Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 112

The design of an extractive system involves considering more than piecing together a probe, pump, and a conditioning or dilution system. The task is more complex since decisions must be made on at least the following minimum components:

1 Sample probe: construction and composition

2 Probe blowback: design and frequency

3 Sample line: composition, length, and diameter

4 Valves and fittings: construction and composition

5 Pressure and vacuum meters: quality

6 Moisture conditioning system: refrigerated, dilution, capacity, design, and construction

7 Filters: coarse, fine, or coalescing

8 Pumps: capacity, type, and quality

9 CEM shelters or cabinets: location, shelter HVAC requirements, enclosed space safety considerations, temperature stability

10 System controller: programmable logic controllers, datalogger, or microprocessor to sequence and control automatic functions

11 Electrical support: fuses, circuit breakers, regulating equipment, and uninterruptible power supplies (UPS)

12 Calibration gases: location, injection point, tubing requirements, regulators, and manifold, certified gases as appropriate, cylinder gas cabinet or weather overhang, cabinet heater/air conditioning as appropriate

13 Automatic calibration system: valves, injection sequencing, interconnections with the DAS and/or DCS

Issues associated with many of these components are discussed in further detail by McNulty et al. (1974) and Podlenski et al. (1984). The resistance of different materials to acid gases, flow rate, condensation requirements is particularly addressed.

Extractive CEM systems are most commonly housed in a temperature‐controlled room or a modular shelter. This adds significantly to the expense of a CEM system, but it does provide a centralized location to conduct system operations. To reduce costs, system manufacturers can also incorporate systems in temperature‐controlled National Electrical Manufacturers Association (NEMA) enclosures, a common practice in process monitoring applications. Alternatively, by close‐coupling the system to the stack, costs associated with sampling line and shelter are essentially eliminated.

To construct a working extractive system that delivers a representative sample to the gas analyzers is not something that can be done without experience, requiring an understanding of the interaction of gases, temperature, and materials. This experience is most often gained through trial and error and may require time to acquire.