Investigation of Hydrodynamics of High‐Temperature Fluidized Beds by Pressure Fluctuations

Abstract

Hydrodynamics of a gas-solid fluidized bed at elevated temperatures was investigated by analyzing pressure fluctuations in time and frequency domains. Sand particles were fluidized with air at various bed temperatures. At a constant gas velocity, the standard deviation, power spectrum density function, and wide-band energy of pressure fluctuations reach a maximum at 300°C. Increasing the temperature to this value causes larger bubble sizes and after the bubbles reach their maximum size, they break into smaller bubbles. The Archimedes number decreases with higher temperature and the type of fluidization becomes closer to that of Geldart A boundary at this maximum temperature. Based on estimation of the drag force acting on the emulsion phase, it was concluded that 300°C was a transition temperature at which the drag force reaches a minimum due to a significant change of interparticle and hydrodynamic forces.

Experimental Investigation of the Effect of Random Packings on Heat Transfer and Particle Segregation in Packed-Fluidized Bed

“…To facilitate understanding, the behavior of a bed with no packing and increasing gas velocity will be considered. The particulate bed can, in this case, be divided into two different phases, the emulsion phase and the bubble phase. , By increasing gas velocity at a fixed temperature, initially, formation of small bubbles will help in increasing the interaction of bed particles with each other and the surface of the water tube. Thus, it will increase heat transfer between the bed material and tube.…”

“…However, increasing the gas velocity to higher values will increase the number of bubbles. Eventually, bubble coalescence will occur and result in the formation of bigger bubbles. , Since heat transfer is a function mainly of particles coming in direct contact with the tube, this will reduce the heat transfer coefficient. A packing with a high void factor, such as RMSR, that does not greatly hinder particle movement but breaks down big bubbles to smaller ones, could therefore conceivably improve the heat transfer coefficient to a submerged tube, as have been observed.…”

Effect of Superficial Gas Velocity on Bubbling Fluidized Bed Behaviour in a Biomass Gasifier

“…With changes in temperature and pressure in the conversion process, the fluid properties as well as the particle-particle interactions may vary, causing changes in the flow velocity. In extreme cases, this may lead to changes in the fluidization type (Nemati et al, 2016). The common observations to these changes is the effect of temperature on the transition of fluidized bed regimes as have been demonstrated in different studies.…”

Numerical Simulations of Solid Circulation Characteristics in an Internally Circulating Elevated Fluidized Bed

“…Fluidized beds are widely applied in many industries and some of their key features are well documented and presented in the literature [1,2]. The process of particle circulation in a fluidized bed can either be accomplished externally such as in the conventional circulating fluidized bed (CFB), or internally like in the non-conventional internally circulating fluidized bed (ICFB).…”