A good sound environment is generally poorly suited to noise emissions from noisy fans, especially when a marked tone is present - when the difference in noise level between adjacent frequency bands is greater than 10 dB (from 50 Hz to 315 Hz) or even greater than 5 dB (from 400 Hz to 8 kHz) because then such acoustic phenomena are clearly perceptible to the human ear, and as such, undesirable.
In a flue gas treatment facility, industrial fans outlet is a very powerful noise source potentially causing sound nuisance for personnel of the operator operating in the vicinity as well as for the neighborhood (including long distance, a fortiori in the case of tall stacks). It is often necessary to use in such cases a soundproofing equipment of high technology to ensure compliance of the installation on the one hand with respect to the legislation on noise at work and on the other hand with respect to the regulation in terms of environmental protection. In fact fans outlet silencers (with such a soundproofing feature) in a flue gas treatment facility must have high acoustic performance (the overall sound power level to consider is often close from 130 dBA and noise emissions are with a very wide frequency spectrum) in a context where high temperatures (around 180 °C or sometimes more) and very high gas flow rates (which are counted in decades of kg/s) must be considered: great care must be taken when sizing to limit the total pressure loss directly impacting the productivity of the plant.
ITS has participated in the soundproofing of an industrial fan in the context of a project of erection of a flue gas treatment unit for of a power generation plant in France, in the area of Lille (Pas de Calais region). A stack with a height close from 40 m was foreseen, of which a noise control was necessary.
Of course, this industrial soundproofing equipment must have a sound transmission loss particularly important, overall sound power level to be accounted being 128 dB(A). But in addition, with a flow rate able to reach 45 kg/s at a temperature of 200°C, the flow rate of exhaust gas into the silencer was very high, requiring a specific design of the silencer in particular with respect to issues related to aerodynamic and to self-noise.
Therefore, the simulation of the insertion loss (with or without flow noise) as well as of the total pressure loss of the soundproofing device (whose splitters will be equipped of extremities with a special aerodynamic shaping) in the foreseen operation conditions was performed by the means of the acoustics simulation software SILDIS®.
Specific absorbent materials wich properties must satisfy both the ambitious goals of acoustic performance and also to requirements related to mechanical and thermal extreme solicitations as well as to physicochemical aggression will be incorporated into the design as required for this soundproofing device for an industrial fan.
In addition, the course of this project shows - once again - the possibilities for design and optimization of soundproofing equipment of the software SILDIS®, whose computing power and reliability, as well as whose versatility made of it a choice tool for the selection of products and construction systems for many projects of sound insulation.