Fire protection for power plant turbine rooms has typically been a game of tradeoffs. Enclosure integrity issues in older facilities can render CO2 and halon systems ineffective. In new and old facilities alike, CO2 systems are a considerable safety hazard. However, a new system available from Victaulic may help protect plants without compromising. The following case study explains the benefits achieved by one plant that switched from a halon system.
Upgrading a Fire Suppression System
The Putnam Power Plant is located in East Palatka, Fla., about 60 miles south of Jacksonville. The plant is owned by Florida Power & Light (FP&L) and was built in the 1950s. Putnam was converted to a gas/oil combined cycle plant in the 1970s, and its two 550-MW units have three turbines each: two combustion and one steam.
When officials at the plant decided to replace their halon system with a Victaulic Vortex Fire Suppression System, it resolved some issues associated with traditional turbine fire protection systems and offered an array of additional benefits.
Putnam was originally outfitted with a halon fire suppression system. For halon to effectively suppress a fire, room integrity is required. Given the age of the building, this was a significant challenge.
Suchat Sonchaiwanich, principal engineer for FP&L technical services department explains, “Every time there is a major outage, we have to take the roof off and haul the turbine out. When complete, we put the roof back. Each time we do this, we have to perform an enclosure integrity test. All of the steel and the roof of the building has to be tight, which makes it difficult to get a positive test back. In fact, it often fails because we have an older building and there is too much leakage.”
With older turbines in the facility that have doors and dampers that do not fully close, the plant couldn’t get a sealed enclosure (Figure 3) without a considerable retrofit expense. Should an incident arise while the doors and dampers are open, the halon system wouldn’t work effectively as designed.
|3. Electrical enclosure zone panel. Courtesy: Victaulic|
With sustainability, safety, and room integrity issues top of mind, FP&L hired Space Coast Fire and Safety to provide a new fire suppression system for the plant. Officials at Putnam investigated several options, including CO2 systems and the Victaulic Vortex Fire Suppression System.
In the fire protection industry, CO2 has been around for awhile and has been used effectively over the years in unoccupied areas. The National Fire Protection Association and U.S. Environmental Protection Agency (EPA), however, have taken an aggressive stand on its use, making it increasingly difficult to install, given the risk factors associated with the gas. According to the EPA, at the minimum design concentration for its use as a total flooding fire suppressant (34%), CO2 is lethal. As a result, it requires pre-discharge alarms and activation delays to allow for the evacuation of personnel. Similar to halon, CO2 systems also require good enclosure integrity to function properly.
A Nontoxic System
With room integrity—or lack thereof—among the top considerations for a new fire suppression system at the Putnam Power Plant, the contractor and plant engineers evaluated and ultimately selected the Victaulic Vortex Fire Suppression System as a replacement for the halon system. Victaulic Vortex is the industry’s first hybrid clean agent/water mist system; in 2009, Factory Mutual established a new category—FM 5580—to classify such systems.
The system extinguishes fires without the use of toxic chemicals or gases by deploying a high-velocity, low-pressure mixture of water and nitrogen. Water is introduced to a jet stream of nitrogen at supersonic speed within the unique emitter (Figure 4). The nitrogen atomizes the water, forming a dense homogeneous suspension that enters the protected space at 40 miles per hour. The unique swirling pattern quickly fills the hazard space and attacks the fire, overcoming aerodynamic forces that typically decelerate and diffuse water droplets, absorbing the heat and starving the fire of oxygen (view the system animation at bit.ly/17dYp0B).
|4. Vortex emitter protection in turbine room. Courtesy: Victaulic|
Although water and turbines generally don’t mix—water can damage or shock the casing, resulting in expensive repairs—the size of the water droplets emitted from the Vortex system is so small that the mist does not damage equipment. At less than 10 microns in size, the water droplets are up to 100 times smaller than water particles delivered through traditional water mist systems. This small size allows for improved heat absorption and total extinguishing. Activation of the three-dimensional total flooding system results in uniform cooling because the water and nitrogen blend is transported throughout the entire hazard area, completely surrounding the equipment. As little as 1 gallon of water is released per emitter per minute. The small water droplets surround the equipment with minimal to no wetting, preventing water damage. Residual moisture is barely detectable following discharge.
Unlike halon and CO2 systems, the Victaulic Vortex system does not require room integrity. The system extinguishes fires in open, naturally ventilated areas, meaning it would work even with doors and dampers open. The turbine enclosures at Putnam did not have to be retrofitted, resulting in significant cost savings for the plant.
“Besides room integrity purposes,” Sonchaiwanich said, “the other big reason for selecting Vortex was for safety purposes. The nitrogen Vortex uses is a friendly gas. It provides adequate and sufficient time for personnel working nearby to get out.”
System activation is immediate when sensors detect smoke or heat. There is no delay in activation to evacuate personnel because the system emits only nontoxic agents. Personnel are safe during activation; reduction of oxygen in the space is at levels within safe breathing tolerances.
The new system was installed in the first unit at the Putnam plant in 2012; installation and commissioning on the second unit was completed in March 2013. The contractor worked within shutdowns to replace the old system, thus reducing the impact on plant operations.
The Vortex system at Putnam is configured with zone control panels to isolate activation to just the unit affected by a fire (Figure 5). The two units share the nitrogen supply, which is stored in cylinders (Figure 6). Nitrogen cylinders simplify long-term maintenance relative to CO2 cylinders. Rather than yearly weight tests, as are needed for CO2 cylinders, gauges indicate adequate nitrogen levels. Maintenance best practices dictate that the cylinders be inspected for possible replacement about every 12 years. Hoses should be inspected every five years.
|5. Mechanical enclosure zone panel. Courtesy: Victaulic|
|6. 80-L nitrogen cylinders and manifold system. Courtesy: Victaulic|
Not long after the Putnam project began, officials at FP&L’s Lauderdale Power Plant, also a two-unit combined cycle facility, selected the Victaulic Vortex system to replace that plant’s CO2 system due to personnel safety concerns.
The CO2 system at the Lauderdale plant was designed with one tank to supply both units, and activation couldn’t be isolated to just one unit. During maintenance, the whole system had to be removed from service, requiring a shutdown of the plant in accordance with site policy. As at the Putnam plant, the Lauderdale plant installed the new system to enable activation in just the affected unit. Lauderdale, however, utilizes bulk tanks instead of cylinders for the nitrogen supply; two tanks supply each turbine. This configuration ensures ample nitrogen supply to each turbine, allowing the plant to keep the nonaffected turbines operating after a fire.
Installation and commissioning at Unit 4 of the Lauderdale plant was completed in April 2013. Installation at Unit 5 is scheduled for completion in 2014.
—Frank Barstow is a Vortex sales representative with Victaulic.