Fluidiseret

Fluidiseret, or fluidized, describes a state in which a bed of solid particles is made to behave like a fluid by passing a gas or liquid upward through the bed at a sufficient velocity. In a gas-solid system, when the superficial gas velocity reaches the minimum fluidization velocity, the particles suspend and mix vigorously, producing enhanced heat and mass transfer compared with a fixed bed. Increasing the velocity further leads to bubbling or circulating regimes that improve mixing and contact between phases.

Common configurations include bubbling fluidized beds (BFB) and circulating fluidized beds (CFB). In a bubbling bed, the gas velocity is near the minimum fluidization value, creating bubbles and a substantial solid–gas contact region. In a circulating bed, a large portion of solids is entrained and continuously circulated by risers and returns, enabling higher solid throughput and better handling of heat release or uptake.

Applications span chemical processing, energy, and materials engineering. Fluidized beds are used as catalysts supports and reactors (notably in some catalytic cracking and hydrogenation processes), as well as in drying, coating, granulation, and polymerization. In energy and environment, circulating fluidized beds are employed for combustion and gasification due to their good heat transfer and fuel flexibility.

Advantages include high interfacial area, excellent temperature control, uniform mixing, and efficient heat and mass transfer. Limitations encompass particle attrition and fines generation, entrainment of fine solids with the gas stream, bed defluidization or channeling, and higher energy consumption. The design and operation depend on particle size and density, gas velocity, temperature, pressure, and scale, as well as the management of solid handling and cyclone or separator systems.