How can biogas be efficiently stripped of CO₂ and thus help to decarbonize? This is the challenge addressed by an international research project in which the Faculty of Mechanical Engineering of the BUT collaborates with colleagues from Berlin and Lodz. The project will focus on understanding biogas enrichment through the so-called Rotating Packed Bed RPB chemical absorption. Methane-rich biogas has become an important point of interest in the realm of renewable energy sources. Biogas fermentation process does not provide pure methane, it is also rich in carbon dioxide, which can constitute up to 45% of its composition. To enrich the biogas, the CO₂ therefore must be removed. The aim of the joint trilateral project is to optimize the RPB process to make biogas treatment more efficient and contribute to more sustainability.

"Rotary absorption is a well-known technology, but the investigation of what happens inside an RPB is limited and very little knowledge about it is available. Among other things, there was a lack of methods to allow experimental observation of the process. Inside, an absorbent liquid is sprayed, which meets the CO₂-containing gas and traps the carbon dioxide. We can use our techniques, such as high-speed cameras and laser systems, to experimentally observe what is happening inside the rotating packing. In addition to experiments, we also develop computer simulations, which can significantly speed up the entire optimization process. This is crucial for us to tune the efficiency of the whole process," says researcher Miroslav Jícha from the Energy Institute of the Faculty of Mechanical Engineering at Brno University of Technology.

While the Brno experts focus mainly the hydrodynamics of the whole process, at the Technical University in Lodz, Poland, they focus on chemical-physical processes at the top level. "There are two main types of absorption: physical and reactive. In reactive, the compound not only dissolves but also undergoes a chemical reaction. In our case, we use solvents that chemically bind the dissolved CO₂, making the process much more efficient," explained Michał Blatkiewicz from TU Lodz. They have already worked with Brno scientists in previous years, and they highly praise the combination of Polish and Czech know-how. In the new project, they also have additional top-notch support from scientists from the Technical University of Berlin. "The Berlin team contributes expertise in modeling and thermodynamics, so together we have a more comprehensive approach to the whole process," adds Blatkiewicz.

The potential of the developing technology is enormous. "We are seeing a growing industry’s interest in this technology. It can contribute to decarbonization and is more flexible than traditional methods. In addition, it can be used decentralized or even as a mobile unit for gas purification on ships," explains Jens-Uwe Repke from the TU Berlin. "We know that there is no one-size-fits-all solution to all the problems, but this technology can be an important piece of the puzzle in the fight against climate change," Jens-Uwe Repke believes.

Decarbonization is a topic that has recently resonated in both politics and industry. Solutions already exist, but they have their limits. "Standard, CO₂ capture is carried out by various methods, but we are working with chemical absorption, which seems to be the most suitable for industrial use in capturing large volumes of CO₂," confirms Jícha, adding: "For example, static absorption columns tens of meters high are commonly used in the chemical industry. These are extremely bulky and expensive devices, and the whole absorption process is not very flexible and is expensive. Rotary absorbers are smaller and speed up the process considerably. Rotation – as opposed to the gravitational force that works in static columns – gives mass transfer up to 40 times greater intensity. The result is more efficient and cheaper technology."

The three-year international project focuses on the carbon capture phase. What to do with it next is a question for experts in other fields. "Europe has so far been more reticent to store CO₂ in the ground. However, storage may not be the only solution; it can be directly utilized in the pharmaceutical and chemical industries, for example, that means to focus on Carbon Capture and Utilization CCU rather than on Carbon Capture and Storage CCS," conclude project leading scientists.