What’s in the air for continuous emissions monitoring?

More attention to mercury and increased acceptance of predictive approaches is emerging. Such monitoring not only can keep plants on the right side of regulators but also can help provide insights for optimizing operation of equipment.

By Mike Spear, editor at large

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Gaining regulatory acceptance

Although not yet universally recognized by regulatory authorities, PEMS’s are accepted for compliance with the EPA’s 40 CFR Parts 60/75 subject to certification requirements that call for either a three- or 30-day test period depending upon application. To further assuage EPA concerns, Pavilion has incorporated a real-time sensor validation system and daily electronic data assessment tests of the PEMS to verify its accuracy.

Meanwhile, CMC Solutions, Wixom, Mich., has gained EPA certification for its SmartCEM PEMS, following trials at two sites operating large-frame gas turbines rated at 160 MW and 80 MW. CMC says these 2005 certifications were the first of their kind in the U.S., each allowing the source site to operate the turbine and PEMS without a CEMS as a non-peaking unit under the regulation.

Another company that started out like Pavilion by developing neural-network-based solutions is Manchester, U.K.-based Cogsys. It has now “evolved into a rotating machinery emissions monitoring company,” says business development manager Chris Dagnall. Part of its portfolio of software solutions is the alert performance and emissions monitoring system, a PEMS in all but name that is aimed mainly at gas turbine applications both on- and offshore in the oil-and- gas and petrochemical industries.

“Our system sits on top of the DCS (distributed control system),” explains Dagnall, “which is very good at bringing in information from all parts of the plant but not so good at generating reports and doing the calculations to meet regulatory requirements.” The alert system has been available through Cogsys’ sister companies Advantica and Stoner Software, Harrisburg, Pa., but Dagnall says Cogsys “is now working with rotating machinery partners in the U.S. to provide solutions.”

Some turbine manufacturers now treat PEMS’s almost as standard equipment. GE Energy, Atlanta, Ga., for example, added PEMS to its “Smart Services” portfolio of turbine tools for remote monitoring and diagnostics and remote NOx tuning. The GE PEMS offering relies on a “first principles” rather than a statistical approach, employing equations that represent various mass and energy balances and thermokinetic reactions in the combustion process. This provides a generalized model that then is tuned to the specific turbine/fuel combination being measured.

Weel & Sandvig, Lyngby, Denmark, has been installing PEMS’s on gas turbines since 1998, with its first installation at an industrial combined-heat-and-power plant. As with most other turbine PEMS’s, the WS.GT-PEMS is easily extended to also provide performance monitoring of the turbine as an aid to optimizing its operation. And, of course, operating plants and equipment at their optimum levels goes a long way towards ensuring that sites stay on the right side of the regulators — leaving the CEMS and PEMS to provide the evidence of that good operation.

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