Fluidized Bed Question 2

[Daniel14]

Craig is setting up a fluidized bed in which a reaction will take place. The reactants are combined with compressed air to act as the fluid in the bed and the particles inside of the bed are catalysts for the reaction. Craig sets up an experiment to determine which particle size is most effective for his reactor.

In experiment 1, Craig utilizes particles that are 1 mm in diameter. In experiment 2, Craig uses particles that are 5 mm in diameter. Craig finds that his reaction reaches completion much faster when the 5 mm diameter particles are used so he decides to go forward with utilizing the larger particles for his reactor.

what is one (1) potential drawback of utilizing the larger particles over the smaller ones?

 

[don1980]

Higher superficial gas velocity for maintaining fluidization.

 

[EdStainless]

And larger reactor needed to get the same surface area.
5mm is getting a bit large to fluidize well without using tons of gas, unless they are low density particles.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[MJCronin]

Could this be a homework problem ? ... It is not nice to trick geezers into doing your homework !!!

Why won't "Craig" explain to you his thinking ?

"Craig" was caught cheating on his last exam .... just wanted you to know....!!!

MJCronin
Sr. Process Engineer

 

[SuperSalad]

Hold the phone, I've heard Craig has an additional problem.

Craig is traveling by train for an important meeting. Craig was late at the station so Craig will miss the scheduled train at the transfer station. The first train is traveling at 60 mph and is 5 miles from the station, whereas the second train he will miss is traveling at 65 mph and has just left the station. Before branching off, the two trains run parallel, in opposite directions, for 10 miles.

What is one (1) potential drawback of Craig jumping from the first train to the second train while they are passing one another in opposite directions in that 10 mile span?

Andrew H.

http://www.MotoTribology.com

 

[0707]

In this kind of reactions catalysts work like a fluid so that the interaction between the fluid catalyst and liquid product to react shall be as good as possible, if you have a catalyst with particles of the measure, you describe it won´t behave like a fluidized reator and your reaction will be very poor.

lm

 

[georgeverghese]

Specific surface area for the 5mm particles is much less than that for the 1mm particles ( m2 of external surface/m3 of particles), so the reaction should have run faster for the 1mm particles if total volume of catalyst is the same in both cases. Does Craig have an explanation why the 5mm particles are better ?

 

[Compositepro]

The only explanation that I can think of is that the gas flow rate is higher through the larger particles. If the particles are actually fluidized the flow rate would have to be higher to fluidize the larger particles.

 

[georgeverghese]

Higher inerts - compressed air rate would have meant lower residence time for a fixed reactor volume, and hence lower conversion rate. Kinetics almost always favors higher conversion with increasing residence time and/or increasing temp, regardless of whether the reaction is endothermic or exothermic. This is because most industrial reversible reactions exit the reactor with the reaction terminated with low residence time and still far from thermodynamic equilibrium.