A Review of Fugitive

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FEATURE

7Sealing Technology October 2006

IntroductionThe average surface temperature of the globe haswarmed appreciably since the late 1800s, byabout 0.6C. Since this warming cannot be ade-quately explained by natural phenomena such asincreased solar activity, human-induced increases inindustrial emissions such as exhaust gas concentra-tions appear to be at least partly responsible. Theparticular gases that lead to this warming, the so-called greenhouse gases, include carbon dioxide(CO2), methane (CH4), nitrous oxide (N2O),ozone (O3), and water vapor.

[1]

A portion of the emissions to atmosphere is rep-

resented by combustion products, along withknown losses of volatile organic compounds(VOCs) and steam. In general, these are all emis-sions anticipated from industrial processes, underthe control of a plant operator.[2]

Fugitive emissions are often defined as follows:any chemical, or a mixture of chemicals, in anyphysical form, which represents an unanticipatedor spurious leak in an industrial site.[35] It alsocovers all of the losses of materials (usually volatile)from a process plant, through evaporation, flaring,spills and unanticipated or spurious leaks.[3]

Fugitive emissions especially VOCs causesignificant environmental concern because some

offer Photochemical Ozone Creation Potential(POCP), Ozone Depletion Potential (ODP),Global Warming Potential (GWP), toxicity, car-cinogenicity and local nuisance from odor.[2] These

properties mean that VOCs are a major contribu-

tor to the formation of summer smog.The prevention of VOC emissions is therefore

one of the most important issues facing theoperation of many industrial processes.[3, 6, 7]

Irrespective of any environmental impact, theymay result in tremendous financial burdens onindustry, because they represent a huge loss ofpotentially valuable materials, and a cause ofplant inefficiency.[6]Yet in many cases, the truecosts are not appreciated, as many of the costsassociated with fugitive emissions are invisible

(Figure 1). The value of fugitive emissions willdepend on:[24]

Equipment design. Age and quality of the equipment. Installation standards. Vapor pressure of the process fluid. Process temperature and pressure. Number and type of sources. Method of determination. Inspection and maintenance routine. Rate of production.

A significant proportion of fugitive emissions can

be losses from unsealed sources, including storage

of liquid and gas tanks, open-ended, non-blanked,

lines, pressure-relief valves, vents, flares, blow-down

systems, spills and evaporation from water treat-

ment facilities. These are part of industrial process-

es, and usually anticipated by the process operator.

In other cases, these losses may be caused by leaks

in the sealing elements of particular items of equip-

ment, such as:

Agitators/mixers. Compressors. Flanges. Pumps. Tank lids.

Valves.

As can be seen inFigure 2, valves are consideredto account for approximately 5060% of

fugitive emissions. Furthermore, the major pro-portion of fugitive emissions comes from onlya small fraction of the sources.[5, 6] Lossesfrom leakage are often hard to determine, asthere are many potential sources and they arevery dependent on how well the installation isoperated, maintained and inspected. Someimportant causes of leakage are:

Improperly fitted seal components. Installation faults. Construction faults. Wear and tear. Ageing. Equipment failure. Contamination of the seal. Excursions out of normal process conditions. Poor maintenance procedures.

The implementation of legislation in the USgoverning emissions of volatile organic com-pounds, together with EU directives, has pro-vided a stimulus for work aimed at reducingfugitive emissions. Industry has respondedthrough improvements in valve sealing tech-

nology and testing to identify high perfor-mance packings.[8] Improvements to overallvalve design and technology, sealing technolo-gy and maintenance techniques have signifi-cantly reduced valve emissions in process

A review of fugitive

emissionsBy Adem Onat Sakarya University, Sakarya, TurkeyWorldwide, fugitive emissions from industrial applications amount to over a mil-lion metric tonnes per year. Many emissions are the result of the actual industrialprocess, and as such, can be controlled by operators. However, a considerable pro-portion of emissions are unanticipated usually referred to as fugitive emissions.Elimination or reduction of fugitive emissions could save industry many millionsof dollars and prolong scarce resources. This feature reviews some of the key liter-ature and techniques involved.

Figure 1. The tip of the iceberg: sources andcosts of fugitive emissions. [Source: ESA]

Figure 2. The proportion of fugitive emissionsfrom different sources: (a) Fugitive emissionpercentages versus type of industrial equip-ment, and (b) fugitive emission percentagesversus type of industry. [Source: ESA]

(a)

(b)


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FEATURE


plant, leading to environmental improvementsthrough reduced hydrocarbon emissions andcost savings through a reduction indischarges.[9]

In order to assist industry in responding tothe challenge of reducing valve emissions, a

requirement is recognized for standardized

methods of qualifying the emission perfor-

mance of valves, and the development of pro-

duction acceptance tests for valve assemblies.

Currently the most widely recognized stan-

dard is the International Standard, ISO 15848

Industrial Valves Fugitive Emissions

Measurement Test and Qualification

Procedures.[10] Other valve emission stan-

dards are:

Environmental Protection Agency (EPA)Method 21.[11]

ISA 93.00.01 Standard Method for the

Evaluation of External Leakage of Manual

and Automated on-off Valves.[12]

Shell MESC SPE 77/312 Industrial Valves:

Fugitive Emission (FE) Measurement,

Classification System, Qualification

Procedures and Prototype and Production

Tests of Valves.[13]

Fugitive emissionmeasurement methodsIn carrying out fugitive emission measurements,

there are two fundamental choices to be made:

Choice of test gas: helium or methane.

Choice of measurement method: mass mea-

surement or sniffing.

Test gasHelium is the widely preferred choice for the test

gas. It is safe in use, and can be readily detected

using a mass spectrometer in either the massmeasurement mode or the sniffing mode. Other

commercial instruments are available to measure

helium concentrations by the sniffing method.

Methane has advantages in that a sniffingmeasurement on methane using an organic

vapor analyzer (OVA) can be directly compared

to site values. Some also consider that graphite

seals perform better when sealing methane, and

so this is a fairer test of performance on hydro-carbons. Mass measurement on methane usually

requires use of the flushing method, although

some mass spectrometers can carry out measure-

ments on methane.

Mass measurementVacuum methodMass measurement of leakage can be carried by the

vacuum method (Figure 3), where the valve top

works are enclosed within a vacuum chamber and

all gas leaking from the valve passes to the mass

spectrometer. This measurement method has sev-

eral advantages as it is accurate, reproducible and is

not equipment-dependent. However, it doesrequire modification to the valve top works to

enable a vacuum to be created to collect emissions.

Flushing methodAlternatively, measurements can be made by the

flushing (or bagging) method, as shown in

Figure 4. The valve top works are enclosed, and a

flush gas is passed through the enclosure.

Measurement of the concentration of the test gas

in the flush stream enables the mass emission of

the test gas to be determined. This method has to

be used if an OVA is used to carry out mass emis-

sion measurements on methane.

SniffingSniffing is a direct method of measuring the con-centration of test gas close to the valve stem. Thisis not a direct method of valve mass emissionmeasurement. It is subject to errors in operatormethod and as a result of external effects such aswind speed, and it is also detector-dependent.

Site measurementsFor site measurements there is no choice of testgas; the hydrocarbon gas in the valve has to beused. Sniffing is the only practicable method,although mass measurement by bagging can becarried out on a limited number of valves.[14]

DiscussionIt is recognized that industry must reduce itsimpact on the environment if we are to continueglobal development for future generations. Themajor contributing factor through the lowering offugitive emissions will be sealing systems. Theyalso play a vital role in the environmental perfor-mance of industrial installations.

A seals primary purpose is to contain a fluid and

so protect the immediate environment from conta-mination and vice versa. This may vary in signifi-cance from innocuous fluid loss such as steam andwater up to nauseous, toxic or hazardous leakage.In the former case, the loss of such innocuous fluidwill lead primarily to reduced plant efficiency forthe operator, although they may still present haz-ards such as leakage of high-pressure water orsteam. Clearly, in the latter case it is not only finan-cially inefficient but also environmentally danger-ous. Consequently, careful selection appropriate forthe specific application, correct installation andoperation according to the performance envelope,regular inspection and maintenance must be con-

sidered for low or zero emission requirements.In most cases, the cost of the actual sealing

technology is infinitesimally small whencompared with the investment made in the plant

Figure 3. Measurement of valve emissions by the vacuum method test setup. [Source: BHR Group]

Figure 4. Schematic diagram of the flushing method test setup for the measurement of valveemissions. [Source: BHR Group]


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as a whole (Figure 5). Indeed, for many sealingtechnologies, the cost per unit may be in theregion of a few cents, completely insignificantwhen the total plant costs are considered.

Importantly, the unit cost of sealing technologyis completely overwhelmed by the labor cost to fitthe seal, let alone plant downtime. Consequently,

the actual cost of the sealing device is immaterial interms of economic considerations for BestAvailable Techniques (BAT). However, for the sakeof completeness,Figure 6provides an overview ofthe relative cost of different types of gasket and theenvironmental impact of sealing system.

ConclusionsIt is now recognized that industry must reduceits environmental impact to allow sustained

global development, and a major contributingfactor will be through lowering emissions. Thiswill be driven by a combination of public pres-sure, environmental legislation and internalcompany requirements to minimize the loss ofvaluable feedstocks. Sealing systems play a vitalrole in the environmental performance of indus-

trial plants. After careful selection appropriate tothe specific application, correct installation andoperation according to the performance enve-lope, there must be regular inspection and main-tenance to ensure low or zero emissions.

The new sealing technologies and materialscan require more careful selection, handling andinstallation than previous asbestos equivalents.These new materials can offer improvedperformance, but are usually less forgiving,

which means that users must exercise more carein selecting the right material for the job andassembling the seal.

References1. T.M.L. Wigley: The science of climate change:Global and US perspective. National Center for

Atmospheric Research, available online at:www. pe wcl imate .org /g loba l -wa rming -basics/basic_science/wigley.cfm2. J. Peters and A. Stephens: New directions:Fugitive emissions identified by chemical finger-printing, Atmospheric Environment 35(7)13471348 (2001).3. Guidelines for safe seal usage Flanges and gas-kets. ESA/FSA Publication No. 009/98, September1998.4. Sealing Technology BAT Guidance Notes.European Sealing Association. ESA PublicationNo. 014/05, June 2005.5. B.S. Ellis: Emission legislation Development

and progress. International Seal Forum at Achema97, Frankfurt, Germany, June 1997.6. R. Szweda: Fugitive emissions: The matter ofimperfect seals, Sealing Technology (November2000) 911.7. C. Alkidas: Combustion-chamber crevices: Themajor source of engine-out hydrocarbon emissionsunder fully warmed conditions, Progress in Energyand Combustion Science25 253273 (1999).8. D. Harrison, B. Kirkman, E. Smith and M.J.Billington: Evaluation of graphite valve packings toreduce fugitive emissions on hydrocarbon duties.Valves & Actuators International Conference, ITC,Manchester, UK, September 1994.

9. B. Kirkman: Winning the battle with leakyvalves. First European Conference on ControllingFugitive Emissions, ESA/BHR Group, Antwerp,Belgium, October 1995.10. (DIS) ISO 15848, Industrial valves Fugitiveemissions Measurement test and qualificationprocedures.11. EPA Method 21, Determination of volatileorganic compound leak. Code of FederalRegulations. Title 40, Part 60, Appendix A.Washington, DC, USA. Revised June 1990.12. ISA93.00.01, Standard method for the evalu-ation of external leakage of manual and automatedon-off valves.

13. Shell MESC SPE 77/312, Industrial valves:Fugitive emission measurement, Classification sys-tem, Qualification procedures and prototype andproduction tests of valves.14. D. Harrison: Valve fugitive emission measure-ment standards, Sealing Technology(February 2004)912.15. Gasket Engineering Manual. ArmstrongIndustry Products Division, USA, 1987.16. W.F. Jones and B.B. Seth: Asbestos-free gasketmaterials for turbines, Journal of Testing andEvaluation21(1) (1993).

Contact:

Adem Onat, Sakarya University, Vocational School of

Sakarya, 54188 Sakarya, Turkey. Email:

[email protected]

FEATURE


Figure 5.The cost of the sealing technology in proportion to overall plant costs. [Source: ESA]

Figure 6. Relative cost of the different gasket types versus environmental impact.
http://www.pewclimate.org/global-warming-basics/basic_science/wigley.cfmhttp://www.pewclimate.org/global-warming-basics/basic_science/wigley.cfmmailto:[email protected]://www.pewclimate.org/global-warming-basics/basic_science/wigley.cfmhttp://www.pewclimate.org/global-warming-basics/basic_science/wigley.cfmmailto:[email protected]

A Review of Fugitive

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