Dampers and Louvers Used in Power Plants, Refineries, Boilers, and Furnaces

Parallel damper with electric actuator.

A damper (otherwise known as a louvre) is a multi-element flow control device generally used to throttle large flows of air at low pressure. Dampers find common application in furnace and boiler draft control, and in HVAC (Heating, Ventilation, and Air Conditioning) systems.

Radial damper.

Common damper designs include parallel and radial. Parallel-vane dampers resemble a Venetian blind, with multiple rectangular vanes synchronously rotated to throttle flow through a rectangular opening. A photograph of a parallel-vane damper is shown above, part of an induced-draft (suction) air fan system on a separator at a cement plant. The vanes are not visible in this photograph because they reside inside the metal air duct, but the electric actuator mechanism and linkages connecting seven vane shafts together are visible.

Pneumatic vane actuator damper drive.

Radial-vane dampers use multiple vanes arranged like petals of a flower to throttle flow through a circular opening. A photograph of a radial-vane damper is shown here (note the levers and linkages on the periphery of the tube, synchronizing the motions of the eight vanes so they rotate at the same angle).

Dampers are opened and closed by electric or pneumatic drives. In recent years, the pneumatic vane actuator  has earned an reputation for modulating dampers. Used in critical applications commonly found in power plants, refineries, boilers, and furnaces, these unique damper drives provide precise combustion gas management, are proven to increase boiler efficiency, lower fuel consumption, reduce emissions, and reduce maintenance cost.


Parts of this post are reprinted from Lessons In Industrial Instrumentation by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.

Boiler Damper Drives: Pneumatic Vane Actuators Excel

Damper drive with pneumatic
vane actuator (Kinetrol).

Industrial and commercial boilers burn much more efficiently when the combustion air is accurately controlled. Reduced emissions and higher BTU/Fuel ratios are achieved through precise draft control. One method to control draft air is with dampers to manage volumetric airflow.  Another role of the damper in industrial boilers is to control the recirculation of flue gases for tighter emissions control. In both cases, improved combustion, through proper air/fuel mixing and controlled recirculation, greatly improves combustion efficiency and also lowers fuel cost (saves money).

Damper drive (side mount) installed.

The mechanical devices used to open, close and modulate dampers are critical to precise control. The “motors” used to move the louvers and dampers can be electrically operated or pneumatic operated. Electrically operated damper drives have historically been favored, but the shift to retro-fit electric drives with pneumatic damper drives has been significant in the last two decades. When pneumatic vane actuators were first introduced for damper drive service, their virtues were quickly discovered. Their inherent design and operating advantages apply perfectly for precise damper control. These design and operating advantages are:

Damper drives on round dampers.

• Precise, smooth signal to movement response
• 100 percent duty cycle
• Continuous modulating service
• No overheating
• High speed/high-torque
• Fast full stroke open/close
• Very easily serviced
• Excels in harsh, high-temperature operating environments
• Effectively zero air consumption in resting state

Along with these performance features, pneumatic vane drives can replace electric damper drives in-place, with the same footprint and mounting dimensions, making retrofit fast and easy. Considering all of the above, one can argue it makes sense to replace all electric drives with pneumatic vane actuator drives.  In the movement toward better environmental control, and greater operating efficiencies, upgrading to pneumatic vane actuator damper drives for boiler damper control is an excellent choice.

Tighter Boiler Emissions Control with Pneumatic Vane Actuator Damper Drives

Pneumatic rotary vane damper drive.

In order to ensure efficient, reliable, and safe boiler operation, it is critical to accurately control the flow of the boiler's combustion air and flue gas. Poor control of airflow results in inefficient burning (wasting money), erratic cycling, flame-outs and even the possibility of toxic and hazardous emissions. In order to reduce the likelihood  of these situations, accurate airflow control is critical.

In the United States, the Environmental Protection Agency's introduction of the MACT (Boiler Maximum Achievable Control Technology) Rule requires operators to institute maintenance procedures annually or bi-annually in an effort to force plant operators toward compliance. This strict new legislation has a large impact on how companies' control their emissions from industrial boilers, process heating systems and furnaces. 

Typical drive applications and designs
(click for larger picture).

Industrial boilers use dampers and louvers to control the quantity of air admitted to the furnace. Tighter boiler draft control significantly improves combustion. Any improvement in controlling the position of the dampers and increasing the positioning speed improves boiler efficiency. Damper operation needs to be precise and fast for the accurate control. 

There are an estimated 15,000 boilers, furnaces, and process heaters running in the USA, and many are using an outdated primary component to control their lovers and dampers - the electric damper drive. Electric damper drives utilize motors and gear-boxes to move and position flue gas and combustion gas dampers. However, because of the inherent movement (sometimes referred to as hysteresis) between gears, linkages and other assorted mechanisms, these drives may not provide the accuracy, power, or signal response time required for optimum control.

Enter the pneumatic vane actuator damper drive. Pneumatic vane actuator drives are a newer, but still proven, method to provide high speed, accurate, and continuous modulation of air dampers for precise control. Replacing outdated electric damper drives with fast acting, pneumatic rotary vane damper drives offers measurable improvement to burner efficiency and cleaner emissions.

Switching out electric drives with their better performing pneumatic cousins is fairly simple. Downtime is not an issue.  The old drive footprint, lever positions, connecting rods, and operational envelop are considered with every design. Any existing mechanical or electrical connection placements are matched. Since the new drive mates to all existing mounting and connections, and the envelope size is typically smaller, installing the pneumatic drive is usually a matter of pulling the old one out, and dropping the new one in.

At the heart of the pneumatic damper drive is the stalwart pneumatic rotary vane actuator. With hundreds of thousands of these devices operating in the toughest process applications around the world, their reputation is well earned. These actuators are known for their incredibly long life, ability to withstand very high cycle rates, and smooth “bump-less” control. They are also designed to handle high ambient temperatures, high vibration, and very dusty environments, typical of where boiler dampers are located. Additionally, rotary vane actuators are available with direct mount pneumatic and electro-pneumatic positioners, manual overrides, network communication modules, limit switches, and spring modules. The direct mount design eliminates external brackets and coupling, and keeps the overall package size small.

Pneumatic vane actuator damper drives are a significant improvement over traditional electric damper drives. They provide fast response to input signal changes, very accurate positioning, a reduction in plant air consumption, and they lower fuel consumption. Engineers tasked with increasingly rigorous boiler emissions requirements must consider pneumatic vane style drives as a compelling alternative to the electric drive. They truly are an example of better form, fit, and function.