Source Testing Association sub groups – A collaborative effort between regulators, accredited test laboratories, process operators and instrument suppliers.
Paul Firth, Tarmac and Process Operator Offi cer of the STA
In the last 25 Years the testing standards, quality of testing, analysis and reporting, CEMS equipment and support have improved signifi cantly, aided by collaborative work at the STA, with input from process operators, regulators, equipment suppliers and test laboratories.
In recent Years with the release of a number of Industrial Emissions Directive, Best Available Techniques (BAT) Reference Documents, a signifi cant number of emission limits, associated with BAT are now getting close to or undercutting measurement uncertainty – unrealistic emission limit values presents a signifi cant risk and disproportionate challenge for both operators and regulators, especially when in some instances current technology does not exist to demonstrate that compliance is being maintained and this remains a current and present day problem.
Lower emission limits not only present a signifi cant measurement challenge, with new lower emission limit values, they also present a signifi cant risk to EN 14181 calibrations, increasing the risk of failure. Both Hydrogen Chloride (HCI) and Particulate Matter (PM) are two components that are currently causing concern to regulators, test organisations, process operators and equipment suppliers.
Hydrogen chloride is well known to be a diffi cult gas to measure accurately, primarily because it is diffi cult to transport through sample lines. The Source Testing Association has also received feedback that the EN 14181 calibration of CEM systems for HCI
10 2
has been problematic. Experience from a number of operator sites and test houses has shown an unexpected high failure rate for both QAL2’s and AST’s and the generation of poor calibration functions and low R2 values. Where a system passes the requirements of a QAL2, calibration functions have been seen to vary from 0.25 to 1.8. This suggests a variance well beyond the defi ned allowable uncertainty of 40% for HCI.
Faced with the issues and challenges around HCI, the STA have set up a sub group with the aim to provide solutions, guidance and best practice.
HCI measurement challenges include cold spots in sampling systems, contamination of sampling systems, pacifi cation of sampling systems, Continuous Emission Monitor (CEM) Interferences. On top of this there is also an issue with the reliability of the Standard Reference Method (SRM). However there is limited information available as anecdotal information suggests that there can be poor agreement between the wet chemistry based SRM (EN 1911) and CEMS results. In particular, agreement appears to be poor where ammonia injection is used for SNCR NOx control by the site.
Additional investigative work is required on the comparison of SRM and FTIR on a variety of processes including with and without ammonia injection, assessing the effect of fi lters, probe types and materials of construction which could lead to losses of HCI during sampling. Looking into the issues surrounding ammonium chloride salts and quantify the effect of cold areas on HCI concentrations at the analyser.
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