The combustion process uses oxygen instead of air and prevents the emission of nitrogen oxides; the CO2 resulting from the combustion may be isolated to be stored underground.
A team of engineers associated to the Research Centre for Gas Innovation – RCGI is creating an advanced natural gas burner to power gas turbines, using the oxy-fuel concept. The combustion is promoted by using pure oxygen instead of using air (largely composed of nitrogen and oxygen). The gases resulting from this new concept are CO2 and water vapour, free from N2 and nitrogen oxides (NOx).
“This process has some benefits in relation to the conventional combustion process. Firstly, it does not form nitrogen oxides, which are air pollutants. Secondly, it allows separating CO2 from the combustion products, facilitating and making Carbon Capture and Storage (CCS) technology more affordable,” explains Guenther C. Krieger Filho, coordinator of the project Development of an advanced gas burner using the oxy-fuel concept. Besides Krieger, who is with the Escola Politécnica (Engineering School) of the USP, there are three other engineers in the team.
Krieger says that the gases have to be compressed for storage, and the process of compressing and separating CO2 from the gases emitted from a conventional gas turbine spend considerable energy. “For those intending to store, compressing nitrogen and water vapour is not worth it. This is only done because these gases are part of the flue gas composition. With the oxy-fuel concept, which allows separating CO2, the compression process is made cheaper, since the amount of gas to be compressed is reduced.”
The project is estimated to last five years, but the researchers intend to have the prototype of the combustion chamber operating in one year. “More than the prototype, we want to generate experimental data of the combustion process to help building computational models, to obtain information that help us build mathematical models for this burning process, which still has unanswered questions,” says Krieger.
The burner consists basically of a combustion chamber, fed by a tube in which natural gas is injected. Oxygen enters by lateral openings. Because of the combustion, the temperature in the central part of the chamber is very high (around 2000 °C). However, at the chamber outlet, the temperature has to be reduced to at about 1000°C, so as not to destroy the turbine rotor. It is thus necessary to decrease the temperature of the flue gas, namely, high temperatures in the combustion chamber and lower ones in the rotor have to be combined. “To accomplish this, these combustion products have to be diluted, so as to lower these temperatures. In the conventional turbine, nitrogen plays the role of lowering the temperatures. In our combustion chamber, we intend to use CO2 for this purpose.”
Krieger affirms that the first step is to conceive a stable burner. “Therefore, at the moment, we are interested in having a model that helps us predict the necessary temperature distribution inside the chamber to provide a stable operation.”
All the experiments will be developed at the Laboratory of Advanced Combustion Diagnosis, which assembling is the goal of one of the projects conducted in the RCGI. “The laboratory will be a multi-user centre, that is, research teams having a demand for using it will be able to do it, even not being connected to the RCGI or to the Polytechnic School, provided they present their proposal and this is also interesting to us. We want more people to use it, the demands to appear.” The laboratory is being equipped with different types of laser diagnostics, which allow accurate analyses of the combustion processes being studied.