Written by Dr Richard Marsh, Senior Lecturer specialising in energy systems, Cardiff University
Principal Investigator on Call 1 Project: Oxyfuel and exhaust gas recirculation processes in gas turbine combustion for improved carbon capture performance
What is ‘Oxyfuel’ ?
‘Oxyfuel’ refers to a chemical reaction between a fuel and pure oxygen, rather than fuel and air. Most people’s experience of oxyfuel will be limited to seeing a welder use an oxy-acetylene torch. The reaction is very concentrated and extremely hot, so hot in fact that the oxyfuel flame can melt metals with ease. Clearly a flame of this intensity would not be directly applicable to a gas turbine engine, since the internal metal components would be damaged by the heat. One solution to this problem would be to inject some of the captured CO2 into the incoming oxygen stream to create a mixture of CO2 / O2, similar to the N2 / O2 mixture we know as air. This would slow down and cool the flame zone, resulting in a more tolerable environment in the engine.
What is this research about?
The aim of this research is to examine some of the operational challenges in using oxygen combustion in gas turbines. The driver for this is that if gas turbines can be operated without atmospheric nitrogen entering the system, then they should theoretically only produce CO2 and steam as a by-product. This is a very tempting concept, since it is accepted that gas turbines will play a significant role in the UK’s future power generation portfolio; therefore gas turbines that produce almost pure (pipeline ready) CO2 will not have the need for CO2 scrubbers. This idea is surrounded by many technical challenges, but undoubtedly the key issue is that there has been very little established research into oxyfuel combustion in gas turbines, so this project is starting with a fairly blank sheet.
What will the research do?
Our plan is to utilise a design for a modern gas turbine burner and observe the changes in the flame’s behaviour as more oxygen is added to the reaction. For example, atmospheric air contains about 21% oxygen, so we will increase this oxygen quantity to higher levels and judge at what point the flame is becoming unstable or too hot for the application. Secondly, the flame will be operated with a mixture of methane, oxygen and carbon dioxide and we will quantify the effect of the CO2 as a diluent in the process. In the research facility we have a gas mixing plant, which allows us to safely and accurately mix the different streams together.
The research will take place on two scales; firstly at atmospheric pressure with a small scale burner in order to define the regions of interest and get a representation of where the operational challenges will be. Secondly a larger burner will be tested at higher pressures, more akin to the conditions in a real engine, where we will also measure the composition of the exhaust gas to check if other pollutants (such as NOX) are being produced in the reaction.