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Environmental monitoring

Stack simulator facilities

Instrument development and personnel training

The stack simulator facility allows manufacturers of new continuous emission monitors to test their equipment over a range of operating conditions. Stack monitoring teams can test their procedures and proficiency under controlled conditions. The facility is available to hire with appropriate back up from NPL experts.

The stack simulator has an across-stack path length of 1.5 m. It has two 5-inch ports at one end of the path-length and two ports at the other end, which are positioned similarly to allow two cross-stack instruments to be attached. Alternatively, four half-length probes could be inserted.

The simulator allows flows of air, nitrogen and a selection of 'pollutant' gases into the 'stack' at controlled rates to create predictable mixture concentrations. It also incorporates a water injector to provide a controlled water vapour concentration.

The gases are recirculated to create a high vertical stack velocity with low gas consumption and low release to the atmosphere. The velocity profile is approximately constant along the length of the test paths, but naturally falls to zero at the walls of the simulated stack. Internal electric heaters allow the 'stack temperature' to be set above the dew point of the recirculating gas mixture.

Performance Summary
Temperature    Up to 180 °C
Gas vertical velocity   Up to 12 metres per second
Water vapour   Up to 25% by volume
Oxygen content   Up to 20% by volume
Input gas flow rate   Up to 150 litres per minute
'Pollutant' gases   Most common pollutant gases, by agreement

The stack simulator forms a key component of a proficiency testing scheme for stack emissions monitoring teams, delivered by NPL for the Source Testing Association.

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