Annual Guide 2017 I SOURCE TESTING ASSOCIATION
Stack Emissions Monitoring – getting the sample location right
Introduction
Stack emissions monitoring requires defi ned fl ow conditions at the sample location. These fl ow conditions are required to measure pollutants that exist in a particulate phase. They are also required to measure velocity, which is used to calculate pollutant mass emissions.
As well as selecting the correct location, it is also important to ensure that sampling facilities are suitable. This includes appropriate access to the sample location and a large enough work area for the sampling equipment and sampling personnel.
If a suitable location and / or sampling facilities are not available, it will mean that sampling of pollutants cannot be done in compliance with the required sampling methods. This means that the uncertainty associated with the results is greatly increased. In these circumstances meaningful results from stack emissions monitoring cannot be achieved.
Designing new plants
It is essential that designers of new plants remember to take account of stack emission monitoring at the plant’s design stage. Once a plant is built it is extremely diffi cult, if not impossible, to retrofi t appropriate sampling facilities.
It is extremely frustrating for all concerned if the sampling location does not comply with the sampling requirements because it is either located in the wrong place or the sampling platforms are too small and do not allow access to the stack.
Permit applications (and Variations for plant extensions) require the operator to assess the monitoring arrangements against the requirements of Environment Agency (EA) Technical Guidance Note M11 (this guidance note is available from
www.mcerts. net. It provides guidance on European Standard 152592). It is essential that this process is carried out at the plant design stage. Once this has been done it is strongly recommended that advice and confi rmation of the monitoring arrangements is sought from the EA.
If the monitoring arrangements (i.e. sample location and facilities) at a newly built plant (or newly built extension to a plant) do not meet the requirements of EA TGN M1 and BS EN 15259, it is possible that the EA would not grant the applicant a permit to operate.
Installing a suitable sample location
The sample location must be positioned such, that there are stable fl ow conditions, which allow representative samples of the stack gas emission to be taken.
In summary, for newly built plant the sampling location should be located according to the recommendations contained in Table 1.
Table 1. Recommended location for meeting sample location requirements
General location of sampling plane
The sampling plane should be situated in a length of straight duct (preferably vertical) with constant shape and constant cross- sectional area. Where possible, the sampling plane should be as far downstream and upstream from any disturbance, which could produce a change in direction of fl ow (e.g. bend, fan or a partially closed damper).
Location of sampling plane in straight section
The sample plane criteria are usually met in sections of duct with fi ve hydraulic diameters of straight duct upstream of the sampling plane and two hydraulic diameters downstream. If the sampling plane is to be located near the top of the stack outlet then the distance from the top should be fi ve hydraulic diameters (making a straight length of 10 hydraulic diameters).
By meeting the recommendations in Table 1 the fl ow stability requirements summarised in Table 2 should be met.
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