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Duct Balloons for Gas Turbine Applications

There are three primary locations for installing duct balloons on Simple Cycle or Combined Cycle Gas Turbine plants with HRSG’s:

  • Inside of the inlet duct in front of the Inlet Guide Vanes (IGV’s)
  • Inside of the duct work just before the exhaust stack
  • Inside of the exhaust stack

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 supply 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.

Many plants do not have stack dampers and during shut downs, the residual heat in the HRSG is lost through the open stack. Down drafts can enter the stack and lower the dew point and ambient temperature inside the HRSG and cause corrosion problems. This installation requires fabricating and installing an access door and a support rod across the diameter of the stack. The balloon can be then installed or removed from outside the stack without entering a confined space.

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’ 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.

To keep rain or snow from accumulating on top of the balloon, it can be installed at a slight angle inside of the stack to permit run off. Different lengths of nylon rope that suspend the balloon from the support rod can be used to attain the desired pitch. Or, the support rod can installed at a slight angle and nylon ropes can then be the same lengths.



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