Duct Balloons
Reduce Maintenance Cost
To reduce outside drafts from entering the inlet duct work, the duct balloon can be installed in duct work that runs horizontally or vertically. The blower is typically placed outside of the duct work and the inflation tube is fed through an existing man way. While only one balloon is required for this type of installation, this artist rendering shows how it would be installed in either a vertical run or horizontal run.
Another installation point can be in the exhaust ductwork just before the exhaust stack. These balloons are typically 7’ to 9’ wide and can be as tall as 50’ or more depending upon the size of the unit. Either of these locations will permit the temporary installation of duct balloons without any modifications to the plant. Your choice may depend upon several factors including which direction the outside air is entering the unit or if certain areas are experiencing off line corrosion.
*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.
Copyright 2010 by G.R. Werth & Associates, Inc. - All rights reserved
To see step-by-step installation pictures in a HRSG Exhaust Stack, click here