Before we begin, let's introduce our panelists. Curtis Ashton is a power maintenance engineer with Qwest Communications, a large telecommunications service provider. He represents a large battery user. Steve McCluer is a senior product manager at American Power Conversion and provides the perspective of original equipment manufacturers (OEMs). Finally, Jose Marrero offers us the view of a large electric utility. He is DC senior systems engineer for the Hatch plant of Southern Company Nuclear. Marrero is vice chairman of the standards coordinating committee on stationary batteries (SCC29) within the Institute of Electrical and Electronics Engineers (IEEE) and a member of several battery working groups. ( Table 1, on page 43, gives the meaning and relevance of frequently used acronyms, and Table 2, on page 44, provides a list of common terms and definitions.)
-PQ. First of all, let's get some background. How do you use batteries in your business?
-CA. We use flooded and valve-regulated lead-acid (VRLA) batteries to provide long-term backup power in case of commercial AC outages and/or engine failures.
We also deploy uninterruptible power supplies (UPSs) with their associated battery backup systems in computer and Internet-related locations. A typical backup for telecom switches is 4 hr to 8 hr.
-SM. Our battery systems can be found everywhere, from huge telephone company central offices to optical interface boxes on the sides of houses. Our AC UPS systems range from small PC backup systems to megawatt 3-phase systems.
-JM. Our applications range anywhere from power plants and substations to data centers, telecom sites, and building facilities.
-PQ. What types and sizes of batteries do you use?
-CA. We use batteries from 2.5Ah (at the C8 rate) up to 4000Ah cells. We also are experimenting with lithium-based batteries and nickel-cadmiums (NiCads).
-SM. Our applications range from a few Ampere-hours to thousands of Ampere-hours. We use lead-acid batteries almost exclusively. Most are valve-regulated, although our larger UPS and DC plants use flooded batteries as well. We're also looking at other energy-reserve technologies.
-JM. We use and maintain tens of thousands of batteries from small 100Ah to large 2700Ah sites. We use lead acid in all its forms (lead calcium and lead antimony/selenium) in vented and VRLA batteries. We also use NiCAds. We're looking into lithium polymer, which we think holds promise for the near future (5 yr).
-PQ. You've mentioned different battery types. What exactly are the design differences between flooded and sealed batteries?
-CA. Let's be very clear on these points. A VRLA battery is not sealed. The electrolyte is held in place and prevented from escaping, so you sometimes hear the terms “immobilized” or “starved” electrolytes. The immobilized nature of the electrolyte allows for better density and easier transport.
A VRLA battery has a one-way pressure relief valve for the escape of hydrogen and oxygen, so it's not sealed completely. It doesn't need watering because most of the water that is electrolyzed into hydrogen and oxygen (by extra charging current) is recombined back into water and kept inside the battery.
Despite some marketers' claims, VRLA batteries are not “maintenance-free.” Other maintenance activities are highly recommended if you want a reliable battery system. Flooded batteries have longer lives and are less susceptible to thermal runaway.
-SM. When we talk about stationary lead-acid batteries, the names vary, but you can characterize them all by the form of electrolyte and whether they give off any gas.
The term “flooded” or “wet-cell” battery comes from the form of its electrolyte. The electrolyte looks like water and, to a large extent, it is. From the off-gasing perspective, these batteries are sometimes called “vented” or “vented lead-acid.” That's because they constantly release gases into the room through normal evaporation or float and recharge activity. These batteries usually have transparent containers — you can see the positive and negative plates and the electrolyte. Maintenance includes visual inspection of the internal plates and occasional electrolyte replenishment.
In your question, you used the term “sealed” for the other type of stationary lead-acid battery. That's true, but only to the extent that you can't see what's going on inside or add water. Even the sealed units have vents to relieve excess internal gas pressure.
-JM. I also refrain from using the word “sealed” because it's a marketing term that can apply to all three battery types or to none of them at all.
We have lead calcium, antimony, and selenium/antimony batteries. These are different types of lead-acid batteries with different requirements for installation, maintenance, and service. What they all have in common is electrolyte concentration between 28% and 34% sulfuric acid. And they come in either excess-free or starved immobilized electrolyte versions.
We use gel-type sealed batteries, where a silica substrate absorbs the electrolyte. If a container with this gel cracks, you won't see liquid running out. But if the cracked container remains in service or is not replaced, all the water will eventually evaporate, and you'll be left with a nasty, explosive condition known as thermal runaway.
We also use absorbed glass mat (AGM) sealed batteries. Here a fiberglass mat separates the cell's plates and absorbs the electrolyte. Just like the gel type, little or no liquid will spill out if the container ruptures, but the threat of thermal runaway exists.
-PQ. What exactly is electrolyte, and what does the term “free electrolyte” mean?
-CA. Electrolyte is a substance or solution placed between dissimilar metals. The solution contains a reactive agent capable of carrying electrons (typically a strong acid or base). People sometimes incorrectly use the terms “acid” and “electrolyte” interchangeably. In a lead-acid battery, the electrolyte is a solution of sulfuric acid diluted in water. The specific gravity rating indicates the acid's strength.
In the case of a lead-acid, Ni-Cad, or similar battery, the electrolyte can be free or immobilized. Free electrolyte is in liquid form. When uncontained, it will flow. VRLA batteries immobilize the electrolyte with a gelling agent or absorb it in a fiberglass mat. In case of a battery break, the immobilized electrolyte will not flow and spread. At worst, it will ooze or drip a small amount.
-JM. I'd add that electrolyte is not only an electron-conduction medium. It can be a reactive agent, in which case it's an intimate part of the cell's chemical reaction — as in lead-acid cells. Or it can take an inactive role, where its sole purpose is for electron transfer.
-PQ. You've had problems in the field caused by a misunderstanding of these basic battery concepts. Can you cite some examples?
-CA. Article 64 of the Uniform Fire Code (UFC) requires neutralization material in the battery room. Some people interpret this to mean you must place neutralizing pillows under each stand. Several of our first installations had these pillows, but power maintenance technicians complained mightily about the dust they created and that people threw trash in with them. Plus, many common neutralizing agents create noxious gasses when reacting with acid, which creates a hazardous environment even with small spills.
We've been able to convince many of our local fire marshals that the code requirement is met with a passive/reactive neutralizing system, rather than an active one. In other words, we meet the code by having separate neutralizing and absorbing materials located within 12 ft of any given battery stand.
For most spills (which mainly occur during installation and removal), we soak up the electrolyte with absorbent pillows, take it to an unenclosed area (typically outside) to neutralize it in containers, then properly dispose of the containers.
-SM. A few months ago, a customer was starting up a large new facility. They installed about 100 flooded lead-acid batteries in a battery room. Each battery jar contained about 10 gal of electrolyte. They followed all installation practices, including spill containment, room ventilation, and fire walls in accordance with Article 64 of the UFC.
The inspector, however, insisted the aggregate volume of electrolyte was so high that Article 80 of the UFC applied. Article 80 is intended for the storage — not use — of large amounts of hazardous liquids, such as fuels or chemicals used in manufacturing processes. Article 64 was written specifically to exempt batteries from Article 80.
In the end, it didn't matter that the batteries were using (not storing) the electrolyte. Even after the company obtained a written statement from the International Conference of Building Officials (ICBO) confirming that Article 64 took precedence, the fire marshal overrode it, asserting his right to create “supplemental requirements.” The customer had no choice but to redo the entire facility by adding full room containment in addition to the barriers around the battery racks. It cost the company a lot of money and put the startup of their services way behind schedule.
Several months later the same customer put in a similar installation a few blocks away. It went in with no problem and no secondary containment — just a different inspector.
-JM. We received a set of lead-selenium batteries installed in a cabinet with only one access door on the front. The top of the second rack measured 7 ft high, with a depth of approximately 3.5 ft. There was a 4-in. containment barrier mounted in the base of the cabinet around the rack.
The barrier prohibits access to the back of the cabinet or the underside of all the bottom cells in the back row. It's even difficult to access the front ones. When we accidentally dropped an intercell connector in the back, the only way to fish it out was to lie on the top row of cells. With the neutralizer pillows added, there is no room for any inspection, and it also cuts down on what little airflow exists.
In this particular application, I can't see how electrolyte containment increased safety, but I can see how it decreased safety for our personnel.
The question is: Where is the documented evidence of a problem? The National Response Center, an organization responsible for tracking chemical spills, has received no reports (out of 145,000) for lead-acid spills since 1989. And as far as I know, no one has performed any risk analyses.
-CA. Here's a story with a happy ending. A fire marshal worked with us on code issues for central offices in his city. He knew we had quite a few controlled environment vaults (CEVs). We didn't have to convince him that spill containment wasn't necessary. When we showed him the space we were dealing with (see photo ), he immediately rescinded the containment requirement.
ConclusionStay tuned. We'll continue our question-and-answer forum on batteries next month in the November issue. In part two, the panelists will discuss spill containment and battery codes and standards in detail.
