Primary Air Shut Off Dampers

Primary air shut off (PASO) dampers are critical to power plant operation and maintenance. The coal pulverizers downstream from the PASO dampers operate in a severe service environment. Because of the severe service condition it is understandable that the pulverizers may require off-line maintenance while the plant remains in operation. That means the dampers that isolate the pulverizers from the incoming air flow must be reliable and efficient.

The coal dust that results from the pulverizer operation is an explosion hazard. It is critical that the PASO dampers be fast acting during a boiler trip so that the pulverizers can be isolated safely and reliably. The thermal shock that results from fast operation must be taken into account if the PASO damper is to perform consistently over the long haul.

Senior Flexonics Pathway has developed a family of PASO damper designs that address the problems so often encountered at coal fired power plants. Unique PASO design features address severe service conditions, fast operation, thermal shock, and reliability with field proven success.

Cold air shut off damper is designed with 1” thick CorTen blade to resist corrosion and survive high pressure surges that can result from operation.

Pneumatic actuators are used for hot and cold air PASO dampers for fast closure rates. Closure rates of 1 second are routinely achieved in factory performance tests.

A cold air PASO damper installed in service with blade open. Note the pneumatic actuator for fast closure.

PASO dampers are designed with fully enclosed bonnets to reduce seal air requirements when the blade is open or closed. At right the bonnet is shown before being assembled to the damper frame.

The image below shows a hot air PASO damper with the bonnet attached in the blade-open configuration.

Pneumatic actuators used on the hot PASO damper result in a closure rate of 1 second during factory performance tests.

The hot PASO damper is designed with an engineered blade to tolerate thermal and pressure shock. The blade has a corrugated face that allows for differential thermal growth across the blade face without excessively straining the blade material. This innovation keeps the blade edges stay flat in service which results in very efficient sealing, up to 99.5% shut off. Reliable, fast, efficient shut off is a critical factor during pulverizer maintenance.