Turbomachinery has experienced a spectacular boom in recent decades, in relation to diversified applications involving an energy transfer between a rotating part (a rotor) and a fluid. This is particularly the case for combustion turbines, which in simple or combined cycle i.e. when a steam turbine and a large capacity industrial boiler - a Heat Recovery Steam Generator (HRSG) - are involved are capable of producing very large quantities of electricity (their unit power is measured in hundreds of MegaWatts). The methods and time frame for building gas-fired power plants, more advantageous than those of many other energy production facilities of comparable power, is an advantage explaining - in the event of increased demand for electrification - the enthusiasm for such investments, especially for facilities in regions being rich in fossil fuels.
The operation of turbomachines is accompanied by very significant noise emissions - the acoustic power level of certain noise sources in question exceeds 140 dB(A), which is considerable - and this implies the implementation of specific noise control measures, both with regard to the protection of workers at the industrial site concerned and with regard to the preservation of the environment.
As a matter of fact, when referring to European Directive 2003/10/EC, it is necessary to consider:
- limit exposure values for workers to noise: exposure level L EX,8h = 87 dB (A) and peak sound pressure pcrête = 200 Pa or 140 dB (C) ref. 20 μPa
- higher exposure values for workers to noise triggering action: exposure level L EX,8h = 85 dB (A) and peak sound pressure pcrête = 140 Pa or 137 dB (C) ref. 20 μPa
- lower exposure values for workers to noise triggering action: exposure level L EX,8h = 80 dB (A) and peak sound pressure pcrête = 112 Pa or 135 dB (C) ref. 20 μPaa
Furthermore, French regulations require control of industrial noise in the environment of such facilities, distinguishing between the daytime period (7 a.m. to 10 p.m. except Sundays and public holidays) and the nighttime period (10 p.m. to 7 a.m. as well as Sundays and public holidays):
- in certain 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
- emergence i.e. the difference between the equivalent continuous A-weighted pressure levels of ambient noise (facity in operation) and residual noise (in the absence of noise generated by the facity, but measured over the period of operation of the facity) is limited in the Regulated Emergence Zones (REZ), which generally include, near the installation: homes, building zones and areas occupied by third parties e.g. Public Access Buildings (PAB), and other industrial establishments. If the ambient noise level in the REZ (including the noise of the facity) 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 REZ (including facility 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 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
In a gas-fired power station, it is therefore often a question of reducing noise:
- of turbines properly speaking
- of load compartments
- of plenum for an air intake duct and for an exhaust duct
- of generators
ITS participated in the construction of soundproof canopies for turbomachines installed in a power plant in North Africa, involving 4 very high capacity combustion turbines in combined cycle; for each, the sub-assemblies mentioned above were treated.
Design and construction of soundproof boxes for turbomachines
The design and construction of soundproof enclosures for turbomachines involved:
- structural calculations: in the case of very large metal structures, it is necessary to consider the site conditions (rain, snow, wind, seismic risks), so that the compulsory stability is guaranteed in all circumstances, including during partial dismantling for maintenance or repair work on turbomachines
- acoustic calculations: to determine the sound reduction index required for the elements constituting the partitions of the envelope (fixed, removable or opening), the insertion loss of the silencers (taking into account the regenerated noise) with a view to obtaining a sound pressure level not exceeding 85 dB(A) at 1 metre to meet the noise level objectives in the near acoustic field as well as in remote locations (at the property boundary and beyond)
- airflow calculations: to size ventilation systems for air renewal and temperature control in relation to the (very significant) heat output dissipated by the turbomachines
- 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: metallic acoustic insulation panel with 1 absorbing face (modular), without roof for constructions realting to generators, already soundproofed when leaving factory (in such cases, noise-reducing walls then complete the soundproofing devices)
- for acces by personnel responsible for maintenance and operation: (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 generators noise barrier walls for which ventilation was natural) have been equipped with ventilation silencers (to ensure the necessary continuity of sound insulation).
Every detail of the design and construction of these soundproof canopies for turbomachines was the subject of all attentions, with the aim of obtaining a high-quality finished product.
In the industrial acoustics sector, the stakes could not be higher than when it comes to designing and building in record time, and without delay (the ship planned for transport would not wait, and the failure to commission the facility on the scheduled date would have immeasurable consequences) soundproof canopies for so many sub-assemblies of such monumental turbomachines, while meeting technical specifications as numerous, as varied, and as demanding as those applicable to the context of the construction of a major power plant by one of the world's largest players in this field, which must not be disappointed at any cost.
Over time, repeated participation in such projects - all successful - has firmly anchored the now widespread opinion that the soundproof canopies for turbomachines marketed by ITS constitute the ultimate.
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Construction of soundproof canopies for turbomachines (in a power plant) similar to those covered by this article |
In addition to soundproof canopies for turbomachines, ITS markets (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 | |