2 replies to this topic

[hirengdesai]

dear all,
i wanted to carry our hydraulics of a column feed which is a mixture of hydrocarbon vapor,liquid and small solid particles of coke.
can anyone guide me abt how should i start for line sizing purposes ?
how much velocity should i keep in these feed line ?
the solid content is 5-10 % bywt in the stream with particle dia of 300 microns.


regards,
hiren.

[Dtan76]

Hi there

Attached here please find line sizing criteria. Basically you need to calculate the fluid velocity and delta P (pressure drop) in milibar. You will find the specific delta P /recommended fluid velocity for different piping sie. Remember, highest fluid velocity will cause erosional happend during surge. Also, if the pipe size is under size you cause high pressure drop.

Regards

[Art Montemayor]

hirengdesai:

I realize that my response won't answer your direct query, but I feel compelled to make what I consider an important remark considering what you have stated:

"....a column feed which is a mixture of hydrocarbon vapor,liquid and small solid particles of coke."

Under no circumstances should an engineer be feeding a distillation column a feed mixture such as you are describing. You are simply asking for trouble. This is not a criticism on my part, but rather a concern and a warning that bad things will happen to your operations and to your column if you persist in carrying out such an operation. I am assuming that you have either trays (valve or bubble cap) or packing (random or structured). It really doesn't matter what is inside. Both type of mass transfer internal will plug up and cause severe and hazardous conditions for your operations. I caution you and would ask you to stop and reconsider what you are proposing. Even a tower designed and built for reactive distillation is not designed to handle solids - or much less a "slurry".

You can forget about worrying about the settling velocity in your feed line. If you have trays or plate distributors inside, the velocity there will be so low that your solids will immediately deposit themselves there and cause you all kinds of hazards and grief.

You should be removing all of the solid particles long before you consider running your 2-phase through a distillation column. I believe this is not a potential problem of handling a slurry; it is an application of common sense: distillation columns cannot be built to handle slurries. The internal velocities inside a distillation column have to be inherently very low in order to allow the successful heat and mass transfer on a stage-to-stage basis.

If I am wrong in assuming you are using a distillation process with solids in the feed stream, let me know; also give us all of the basic data that applies to this application.

What Dtan has supplied are general guidelines for velocities of fluids - but not for slurries. So the information does not apply. Slurry handling is much more specific and empirical than other fluids and must be handled and designed by experienced engineers in that field. Factors that will present problems in designing for a slurry system are how to calculate the effective viscosity and density of the fluid while maintaining the mixture in a homogeneous state in order to avoid precipitation or segregation of the solids. A 10% wt mixture of 300 micron solids is a very heavy slurry, in my opinion, and one that should be kept as far away from a distillation process as one can keep it. The solids do not contribute to the separation. They are, if successful, only going to go through your distillation tower as inerts. So why put them in there in the first place? Can you furnish more and detailed data/description on your system? Perhaps we can help if you tell us what/why you are doing this.