A continuous emission monitoring system (CEMS) is used to continuously measure and monitor gases released from combustion and industrial processes. A CEMS emissions monitoring system can measure gases such as oxygen (O₂), carbon monoxide (CO), and carbon dioxide (CO₂), providing valuable information about combustion performance and emissions.
Emissions monitoring systems are also used to help facilities monitor compliance with applicable air-quality regulations and permitted emission limits. Depending on the application, a CEMS monitoring system can continuously collect, record, and report emissions data for regulatory compliance, process monitoring, combustion optimization, and environmental reporting.
What Does a CEMS Emission Monitoring System Measure?
A CEMS emission monitoring system can be configured to measure different gases and other parameters depending on the industrial process and regulatory requirements. Commonly monitored emissions include:
Sulfur dioxide (SO₂)
Nitrogen oxides (NOₓ)
Carbon monoxide (CO)
Carbon dioxide (CO₂)
Oxygen (O₂)
Hydrogen chloride (HCl)
Hydrogen sulfide (H₂S)
Mercury
Volatile organic compounds (VOCs)
Particulate matter
Some emissions monitoring systems can also measure parameters such as stack gas flow, moisture, temperature, and opacity. The specific measurements required depend on the facility, combustion process, pollutants being regulated, and applicable permit requirements.
CEMS Monitoring for Industrial Emissions
CEMS monitoring systems are commonly used in industrial facilities where continuous information about stack or process emissions is required. Rather than taking occasional manual measurements, a continuous emission monitoring system can collect data at regular intervals and maintain an ongoing record of emissions.
A typical CEMS consists of a sampling probe, filter, sample line or umbilical, gas conditioning system, calibration gas system, and one or more gas analyzers. Together, these components allow the system to collect a representative gas sample, prepare it for analysis, measure the required gases, and record the resulting data.
A Data Acquisition and Handling System (DAHS) can collect and store measurements from the analyzers and perform calculations required for emissions reporting and monitoring.
Hydrogen Sulfide (H₂S) in Emissions Monitoring
Hydrogen sulfide (H₂S) is an important gas to consider in certain industrial emissions monitoring systems. H₂S is a colorless gas with a characteristic odor and can be associated with processes involving sulfur-containing fuels, biogas, wastewater treatment, petroleum processing, and other industrial applications.
Monitoring H₂S can help facilities evaluate process conditions, identify potential emissions, and maintain appropriate environmental and workplace safety controls. The measurement of H₂S may be particularly important in applications where sulfur compounds are present in the process gas or exhaust stream.
The appropriate H₂S analyzer and measurement method depend on the concentration range, gas composition, temperature, moisture, and other characteristics of the application.
How Does a Continuous Emission Monitoring System Work?
A typical continuous emission monitoring system removes a small sample of exhaust or process gas through a sampling probe. A pump transports the sample through the CEMS for conditioning and analysis.
Facilities that combust fossil fuels or other materials may use extractive sampling systems. Depending on the application, the sample may be diluted with clean, dry air to reduce the effects of high temperatures, moisture, and potentially interfering components.
After the sample has been conditioned, it travels through the sample line to the gas analyzers. Different analyzers use different measurement technologies depending on the gas being measured and the required accuracy.
Gas Analysis Technologies Used in CEMS
A CEMS monitoring system can use several different analytical technologies to measure gas concentrations. The appropriate technology depends on the target gas and the requirements of the application.
Common gas-analysis methods include infrared absorption, ultraviolet absorption, chemiluminescence, fluorescence, and beta-ray absorption for certain measurements.
Infrared analysis, for example, can be used for gases that absorb infrared radiation, while chemiluminescence is commonly associated with nitrogen oxide measurements. Different technologies offer different advantages depending on the gases being monitored and the conditions of the sample stream.
CEMS Emission Sampling and Gas Conditioning
Accurate CEMS emissions monitoring depends on obtaining a representative sample and delivering it to the analyzer without changing its composition. The sampling system therefore plays an important role in overall measurement performance.
A CEMS may include filters, pumps, heated sample lines, moisture removal, dilution equipment, and other conditioning components. These components help protect the analyzers and reduce potential interference from water vapor, particulates, condensation, or other substances in the exhaust gas.
Proper sample conditioning is especially important when monitoring hot, wet, corrosive, or particulate-laden exhaust streams.
Data Acquisition and Emissions Reporting
The data acquisition and handling system is an important part of an emissions monitoring system. It receives measurement information from the gas analyzers and stores the resulting data for analysis and reporting.
Depending on the configuration, CEMS software can calculate emissions concentrations, correct measurements based on parameters such as oxygen or moisture, track operating conditions, and generate reports.
Continuous data collection allows operators to identify changes in emissions and combustion performance while also maintaining records needed for applicable regulatory requirements.
Choosing an Emissions Monitoring System
Selecting the right emissions monitoring system depends on the application, gases being measured, required measurement ranges, sampling conditions, and regulatory requirements. A system designed for a relatively clean combustion exhaust may have very different requirements from one used with a hot, wet, corrosive, or high-particulate process stream.
MRU Instruments offers gas analysis and emissions measurement equipment for a variety of industrial applications. When evaluating a CEMS emission monitoring solution, consider the gases that need to be measured, the expected concentrations, sample conditions, required accuracy, and whether continuous or periodic measurements are appropriate.
A properly configured continuous emission monitoring system can provide valuable information for combustion control, process optimization, environmental monitoring, and emissions compliance.
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