Title: Advances in the Design and Application of Catalysts for VRLA Batteries
1Advances in the Design and Application of
Catalysts for VRLA Batteries
Philadelphia Scientific
- Harold A. Vanasse Philadelphia Scientific
- Robert Anderson Andersons Electronics
2Presentation 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 Test Site
3Catalyst 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.
4Catalyst Basics
5Advances in the Catalyst Design
6Catalysts 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.
7Dead 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.
8H2S 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.
9Test Results
- High concentration of H2S produced.
- H2S concentration independent of voltage.
- H2S produced at normal cell voltage!
10H2S Absorbed by Positive Plate
11Test Results
- Lead oxides make up positive plate active
material. - Lead oxides absorb H2S.
Test Material Amount (grams) Breakthrough Time(minutes)
Empty 0.0 0.01
PbO 2.2 120
PbO2 2.0 360
12H2S Absorbed in a VRLA Cell
13Test 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!
14GC 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
25C 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.
15H2S 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.
16How 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.
17Basic 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.
18Our 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. -
19Slowing 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.
20Microcat 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
21How long will it last?
- Theoretical Life Estimate
- Empirical Life Estimate
22Theoretical 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.
23Empirical 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.
24Stubby 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.
25Catalyst 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.
26Catalyst 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.
27Advances in the Field Application of Catalysts
28Catalysts in Canada Lessons Learned
- Andersons 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 Andersons
from sites in Canada.
29Steps 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.
30Factors 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.
31Do 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.
32Ohmic Change after Catalyst/Rehydration
Process(1995) 530 Ah Cells
33A More Exact Way to Rehydrate VRLA Cells?
- Andersons 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.
34Example of Uniform Rehydration(1994) 615 Ah
Cells
35Observations after Rehydrating 3,500 Canadian
VRLA cells.
- Age of cells worked on 1994 to 1998.
- All cells showed signs of improvement.
- Newer cells (19971998) 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.
36Average Ohmic Improvement after Catalyst/Water
Addition
37Update on 3 Year Old Test Site
- 2 year old data from this Canadian site presented
at last years 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.
38W Site Conductance Change
39W Site Load Test Run Time Change(Minutes before
1.90 VPC at 3 Hour Rate)
40W 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.
41Conclusions
- 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?