Measure Efficiency: Mobile Video Imaging Spectral Radiometry – (VISR)

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

Feature image courtesy of Zeeco, Inc.® – all rights reserved.

Summary 

A  spectrometer that provides direct and real-time measurement of flare combustion efficiency by measuring the ratio of methane to carbon dioxide.  Energy radiated by the flare is used to measure CO2 and CH4 intensity in the combustion zone.  It has been tested against established reference methods including extractive sampling. VISR works for flares of all sizes and locations provided the flame can be isolated within the field of view

It can be deployed as a survey method or used as a permanently installed system (see separate entry).

 

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 zone.
  • Provides a real-time direct measurement of CE and empirically derives DE

 

Mobile deployment in an offshore setting (Image courtesy of Zeeco, Inc.® – all rights reserved.)

Advantages

  • Results have been compared to the reference extractive method (see separate entry) with a mean difference - 0.07% in the 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
  • Can be run from outside process boundary, camera being positioned 100-1000ft 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 temperature, smoke index and flow rates

Limitations

  • Needs a clear line of sight of the full combustion envelope
  • 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

VISR survey on an onshore gas processing facility and associated gas wells

VISR was deployed for testing of flare destruction efficiency alongside four other performance indicators in an onshore conventional gas production site. Three flares were tested, two in the central processing facility and one well pad flare. Tests were performed at ~1000ft distance to flare, conducted over two days with each flare measurement lasting approx. 1 hour. Tests done during daytime with calm wind.

Flare Types:

  1. Permanently installed LP single-tip non-assisted flare – methane content >90%
  2. Permanently installed HP flare with ultrasonic tips and air assist – methane content >90%
  3. Temporary well pad clean-up flare – oil/gas mixed composition

Example data

 

Flare type

Indicative flowrate (MMSCFD)

VISR Destruction efficiency (DE) (%)

DE Standard Deviation (%)

LP

0.65

99.0 0.5

HP

1.6 97.0

0.8

Well pad

3.6 98.2

2.1

Observations

  • It was identified that the HP flare would benefit from reduced air assist flowrates.
  • Well pad flare was less stable during the tests, yet its destruction efficiency was at acceptable level.

 

Spectrometry

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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