Gas Turbine Handbook : Principles and Practices

156 Gas Turbine Handbook: Principles and Practices
It is always recommended to wear hearing protection around
any moderately loud equipment, even at home. The interested reader
is directed to Appendix C-13 for more information.
NOISE CONTROL
Noise control or mitigation involves several steps. First of course
is, “does it need to be quiet and if so, how much?” The amount of
noise reduction is driven by having to meet an environmental noise
limit or some regulatory limit as discussed. Frequently, more silencing
is needed than what can be described as the bare minimum in
order to account for noise from other equipment or sources that all
combine to create a total sound level (see equation, 10-5); thus, a
balance of plant noise analysis must be performed. There is also a
certain amount of uncertainty, particularly with turbine sound power
levels, and there may be some design margin incorporated, perhaps
3 decibels or more depending on the acoustical performance risks
and guarantees that must be met. The following figure illustrates
the classical approach to noise control.
Figure 10-3. Source-Path-Receiver Noise Control Model
Applying noise control involves affecting one of these three elements.
For turbine inlet and exhaust noises, the noise is reduced near
the Source location by installing silencers in the gas Path. Controlling
the Path by use of a turbine enclosure or turbine building reduces
the casing noise. The Receiver noise or sound level results from controlling
either the Source or Path elements and in some situations,
the Receiver may be placed inside an enclosure.
As discussed, the turbine has three main sources of noise: inlet,
exhaust and casing. In this section we will mainly focus on the inlet
and exhaust noise, as those are the most demanding and costly for
noise control. The casing noise, as mentioned, is usually not a major
concern since the turbine is either inside a building or an enclosure.