Some basics about noise

Noise is commonly defined as unwanted sound. A typical noise control problem includes three basic components: the noise source (machines, fans, pumps, processes etc.), the receiver (persons subjected to the noise); and the path (the route the noise travels between the source and the receiver indoors or outdoors).

Noise can be classified in two different forms: airborne and structure-borne.

The first one goes from a source to a receiver as a differential in atmospheric pressure, traveling in all directions. Structure-borne instead is unwanted vibration, which is transmitted from a vibrating source to a receiver through a solid material and regenerated as airborne noise. Once the three main elements (source, path and receiver) have been identified, four ways can be adopted to control the noise: absorption, barriers (blocking), damping and vibration isolation.

Perhaps the greatest single contribution of unnecessary noise is the lack of proper maintenance and corresponding preventive maintenance intervals. Equipment that is poorly maintained eventually becomes inefficient. One manifestation of inefficiency is noise (misdirected energy), which, ultimately, becomes the subject of replacement. Typical energy wasters and noise producers are:

• Steam leaks
• Slipping belts
• Worn bearings/gears
• Improperly aligned belts
• Unbalanced rotating parts
• Reciprocating striking parts
• Insufficiently lubricated parts
• Contact between moving and stationary parts
• Compressed air leaks
• Vibrating sheet metal, such as streamlining
• Improperly adjusted linkages or cams

How to choose the most appropriate Steam Vent Silencer provider

Which are the most relevant data to be considered in order to identify the correct roles within the supply chain of acoustic manufacturers. Understanding all of the factors involved could simplify the selection of the rightest vent silencer for the application required. But first, it’s important to introduce vent and blowdown silencers, reviewing the factors involved in predicting the noise generated by high-pressure vents.

Here below a list about the blowdown and vent applications that require silencers:

• Steam venting in power generation applications
• Process control and relief valves in industrial applications
• Pipeline blowdowns and Natural Gas compressor station
• Blowdown tanks and autoclaves
• Bypass valves on blowers and compressors
• Discharge of high-pressure gas to substantially lower pressure environment (atmosphere).
• Steam ejectors and hogging vents

Vent Silencers and their applications

The terms “vent silencer” and “blowdown silencer” refer to the relative application for which each one is used. For both of them the design is similar, since we refer to vent silencers when being used to vent at a constant flow rate, for a period of time. The word silencer is instead referred to as blowdown, when they are blowing down a finite volume of gas starting at a high pressure, and ending at a low pressure over a given time. Vent silencers are sized for constant flow and blowdown silencers are sized for maximum flow.

Vent silencers find wide applications in high pressure vents, steam vents, safety relief valve outlets, system blow downs and purge outlets etc. Vent and blowdown noise is a function of upstream pressure and temperature, type of gas being vented, the valve size and type, plus the effect of downstream piping.

Stopson Italiana designs and manufactures high quality Vent Silencers that attenuate the high noise produced by the expansion of Gas, Steam or Air at elevated temperatures to atmospheric pressure.

When it’s required the installation of a Vent Silencer, here below all the data required in order to obtain a precise offer:

• Application (Vent, Blow down, Relief)
• Fluid Composition (Steam, Gas, Air)
• Molecular Weight or Specific Gravity
• Process conditions upstream of valve and units (lb/hr, SCFM, ACFM)
• Temperature Pressure (P1)
• Atmospheric pressure ( Pa ) / Temperature (T2)
• Line size between valve and silencer
• Line size from silencer discharge
• Attenuation required (silencer performance)
• Allowable pressure drop

Noise Generated by High-Pressure Vents

Over the years, there has been a good deal of work done in the field of predicting the noise generated by the high-pressure venting of gases.

Factors Influencing Noise Generated by High-Pressure Vents:

• Mass flow – the higher the mass flow, the noisier it becomes.
• The type of gas and its molecular weight/specific gravity – lighter gases are noisier.
• Temperature – higher temperatures result in lighter gas flows, and therefore, higher noise levels.
• Upstream versus downstream pressure – the higher the upstream pressure is relative to downstream pressure, the louder it will be.
• Choke flow (critical flow or sonic flow) – occurs when upstream pressure is roughly two times or greater than downstream pressure, making things much noisier.
• Orifice/opening size of valves, vents, orifice plates, diffusers, etc. – larger diameters result in low frequency noise, while smaller diameters produce higher frequency noise. For instance, diffusers create a shift in the noise spectrum from low frequency (one large vent opening) to high frequency (many smaller openings), which is much easier to attenuate.

Elements Creating Noise in High-Pressure Venting Systems

The noise at the end of a high-pressure vent pipe is a combination of the noise generated by the high-pressure-drop elements in the system. Essentially, any element that has a high-pressure drop across it or large change in area will create noise and should be included in the noise model to accurately predict overall noise level.

The major elements that create noise in high-pressure venting systems are:

• Pressure relief and control values – present in virtually all venting systems.
• Vent pipes/nozzles – last element in venting systems, except for those using high-pressure silencer diffusers.
• High-pressure silencer diffusers – when included, usually designed to provide a specific backpressure at the rated flow (sometimes used as fail-safe device).
• Orifice plates – included in many systems as a flow regulator or fail-safe device.
• Enlargers (reducers), headers and abrupt transitions – included in pipe systems for various reasons. Shock Noise Versus Turbulent Mixing.

There are two phenomena that produce noise in a high-pressure venting system:

• Shock noise – occurs when a choked flow condition exists
• Turbulent mixing – caused by the ripping of the air as the vent gas decelerates to lower velocity, such as the atmosphere. Shock noise is the louder of the two. By adjusting the elements in a piping system it is possible to reduce the shock noise by reducing the magnitude or quantity of choked flow conditions present. Turbulent mixing, on the other hand, is always present, though less of an issue.

The Sound Vibration Control Magazine released a full report with all the specifications needed (listed in a Data Sheet) in order to proceed with the right purchase of a industrial silencer.

Industrial silencers: an increase of demand due to a more strict regulation for industries

An integral part of today’s industrial process and ventilation systems, industrial fans, blowers, and compressors are leading causes of noise problems. If unaddressed, these issues can lead to health and safety concerns, as well as environmental regulation violation. With the tightening of noise regulations, industrial facilities are required to stay in compliance with regulations. Industrial silencers are typical being used to attenuate noise coming from intake and exhaust systems of industrial facilities. These silencers may be built in limited space.  Inside an industrial area, fan installation is one of the most predominant source.

Industrial silencers are engineered to control noise in specific applications, and can alleviate problems in work facilities. With more than 50 years of experience Stopson Italiana soundproofed plants in a broad range of installations, such as:

• Fan Silencers
• Duct Silencers
• Blower Silencers
• Sound Enclosures

Gas Turbine Engine Exhaust Silencers

Silencers are required for almost all installations that particularly include gas turbines and heat recovery steam generators. Our Gas Turbine Exhaust Silencers are especially designed to work in an environment where they are simultaneously exposed to high temperatures and to high velocity turbulent flow.

Stopson Italiana provides full custom engineered Inlet Exhaust Silencers for Gas Turbines, DG sets Turbo Compressors and Turbo Blowers. They entail complete solutions in the field of Machinery filtration and acoustic solutions for Gas turbines and compressors.

Stopson Italiana Gas Turbine Silencers provide the ideal solution to keep noise at a manageable level, while maintaining the operating efficiency of your turbine intake system.

Stopson Italiana designs and manufactures all types of discharge silencers in compliance with the international quality standards. Our discharge silencers are very much effective in reducing the noise for entire systems that receives air for heavy engines & turbine.

Stopson Italiana engineers have been designing application-specific products and services for industrial plants and processes since 1965.
Each product manufactured is tested and inspected to meet all applicable industry standards in terms of quality, longevity and safety.

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The noise pollution’s matter has become a well-documented public domain anthology by now.

The World Health Organisation has reported that 40% of Europe’s population is exposed to noise levels in excess of 55dB. Moreover, noise pollution is ranked as second to air pollution, in terms of affecting our health and wellbeing, including diabetes, tinnitus and risk of heart disease.

Noise pollution in Oil and Gas

According to recent study achieved by PSE Healthy Energy and West Virginia University, some modern Oil and Gas techniques – such as hydraulic fracturing (or “fracking”) – produce noise that may increase adverse effects on human health. 

Fracking can create noise at levels high enough to harm the health of people living nearby (source phys.org). “Oil and gas operations produce a complex symphony of noise types, including intermittent and continuous sounds and varying intensities,” argued PSE Healthy Energy Executive Director Seth Shonkoff.

An adequate set of policies should be specified, in order to safeguard residents and communities, such as particularly vulnerable populations (e.g. schools and hospitals). Noise mitigation techniques like perimeter sound walls, noise barriers and acoustic enclosures could represent the most appropriate solutions to hold back this phenomenon.

Noise impact on marine species

This is not all. A recent study led by International Fund for Animal Welfare, reveals the damaging impact of Oil

and Gas noise pollution on whales and dolphins. In the report, they put in evidence how new technologies should reduce their impact on marine environment during the exploration phase (source: International Fund for Animal Welfare).

Noise and Diseases

Numerous epidemiological studies have linked noise to adverse health outcomes too. They include diabetes, depression, birth complications and cognitive impairment in children.

In facts, apart from damage to hearing, exposure to excessive and constant noise can cause other health problems including:

• Headache
• Sleep and heart disease
• Stress
• Elevated blood pressure
• Fatigue
• Irritability
• Digestive disorders
• Increased susceptibility to colds and other minor infections

Noise in Europe: limits and human tolerance

As we know, the loudness of noise is measured in decibels. Sensitivity to noise differs from one individual to the next, but experts believe that damage to hearing occurs when noise levels are higher than 85 decibels, which is about the loudness of heavy traffic.

Every year, 7 million people in Europe die from heart disease, which would put the toll from exposure to noise at around 210,000 deaths. In England heart disease kills 110,000 people annually, so the deaths linked to noise could be around 3,300.

2% of Europeans suffer severely disturbed sleep because of noise pollution. The researchers calculate that chronic exposure to loud traffic noise causes three percent of all cases of tinnitus, in which sufferers hear constant noise. Length of exposure is important too. In facts, it is not recommendable to listen to noises of 109 decibels for any longer than two minutes in row.

Noise and public health in U.S.

In US the noise phenomena has been studied deeply, causing a direct response by public health. The Health Impacts Project (HIP) provides since 2013 guidance for policy makers to identify the health consequences of potential projects by making public a national sample of health impact assessment.

Exposure Limits in U.S.

The U.S. EPA recommends an average 24-hr exposure limit of 55 A-weighted decibels (dBA) to protect the public from all adverse effects on health and welfare in residential areas. This limit is a day–night 24-hr average noise level (LDN), with a 10-dBA penalty applied to nighttime levels between 2200 and 0700 hours to account for sleep disruption and no penalty applied to daytime levels.

More info about the Noise sources and Soundproofing solutions in industrial sector can be found here.

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Industrial soundproofing covers various sectors and applications. Thanks to its expertise, Stopson Italiana is able to provide turnkey service in the acoustic insulation applied to Power Generation, Oil & Gas, Marine and Avio sectors.

For this latter, several noteworthy installations have been delivered. Among these a huge supply of vent silencers with their respective jet air turbine test chambers has been developed to for GE Avio.

The installation of “PoloniAero” was inaugurated at the end of 2015, and it still represents a unique example of cooperation between universities and industry. The structure – one of the largest and most avant-garde laboratories in the world – was financed by EU funds. The objective is the turbine test for low pressure (and next-generation) aeronautical engines, as well as technological demonstrators used for the construction of aeronautical engines.

The Cold Flow Turbine Test Facility combines the scientific expertise of Poland with the aerospace industry innovation. The partners of the Polish Aero scientific-industrial company are Avio Aero, Military Aircraft Works No. 4, the Warsaw University of Technology and the Military University of Technology. The ultimate goal of the choral project concerns the development of aerospace industry activities, including aeronautical turbine testing.

Stopson Vent Silencers are designed to reduce the noise level of exhaust pipes in the atmosphere for pressurized gaseous fluids. They can be installed downstream of any device that acts as a connection between a pressurized gaseous fluid reservoir and the atmosphere. The Steam Vent Silencer can also provide a high or low backpressure to ensure the proper operation of the system.

Noise reduction is achieved by two principles: a reactive section, useful for attenuating low frequencies; and a high frequency absorption section possible by inserting a sound-absorbing material.

Ventilation silencers can be reactive, absorbent or combined, according to the applications and required attenuation, which can reach up to 75 dB (A).

Typical applications for vent silencers are:

• Safety Valve (PSV)
• Ventilation Valve (PRV)
• Control valve
• Ejector
• Starting valve
• Snort valve
• Flash and Blow Down Tanks

To see all the features in detail, visit Stopson Italiana Vent Silencers page.

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