Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 13

A CEM system is actually composed of several subsystems: the sampling interface, the gas analyzer(s), and the data acquisition/controller system. The sampling interface is a subsystem that either transports or separates the flue gas from the analyzer. CEM systems are characterized in terms of the design of this interface. In extractive systems, the interface consists of a system that extracts and conditions the gas before entering the analyzer. In in‐situ systems, the interface is simpler, composed of flanges designed to align or support the monitor and blower systems used to minimize interference from particulate matter. The data acquisition/controller subsystem is integral to the proper operation of the total system. The control system controls automatic functions of the system, such as calibration, probe purging, and alarming. The data acquisition system receives the analyzer data, converts it into appropriate units, records it, and provides reports for both internal and external use. Today, CEM data acquisition systems are frequently networked to engineering, corporate, and even agency offices, where the data are used for a variety of operational and management purposes.

Both extractive and in‐situ systems operate in the source environment and must operate continually under changing stack and ambient conditions. Although this is not necessarily a problem for properly designed and maintained systems, alternative approaches have been sought. One of these approaches, remote sensing, has been applied with limited success, but has not been used widely. Another alternative, the correlation of stack emissions to process parameter data, has led to computerized “predictive emission monitoring systems” or PEMS. These systems have been employed successfully in a number of applications and have considerable potential if used in tandem with extractive or in‐situ monitoring hardware. The monitoring methods discussed earlier are classified in Figure 1‐2 and discussed further in the following sections.