Reducing the sound impact of a facility is motivated by different considerations :
- the obligation to protect personnel assigned to process control and maintenance of the machines and production equipment concerned against excessive exposure of these workers to noise-related risks [1]
- the need to preserve the neighborhood from undesirable noise, in relation to exceeding the permissible levels at the property boundary [2] or the values authorized for emergence in Regulated Emergence Zones (REZ) [3]
ITS participated in the reduction of the sound impact of an electricity production facility in the Middle East (in the Persian Gulf) in combined cycle, involving (for 3 sets) many particularly noisy equipment :
- combustion turbines
- lubrication and load compartments
- steam turbines
- generators
With regard to the first three types of equipment in the list above, the reduction of the sound impact was based on a reduction at the source of the sound power level - initially of the order of 135 dB(A) for some equipment, which is considerable - by means of ventilated sound enclosures.
As far as the generators are concerned, the noise impact was reduced by means of noise-barrier walls (constituting acoustic screens), making it possible to reduce the noise level at a short distance from noisy equipment.
The works to reduce the sound impact of this installation were made in the form of metal constructions (some: very large) with :
- a framework that should be designed and dimensioned not only taking into account the risks associated with the site (climate hazards, earthquakes) but also to ensure the stability required during maintenance operations which require the dismantling of elements (beams, posts) which should not be problematic for the proper maintenance of the whole
- panels constituting an envelope that should not only be perfectly sealed to protect the (sensitive) high-tech hardware enclosed (against bad weather, including sandstorms), but also capable of limiting the transmission of sounds towards the outside (i.e. with a high sound reduction index: of the order of 35 dB(A) for noise with spectral energy equalization. Constitution and principle of assembly of the panels, doors and removable elements have therefore made the subject of meticulous study and manufacturing work, the filling being made of high-density rock wool and the facings being made of very thick steel.
- (except for generators for which air renewal has been, in the absence of a roof for soundproofing equipment, based on the phenomenon of natural convection) silencers to limit noise transmission through openings required for the indispensable evacuation - by means of fans, themselves noisy because they are very powerful - of the heat output dissipated by the equipment enclosed in the sound enclosure. These were dissipative noise reduction devices, i.e. the effectiveness of which is linked to the presence of a porous sound-absorbing material (mineral wool) forming, in a welded construction, the filling of splitters in contact with which noise propagating in airways is attenuated.
The study and manufacture of these hardware for reducing the sound impact of a facility, made available in the form of kits ready to be assembled by local labor, supplied by the end customer, was a once again the opportunity to see the level of expertise of ITS and its business partners for such projects of industrial acoustical insulation, all the stages of which were carried out without a hitch.
Designed to last, this quality soundproofing equipment will therefore allow the reduction of the sound impact of this facility for a long time.
[1] according to European directive 2003/10/EC, for the daily noise exposure level L EX, 8hours.: 80 dB(A) and 85 dB(A) are the thresholds, respectively lower and upper, triggering the action; 87 dB(A) is the authorized limit value
[2] in France, a limit is set by a prefectural decree e.g. 60 dB(A)
[3] in France difference (using A-weighting) between the noise level of ambient noise (facillity in operation) and the residual noise level (in the absence of noise produced by the facility), is legally limited: depending on the case 5 or 6 dB(A) during the day and 3 or 4 dB(A) during the night