TUV NEL targets flow measuremment for carbon capture, stack emissions

Glasgow, UK - TUV NEL has started a new project  to investigate measurement issues and challenges associated with the accurate monitoring of CO2 for different CCS applications.  The work is being carried out within the Engineering and Flow Programme of the Department for Innovation, Universities and Skills.

With fossil fuels remaining the main source of energy for many decades to come, reducing associated carbon dioxide (CO2) emissions using carbon capture and storage (CCS) technologies is seen as one of the greatest solutions in combating climate change.

This is reflected in the UK government’s current stance on CCS and forthcoming legislation which will make CCS compulsory for all new power plants, and CCS provisions (‘CCS ready’) necessary for all new combustion plant. The inclusion of CCS in Phase 3 of the EU Emissions Trading Scheme will also impact on many industrial sectors.

It is anticipated that the accurate measurement of CO2 to meet legislative requirements will present many challenges. Several organisations currently engaged in CCS projects and CO2 measurement, have identified problematic behaviour of CO2 under high pressure conditions.

CO2 is unusual because the relationship and closeness of its triple point and critical point to the temperature and pressures commonly found in industrial processes. At the pressures and temperatures necessary to pump CO2 into oil fields and for sequestering CO2 from CCS applications, the CO2 is compressed between phases, from a gas to a liquid to a supercritical fluid, where it then behaves in ways analogous to a gas but with densities more associated with liquids.

Due to its physical properties it can also undergo rapid phase changes which can make the measurement of flow rate extremely difficult. To date there has been limited experience and information relating to the performance and accuracy of flowmeters in various CO2 phases and transitions.

The project, currently underway at TUV NEL will involve collaboration with industry to identify CCS measurement requirements and needs and to identify and assess the suitability of existing metering technologies to accurately measure CO2 under given conditions.

Also as part of DIUS’ Engineering and Flow Programme, TUV NEL is researching the accurate measurement of emissions from industrial stacks. This is required to monitor harmful pollutants and to comply with environmental legislation, such as the EU Emissions Trading Scheme and IPPC Directive.

Pitots tubes are commonly used in emissions monitoring to determine gas flow in the stack. Although cost effective and relatively simplistic in design and installation, the Pitot tube has a very limited range of operation where it can be used with an acceptable level of confidence.

Furthermore, laboratory calibrations which are carried out at single point and under perfect flow conditions, are generally not comprehensive enough or representative of the true conditions found in stacks, according to TUV NEL. Previous studies, ti noted, have indicated a need for further research into the use of Pitot tubes for stack emissions monitoring applications to validate performance and accuracy when used outside the accepted range.

TUV NEL recently initiated a study to evaluate a range of representative stack conditions using computer modelling and analysis software to assess how various flow conditions impact on measurement uncertainty. The work is intended to provide better insight into the flow measurement issues surrounding Pitot tubes and help establish useful reference data and correction factors to assist industry in emissions measurement calculations.