Valves & Flare Stack

8/13/2019 Valves & Flare Stack

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Water Transmission and DistributionBy American Water Works Association


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Relief valve

From Wikipedia, the free encyclopedia

(Redirected fromPressure relief valve)

For other uses, seeRelief valve (disambiguation).

A relief valve
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Schematic diagram of a conventional spring-loaded pressure relief valve.

The relief valve(RV) is a type ofvalveused to control or limit thepressurein a system or vessel which can

build up by a process upset, instrument or equipment failure, or fire.

The pressure is relieved by allowing the pressurised fluid to flow from an auxiliary passage out of the

system. The relief valve is designed or set to open at a predetermined set pressure to protectpressure

vesselsand other equipment from being subjected to pressures that exceed their design limits. When the

set pressure is exceeded, the relief valve becomes the "path of least resistance"as the valve is forced

open and a portion of the fluid is diverted through the auxiliary route. The diverted fluid (liquid, gas or

liquidgas mixture) is usually routed through apipingsystem known as a flare headeror relief headerto a

central, elevatedgas flarewhere it is usually burned and the resultingcombustiongases are released to

the atmosphere.[1]As the fluid is diverted, the pressure inside the vessel will drop. Once it reaches the

valve's reseating pressure, the valve will close. The blowdownis usually stated as a percentage of set

pressure and refers to how much the pressure needs to drop before the valve reseats. The blowdown can

vary from roughly 220%, and some valves have adjustable blowdowns.

In high-pressure gas systems, it is recommended that the outlet of the relief valve is in the open air. In

systems where the outlet is connected to piping, the opening of a relief valve will give a pressure build up in

the piping system downstream of the relief valve. This often means that the relief valve will not re-seat once

the set pressure is reached. For these systems often so called "differential" relief valves are used. This

means that the pressure is only working on an area that is much smaller than the openings area of the
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valve. If the valve is opened the pressure has to decrease enormously before the valve closes and also the

outlet pressure of the valve can easily keep the valve open. Another consideration is that if other relief

valves are connected to the outlet pipe system, they may open as the pressure in exhaust pipe system

increases. This may cause undesired operation.

In some cases, a so-called bypass valveacts as a relief valve by being used to return all or part of the fluid

discharged by apumporgas compressorback to either a storage reservoir or the inlet of the pump or gas

compressor. This is done to protect the pump or gas compressor and any associated equipment from

excessive pressure. The bypass valve and bypass path can be internal (an integral part of the pump or

compressor) or external (installed as a component in the fluid path). Many fire engineshave such relief

valves to prevent the overpressurization offire hoses.

In other cases, equipment must be protected against being subjected to an internalvacuum(i.e., low

pressure) that is lower than the equipment can withstand. In such cases, vacuum relief valvesare used toopen at a predetermined low pressure limit and to admit air or an inert gasinto the equipment so as control

the amount of vacuum.

Contents

[hide]

1 Technical terms

2 Legal and code requirements in industry

3 DIERS

4 See also

5 References

6 External links

Technical terms[edit]

In thepetroleum refining,petrochemicalandchemical manufacturing,natural gas processingandpower

generationindustries, the term relief valveis associated with the terms pressure relief valve

(PRV),pressure safety valve (PSV)and safety valve:

Pressure relief valve (PRV) or pressure safety valve (PSV): The difference is that PSVs have a manual

lever to activate the valve in case of emergency. Most PRVs are spring operated. At lower pressures

some use a diaphragm in place of a spring. The oldest PRV designs use a weight to seal the valve.

Set pressure: When the system pressure increases to this value, the PRV opens. The accuracy of the

set pressure often follows guidelines set by theAmerican Society of Mechanical Engineers(ASME).

Relief valve (RV): A valve used on a liquid service, which opens proportionally as the increasing

pressure overcomes the spring pressure.
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Safety valve(SV): Used in gas service. Most SVs are full lift or snap acting, in that they pop completely

open.

Safety relief valve (SRV): A relief valve that can be used for gas or liquid service. However, the set

pressure will usually only be accurate for one type of fluid at a time.

Pilot-operated relief valve(POSRV, PORV, POPRV): A device that relieves by remote command from

a pilot valve which is connected to the upstream system pressure.

Low-pressure safety valve (LPSV): An automatic system that relieves by the static pressure of a gas.

The relieving pressure is small and near the atmospheric pressure.

Vacuum pressure safety valve (VPSV): An automatic system that relieves by the static pressure of a

gas. The relieving pressure is small, negative and near the atmospheric pressure.

Low and vacuum pressure safety valve (LVPSV): An automatic system that relieves by the static

pressure of a gas. The relieving pressure is small, negative or positive, and near the atmospheric

pressure.

Pressure vacuum release valve (PVRV): A combination of a vacuum pressure and a relief valve in one

housing. Used on storage tanks for liquids to prevent implosionor over pressure.

Snap acting: The opposite of modulating, refers to a valve that "pops" open. It snaps into full lift in

milliseconds. Usually accomplished with a skirt on the disc so that the fluid passing the seat suddenly

affects a larger area and creates more lifting force.

Modulating: Opens in proportion to the overpressure.

Gas flareFrom Wikipedia, the free encyclopedia

Flare stack at theShell Havenrefinery in England.
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A gas flare, alternatively known as a flare stack, is a gascombustiondevice used in industrial plants such

aspetroleum refineries,chemical plants,natural gas processingplants as well as at oil or gas production

sites havingoil wells,gas wells,offshore oil and gas rigsandlandfills.

North Dakota Flaring of Gas

In industrial plants, flare stacks are primarily used for burning offflammablegas released bypressure relief

valvesduring unplanned over-pressuring of plant equipment.[1][2][3][4][5]During plant or partial plant startups

and shutdowns, flare stacks are also often used for the planned combustion of gases over relatively short

periods.

A great deal of gas flaring at many oil and gas production sites has nothing to do with protection against the

dangers of over-pressuring industrial plant equipment. Whenpetroleum crude oilis extracted and produced

from onshore or offshoreoil wells,raw natural gasassociated with the oil is produced to the surface as

well. Especially in areas of the world lackingpipelinesand other gas transportation infrastructure, vast

amounts of suchassociated gasare commonly flared as waste or unusable gas. The flaring of associated

gas may occur at the top of a vertical flare stack (as in the adjacent photo) or it may occur in a ground-level

flare in an earthen pit.

Contents

[hide]

1 Overall flare system in industrial plants

2 Impacts of waste flaring associated gas from oil drilling sites and other facilities

3 See also

4 References

5 External links

6 Media

Overall flare system in industrial plants[edit]
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Schematic flow diagram of an overall vertical, elevated flare stack system in an industrial plant.

Whenever industrial plant equipment items are over-pressured, thepressure relief valvesprovided as

essential safety devices on the equipment automatically release gases and sometimes liquids as well.

Those pressure relief valves are required by industrial design codes and standards as well as by law.

The released gases and liquids are routed through largepipingsystems called flare headersto a vertical

elevated flare. The released gases areburnedas they exit the flare stacks. The size and brightness of the

resulting flame depends upon the flammable material's flow rate in terms ofjoulesper hour (orbtuper

hour).[4]

Most industrial plant flares have avapor-liquid separator(also known as a knockout drum) upstream of the

flare to remove any large amounts of liquid that may accompany the relieved gases.

Steamis very often injected into the flame to reduce the formation of black smoke. When too much steam

is added to the flame, a condition known as "over steaming" can occur resulting in reduced combustion

efficiency and higher emissions. In order to keep the flare system functional, a small amount of gas is

continuously burned, like a pilot light, so that the system is always ready for its primary purpose as an over-

pressure safety system.

The adjacent flow diagram depicts the typical components of an overall industrial flare stack system :[1][2][3]

A knockout drum to remove any oil and/or water from the relieved gases.

A water seal drum to prevent any flashback of theflamefrom the top of the flare stack.
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An alternative gas recovery system for use during partial plant startups and/or shutdowns as well as

other times when required. The recovered gas is routed into the fuel gas system of the overall

industrial plant.

A steam injection system to provide an externalmomentumforce used for efficient mixing ofairwith

the relieved gas, which promotes smokeless burning.

Apilot flame(with itsignition system)that burns all the time so that it is available to ignite relieved

gases whenever needed.[6]

The flare stack, including a flashback prevention section at the upper part of the flare stack.

Impacts of waste flaring associated gas from oil drilling sites and otherfacilities[edit]

Flaring of associated gas from an oil well site in Nigeria.

Flaring gases from an oil platform in the North Sea.

Flaring is a contributor to the worldwide anthropogenic emissions ofcarbon dioxide.Improperly operated

flares may emitmethaneand othervolatile organic compoundsas well assulfur dioxideand

othersulfurcompounds, which are known to exacerbate asthma and other respiratory problems. Other

emissions from improperly operated flares may include,aromatic

hydrocarbons(benzene,toluene,xylenes)andbenzapyrene,which are known to be carcinogenic.
http://en.wikipedia.org/wiki/Momentumhttp://en.wikipedia.org/wiki/Momentumhttp://en.wikipedia.org/wiki/Momentumhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Pilot_lighthttp://en.wikipedia.org/wiki/Pilot_lighthttp://en.wikipedia.org/wiki/Pilot_lighthttp://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Gas_flare#cite_note-6http://en.wikipedia.org/wiki/Gas_flare#cite_note-6http://en.wikipedia.org/wiki/Gas_flare#cite_note-6http://en.wikipedia.org/w/index.php?title=Gas_flare&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Gas_flare&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Gas_flare&action=edit&section=2http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Volatile_organic_compoundshttp://en.wikipedia.org/wiki/Volatile_organic_compoundshttp://en.wikipedia.org/wiki/Volatile_organic_compoundshttp://en.wikipedia.org/wiki/Sulfur_dioxidehttp://en.wikipedia.org/wiki/Sulfur_dioxidehttp://en.wikipedia.org/wiki/Sulfur_dioxidehttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Benzenehttp://en.wikipedia.org/wiki/Benzenehttp://en.wikipedia.org/wiki/Benzenehttp://en.wikipedia.org/wiki/Toluenehttp://en.wikipedia.org/wiki/Toluenehttp://en.wikipedia.org/wiki/Toluenehttp://en.wikipedia.org/wiki/Xyleneshttp://en.wikipedia.org/wiki/Xyleneshttp://en.wikipedia.org/wiki/Xyleneshttp://en.wikipedia.org/wiki/Benzapyrenehttp://en.wikipedia.org/wiki/Benzapyrenehttp://en.wikipedia.org/wiki/Benzapyrenehttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:First_gas_from_the_Oselvar_module_on_the_Ula_platform_on_April_14th,_2012.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/File:Niger_Delta_Gas-Flares.jpghttp://en.wikipedia.org/wiki/Benzapyrenehttp://en.wikipedia.org/wiki/Xyleneshttp://en.wikipedia.org/wiki/Toluenehttp://en.wikipedia.org/wiki/Benzenehttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Aromatic_hydrocarbonshttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfur_dioxidehttp://en.wikipedia.org/wiki/Volatile_organic_compoundshttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/w/index.php?title=Gas_flare&action=edit&section=2http://en.wikipedia.org/wiki/Gas_flare#cite_note-6http://en.wikipedia.org/wiki/Ignition_systemhttp://en.wikipedia.org/wiki/Pilot_lighthttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Momentum


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Flaring can impact wildlife by attracting birds and insects to the flame. Approximately 7,500 migrating

songbirds were attracted to and killed by the flare at the liquefied natural gas terminal in Saint John, New

Brunswick, Canada on September 13, 2013.[7]Similar incidents have occurred at flares on offshore oil and

gas installations.[8]Moths are known to be attracted to lights. A brochure published by the Secretariat of the

Convention on Biological Diversity describing the Global Taxonomy Initiative describes a situation where " a

taxonomist working in a tropical forest noticed that a gas flare at an oil refinery was attracting and killing

hundreds of these [hawk or sphinx] moths. Over the course of the months and years that the refinery was

running a a vast number of moths must have been killed, suggesting that plants could not be pollinated

over a large area of forest".[9]

As of the end of 2011, 150 109cubic meters (5.3 1012cubic feet) of associated gas are flared annually.

That is equivalent to about 25 per cent of the annual natural gas consumption in theUnited Statesor about

30 per cent of the annual gas consumption in theEuropean Union.[10]If it were to reach market, this

quantity of gas (at a nominal value of $5.62 per 1000 cubic feet) would be worth $29.8 billion USD.[11]

Also as of the end of 2011, 10 countries accounted for 72 per cent of the flaring, and twenty for 86 per cent.

The top ten leading contributors to world gas flaring at the end of 2011, were (in declining

order):Russia(27%),Nigeria(11%),Iran(8%),Iraq(7%),USA(5%),Algeria(4%),Kazakhstan(3%),Ango

la(3%),Saudi Arabia(3%) andVenezuela(3%).[12]

That amount of flaring and burning of associated gas from oil drilling sites is a significant source ofcarbon

dioxide(CO2) emissions. Some 400 106tons of carbon dioxide are emitted annually in this way and it

amounts to about 1.2 per cent of the worldwide emissions of carbon dioxide. That may seem to be

insignificant, but in perspective it is more than half of the Certified Emissions Reductions(a type of carbon

credits) that have been issued under the rules and mechanisms of the Kyoto Protocol as of June 2011 .[10][13]

Satellite data show that from 2005 to 2010, global gas flaring decreased by about 20%. The most

significant reductions in terms of volume were made in Russia and Nigeria.[
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Valves & Flare Stack

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