Acoustic and flow analysis to reduce boiler hum
Regular paper
LBPSIGHT
Monday 1 june, 2015, 18:20 - 18:40
0.6 Madrid (49)
Abstract:
A forced draft boiler installation showed serious low frequency noise problems. The installation consists of an air intake, fan, air ducting, a furnace and a stack with the exhaust at 40 m above ground level. Noise measurements showed that the problem occurred between 66% and 80% of the boiler load. The dominant frequencies were around 30Hz. This hum caused serious annoyance in the surrounding, and therefore the problematic load range was avoided as much as possible.
With a Finite Element acoustic study, resonances were found around 30 Hz. It was expected that flow turbulences at the inlet and outlet of the fan caused the excitation. CFD calculations showed that both the inlet and outlet flow contained large vortices. Several possible solutions were studied with the aim to reduce these vortices. Based on the calculations, changes in the design were determined. The proposed changes consist of changing the overal shapes of the inlet and outlet duct, in combination with several flow guiding vanes.
To have more assurance to reduce the hum, additional silencing was designed, resulting in a large absorbent section directly behind the fan. The acoustic responses of the original situation and the situation with absorption were calculated.
In July 2014, the changes in the installation were made in a major overhaul of the installation. Measurements showed that the changes had resulted in a reduction of 8 dB at the low frequencies.