

• The project was presented as the capstone project for the senior class.

• The students used a previously developed model to determine the device parameters and device cost.

• The sizing method was determined by Moore et al.

Method

• The technology was costed using tables and methods laid out in Dr. Gael Ulrich’s textbook Chemical Engineering: Process Design and Economics A Practical Guide and information provided by Moore et al.

Assumptions

• The pressure drop due to the manifold spreading the vanadium electrolyte into the cells would be equal to the gains when the flows were rejoined.

• The cells were modeled as fully developed linear flow infinite plates.

• The pressure drop in the different cells is assumed the same, so the pressure drop of the liquid flow through one cell is equal to the total pressure drop.

Assumptions

• The costs and additional effects of enlarging the flow channel are neglected.

• It is assumed the current density is independent of the channel thickness.

• The flow rate of hydrogen is the flow rate required to keep the hydrogen gas at 1 atm.

• Hydrogen is the dominant gas in the gas flow stream. The presence of any other substance is negligible.

Electrolyte Flow Rate

• The flow rate of the vanadium electrolyte has an effect on the overall efficiency of the battery.

• In order to generate any power, and consistently achieve positive voltage, a minimum flow rate is required.

• The analyzed flow rates were 20 and 50 times the minimum theoretical flow rate.

Efficiency VS Flow Rate and Current Density

1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Flow Rate of Vanadium(L/s)

Effi

cien

cy (%

)

100 mA/cm2

200 mA/cm2

300 mA/cm2

400 mA/cm2

Effects of Electrolyte Flow Rate on Capital Cost

Effects of Electrolyte Flow Rate on Capital Cost

• The observed effects of the flow rate on the price of the battery were minimal.

Flow Channel Thickness

• Traditionally the cost of pumps are a small percentage of the total device cost.

• The analyzed flow channel thickness were: 0.5 cm, 1 cm, 1.5 cm, and 2 cm.

Effects of Flow Channel Thickness on Capital Cost

Effects of Flow Channel Thickness on Capital Cost

• A small effect of the flow channel was observed.

• The thicker flow channels resulted in the smallest cost, however, the returns diminished after the 1 cm thickness.

Current Density

• The current density is assumed to be constant through all the stacks

• The current density is a parameter that determines many other important parameters such as flow rate and the total number of required cells

Current Density

• An efficiency is associated with the 4 current densities that were analyzed

• The 4 current densities analyzed were: 100 mA/cm², 200 mA/cm², 300 mA/cm², and 400 mA/cm².

Current Density

Table 1. The efficiency of the due to electrical resistances at different current densities.

Current Density(mA/cm2)

Efficiency

100 93.54%200 87.16%300 80.77%400 74.40%

Effect of Current Density on Capital Cost

Effect of Current Density on Capital Cost

Effect of Current Density on Capital Cost

• The optimal current density is a function of the power capacity of the battery

• The current density has the greatest effect on the over cost of the device

Conclusions

• Flow rates have a small effect on the overall efficiency.

• The flow rate has a small overall impact on the overall cost of the device.

Conclusions

• The channel thickness had the least impact on the overall device cost of the three variables analyzed.

• Larger flow channels resulted in decreased overall costs.

• Extremely thin channel thicknesses will result in drastically increasing costs.

Conclusions

• The current density had the greatest effect of the three variables.

• The ideal current density is a function of the power capacity of the battery. – 200 mA/cm² for a 4 MW battery, 300 mA/cm²

for a 6 MW battery.

Conclusions

• The ideal current density would be dependant on the desired power of the.

• The optimal flow channel is around a thickness of 2 cm.

• The flow rate should be at least 20 times the minimum theoretical flow rate.

Acknowledgements

• My primary advisor – Dr. Robert Counce

• Dr. Jack Watson• Dr. Thomas Zawodzinski

Acknowledgement

• Mark Moore

References• REFERENCES• 1 D. Aaron, Z. J. Tang, A. B. Papandrew, and T. A. Zawodzinski, 'Polarization Curve Analysis of All-

Vanadium Redox Flow Batteries', Journal of Applied Electrochemistry, 41 (2011), 1175-82.• 2 Christie John Geankoplis, Transport Processes and Separation Process Principles. 4 edn (Bernard

Goodwin, 2003), p. 1026.• 3 'Hydraulic Diameter of Ducts and Tubes', 2014) <

http://www.engineeringtoolbox.com/hydraulic-equivalent-diameter-d_458.html> [Accessed June 4 2014].• 4 M. Moore, J. S. Watson, T. A. Zawodzinski, M. Q. Zhang, and R. M. Counce, 'Capital Cost Sensitivity

Analysis of an All-Vanadium Redox-Flow Battery', Industrial Electrochemistry and Electrochemical Engineering (General) - 220th Ecs Meeting, 41 (2012), 1-19.

• 5 M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli, and M. Saleem, 'Progress in Flow Battery Research and Development', Journal of the Electrochemical Society, 158 (2011), R55-R79.

• 6 A. Tang, S. M. Ting, J. Bao, and M. Skyllas-Kazacos, 'Thermal Modelling and Simulation of the All-Vanadium Redox Flow Battery', Journal of Power Sources, 203 (2012), 165-76.

• 7 A. Z. Weber, M. M. Mench, J. P. Meyers, P. N. Ross, J. T. Gostick, and Q. H. Liu, 'Redox Flow Batteries: A Review', Journal of Applied Electrochemistry, 41 (2011), 1137-64.

• 8 V. Yufit, B. Hale, M. Matian, P. Mazur, and N. P. Brandon, 'Development of a Regenerative Hydrogen-Vanadium Fuel Cell for Energy Storage Applications', Journal of the Electrochemical Society, 160 (2013), A856-A61.

 

Questions

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