Due to environmental regulations, Nitrogen oxides (NOx), Carbon Monoxide (CO) and Sulfur Dioxide (SO2) emissions are key issues for gas turbine plants. Regulators are becoming more and more involved and they often require complete and real-time emission information.
The measurements can be done with gas analyzers, this technology is called CEMS: Continuous Emissions Monitoring System. An alternative method  is to use a calculation based on the turbine instrumentation. This technology is called PEMS: Predictive Emissions Monitoring System. But these technologies do not provide all the information required by the regulator.
GRTgaz, the main gas transmission company in France managing 44 turbines spread over 27 stations across France, has decided to monitor its emissions by PEMS for many years. Two years ago, GRTgaz developed successfully its own PEMS equations, organized answers to regulators around this technology and decided to spread the technology across its gas turbine fleet. The complete intellectual path followed is described in the paper GT2014-25242. This 2016 3-part paper describes the PEMS project steps forward.
In the first part of the paper, a review is done of the PEMS equations used at GRTgaz for NOx and CO concentrations. The various lean premixed combustion turbines differ in terms of combustion design, control and instrumentation. These differences are analyzed considering their influence on combustion and their impact on the PEMS results accuracy.
In order to comply with regulators requirements a calibration of the PEMS results is done every quarter. The results of the first 2 stations equipped with PEMS are described in this first part.
The second part of the paper introduces the smoke developed and the neutral air flow to complete the real time calculation required by the regulators: SO2 concentration and the mass flowrates for NOx, CO and SO2. The final calculation integrates the mass flowrate in order to elaborate the total mass emitted into the atmosphere over different time periods.
The last part deals with developing personnel involvement, managing the data and compiling the results given to regulators. These aspects were more difficult to implement than expected. The importance of these aspects should not be underestimated because the scientific credibility of PEMS cannot be confirmed without them.