2 replies to this topic

[sumit mate]

hello all,
i hav problem that i m not geting sufficient reflux to column due to that i can no increase distillate flow rate and this lead to low capacity.
our operating condition of column(under vacuume) is top pres 10 to 40 torr(abs) & temp 115 to 120 , mid temp is 130 to 135 and bott. press 130 to 160torr(abs) & temp. 180 to 185 which is match with vap press data and found ok.
our require press drop is 120 to 130 torr(abs) and im also mentain the same.
when i increase the steam to reboiler the bott press is increasing to 170 to 175 torr(abs) and top press remains 10 to 12 torr now due to this im not able to mentain the press dropp and lead to less reflux still i have increase the steam to reboiler.
and secondly not able to mentain level in rebioler( it is going down to overflow line)
column has open and thermosyfen line to reboiler has also open has found nothing in it.
the distillate temp also mentain to require temp.
what i think is that vapoure which are genrating to reboiler is not going up(which is very contrdictory as top press is 10 tor).due to this less vap reaching to condenser and result in less reflux.

please rep

[Art Montemayor]

Sumit:

I have taken the liberty of redacting and correcting some language in your original post in order to make sure we all understand what you are describing. Please read my version at the bottom very carefully and correct it if I have mis-interpreted what your wrote. Also, please furnish some basic data in order to be able to try to help you resolve this problem. The minimum basic data needed is:

• A detailed sketch of your vacuum distillation unit - including reboiler, overheads condenser, reflux system, and vacuum unit; state the type of column internals used;
• Vacuum control method;
• Identification of the fluids involved;
• Flow rates of feed, distillate, and bottoms products;
• Location of temperature and pressure data shown on sketch.

Await your reply.


"Hello all,

I have a problem with a vacuum distillation unit. I am not able to furnish sufficient reflux to the column because I cannot increase the distillate flow rate at the top of the column and this is causing a low distillate production.

Our vacuum column operating conditions are:

Top section pressure = 10 to 40 torr (abs)
Top section temperature = 115 to 120 ^oC
Mid-section temperature = is 130 to 135 ^oC
Bottom section pressure = 130 to 160 torr (abs)
Bottom section temperature = 180 to 185 ^oC (which matches with vapor pressure data and is found OK).

Our require press drop across the column is 120 to 130 torr (abs) and I am maintaining the same.

When I increase the steam flow rate to the reboiler the, bottom pressure increases to 170 to 175 torr (abs) and the top section pressure remains at 10 to 12 torr. Because of this, I am not able to maintain the press drop across the column and this lead to less reflux – even though I have to increase the steam flow to the reboiler.

Additionally, I am not able to maintain a constant level in the reboiler (it is going down the overflow line). The column and the thermosyphon line to the reboiler have been opened and inspected and nothing has been found in them.

The overhead distillate temp is also maintained at the required temperature

What I think is happening is that the vapor generated in the reboiler is not going up into the column (which is very contradictory to the top section pressure being at 10 torr). Due to this effect, less vapor is reaching the overhead condenser and this results in less reflux.

Please reply"

[sundutt]

Dear Sumit;

On behalf of of community members I must say thank you for Mr.Art for elaborating & presenting the problem in professional way. now it is very easy for understanding. however you must provide all details with sketch as per Mr. Art's recommendation.

From the understanding of the problem. I am feeling that you are now operating the column at higher pressure as you facing limitation in refulx flow.You feel that vapors are not reaching in reflux drum as per your observation on pressure which remained same. I feel that you can refer top temperature also & compare with earlier condition.
For the vacuum distillation if your steam consumption for same feed rate increased, it means you are operating column at higher pressure. so calibrate your pressure transmitter.
You mentioned that your level is falling when you increasing steam--- it means your column bottom temperature may be in cascade which is drawing more bottom flow when bottom temperature increases.

just interpret these my observations for your column operations.

Best Wishes;
santosh
santosh_khopade@rediffmail.com