Correction from Actual to Normal Stack Data Calculator
Why correct measured stack data from actual conditions to normal conditions?
Stack testing usually includes the measurement of a pollutant as well as a range of other parameters (e.g. oxygen, moisture, temperature and pressure) to allow measured data to be corrected or ‘Normalised’, denoted ‘N’, or ‘Normal’ to be undertaken. This is to allow measured data obtained through stack testing (defined as ‘Actual’, or denoted ‘A’) to be compared directly to standards or guidelines which are at ‘reference conditions’ set by governments and other regulatory bodies.
For example, the World Bank EHS Guidelines Table 1.1.2 (2007) defines a NOx emission limit for gas fired boilers (between 3MW and 50MW thermal input) of 320 mg/Nm3 where ‘N’ defines the following reference conditions:
- 3% excess oxygen
- Dry
- 1 Atmosphere
- 273.15 K
These are known as ‘reference conditions’ and apply to most combustion equipment emission limits.
Similarly, design data for new equipment may need to be corrected to reference conditions if, for example, vendor data is provided at alternative excess oxygen, wet conditions, or alternative pressures and temperatures to Normal conditions set by regulatory authorities.
See the Environmental Protection Agency of Ireland‘s site for more information on the calculation methods applied in this stack gas concentration measurement correction calculator. See our tools room for more air quality tools.
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