SOURCE TESTING ASSOCIATION I Annual Guide 2021
As with any measurement system, regular calibration is required to ensure the CEMS is performing as expected. Even before the calibration procedure is conducted, the UK Environment Agency (EA) recommends checking its functionality and verifying its performance. Typical recommended performance checks include a leak test, the CEMS response time, linearity, interference, zero and span drift and comparison with a reference method.
The standard governing quality assurance of permanently installed CEMS is EN 14181, which applies particularly to large combustion plant and waste incineration facilities. It may also apply to certain installations producing or using organic solvents and titanium dioxide.
The EA also cites certain performance criteria for CEMS.[2] For example, with the parameter for availability, a CEMS that is measuring gases other than oxygen must demonstrate an availability equal to or greater than 95 percent.
For example, the most recent Chinese ‘Blue Sky’ legislation demands the measurement of particulate matter, carbon monoxide, chlorine, oxides of nitrogen, sulfur dioxide, hydrogen chloride, and ammonia, amongst others. Most of these can be monitored with modern FTIR gas analysers with appropriate data processing software. Systems that can measure multiple components reduce the cost of ownership, with fewer detection elements and less equipment to maintain and calibrate.
Calibration is a signifi cant cost for CEMS operators, accounting for some 24 percent of operating expenses. It is needed for all types of gas analysers but the frequency of calibration can be much higher in some types than for others, while the effort and costs involved can also vary widely depending on the approach. For example, the cost of calibration gas cylinders is often underestimated, while the US EPA regulations demand daily calibration.
One approach to reducing this cost, adopted by ABB, is the use of internal gas fi lled cells. Filled with a test gas of known concentration and sealed to prevent any permeation of the gas to the outside atmosphere, these offer a stable sample against which to test instrumentation performance. They are also accepted as a viable alternative to fl owing test gas, meeting the requirements of both EN 14181 and US EPA 40 CFR part 60. Using internal calibration cells can reduce calibration costs by up to 95 percent.
Another alternative to test gas, particularly suited to FTIR based CEMS, is that of internal validation cells, which use fi lms or cells for all FTIR components. Designed to conduct automated drift checks, these cells rotate into the optical path to check precision and drift of all FTIR components.
Digital solutions are also making major inroads in the world of CEMS. For example, ABB offers its Ability range of digital solutions that allow CEMS operators to control compliance costs, reduce complexity and make more cost-effective use of their CAPEX investments.
Breaches of environmental law can lead to the EA closing or suspending the business until the breach has been rectifi ed – it can also order the offending organization to clean up any contamination resulting from the incident. Serious incidents or willfully negligent companies can expect serious penalties, including large fi nes and the imprisonment of offending individuals. They can also lead to directors being banned from taking up further directorial positions. The EA will also publish the names of offenders, bringing the potential for signifi cant reputational damage.
Trends and expectations
In the past, systems that monitored a single gas were popular with many CEMS users, in the belief that these were less complex than systems that can measure multiple gases and so less prone to failure. With the requirement for more plants to monitor their gas emissions and the need to monitor a greater range of gases, many users are looking at FTIR spectroscopy, a technique that can measure multiple gases without the need for frequent calibration.
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These innovations include remote assistance. Allowing rapid solving of problems, this solution cuts costs and reduces both downtime and the training needs of staff. Remote Insights is a solution that makes maintenance safer and more effective, while dynamic QR Codes allow the user to share instrumentation with ABB to enable remote trouble shooting.
There is a growing awareness of the need for gas emissions monitoring, with the result that legislation is being tightened up and extended across the globe. Yet with new technologies that are more capable and accurate than ever and the support of vendors offering convenient digital services to keep CEMS operational, keeping your emissions within limits has never been easier.
References
[1]
https://assets.publishing.service.gov.uk/government/uploads/system/ uploads/attachment_data/fi le/730225/TGN_M20_Quality_assurance_of_ continuous_emission_monitoring_systems.pdf
[2]
https://assets.publishing.service.gov.uk/government/uploads/system/ uploads/attachment_data/fi le/725557/Performance_Standards_and_ Test_Procedures_for_Continuous_Emission_Monitoring_Systems.pdf
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