Inflatable Isolation Barriers
It’s an inflatable barrier that can be inserted through most existing access doors in duct work and will perform much better than wood, or wood frame and plastic sheeting. They are constructed out of a variety of durable wear resistant fabrics with some rated up to 500°F (260ºC). Fabric selection is based on the type of application, existing access door size, operating temperature and duration of intended use. Since they are very durable, they can be reused outage after outage. They are designed so that they will
This is a 24’0” (7.3m) high x 20’0” (6.0m ) wide x 3’0” (.9m) deep Duct Balloon being tested before shipment. Even though it’s quite large, it will collapse down small enough so that it can pass through an existing 24” (609mm) x 30” (762mm) man way for quick installation and removal. It weighs about 95 lbs. (43 kg.) and can be inflated in less than five minutes. Deflation is accomplished by turning of the blower and opening the deflation zipper.
This is a 36’0” (10.9m) wide x 14’10” (4.52m) high x 3’0” (.9m) deep Duct Balloon that is installed in a FGD Absorber outlet duct. It weighs <100 lbs. (45 kg.) and can be installed in minutes. Due to the leaky isolation damper, it is used down stream (on the non-gas side) of it and was used during inspection and maintenance of the FGD Absorber on an annual basis. To read more, click here
This is a 31’0” (9.44m) wide x 12’0” (3.65m) high x 3’0” (.9m) deep Duct Balloon that is made in Silicone Coated Fiberglass Fabric. This material is rated to 500ºF (260ºC) continuous and meets NFPA 701. The application is in a SCR Reactor on the man safe side of an existing damper to provide secondary isolation while in a bypass mode.
This one measures 9’7” (2.9m) x 3’6” (1.1m) x 2’6” (.76m) deep and is also made in Silicone Coated Fiberglass Fabric. The application is for ID Fan suction isolation where it will be installed in the inlet side of the ID fan, upstream of the inlet guide vanes.
Many plants that have added scrubbers and baghouses have discovered that the isolation dampers do not seal properly during maintenance of forced draft or booster fans. While waiting for the next major outage is usually not an option, a method was developed to provide secondary isolation to an existing guillotine damper. This was accomplished by installing an access door below the damper, and then support pipes above and below the access door. A Duct Balloon is inserted inside the duct and inflated from outside the confined space. Note the open area above the access door which becomes the vent in a “double block and bleed” arrangement. This method creates additional isolation and allows work to be done in the confined space below the duct balloon while the unit remains on line.
Copyright 2013 by G.R. Werth & Associates, Inc. - All rights reserved
Due to plant cycling, weekend shut downs may occur many times during one year. If the plant will be down for a few days, a Stack Balloon can be inserted inside the exhaust stack after a 24 hour period to keep the residual heat “bottled up” inside the HRSG. Some plants use a combination of one Duct Balloon in the inlet duct in front of the IGV’s and one in the HRSG Exhaust Stack. The quantity and location on where to use them are based on the operating cycles of the plant, geographic location, corrosion prevention goals, outage requirements, etc. For more information, please click here.
*HRSGs that sit idle for extended periods of time are at risk of gas side corrosion from the humidity in ambient air. In North America, HRSG’s tend to sit idle more frequently in the fall and spring, which also coincide with wetter weather, increasing potential for damage unless preventative action is taken. Rain water and humidity entering through an open stack helps drive the corrosion process.
*Excerpt taken from the HRSG Users Handbook, 2nd Edition (Chapter 9.1), distributed by the HRSG User's Group. Another driver is the change in ambient temperatures between day time and night time, where tube metal temperatures lag behind the daily high ambient temperature. When humid air contacts the cool tubes, condensation can occur, causing corrosion. This can be considered another form of “dew point corrosion”, except that entire sections of the HRSG’s typically are affected, not just a few rows of preheater tubes receiving cool feed water.