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Hydrogen Sulfide in VRLA Cells

Hydrogen Sulfide in VRLA Cells Harold A. Vanasse Frank J. Vaccaro Volen R. Nikolov INTELEC 2001 Presentation Outline H 2 S is produced in VRLA Cells. H 2 S is absorbed on the lead dioxide of the positive plate. Resultant H 2 S equilibrium concentration is less than 1 ppm. Background

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Hydrogen Sulfide in VRLA Cells

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  1. Hydrogen Sulfide in VRLA Cells Harold A. Vanasse Frank J. Vaccaro Volen R. Nikolov INTELEC 2001

  2. Presentation Outline • H2S is produced in VRLA Cells. • H2S is absorbed on the lead dioxide of the positive plate. • Resultant H2S equilibrium concentration is less than 1 ppm.

  3. Background • H2S is known in: • Flooded cells. • VRLA cells in thermal runaway. • Measured in our lab in Negative Active Material testing (Intelec 2000). • Supported in literature: • Reduction reaction. • MeS + 2H+ = H2S + Me2+

  4. Finding H2S • Goals: • Prove that H2S could be produced at normal float voltages and temperatures. • Identify sources. • Early testing eliminated many candidates as main factors. • Reaction between pure lead and acid became our focus.

  5. Test Rig • Test run at 40ºC. • 1.300 specific gravity acid. • Test run at a variety of voltages. • Three identical test rigs used.

  6. Results • H2S Concentration independent of voltage. • Results repeated over multiple tests.

  7. Another Surprise • H2S concentration declines over time or repeated rounds of testing. • Results repeated over multiple tests.

  8. Interim Findings • Sulfuric acid + charged negative plate = H2S. • Liberation of H2S is not voltage dependent. • H2S concentration high at first, but decreases over time. • If this were the case, we would smell rotten eggs around new VRLA cells.

  9. H2S is removed by Positive Plate • Lead dioxide reactions predict absorption: • PbO + H2S = PbS + H2O • 4PbO2 + H2S = PbSO4 + 3PbO + H2O • 4PbO2 + 3H2SO4 + H2S = 4PbSO4 + 4H2O • Two experiments lead to proof.

  10. Experiment 1: Reactor Test

  11. Input: 108 ppm H2S in H2 @ 50 ml/min. Output: Connected to GC. Measurements taken every 15 minutes. Experiment 1: Reactor TestResults

  12. Experiment 2: H2S Through a VRLA Cell

  13. Experiment 2: Results • H2S clearly being removed in the cell. • Output H2S significantly lower than input concentration.

  14. H2S Interactions • H2S Generated at the Negative Plate. • H2S Absorbed or Oxidized at the Positive Plate. • Follow on Questions: • Which process is dominant? • What H2S equilibrium concentration level is established?

  15. GC Analysis of VRLA Cells • Multiple cells from multiple manufacturers sampled weekly for H2S. • All cells on float service at 2.27 VPC at either 25°C or 32° C. • Age of cells: New to 6 years old.

  16. Results of GC Sampling • H2S concentration: 0 ppm < 1 ppm, but always less than 1 ppm. • Found across all cells tested. • Analytical proof of the presence of H2S in VRLA cells. • Maximum equilibrium threshold established for float conditions.

  17. Conclusions • H2S can be produced by VRLA cells through the reduction of sulfur-containing compounds. • H2S can be absorbed within a VRLA cell by the positive plate active material. • In cells on float, H2S concentration levels are less than 1 ppm.

  18. Impact • H2S is a poisonous gas that corrodes metal. • H2S can poison precious metal catalysts. • We have built a filter into our latest catalyst design to protect against H2S.

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