A new high-frequency radar technique can provide a detailed characterisation of the flow of solids in fluidised beds, one of the leading technologies used in thermal power plants.

The method could lead to “completely new and more efficient processes in several industries, including energy conversion”, according to its developers at Chalmers University of Technology in Sweden.

Fluidised bed combustion is used to burn solid fuels, such as biomass and waste, for district heating and electricity. Fluidisation technology is also fundamental to many other processes that are expected to play an important role in the transition to ‘net zero’, such as carbon capture, energy storage, and the production of hydrogen and other fossil-free fuels.

Fluidisation technology is based on a gas being blown through a bed of small sand-like particles in a reactor, thoroughly mixing the solid particles, fuel and gas.

“To achieve even greater efficiencies in this process, you need to be able to understand and control how the solid particles behave in the mixture,” the Chalmers researchers said. “But the reactor environment is often hot, dirty and corrosive – like a sandstorm and a wildfire in one – effectively preventing any type of measurement and thus limiting our understanding of what is actually happening inside the reactor.”

The team’s solution to this problem is an extremely high-frequency radar technique that can measure the flows of solid particles in fluidised beds with high precision. The method was inspired by the pulse-Doppler radar, which is used to track precipitation.

“The use of the high-frequency terahertz radar instrument demonstrated in our study has the potential to revolutionise how fluidised bed technology can be designed and used in many different industrial sectors – from energy conversion to the food industry and drug production.

“This is one of very few demonstrations of the use of pulse-Doppler radar technique at submillimetre wave frequencies, and it is the first time ever that it has been used for making measurements in a fluidised bed,” said Diana Carolina Guío Pérez, researcher in energy technology at Chalmers.

The measurement techniques used in fluidised beds are normally low-resolution, produce results that are difficult to interpret, or cause disturbances in the flow, the researchers said. In contrast, they said their technique can penetrate the reactor from the outside and measure the behaviour of the particles inside without disturbing the flow.

The radar technique can also measure the velocity and concentration of the solid particles with high precision and resolution, meaning that even minimal changes in the flow can be detected in real-time.

The method was demonstrated in a three-metre high circulating fluidised bed boiler in the researchers’ study. The findings reportedly showed a measurement quality that exceeded the quality achieved by the methods previously used in the field by a “big margin”.

“We have been able to show that pulse-Doppler radar technique at frequencies up to 340GHz can measure both the distribution of particles and their velocity inside a process reactor at a much higher resolution than other technologies can. This is information that has long been lacking in the field and will make it possible to improve and scale up process reactors and – in the case of energy conversion – reduce emissions of unwanted residual products,” said Marlene Bonmann, post-doc researcher at the Terahertz and Millimetre Wave Laboratory at Chalmers.

Pérez added: “The knowledge that can be acquired with our high-frequency terahertz radar technique has the potential to break new ground in our understanding of solids flows in fluidised bed reactors and other solids handling units. For example, it can lead to improved operation and design of the reactors needed in existing and completely new fluidised bed-based conversion processes, such as carbon capture and storage, energy storage and thermal cycling.”

Extracted from IMechE website, read more here

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