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Duct Balloons for use in SCR Applications

In recent years, many coal fired power plants have installed pollution control devices on their boilers known as Selective Catalytic Reduction equipment. Often referred to as SCR’s, this equipment is installed as an integral part of the flue gas duct work. Large louver dampers are installed at the inlet and outlet locations of the SCR to provide a way to isolate the SCR during inspection and maintenance of the catalyst elements.

These large louver dampers are usually equipped with a seal air system and lamella seals on the blades to help provide a tight shut off. But over time, these seals lose their ability to provide a tight seal. Replacing them would require that the unit be shut down in order to change them out.

As a solution to these leaky blade seals, a duct balloon can be installed on top of or in front of the existing louver dampers. Even though the balloon material is rated to 485º F, insulation between the damper and the balloon is required to protect it from any high heat surfaces for which it could come in contact.

After the insulation is laid down on the existing dampers, the balloon is brought into the duct work and placed in position prior to inflating it. Grab handles are sewn into the balloon to provide a means to maneuver it in place. The supply tube is permanently attached to the balloon at a location specified by the customer, usually near the manway. The end of the supply tube is then connected to the blower system, which is normally placed outside the SCR on the floor grating. Once the blower is activated the balloon will inflate in about 5-10 minutes depending on it’s size.

Duct balloons for these applications can be as large 12’0” high x 70’0” wide. But even a large duct balloon of this size would still weigh less than 150 pounds and still be able to be installed through an existing man way as small as 24” x 30”.

More....see below (click on photos to enlarge)


This balloon measured 9’0” high x 91’6” wide, but was made in four sections. Each section measured 9’0” high x 23’0” wide and weighed about 45 lbs. each which made them easy to carry up stairways and through access doors.


Each section has mating air supply connections so that the air from the blower can pass through each section.


Close up shot of the supply tubes and side lacings


Two of the four sections zipper together and form one half of the 91’6” width. The remaining section is laced together to complete the 91’6” width. Total weight of all four section is about 180 lbs.

Application Notes:

Two balloons were supplied on this project to provide auxiliary sealing of existing dampers during change out of the honeycomb catalyst elements. One balloon measured 12’0 high x 47’0” wide x 3’0” deep, and the other measured 11’0” high x 44’0” wide x 3’0” deep. The duct work that was to be isolated ran vertical up, so the balloons were installed on top of the existing dampers. The dampers were pinned closed, and the seal air systems were activated. Mineral wool insulation was first installed on top of the dampers, and then the balloons were laid down on top of the insulation. Grab handles and “D” rings are sewn into the balloon to help maneuver the balloon in place during inflation. Inflation time for these large balloons is less than 10 minutes.

Two high pressure blowers were supplied using a “Y” fitting near the connection point to the blowers. The two blowers were connected to separate electrical circuits. While it only requires one blower per balloon to keep it continuously inflated, the second blower was used as a backup in case of a circuit breaker trip.


his balloon measures 12’0” high x 47’0” wide x 3’0” deep (Damper Side)

Same picture showing inflation tube side (Note “D” Rings and Grab Handles)

 


Power Products Sales and Service, Inc.


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