CEMS — continuous emissions monitoring

A continuous emissions monitoring system exists to answer one question, repeatedly, in a form a regulator will accept: what came out of the stack, and can you prove it. The analysers do the measuring. Everything that turns those readings into a defensible record is the system around them — and that is the part we build.

What the system has to get right

RequirementWhy it is harder than it looks
ContinuityA gap in the record is treated as a failure to monitor, not as missing data. Availability targets apply to the data, not just to the hardware
ValidityA reading taken while the analyser is calibrating, faulted or out of range is not a valid emission reading and must not be averaged in as one
TraceabilityEvery reported figure has to trace back to a raw measurement and to the analyser state at that moment
Reporting formatThe regulator specifies averaging period, units and file format. Having the data is not the same as being able to report it

Data validity handling

This is where home-grown emissions reporting usually falls apart. Raw analyser output is not emissions data until the system knows what state the analyser was in.

StateHow it is treated
Normal operationRecorded as valid
Zero and span calibrationPeriod flagged and excluded from emission averages; drift recorded
Fault or out of servicePeriod flagged; substitution rules applied only where the regulator permits them
Out of rangeRecorded with the exceedance marked rather than clipped
Plant not operatingDistinguished from monitoring downtime — for compliance these are not the same thing

Where it sits

InterfacePurpose
Analyser shelterReads the analysers and their status contacts
Plant control systemProcess state, so emissions can be attributed to operating condition
HistorianLong-term retention alongside the rest of the plant record
Reporting outputFiles in the format and on the cycle the authority requires

What we take responsibility for

IncludedNot included
Acquisition, validation, averaging, retention and reportingSupply and certification of the analysers themselves
Analyser shelter integration and cabinet buildStack sampling system design and probe installation
Interfacing to the control system and historianRegulatory approval of the installation

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The useful conversation starts with which authority you report to, what analysers are installed, and how that data becomes a report today. Contact us.

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