Lowering the effect of low‐frequency noise generated from boiler exhaust stacks.

Abstract

Low‐frequency noise from exhaust boiler stacks at a semiconductor plant was measured and the low‐frequency noise spectrum was predicted using an analytical impedance model. Nearby residents complained that noise was rattling household items, such as windows and light fixtures. The semiconductor plant speculated that noise from two boiler exhaust stacks was the source of the problem. Sound pressure level measurements conducted at the plant revealed strong tones in the infrasound and low‐audible frequency range. The boiler exhaust stack noise source was theoretically characterized by deriving the mechanical impedance of the boiler exhaust stack and the radiation impedance of the top of the boiler exhaust stack as a simple unbaffled source. The analytical model predicted the resonant frequencies of the boiler exhaust stacks and these resonances closely matched the strong low‐frequency tones measured. Using this model, possible changes in controlling parameters of common exhaust boiler stack design are described that could decrease the overall noise radiating from the exhaust stacks. As one example, the plant appreciably decreased the sound power contribution from the upper exhaust stack resonances by lowering the overall output of the exhaust boilers. This change lowered the overall noise levels without the use of silencers.