Air Monitoring 25
and AST. The on-going quality assurance procedure under QAL 3 is typically carried out internally under the responsibility of the plant manager. In this case the composition of the calibration gases is defi ned according to the measuring range at which the AMS is set to operate. Certifi ed calibration mixtures – e.g. prepared according to ISO 6142 – are usually suffi cient for zero and span checks.
The instrumentation gases should meet the purity and maximum impurities content requirements, depending on the instrumentation in use. In general, higher the purity and lower the content of critical impurities, higher the accuracy of the measurements.
Calibration and instrumentation gases place demands on components for distribution, control and monitoring. This is either because the analytical methods require that the gas shall maintain its high purity though to the point of use or the chemical and physical properties require special design of the equipment e.g. compatibility with the use with reactive components.
Innovative technologies from the gas companies can support the industry to meet the new requirements. An example is the HiQ®
Multimix gas diluter based on the principle of dynamic
preparation of calibration gas mixtures described in ISO 6145- 6. Thanks to its 1/100 dilution factor, the portable diluter can generate multiple points calibration curves and mixtures with low concentration (ppb-range) of reactive components such as ammonia, sulfur dioxide, nitric oxide.
Figure 2 – Installed capacity in 2017 by country according to the European Environment Agency (
eea.europa.eu)
Figure 3 – The quality assurance procedures according to EN 14181 Quality Assurance Procedures
The key EN standards to refer to are the EN 15267 about the certifi cation of Automated Measuring Systems (AMS) and the EN 14181 about the quality assurance of AMS that identify three different quality assurance levels – QAL 1, QAL 2 and QAL 3 – and an annual surveillance test.
QAL 1 procedure ensures that the AMS is suitable for the defi ned measuring tasks. The certifi cation according to EN 15267 shall prove that the total uncertainty of the AMS results meet the uncertainty specifi cation stated in the applicable regulations (IED and BREF). In QAL 2 the AMS is calibrated and validated by using a parallel measurement with the relevant Standard Reference Method (SRM) – e.g. SRM for NOx and SO2 are defi ned in EN 14211 and EN 14212. QAL 3 demonstrates that the requirements for the stated zero and span repeatability and drift values are met during ongoing operation and the AMS is maintained in the same operational condition as when it was
installed and calibrated in QAL 2. This procedure is repeated more often than QAL 2 to identify as soon as possible potential random and systematic deviations. Finally, the purpose of the Annual Surveillance Test (AST) is to verify whether the calibration function of the AMS is still valid and its precision is still within the required limits. In case of test failure, the QAL 2 step needs to be repeated.
Calibration and Instrumentation Gases
The AMS certifi cation is typically carried out by the equipment manufacturer, while the calibration curve, the linearity check and the yearly validation are usually carried out by an ISO 17025 accredited laboratory and accredited calibration gases might be required. The composition of the calibration gases is defi ned according to the certifi cation range for QAL 1 (e.g. the EN 15267- 3 requires for LCP that the certifi cation range is not greater than 2.5 times the daily ELV) and to the calibration range for QAL 2
Author Contact Details Roberto Parola, Linde GmbH • Dr-Carl-von-Linde-Strasse 6-14, 82049 Pullach, Germany • Tel: +49 89 7446-2167 • Email:
roberto.parola@
linde.com • Web:
http://hiq.linde-gas.com
Figure 4 – HiQ®
Multimix gas diluter based on two ECOCYL® Conclusions
In the context of the air quality, continued improvements in air pollution levels are expected under current and future legislation. The IED has been introducing more stringent requirements via the BREF documents related to specifi c industry (e.g. LCP) and agriculture sectors. In all cases robust quality assurance procedures are required to ensure that emission measurements are always accurate and reliable. Proper calibration, instrumentation gases and specialty equipment are crucial to ensure compliance and efforts from the gas suppliers are necessary to continuously support the industry meeting the new requirements.
cylinders
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