Normalisation in Emissions Monitoring – What Does It Mean?

Emission sources (stack emissions) are found across different industries including power generation, cement production, steel making, energy from waste, chemicals processing, oil and gas refining and food processing.

Emission monitoring systems that measure emissions released into the atmosphere are used to demonstrate compliance with environmental regulations.

It is preferred, to report gaseous or solid emissions in a format that allows for a comparison of emissions from different sources, taken at different times and in different process conditions.

Therefore, in most cases, concentrations are reported at standard levels, standard temperature, standard pressure, on a dry gas basis, and at a defined air dilution.

Standard levels are agreed values, within a country or group of countries. European countries follow Standard Temperature 0 C°, Standard Pressure 101.3 kPa, Dry basis. Reference oxygen depends on the type of process, levels of oxygen in emitted gas.

Emission limits are defined under the standard conditions of temperature, pressure and air dilution specific to the emission source (air dilution is defined using the waste gas O₂ or CO₂ concentration). Legislation also requires concentrations to be reported on a “dry gas” basis (water vapour in the flue gas is not permitted to dilute the measurement). Correction of the measurement from ‘as measured’ conditions to ‘standard’ conditions is known as ‘normalisation’. Like all in-situ gas analysers, GCEM40 series analysers measure the concentration of pollutants in ppm (parts per million) or %, under the conditions that exist at the measurement position.

This basic ppm measurement is always corrected for the stack pressure and presented as vpm by the analyser. CODEL GCEM40 series analysers have the capability for the outputs and display to be configured in vpm (or %) or mg/m³ (conversion from ratio based concentration to a mass per volume based concentration), or in mg/Nm³ ( ’normalised’ to the required standard conditions).

When the outputs are required to be normalised to a pre-defined reference O₂ concentration (as opposed to a measured CO₂ level), then an external 4-20mA signal representing % oxygen levels can be input into the GCEM40 series system. All other normalising parameters i.e. pressure, temperature, H₂O and CO₂ (if used) are measured as standard by the GCEM40 series.

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