Abstract
Induced-draft fans are commonly the most annoying sources of community noise associated with fossil-fuel power plants. The low frequency tones generated by the fans are usually radiated to the community from the top of a tall stack. Measurements of the tone levels in the community are hampered by environmental effects such as strong wind and thermal gradients. Measurements within the flue gas ducting are therefore desirable. However, the flue gas environment is hostile to microphones due to elevated temperatures, particulates, and the presence of gas flow. The interpretation of in-duct data is complicated by the possible effects of standing waves and cross modes in the duct and turbulence generated noise. The recent installation of a dissipative-reactive muffler in a coal-fired plant offered the opportunity to (1) investigate techniques for measuring noise in stacks, (2) evaluate the performance of the muffler under operating conditions, and (3) check the in-stack results against limited farfield data. Good agreement was obtained between reductions in tone levels measured in the stack and in the community.
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