A CEMS is a system that retrieves data on air pollutants emitted by a specific facility. These systems are used to comply with regulations that aim to reduce outdoor air pollution concentrations such as smog, haze, and acid rain.
A full extractive CEMS has several components that work together to monitor stack emissions. The first component is the probe which collects the gas sample and delivers it to the umbilical line or CEMS shelter.
Continuous Emissions Monitoring System
A continuous emissions monitoring system, or CEMS, is a series of components that retrieve data on air pollutants and emissions from a specific source in real time. These systems help facilities comply with EPA regulations such as Title 40, Part 60, and 63 of the Code of Federal Regulations. These regulations aim to reduce outdoor ambient air pollutant concentrations that cause issues like acid rain, haze, and smog and eliminate toxic and carcinogenic gases that pose health problems and ozone-depleting chemicals that harm the environment.
Most power stations and industrial sites that use fossil fuels have CEMS to monitor their smokestack emissions. These systems are critical as they help ensure that the site stays within legal limits and does not release dangerous chemicals into the environment. The systems also provide a record of any problems and when they were fixed to avoid future incidents.
The sampling probe is one of the most important parts of any CEMS system. The probe carries the sample from the flue gas stream to the analyzers. The sample is usually diluted by mixing it with clean, dry air, as pure flue gas can be hot, wet, or sticky depending on the mix of pollutants that are in it. The diluted sample is then sent to a manifold where the analyzers extract it and send it to a data acquisition and handling system (DAHS) to record its FTIR spectrum.
The umbilical tubes that carry the samples to and from the samplers are normally made of Teflon, stainless steel, or another material. The tubes are insulated and wrapped in a jacket to keep the temperature of the sample within its optimal range for analysis. The stinger, which extends from the probe and collects samples from the stack, is made of stainless steel or other materials.
The purpose of this guide is to educate plant technicians on how to properly maintain CEMS systems that are used for regulatory reporting. It reviews the hands-on common-sense techniques that should be used to maintain instrumentation and how these maintenance practices can improve the reliability of monitoring programs by reducing corrective maintenance events and increasing equipment availability.
Continuous Emissions Measurement System
A CEMS is an instrument used to measure the emissions of pollutants and gases emitted from a specific source. This system, regulated by the Environmental Protection Agency (EPA), helps businesses comply with 40 CFR Part 60 and ensure that they are not contributing to smog, acid rain, or other environmental issues.
The CEMS requires several components to operate. The probe is the main component in the system and serves to collect gas samples from a facility’s stack. It is a metal cylinder with an internal diameter that varies depending on EPA regulations. The sample is then drawn to the system’s analyzers through an umbilical.
A CEM must be calibrated on a daily basis. This is achieved by introducing a known concentration of calibration gas, or cal gas, into the system and measuring its accuracy. The results are calculated as a percentage and compared to the CEMS’s zero gas reading. If the calibration error is above a certain percentage, a “bad cal” will be recorded, and the CEMS will need to undergo data substitution for that day until it is brought back into control.
While a CEMS does not require a permit as it does not produce pollution, it must be certified by an AQMD engineer in order to be utilized at a plant. In addition, a facility must follow a set of rules and regulations for installation, operation, maintenance, and testing of the CEMS.
The simplest way to install a CEMS is by having an Environmental Engineer study your plant and identify requirements based on your Permit and current activity. This allows for a tailored solution to be designed that will best meet your site’s needs.
In-situ systems are also available, allowing the analyzers to be installed in the stack. This provides cost savings as well as a less invasive installation process.
Continuous Emissions Monitoring Equipment
A continuous emissions monitoring equipment system measures and records the concentrations of industrial combustion processes’ gases. It is used to help maintain compliance with environmental regulations, such as the US EPA Acid Rain program or local air quality permits. These systems can be a necessity for large facilities and may have high capital and operating costs. However, smaller plants may not have the resources to implement and operate such a complex system.
There are several types of CEMS equipment, but the most common is a full-extractive system that begins with a probe in the stack. The sample then travels through a heated umbilical line, which delivers it to the analyzer. Depending on the type of gas, it can also go through other components, including a Peltier cooler and a sample pump. This process removes moisture and contaminants before the sample enters the analyzer.
After the sample is measured by the analyzer, it can be released back into the stack or sent to the ambient air. This is determined by the protocols set out in the CEMS’s permit. CEMS systems can also be a useful tool to track performance, such as identifying trends in emission rates or peak loads. This data can then be used to adjust equipment or control strategies to reduce overall emissions.
In addition to measuring the concentrations of a wide range of pollutants, some CEMS can also measure oxygen and flow. Flow sensors are typically positioned at least two stack/duct diameters downstream from the point of measurement and upstream of any bends or disruptions in the stack/duct. Oxygen sensors are most commonly zirconia cells, the same technology that stack-test crews use to measure oxygen. On the other hand, Mercury is often measured via an integrated thermal converter which converts all forms of mercury to elemental mercury.
In addition to the probe, umbilical, and various components to deliver a gas sample, a CEMS system can also include control and power wiring for the stack J-box and AC voltage for the pride and umbilical heaters. The umbilical itself is typically a Teflon tubing that is insulated and jacketed to keep the temperature stable.
Continuous Emissions Monitoring Software
A continuous emissions monitoring system (CEMS) is a comprehensive set of components to collect and retrieve air pollution data from industrial combustion processes. CEMS systems are used to ensure that emissions are in compliance with federal ambient air quality standards and EPA regulations. Some of the most common pollutants measured by CEMS include carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxides, hydrocarbons, volatile organic compounds, ozone, and heavy metals such as mercury.
The primary function of a CEMS is to monitor the concentrations of various gases and particulates in a flue gas effluent stream from an emission source. Unlike continuous opacity monitoring systems (COMS) and continuous parametric monitoring systems (CPMS), CEMS extracts a sample of flue gas from the smokestack and analyzes it for the presence of targeted contaminants.
Depending on the location and regulations, a CEMS may be configured to measure either one or multiple gases or particulates. To do this, the system includes a probe inside the smokestack that is heated to extract a small sample of flue gas, a sample line to deliver the sample into the system, an air conditioning system to remove moisture from the sample, and a spectrometer or other gas analysis device that measures the concentrations of the target contaminant(s).
Most CEMS are designed to be as simple as possible for plant personnel to maintain and repair. This is especially important for systems used to meet regulatory reporting requirements, such as the EPA’s Title V program.
A CEMS is composed of a number of components, the most important being the gas analyzers. To ensure the accuracy of these devices, it is recommended that a calibration and maintenance system be installed. This set of tools allows the introduction of calibration gases into the sampling system to verify that the analyzers are accurate.
Some CEMS systems are fully extractive, which means that the probe is inside the stack, collecting the sample and delivering it to the sample line through an umbilical. Depending on the type of gas being analyzed, the sample can then be routed through the spec metering systems or through a full-extractive analyzer cabinet/rack/shelter, where it is conditioned to remove moisture and other contaminants that could interfere with the measurements.
