Elimination of Thermoacoustic Furnace Vibration in a Gas-Fired Package Boiler: A Case Study

A severe furnace vibration was developed in a gas-fired package boiler during an initial operation. The vibration occurred at higher loads and was characterized by an acoustic standing wave residing inside the furnace in the front-to-rear direction along a burner axis. Theoretical predictions indicated that the thermoacoustic behavior of the burner/furnace system operated in an unstable range explaining the underlying cause of the vibration problem. For the elimination of the vibration problem, a two-step solution was envisioned: (1) The mode of fuel injection was modified in order to affect the flame’s oscillatory behavior and its interaction with the acoustic waves in the enclosed spaces of the burner conduits and the furnace. This step was successful in mitigating the vibration in a still thermoacoustically unstable system. (2) A full elimination of the vibration may be achieved by making the system thermoacoustically stable by modifying the cold air portion of the system. Both the step 1 solution, which suppressed the thermoacoustic oscillation, and the step 2 solution of making the system thermoacoustially stable will allow the boiler to operate without vibration at all loads. This paper gives a detailed description of the issues involved.