It is important to model the sound emissions of aeraulic systems such as those that must be considered for the exhaust of gas turbines taking into account the contribution of the various elements: the study and sizing of exhaust silencers for gas turbines are obviously major aspects of such an engineering work, since the expected feature of this component is the compliance of the facility with the noise level at the outlet of the stack of a gas-fired power plant.
Indeed, 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 study and sizing of exhaust silencers for 5 heavy duty gas turbines / combustion turbines - more than 120 MW for operation in simple cycle, more than 190 MW for operation in combined cycle - (each) in the context of a project of refurbishment (conversion for combined cycle operation) of a power generation unit near Dubai (United Arab Emirates).
In the context of this project, it is envisaged that the noise reduction devices will be installed partly in a stack with a height of 40 meters.
Of course, this soundproofing equipment must have a sound transmission loss particularly important (the sound power level of the gas turbine exhaust reaches almost 143 dBA). But in addition, with a flow rate of 395 kg/s at a temperature of 580°C, the flow speed of exhaust gas into the silencer is 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 (whose splitters will be equipped of extremities with a special aerodynamic shaping) in the foreseen operation conditions was performed by the means of the software SILDIS® (cf. acoustics simulation software).
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 for those exhaust silencers for gas turbines / combustion turbines.
In addition, the course of this project shows - once again - the possibilities for design and optimization of soundproofing equipment of the software SILDIS®, whose computing power and reliability, as well as whose versatility made of it a choice tool for the selection of products and construction systems for many projects of sound insulation.
Indeed, the software developed by the human resource of ITS allows the simulation of the acoustic and aeraulic performances of silencers (including: those with discontinuous splitters cf. Modules 1 and 1A). However, it also allows the computation of the performance of plane partitions and of duct walls (cf. Modules 2 and 3), the prediction of the acoustic performance of straight ducts (cf. Module 4), the prediction of break-out noise, namely in case of ducts of variable section (Modules 5 and 5A), the prediction of the acoustic performance of the bends (Module 6), the prediction of nozzle reflection (Module 7), the prediction of the sound impact of duct systems (Module 8), the prediction of stack directivity (Module 9).