Particle Entrainment in a Counter-Current Flow Reactor

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SUMMARY

The discussion centers on the challenges of particle entrainment in a counter-current flow reactor, specifically a rotating kiln designed to process fine, low-density solid feedstock. The key issue is determining the maximum gas velocity that can be used without causing the solid particles to be entrained and exit through the gas outlet. Participants suggest that parameters such as particle size, density, and shape are critical, and recommend researching Stokes' law and pneumatic conveying systems for further insights.

PREREQUISITES
  • Understanding of counter-current flow dynamics
  • Knowledge of particle size distribution (PSD) and density
  • Familiarity with Stokes' law and its applications
  • Basic principles of rotary kiln operation
NEXT STEPS
  • Research Stokes' law and its implications for particle settling in gas flows
  • Explore pneumatic conveying systems and their design considerations
  • Study the principles of rotary kiln design and operation
  • Investigate empirical relationships between gas velocity and particle entrainment
USEFUL FOR

Engineers and researchers involved in chemical engineering, particularly those focusing on rotary kiln design, particle processing, and gas-solid interactions in reactors.

davidgrant23
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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
 
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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?
 
anorlunda said:
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
 
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.
 
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.
 
Try to check textbooks on cement production.
Regards,
 

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