In a power plant with gas turbines (combustion turbines), exhaust is a very powerful noise source potentially causing sound nuisance for personnel of the operator operating in the vicinity as well as for the neighborhood (including long distance, a fortiori in the case of tall stacks). It is often necessary to use in such cases a soundproofing equipment of high technology to ensure compliance of the installation on the one hand with respect to the legislation on noise at work and on the other hand with respect to the regulation in terms of environmental protection. In fact gas turbines exhaust silencers must often have outsized acoustic performance (the overall sound power level to consider is often greater than 135 dBA and noise emissions are with a very wide frequency spectrum) in a context where very high temperatures (around 550 °C or sometimes more) and very high gas flow rates (which are sometimes counted in hundreds of kg/s) must be considered: great care must be taken when sizing to limit the total pressure loss directly impacting the productivity of the plant.
ITS has participated in the design of exhaust silencers for 3 gas turbines (combustion turbines) with a power above 40 MW for simple cycle operation and above 60 MW for combined cycle operation (each) in the context of a project of refurbishment (conversion for simple cycle operation) of a power generation unit near Kingston upon Hull (North Lincolnshire) in England.
Of course, this soundproofing equipment must have a sound transmission loss particularly important. But in addition, with a flow rate being above 140 kg/s at a temperature of nearly 550°C, the flow speed of exhaust gas into the silencer was extremely high, requiring a specific design of the silencer in particular with respect to issues related to aerodynamic and to self-noise.
Therefore, the simulation of the insertion loss (with or without flow noise) as well as of the total pressure loss of the silencer (with splitters equipped of extremities with a special aerodynamic shaping) in the foreseen operation conditions was performed.
Specific absorbent materials wich properties must satisfy both the ambitious goals of acoustic performance and also to requirements related to mechanical and thermal extreme solicitations have been incorporated into the design as required.