Measure Efficiency: Video Imaging Spectral Radiometry – VISR

Can I measure flare efficiency? > Measure Efficiency: Video Imaging Spectral Radiometry – VISR


A  spectrometer  that provides direct and real-time measurement of flare combustion efficiency by measuring the ratio of methane to carbon dioxide. It has been tested against established reference methods including extractive EPA methods typically used for stack testing. It can be permanently installed or deployed as a survey method (see separate entry). It works for flares of all sizes and locations provided the flame can be isolated within the field of view.


How it Works

  • A multi-spectral 2D imager measures radiance in the mid-wave infrared spectrum to obtain the relative concentrations of CO2 and unburnt hydrocarbons.
  • Relative concentration measurement is based on spatial averaging of CO2 & unburnt HC presence across the whole combustion envelope.
  • Provides a real-time direct measurement of Combustion efficiency and empirically derives Destruction efficiency (to include CO and soot)
  • Also provides data on flare heat release from which flare volumes can be approximated.

Comparison between flare combustion efficiency measurements taken by extractive method and by VISR


  • Results have been compared to the reference extractive method (with a mean difference - 0.07% in 95-100% CE range)

  • Tested against flares of variable size, design and with/without assist features

  • Quick (~30mins) setup, can be mobilised to provide measurements both onshore & offshore or run continuously to help conform to visual impact legislation

  • Can be run from outside process boundary, camera being positioned 100-1500ft from flare

  • Directly measuring CE eliminates the uncertainty of using surrogate parameters (e.g. NHVcz)

  • Operates in a range of environmental conditions, day & night

  • Provides data on other flare parameters, including heat release, flame size, smoke index and flow rates


  • Needs a clear line of sight of the post combustion gas with a minimum temperature of 300C

  • Cannot measure the concentration of CO, hence, DE has to be empirically derived

  • Some limitations in severe weather conditions (e.g. heavy fog)

Case study

Research article:

Validation of a new method for measuring and continuously monitoring the efficiency of industrial flares

Yousheng Zeng, Jon Morris & Mark Dombrowski (2016)

Journal of the Air & Waste Management Association, 66:1, 76-86


Validation of a new method for measuring and continuously monitoring the efficiency of industrial flares (


Spectrometry is the observation and measurement of wavelengths of light or other electromagnetic radiation. Once a range of wavelengths, or a spectrum, for a gas mixture has been measured, by observing the intensity or amplitude of individual wavelengths, the method allows for determination of chemical composition of that gas mixture. Spectrometry is typically performed with the use of a spectrometer which is an instrument that separates and measures the spectral components of the sample or object being studied. Various types exist, but the most used are either a mass spectrometer or an optical spectrometer. Spectrometry techniques may be used for process control - such as determining the composition of flared gas, or for environmental measurements such as determination of combustion efficiency.

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