Particulate emissions by extractive sampling

Abstract

In contrast to the measurement of gaseous emissions which can be routinely undertaken with an accuracy of a few percent, the measurement of particulate emissions is far more difficult. This arises primarily from the maldistribution of particle concentration within the duct or chimney coupled to the non-uniformity of the gas velocity. It is also partly due to sampling difficulties. Variations in the particle concentration from point to point within a duct or flue may arise for several reasons. These include incomplete mixing downstream of a junction if the two gas streams bear different particle loads, or incomplete mixing downstream of a point where air has leaked into the process gas stream. Since the air is likely to be relatively cool this problem should be detected during the preliminary probing of the gas temperature which is a normal part of the testing procedure. It may then be necessary to seal the leak or to move the sampling position. The other factors which upset the uniformity of the particle distribution are sedimentation and inertial effects when the gas passes round bends or obstacles to the flow. These factors are discussed in the next section.