Precipitator Isolation Dampers—What You Need to Know

dampers

Precipitator isolation dampers, such as isolation gates, slide gates, guillotine dampers, and louver dampers, are a mechanical device to stop or regulate the fluid flow into and out of an electrostatic precipitator.

Isolation dampers may be used to divert hot exhaust or to shut off process for precipitator maintenance, or to regulate or balance airflow. Precipitator systems having one or more chambers or auxiliary precipitators can use isolation dampers to isolate a particular chamber of the precipitator from boiler exhaust so that internal precipitator access can be gained for maintenance, repairs of internal precipitator components, or to correct an operating deficiency. This saves equipment downtime by not having to take the boiler off line.

Inlet and outlet dampers can be used either as a backdraft damper to restrict flow in one precipitator chamber or to regulate or control the amount of flow through multiple precipitator chambers. Zero Leak isolation dampers installed on precipitator inlet flues provide personnel protection from exposure to dust, vapors, fumes, and heat during internal maintenance work.

The risks posed by these disc dampers are multifaceted:

  • The disc damper construction allows for up to 6% leakage. This does not meet the OSHA standard (double block and bleed) for safe vessel entry.  
  • Maintenance programs, parts replacement, or inspections are often overlooked on the sealing surfaces or linkage arms.
  • Dampers installed in the “Fail Open” position could have a linkage failure that would cause the damper to open unexpectedly and fatally endanger any personnel in the confined space.   
  • Dampers installed in the “Fail Closed” position could have a linkage failure that would cause the damper to close unexpectedly and trip the boiler or ID fan and possibly endanger personnel in an upset condition.   
  • The sealing surface could be occluded by ash buildup, providing some unknown amount of blow by. Inspection of the seal is only possible with the damper open and the boiler down.  

There are several large companies who have recently enacted policies stating that no work can be done inside the precipitator without a furnace lockout because of risks the disc dampers are posing.  

The industry standard for large flue gas streams is the double block and bleed guillotine slide gate, where a pressurized chamber of purge air is held between the vessel being entered and the flue gas. In the proper operation condition these dampers are “zero leak by.”  

ProcessBarron guillotine dampers incorporate dual jackscrew style drives coupled to a TEFC motor. Horsepower is calculated based on loading and service intended with a 2:1 safety margin, and then is compared to the jackscrew column load.

The largest motor size to prevent buckling is then selected. While other designs may use a wormgear actuator that can be limited by the use of internal torque switches, our design provides a healthy margin on force output plus the added feature of 220% of rated force if there’s an obstruction in the duct. Although it’s not always necessary, the added force is a great safety net as opposed to the wormgear stalling out.

Another key feature is the use of 1/4” stainless steel angle seals as a standard for internal blade seals. Many designs incorporate thin gauge spring seals that may be easily damaged when in contact with salt cake or other duct debris relegating the damper to “low leakage” status in operation.

Installing New Dampers

Southern Field–EEC has an exceptional track record replacing these disc dampers with ProcessBarron isolation dampers on the inlets of electrostatic precipitators across the country. These are often in difficult-to-access positions and require significant rigging and safety considerations. Damper replacement can be done in a standard outage window. A damper replacement project can ensure that your equipment will be ready for safe access and eliminate costly boiler downtime caused by downstream equipment.

Need more information about dampers? Contact Southern Field-EEC today.