Particle Entrainment in a Counter-Current Flow Reactor

[davidgrant23]

Hi there,

I am currently looking to build a rotating kiln to provide the necessary heat/res. time/gases to react a solid feedstock. The problem that I can envision, however, is that the solid (which is fed as small particles) may become entrained in the counter-current gas flow inside the rotating kiln.

Is there some fundamental or empirical relationship between the velocity of the counter-current gas flow and the rate of entrainment of the solid particles?

Cheers

 

[anorlunda]

Your query sounds a little bit like a fluidized bed.

Where does gravity act in relation to your kiln?

Can you elaborate on what you visualize as entrained?

 

[davidgrant23]

Your query sounds a little bit like a fluidized bed.

Where does gravity act in relation to your kiln?

Can you elaborate on what you visualize as entrained?

Hi Anorlunda,

The rotating kiln is inclined slightly away from horizontal (1-5 degrees). The solid particles are fed at the elevated end and travel towards the lower end through rotation of the kiln. While they are traveling a counter-current gas flow is passed through the kiln.

The problem I can envision is that my feedstock (which are fine, low density particles) may become entrained in the counter-current gas flow if the gas velocity is sufficiently high. This will affect the residence time inside the kiln, as well as the mass transfer characteristics. What I'm not sure of, however, is how to take the gas velocity inside the kiln (which I can calculate) and combine that information with the flow properties of the solid particles (density, PSD, shape etc.) to calculate what is the MAXIMUM gas velocity I can run at without having the particles get picked up by the counter current flow and exit the reactor via the gas outlet (instead of the solid outlet).

This problem differs from a fluidized bed reactor as in that case the gas is passed vertically through a stationary bed (inducing fluidization). In this case the particles are traveling horizontally and the flow is counter-current.

Hopefully this cleared up the problem a little.

Cheers,
Dave

 

[anorlunda]

That sounds very non-trivial. I'm not sure there is a straightforward way to calculate that max velocity.
The size and density of the solid particles would be critical parameters. centimeters? MIcrons?

I'm afraid your question is over my head. Hopefully, others can help.

 

[jrmichler]

If your gas is flowing upward, the particles settling downward, the particles are well separated, the particles are roughly spherical, and the particles are small, then google Stokes' law. You might also google pneumatic conveyor for cases where flow velocities are higher.

 

[zbikraw]

Try to check textbooks on cement production.
Regards,