Continuous emission monitoring systems measure flue gas composition in industrial settings like boiler stacks, thermal oxidizers, and exhausts. The system is designed to help companies meet strict environmental regulations regarding air quality, pollution, and climate change.

A CEMS typically consists of the following components: analyzers to measure pollutants in the gas stream, a sampling system to extract and transport the sample to the analyzers, and a data acquisition and handling system to record and calculate contaminants concentration.

What is a CEMS?

A CEMS, or continuous emission monitoring system, is a comprehensive package of hardware and software that provides measurement and reporting on air pollutants, such as carbon monoxide, nitrogen oxides, sulfur dioxide, hydrogen chloride, volatile organic compounds, airborne particulate matter, air flow rate, and flue gas opacity. The specific contaminants monitored will depend upon the site in question and are typically dictated by regulatory requirements.

A typical system includes a sampling probe, sample line (umbilical), a gas conditioning system that removes water and other contaminants that could interfere with the analysis instrumentation, a data acquisition system for recording measurements, and a set of emissions analyzers that reflect the type of gases being measured. A CEMS also includes an internal quality assurance (IQA) program, which involves daily introduction of calibration gases that are known to be within the specified performance specifications, and a comparison of those readings with the results from the CEMS to demonstrate its accuracy.

The QA process is critical to maintaining the proper operation of the system. The data acquired by a CEMS must be reviewed regularly by both the company and regulatory authorities, and any errors must be rectified immediately. Having the correct tools in place to do so is essential, and this is where a good data management solution becomes crucial.

This kind of software enables plant owners to validate environmental data and create reports both for their own use and for regulators, providing a robust and accurate record of any issues that may occur. The record will also highlight the precise moment any problems occurred and again when they were resolved, enabling the site owner to provide accurate noncompliance notifications to regulators as required.

A good CEMS should be as easy as possible to operate, and it is important that the equipment is located close enough to the source so that readings are not affected by factors such as weather conditions. The design of a CEMS should also consider material compatibility, onsite conditions, minimum maintenance, and redundancy to ensure long-term function and reliability. The system should be designed to meet EPA requirements and those of local air districts, and it should be compatible with any future changes in regulations.

CEMS Installation

Many EPA-regulated sites must install CEMS to stay compliant with certain regulations. A good CEMS can make it far easier to prove compliance, and it can help a plant take steps to improve efficiency. It can also be invaluable in the event that a problem arises, as it may be able to provide minute-by-minute readings that show the exact moment any pollution occurred and when that contamination was cleared up.

The main types of pollutants monitored by a CEMS are carbon monoxide, nitrogen oxides, sulfur dioxide, particulate matter, and hydrogen chloride. A typical system will also monitor the concentrations of a few volatile organic compounds and other gases such as chlorine, ammonia, and hydrogen fluoride. The specific parameters measured will depend on the site and its industry, with most systems being built around a specific set of requirements defined by the EPA (under 40 CFR Part 60 Appendix F) or a local air district.

Each system is designed and assembled by a systems integrator and is customized for the particular facility. There are nearly limitless combinations of parameters and analyzers, and the exact system will differ from one facility to the next. This customization allows the system to meet the EPA’s performance specifications and any additional requirements that the air district might have.

A full-extractive CEMS will usually consist of a sample probe at the top of the stack that draws a sample from the gas stream, a gas cabinet or shelter where the analyzers are located to protect them from weather and other contaminants, a piping network with pneumatic plumbing that a PLC can control to route the sample to and away from the analyzers, equipment to condition the sample gas by removing water and other components that could interfere with the measurements, and a data acquisition and handling system to store the data points and perform calculations to determine the total mass emissions.

There are a number of advantages to installing a CEMS at a plant, and it is worth considering whether the cost and complexity of the system can be justified based on its potential to improve efficiency. The data provided by the system can also be used to identify problems in a plant and make adjustments that will decrease pollution levels or increase process output.

CEMS Maintenance

As we all know, pollutants are detrimental to our environment and are therefore regulated by government agencies. This means that industrial sites need to carefully monitor their emissions levels to ensure they do not exceed the set limit. This is why continuous emission monitoring systems, or CEMS, are an essential tool for industrial sites to use.

In order to keep your CEMS functioning at an optimal level, you must perform regular maintenance and calibrations on the system. These routine tasks will help ensure that your system is accurate and will provide you with reliable data. Depending on your system design, the types of maintenance and calibrations that you need to carry out will vary.

For example, if your CEMS uses UV light to measure the sample gas, you will need to replace the ultraviolet lamp periodically, usually every 12 months. This will keep the light from becoming contaminated with water vapor and carbon dioxide, which can cause false readings and inaccurate measurements. Similarly, you will need to change the calibration tube regularly as this can become blocked by corrosion or contamination. This will prevent the calibration from being invalid and will allow for a more accurate reading of your plant’s emissions levels.

To calibrate your CEMS, you will need to introduce a known concentration of gas into the system. The sample probe will then be compared to this, and a calibration error percentage calculated. This percentage is used to determine whether your CEMS is within the specified limits. If the calibration error is higher than the performance specification limit, then your system will need to be brought back into compliance using data substitution until the calibration error is within the specified limits.

The final component of a CEMS is the data acquisition system (DAS). This will collect the results from all of the analyzers, perform the calculations, highlight any exceedances, and much more. The DAS will use a data controller or PLC to bring in all of the information from the analyzers. ESC Spectrum offers three different data acquisition systems: StackVision, Prism, and CEMDAS.

CEMS Reporting

The data gathered by a CEMS must be reported to authorities on a regular basis. This is why it is essential that the system is highly accurate and easy to interpret by plant staff. In addition to being able to report to the government, an accurate CEMS can help site owners optimize their processes and prevent unnecessary downtime due to unforeseen issues.

For this reason, a CEMS must be designed to provide reliable results even when the facility experiences a system failure. The system must also be able to track down exactly when the problem occurred and when it was corrected so that the correct measurements can be made in the future.

An important feature of a CEMS is that it can monitor a wide range of pollutants, including carbon monoxide, hydrogen chloride, particulate matter, and nitrogen oxides. These are all harmful chemicals that can cause damage to the environment and human health, so it is vital to know what levels they are releasing into the air at any given time.

CEMS uses a sample probe to draw a gas sample from the effluent stream and transfer it to an analyzer. The probe is usually surrounded by a dilution system that can dilute the flue gas with clean, dry air to remove any contaminants that may interfere with the analyzer’s reading. Once the sample is diluted, it passes through a manifold, where it can be extracted by several analyzers to measure specific pollutant concentrations. A data acquisition and handling system then records the results from each of the analyzers.

Regardless of what pollutants are being measured, all CEMS systems will include a PLC to control the analyzers and sample probe, equipment to direct the gas stream to the analyzers if it is not at the same location, a dilution system that can inject calibration gases into the sampling line and pneumatic plumbing with valves that a PLC can control to route the gas to and from the analyzers. In addition, a PEMS will need a data acquisition and handling system that can record each measurement and perform the necessary calculations to determine total mass emissions.


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