Extractive samplingThe process of measuring flaring combustion by extracting part of the plume and analysing the absolute quantities of burnt and unburnt gas by measn of a traceable method such as… has for several decades been considered the nearest technique to a reference method for measuring flare combustion efficiency and destruction efficiency. The method involves taking gas samples in the vicinity of a test flare by means of an extractive hood suspended over the flare. Gas samples are analysed for hydrocarbons and combustion products by means of gas chromatography (GC-MS).
The key advantage is the ability to directly measure the composition of gas relative to traceableWherby a measurement is calibrated to a reference standard and when the uncertainties of th calibration are insignificant compared to the uncertainties arising from random effects or from a limited number… reference gases. However, the limitations are that it is resource intensive, requires experienced operators and specially built test facilities. It cannot be deployed in the field to measure combustion from existing flares. Test facilities do not cover the full range of flare sizes in use today.
Texas Commission on Environmental Quality (TCEQ) has conducted a thorough study in 2010 (TCEQ 2010 Flare Study) of various flare destruction efficiency measurement techniques using extractive samplingThe process of measuring flaring combustion by extracting part of the plume and analysing the absolute quantities of burnt and unburnt gas by measn of a traceable method such as… as a reference method. It was also used to investigate optimal operating parameters for air and steam assisted flares.
Figure 1 shows that while steam is used to increase the flare performance, excessive steam supply to the flare tip can dramatically reduce the flare destruction efficiency. Figure 2 indicates the results obtained using extractive sampling method, which allows to directly measure different gas species compositions.
The challenges in measuring flare efficinecy in the field have led to a number of empirical studies being designed using both full scale and reduced sacale flares with additional instrumentation designed to analyse the flare products. Whilst these provide useful insights in to flare performance cautuion is required to consider how close the experimental design replicates in-field conditions including environmental effects.
