Vibration Control
To prevent damage to a stack due to excessive or prolonged vibration from wind induced vibration forces several treatments may be utilized. The most common two methods used today are to employ Spoilers (strakes) or to utilize a Tuned Mass Damper (TMD). The two methods work entirely different and have various advantages and disadvantages.
Spoilers (strakes)
As the name indicates spoilers, or strakes, spoil the effect of the wind forces acting on a stack structure by creating a disturbance at the stack wall, thus preventing the wind from creating a negative pressure on the downwind side and therefore preventing any stack vibrations at or above critical wind speeds.
Tuned Mass Damper (TMD)
The tuned mass damper work by creating a resistance to stack movement or vibrations from wind speeds at or above critical wind speeds. The damper is mounted near the top of the stack. The damper consists of a mass (weight) constructed by rolled plate several inches larger than the stack diameter. The weight is sized specifically for each stack. It is supported by three or more pendulum style hangers, so it is free to move. Mounted between the ring mass and the stack shell are a series of cable springs. As the stack tries to move from the wind forces, it is resisted by movement against the cable spring, which is held in place by the ring mass (weight). The ring or mass is held in place by gravity.
Spoilers
Tuned Mass Damper
FAA Lighting
AThe Federal Aviation Administration (FAA) Advisory for stack systems requires that all stacks reaching a height of 200 feet or higher be lighted with an anti-collision aviation light system. These systems are available from a number of our vendors that specialize in these products to provide a complete system with the stack. It is important to provide additional stack access facilities for maintenance to the stack light system.
Davit Cranes
Although not required by the stack code, Davit Cranes can be supplied at the stack platform elevation. Davits are used to assist in hoisting equipment to the test platform level by emissions testing and sampling personnel. Davit Cranes can be supplied with manual or electric motor driven winches and range in capacity from 250 lbs. to 500 lbs. or even higher if the need arises.
Stack Testing
Air Techniques holds the unique position as the only stack producer that is also in the stack testing, and stack monitoring business. Other departments of our company mirror our history as a steel stack producer dating back to earlier years when a customer’s request led to growth into these other fields. We provide stack testing services using EPA manual and in instrumental methods to perform stack emission tests. Our CEMS group designs, supplies and installs Continuous Emission Monitoring Systems (CEMS) on new or existing stack systems. In addition, we do quarterly service and reporting for any CEMS user. When you come to ATI you can expect to use our 30 years of experience to help optimize your stack test or monitoring facilities. As an example, we commonly see this item repeated, stack test facilities located 8 diameters from an upstream disturbance, when the regulations published in 40CFR60 allow the test location as close as 2 diameters. This saves the client expense for extra ladders and rest platforms and the stack test firm set up time placing the test platform at a lower elevation. Contact us for more details and specifics for your stack project
