More stringent clean air standards require more stringent monitoring of the release of pollutants into the atmosphere. The need is growing for reliable continuous emission monitoring (CEM) capabilities and for documenting the release amount from process plants. Therefore, a CEM system is an integral part of utility and industrial operations. For operators, collecting real-time emission data is the first step to attaining the nationally mandated reduction in SOx and NOx emissions. A company uses CEM to ensure compliance with the Acid Rain Program requirements of the CAAA.

A CEM system is defined by the U.S. EPA in Title 40, Part 60, Appendix B, Performance Specification 2 of the Code of Federation Regulations, as all equipment required to determine a gas concentration or emission rate. The regulation also defines a CEM system as consisting of subsystems that acquire, transport, and condition the sample, determine the concentration of the pollutant, and acquire and record the results. For the measurement of opacity, the specifics of the major subsystems are slightly different but basically the same.

The EPA has codified the standards of performance, equipment specifications, and installation and location specifications for the measurement of opacity, total reduced sulfur (TRS), sulfur dioxide, carbon dioxide, and hydrogen sulfide. These standards include requirements for the data recorder range, relative accuracy, calibration drift and frequency of calibration, test methods, and quarterly and yearly audits. The regulations also require opacity to be measured every 10 sec, the average to be recorded every 6 min, and pollutants to be measured a minimum of one cycle of sampling, analyzing, and data recording every 15 min. The readings from the gas analyzer must agree with a stack sampler to within 20% relative accuracy.

This section provides an overview of the CEM technology, the components of a proper analysis system, and some details in the reliable and accurate operation of CEM.

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