Industrial generators (gensets consisting mainly of a heat engine and an alternator) are widely used for the decentralized production of electrical energy in different contexts, when there is, locally, no alternating current distribution network (on land, including in a cogeneration context or at sea: boats, off-shore platforms) or when it comes to overcoming its possible failure (emergency installations) on sensitive sites of different natures (e.g. hospitals and transport infrastructures, data centers, industries).
The reduction of noise and oxides of nitrogen NOx - monoxide (NO) and dioxide (NO2) - linked to the exhaust of combustion gases from thermal generators constitute two fundamental aspects of the management of environmental issues linked to the installation of such equipment :
- noise reduction responds to the dual need to protect personnel on the site from the risk of hearing trauma [1] and to protect the neighborhood in terms of noise impact [2] ; inside a given site, the short distance to buildings in which personnel carry out an activity requiring a certain concentration (e.g. offices) can make it useful to consider an additional issue related to acoustic comfort inside premises
- the reduction of nitrogen oxides responds to a public health issue with respect to pollutants whose toxicity is well-known [3]
The reduction of the exhaust noise of thermal generators can be achieved by the implementation of silencers :
- reactive: performance is linked to the reflection of acoustic waves resulting from section changes (in chambers connected by perforated or unperforated tubes) ; efficient at low and medium frequency and involving a total pressure loss which is increasing with the complexity of the geometry of the internal parts
- dissipative: performance is linked to the presence of sound-absorbing materials; efficient at medium and high frequency and involving low total pressure loss
ITS markets a wide range of exhaust silencers for generating sets, possibly combining the two operating principles [4].
The reduction of nitrogen oxides NOx linked to the exhaust of combustion gases from industrial generators can be achieved by means of a Selective Catalytic Reduction (SCR) device :
- combined with ammonia (NH3) as present in an aqueous solution of urea (CO(NH2)2) they are transformed, by chemical reaction, into nitrogen (N2) and water (H2O)
ITS markets Selective Catalytic Reduction (SCR) devices, based on this principle [5].
In some cases, the reduction of noise and NOx emissions from industrial generators by means of a silencer + SCR catalyst assembly is a practical way to combine the different functionalities required :
- by means of a skid combining the two sub-assemblies in the form of a single module (respectively intended for noise and NOx reduction) :
- sometimes, with the possibility of using a (reactive) primary silencer for the mixture of the components basing the chemical reaction of catalytic reduction
- always in a compact form, well suited to the requirements associated with installation on containers roofs
ITS will participate in the reduction of noise and NOx emissions from industrial generators by means of silencers + selective SCR catalysts in the form of skids.
These will be motors with a power greater than 3.5 MW, in number more than half a dozen installed on a high-tech site in Western Europe.
With complications related to the smallness of the location planned for the installation, the performance of this assembly will meet all project specifications, namely :
- a sound pressure level at 1 m limited to a maximum value of 85 dB(A)
- NOx emissions reduced to a maximum value of 0.5 mg/Nm3
A careful design with respect to all technical requirements (acoustics, fluid mechanics, chemistry, resistance of materials, electricity), a demanding choice of raw materials (mostly stainless steel), manufacturing and assembly flawless from a technological aspect will make this set silencer + SCR reactor + electrical box with sensors installed on a mechanically welded self-supporting frame equipment built to last.
All noise reduction devices (mufflers) and pollution control devices (SCR) for industrial engines exhaust gases are marketed by ITS with high-quality and affordable hardware.
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[1] in Europe, the Directive 2003/10/EC of the European Parliament and of the Council, of February 6, 2003, on the minimum health and safety requirements relating to the exposure of workers to the risks due to physical agents (noise) is applicable :
- for the daily noise exposure level L EX, 8h: 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
- for the peak sound pressure ρpeak: 112 Pa i.e. 135 dB(C) and 140 Pa i.e. 137 dB(C) are the thresholds, respectively lower and upper, triggering the action; 200 Pa i.e. 140 dB(C) is the permitted limit value
[2] in France, for an establishment classified for environmental protection (ECEP) a prefectural decree is imposing a sound pressure level not to be exceeded at the property boundary e.g. 60 dB(A) and emergence is regulated; this is the difference between the A-weighted equivalent continuous pressure levels of ambient noise (site considered in operation) and residual noise (in the absence of noise generated by the considered site, but measured over its period of operation) in regulated emergence zones (REZ), and depending on the context :
- 5 or 6 dB(A) during the day
- 3 or 4 dB(A) at night
[3] In France, the limitation of emissions of certain pollutants into the air is the subject of a Decree : cf. link Limitation of emissions of certain pollutants into the air
[4] cf. link Exhaust silencer for generator sets
[5] cf. link Selective Catalytic Reduction Device SCR - catalytic converter