STATIONARY SOURCE EMISSIONS
EMISSION MONITORING AND MEASUREMENT OF FLUE GAS FLOW RATE
EN ISO 16911 ‘Stationary Source Emissions – Manual and automatic determination of velocity and volume fl ow rate in ducts.
Operators of combustion plant need to know the fl ue gas fl ow rate in order to calculate the mass release of pollutant emissions. The fl ue gas fl ow rate (m3/s) is multiplied by the concentration (mg/m3) of pollutant, e.g., NOx, to give the mass release rate in mg/s. This information may be required for emissions trading, compliance or inventory reporting, or for air quality modelling purposes.
The standard on fl ue gas fl ow rate measurement was published in 2013: EN ISO 16911 ‘Stationary Source Emissions – Manual and automatic determination of velocity and volume fl ow rate in ducts. The scope of the standard, based on the original mandate from the European Union, is linked to the requirements of European Directives, including the Industrial Emissions Directive (IED) and the EU Emissions Trading System (EU ETS) which allow this alternative ‘measurement’ approach for CO2 and requires it for emissions of N2O and CH4 from other sectors, all subject to defi ned uncertainty requirements. European Directives require the use of CEN standards when available.
The standard is divided into two parts. Part 1 defi nes manual Standard Reference Methods (SRM) to be used for the calibration of continuous stack fl ow monitors and for other compliance purposes, such as periodic testing. Part 2 of the standard applies to continuous monitoring and specifi es the requirements for the certifi cation, calibration and ongoing control of continuous fl ow monitors.
Part 1: Manual reference method
Part 1 of the standard is performance based, that is, a number of different techniques may be used as the manual reference method provided that the specifi ed performance requirements are satisfi ed. The alternative techniques include: velocity traverses with Pitot probes (various designs) or vane anemometers; tracer (dilution) and tracer (time-of-fl ight) methods. Under certain circumstances, fl ow calculation from fuel consumption can be used to perform compliance checks and a mandatory calculation approach is also provided in Part 1 (Annex E).
Table 1 summarises the applicability of the different techniques.
Measurement Objective Applicable Techniques Velocity profi le
Point velocity measurement: - Pitot tubes (ΔP measurement) - Vane anemometer
Swirl angle
Point swirl angle measurement: - S-type Pitot tubes - 3D or 2D Pitot tubes
Periodic measurement of average velocity
(fl ow rate) - Pitot tube traverse (ΔP) (averaged)
- Vane anemometer traverse (averaged)
Calibration of fl ow monitors for average velocity
(fl ow rate)
- Tracer dilution technique - Tracer transit time technique - Calculation from fuel consumption - Pitot tube traverse (ΔP) (averaged)
- Vane anemometer traverse (averaged)
- Tracer dilution technique - Tracer transit time technique
- Calculation from fuel consumption
Figure 1a: Spherical (5-hole) Pitot head
Table 1: Applicability of manual reference techniques
Point velocity measurements are, evidently, required when measuring the velocity profi le in order to determine if a given measurement plane is suitable for the installation of a fl ow monitor, for example. Any type of Pitot tube or vane anemometer with a traceable calibration can be used for this purpose, provided that the level of swirl is low (nominally less than 15° swirl angle at all traverse points). If the level of swirl is signifi cant, then the traverse must be conducted using a 3D or 2D Pitot, noting that a conventional S-type Pitot can be operated as a 2D Pitot with measurement of the swirl angle. The 3D approach, as the name
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suggests, measures all three velocity components, including the axial velocity that is required for an unbiased fl ow rate determination.
The spherical (5-hole) Pitot, shown in Figure 1a, is an example of a 3D device. This is inserted into the fl ow and turned until one of the ΔP measurements is nulled. Wind tunnel calibration relationships are then used to calculate all three velocity components from the various measured ΔPs. The operation of 3D Pitots is described in detail in US EPA Method 2F.
Figure 1b: S type Pitot head
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