Stationary Source Sampling

Evaluating the characteristics of industrial waste gas emissions

Stationary source sampling or ‘stack-emission testing’ is the experimental process for evaluating the characteristics of industrial waste gas emissions into the atmosphere. Materials emitted to the air from these sources can be solid, liquid, or gaseous; organic or inorganic.

The effluent pollutants emitted to the atmosphere from a source may contain many different pollutant materials. The quantity and type of each pollutant must be known so that a control strategy can be formed and emissions regulated. There is a variety of European, International and National procedures for evaluating these emissions.

The gaseous or isokinetic source sampling procedures give the environmental and industrial engineer a great deal of data on the operation of an individual process. The sampling system measures a number of variables at the source while extracting from the gas stream a sample of known volume. The information on source parameters in conjunction with quantitative and qualitative laboratory analysis of the extracted sample makes possible calculation of the total amount of pollutant material entering the atmosphere.

These data are important for controlling pollutant emissions, evaluating source compliance with regulations or providing information upon which control regulations can be based. The industry performing source sampling gains information on the operation of the process tested. The sampling of source emissions gives valuable process data, which can be used to evaluate process economics and operation control. Information gathered during a source test experiment may also be used for determining existing control device efficiency or for designing new process and emissions control equipment.

Source sampling provides a great deal of important data on the operating parameters and emissions of an industrial stationary source. This information is used as the basis for decisions on a variety of issues. The data taken during a source test experiment must, therefore, be an accurate representation of the source emissions. This task requires a thorough knowledge of the recommended sampling procedures in conjunction with an understanding of the process operation.

The typical industrial process may vary conditions at the source for a variety of economic or logistical reasons. The source sampling experiment must be designed to prevent process variation from biasing the source sample. The test engineer has the additional problem of carrying out an important experiment under extremely difficult working conditions. These problems make source testing an endeavour that should be performed only be trained personnel.

The Environment Agency MCERTS scheme

One aspect of the MCERTS scheme applies to Manual Stack Emission Monitoring. The Environment Agency has recognised the difficulties involved in stack-emission monitoring and has stipulated that it should only be carried out by accredited test laboratories, using certified staff, or industrial process operators with their own certified staff.

Accreditation of laboratories and certification of staff comes under the MCERTS scheme for Manual Stack Emissions Monitoring. This two part scheme ensures that industrial stack-emission monitoring is performed to appropriate and consistent standards.

Stack testing methods

Testing of emissions can be broadly broken down into two categories

• Isokinetic sampling
• Gaseous sampling

Isokinetic sampling

A dictionary defines ‘iso’ as denoting equality, similarity, and uniformity. Kinetic is defined as of, pertaining to, or due to motion. Isokinetic sampling is an equal or uniform sampling of particles and gases in motion within a stack.

Isokinetic source sampling is achieved when the velocity of gas entering a sampling nozzle is exactly equal to the velocity of the approaching gas stream. This provides a uniform, unbiased sample of the pollutants being emitted by the source. Isokinetic source sampling closely evaluates and defines various parameters in the stack as they actually exist at the time of sampling.

Isokinetic sampling was primarily developed for determination of particulate (dust) emitted from stationary sources. One of the first standards to be developed was BS 893 first published in 1940 for the determination of dust from coal fired power stations and later BS3405 for monitoring of small coal fired installations.

These standards encompassed the basic principles of sampling which have been carried through into the modern day standards and methods.

Isokinetic sampling is now used for, not only the determination of particulate but also, other pollutants that exist in particulate, aerosols or droplet phase and can be combined with gas phase components. A typical sample train is shown in figure 1.

Gaseous sampling

Sampling of species in the gaseous phase in chimney stacks (e.g. oxides of nitrogen, oxides of sulphur, volatile organic compounds etc) is either carried out by the use of extractive, (e.g. wet chemical methods) or by continuous analysers. The DTI commissioned a technology status report on Emission Monitoring Technologies for Combustion and Gasification plant, TSR021, which can be found at http://www.dti.gov.uk/files/file20909.pdf. This document gives details on all the technologies available for continuous monitoring of emissions from stationary sources.

Directives, methods and standards

The industrial activities in the UK covered by the Pollution Prevention Control (PPC) regulations and are split into three categories:

• Part A(1) – Regulated by the Environment Agency The Environment Agency regulates what are considered to be the potentially most polluting of the three industrial categories – A(1) activities. The regulations cover emissions to air, land, and water and other environmental considerations
• Part A(2) and Part B – Regulated by the Local Authorities Local authorities regulate the potentially less polluting Part A(2) activities (which also have regulations to cover emissions to air, land, and water) and the lesser polluting Part B activities (these are regulated for emissions to air only)

Within the regulations there is a requirement to follow published standards when carrying out stack-emission monitoring.

Standards

Standard reference methods are essential for the effective measurement and control of air pollution. Such standards are developed at National, European and International level. The robustness and fitness for purpose of these standards is a function of the accumulated expertise and experience of the people who work together in committee to produce them. Where internationally derived standards are binding on the UK, as European (CEN) standards are, it is particularly important that they should recognise UK interests and sensitivities. BSI manages the UK input to new standards via its technical committees and the UK experts they nominate to CEN and ISO working groups.

ISO standards are accepted on a case by case principle, although there is representation on the majority of working groups it is not mandatory for a member country to adopt a standard.

CEN standards are mandatory and must be adopted by a member state of the European Union. If a conflicting standard is in existence this must be withdrawn.

The BSI technical committee responsible for air quality issues is EH/2. Its sub-group EH/2/1 is specifically charged with stationary source emission measurement standardisation. BSI EH2/1 nominates experts to the technical committees of CEN/TC 264 (Air Quality) and ISO TC 146 (Air Quality). BSI EH2/1 also oversees a portfolio of existing BSI, CEN and ISO standards to ensure that they are regularly reviewed for technical relevance and continued suitability for purpose. In order that existing and developing standards reflect the full range of UK needs it is imperative that BSI EH2/1, like other BSI committees, reflects the widest possible range of users.

Standards developed and published by CEN are generally accepted as being the most robust. However, other standards are still important, as there are substances that are not, as yet, covered by CEN Standards. The choice of the method is often dictated by the requirements of a relevant EU Directive, where the use of the relevant CEN standards is mandatory. If the standard is not dictated by mandatory requirements then monitoring standards should be used in the following order of priority as given in the European IPPC Bureau’s Reference Document on the General Principles of Monitoring:

• Comité European de Normalisation (CEN)
• International Standardisation Organisation (ISO)

If the substance cannot be monitored using standards covered by the above then a method can be selected from any one of the following:

• American Society for Testing and Materials (ASTM)
• Association Francaise de Normalisation (AFNOR)
• British Standards Institution (BSI)
• Deutsches Institute fur Normung (DIN)
• United States Environmental Protection Agency (US EPA)
• Verein Deustcher Ingenieure (VDI)

If the substance cannot be monitored using standards covered by the above then the following occupational methods may be developed, following the requirements of ISO 17025, for stack emission monitoring:

• Method for the Determination of Hazardous Substances (MDHS) series published by the Health and Safety Executive (HSE)
• National Institute of Occupational Safety and Health (NIOSH)
• Occupational Safety and Health Administration (OSHA)

The intended application of the standard method must always be taken into account; for example, a CEN method may be less suitable than another less-rigorously validated standard method if the application is not one for which the CEN method was developed. The Environment Agency produces, wherever required, Method Implementation Documents (MIDs) which detail the applicability of methods. The methods detailed in Environment Agency Technical Guidance Note (Monitoring) M2 ‘Monitoring of Stack Emissions to Air’ should be used unless it can be demonstrated that they are not fit for purpose for the particular application.

Published: 10th Sep 2007 in AWE International