|Abstract Title:||Opacity Monitoring at Very Low Levels|
|Session Choice:||Monitoring Techniques: Particulate|
|Presenter Name:||Mr Derek Stuart|
Abstract Information :
Opacity monitoring remains the most widely-used method for measuring emissions of smoke and particulate matter from stacks. Although more sensitive techniques are available, opacity monitors have a number of features which make them especially attractive, including the ability to calibrate the analyser using a traceable neutral density filter. Opacity measurements can also be compared to a visual estimate made using the Ringelmann method, giving a simple remote check of the indicated value.
Traditionally, opacity monitors have been used only in applications where the emission limit value is at least 10% opacity. However, there have been a number of applications in electric arc furnaces and elsewhere where emission limit values of 6% or even 3% opacity have been applied. These values present serious challenges even to the latest generation of opacity monitors.
US Federal law requires all opacity monitors to comply with ASTM D6216. The specification limits for the various measurement uncertainties given in D6216 set a minimum uncertainty budget. However, the standard omits a number of significant sources of uncertainty which cannot readily be evaluated in the laboratory and so tends to underestimate the actual uncertainty.
A full understanding of opacity measurement requires an accurate determination of the sources of uncertainty and their contribution to the overall uncertainty budget. This paper will discuss these sources and what can be done to minimize their contribution.