Print page

Print page

Solving Problems with Vacuum Distillation Systems

Q: In our vacuum distillation system, we are getting 0.4 Torr vacuum while in reactor we are getting 8 Torr. Our client requirement is 1 Torr. Do you think there is any problem from the vacuum system side?

System volume is 5,000 liters; air leakage is 1kg/hour; and carry over load of 1kg/hr (MW 137). Vacuum system of 570 ACFM (Mech booster backed by Dry Vacuum pump)supplied. We have 4-inch pipe line.

A:

This is a bit out of my area, but here are my thoughts:

1.) If I did the calculation correct, I calculate the unit is generating 1,108 ACFM (air + carry-over) at 60F and 0.4 Torr.  (This ACFM calculation needs confirmed.)  The calculated ACFM is greater than the stated capacity of the vacuum system given as 570 ACFM.  If the temperature is lower than 60 F, the volume would be less but I doubt it is low enough to reduce the ACFM to half and if the temperature is greater than 60 F the ACFM would be higher.  If the gas/vapor load on the vacuum system is not the problem or the whole problem, and it may not be since the pressure is 0.4 Torr at the pump, then in addition to vacuum system load evaluation the other equipment in the system needs its pressure drop evaluated.

2.) I don't know the equipment arrangement, but if I assume that the vacuum is being drawn through the overhead condenser and that the distillation column is between the reactor and vacuum system then the pressure drop of various components need to be evaluated.   Some of the components may be a packed or trayed tower, overhead condenser and the connecting piping.

If you already considered these possibilities, you may want to contact a distillation consultant. 

Here are more of the latest questions on: Distillation

Is there a guideline for setting the height of the conical section of a column?
I have designed a column with two sections of different diameters (enriching section 1,900 mm and stripping section 3,500 mm). Is there any rule or guideline to be followed to set the height of conical section of column between these two diameters? Presently I have considered height of conical section as 500 mm approx (equivalent to one manhole) between these two diameters.

Is vacuum distillation best to recover iso amyl alcohol and manufacturing esters?
I'm planning to set up a distillation unit for distilling fusel oil to recover iso amyl alcohol and manufacturing esters from it. I've been suggested to go for vacuum distillation through use of watering pump and reboiler of falling film evaporator type. The column will be about 10m high having a diameter of 0.6m. Is this the right way to go? Which packing should I consider? Will vacuum distillation break the azeotrope formed between water and ethanol?

Is there a good way to calculate the height of stage in a distillation column?
I'm working on a distillation column for a six-part multi-component distillation column. It contains structured packing. I estimated about eight stages with a model and came up with approximately the same answer with pseudo-McCabe-Thiele. I was careful to pick the correct heavy key and light key. Then, I realized I did not have a good way to calculate the height of stage. The model, like most, only tells you the number of stages not the height of stage or Z, the final height of theoretical packing.

Kister would say 1-3 feet as an assumption (based on gas resistance), or I could estimate it using a KG or KL. Empirical data would help.

I assume that the oil, a collection of C10+, would pose the greatest resistance, which makes calculating an H stage even more difficult. The feed is trace water, toluene and oils.

Any advice or reference that might be useful in solving this dilemma?

How do I calculate the void space in a column?
How do I calculate the void space in a column? Actually we are putting ½-inch balls in a 14-inch pipe. Height of packing will be 3 inches. Above the ½-inch balls we will put ¼-inch balls and the packing height will be the same (3 inches). How many balls can I put in the column?

How does a water draw off vessel work?
I need to design water draw off vessel. How does a water draw off vessel work?

Back to Ask the Experts