Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 94

Many of the problems associated with source‐level extractive systems can be resolved by coupling the extractive and analytical system directly to the stack or duct. This technique minimizes problems associated with reactive, condensable, or adsorbing gases by essentially eliminating the sampling line. The method is especially appropriate for the extraction and measurement of volatile organic compounds. Close‐coupled systems have also been designed for monitoring criteria pollutants (Mandel and Gottlieb 1995), the most recent incorporating modular gas sensors with internal microprocessor control to regulate temperature, flows, and calibration sequencing (Jahnke 1997). A typical close‐coupled system is illustrated in Figure 3‐16.

Close‐coupled systems allow the use of analytical techniques that may need a more controlled sampling volume than is afforded in in‐situ measurements. By measuring the sample directly outside of the stack, sampling conditions can be controlled, while minimizing reactivity and sample line problems. Close‐coupled systems can be designed as either cool/dry or hot/wet systems.

Figure 3‐16 A close‐coupled extractive systems.

Costs of such systems are lower due to the elimination of the sampling line and the use of temperature‐controlled cabinets, which removes the need for a CEM shelter. However, challenges of the ambient environment, such as lightning, rain, ice, or extremes in temperature, may compromise its operation unless it is designed to accommodate such varying conditions.