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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

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
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
catalyst basics
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.
catalysts in the field
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.
dead catalysts
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.
h 2 s produced on negative plate
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.
test results
Test Results
  • High concentration of H2S produced.
  • H2S concentration independent of voltage.
  • H2S produced at normal cell voltage!
test results13
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!
gc analysis of vrla cells
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.
h 2 s in vrla cells
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.
how do we protect the catalyst
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.
basic filter science
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.
our filter selection
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.
slowing down the reaction
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.
microcat catalyst design
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

how long will it last
How long will it last?
  • Theoretical Life Estimate
  • Empirical Life Estimate
theoretical life estimate
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.
empirical life estimate
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.
stubby microcat catalyst test results
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.
catalyst life estimate
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.
catalyst design summary
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.
catalysts in canada lessons learned
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.
steps to reverse capacity loss
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.
factors to consider when qualifying a vrla cell
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.
do ohmic readings change after catalyst addition rehydration
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.
a more exact way to rehydrate vrla cells
A More Exact Way to 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.
observations after rehydrating 3 500 canadian vrla cells
Observations after Rehydrating 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.
update on 3 year old test site
Update on 3 Year Old Test Site
  • 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.
w test site summary
W Test Site Summary
  • 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.
conclusions
Conclusions
  • 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?