Air Monitoring


Oct 06 2014

Author: John G. Hiss and Jim Mills on behalf of CEM

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Presently, particulate emissions from stacks are measured by sample and weigh methodology, which despite their status as ‘reference methods’ are often slow and sometimes not very repeatable. These methods use comparisons of before and after filter weighing to yield an average particulate concentration for a given sample period. The procedures require a great deal of care to give repeatable results because of the many inherent sources of error such as filter handling, transport, conditioning and weighing. Another disadvantage of gravimetric methods is that useful time history information, describing transients and stack stratification, is not possible.

Virtually all existing continuous stack particulate monitors (opacity, triboelectric, acoustical, and beta attenuation) suffer from potential inaccuracy in that they do not directly weigh particulate and must be periodically calibrated using the above reference methods. An easier, faster, more repeatable ‘reference’ technique would allow for more accurate and frequent calibrations of the present continuous monitors.

Rupprecht and Patashnick Co., Inc. (R&P) has developed a new instrument based on its TEOMâ tapered element oscillating microbalance technology that accurately weighs the particulate mass in real-time. It consists of an inertial mass detector supported at the end of a sampling boom that is placed in the stack, and a control unit remotely located. An umbilical cable interfaces the mass detector with the control unit. The instrument features online direct mass concentration measurement in the stack, and eliminates the need for pre-test and post-test laboratory work. This reduces many of the error sources associated with manual sampling, providing a less labour intensive technique and more representative data. It also enables decisions relating to efficiency of abatement techniques to be taken ‘on the spot’ allowing optimisation in real time.

Because of the increasing emphasis of particulate matter on health issues, and the impending legislation from the European Union, R&P believes that there is a need for an improved monitoring protocol for particulate mass emissions from industrial sources. In answer to this need we have applied our well proven TEOM inertial mass measurement technology, resulting in an instrument that directly measures source particulate mass concentrations in real time. The instrument may be used to perform tests equivalent to many of the current reference standards, as well as short term continuous tests. In addition, because it resolves mass in real time, it provides useful plant process information such as transient particulate mass concentrations during ramped loading, stratification in ducts and control device efficiencies. Another valuable use of the instrument is to calibrate existing continuous monitors such as opacity, triboelectric, acoustic and beta attenuation that, unlike the TEOM system, do not possess a direct relationship with particulate mass.

Continuous emissions monitoring accuracy and frequency of calibration are very important because regulatory action against power plants is often based on continuous emission particulate data. Even a relatively high compliance rate, can result in significant fines to some industries because of potentially high mass emissions represented by being out of compliance for only a small fraction of the time. It is important that the monitoring protocol be accurate, repeatable and inexpensive to ease the burden of demonstration and provide industry with watertight results.


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