Low NOx Solution for Power Stations and Other Large Combustion Plants

Successful emissions monitoring from gas turbine power generators requires appropriate consideration of their unique characteristics and how they differ from other large combustion processes. When selecting CEMS equipment for gas turbines, it is important to choose a system designed specifically for this application.

In particular, the emission limit values (ELVs) for NOx are typically around 60mg/m3 (expressed as NO2 equivalent), which equates to just 30ppm of NO2. Following EA guidance, which specifies that the maximum operating range should be 2.5 times the ELV, a 60mg/m3 ELV would allow a maximum range of 75ppm NOx, considerably below that available on many gas analysers.

In addition, the NO2 fraction of the NOx is much higher when compared to other large combustion processes. This is as a result of the high air dilution in gas turbines, which allows oxidation of NO to NO2 prior to flue exit.
There can also be a high level of water vapour, due to the levels of hydrogen in natural gas. With higher levels of NO2 and water vapour, it is important not to allow condensing water vapour in the sample to cause loss of NO2 due to its solubility.

Among the various techniques for measuring NOx, chemiluminescence is preferred for low levels and it is also the standard reference method (SRM). The Signal Emirak is a heated,extractive system, which utilises a chemiluminescent NOx analyser with sensitivity to NOx well within the 75ppm range noted above and it is now being tested for MCERTS approval in the UK. This approval is expected such that the system fully complies with EN14181 within the implementation timescale set out by the Environment Agency.

The Signal Ambitech “Emirak” CEM has been successfully employed in gas turbine power generator applications throughout the world for the past 20 years. Currently over 3000MW of electricity is being generated in the UK by plants using this equipment including a recent installation in Baglan Bay, South Wales, for the advanced 9H gas turbine manufactured by General Electric.

For further information on the Emirak or any of Signal’s products and services please call 01276 682841 or visit www.signalgroup.com.