Acoustic resonance in a package boiler and its solution - A case study

Strong acoustic resonance with acoustic pressures reaching up to 165 dB developed in the boiler bank of a package boiler at full load. At first, the resonance developed at a lower frequency in the downstream portion of the tube bank and was suppressed by an acoustic baffle covering the downstream section of the flow channel. After about one year of operation, a second resonant condition developed. Tests confirmed that, again, a strong resonant condition developed at a higher firequency in the unbaffled upstream portion of the flow channel. Computer analysis confirmed that the initial resonance occurred at the first acoustic mode of the flow channel while the follow-up resonance occurred at the second mode of the flow channel expressed as a first-mode resonance in a different (upstream) location. An extension of the acoustic baffle covering the entire depth of the tube bank eliminated the vibration. This paper gives a description of the problem and summarizes the theoretical and experimental results substantiating the findings.