Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 93

Designing and assembling a cool/dry extractive system is a relatively straightforward process. System components, such as probes, chillers, filters, and pumps are available from many suppliers and can be purchased individually to incorporate into a system design. Alternatively, several suppliers provide modular conditioning systems and modular calibration gas distribution systems that simplify the assembly. An example of a plumbing system for a cool‐dry extractive system is shown in Figure 3‐15.

Figure 3‐15 A cool/dry extractive system for monitoring CO.

The example shows a simple sample probe (stinger) attached to a heated, coarse filter external to the stack. Instrument air is provided for particulate blowback from the filter. Two sets of impingers, cooled with a Peltier cooler, condense moisture from the flue gas sample. The condensed water vapor is removed from the system using peristaltic pumps. A water break‐through detector is incorporated into the line after the first set of impingers and before the sampling pump. The sampling pump transports the dry sample gas to the analyzer after passing through a fine filter. The sample system control panel monitors vacuum, pressures, and flow rates at various points in the system. The control panel may provide for either manual or automatic control of the gas distribution although today most systems are automatically controlled. The system illustrated shows only one gas analyzer, but can be expanded to monitor multiple gases.

Although assembling such components to construct a CEM system may appear straightforward, it is important that the system design be appropriate for the application. If emissions need to be reported on a mass rate basis (kg/hr), if the pollutant is partially soluble in water and the emission limit is 10 ppm instead of 200 ppm, a hot/wet or dilution extractive system might be more appropriate. Other factors such as flue gas temperature, moisture content, and particulate concentration must also be considered in the system design. High temperatures and/or high levels of particulate matter or sticky particulate matter may limit the choice of probes and filters. Similarly, high moisture levels or the presence of acid gases may limit the choice of sample coolers. For challenging applications, experience in system design is important. It is this experience that distinguishes CEM system integrators from each other. It also may make a difference in the success of the system in passing its initial certification test and its success in operating continually without excessive maintenance demands.

Not shown in the diagram are the electrical and communication systems necessary for system control and data utilization. These aspects of the CEM system are the most difficult to accommodate into a CEM system installation because they must be integrated into existing plant networks. Most CEM systems do not stand alone, but are often used for control and optimization of the monitored operating unit. Alarms, emission values, calibration results, and real‐time as well as summary data are typically routed to the plant distributed control system, or separately to the environmental manager or corporate office. All of this takes coordination and collaboration with plant personnel and contractors to assure that CEM system electrical connections and communications are properly integrated into the existing systems of the plant. Compared to these challenges, assembly of monitoring system hardware is the simplest part of the installation program.