Researchers will work with oxy-combustion and Chemical Looping Combustion (CLC), which are relatively unknown in Brazil

Two little-known technologies in Brazil capable of generating energy and of capturing and purifying carbon dioxide (CO2), which is one of the most significant villains of global warming, are under study by researchers from the Research Center for Innovation in Greenhouse Gases (RCGI), headquartered in the University of São Paulo (USP) and funded by the São Paulo Research Foundation (FAPESP) in a partnership with Shell of Brazil.

“Both technologies use combustion and manage to generate virtually pure CO2, with no need for such subsequent processes as membrane separation. In other words, the CO2 comes ready to be stored or reused,” states Guenther Carlos Krieger Filho, Professor in the Department of Mechanical Engineering at USP’s Polytechnic School (Poli-USP) and Coordinator of the Chemical Looping Combustion (CLC) and Oxy-Combustion Project with Natural Gas (NG) and Biogas.

The project will work along two lines of study. In one of them, the researchers want to reduce CO2 emissions through oxy-combustion, in such mills as thermoelectric plants powered by natural gas (NG) or biogas. “Conventional combustion is usually done with air, and the exhaust gases resulting from the burning process produce not only CO2, but also such pollutants as Nitrogen (N2) and others. In the case of oxy-combustion, the burning is carried out with pure oxygen (O2), instead of common air, and this results only in CO2 and water vapor,” Krieger Filho explains.

He says that this is one of the special advantages of oxy-combustion. “In conventional combustion, more than 70% of the gas resulting from the process is composed of nitrogen. However, it is highly expensive to compress all that gas and store it. Not to mention the fact that the intent of the process is to be able to store the CO2 or to use it for another purpose. With oxy-combustion technology it is easy to separate the CO2, because you only need to condense the water and you are done.”

The focus of the project will be on developing combustion chambers capable of performing this operation. “Oxy-combustion demands extremely high temperatures and the reactor must withstand that thermal stress. Ensuring the stability of this type of combustion is our challenge,” says Krieger Filho. The experiments are performed both through modeling and, empirically, on a laboratory scale. In the latter case, the researchers will develop an oxy-combustion chamber coupled to a mini gas turbine, which will generate the CO2 already separated from the water vapor.

As for the computations, the project team will initially use several studies performed by the Massachusetts Institute of Technology (MIT), in the United States. “This is just the kickoff. We will replicate the combustion chamber developed by MIT on the computer and, from there, perform our own studies using laser-optical techniques to measure velocity fields and identify the structure of the flame, for example,” the researcher adds. “We are going use this data to improve and modify the computational models that will allow the future construction of an industrial-scale combustion chamber.”

Retrofitting the mills – In order to adopt the oxy-combustion process, the mill must be retrofitted. “This technology can be incorporated into the existing structure. However, it requires the implantation of a cryogenic plant to produce pure O2,” says Krieger Filho. “The project also intends to test what would be a tolerable concentration of nitrogen for this process, in order to attempt to reduce plant costs.”

According to the expert, the team of researchers at the RCGI did not find studies concerning the use of oxy-combustion with biogas. “It seems that our project is a pioneer with regard to this issue. Because of the need to reduce greenhouse gas emissions, biogas production will likely grow in Brazil, since it makes use of agribusiness waste. If the mill uses biogas and oxy-combustion, it could be negative in terms of CO2 emissions.

The other technology that will be studied by the project researchers is Chemical Looping Combustion (CLC). “In this process, we have two interconnected reactors. In one of them, using air, a metallic particle oxidizes, which is then sent to the other reactor and provides the O2 for burning the fuel,” explains Fernando Luiz Sacomano Filho, Professor in the Department of Mechanical Engineering of Poli-USP and Deputy Project Coordinator. “When the exhaust gases cool, the water condenses and pure CO2 is obtained.”

In this case, the mill does not need to install a cryogenic plant, since the O2 is generated by the combustion process itself. “However, CLC is not suitable for retrofitting and anyone who wants to adopt it needs to modify the industrial plant,” adds the expert who learned about the technology during his Doctoral studies at the Technical University of Darmstadt, Germany, which he completed in 2017.

The researchers’ objective, as it is in the oxy-combustion phase of the project, is to build reactors through modeling and, empirically, in the laboratory. In terms of computation, a pilot plant located at the Technical University of Darmstadt will be used as a starting point, which will then be worked on by the RCGI team. “Although it emerged in the 1950s, this technology has gained momentum over the last 20 years as an alternative for capturing CO2. For that purpose, this is a technology under development throughout the world, where commercialization is still at an embryonic stage,” says Sacomano Filho.

During the project, the researchers intend to test various types of ores that can be used in reactors, such as ilmenite (FeTiO3). “There are several possibilities. For example, several studies, worldwide, deal with transforming waste from the electronics industry into metallic particles for the CLC reactors, but this is not our immediate objective,” he reports.

Sacomano Filho adds that Brazil has great renewable energy potential, if we take hydroelectric plants into account. “But when we consider primary energy sources, which feed the industry, we are very dependent on fossil fuels.” According to him, one of the goals of the project is to test the CLC powered by natural gas, biogas, and biomass. “That will be a brand-new area.”