Transcript H2S in VRLA Cells - Philadelphia Scientific | industrial

Hydrogen Sulfide in VRLA Cells
Harold A. Vanasse
Frank J. Vaccaro
Volen R. Nikolov
INTELEC 2001
© Philadelphia Scientific 2001
Philadelphia Scientific
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.
© Philadelphia Scientific 2001
Philadelphia Scientific
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+
© Philadelphia Scientific 2001
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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.
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Test Rig
• Test run at 40ºC.
• 1.300 specific gravity
acid.
• Test run at a variety of
voltages.
• Three identical test rigs
used.
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Philadelphia Scientific
Results
H2S concentration (ppm)
600
500
• H2S Concentration
independent of
voltage.
• Results repeated
over multiple tests.
400
300
200
100
0
2.25
2.35
2.45
2.55
2.65
2.75
Cell voltage (V)
© Philadelphia Scientific 2001
Philadelphia Scientific
H2S m easured in the collected gas
(ppm )
Another Surprise
600
500
• H2S concentration
declines over time
or repeated rounds
of testing.
• Results repeated
over multiple tests.
400
300
200
100
0
1
2
3
4
Test round #
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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.
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Philadelphia Scientific
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.
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Experiment 1: Reactor Test
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Experiment 1: Reactor Test
Results
• Input: 108 ppm H2S in
H2 @ 50 ml/min.
• Output: Connected to
GC.
• Measurements taken
every 15 minutes.
© Philadelphia Scientific 2001
Test
Material
Amount
(grams)
Breakthrough
Time
(minutes)
Empty
0.0
0.01
PbO
2.2
120
PbO2
2.0
360
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Experiment 2: H2S Through a VRLA
Cell
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Experiment 2: Results
H2S concentration (ppm)
120
Inlet Concentration
100
80
Outlet Concentration
60
40
20
0
0
5
10
15
20
25
30
25
30
Elapsed Time (hours)
Gas flowrate (ml/min)
160
• H2S clearly being
removed in the cell.
• Output H2S significantly
lower than input
concentration.
140
Gas Flowrate
through the
VRLA Cell
120
100
80
60
40
20
0
0
5
10
15
20
Elapsed Time (hours)
© Philadelphia Scientific 2001
Philadelphia Scientific
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?
© Philadelphia Scientific 2001
Philadelphia Scientific
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.
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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.
© Philadelphia Scientific 2001
Philadelphia Scientific
Conclusions
• H2S can be produced by VRLA cells
through the reduction of sulfurcontaining 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.
© Philadelphia Scientific 2001
Philadelphia Scientific
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.
© Philadelphia Scientific 2001
Philadelphia Scientific