The reduction of industrial noise in the environment is all the more necessary as the number and power of some machines and various processes is accompanied by an increase in their noise emissions, which would then be likely - if nothing were done - to negatively impact the quietness of neighbors, not only at short distances (e.g. at the property boundary), but also in more distant locations (in a variable manner depending on the configuration of the locations e.g. relief, land use, obstacles and depending on climatic conditions e.g. wind, air humidity which influence sound propagation outdoors).
The list of noise sources that can be incriminated, depending on the case, is endless - whether it is building envelopes housing production or processing activities, equipment installed outside (e.g. motors, fans, coolers, dust collectors, grinders), ends of air networks (e.g. ventilation air inlets and outlets, chimney outlets) or gas decompression vents.
French regulations require a reduction in industrial noise in the environment of factories, distinguishing between the daytime period (07:00 to 22:00 except Sundays and public holidays) and the nighttime period (22:00 to 07:00 as well as Sundays and public holidays):
- in some cases, a prefectural decree (when it is not ministerial) sets the noise levels not to be exceeded at the property boundary: this is particularly the case for Facilities Classified for the Protection of the Environment (FCPE) e.g. 70 dB(A) during the day and 60 dB(A) at night
- the emergence i.e. the difference between the A-weighted equivalent continuous pressure levels of ambient noise (factory in operation) and residual noise (in the absence of noise generated by the factory, but measured over the period of operation of the factory) is limited in the Zones with Regulated Emergencies (ZRE), which generally include, near the industrial plant: homes, building zones and areas occupied by third parties e.g. Public Access Buildings (PAB), other industrial establishments. If the ambient noise level in the ZER (including factory noise) is between 35 dB(A) and 45 dB(A) then the admissible emergence is 6 dB(A) during the day and 4 dB(A) at night. If the ambient noise level in the ZER (including factory noise) is greater than 45 dB(A) then the admissible emergence is 5 dB(A) during the day and 3 dB(A) at night
- in the case of a Facility Classified for the Protection of the Environment (FCPE), a marked tone, the presence of which is linked to the difference between the sound pressure level in a given 1/3 octave frequency band and the adjacent frequency bands, is considered undesirable if it exceeds 10 dB in the frequency range 50 Hz-315 Hz or 5 dB in the frequency range 400 Hz-8000 Hz
ITS participated in the reduction of industrial noise in the environment of a power plant in the Maghreb, involving a combustion turbine coupled to a steam turbine and to a generator, for the production of electricity (the power of such an installation is greater than 0.5 TeraWatt) with, in particular, the following sound sources:
- the turbine itself
- a compartment for the load
- a plenum for an air intake duct and for an exhaust duct
- a generator
- a steam turbine
Design and construction of structures for industrial noise reduction in the environment
The design and construction of structures for the reduction of industrial noise in the environment of this power plant involved:
- a structural study: when it comes to very large metal structures, it is necessary to take into account the site conditions (rain, snow, wind, seismic activity), to ensure the necessary stability, including in the event of partial dismantling during maintenance or repair work on the soundproofed hardware and machines
- sound insulation calculations: to determine the sound reduction index required for the elements of the envelope (fixed, removable or opening), the insertion loss of the silencers (taking into account the regenerated noise) in order to obtain a sound pressure level not exceeding 85 dB(A) at 1 meter, which is ambitious when some noise sources have a weighted overall sound power level greater than 135 dB(A); in addition to meeting the environmental objectives mentioned above, this also allows - and this is not secondary - the protection against noise of personnel (e.g. dedicated to supervision, maintenance) of the industrial establishment e.g. for compliance with European Directive 2003/10/EC:
- limit values of exposure of workers to noise: exposure level L EX,8h = 87 dB (A) and peak sound pressure ppeak = 200 Pa or 140 dB (C) ref. 20 μPa
- higher exposure values of workers to noise triggering action: exposure level L EX,8h = 85 dB (A) and peak sound pressure ppeak = 140 Pa or 137 dB (C) ref. 20 μPa
- lower exposure values of workers to the noise triggering the action: exposure level L EX,8h = 80 dB (A) and a peak sound pressure pcrest = 112 Pa or 135 dB (C) ref. 20 μPa
- airflow calculations: to ensure air renewal and temperature control in relation to the (very high) heat output dissipated by soundproofed equipment and machines of which noise shall be limited
- electrical studies: for components such as fans, sensors
A metal frame (in steel) was therefore foreseen and:
- for fixed or easily removable parts, by elements: industrial soundproofing panels with an absorbing face (modular), without roof for the structure relating to the generator, already soundproofed when it left the factory (what was added was a noise-barrier wall to get an additionnal effect of acoustical screening)
- for acces for employees: (rotating) acoustic doorsets with, for translucent parts (with glazing guaranteeing residual safety in the event of accidental breakage): acoustic window sets
In addition, the ventilation air inlets and outlets (the latter: with fans, except for generator for which ventilation is natural) have been equipped with ventilation silencers (to ensure the necessary continuity of sound insulation).
All aspects of such a project have been carefully considered, and every detail has been designed with maximum performance in all areas, ease of implementation and durability in mind.
The design and construction of such industrial noise reduction works in the environment have long been at the heart of the activity of ITS and its business partners for a wide variety of applications, illustrating once again the power of the ITS slogan: "Choice sounscapes, everywhere".
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Structures for reduction of industrial noise in the environment of an industrial facility (a power plant) similar to those covered by this article |
In addition to sound enclosures and noise-barrier walls, ITS markets, for reduction of industrial noise in the environment (visible in the photo opposite but not delivered as part of the project subject of this article) soundproofed air intake systems for combustion turbines / gas turbines, exhaust silencers for combustion turbines / gas turbines, and also Vent silencers for pressurized gas | |