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

Severe furnace vibration developed in a gas-fired package boiler during 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 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 utilized: 1. The mode of fuel injection was modified with the aim of disrupting the interface between the hot furnace gases and the cold burner air region in order to minimize the principal thermoacoustic hot-to-cold driving mechanism. This step was successful in mitigating the vibration in a still thermoacoustically unstable system. 2. A full elimination of the vibration was 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 excitation source and the step 2 solution of making the system thermoacoustially stable allowed the boiler to operate without vibration at all loads. The paper gives a detailed description of the issues involved.