CEMS typically consist of analyzers to measure gas concentrations within the stream, equipment to direct a sample of that gas stream to the analyzers if they are remote, equipment to condition the sample gas by removing water and other components that could interfere with the reading, pneumatic plumbing with valves that can be controlled by a PLC to route the sample gas to and away from the analyzers, a calibration and maintenance system that allows for the injection of calibration gases into the sample line, and a Data Acquisition and Handling System (DAHS) that collects and stores each data point and can perform necessary calculations required to get total mass emissions.
They can continuously collect, record and report emissions data for process monitoring and/or for compliance purposes.
Typical monitored emissions include: sulfur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, hydrogen chloride, airborne particulate matter, mercury, volatile organic compounds, and oxygen.
CEM systems can also measure air flow, flue gas opacity and moisture.
Facilities that combust fossil fuels often use a dilution-extractive probe to dilute the sample with clean, dry air to a ratio typically between 50:1 to 200:1, but usually 100:1.
Some commonly used techniques include: infrared and ultraviolet adsorption, chemiluminescence, fluorescence and beta ray absorption.
The amount of current required to move the mirror back to center is proportional to the O2 concentration.
An internal quality assurance check is achieved by daily introduction of a certified concentration of gas to the sample probe.
The data substitution method is generally not advantageous so it is critical to get the CEMS back into control as soon as possible.
In power stations affected by the Acid Rain Program, annual (or bi-annual) certification of the system must be performed by an independent firm.
In such cases, a facility will install non-EPA compliant analysis equipment at the emissions point.