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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
Hydrogen Sulfide in VRLA Cells

Harold A. Vanasse

Frank J. Vaccaro

Volen R. Nikolov

INTELEC 2001

presentation outline
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.
background
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+
finding h 2 s
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.
test rig
Test Rig
  • Test run at 40ºC.
  • 1.300 specific gravity acid.
  • Test run at a variety of voltages.
  • Three identical test rigs used.
results
Results
  • H2S Concentration independent of voltage.
  • Results repeated over multiple tests.
another surprise
Another Surprise
  • H2S concentration declines over time or repeated rounds of testing.
  • Results repeated over multiple tests.
interim findings
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.
h 2 s is removed by positive plate
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.
experiment 1 reactor test results
Input: 108 ppm H2S in H2 @ 50 ml/min.

Output: Connected to GC.

Measurements taken every 15 minutes.

Experiment 1: Reactor TestResults
experiment 2 results
Experiment 2: Results
  • H2S clearly being removed in the cell.
  • Output H2S significantly lower than input concentration.
h 2 s interactions
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?
gc analysis of vrla cells
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.
results of gc sampling
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.
conclusions
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.
impact
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.