Low-cost, effective engineering noise reduction techniques
Extensive experience across these industries has revealed the key issue to be one of attitude. As a result of the lack of knowledge of the diagnostic process and modern low-cost engineering noise control technology, site engineers are generally reluctant even to consider noise control as an option, as for them it is associated with high-cost acoustic enclosures and other palliatives that are a hassle that makes maintenance etc difficult.
The Energy Institute has launched a project to address this issue in conjunction with INVC.
There are numerous elegant, low-cost and highly effective engineering noise control techniques that have no effect on maintenance or performance. For example, applying this approach to a refinery project in the USA saved over $1 million from the previously quoted $1.25 million for conventional noise control measures. In some cases, they can actually improve efficiency and reduce running costs...
The noise control process and example case studies are detailed below. There is considerable pressure on all noisy industries for urgent action due to the recent changes that will cause a very dramatic increase in both the number of hearing damage claims and the settlement costs - see below...
Urgency - will >£700k claims become the new normal?
- the health effects of hearing damage have been seriously underestimated
- the legal framework for hearing damage claims has changed
- HSE inspection noise focus has resulted in a 300% increase in enforcement actions
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Noise Control Audit - cost/benefit analysis process
PPE cannot be used for long term hearing conservation unless you can prove that noise control is not practical. The evaluation of the practical noise control options is conspicuous by its absence – largely due to lack of knowledge and the prevailing attitude to noise control described above.
The Hierarchy of Control (HoC) that is standard for health and safety risk management has been inverted for noise as shown here. As the noise consultancy industry is dominated by measurement, virtually the only risk mitigation measure ever recommended in the energy and petrochem industries is based on PPE. The fact that noise control should be the priority requirement is almost invariably ignored.
Consequently, organisations currently waste resources on measures that are not cost-effective, are not best practice, and do not adequately protect against Noise Induced Hearing Loss (NIHL). There is only one approach that must be used to determine whether noise control is practical and what constitutes best practice.
- Rank the noisy plant in an area by contribution to noise risk
- Rank the sources within the highest ranked plant in terms of their contribution to the noise produced e.g. fan, motor, gearbox etc
- Determine the best practice engineering source control options for the dominant source
- If you prove that source control is not practical for the dominant source, then, and only then, consider falling back on traditional palliatives (enclosures, barriers etc)
- Repeat for all significant noise sources
- Discuss the noise control options with site engineers
- Generate an accurate noise control cost/benefit analysis for the area/site that includes cost v field performance data for PPE. This provides the information required to make informed decisions on the optimum risk reduction strategy.
This Noise Control Audit (NCA) process is a regulatory requirement that will often pay for itself within a few years. Much of the above can be described and quickly taught to non- specialist engineers.
Energy and Petrochem plant noise control examples
In conjunction with the INVC, the Energy Institute has launched a project to develop a guide to the optimal noise reduction options and strategies for the energy and petrochemical industries. This will also include practical online webinars detailing the approach and techniques.
A BP refinery in the USA had been quoted $1.25 million for five 1.5MW double entry ID combustion fan silencers to address the cause of extensive noise complaints. Their acoustic consultant had come across our aerodynamic fan noise control technology on the web and contacted us for advice. He sent his noise data to us by email and we identified that our technology would be ideal as an alternative to fitting fan silencers.
We used the information provided to design the aerodynamic modifications to generate drawings that would allow the components to be made by local contractors. After an installation process that required a tiny fraction of the downtime associated with fitting attenuators, the 180Hz blade pass tone had been completely eliminated (>12dB reduction), preventing any further noise complaints.
The quotation for fitting conventional silencers or mufflers totaled $1.25 million with additional costs associated with the extensive downtime required to fit the attenuators plus increased running costs.
The total project cost for all the aerodynamic modifications not only saved over $1,000,000 from the $1.25 million quotation for conventional silencers, but, in contrast with traditional mufflers, the modifications had no effect on fan efficiency (reduced running costs) and will last the lifetime of the fan with zero maintenance.
No site visits were required, saving time, resources and carbon (transatlantic flights etc). A very self-financing project...
More details of how to reduce ID fan noise using our aerodynamic noise control technology.
More information about our remote control of noise technology used for this ID fan project.
The Power Industry International journal published an article about the application of our innovative aerodynamic fan noise attenuation technology to cut not just the cost of noise control projects to reduce the noise from large fans feeding into stacks in the power industry, but also to improve fan efficiency.
The suggestion was that the widespread adoption of the technology could substantially reduce capital and running costs compared with traditional fan noise attenuation techniques such as attenuators, acoustic enclosures and lagging.
The journalist uses the application of the technology to the 50MW Schiller biomass power station in the US as an example. This is the largest power station of its type and uses a huge, house-sized ID combustion fan connected to a stack. The aerodynamic fan noise attenuation was installed within a time window of just 12 hours - compare that with the costly weeks of downtime required to install conventional mufflers. This cut the fan noise by 10dB at fraction of the cost and the fan efficiency was substantially improved.
An interesting point made in the article is that the noise control installation may seem too simple. The industry is used to the idea of massive noise control structures and extensive downtime. Compare that with the option to install elegant aerodynamic inserts inside the fan casing in a few hours to eliminate the noise problem at source without compromising fan efficiency.
Exactly the same point applies to many other industries such as steel and cement industry fans and the associated signature stacks that broadcast the fan noise far and wide.
Read the Power Engineering International fan noise control article
The noise from a 3m, 1.5MW wood-burning biomass boiler combustion ID fan installed at the Schiller power station in New Hampshire (one of the largest renewable energy projects in the U.S.) was dramatically reduced using innovative technology to replace the traditional silencer fitted to the power station fan. Our aerodynamic noise control technology not only cut the noise at source, but also substantially increased the fan efficiency.
The ID fan feeds a stack through a system that included a very large conventional silencer to prevent noise complaints from local residents. As this muffler had a drastic impact on fan efficiency, it had to be removed. This had a serious impact on the local environment, generating a host of complaints for which a very urgent solution was required.
Our aerodynamic source control technology was retrofitted instead of the attenuator within an incredibly short 12-hour downtime window. This not only eliminated the low-frequency tonal noise problem from this large industrial boiler system at a minute fraction of the cost of the silencer it had usurped, but as it also reduced the fan power consumption, the project was self-financing.
"The ID combustion fan created a low frequency tonal noise that could be heard on the other side of the river and was the cause of complaints. The installation process took only 12 hours, after which we recorded a huge 10dB drop in noise and measured a reduction in the power used by the ID fan.." Jim Granger, Senior Engineer, Schiller
This international project was managed remotely from our UK offices. By analysing and interpreting data acquired locally to our specifications, we were able to dispense with site visits and reduce the entire process, from initial contact to problem solved, to a matter of a few weeks.
Filtration (bag filters etc) and conventional attenuators reduce fan efficiency by adding back pressure. We use Computational Fluid Dynamics (CFD) modeling and past experience to determine exactly where changes can be made to reduce back pressure and hence improve system efficiency. For example, it is often possible to modify existing silencers to reduce back pressure - or even to eliminate these attenuators altogether by using alternative techniques to cut broadband noise without the hit on fan efficiency associated with conventional noise control measures..
The approach not only reduces noise, but it also cuts running costs and increases productivity. This renders noise control projects of this type highly profitable so that implementing the modifications would be a valuable exercise, even if there was no noise issue...
Boiler burner noise complaints
The cause of complaints about environmental noise levels was traced to this dual fuel burner boiler on a Heinz site. The company contacted us to assess the noise control options as the conventional palliative noise control techniques for this sort of problem involve fitting large silencers into the stack and converting the boiler house into an acoustic enclosure – eye-wateringly expensive with extensive downtime (which would have caused serious production problems).
The (blackcurrent) solution
The source was diagnosed as a 116Hz low frequency “drone”, a very common type of burner noise control problem. We developed a stunning simple alternative solution that comprised a set of aerodynamic modifications that fitted inside the combustion head. The initial trials were conducted using an adapted yoghurt pot fitted inside the burner head – as far as we know, this is the only known yoghurt-based noise control application…
The modified pot reduced the drone by 16dB, completely eliminating the problem.
The cost? Less than £2k with a downtime of a few hours (aluminium version of the yoghurt pot). This new approach and technology can be an incredibly cost-effective solution to many burner or combustion noise problems - and can reduce fuel consumption...
Industrial boiler burner noise attenuation
There are usually only 2 noise sources on industrial boilers and burners:-
- combustion fan: broadband and/or tonal noise at the fan blade pass frequency. Easily controlled using a simple silencer and/or aerodynamic fan noise control technology
- combustion noise in the boiler burner: broadband sound - but very often with a pronounced low-frequency signature (and sometimes pure tones) that can travel large distances (a common cause of complaints). Traditionally, the suggestion is often to spend a large fortune to turn the boiler house into an effective acoustic enclosure. Our alternative is to address the problem at the source - as above...
Buy Quiet specification not met
This pair of water pumps generated 95 – 99 dB(A) -which exceeded the noise level specified in the Buy Quiet procurement contract. The two contractors involved both blamed the other for the high level of noise, leading to a prolonged dispute over responsibilities and payment.
Conventional noise control measures
Various acoustic barriers and partial enclosures were being considered – at high cost and with considerable access and maintenance issues, not to mention the hassle involved.
Accurate noise source diagnosis
We requested a couple of smartphone video clips of the units. Our detailed analysis of the soundtracks revealed the dominant noise to be a 100Hz mains frequency toothcomb.
Consequently, we could determine that the problem was caused by electromagnetic vibration radiated as noise by the thin steel access panels.
Simple, low-cost engineering solution
We provided details of the high performance retrofit constrained layer damping that could be applied to achieve the required noise reduction plus laminated close shields. These provided a 12dB(A) noise reduction with no effect on access, operation or maintenance – and at a tiny fraction of the previously proposed costs.
This is an example of the efficacy of accurate diagnosis coupled with good engineering and knowledge of materials. More information is available on the Sound Damped Steel installer website here.
Noise levels from a power station were uncomfortably close to the environmental noise planning conditions, but it was unclear which were the dominant noise sources.
Noise diagnosis
Detailed diagnosis proved that the dominant contribution was high-frequency noise (>500Hz) radiated by the Gas Reception Facility. Vibration measurements were used to calculate the proportion of the noise from the various plant elements so that their contributions could be ranked. The results were used to determine the minimum parts of the plant that would require attenuation in order to meet the noise specification.
This process showed that is was only necessary to treat the reducer, expander and associated valve section of the facility instead of the much larger areas previous considered, saving a considerable sum.
Noise mitigation measures
We provided details of our innovative, high-performance acoustic lagging that was manufactured and installed by Sound Damped Steel. This has an outer skin constructed from highly damped laminated steel, making it very tolerant of installation practicalities. Moreover, we have also developed versions that eliminate the corrosion problems inherent in conventional lagging designs that almost invariable leak, causing hidden corrosion.
The diagnostic process illustrates how costs can be kept to an absolute minimum by precisely ranking noise contributions from different components, even amidst complex arrays of pipework, valves and other sources.
The effect of the treatment was to reduce the noise from this source by 16 -19dB(A), eliminating it as a contributor off-site. Occupational noise levels in the area were also reduced by an average of 8dB(A). More information is available on the Sound Damped Steel installer website here.
