MET-80 Hangs Tough Amidst the Winds of Regulatory Change

The U.S. EPA regulatory requirements for mercury (Hg) monitoring effectively went into limbo after the Washington D. C. District Court of Appeals vacated the Clean Air Mercury Rule on February 8, 2008. This ruling was mandated on March 14, 2008, but the mandate was subsequently appealed on March 24, 2008. The outcome of this appeal is still pending.

If the ruling to vacate the CAMR stands, the federal requirements for continuous mercury monitoring under 40 CFR Part 75 may disappear. However, most experts agree that control of mercury emissions from coal-fired power plants will remain a high priority both nationally and world-wide. Any plan to curb power plant Hg emissions will require the accurate monitoring of the Hg content in combustion flue gas streams.

Although future monitoring requirements may change slightly from those currently specified, the overall technological requirements and challenges of mercury monitoring remain essentially the same. Appendix K sorbent trap monitoring remains a viable option for facilities that are required to monitor mercury emissions, regardless of the underlying regulatory driver. CleanAir's MET-80 system, with its design based on maximum versatility over a wide range of installation requirements, will continue to lead this charge.

A Brief Introduction to the MET-80 Sorbent Trap Monitoring Systems

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.