Problems with Pitots. Issues with flow measurement in stacks

Reliable and accurate measurements of gas flows in stacks underpin the monitoring of emissions. However, flow measurement has often been the poor relation in stack sampling. The measurement of flow has significant impact on stack emissions monitoring in a number of ways. In addition to enabling concentration measurements to be converted to emission fluxes, flow measurement is also necessary to demonstrate that the gas flow profile in the stack meets the requirements of the method. The most routinely used stack and duct gas flow monitoring techniques are based on the use of Pitot tubes. Pitot tube measurements are also used to enable isokinetic sampling to be achieved and verified. Issues with Pitot tube measurements can therefore result in significant errors in reported emissions.