×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pressure drop calculation

Pressure drop calculation

Pressure drop calculation

(OP)
I have a vacuum distillation column with vacuum of 15 inHG being pulled from overheads condensate receiver. There is a pressure equalization line from overheads condenser to this receiver.

At increased vapor loads, condenser will not handle so I am installing a vent condenser on vacuum line from receiver to vacuum pump. At high vapor rates, about 3000 lbs/hr of acetone flows through equalization line ( condenser to condensed liquid receiver) How should I calculate pressure drop across this 2" line?

Does pressure in my receiver and condenser will be same due to equalization line?

Thank You
Koshy

RE: Pressure drop calculation

You shall try to find a copy of Crane Technical Paper #410 and if and when you do, you will be able to get on with the calculations.

rmw

RE: Pressure drop calculation

The liquid from the condenser should not flow via the equalization line to the receiver.  The liquid should flow from a nozzle at the bottom of the condenser to a point below the liquid surface level in the receiver.  There is often a U-bend seal in this line to ensure that it is always sealed with liquid, preventing vapor from flowing back up the line.

The equalization line should be a separate line and it should see vapor only.  It should be connected from the top of the condenser (or the line to the vacuum pump) down to the vapor space at the top of the receiver.

You are correct that the pressures in the condenser and receiver are (or should be) the same.  That is what the equalization line is for.  The head that drives the liquid from the condenser to the receiver is the static head due to the difference in heights - the receiver is placed below the condenser.

I suppose it would be possible to combine the liquid drain line and the equalization line into one if the line was sized for self venting flow. The line would have to run from the bottom of the condenser to the vapor space of the receiver and have no low points in it.  It sounds as though this is what you have and 3000 lb/h of acetone in a 2" line is just at the limit of self venting flow.  In my opinion you are lucky that this system works and this type of arrangement should be avoided.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Pressure drop calculation

(OP)
Thanks Katmar. I might have not expressed my clarifications in detail. Please look at the attachment for better explanation of my process.

Liquid flows through bottom discharge. At high rates, excess vapors will flow through equalization line  to receiver and will be pulled by vacuum pump. My intention is to condense these excess vapors using a BEM type condenser installed on vacuum line between receiver and vacuum pump.

I request for how to calculate pressure drop in eqalization line( flow is 3000 lbs/hr). IS the type of configuration have success? what is momentum factor? ( used in vapor nozzle sizing)

Thanks a Lot
Koshy

RE: Pressure drop calculation

OK - I misunderstood what you were trying to do.  rmw gave you the right advice - calculating this pressure drop is not any different from any other.  3000 lb/h is too much for the 2" line.  Why not put the new condenser in parallel with the existing unit?

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Pressure drop calculation

(OP)


Katmar,

I agree with you on pipe size. Existing condenser nozzle is 2" and 3.5" pipe will work at 3000 lbs/hr.

Can I still use 2" condenser nozzle and upsize my pipe to 3" with a reducer? Please advice me

Thank You very much

RE: Pressure drop calculation

Koshy, there is a chance that it will work but it all depends on the details of your pipe and equipment layout, your process conditions and requirements and so on.  You need to do the calculations and satisfy yourself that it is adequate. I still think that putting the condensers in parallel is a better option.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Pressure drop calculation

(OP)
Thanks Katmar.

I guess I did my home work after some inputs from this post.

Maximum vapor flow rate handled by main condenser is 23,500 lbs/hr of acetone. At high rates, ( 26,000 lb/hr) I need another small condenser ( this rate is limited by flooding in columns with high efficiency trays, superfrac) to handle this rate.

Option 1: Installing vent condenser on vacuum line to pump requires more piping and hence pressure drop.

Option 2: Parallel condenser requires vapor flow meter and control valves on chilled water and vapor side( pressure drop and cost)

Option 3: To install condenser on  pressure equalization line. This seems to be better as I have to upsize only one nozzle on main condenser and ofcourse piping too.

I have attached drawing in my previous post. Please help me with your advice/ recommendations on above options.

Thank you Katmar and rmw.

Koshy

RE: Pressure drop calculation

(OP)
Can someone please help me recommend on above options (no 2 and 3).

Thank You
Koshy

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources