Porosity and Pressure Waves in a Fluidized Bed of FCC Particles

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• 作者：Dimitri Gidaspow ; Michael Driscoll*
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2009
• 出版时间：March 4, 2009
• 年：2009
• 卷：48
• 期：5
• 页码：2422-2429
• 全文大小：223K
• 年卷期：v.48,no.5(March 4, 2009)
• ISSN：1520-5045

文摘

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.