FUGITIVE EMISSION CONTROL

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Emission measurements ofindustrial valves according toTA Luft and EN ISO 15848-1As the title suggests, in this article Professor Dr.-Ing Alexander Riedl looks into theimplications of measuring emissions according to TA Luft and EN ISO 15848-1 andpoints out some important conclusions.

Professor Dr.-Ing. Alexander Riedl, University of Applied Sciences Muenster, Germany

TA Luft Inasmuch as they relate to Germany, the“Technische Anleitung zur Reinhaltungder Luft” (Technical Guidelines for AirPollution Control, or TA Luft for shortand referred to hereinafter as TA Luft) [1]are like a law in character. Among otherthings, they pursue the objective ofreducing emissions with gasket systems as

normally used in the chemicals andpetrochemical industries.TA Luft onlygives guidelines in respect of compliancewith permissible leakage limits and refersto regulations which define basicconditions for inspections. For shutoffand regulating valves, this affects VDI(Association of German Engineers)Guideline 2440 [2], which may be

regarded as state-of-the-art from a legalperspective.

VDI 2440Guideline VDI 2440 refers to averagegas-like emissions for differing gasketsystems but these are not upper limits(see Table 1).

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Table 1 – Average gaseous emissions (leakage) and valve gaskets [1]

Gasket system Leakage related to the average sizeof the gasket [mg/(s x m)]

Stuffing box with packing 1.0

Stuffing box with cup leather, O-ring 0.1

Stuffing box with packing, stuffing box with cup leather, 0.01O-Ring (with "TA Air Certificate" according toVDI 2440, Section 3.3.1.3)

Metallic bellows, sealed 0.01

Metallic bellows, sealed (with flat gasket possessing 0.001a TA Luft Certificate according to VDI 2440)

Stuffing box with packing and sealing medium/suction, No emissionmetallic bellows, welded on both sides (technically leak-proof)

VDI 2440 refers to the use of high-quality metallic bellows with adownstream safety stuffing box orequivalent gasket systems as aparticularly effective means of reducingemissions. In other words, metallicbellows and so-called “equivalent gasketsystems” are established as conforming toTA Luft.This means that only these kindsof gasket systems may be used inGermany on shutoff and regulatingvalves when a TA Luft medium issubsidised.

Gasket systems may be regarded asequivalent if they fulfil the followingconditions:

(1) The construction of the gasket systemcan be expected to permit itsregulation function under operatingconditions.

(2) Compliance with specific leakage ratewith reference to the average size ofthe gasket, from 10-4 mbar x l/(s x m)at temperatures of less than 250°Cand from 10-2 mbar x l/(s x m) attemperatures on the gasket system ofgreater than 250°C is proven at thefirst inspection.

No specific explanation is given onconstruction under (1) as to why thisguideline is difficult to understand. Onthe other hand, the determination of aleakage rate to be complied with under(2) for all gaskets except metallic bellowsis crucial in order to get valves that fulfilthe conditions of this certificate onto themarket.

Guideline VDI 2440 describes a testingprocedure with which the above-mentioned certificate can be shown.Theancillary conditions here are:

(1) testing medium: helium;(2) testing pressure: nominal pressure;(3) testing temperature: permissible

operating temperature;(4) before the test, a representative

number of switching cycles is carriedout depending on the operatingconditions (switching rate);

(5) test: with static and movingspindle/shaft;

(6) leak rate: leakage resulting after atleast 24-hour admission flow withhelium under the given testingconditions.

If the leak in (6) is less than 10-4 mbar xl/(s x m) (up to 250°C) or 10-2 mbar xl/(s x m) (over/the same as 250°C), thevalve may be regarded as TA Luftcompliant and may be used with TA Luftmedia.

EN ISO 15848-1ISO norm EN ISO 15848-1 [3] has beenvalid since 2006. It refers exclusively tovalves and describes, independent of theguidelines of TA Luft and VDI 2440respectively, detailed tests fordetermining leakage and the creepbehaviour of valves.The norm wasdeveloped under the overall control ofthe CEN/TC 69 “Industrial Valves”Committee.The norm distinguishesbetween the following parameters:

(1) 3 grades of imperviousness for thespindle/shaft;

(2) a grade of imperviousness for thebody gasket;

(3) 2 testing media (helium and methane);(4) 3 grades of firmness;(5) 5 grades of temperature; and1 distinction between shutoff andregulating valves.

Table 2 [3] shows the following grades ofimperviousness for die spindle and theshaft:

Table 2 – Grade of imperviousness/leakage areas

Grade Measured leakage Remarksrate mg/(s x m)

A Typically achieved with bellows gaskets or an equivalent(helium only) ≤ 10-6 spindle/shaft gasket system for swivel valves.

B ≤ 10-4 Typically achieved with packing on a PTFE basisor elastomer packing.

C ≤ 10-2 Typically achieved with packing on the basis offlexible graphite.

The required imperviousness for the bodygasket, measured using the sniffing method,may not exceed 50 ppmv (1 ppmv = 1cm3

x /m3). In respect of the media, the normis not intended to achieve anycomparability, but less leakage may beexpected than with helium. However, thisstatement requires testing.The leakage testsare conducted both at room temperatureand at maximum operating temperature,taking cycles of differing lengths.The gasketconnection may only be re-tightened to alimited extent.At the moment the author does not knowwhether any European country or the EUhas adopted the norm in order to convertthe limits described here into national orEuropean law.Through the preciseguidelines, however, it is expected that thiswill be carried out within the foreseeablefuture.The same applies to the stability andtemperature grades described below.The shutoff and regulating valves differ bystability grades, but the classification to agrade of stability is given by the number ofcycles in which a certain grade ofimperviousness (see Table 1) has not beenexceeded.With the shutoff valves the normassumes a maximum cycle of 2500 andwith the regulating valves, a maximumcycle of 105 cycles. Differences aredescribed in three grades of firmnessshown in Table 3 below.

FUGITIVE EMISSION CONTROL

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HEADINGFUGITIVE EMISSION CONTROL

Comparison of regulationsThe guidelines in EN ISO 15848-1 arevery precise and easy to understand. It isimportant to note here that clearguidelines are given in respect of thetesting procedure. As well, thesubdivision into grades of stability,imperviousness and temperature aresignificant in order to also enable theusers of valves to differentiate betweenthem.The same applies to the subdivisioninto shutoff (low number of expectedcycles) and regulating valves (highnumber of expected cycles).The TA Luft and Guideline VDI 2440give a maximum permissible leakage asthe only criterion which may not beexceeded; however, the marginalconditions (cycle etc.) are not clearlydefined. In addition, the constructionrequirement which allows it to functionaccording to the purpose for which itwas built, is not really a clear guideline.But what is important is the question ofthe usefulness of EN ISO 15848-1 forverifying TA Luft. If we compare thedegree of leakage in the ISO norm withthe guidelines of TA Luft/VDI 2440, wearrive at the following interrelationship[4]:

T = temperature of the gases (K)X = leakage rate (mbar x l/s)Y = leakage rate (mg/m x s)

Note: the dependence of the leakage onthe temperature of the gas is not takeninto account in EN ISO 15848-1.

Accordingly, the conversion factor forleaks at room temperature, taking intoaccount the relationship to the size of thespindle/shaft, is:

Y = 0,164 . X (2)

Y = leakage [mg/(s x m)]X = leakage [mbar x l/(s x m)]

If one takes into account the fact that,according to TA Luft, the average size ofthe sealing material for inspecting theleakage is the determining factor andthat, by contrast, EN ISO 15848-1includes the size of the spindle/shaft, wearrive at the following interrelationship:

Ydm = 0,164 D + d Xd (3)

Ydm = leakage according to VDI 2440, inrelation to the average size of the gasket[mg/(s x m)] Xd = leakage according to EN ISO

15848-1, in relation to thediameter of the spindle/shaft[mbar x l/(s x m)]

D = outside diameter of the sealingelement (corresponds to theinterior diameter of the body) [mm]

D = exterior diameter of thespindle/shaft [mm].

In most cases this probably means that,on achieving grade B imperviousnessaccording to EN ISO 15848-1, theguidelines of TA Luft are probably alsofulfilled.The same applies toimperviousness grade C at temperaturesof over 250°C.

Essentially, it may be assumed that ENISO 15848-1 constitutes a tightening ofthe criteria in contrast to TALuft/VDI2440, as more temperaturecycles can be carried out with the ISO-Norm.

Table 3 – Stability grade for shutoff and regulating valves

Type Stability grade Cycle Temperature cycles

C01 500 2Regulating valve C02 1,500 3

C03 2,500 4CC1 20,000 2

Regulating valve CC2 60,000 3CC3 100,000 4

Table 4 – Grade of temperature

Grade of temperature (t-196°C) (t-46°C) (tRT) (t 200°C) (t 400°C)

Temperature -196°C -46°C Atmospheric 200°C 400°Ctemperature

The testing temperatures are subdivided into five grades and an area of -29°C x 40°Cis given for room temperature (see Table 4).

M • fY =

R • T • π • D X (1)

where:D = average gasket diameter (m)f = conversion factor (=100) (mg x Pa

x m3/g x mbar x l)M = molecular mass (g/mol)R = general gas constant (8,314)

(J/mol x K)

2d

Literature

[1] TA Luft:Technical Guidelines forAir Pollution Control (TA Luft).Heymanns Verlag, Cologne, 2002.

[2]VDI 2440: Reducing Emissionsfrom Mineral Oil Refineries. BeuthVerlag, Berlin, 2000.

[3] DIN EN ISO 15848-1: IndustrialValves - Measuring,Testing andQualification Procedures forEscaping Emissions - Part 1: AClassification System andQualification Procedures for theTesting the Design of Valves. BeuthVerlag, Berlin, 2006.

[4] D. Bathen, C. Hummelt, J.Meisel: Emissions on Flanged Joints.Vulkan Verlag, Essen, 2000.

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