Robert Lomax examines existing technologies addressing industrial noise emissions from CHP plants.
As more organisations turn their attention to clean energy alternatives and reliable off-grid electricity ” in the midst of power irregularity ” there has been a notable upturn in onsite power generation adoption.
Thisà‚ articleà‚ wasà‚ originallyà‚ publishedà‚ in Power Engineering International Issue 2 -2020, a supplement in à‚ Smart Energy International.
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A recent survey found that 81 per cent of companies already generating energy onsite have plans or aspirations in place to increase self-generation capacity over the next five years, in a move to become a “power plant of the future”.
It is perhaps little surprise, given its well-defined benefits, that onsite generation continues to prove popular across a broad range of sectors.
The wider benefits of CHP plants are indisputable. However, by virtue of their proximity to nearby sensitive properties and users of the plant, they have the potential to produce excessive and potentially harmful noise output.
Addressing those challenges, therefore, becomes a balancing act to optimise power generation performance, while at the same time limiting the acoustical footprint of equipment.
Traditionally, the focus of onsite generation installations has centred on critical areas of improvement for end-users such as energy efficiency and emissions control. Industry professionals also have a crucial responsibility to consider any potential noise emissions from new developments, starting at the initial planning stage to help comply with noise regulations and protect those in the vicinity of their systems.
Advanced noise control solutions
Large scale CHP systems use a main driver such as a gas engine to operate, emitting noise which far exceeds levels permitted under regulations, such as the UK’s Control of Noise at Work Regulations 2005.
A-weighted decibels, or dB(A), are an expression of the relative loudness of sounds in air as perceived by the human ear. In the A-weighted system, the decibel values of sounds at low frequencies are reduced, compared with unweighted decibels, in which no correction is made for audio frequency.
The continuous noise levels from engines within CHP systems can reach levels of 110dB(A), which significantly surpasses the upper exposure action value of 85dB(A) for an eight hour working day, as outlined in the regulations.
In instances where machinery is housed in a reverberant area with reflective surfaces, noise levels can be further exacerbated and have the potential to reach 120dB(A), limiting workers to far less than a minute of exposure in any eighthour period unless suitable noise protection measures are employed.
Therefore, it is usual practice for such systems to be paid special attention to reduce noise to operatives undertaking general maintenance activities in nearby plant areas.
For organisations across a myriad of industries, there is a positive outlook. Just as onsite generation has advanced, so too have the noise control technologies developed to mitigate excessive noise.
With noise control standards in place for the UK and Europe, CHP system operators and installers need to deploy the latest innovative noise control solutions, to comply with varying regulations and reduce the risks to exposure.
The use of acoustically tested panel systems will help to ensure correct design and selection of noise control measures, and thus alleviate concerns with regards to noise.
Given that no two plant installations are completely identical, careful consideration needs to be given to each system’s function, location and permitted noise levels, in order to determine the most effective noise control solution for the specific application.
The bottom line is that, for mission-critical environments in particular, there is no off-the-shelf solution when it comes to specifying noise mitigation products for CHP systems.
The first consideration is that most cogeneration systems installed in critical environments are located inside, or within close vicinity of, a building and this substantially increases operators’ and visitors’ exposure to the risk of breakout noise. In addition to noise at work considerations, critical facilities are having more stringent noise emission limits imposed on them and local authorities are increasingly meticulous about policing them. Environmental noise emissions for ventilation and exhaust systems on CHP systems need to be contemplated from the project planning stage.
Noise mitigation for onsite power
The greatest level of noise reduction for the main noise generating equipment can be achieved by deploying full acoustic enclosures, or installing CHP systems into acoustically insulated containers.
With a correctly designed and acoustically tested panel system, such systems will ensure breakout noise falls below levels set within the regulations and project requirements.
As well as breakout from the main engine cell, there are other factors which require consideration, such as noise passing through the associated ventilation system, breakout from pipework and engine silencers, as well as noise emissions from associated cooling plant and radiators.
Noise from all paths and potential sources needs to be considered at the initial design stage, to ensure compliance with specifications and regulations.
The prime mover (engine), for instance, will require a silencer for its gas exhaust which is capable of withstanding its gas flow rate, its temperature and pressure. Additionally, noise is created when the CHP system’s ventilation air is ducted into and out of an associated enclosure. This means both the supply and return ducts will require noise attenuation.
To facilitate regular access and maintenance, a correctly designed enclosure can also be constructed with incorporated lifting beams, maintenance access doors and removable walls.
Acoustic sealing around access points and penetrations is essential, as a single weak point can compromise the entire installation.
When power generation plants are externally sited, high performance composite acoustic panelling to form enclosures or housings enables systems to be used in the vicinity of residential buildings, 24 hours a day, making them ideal for organisations such as hospitals and large scale manufacturing facilities alike.
ABOUT THE AUTHOR
Robert Lomax is a director at Wakefield Acoustics.