New Radar Technique Offers Window into Fluidized Beds

Swedish researchers from the Chalmers University of Technology have demonstrated a high-frequency radar technique that measures the complex processes occurring during fluidized bed combustion.

 

A radar transmitter and receiver convert low frequencies into high ones reaching 340 GHz. The signal is sent through the antenna, and a gold mirror points the beam toward the fluidized bed. Image used courtesy of Chalmers University of Technology/Anna-Lena Lundqvist

 

Common in thermal power plants for converting solid fuels into heating and electricity, fluidization provides efficient combustion by sending gas through a bed of small particles in a reactor, mixing the fuel and gas. It’s used in several applications with circular resource flows. 

In carbon capture and storage, fluidized beds assist in chemical and calcium looping. In energy storage systems, they convert solar and wind energy and store it as bulk solid particles. They’re also used in gasification processes for hydrogen production. 

The new technique is based on pulse-Doppler radar technology long used in weather applications, but this is the first time it has been used to conduct measurements in a fluidized bed. The researchers detailed the results in a study published in Fuel. 

Diana Carolina Guío Pérez, an energy technology researcher at Chalmers and one of the study’s authors, stated this is one of the few demonstrations of pulse-Doppler radar techniques at submillimeter wave frequencies. Co-author Marlene Bonmann, a post-doc at Chalmers’ Terahertz and Millimeter Wave Laboratory, added that particle distribution and velocity measurements have long been a challenge in the field. The new technique can help improve and scale up process reactors and address residual product emissions in energy conversion. 

Overall, the findings represent a promising method to improve the design and operation of reactors used in fluidized bed conversion processes, including energy storage, thermal cycling, carbon capture and storage, and other renewable energy applications. It can also apply to other industries, such as food and pharmaceutical production. 

 

The radar technique measures the velocity and concentration of solid particles in a circulating fluidized bed boiler. Image used courtesy of Chalmers

 

Here’s How the Technique Works

The technique offers a high-precision window into the behavior of solid particles as they flow through the mixture inside a fluidized bed. Due to the extreme environment inside the reactor, such measurements are typically difficult to gather. Existing techniques are low-resolution and can create disturbances in the flow. 

The Chalmers researchers’ technique gets around these challenges by penetrating the reactor on the outside to understand the air flows within, measuring the distribution and velocity of solid particles with high spatial and temporal resolution. It can even detect small flow changes in real-time, a feature helpful in monitoring and controlling processes in industrial applications. 

 

The position of the radar antenna is shown in these two schematics of the experimental assembly used for vertical (left) and horizontal (right) measurements. (Side-by-side placement added by EE Power.) Images used courtesy of the study authors (Creative Commons)

 

The technique was demonstrated at frequencies up to 340 gigahertz in a circulating fluidized bed boiler three meters (nearly 10 feet) in height. The quality beats that of existing methods. 

In the study’s conclusion, the authors wrote that further work would be needed to raise the penetration levels at high solid concentrations. The technique and radar setup could also be refined to narrow the radar beam and minimize effects from static reflections.