Hg emissions can be monitored via continuous emissions monitoring systems (Hg CEMS) or a less complex sorbent-based monitoring system (STMS) approach. There are several sorbent-based monitoring systems available that are based on similar operating principles. Clean Air Engineering’s monitoring system, the MET-80, consists of the following main components:
- Sampling probe housing the actual sampling media (sorbent traps) in a temperature controlled compartment
- Multiple-zone heated sampling line that is integrated with the probe to reduce the number of connections
- Gas conditioning module with acid mist filters removing flue gas moisture and preventing acid mist breakthrough
- Condensate retrieval module facilitating a direct measurement approach for the sample gas moisture content
- Gas sampling and the control module governing the instrument operation, data handling and network connectivity
The picture above shows two typical layouts of sorbent trap based monitoring equipment installations. Sorbent trap monitoring systems were traditionally installed at stack platforms in close vicinity to the sampling port and housed in a rugged and environmentally controlled cabinet (figure on right). As an alternative, these systems can also be installed at the bottom of the stack with an extended heated sample line connecting the sampling system to the sampling probe at the stack platform (figure on left). Sampling line lengths at these installations can typically extend up to several hundred feet. In case of a remote installation, the system usually includes distributed control equipment at the top of the stack connected to the main control system via fiber-optic cabling. Network connectivity to the plant, in either configuration, is achieved via Ethernet-based Modbus TCP.
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