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Philadelphia Scientific Advances in the Design and Application of Catalysts for VRLA Batteries Harold A. Vanasse – Philadelphia Scientific Robert Anderson – Anderson’s Electronics Presentation Outline A Review of Catalyst Basics Advances in the Catalyst Design

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Advances in the design and application of catalysts for vrla batteries l.jpg

Philadelphia Scientific

Advances in the Design and Application of Catalysts for VRLA Batteries

Harold A. Vanasse – Philadelphia Scientific

Robert Anderson – Anderson’s Electronics


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Presentation Outline

  • A Review of Catalyst Basics

  • Advances in the Catalyst Design

    • Hydrogen Sulfide in VRLA Cells

    • Catalyst Poisoning

    • A Design to Survive Poisons

  • Advances in the Field Application

    • Catalysts in Canada – Lessons Learned

    • Review of 3 Year Old Canadian TestSite


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Catalyst Basics

  • By placing a catalyst into a VRLA cell:

    • A small amount of O2 is prevented from reaching the negative plate.

    • The negative stays polarized.

    • The positive polarization is reduced.

    • The float current of the cell is lowered.




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Catalysts in the Field

  • 5 years of commercial VRLA Catalyst success.

  • A large number of cells returned to good health.

  • After 2-3 years, we found a small number of dead catalysts.

    • Original unprotected design.

    • Indicated by a rise in float current to pre-catalyst level.


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Dead Catalysts

  • No physical signs of damage to explain death.

  • Unprotected catalysts have been killed in most manufacturers’ cells in our lab.

    • Catalyst deaths are not certain.

    • Length of life can be as short as 12 months.

  • Theoretically catalysts never stop working …. unless poisoned.

  • Investigation revealed hydrogen sulfide (H2S) poisoning.


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H2S Produced on Negative Plate

  • Test rig collects gas produced over negative plate.

  • Very pure lead and 1.300 specific gravity acid used.

  • Test run at a variety of voltages.

  • Gas analyzed with GC.


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Test Results

  • High concentration of H2S produced.

  • H2S concentration independent of voltage.

  • H2S produced at normal cell voltage!


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H2S Absorbed by Positive Plate


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Lead oxides make up positive plate active material.

Lead oxides absorb H2S.

Test Results


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H2S Absorbed in a VRLA Cell


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Test Results

  • H2S clearly being removed in the cell.

  • 10 ppm of H2S detected when gassing rate was 1,000 times normal rate of cell on float!


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GC Analysis of VRLA Cells

  • Cells from multiple manufacturers sampled weekly for H2S since November 2000.

  • All cells on float service at 2.27 VPC at either 25°C or 32° C.

  • Results:

    • H2S routinely found in all cells.

    • H2S levels were inconsistent and varied from 0 ppm to 1 ppm, but were always much less than 1 ppm.


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H2S in VRLA Cells

  • H2S can be produced on the negative plate in a reaction between the plate and the acid.

  • H2S is absorbed by the PbO2 of the positive plate in large quantities.

  • An equilibrium condition exists where H2S concentration does not exceed 1 ppm.


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How do we protect the Catalyst?

  • Two possible methods:

    • Add a filter to remove poisons before they reach the catalyst material.

    • Slow down the gas flow reaching the catalyst to slow down the poisoning.


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Basic Filter Science

  • Precious metal catalysts can be poisoned by two categories of poison:

    • Electron Donors: Hydrogen Sulfide (H2S)

    • Electron Receivers: Arsine & Stibine

  • A different filter is needed for each category.


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Our Filter Selection

  • We chose a dual-acting filter to address both types of poison.

    • Proprietary material filters electron donor poisons such as H2S.

    • Activated Carbon filters electron receiver poisons.


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Slowing Down the Reaction

  • There is a fixed amount of material inside the catalyst unit.

  • Catalyst and filter materials both absorb poisons until “used up”.

  • Limiting the gas access to the catalyst slows down the rate of poisoning and the rate of catalyst reaction.


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Microcat® Catalyst Design

  • Chamber created by non-porous walls.

  • Gas enters through one opening.

  • Microporous disk further restricts flow.

  • Gas passes through filter before reaching catalyst.

Gas / Vapor Path

Porous

Disk

Filter

Material

Catalyst

Material

Housing


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How long will it last?

  • Theoretical Life Estimate

  • Empirical Life Estimate


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Theoretical Life Estimate

  • Microcat® catalyst theoretical life is 45 times longer than original design.

    • Filter improves life by factor of 9.

    • Rate reduction improves life by factor of 5.


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Empirical Life Estimate:

  • Stubby Microcat® catalysts developed for accelerated testing.

    • 1/100th the H2S absorption capacity of normal.

    • All other materials the same.

    • Placed in VRLA cells on float at 2.25 VPC & 90ºF (32ºC).

    • Two tests running.

  • Float current and gas emitted are monitored for signs of death.


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Stubby Microcat®Catalyst Test Results

  • Stubby Microcats lasted for:

    • Unit 1: 407 days.

    • Unit 2: 273 days.

  • Translation:

    • Unit 1: 407 x 100 = 40,700 days = 111 yrs

    • Unit 2: 273 x 100 = 27,300 days = 75 yrs.


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Catalyst Life Estimate

  • Life estimates range from 75 years to 111 years.

  • We only need 20 years to match design life of VRLA battery.

  • A Catalyst is only one component in battery system and VRLA cells must be designed to minimize H2S production.

    • Fortunately this is part of good battery design.


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Catalyst Design Summary

  • Catalysts reduce float current and maintain cell capacity.

  • VRLA Cells can produce small amounts of H2S, which poisons catalysts.

  • H2S can be successfully filtered.

  • A catalyst design has been developed to survive in batteries.



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Catalysts in Canada – Lessons Learned

  • Anderson’s Electronics has been adding water and catalysts to VRLA cells in Canada for over 3 years.

    • Main focus with catalysts has been the recovery of lost capacity of installed VRLA cells.

  • Their technique has been refined and improved over time.

  • The following data was collected by Anderson’s from sites in Canada.


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Steps to Reverse Capacity Loss

  • Assess the state of health of the cells.

    • Trended Ohmic Measurements & Capacity Testing

  • If necessary, rehydrate the affected cells to gain immediate improvement.

  • Install a Catalyst Vent Cap into each cell to address root cause of problem.

  • Inspect cells over time.


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    Factors to Consider when Qualifying a VRLA Cell

    • Age of cell: Cells from 1994 to 1998 were successfully rehydrated this year.

    • Cell Leaks: The cell must pass an inspection including a pressure test in order to qualify for rehydration.

    • Physical damage: Positive Plate growth should not be in an advanced stage – no severely bulging jars or covers.


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    Do Ohmic Readings Change After Catalyst Addition & Rehydration?

    • “Ohmic” refers to Conductance, Impedance or Internal Resistance.

    • Data must be collected over time and trended to get best results.

    • Rehydration significantly improves ohmic readings for cells that are experiencing the “dry-out” side effect of negative plate self discharge.


    Ohmic change after catalyst rehydration process 1995 530 ah cells l.jpg
    Ohmic Change after Rehydration?Catalyst/Rehydration Process(1995) 530 Ah Cells


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    A More Exact Way to Rehydration?Rehydrate VRLA Cells?

    • Anderson’s Electronics believes that VRLA cells dry out at different rates and should not be rehydrated using the same amount of water in each cell.

    • The rehydration tuning procedure has been further refined since last year to produce even more uniform readings.


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    Example of Rehydration?Uniform Rehydration(1994) 615 Ah Cells


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    Observations after Rehydrating Rehydration?3,500 Canadian VRLA cells.

    • Age of cells worked on: 1994 to 1998.

    • All cells showed signs of improvement.

    • Newer cells (1997–1998) did not exhibit the same amount of ohmic improvement.

      • We believe that these cells were not as dried out as older cells.

    • Older cells (1994-1996) recovered with enough capacity to remain in service and provide adequate run times for the site loads.



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    Update on 3 Year Old Test Site Rehydration?

    • 2 year old data from this Canadian site presented at last year’s conference.

    • All cells are VRLA from 1993 and same manufacturer.

    • Cells were scheduled to be replaced but catalysts and water were added to each cell as a test.


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    W Site Rehydration?Conductance Change


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    W Site Rehydration?Load Test Run Time Change(Minutes before 1.90 VPC at 3 Hour Rate)


    W test site summary l.jpg
    W Test Site Summary Rehydration?

    • The improvements are still being maintained after 3 years.

    • This string was about to be recycled, however 3 years later it remains in service.

    • Site load being protected for the required amount of time (8 hours).

    • During the recent blackout this site was without power for 5 hours and the load was successfully carried by this string.


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    Conclusions Rehydration?

    • The new generation of Microcat®catalyst product is engineered to survive real world conditions for the life of the cell.

    • Retrofitting your cells and rehydrating can:

      • Restore significant capacity for 3 years or more.

      • Save money on replacement batteries.

      • Help you get the capacity you need.

    • How did your non-Catalyst “protected” VRLA cells perform in the blackout?


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