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© Philadelphia Scientific 2003 Philadelphia Scientific Advances in the Design and Application of Catalysts for VRLA Batteries Harold A. Vanasse – Philadelphia Scientific Robert Anderson – Andersons Electronics Philadelphia Scientific
© Philadelphia Scientific 2003 Philadelphia Scientific 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 Test Site
© Philadelphia Scientific 2003 Philadelphia Scientific Catalyst Basics By placing a catalyst into a VRLA cell: –A small amount of O 2 is prevented from reaching the negative plate. –The negative stays polarized. –The positive polarization is reduced. –The float current of the cell is lowered.
© Philadelphia Scientific 2003 Philadelphia Scientific Catalyst Basics
© Philadelphia Scientific 2003 Philadelphia Scientific Advances in the Catalyst Design
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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 (H 2 S) poisoning.
© Philadelphia Scientific 2003 Philadelphia Scientific H 2 S Produced on Negative Plate Test rig collects gas produced over negative plate. Very pure lead and specific gravity acid used. Test run at a variety of voltages. Gas analyzed with GC.
© Philadelphia Scientific 2003 Philadelphia Scientific Test Results High concentration of H 2 S produced. H 2 S concentration independent of voltage. H 2 S produced at normal cell voltage!
© Philadelphia Scientific 2003 Philadelphia Scientific H 2 S Absorbed by Positive Plate
© Philadelphia Scientific 2003 Philadelphia Scientific Test Results Lead oxides make up positive plate active material. Lead oxides absorb H 2 S. Test Material Amount (grams) Breakthrough Time (minutes) Empty PbO PbO
© Philadelphia Scientific 2003 Philadelphia Scientific H 2 S Absorbed in a VRLA Cell
© Philadelphia Scientific 2003 Philadelphia Scientific Test Results H 2 S clearly being removed in the cell. 10 ppm of H 2 S detected when gassing rate was 1,000 times normal rate of cell on float!
© Philadelphia Scientific 2003 Philadelphia Scientific GC Analysis of VRLA Cells Cells from multiple manufacturers sampled weekly for H 2 S since November All cells on float service at 2.27 VPC at either 25°C or 32° C. Results: –H 2 S routinely found in all cells. –H 2 S levels were inconsistent and varied from 0 ppm to 1 ppm, but were always much less than 1 ppm.
© Philadelphia Scientific 2003 Philadelphia Scientific H 2 S in VRLA Cells H 2 S can be produced on the negative plate in a reaction between the plate and the acid. H 2 S is absorbed by the PbO 2 of the positive plate in large quantities. An equilibrium condition exists where H 2 S concentration does not exceed 1 ppm.
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific Basic Filter Science Precious metal catalysts can be poisoned by two categories of poison: –Electron Donors: Hydrogen Sulfide (H 2 S) –Electron Receivers: Arsine & Stibine A different filter is needed for each category.
© Philadelphia Scientific 2003 Philadelphia Scientific Our Filter Selection We chose a dual-acting filter to address both types of poison. –Proprietary material filters electron donor poisons such as H 2 S. –Activated Carbon filters electron receiver poisons.
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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 PathPorous Disk Filter Material Catalyst Material Housing
© Philadelphia Scientific 2003 Philadelphia Scientific How long will it last? Theoretical Life Estimate Empirical Life Estimate
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific Empirical Life Estimate: Stubby Microcat ® catalysts developed for accelerated testing. –1/100 th the H 2 S 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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 H 2 S production. –Fortunately this is part of good battery design.
© Philadelphia Scientific 2003 Philadelphia Scientific Catalyst Design Summary Catalysts reduce float current and maintain cell capacity. VRLA Cells can produce small amounts of H 2 S, which poisons catalysts. H 2 S can be successfully filtered. A catalyst design has been developed to survive in batteries.
© Philadelphia Scientific 2003 Philadelphia Scientific Advances in the Field Application of Catalysts
© Philadelphia Scientific 2003 Philadelphia Scientific Catalysts 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.
© Philadelphia Scientific 2003 Philadelphia Scientific Steps to Reverse Capacity Loss 1.Assess the state of health of the cells. Trended Ohmic Measurements & Capacity Testing 2.If necessary, rehydrate the affected cells to gain immediate improvement. 3.Install a Catalyst Vent Cap into each cell to address root cause of problem. 4.Inspect cells over time.
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific Ohmic Change after Catalyst/Rehydration Process (1995) 530 Ah Cells
© Philadelphia Scientific 2003 Philadelphia Scientific A 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.
© Philadelphia Scientific 2003 Philadelphia Scientific Example of Uniform Rehydration (1994) 615 Ah Cells
© Philadelphia Scientific 2003 Philadelphia Scientific Observations after Rehydrating 3,500 Canadian VRLA cells. Age of cells worked on: 1994 to 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 ( ) recovered with enough capacity to remain in service and provide adequate run times for the site loads.
© Philadelphia Scientific 2003 Philadelphia Scientific Average Ohmic Improvement after Catalyst/Water Addition
© Philadelphia Scientific 2003 Philadelphia Scientific Update 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.
© Philadelphia Scientific 2003 Philadelphia Scientific W Site Conductance Change
© Philadelphia Scientific 2003 Philadelphia Scientific W Site Load Test Run Time Change (Minutes before 1.90 VPC at 3 Hour Rate)
© Philadelphia Scientific 2003 Philadelphia Scientific 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.
© Philadelphia Scientific 2003 Philadelphia Scientific 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?
© Philadelphia Scientific 2002 Philadelphia Scientific Catalysts in Canada: The Science Behind 2 Years of Canadian VRLA Cell Rehydration and Catalyst Addition.
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