Air Monitoring

Plant Operator Problems with CEM’s - A Common Evaluation

Oct 06 2014

Author: M L Yeoman and A D Leonard on behalf of CEM

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In situations where continuous monitoring systems (CEM’s) are available which have been ‘proven’ by regular use, the Regulator will normally require their use for the monitoring of airborne pollutants emitted by large plant. Disputes which arise between operators who purchase CEM systems and the system suppliers over the level of performance achieved are often difficult to resolve. Since the payment or non-payment of a significant amount of money is integral to these disputes a third party such as AEA Technology Environment is often brought in to give an expert opinion.

The range of CEM’s problems and the types of plant on which such disputes can occur are illustrated by four case studies. In each case study the independent assessment of performance which was subsequently performed selected appropriate performance criteria to evaluate the installed system from a small set of performance standards with national or international recognition.

A different result emerged from each of the four case studies illustrating the complexity of the reasons for poor CEM’s performance.

In all cases the causes for inadequate or poor performance were identified. The success of such assessments relies critically on selecting the right approach, on the relevance and quality of the reference measurements performed and on the quality of staff, equipment and procedures.

The process of minimising emissions to the atmosphere of gaseous or particulate pollutants is not a cost benefit to operators of production plants, but the failure to do so could result in severe cost penalties. Since the range of instrumentation available on the market to monitor airborne pollutants is very wide with prices ranging from a few hundred pounds to tens of thousands of pounds the operator is faced with a difficult choice. On the one hand he could purchase an inexpensive system with little support and risk breakdown or he can purchase an expensive well supported system with good guarantees and expect to have a trouble free performance. In some parts of the world eg Germany, USA the operator’s choice of system is constrained, by regulations, to systems which have proved that they can achieve a well specified level of performance on that type of application. In the UK there is no such constraint and operators are quite frequently disappointed by the performance of a CEM system purchased and installed as part of the requirement of the Authorisation to operate the plant issued by the Environment Agency.

When disputes arise between plant operators, instrument manufacturers the Regulator or interest groups a clear specification of what performance should be expected from the installed CEM system is required. Unfortunately this is usually not available. A CEM system may perform faultlessly in the laboratory, but the matrix of conditions on a plant can be very severe with high moisture, high acidity, complicated flow patterns and concentration levels of pollutants which can suddenly increase to many times the typical values.

This paper discusses four case studies in which AEA Technology has been asked to assess the performance of an installed CEM system. Sometimes the design and construction of the CEM system makes it unsuitable for the application and this showed up in one of these case studies. At other times the installation and maintenance procedures were inadequate and did not allow the system to reach the level of performance of which it was capable. In another example the ancillary equipment on the plant, which was connected to the CEM system installed, namely the data logging arrangement, was the feature which caused the apparent poor performance of the CEM system.

When carrying out assessments of CEM systems the procedures and standards employed as the basis of the assessment were selected from a small range of criteria such that the testing programme proposed was applicable to the installation in question. This approach helped to minimise cost and to quickly identify the cause of the concern over the quality of the data. All of the criteria employed are available in published form, but to ensure an accurate assessment of the CEM system the testing organisation should itself have third party verification of the quality of its staff and procedures. Such verifications of test organisations by for example UKAS, STA are becoming more common and prospective litigants in dispute procedures can now be confident that an assessment carried out by a verified test organisation will produce robust data and conclusions which will stand up to scrutiny.

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