Natural gas is a generic designation for various qualities of gas based on the main gas component methane (CH4). As such, it covers many different qualities linked to the gas composition including the source of raw gas and refinery processes. Natural gas can be manufactured from synthesis technologies, natural processes, or “renewable power-to-gas” technologies.

Gas networks are interconnected and strategically linked to multiple sources. Because of this, the quality of gas can change at a given location and these changes could be rapid when switching from one source to another. As well, rapid changes of gas quality can occur in other situations faced by end users, such as onsite switching from a gas tank to the gas network, or vice-versa. Also, when gas is only available in tanks, switching from an empty tank to a full tank can result in significant changes of gas quality, as an empty tank will deliver the heaviest molecules contained in natural gas, and a full tank may deliver the lightest molecules.

Gas fired gas turbine builders are very much aware of these situations that deeply affect the combustion inside the gas turbines. Gas fired gas turbines  are sensitive to Wobbe index, calorific value of the fuel gas and flame  speed of the combustion as flashback or flame extinction can result from fuel gas quality change..  To combat this, oxygen sensors in the chimney, and temperature sensors in the combustion chamber are used by engine builders to monitor the combustion. As often the case, such management loops are not always fast enough to match sudden changes of gas quality, resulting in an emergency stop of the turbine. Additional margin is usually obtained by conservative tuning of the turbine, such as derating of the turbine output.  

To overcome the combustion instability of gas fuel gas turbines, a new sensor, called NIRIS NG, has been designed to analyse the natural gas composition at the inlet of the turbine burners. Design of the NIRIS NG sensor boasts a short response time – less than one second – easy installation, simple maintenance, and low cost in order to be standardised on all gas fired gas turbines. The NIRIS NG sensor is based on spectrometry, which has been specifically engineered for installation ON turbines. Compared to other gas quality analysers, the NIRIS NG sensor is performing a technological breakthrough by using low cost optical components and proprietary signal treatment software within robust packaging able to sustain vibration and heat. It is a gas-pipe-plugged sensor to provide fast response times. Measurement data are provided through CAN protocol to the turbine controller. The paper will describe sensor hardware and software technologies, validation testing, and expected advantages on industrial gas fired gas turbines.


A Novel Sensor for Improving Flame Stability of Gas Fired Gas Turbine by Continuously Monitoring Fuel Gas Quality

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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