Inflatable duct balloons can be inserted in any size duct work and perform much better than wood frame and plastic barriers. They are constructed out of a durable acid resistant fabric rated to 485°F (251º C) which is resistant to tears, and can be reused outage after outage. They are designed to collapse down small enough to fit through most existing man ways for ease
of installation and removal. Using the supplied 120-V blower system, they can be installed quickly and become fully inflated in ten minutes or less. They can be quickly removed from the duct work by turning off the blower and then opening a large zipper. Applications are in SCR’s, FGD Scrubbers, Gas Turbines with HRSG Exhaust Stacks, and many others.
Units that share a common stack often experience opacity excursions that are aerosols rather than particulates. These aerosols form when the stack flue gas temperature falls below the dew point temperature because of air in-leakage from out of service units, especially at reduced loads. Although zero leakage dampers are available, most units are not equipped with this type of damper. To alleviate this
operational problem, the plant personal or their designated contractor will install a temporary barrier made of wood and plastic sheeting in front of the leaky isolation damper to try and seal off this air in-leakage. These temporary wood frame and plastic barriers are very time and labor intensive to make on site and rarely work very well. They are usually discarded at the end of the outage.
*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, HRSGs 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. 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
HRGSs typically are affected, not just a few rows of preheater tubes receiving cool feed water. *Excerpt from the HRSG Users Handbook, 2nd Edition (Chapter 9.1), distributed by the HRSG User's Group.
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 HRSGs. Some plants use a combination of duct balloons at the front end and back end, and sometimes at the back end only. The location on where to use them are based on the operating cycles of the plant, geographic location, corrosion prevention goals, etc.
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 HRSGs. Some plants use a combination of duct balloons at the front end and back end, and sometimes at the back end only. The location on where to use them are based on the operating cycles of the plant, geographic location, corrosion prevention goals, etc.
This is a 24’0” high x 20’0” wide x 3’0” deep duct balloon being tested before shipment. It will collapse down small enough so that it can pass through an existing 24” x 30” man way. It weighs about 95 lbs and inflates in less than four minutes.
Many plants do not have stack dampers and during shut downs, the residual heat in the HRSG is lost through the open stack. According to HRSG vendors, fatigue damage resulting from cold starts is 20 times to 40 times greater than from warm starts. Down drafts can enter the stack and lower the dew point and the ambient temperature inside the HRSG and cause
corrosion. This type of installation requires installing a 30” x 30” access door at the CEMS platform level and a support rod and hardware across the diameter of the stack. The balloon can then be installed or removed from outside the stack without entering a confined space. Complete installation pictures for this application can be found here.
Duct Balloons
Reduce Maintenance Cost