Multiphase Fluidized-Bed Chemical Reactions Imbalance

Jack_lumber · July 27, 2016, 19:28

Hi everyone!

I'm trying to model gasification and combustion in a fluidized bed in Fluent.
I've defined the rate of the reactions into the "phase interaction" panel through the use of UDFs.

The kinetics work fine for the primary phase (gas phase composed of co,co2,h2,h2o,o2 and argon) I obtain good results for the species in the primary phase i.e. for h2o gasification the h2o mole shrinks and h2 and co are produced.

However, the model doesn't work for the secondary phase consisting of only pure carbon. When the reactions take place, the carbon content increases instead of decreasing.

Any suggestions? Anybody experienced/resolved the same issue?

cheers

Jack_lumber · July 28, 2016, 15:49

So the problem seems to come from the density definition:

when I set the solid phase density as "incompressible ideal gas" the reaction works as expected, however, the density of the solid phase becomes very low (way below the 350 kg/m3 I measured for my feedstock). This is the reason I was assuming a constant density of 350 kg/m2 before.

How could I overcome this? I need to define a solid phase density of 350 kg/m3 but the reactions only work by considering the solid phase as an incompressible ideal gas... I'm a bit confused...

Jay Yin · October 23, 2016, 23:41

Could you make it more clear why you think carbon is increasing instead of decreasing? From my experience, if solid phase include only carbon, its mass fraction will keep unity, however its volume fraction will decrease as expected.

Dri · December 3, 2016, 13:18

What is the volume fraction of the secondary phase, and what are your boundary conditions?

July 27, 2016, 19:28	Multiphase Fluidized-Bed Chemical Reactions Imbalance	#1
Jack_lumber New Member Join Date: Jun 2016 Posts: 3 Rep Power: 10	Hi everyone! I'm trying to model gasification and combustion in a fluidized bed in Fluent. I've defined the rate of the reactions into the "phase interaction" panel through the use of UDFs. The kinetics work fine for the primary phase (gas phase composed of co,co2,h2,h2o,o2 and argon) I obtain good results for the species in the primary phase i.e. for h2o gasification the h2o mole shrinks and h2 and co are produced. However, the model doesn't work for the secondary phase consisting of only pure carbon. When the reactions take place, the carbon content increases instead of decreasing. Any suggestions? Anybody experienced/resolved the same issue? cheers

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July 28, 2016, 15:49		#2
Jack_lumber New Member Join Date: Jun 2016 Posts: 3 Rep Power: 10	So the problem seems to come from the density definition: when I set the solid phase density as "incompressible ideal gas" the reaction works as expected, however, the density of the solid phase becomes very low (way below the 350 kg/m3 I measured for my feedstock). This is the reason I was assuming a constant density of 350 kg/m2 before. How could I overcome this? I need to define a solid phase density of 350 kg/m3 but the reactions only work by considering the solid phase as an incompressible ideal gas... I'm a bit confused...

October 23, 2016, 23:41		#3
Jay Yin New Member Join Date: Oct 2016 Posts: 4 Rep Power: 10	Could you make it more clear why you think carbon is increasing instead of decreasing? From my experience, if solid phase include only carbon, its mass fraction will keep unity, however its volume fraction will decrease as expected.

December 3, 2016, 13:18		#4
Dri New Member Adriana Join Date: Oct 2012 Location: Canada Posts: 7 Rep Power: 14	What is the volume fraction of the secondary phase, and what are your boundary conditions?