Continuous emission monitoring—sometimes abbreviated to CEM—is a requirement established by the US Environmental Protection Agency (EPA) to ensure compliance with the appropriate emission standards. It is not mandated for all stack emission monitoring applications, but it is necessary for companies that need to demonstrate continual compliance or to determine exceedances of standards according to specific EPA limitations.

But what are continuous emission monitoring systems (CEMS), how do they work, and what methods are available for validating CEMS results?

What is Stack Emission Monitoring?

Stack emission monitoring is the process of monitoring the composition of the air exhausted from a chimney stack in industrial settings. Emissions discharged from boiler stacks, exhausts, thermal oxidizers, and so on, typically contain pollutant gases and particulates which can have a detrimental impact on local air quality and contribute to the greenhouse effect.

Consequently, strict controls are established by various regional and international governing bodies to limit hazardous emissions. Some processes can satisfy regulatory requirements through periodic testing, but others require continuous emission monitoring.

How Does Continuous Emission Monitoring Work?

A typical continuous emission monitoring system comprises several interconnected parts:

  • A sample probe
  • A sample line
  • A conditioning system
  • A gas analyser, or multiple gas analysers

Various methods of operation exist, with different protocols for sampling, conditioning, and analyzing flue gases, but most continuous emission monitoring systems use a probe and pump to sample gases directly from a flue. Consequently, the gas stream tends to be hot—and in many cases extremely humid, sticky, and loaded with pollutants that may be harmful to the sensitive gas sensing equipment. The gas is usually conditioned with clean, dry air before it is transferred via the sample line to the analyzer/s. Some CEMCSs sample the gas stream directly, without conditioning, but even direct continuous emission monitoring systems filter out hazardous particulate matter.

Once sampled and conditioned, the gas stream can be analyzed using a choice of techniques. A data acquisition system collects the signal outputs from each analyser, the strength of each signal indicating the relative concentration of specific analytes. Continuous emission monitoring systems thus provide a spectrum of gas/pollutant composition over time, allowing businesses to validate stack emissions continuously according to the relevant regulations. Additionally, flue gas composition can indicate process efficiency, particularly for combustion processes. Continuous emission monitoring can, therefore, be crucial to ongoing quality assurance and control (QA/QC).

Interested in CEMCS Monitoring and Calibration?

Continuous emission monitoring systems determine gas/particulate concentration as a function of relative signal intensity. The output signals of CEM gas analysers would largely be meaningless without the use of some internal—or certified—calibration standard, and a robust QA check.

At Environics, we specialize in the development of CEM calibration systems (CEMCS) that meet or exceed the performance requirements of EPA 40 CFR Part 51 Method 205 Appendix M. All our systems are bespoke built to custom specifications, using mass flow controllers to enable users to dilute high concentration cylinders to low level gas blends with typical ratios as low as 10,000:1 and increased ranges available. Want to learn more? Simply contact a member of the Environics team today.