|Abstract Title:||Stack Gas Flow Rate Validation and Verification|
|Session Choice:||Industrial Case Studies|
|Presenter Name:||Mr Jonathan Spence|
|Co-authors:||Mr David Graham|
Abstract Information :
Stack gas flow rate can either be measured directly or calculated from fuel consumption (for well-defined fuels) according to EN ISO 16911:2013. Stack gas flow rate is required for mass emissions reporting and in order to calculate stack exit conditions for dispersion modelling purposes. Part 1 of the standard specifies the requirements for manual stack testing methods which include a tracer gas dilution reference method that has been used extensively in the UK. Part 1 also specifies the methodology and performance characteristics required for stack gas flow rate calculation. Part 2 of the standard describes the Quality Assurance (QA) procedures that are applicable to continuous flow monitoring using either an instrument or a calculation method. Part 2 of the standard is based upon the requirements of EN 14181 which defines three QA Levels: QAL1 (certification); QAL2 (calibration) and QAL3 (control) and an Annual Surveillance Test (AST calibration check).
When the flow rate is calculated, it is important that the calculation is audited in order to demonstrate compliance with EN ISO 16911- Part 1 and that the uncertainty of the calculated hourly average flow rate is compliant with the specified performance requirements. This process can be regarded as a validation exercise that is equivalent to the certification of an instrument under QAL1. However, the flow rate calculation must also be subject to verification by means of stack testing such that the QAL2 and AST requirements specified in EN ISO 16911- Part 2 are satisfied.
Experience of applying this standard in the UK has identified common issues that have been highlighted by these complementary validation and verification processes. Inconsistencies in the adopted calculation approach at a range of sites, firing either natural gas or solid fuels, are mostly related to the quality of the input parameters used for the calculation. Despite these findings, stack gas flow rate calculation remains a robust and accurate means of continuous flow monitoring provided that it is properly validated and verified.