ANSYS FLUENT Simulation;
Fluidization of solid particles in fluidized-bed gasifier;
2D geometry;
a region of 40% from the whole domain (gasifier cylinder) has been adapted to patch with sands. solid particles are located above the sands and the air stream enters from the bottom of the gasifier and drives the solid particles to fluidize.
the attached picture shows the contour of solid volume fraction, resulted after 1 sec of the run-time calculations.
the target is to monitor merely the fluidization of solid particles.
I am not sure I understand your question, but in fluid beds, the bed material (sand) fluidizes in addiition to any particles that you add.
I think I made the wrong choice of words to deliver my point
my question is:
since the density and particle size of the sand and solid element are different , is there any options that allows me to monitor the distribution of each of the elements individually during the fluidization from the contour of solid volume fraction?
My appreciation in advance for your answerings
Ramin Khezri, my answer here is not to address the CFD related question you ask, but to have a system that will work well. For co-fluidizing of two solids of different sizes and densities, you need to ensure that both have the same Umf. This may happen when the (density x Dp) of both particles is nearly the same for low Re numbers. For higher Reynolds numbers, the relationship is more complicated and also depends on the Geldart classification of the particles. (See the correlation of Wen and Yu for Umf). Particles with larger (density x Dp) will tend to fluidize later. This may mean (i) stratification and segregation of the particles in the bed, or (ii) pneumatic carryover of the lighter phase. Both cases mean poor contact between the two types of particles and the system will not work well.
In a combustor we designed we used lump coal +6mm -25mm in a graded 4 - 6mm sand bed. The coal was added on top and the lumps tended to stay on top while they were big. As the diameter got smaller, the lumps tended to enter the bed and were well distributed. I guess this was possibly the "Brazil Nut Effect" that I just did not recognize at the time. So sometimes there are interesting anomalies that come out albeit that coal has a lower density than sand. Also, as the carbon in the coal burnt, it was slowly being converted to ash that has an SG similar to that of the sand.
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