The reduction of the sound level of noisy industrial equipment is a necessity in view of various requirements:
- the protection of workers (e.g. assigned to production, operation of machines, process controls and supervision, maintenance) on the considered site: their health is at stake when they are exposed to noise (both with regard to their hearing and to the risks of accident they run when warning and traffic signals for vehicles and machines are not correctly perceived); in terms of working conditions, European directive 2003/10/EC sets noise exposure limit values:
- limit exposure values for 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 the noise triggering the 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 ppeak = 112 Pa or 135 dB(C) ref. 20 μPa
- the tranquility of the neighborhood (near the industrial site or at a longer distance depending on the conditions of sound propagation resulting in particular from the topology, land use and climatic conditions); French regulations distinguish the daytime period (7:00 a.m. to 10:00 p.m. except Sundays and public holidays) and the nighttime period (10:00 p.m. to 7:00 a.m. as well as Sundays and public holidays) and, 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 Environmental Protection (FCEP) e.g. 70 dB(A) during daytime periods and 60 dB(A) during nocturnal. Emergence i.e. the difference between the equivalent A-weighted continuous pressure levels of ambient noise (industrial site in operation) and residual noise (in the absence of noise generated by the industrial site, but measured over the period of operation of the industrial site) is limited in Regulated Emergence Zones (REZ), which generally include, nearby: homes, building areas and areas occupied by third parties e.g. Public Acces Buildings (PAB), other industrial establishments. If the ambient noise level in the REZ (including industrial site 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) during the night. If the ambient noise level in the ZER (including industrial site noise) is greater than 45 dB(A) then the admissible emergence is 5 dB(A) during the day and 3 dB(A) during the night . In the case of a Facility Classified for Environmental Protection (FCEP), the 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 adjacent frequency bands, is considered undesirable if it exceeds 10 dB in the frequency interval 50 Hz-315 Hz or 5 dB in the frequency interval 400 Hz-8000 Hz.
ITS participated in the reduction of the noise level of noisy industrial equipment in a gas-fired power plant in Central Europe, by marketing ventilated acoustic enclosures and noise barriers.
Design and construction of structures for the reduction of noise level of noisy industrial equipment
Ventilated sound enclosures are an effective mean for the reduction of the sound level of noisy industrial equipment, since they make it possible to act on noise "at the source" by reducing the sound power level, which is an intrinsic characteristic of a noise source (not dependent on its environment).
Noise barriers can usefully be installed to protect specified locations from noise, for which the effectiveness (variable with frequency) depends in particular on the dimensions, on the respective distance to the acoustic screen that they constitute of on the one hand the noise source and on the other hand the measurement point, and also on any surfaces reflecting the sounds.
As always in such cases, the design and construction of structures for the reduction of the sound level of noisy industrial equipment, being the subject of this article, have made it necessary:
- structural sizing: taking into account site conditions (for outdoor installation: rain, snow, wind, seismic activity), to ensure the necessary stability, including in the event of partial dismantling during maintenance or repair works of enclosed hardware
- predictive acoustics calculations: for the evaluation of the sound pressure level at 1 m from the partitions of the structures, based on the sound reduction index of the elements constituting them (fixed, removable or with openings), and on the insertion loss of the silencers (taking into account the regenerated noise)
- an aeraulic study: for ventilation systems (with filtration) suitable for the evacuation of the heat power (very important in the case of compressors or other large capacity turbomachines)
- electrical engineering: for components such as fans, sensors
The project subject of this article concerned:
- ventilated sound enclosures for 2 combustion turbines (even of small power - 35 MW per unit - these are very large industrial equipment justifying the construction of very big soundproofed buildings), with their associated gas modules and water injection module (each equipped with an enclosure)
- anti-noise walls for 2 generators, delivered with a cover whose effectiveness had to be increased in terms of sound impact limitation
The objective was to obtain a sound pressure level at most equal to 85 dB(A) at 1 m from the partitions of the structures for the reduction of noise level.
A metal frame (made of 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 generators
- 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 - hot air being evcuated by natural convection -) have been equipped with ventilation silencers (to ensure the necessary continuity of sound insulation for those openings).
Such a project for the reduction of the sound level of noisy industrial equipment was, once again, an opportunity for ITS and its commercial partners to mobilize their human and material resources to contribute to the success of constructions with multiple issues (technical, organizational, financial) inherent to the installation of soundproofing means in a power plant.
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Structures for the reduction of sound level of noisy industrial equipment similar to those covered by this article |
In addition to sound enclosures and noise-barrier walls, ITS markets, for the reduction of sound levels of noisy equipment (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 | |