Technical Guidance Note (Monitoring) Sampling Requirements .
Technical Guidance Note(Monitoring)M1Sampling requirements for stack emissionmonitoringEnvironment AgencyVersion 8August 2017
ated information on inspections of permanent platforms (section9.7.7.1)Status of this documentThis TGN may be subject to review and amendment following publication. The mostrecent version of this note is available at:www.mcerts.netFeedbackIf you have any comments on this standard please contact our National CustomerContact Centre at:Email: enquiries@environment-agency.gov.uk
ForewordPurposeThis Technical Guidance Note (TGN) on sampling requirements for monitoring stackemissions to air is one of a series providing guidance to our staff, monitoringcontractors, industry and other parties interested in stack emission monitoring. It isalso a guidance document in support of our Monitoring Certification Scheme(MCERTS) and Operator Monitoring Assessment (OMA).It provides guidance on European standard BS EN 15259:2007 Requirements formeasurement sections and sites and for the measurement objective, plan and report.It focuses on the parts of the standard that deal with measurement sections andsites.This TGN also provides guidance on risk management in stack emission monitoring.Throughout the document, references to sampling from stacks should be interpretedas also meaning sampling from vents, ducts and flues, unless otherwise stated.
Contents1. Monitoring guidance and MCERTS . 12. EN 15259 – Requirements for measurement sections and sites and forthe measurement objective plan and report . 13. Designing a representative measurement location . 2Box 3.1 Definitions of important terms in stack emission monitoring . 24. Principles of representative sampling . 35. Periodic sampling using grid measurements . 45.1 Grid measurement positional requirements . 45.2 Criteria for locating the sampling plane . 45.3 Surveying the proposed sampling plane . 55.4 Preliminary velocity survey . 55.5 Number of sampling points . 65.6 Position of sampling points along the sample lines . 66. Representative sampling of gases . 67. Sampling requirements: continuous emissions monitoring systems . 78. Sampling facilities for stack-emission monitoring . 78.1 Permanent platforms. 78.2 Space for the equipment and personnel. 78.3 Means of entry into the stack (measurement ports) . 88.6 Sampling facilities for periodic monitoring of gases . 88.7 Sampling facilities for CEMs . 88.8 Essential services . 98.9 Installing and upgrading sampling platforms at existing stacks. 98.10 Alternatives to permanent platforms . 99. The risk-management approach to site work . 99.1 Safety has the highest priority . 99.2 Prominent hazards encountered when stack-emission monitoring . 109.3 The risk-assessment process. 119.4 Responsibilities . 129.5 When to carry out a risk assessment . 129.6 Getting the operator involved . 139.7 Working at heights . 13Annex 1 - Check sheet of sample facility requirements for plant designers /operators. 19Annex 2 Examples of platforms and sampling ports . 22References . 27
1. Monitoring guidance and MCERTSThis Technical Guidance Notes (TGNs) covers sampling and safety requirements forstack emission monitoring. It is one of a series of TGNs in the ‘M’ series providingguidance on regulatory monitoring and support to our Monitoring Certification SchemeMCERTS.MCERTS for manual stack emission monitoring (see box 1.1) provides for theassessment of the quality and reliability of organisations, and the competence ofindividuals carrying out stack emission monitoring against published performancestandards for organisations1 and personnel2.Box 1.1 MCERTSMCERTS is our Monitoring Certification Scheme for instruments, monitoring andanalytical services. The scheme is built on proven international standards and providesindustry with a framework for choosing monitoring systems and services that meet ourperformance specifications. MCERTS reflects the growing requirement for regulatorymonitoring to meet European and international standards. It brings together relevantstandards into a scheme that can be easily accessed by manufacturers, operators,regulators and laboratories. Further information on MCERTS is available atwww.mcerts.net2. EN 15259 – Requirements for measurement sections andsites and for the measurement objective plan and reportComité Européen de Normalisation (CEN) standard BS EN 152593 is a Europeanstandard that is of importance to plant designers, plant operators and stack emissionmonitoring organisations.In summary BS EN 15259: specifies requirements for stack emission monitoring measurement locationsapplies to both periodic measurements and to continuous emissionmeasurement systems (see Box 2.1)outlines the sampling strategy required to obtain a representative sampleThis TGN provides guidance on meeting the requirements of BS EN 15259. It doesnot repeat text, tables or diagrams from BS EN 15259; instead it refers to the relevantsections of this standard. It is therefore strongly recommended that the reader has acopy of BS EN 15259.TGN M1, Version 8, August 2017Page 1 of 27
Box 2.1: Periodic and continuous measurementsPeriodic measurements – a measurement campaign is carried out at periodic intervals,for example, once every three months. The sample is withdrawn from the stack (extractivesampling). An instrumental or automated technique may be used, where the samplingand analysis of the substance is fed to an on-line analyser. Alternatively, a techniquemay be used where a sample is extracted on site and analysed later in a laboratory.Samples may be obtained over several hours, or may be so-called “spot” or “grab”samples collected over a period of seconds to several minutes.Continuous emissions monitoring systems (CEMs) – automated measurementscarried out continuously, with few if any gaps in the data produced. Measurement may becarried out in situ in the stack (for example, cross-duct monitoring), or extractive samplingmay be used with an instrument permanently located at or near the stack. CEMs are alsoreferred to as Automated Measuring Systems (AMS), particularly in a European context.3. Designing a representative measurement locationSuitable measurement sections and measurement sites are necessary to obtainreliable and comparable emission measurement results. Therefore, appropriatemeasurement sections and sites should be planned when designing a plant. Termsrelated to the measurement section and site are given in Box 3.1Box 3.1 Definitions of important terms in stack emission monitoringStack, duct or flue – a structure through which gases pass. Typically stacks areintended to be of sufficient height to adequately disperse emissions in the atmosphere.The terms duct and flue are synonymous.Measurement section - region of the stack or duct that includes the sampling plane andthe inlet and outlet sections.Measurement plane – the plane normal to the centreline of the stack or duct at thesampling location.Measurement location or site – the working area around the sampling plane on a stackor duct.Sampling lines – imaginary lines in the sampling plane along which sampling points arelocated, bounded by the inner wall of the stack or duct.Measurement ports or access ports – points in the wall of the stack or duct throughwhich access to the emission gas can be gained.Measurement point – the specific position on the sample plane from where the sampleis extracted.Emission measurements require appropriate measurement ports and workingplatforms. Therefore, the installation of measurement ports and working platformsshould be taken into account at the planning phase of a measurement section.TGN M1, Version 8, August 2017Page 2 of 27
4. Principles of representative samplingThe mass concentration of a stack emission is the concentration of the measuredcomponent averaged over the cross section of the stack, averaged over a defined timeperiod.Concentration distributions may differ across a stack and over time. If concentrationand / or velocity profiles, which are variable in space and time occur, the emissions aredetermined as the integral for time and space over the stack area. This means that theaverage concentration and velocity at several measurement points across a stack mayneed to be determined.For gases carrying particulates, inertial effects introduced by gravity and the ductgeometry lead to the particles being unevenly distributed in the stack. Samples mustbe obtained from multiple sample points (a grid measurement) across the samplingplane to give an overall average of the particulate emission. Rules have beendeveloped specifying where these sampling points should be located. Rules have alsobeen developed for determining the flow criteria that a cross section must comply within order to carry out a grid measurement – these rules are based on having an evenflow profile.For extractive particulate methods, the sample must be collected isokinetically (seeBox 4.1) using a grid measurement approach.Stack gases may be non-homogeneous due to differences in chemical composition,or differences in temperature and velocity, which may lead to stratification and swirling.However, simplifications for gas sampling can be made if the concentration does notchange over the cross section of the stack.Therefore, where the measurement is of concentrations of gaseous species alone, asampling location can be chosen that does not have to take into account therequirements to measure flow and particulates. This means requirements on designinga measurement section to measure gas concentrations alone can be less stringentthan for measuring flow or particulates. Also, provided the gases are well mixed thesampling approach is more straightforward because single point sampling may becarried out rather than grid sampling.However, these simplifications for gas sampling can only be made if it can be proventhat the stack gas is homogenous (i.e. well mixed).If the gases are not well mixed, it is necessary to sample the gases using a gridmeasurement technique. When a grid measurement technique is required it isnecessary to be able to measure the velocity at several points across the sampleplane. This means that it is advisable to consider, at the design stage, the possibilityof the gases being heterogeneous.Also, if the mass emission rate of a gas is to be calculated, the gas volumetric flow ratewill need to be measured; this will require velocity measurements to be made at severalpoints across the sampling plane using a grid measurement approach.Some pollutants, for example, metals and dioxins, are present in both particulate andvapour phases. Other pollutants for example, hydrogen chloride, may be present in anaerosol phase and vapour phase. Aerosols are normally treated as particulates. In allsuch cases grid measurement sampling is required.TGN M1, Version 8, August 2017Page 3 of 27
Box 4.1 The importance of isokinetic sampling for particulatesIsokinetic sampling is achieved when the gas enters the sampling nozzle at the samevelocity and direction as the gas travelling in the stack or duct.Periodic sampling of particulates requires extractive isokinetic sampling methods. Theprinciple of isokinetic sampling is that a sharp-edged nozzle is positioned in the stackfacing into the moving gas stream and a sample of the gas is extracted through it, at thesame velocity as the gas in the stack, for a measured period of time. To allow for nonuniformity of particulate distribution, samples are taken at a pre-selected number of pointsacross the sample plane. The particulates collected in the sampler are later weighed, andthe concentration of particulate matter in the stack is calculated using the volume of gassampled. The mass flow rate of particulate matter in the stack can be calculated from theconcentration and the velocity of gas in the stack.Due to the wide range of particle sizes normally present in process emission streams, itis necessary to sample isokinetically to ensure that a representative sample of theparticulate emission is obtained.If the sampling velocity is less than the isokinetic rate, at first sight it would appear, thatthe emission will be underestimated. However, because the sampling rate is too low,there is a divergence in flow around the sampling inlet. Small particles are able to followthe flow and a percentage of them will not be sampled. Larger particles, on the otherhand, are not able to follow the flow because of their greater inertia and more of theseparticles will enter the sampler. Thus a sub-isokinetic sampling rate will lead to a bias inthe sampled particle size distribution towards the larger particles. This could lead to anoverestimate of the particulate concentration depending on the original size distribution.Sampling at a rate in excess of the isokinetic rate will lead to a bias in the sampledparticle size distribution towards the smaller particles. This could lead to anunderestimate of the emission concentration depending on the original size distribution.5. Periodic sampling using grid measurements5.1 Grid measurement positional requirementsBS EN 15259 details the positional requirements for carrying out a grid measurement.This approach is used for: sampling particulatessampling multiphase pollutantssampling using wet chemistry when droplets are presentvelocity measurements for reporting mass emissionsampling gases that are distributed heterogeneously, due to effects, such asstratificationdetermining a representative sample location for CEMs5.2 Criteria for locating the sampling planeThe general approach for locating a sample plane for grid measurements can besummarised as:TGN M1, Version 8, August 2017Page 4 of 27
Identify a potentially suitable samplinglocation.Access the stack and check that theflow criteria are met by carrying out anexploratory survey.Decide the number and position of thesampling points and install ports andaccess to the sampling location.Carry out preliminary velocity traverseto confirm it is satisfactory. Proceedwith sampling.Sampling must be carried out at a suitable location on the stack. Bends, branches,obstructions, fans and leaks can all cause undesirable variations in the velocityprofiles, which may make the location unsuitable for sampling.Detailed information on locating a measurement plane in a stack is given in section 6of BS EN 15259. Annexes 1 and 2 of this document provide a summary of thisinformation.5.3 Surveying the proposed sampling planeAn exploratory survey of the proposed sample plane should be undertaken. Thisshould include a stack gas velocity survey. For metal or other thin walled stacks, 13mmdiameter pilot holes, drilled through the flue wall on the centres of the proposed sampleaccess holes, may enable a small bore Pitot-static tube and thermocouple probe ofsuitable length to be used for this purpose. The use of such temporary access holesdistinguishes the exploratory velocity traverse from the preliminary velocity survey. Thelatter should be performed through permanent access ports.Wherever possible, it is important that this approach is followed, so that the sampleplane location is shown to be suitable before installing comprehensive and expensivesampling access and facilities on a stack.5.4 Preliminary velocity surveyA preliminary velocity traverse should be completed before sampling is carried out ata location for the first time. To establish that a sampling location is suitable,measurements of gas velocity should be carried out at equally spaced points alongeach proposed sampling line (a grid measurement). Measurements at these samplingTGN M1, Version 8, August 2017Page 5 of 27
points must demonstrate that the gas stream at the sampling plane meets the flowstability criteria requirements. If the results do not conform to the flow stability criteria,another sample location should be found.Detailed information on the required flow criteria is given in section 6 of BS EN 15259.5.5 Number of sampling pointsThe number of sampling points required is determined by the size of the stack. Theminimum number of sampling points and sample lines are given in section 8 of BS EN15259.5.6 Position of sampling points along the sample linesThe sampling plane is divided into equal areas and sampling is carried out from pointsin the centres of these areas. Further details are provided in section 8 of BS EN 15259.6. Representative sampling of gasesGases can be sampled using a grid measurement approach. The sampling points inthe grid are determined in the same way as for flow stability checks and isokineticsampling. However, when an instrumental technique is used the length of time spentat each point is proportional to the concentration of the gas in the stack and the velocityat the sample point.As gases are often well mixed, it may be possible to prove that a grid measurementmay not be required and that sampling from a single point may be carried out. This isdone by assessing spatial and temporal variations in the gas concentration. Theprocedure for doing this is given in section 8 of BS EN 15259.If the distribution is heterogeneous, it may still be possible to sample from a singlepoint provided that a single representative point can be found. The approach is basedon assessing whether the variations in concentration across the stack are within theallowable measurement uncertainty. The procedure to determine if a representativepoint can be found is given in section 8 of BS EN 15259.If a representative point cannot be found due to the gas being heterogeneous, gridmeasurements must be carried out. Where grid measurements are required it isnecessary to measure the velocity at each sample point, so that representativesampling can be achieved.Once the homogeneity test has been completed it does not need repeating unlessthere is a significant change in the fuel type, structure of the stack or processabatement systems.Further information on the application of the homogeneity test is available inEnvironment Agency Method Implementation Document (EA MID
This Technical Guidance Note (TGN) on sampling requirements for monitoring stack emissions to air is one of a series providing guidance to our staff, monitoring contractors, industry and other parties interested in stack emission monitoring. It is also a guidance document in support of our Monitoring Certification Scheme
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