27-02-2024

NETL discovers breakthrough scaling approach for circulating fluidized bed technology

NETL researchers have developed a new scaling methodology for measuring and understanding the performance of key elements used in circulating fluidized bed technologies (CFB) that can speed the development of CFBs for more widespread use.

Scaling is the process of taking laboratory experimental data and using it to build a commercial process. This specific scaling work takes all the performance obtained in the laboratory experiment and maintains that performance in commercial reactors that could be 1 to 2 m in diameter or even larger.

CFB systems have two parts, the riser where chemical reactions take place and the downer, which returns solids to the riser. CFB systems feeds solids like biomass or coal into a reactor, which is then aerated by an upward flow of air so that the solids, supported by the upward flowing gas, behaves like a fluid, thus the term “fluidized bed.” Combustion, or other chemical reactions, take place in the bed with very intense mixing of gases and solids.

Advantages of CFB include fuel flexibility; capability for firing low-grade fuels like biomass; desulfurization during combustion; low NOx emissions; intense heat transfer characteristics; use of crushed fuel with relatively large particles; and small installation capabilities.

CFB has been used in some industries to burn low-grade solid fuels and recovering energy as a proven technology for power generation. However, a greater understanding of the effectiveness of the risers that contain the upward movement of solids and gas in CFBs can lead to greater use of the technology.

NETL’s Ron Breault explained that scaling circulating fluidized bed risers effectively, has been a point of contention for nearly a century. There have been numerous attempts to define various methodologies. These have all fallen short of providing a robust approach, primarily due to a lack of maintaining microstructure dynamics – a key factor in maintaining heat and mass transfer.

“Circulating fluidized beds have been used for petroleum refining, chemicals production, solids fuel gasification and combustion, and emission reduction,” Breault explained. “Even for such a vast and lengthy history, scale-up of these systems is a difficult process due to the non-linear and chaotic flow behavior within the risers.”

Breault, who led the NETL research effort, added that a scale-up procedure is based upon maintaining the bed behavior that retains the heat and mass transfer when scaling the technology, which is key to broadening potential for wider use of CFBs.

“The new approach overcomes shortcomings of previous scaling methodologies by maintaining statistical and chaotic parameters across the scales,” he said. “Through this work, developers of fluidized bed technologies can successfully speed development and scale up to commercialization.”