Porosity and Pressure Waves in a Fluidized Bed of FCC Particles

Abstract

The speeds of motion of compression waves through a fluidized bed of 75-µm FCC particles between the minimum bubbling and the minimum fluidization velocities were determined by measuring the times of arrival of compression zones using a γ-ray densitometer. The theory of characteristics shows that this speed, which is on the order of 1.4 m/s, represents the maximum velocity of discharge of nonfluidized FCC particles. The velocity of these compression waves was used to calculate the solids stress modulus of the fluidized bed via the one-dimensional mass and momentum balances for granular flow. In addition, measurements of the pressure wave propagation produced a mixture sonic velocity that is an order of magnitude higher than the speeds of the solids compression wave. The sonic velocity of the homogeneous mixture, which is on the order of 20 m/s, gives the maximum achievable velocity for the circulation of FCC particles in a standpipe of a refinery. This study shows that there are two distinct waves that travel through the fluidized bed at significantly different velocities when the bed is subjected to a shock. A correlation for the solids stress modulus was determined as a function of void fraction. This new correlation was an input into the viscosity input gas-solid hydrodynamic model and yielded simulations that were consistent with the experimental observations and results. Using the complete equation of state for FCC particles and the relationship between the compression wave velocity and the solids stress modulus, the computed granular temperature is two orders of magnitude lower than the square of the wave propagation velocity and is consistent with literature values.

Fluid dynamics of the 1997 Boxing Day volcanic blast on Montserrat, West Indies

“…Moreover, as a first‐order estimate, we did not include a slip velocity correction due to its relatively small value compared to the horizontal flow speed. The above equation has been validated by Gidaspow and Driscoll [2008] by showing it appropriately describes the propagation of pressure waves through a fluidized bed over a wide range of void fractions. According to it, the sound speed of the mixture decreases with increasing particle volume fraction until a minimum is reached at a void fraction of 0.5.…”

Comprehensive Theoretical Investigation of the Mechanism of Methanol to Aromatics Catalyzed by Gallium-Modified FAU Zeolite

“…The propene molecules in Scheme could originate from the products in the well-known methanol to olefin (MTO) conversion. A great number of experimental and theoretical studies reported that light olefins such as propene and ethene could be produced from the MTO process on acidic zeolites. − …”

Evaluation of Drag Models for Predicting the Fluidization Behavior of Silver oxide Nanoparticle Agglomerates in a Fluidized Bed

“…The bed expansion characteristics of these FCC particles follow the Richardson–Zaki model in a homogeneous fluidization regime . Nevertheless, the interparticle drag force was identified as the dominant factor for FCC particles with a mean diameter of 75 μm. ,, The drag force between the gas and solid particles is one of the dominant forces in a fluidized bed. The drag laws on modeling the interphase momentum exchange are usually developed empirically.…”

“…Nanoparticles are 3 orders of magnitude smaller than traditional Geldart group C fine powders (<30 μm), and during fluidizing, they form large agglomerates that can lead to severe channeling and heterogeneous fluidization or even complete defluidization. These agglomerates fluidize smoothly when the gas velocity is increased several orders of magnitude above the minimum fluidization velocity of primary nanoparticles. − Few experimental studies have been carried out to investigate the fundamental hydrodynamics of fluidized beds containing micrometer-scale particles and nanoparticles. Nanoparticles with a low bulk density generally form porous agglomerates providing fluidlike fluidization with no bubbles, that is, agglomerate particulate fluidization (APF).…”