What does a typical CEMS consist of?

There are a variety of different sampling and analyzing methods and protocols when it comes to installing a CEMS at regulated industrial facilities. The design mandates by owners and federal and local authorities needs to be taken into accounts during the design phase for the required monitoring of the pollutants in the stack flue gas.

• Although the exact components of a CEMS can vary from plant to plant and depending on the properties of the stack flue gas and which pollutants and diluents are to be monitored, a typical CEMS consists of the following elements: A Sample Probe, which is responsible for extracting the gas sample from the flue gas stream. There are 2 typical probe types available, dilution probe and extraction probe.
• A Sample Line, through which the sample is transported to the sample conditioning and analyzing hardware. The sample line is heated above the sample dew point to avoid any condensation that will affect the sample integrity.
• Sample Conditioning System (SCS), which conditions the gas sample as required for the analyzers. The SCS typically contains a sample pump to draw the sample from the stack, sample chiller to remove moisture, and any other instruments and components such as moisture sensor, filter, pressure switch, flow switch, pressure regulators, valves, etc. as needed for regulating the sample flow rate and distributing of the sample to the analyzers. The SCS also includes a provision for selecting and routing the calibration gasses.
• Calibration Gasses in cylinders, which are routed to the probe or directly to the gas analyzers according to the quality assurance protocol such as daily calibration error check.
• A gas analyzer (or gas analyzers), which measure the concentrations of monitored pollutants and diluents in the gas sample.
• The entire system is typically controlled by a programmable logic controller (PLC). The PLC controls the selecting and routing of the calibration gasses for the ongoing certification, monitor the system operating status,  trigger the system fault alarms, and gather data from the analyzers and pass them to DAS below.
• Stack Flow Monitoring System, which measures the stack flue gas rate for calculating the heat input rate and NOx, SO₂ and/or CO₂ mass emissions.
• A Data Acquisition and Handling System (DAS), which is a centralized computer system that can collect, store, and analyze the data, including the ability to perform calculations of the pollutant emissions to be reported in an electronic format to EPA and local air quality management agency.

While all these analytical equipment and components may not be present and in operation at every regulated site, some of them such as sample probe, sample line, sample conditioning system, and analyzers are mandatory for all facilities and for all pollutants. Additionally, DAS is also a legal requirement in many sites and takes the flue gas flow rate data to convert the concentration measures to the required reporting format such as tons per hour.